Acoustic Wave Devices, Filters and Multiplexers

Abstract

To provide an elastic wave device which suppresses migration of copper or silver.SOLUTION: An elastic wave device comprises: a first substrate 10 in which at least of a portion of a first face is a piezoelectric layer; an elastic wave element 12 provided on the first face of the piezoelectric layer; a second substrate 20 which is provided while interposing a cavity 28 with the elastic wave element 12; a first metal layer 14 provided on the first face and connected so as to be conducted with the elastic wave element 12; a second metal layer 24 provided on a second face of the second substrate 20 at a side of the first substrate 10; a third metal layer 30 connecting the first metal layer 14 and the second metal layer 24, being thicker than the first metal layer 14 and the second metal layer 24 and containing copper or silver as a main component; and a first conductive layer covering a side face of the third metal layer 30 and a third face of the first metal layer 14 at a side of the second substrate 20 in a region 50 enclosing a region 51 where the third metal layer 30 is joined to the first metal layer 14, being thinner than the first metal layer 14 and containing any other than copper, silver and thin as a main component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to acoustic wave devices, filters and multiplexers. [Background technology]

[0002] There is known an acoustic wave device in which an acoustic wave element is provided on a substrate, and another substrate such as a lid is placed on the acoustic wave element, and the substrate and the other substrate are connected using a metal layer (e.g., Patent Documents 1 to 4). It is also known that in an under-bump metal layer, another metal layer is provided so as to cover the side and top surfaces of the metal layer (e.g., Patent Documents 5 and 6). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-364041 A [Patent Document 2] JP 2007-89143 A [Patent Document 3] JP 2015-146523 A [Patent Document 4] Special Publication No. 2010-526456 [Patent Document 5] Japanese Patent Application Publication No. 10-13184 [Patent Document 6] JP 2002-100951 A Summary of the Invention [Problem to be solved by the invention]

[0004] Piezoelectric substrates are prone to become charged, and when a metal layer connecting one substrate to another is mainly composed of copper or silver, the copper or silver may migrate into the acoustic wave element.

[0005] The present invention has been made in consideration of the above problems, and has an object to suppress the migration of copper or silver. [Means for solving the problem]

[0006] The present invention is an acoustic wave device comprising: a first substrate, at least a portion of whose first surface is a piezoelectric layer; an acoustic wave element provided on the first surface of the piezoelectric layer; a second substrate provided with a gap between the acoustic wave element and the first metal layer; a first metal layer provided on the first surface and electrically connected to the acoustic wave element; a second metal layer provided on a second surface of the second substrate facing the first substrate; a third metal layer connecting the first metal layer and the second metal layer, being thicker than the first metal layer and the second metal layer and containing copper or silver as its main component; and a first conductive layer covering side surfaces of the third metal layer and a third surface of the first metal layer facing the second substrate in a region surrounding the region where the third metal layer is joined to the first metal layer, being thinner than the third metal layer and containing a component other than copper, silver and tin as its main component.

[0007] In the above configuration, the first conductive layer covering the third surface may be thicker than the first conductive layer covering a side surface of the third metal layer.

[0008] In the above configuration, the first conductive layer may further cover a surface of the third metal layer facing the second substrate, and be directly bonded to the second metal layer.

[0009] In the above configuration, the first conductive layer includes a second conductive layer that is directly bonded to the second metal layer, and the second conductive layer is bonded to the second metal layer. Conductive Layer and a third conductive layer provided between the third metal layer.

[0010] In the above configuration, a region of the second metal layer that is in contact with the second conductive layer may have the same main component as the main component of the second conductive layer.

[0011] In the above configuration, the second conductive layer may be composed mainly of gold or aluminum.

[0012] In the above configuration, the third conductive layer may be mainly composed of at least one element selected from the group consisting of titanium, chromium, tantalum, nickel, tungsten, and ruthenium, or a nitride of the at least one element.

[0013] The above configuration may further include a metal pillar including the third metal layer.

[0014] In the above configuration, the first substrate may include a support substrate and the piezoelectric layer provided on the support substrate.

[0015] The above configuration may include an element provided on a surface of the second substrate facing the first substrate.

[0016] In the above configuration, at least a portion of the second surface of the second substrate is another piezoelectric layer, and the acoustic wave device can be configured to include another acoustic wave element provided on the other piezoelectric layer, a fourth metal layer connecting the second metal layer and the third metal layer, being thicker than the first metal layer and the second metal layer and containing copper or silver as its main component, and a fourth conductive layer covering a side surface of the fourth metal layer and a fourth surface of the second metal layer facing the first substrate in a region surrounding the region where the fourth metal layer is joined to the second metal layer, being thinner than the fourth metal layer and containing a component other than copper, silver and tin as its main component.

