Circuit changeover switch

Abstract

A circuit changeover switch 60, which includes a drive device 10, includes ceramic pumps 18a and 18b, which alternately pressurize and depressurize operation fluid 100 within a fluid chamber 13a on opposite sides of an electrically conductive movable body 110, to thereby move the movable body 110 within the flow chamber 13a, whereby one of changeover electrodes 62a and 62b is electrically connected to a common electrode 61. When the pressure of the operation fluid is increased and decreased at high speed by the ceramic pumps, micro channels 16a and 16b exhibit a high passage resistance, so that the pressure within the channel does not escape to an internal-pressure buffering chamber 15a, and the movable body moves without fail. When the pressure of the operation fluid increases slowly due to expansion of the operation fluid, the micro channels exhibit a low passage resistance, so that an expanded portion of the operation fluid is led to the internal-pressure buffering chamber, and the pressure increase of the operation fluid is suppressed. A drive device which does not cause breakage of a pump chamber or a seal due to thermal expansion of operation fluid is provided.

Description

TECHNICAL FIELD

[0001] The present invention relates to a circuit changeover switch which switches an electrical path by use of a drive device for moving a movable body through utilization of operation fluid.

BACKGROUND ART

[0002] In recent years, there have been developed micro motors, micro sensors, micro switches, etc. which have sizes of several millimeters to several tens of microns and which are fabricated through utilization of a technique for micro-machining of materials, such as a semiconductor fabrication technique, or by making use of piezoelectric material or a like material which can effect mutual conversion between electrical energy and mechanical energy. These elementary devices can be widely applied to, for example, ink-jet printer heads, micro valves, flow sensors, pressure sensors, recording heads, actuators for tracking servos, on-chip biochemical analyzers, micro reactors, high-frequency components, micro magnetic devices, micro relays, acceleration sensors, gyroscopes, drive devices, displays, and optical scanners (Nikkei Micro Device, July 2000, pp 164-165).

[0003] In these micro machines, electrostatic force is often used as drive force. Further, various types of drive sources have been studied, such as a type which utilizes distortion deformation of a piezoelectric material caused through application of voltage thereto, a type which utilizes changes in shape of a shape memory alloy, and a type which utilizes changes in volume of liquid caused by phase change thereof induced by heating. However, in micro mechanisms, force generated by a drive source and drive stroke become extremely small, and therefore, in some applications a mechanical amplification mechanism such as a lever must be combined with a drive source.

[0004] However, when the size of such a mechanical amplification mechanism is reduced to that of a micro machine, wear or sticking, which does not raise any problem in the case of a machine of ordinary size, raises a big problem. Further, since a micro machine having an amplification mechanism (drive function) such as a lever inevitably requires formation of a three-dimensional structure having a depth (height), micro machining of such a micro machine requires a longer time, and assembly of micro components requires a greater number of steps. For this reasons, some micro machines involve the problem of not being suitable for mass production.

[0005] Meanwhile, in order to be used as a circuit changeover switch that functions as an electrical switch (or a relay), among the above-described devices, there has been developed a mercury micro relay of a type which realizes switching operation through movement of a mercury droplet and which utilizes, as a drive force for moving the mercury droplet, pressure created upon instantaneous generation of a bubble by means of heating by a micro heater (see, for example, J. Kim et al., Proc. 46th Annual Int. Relay Conf., Oak Brook, Ill., April 1998, pp. 19-1-19-8). This switch is reported to have various features, such as a wide frequency range of DC to 10 GHz, high insulating resistance and low insertion loss in the GHz band, and no signal bounce.

[0006] However, the above-described mercury micro relay of a bubble generation type has drawbacks, in that heat accumulates through heating operation and that a large amount of electrical power is consumed.

[0007] Accordingly, an object of the present invention is to provide a circuit changeover switch which is a device using operation fluid, which maintains the features of micro machines such as small size and low power consumption, which does not include a mechanical amplification mechanism having intrinsic problems of wear and sticking, which facilitates mass production, and which hardly causes leakage of operation fluid under variation in atmospheric temperature. Another object of the present invention is to provide a circuit changeover switch which is free from the problem of heat accumulation and which enables high-speed changeover operation.

DISCLOSURE OF THE INVENTION

[0008] In order to achieve the above-described object, the present invention provides a circuit changeover switch comprising: a channel forming portion for forming a channel (i.e. a flow-passage forming portion for forming a flow passage), the channel accommodating an incompressible operation fluid and a movable body made of a substance different from that of the operation fluid, and being substantially divided into two operation chambers by means of the movable body; a pair of pumps each including a pump chamber communicating with the corresponding operation chamber and being filled with the operation fluid, an actuator provided for the pump chamber, and a diaphragm deformed by the actuator, the operation fluid within the pump chamber being pressurized or depressurized through deformation of the diaphragm; an internal-pressure-buffering-chamber-forming portion for forming an internal-pressure buffering chamber which accommodates the operation fluid and a compressible fluid for pressure buffering; and a micro channel portion for forming a micro channel which connects the channel of the channel forming portion and the internal-pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion, the micro channel exhibiting a high passage resistance against abrupt pressure change of the operation fluid within the channel, to thereby substantially prohibit passage of the operation fluid through the micro channel and exhibiting a low passage resistance against slow pressure change of the operation fluid within the channel, to thereby substantially permit passage of the operation fluid through the micro channel. The micro channel may connect the channel of the channel-forming portion and the internal-pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion directly, or via another portion (e.g., a connection passage for connecting the channel and the pump chamber, or a pump chamber). Further, three or more pumps may be provided.

[0009] By virtue of the above-described configuration, when the diaphragm is deformed by the actuator, the operation fluid within the channel is pressurized or depressurized. At this time, when the pressure of the operation fluid changes abruptly, the micro channel exhibits a high passage resistance in order to substantially prohibit passage of the operation fluid through the micro channel. Therefore, the pressure change of the operation fluid is transmitted to the movable body within the channel, so that the movable body moves. In contrast, when the pressure of the operation fluid changes slowly due to thermal expansion of the operation fluid caused by variation in the ambient temperature or due to slow operation of the actuator, the micro channel exhibits a low passage resistance in order to substantially permit passage of the operation fluid through the micro channel. Therefore, the operation fluid moves via the micro channel to the internal-pressure buffering chamber, which accommodates a compressible fluid for pressure buffering. As a result, pressure increase of the operation fluid within the channel is suppressed, and it becomes possible to avoid breakage of the device (switch) due to excessive pressure of the operation fluid and to prevent leakage of the operation fluid due to breakage of the device.

[0010] Preferably, the actuator includes a film-type piezoelectric element comprising a piezoelectric/electrostrictive film or an antiferroelectric film and electrodes; and the diaphragm is formed of ceramic.

[0011] In this case, micro machining can be performed more easily, and circuit changeover switches which are well suited for mass production and which have excellent durability can be provided.

[0012] Preferably, the circuit changeover switch according to the present invention includes a first changeover electrode exposed to a portion of the channel of the channel forming portion; a second changeover electrode exposed to another portion of the channel of the channel forming portion and electrically isolated from the first changeover electrode; and an electrode (common electrode) exposed to the channel of the channel forming portion to face the first changeover electrode and the second changeover electrode via the channel (to be connected with the first changeover electrode and the second changeover electrode through the movable body within the channel), wherein at least a surface portion of the movable body is formed of an electrically conductive material. In this case, the operation fluid must be electrically non-conductive.

[0013] Preferably, the circuit changeover switch according to the present invention includes a first changeover electrode exposed to a portion of the channel of the channel forming portion; a second changeover electrode exposed to another portion of the channel of the channel forming portion and electrically isolated from the first changeover electrode; an electrode exposed to the channel of the channel forming portion to face the first changeover electrode via the channel (to be connected with the first changeover electrode through the movable body within the channel); and another electrode exposed to the channel of the channel forming portion to face the second changeover electrode via the channel (to be connected with the second changeover electrode through the movable body within the channel), wherein at least a surface portion of the movable body is formed of an electrically conductive material.

[0014] Notably, in such a switch, no limitation is imposed on the number of the changeover electrodes, so long as the number is not less than two.

[0015] By virtue of the above-described structure, the movable body is moved between the first changeover electrode and the second changeover electrode by pumps each comprising a film-type piezoelectric element and a ceramic diaphragm, whereby an electric circuit (electric path) is switched. Thus is provided a circuit changeover switch which exhibits reduced electrical power consumption and which does not involve a problem of heat accumulation, which would otherwise be caused by heating by a micro heater. Further, since such a pump can be operated at high speed and has excellent durability, a circuit changeover switch suitable for portable information terminals, etc. can be provided.

[0016] In the above-described circuit changeover switch, preferably, each of the diaphragms of the pumps constitutes a portion of the walls of the corresponding pump chamber and has a film surface in a common plane; the channel of the channel forming portion forms a space whose longitudinal axis lies in a plane parallel to the film surfaces of the diaphragms; the micro channel of the micro channel portion extends along a direction parallel to the film surfaces of the diaphragms; and the internal-pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion forms a space whose longitudinal axis lies in a plane parallel to the film surfaces of the diaphragms and is connected with the channel of the channel forming portion via the micro channel of the micro channel portion.

[0017] When each of the pumps is configured in such a manner that a diaphragm formed of a single deformable plate member such as a ceramic sheet forms a portion of the walls of the pump chambers, the volume of each pump chamber is changed directly upon operation of the corresponding actuator, whereby the operation fluid can be pressurized or depressurized efficiently. Accordingly, it is preferable that each of the diaphragms of the pumps form a portion of the walls of the corresponding pump chamber and have a film surface in the common plane.

[0018] Meanwhile, in order to produce a passage resistance having the above-described characteristics, the micro channel must have a small cross section. However, when the cross section of the micro channel is extremely small, high machining accuracy is required, thereby increasing the production cost of the circuit changeover switch. By contrast, the micro channel can produce a passage resistance having the above-described characteristics when the micro channel has an increased length. However, when the micro channel is extended only along a direction intersecting the film surface of the diaphragm (e.g., a direction perpendicularly intersecting the film surface of the diaphragm), the thickness of the circuit changeover switch increases.

[0019] In order to solve the above problem, the circuit changeover switch of the present invention employs the above-described structure in which the micro channel of the micro channel portion extends along a direction parallel to the film surface of the diaphragm; and the micro channel connects the channel of the channel forming portion and the internal-pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion, each being a space whose longitudinal axis lies in a plane parallel to the film surface of the diaphragm. Since the above arrangement and configuration enable formation of the channel, the internal-pressure buffering chamber, and the micro channel within a certain thickness, a circuit changeover switch (drive device) of small thickness (a thin type) can be provided. Further, since such a thin-type circuit changeover switch increases the surface area of the circuit changeover switch relative to the overall volume of the circuit changeover switch, heat generated upon operation can be dissipated to the outside with ease, and the circuit changeover switch can operate stably.

BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a sectional view of a drive device which serves as a portion of a circuit changeover switch according to a first embodiment of the present invention.

[0021] FIG. 2 is a plan view of the drive device shown in FIG. 1.

[0022] FIG. 3 is a sectional view of the drive device taken along line 2-2 in FIG. 1.

[0023] FIG. 4 is a sectional view of the drive device shown in FIG. 1, showing an initial state thereof.

[0024] FIG. 5 is a sectional view of the drive device shown in FIG. 1, showing an operated state thereof.

[0025] FIG. 6 is a sectional view of the drive device shown in FIG. 1, showing another operated state thereof.

[0026] FIG. 7 is a sectional view of the drive device shown in FIG. 1, showing flow of operation fluid when the ambient temperature increases.

[0027] FIG. 8 is a sectional view of the drive device shown in FIG. 1, showing flow of the operation fluid when the ambient temperature decreases.

[0028] FIG. 9 is a view used for explaining an operation for finely adjusting the position of a movable body of the drive device shown in FIG. 1.

[0029] FIG. 10 is a pair of time charts showing waveforms of voltages which are applied to piezoelectric films of the drive device shown in FIG. 1 for the purpose of fine adjustment of the position of the movable body of the drive device.

[0030] FIG. 11 is a view used for explaining an operation for finely adjusting the position of the movable body of the drive device shown in FIG. 1.

[0031] FIG. 12 is a view used for explaining an operation for finely adjusting the position of the movable body of the drive device shown in FIG. 1.

[0032] FIG. 13 is a sectional view of a modification of the drive device shown in FIG. 1.

[0033] FIG. 14 is a sectional view showing a modification of a channel of the drive device shown in FIG. 1.

[0034] FIG. 15 is a sectional view of a drive device which serves as a portion of a circuit changeover switch according to a second embodiment of the present invention. FIG. 16 is a plan view of the drive device shown in FIG. 15.

[0035] FIG. 17 is a conceptional diagram showing a process of fabricating a piezoelectric/electrostrictive actuator of the drive device shown in FIG. 15.

[0036] FIG. 18 is a conceptional diagram showing a different process of fabricating a piezoelectric/electrostrictive actuator of the drive device shown in FIG. 15.

[0037] FIG. 19 is a conceptional diagram showing a process of fabricating the drive device shown in FIG. 15.

[0038] FIG. 20 is a conceptional diagram showing a process of fabricating the drive device shown in FIG. 15.

[0039] FIG. 21 is a sectional view of a drive device which serves as a portion of a circuit changeover switch according to a third embodiment of the present invention.

[0040] FIG. 22 is a sectional view of a drive device which serves as a portion of a circuit changeover switch according to a fourth embodiment of the present invention.

[0041] FIG. 23 is a sectional view of a drive device which serves as a portion of a circuit changeover switch according to a fifth embodiment of the present invention.

[0042] FIG. 24 is a plan view of the drive device shown in FIG. 23.

[0043] FIG. 25 is a sectional view of the drive device shown in FIG. 23, showing an operated state thereof.

[0044] FIG. 26 is a plan view of a modification of the drive device which serves as a portion of the circuit changeover switch according to the fifth embodiment of the present invention.

[0045] FIG. 27 is a sectional view of one embodiment of the circuit changeover switch of the present invention, showing an initial state thereof.

[0046] FIG. 28 is a sectional view of the circuit changeover switch shown in FIG. 27, showing a driven state thereof.

[0047] FIG. 29 is a system block diagram of a portable information terminal to which the circuit changeover switch shown in FIG. 27 is applied.

[0048] FIG. 30 is a sectional view of another embodiment of the circuit changeover switch of the present invention, showing an initial state thereof.

[0049] FIG. 31 is a conceptional diagram showing a process of fabricating the circuit changeover switch shown in FIG. 30.

[0050] FIG. 32 is a conceptional diagram showing a different process of fabricating the circuit changeover switch shown in FIG. 30.

[0051] FIG. 33 is a sectional view of still another embodiment of the circuit changeover switch of the present invention, showing an initial state thereof.

[0052] FIG. 34 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to a sixth embodiment of the present invention.

[0053] FIG. 35 is a sectional view of the drive device taken along line A5-A5 in FIG. 34.

[0054] FIG. 36 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to a seventh embodiment of the present invention.

[0055] FIG. 37 is a sectional view of the drive device taken along line A6-A6 in FIG. 36.

[0056] FIG. 38 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to an eighth embodiment of the present invention.

[0057] FIG. 39 is a sectional view of the drive device taken along line A7-A7 in FIG. 38.

[0058] FIG. 40 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to a ninth embodiment of the present invention.

[0059] FIG. 41 is a sectional view of the drive device taken along line A8-A8 in FIG. 40.

[0060] FIG. 42 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to a tenth embodiment of the present invention.

[0061] FIG. 43 is a sectional view of the drive device taken along line A9-A9 in FIG. 42.

[0062] FIG. 44 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to an eleventh embodiment of the present invention.

