ACOUSTIC WAVE DEVICE AND COMMUNICATION MODULE

An acoustic wave device includes a first substrate having first and second surfaces opposite from each other, and side surfaces connecting the first and second surfaces, a first acoustic wave element disposed on the first surface of the first substrate, a second substrate that is provided over the first surface of the first substrate and over the first acoustic wave element and has a first air gap between the second and first substrates, a second acoustic wave element disposed on the second substrate, a ground terminal disposed on the second surface of the first substrate, a first metal layer provided between the first and second acoustic wave elements and located in the first air gap, and a second metal layer that covers half or more of a total area of the side surfaces of the first substrate and electrically connects the first metal layer and the ground terminal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2020-181579, filed on Oct. 29, 2020, the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the present embodiments relates to an acoustic wave device and a communication module.

BACKGROUND

It is known to obtain the electromagnetic shielding effect by providing a metal layer connected to a ground to an opposite surface of an acoustic wave device from the surface having an acoustic wave element formed thereon, as disclosed in Japanese Patent Application Publication No. 2006-211613. In addition, it is known to mount a first substrate having a first acoustic wave element formed thereon over a second substrate having a second acoustic wave element formed thereon to miniaturize the acoustic wave device. In this case, it is known to provide a metal layer connected to a ground between the first acoustic wave element and the second acoustic wave element for electromagnetic shielding as disclosed in Japanese Patent Application Publication Nos. 2008-546207 and 2017-118273.

SUMMARY

However, simply providing the metal layer connected to the ground between the first acoustic wave element and the second acoustic wave element may be insufficient to provide electromagnetic shielding effect, which may result in deterioration in characteristics.

According to a first aspect of the present disclosure, there is provided an acoustic wave device including: a first substrate having a first surface, a second surface opposite from the first surface, and side surfaces connecting the first surface and the second surface; a first acoustic wave element disposed on the first surface of the first substrate; a second substrate that is provided over the first surface of the first substrate and over the first acoustic wave element and has a first air gap between the second substrate and the first substrate; a second acoustic wave element disposed on the second substrate; a ground terminal disposed on the second surface of the first substrate; a first metal layer provided between the first acoustic wave element and the second acoustic wave element and located in the first air gap; and a second metal layer that covers half or more of a total area of the side surfaces of the first substrate and electrically connects the first metal layer and the ground terminal.

According to a second aspect of the present disclosure, there is provided a communication module including: a circuit substrate; and the above acoustic wave device mounted on the circuit substrate.

DETAILED DESCRIPTION

Hereinafter, with reference to the accompanying drawings, embodiments of the present disclosure will be described.

First Embodiment

FIG. 1is a cross-sectional view of an acoustic wave device in accordance with a first embodiment. As illustrated inFIG. 1, in an acoustic wave device100of the first embodiment, a substrate20having acoustic wave elements26disposed thereon is mounted over a substrate10having acoustic wave elements16disposed thereon. The substrate10is formed of an insulating member, and includes a support substrate11and a piezoelectric layer12. Similarly, the substrate20is formed of an insulating member, and includes a support substrate21and a piezoelectric layer22.

The support substrates11and21are, for example, sapphire substrates, alumina substrates, spinel substrates, quartz substrates, crystal substrates, silicon substrates, zirconium oxides substrate, or resin substrates, and have thicknesses of approximately 50 μm to 150 μm. The sapphire substrate is a substrate mainly composed of monocrystalline Al2O3. The alumina substrate is a substrate mainly composed of polycrystalline Al2O3. The spinel substrate is a substrate mainly composed of monocrystalline or polycrystalline MgAl2O4. The quartz substrate is a substrate mainly composed of amorphous SiO2. The crystal substrate is a substrate mainly composed of monocrystalline SiO2.

An insulating film having acoustic impedance different from those of the support substrate and the piezoelectric layer may be provided between the support substrate11and the piezoelectric layer12and/or between the support substrate21and the piezoelectric layer22to improve the acoustic characteristics of the acoustic wave element. As described above, the piezoelectric layer12is directly or indirectly bonded to the surface of the support substrate11, and the piezoelectric layer22is directly or indirectly bonded to the surface of the support substrate21. The insulating film having acoustic impedance different from those of the support substrate and the piezoelectric layer may have a temperature coefficient of an elastic constant opposite in sign to the temperature coefficient of the elastic constant of the piezoelectric layer, and may be, for example, an additive-free silicon oxide layer or a silicon oxide layer containing additive elements such as fluorine. This configuration can reduce the temperature coefficient of frequency. The insulating film having acoustic impedance different from those of the support substrate and the piezoelectric layer may be, for example, polycrystalline or amorphous, and may be, for example, an aluminum oxide layer, a silicon layer, an aluminum nitride layer, a silicon nitride layer, or a silicon carbide layer.

The acoustic wave elements16are disposed on an upper surface13of the substrate10. The acoustic wave elements26are disposed on a lower surface24of the substrate20. The upper surface13of the substrate10is uneven due to the piezoelectric layer12. Similarly, the lower surface24of the substrate20is uneven due to the piezoelectric layer22. The upper surface13of the substrate10is opposite to the lower surface24of the substrate20across an air gap82(a first air gap). Thus, the acoustic wave elements16and the acoustic wave elements26are opposite to each other in the air gap82between the substrate10and the substrate20.