[0017] The present invention is a filter including the above acoustic wave device.

[0018] The present invention is a multiplexer including the above filter. Effect of the Invention

[0019] According to the present invention, migration of copper or silver can be suppressed. [Brief description of the drawings]

[0020] [Figure 1]FIG. 1(a) is a cross-sectional view of an acoustic wave device in accordance with a first embodiment, and FIG. 1(b) is an enlarged view of the vicinity of a metal pillar in FIG. 1(a). [Diagram 2] FIG. 2 is a plan view of the acoustic wave device in accordance with the first embodiment. [Diagram 3] 3A and 3B are plan views of the acoustic wave device in accordance with the first embodiment. [Figure 4] 4(a) to 4(d) are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Diagram 5] 5(a) and 5(b) are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 6] FIG. 6 is an enlarged view of the vicinity of the metal pillar in Comparative Example 1. As shown in FIG. [Figure 7] FIG. 7(a) is a cross-sectional view of an acoustic wave device in accordance with a first modification of the first embodiment, and FIG. 7(b) is an enlarged view of the vicinity of a metal pillar in FIG. 7(a). [Figure 8] 8A and 8B are cross-sectional views of acoustic wave devices according to second and third modifications of the first embodiment, respectively. [Figure 9] FIG. 9 is a cross-sectional view of an acoustic wave device in accordance with a fourth modification of the first embodiment. [Figure 10] FIG. 10 is a cross-sectional view of an acoustic wave device according to a fourth modification of the first embodiment. [Figure 11] FIG. 11 is a cross-sectional view of an acoustic wave device in accordance with a fifth modification of the first embodiment. [Figure 12] FIG. 12(a) is a circuit diagram of a filter in accordance with the second embodiment, and FIG. 12(b) is a circuit diagram of a duplexer in accordance with a first modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0022] Fig. 1(a) is a cross-sectional view of an acoustic wave device in accordance with a first embodiment, and Fig. 1(b) is an enlarged view of the vicinity of a metal pillar in Fig. 1(a). The thickness direction of the substrate 10 is the Z direction, and the planar directions of the substrate 10 are the X direction and the Y direction.

[0023] As shown in FIG. 1(a), the substrate 10 includes a support substrate 10b and a piezoelectric substrate 10a provided on the support substrate 10b. One or more insulating layers, such as a silicon oxide film or an aluminum oxide film, may be provided between the support substrate 10b and the piezoelectric substrate 10a. An acoustic wave element 12 and a metal layer 14 are provided on the piezoelectric substrate 10a. The acoustic wave element 12 is, for example, a surface acoustic wave element. The metal layer 14 functions as wiring and a pad electrically connected to the acoustic wave element 12. The piezoelectric substrate 10a is removed from the periphery of the substrate 10, and a metal layer 15 is provided on the support substrate 10b in the periphery of the substrate 10 so as to surround the acoustic wave element 12. A via wiring 16 is provided to penetrate the substrate 10. A terminal 18 is provided on the lower surface of the substrate 10. The terminal 18 functions as an input terminal Tin, an output terminal (not shown), and a ground terminal Tgnd. The via wiring 16 electrically connects the metal layer 14 and the terminal 18. A substrate 20 is provided above the substrate 10. Metal pillars 36 are provided on metal layer 14. A ring-shaped metal layer 38 is provided on metal layer 15 so as to surround acoustic wave element 12.

[0024] The piezoelectric substrate 10a is, for example, a piezoelectric substrate such as a single crystal lithium tantalate substrate, a single crystal lithium niobate substrate, or a single crystal quartz substrate. The single crystal lithium tantalate substrate and the single crystal lithium niobate substrate are, for example, rotated Y-cut X-propagation substrates. The support substrate 10b is, for example, a sapphire substrate, an alumina substrate, a quartz substrate, a quartz substrate, a spinel substrate, a SiC substrate, or a silicon substrate. The metal layer 14, the metal layer 15, the via wiring 16, and the terminal 18 are, for example, a single layer of a metal layer such as a copper layer, a gold layer, a silver layer, a titanium layer, a nickel layer, or a tungsten layer, or a laminate of these layers.

[0025] The substrate 20 is provided above the substrate 10 with a gap 28 therebetween. The substrate 20 has an element 21 and a metal layer 24 provided on its lower surface. The element 21 is, for example, a passive element such as an inductor or a capacitor. The metal pillar 36 connects the metal layer 14 to the metal layer 24. The annular metal layer 38 connects the metal layers 15 to 24. The annular metal layer 38 and the substrates 10 and 20 seal the acoustic wave element 12 and the element 21 in the gap 28. The metal pillar 36 and the annular metal layer 38 include a metal layer 30 and a metal layer 33 covering the metal layer 30. The substrate 20 is, for example, a sapphire substrate, an alumina substrate, a quartz substrate, a crystal substrate, a spinel substrate, a SiC substrate, or a silicon substrate. The metal layer 24 is, for example, a single layer of a metal layer such as a copper layer, a gold layer, a silver layer, a titanium layer, a nickel layer, or a tungsten layer, or a laminate of these layers.

