Acoustic wave device

An acoustic wave device includes: a first substrate; a first acoustic wave filter located on a first surface of the first substrate; a pad that is located on the first surface and electrically separated from the first acoustic wave filter in the first surface; a ground pattern that is located on the first surface, and is located between the pad and the first acoustic wave filter in the first surface; and a second acoustic wave filter that is electrically connected to the pad, and at least partially overlaps with the first acoustic wave filter in plan view.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2016-097206, filed on May 13, 2016, the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the present invention relates to an acoustic wave device.

BACKGROUND

As a packaging method of an acoustic wave device, there has been known a method that face-down mounts a chip including an acoustic wave element, and then covers the periphery of the chip with a sealing member. Japanese Patent Application Publication No. 2008-546207 (Patent Document 1) describes that two substrates each including an acoustic wave element formed on the surface thereof are bonded together through an interlayer so that the acoustic wave elements face each other across an air gap.

The acoustic wave device can be downsized by forming acoustic wave filters on different surfaces and staking them. However, the acoustic wave filters interfere with each other, and thereby, the isolation characteristic deteriorates.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided an acoustic wave device including: a first substrate; a first acoustic wave filter located on a first surface of the first substrate; a pad that is located on the first surface and electrically separated from the first acoustic wave filter in the first surface; a ground pattern that is located on the first surface, and is located between the pad and the first acoustic wave filter in the first surface; and a second acoustic wave filter that is electrically connected to the pad, and at least partially overlaps with the first acoustic wave filter in plan view.

DETAILED DESCRIPTION

Hereinafter, a description will be given of embodiments of the present invention with reference to the accompanying drawings.

First Embodiment

FIG. 1is a cross-sectional view of an acoustic wave device in accordance with a first embodiment. As illustrated inFIG. 1, a substrate20is mounted on a substrate10. The upper surface of the substrate10corresponds to a first surface70, the lower surface of the substrate20corresponds to a second surface72, and the lower surface of the substrate10corresponds to a third surface74. The substrate10includes a support substrate10aand a piezoelectric substrate10b.The support substrate10ais, for example, a sapphire substrate, a spinel substrate, an alumina substrate, or a silicon substrate. The piezoelectric substrate10bis, for example, a lithium tantalate substrate or a lithium niobate substrate. The piezoelectric substrate10bis bonded on the upper surface of the support substrate10a.The bonded surface of the piezoelectric substrate10band the support substrate10ais a plane surface and flat.

Located on the upper surface of the substrate10(i.e., on the first surface70) are an acoustic wave resonator12, wiring lines34, pads35aand35b,and a ground pattern37. The acoustic wave resonator12is formed of a metal layer17, and the wiring lines34, the pads35aand35b,and the ground pattern37are formed of the metal layer17and a metal layer18formed on the metal layer17. The metal layer17is, for example, an aluminum layer or a copper layer. The metal layer18is, for example, a copper layer or a gold layer. Located on the lower surface of the substrate10(i.e., on the third surface74) are terminals30athrough30c.The terminals30athrough30care foot pads for connecting the acoustic wave resonators12and22to external devices. Via wirings32athrough32cpenetrating through the substrate10are provided. The via wirings32aand32belectrically connect the pads35aand35bto the terminals30aand30b,respectively. The via wiring32celectrically connects the ground pattern37and the terminal30c.The terminals30athrough30cand the via wirings32athrough32care formed of, for example, a metal layer such as a copper layer, an aluminum layer, or a gold layer.

