Surface acoustic wave device and method of fabricating the same
A surface acoustic wave device includes a piezoelectric substrate having a first surface on which comb-like electrodes, first pads connected thereto, and a first film are provided. The first film is located so as to surround the comb-like electrodes. A base substrate has a second surface on which second pads joined to the first pads and a second film joined to the first film are provided. The first and second films joined by a surface activation process define a cavity in which the comb-like electrodes and the first and second pads are hermetically sealed.
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1. Field of the Invention
The invention generally relates to surface acoustic wave devices and methods of fabricating the same, and more particularly, to a surface acoustic wave device having a SAW chip hermetically sealed, and a method of fabricating the same.
2. Description of the Related Art
Recently, there has been a demand to downsize electric parts mounted to electronic devices and improve the performance thereof with downsizing and high performance of the electronic devices. For instance, there have been similar demands on surface acoustic wave (SAW) devices that are electric parts used as filters, delay lines, oscillators in electronic devices capable of transmitting and receiving radio waves.
A description will now be given of a filter device equipped with a conventional SAW device.
Referring to
There is another proposal to mount the SAW chip in flip-chip fashion (see, for example, Japanese Patent Application Publication No. 2001-110946).
As shown in
A duplexer equipped with a transmit filter and a receive filter may be formed by using SAW filters as mentioned above. Such a duplexer will now be described with reference to
Referring to
The SAW filter or duplexer as mentioned above is required to have the SAW chip hermetically sealed. The metal cap is used, along with bonding material or resin, to accomplish hermetically sealing.
However, there are drawbacks to be solved. A large joining area (seal width) at the interface between the package and the cap is needed to hermetically seal the cavity with high reliability. However, this prevents downsizing of the package. Downsizing of package is also restricted due to the use of wires because the wires need a relatively wide pattern for bonding. The package is the multilayer substrate made of ceramics, which is comparatively expensive. The device needs the process of assembling the cap, chip and package device, and is therefore costly.
It is an object of the present invention to provide a downsized, less expensive, productive SAW device and a method of fabricating the same.
This object of the present invention is achieved by a surface acoustic wave device comprising: a piezoelectric substrate having a first surface on which comb-like electrodes, first pads connected thereto, and a first film are provided, the first film being located so as to surround the comb-like electrodes; and a base substrate having a second surface on which second pads joined to the first pads and a second film joined to the first film are provided, the first and second films joined by a surface activation process defining a cavity in which the comb-like electrodes and the first and second pads are hermetically sealed.
The above objects of the present invention are also achieved by a method of fabricating a surface acoustic wave device comprising the steps of: (a) forming a first film on a first surface of a piezoelectric substrate on which comb-like electrodes and first pads are formed so as to be surround by the first film; (b) forming a second film on a second surface of a base substrate, the second film corresponding to the first film in position; (c) subjecting a surface activation process to surfaces of the first and second films; and (d) joining the first and second films so as to join activated surfaces thereof, the comb-like electrodes being hermetically sealed in a cavity defined by the first and second films.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:
A description will now be given of the fundamental concepts of the present invention.
The SAW device 1 has a piezoelectric substrate 11A and a base substrate 2A. On the main (upper) surface of the piezoelectric substrate 11A, provided are comb-like electrodes (IDT) 13, electrode pads 14 and wiring patterns 15. Electrode pads 5 are provided on a main surface of the base substrate 2A. The electrode pads 5 are provided at positions that correspond to the electrode pads 14.
A metal film 16 is provided on a peripheral potion on the main surface of the piezoelectric substrate 11A. The metal film 16 is located further out than the IDT 13 and the pads 14 so as to surround these patterns. Similarly, a metal film 4 is provided on a peripheral portion on the main surface of the base substrate 2A. The metal films 16 and 4 are joined so that a cavity 9 defined by the piezoelectric substrate 11A and the base substrate 2A can be hermetically sealed. In the cavity 9 thus sealed hermetically, there are the IDT 13, the electrode pads 14 and the wiring patterns 15.