[0063] FIG. 45 is a sectional view of the drive device taken along line AA-AA in FIG. 44.

[0064] FIG. 46 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to a twelfth embodiment of the present invention.

[0065] FIG. 47 is a sectional view of the drive device taken along line AB-AB in FIG. 46.

[0066] FIG. 48 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to a thirteenth embodiment of the present invention.

[0067] FIG. 49 is a sectional view of the drive device taken along line AC-AC in FIG. 48.

[0068] FIG. 50 is a sectional view of the drive device taken along line AD-AD in FIG. 48.

[0069] FIG. 51 is a plan view of a drive device which serves as a portion of a circuit changeover switch according to a fourteenth embodiment of the present invention.

[0070] FIG. 52 is a sectional view of the drive device taken along line AE-AE in FIG. 51.

[0071] FIG. 53 is an enlarged sectional view of a modification of the piezoelectric/electrostrictive film actuator applied to the drive device shown in FIG. 34, taken along line A5-A5 in FIG. 34.

[0072] FIG. 54 is an enlarged sectional view of the modification of the piezoelectric/electrostrictive film actuator applied to the drive device shown in FIG. 34, taken along line AF-AF in FIG. 34.

BEST MODE FOR CARRYING OUT THE INVENTION

[0073] Embodiments of the circuit changeover switch containing the drive device according to the present invention will now be described with reference to the drawings. However, the present invention is not limited to these embodiments, and on the basis of knowledge of persons with ordinary skill in the art, various changes, modifications, and improvements can be made without departing from the scope of the present invention. Notably, when the drive device is described, descriptions of electrodes are omitted.

[0074] FIG. 1 is a vertical sectional view of a drive device 10, which serves as a portion of a circuit changeover switch according to a first embodiment of the present invention; and FIG. 2 is a plan view of the drive device 10. Notably, FIG. 1 is a sectional view of the drive device 10 taken along line 1-1 in FIG. 2.

[0075] The drive device 10 comprises a ceramic base body 11 of a substantially rectangular parallelepiped shape having sides which respectively extend along the X-axis, Y-axis, and Z-axis directions, which are mutually perpendicular; and a pair of piezoelectric films (piezoelectric/electrostrictive elements) 12a and 12b. The base body 11 includes a channel forming portion 13, a pair of pump chambers 14a and 14b, an internal-pressure-buffering-chamber-forming portion 15, and a pair of micro channel portions 16a and 16b.

[0076] The channel forming portion 13 has a long axis along the X-axis direction. As shown in FIG. 3, which is a sectional view of the base body 11 taken along line 2-2 in FIG. 1 (along a plane parallel to the Y-Z plane), the channel forming portion 13 forms a channel 13a having a substantially rectangular cross section. For example, the channel 13a has dimensions such that the width (along the Y-axis direction) W of the substantially rectangular cross section is 100 &mgr;m, the depth (along the Z-axis direction; i.e., height) H is 50 &mgr;m, and the longitudinal length (in the X-axis direction) L is 1 mm. Incompressible operation fluid (e.g., liquid such as water or oil) 100 and a movable body 110 are accommodated within the channel 13a. The movable body 110 is formed from a material ,such as magnetic material or liquid metal (e.g., gallium alloy), differing from the operation fluid 100 and having electric conductivity at least at its surface portion. The channel 13a is divided substantially into two operation chambers 13a1 and 13a2 by means of the movable body 110. Within the channel 13a, the movable body 110 is present in the form of a single mass (liquid mass (vacuole), bubble, or micro solid) and, as shown in FIG. 3, forms very small clearances S at the four corners of the rectangular cross section of the channel 13a in order to permit passage of the operation fluid 100 therethrough.

[0077] The pump chamber 14a is a space in the form of a cylinder which has a center axis extending along the Z-axis direction and is filled with the operation fluid 100, the space being formed above the channel 13a in such a manner that a lower portion of the space communicates with one end portion of the passage 13a, located at the negative side in the direction of the X-axis. For example, the pump chamber 14a has dimensions such that the bottom and top surfaces of the cylinder have a radius R of 0.5 mm, and the depth (height) h is 10 &mgr;m. A ceramic diaphragm (diaphragm portion) 17a having a thickness (height) d of 10 &mgr;m is formed above the pump chamber 14a.

[0078] The pump chamber 14b has the same shape as the pump chamber 14a and is formed above the channel 13a in such a manner that a lower portion of the space communicates with the other end portion of the passage 13a, located at the positive side in the direction of the X-axis. The pump chamber 14b is filled with the operation fluid 100. A ceramic diaphragm 17b having the same shape as that of the diaphragm 17a is formed above the pump chamber 14b.

[0079] The piezoelectric film 12a constitutes a ceramic pump 18a together with the pump chamber 14a and the diaphragm 17a. The piezoelectric film 12a has a thickness D of 20 microns and assumes the shape of a circular thin plate which has a radius r slightly smaller than the radius R of the pump chambers as viewed from above. The piezoelectric film 12a is fixed to the upper surface of the diaphragm 17a in such a manner that the piezoelectric film 12a is located above the pump chamber 14a and that the center of the circular bottom surface of the piezoelectric film 12a coincides with the center of the pump chamber 14a as viewed from above. When a voltage is applied to unillustrated paired electrodes formed to sandwich the piezoelectric film 12a, the piezoelectric film 12a increases and decreases the volume of the pump chamber 14a by deforming the diaphragm 17a, to thereby pressurize or depressurize the operation fluid 100 within the pump chamber 14a. Notably, the piezoelectric film 12a is polarized in the positive direction of the Z-axis.

[0080] The piezoelectric film 12b has the same shape as the piezoelectric film 12a. The piezoelectric film 12b constitutes a ceramic pump 18b together with the pump chamber 14b and the diaphragm 17b. That is, the piezoelectric film 12b is fixed to the upper surface of the diaphragm 17b in such a manner that the piezoelectric film 12b is located above the pump chamber 14b. When a voltage is applied to unillustrated paired electrodes, the piezoelectric film 12b increases and decreases the volume of the pump chamber 14b by deforming the diaphragm 17b, to thereby pressurize or depressurize the operation fluid 100 within the pump chamber 14b. Notably, the piezoelectric film 12b is also polarized in the positive direction of the Z-axis.

[0081] The internal-pressure-buffering-chamber-forming portion 15 forms an internal-pressure buffering chamber 15a which assumes a substantially elliptical shape having a major axis along the X-axis direction as viewed from above. The internal-pressure buffering chamber 15a has a length along the X-axis greater than the length L of the channel 13a and a length along the Y-axis (minor axis) direction greater than the width W of the channel 13a, and has a substantially rectangular cross section, as shown in FIG. 3. The internal-pressure buffering chamber 15a is formed within the base body 11 to be located below the channel 13a (on the Z-axis negative direction side of the channel 13a) in such a manner that the major axis of the chamber 15a coincides with the center axis of the channel 13a as viewed from above. The above-described operation fluid 100 fills a substantially central portion of the chamber 15a with respect to the X-axis direction. A compressible fluid for pressure buffering (hereinafter may be referred to as a “compressible fluid”) 120 (having a compressibility considerably lower than that of the operation fluid 100) fills the peripheral portions of the chamber 15a. In the present embodiment, the compressible fluid 120 is vapor of the operation fluid 100. However, a predetermined amount of an inert gas may be mixed into the vapor, or the vapor may be replaced with a gas not containing the vapor.

[0082] The micro channel portion 16a forms a micro channel 16a1 which extends along the Z-axis direction and assumes the shape of a hollow cylinder. The micro channel 16a1 connects the left-hand operation chamber 13a1 of the channel 13a with the internal-pressure buffering chamber 15a. The micro channel 16a1 is also filled with the operation fluid 100. For example, the micro channel 16a1 has dimensions such that the cylinder has a radius of 15 &mgr;m, and the length along the Z-axis direction (height of the cylinder) is 100 &mgr;m. The shape of the micro channel 16a1 is selected to produce a fluid resistance greater than that produced by the channel 13a. Specifically, the micro channel 16a1 has a so-called throttle function which produces a high passage resistance against abrupt pressure change of the operation fluid 100 within the channel 13a, to thereby substantially prohibit passage (movement) of the operation fluid 100 toward the internal-pressure buffering chamber 15a, and which produces only a small passage resistance against slow pressure change of the operation fluid 100 within the channel 13a, to thereby substantially permit passage (movement) of the operation fluid 100 toward the internal-pressure buffering chamber 15a.

[0083] The micro channel portion 16b forms a micro channel 16b1, which has the same shape as the micro channel 16a1. The micro channel 16b1 connects the right-hand operation chamber 13a2 of the channel 13a with the internal-pressure buffering chamber 15a. The micro channel 16b1 is also filled with the operation fluid 100. The micro channel 16b1 also has a throttle function identical to that of the micro channel 16a1.

[0084] As described above, the operation fluid 100 continuously fills the channel 13a, the pair of pump chambers 14a and 14b, the pair of micro channels 16a1 and 16b1, and a portion of the internal-pressure buffering chamber 15a, which communicates with the channel 13a via the pair of micro channels 16a1 and 16b1. Further, the vapor 120 of the operation fluid 100 fills the spaces of the internal-pressure buffering chamber 15a that are not filled with the operation fluid 100.

[0085] Next, operation of the drive device 10 configured as described above will be described with reference to FIGS. 4 to 7, which show different operation states. FIG. 4 shows an initial state of the drive device 10 in which drive voltage is applied to none of the electrodes of the piezoelectric films 12a and 12b. In this case, since both the pump chambers 14a and 14b maintain their initial volumes, the operation fluid 100 charged into the pump chambers 14a and 14b and the channel 13a is neither pressurized or depressurized. Consequently, the movable body 110 accommodated within the channel 13a remains at the initial position (at the substantially central portion of the channel 13a with respect to the X-axis direction).

[0086] During drive, as shown in FIG. 5, a voltage is applied to the upper and lower electrodes of the piezoelectric film 12a disposed on the diaphragm 17a of the pump chamber 14a in such a manner that the upper electrode assumes a positive polarity and the lower electrode assumes a negative polarity. Simultaneously, a voltage is applied to the upper and lower electrodes of the piezoelectric film 12b disposed on the diaphragm 17b of the pump chamber 14b in such a manner that the upper electrode assumes a negative polarity and the lower electrode assumes a positive polarity.

[0087] As a result, the piezoelectric film 12a contracts along the transverse direction (i.e., in a plane substantially parallel to the X-Y plane, or in the direction perpendicular to the direction of the thickness D of the piezoelectric film 12a), so that the diaphragm 17a above the pump chamber 14a bends and deforms downward to thereby reduce the volume of the pump chamber 14a. As a result, the operation fluid 100 within the pump chamber 14a is pressurized, so that the operation fluid 100 flows from the pump chamber 14a to the operation chamber 13a1 of the channel 13a. Simultaneously, the piezoelectric film 12b expands along the transverse direction (i.e., in a plane substantially parallel to the X-Y plane), so that the diaphragm 17b bends and deforms upward to thereby increase the volume of the pump chamber 14b. As a result, the operation fluid 100 within the pump chamber 14b is depressurized, so that the operation fluid 100 flows from the operation chamber 13a2 of the channel 13a to the pump chamber 14b. Accordingly, due to the pressure difference between the pump chambers 14a and 14b, the movable body 110 accommodated within the channel 13a moves from the operation chamber 13a1 (pump chamber 14a) toward the operation chamber 13a2 (pump chamber 14b) (i.e., in the positive direction of the X-axis).

[0088] Further, when, as shown in FIG. 6, a voltage is applied to the upper and lower electrodes of the piezoelectric film 12a in such a manner that the upper electrode assumes a negative polarity and the lower electrode assumes a positive polarity, and simultaneously, a voltage is applied to the upper and lower electrodes of the piezoelectric film 12b in such a manner that the upper electrode assumes a positive polarity and the lower electrode assumes a negative polarity, the operation fluid 100 within the pump chamber 14b is pressurized, and the operation fluid 100 within the pump chamber 14a is depressurized. Due to the pressure difference, the movable body 110 moves from the operation chamber 13a2 (pump chamber 14b) toward the operation chamber 13a1 (pump chamber 14a) (i.e., in the negative direction of the X-axis).

[0089] During such ordinary driving, pressurization and depressurization of the pump chambers 14a and 14b are performed at high speed by varying the voltages applied to the piezoelectric films 12a and 12b at high speed (i.e., by having larger speed at which the applied voltages are increased and decreased). As a result, the passage resistances of the micro channels 16a1 and 16b1 become sufficiently large, and the operation fluid 100 within the channel 13a does not move to (go through), or return from, the micro channels 16a1 and 16b1. Therefore, the pressure difference generated between the operation chambers 13a1 and 13a2 of the channel 13a acts on the movable body 110 without decreasing (without generation of so-called pressure escaping). Accordingly, the movable body 110 moves without fail.

[0090] Incidentally, in the case of a drive device which does not include the micro channels 16a1 and 16b1 and the internal-pressure buffering chamber 15a, when the operation fluid 100 thermally expands due to an increase in the environment temperature of the drive device, the pressure of the operation fluid 100 becomes excessive, possibly raising a problem such that the pump chambers 14a and 14b increase in volume, and the diaphragms 17a and 17b are pushed up and broken. Further, in the case in which the base body 11 is formed of an assembly of bonded ceramic sheets, there may arise the problem such that a bonded portion (the seal of the bonded portion) is broken, and the operation fluid 100 leaks.

[0091] By contrast, the drive device 10 according to the present invention is provided with the micro channels 16a1 and 16b1 and the internal-pressure buffering chamber 15a. In addition, since the temperature increase of the operation fluid 100 occurs slowly, the pressure of the operation fluid 100 increases slowly. Accordingly, as indicated by arrows in FIG. 7, an amount of the operation fluid 100 corresponding to expansion due to temperature elevation flows into the internal-pressure buffering chamber 15a via the micro channels 16a1 and 16b1, which produce an extremely low passage resistance against such slow increase in pressure of the operation fluid 100. Within the internal-pressure buffering chamber 15a, the vapor 120 of the operation fluid 100 is compressed, and pressure increase occurs. However, the pressure increase of the operation fluid 100 is slight, because the compressibility of gas is lower than that of liquid. Accordingly, there can be avoided the situation in which the diaphragms 17a and 17b above the pump chambers 14a and 14b are pushed up and broken and the situation in which a seal of the bond-assembled portion is broken, with resultant leakage of the operation fluid 100. Further, when the operation fluid 100 thermally contracts due to a decrease in the environmental temperature of the drive device 10, as indicated by arrows in FIG. 8, the operation fluid 100 returns from the internal-pressure buffering chamber 15a to the channel 13a via the micro channels 16a1 and 16b1, because the temperature decrease of the operation fluid 100 occurs slowly.

[0092] As described above, by virtue of provision of the micro channels 16a1 and 16b1 and the internal-pressure buffering chamber 15a, the drive device 10 can be used within a wide temperature range, and can have enhanced reliability and durability.

[0093] Next, an operation which the drive device 10 performs in the initial state in order to finely adjust the position of the movable body 110 will be described by reference to FIGS. 9 to 12. Here, it is assumed that, as shown in FIG. 9, in the initial state the movable body 110 remains at a position deviated to the side toward the piezoelectric film 12a. Such a state may result from variation, or erroneous work, involved in a fabrication process which will be described later; specifically, in a step of placing the movable body 110 in the channel 13a.