Located on the lower surface of the substrate20(i.e., on the second surface72) are an acoustic wave resonator22, a wiring line27, and a pad28. The substrate20is, for example, an insulating substrate such as a glass substrate or a semiconductor substrate such as a silicon substrate. The acoustic wave resonator22includes a lower electrode23, a piezoelectric film24, and an upper electrode25. An air gap21is located between the lower electrode23and the substrate20. The pad28is formed of, for example, a metal layer such as a copper layer, an aluminum layer, or a gold layer. A bump36and a ring-shaped sealing portion38are located between the substrates10and20. The substrate20is flip-chip mounted (face-down mounted) on the substrate10through the bump36. The bump36is, for example, a gold bump, a solder bump, or a copper bump. The ring-shaped sealing portion38is formed of a metal layer such as a gold layer, a copper layer, or a solder layer, or an insulating layer such as a resin layer. The acoustic wave resonators12and22face each other across an air gap26. The air gap26is sealed by the ring-shaped sealing portion38, and the substrates10and20. The bump36is surrounded by the air gap26.

The terminal30ais electrically connected to the acoustic wave resonator12through the via wiring32a,the pad35a,and the wiring line34. The terminal30bis electrically connected to the acoustic wave resonator22through the via wiring32b,the pad35b,the bump36, the pad28, and the wiring line27. The terminal30bis not electrically connected to the acoustic wave resonator12. The terminal30cis electrically connected to the ground pattern37through the via wiring32c.When a ground potential is supplied to the terminal30c, the ground pattern37is grounded.

FIG. 2Ais a plan view of the acoustic wave resonator12, andFIG. 2Bis a cross-sectional view of the acoustic wave resonator22. As illustrated inFIG. 2A, the acoustic wave resonator12is a surface acoustic wave resonator. An Interdigital Transducer (IDT)15and reflectors16are located on the substrate10. The IDT15includes a pair of comb-shaped electrodes14facing each other. The comb-shaped electrode14includes electrode fingers11and a bus bar13to which the electrode fingers11are connected. The reflectors16are located at both sides of the IDT15. The IDT15excites a surface acoustic wave on the piezoelectric substrate10b.The IDT15and the reflectors16are formed of the metal layer17inFIG. 1. A protective film or a temperature compensation film made of an insulating material may be located on the metal layer17.

As illustrated inFIG. 2B, the acoustic wave resonator22is a piezoelectric thin film resonator. The piezoelectric film24is located on the substrate20. The lower electrode23and the upper electrode25are located so as to sandwich the piezoelectric film24. The air gap21is formed between the lower electrode23and the substrate20. The lower electrode23and the upper electrode25excites an acoustic wave in the thickness extension mode in the piezoelectric film24. The lower electrode23and the upper electrode25are formed of a metal film such as, for example, a ruthenium film. The piezoelectric film24is, for example, an aluminum nitride film. The acoustic wave resonators12and22include electrodes exciting acoustic waves. Thus, the acoustic wave resonators12and22are covered with the air gap26so as not to restrain the acoustic waves.

FIG. 3is a plan view of the upper surface of the substrate10in the first embodiment.FIG. 1corresponds to a cross-sectional view taken along line A-A inFIG. 3. As illustrated inFIG. 3, located on the upper surface of the substrate10are a plurality of the acoustic wave resonators12, the wiring lines34, pads35, and the ring-shaped sealing portion38. The bumps36are located on the pads35. Via wirings32connecting to the pads35are formed in the substrate10. The pads35include a common pad Pa1, a transmit pad Pt1, a receive pad Pr1, and ground pads Pg1. The transmit pad Pt1corresponds to the pad35ainFIG. 1, and the receive pad Pr1corresponds to the pad35binFIG. 1. A transmit filter60is a ladder-type filter, and includes series resonators S11and S12and parallel resonators P11and P12that are the acoustic wave resonators12. The series resonators S11and S12are connected in series between the common pad Pa1and the transmit pad Pt1through the wiring lines34. The parallel resonators P11and P12are connected in parallel between the common pad Pa1and the transmit pad Pt1through the wiring lines34. The parallel resonators P11and P12are connected to the ground pads Pg1through the wiring lines34.

The ground pattern37is located on the upper surface of the substrate10so as to surround the receive pad Pr1. The ground pattern37is coupled to the ground pad Pg1. This structure connects the ground pattern37to a ground.

