Acoustic wave device

Abstract

To provide an acoustic wave device where a bonding strength of a via conductor is improved.SOLUTION: An acoustic wave device 1 comprises: a substrate 10 having main surfaces 10a and 10b; a substrate 20 having a main surface 20a that is faced to the main surface 10a; a function electrode 34 arranged on the main surface 20a; a support part arranged between the main surface 10a and the main surface 20a; and a via conductor 11 arranged on the substrate 10 toward the main surface 10b from the main surface 10a. The support part has: a metal film 31 arranged on the main surface 10a, and contacting with the via conductor 11; and a metal film 32 arranged on the side opposite to the via conductor 11 with the metal film 31 interposed therebetween. In a plan view of the main surface 10a, a region of the metal film 31 includes a region of the via conductor 11, and an area of the metal film 31 is larger than an area of the via conductor 11. A region of the metal film 32 includes a region of the via conductor 11, and an area of the metal film 32 is larger than the area of the via conductor 11.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acoustic wave device. [Background technology]

[0002] Patent Document 1 discloses an electronic device including a piezoelectric thin film resonator, a first substrate (piezoelectric substrate) on which the piezoelectric thin film resonator is arranged, a second substrate (lid substrate) arranged so as to sandwich the piezoelectric thin film resonator between the first substrate, a thin film of a high resistivity material formed on the second substrate, and a via conductor provided on the first substrate. According to this, it is possible to input and output a signal of the piezoelectric thin film resonator from the first substrate side while suppressing the signal from being coupled to the second substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-137742 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a via conductor is formed by processing a substrate made of a piezoelectric material as a structure for inputting and outputting signals from a piezoelectric thin-film resonator (elastic wave resonator), there is a concern that the signal degradation of the elastic wave resonator may occur.

[0005] In contrast, there is a structure in which via conductors are formed in the lid substrate to input and output signals from the acoustic wave resonator. However, in this structure, in order to suppress signal degradation of the acoustic wave resonator, it is necessary to improve the bonding strength of the via conductors formed in the lid substrate.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS In view of the above, an object of the present invention is to provide an acoustic wave device in which the bonding strength of via conductors is improved. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, an elastic wave device according to one embodiment of the present invention comprises a first substrate having first and second substrates facing each other, a second substrate having a third substrate facing the first substrate, a functional electrode arranged on the third substrate, a support portion arranged between the first substrate and the third substrate so as to provide a space between the first substrate and the third substrate, and a via conductor arranged on the first substrate from the first substrate to the second substrate, wherein the support portion has a first metal film arranged on the first substrate and in contact with the via conductor, and a second metal film arranged on the opposite side of the first metal film from the via conductor and in contact with the first metal film, wherein in a plan view of the first substrate, a region of the first metal film includes a region of the via conductor and an area of ​​the first metal film is larger than an area of ​​the via conductor, and a region of the second metal film includes a region of the via conductor and an area of ​​the second metal film is larger than an area of ​​the via conductor. Effect of the Invention

[0008] According to the present invention, it is possible to provide an acoustic wave device having improved bonding strength of via conductors. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of an elastic wave device according to an embodiment. [Figure 2A] 1 is a first plan view of an elastic wave device according to an embodiment. [Figure 2B] 4 is a second plan view of the elastic wave device according to the embodiment. FIG. [Figure 2C] 11 is a third plan view of the elastic wave device according to the embodiment. FIG. [Figure 3A] 1A and 1B are a plan view and a cross-sectional view illustrating a first example of an elastic wave resonator included in an elastic wave device according to an embodiment of the present invention. [Figure 3B] 10 is a cross-sectional view illustrating a schematic diagram of a second example of an elastic wave resonator included in an elastic wave device according to an embodiment. FIG. [Figure 3C] 11 is a cross-sectional view illustrating a schematic diagram of a third example of an elastic wave resonator included in an elastic wave device according to an embodiment. FIG. [Figure 4]2 is an enlarged cross-sectional view of a via conductor and its surroundings in an elastic wave device according to an embodiment. FIG. [Diagram 5] 1 is a cross-sectional view illustrating an example of a laminated structure of metal films constituting an elastic wave device according to an embodiment. [Figure 6] 4 is a cross-sectional view illustrating an interface between a via conductor and a first substrate in an elastic wave device according to an embodiment. [Figure 7] 10 is a cross-sectional view illustrating an interface between a via conductor and a first substrate in an elastic wave device according to a comparative example. [Figure 8] 4A to 4C are cross-sectional views of a via conductor opening portion of an elastic wave device according to an embodiment. [Figure 9] 11 is a cross-sectional view of an elastic wave device according to a modified example of an embodiment. [Figure 10] 11 is a first plan view of an elastic wave device according to a modified example of an embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangements and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present invention. Among the components in the following embodiments, components that are not described in the independent claims are described as optional components. Also, the size or size ratio of the components shown in the drawings is not necessarily strict.

[0011] In addition, each figure is a schematic diagram in which emphasis, omission, or adjustment of the ratio is appropriately performed in order to illustrate the present invention, and is not necessarily a strict illustration, and may differ from the actual shape, positional relationship, and ratio. In each figure, the same reference numerals are given to substantially the same configurations, and duplicated explanations may be omitted or simplified.

[0012] In the circuit configuration of the present disclosure, "connected" includes not only direct connection by electrodes and / or wiring conductors, but also electrical connection via matching elements such as inductors and capacitors, and switch circuits. "Connected between A and B" means connected to both A and B between A and B.

[0013] In addition, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of an element, such as "rectangle," and numerical ranges do not only indicate the strict meaning, but also include a substantially equivalent range, for example, an error of about a few percent.

[0014] (Embodiment) [1 Structure of Elastic Wave Device 1] FIG. 1 is a cross-sectional view of an elastic wave device 1 according to an embodiment. FIG. 2A is a first plan view of an elastic wave device 1 according to an embodiment. FIG. 2B is a second plan view of an elastic wave device 1 according to an embodiment. FIG. 2C is a third plan view of an elastic wave device 1 according to an embodiment. FIG. 2A is a plan view (see-through) of main surface 20a of substrate 20 from the positive side of the z axis, FIG. 2B is a plan view (see-through) of main surface 10a of substrate 10 from the positive side of the z axis, and FIG. 2C is a plan view of main surface 10b of substrate 10 from the positive side of the z axis. FIG. 1 is a cross-sectional view taken along line II in FIGS. 2A, 2B, and 2C.

