Piezoelectric device and acousto-electric transducer and method for manufacturing the same
A lens shape piezoelectric device which is thinner than the manufacture limit thickness, which is conventionally difficult to manufacture, and a method for manufacturing the same. The piezoelectric device has a oscillation part having at least two steps where one side thereof is planar and the opposite side is thickest at a peripheral holding portion and thinner toward the central portion. A piezoelectric element of another embodiment has an oscillation part of at least two steps where the peripheral holding portion is thickest on both sides and the thickness decreases toward the central portion. In these piezoelectric devices, at least one side of the thinnest central portion of the oscillation part has a convex lens shape. A pair of electrodes are vacuum deposited in the center of these oscillation parts on both sides, and a gold wire is led as a lead wire from each electrode.
This is a divisional application of Ser. No. 10/333,130, filed Jan. 16, 2003.
BACKGROUND OF THE INVENTION1. Technical Field
This invention is related to a piezoelectric device and an acousto-electric transducer, and the method for manufacturing the same, which enables the characteristic frequency to be extremely higher.
2. Description of Related Art
Quartz oscillators (resonators), as one of piezoelectric devices, are used for a wide variety of application fields such as fundamental frequency generators of communication apparatus and sensing instrumentation and clock sources of general computers, office automation information equipment, home appliances, and so forth. It has been required for those characteristic frequencies to be higher by decreasing the thickness of their oscillators (resonators) in order to achieve the high performance of the information processing and transfer capabilities. Also the lens-line type finishing was proposed to produce higher quality oscillators (resonators), and these performances were accomplished for those relatively lower frequency domains.
Quartz oscillators are the essential electronic devices for digital machines such as communication equipment, computers, and so forth. It is demanded for those oscillators to increase the primary oscillation frequency by decreasing the thickness in order to achieve the high performance of the information processing and transfer abilities. Especially for mobile communication, the fundamental frequency is required to be higher for the small sizing and power saving management.
Quartz oscillators have been generally manufactured by the mechanical polishing and chemical wet etching processes. The former polishing shows the fine surface finish, however it cannot machine in lower than 30 μm. The latter etching has the advantage of decreasing deteriorated surface in principle, but it has the limitation of thickness due to the etching channel generation and so forth. On the other hand, the reactive ion etching (RIE), inductive coupled plasma etching (ICP) or plasma-etching process (abbreviated as chemical dry etching) makes the damaged surface layer, however the dry etching allows the device to be thin without the inconvenient surface roughness.
The novel mass-productive manufacturing method of high frequency quartz oscillator is developed, by combining efficiently the advantages of these processes. However the problem of reducing the thickness of those oscillators (resonators) by the dual-face polishing method (dual-face polishing machine) is presently incapable reducing the thickness to less than 30.0 μm (=55.6 MHz).
Furthermore, when oscillators were finishing in lens shape, it was extremely difficult to make the curved surface on the thin plate, and there existed no machining method of mass production with low cost.
SUMMARY OF THE INVENTIONThereafter the present invention was developed to solve these problems, and shall make possible the manufacture the lens shape piezoelectric device, which is thinner than the thickness limitation in the conventional method.
In order to solve previously mentioned problems, the piezoelectric device of present invention has one flat surface, and the other side has the thickest peripheral holding portion and a central oscillation part connected by at least two steps, which one side is decreasing the thickness toward the central region. Also another type of piezoelectric device has the thickest peripheral holding portion and the central oscillation part at least with two steps, and both sides are decreasing in thickness toward the central region.
The oscillating part at the thinnest center of piezoelectric device is in convex lens shape at least for the one surface.
Furthermore the present invention enables the piezoelectric device to be manufactured to make the first oscillating part to be seen toward the crystal orientation of the piezoelectric material at the central part of a nearly rectangular quartz blank, and afterward to make the second oscillating part so as not to be seen toward the crystal orientation of the piezoelectric material.
Furthermore, an acousto-electric transducer of the present invention is manufactured so as to make the final shape profile at both end surfaces of piezoelectric rod, and to make the end surface of above stick as homogeneously and relatively decreasing the thickness toward the central direction of the rod in the similar geometric shape by a dry etching process such as RIE, without machining the outer wall thickness of the rod. Then the oscillating part at the inner central region of the cylindrical rod is made the oscillation device with the final thickness and profile.
A pair of electrodes is vacuum deposited in the center of these vibrating parts on both sides, and a gold wire is led as a lead wire from each electrode.
BRIEF DESCRIPTION OF DRAWINGS
As the next step, the whole lower surface is processed by a dry etching as ion etching (hereafter ion etching process) with hydrogen fluoride, and the quartz blank 100 becomes thinner
As mentioned previously, it is not possible for the sole chemical wet etching to decrease the thickness thinner than 20 μm. Afterwards the ion etching process will decrease the thickness down to approximately 10.3 μm.
The target thickness is 10 μm. However, the ion etching process alone will not achieve the target thickness. The ion etching can decrease the thickness, however this has the disadvantage of forming an ion-damaged layer, which is unknown defect with non-crystalline component at the mono-crystalline surface, since the ion etching process uses atomic collisions. The thickness of the layer is approximately 0.2-0.3 μm.
Therefore we employed the mechanical polishing. The dual face polishing machine does the job to polish the final processing (
Thereafter, cerium oxide whetstone powder is streaming with water, the quartz blank 100 held by carrier 106 rotates around its own axis between the lower and upper tables 103, 104, also the upper table 103 rotates, and then the quartz 100 can be polished.
As shown in
The polished quantity is proportional to the polishing pressure. The frame 102 of concave quartz blank 100 after the ion etching is strongly pressurized to be polished between the upper table 103 and lower table 104, and the grooved part for oscillation is slightly impressed only by the lower table 104. Furthermore the polishing force at the central region of the concaved structure part 101 is weaker (
As understood from the above, the dual polishing machine cuts only 0.3 μm. This small amount of polishing enables the damaged layer to be removed and shaped in a convex lens shape. In other words, the chemical etching and dry etching process corresponds to the coarse machining, and the dual face polishing processing corresponds to the fine machining.