FIG. 4is a plan view of the lower surface of the substrate20in the first embodiment. To make the correspondence betweenFIG. 4andFIG. 3easier to understand,FIG. 4is a plan view transparently illustrated from above the substrate20. As illustrated inFIG. 4, located on the lower surface of the substrate20are a plurality of the acoustic wave resonators22, the wiring lines27, the pads28, and the ring-shaped sealing portion38. The bumps36are located on the pads28. The pads28include a common pad Pa2, a receive pad Pr2, and ground pads Pg2. A receive filter62is a ladder-type filter, and includes series resonators S21through S24and parallel resonators P21through P23that are the acoustic wave resonators22. The series resonators S21through S24are connected in series between the common pad Pa2and the receive pad Pr2through the wiring lines27. The parallel resonators P21through P23are connected in parallel between the common pad Pa2and the receive pad Pr2through the wiring lines27. The parallel resonators P21through P23are coupled to the ground pads Pg2through the wiring lines27.

FIG. 5is a plan view of the lower surface of the substrate10in the first embodiment. To make the correspondence betweenFIG. 5andFIG. 3easier to understand,FIG. 5is a plan view transparently illustrated from above the substrate10. As illustrated inFIG. 5, terminals30are located on the lower surface of the substrate10. The terminals30include a common terminal Ant, a transmit terminal Tx, a receive terminal Rx, and a ground terminal Gnd. As illustrated inFIG. 3throughFIG. 5, the common terminal Ant is electrically connected to the common pad Pa1through the via wiring32, and is further electrically connected to the common pad Pa2through the bump36. The transmit terminal Tx is electrically connected to the transmit pad Pt1through the via wiring32a.The receive terminal Rx is electrically connected to the receive pad Pr2through the via wiring32b,the receive pad Pr1, and the bump36. The ground terminal Gnd is electrically connected to the ground pad Pg1through the via wiring32c, and is further electrically connected to the ground pad Pg2through the bump36.

As described above, the acoustic wave device of the first embodiment functions as a duplexer including: the transmit filter60connected between the common terminal Ant and the transmit terminal Tx; and the receive filter62connected between the common terminal Ant and the receive terminal Rx. The transmit filter60transmits signals in the transmit band to the common terminal Ant among high-frequency signals input from the transmit terminal Tx, and suppresses other signals. The receive filter62transmits signals in the receive band to the receive terminal Rx among high-frequency signals input from the common terminal Ant, and suppresses other signals.

FIG. 6is a cross-sectional view of an acoustic wave device in accordance with a first comparative example.FIG. 7is a plan view of the substrate10in the first comparative example. As illustrated inFIG. 6andFIG. 7, a ground pattern is not formed on the first surface70. Other structures are the same as those of the first embodiment, and the description thereof is omitted.

In the first comparative example and the first embodiment, the first surface70on which the transmit filter60is formed, the second surface72on which the receive filter62is formed, and the third surface74on which the terminals30are formed are stacked. The receive terminal Rx is electrically connected to the receive filter62, but is not electrically connected to the transmit filter60. However, when the first surface70is located between the second surface72and the third surface74, the receive pad Pr1is to be located on the first surface70. The receive pad Pr1is not electrically connected to the transmit filter60in the first surface70. As indicated by arrows80inFIG. 6andFIG. 7, the receive pad Pr1and the transmit filter60are capacitively coupled. Since the air gap26has a relative permittivity of approximately 1 while the substrate10has a relative permittivity greater than 1, the capacitive coupling between the receive pad Pr1and the transmit filter60is large. Accordingly, the transmit filter60and the receive pad Pr1interfere with each other, and the isolation characteristic between the transmit filter60and the receive filter62deteriorates. For example, through the capacitive coupling, transmission signals leak to the receive pad Pr1.

As described above, as in the first comparative example, the substrate20, which is one of the substrate10on which the transmit filter60is formed and the substrate20on which the receive filter62is formed, goes through above the substrate10, which is the other of the substrate10and the substrate20, and connects to an external terminal. At this time, unlike a case where the substrates10and20are mounted on a circuit board in the same direction, the inventor found that the isolation deteriorates because of the permittivity of the substrate10since the transmit filter60and the wiring line become close to each other when the substrate20goes through the substrate10.