[0026] As shown in FIG. 1(b), the metal layer 33 covers a region 50 on the surface of the metal layer 14 and the upper and side surfaces of the metal layer 30. The region 50 is a region surrounding a bonding region 51 where the metal layer 30 is bonded to the metal layer 14. The metal layer 33 may be provided at least in a region of the region 50 between the metal layer 30 and the acoustic wave element 12. The metal layer 33 includes a metal layer 32 that contacts the region 50 and the upper and side surfaces of the metal layer 30, and a metal layer 34 that covers the metal layer 32 and contacts the metal layer 32. The metal layer 30 is mainly composed of copper or silver. The metal layer 34 is mainly composed of, for example, gold or aluminum. The metal layer 32 is a barrier layer that suppresses migration of copper or silver, and is mainly composed of, for example, at least one element selected from the group consisting of titanium, chromium, tantalum, nickel, tungsten, and ruthenium, or a nitride of the at least one element.

[0027] The metal layer 24 includes metal layers 24a to 24c. The metal layer 24a is electrically connected to the element 21. The metal layer 24c is directly bonded to the metal layer 34. The metal layer 24b is provided between the metal layers 24a and 24c. Since the metal layer 24c is directly bonded to the metal layer 34, the main components of the metal layers 24c and 34 are the same, for example. The metal layer 24c is mainly composed of, for example, gold or aluminum. The metal layer 24b is a diffusion prevention barrier layer between the metal layers 24a and 24c, and is mainly composed of, for example, at least one element selected from the group consisting of titanium, chromium, tantalum, nickel, tungsten, and ruthenium, or a nitride of the at least one element.

[0028] The thicknesses of metal layers 14, 24, and 30 are T1 to T3, respectively. The thicknesses of metal layer 32 covering the upper surface and side surfaces of metal layer 30 are T4c and T4a, respectively, and the thicknesses of metal layer 34 covering the upper surface and side surfaces of metal layer 32 are T5c and T5a, respectively. The thickness of metal layer 32 covering region 50 is T4b. The thickness of metal layer 34 covering region 50 is T5b.

[0029] The thicknesses T1 and T2 of the metal layers 14 and 24 are, for example, 0.1 μm to 5 μm. The thickness T3 of the metal layer 30 is, for example, 10 μm to 100 μm. The thicknesses T1 and T2 of the metal layers 14 and 24 are relatively thin because they function as wiring extending in the planar direction. The thickness T3 of the metal layer 30 is relatively thick because it connects the substrates 10 and 20 and increases the width of the gap 28 in the Z direction. The thickness T3 is, for example, 2 times or more, and 5 times or more, of the thickness T1+T2. The thickness T3 of the metal layer 30 is, for example, 1 / 2 or more, and 4 / 5 or more of the height H1 in the Z direction between the substrates 10 and 20. The width W1 of the metal layer 30 is, for example, 20 μm to 200 μm. When the width W1 is large, the chip planar area is large. For this reason, the aspect ratio T3 / W1 is 0.4 or more, preferably 0.6 or more, and more preferably 1.0 or more. Each of thicknesses T4a to T4c and T5a to T5c is 20 nm to 200 nm. Thickness T4b is smaller than thicknesses T4a and T4c, and thickness T5b is smaller than thicknesses T5a and T5c. For example, T4a:T4b=T5a:T5b=2:5. In order to cover the side surface of metal layer 30 with metal layer 33, the cross-sectional shape of metal layer 30 is, for example, trapezoidal, and the taper angle of the side surface is, for example, 70° or more and less than 90°.

[0030] FIG. 2 is a plan view of the acoustic wave element in the first embodiment. As shown in FIG. 2, the acoustic wave element 12 is a surface acoustic wave resonator or a Lamb wave resonator. An IDT (Interdigital Transducer) 40 and a reflector 42 are formed on a piezoelectric substrate 10a. The IDT 40 has a pair of comb electrodes 40a facing each other. The comb electrodes 40a have a plurality of electrode fingers 40b and a bus bar 40c connecting the plurality of electrode fingers 40b. The reflectors 42 are provided on both sides of the IDT 40. The IDT 40 excites a surface acoustic wave on the substrate 10, which is a piezoelectric substrate. The wavelength of the acoustic wave is approximately equal to the pitch of the electrode fingers 40b of one of the pair of comb electrodes 40a. That is, the wavelength of the acoustic wave is approximately equal to twice the pitch of the electrode fingers 40b of the pair of comb electrodes 40a. The IDT 40 and the reflector 42 are formed of, for example, an aluminum film, a copper film, or a molybdenum film. A protective film or a temperature compensation film may be provided on piezoelectric substrate 10a to cover IDT 40 and reflector 42. Acoustic wave element 12 includes an electrode that excites an acoustic wave. For this reason, acoustic wave element 12 is covered with gap 28 so as not to restrict the acoustic wave.