[0015] As shown in FIGS. 1 to 2C, acoustic wave device 1 includes substrates 10 and 20, metal films 31, 32, and 33, a functional electrode 34, a via conductor 11, insulating films 13 and 23, a planar electrode 12, and a bump electrode 40.

[0016] The substrate 10 is an example of a first substrate, and has main surfaces 10a (first main surface) and 10b (second main surface) opposed to each other. In the present embodiment, the substrate 10 contains silicon.

[0017] The substrate 20 is an example of a second substrate, and has principal surfaces 20a (third principal surface) and 20b that face each other. The principal surface 10a and the principal surface 20a face each other. In this embodiment, the substrate 20 has piezoelectricity.

[0018] 1, the via conductor 11 is an electrode disposed on the substrate 10 from the principal surface 10a to the principal surface 10b. In the present embodiment, the via conductor 11 is a through electrode filled in a cavity penetrating the substrate 10 between the principal surface 10a and the principal surface 10b. The via conductor 11 is made of, for example, a metal member mainly composed of Cu (copper).

[0019] In addition, via conductor 11 does not have to be a single via conductor extending from principal surface 10a to principal surface 10b, and may have a configuration in which multiple via conductors are connected via a planar electrode formed in substrate 10.

[0020] 1 and 2B, the metal film 31 is an example of a first metal film, and is a planar electrode disposed on the main surface 10a and in contact with the via conductors 11. The metal film 31 is, for example, a laminate of a plurality of metal layers. A specific example of the laminate structure of the metal film 31 will be described with reference to FIG.

[0021] 1 and 2B, the metal film 32 is an example of a second metal film, and is a planar electrode disposed on the opposite side of the metal film 31 from the via conductor 11 and in contact with the metal film 31. The metal film 32 is, for example, a laminate of a plurality of metal layers. A specific example of the laminate structure of the metal film 32 will be described with reference to FIG.

[0022] The metal film 33 is an example of a third metal film, and is a planar electrode disposed on the main surface 20a, connected to the functional electrode 34, and in contact with the metal film 32, as shown in Fig. 1 and Fig. 2A. The metal film 33 is, for example, a laminate of a plurality of metal layers. A specific example of the laminate structure of the metal film 33 will be described with reference to Fig. 5.

[0023] The functional electrode 34 is disposed on the main surface 20a, and performs electromechanical transduction with the substrate 20. Examples of the structures of the functional electrode 34 and the metal film 33 will be described with reference to Figs. 3A to 3C.

[0024] As shown in FIG. 1, metal films 31, 32, and 33 form a support portion, and are laminated in this order between main surface 10a and main surface 20a, so that a space is provided between main surface 10a and main surface 20a.

[0025] The insulating film 13 is disposed on the main surface 10b and is, for example, a silicon oxide film. The insulating film 23 is disposed on the main surface 20a and is, for example, a silicon oxide film. At least one of the insulating films 13 and 23 may be omitted.

[0026] [2 Structure of the substrate 20, the functional electrode 34 and the metal film 33] Next, exemplary structures of substrate 20, functional electrode 34, and metal film 33 will be described. Fig. 3A is a plan view and a cross-sectional view that typically show a first example of elastic wave resonator 60 constituting elastic wave device 1 according to an embodiment. This figure illustrates the basic structure of elastic wave resonator 60 constituting elastic wave device 1. Note that elastic wave resonator 60 shown in Fig. 3A is intended to illustrate a typical structure of an elastic wave resonator constituting elastic wave device 1, and the number and length of electrode fingers constituting the electrodes are not limited thereto.

[0027] The acoustic wave resonator 60 is composed of a substrate 20 and comb-shaped electrodes 60a and 60b.

[0028] As shown in FIG. 3A(a), a pair of comb-shaped electrodes 60a and 60b facing each other are formed on the substrate 20. The comb-shaped electrode 60a is composed of a plurality of electrode fingers 61a (first electrode fingers) parallel to each other and a busbar electrode 62a (first busbar electrode) connecting one ends of the plurality of electrode fingers 61a. The comb-shaped electrode 60b is composed of a plurality of electrode fingers 61b (second electrode fingers) parallel to each other and a busbar electrode 62b (second busbar electrode) connecting one ends of the plurality of electrode fingers 61b. The plurality of electrode fingers 61a and 61b are formed along a direction perpendicular to the acoustic wave propagation direction (X-axis direction). The busbar electrode 62a and the busbar electrode 62b are arranged facing each other with the electrode fingers 61a and 61b in between. The comb-shaped electrodes 60a and 60b form an IDT (InterDigital Transducer) electrode 54.

[0029] When acoustic wave device 1 according to the present embodiment performs electromechanical transduction using surface acoustic waves, functional electrode 34 shown in Fig. 1 and 2A includes a plurality of electrode fingers 61a and a plurality of electrode fingers 61b. Moreover, metal film 33 shown in Fig. 1 and 2A includes bus bar electrodes 62a and 62b.

[0030] The acoustic wave resonator 60 may have reflectors on both ends of the IDT electrode 54 in the acoustic wave propagation direction (X-axis direction).

[0031] As shown in FIG. 3B, the IDT electrode 54 has a laminated structure of an adhesive layer 540 and a main electrode layer 542, for example.

[0032] The adhesion layer 540 is a layer for improving adhesion between the substrate 20 and the main electrode layer 542, and is made of, for example, Ti. The main electrode layer 542 is made of, for example, Al containing 1% Cu. The protective layer 55 is formed so as to cover the comb-shaped electrodes 60a and 60b. The protective layer 55 is a layer intended to protect the main electrode layer 542 from the external environment, adjust the frequency-temperature characteristics, and increase moisture resistance, and is, for example, a dielectric film whose main component is silicon dioxide.