[0094] First, during a period of time from t1 to t2 shown in FIG. 10, voltages Va and Vb, which change at high speed, are applied to (the electrodes of) the piezoelectric films 12a and 12b, respectively. For example, the applied voltage Va is a drive voltage whose absolute value increases from 0 V to 50 V during a period of 1 to 20 &mgr;sec and which has a polarity such that the upper electrode becomes the positive side and the lower electrode becomes the negative side. Similarly, the applied voltage Vb is a drive voltage whose absolute value increases from 0 V to 50 V during a period of 1 to 20 &mgr;sec and which has a polarity such that the upper electrode becomes the negative side and the lower electrode becomes positive side. As a result, as shown in FIG. 11, the operation fluid 100 is pressurized in the pump chamber 14a and is depressurized in the pump chamber 14b, so that the movable body 110 moves toward the center (toward the pump chamber 14b). In this case, since the applied voltages Va and Vb change at high speed, the passage resistances of the micro channels 16a1 and 16b1 become sufficiently large, and thus the operation fluid 100 within the channel 13a does not move to, or return from, the micro channels 16a1 and 16b1.

[0095] Subsequently, during a short period of time from t2 to t3 shown in FIG. 10, the applied voltages Va and Vb are maintained constant; and during a subsequent period of time from t3 to t4, the absolutes values of the applied voltages Va and Vb are decreased slowly to 0 V over a period of, for example, about 0.1 to 1 sec. In this case, since the passage resistances of the micro channels 16a1 and 16b1 become small, as shown in FIG. 12, the operation fluid 100 within the right-hand operation chamber 13a2 of the channel 13a flows into the internal-pressure buffering chamber 15a via the micro channel 16b1, and the operation fluid 100 within the internal-pressure buffering chamber 15a flows into the left-hand operation chamber 13a1 of the channel 13a via the micro channel 16a1. That is, the pressure change of the operation fluid 100 becomes sufficiently slow such that pressure escapes via the micro channels 16a1 and 16b1, and the internal pressure of the pump chamber 14a and 14b and the channel 13a hardly changes. Thus, the movable body 110 can be maintained stationary. Alternatively, as compared with the moving distance L0 of the movable body 110 upon application of voltages during the period of t1 to t2, the return distance L1 of the movable body 110 during the period of t3 to t4 can be reduced to about one-tenth (L1=L0/10).

[0096] Through performing the above-described operation once or a plurality of times, the movable body 110 can be positioned at a desired initial position. Further, the movable body 110 can be moved to stop at a desired position through appropriate selection of the peak values Vp and −Vp of the applied voltages Va and Vb shown in FIG. 10, the voltage change speed at which the applied voltages Va and Vb are changed to the peak values Vp and −Vp, and the voltage change speed at which the applied voltages Va and Vb are changed from the peak values Vp and −Vp to 0 V.

[0097] In the above-described embodiment, through application of voltages to the piezoelectric films 12a and 12b, electric fields are applied to the piezoelectric films 12a and 12b in the positive direction (in the present embodiment, Z-axis positive direction) and the negative direction (Z-axis negative direction), respectively. However, in some cases, application of such electric fields is not desirable, because an electric field of a direction opposite the polarization direction of the piezoelectric films 12a and 12b cancels the polarization if the intensity of the electric field exceeds that of a coercive field. In view of this, a bias voltage may be applied so as to establish the initial state of the drive device 10. In this case, the drive device 10 can be driven through use of electric fields of the same direction as that of the polarization. Specifically, for example, the potential of the lower electrode is maintained at 0 V, which is a reference potential, and a bias voltage of 25 V is applied to the upper electrode to establish an initial state. When the potential of the upper electrode of either one of piezoelectric film 12a or 12b is increased to 50 V, an electric field is applied to that piezoelectric film in the same direction as the polarization direction, so that the piezoelectric film contracts. As a result, the diaphragm 17a or 17b located under the piezoelectric film bends and deforms downward, and the corresponding pump chamber 14a or 14b pressurizes the operation fluid 100. Simultaneously, when the potential of the upper electrode of the other of the piezoelectric films 12a and 12b is decreased to 0 V, the contraction of that piezoelectric film is cancelled. Accordingly, the diaphragm 17a or 17b located under the piezoelectric film bends and deforms upward with respect to the initial state, and the corresponding pump chamber 14a or 14b depressurizes the operation fluid 100.

[0098] Next, a modification of the drive device according to the first embodiment will be described with reference to FIG. 13. The drive device 10-1 according to this modification differs from the drive device 10 shown in FIG. 1 only in that a base body 11-1 of the drive device 10-1 includes a single micro channel 16a1, whereas the base body 11 of the drive device 10 has the pair of micro channels 16a1 and 16b1. This configuration can be employed only in the case in which the gap (clearance S shown in FIG. 3) between the movable body 110 and the channel 13a can have a cross section equal to or greater than a predetermined value. Since this configuration can halve labor and time required to machine the micro channels, the drive device 10-1 can be fabricated at lower cost. However, in this modification, the stationary position of the movable body 110 in the initial state in which no voltage is applied to the drive device 10-1 is difficult to control. In relation to this point, the drive device 10 of the first embodiment is considered superior.

[0099] Note that in addition to the above-described gap (clearance S), a micro groove M may be formed in the wall surface of the channel 13a, as shown in, for example, FIG. 14, which shows a cross section of the channel 13a. The micro groove M may be configured in such a manner that the operation fluid 100 can enter the groove M insofar as the pressure change of the operation fluid 100 is slow and the surface of the movable body 110 cannot enter the micro groove M. Notably, the micro groove M can be applied to other embodiments of the present invention, and the number and shape of the micro grooves may be selected appropriately.

[0100] Further, the piezoelectric/electrostrictive film type actuator for a display device disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 10-78549 can be applied to the piezoelectric films 12a and 12b, the diaphragms 17a and 17b, and the pump chambers 14a and 14b of the above-described drive devices 10 and 10-1 (and drive devices of other embodiments which will be described later). Since this actuator is small and can produce a large pressurizing force, it is suitable for the drive device of the present invention. Further, when the drive operation which has been described with reference to FIGS. 4 to 6 is performed, an important consideration is that the piezoelectric films 12a and 12b be formed of a piezoelectric material which has a large coercive electric field, because of occurrence of a state in which voltage is applied to the piezoelectric films 12a and 12b in the direction opposite the polarization direction of the piezoelectric films 12a and 12b. When the intensity of a coercive electric field is low, the polarization may be disturbed through application of voltage in the direction opposite the polarization direction.

[0101] In order to reduce the amount of thermal expansion and contraction of the operation fluid 100 stemming from variation in the environmental temperature, it is desirable that the volumes of the pump chambers 14a and 14b be close to a minimum required value. In order to achieve this, the method disclosed in Japanese Patent Application Laid-Open (kokai) No. 9-229013 is preferably used to fabricate a diaphragm substrate used in the process of fabricating the above-described piezoelectric/electrostrictive film type actuator, because the disclosed method can reduce the depths of the pump chambers 14a and 14b to about 5 (minimum) to 10 &mgr;m.

[0102] Next, a drive device 20, which serves as a portion of a circuit changeover switch according to a second embodiment of the present invention, will be specifically described, together with a method of fabricating the device. FIG. 15 is a vertical sectional view of the drive device 20, and FIG. 16 is a plan view of the drive device 20. Notably, FIG. 15 is a sectional view of the drive device 20 taken along line 3-3 in FIG. 16. In the following description, the same structural portions in respective embodiments are denoted by the same reference numerals, and their detailed descriptions are not repeated.

[0103] The drive device 20 includes a base body 21 having a channel 13a which is formed to be exposed at the upper surface thereof; a connection plate (connection substrate) 22 disposed on the base body 21 and formed of a ceramic thin plate; and a pair of ceramic pumps 23a and 23b disposed on the connection plate 22.

[0104] The connection plate 22 includes left-hand and right-hand channel connection holes 22a and 22b, which are formed at positions separated from each other along the X-axis direction and each assume the shape of a hollow cylinder. The bottom ends of the channel connection holes 22a and 22b are connected to the opposite end portions of the channel 13a with respect to the X-axis direction.

[0105] The ceramic pumps 23a and 23b are each formed of a ceramic thin plate(s). The ceramic pumps 23a and 23b include pump-chamber forming portions 24a and 24b having a substantially square shape as viewed from above; and piezoelectric films 25a and 25b fixed to the upper surfaces of the pump-chamber forming portions 24a and 24b, respectively. The pump-chamber forming portions 24a and 24b include pump chambers 24a1 and 24b1 having a shape similar to that of the pump chambers 14a and 14b of the drive device 10 according to the first embodiment; thin-plate-shaped diaphragms 26a and 26b formed on the pump chambers 24a1 and 24b1, respectively; and pump-chamber connection holes 24a2 and 24b2 which each assume the shape of a hollow cylinder and which connect bottom portions of the pump chambers 24a1 and 24b1 with the upper portions of the channel connection holes 22a and 22b. The pump chambers 24a1 and 24b1 and the pump-chamber connection holes 24a2 and 24b2 are filled with the operation fluid 100 as in the case of the channel connection holes 22a and 22b and the channel 13a.

[0106] The ceramic pumps 23a and 23b are piezoelectric/electrostrictive film type actuators which are fabricated by utilization of the method and structure disclosed in Japanese Patent Application Laid-Open Nos. 10-78549 and 7-214779, etc. The ceramic pumps 23a and 23b are formed on the base body 21 serving as a channel substrate and the connection plate 22, in a stacked configuration.

[0107] The operation of the drive device 20 for driving (moving) the movable body 110 is the same as that of the drive device 10. Further, the operation of the drive device 20 for absorbing changes in the internal pressure due to thermal expansion and contraction of the operation fluid 100 charged into the pump chambers 24a1 and 24b1, the pump-chamber connection holes 24a2 and 24b2, the channel connection holes 22a and 22b, and the channel 13a is also the same as that of the drive device 10.

[0108] Next, a method of fabricating the drive device 20 will be described. First, a fabrication process of the ceramic pumps 23a and 23b, which are piezoelectric/electrostrictive film type actuators, will be described. As shown in FIG. 17, ceramic green sheets 201, 202, and 203 are prepared. Subsequently, by means of mechanical machining such as punching, a window portion 202a for forming the pump chamber 24a1 (24b1) is formed in the green sheet 202, and a hole portion 203a is formed in the green sheet 203. The hole portion 203a is to serve as the pump-chamber connection hole 24a2 (24b2) for connecting the pump chamber 24a1 (24b1) with the channel 13a via the channel connection hole 22a (22b).

[0109] Subsequently, the green sheets 201, 202, and 203 are stacked and heated under pressure to thereby be fired. Thus, the green sheets 201, 202, and 203 are integrated together to thereby form a diaphragm substrate 204. Subsequently, a lower electrode 205 and an auxiliary electrode 206 as disclosed in Japanese Patent Application Laid-Open (kokai) No. 5-267742 are formed on the substrate 204 The electrode 205 and the electrode 206 are formed from a high-melting-point metal and in accordance with a thick-film forming process, such as screen printing. If necessary, the substrate is subjected to heat treatment such as firing. A piezoelectric film 207 is formed on the electrodes in accordance with a thick-film forming process, and finally an upper electrode 208 is formed. In forming the upper electrode 208, a thin-film forming process such as sputtering may be used instead of the thick-film forming process. In the above-described manner, portions corresponding to the ceramic pumps 23a and 23b are fabricated.

[0110] FIG. 18 shows a different method for fabricating the portions corresponding to the above-described ceramic pumps 23a and 23b. In this method, during the process of fabricating the diaphragm substrate, in place of using the above-described green sheet 202, a spacer layer 202b is formed on the green sheet 203 by means of screen printing in such a manner that the spacer layer 202b has a window portion 202a for forming the pump chamber 24a1 (24b1) . The remaining portion is the same as that of the fabrication method having been described with reference to FIG. 17. The details of this fabrication method are disclosed in Japanese Patent Application Laid-Open No. 9-229013. The technique disclosed in the patent publication enables the depth of the pump chamber 24a1 (24b1) (the height of the hollow cylinder along the Z-axis direction in the assembled state) to be reduced to about 10 &mgr;m. Therefore, the diaphragm substrate (i.e., the ceramic pumps 23a and 23b) can have a pump chamber 24a1 (24b1) of small volume.

[0111] Next, a method of fabricating the base body (channel substrate) 21 will be described with reference to FIG. 19. First, an appropriate material is selected from plastic, glass, metal, and ceramics, and then substrates 211, 212, and 213 are made using the selected material. Subsequently, the channel 13a, the micro channels 16a1 and 16b1, and the internal-pressure buffering chamber 15a are formed in the substrates 211, 212, and 213, respectively. Further, an operation fluid injection hole 213a is formed in the substrate 213 in such a manner that the operation fluid injection hole 213a penetrates from the bottom wall surface of the internal-pressure buffering chamber 15a to the lower surface of the substrate 213. A machining method suitable for forming channels, etc. in the substrates 211, 212, and 213 is selected from among punching, etching, laser machining, coining, sandblasting, etc. Subsequently, the substrates 211, 212, and 213 are stacked and bonded by use of epoxy resin or the like to thereby complete the base body 21.

[0112] Notably, in order to make the thermal expansion coefficient of the base body 21 equal, to the extent possible, to that of the ceramic pumps 23a and 23b, which are piezoelectric/electrostrictive film type actuators, the substrates 211, 212, and 213 are preferably formed of ceramic or glass whose expansion coefficient is close to that of the ceramic pumps. Further, etching or coining is preferably used for depression machining; i.e., forming the channel 13a and the internal-pressure buffering chamber 15a having a depth of 200 &mgr;m. Alternatively, the substrate 211 having the channel 13a may be obtained through bonding plates each having a punched window portion corresponding to the channel 13a, and a closure plate. Similarly, the substrate 213 having the internal-pressure buffering chamber 15a may be obtained through bonding plates each having a punched window portion corresponding to the internal-pressure buffering chamber 15a, and a closure plate. Meanwhile, the micro channels 16a1 and 16b1, which must have a high aspect ratio, are preferably formed by means of laser machining or by means of a process of punching a ceramic green sheet in order to form holes having a high aspect ratio therein, and then firing the green sheet.

[0113] Meanwhile, as shown in FIG. 20, as in the case of the substrate 211, the pair of channel connection holes 22a and 22b are formed in a connection substrate 214, which is to serve as the connection plate 22; and finally, the ceramic pumps 23a and 23b (piezoelectric/electrostrictive film type actuators), the connection substrate 214, and the base body 21 are stacked and united by use of joining means such as adhesion-bonding, press-bonding, or diffusion joining.

[0114] During this process, the movable body 110 is placed at a predetermined position within the channel 13a. When the movable body 110 is a vacuole (liquid mass), a material that is insoluble against the vacuole is selected for the operation fluid 100, and the movable body 110 is placed at the predetermined position within the channel 13a by use of a dispenser or the like. When the movable body is a bubble, an injection hole for injecting a gas is branched from the channel 13a, and the bubble and the operation fluid 100 are injected into the channel 13a via the injection hole. There after, the injection hole is sealed.

[0115] Subsequently, the thus-obtained stacked product is placed under vacuum by use of, for example, a vacuum chamber, and a predetermined amount of the operation fluid 100 is injected from the injection hole 213a into the internal-pressure buffering chamber 15a by use of metering means such as a dispenser. Notably, before injection, the operation fluid 100 is preferably subjected to vacuum degassing in order to remove dissolved gases. In order to charge the injected operation fluid 100 into the channel 13a, the pump chambers 24a1 and 24b1, etc., via the micro channels 16a1 and 16b1, the pressure within the channel is increased to a predetermined level by means of a seal gas 120, which is a compressible fluid such as an inert gas, vapor of the operation fluid 100, or a mixture thereof. Finally, the injection hole 213a is sealed by use of adhesive or the like to thereby obtain the drive device 20 of the present invention.