[0031] 3(a) and 3(b) are plan views of the acoustic wave device according to the first embodiment. FIG. 3(a) is a plan view of the upper surface of the substrate 10, and FIG. 3(b) is a plan view of the lower surface of the substrate 10 seen through from above. As shown in FIG. 3(a), the piezoelectric substrate 10a at the periphery of the substrate 10 is removed, and the annular metal layer 38 is provided at the periphery of the substrate 10. The annular metal layer 38 is connected to a ground terminal provided at the lower surface of the substrate 10 through the via wiring 16. An acoustic wave element 12 and a metal layer 14 are provided on the piezoelectric substrate 10a. The acoustic wave element 12 is an acoustic wave resonator and includes an IDT 40 and a reflector 42. The metal layer 14 functions as a wiring for connecting the acoustic wave element 12 and a pad to which the via wiring 16 is connected. The acoustic wave element 12 includes series resonators S1 and S2 and a parallel resonator P1. The metal layer 14 functions as an input pad In, an output pad Out, and a ground pad Gnd. The input pad In, the output pad Out, and the ground pad Gnd are electrically connected to an input terminal, an output terminal, and a ground terminal provided on the lower surface of the substrate 10 through via wiring 16. A metal pillar 36 is provided on the input pad In. The series resonators S1 and S2 are connected in series between the input pad In and the output pad Out, and the parallel resonator P1 is connected between the input pad In and the output pad Out. parallel is connected to.

[0032] As shown in Fig. 3(b), an annular metal layer 38 is provided on the periphery of the substrate 20. An inductor is formed as the element 21 by the metal layer 24. One end of the element 21 is electrically connected to the input pad In of Fig. 3(a) via the metal pillar 36. The other end of the element 21 is connected to the annular metal layer 38 by the metal layer 24, and is connected to the ground terminal via the via wiring 16 of Fig. 3(a). As a result, the inductor is connected between the input terminal Tin and the ground terminal Tgnd.

[0033] 4(a) to 5(b) are cross-sectional views showing a method for manufacturing an acoustic wave device according to Example 1. As shown in Fig. 4(a), the piezoelectric substrate 10a is removed from the peripheral portion of the substrate 10, in which the piezoelectric substrate 10a is bonded to the upper surface of the support substrate 10b. Holes are formed in the substrate 10, and via wiring 16 is formed in the holes. The via wiring 16 does not penetrate the substrate 10. An acoustic wave element 12 and metal layers 14 and 15 are formed on the substrate 10.

[0034] As shown in FIG. 4(b), a metal layer 30 is formed on the metal layers 14 and 15. A plating method is used to form the metal layer 30. The side of the opening in the photoresist, which serves as a mask for plating, is reverse tapered (the width at the top of the opening is smaller than the width at the bottom of the opening), so that the side of the metal layer 30 is tapered (the width at the top of the metal layer 30 is smaller than the width at the bottom of the metal layer 30). The distance from the support substrate 10b to the top surface of the metal layer 30 is different between the metal layer 30 provided on the piezoelectric substrate 10a and the metal layer 30 provided on the support substrate 10b from which the piezoelectric substrate 10a has been removed.

[0035] As shown in FIG. 4(c), the upper surface of the metal layer 30 is ground. As a result, the distance from the support substrate 10b to the upper surface of the metal layer 30 becomes the same. The upper surface of the metal layer 30 is planarized, for example, by using a chemical mechanical polishing (CMP) method. As a result, the arithmetic mean roughness of the upper surface of the metal layer 30 is set to, for example, 1 nm or less.

[0036] As shown in FIG. 4(d), a metal layer 33 is formed so as to cover the metal layer 30. For example, a sputtering method and a lift-off method are used to form the metal layer 33. The side surface of the metal layer 30 does not need to be tapered, but if the side surface is tapered, the coverage of the metal layer 33 is improved. Depending on the deposition conditions of the metal layer 33, the thickness of the metal layer 33 on the metal layer 14 (T4b and T5b in FIG. 1(b)) can be made thicker than the thickness of the metal layer 33 on the side surface of the metal layer 30 (T4a and T5a in FIG. 1(b)).