[0033] The materials constituting the adhesion layer 540, the main electrode layer 542, and the protective layer 55 are not limited to the above-mentioned materials. Furthermore, the IDT electrode 54 does not have to have the above-mentioned laminated structure. The IDT electrode 54 may be made of a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or may be made of a laminate of multiple layers made of the above-mentioned metals or alloys. Furthermore, the protective layer 55 does not have to be formed.

[0034] Next, the layered structure of the substrate 20 will be described.

[0035] As shown in (c) of Figure 3A, the substrate 20 has a high acoustic speed support substrate 51, a low acoustic speed film 52, and a piezoelectric film 53, and has a structure in which the high acoustic speed support substrate 51, the low acoustic speed film 52, and the piezoelectric film 53 are laminated in this order.

[0036] The piezoelectric film 53 is made of, for example, θ°Y-cut X-propagation LiTaO3 piezoelectric single crystal or piezoelectric ceramics (lithium tantalate single crystal or ceramics cut on a plane whose normal is an axis rotated θ° from the Y axis around the X axis, and whose surface acoustic wave propagates in the X axis direction). Note that the material and cut angle θ of the piezoelectric single crystal used as the piezoelectric film 53 are appropriately selected depending on the required specifications of each filter.

[0037] The high acoustic velocity support substrate 51 is a substrate that supports the low acoustic velocity film 52, the piezoelectric film 53, and the IDT electrode 54. The high acoustic velocity support substrate 51 is a substrate in which the acoustic velocity of the bulk waves in the high acoustic velocity support substrate 51 is faster than that of the surface waves and boundary waves propagating through the piezoelectric film 53, and functions to confine the surface acoustic waves to the portion where the piezoelectric film 53 and the low acoustic velocity film 52 are laminated, and to prevent the surface acoustic waves from leaking below the high acoustic velocity support substrate 51. Examples of materials that can be used for the high acoustic velocity support substrate 51 include piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon, dielectric materials such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond, semiconductors such as silicon, and materials mainly composed of the above materials. The spinel includes an aluminum compound containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0038] The low acoustic velocity film 52 is a film in which the acoustic velocity of the bulk waves in the low acoustic velocity film 52 is slower than that of the bulk waves propagating through the piezoelectric film 53, and is disposed between the piezoelectric film 53 and the high acoustic velocity support substrate 51. This structure and the property of the acoustic wave concentrating energy in a medium with an essentially low acoustic velocity suppress leakage of the surface acoustic wave energy outside the IDT electrode. The low acoustic velocity film 52 can be made of a dielectric material such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a compound in which fluorine, carbon, or boron is added to silicon oxide, or a material mainly composed of the above materials.

[0039] The laminated structure of substrate 20 makes it possible to significantly increase the Q value at the resonant frequency and anti-resonant frequency, compared to a conventional structure using a single layer of piezoelectric substrate. In other words, an elastic wave resonator with a high Q value can be configured, and a filter with low insertion loss can be configured using the elastic wave resonator.

[0040] The high acoustic velocity support substrate 51 may have a structure in which a support substrate and a high acoustic velocity film in which the acoustic velocity of the propagating bulk wave is faster than that of the elastic wave such as the surface wave and boundary wave propagating through the piezoelectric film 53 are laminated. In this case, the material of the high acoustic velocity film can be the same as the material of the high acoustic velocity support substrate 51. The material of the support substrate can be, for example, a piezoelectric material such as aluminum nitride, lithium tantalate, lithium niobate, or quartz; a ceramic material such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, or forsterite; a dielectric material such as diamond or glass; a semiconductor material such as silicon or gallium nitride; or a resin; or a material mainly composed of the above-mentioned material.

[0041] In this specification, the term "major component of a material" refers to a component that accounts for more than 50% by weight of the material. The major component may be in any of the following states: single crystal, polycrystalline, or amorphous, or a mixture of these.

[0042] Fig. 3B is a cross-sectional view illustrating a schematic diagram of a second example of an acoustic wave resonator 60 constituting an acoustic wave device 1 according to an embodiment. In the acoustic wave resonator 60 illustrated in Fig. 3A, the IDT electrode 54 is formed on the substrate 20 having the piezoelectric film 53. However, the substrate on which the IDT electrode 54 is formed may be a piezoelectric single crystal substrate 57 consisting of a single piezoelectric layer, as illustrated in Fig. 3B.

[0043] The piezoelectric single crystal substrate 57 is made of, for example, a piezoelectric single crystal of LiNbO3. The elastic wave resonator according to this example is made of the piezoelectric single crystal substrate 57 made of LiNbO3, an IDT electrode 54, and a protective layer 58 formed on the piezoelectric single crystal substrate 57 and the IDT electrode 54.

[0044] The laminate structure, material, cut angle, and thickness of the piezoelectric film 53 and piezoelectric single crystal substrate 57 described above may be changed as appropriate depending on the required transmission characteristics of the acoustic wave device 1. Even an acoustic wave resonator using a LiTaO3 piezoelectric substrate having a cut angle other than the above-mentioned cut angle can achieve the same effect as acoustic wave resonator 60 using the piezoelectric film 53 described above.

[0045] The piezoelectric substrate on which the IDT electrode 54 is formed may have a structure in which a support substrate, an energy trapping layer, and a piezoelectric film are laminated in this order. The IDT electrode 54 is formed on the piezoelectric film. For example, a LiTaO3 piezoelectric single crystal or a piezoelectric ceramic is used for the piezoelectric film. The support substrate is a substrate that supports the piezoelectric film, the energy trapping layer, and the IDT electrode 54.

[0046] The energy trapping layer is composed of one or more layers, and the speed of the bulk acoustic wave propagating through at least one of the layers is greater than the speed of the acoustic wave propagating near the piezoelectric film. For example, the energy trapping layer may have a laminated structure of a low acoustic velocity layer and a high acoustic velocity layer. The low acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the low acoustic velocity layer is slower than the acoustic velocity of the acoustic wave propagating through the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the high acoustic velocity layer is faster than the acoustic velocity of the acoustic wave propagating through the piezoelectric film. The support substrate may be the high acoustic velocity layer.