When the substrates 11A and 2A are joined so that the metal films 16 and 4 are joined, the electrode pads 14 and 5 are joined. An electric contact with the pads 14 on the substrate 11A can be made on the backside of the base substrate 2A via a via-hole 6a that penetrates the base substrate 2A. The via-hole 6a may be full of a conductor such as a metal bump, so that a via-wiring line can be made. The input and output terminals of the IDT 13 can be extended up to the backside of the base substrate 2A.
The piezoelectric substrate 11A may be a piezoelectric single-crystal substrate of a 42° Y-cut X-propagation lithium tantalate (LiTaO3:LT). The LT substrate has a linear expansion coefficient of 16.1 ppm/° C. in the X direction in which the SAW is propagated. The LT substrate may be replaced by a piezoelectric single-crystal substrate of Y-cut lithium niobate (LiNbO3:LN).
The IDT 13, the electrode pads 14, the wiring patterns 15 and the metal film 16 may be made of a conductor that contains, as the major component, at least one of gold (Au), aluminum (Al), copper (Cu), titanium (Ti), chromium (Cr) and tantalum (Ta). The patterns may be a single layer or a laminate composed of at least two conductive layers, each of which contains at least one of Au, Al, Cu, Ti, Cr and Ta. The conductors may be deposited by, for instance, sputtering.
The base substrate 2A may be made of an insulator that contains, as the major component, at least one of silicon, ceramics, aluminum ceramics, BT (Bismuthimido-Triazine) resin, PPE (Polyphenylene-Ethel), polyimide resin, glass-epoxy and glass-cloth. The first embodiment employs silicon for the base substrate 2A because silicon can easily be processed and handled at the stage of wafer. Preferably, the base substrate 2A is made of a silicon substance that has a resistivity as low as 1000 Ω·m or greater in order to avoid degradation of the filter characteristic stemming from the resistance of silicon.
The electrode pads 5 and the metal film 4 on the main surface of the base substrate 2A may be made of a conductor that contains, as the major component, at least one of Au, Al, Cu, Ti, Cr and Ta. The conductors may be deposited by, for instance, sputtering. The pads 5 and the film 4 may be a single layer or a laminate of at least two layers.
An adhesive may be used to join the substrates 11A and 2A. However, it is preferable to directly bond the substrates 11A and 2A metal films 16 and 4 at room temperature. In this case, the bonding strength can be enhanced by applying a surface activation process to the joining surfaces of the substrates 11A and 2A. Now, a description will be given, with reference to
Referring to
After the cleaned substrates are dried (drying process), as shown in
The piezoelectric substrate 11A and the silicon substrate 2A are then positioned and joined to each other (joining process) in such a manner that the metal films 16 and 4 are positioned and the electrode pads 14 and 5 are positioned. For most materials, this joining process may be carried out in a vacuum or in an atmosphere of a high purity gas such as an inert gas, though it may be carried out in the air. Also, it might be necessary to press the substrates 11A and 2A from both sides. This joining process can be carried out at room temperature or by heating the substrates 11A and 2A at a temperature of 100° C. or lower. The use of heating may increase the joining strength of the substrates 11A and 2A.
The present method does not need an annealing process at 1000° C. or higher after the substrates 11A and 2A are joined. Thus, the substrates 11A and 2A can be reliably joined without any damage. In addition, the method with the surface activation process does not need any adhesive agent such as resin or metal and realizes a height-reduced package, so that downsizing of package can be achieved. Further, a sufficient joining strength can be obtained by a smaller joining interface area than that for the adhesive, so that the package can be miniaturized. The joining process employed in the invention can be applied to the wafer. Thus, a large number of SAW devices 1 can be produced at a time by using a wafer-level piezoelectric substrate having multiple piezoelectric substrates integrally arranged in rows and columns and a wafer-level base substrate having multiple base substrates integrally arranged in rows and columns. This realizes a simplified production process and an improved yield.
When the metal films 4 and 16 contain gold, these films can be joined more tightly because gold is comparatively soft. The films 4 and 16 are joined via joining surfaces that contain gold by the surface activation process. Only one of the metal films 4 and 16 may contain gold.