FIG. 2is a plan view of the acoustic wave element in the first embodiment.FIG. 2illustrates the acoustic wave element16as an example, but the same applies to the acoustic wave element26. As illustrated inFIG. 2, the acoustic wave element16is, for example, a surface acoustic wave resonator, and includes an interdigital transducer (IDT)30and reflectors34on the piezoelectric layer12. The IDT30includes a pair of comb-shaped electrodes31opposite to each other. The comb-shaped electrode31includes electrode fingers32, and a bus bar33to which the electrode fingers32are coupled. The reflectors34are located at both sides of the IDT30. The IDT30excites a surface acoustic wave on the piezoelectric layer12. The reflectors34reflect the surface acoustic wave. The IDT30and the reflectors34are formed of a metal film such as, but not limited to, an aluminum film or a copper film.

In the acoustic wave device100of the first embodiment, the acoustic wave elements16disposed on the piezoelectric layer12form a transmit filter, and the acoustic wave elements26disposed on the piezoelectric layer22form a receive filter. This will be described later.

As illustrated inFIG. 1, wiring lines17electrically connected to the acoustic wave elements16are provided on the upper surface13of the substrate10. Wiring lines27electrically connected to the acoustic wave elements26are provided on the lower surface24of the substrate20. The wiring lines17and27are metal layers including, for example, copper layers, aluminum layers, or gold layers. Terminals, which are foot pads for connecting the acoustic wave device100to an external device, are provided on a lower surface14opposite from the upper surface13of the substrate10. The terminals include a receive terminal41and a ground terminal44. The terminal is a metal layer including a copper layer, an aluminum layer, a gold layer, or the like, and has a thickness of approximately several micrometers.

The acoustic wave elements16disposed on the upper surface13of the substrate10are electrically connected to the ground terminal44through the wiring lines17and a via wiring54provided in the substrate10. The acoustic wave elements26disposed on the lower surface24of the substrate20are electrically connected to the receive terminal41through the wiring lines27, a pillar61provided between the substrate10and the substrate20, and a via wiring51provided in the substrate10. The pillar61is bonded to a metal layer18provided on the upper surface13of the substrate10and the wiring line27provided on the lower surface24of the substrate20by solder.

A ring-shaped metal layer60surrounding the acoustic wave elements16and the acoustic wave elements26is provided between the substrate10and the substrate20. Additionally, a shield metal layer70is provided between the substrate10and the substrate20and located in the air gap82between the acoustic wave elements16and the acoustic wave elements26. The ring-shaped metal layer60includes a part71of the shield metal layer70and post portions65aand65bsandwiching the part71therebetween. The post portion65ais bonded to the metal layer18provided on the upper surface13of the substrate10by solder, and the post portion65bis bonded to a metal layer28provided on the lower surface24of the substrate20by solder. The shield metal layer70preferably extends across the entire region where the acoustic wave elements16and the acoustic wave elements26are provided and is located between the acoustic wave elements16and the acoustic wave elements26. However, the shield metal layer70may extend across ⅔ or more of the region where the acoustic wave elements16and the acoustic wave elements26are provided, or may extend across ¾ or more of the region where the acoustic wave elements16and the acoustic wave elements26are provided.

The acoustic wave elements16and the acoustic wave elements26are sealed in the air gap82between the substrate10and the substrate20by the ring-shaped metal layer60. The shield metal layer70is in contact with the ring-shaped metal layer60and is electrically connected to the ring-shaped metal layer60. The shield metal layer70has an aperture, and the pillar61passes through the aperture. An insulating resin film72is embedded between the pillar61and the shield metal layer70. This configuration electrically insulates the pillar61and the shield metal layer70from each other. When the shield metal layer70and the pillar61can be sufficiently distanced from each other, the resin film72may be omitted, and the shield metal layer70and the pillar61may be insulated from each other across the air gap. In this case, the air gap82between the substrate10and the shield metal layer70is communicated with the air gap82between the substrate20and the shield metal layer70.

The post portions65aand65bare formed of metal layers including, for example, nickel layers, copper layers, or gold layers, and have heights of approximately 10 μm to 30 μm. The shield metal layer70is a metal layer including a conductive metal layer such as, but not limited to, a copper layer, a gold layer, a silver layer, a tungsten layer, an aluminum layer, or a titanium layer, or a magnetic metal layer such as, but not limited to, an iron layer, a nickel layer, or an iron-nickel alloy layer (such as a kovar layer). The thickness of the shield metal layer70is preferably equal to or greater than the skin depth of the electromagnetic wave to be shielded, and is, for example, approximately 1 μm to 40 μm.

FIG. 3AandFIG. 3Care plan views of the substrate in the first embodiment, andFIG. 3Bis a plan view of the shield metal layer.FIG. 3Ais a plan view of the substrate20, and is a transparent plan view as viewed from above the substrate20to clarify correspondence withFIG. 3BandFIG. 3C.FIG. 3Cis a plan view of the substrate10, and indicates the terminals disposed on the lower surface14of the substrate10by dotted lines. In addition, for clarity of the drawings, pillars61to63are not illustrated inFIG. 3C.