The combination of these polishing processes in this invention makes the piezoelectric device thinner than the conventional one, and also the oscillation part in a convex lens shape makes it steady in electric vibration without the spurious one.
This invention presents the manufacturing method of a high frequency quartz oscillator with an efficient combination of chemical wet etching (abbreviated as chemical etching), reactive ion etching (RIE), inductive coupled plasma etching (dry etching) and mechanical polishing. As a result, we could manufacture the high frequency quartz oscillator in a piano-convex type with a general dual face polishing machine, when the quartz blank was in one step single-sided inverted mesa type.
In order to mass-produce quartz blanks in one step single sided inverse mesa type by chemical etching, quartz wafers were masked and chemically etched. The shape is shown in
A reactance-frequency property of this quartz blank is seen in
In order to achieve higher frequency, the dry etching process of the mechanical polishing process with the dual face polishing machine was employed to decrease the thickness. Here before the ion-damaged layer must be removed, the surface side of dry etching was selected to be the planar surface of quartz blank in single-sided inverse mesa type. This RIE processing condition was the standard one. It is possible for the ion damage to be decreased by small RF power and high pressure. However this means a slower ion etching rate, and the first dry etching was performed in the high efficient mode, and the third one was performed in the low damage condition. By the way, the removed mass was controlled by the processing time of the first dry etching process.
When the mechanical polishing was executed with the dual face polishing machine, the blank could be machined without any fear of the first problem of breaking the thin oscillation part. The second target of forming the shape was successfully accomplished as shown in
The principle of this shaping mechanism is seen as follows. When the quartz blank in one step single-sided inverse mesa type with thin oscillation part is impressed with the polishing pressure, the thin part is distorted toward the cavity direction and this part cannot be substantially polished. After the polishing process is finished and the polishing pressure is relieved, the thin part (which is distorted toward the pit) rebounds to the opposite side, and this shape becomes the protruded lens shape.
Also
Based on these results, the electrically high performance quartz oscillator was proved to be made above 334 MHz high frequency, when the aperture thickness ratio (d/t) was from 50 to 150 (optimum 80).
The following theme concerns the acousto-electric transducer as an application of the piezoelectric device of this invention.
While a conventional detection and prediction of earthquake was executed by ocean observation, underground structure probe, earth magnetic observation, ground movement measurements between two points with GPS and Laser, and so forth, acoustic wave observation due to the earthquake and Tsunami will be one of these detection and prediction. A focused microphone can transform the acoustic wave to an electric signal, which is convenient to record and analyze, but it is difficult to detect the acoustic wave at the specific frequency due to the picking up of noises.
FIGS. 11 from (a) to (e) illustrate variously executed examples of acousto-electric transducer of piezoelectric device in this invention. In
In this paragraph, the method, which was proposed in the previous invention by the present applicant, is described to explain the mechanical formation of the pressure receiver 22. In the fundamental method, the circular rod 30, which is made from a piezoelectric material such as quartz, barium titan oxide, lithium niobium or other ceramics and so on as shown in
Also when the polishing surface of pressured surface 22 is convex as shown in
At the same time, a chuck 31 rotates and polishes the pressured surface with a circular rod 30. Also the tool to make the hole or space part 47 is a whetstone 32″ in
Also the circular hole of the machining tool can be the usual rotating one around the axis, for example, a spherical whetstone as shown in
- {circumflex over (1)} Air pressure is 0.5 atmosphere, and rotation of whetstone 32 is about 12,200 rpm.
- {circumflex over (2)} Air pressure is 1.0 atmosphere, and rotation of whetstone 32 is about 22,000 rpm.
- {circumflex over (3)} Air pressure is 2.0 atmosphere, and rotation of whetstone 32 is about 37,500 rpm.
- {circumflex over (4)} Air pressure is 3.0 atmosphere, and rotation of whetstone 32 is about 47,800 rpm.
- {circumflex over (5)} Air pressure is 4.0 atmosphere, and rotation of whetstone 32 is about 50,000 rpm, which is the bearing limitation.
Also, instead of the cutting whetstone 32 the cutting and polishing machine in
The above paragraph explains the manufacturing method, which was previously invented by us, and the following introduces newly invented acousto-electric transducer.
Initially, we will explain the method of forming the convex lens type pressure receiver 22 (oscillation surface) in
- (a) The first product, the target of which is to form the convex lens shape 20a, is made from both ends of cylindrical piezoelectric material 20 by means of mechanical polishing, etching process, or the like.
- (b) Only a cylindrical part of the first product in the convex lens shape is processed by the dry etching process (RIE or CIP process), other parts are not etched. This process can be executed by setting the ring mask, which is made from glass, quartz, tungsten, nickel, pure iron, plastic or other materials, on the end of the cylindrical piezoelectric material 20.
- (c) This process continues to the central part of the piezoelectric material 20 as shown in
FIG. 23 (c). - (d) After the dry etching process reaches the predetermined length at the central part, the same dry etching process is undertook from the opposite surface. In practice, this is done by inverting the piezoelectric material 20, not by moving the dry etching machine.
- (e) As shown in
FIG. 23 (e), after the convex lens shape is formed at the central part of piezoelectric material 20, the ion-damaged layer, which is generated by the dry etching process in 0.2 μm-0.3 μm depth, is removed by the mechanical polishing method. Then we have the oscillator (resonator) with electrically excellent performance, since the lens shape of ring support type is formed at the cylindrical central part as shown inFIG. 23 (f).
- (a) The first product, the target of which is to form the convex lens shape 20a, is made from both ends of cylindrical piezoelectric material 20 by means of mechanical polishing, etching process, or the like.
- (b) Only a cylindrical part of the first product in the convex lens shape is processed by the dry etching (RIE or CIP process), other parts are not etched. This process can be executed by setting a hollow cylinder 52, which is smaller than the material 20 and made from glass, quartz, tungsten, nickel, pure iron, plastic, or other material, on the end of the cylindrical piezoelectric material 20. Then the dry etching process is simultaneously performed at the inner and outer surfaces of piezoelectric hollow cylinder 52. At the same time, the end surface of the cylinder 52 is shaven.