[0047] The energy trapping layer may be an acoustic impedance layer having a configuration in which low acoustic impedance layers having a relatively low acoustic impedance and high acoustic impedance layers having a relatively high acoustic impedance are alternately laminated.

[0048] 3C is a cross-sectional view that typically illustrates a third example of an elastic wave resonator 60 constituting an elastic wave device 1 according to an embodiment. In FIG. 3C, a bulk elastic wave resonator is illustrated as the elastic wave resonator of the elastic wave device 1. As illustrated in the figure, the bulk elastic wave resonator has, for example, a support substrate 65, a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68, in which the support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are laminated in this order.

[0049] The support substrate 65 is a substrate for supporting the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68, and is, for example, a silicon substrate. The support substrate 65 has a cavity in an area in contact with the lower electrode 66. This allows the piezoelectric layer 67 to vibrate freely.

[0050] The lower electrode 66 is an example of a first planar electrode, and is formed on one surface of the support substrate 65. The upper electrode 68 is an example of a second planar electrode, and is formed on one surface of the support substrate 65. The lower electrode 66 and the upper electrode 68 are made of a material, for example, Al containing 1% Cu.

[0051] The piezoelectric layer 67 is an example of a piezoelectric thin film, and is formed between the lower electrode 66 and the upper electrode 68. The piezoelectric layer 67 is mainly composed of at least one of ZnO (zinc oxide), AlN (aluminum nitride), PZT (lead zirconate titanate), KN (potassium niobate), LN (lithium niobate), LT (lithium tantalate), quartz crystal, and LiBO (lithium borate).

[0052] A bulk acoustic wave resonator having the above-described laminated structure generates resonance by inducing bulk acoustic waves in the piezoelectric layer 67 by applying electrical energy between the lower electrode 66 and the upper electrode 68. The bulk acoustic waves generated by this bulk acoustic wave resonator propagate between the lower electrode 66 and the upper electrode 68 in a direction perpendicular to the film surface of the piezoelectric layer 67. In other words, the bulk acoustic wave resonator is a resonator that utilizes bulk acoustic waves.

[0053] When acoustic wave device 1 according to the present embodiment performs electromechanical transduction using bulk acoustic waves, functional electrode 34 shown in Fig. 1 and Fig. 2A includes lower electrode 66, piezoelectric layer 67, and upper electrode 68. Substrate 20 shown in Fig. 1 and Fig. 2A may not have piezoelectricity and may include support substrate 65.

[0054] [3. Bonding structure of substrate 10, via conductor 11, and metal films 31 to 33] Next, the joining structure of the substrate 10, the via conductor 11, and the metal films 31 to 33 will be described. Fig. 4 is an enlarged cross-sectional view of the via conductor 11 and its periphery in the elastic wave device 1 according to the embodiment. This figure is a microscope image of region IV in Fig. 1. As shown in the figure, the via conductor 11 is formed inside the substrate 10, a planar electrode 12 is joined to the upper opening (positive z-axis direction) of the via conductor 11, and a metal film 31 is joined to the lower opening (negative z-axis direction) of the via conductor 11. In addition, a metal film 32, a metal film 33, and the substrate 20 are joined in this order to the negative z-axis side of the metal film 31.

[0055] Here, as shown in Fig. 2B, in a plan view of the main surface 10a, the region of the metal film 31 (at the upper right of Fig. 2B) includes the region of the via conductor 11 (at the upper right of Fig. 2B), and the area of ​​the metal film 31 (at the upper right of Fig. 2B) is larger than the area of ​​the via conductor 11 (at the upper right of Fig. 2B). In addition, in a plan view of the main surface 10a, the region of the metal film 32 (at the upper right of Fig. 2B) includes the region of the via conductor 11 (at the upper right of Fig. 2B), and the area of ​​the metal film 32 (at the upper right of Fig. 2B) is larger than the area of ​​the via conductor 11 (at the upper right of Fig. 2B).

[0056] In other words, as shown in FIG. 4, in a cross section (cross section II in FIGS. 2A to 2C) that is perpendicular to the main surface 10a (z-axis direction) and passes through the via conductor 11, the length L 31 is the length D of the via conductor 11 11 (diameter) and the length L of the metal film 32 32 is the length D of the via conductor 11 11 (diameter) is larger than

[0057] When the regions of the metal films 31 and 32 are included in the region of the via conductor 11 in a plan view of the principal surface 10a, all of the compressive stresses of the metal films 31 and 32 are applied to the via conductor 11, which may cause the via conductor 11 to deform or peel off from the substrate 10. In contrast, according to the above-described configuration of the elastic wave device 1 according to the present embodiment, when viewed in a plan view of the principal surface 10a, the region of the via conductor 11 is included in the regions of the metal films 31 and 32, the area of ​​the metal film 31 is larger than the area of ​​the via conductor 11, and the area of ​​the metal film 32 is larger than the area of ​​the via conductor 11. As a result, the substrate 10 adjacent to the via conductor 11 in the x-axis direction is joined to the metal film 31, and the substrate 10 joined to the metal film 31 can absorb the compressive stresses of the metal films 31 and 32, thereby suppressing deformation and peeling of the via conductor 11. In other words, fixation of the via conductor 11 can be promoted. Furthermore, since metal film 32 is joined to metal film 33, and metal film 33 is joined to substrate 20, the compressive stress generated in metal films 31 and 32 can be dispersed to substrate 20 as well. This makes it possible to provide an acoustic wave device 1 with improved bonding strength of via conductors 11.

[0058] In this specification, region A including region B is defined as the entirety of region B being disposed within region A.

[0059] Next, a description will be given of the layered structure of the metal films 31 to 33. Fig. 5 is a cross-sectional view showing an example of the layered structure of the metal films 31 to 33 constituting the elastic wave device 1 according to an embodiment. The drawing is a cross-sectional view that shows a schematic enlargement of a region V in Fig. 4.

[0060] As shown in FIG. 5, the metal film 31 has an intermediate layer 316, an intermediate layer 315, a main electrode layer 314, an intermediate layer 313, an intermediate layer 312, and a bonding layer 311 from the main surface 10a side.