As illustrated inFIG. 3A, the acoustic wave elements26, the wiring lines27, and the pillars61to63are disposed on the substrate20(on the lower surface inFIG. 1). The acoustic wave elements26include series resonators S21and S22and a parallel resonator P21. The pillars61to63are connected to the wiring lines27. The ring-shaped metal layer60surrounds the series resonators S21and S22, the parallel resonator P21, and the wiring lines27. The pillars61to63are metal layers including, for example, copper layers, gold layers, silver layers, tungsten layers, aluminum layers, titanium layers, iron layers, nickel layers, or iron-nickel alloy layers, and have heights approximately equal to that of the ring-shaped metal layer60.

As illustrated inFIG. 3B, the insulating resin film72is provided between the shield metal layer70and the pillar61and between the shield metal layer70and the pillar62, and the pillars61and62are electrically insulated from the shield metal layer70. The pillar63is in contact with the shield metal layer70and is electrically connected to the shield metal layer70. The shield metal layer70is provided across the entire region where the substrate10and the substrate20are opposite to each other in a plan view.

As illustrated inFIG. 3C, the acoustic wave elements16, the wiring lines17, and the ring-shaped metal layer60are provided on the substrate10. The acoustic wave elements16include series resonators S11and S12and a parallel resonator P11. Via wirings50to54are provided in the substrate10. The via wiring50, the via wiring52, and the via wiring54are coupled to the wiring lines17. The via wiring51is coupled to the pillar61, the via wiring52is coupled to the pillar62, and the via wiring53is coupled to the pillar63. The ring-shaped metal layer60surrounds the series resonators S11and S12, the parallel resonator P11, and the wiring line17. The via wirings50to54are metal layers including, for example, copper layers, aluminum layers, or gold layers.

The via wiring50is coupled to a transmit terminal40, the via wiring52is coupled to a common terminal42, and the via wiring54is coupled to the ground terminal44. Thus, the series resonators S11and S12are connected in series between the transmit terminal40and the common terminal42. The parallel resonator P11is connected in parallel between the transmit terminal40and the common terminal42. The parallel resonator P11is connected between the wiring lines17, which is between the series resonator S11and the series resonator S12, and the ground terminal44. As seen from the above, a transmit filter19, which is a ladder-type filter, is provided to the substrate10.

The via wiring51is coupled to the receive terminal41, the via wiring52is coupled to the common terminal42, and the via wiring53is coupled to a ground terminal43. Thus, the series resonators S21and S22disposed on the substrate20are connected in series between the common terminal42and the receive terminal41. The parallel resonator P21is connected in parallel between the common terminal42and the receive terminal41. The parallel resonator P21is connected between the wiring line27, which is between the series resonator S21and the series resonator S22, and the ground terminal43. As seen from the above, a receive filter29, which is a ladder-type filter, is provided to the substrate20.

The transmit filter19transmits signals in the transmit band, as transmission signals, to the common terminal42among high-frequency signals input from the transmit terminal40, and suppresses signals with other frequencies. The receive filter29transmits signals in the receive band, as reception signals, to the receive terminal41among high-frequency signals input from the common terminal42, and suppresses signals with other frequencies. As seen from the above, the acoustic wave device100is a duplexer. In addition, ground terminals45to47are also disposed on the lower surface14of the substrate10.

As illustrated inFIG. 1, a covering metal layer75is provided to cover half or more of the total area of side surfaces15of the substrate10. The side surfaces15are surfaces connecting the upper surface13and the lower surface14. The upper surface13and the lower surface14of the substrate10have substantially rectangular shapes in a plan view, and the substrate10has four side surfaces15. The covering metal layer75extends from the side surfaces15of the substrate10to the ring-shaped metal layer60, and covers at least a part of the surface of the ring-shaped metal layer60. In the first embodiment, the covering metal layer75covers the entire surfaces of all side surfaces15of the substrate10, the entire outer surface of the ring-shaped metal layer60, the entire surfaces of all side surfaces25of the substrate20, and an entire upper surface23of the substrate20. The upper surface23of the substrate20is the surface opposite from the lower surface24, and the side surface25is a surface connecting the upper surface23and the lower surface24. The substrate20has four side surfaces25.

The covering metal layer75is a single-layer film or multilayered film made of a highly conducting metal such as, but not limited to, silver, copper, gold, or aluminum. The shield metal layer70may be formed of a non-magnetic material such as, but not limited to, titanium, or may be formed of a magnetic material such as, but not limited to, iron or nickel. The covering metal layer75has a thickness of, for example, approximately 1 μm to 5 μm. The thickness of the covering metal layer75is preferably equal to or greater than the skin depth of the electromagnetic wave to be shielded to allow the covering metal layer75to have electromagnetic shielding effect.

FIG. 4Ais a perspective view of the acoustic wave device illustrating the covered region with the covering metal layer in the first embodiment, andFIG. 4Bis a plan view illustrating the lower surface of the substrate. InFIG. 4AandFIG. 4B, for clarity of the drawings, the region where the covering metal layer75is provided is indicated by hatching.FIG. 4Bis a transparent plan view of the lower surface14as viewed from above the substrate10. As illustrated inFIG. 4A, in the first embodiment, the covering metal layer75covers the entire surfaces of all side surfaces15of the substrate10, the entire outer surface of the ring-shaped metal layer60, the entire surfaces of all side surfaces25of the substrate20, and the entire upper surface23of the substrate20. As illustrated inFIG. 4B, the covering metal layer75extends from the side surfaces15of the substrate10to the lower surface14, and is in contact with the ground terminals43to47. Therefore, the shield metal layer70is electrically connected to a ground through the covering metal layer75.