- (c) This process continues to the central part of the piezoelectric material 20 as shown in
FIG. 27 (c). - (d) After the dry etching process reaches the predetermined length of the central part, the same dry etching process is undertook from the opposite surface. In practice, this is done by inverting the piezoelectric material 20, not by moving the dry etching machine.
- (e) As shown in
FIG. 27 (e), after the convex lens shape is formed at the central part of piezoelectric material 20, the ion-damaged layer, which is generated by the dry etching process in 0.2 μm˜0.3 μm depth, is removed by the mechanical polishing method. Then we have the oscillator (resonator) with electrically excellent performance, since the lens shape of ring support type is formed at the cylindrical central part, and a lens shape shown inFIG. 27 (f) is formed at the central part of hollow cylinder, we get the oscillator (resonator), which contains the holding part in a ring-support shape and is electrically excellent.
Although
The following paragraph introduces a processing method to make the convex lens shape oscillator (resonator), which is connected to an extremely thin connector.
- (1) The first product, the target of which is to form the convex lens shape 20a, is made from both ends of a thick piezoelectric plate 20 by means of mechanical polishing, etching process, or the like.
- (2) Only a cylindrical part of the first product in the convex lens shape is processed by the dry etching process, as other parts are not etched. This process can be executed by setting a hollow cylindrical auxiliary tool 50 (on the top of the first product), which is smaller than the hollow cylinder 20 and made from glass, quartz, tungsten, nickel, pure iron, plastic or other material, and the surface of the tool 50 and the both ends are shaven by the dry etching process at the same time or successively (step one end in this sample). Then, after the convex lens shape is formed at the central part of piezoelectric material 20, the ion-damaged layer, which is generated by the dry etching process in 0.2 μm˜0.3 μm depth, is removed by the mechanical polishing method. Then we have the oscillator with electrically excellent performance, since the lens shape of ring support type is formed at the cylindrical central part, and a lens shape in
FIG. 27 (f) is formed at the central part of hollow cylinder, we get the oscillator (resonator), which outer surface is in a ring-support shape with the holding part.
Although
- (1) At both ends of the piezoelectric disk, a convex lens type auxiliary blank 51 is pressingly set by using the mechanical polishing process, press formation (to make lens), etching process, or other means. Otherwise, the auxiliary blank 51 is pasted on the piezoelectric material 20 by using resist (for instance OSPR resist made in Tokyo Ohka Kogyo Ltd.) or other adhesives. Here the material of the auxiliary blank 51 is glass, optical glass, lens, quartz, tungsten, nickel, pure iron, plastics, or other material.
- (2) Only the convex lens shape part of auxiliary blank 51 is dry etched, a hollow cylindrical auxiliary tool 50, which is made from glass, optical glass, lens, quartz, tungsten, nickel, pure iron, plastics or other material, is set on the top of the auxiliary blank 51, in order not to etch other part of the convex lens shape. And the surface of auxiliary tool 50 is homogeneously shaven by dry etching process at the same time. Then the surface of blank 51 is etched at first, next the surface of piezoelectric material 20 is shaven, and an ultra thin convex lens shape is formed at the central part in hollow cylindrical shape. After the mechanical lapping process removes the 0.2 μm˜0.3 μm ion-damaged layer, which is followed by the dry etching, and finally formed is the electrically excellent oscillator, which has the lens shape in the hollow cylindrical central part and the ring-support type holder at the outer part.
The material of the auxiliary blank 51 can be made from glass, optical glass, lens, quartz, tungsten, nickel, pure iron, plastics or others, however the best material is quartz glass similar to quartz crystal to press the auxiliary blank 51, but other material is to be useful. In
Electrodes 23 and 24 in
Other examples are illustrated in
In these examples, an 80 μm thick quartz wafer is masked as the first step, then the oscillation part is processed in every 25 μm from both sides of the quartz wafer by chemical etching or dry etching as shown in FIGS. 32(b), 33(b), 34(b) and 35(b), and the thickness of oscillation part becomes 30 μm after these etching processes. Then, the quartz wafer an masked as the second step, the 30 μm oscillation part is processed in every 13 μm from both sides by chemical etching or dry etching as shown in FIGS. 32(c), 33(c), 34(c) and 35(c), and the thickness of the oscillation part becomes 4 μm after these etching processes.
Like the circle shapes shown in FIGS. 32(a) and 33(a), hexagonal shape shown in
This method has the following merits.
- {circumflex over (1)} Although the outer shape is square or rectangular, the shape of the oscillation part becomes pure circular or circle, which is electrically excellent.
- {circumflex over (2)} As shown in
FIGS. 32 and 33 , when the outer shape of quartz blank is square or rectangular, and the shape of the oscillation part is purely circular or in circle, it becomes difficult for the crystal orientation to be seen, since the crystal orientation has no mark. Then the crystal orientation is marked by etching in a specific shape as shown inFIG. 32 (a) andFIG. 33 (a), when the shape of the oscillation part is processed to be circular. - {circumflex over (3)} As shown in
FIGS. 32, 33 , 34 and 35, when the outer shape of quartz blank is square, mass production becomes easy compared to the circular case, because the cutting is conveniently done. - {circumflex over (4)} The outer shape of the quartz blank can be square, however the electric property of quartz oscillator becomes more excellent, when the shape of oscillation part is purely circular or in circle.
- {circumflex over (5)} As shown in FIGS. 32(c), 33(c), 34(c), and 35 (c), the ratio of diameter over the thickness (d/t) is to be approximately 80 and the optimum diameter of the oscillation part is 4 μm×80=0.32 mm in order to get the best electric performance, when the oscillation part is 4 μm thick. When the initial quartz blank is 80 μm thick and the oscillation diameter is 0.32 mm, it is impossible for the circular oscillation part to be processed down to 4 μm thick by only one masking after the chemical etching of 76 μm. When the diameter of oscillation part becomes as small as 0.32 mm, the chemical etching cannot be homogeneously processed due to the surface tension of solution as hydrogen fluoride and the crystalline anisotropy. When the chemical etching is successively processed more than two times, it become possible for the blank of the small diameter less than 0.32 mm to be shaved.