As illustrated inFIG. 1andFIG. 3, in the first embodiment, the ground pattern37is located between the transmit filter60and the receive pad Pr1. This structure capacitively couples the receive pad Pr1to the ground pattern37as indicated by the arrows80. Thus, the interference between the transmit filter60and the receive pad Pr1can be inhibited, and the isolation characteristic can be improved.

In the first embodiment, the transmit filter60(a first acoustic wave filter), the receive pad Pr1, and the ground pattern37are located on the first surface70of the substrate10(a first substrate). The transmit filter60and the receive pad Pr1are electrically separated in the first surface70. The receive filter62at least partially overlaps with the transmit filter60in plan view, and is electrically connected to the receive pad Pr1. In such a structure, the ground pattern37is located between the receive pad Pr1and the transmit filter60in the first surface70. As described above, the ground pattern37separates the receive pad Pr1and the transmit filter60. Accordingly, the capacitive coupling between the transmit filter60and the receive pad Pr1in the first surface70can be inhibited, and the isolation characteristic between the transmit filter60and the receive filter62can be improved.

Moreover, the transmit terminal Tx (a first signal terminal) is electrically connected to the transmit filter60. The receive terminal Rx (a second signal terminal) is electrically connected to the receive filter62through the receive pad Pr1. The ground terminal Gnd is electrically connected to the ground pattern37. The substrate20(a second substrate) is mounted above the first surface70of the substrate10. The receive filter62is located on the second surface72of the substrate20. The transmit terminal Tx, the receive terminal Rx, and the ground terminal Gnd are located on the third surface74that is an opposite surface of the substrate10from the first surface70. In such a structure, the receive pad Pr1is located on the first surface70of the substrate10. Thus, the isolation characteristic between the transmit filter60and the receive filter62deteriorates. Thus, the provision of the ground pattern37can improve the isolation characteristic.

Furthermore, the substrate20is mounted above the first surface70so that the second surface72and the first surface70face each other, and the receive filter62is electrically connected to the receive pad Pr1through the bump36. In such a structure, the isolation characteristic between the transmit filter60and the receive filter62deteriorates. Accordingly, the provision of the ground pattern37can improve the isolation characteristic.

Furthermore, the via wiring32a(a first via wiring) penetrates through the substrate10, and electrically connects the transmit filter60and the transmit terminal Tx. The via wiring32b(a second via wiring) penetrates through the substrate10, and electrically connects the receive pad Pr1and the receive terminal Rx.

Furthermore, the ring-shaped sealing portion38is located on the substrate10so as to surround the transmit filter60, the receive pad Pr1, and the ground pattern37, and seals the transmit filter60and the receive filter62in the air gap26.

Furthermore, the ground pattern37is preferably electrically separated from the transmit filter60in the first surface70. This structure can inhibit the interference between the transmit filter60and the receive pad Pr1through the ground pattern37. Therefore, the isolation characteristic between the transmit filter60and the receive filter62can be further improved.

The film thickness of the ground pattern37is preferably equal to or greater than the film thickness of the pad35b.This structure can further inhibit the capacitive coupling between the pad35band the transmit filter60. As illustrated inFIG. 1, the pad35bincludes the metal layer18for bonding the bump36. Thus, even when a wiring line interconnecting the acoustic wave resonators12is formed of the metal layer17, the pad35bbecomes thicker than the wiring line interconnecting the acoustic wave resonators12. At this time, the ground pattern37is preferably formed of the metal layers17and18. This structure allows the ground pattern37and the pad35bto have approximately the same film thickness. Therefore, the capacitive coupling between the pad35band the transmit filter60can be further inhibited.