Manufacturing Method

FIG. 5AtoFIG. 6Bare cross-sectional views illustrating a method of manufacturing the acoustic wave device in accordance with the first embodiment. The acoustic wave devices are simultaneously manufactured in a wafer state. However, for clarity of the drawings, one acoustic wave device will be illustrated inFIG. 5AtoFIG. 6A. As illustrated inFIG. 5A, after via holes are formed in the support substrate11, the via wirings50to54(only the via wirings51and54are illustrated inFIG. 5A) are formed in the via holes. The via hole is formed by, for example, laser beam irradiation or etching. The via wirings50to54are formed by, for example, electrolytic plating. Thereafter, after a piezoelectric substrate is bonded to the surface of the support substrate11, the piezoelectric substrate is thinned by polishing or grinding to form the piezoelectric layer12. The support substrate11and the piezoelectric substrate are bonded to each other using, for example, a direct bonding method in which the surface of the support substrate11and the surface of the piezoelectric substrate are activated and bonded at room temperature. The support substrate11and the piezoelectric layer12form the substrate10.

Then, the terminals40to47(only the terminals41and44are illustrated inFIG. 5A) are formed on the lower surface14of the substrate10. The piezoelectric layer12is etched to be patterned. The acoustic wave element16is formed on the piezoelectric layer12. The wiring lines17electrically connected to the acoustic wave elements16are formed. The metal layer18is formed in the region to which the ring-shaped metal layer60and the pillars61to63are bonded. The acoustic wave elements16, the wiring lines17, the metal layer18, and the terminals40to47are formed using a commonly known method. Through the above steps, the substrate10having the acoustic wave elements16and the like is formed.

As illustrated inFIG. 5B, after a piezoelectric substrate is bonded to the surface of the support substrate21, the piezoelectric substrate is thinned by polishing or grinding to form the piezoelectric layer22. The support substrate21and the piezoelectric substrate are bonded to each other using, for example, a direct bonding method in which the surface of the support substrate21and the surface of the piezoelectric substrate are activated and bonded at room temperature. The support substrate21and the piezoelectric layer22form the substrate20. Then, the piezoelectric layer22is etched to be patterned. The acoustic wave elements26are formed on the piezoelectric layer22. The wiring lines27electrically connected to the acoustic wave elements26are formed. The metal layer28is formed in the region to which the ring-shaped metal layer60is bonded. The acoustic wave elements26, the wiring lines27, and the metal layer28are formed using a commonly known method. Through the above steps, the substrate20having the acoustic wave elements26and the like is formed.

As illustrated inFIG. 5C, after a metallic foil90is processed so as to have the same outer shape as the substrate10and the substrate20, toric apertures are formed by removing the metallic foil90around the regions where the pillars61and62are to be formed. An insulating resin is filled in the aperture and cured to form the insulating resin film72. The aperture has a width of, for example, 60 μm, and the metallic foil90in the inner region of the hollow circular aperture has a diameter of, for example, 120 μm. The metallic foil90is removed by, for example, wet etching.

As illustrated inFIG. 5D, metal layers are formed on both surfaces of the metallic foil90by, for example, electroforming. This forms the shield metal layer70formed of the metallic foil90, the ring-shaped metal layer60including the part71of the shield metal layer70and the post portions65aand65b, and the pillars61to63(only the pillar61is illustrated inFIG. 5D) including a part of the metallic foil90. The diameters of the pillars61to63and the width of the ring-shaped metal layer60are, for example, 100 μm. The pillars61to63and the ring-shaped metal layer60have a structure in which, for example, a copper layer with a thickness of 20 μm, a nickel layer with a thickness of 5 μm, and a tin layer with a thickness of 5 μm are stacked in this order from the shield metal layer70side.

As illustrated inFIG. 6A, the pillars61to63and the ring-shaped metal layer60are bonded to the metal layer18of the substrate10. For example, the pillars61to63and the ring-shaped metal layer60are heated to 250° C. and pressurized under a nitrogen atmosphere to be solder-bonded to the metal layer18of the substrate10. Similarly, the pillars61to63are bonded to the wiring lines27of the substrate20, and the ring-shaped metal layer60is bonded to the metal layer28. For example, the pillars61to63are heated to 250° C. and pressurized under a nitrogen atmosphere to be solder-bonded to the wiring lines27of the substrate20, and the ring-shaped metal layer60is heated to 250° C. and pressurized under a nitrogen atmosphere to be solder-bonded to the metal layer28.

As illustrated inFIG. 6B, a resist film91covering the region other than the region where the covering metal layer75is to be formed is formed on the lower surface14of the substrate10. After the substrate10and the substrate20are separated into individual chips by dicing, the chip is fixed to a protrusion portion93of a substrate92, which has a protrusion, using a tape94or the like. The width of the protrusion portion93is less than the chip size (for example, less than the chip size by 200 μm or greater), only the region where the resist film91is formed is attached to the tape94, and the region where no resist film91is formed is separated from the tape94. Then, a metal film is deposited on the chip fixed to the substrate92by sputtering. The metal film is formed across the entire surface of the chip except the region where the resist film91is formed. In this manner, the acoustic wave device100of the first embodiment having the covering metal layer75on the surface thereof is formed. Finally, the acoustic wave device100is detached from the tape94, and the resist film91is removed to complete the acoustic wave device100.