- {circumflex over (6)} In the case of the dry etching process, there exists no problem for the diameter of the oscillation part to be as small as 0.32 mm.
- {circumflex over (7)} When this is in two steps wise shape and the thickness is decreased step by step, the mechanical polishing process can easily remove the damaged layer, which is generated during the chemical or dry etching.
These processes serve to reduce the oscillation part to 4 μm, and have the following merits in addition to those shown in
- {circumflex over (1)} After this is masked twice or more than two times to make the aperture ratio larger, processed by chemical etching and dry chemical etching, and then mechanically polished as shown in
FIG. 2 (a), the aperture ratio(d/t) becomes approximately 80 and the electrical property is at an optimum.FIG. 38 (c) illustrates the cross section, and this structure is concave in order to widen the pressure distribution. This concave structure is not plano-convex with a larger curvature, it really becomes like a convex lens similar to concavo-convex or bi-convex shape, which electric property is ideal, and we complete the ultra thin quartz oscillator less than 0.5 μm. For example of BT-cut, the primary frequency of fundamental wave becomes approximately 5.0 GHz. Also, it is possible to use other materials such as AT-cut, SC-cut, FC-cut, IT-cut, and other cuts. - {circumflex over (2)} When the outer region of oscillation part is structured so as to be another concave shape or stepwise, this electrode can be easily made, even if the target diameter of the oscillation part is extremely small.
- {circumflex over (3)} After the chemical etching and dry etching processes are completed, the polishing process to remove the ion damaged layer (changed layer due to the process) is conveniently executed, since the thickness of quartz blank is, step by step, decreasing toward the center.
Also, the mechanically polished shape as shown in FIGS. 40(c), 41(c), 42(c), and 43(c) can remarkably improve the electrical performance, after the chemical etching and dry etching processes are done and the polishing process to remove the ion damaged layer due to the etching is properly executed.
As shown in FIGS. 44 (b), 45 (b), 46 (b) and 47 (b), one surface of 80 μm thick quartz wafer is masked in the first stage, and one side of the wafer, which diameter is 0.32 mm and pure circular (otherwise nearly circular), is shaved 12 μm by chemical etching and dry etching. Then the quartz wafer is masked in the second stage, and both sides of the wafer are shaved 26 μm by chemical etching and dry etching as shown in FIGS. 44(c), 45(c), 46(c), and 47(c), where the diameter is 1.6 mm and the shape is circular, square, hexagonal, or others. The thickness becomes 4 u m and the diameter of the oscillation part is 0.32 mm.
The oscillation part becomes the shape as shown in FIGS. 44(c), 45(c), 46(c), 47(c), and 48(c), after the chemical etching, dry etching and mechanical polishing process by a dual-face polishing machine (polishing table) and other polishing means to remove the damaged layer due to the etching. In this case, since the oscillation part of the quartz blank becomes stepwise and the oscillating diameter is large as illustrated in FIGS. 44(c), 45(c), 46(c), 47 and 48(c), the polishing agent such as cerium oxide can smoothly penetrate from both sides during the polishing process by the polishing table, barrel polishing machine, or ultrasonic polishing method. Therefore, the mechanical polishing process becomes efficient, and the electric performance of the quartz oscillator becomes ideal.
Here the following three problems occur during mass production.
- {circumflex over (1)} From the result of the examination, when a single-sided grooved type oscillator with two steps is processed to be piano-convex shape, the optimum aperture ratio (d/t) is approximately 80.
- {circumflex over (2)} The dimension of the blank is bigger than 1 inch×1 inch, and the thickness becomes larger than 80 μm.
- {circumflex over (3)} The quartz crystal is anisotropy, and the anisotropy appears when the chemical etching shaves more deeply than 1/20 of the oscillation diameter.
In order to clear these three problems, two chemical etching processes in
- {circumflex over (1)} As demonstrated in the above examples, there exists no anisotropy of quartz oscillators in every case of the first manufactured sample of two steps single-sided grooved type in
FIGS. 55 and 56 , the second sample of two steps single-sided grooved type inFIGS. 60 and 61 , and the third sample of two steps double-sided grooved type inFIGS. 65 and 66 . - {circumflex over (2)} The surface accuracy and shape accuracy of the fourth quartz oscillator sample in steps double-sided grooved type in
FIG. 71 and of the fifth quartz oscillator sample in steps single-sided grooved type inFIG. 76 are measured to be worse than those of the first, second, and third samples. This is found to be due to the quartz anisotropy. - {circumflex over (3)} It is found to be the reason for the quartz anisotropy of first, second, and third samples not to observed (not for the fourth and fifth samples), why the larger diameter oscillation part (the second oscillation part) of the first, second, and third samples in
FIGS. 54, 59 , and 64 are chemically etched at first, and the smaller first oscillation part is done secondly, and why the smaller diameter oscillation part (the first oscillation part) of the fourth and fifth samples inFIGS. 70 and 75 are chemically etched at first, and the larger second oscillation part is done secondly (these are etched relatively at the same time). - {circumflex over (4)} The first, second, and third samples are proved to be machined in ultra fine accuracy, the fourth and fifth samples are not, however the latter devices can be used as the lower grade quartz oscillator. On the contrary, the first, second, and third oscillators show more than one hundred times better accuracy compared to the fourth and fifth cases. Therefore the former three manufacturing methods should be utilized for the ultra accurate quartz oscillator as shown in
FIGS. 54, 59 , and 64.
The following paragraph shows the frequency, wave shape and resonance characteristics of quartz oscillator in two steps shape.