[0061] Intermediate layer 313 (first intermediate layer) and intermediate layer 316 are, for example, metal layers containing Ti (titanium) as a main component, and function as diffusion prevention layers.

[0062] Intermediate layers 312 and 315 are metal layers containing, for example, platinum (Pt) as a main component, and function, together with intermediate layers 313 and 316, as diffusion prevention layers.

[0063] The main electrode layer 314 is an example of a first main electrode layer, and is a metal layer containing, for example, aluminum (Al) and copper (Cu) as main components, and functions as a main medium in the metal film 31 for transmitting high-frequency signals.

[0064] The bonding layer 311 is an example of a first bonding layer, and is, for example, a metal layer containing Au (gold) as a main component, and has a function of forming a good electrical and mechanical bond with the metal film 32.

[0065] In the metal film 31 according to the present embodiment, the intermediate layers 312 and 315 may be omitted. Furthermore, the metal film 31 may be composed of the main electrode layer 314 alone.

[0066] As shown in FIG. 5, the metal film 32 has a bonding layer 321, an intermediate layer 322, an intermediate layer 323, a main electrode layer 324, and an intermediate layer 325 from the main surface 10a side.

[0067] The bonding layer 321 is an example of a second bonding layer, and is, for example, a metal layer containing Au (gold) as a main component, and has a function of forming a good electrical and mechanical bond with the metal film 31.

[0068] The intermediate layer 322 is a metal layer containing, for example, platinum (Pt) as a main component, and functions together with the intermediate layer 323 as a diffusion prevention layer.

[0069] Intermediate layer 323 (second intermediate layer) and intermediate layer 325 are, for example, metal layers containing Ti (titanium) as a main component, and function as diffusion prevention layers.

[0070] The main electrode layer 324 is an example of a second main electrode layer, and is a metal layer containing, for example, aluminum (Al) and copper (Cu) as main components, and functions as a main medium in the metal film 32 for transmitting high-frequency signals.

[0071] It should be noted that the metal film 32 according to this embodiment does not necessarily have to include the intermediate layer 322. Furthermore, the metal film 32 may be composed of only the main electrode layer 324.

[0072] As shown in FIG. 5, the metal film 33 has an intermediate layer 331, a main electrode layer 332, and an intermediate layer 333 from the main surface 10a side.

[0073] The intermediate layers 331 and 333 are, for example, metal layers containing Ti (titanium) as a main component, and function as diffusion prevention layers.

[0074] The main electrode layer 332 is a metal layer containing, for example, aluminum (Al) and copper (Cu) as main components, and functions as a main medium in the metal film 33 for transmitting high-frequency signals.

[0075] In the metal film 33 according to the present embodiment, the intermediate layers 331 and 333 may be omitted, and the metal film 33 may be composed of the main electrode layer 332 only.

[0076] 5 corresponds to, for example, the main electrode layer 542 in FIG. 3A, and the intermediate layer 333 in FIG. 5 corresponds to, for example, the adhesion layer 540 in FIG. 3A.

[0077] Also, as shown in FIG. 2B, in a planar view of main surface 10a, the region of metal film 31 (in the upper right corner of FIG. 2B) includes the region of metal film 32 (in the upper right corner of FIG. 2B), and the area of ​​metal film 31 (in the upper right corner of FIG. 2B) is larger than the area of ​​metal film 32 (in the upper right corner of FIG. 2B).

[0078] In other words, as shown in FIG. 4, in a cross section (cross section II in FIGS. 2A to 2C) that is perpendicular to the main surface 10a (z-axis direction) and passes through the via conductor 11, the length L 31 is the length L of the metal film 32 32 Greater than.

[0079] According to this, the end shape of metal film 31 is not deformed by bonding of metal film 32, so that the bonding between substrate 10 and metal film 31 can promote the reduction of the compressive stress applied to via conductor 11.

[0080] As shown in FIGS. 2A and 2B, the region of metal film 33 includes the region of metal film 32 in plan view of main surface 20a, and the area of ​​metal film 33 is larger than the area of ​​metal film 32.

[0081] In other words, as shown in FIG. 4, in a cross section (cross section II in FIGS. 2A to 2C) that is perpendicular to main surface 20a (z-axis direction) and passes through via conductor 11, length L 33 is the length L of the metal film 32 32 Greater than.

[0082] In this way, the metal film 32 does not limit the arrangement area of ​​the functional electrodes 34 and the metal film 33 on the main surface 20a, and the arrangement layout of the functional electrodes 34 and the metal film 33 can be prioritized.

[0083] Next, a bonding state between via conductor 11 and substrate 10 will be described. Fig. 6 is a cross-sectional view showing an interface between via conductor 11 and substrate 10 of elastic wave device 1 according to an embodiment. This figure is a cross-sectional view that shows a schematic enlargement of region VI in Fig. 4.

[0084] 6, the acoustic wave device 1 has a metal layer 14 disposed between the substrate 10 and the via conductor 11. The metal layer 14 is mainly composed of Ti, for example. The metal layer 14 has a linear expansion coefficient between the linear expansion coefficient of Cu, which is the main component of the via conductor 11, and the linear expansion coefficient of Si, which constitutes the substrate 10.

[0085] This allows the metal layer 14 to function as a buffer material that prevents the via conductors 11 from peeling off from the substrate 10 due to stress applied to the via conductors 11 caused by thermal history. The metal layer 14 also functions as a diffusion barrier film for Cu and Si.

[0086] Furthermore, due to the process of forming a cylindrical cavity in substrate 10 made of Si for filling with via conductor 11, a shell-shaped uneven structure called a scallop is generated on the inner wall of the cylindrical cavity in substrate 10. Fig. 7 is a cross-sectional view showing the interface between via conductor 11 and substrate 10 in an elastic wave device according to a comparative example. The elastic wave device according to the comparative example differs from elastic wave device 1 according to the present embodiment only in the shape of the interface between via conductor 11 and substrate 10.

[0087] 7, the interface between via conductor 11 and substrate 10 has a scalloped uneven structure with sharp tips. This increases electrical resistance at the tips of the uneven structure, making them more susceptible to heat generation and reducing the bonding strength of via conductor 11. Furthermore, the uneven structure makes it easier for voids to form at the interface between via conductor 11 and substrate 10, reducing the bonding strength of via conductor 11.