First Variation of the First Embodiment

FIG. 7is a cross-sectional view of an acoustic wave device in accordance with a first variation of the first embodiment.FIG. 8Ais a perspective view of the acoustic wave device illustrating the covered region with the covering metal layer in the first variation of the first embodiment, andFIG. 8Bis a plan view illustrating the lower surface of the substrate. InFIG. 8AandFIG. 8B, for clarity of the drawings, the region where the covering metal layer75is provided is indicated by hatching.FIG. 8Bis a transparent plan view of the lower surface14as viewed from above the substrate10. As illustrated inFIG. 7andFIG. 8A, in an acoustic wave device110of the first variation of the first embodiment, the covering metal layer75covers the entire surfaces of all side surfaces15of the substrate10, the outer surface of the post portion65a, which is a part of the outer surface of the ring-shaped metal layer60, and the entire outer surface of the part71of the shield metal layer70. As illustrated inFIG. 8B, the covering metal layer75extends from the side surfaces15to the lower surface14of the substrate10as in the first embodiment, and is in contact with the ground terminals43to47and is electrically connected to the ground terminals43to47. Other configurations are the same as those of the first embodiment, and the description thereof is thus omitted.

COMPARATIVE EXAMPLES

FIG. 9Ais a cross-sectional view of an acoustic wave device in accordance with a first comparative example,FIG. 9Bis a cross-sectional view of an acoustic wave device in accordance with a second comparative example, andFIG. 10is a cross-sectional view of an acoustic wave device in accordance with a third comparative example. As illustrated inFIG. 9A, in an acoustic wave device500of the first comparative example, no shield metal layer70is provided between the substrate10and the substrate20, and no covering metal layer75electrically connected to the shield metal layer70is provided. The ring-shaped metal layer60is electrically connected to the ground terminal44through a via wiring55provided in the substrate10. Other configurations are the same as those of the first embodiment, and the description thereof is thus omitted.

As illustrated inFIG. 9B, in an acoustic wave device600of the second comparative example, no covering metal layer75is provided, and the ring-shaped metal layer60and the shield metal layer70are electrically connected to the ground terminal44through the via wiring55provided in the substrate10. Other configurations are the same as those of the first embodiment, and the description thereof is thus omitted.

As illustrated inFIG. 10, in an acoustic wave device700of the third comparative example, no shield metal layer70is provided between the substrate10and the substrate20. Other configurations are the same as those of the first embodiment, and the description thereof is thus omitted.

The isolation of the acoustic wave devices of the first embodiment, the first comparative example, and the second comparative example was simulated. The simulation conditions are as follows.

Support substrates11and21: Sapphire substrate with a thickness of 75 μm

Via wirings50to55: Copper film with a diameter of 40 μm

Ring-shaped metal layer60: Multilayered film in which a kovar layer with a thickness of 30 μm is sandwiched between copper layers with a thickness of 20 μm

Shield metal layer70: Kovar layer with a thickness of 30 μm

Covering metal layer75: Gold layer with a thickness of 1 μm

Transmit band of the transmit filter19: 2500 MHz to 2570 MHz

Receive band of the receive filter29: 2620 MHz to 2690 MHz

FIG. 11illustrates isolation characteristics of the acoustic wave devices of the first embodiment, the first comparative example, and the second comparative example. The horizontal axis inFIG. 11represents frequency [MHz], and the vertical axis represents attenuation [dB]. The attenuation indicates the leakage of the transmission signal to the receive terminal41. The larger absolute value of the attenuation indicates higher isolation, and the smaller absolute value of the attenuation indicates lower isolation (hereinafter, the same applies to similar drawings).

As illustrated inFIG. 11, in the transmit band of 2500 MHz to 2570 MHz and the receive band of 2620 MHz to 2690 MHz, the isolation characteristics of the first embodiment and the second comparative example are improved compared with that of the first comparative example. This is considered because in the first embodiment and the second comparative example, the shield metal layer70, to which a ground potential is supplied, is provided between the acoustic wave elements16forming the transmit filter19and the acoustic wave elements26forming the receive filter29. In other words, this is considered because the shield metal layer70shields the electromagnetic wave of the transmit filter19, and thereby the electromagnetic field coupling between the transmit filter19and the receive filter29is inhibited.

In the lower-side floor region (around 2350 MHz to 2450 MHz) lower in frequency than the transmit band and the higher-side floor region (around 2750 MHz to 2850 MHz) higher in frequency than the receive band, the isolation characteristic of the first embodiment is improved compared with that of the second comparative example. This reason is considered as follows. In the second comparative example, the shield metal layer70is supplied with a ground potential by being connected to the ground terminal44through the via wiring55provided in the substrate10. In this case, the inductance component of the via wiring55inhibits the grounding performance of the shield metal layer70from being sufficiently high, and as a result, the isolation characteristic is difficult to improve in the lower-side floor region and the higher-side floor region in the second comparative example. On the other hand, in the first embodiment, the shield metal layer70is supplied with a ground potential by being connected to the ground terminals43to47through the covering metal layer75covering the side surfaces15of the substrate10. This reduces the inductance component and improves the grounding performance of the shield metal layer70, and as a result, the isolation characteristics in the lower-side floor region and the higher-side floor region are improved in the first embodiment. In addition, in the first embodiment, the grounding performance of the shield metal layer70is improved. Thus, compared with the second comparative example, the isolation characteristic in the transmit band is also improved.