Based on the above-mentioned concepts of the present invention, the cavity 9 that houses the IDT 13 can be minimized. The use of the surface activation process for joining the piezoelectric substrate 11A and the base substrate 2A realizes a reduced joining interface area while a sufficient joining strength can be secured. This contributes to downsizing the SAW device. The base substrate 2A can be processed at the wafer level and may be made of silicon that is less expensive. This simplifies the fabrication process and produces the less-expensive SAW device at an improved yield. Now, a description will be given of embodiments of the present invention based on the above-mentioned concepts.
(First Embodiment)
A description will now be given of a first embodiment of the present invention.
As shown in
As is shown in
The metal film 4 is formed on the base substrate 22 so as to surround the electrode pads 5. The metal film 4 corresponds to the metal film 16 in position. The metal film 4 is electrically extended to the backside of the silicon substrate 2 by means of the via conductors 7 that penetrate the silicon substrate 2. The metal film 4 may be grounded on the backside of the silicon substrate 2 through the via conductors 7. In the assembled state, the IDTs 13, the electrode pads 14 and 5 and the metal films 16 and 4 are all grounded.
The SAW chip 20 is joined to the base substrate 22 so that the main surface of the SAW chip 20 faces the main surface of the base substrate 22. That is, the SAW chip 20 is mounted in the facedown state. This joining results in the SAW device 21 shown in
A description will now be given of a method of fabricating the SAW device 21 with reference to
The step of
The patterned film 13B is the underlying layer of the IDTs 13, the electrode pads 14, the wiring patterns 15 and the metal film 16. The mask 25 that remains after etching is removed, and an insulating film such as silicon oxide (SiO2) is provided so as to cover the entire surface including the patterned electrode film 13B. Then, as shown in
Then, as shown in
The electrode pads 14 and the metal film 16 are connected by the wiring patterns 17. However, the wiring patterns 17 may be omitted when the LT substrate 11 has a resistivity as high as 10−14 to 10−7 Ω·m. This further facilitates to simplification of the production process.
The base substrate 22 is produced as follows. The step of
Then, as shown in
The vias 6a and 7a are formed as follows. A mask 36 patterned into the vias 6a and 7a is photolithographically formed, as shown in
The SAW chip 20 and the base substrate 22 thus produced are joined by the process that has been described with reference to
All the steps of
The steps of
Then, as shown in
The above process does not each the metal film 4′ and the electrode patterns 5′, so that the metal films 4′ and 16 and the electrode pads 5′ and 14 can be self-aligned in joining. This simplifies the production process greatly. In the above-mentioned alternative process, the SAW chip 20 produced by the process shown in
The above-mentioned fabrication methods complete the SAW chip 20 and the base substrate 22 separately, and then join them. Besides, some process may be applied after the SAW chip 20 and the base substrate 22 are joined. For example, the vias 6a and 7a may be formed in the silicon substrate 2 after joining. This will now be described with reference to
The steps of
The above process does not etch the metal film 4′ and the electrode pads 5′. Thus, the metal films 4′ and 16 and the electrode pads 5′ and 14 can be self-aligned at the time of joining. This simplifies the production process. The SAW device 21 thus produced has the aforementioned structure and effects.
(Second Embodiment)
A given electric element is formed on the main surface of the base substrate 32. The electric element may, for example, be a matching circuit, which changes the input impedance of the SAW chip 20 so as to make impedance matching with an external circuit (impedance conversion). In
The electric element may be simultaneously formed along with the electrode pads 5 and the metal film 4 or may be formed before or after these patterns are formed. The electric element may be made of copper (Cu), aluminum (Al) or gold (Au) deposited by sputtering or the like.
The SAW device includes the electric element so that it does not need it externally. The SAW device is thus usable to various applications. The other structures, fabrication method and effects of the SAW device according to the second embodiment are the same as those of the first embodiment.
(Third Embodiment)
The SAW chip 40 has a piezoelectric substrate 41a like an LT substrate, to the backside of which is joined another substrate 41b made of a material different from the piezoelectric substrate 41a. The substrate 41b serves as a support substrate, and may, for example, be a silicon substrate. The substrates 41a and 41b form a joined substrate.