- {circumflex over (1)}
FIGS. 83, 84 , 85 and 86 show measured resonance characteristics of the second quartz oscillator in two steps single-sided grooved type inFIGS. 59, 64 , and 70, and of the third and fourth ones in two steps double-sided grooved type. - {circumflex over (2)} Resonance characteristics in
FIGS. 83, 84 , 85, and 86 are measured at the first oscillation part in FIGS. 54(c), 64(c) and 70(c), not at the larger second grooved region (second oscillation part) in FIGS. 54(b), 64(b) and 70(b). - {circumflex over (3)}
FIGS. 83 and 84 are measured resonance characteristics of the second quartz oscillator example, which are made based on the diagrams inFIG. 59 for two steps single-sided grooved type. When a material blank is AT-cut, it is thought to be the most excellent electrical performance in the world at present for the resonant point at 184.872 MHz inFIG. 83 and 181.232 MHz inFIG. 84 to see the resonance characteristics inFIGS. 83 and 84 . - {circumflex over (4)}
FIG. 85 shows measured resonance characteristics of the fourth quartz oscillator example, which is made based on the diagram inFIG. 70 for two steps double-sided grooved type. When the material blank is AT-cut, it is thought to be the most excellent electrical performance in the world at present for the resonant point at 257.369 MHz to see the resonance characteristics inFIG. 85 . - {circumflex over (5)}
FIG. 86 shows measured resonance characteristics of the third quartz oscillator example, which is made based on the diagram inFIG. 64 for two steps double-sided grooved type. It is thought to be the most excellent electrical performance in the world at present for the resonant point at 283.178 MHz to see the resonance characteristics inFIG. 86 . - {circumflex over (6)}
FIG. 87 is measured resonance characteristics of the sixth quartz oscillator example, which is made by Hoffman Inc. in USA for one step double-sided inverse mesa type and oscillation part is approximately 5 u m. - {circumflex over (7)} When the resonance property of one step double-sided inverse mesa type in
FIG. 87 is compared both to those of two steps single-sided grooved type inFIGS. 83 and 84 and to two steps double-sided grooved type inFIGS. 85 and 86 , the electrical resonance characteristics inFIGS. 83, 84 , 85, and 86 is much better than that inFIG. 87 , although these frequencies are slightly different. - {circumflex over (8)} It is thought to be due to the present two steps grooved shape for electrical resonance characteristics of two steps single-sided grooved type in
FIGS. 83 and 84 and of two steps double-sided grooved type inFIGS. 85 and 86 , to be much better than that of Hoffman's resonator in one step inverse mesa type inFIG. 87 . - {circumflex over (9)} The large area of the second grooved part (second oscillation part) in two steps grooved stereo type in FIGS. 59(b), 64(b), and 70(c) is not vibrated, the first oscillation part in very small diameter is only vibrated, and the first oscillation part is demonstrated to contribute solely for the electrical resonance.
- {circumflex over (10)} The above discovery implies that the ultra high frequency resonance over 160 GHz primary wave (approximately 0.015 μm thick), with BT-cut, for example, can be oscillated in near future, and that it can be possible for electrically ideal quartz oscillator to be made in concavo-convex lens shape rather than in two steps single-grooved plano-convex type.
The quartz oscillator in
The quartz oscillator in
The reason to become nearly concavo-convex lens shape in
The single-sided grooved type is seen as the second manufactured examples in
Therefore, the protruding grade is found to be proportional to the polishing time.
The electrical property of the eighth quartz oscillator example in
Based on these results for the seventh and eighth manufacturing cases, the quartz oscillators in the two-stepped single-sided grooved type are found to become convex lens shape, which is introduced in
The dotted line a-b in
Therefore, three steps or more than three steps single-sided grooved type becomes larger curvature shape (the lower line is widen), and concavo-convex shape in more protruding convex lens type than those of two steps single-sided grooved type.
It must be parallel or in convex lens shape for the quartz oscillator to perform ideal electrical characteristics. The best parallel error is ideally 0, however it is practically impossible to make the plate with zero error of parallelism. Besides, the size of wafer becomes larger in these years, and the thickness becomes thicker as the size becomes bigger. The typical wafer size is 60 mm high, 30 mm wide, and 80 μm thick at the present. As the size of wafer becomes larger, the parallel error is inversely bigger.
When a quartz blank is chemically etched, the quartz anisotropy generates. As the method for avoiding this anisotropy, this must not be chemically etched more than 1/20 of the aperture (diameter). For example, if the thickness of the oscillation part is 5 μm of an 80 μm thick wafer, and the remaining 75 μm is chemically etched, the aperture (diameter) should be 1500 μm=1.5 mm, which is 20 times of 75 μm.
When the oscillation part of a quartz oscillator is 5 μm thick, the diameter of the oscillation part is enough to be 80 times of the thickness both for parallel plate and convex lens shape since the aperture (diameter) is sufficient to be 0.4 mm for the 5 μm thick oscillation part.
When the same parallel plate is used, the parallel error of 1.5 mm diameter is quite different from that of 0.4 mm diameter. In conclusion, the smaller the aperture is, the smaller the parallel error of the oscillation part is relatively, when parallel error of the wafer is same. In order to make a small aperture quartz oscillator, it is necessary to avoid the original quartz anisotropy, and it is found to be the most optimum for two or three steps single-sided grooved or double-sided grooved shape, since the minimum thickness of wafer is 80 μm.
The resonance characteristics is best in
When quartz oscillator in
Effect of Invention
- (1) When both ends of a cylindrical blank are made at first to be the final target as lens, single-sided convex, single-sided groove, or planar shape, the oscillation part with a predetermined thickness can be shaped in the hollow cylindrical piezoelectric element, by shaving homogeneously to be circular from the cylinder end with a dry etching process.