[0116] Notably, the depth (height along the Z-axis direction) of the internal-pressure buffering chamber 15a is desirably rendered greater than the depth of the pump chambers 24a1 and 24b1, as well as greater than the depth of the channel 13a, so as to enable smooth charging. With this configuration, when the operation fluid 100 is liquid, the radius of curvature of the gas-liquid interface within the internal-pressure buffering chamber 15a becomes greater than those of the gas-liquid interfaces formed within the pump chambers 24a1 and 24b1 and the channel 13a under charging, whereby charging can be performed more smoothly.

[0117] Next, a drive device 30, which serves as a portion of a circuit changeover switch according to a third embodiment of the present invention, will be described. As shown in FIG. 21, which shows a vertical cross section of the drive device 30, the drive device 30 differs from the drive device 20 of the second embodiment shown in FIG. 15 only in that the two pump-chamber forming portions 24a and 24b of the two ceramic pumps 23a and 23b (piezoelectric/electrostrictive film type actuators) are replaced with a single pump-chamber forming portion 24c and in that the connection plate 22 provided in the drive device 20 is omitted. The drive device 30 can achieve the effect of lowering fabrication cost, by virtue of employing fewer bonded portions and components. In the drive device 20 shown in FIG. 15, the connection plate 22 can be formed of a transparent glass or a metal plate which also serves as an electrode. However, in the drive device 30 shown in FIG. 21, since the connection plate 22 does not exist, the material of the pump-chamber forming portion 24c is restricted to the material of the ceramic substrate of the piezoelectric/electrostrictive film type actuators.

[0118] Next, a drive device 40, which serves as a portion of a circuit changeover switch according to a fourth embodiment of the present invention, will be described. In the drive device 40, whose vertical cross section is shown in FIG. 22, a base body 41 includes a porous member 16c in place of the micro channels 16a1 and 16b1 of the drive device 20 of the second embodiment shown in FIG. 15; and the channel 13a and the internal-pressure buffering chamber 15a are connected together via the porous member 16c. Provision of the porous member 16c achieves the same effect as that obtained through formation of a large number of extremely fine (thin) micro channels 16a1 and 16b1. In order to facilitate assembly and improve seal performance, the porous member 16c preferably has a tapered or stepped side surface, as shown in FIG. 22.

[0119] Next, a drive device 50, which serves as a portion of a circuit changeover switch according to a fifth embodiment of the present invention, will be described. FIG. 23 is a vertical sectional view of the drive device 50, and FIG. 24 is a plan view of the drive device 50. Notably, FIG. 23 is a sectional view of the drive device 50 taken along line 4-4 in FIG. 24. In the drive device 50, in place of the piezoelectric film 25b of the ceramic pump 23b provided in the drive device 30 shown in FIG. 21, a ceramic pump 23c having a pair of piezoelectric films 25c1 and 25c2 is provided. Like the piezoelectric film 25a, the piezoelectric films 25c1 and 25c2 are polarized in the positive direction of the Z-axis.

[0120] The piezoelectric films 25c1 and 25c2 each assume an elliptical shape having a long axis along the Y-axis direction as viewed from above. The piezoelectric films 25c1 and 25c2 are fixed onto the diaphragm 26b, which is a ceramic thin plate, in such a manner that their long axes become parallel to each other while being separated by a predetermined distance along the direction of the X-axis. A pump chamber 27, which is formed under the diaphragm 26b, assumes an elliptical shape having its long axis along the Y-axis direction as viewed from above, as in the case of the piezoelectric films 25c1 and 25c2. The piezoelectric films 25c1 and 25c2 are disposed in such a manner that they sandwich the pump chamber 27 as viewed from above, and that about one-half of the piezoelectric film 25c1 and one-half of the piezoelectric film 25c2 overlap the pump chamber 27 as viewed from above. The pump chamber 25a is also formed such that it assumes an elliptical shape having a long axis along the Y-axis direction as viewed from above.

[0121] Next, operation of the drive device 50 configured as described above will be described. As shown in FIG. 25, voltages of the same polarity are applied to the piezoelectric films 25c1 and 25c2 and the piezoelectric film 25a. That is, a drive voltage which changes at high speed is applied to each of the piezoelectric films 25a, 25c1, and 25c2 in such a manner that a positive voltage is applied to the upper electrode and a negative voltage is applied to the lower electrode. Thus, the diaphragm 26a bends and deforms downward due to contraction of the piezoelectric film 25a. In contrast, the diaphragm 26b displaces upward at the central portion due to contraction of the piezoelectric films 25c1 and 25c2. As a result, the operation fluid 100 is pressurized in the pump chamber 24a1 and is depressurized in the pump chamber 27, so that the movable body 110 moves from the pump chamber 24a1 toward the pump chamber 27 (in the positive direction of the X-axis)

[0122] Piezoelectric/electrostrictive film type actuators (ceramic pumps) which operate in the above-described manner are disclosed in Japanese Patent Application Laid-Open (kokai) No. 7-202284. Unlike the case of first through fourth embodiments, in the fifth embodiment (drive device 50), voltages of constant polarity are applied to the piezoelectric films 25c1, 25c2, and 25a, and the piezoelectric films 25c1, 25c2, and 25a can be driven at all times in the same polarity as that of the polarization electric field thereof. Therefore, the piezoelectric films 25c1, 25c2, and 25a can be formed of a material of weak coercive field. Further, it should be understood that even in the case in which the drive device is configured in such a manner that one of the pair of pumps can provide only pressurization or both pressurization and depressurization and the other pump can provide depressurization only, and the pumps are operated in such a manner, the drive device may sufficiently provide required functions and performance. By contrast, when the pump structure of the drive devices 10, 20, 30, and 40 of the first through fourth embodiments is employed, film of an electrostrictive material cannot be used as a piezoelectric film of a pump which provides depressurization only, unless a special drive scheme, such as application of bias voltage, is employed. This is because an electrostrictive material does not expand, irrespective of the direction of an applied electric field, although it contracts along a direction perpendicular to the applied electric field, and therefore, the electrostrictive material cannot bend or deform a diaphragm upward. By contrast, in the case of the piezoelectric films 25c1 and 25c2 of the pump 23c of the drive device 50 according to the fifth embodiment, since the piezoelectric films 25c1 and 25c2 can bend and deform the diaphragm 26b upward through their contracting actions to thereby reduce the internal pressure of the pump chamber 27, film of an electrostrictive material can be used as the piezoelectric films 25c1 and 25c2.

[0123] Notably, as shown in FIG. 26, there may be provided a necessary number of pumps 23d which are similar to the pump 23c and which have pump chambers of an appropriate shape, depending on the performance of each device. In such a case, if a configuration for driving the pumps individually is employed, the differential pressure acting on the movable body 110 can be adjusted by, for example, properly changing the number of driven pumps, to thereby control the amount of movement and/or moving speed of the movable body 110.

[0124] Next, an example application of the above-described circuit changeover switches (drive devices) of the first to fifth embodiments will be described. A circuit changeover switch 60 shown in FIG. 27 includes the above-described drive device 10, and is provided with a common electrode 61 formed of platinum, gold, nickel, or any other suitable material, and a pair of changeover electrodes 62a and 62b formed of platinum, gold, nickel, or any other suitable material.

[0125] The common electrode 61 is formed on a lower wall surface (wall surface on the negative side with respect to the Z-axis direction) 13a-1, which is one of the wall surfaces constituting the channel 13a, in such a manner that the common electrode 61 is exposed to the channel 13a at a position between the micro channels 16a1 and 16b1. The common electrode 61 is electrically connected to an external electric component via an unillustrated connection line (terminal electrode) so that the electrical potential of the common electrode 61 is transmitted to the electric component.

[0126] The changeover electrodes 62a and 62b have the same shape and are formed on an upper wall surface (wall surface on the positive side with respect to the Z-axis direction) 13a-2, which is another one of the wall surfaces constituting the channel 13a, in such a manner that the changeover electrodes 62a and 62b are exposed to the channel 13a so as to face the common electrode 61. The changeover electrodes 62a and 62b are mutually separated along the X-axis direction. The changeover electrodes 62a and 62b are electrically isolated from each other, and electrically connected to the external electric component via unillustrated connection lines (terminal electrodes) so that their electrical potentials are transmitted to the electric component. Notably, in the following description, the changeover electrode 62a will be called the first changeover electrode 62a, and the changeover electrode 62b will be called the second changeover electrode 62b.

[0127] The movable body 110 is formed of an electrically conductive liquid metal such as mercury or Ga-base alloy and has a size substantially the same as that of the first changeover electrode 62a (or the second changeover electrode 62b) when viewed from the side. The movable body 110 moves within the channel 13a while maintaining contact with the common electrode 61, and selectively comes into contact with the first changeover electrode 62a or the second changeover electrode 62b. In other words, the first changeover electrode 62a and the second changeover electrode 62b are electrically connected to the common electrode 61 via the movable body 110.

[0128] Next, operation of the circuit changeover switch 60 will be described. FIG. 27 shows an initial state of the drive device 10 in which drive voltage is applied to none of the electrodes of the piezoelectric films 12a and 12b. In this state, the movable body 110 comes into contact with the first changeover electrode 62a and the common electrode 61 and does not come into contact with the second changeover electrode 62b. Thus, the first changeover electrode 62a and the common electrode 61 are electrically connected to each other. Notably, the position of the movable body 110 in such an initial state is adjusted by the method having been described with reference to FIGS. 9 to 12.

[0129] Meanwhile, during drive, as shown in FIG. 28, a voltage is applied to the upper and lower electrodes of the piezoelectric film 12a by means of an unillustrated control circuit in such a manner that the upper electrode assumes a positive polarity and the lower electrode assumes a negative polarity. Simultaneously, a voltage is applied to the upper and lower electrodes of the piezoelectric film 12b in such a manner that the upper electrode assumes a negative polarity and the lower electrode assumes a positive polarity. As a result of application of the drive voltage, the pump chambers 14a and 14b operate; and by virtue of a pressure difference of the operation fluid 100 generated upon operation of the pump chambers 14a and 14b, the movable body 110 moves from the operation chamber 13a1 (pump chamber 14a) toward the operation chamber 13a2 (pump chamber 14b) (i.e., in the positive direction of the X-axis) up to a position where the movable body 110 comes into contact with the second changeover electrode 62b, to thereby electrically connect the second changeover electrode 62b and the common electrode 61.

[0130] Subsequently, the control circuit removes the drive voltage applied to the respective electrodes of the piezoelectric films 12a and 12b. As a result, the pump chambers 14a and 14b return to their original states; and, by virtue of a pressure difference of the operation fluid 100 generated while the pump chambers 14a and 14b return to their original states, the movable body 110 moves from the operation chamber 13a2 toward the operation chamber 13a1 (i.e., in the negative direction of the X-axis) up to a position where the movable body 110 comes into contact with the first changeover electrode 62a, to thereby electrically connect the first changeover electrode 62a and the common electrode 61.

[0131] As described above, the circuit changeover switch 61 selectively connects the first changeover electrode 62a or the second changeover electrode 62b to the common electrode 61 in order to establish electrical continuity therebetween, by moving the movable body 110. The movable body 110 exhibits a higher degree of wettability for each of the first and second changeover electrodes 62a and 62b and a lower degree of wettability for the wall surface of the channel 13a at portions where the first and second changeover electrodes 62a and 62b are not provided. Therefore, the movable body 110 reliably maintains contact with the first changeover electrodes 62a in the initial state and contact with the second changeover electrodes 62b in the driven state.

[0132] Next, a specific application of the above-described circuit changeover switch 60 will be described with reference to FIG. 29. The system shown in FIG. 29 includes two circuit changeover switches each having the same structure as that of the circuit changeover switch 60. These switches are used as a diversity antenna changeover switch and a transmission/reception changeover switch of a portable information terminal called PDA (Personal Digital Assistant) that is configured to enable radio communications.

[0133] More specifically, the system includes a main antenna 301, a diversity antenna 302, a diversity antenna changeover switch 303 having the same structure as that of the circuit changeover switch 60, d transmission/reception changeover switch 304 having the same structure as that of the circuit changeover switch 60, a power amplifier 305, an RF-IF converter 306, an IF modem 307, and a baseband processor 308.

[0134] The main antenna 301 and the diversity antenna 302 are electrically connected to a first changeover electrode 303a and a second changeover electrode 303b, respectively, of the diversity antenna changeover switch 303. A common electrode 303c of the diversity antenna changeover switch 303 is electrically connected to a common electrode 304c of the transmission/reception changeover switch 304. A first changeover electrode 304a of the transmission/reception changeover switch 304 is electrically connected to the RF-IF converter (radio frequency—intermediate frequency converter) 306; and a second changeover electrode 304b of the transmission/reception changeover switch 304 is electrically connected to the power amplifier 305. The baseband processor 308 is electrically connected to the RF-IF converter 306 via the IF modem 307 and is electrically connected to the power amplifier 305. The power amplifier 305 is further connected to the RF-IF converter 306. The upper and lower electrodes of the respective piezoelectric films of the diversity antenna changeover switch 303 and the transmission/reception changeover switch 304 are connected to an unillustrated control circuit.

[0135] Next, operation of the system will be described. When the system is in a “reception wait state” in which the system awaits arrival of radio waves from the outside, the control circuit does not apply any drive voltage to the upper and lower electrodes of the respective piezoelectric films of the diversity antenna changeover switch 303. As a result, the diversity antenna changeover switch 303 maintains its initial state, and a movable body 303d of the switch 303 stays at the position shown in FIG. 29 in order to maintain connection between the first changeover electrode 303a and the common electrode 303c.

[0136] When the system is in the reception wait state, the control circuit does not apply any drive voltage to the upper and lower electrodes of the respective piezoelectric films of the transmission/reception changeover switch 304. As a result, the transmission/reception changeover switch 304 maintains its initial state, and a movable body 304d of the switch 304 stays at the position shown in FIG. 29 in order to maintain connection between the first changeover electrode 304a and the common electrode 304c.

[0137] As described above, the present system operates in such a manner that when the system in the reception wait state, the diversity antenna changeover switch 303 and the transmission/reception changeover switch 304 electrically connect the main antenna 301 to the RF-IF converter 306 without consuming electrical power.

[0138] In a reception mode, the control circuit selects from the main antenna 301 and the diversity antenna 302 an antenna suitable for reception (e.g., an antenna which provides high received-radio-wave intensity) . When the main antenna 301 is selected, the control circuit does not apply any drive voltage to the upper and lower electrodes of the respective piezoelectric films of the diversity antenna changeover switch 303. As a result, the diversity antenna changeover switch 303 maintains its initial state, and the movable body 303d of the switch 303 stays at the position shown in FIG. 29 in order to maintain connection between the first changeover electrode 303a and the common electrode 303c.

[0139] In contrast, when the diversity antenna 302 is selected, the control circuit applies drive voltages to the upper and lower electrodes of the respective piezoelectric films of the diversity antenna changeover switch 303. As a result, the movable body 303d of the diversity antenna changeover switch 303 moves rightward in FIG. 29 in order to electrically connect the second changeover electrode 303b and the common electrode 303c. Thus, there is established a state in which the diversity antenna 302 can be electrically connected to the RF-IF converter 306 or the power amplifier 305. Further, in accordance with needs, the control circuit applies drive voltages to the upper and lower electrodes of the respective piezoelectric films of the transmission/reception changeover switch 304 in order to move the movable body 304d of the transmission/reception changeover switch 304 leftward in FIG. 29, to thereby connect the common electrode 304c to the power amplifier 305 via the movable body 304d and the second changeover electrode 304b. As a result, the received signal is amplified to an appropriate level. Notably, the control circuit may be configured in such a manner that no drive voltage is applied to the upper and lower electrodes of the respective piezoelectric films of the transmission/reception changeover switch 304 throughout the entire reception period, in order to maintain the switch 304 in the initial state.