[0088] In contrast, in elastic wave device 1 according to the present embodiment, the tips of the convex portions of the scalloped concave-convex structure are flattened as shown in Fig. 6. This reduces the electrical resistance at the tips of the concave-convex structure to suppress heat generation, and also suppresses the generation of voids at the interface between via conductor 11 and substrate 10, thereby improving the bonding strength of via conductor 11.

[0089] Next, a description will be given of the shape of via conductor 11. Fig. 8 is a cross-sectional view of the vicinity of the opening of via conductor 11 in elastic wave device 1 according to this embodiment. This figure is an enlarged microscope image of region VIII in Fig. 4.

[0090] 1, an elastic wave device 1 according to this embodiment includes an insulating film 13 disposed on a principal surface 10b. The insulating film 13 is, for example, a silicon oxide film, and has a function of suppressing leakage of high-frequency signals between adjacent planar electrodes 12 on the principal surface 10b.

[0091] Here, as shown in FIGS. 4 and 8, in a cut surface (cut surface II in FIGS. 2A to 2C) perpendicular to the main surface 10b (z-axis direction) and passing through the central axis of the via conductor 11, the length D of both ends of the via conductor 11 that are in contact with the insulating film 13 and face each other in a direction parallel to the main surface 10b is 13 is the length D of both ends of the via conductor 11 that are in contact with the substrate 10 and face each other in a direction parallel to the main surface 10b. 11 Less than.

[0092] According to this, the ends of the via conductors 11 near the main surface 10b are covered with the insulating film 13, so that the via conductors 11 can be prevented from peeling off from the substrate 10 at the openings due to thermal history.

[0093] [4. Structure of Elastic Wave Device 1A According to Modification] FIG. 9 is a cross-sectional view of an elastic wave device 1A according to a modified embodiment of the present invention. FIG. 10 is a first plan view of an elastic wave device 1A according to a modified embodiment of the present invention. FIG. 10 is a plan view (see-through) of main surface 20a of substrate 20 from the positive side of the z axis. Note that in elastic wave device 1A, the plan view (see-through) of main surface 10a of substrate 10 from the positive side of the z axis is the same as the second plan view of FIG. 2B, and the plan view of main surface 10b of substrate 10 from the positive side of the z axis is the same as the third plan view of FIG. 2C. FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 10.

[0094] 9 and 10 , elastic wave device 1A includes substrates 10 and 20, metal films 31, 32, and 33, a functional electrode 34, via conductor 11, insulating films 13 and 23, a planar electrode 12, and a bump electrode 40. Elastic wave device 1A of this modification differs from elastic wave device 1 of the embodiment in the relative positions of via conductor 11 and metal films 31, 32, and 33. Hereinafter, a description of the same configuration as elastic wave device 1A of the embodiment will be omitted and different configurations will be mainly described.

[0095] 9, the metal film 31 is an example of a first metal film, and is a planar electrode disposed on the main surface 10a and in contact with the via conductors 11. The metal film 31 is, for example, a laminate of a plurality of metal layers.

[0096] The metal film 32 is an example of a second metal film, and is a planar electrode in contact with the metal film 31, as shown in Fig. 9. The metal film 32 is, for example, a laminate of a plurality of metal layers.

[0097] 9 and 10, the metal film 33 is an example of a third metal film, and is a planar electrode disposed on the main surface 20a, connected to the functional electrode 34, and in contact with the metal film 32. The metal film 33 is, for example, a laminate of multiple metal layers.

[0098] The functional electrode 34 is disposed on the main surface 20 a and performs electromechanical transduction with the substrate 20 .

[0099] As shown in FIG. 9, metal films 31, 32, and 33 form a support portion, and are laminated in this order between main surface 10a and main surface 20a, so that a space is provided between main surface 10a and main surface 20a.

[0100] In FIG. 9, of the two via conductors 11, the right-hand via conductor 11 does not overlap with the functional electrode 34 when the main surfaces 10a and 20a are viewed in plan.

[0101] [5 Effects, etc.] As described above, the elastic wave device 1 in accordance with the present embodiment includes the substrate 10 having principal surfaces 10a and 10b opposing each other, the substrate 20 having the principal surface 20a facing the principal surface 10a, the functional electrode 34 arranged on the principal surface 20a, the supporting portion arranged between the principal surfaces 10a and 20a so as to provide a space between the principal surfaces 10a and 20a, and the via conductor 11 arranged on the substrate 10 from the principal surface 10a to the principal surface 10b. The support portion has a metal film 31 arranged on the main surface 10a and in contact with the via conductor 11, and a metal film 32 arranged on the opposite side of the metal film 31 from the via conductor 11 and in contact with the metal film 31, and in a planar view of the main surface 10a, the region of the metal film 31 includes the region of the via conductor 11 and the area of ​​the metal film 31 is larger than the area of ​​the via conductor 11, the region of the metal film 32 includes the region of the via conductor 11 and the area of ​​the metal film 32 is larger than the area of ​​the via conductor 11.

[0102] According to this, the substrate 10 adjacent to the via conductor 11 in the x-axis direction is joined to the metal film 31, and the substrate 10 joined to the metal film 31 can absorb the compressive stress of the metal films 31 and 32, thereby suppressing deformation and peeling of the via conductor 11.

[0103] For example, in elastic wave device 1, when principal surface 10a is viewed in plan, the region of metal film 31 includes the region of metal film 32, and the area of ​​metal film 31 is larger than the area of ​​metal film 32.

[0104] According to this, the end shape of metal film 31 is not deformed by bonding of metal film 32, so that the bonding between substrate 10 and metal film 31 can promote the reduction of the compressive stress applied to via conductor 11.

[0105] For example, in the elastic wave device 1, the metal film 31 has, in order from the principal surface 10a side, a main electrode layer 314, an intermediate layer 313, and a bonding layer 311, and the metal film 32 has, in order from the principal surface 10a side, a bonding layer 321, an intermediate layer 323, and a main electrode layer 324.