[0037] As shown in FIG. 5(a), the substrate 10 is placed on the substrate 20, upside down from FIG. 4(d). The upper surface of the metal layer 33 (i.e., the upper surface of the metal layer 32) and the lower surface of the metal layer 24c are irradiated with a beam of an inert gas such as argon to activate the upper surface of the metal layer 33 and the lower surface of the metal layer 24c. At this time, the arithmetic mean roughness Ra of the upper surface of the metal layer 33 and the lower surface of the metal layer 24c is 1 nm or less. Thereafter, as shown in FIG. 5(b), the metal layer 33 on the metal layer 30 and the metal layer 24c (see FIG. 1(b)) are pressed together to bond them. Such a surface activation method is performed at room temperature (for example, 0° C. or higher and 100° C. or lower). By making the main component of the upper part of the metal layer 33 and the metal layer 24c the same, it becomes easy to bond the metal layers 33 and 24c at room temperature by the surface activation method. Thereafter, the lower surface of the support substrate 10b is polished until the via wiring 16 is exposed. A terminal 18 is formed on the lower surface of the support substrate 10b. In this manner, the acoustic wave device in accordance with the first embodiment is manufactured.

[0038] [Comparative Example 1] FIG. 6 is an enlarged view of the vicinity of the metal pillar in Comparative Example 1. In Comparative Example 1, the metal pillar 36b and the metal layer 24 are joined by the solder 37. The metal layer 24 includes a metal layer 24d between the metal layer 24a and the solder 37. The metal layer 24d is a layer with good solder wettability, for example, a nickel layer. The piezoelectric substrate 10a is charged by temperature and stress. This applies an electric field to the metal pillar 36b. When moisture is supplied in a state where an electric field is applied, ion migration occurs in which the metal of the metal pillar 36 moves. Copper and silver are elements that are prone to ion migration. Similarly, tin in the solder 37 is an element that is prone to ion migration. When copper or silver ions move to the acoustic wave element 12 as indicated by the arrow 52a, or tin ions move to the acoustic wave element 12 as indicated by the arrow 52b, the acoustic wave element 12 deteriorates. For example, the electrode fingers of the acoustic wave element 12 are short-circuited. When the acoustic wave device is manufactured or used, if the temperature changes or stress is applied, ion migration of copper or silver occurs, causing deterioration of acoustic wave element 12.

[0039] 1(b), at least a part of the upper surface (first surface) of substrate 10 (first substrate) is piezoelectric substrate 10a (piezoelectric layer), and acoustic wave element 12 is provided on piezoelectric substrate 10a. Substrate 20 (second substrate) is provided with acoustic wave element 12 via gap 28. Metal layer 14 (first metal layer) is provided on the upper surface (first surface on substrate 20 side) of substrate 10 and is electrically connected to acoustic wave element 12. Metal layer 24 (second metal layer) is provided on the lower surface of substrate 20 (second surface on substrate 10 side). Metal layer 30 (third metal layer) connects metal layers 14 and 24 together.

[0040] In this structure, in order to reduce the resistance of metal pillar 36, metal layer 30, which is thicker than metal layers 14 and 24, is mainly composed of copper or silver. If metal layer 14 is conductive to acoustic wave element 12 provided on piezoelectric substrate 10a, which is easily charged, an electric field is applied to metal layer 30. This may cause the copper or silver of metal layer 30 to migrate to acoustic wave element 12 due to ion migration, as in Comparative Example 1, resulting in deterioration of acoustic wave element 12.

[0041] Therefore, a metal layer 33 (first conductive layer) is provided that is thinner than metal layer 30 and contains a component other than copper, silver, and tin (i.e., does not contain copper, silver, and tin as its main components) so as to cover the side surface of metal layer 30 and the top surface (third surface) of metal layer 30 in region 50 surrounding bonding region 51 where metal layer 30 is bonded to metal layer 14. This allows metal layer 33 to function as a barrier against migration of copper or silver as indicated by arrow 52a in FIG. 6. This makes it possible to suppress migration of copper or silver to acoustic wave element 12. Note that metal layer 30 preferably contains copper as its main component. This allows metal layer 30 to be formed more easily by plating than when metal layer 30 contains silver as its main component.

[0042] A thickness T4b+T5b of metal layer 33 covering region 50 is thicker than a thickness T4a+T5a of metal layer 33 covering the side surfaces of metal layer 30. This allows metal layer 33 in region 50 to further suppress migration of copper or silver from metal layer 30 to acoustic wave element 12.

[0043] Metal layer 33 further covers the upper surface (surface on the substrate 20 side) of metal layer 30 and is directly bonded to metal layer 24. Metal layer 33 does not contain tin as a main component, and therefore does not require solder 37 as in Comparative Example 1. This makes it possible to suppress the migration of tin into acoustic wave element 12 as indicated by arrow 52b.