Since the via wiring32is formed by processing the substrate10, a fine crack may exist. Thus, the crack may expand because of the stress or the like caused by the stress and/or the temperature change at the time of bonding the bumps36. As illustrated inFIG. 1andFIG. 3, the via wiring32and the bump36coupled to the same pad35do not overlap in plan view. Accordingly, the expanding of a crack due to the stress caused by the stress and/or the temperature change at the time of bonding the bumps36can be inhibited.

FIG. 8is a plan view of the upper surface of the substrate10in a first variation of the first embodiment. As illustrated inFIG. 8, the ground pattern37surrounds three sides of the receive pad Pr1in the first surface70, but does not surround one side of the receive pad Pr1. Other structures are the same as those of the first embodiment, and the description thereof is thus omitted.

FIG. 9is a plan view of the upper surface of the substrate10in a second variation of the first embodiment. As illustrated inFIG. 9, the ground pattern37surrounds the transmit filter60in the first surface70. Other structures are the same as those of the first embodiment, and the description thereof is thus omitted.

It is only required that the ground pattern37is located between the transmit filter60and the receive pad Pr1. The ground pattern37is preferably located so as to block all the lines connecting, for example, the transmit filter60and the receive pad Pr1. As described in the first embodiment and the first variation thereof, the ground pattern37preferably surrounds the receive pad Pr1in the first surface70. This structure can further improve the isolation characteristic between the transmit filter60and the receive filter62. As described in the first embodiment, the ground pattern37preferably completely surrounds the receive pad Pr1in the first surface70. As described in the second variation of the first embodiment, the ground pattern37may completely surround the transmit filter60in the first surface70.

The first embodiment has described a duplexer as an example, but a filter located on the substrate10and a filter located on the substrate20may not necessarily be interconnected. An exemplary case where the receive filter62and the transmit filter60are ladder-type filters has been described, but at least one of the receive filter62and the transmit filter60may be a multimode type filter. A receive filter may be located on the first surface70, and a transmit filter may be located on the second surface72. An exemplary case where the acoustic wave resonator12is an surface acoustic wave resonator and the acoustic wave resonator22is a piezoelectric thin film resonator has been described, but the acoustic wave resonators12and22may be any one of the surface acoustic wave resonator and the piezoelectric thin film resonator. An exemplary case where the piezoelectric substrate10bis bonded to the support substrate10a, but the support substrate may not necessarily be provided.

The transmit filter60and the receive filter62have been described as examples, but filters located on the substrate10and the substrate20may not be necessarily a transmit filter or a receive filter, and may be filters each being connected between the input terminal and the output terminal. For example, the transmit band and the receive band of the Frequency Division Duplex (FDD) system do not overlap. As described above, when filters have different passbands (for example, when the center frequencies of the passbands differ from each other, or when the passbands do not overlap), the isolation characteristic between the filters is important. Therefore, the provision of the ground pattern is preferable.

Second Embodiment

FIG. 10is a cross-sectional view of an acoustic wave device in accordance with a second embodiment. As illustrated inFIG. 10, in the edge portion of the substrate10, the piezoelectric substrate10bis removed, and a ring-shaped metal layer46is formed. A ring-shaped electrode44is located on the ring-shaped metal layer46. A ring-shaped sealing portion40is located on the ring-shaped electrode44. The ring-shaped sealing portion40surrounds the substrate20. A flat plate-like lid42is located on the upper surface of the substrate20and the upper surface of the ring-shaped sealing portion40. A protective film48is formed so as to cover the ring-shaped metal layer46, the ring-shaped electrode44, the ring-shaped sealing portion40, and the lid42. The ring-shaped sealing portion40is formed of, for example, a metal layer such as a solder layer or an insulating layer such as a resin layer. The ring-shaped metal layer46is a copper layer or a gold layer, and the ring-shaped electrode44is formed of a metal layer such as a nickel layer. The lid42is made of, for example, a metal plate or an insulating plate. The protective film48is a metal film or an insulating film.