The simulation obtained results where the isolation at 2400 MHz (the lower-side floor region) in the first embodiment was improved by approximately 5.3 dB compared with that in the second comparative example, and the isolation at 2800 MHz (the higher-side floor region) in the first embodiment was improved by approximately 7.4 dB compared with that in the second comparative example. In addition, the isolation characteristic in the transmit band of the first embodiment was improved by approximately 3.7 dB compared with that in the second comparative example.

In the second comparative example, it may be considered to improve the grounding performance of the shield metal layer70by increasing the number of the via wirings that are provided in the support substrate11to electrically connect the ring-shaped metal layer60and the shield metal layer70to the ground terminal. However, due to the influence of the inductance components of the via wirings and the like, the grounding performance of the shield metal layer70is not sufficiently improved, and the improvement in the isolation characteristics does not become sufficiently high. In addition, since a plurality of via wirings are formed, the locations where the via wirings can be formed are limited by the locations where terminals are formed and the like. Thus, the improvement in isolation characteristics varies depending on the device, and it is difficult to obtain a stable improvement effect. Further, formation of a plurality of via wirings results in decrease in the strength of the substrate. In addition, when the ring-shaped metal layer60and the shield metal layer70are electrically connected to the ground terminal using a via wiring and/or a through-hole, increase in the number of via wirings and/or the number of through-holes may reduce the area that can be designed on the substrate. However, by connecting the ring-shaped metal layer60and the shield metal layer70to the ground terminal through not only the via wiring but also the covering metal layer75, the area that can be designed is secured.

The isolation of the acoustic wave devices of the first embodiment, the first variation of the first embodiment, and the second comparative example was simulated. The simulation conditions were the same as those of the above simulation 1.

FIG. 12illustrates isolation characteristics of the acoustic wave devices of the first embodiment, the first variation of the first embodiment, and the second comparative example. InFIG. 12, the horizontal axis represents frequency [MHz], and the vertical axis represents attenuation [dB]. As illustrated inFIG. 12, the first variation of the first embodiment improves the isolation characteristics to the same extent as the first embodiment. In the first variation of the first embodiment, the covering metal layer75covers only the side surfaces15of the substrate10, the post portion65a, which is located closer to the substrate10, of the ring-shaped metal layer60, and the part71of the shield metal layer70. Thus, the simulation result ofFIG. 12indicates that the isolation characteristic can be improved sufficiently even by covering only a part of the acoustic wave device with the covering metal layer75.

The isolation of the acoustic wave devices of the first embodiment, the first comparative example, and the third comparative example was simulated. The simulation conditions were the same as those of the above simulation 1.

FIG. 13illustrates isolation characteristics of the acoustic wave devices of the first embodiment, the first comparative example, and the third comparative example. InFIG. 13, the horizontal axis represents frequency [MHz], and the vertical axis represents attenuation [dB]. As illustrated inFIG. 13, the first comparative example and the third comparative example have similar isolation characteristics. In the third comparative example, the covering metal layer75is provided, but no shield metal layer70is provided. Therefore, the simulation result ofFIG. 13indicates that the improvement in isolation characteristics is small when only the covering metal layer75is provided without providing the shield metal layer70. That is, the simulation result indicates that the isolation characteristics can be improved by providing both the shield metal layer70and the covering metal layer75to improve the grounding performance of the shield metal layer70.

Second and Third Variations of the First Embodiment

FIG. 14AandFIG. 14Bare perspective views of acoustic wave devices illustrating the covered region with the covering metal layer in second and third variations of the first embodiment, respectively. InFIG. 14AandFIG. 14B, for clarity of the drawings, the region where the covering metal layer75is provided is indicated by hatching, and the outer shape of the covering metal layer75is indicated by a bold line. As illustrated inFIG. 14A, in an acoustic wave device120of the second variation of the first embodiment, the covering metal layer75is provided on two side surfaces15opposite to each other among the side surfaces15of the substrate10. The side surfaces15provided with the covering metal layer75are not limited to the side surfaces15opposite to each other, and may be the side surfaces15next to each other. Although the illustration is omitted, the covering metal layer75may be provided on three side surfaces15among the side surfaces15of the substrate10. As illustrated inFIG. 14B, in an acoustic wave device130of the third variation of the first embodiment, the covering metal layer75is provided on the side surfaces15of the substrate10so as to linearly extend from the parts adjacent to the ground terminals43to47among sides of the lower surface14of the substrate10to the respective side surfaces15of the substrate10. As described above, as long as the covering metal layer75covers half or more of the total area of the side surfaces15of the substrate10, how the covering metal layer75covers the side surfaces15is not limited.