[0044] Metal layer 34 (second conductive layer) is bonded to metal layer 24, and metal layer 32 (third conductive layer) is provided between metal layers 34 and 30. This allows metal layer 34 to be made of a material that easily bonds to metal layer 24, and metal layer 32 to be made of a material that easily acts as a barrier for copper or silver.

[0045] The metal layer 24c in the region of the metal layer 24 that is bonded to the metal layer 34 has the same main component as the main component of the metal layer 34. This makes it possible to suppress the generation of an intermetallic compound between the metal layers 24c and 34. As a result, the bonding quality between the metal layers 24c and 34 can be improved.

[0046] At high temperatures, the piezoelectric substrate 10a is easily charged by stress and the like. At high temperatures, moisture is released into the gaps 28 from the metal layer 30 formed by plating and the like. Moisture in the gaps 28 makes it easier for ion migration of copper or silver to occur in the metal layer 30. If the metal layers 34 and 24 are bonded at high temperatures, the above-mentioned migration of copper or silver is more likely to occur. Therefore, the metal layers 24 and 34 are bonded at room temperature using a surface activation method. This makes it possible to suppress migration.

[0047] The metal layer 34 is mainly composed of gold or aluminum. This facilitates direct bonding between the metal layers 24 and 30. The metal layer 34 is preferably mainly composed of gold. This facilitates direct bonding between the metal layers 24 and 30. In addition, gold and aluminum are less susceptible to ion migration than copper or silver.

[0048] The metal layer 32 is mainly composed of at least one element selected from the group consisting of titanium, chromium, tantalum, nickel, tungsten, and ruthenium, or a nitride of these elements. As a result, these elements or nitrides function as a barrier against ion migration of copper or silver, thereby further suppressing migration.

[0049] Metal pillar 36 including metal layer 30 connects substrates 10 and 20. Metal pillar 36 is preferably made mainly of copper or silver to electrically connect substrates 10 and 20. Therefore, it is preferable to provide metal layer 33 that suppresses migration. Note that there is a possibility that copper or silver may migrate from metal layer 30 of annular metal layer 38 to acoustic wave element 12. Therefore, it is preferable to provide metal layer 33 on annular metal layer 38.

[0050] Substrate 10 includes support substrate 10b and piezoelectric substrate 10a provided on support substrate 10b. The thermal expansion coefficient of support substrate 10b is set to be smaller than the thermal expansion coefficient of piezoelectric substrate 10a in the propagation direction of the elastic wave. This makes it possible to suppress temperature changes in acoustic wave element 12. However, since thermal stress is applied to piezoelectric substrate 10a, piezoelectric substrate 10a becomes more likely to be charged. This increases the electric field in metal layer 30, making ion migration more likely to occur. Therefore, it is preferable to provide metal layer 33 that suppresses migration.

[0051] When the metal layer 30 is provided on the piezoelectric substrate 10a, the piezoelectric substrate 10a is charged by stress applied from the metal layer 30 to the piezoelectric substrate 10a, and the electric field applied to the metal layer 30 is likely to become large. This makes it easier for migration of copper or silver in the metal layer 30 to occur. Therefore, it is preferable to provide the metal layer 33.

[0052] Substrate 20 may not have any elements and may simply be a lid. However, if substrate 20 has passive elements or the like, metal layer 30 is preferably made mainly of copper or silver to electrically connect element 21 and acoustic wave element 12. Therefore, it is preferable to provide metal layer 33 that suppresses migration.

[0053] No solder layer containing tin is provided between the substrates 10 and 20. This makes it possible to suppress ion migration of tin, as indicated by arrow 52b in FIG.

[0054] A metal layer consisting primarily of a certain element or compound includes the unintentional or intentional inclusion of impurities in the metal layer, for example, the concentration of a certain element or compound in the metal layer being 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more.

[0055] [Modification 1 of Example 1] FIG. 7(a) is a cross-sectional view of an acoustic wave device according to a first modification of the first embodiment, and FIG. 7(b) is an enlarged view of the vicinity of the metal pillar in FIG. 7(a). As shown in FIG. 7(a) and FIG. 7(b), the piezoelectric substrate 10a below the metal pillar 36 is removed. The metal pillar 36 is provided on the support substrate 10b from which the piezoelectric substrate 10a has been removed. Even if the metal pillar 36 is not provided on the piezoelectric substrate 10a as in the first modification of the first embodiment, an electric field is applied to the metal layer 30 due to the charging of the piezoelectric substrate 10a, as long as the acoustic wave element 12 and the metal layer 30 are electrically connected via the metal layer 14. Therefore, migration of copper or silver in the metal layer 30 may occur. Therefore, it is preferable to provide the metal layer 33. The other configurations are the same as those of the first embodiment, and description thereof will be omitted.