FIG. 11is a plan view of the upper surface of the substrate10in the second embodiment.FIG. 12is a plan view of the lower surface of the substrate20in the second embodiment. The substrate20is smaller than the substrate10in plan view. The ring-shaped sealing portion40is formed so as to surround the substrate20. The ring-shaped sealing portion40is electrically connected to the ground terminal Gnd through the via wiring32. Other structures are the same as those of the first embodiment, and the description thereof is omitted.

FIG. 13AthroughFIG. 15Care cross-sectional views illustrating a method of fabricating the acoustic wave device in accordance with the second embodiment. As illustrated inFIG. 13A, the lower surface of the piezoelectric substrate10bis bonded onto the upper surface of the support substrate10a.This bonding is performed in a wafer state.

This bonding may be performed by activating the upper surface of the support substrate10aand the lower surface of the piezoelectric substrate10band then bonding them at normal temperature, or by bonding them with an adhesive agent.

As illustrated inFIG. 13B, desired apertures50are formed in the piezoelectric substrate10b.The apertures50are formed by, for example, blasting using a patterned photoresist as a mask. The apertures50may be formed by ion milling or wet etching instead of blasting.

As illustrated inFIG. 13C, via holes are formed in the piezoelectric substrate10band the support substrate10a.The via holes are formed by, for example, irradiating the piezoelectric substrate10band the support substrate10awith a laser beam. A seed layer (not illustrated) is formed in the via holes and the apertures50. An electric current is supplied to the seed layer, and the via wirings32are formed in the via holes and the ring-shaped metal layer46is formed in the apertures50by electrolytic plating. When the via wirings32and the ring-shaped metal layer46are made of a copper layer, the seed layer may be made of, for example, a titanium film with a film thickness of 100 μm and a copper layer with a film thickness of 200 μm stacked in this order from the substrate10side. Unnecessary plated layers are removed by Chemical Mechanical Polishing (CMP) or the like.

As illustrated inFIG. 13D, formed on the upper surface of the piezoelectric substrate10bare the acoustic wave resonators12, the wiring lines34, and the pads35. The acoustic wave resonator12is made of, for example, a titanium film and an aluminum film stacked in this order from the substrate10side. The wiring line34and the pad35are made of, for example, a titanium film and a gold film stacked in this order from the substrate10side.

As illustrated inFIG. 14A, the ring-shaped electrodes44are formed on the ring-shaped metal layer46. The ring-shaped electrode44is formed of, for example, a titanium film and a nickel film stacked in this order from the substrate10side, and is formed by evaporation and liftoff. As illustrated inFIG. 14B, the lower surface of the substrate10is polished or ground. This process exposes the via wirings32from the lower surface of the substrate10.

As illustrated inFIG. 14C, the terminals30are formed so as to make contact with the via wirings32. For example, a seed layer is formed on the lower surface of the substrate10. A photoresist including apertures is formed under the seed layer. An electric current is supplied to the seed layer, and a plated layer is formed in the apertures by electrolytic plating. Then, the seed layer other than the plated layer is removed. The seed layer may be formed of, for example, a titanium film and a copper film stacked in this order from the substrate10side. The plated layer may be formed of, for example, a copper layer, a nickel layer, and a gold layer stacked in this order from the substrate10side.

As illustrated inFIG. 14D, the substrate20is flip-chip mounted on the substrate10. The substrate20is a chip after the separation into individual chips, and gold stud bumps as the bumps36are formed on the lower surface of the substrate20.

As illustrated inFIG. 15A, a solder plate is placed above the substrate10so as to cover the substrate20. The lid42is placed on the solder plate. The solder plate is pressed to the substrate10by the lid42, and the lid42is heated to a temperature equal to or greater than the melting point of the solder plate. This process melts the solder plate, forming the ring-shaped sealing portion40. The upper surface of the ring-shaped electrode44has a good solderability, and thus, the ring-shaped sealing portion40is bonded to the substrate10through the ring-shaped electrode44. The surface of the substrate20has a poor solderability, and thus the ring-shaped sealing portion40is not bonded to the side surface of the substrate20even when making contact with the side surface of the substrate20. The lid42has a good solderability, and thus the ring-shaped sealing portion40is bonded to the lid42. The lid42makes contact with the upper surface of the substrate20, but is not bonded to the upper surface of the substrate20.