In the first embodiment and the variations thereof, the shield metal layer70(a first metal layer) is provided between the acoustic wave elements16disposed on the substrate10and the acoustic wave elements26disposed on the substrate20. The shield metal layer70is electrically connected to the ground terminal44by the covering metal layer75(a second metal layer) covering half or more of the total area of the side surfaces15of the substrate10. This improves the grounding performance of the shield metal layer70, which enhances the electromagnetic shielding effect and improves the isolation characteristics. In addition, since the covering metal layer75covering the side surfaces15of the substrate10is provided, the electromagnetic field coupling between the acoustic wave elements16disposed on the substrate10and a device outside the acoustic wave device100is inhibited. The ratio of the area covered with the covering metal layer75to the total area of the side surfaces15can be obtained as follows, for example. The limits of the substrate10is determined in the X-ray image, the optical microscope image, or the SEM image of the cross-section of the acoustic wave device, and then the area defined by the limits is measured in the X-ray image, the optical microscope image, or the SEM image.

The covering metal layer75preferably covers a plurality of the side surfaces15from first ends, which are at the upper surface13side, of the side surfaces15of the substrate10to second ends, which are at the lower surface14side, of the side surfaces15. To improve the grounding performance of the shield metal layer70, it is preferable that the covering metal layer75is provided on two or more side surfaces15of the side surfaces15of the substrate10and covers at least a part of each of the two or more side surfaces15, and it is more preferable that the covering metal layer75is provided on three or more side surfaces15and covers at least a part of each of the three or more side surfaces15. It is further preferable that the covering metal layer75is provided on each of the side surfaces15of the substrate10and covers at least a part of each of the side surfaces15.

To improve the grounding performance of the shield metal layer70, the covering metal layer75covers preferably 60% or more of the total area of the side surfaces15of the substrate10, more preferably 75% or more of the total area of the side surfaces15of the substrate10, further preferably 90% or more of the total area of the side surfaces15of the substrate10, yet further preferably the entire surfaces of the side surfaces15of the substrate10. That is, it is yet further preferable that the covering metal layer75is provided on each of the side surfaces15of the substrate10and covers the entire of each of the side surfaces15.

The covering metal layer75is preferably in contact with at least a part of the surface of the ring-shaped metal layer60from the side surface15of the substrate10. This allows the shield metal layer70to be electrically connected to the ground terminal44through the covering metal layer75by a simple structure. The post portions65aand65bmay be formed of an insulating material instead of a metal material. In this case, the covering metal layer75preferably extends from the side surface15of the substrate10to the surface of the part71of the shield metal layer70.

When the acoustic wave elements16and26are sealed in the air gap82between the substrate10and the substrate20by the ring-shaped metal layer60, the covering metal layer75preferably covers surfaces extending from the side surfaces15of the substrate10to the side surfaces25and the upper surface23of the substrate20through the surface of the ring-shaped metal layer60. Since the covering metal layer75is provided on the side surfaces15and the upper surface23of the substrate20, the electromagnetic field coupling between the acoustic wave elements26disposed on the substrate20and an external device can be inhibited. Thus, the deterioration in characteristics can be reduced. The covering metal layer75covers preferably half or more of the total area of the side surfaces25and the upper surface23of the substrate20, more preferably ¾ or more of the total area of the side surfaces25and the upper surface23of the substrate20, further preferably the entire of each of the side surfaces25and the entire upper surface23of the substrate20.

The shield metal layer70may be electrically connected to the ground terminal44by both the covering metal layer75and the via wiring55(seeFIG. 9AandFIG. 9B) penetrating through the substrate10. This allows the area that can be designed on the substrate10to be satisfactory secured.

Second Embodiment

FIG. 15is a cross-sectional view of an acoustic wave device in accordance with a second embodiment. As illustrated inFIG. 15, in an acoustic wave device200of the second embodiment, the acoustic wave elements16disposed on the substrate10and the acoustic wave elements26disposed on the substrate20are not opposite to each other. That is, the piezoelectric layer22is provided on the opposite surface of the support substrate21from the surface opposite to the substrate10, and the acoustic wave elements26are disposed on the upper surface23of the substrate20. The acoustic wave elements26disposed on the substrate20are electrically connected to the receive terminal41through a via wiring81penetrating through the substrate20, the pillar61, and the via wiring51.

A ring-shaped metal layer60ais provided between the substrate10and the substrate20and surrounds the acoustic wave elements16. The acoustic wave elements16are sealed in an air gap83(a first air gap) formed between the substrate10and the substrate20by the ring-shaped metal layer60a. A ring-shaped metal layer60bis provided over the upper surface23of the substrate20and surrounds the acoustic wave elements26. A lid66is provided on the ring-shaped metal layer60b. The acoustic wave elements26are sealed in an air gap84(a second air gap) formed between the substrate20and the lid66by a sealing portion formed of the ring-shaped metal layer60band the lid66.

The shield metal layer70is provided on the lower surface24of the substrate20and is located in the air gap83. The covering metal layer75covers the entire surfaces of all side surfaces15of the substrate10, the entire outer surface of the ring-shaped metal layer60a, the entire outer surface of the shield metal layer70, the entire surfaces of all side surfaces25of the substrate20, the entire outer surface of the ring-shaped metal layer60b, and the entire outer surface of the lid66. Other configurations are the same as those of the first embodiment, and the description thereof is thus omitted.