- (2) The following effect will arise, when the planar piezoelectric blank is attached by an auxiliary mold in convex lens or convex lens shape, or when the auxiliary mold shape is pressed to the end of piezoelectric material by dry etching process after the auxiliary mold is pasted to the piezoelectric material with dry etching process. When the press forming makes the optical lens of flat and convex (or concave) shape with the outer ring-support (in frame shape) holder, and the auxiliary mold as the optical lens is attached to the planar piezoelectric material and shaved by the dry etching process, the planar piezoelectric surface is processed to be in the same lens shape with the high surface accuracy as the conventional lens, which is machined by press forming or other mechanical polishing processes. Then we can conveniently manufacture the ultra accurate quartz oscillator (quartz resonator), which is in lens shape at the central part and accompanied by the outer holder in the ring-support shape (frame shape or hollow bamboo cylinder shape).
- (3) Furthermore, since the crystal axis of quartz can be easily identical to the machining axis of optical lens, the quartz oscillator becomes electrically excellent.
- (4) The final surface accuracy becomes equal to the original surface accuracy at both ends of the cylinder shape. However, the intrinsic electrical characteristics of the piezoelectric element will not restore, if the ion-damaged layer due to the dry etching process is removed.
- (5) If the cylinder is machined to be in the hollow cylinder shape by the mechanical process, it is difficult for the deep groove to be machined.
- (6) When the piezoelectric material is formed to be in hollow cylinder shape by the dry etching process, the lens shaped oscillator is made at the central part of hollow cylinder, which hole diameter is approximately 10 mm, hole length is from 1.0 cm to 15 cm, and thickness is around 1 mm.
- (7) It is actually extremely difficult for the hollow cylinder thickness to be machined only by the mechanical process, however the present invention to use the dry etching can manufacture oscillators in ultra high performance, since this invention enables the processing to be in lens shape at the central part with the holder of extremely thin bamboo hollow cylinder and ring-support shape (bamboo type hollow cylinder shape) at the outer part.
- (8) The thickness of the bamboo type hollow cylinder can be polished to be extremely thin, since the dry etching process is performed at the same time both for outer and inner surfaces of the bamboo type ring-support shape.
- (9) If the ion-damaged layer is not considered during the dry etching process (RIE or CIP), the ultra thin lens shape can be manufactured after both ends are shaved in the same accuracy as the original one at the end of the cylinder.
- (10) Since we can manufacture oscillators, whose walls are quite thin, hole diameter is small, hole length of bamboo hollow cylinder is long, central pressure sensor part is in the convex or concave lens shape, and it makes high performance to catch an acoustic wave.
- (11) When the outer diameter of small oscillator in bamboo type hollow cylinder shape is less than ½ inch, for example, the pressure or the temperature of oil, methane gas, and so on is always measured at the same time, after this is inserted into the pipe under say 5000 m of ground to pump oil, methane etc.
- (12) The diameter of a conventional pressure sensor (called quartz sensor) is as large as about ¾ inch, and this cannot always be inserted into the drilling pipe to get oil and methane.
- (13) This high performance of the pressure sensor can detect oil and methane gas in extremely deep underground.
If it is two steps single-sided grooved type or double-sided grooved type (abbreviation for grooved type or grooved resonators), after the second oscillation part (second grooved part) in circular, triangular, rectangular, hexagonal, or other shapes to mark the crystal orientation of piezoelectric material is machined inside or at the central part in square or rectangular shape, the inside or the central region of the second oscillation part is again formed so as to be pure circular, quasi-circular, triangular, square, hexagonal, or other shapes. The following effects are observed.
- {circumflex over (1)} Since the shape of the rectangular quartz blank is machined to be pure circular, quasi-circular or other shapes, the piezoelectric device achieves more excellent electric performance.
- {circumflex over (2)} Since the outer shape of the quartz blank can be in the form of a rectangular shape even if the oscillation part is purely circular or quasi-circular, the quartz wafer can be automatically cut, and then mass production becomes easy.
- {circumflex over (3)} Even when the oscillation part is in accurately circular or quasi-circular shape, the crystal axis direction can be conveniently recognized.
- {circumflex over (4)} When the extremely small oscillation part is manufactured by the chemical etching process, the shape is formed to avoid to be affected by the surface tension and crystal anisotropy due to the chemical etching step by step.
- {circumflex over (5)} Since the most ideal frequency of oscillation energy at the first circular vibrating part is dissipated from the outer second oscillation part (second grooved part) toward the outer periphery step by step, the quartz oscillator becomes to show the excellent ideal electrical performance.
- {circumflex over (6)} As the oscillation part is made to be very small and the aperture ratio (d/t) is set to around 80 by forming the oscillation part to be stepwise thin, the electrically excellent quartz oscillator can be manufactured, when the primary frequency is more than 400 MHz (less than 4 μm thick for AT-cut) for the AT-cut case.
- {circumflex over (7)} After the quartz oscillator is cut to be rectangular, the pure circular or quasi-circular first oscillation part is made, and another circular second oscillation part (second grooved part) is also made inside or at the central region of the first oscillation part to mark the crystal orientation. By this manufacturing method, after the direction marking slit is cut to find the crystal orientation as shown in FIGS. 32(a), 36(a), 40(a), and 44(a). By forming a crescent shape type in FIGS. 33(a), 37(a), 41(a), and 45(b), both the first oscillation part and the second one (second grooved part) can be formed to be pure-circular or quasi-circular, and the quartz blank is conveniently cut and massively produced from the quartz wafer to be in the rectangular outer shape.
- {circumflex over (8)} If the oscillation part is not made to be in thin at least two steps shape by chemically etching the first oscillation part and the second one (second grooved part), the wafer is thick as 80 μm. When the frequency of oscillation part is high as 2.1 GHz at AT-cut, the oscillation part is approximately 0.8 μm, the aperture ratio is found to be around 80 to resonate the best wave. Then the diameter of the oscillation part is extremely small as 0.8 μm×80=64 μm, the homogeneous chemical etching becomes impossible due to the surface tension of liquid solution as hydrogen fluoride etc for the chemical etching or crystal anisotropy, if the oscillation parts are not chemically etched to be thin step by step.