[0140] Further, the control circuit may be configured in such a manner that in the above-described reception wait state as well, the control circuit selects an appropriate antenna as in the reception mode. Even in the case where the control circuit is configured in the above-described manner, the diversity antenna changeover switch 303 can maintain the reception wait state without consuming electrical power, at least when the main antenna 301 is determined (selected) to be an appropriate antenna.

[0141] In a transmission mode, the control circuit does not apply any drive voltage to the upper and lower electrodes of the respective piezoelectric films of the diversity antenna changeover switch 303, whereby the diversity antenna changeover switch 303 selects the main antenna 301 as a transmission antenna. Further, the control circuit applies drive voltages to the upper and lower electrodes of the respective piezoelectric films of the transmission/reception changeover switch 304 in order to connect the common electrode 304c to the power amplifier 305 via the movable body 304d and the second changeover electrode 304b. As a result, a transmission signal amplified by the power amplifier 305 is transmitted from the main antenna 301. Of course, in the transmission mode as well, drive voltages may be applied to the upper and lower electrodes of the respective piezoelectric films of the diversity antenna changeover switch 303 so as to select the diversity antenna 302 through the diversity antenna changeover switch 303.

[0142] Next, a circuit changeover switch 70 according to the present invention which includes a drive device 20′ similar to the drive device 20 will be described with reference to FIG. 30. In the circuit changeover switch 70, a common electrode 71, a first changeover electrode 72a, and a second changeover electrode 72b, which are similar to those of the circuit changeover switch 60, are provided on the drive device 20′. The circuit changeover switch 70 operates in the same manner as the circuit changeover switch 60.

[0143] A method of fabricating the circuit changeover switch 70 will be described. The ceramic pumps 23a and 23b, which are piezoelectric/electrostrictive film-type actuators, are fabricated by the method illustrated in FIG. 17 or FIG. 18. A substrate 21′ is fabricated by the fabrication method illustrated in FIG. 31. The fabrication method illustrated in FIG. 31 is identical with the fabrication method illustrated in FIG. 19, except that before lamination and bonding of the substrate 211, a substrate 212′ corresponding to the substrate 212, and a substrate 213′ corresponding to the substrate 213, a terminal electrode 71a for leading out (providing) electrical potential of the common electrode 71, a terminal electrode 72a1 for leading out (providing) electrical potential of the first changeover electrode 72a, and a terminal electrode 72b1 for leading out (providing) electrical potential of the second changeover electrode 72b are formed on the upper surface of the substrate 212′ by means of a thick-film forming technique such as screen printing.

[0144] Subsequently, the circuit changeover switch 70 is fabricated by the fabrication method illustrated in FIG. 32. The fabrication method illustrated in FIG. 32 is identical with the fabrication method illustrated in FIG. 20, except that the first changeover electrode 72a and the second changeover electrode 72b are formed on the lower surface of a substrate 214′ corresponding to the substrate 214, by means of a thick-film forming technique such as screen printing, and that the first changeover electrode 72a and the second changeover electrode 72b are electrically connected to the terminal electrodes 72a1 and the terminal electrode 72b1, respectively, by use of, for example, electrically conductive adhesive, when the ceramic pumps 23a and 23b, the connection substrate 214′, and the substrate 21′ are laminated and unified by coupling means such as bonding, compression bonding, or diffusion joining. In this manner, the circuit changeover switch 70 is fabricated.

[0145] As described above, a small switch or small relay can be fabricated through modification of the drive device of the present invention in such a manner that the movable body 110 is formed of a liquid droplet of liquid metal; and a plurality of electrodes 62a, 62b, etc., which are connected to an external circuit by means of lead wires, are provided on the wall surfaces of the channel 13a.

[0146] An example of such a switch is a mercury micro relay of a type which realizes switching operation through movement of a mercury droplet and which utilizes, as a drive force for moving the mercury droplet, pressure created upon instantaneous generation of a bubble by means of heating by a micro heater (see, for example, J. Kim et al., Proc. 46th Annual Int. Relay Conf., Oak Brook, Ill., April 1998, pp. 19-1-19-8). This switch is reported to have various features such as a wide frequency range of DC to 10 GHz, high insulating resistance and low insertion loss in the GHz band, and no signal bounce.

[0147] In contrast with such a conventional switch, the above-described circuit changeover switch of the present invention utilizes piezoelectric/electrostrictive actuators for generating drive force for moving the movable body 110, which is a droplet of mercury. As a result, as compared with the above-described mercury micro relay of the type which utilizes pressure at the time of generation of a bubble, the above-described circuit changeover switch of the present invention has advantages of no heat accumulation and reduced consumption of electrical power. Therefore, as having been described with reference to FIG. 29, the circuit changeover switch of the present invention can be suitably used in, for example, PDAs, which have recently been developed to improve functions and capability of radio communications, in order to serve as an antenna changeover switch for switching antennas used for both reception and sending (transmission), a circuit changeover switch for selectively connecting one of a sending (transmission) circuit and a reception circuit to an antenna, or any other switch.

[0148] When the circuit changeover switch of the present invention is used in the above-described application, unlike conventional semiconductor switches, the circuit changeover switch of the present invention provides the following advantages. (a) Since standby or idle electrical power is not consumed unless reception or transmission is performed, the overall electrical power consumption of the system can be reduced, and battery life can be extended. (b) Transmission and reception signals hardly deteriorate even in a high frequency band of 1 GHz or higher or even 5 GHz or higher. Further, as compared with a wet-type mercury lead switch, the circuit changeover switch of the present invention has advantages in that no restriction is imposed on inclination angle during use, and a greatly extended life is attained, because the drive sections (movable sections such as pump chambers) are integrally formed of ceramic.

[0149] Additionally, the circuit changeover switch of the present invention is suitable for use as a DC changeover switch. In other words, application of the circuit changeover switch of the present invention is not limited to switches for high frequency bands.

[0150] Although the common electrode 61 (71) of the above-described circuit changeover switch 60 (70) has been described as being a single electrode, the common electrode 61 (71) is preferably divided into two pieces corresponding to the first changeover electrode 62a (72a) and the second changeover electrode 62b (72b) (i.e., an electrode 61a facing the first changeover electrode 62a and an electrode 61b facing the second changeover electrode 62b are provided), as shown in FIG. 33; and the electrodes 61a and 61b are electrically connected together outside the circuit changeover switch 60 (70). This configuration is preferable, because the movable body 110, which is formed of, for example, mercury having a high degree of wettability for the electrode surfaces, can move within the channel 13a with reduced resistance. Further, the first and second changeover electrodes and the common electrodes may be exposed to any wall surface (upper surface, lower surface, side wall surface) of the channel, so long as the insulation among the electrodes is secured.

[0151] Next, a drive device 500, which serves as a portion of a circuit changeover switch according to a sixth embodiment of the present invention, will be described. FIG. 34 is a plan view of the drive device 500; and FIG. 35 is a sectional view of the drive device 500 taken along line A5-A5 in FIG. 34. The drive device 500 differs from the drive device 10 of the first embodiment mainly in that an internal-pressure buffering chamber is provided at the same vertical position as that of the channel and that micro channels extend along the Y-axis (maintaining the same vertical position) so as to connect the channel and the internal-pressure buffering chamber.

[0152] Specifically, the drive device 500 comprises a ceramic base body 501 of a substantially rectangular parallelepiped shape having sides which respectively extend along the X-axis, Y-axis, and Z-axis directions, which are mutually perpendicular; and a pair of piezoelectric films (piezoelectric/electrostrictive elements) 502a and 502b. As shown in FIG. 35, the base body 501 is formed through a process of successively laminating thin plates of ceramic (hereinafter referred to as “ceramic sheets”) 501-1 to 501-4 and firing the resultant laminate in such a manner that the base body 501 contains therein a channel forming portion 503, a pair of pump chambers 504a and 504b, an internal-pressure-buffering-chamber-forming portion 505, and a pair of micro channel portions 506a and 506b.

[0153] The channel forming portion 503 forms a channel 503a similar to the channel 13a of the drive device 10 according to the first embodiment. The channel 503a is a hollow space which is defined by side wall surfaces of a substantially rectangular parallelepiped through hole formed in the ceramic sheet 501-2, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 501-3. The space has a substantially rectangular parallelepiped shape having sides extending along the X-axis, Y-axis, and Z-axis directions, respectively, and has a long axis along the X-axis direction (a rectangular columnar space whose longitudinal axis lies in a plane parallel to the X-Y plane). As in the case of the channel 13a, an operation fluid 100 and a movable body 110 are accommodated within the channel 503a, whereby the channel 503a is divided substantially into two operation chambers 503a1 and 503a2 by means of the movable body 110. Within the channel 503a, the movable body 110 is present in the form of a single mass and forms very small clearances S at the four corners of the rectangular cross section of the channel 503a in order to permit passage of the operation fluid 100 therethrough (see FIG. 3). Notably, a groove similar to the groove M shown in FIG. 14 may be formed on the wall of the channel 503a.

[0154] The pump chambers 504a and 504b are similar to the pump chambers 14a and 14b, respectively, of the drive device 10. The pump chambers 504a and 504b are cylindrical spaces defined by side wall surfaces of through holes formed in the ceramic sheet 501-3, the upper surface of the ceramic sheet 501-2, and the lower surface of the ceramic sheet 501-4. Thin-plate shaped ceramic diaphragms 507a and 507b formed of the ceramic sheet 501-4 are provided above the pump chambers 504a and 504b, respectively. In other words, the diaphragms 507a and 507b are disposed to constitute respective walls (upper walls) of the pump chambers 504a and 504b (the diaphragms 507a and 507b constitute portions of the walls of the pump chambers 504a and 508b and to have respective film surfaces in a common X-Y plane. The ceramic diaphragms 507a and 507b are identical in configuration with the diaphragms 17a and 17b of the above-described drive device 10.

[0155] The piezoelectric film 502a is formed on the upper surface of the diaphragm 507a, and constitutes a ceramic pump 508a together with the pump chamber 504a and the diaphragm 507a. The piezoelectric film 502b is formed on the upper surface of the diaphragm 507b, and constitutes a ceramic pump 508b together with the pump chamber 504b and the diaphragm 507b. The ceramic pumps 508a and 508b are identical in configuration with the ceramic pumps 18a and 18b of the drive device 10. When a voltage is applied to unillustrated paired electrodes for the piezoelectric film 502a (502b), the piezoelectric film 502a (502b) deforms the diaphragm 507a (507b) in order to increase or decrease the volume of the pump chamber 504a (504b), to thereby pressurize or depressurize the operation fluid 100 within the pump chamber 504a (504b). Notably, the piezoelectric films 502a and 502b are each polarized in the positive direction of the Z-axis.

[0156] The internal-pressure-buffering-chamber-forming portion 505 forms an internal-pressure buffering chamber 505a. As in the case of the channel 503a, the internal-pressure buffering chamber 505a is a hollow space which is defined by side wall surfaces of a through hole of the ceramic sheet 501-2, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 501-3. The space has a substantially rectangular parallelepiped shape having sides extending along the X-axis, Y-axis, and Z-axis directions, respectively, and has a long axis along the X-axis direction (a rectangular columnar space whose longitudinal axis lies in a plane parallel to the X-Y plane in which the film surfaces of the diaphragms 507a and 507b are present; i.e., a rectangular columnar space having a long axis which is parallel to the long axis of the channel 503a and is located at the same vertical position as the long axis of the channel 503a). The internal-pressure buffering chamber 505a is formed at a position separated from the channel 503a in the Y-axis negative direction. The length of the internal-pressure buffering chamber 505a as measured along the X-axis direction is greater than that of the channel 503a; the length (width) of the internal-pressure buffering chamber 505a as measured along the Y-axis direction is greater than that of the channel 503a; and the length (height) of the internal-pressure buffering chamber 505a as measured along the Z-axis direction is equal to that of the channel 503a. A substantially central portion of the chamber 505a with respect to the X-axis direction is filled with the above-described operation fluid 100; and the peripheral portions thereof are filled with the above-described compressible fluid for pressure buffering 120.

[0157] The micro channel portion 506a forms a micro channel 506a1. As in the case of the pump chambers 504a and 504b, the micro channel 506a1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 501-3, the upper surface of the ceramic sheet 501-2, and the lower surface of the ceramic sheet 501-4 and which has a long axis along the Y-axis direction. The micro channel 506a1 connects a left-hand operation chamber 503a1 (an upper portion of the operation chamber 503a1) of the channel 503a with the internal-pressure buffering chamber 505a (an upper portion of the internal-pressure buffering chamber 505a). In other words, the micro channel 506a1 extends only along a direction (Y-axis direction) parallel to the X-Y plane in which the film surfaces of the diaphragms 507a and 507b are present, to thereby connect the flow chamber 503a with the internal-pressure buffering chamber 505a. The micro channel 506a1 is also filled with the operation fluid 100.

[0158] For example, the micro channel 506a1 has specific dimensions such that when the micro channel 506a1 is sectioned along a plane (i.e., an X-Z plane) perpendicular to the long axis, the height (length as measured along the Z-axis direction) of the rectangular cross section is 10 &mgr;m, and the width (length as measured along the X-axis direction) of the rectangular cross section is 10 &mgr;m, and that the length as measured along the Y-axis direction (excluding a portion above the channel 503a and a portion above the internal-pressure buffering chamber 505a) is 500 &mgr;m. As in the case of the micro channel 16a1, the shape and the dimensions of the micro channel 506a1 are selected in such a manner that a high passage resistance is produced against abrupt pressure change of the operation fluid 100 within the channel 503a in order to substantially prohibit passage (movement) of the operation fluid 100 toward the internal-pressure buffering chamber 505a, and only a small passage resistance is produced against slow pressure change of the operation fluid 100 within the channel 503a, in order to substantially permit passage (movement) of the operation fluid 100 toward the internal-pressure buffering chamber 505a (that is, the shape and the dimensions of the micro channel 506a1 are selected so as to provide a throttle function).

[0159] The micro channel portion 506b forms a micro channel 506b1 having the same shape as that of the micro channel 506a1 at a position separated from the micro channel 506a1 by a predetermined distance along the X-axis direction. The micro channel 506b1 extends only along a direction (Y-axis direction) parallel to the X-Y plane in which the film surfaces of the diaphragms 507a and 507b are present, to thereby connect a right-hand operation chamber 503a2 (an upper portion of the operation chamber 503a2) of the channel 503a with the internal-pressure buffering chamber 505a (an upper portion of the internal-pressure buffering chamber 505a). The micro channel 506b1 is also filled with the operation fluid 100. That is, the micro channel 506b1 also extends only along the direction (Y-axis direction) parallel to the X-Y plane in which the film surfaces of the diaphragms 507a and 507b are present, connects the flow chamber 503a with the internal-pressure buffering chamber 505a, and has the throttle function described in connection with the micro channel 506a1.

[0160] As described above, the operation fluid 100 continuously fills the channel 503a, the pair of pump chambers 504a and 504b, the pair of micro channels 506a1 and 506b1, and a portion of the internal-pressure buffering chamber 505a, which communicates with the channel 503a via the pair of micro channels 506a1 and 506b1. Further, the compressible fluid for pressure buffering 120 fills the spaces of the internal-pressure buffering chamber 505a that are not filled with the operation fluid 100.

[0161] The operation of the drive device 500 for driving (moving) the movable body 110 is the same as that of the drive device 10. Further, the operation of the drive device 500 for absorbing changes in the internal pressure of the channel 503a resulting from thermal expansion and contraction of the operation fluid 100 is also the same as that of the drive device 10.