Preferably, the support substrate 41b has a smaller Young's modulus and a smaller linear expansion coefficient than those of the piezoelectric substrate 41a. A sapphire substrate or silicon substrate may be used as the supporting substrate 41b. The use of the above support substrate 41b restricts thermal expansion of the piezoelectric 41a, and reinforces the strength thereof so that the required strength of the piezoelectric substrate can be achieved by the support substrate. Thus, the joined substrate can be made thinner than the piezoelectric substrate conventionally used, so that the SAW chip can be thinned. When the support substrate 41b is made of silicon, which is easily processible, the SAW device can be produced more easily and precisely. Further, the wafer-level process can be used, so that the productivity can be improved. From the aforementioned viewpoints, preferably, the support substrate 41 is a silicon substance that has a resistivity as low as 1000 Ω·m or greater in order to avoid degradation of the filter characteristic stemming from the resistance of silicon.
It is preferable that the piezoelectric substrate 41a and the support substrate 41b are joined by the joining method based on the surface activation process. Thus, the substrates 41a and 41b can be joined more strongly and even at room temperature. This prevents occurrence of any damages during process and degradation of the characteristic. Improved joining strength enables a reduced joining interface area, so that the SAW chip 40 can be downsized. Further, improved joining strength effectively restricts thermal expansion of the LT substrate 41a by the silicon substrate 41b, so that the frequency stability for temperature variation can be improved.
The SAW chip 40 can be produced as shown in
The joined substrate is grinded and polished from both sides thereof, so that the joined substrate 41 composed of the substrates 41a and 41b can be produced. The joined substrate 41 is thinner than the LT substrate alone. Then, the joined substrate 41 is processed in such a manner as shown in
(Fourth Embodiment)
A fourth embodiment of the present invention is directed to fabricating a large number of SAW devices at a time. For this purpose, substrates 50A and 52A respectively shown in
Holes for dicing may be formed simultaneously when the vias 6a and 7a are formed in the step of
(Fifth Embodiment)
The SAW device of the third embodiment may be produced by a process similar to that of the fourth embodiment. In this case, a substrate 60A as shown in
The other structures, fabrication method and effects of the fifth embodiment are the same as those of the previous embodiments.
(Sixth Embodiment)
A sixth embodiment of the present invention is directed to joining the base substrate 22 or 42 directly to a substrate of low-temperature co-fired ceramics (LTCC) or a printed-circuit board.
(Seventh Embodiment)
A seventh embodiment of the present invention is a SAW device equipped with two or more SAW filters, whereas any of the aforementioned embodiments is equipped with only one SAW filter.
The present invention is not limited to the specifically disclosed embodiments, and other embodiments, variations and modifications may be made without departing from the scope of the present invention.
The present application is based on Japanese Patent Application No. 2003-096577 filed on Mar. 31, 2003, the entire disclosure of which is hereby incorporated by reference.
Claims
1. A surface acoustic wave device comprising:
- a piezoelectric substrate having a first surface on which comb-like electrodes, first pads connected thereto, and a first film are provided, the first film being located so as to surround the comb-like electrodes;
- a base substrate having a second surface on which second pads joined to the first pads and a second film joined to the first film are provided;
- an electronic element provided on an area of the second surface facing the first surface; and
- a ceramic substrate supporting the base substrate, a chip electronically coupled to the second pads being mounted on the ceramic substrate, the base substrate having a plate shape, and the first and second films joined by a surface activation process defining a cavity in which the comb-like electrodes, the first and second pads, and the electronic element are hermetically sealed.
2. The surface acoustic wave device as claimed in claim 1, wherein each of the first and second films contains a metal as a major component.
3. The surface acoustic wave device as claimed in claim 1, wherein the first and second films are joined via joining surfaces that contain gold.
4. The surface acoustic wave device as claimed in claim 1, wherein the base substrate is one of a semiconductor substrate and an insulator substrate.