[0106] According to this, since each of the metal films 31 and 32 is composed of a plurality of metal layers having different functions, good bonding between the metal films 31 and 32 can be achieved.

[0107] For example, in the elastic wave device 1, the support portion further has a metal film 33 arranged on the principal surface 20a, connected to the functional electrode 34, and in contact with the metal film 32, and in a planar view of the principal surface 20a, the region of the metal film 33 includes the region of the metal film 32, and the area of ​​the metal film 33 is larger than the area of ​​the metal film 32.

[0108] In this way, the metal film 32 does not limit the arrangement area of ​​the functional electrodes 34 and the metal film 33 on the main surface 20a, and the arrangement layout of the functional electrodes 34 and the metal film 33 can be prioritized.

[0109] Also, for example, in the elastic wave device 1, the substrate 20 has piezoelectricity, an IDT electrode 54 is arranged on the main surface 20a, the IDT electrode 54 has a plurality of electrode fingers 61a and a plurality of electrode fingers 61b arranged parallel to each other, a busbar electrode 62a configured to connect one ends of the plurality of electrode fingers 61a, and a busbar electrode 62b configured to connect one ends of the plurality of electrode fingers 61b and arranged opposite the busbar electrode 62a across the plurality of electrode fingers 61a and the plurality of electrode fingers 61b, and the functional electrode 34 includes the plurality of electrode fingers 61a and the plurality of electrode fingers 61b.

[0110] This makes it possible to provide a surface acoustic wave device with improved bonding strength of the via conductors 11.

[0111] For example, in the elastic wave device 1, the support portion further has a metal film 33 arranged on the principal surface 20a, connected to the functional electrode 34, and in contact with the metal film 32, the metal film 33 includes busbar electrodes 62a and 62b, and in a planar view of the principal surface 20a, the region of the metal film 33 includes the region of the metal film 32, and the area of ​​the metal film 33 is larger than the area of ​​the metal film 32.

[0112] In this way, the metal film 32 does not limit the arrangement area of ​​the functional electrodes 34 and the metal film 33 on the main surface 20a, and the arrangement layout of the functional electrodes 34 and the metal film 33 can be prioritized.

[0113] For example, in the acoustic wave device 1, the functional electrode 34 includes a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68 in this order from the principal surface 20a.

[0114] This makes it possible to provide a bulk acoustic wave device with improved bonding strength of the via conductors 11.

[0115] Furthermore, for example, in the acoustic wave device 1, the substrate 10 includes silicon.

[0116] This improves the processing accuracy of the substrate 10.

[0117] For example, the elastic wave device 1 further includes a metal layer 14 arranged between the substrate 10 and the via conductor 11, the via conductor 11 containing Cu, and the metal layer 14 having a linear expansion coefficient between the linear expansion coefficient of copper and the linear expansion coefficient of Si.

[0118] This allows the metal layer 14 to function as a buffer material that prevents the via conductors 11 from peeling off from the substrate 10 due to stress applied to the via conductors 11 caused by thermal history. The metal layer 14 also functions as a diffusion barrier film for Cu and Si.

[0119] For example, the elastic wave device 1 further includes an insulating film 13 disposed on the principal surface 10b. In a fifth cut plane perpendicular to the principal surface 10b and passing through the central axis of the via conductor 11, the length D of both ends of the via conductor 11 that are in contact with the insulating film 13 and face each other in a direction parallel to the principal surface 10b is 13 is the length D of both ends of the via conductor 11 that are in contact with the substrate 10 and face each other in a direction parallel to the main surface 10b. 11 Less than.

[0120] According to this, the ends of the via conductors 11 near the main surface 10b are covered with the insulating film 13, so that the via conductors 11 can be prevented from peeling off from the substrate 10 at the openings of the main surface 10b due to thermal history.

[0121] (Other embodiments) Although the elastic wave device according to the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments. The present invention also includes modifications that can be made by those skilled in the art without departing from the spirit of the present invention, and various devices incorporating the elastic wave device according to the present invention.

[0122] The characteristics of the elastic wave device described based on the above embodiment will be described below.

[0123] <1> A first substrate having a first main surface and a second main surface opposed to each other; a second substrate having a third main surface facing the first main surface; a functional electrode disposed on the third principal surface; a support portion disposed between the first main surface and the third main surface and configured to provide a space between the first main surface and the third main surface; a via conductor disposed on the first substrate from the first main surface to the second main surface, The support portion is a first metal film disposed on the first main surface and in contact with the via conductor; a second metal film disposed on an opposite side of the first metal film from the via conductor and in contact with the first metal film; In a plan view of the first main surface, a region of the first metal film includes a region of the via conductor, and an area of ​​the first metal film is larger than an area of ​​the via conductor; An acoustic wave device, wherein a region of the second metal film includes a region of the via conductor, and an area of ​​the second metal film is larger than an area of ​​the via conductor.

[0124] <2> In a plan view of the first main surface, a region of the first metal film includes a region of the second metal film, and an area of ​​the first metal film is larger than an area of ​​the second metal film; <1> The acoustic wave device according to claim 1 .

[0125] <3> The first metal film is a first main electrode layer, a first diffusion prevention layer, and a first bonding layer in this order from the first main surface side; The second metal film is The semiconductor device has, in order from the first main surface side, a second bonding layer, a second diffusion prevention layer, and a second main electrode layer. <1> or <2> The acoustic wave device according to claim 1 .

[0126] <4> The support portion further includes: a third metal film disposed on the third main surface, connected to the functional electrode, and in contact with the second metal film; In a plan view of the third main surface, a region of the third metal film includes a region of the second metal film, and an area of ​​the third metal film is larger than an area of ​​the second metal film; <1> ~ <3> 2. The acoustic wave device according to claim 1 ,

[0127] <5> the second substrate has piezoelectric properties; an IDT electrode is disposed on the third principal surface; The IDT electrode is a plurality of first electrode fingers and a plurality of second electrode fingers arranged parallel to each other; a first bus bar electrode configured to connect one ends of the first electrode fingers to each other; a second bus bar electrode configured to connect one ends of the second electrode fingers to each other and disposed opposite the first bus bar electrode with the first electrode fingers and the second electrode fingers interposed therebetween, the functional electrode includes the plurality of first electrode fingers and the plurality of second electrode fingers; <1> ~ <3> 2. The acoustic wave device according to claim 1 ,

[0128] <6> The support portion further includes: a third metal film disposed on the third main surface, connected to the functional electrode, and in contact with the second metal film; the third metal film includes the first bus bar electrode and the second bus bar electrode, In a plan view of the third main surface, a region of the third metal film includes a region of the second metal film, and an area of ​​the third metal film is larger than an area of ​​the second metal film; <5> The acoustic wave device according to claim 1 .