[0162] The thickness (height or length as measured along the Z-axis direction) of the drive device 500 of the sixth embodiment can be very small (reduced), because the drive device 500 is configured to have the micro channels 506a1 and 506b1 each having a long axis along the Y-axis direction, to have the channel 503a and the internal-pressure buffering chamber 505a formed at the same vertical position (in the common plane or within the common ceramic sheet 501-2), and to establish communication between an upper portion of the channel 503a and an upper portion of the internal-pressure buffering chamber 505a by means of the micro channels 506a1 and 506b1. Further, the drive device 500 can be made compact, because of a large volume of the space (the total sum of the volume of the channel 503a, those of the pump chambers 504a and 504b, that of the internal-pressure buffering chamber 505a, and those of the micro channels 506a1 and 506b1), as compared with the volume of the base body 501. Further, since the drive device 500 can have a small thickness and/or an increased surface area relative to the volume thereof, heat generated upon operation can be dissipated to the outside with ease. Accordingly, since the entirety of the drive device 500 heats uniformly (that is, temperature differences among different portions of the device are small), the drive device 500 operates stably by virtue of uniform heating, and has enhanced durability against heat. Next, a drive device 510, which serves as a portion of a circuit changeover switch according to a seventh embodiment of the present invention, will be described. FIG. 36 is a plan view of the drive device 510; and FIG. 37 is a sectional view of the drive device 510 taken along line A6-A6 in FIG. 36. The drive device 510 differs from the drive device 500 mainly in that a pair of micro channels 516a1 and 516b1 and a pair of pump-chamber communication holes 519a and 519b are formed in a ceramic sheet 511-3, which is disposed between a ceramic sheet 511-2 in which a channel 513a is formed and a ceramic sheet 511-4 in which pump chambers 514a and 514b are formed.

[0163] Specifically, the drive device 510 comprises a ceramic base body 511 of a substantially rectangular parallelepiped shape having sides which respectively extend along the X-axis, Y-axis, and Z-axis directions, which are mutually perpendicular; and a pair of piezoelectric films (piezoelectric/electrostrictive elements) 512a and 512b. As shown in FIG. 37, the base body 511 is formed through a process of successively laminating ceramic sheets 511-1 to 511-5 and firing the resultant laminate in such a manner that the base body 511 contains therein a channel forming portion 513, an internal-pressure-buffering-chamber-forming portion 515, the pair of pump chambers 514a and 514b, and the pair of micro channel portions 516a and 516b.

[0164] The channel forming portion 513 forms a channel 513a similar to the channel 503a of the drive device 500. The channel 513a is a space which is defined by side wall surfaces of a through hole formed in the ceramic sheet 511-2, the upper surface of the ceramic sheet 511-1, and the lower surface of the ceramic sheet 511-3 and whose longitudinal axis coincides with the X-axis direction (which has a long axis extending along the X-axis direction). As in the case of the channel 503a, an operation fluid 100 and a movable body 110 are accommodated within the channel 513a, whereby the channel 513a is divided substantially into two operation chambers 513a1 and 513a2 by means of the movable body 110.

[0165] The pump chambers 514a and 514b are identical in configuration with the pump chambers 504a and 504b. The pump chambers 514a and 514b are cylindrical spaces defined by side wall surfaces of through holes formed in the ceramic sheet 511-4, the upper surface of the ceramic sheet 511-3, and the lower surface of the ceramic sheet 511-5. Ceramic diaphragms 517a and 517b formed of the ceramic sheet 511-5 are provided above the pump chambers 514a and 514b, respectively. The diaphragms 517a and 517b are identical in configuration with the diaphragms 507a and 507b, and are disposed to constitute portions of the walls (upper walls) of the pump chambers 514a and 514b and to have respective film surfaces in a common X-Y plane. Piezoelectric films 512a and 512b are formed on the upper surfaces of the diaphragms 517a and 517b, respectively. The piezoelectric films 512a and 512b are identical in configuration with the piezoelectric films 502a and 502b. As a result, the pump chamber 514a, the diaphragm 517a, and the piezoelectric film 512a constitute a ceramic pump 518a; and the pump chamber 514b, the diaphragm 517b, and the piezoelectric film 512b constitute a ceramic pump 518b. The ceramic pumps 518a and 518b are identical in configuration with the ceramic pumps 508a and 508b.

[0166] The internal-pressure-buffering-chamber-forming portion 515 forms an internal-pressure buffering chamber 515a. The internal-pressure buffering chamber 515a is a hollow space which is defined by side wall surfaces of a through hole of the ceramic sheet 511-2, the upper surface of the ceramic sheet 511-1, and the lower surface of the ceramic sheet 511-3, which is identical in configuration with the internal-pressure buffering chamber 505a, and whose longitudinal axis coincides with the X-axis direction (which has a long axis extending along the X-axis direction). The internal-pressure buffering chamber 515a is also formed at a position separated from the channel 513a in the Y-axis negative direction. As in the case of the size of the internal-pressure buffering chamber 505a relative to the channel 503a, the internal-pressure buffering chamber 515a is greater in size than the channel 513a. A substantially central portion of the chamber 515a with respect to the X-axis direction is filled with the above-described operation fluid 100; and the peripheral portions thereof are filled with the above-described compressible fluid for pressure buffering 120.

[0167] The micro channel portions 516a and 516b respectively form micro channels 516a1 and 516b1, which are of the same shape and parallel with each other. Each of the micro channels 516a1 and 516b1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 511-3, the upper surface of the ceramic sheet 511-2, and the lower surface of the ceramic sheet 511-4 and which has a long axis along the Y-axis direction. The micro channel 516a1 extends from an upper portion of a left-hand operation chamber 513a1 of the channel 513a to an upper portion of the internal-pressure buffering chamber 515a to thereby connect the left-hand operation chamber 513a1 with the internal-pressure buffering chamber 515a. The micro channel 516b1 extends from an upper portion of a right-hand operation chamber 513a2 of the channel 513a to an upper portion of the internal-pressure buffering chamber 515a to thereby connect the right-hand operation chamber 513a2 with the internal-pressure buffering chamber 515a. The micro channels 516a1 and 516b1 are also filled with the operation fluid 100.

[0168] For example, the micro channel 516a1 (516b1) has specific dimensions such that when the micro channel 516a1 is sectioned along a plane (i.e., an X-Z plane) perpendicular to the long axis, the height (length along the Z-axis direction) and width (length along the X-axis direction) of the rectangular cross section are each 15 &mgr;m, and the length as measured along the Y-axis direction (excluding a portion above the channel 513a and a portion above the internal-pressure buffering chamber 515a) is 500 &mgr;m. As in the case of the channel 506a1, the shape and the dimensions of the micro channel 516a1 (516b1) are selected so as to provide a throttle function such that a high passage resistance is produced against abrupt pressure change of the operation fluid 100 within the channel 513a in order to substantially prohibit passage (movement) of the operation fluid 100 toward the internal-pressure buffering chamber 515a, and only a low passage resistance is produced against slow pressure change of the operation fluid 100 within the channel 513a, in order to substantially permit passage (movement) of the operation fluid 100 toward the internal-pressure buffering chamber 515a.

[0169] The pump chamber communication holes 519a and 519b are cylindrical spaces formed of through holes, which are formed in the ceramic sheet 511-3, as in the case of the micro channels 516a1 and 5161b. The pump chamber communication hole 519a connects an upper portion of the left-hand operation chamber 513a1 of the channel 513a with the pump chamber 514a. The pump chamber communication hole 519b connects an upper portion of the right-hand operation chamber 513a2 of the channel 513a with the pump chamber 514b. The pump chamber communication holes 519a and 519b are also filled with the operation fluid 100.

[0170] As described above, the operation fluid 100 continuously fills the channel 513a, the pair of pump chambers 514a and 514b, the pair of micro channels 516a1 and 516b1, the pump chamber communication holes 519a and 519b, and a portion of the internal-pressure buffering chamber 515a, which communicates with the channel 513a via the pair of micro channels 516a1 and 516b1. Further, the compressible fluid for pressure buffering 120 fills the spaces of the internal-pressure buffering chamber 515a that are not filled with the operation fluid 100.

[0171] The operation of the drive device 510 for driving (moving) the movable body 110 is the same as that of the drive device 10. Further, the operation of the drive device 510 for absorbing changes in the internal pressure of the channel 513a resulting from thermal expansion and contraction of the operation fluid 100 is also the same as that of the drive device 10.

[0172] The thickness (height or length as measured along the Z-axis direction) of the drive device 510 of the seventh embodiment can be very small (reduced), because the drive device 510 is configured to have the micro channels 516a1 and 516b1 each having a long axis along the Y-axis direction, to have the channel 513a and the internal-pressure buffering chamber 515a formed at the same vertical position (in the common plane or within the common ceramic sheet 511-2), and to establish communication between an upper portion of the channel 513a and an upper portion of the internal-pressure buffering chamber 515a by means of the micro channels 516a1 and 516b1. Further, the drive device 510 can be made compact, because of a large volume of the space (the total sum of the volume of the channel 513a, those of the pump chambers 514a and 514b, that of the internal-pressure buffering chamber 515a, those of the micro channels 516a1 and 516b1, and those of the pump chamber communication holes 519a and 519b), as compared with the volume of the base body 511. Further, since the drive device 510 can have a small thickness and/or an increased surface area relative to the volume thereof, heat generated upon operation can be dissipated to the outside with ease. Accordingly, the entirety of the drive device 510 heats uniformly (that is, temperature differences among different portions of the device are small), the drive device 510 operates stably by virtue of uniform heating, and has enhanced durability against heat.

[0173] Next, a drive device 520, which serves as a portion of a circuit changeover switch according to an eighth embodiment of the present invention, will be described. FIG. 38 is a plan view of the drive device 520; and FIG. 39 is a sectional view of the drive device 520 taken along line A7-A7 in FIG. 38. The drive device 520 differs from the drive device 500 mainly in that a pair of micro channels are formed in a ceramic sheet 521-1, which forms a channel and an internal-pressure buffering chamber in cooperation with a ceramic sheet 521-2. Therefore, in the following description, structural portions identical with those of the drive device 500 are denoted by the same reference numerals, their detailed descriptions are not repeated, and the above-described difference will be mainly described.

[0174] The drive device 520 can be obtained through replacement of the ceramic sheets 501-2 and 501-3 of the drive device 500 with ceramic sheets 521-1 to 521-3, which are successively laminated on the ceramic sheet 501-1 and fired integrally. The drive device 520 comprises a base body 521 and a pair of piezoelectric films (piezoelectric/electrostrictive elements) 502a and 502b. The base body 521 contains therein a channel forming portion 503, an internal-pressure-buffering-chamber-forming portion 505, a pair of pump chambers 524a and 524b, and a pair of micro channel portions 526a and 526b.

[0175] The channel forming portion 503 forms a channel 503a, which is defined by side wall surfaces of substantially rectangular parallelepiped through holes formed in the ceramic sheets 521-1 and 521-2, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 521-3.

[0176] The pump chambers 524a and 524b are identical in configuration with the pump chambers 504a and 504b. The pump chambers 524a and 524b are cylindrical spaces defined by side wall surfaces of through holes formed in the ceramic sheet 521-3, the upper surface of the ceramic sheet 521-2, and the lower surface of a ceramic sheet 501-4. Ceramic diaphragms 507a and 507b formed of the ceramic sheet 501-4 are provided above the pump chambers 524a and 524b, respectively, in such a manner that the ceramic diaphragms 507a and 507b constitute portions of the walls (upper walls) of the pump chambers 524a and 524b, respectively. Piezoelectric films 502a and 502b are formed on the upper surfaces of the diaphragms 507a and 507b, respectively. As a result, the pump chamber 524a, the diaphragm 507a, and the piezoelectric film 502a constitute a ceramic pump 528a; and the pump chamber 524b, the diaphragm 507b, and the piezoelectric film 502b constitute a ceramic pump 528b. The ceramic pumps 528a and 528b are identical in configuration with the ceramic pumps 508a and 508b.

[0177] The internal-pressure-buffering-chamber-forming portion 505 forms an internal-pressure buffering chamber 505a, which is defined by side wall surfaces of substantially rectangular parallelepiped through holes formed in the ceramic sheets 521-1 and 521-2, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 521-3, as in the case of the channel 503a.

[0178] The micro channel portion 526a forms a micro channel 526a1. The micro channel 526a1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 521-1 the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 521-2 and which has a long axis along the Y-axis direction. The micro channel 526a1 connects a left-hand operation chamber 503a1 (a side wall portion of the operation chamber 503a1 formed in the ceramic sheet 521-1) of the channel 503a with the internal-pressure buffering chamber 505a (a side wall portion of the internal-pressure buffering chamber 505a formed in the ceramic sheet 521-1). Notably, the micro channel 526a1 has the same dimensions as the micro channel 506a1.

[0179] The micro channel portion 526b forms a micro channel 526b1. The micro channel 526b1 is identical in shape with the micro channel 526a1, and is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 521-1, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 521-2, which is located at a position separated from the micro channel 526a1 by a predetermined distance along the X-axis positive direction, and which has a long axis along the Y-axis direction. The micro channel 526b1 connects a right-hand operation chamber 503a2 (a side wall portion of the operation chamber 503a2 formed in the ceramic sheet 521-1) of the channel 503a with the internal-pressure buffering chamber 505a (a side wall portion of the internal-pressure buffering chamber 505a formed in the ceramic sheet 521-1).

[0180] As in the case of the micro channels 506a1, 506b1, etc., the shape and the dimensions of the micro channels 526a1 and 526b1 are selected so as to provide a throttle function such that a high passage resistance is produced against abrupt pressure change of the operation fluid 100 within the channel 503a in order to substantially prohibit passage (movement) of the operation fluid 100 toward the internal-pressure buffering chamber 505a, and only a low passage resistance is produced against slow pressure change of the operation fluid 100 within the channel 503a in order to substantially permit passage (movement) of the operation fluid 100 toward the internal-pressure buffering chamber 505a.

[0181] In the drive device 520 as well, the operation fluid 100 continuously fills the channel 503a, the pair of pump chambers 524a and 524b, the pair of micro channels 526a1 and 526b1, and a portion of the internal-pressure buffering chamber 505a, which communicates with the channel 503a via the pair of micro channels 526a1 and 526b1. Further, the compressible fluid for pressure buffering 120 fills the spaces of the internal-pressure buffering chamber 505a that are not filled with the operation fluid 100.

[0182] The operation of the drive device 520 for driving (moving) the movable body 110 is the same as that of the drive device 10. Further, the operation of the drive device 520 for absorbing changes in the internal pressure of the channel 503a resulting from thermal expansion and contraction of the operation fluid 100 is also the same as that of the drive device 10. As a result, the drive device 520 have the same advantages as does the drive device 500. Further, since the drive device 520 is small (thin), as is the drive device 500, the drive device 520 provides the same effects as does the drive device 500.

[0183] Next, a drive device 530, which serves as a portion of a circuit changeover switch according to a ninth embodiment of the present invention, will be described. FIG. 40 is a plan view of the drive device 530; and FIG. 41 is a sectional view of the drive device 530 taken along line A8-A8 in FIG. 40. The drive device 530 differs from the drive device 520 only in that the ceramic sheets 521-1 and 521-2 of the drive device 520 have been replaced with ceramic sheets 531-1 and 531-2 successively laminated on a ceramic sheet 501-1 and fired integrally. Therefore, in the following description, structural portions identical with those of the drive device 520 are denoted by the same reference numerals, their detailed descriptions are not repeated, and the above-described difference will be mainly described.

[0184] In the drive device 530, a channel 503a and an internal-pressure buffering chamber 505a are formed by means of side wall surfaces of through holes formed in the ceramic sheets 531-1 and 531-2, the upper surface of the ceramic sheet 501-1, and the lower surface of a ceramic sheet 521-3.