As illustrated inFIG. 15B, the lower surface of the substrate10is protected by a protective material52such as a photoresist. The lid42, the ring-shaped sealing portion40, and the substrate10are cut by dicing. As illustrated inFIG. 15C, the protective film48is formed so as to cover the side surface of the ring-shaped sealing portion40. The protective film48is formed by, for example, barrel plating.

As described in the second embodiment, the ring-shaped sealing portion40may be formed on the substrate10so as to surround the substrate20.

FIG. 16is a plan view of the upper surface of the substrate10in a first variation of the second embodiment.FIG. 17is a plan view of the lower surface of the substrate20in a second variation of the second embodiment.FIG. 18Ais a cross-sectional view taken along line A-A inFIG. 16andFIG. 17, andFIG. 18Bis a cross-sectional view taken along line B-B inFIG. 16andFIG. 17.

As illustrated inFIG. 16throughFIG. 18B, a ground pattern37alocated on the upper surface of the substrate10is bonded to a pattern29formed on the lower surface of the substrate20. As illustrated inFIG. 16, the ground pattern37asurrounds the pad35b.As illustrated inFIG. 17, the pattern29surrounds the pad28in three directions. The wiring line27connecting the pad28and the acoustic wave resonator22is not electrically connected to the ground pattern37a.As illustrated inFIG. 18A, an insulating layer39is located between the ground pattern37aand the wiring line27. The ground pattern37aand the pattern29are formed of, for example, a metal layer such as a copper layer, an aluminum layer, or a gold layer. The ground pattern37ais formed by, for example, plating. The pattern29is formed at the same time as, for example, the wiring line27and the pad28. The insulating layer39is formed of, for example, a silicon oxide film or a resin film. The insulating layer39electrically separates the ground pattern37aand the wiring line27. Other structures are the same as those of the second embodiment, and the description thereof is omitted.

As described in the first variation of the second embodiment, the ground pattern37amay be formed in an area from the substrate10to the substrate20. This structure can inhibit the capacitive coupling between the transmit filter60and the receive pad Pr1through the air gap26. Thus, the isolation characteristic can be further improved.

Also in the first embodiment and the first variation of the embodiment, the ground pattern37amay be formed.

Third Embodiment

FIG. 19AandFIG. 19Bare cross-sectional views of acoustic wave devices in accordance with a third embodiment and a first variation of the third embodiment, respectively. As illustrated inFIG. 19A, the substrate10is mounted on a mounting board90. The upper surface and the lower surface of the substrate10correspond to the first surface70and the second surface72, respectively. The lower surface of the mounting board90corresponds to the third surface74. The mounting board90is made of an insulating layer such as, for example, ceramic or resin. Terminals30athrough30care located on the lower surface of the mounting board90. Pads93athrough93care located on the upper surface of the mounting board90. Via wirings94athrough94cpenetrating through the mounting board90are formed. The via wirings94athrough94celectrically connect the terminals30athrough30cto the pads93athrough93c,respectively.

The substrate10is a piezoelectric substrate. Formed on the lower surface of the substrate10are the acoustic wave resonator12, the wiring lines34, the pads35aand35b,and the ground pattern37. Formed on the upper surface of the substrate10are the acoustic wave resonator22, the wiring lines27, and the pads28, and a via wiring95penetrating through the substrate10is formed. The via wiring95electrically connects the pad28and the pad35b. The pads35aand35band the ground pattern37are bonded to the pads93athrough93cthrough bumps91athrough91c,respectively. A ring-shaped sealing portion92ais located between the mounting board90and the substrate10, and seals the acoustic wave resonator12in an air gap26a.A ring-shaped sealing portion92bis located between the substrate10and a lid96, and seals the acoustic wave resonator22in an air gap26b.