5. The surface acoustic wave device as claimed in claim 1, wherein the base substrate is made of silicon.
6. The surface acoustic wave device as claimed in claim 1, wherein the first film is provided on peripheral portions on the first surface of the piezoelectric substrate, and the second film is provided on peripheral portions on the second surface of the base substrate.
7. The surface acoustic wave device as claimed in claim 1, further comprising an impedance matching circuit on the second surface of the base substrate, the impedance matching circuit being coupled to at least one of the comb-like electrodes.
8. The surface acoustic wave device as claimed in claim 1, wherein the comb-like electrodes and the first pads form a transmit filter and a receive filter.
9. The surface acoustic wave device as claimed in claim 1, wherein:
- the comb-like electrodes and the first pads form a transmit filter and a receive filter;
- the surface acoustic wave device comprises an impedance matching circuit coupled to at least one of the transmit filter and the receive filter, and a common terminal via which an external connection with the impedance matching circuit can be made.
10. The surface acoustic wave device as claimed in claim 1, wherein the base substrate has via-wiring lines connected to the second pads, so that electric connections with the first pads can be made on a surface of the base substrate opposite to the second surface.
11. A surface acoustic wave device comprising:
- a piezoelectric substrate having a first surface on which comb-like electrodes, first pads connected thereto, and a first film are provided, the first film being located so as to surround the comb-like electrodes; and
- a base substrate having a second surface on which second pads joined to the first pads and a second film joined to the first film are provided,
- the first and second films joined by a surface activation process defining a cavity in which the comb-like electrodes and the first and second pads are hermetically sealed,
- wherein the surface acoustic wave device further comprises a support substrate joined to a third surface of the piezoelectric substrate opposite to the first surface;
- the piezoelectric substrate and the support substrate have been subjected to the surface activation process; and
- the support substrate is one of a silicon substrate and a sapphire substrate.
12. A method of fabricating a surface acoustic wave device comprising the steps of:
- (a) forming a first metal film on a first surface of a piezoelectric substrate on which comb-like electrodes and first pads are provided, wherein the first metal film surrounds the comb-like electrodes and the first pads and is provided along edges of the piezoelectric substrate;
- (b) forming a second metal film on a second surface of a base substrate other than a piezoelectric substrate, the base substrate comprising second pads, wherein the second metal film is provided along edges of the base substrate, and a position of the second metal film and the second pads corresponds to a position of the first metal film and the first pads respectively;
- (c) applying a surface activation process to surfaces of the first metal film and surfaces of the second metal film so that residual impurities are removed; and
- (d) joining the first metal film and the second metal film so as to join bond the activated surfaces thereof directly, wherein the comb-like electrodes, the first pads and the second pads are hermetically sealed in a cavity defined by the first metal film and the second metal film,
- edges of the first and second metal films being flush with side surfaces of the piezoelectric substrate and those of the base substrate and forming parts of side surfaces of the surface acoustic wave device,
- the base substrate having a contact hole for making an external connection with the first and second metal films.
13. A method of fabricating a surface acoustic wave device comprising the steps of:
- (a) forming a first film on a first surface of a piezoelectric substrate on which comb-like electrodes and first pads are formed so as to be surrounded by the first film;
- (b) forming a second film on a second surface of a base substrate on which second pads and an electronic element are formed so as to be surrounded by the second film, the second film and the second pads corresponding to the first film and the first pads in position, the base substrate having a plate shape and is being supported by a ceramic substrate on which a chip electronically coupled to the electronic element is mounted;
- (c) subjecting a surface activation process to surfaces of the first and second films; and
- (d) joining the first and second films so as to join activated surfaces thereof,
- the comb-like electrodes, the first and second pads and the electronic element being hermetically sealed in a cavity defined by the first and second films.
14. The method as claimed in claim 13, wherein the steps (a) and/or (b) forms the first and/or second film that contains a metal as a major component.
15. The method as claimed in claim 13, further comprising a step of forming an electric element on the second surface.
16. The method as claimed in claim 13, further comprising a step of forming via-wiring lines in the base substrate so that the second pads can be extended to a third surface of the base substrate opposite to the second surface.