[0185] Meanwhile, a micro channel 536a1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 531-2, the upper surface of the ceramic sheet 531-1, and the lower surface of the ceramic sheet 521-3 and which has a long axis along the Y-axis direction. The micro channel 536a1 connects a left-hand operation chamber 503a1 (a side wall portion of the operation chamber 503a1 formed in the ceramic sheet 531-2) of the channel 503a with the internal-pressure buffering chamber 505a (a side wall portion of the internal-pressure buffering chamber 505a formed in the ceramic sheet 531-2). Notably, the micro channel 536a1 has the same dimensions as the micro channel 506a1.

[0186] A micro channel 536b1 is identical in shape with the micro channel 536a1. The micro channel 536b1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 531-2, the upper surface of the ceramic sheet 531-1, and the lower surface of the ceramic sheet 521-3, which is located at a position separated from the micro channel 536a1 by a predetermined distance along the X-axis positive direction, and which has a long axis along the Y-axis direction. The micro channel 536b1 connects a right-hand operation chamber 503a2 (a side wall portion of the operation chamber 503a2 formed in the ceramic sheet 531-2) of the channel 503a with the internal-pressure buffering chamber 505a (a side wall portion of the internal-pressure buffering chamber 505a formed in the ceramic sheet 531-2). The functions of the micro channels 536a1 and 536b1 are the same as those of the micro channels 526a1 and 526b1.

[0187] The drive device 530 accommodates a movable body 110, an operation fluid 100, and a compressible fluid for pressure buffering 120 in the same manner as the drive device 520. The drive device 530 provides the same operation and advantages as those provided by the drive device 520, and is a small, reliable device.

[0188] Next, a drive device 540, which serves as a portion of a circuit changeover switch according to a tenth embodiment of the present invention, will be described. FIG. 42 is a plan view of the drive device 540; and FIG. 43 is a sectional view of the drive device 540 taken along line A9-A9 in FIG. 42. The drive device 540 differs from the drive device 520 only in that the ceramic sheets 521-1 and 521-2 of the drive device 520 have been replaced with ceramic sheets 541-1, 5412, and 541-3 successively laminated on a ceramic sheet 501-1 and fired integrally. Therefore, in the following description, structural portions identical with those of the drive device 520 are denoted by the same reference numerals, their detailed descriptions are not repeated, and the above-described difference will be mainly described.

[0189] In the drive device 540, a channel 503a and an internal -pressure buffering chamber 505a are formed by means of side wall surfaces of through holes formed in the ceramic sheets 541-1, 541-2, and 541-3, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 521-3.

[0190] Meanwhile, the micro channel 546a1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 541-2, the upper surface of the ceramic sheet 541-1, and the lower surface of the ceramic sheet 541-3 and which has a long axis along the Y-axis direction. The micro channel 546a1 connects a left-hand operation chamber 503a1 (a side wall portion of the operation chamber 503a1 formed in the ceramic sheet 541-2) of the channel 503a with the internal-pressure buffering chamber 505a (a side wall portion of the internal-pressure buffering chamber 505a formed in the ceramic sheet 541-2).

[0191] For example, the micro channel 546a1 has specific dimensions such that when the micro channel 546a1 is sectioned along a plane (i.e., an X-Z plane) perpendicular to the long axis, the height (length along the Z-axis direction) of the rectangular cross section is 30 &mgr;m, and the width (length along the X-axis direction) of the rectangular cross section is 15 &mgr;m, and that the length as measured along the Y-axis direction (the length of a portion not including the channel 503a and the internal-pressure buffering chamber 505a) is 500 &mgr;m.

[0192] A micro channel 546b1 is identical in shape with the micro channel 546a1. The micro channel 546b1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 541-2, the upper surface of the ceramic sheet 541-1, and the lower surface of the ceramic sheet 541-3, which is located at a position separated from the micro channel 546a1 by a predetermined distance along the X-axis positive direction, and which has a long axis along the Y-axis direction. The micro channel 546b1 connects a right-hand operation chamber 503a2 (a side wall portion of the operation chamber 503a2 formed in the ceramic sheet 541-2) of the channel 503a with the internal-pressure buffering chamber 505a (a side wall portion of the internal-pressure buffering chamber 505a formed in the ceramic sheet 541-2). The functions of the micro channels 546a1 and 546b1 are the same as those of the micro channels 526a1 and 526b1.

[0193] The drive device 540 accommodates a movable body 110, an operation fluid 100, and a compressible fluid for pressure buffering 120 in the same manner as the drive device 520. The drive device 540 provides the same operation and advantages as those provided by the drive device 520, and is a small, reliable device.

[0194] Next, a drive device 550, which serves as a portion of a circuit changeover switch according to an eleventh embodiment of the present invention, will be described. FIG. 44 is a plan view of the drive device 550; and FIG. 45 is a sectional view of the drive device 550 taken along line AA-AA in FIG. 44. The drive device 550 differs from the drive device 520 only in that the ceramic sheets 521-1 and 521-2 of the drive device 520 have been replaced with a ceramic sheet 551-1 laminated on a ceramic sheet 501-1. Therefore, in the following description, structural portions identical with those of the drive device 520 are denoted by the same reference numerals, their detailed descriptions are not repeated, and the above-described difference will be mainly described.

[0195] In the drive device 550, a channel 503a and an internal-pressure buffering chamber 505a are formed by means of side wall surfaces of through holes formed in the ceramic sheet 551-1, the upper surface of the ceramic sheet 501-1, and the lower surface of a ceramic sheet 521-3.

[0196] Meanwhile, a micro channel 556a1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 551-1, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 521-3 and which has a long axis along the Y-axis direction. The micro channel 556a1 connects a left-hand operation chamber 503a1 (a side wall portion of the operation chamber 503a1 formed in the ceramic sheet 551-1) of the channel 503a with the internal-pressure buffering chamber 505a (a side wall portion of the internal-pressure buffering chamber 505a formed in the ceramic sheet 551-1).

[0197] For example, the micro channel 556a1 has specific dimensions such that when the micro channel 556a1 is sectioned along a plane (i.e., an X-Z plane) perpendicular to the long axis, the height (length along the Z-axis direction) of the rectangular cross section is 50 &mgr;m, and the width (length along the X-axis direction) of the rectangular cross section is 15 &mgr;m, and that the length as measured along the Y-axis direction (the length of a portion not including the channel 503a and the internal-pressure buffering chamber 505a) is 500 &mgr;m.

[0198] A micro channel 556b1 is identical in shape with the micro channel 556a1. The micro channel 556b1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 551-1, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 521-3, which is located at a position separated from the micro channel 556a1 by a predetermined distance along the X-axis positive direction, and which has a long axis along the Y-axis direction. The micro channel 556b1 connects a right-hand operation chamber 503a2 (a side wall portion of the operation chamber 503a2 formed in the ceramic sheet 551-1) of the channel 503a with the internal-pressure buffering chamber 505a (a side wall portion of the internal-pressure buffering chamber 505a formed in the ceramic sheet 551-1). The functions of the micro channels 556a1 and 556b1 are the same as those of the micro channels 526a1 and 526b1.

[0199] The drive device 550 accommodates a movable body 110, an operation fluid 100, and a compressible fluid for pressure buffering 120 in the same manner as the drive device 520. The drive device 550 provides the same operation and advantages as those provided by the drive device 520, and is a small, reliable device. Further, by contrast with the drive devices 520, 530, and 540, the side wall surfaces of the channel 503a and the internal-pressure buffering chamber 505a can be formed by use of the single ceramic sheet 551-1, so that the drive device 550 can be fabricated with ease and at low cost.

[0200] Next, a drive device 560, which serves as a portion of a circuit changeover switch according to a twelfth embodiment of the present invention, will be described. FIG. 46 is a plan view of the drive device 560; and FIG. 47 is a sectional view of the drive device 560 taken along line AB-AB in FIG. 46. The drive device 560 differs from the drive device 520 only in that the ceramic sheets 521-1 and 521-2 of the drive device 520 have been replaced with ceramic sheets 561-1 and 561-2 laminated on a ceramic sheet 501-1 and then fired integrally. Therefore, in the following description, structural portions identical with those of the drive device 520 are denoted by the same reference numerals, their detailed descriptions are not repeated, and the above-described difference will be mainly described.

[0201] In the drive device 560, a channel 503a and an internal-pressure buffering chamber 505a are formed by means of side wall surfaces of through holes formed in the ceramic sheet 561-2, the upper surface of the ceramic sheet 561-1, and the lower surface of the ceramic sheet 521-3.

[0202] Meanwhile, a micro channel 566a1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 561-1, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 561-2 and which has a long axis along the Y-axis direction. The micro channel 566a1 connects a left-hand operation chamber 503a1 (a lower portion of the operation chamber 503a1) of the channel 503a with the internal-pressure buffering chamber 505a (a lower portion of the internal-pressure buffering chamber 505a). The micro channel 566a1 has the same dimensions as does the micro channel 506a1 shown in FIG. 35.

[0203] A micro channel 566b1 is identical in shape with the micro channel 566a1. The micro channel 566b1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a slit-like through hole formed in the ceramic sheet 561-1, the upper surface of the ceramic sheet 501-1, and the lower surface of the ceramic sheet 561-2, which is located at a position separated from the micro channel 566a1 by a predetermined distance along the X-axis positive direction, and which has a long axis along the Y-axis direction. The micro channel 566b1 connects a right-hand operation chamber 503a2 (a lower portion of the operation chamber 503a2) of the channel 503a with the internal-pressure buffering chamber 505a (a lower portion of the internal-pressure buffering chamber 505a). The functions of the micro channels 566a1 and 566b1 are the same as those of the micro channels 526a1 and 526b1.

[0204] The drive device 560 accommodates a movable body 110, an operation fluid 100, and a compressible fluid for pressure buffering 120 in the same manner as the drive device 520. The drive device 560 provides the same operation and advantages as those provided by the drive device 520, and is a small, reliable device.

[0205] Next, a drive device 570, which serves as a portion of a circuit changeover switch according to a thirteenth embodiment of the present invention, will be described. FIG. 48 is a plan view of the drive device 570; FIG. 49 is a sectional view of the drive device 570 taken along line AC-AC in FIG. 48; and FIG. 50 is a sectional view of the drive device 570 taken along line AD-AD in FIG. 48.

[0206] The drive device 570 differs from the drive device 560 in that the ceramic sheets 501-1 and 561-1 of the drive device 560 have been replaced with a ceramic sheet 571-1; the ceramic sheet 561-2 of the drive device 560 have been replaced with a ceramic sheet 571-2; and a single micro channel is provided. Therefore, in the following description, structural portions identical with those of the drive device 560 are denoted by the same reference numerals, their detailed descriptions are not repeated, and the above-described difference will be mainly described.

[0207] In the drive device 570, a channel 503a and an internal-pressure buffering chamber 505a are formed by means of side wall surfaces of through holes formed in the ceramic sheet 571-2, the upper surface of the ceramic sheet 571-1, and the lower surface of the ceramic sheet 521-3. Further, as shown in FIGS. 48 and 50, a groove 570M is formed on the upper surface of the ceramic sheet 571-1. The groove 570M having a long axis extending along the X-axis direction is disposed at a substantially central portion of a lower wall surface of the channel 503a with respect to the X-axis direction, and provides the same function as that provided by the groove M shown in FIG. 14.

[0208] Meanwhile, the micro channel 576a1 is a substantially rectangular parallelepiped space which is defined by side wall surfaces of a rectangular groove formed, through laser machining, on the upper surface of the ceramic sheet 571-1 and the lower surface of the ceramic sheet 571-2 and which has a long axis along the Y-axis direction. The micro channel 576a1 connects a lower portion of a left-hand operation chamber 503a1 of the channel 503a and the groove 570M with the internal-pressure buffering chamber 505a (a lower portion of the internal-pressure buffering chamber 505a). The micro channel 576a1 has the same dimensions as the micro channel 506a1 shown in FIG. 35, and provides the same function as that provided by the micro channel 506a1.

[0209] The drive device 570 accommodates a movable body 110, an operation fluid 100, and a compressible fluid for pressure buffering 120 in the same manner as the drive device 520. The drive device 570 provides the same operation as that provided by the drive device 10-1, which is a modification of the first embodiment and is shown in FIG. 13. As a result, the drive device 570 can serve as a small, reliable device as in the case of the drive device 520. Further, since the drive device 570 has the single micro channel 576a1, labor and time needed for machining of the micro channel can be halved, and the drive device can be provided inexpensively.

[0210] Next, a drive device 580, which serves as a portion of a circuit changeover switch according to a fourteenth embodiment of the present invention, will be described. FIG. 51 is a plan view of the drive device 580; and FIG. 52 is a sectional view of the drive device 580 taken along line AE-AE in FIG. 51.

[0211] The drive device 580 differs from the drive device 500 of the sixth embodiment shown in FIGS. 34 and 35 in that the ceramic sheet 501-3 of the drive device 500 has been replaced with a ceramic sheet 581-1 in order to provide bent micro channels. Therefore, in the following description, structural portions identical with those of the drive device 500 are denoted by the same reference numerals, their detailed descriptions are not repeated, and the above-described difference will be mainly described.

[0212] In the drive device 580, micro channels 586a1 and 586b1 are defined by side wall surfaces of slit-like through holes formed in the ceramic sheet 581-1, the upper surface of a ceramic sheet 501-2, and the lower surface of a ceramic sheet 501-4.

[0213] The micro channel 586a1 communicates with an upper portion of a left-hand operation chamber 503a1 of the channel 503a, extends in the Y-axis negative direction from the upper portion of the operation chamber 503a1, bends at a substantially central portion of the base body 581 with respect to the Y-axis direction toward the X-axis negative direction, then extends again in the Y-axis negative direction in order to communicate with an upper portion of the internal-pressure buffering chamber 505a. Similarly, the micro channel 586b1 communicates with an upper portion of a right-hand operation chamber 503a2 of the channel 503a, extends in the Y-axis negative direction from the upper portion of the operation chamber 503a2, bends at a substantially central portion of the base body 581 with respect to the Y-axis direction toward the X-axis positive direction, then extends again in the Y-axis negative direction in order to communicate with an upper portion of the internal-pressure buffering chamber 505a.

[0214] The micro channels 586a1 and 586b1 each have a substantially rectangular cross section when taken along a plane (i.e., an X-Z plane) perpendicular to the axial direction. Example dimensions at a portion extending in the Y-axis negative direction are such that the height (length along the Z-axis direction) of the rectangular cross section is 10 &mgr;m, and the width (length along the X-axis direction) of the rectangular cross section is 10 &mgr;m. Further, the overall axial length (the overall length of a channel excluding a portion above the channel 503a and a portion above the internal-pressure buffering chamber 505a) is 700 &mgr;m.

[0215] The drive device 580 accommodates a movable body 110, an operation fluid 100, and a compressible fluid for pressure buffering 120 in the same manner as the drive device 500. The drive device 580 provides the same operation and advantages as those provided by the drive device 500, and is a small, reliable device. Further, in the drive device 580, the axial length (channel length) of each micro channel is increased and/or the micro channel is bent in order to attain an effect of increasing passage resistance which is similar to that obtained through reduction of the cross sectional area of the micro channel. As a result, in the drive device 580, even when a higher passage resistance must be produced against abrupt pressure change of the operation fluid 100, drastic reduction in the cross sectional areas of the micro channels 586a1 and 586b1 is not required. Therefore, machining accuracy involved in formation of micro slits in the ceramic sheet 581-1 is not required to increase very much, whereby the drive device can be fabricated at low cost.

[0216] Next, a modification of the piezoelectric/electrostrictive actuators employed in the above-described embodiments will be described with reference to an example in which a modified piezoelectric/electrostrictive actuator is used for the drive device 500 of the sixth embodiment shown in FIGS. 34 and 35 in order to replace the ceramic pump 508b (508a). The modified piezoelectric/electrostrictive actuator includes a plurality of layered piezoelectric films to serve as a pump, and, needless to say, can be used not only as the ceramic pumps 508a and 508b, but also as actuators (pumps) of other embodiments.