- {circumflex over (9)} Furthermore, when the aperture diameter is 64 μm, the chemically etched depth by hydrogen fluoride is at most 3.2 μm (for instance approximately 1/20 of the diameter). If the chemical etching is deeper than this, the quartz crystal anisotropy appears, and the flat surface accuracy becomes poor. Therefore, the ultra high frequency quartz oscillator must be manufactured by forming at least two steps shape with the chemical etching, since the aperture ratio is found to be about 80 to make electrically high-level quartz oscillator.
- {circumflex over (10)} When the diameter of the first oscillation part becomes extremely small as 64 μm or 0.32 mm, the shape of the second oscillation part becomes triangular, rectangular, or hexagonal except pure-circular or quasi-circular. Since the shape is too small, this can be better to be pure circular or quasi circular, however this can be triangular, rectangular, hexagonal, or other shapes.
- {circumflex over (11)} Since the electrode to oscillate only the second oscillation part is attached by photo resist chemical etching process to the front and rear surfaces of the first oscillation part, whose diameter is very small as approximately 0.32 mm and shape is pure-circular or quasi-circular, the second part does not oscillate, and the electrically ideal oscillator (resonator) is made to resonate at more high frequency without the spurious signal.
- {circumflex over (12)} When the quartz is relatively and chemically etched by using two or three steps or the plural steps shape, the chemical etching can shave the deep groove, which must be deeper than 1/20 of the oscillation part diameter to avoid the quartz crystal anisotropy.
- {circumflex over (13)} After the first chemical etching makes at first the pure circular or quasi circular shape, whose first oscillation part diameter is 0.32 mm and depth is 16 μm for example, the first and second oscillation parts are chemically and relatively etched step by step in order to make form the rectangular, hexagonal, or other shapes with 1.6 mm diameter at the outer part of circular shape, and the anisotropy problem can be solved.
- {circumflex over (14)} As discussed above, since the quartz anisotropy problem is relatively solved by chemical etching process with two steps more deeply than 1/20 of the aperture diameter, it becomes possible for mass production of high frequency quartz oscillator by using over 80 μm thick and more than 1 inch×1 inch wafer plate.
After the blank is selected to be the quartz crystal unit in the chemically etched single-sided grooved type of more than two steps shape, this is etched by the reactive ion etching (RIE) and polished by dual-face polishing machine, the AT-cut quartz oscillator is successfully developed over 467 MHz fundamental frequency. This quartz oscillator processed by this method is nearly in the concavo-convex or bi-convex shape rather than plano-convex shape as the ideal convex lens type, and this shows the excellent reactance-frequency characteristics.
This machining method demonstrates that the optimum aperture ratio d/t (diameter/thickness) is 80. As the consequence, when the quartz oscillator with very high frequency is required to be manufactured, the aperture diameter d becomes small, since the diameter d is proportional to the thickness t, which is extremely thin. When the diameter becomes small, the quartz oscillator shows the anisotropy problem, the parallel accuracy cannot be maintained due to the chemical etching process, since the quartz wafer is shaved to be deeper than 1/20 of the diameter d. This problem was solved in the following methods. At first, the first chemical etching is done, after the depth of the first oscillation part is selected to be less than 1/20 of the aperture diameter d which is 80 times of the thickness t corresponding to the frequency, and next we chemically etched the second oscillation part (second grooved part), whose diameter is much larger than the first oscillation part (outer region of the first oscillation part) and is not affected by d/t (80:1 or 100:1) problem. Since the first and second oscillation part (grooved part) is chemically and respectively etched with two steps, the quartz anisotropy property is solved.
Also, even if the quartz wafer blank is thick, the aperture d of oscillation part can be very small. Therefore we can mass-produce the ultra high frequency quartz oscillator whose electric characteristic is ideal and extremely thin in the plano-convex shape. This problem was solved in the following way. At first, the first chemical etching is done, after the depth of the first oscillation part is selected to be less than 1/20 of the aperture diameter d which is 80 or 100 times of the thickness t corresponding to the frequency, and secondly we chemically etched the second oscillation part (second grooved part), whose diameter is much larger than the first oscillation part (outer region of the first oscillation part) and is not affected by d/t problem. Since the first and second oscillation part (grooved part) is chemically and respectively etched step by step, the quartz anisotropy property is finally solved. When another method from
By the way, even if the quartz wafer blank is thick, the aperture d of oscillation part can be very small. Therefore we can mass-produce the electrically ideal ultra high frequency quartz oscillator, which is extremely thin in the plano-convex shape.
As shown on U.S. Pat. No. 3,694,677 On Sep. 26, 1972, Dr. Gunter K. Guttwein, Dr. Arthur D. Ballato, Dr. Theodre J. Lukaszek invented quartz oscillators of one step inverted mesa type (single-sided inverted mesa type and double-sided inverted mesa type) at US Army. This time we manufactured novel quartz oscillators of single-sided grooved type in two steps shape by using the chemical etching process or dry etching, which were found to have the following advantages over the former quartz oscillators in one step shape.
- {circumflex over (1)} When the aperture ratio (d/t) is chosen to be optimum, the oscillation area is made to be small as possible. Then the waved shape is prevented and becomes small on the oscillation surface, when the oscillation part is made to be thin as 5 μm. Also the surface accuracy becomes at least ten times better.
- {circumflex over (2)} Since the quartz anisotropy is avoided by selecting the aperture ratio to be 80:1 (d/t), the surface accuracy is improved for any quartz blank thickness.
- {circumflex over (3)} The latter new two steps oscillator has the structure of the optimum aperture ratio as 80:1 (d/t) regardless of quartz plate thickness t.
- {circumflex over (4)} Tough resonators against the mechanical shock and acceleration can be made, since the thick plate improves the structural and dynamic strength. Furthermore the step type quartz oscillators of two or more than two steps shape enables us to resist more strong shock.
- {circumflex over (5)} Since the former one step quartz oscillator in single-sided inverse mesa type and double-sided inverted mesa type are apt to make pin holes, the one step resonator etched down to 5 μm cannot be mass-produced. The latter two steps one can be mass-produced down to 5 μm.