Also in the acoustic wave device200of the second embodiment, the shield metal layer70is electrically connected to the ground terminal44by the covering metal layer75covering half or more of the total area of the side surfaces15of the substrate10. This improves the grounding performance of the shield metal layer70, which enhances the electromagnetic shielding effect and improves the isolation characteristics.

When the acoustic wave elements16are disposed on the upper surface13of the substrate10and the acoustic wave elements26are disposed on the upper surface23of the substrate20, the covering metal layer75preferably covers the surfaces extending from the side surfaces15of the substrate10to the side surfaces25of the substrate20and the surface of the sealing portion (the ring-shaped metal layer60band the lid66) through the surface of the ring-shaped metal layer60a. The covering metal layer75provided on the side surfaces25of the substrate20and the surface of the sealing portion (the ring-shaped metal layer60band the lid66) inhibits the electromagnetic field coupling between the acoustic wave elements26disposed on the substrate20and an external device. Therefore, the deterioration in characteristics can be reduced. The covering metal layer75covers preferably half or more of the total area of the side surfaces25of the substrate20and the surface of the sealing portion, more preferably ¾ or more of the total area of the side surfaces25of the substrate20and the surface of the sealing portion, further preferably the entire of each of the side surfaces25of the substrate20and the entire surface of the sealing portion.

The first embodiment and the second embodiment describe a case where the acoustic wave elements16and26excite surface acoustic waves, as an example, but the acoustic wave elements16and26may excite Love waves or boundary acoustic waves.

Third Embodiment

FIG. 16Ais a cross-sectional view of an acoustic wave device in accordance with a third embodiment, andFIG. 16Bis a cross-sectional view of an acoustic wave element in accordance with the third embodiment.FIG. 16Billustrates an acoustic wave element16a, as an example, but the same applies to an acoustic wave element26a. As illustrated inFIG. 16A, in an acoustic wave device300of the third embodiment, the acoustic wave elements16aare disposed on the upper surface13of a substrate10a, and the acoustic wave elements26aare disposed on the lower surface24of a substrate20a. The substrates10aand20aare insulating substrates such as, for example, silicon oxide substrates. As illustrated inFIG. 16B, the acoustic wave element16ais a piezoelectric thin film resonator where a lower electrode35, a piezoelectric film36, and an upper electrode37are provided on the substrate10a, and the lower electrode35and the upper electrode37sandwich the piezoelectric film36therebetween. An air gap38is formed between the lower electrode35and the substrate10a. The region where the lower electrode35and the upper electrode37sandwich the piezoelectric film36therebetween is the resonance region, and the lower electrode35and the upper electrode37excite an acoustic wave in the thickness extension mode within the piezoelectric film36in the resonance region. The lower electrode35and the upper electrode37are, for example, metal films made of, for example, ruthenium. The piezoelectric film36is, for example, an aluminum nitride film. Other configurations are the same as those of the first embodiment, and the description thereof is thus omitted.

The first and second embodiments describe a case where the acoustic wave elements16and26are surface acoustic wave resonators, as an example, but the acoustic wave elements16aand26amay be piezoelectric thin film resonators as in the third embodiment. Alternatively, one of the acoustic wave elements disposed on the two substrates may be a surface acoustic wave resonator, and the other may be a piezoelectric thin film resonator.

The first to third embodiments describe a case where the acoustic wave elements16or16adisposed on the substrate10or10aform the transmit filter19and the acoustic wave elements26or26adisposed on the substrate20or20aform the receive filter29, but does not intend to suggest any limitation. For example, the acoustic wave elements16or16amay form the receive filter and the acoustic wave elements26or26amay form the transmit filter. Alternatively, the acoustic wave elements16or16amay form one of two transmit filters having different passbands, and the acoustic wave elements26or26amay form the other of the two transmit filters where one of the two transmit filters is for a first band, the other of the two transmit filters is for a second band different from the first band, and a signal of the first band and a signal of the second band are transmitted simultaneously. Alternatively, the acoustic wave elements16or16amay form one of two receive filters having different passbands, and the acoustic wave elements26or26amay form the other of the two receive filters where one of the two receive filters is for a first band, the other of the two receive filters is for a second band different from the first band, and a signal of the first band and a signal of the second band are received simultaneously. Alternatively, the transmit filter19and the receive filter29may form a multiplexer.

Fourth Embodiment

FIG. 17is a perspective view of a communication module in accordance with a fourth embodiment. As illustrated inFIG. 17, in a communication module400of the fourth embodiment, one or more integrated circuits (ICs)86, one or more chip inductors87, one or more chip capacitors88, and one or more acoustic wave devices100of the first embodiment are mounted on a circuit substrate85. Since the covering metal layer75is provided on the surface of the acoustic wave device100, the electromagnetic field coupling between the acoustic wave device100and another device mounted on the circuit substrate85is inhibited. That is, the influence of the electromagnetic field on the external device from the acoustic wave device100can be reduced, and the influence of the electromagnetic field on the acoustic wave device100from the external device can be reduced. The fourth embodiment describes a case where the acoustic wave device100of the first embodiment is mounted, but the acoustic wave device of any one of the first to third variations of the first embodiment and the second and third embodiments may be mounted.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to such a specific embodiment, and it is to be understood that the various change, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.