17. A method of fabricating a surface acoustic wave device comprising the steps of:
- (a) forming a first film on a first surface of a piezoelectric substrate on which comb-like electrodes and first pads are formed so as to be surrounded by the first film;
- (b) forming a second film on a second surface of a base substrate, the second film corresponding to the first film in position;
- (c) subjecting a surface activation process to surfaces of the first and second films; and
- (d) joining the first and second films so as to join activated surfaces thereof,
- the comb-like electrodes being hermetically sealed in a cavity defined by the first and second films,
- wherein the method further comprises a step of joining a support substrate to a backside of the piezoelectric substrate opposite to the first surface after an interface between the piezoelectric substrate and the support substrate is subjected to the surface activation process,
- the support substrate being one of a silicon substrate and a sapphire substrate.
18. A surface acoustic wave device comprising:
- a piezoelectric substrate having a first surface on which comb-like electrodes, first pads connected thereto, and a first film are provided, the first film surrounding the comb-like electrodes;
- a base substrate having a second surface on which second pads joined to the first pads and a second film joined to the first film are provided; and
- an electronic element provided on an area of the second surface facing the first surface, wherein the first film and the second film are configured to be joined by a surface activation process and to define a cavity in which the comb-like electrodes, the first pads, the second pads, and the electronic element are hermetically sealed,
- the second pads being electrically extended via a through hole penetrating the base substrate, to a third surface of the base substrate opposite to the second surface thereof,
- the first and second films being electrically extended, via another through hole penetrating the base substrate, to the third surface,
- the piezoelectric substrate and the base substrate having an identical width and length forming flat side surfaces of the surface acoustic wave device.
19. A method of fabricating a surface acoustic wave device, comprising the steps of:
- (a) forming a first film on a first surface of a piezoelectric substrate comprising comb-like electrodes and first pads, wherein the first film surrounds the comb-like electrodes and the first pads;
- (b) forming a second film on a second surface of a base substrate comprising second pads and an electronic element, wherein the second film surrounds the second pads and the electronic element, and a position of the second film and the second pads corresponds to a position of the first film and the first pads, respectively;
- (c) applying a surface activation process to surfaces of the first film and surfaces of the second film; and
- (d) joining the first film and the second film so as to join the activated surfaces thereof, wherein the comb-like electrodes, the first pads, the second pads, and the electronic element are hermetically sealed in a cavity defined by the first film and the second film,
- the second pads being electrically extended, via a through hole penetrating the base substrate, to a third surface of the base substrate opposite to the second surface thereof,
- the first and second films being electrically extended, via another through hole penetrating the base substrate, to the third surface,
- the piezoelectric substrate and the base substrate having an identical width and length forming flat side surfaces of the surface acoustic wave device.
20. A surface acoustic wave device comprising:
- a piezoelectric substrate having a first surface on which comb-like electrodes, first pads connected thereto, and a first metal film are provided, the first metal film being provided along edges of the piezoelectric substrate and being located so as to surround the comb like electrodes; and
- a base substrate other than a piezoelectric substrate, the base substrate having a second surface on which second pads joined to the first pads and a second metal film joined to the first metal film are provided, the second metal film being provided along edges of the base substrate,
- wherein the first and second metal films are configured to be joined by a surface activation process directly bonded and define a cavity in which the comb-like electrodes and the first and second pads are hermetically sealed,
- edges of the first and second metal films being flush with side surfaces of the piezoelectric substrate and those of the base substrate and forming parts of side surfaces of the surface acoustic wave device,
- the base substrate having a contact hole for making an external connection with the first and second metal films.
21. The surface acoustic wave device of claim 20, wherein the first and second metal films each comprise at least one metal selected from a group consisting of Au, Al, Cu, Ti, Cr, and Ta.
22. The surface acoustic wave device of claim 20, wherein the base substrate is one of a semiconductor substrate and an insulator substrate.
23. The surface acoustic wave device of claim 20, wherein the comb-like electrodes and the first pads form a transmit filter or a receive filter.
24. The surface acoustic wave device of claim 20, wherein the piezoelectric substrate and the base substrate have an identical width and length forming flat side surfaces of the acoustic wave device.