- {circumflex over (6)} While one step inverted mesa type device needs only one chemical etching process, the two steps double-sided grooved type requires two etching processes. However the electrical property becomes improved, and the quartz oscillator device over 70 MHz will become two steps double-sided grooved type in the near future.
- {circumflex over (7)} When the single-sided inverted mesa type or doubled sided inverted mesa type in one step shape becomes thinner than 5 μm, the aperture ratio (d/t) must be larger due to the quartz anisotropy, and then there appears the wave shape (like up and down hills) on the oscillation part. Also the surface accuracy on the oscillation part becomes worse than 0.02 μm.
- {circumflex over (8)} In case of grooved type in two steps shape, there are few waves, and the surface accuracy is approximately 0.003 μm. And these are ten times better than those of inverted mesa type in one step shape.
- {circumflex over (9)} In case of grooved type in two or more steps, since there are the second grooved part (second oscillation part) and third grooved part (third oscillation part), the oscillation energy impressed on the small first central oscillation part (oscillating surface with electric voltage) is efficiently and smoothly used at the second and third outer oscillation part step by step, and the resonator shows the excellent electrical performance.
- {circumflex over (10)} In case of the single-sided grooved type in two steps shape, the device can be mass-produced to be thinner than 5 μm. After the oscillation surface of the blank is made to be thinner than 5 μm, the blank is polished by the polishing machine to impress mechanical pressure on the quartz plate both from upper and lower sides in order to confine the energy. As a consequence, ideal quartz oscillators in the concavo-convex or bi-convex lens shape, rather than the conventional piano-convex, are thought to be made to show better electric property approximately as 5.0 GHz fundamental frequency for BT-cut below 0.5 μm. Furthermore, in the near future, it will be possible for the quartz oscillator to be developed as thin as approximately 0.015 μm (primary frequency as 160 GHz for BT-cut).
The accurate name of the single-sided inverted mesa type or double-sided inverted mesa type with two steps in this invention should be called as the single-sided grooved type or double-sided grooved type (abbreviated as grooved type or grooved resonators type). The reasons of these names are as follows.
- {circumflex over (1)} Even when the outer shape is pure circular, the central oscillation part can be in purely circular shape, which contributes to better electrical performance.
- {circumflex over (2)} The oscillation energy impressed on the small first central oscillation part is efficiently and smoothly used at the second grooved part (second oscillation part) and third outer grooved part (third oscillation part) step by step.
- {circumflex over (3)} The electrode can be made smoothly in step shape.
- {circumflex over (4)} The quartz blank can be made to be thick, while the oscillation part is processed to be very thin.
- {circumflex over (5)} Based on the above items, the one step inverted mesa type invented by the US Army is quite different from the grooved type in this invention. Therefore, this is named as the grooved type or grooved resonators type.
The following papers were introduced to show that the aperture ratio (d/t) should be approximately 80 in order to achieve the best electrical performance.
- {circumflex over (1)} 1999 IEEE International Frequency Control Symposium, pp. 425-428.
- {circumflex over (4)} 21st (1999) Piezoelectric Devices Conference and Exhibition, pp. 4/1-4/6.
- {circumflex over (3)} 2000 IEEE/EIA International Frequency Control Symposium & Exhibition, pp 255-259.
This invention is related to the manufacturing process of a grooved type device in two or more than two steps stereo shape by using the chemical etching, and then this can apply to a wide variety of semi-conducting electronic materials such as silicone, gallium arsenate, and so forth in addition to the piezoelectric material as quartz, lithium niobium, etc.
INDUSTRIAL APPLICABILITYThis invention can be used for a wide variety of fields such as communication equipment, instrumentation, general computer, office automation information technology, home appliance microcomputer, and so forth.
Claims
1. A manufacturing method of said acousto-electric transducer, which makes the oscillation part of a final thickness and target profile, after the final profile is formed on the surface of piezoelectric material which is thicker than the final thickness, and the surface of said piezoelectric material is reactively etched and homogeneously decreasing the thickness from both ends toward the central region of said piezoelectric material.
2. A manufacturing method of said piezoelectric device, which makes the oscillation part of a final thickness and target profile inside the central region of a rod in hollow cylindrical shape, after the final profile is formed on the surface of a rod made from the piezoelectric material, and the surface of said rod except the wall of said rod is processed by the dry etching and homogeneously decreasing the thickness from both ends toward the central region of said rod.
3. A manufacturing method of said acousto-electric transducer, which makes the oscillation part of a final thickness and target profile, after the final profile is formed on the surface of piezoelectric material which is thicker than the final thickness, and the surface of said piezoelectric material is processed by the dry etching and homogeneously decreasing the thickness from both ends toward the central region of said piezoelectric material.
4. A manufacturing method of said piezoelectric device, which makes the oscillation part of a final thickness and target profile inside the central region of a rod in hollow cylindrical shape, after the final profile is formed on the surface of a rod made from the piezoelectric material, and the surface of said rod except the wall of said rod is processed by the dry etching and homogeneously decreasing the thickness from both ends toward the central region of said rod.
5. A manufacturing method of said piezoelectric device, which makes the piezoelectric material in a lens shape identical to an auxiliary blank, after said auxiliary blank in the final lens shape is closely attached to both ends of the rod made from the piezoelectric material, and the surface of said auxiliary blank attached to the rod is processed by the dry etching, and then the surface of said auxiliary blank is shaved at first and next the surface of the piezoelectric material.
6. A manufacturing method of said piezoelectric device, which makes the piezoelectric material in a lens shape with a holder identical to an auxiliary blank, after said auxiliary blank in the final lens shape is closely attached to both ends of the rod made from the piezoelectric material, and the surface of said auxiliary blank attached to the rod is processed by the dry etching, and then the surface of said auxiliary blank is shaved at first, and next the surface of the piezoelectric material is also shaved.
Type: Application
Filed: Jul 1, 2005
Publication Date: Jan 26, 2006
Inventor: Yoshiaki Nagaura (Chikushino-shi)
Application Number: 11/171,449
International Classification: H01L 41/04 (20060101);