[0056] [Modification 2 of Example 1] Fig. 8(a) is a cross-sectional view of an acoustic wave device according to Modification 2 of Example 1. As shown in Fig. 8(a), the substrate 10 is a piezoelectric substrate, and the metal pillars 36 and the annular metal layer 38 are provided on the piezoelectric substrate. The other configurations are the same as those of Example 1, and therefore description thereof will be omitted.

[0057] [Modification 3 of Example 1] FIG. 8(b) is a cross-sectional view of an acoustic wave device according to Modification 3 of Example 1. As shown in FIG. 8(b), the substrate 20 includes a support substrate 20b and a piezoelectric substrate 20a provided under the support substrate 20b. An acoustic wave element 22 and a metal layer 24 are provided on the lower surface of the piezoelectric substrate 20a. The piezoelectric substrate 20a, the support substrate 20b, the acoustic wave element 22, and the metal layer 24 have the same configurations as the piezoelectric substrate 10a, the support substrate 10b, the acoustic wave element 12, and the metal layer 14, and therefore their description will be omitted. A metal pillar 36a and an annular metal layer 38a are provided under the metal layer 24. The metal pillar 36a and the annular metal layer 38a include metal layers 30a and 33a. The metal layers 30a and 33a have the same configurations as the metal layers 30 and 33, and therefore their description will be omitted. The metal layer 33 on the upper surface of the metal pillar 36 and the metal layer 33a on the lower surface of the metal pillar 36a are directly bonded to each other, and the metal layer 33 on the upper surface of the annular metal layer 38 and the metal layer 33a on the lower surface of the annular metal layer 38a are directly bonded to each other. The other configurations are the same as those in the first embodiment, and therefore the description will be omitted.

[0058] [Variation 4 of Example 1] 9 is a cross-sectional view of an acoustic wave device according to Modification 4 of Example 1. As shown in FIG.

[0059] FIG. 10 is a cross-sectional view of an acoustic wave element in Modification 4 of Example 1. As shown in FIG. 10, in acoustic wave element 22, which is a piezoelectric thin film resonator, piezoelectric film 46 is provided on substrate 20. Lower electrode 44 and upper electrode 48 are provided to sandwich piezoelectric film 46. A gap 45 is formed between lower electrode 44 and substrate 10. A region where lower electrode 44 and upper electrode 48 face each other with at least a part of piezoelectric film 46 sandwiched therebetween is resonance region 47. In resonance region 47, lower electrode 44 and upper electrode 48 excite an acoustic wave in thickness longitudinal vibration mode in piezoelectric film 46. Lower electrode 44 and upper electrode 48 are metal films such as ruthenium films. Piezoelectric film 46 is, for example, an aluminum nitride film. An acoustic reflection film that reflects acoustic waves may be provided instead of gap 45. The other configurations are the same as those of Modification 3 of Example 1, and description thereof will be omitted.

[0060] As in the third and fourth modified examples of the first embodiment, at least a part of the lower surface (second surface) of the substrate 20 is a piezoelectric substrate 20a (another piezoelectric layer), and an acoustic wave element 22 (another acoustic wave element) is provided on the piezoelectric substrate 20a. The metal layer 30a (fourth metal layer) connects the metal layers 24 and 30, is thicker than the metal layers 14 and 24, and is mainly composed of copper or silver. The metal layer 33a (fourth conductive layer) covers the side surface of the metal layer 30a, the lower surface (fourth surface) of the metal layer 24 in the region surrounding the region where the metal layer 30a is bonded to the metal layer 24, is thinner than the metal layer 24, and is mainly composed of materials other than copper, silver, and tin. This can suppress the migration of copper or silver of the metal layer 30a to the acoustic wave element 22. Since the annular metal layers 38 and 38a are bonded to each other, the strength is easily weakened. Therefore, it is preferable to make the width of the annular metal layers 38 and 38a larger than the width of the annular metal layer 38 in the first embodiment.

[0061] [Modification 5 of Example 1] FIG. 11 is a cross-sectional view of an acoustic wave device according to a fifth modification of the first embodiment. As shown in FIG. 11, the piezoelectric substrate 20a in the substrate 20 is provided on the upper surface of the support substrate 20b. Metal layers 27a and 27b are provided on the lower surface of the substrate 20. The metal pillars 36 and the annular metal layer 38 are bonded to the metal layers 27a and 27b, respectively. The metal layer 27a functions as a shield. A lid 54 is provided on the substrate 20. A metal layer 55 is provided on the lower surface of the lid 54. A via wiring 56 penetrating the lid 54 is provided. A metal layer 58 is provided on the lid 54. The via wiring 56 connects the metal layers 55 and 58. The metal pillars 36a and the annular metal layer 38a are bonded to the metal layer 55. The lid 54 and the annular metal layer 38a seal the acoustic wave element 22 in the gap 28a. The other configurations are the same as those of the third modification of the first embodiment, and therefore description thereof will be omitted. As in the fifth modification of the first embodiment, an element may be provided on the substrate 20.