25. An acoustic wave device comprising:
- a first substrate having a first surface on which electrodes of an acoustic wave filter are provided, first pads connected thereto, and a first film made of a metal are provided, the first film located so as to surround the electrodes; and
- a base substrate other than the first substrate, the base substrate having a second surface on which second pads joined to the first pads and a second film made of a metal joined to the first film are provided,
- wherein the first and second films are directly bonded without solder and define a cavity in which the electrodes and the first and second pads are hermetically sealed,
- edges of the first and second films being flush with side surfaces of the first substrate and those of the base substrate and forming parts of side surfaces of the acoustic wave device,
- the base substrate having a contact hole for making an external connection with the first and second films.
26. The acoustic wave device of claim 25, wherein the first and second films each comprise at least one metal selected from a group consisting of Au, Al, Cu, Ti, Cr, and Ta.
27. The acoustic wave device of claim 25, wherein the base substrate is one of a semiconductor substrate and an insulator substrate.
28. The acoustic wave device of claim 25, wherein the first film is provided on peripheral portions on the first surface of the first substrate, and the second film is provided on peripheral portions on the second surface of the base substrate.
29. The acoustic wave device of claim 25, wherein the electrodes and the first pads form a transmit filter and a receive filter.
30. The acoustic wave device of claim 25, wherein the first substrate and the base substrate have an identical width and length forming flat side surfaces of the acoustic wave device.
31. The method of claim 12, wherein the first and second metal films each comprise at least one metal selected from a group consisting of Au, Al, Cu, Ti, Cr, and Ta.
32. The method of claim 12, wherein the base substrate is one of a semiconductor substrate and an insulator substrate.
33. The method of claim 12, wherein the comb-like electrodes and the first pads form a transmit filter or a receive filter.
34. The method of claim 12, wherein the piezoelectric substrate and the base substrate have an identical width and length forming flat side surfaces of the acoustic wave device.
35. A method of fabricating an acoustic wave device comprising the steps of:
- (a) forming a first film made of a metal on a first surface of a first substrate on which electrodes of an acoustic wave filter and first pads are provided, wherein the first film surrounds the electrodes and the first pads;
- (b) forming a second film made of a metal on a second surface of a base substrate other than the first substrate, the base substrate comprising second pads, wherein a position of the second film and the second pads corresponds to a position of the first film and the first pads respectively;
- (c) applying a surface activation process to surfaces of the first film and surfaces of the second film so that residual impurities are removed; and
- (d) joining the first film and the second film so as to bond the activated surfaces thereof directly, wherein the electrodes, the first pads and the second pads are hermetically sealed in a cavity defined by the first metal film and the second metal film,
- edges of the first and second metal films being flush with side surfaces of the first substrate and those of the base substrate and forming parts of side surfaces of the acoustic wave device,
- the base substrate having a contact hole for making an external connection with the first and second films.
36. The method of claim 35, wherein the first and second films each comprise at least one metal selected from a group consisting of Au, Al, Cu, Ti, Cr, and Ta.
37. The method of claim 35, wherein the base substrate is one of a semiconductor substrate and an insulator substrate.
38. The method of claim 35, wherein the first film is provided on peripheral portions on the first surface of the first substrate, and the second film is provided on peripheral portions on the second surface of the base substrate.
39. The method of claim 35, wherein the electrodes and the first pads form a transmit filter and a receive filter.
40. The method of claim 35, wherein the first substrate and the base substrate have an identical width and length forming flat side surfaces of the acoustic wave device.
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Type: Grant
Filed: Nov 22, 2008
Date of Patent: Mar 17, 2015
Assignee: Taiyo Yuden Co., Ltd. (Tokyo)
Inventors: Osamu Kawachi (Yokohama), Osamu Ikata (Yokohama), Masanori Ueda (Yokohama), Suguru Warashina (Kawasaki)
Primary Examiner: Barbara Summons
Application Number: 12/276,319
International Classification: H03H 9/72 (20060101); H03H 9/64 (20060101); H03H 3/08 (20060101); H03H 9/54 (20060101);