[0129] <7> the functional electrode includes, in order from the third principal surface, a first planar electrode, a piezoelectric thin film, and a second planar electrode; <1> ~ <4> 2. The acoustic wave device according to claim 1 ,

[0130] <8> The first substrate comprises silicon. <1> ~ <7> 2. The acoustic wave device according to claim 1 ,

[0131] <9> moreover, a metal layer disposed between the first substrate and the via conductor; the via conductor contains copper; The metal layer has a linear expansion coefficient between that of copper and that of silicon. <1> ~ <8> 2. The acoustic wave device according to claim 1 ,

[0132] <10> moreover, an insulating film disposed on the second main surface; In a fifth cut plane perpendicular to the second main surface and passing through a central axis of the via conductor, the length of both ends of the via conductor that are opposed in a direction parallel to the second main surface and that are in contact with the insulating film is smaller than the length of both ends of the via conductor that are opposed in a direction parallel to the second main surface and that are in contact with the first substrate. <1> ~ <9> 2. The acoustic wave device according to claim 1 , [Industrial Applicability]

[0133] INDUSTRIAL APPLICABILITY The present invention, as a small-sized acoustic wave device, can be widely used in communication devices such as mobile phones. [Explanation of symbols]

[0134] 1. 1A Elastic Wave Device 10, 20 board 10a, 10b, 20a, 20b main surface 11 Via conductor 12 Planar electrode 13, 23 Insulating film 14 Metal layer 31, 32, 33 Metal film 34 Functional Electrode 40 Bump electrode 51 High-sonic support substrate 52 Low sound velocity membrane 53 Piezoelectric film 54 IDT electrode 55, 58 protective layer 57 Piezoelectric single crystal substrate 60 Elastic Wave Resonator 60a, 60b comb-shaped electrode 61a, 61b electrode fingers 62a, 62b Busbar electrodes 65 Support substrate 66 Lower electrode 67 Piezoelectric layer 68 Upper electrode 314, 324, 332, 542 Main electrode layer 312, 313, 315, 316, 322, 323, 325, 331, 333 Middle class 311, 321 bonding layer 540 Adhesion layer

Claims

1. A first substrate having a first main surface and a second main surface opposed to each other; a second substrate having a third main surface facing the first main surface; a functional electrode disposed on the third principal surface; a support portion disposed between the first main surface and the third main surface and configured to provide a space between the first main surface and the third main surface; a via conductor disposed on the first substrate from the first main surface to the second main surface, The support portion is a first metal film disposed on the first main surface and in contact with the via conductor; a second metal film disposed on an opposite side of the first metal film from the via conductor and in contact with the first metal film; In a plan view of the first main surface, a region of the first metal film includes a region of the via conductor, and an area of ​​the first metal film is larger than an area of ​​the via conductor; a region of the second metal film includes a region of the via conductor, and an area of ​​the second metal film is larger than an area of ​​the via conductor; Elastic wave device.

2. In a plan view of the first main surface, a region of the first metal film includes a region of the second metal film, and an area of ​​the first metal film is larger than an area of ​​the second metal film; The acoustic wave device according to claim 1 .

3. The first metal film is a first main electrode layer, a first diffusion prevention layer, and a first bonding layer in this order from the first main surface side; The second metal film is a second bonding layer, a second diffusion prevention layer, and a second main electrode layer, in this order from the first main surface side; The acoustic wave device according to claim 1 .

4. The support portion further includes: a third metal film disposed on the third main surface, connected to the functional electrode, and in contact with the second metal film; In a plan view of the third main surface, a region of the third metal film includes a region of the second metal film, and an area of ​​the third metal film is larger than an area of ​​the second metal film; The acoustic wave device according to claim 1 .

5. the second substrate has piezoelectric properties; an IDT electrode is disposed on the third principal surface; The IDT electrode is a plurality of first electrode fingers and a plurality of second electrode fingers arranged parallel to each other; a first bus bar electrode configured to connect one ends of the first electrode fingers to each other; a second bus bar electrode configured to connect one ends of the second electrode fingers to each other and disposed opposite the first bus bar electrode with the first electrode fingers and the second electrode fingers interposed therebetween, the functional electrode includes the plurality of first electrode fingers and the plurality of second electrode fingers; The acoustic wave device according to claim 1 .

6. The support portion further includes: a third metal film disposed on the third main surface, connected to the functional electrode, and in contact with the second metal film; the third metal film includes the first bus bar electrode and the second bus bar electrode, In a plan view of the third main surface, a region of the third metal film includes a region of the second metal film, and an area of ​​the third metal film is larger than an area of ​​the second metal film; The acoustic wave device according to claim 5 .

7. the functional electrode includes, in order from the third principal surface, a first planar electrode, a piezoelectric thin film, and a second planar electrode; The acoustic wave device according to claim 1 .

8. The first substrate comprises silicon. The acoustic wave device according to claim 1 .

9. moreover, a metal layer disposed between the first substrate and the via conductor; the via conductor contains copper; The metal layer has a linear expansion coefficient between that of copper and that of silicon. The acoustic wave device according to claim 1 .

10. moreover, an insulating film disposed on the second main surface; In a cut surface perpendicular to the second main surface and passing through a central axis of the via conductor, the length of both ends of the via conductor that are opposed in a direction parallel to the second main surface and are in contact with the insulating film is smaller than the length of both ends of the via conductor that are opposed in a direction parallel to the second main surface and are in contact with the first substrate. The acoustic wave device according to claim 1 .

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