The terminal30ais electrically connected to the acoustic wave resonator12through the via wiring94a,the pad93a,the bump91a,the pad35a,and the wiring line34. The terminal30bis electrically connected to the acoustic wave resonator22through the via wiring94b,the pad93b,the bump91b,the pad35b,the via wiring95, the pad28, and the wiring line27. The terminal30cis electrically connected to the ground pattern37through the via wiring94c,the pad93c,and the bump91c.Other structures are the same as those of the first embodiment, and the description thereof is omitted.

As illustrated inFIG. 19B, the substrate10includes the support substrate10a,the piezoelectric substrate10bbonded to the lower surface of the support substrate10a,and the piezoelectric substrate10cbonded to the upper surface of the support substrate10a.The acoustic wave resonators12and22are respectively located on the piezoelectric substrates10band10c.Other structures are the same as those of the third embodiment, and the description thereof is thus omitted.

In the third embodiment and the variations thereof, the mounting board90(a second substrate) includes the third surface74on which the transmit terminal Tx, the receive terminal Rx, and the ground terminal Gnd are located. The substrate10(a first substrate) is mounted on the mounting board90, and includes the first surface70and the second surface72that are opposing surfaces. In addition, the substrate10is mounted on the mounting board90so that the first surface70faces the surface opposite from the third surface74. In such a structure, the pad35bcoupled to the acoustic wave resonator22is formed on the first surface70of the substrate10. Thus, the isolation characteristic between the transmit filter60and the receive filter62deteriorates. Therefore, the isolation characteristic can be improved by providing the ground pattern37.

Fourth Embodiment

FIG. 20AandFIG. 20Bare cross-sectional views of acoustic wave devices in accordance with a fourth embodiment and a first variation of the fourth embodiment, respectively. As illustrated inFIG. 20A, the ring-shaped metal layer46is located on the side surface of the substrate10, and is coupled to the terminal30a.The terminal30cis coupled to the ground pattern37through the ring-shaped metal layer46and the ring-shaped electrode44. Other structures are the same as those of the second embodiment, and the description thereof is thus omitted. As described in the fourth embodiment, the ground pattern37may be coupled to a ground through the ring-shaped metal layer46.

As illustrated inFIG. 20B, a substrate82is located between the substrate10and the substrate20. Pads81are located on the lower surface of the substrate82. Pads83are located on the upper surface of the substrate82. Via wirings84penetrating through the substrate82and electrically connecting the pads81and83are formed. The pads35band81are bonded together by a bump36a.The acoustic wave resonator12is sealed in the air gap26aby a ring-shaped sealing portion38alocated between the substrates10and82. The pads83and28are bonded together by a bump36b.The acoustic wave resonator22is sealed in the air gap26bby a ring-shaped sealing portion38blocated between the substrates20and82. The terminal30bis electrically connected to the acoustic wave resonator22through the via wiring32b,the pad35b,the bump36a,the pad81, the via wiring84, the pad83, the bump36b, the pad28, and the wiring line27. Other structures are the same as those of the first embodiment, and the description thereof is omitted.

As described in the first variation of the fourth embodiment, the substrate82may be located between the first surface70and the second surface72.

Fifth Embodiment

FIG. 21is a cross-sectional view of an acoustic wave device in accordance with a fifth embodiment. As illustrated inFIG. 21, the substrate20is mounted on the substrate10so that the second surface72faces upward. Pads87are located on the lower surface of the substrate20. The bump36is bonded to the pad87, and is bonded to the pad35aand the ground pattern37. The bump36mechanically supports the substrate20. The pads35band28are electrically connected through a bonding wire88. Other structures are the same as those of the first embodiment, and the description thereof is omitted.

In the fifth embodiment, the substrate20is mounted above the first surface70so that the surface opposite from the second surface72faces the first surface70. Even such a structure can improve the isolation characteristic by providing the ground pattern37.