[0217] FIGS. 53 and 54 are enlarged sectional views of a piezoelectric/electrostrictive film actuator 300 of the modification applied to the drive device 500 shown in FIGS. 34 and 35, taken along lines A5-A5 and AF-AF, respectively, in FIG. 34.

[0218] As shown in these drawings, the piezoelectric/electrostrictive film actuator 300 includes a first electrode film 301-1, a first piezoelectric/electrostrictive film 302-1, a second electrode film 301-2, a second piezoelectric/electrostrictive film 3022, a third electrode film 301-3, a third piezoelectric/electrostrictive film 302-3, and a fourth electrode film 301-4, which are successively stacked on the upper surface of the ceramic diaphragm 507b formed of the ceramic sheet 501-4.

[0219] The first electrode film 301-1 and the third electrode film 301-3 are connected together to assume the same potential to thereby constitute a first electrode section. The second electrode film 301-2 and the fourth electrode film 301-4 are connected together to assume the same potential to thereby constitute a second electrode section. The first electrode section and the second electrode section are mutually isolated by means of the piezoelectric/electrostrictive films; and as in the case of the above-described upper and lower electrodes, a drive voltage is applied to the first and second electrode sections in such a manner that the first and second electrode sections assume different polarities.

[0220] The first to fourth electrode films 301-1 to 301-4 are preferably formed of a metallic material which is solid at room temperature, which can endure an oxidizing atmosphere at high temperature of about firing temperature employed during fabrication of the piezoelectric/electrostrictive film actuator 300, and which has excellent electrical conductivity. Examples of such a metallic material include pure metals such as aluminum, titanium, chromium, iron, cobalt, nickel, copper, zinc, niobium, molybdenum, ruthenium, palladium, rhodium, silver, tin, tantalum, tungsten, iridium, platinum, gold, and lead; and alloys of these metals. The first to fourth electrode films 301-1 to 301-4 may be formed of a cermet material which contains any of the above-described materials and into which the same material as that of the piezoelectric/electrostrictive films or the base body 501 is dispersed. Alternatively, the first to fourth electrode films 301-1 to 301-4 may be formed of gold resinated paste, platinum resinated paste, silver resinated paste, or a like material which enables formation of dense, thin electrode Further, in the above-described multilayer-type piezoelectric/electrostrictive film actuator, the lowermost electrode (first electrode film 301-1) and intermediate electrodes (second and third electrode films 301-2 and 301-3) provided between the piezoelectric/electrostrictive films are preferably formed of an electrode material that contains platinum, etc., as a main component, and an additive such as zirconia oxide, cerium oxide, or titanium oxide. Although the reasons are unknown, when the lowermost and intermediate electrodes are formed of these materials, separation between the electrodes and the piezoelectric/electrostrictive films can be prevented. Notably, the above-mentioned additive is preferably added in an amount of 0.01 to 20% by mass with respect to the entirety of the electrode material in order to obtain a desired separation prevention effect.

[0221] Since, in some cases, an increase in thickness of the electrode films results in a reduced amount of displacement of the piezoelectric/electrostrictive film actuator, the electrode films are preferably thin, in order to maintain a large amount of displacement. Therefore, in general, each of the electrode films preferably has a thickness of 15 &mgr;m or less, more preferably, 5 &mgr;m or less.

[0222] The first to third piezoelectric/electrostrictive films 302-1 to 302-3 must be formed of a material which generates electric-field induced distortion such as that due to the piezoelectric effect or that due to the electrostrictive effect, but no restriction is imposed in terms of whether the material is crystalline or amorphous. Also, a semiconductor, ferroelectric ceramic, or antiferroelectric ceramic may be used.

[0223] Examples of materials for producing piezoelectric/electrostrictive film include ceramic materials formed from lead zirconate, lead titanate, lead magnesium niobate, lead nickel niobate, lead zinc niobate, lead manganese niobate, lead antimony stannate, lead manganese tungustate, lead cobalt niobate, barium titanate, sodium bismuth titanate, potassium sodium niobate, strontium bismuth tantalate, and mixtures thereof.

[0224] Each of the first to third piezoelectric/electrostrictive films 302-1 to 302-3 preferably has a small thickness, in order to obtain large displacement at low voltage. For example, each piezoelectric/electrostrictive film is designed to have a thickness of 100 &mgr;m or less, more preferably a thickness of about 3 to 30 &mgr;m. Further, when a plurality of piezoelectric/electrostrictive films are layered on a diaphragm, the thicknesses of the piezoelectric/electrostrictive films are preferably determined in such a manner that the film thickness decreases gradually toward the uppermost layer (i.e., with increasing distance from the diaphragm). More specifically, the piezoelectric/electrostrictive films are preferably formed so as to satisfy the following relation:

tn≦tn-1×0.95

[0225] where tn represents the thickness of the n-th piezoelectric/electrostrictive film as counted from the lowermost piezoelectric/electrostrictive film (the piezoelectric/electrostrictive film formed immediately on the diaphragm via an electrode film).

[0226] The reason why the thicknesses of the piezoelectric/electrostrictive films are determined in such a manner that the film thickness decreases toward the uppermost layer is as follows. The amount of distortion of a piezoelectric/electrostrictive film increases with the strength of an applied electric field (in other words, when a constant drive voltage is applied to the piezoelectric/electrostrictive film, the amount of distortion increases with decreasing thickness of the piezoelectric/electrostrictive film) . Accordingly, when the thicknesses of the piezoelectric/electrostrictive films are determined as described above; i.e., in such a manner that film thickness decreases toward the uppermost layer, a piezoelectric/electrostrictive film formed on an upper portion distorts to a greater extent than does a piezoelectric/electrostrictive film formed on a lower portion. As a result, the efficiency in bending the diaphragm increases, whereby the amount of bending displacement of the diaphragm can be increased.

[0227] The piezoelectric/electrostrictive film actuator 300 can be fabricated by a method similar to the fabrication method having been described with reference to FIG. 17 or 18.

[0228] Specifically, the first electrode film 301-1 is first formed on the upper surface of the ceramic member 501-4 serving as a diaphragm 507b, by means of a method similar to that used to form the above-described lower electrode 205; and the first piezoelectric/electrostrictive film 302-1 is formed on the upper surface of the electrode film 301-1 by means of a method similar to that used to form the piezoelectric film 207. Subsequently, the second electrode film 301-2 is formed on the upper surface of the first piezoelectric/electrostrictive film 302-1 by means of a method similar to that used to form the above-described lower electrode 205 or the above-described upper electrode 208; and the second piezoelectric/electrostrictive film 302-2 is formed on the upper surface of the electrode film 301-2 by means of a method similar to that used to form the piezoelectric film 207. Subsequently, the third electrode film 301-3 is formed on the upper surface of the second piezoelectric/electrostrictive film 302-2 by means of a method similar to that used to form the above-described lower electrode 205 or the above-described upper electrode 208; and the third piezoelectric/electrostrictive film 302-3 is formed on the upper surface of the electrode film 301-3 by means of a method similar to that used to form the piezoelectric film 207. Finally, the fourth electrode film 301-4 is formed by means of a method similar to that used to form the above-described upper electrode 208.

[0229] As described above, a modification of the piezoelectric/electrostrictive film actuator, which is applicable to the respective drive devices of the present invention, is the piezoelectric/electrostrictive film actuator 300, which includes a piezoelectric/electrostrictive element provided on the diaphragm 507b and consisting of piezoelectric/electrostrictive films and electrode films, which deforms the diaphragm 507b by means of displacement (deformation) of the piezoelectric/electrostrictive element, and in which the piezoelectric/electrostrictive element is formed in such a manner that the electrode films and the piezoelectric/electrostrictive films are laminated alternately, and the uppermost layer and the lowermost layers are formed of electrode films (the first electrode film.301-1 and the fourth electrode film 301-4).

[0230] Since the actuator 300 includes a plurality of piezoelectric/electrostrictive films, each of which generates force, a greater drive force (a force for deforming the diaphragm) can be generated upon application of an electrical potential difference between the electrodes (i.e., between the first and second electrode sections), as compared with the case where the same electrical potential difference is applied between the electrodes (i.e., between the upper and lower electrodes) of a piezoelectric/electrostrictive film actuator which includes only a single piezoelectric/electrostrictive film between the electrodes.

[0231] Further, in the piezoelectric/electrostrictive film actuator 300, a plurality of piezoelectric/electrostrictive films are stacked. This configuration enables easy fabrication of a piezoelectric/electrostrictive element having a high aspect ratio, in which the ratio of the dimension in the vertical direction (as measured along the Z-axis direction) to the dimensions in the horizontal direction (as measured along an X-Y plane) is high. Since a piezoelectric/electrostrictive element having a high aspect ratio has high rigidity at a portion which causes bending displacement, the element exhibits an increased response speed. Therefore, through employment of the actuator 300, a drive device of enhanced responsiveness can be obtained.

[0232] Notably, although the piezoelectric/electrostrictive film actuator 300 includes three piezoelectric/electrostrictive films (and four electrode films), no limitation is imposed on the number of the piezoelectric/electrostrictive films, so long as the number is not less than two.

[0233] As described above, according to the embodiments of the present invention and their modifications, there can be provided drive devices and circuit changeover switches using the same, which can maintain the features of micro machines such as small size and low power consumption; do not include a mechanical amplification mechanism involving intrinsic problems of wear and sticking; and can facilitate mass production. In addition, since the drive devices (switches) hardly break even when the atmospheric temperature increases, the drive devices (circuit changeover switches) have enhanced reliability and durability.

[0234] Notably, the present invention is not limited to the above-described embodiments, and various modifications may be employed within the scope of the present invention. For example, although the above-described circuit changeover switches each have two changeover electrodes, each of the circuit changeover switches may have three or more changeover electrodes. Further, the changeover electrodes and the common electrode may be provided on any wall surface of the channel 13a so long as these electrodes are exposed to the channel 13a and are isolated from one another. For example, the changeover electrodes and the common electrode may be provided on the opposite side wall surfaces. Alternatively, the changeover electrodes may be provided on a side wall surface, and the common electrode may be provided on the lower wall surface or the upper wall surface.

[0235] Moreover, while the basic configurations of the respective drive devices of the present invention are maintained, the films of a piezoelectric/electrostrictive material for deforming diaphragms may be replaced with films of an antiferroelectric material (antiferroelectric film). Further, electrostatic force which is generated between electrodes opposed via a gap and deforming force which is generated in a shape memory alloy heated through application of voltage thereto—which have been actively studied in the field of micro machines—may be used in place of deforming force of piezoelectric film, in order to deform a diaphragm. Even in such a configuration, the combined use of the micro channels 16a1, 16b1, 16c and the internal-pressure buffering chamber 15a as in the above-described embodiments prevents breakage of the drive devices due to variation in atmospheric temperature. In addition, the position of the movable body in the initial state can be controlled through control of the drive voltage (applied voltage).

[0236] Notably, the drive device of the present invention can be used as a device for constructing a so-called rod-less cylinder in the form of a micro machine. As disclosed in, for example, U.S. Pat. No. 3,779,401, a rod-less cylinder is configured as follows. A cylinder working section is sealed completely; an operation member, which is magnetically coupled with the working member (the movable body of the present invention) moving within the sealed space, reciprocates outside the sealed space; and movement of the operation member is transmitted to the outside of the rod-less cylinder system.

[0237] Accordingly, when the movable body 110 of the present invention is formed of a magnetic material, and an operation member magnetically coupled with the movable body 110 is provided outside, there can be obtained a micro rod-less cylinder to which the drive device according to the present invention is applied. Further, the drive device of the present invention may be configured in such a manner that very small electrodes (detection electrodes) are provided within the channel 13a at numerous locations, and the movable body 110 is formed of an electrically conductive magnetic material. This configuration enables detection of the position of the movable body 110 on the basis of an “ON (close)” or “Off (open)” state of each electrode, to thereby enable control of the stroke position of the micro rod-less cylinder.

[0238] The drive device of the present invention can be applied not only to micro machines, such as a micro motor, which are adapted for simple mechanical movement of an object, but also to a wide range of uses of various types of micro machines. For example, a portion or the entirety of the wall surface of the channel 13a may be formed of a transparent material, and the movable body 110 may be formed of a bubble, a colored liquid, a vacuole of a fluorescent liquid, or a very small metal piece capable of reflecting light. In this case, the drive device can be used as an optical display element. Moreover, when magnetic, optical, or electrical means for detecting the position of the movable body 110 from the outside is provided, the drive device of the present invention can be used as a memory element. Further, the movable body 110 may be forced to undergo oscillation motion, and the influence of an external force, such as Coriolis force, exerted on the oscillation motion may be sensed by electrical or optical means. Thus, the drive device can be used as a sensor such as a gyroscope.

[0239] The above-described drive device (circuit changeover switch) of the present invention can be said to have the following features. Ceramic pumps (23a, 23b, 23c) each including a ceramic diaphragm and a film-type piezoelectric element comprising (consisting of) a piezoelectric/electrostrictive film or an antiferroelectric film and electrodes are provided on a substrate (11, 21, 41) having a channel (13a). This channel is formed to have a shape for connecting the ceramic pumps, and accommodates a liquid (100) and a movable body (110), such as a bubble, a vacuole, or a micro solid, to be moved. The channel is connected to a buffering space (15a) via micro channels (16a1, 16b1, 16c). When pressurization or depressurization is effected at high speed by the ceramic pump, the speed at which the liquid enters and returns from the micro channels is low, so that the micro channels exhibit an effect for reducing the pressurization or depressurization with a time delay. When pressurization or depressurization is effected at low speed, the liquid freely enters and returns from the micro channels, so that the micro channels exhibit a buffering effect for suppressing pressure variation within the channel to substantially zero.

Claims

1. A circuit changeover switch comprising:

a channel forming portion for forming a channel, the channel accommodating an incompressible operation fluid and a movable body made of a substance different from that of the operation fluid, and being substantially divided into two operation chambers by means of the movable body;

a pair of pumps each including a pump chamber communicating with the corresponding operation chamber and being filled with the operation fluid, an actuator provided for the pump chamber, and a diaphragm deformed by the actuator, the operation fluid within the pump chamber being pressurized or depressurized through deformation of the diaphragm;

an internal-pressure-buffering-chamber-forming portion for forming an internal-pressure buffering chamber which accommodates the operation fluid and a compressible fluid for pressure buffering; and

a micro channel portion for forming a micro channel which connects the channel of the channel forming portion and the internal-pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion, the micro channel exhibiting a high passage resistance against abrupt pressure change of the operation fluid within the channel, to thereby substantially prohibit passage of the operation fluid through the micro channel and exhibiting a low passage resistance against slow pressure change of the operation fluid within the channel, to thereby substantially permit passage of the operation fluid through the micro channel.

2. A circuit changeover switch according to claim 1, wherein the actuator includes a film-type piezoelectric element comprising a piezoelectric/electrostrictive film or an antiferroelectric film and electrodes; and the diaphragm is formed of ceramic.

3. A circuit changeover switch according to claim 1 or 2, wherein

each of the diaphragms of the pumps constitutes a portion of the walls of the corresponding pump chamber and has a film surface in a common plane;

the channel of the channel forming portion forms a space whose longitudinal axis lies in a plane parallel to the film surfaces of the diaphragms;

the micro channel of the micro channel portion extends along a direction parallel to the film surfaces of the diaphragms; and

the internal-pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion forms a space whose longitudinal axis lies in a plane parallel to the film surfaces of the diaphragms and is connected with the channel of the channel forming portion via the micro channel of the micro channel portion.