[0062] In the first embodiment and its modified example, an example of an inductor and an acoustic wave element 22 (a piezoelectric thin film resonator or a surface acoustic wave resonator) has been described as the element 21, but the element 21 may be a passive element such as an inductor or a capacitor, an active element including a transistor, or a MEMS (Micro Electro Mechanical Systems) element. EXAMPLES

[0063] FIG. 12(a) is a circuit diagram of a filter according to a second embodiment. As shown in FIG. 12(a), one or more series resonators S1 to S4 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 to P4 are connected in parallel between the input terminal Tin and the output terminal Tout. The filter of the second embodiment may be formed of an acoustic wave element 12. The numbers of the series resonators and parallel resonators can be set appropriately. Although a ladder-type filter has been described as an example of the filter, the filter may be a multimode filter.

[0064] FIG. 12(b) is a circuit diagram of a duplexer according to a first modified example of the second embodiment. As shown in FIG. 12(b), a transmission filter 60 is connected between a common terminal Ant and a transmission terminal Tx. A reception filter 62 is connected between the common terminal Ant and a reception terminal Rx. The transmission filter 60 passes a signal in a transmission band among high-frequency signals input from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 62 passes a signal in a reception band among high-frequency signals input from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 60 and the reception filter 62 can be the filter of the second embodiment.

[0065] Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0066] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0067] 10 Substrate 12, 22 Acoustic Wave Device 14, 15, 24, 24a~24c, 30, 32, 33, 33a, 34, 55, 58 metal layer 16 Via wiring 18 Terminals 28, 28a void 36, 36a metal pillar 38, 38a Annular metal layer 60 Transmission Filter 62 Receiving Filter

Claims

1. A first substrate having at least a portion of a first surface which is a piezoelectric layer; an acoustic wave element provided on the first surface of the piezoelectric layer; a second substrate provided with a gap between the acoustic wave element and the second substrate; a first metal layer provided on the first surface and electrically connected to the acoustic wave element; a second metal layer provided on a second surface of the second substrate facing the first substrate; a third metal layer connecting the first metal layer and the second metal layer, being thicker than the first metal layer and the second metal layer, and containing copper or silver as a main component; a first conductive layer covering a side surface of the third metal layer and a third surface of the first metal layer on the second substrate side in a region surrounding a region where the third metal layer is bonded to the first metal layer, the first conductive layer being thinner than the third metal layer and containing a component other than copper, silver, and tin as a main component; 1. An acoustic wave device comprising:

2. The acoustic wave device according to claim 1 , wherein the first conductive layer covering the third surface is thicker than the first conductive layer covering a side surface of the third metal layer.

3. The acoustic wave device according to claim 1 , wherein the first conductive layer further covers a surface of the third metal layer facing the second substrate and is directly bonded to the second metal layer.

4. The acoustic wave device according to claim 3 , wherein the first conductive layer comprises a second conductive layer that is directly bonded to the second metal layer, and a third conductive layer that is provided between the second conductive layer and the third metal layer.

5. The acoustic wave device according to claim 4 , wherein a region of the second metal layer that is in contact with the second conductive layer has the same main component as a main component of the second conductive layer.

6. The acoustic wave device according to claim 4 , wherein the second conductive layer is mainly composed of gold or aluminum.

7. The acoustic wave device according to claim 4 , wherein the third conductive layer is mainly composed of at least one element selected from the group consisting of titanium, chromium, tantalum, nickel, tungsten, and ruthenium, or a nitride of the at least one element.

8. The acoustic wave device according to claim 1 , further comprising a metal pillar including the third metal layer.

9. The acoustic wave device according to claim 1 , wherein the first substrate comprises a support substrate and the piezoelectric layer provided on the support substrate.

10. The acoustic wave device according to claim 1 , further comprising an element provided on a surface of the second substrate facing the first substrate.

11. at least a portion of the second surface of the second substrate is another piezoelectric layer; The acoustic wave device comprises: Another acoustic wave element provided on the other piezoelectric layer; a fourth metal layer connecting the second metal layer and the third metal layer, being thicker than the first metal layer and the second metal layer, and containing copper or silver as a main component; a fourth conductive layer covering a side surface of the fourth metal layer and a fourth surface of the second metal layer on the first substrate side in a region surrounding a region where the fourth metal layer is bonded to the second metal layer, the fourth conductive layer being thinner than the fourth metal layer and containing a component other than copper, silver, and tin as a main component; The acoustic wave device according to claim 1 , further comprising:

12. A filter comprising the acoustic wave device according to claim 10 or 11.

13. A multiplexer including a filter according to claim 12.

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