Elastic wave device

Abstract

An elastic wave device (1) comprises: a substrate (10) having main surfaces (10a, 10b) that are opposed to each other; a substrate (20) having a main surface (20a) that faces the main surface (10a); a functional electrode (34) disposed on the main surface (20a); a support part disposed between the main surface (10a) and the main surface (20a) and configured so that a space is provided between the main surface (10a) and the main surface (20a); and a via conductor (11) disposed in the substrate (10) from the main surface (10a) toward the main surface (10b). The support part has: a metal film (31) that is disposed on the main surface (10a) and is in contact with the via conductor (11); and a metal film (32) that is disposed on the side opposite to the via conductor (11) with the metal film (31) therebetween, and that is in contact with the metal film (31). In a plan view of the main surface (10a), a region of the metal film (31) includes a region of the metal film (32), the area of the metal film (31) is larger than the area of the metal film (32), and the hardness of the metal film (32) is greater than the hardness of the metal film (31).

Description

Elastic Wave Device

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

[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 and the first substrate, a thin film made 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 signals from the piezoelectric thin film resonator from the first substrate side while suppressing coupling of the signals to the second substrate.

[0003] Japanese Patent Application Laid-Open No. 2018-137742

[0004] When via conductors are 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 cover substrate to input and output signals from the acoustic wave resonator. However, in this structure, to suppress signal degradation of the acoustic wave resonator, it is necessary to improve the bonding strength of the support part that connects the via conductors to the electrodes of the piezoelectric substrate while ensuring a space between the piezoelectric substrate and the cover substrate.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an acoustic wave device in which the bonding strength of the support portion is improved.

[0007] In order to achieve the above object, an elastic wave device according to one aspect of the present invention comprises a first substrate having a first main surface and a second main surface opposing each other, a second substrate having a third main surface facing the first main surface, a functional electrode arranged on the third main surface, a support portion arranged 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, and via conductors arranged on the first substrate from the first main surface toward the second main surface, wherein the support portion has a first metal film arranged on the first main surface 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 planar view of the first main surface, a region of the first metal film includes a region of the second metal film, the area of ​​the first metal film is larger than the area of ​​the second metal film, and the hardness of the second metal film is higher than the hardness of the first metal film.

[0008] According to the present invention, it is possible to provide an acoustic wave device having a support portion with improved bonding strength.

[0009] FIG. 1 is a cross-sectional view of an elastic wave device according to an embodiment. FIG. 2A is a first plan view of an elastic wave device according to an embodiment. FIG. 2B is a second plan view of an elastic wave device according to an embodiment. FIG. 2C is a third plan view of an elastic wave device according to an embodiment. FIG. 3A is a plan view and a cross-sectional view schematically illustrating a first example of an elastic wave resonator constituting an elastic wave device according to an embodiment. FIG. 3B is a cross-sectional view schematically illustrating a second example of an elastic wave resonator constituting an elastic wave device according to an embodiment. FIG. 3C is a cross-sectional view schematically illustrating a third example of an elastic wave resonator constituting an elastic wave device according to an embodiment. FIG. 3D is a cross-sectional view schematically illustrating a fourth example of an elastic wave resonator constituting an elastic wave device according to an embodiment. FIG. 4 is a cross-sectional view illustrating an enlarged view of a via conductor and its periphery in an elastic wave device according to an embodiment. FIG. 5 is a cross-sectional view illustrating an example of a layered structure of metal films constituting an elastic wave device according to an embodiment. FIG. 6 is a cross-sectional view illustrating an enlarged view of a layered interface of a metal film in an elastic wave device according to an embodiment. FIG. 7 is a cross-sectional view of an elastic wave device according to a first modification of the embodiment. FIG. 8 is a first plan view of an elastic wave device according to a first modification of the embodiment. FIG. 9 is a cross-sectional view of a support portion showing hardness measurement points. FIG. 10A is a cross-sectional schematic view showing an interface between a via conductor and a first substrate in an elastic wave device according to an embodiment. FIG. 10B is an SEM image showing an interface between a via conductor and a first substrate in an elastic wave device according to an embodiment. FIG. 11A is a cross-sectional view of an elastic wave device according to a second modification of the embodiment. FIG. 11B is a cross-sectional view of an elastic wave device according to a third modification of the embodiment. FIG. 11C is a cross-sectional view of an elastic wave device according to a fourth modification of the embodiment. FIG. 11D is a cross-sectional view of an elastic wave device according to a fifth modification of the embodiment. FIG. 12 is a cross-sectional view showing a layered structure of metal films constituting an elastic wave device according to a sixth modification of the embodiment. FIG. 13 is a cross-sectional view showing a layered structure of metal films constituting an elastic wave device according to a comparative example.

[0010] Hereinafter, 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, component arrangements, and connection forms 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 recited in independent claims will be described as optional components. Furthermore, the sizes or size ratios of the components shown in the drawings are not necessarily strict.

[0011] It should be noted that the drawings are schematic diagrams in which emphasis, omission, or adjustment of proportions has been appropriately made to illustrate the present invention, and are not necessarily strictly illustrated, and may differ from the actual shapes, positional relationships, and proportions. In the drawings, the same reference numerals are used to denote substantially the same components, and redundant 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] Furthermore, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of elements, such as "rectangle," and numerical ranges do not only represent strict meanings, but also include substantially equivalent ranges, for example, including an error of a few percent.

[0014] (Embodiments) [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 planar (transparent) view of a main surface 20a of a substrate 20 from the positive side of the z axis. FIG. 2B is a planar (transparent) view of a main surface 10a of a substrate 10 from the positive side of the z axis. FIG. 2C is a planar view of a main surface 10b of a 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 a main surface 10a (first main surface) and a main surface 10b (second main surface) that face each other. In this embodiment, the substrate 10 contains silicon.

[0017] The substrate 20 is an example of a second substrate and has two opposing principal surfaces 20a (third principal surface) and 20b. The principal surfaces 20a and 20b 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 main surface 10a toward the main surface 10b. In this embodiment, the via conductor 11 is a through electrode filled in a cavity that penetrates the substrate 10 between the main surface 10a and the main surface 10b. The via conductor 11 is made of, for example, a metal member whose main component is Cu (copper).

[0019] In addition, via conductor 11 does not have to be a single via conductor extending from main surface 10a to main surface 10b, but may have a configuration in which multiple via conductors are connected via a planar electrode formed within 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 multiple metal layers. A specific example of the laminate structure of the metal film 31 will be described with reference to FIG. 5.

[0021] 1 and 2B , the metal film 32 is an example of a second metal film, and is a planar electrode that is disposed on the opposite side of the metal film 31 from the via conductor 11 and is in contact with the metal film 31. The metal film 32 is, for example, a laminate of multiple metal layers. A specific example of the laminate structure of the metal film 32 will be described with reference to FIG. 5 .

[0022] 1 and 2A, 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. 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 stacked in this order between main surface 10a and main surface 20a, so as to provide a space 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 Structures of the Substrate 20, Functional Electrode 34, and Metal Film 33] Next, exemplary structures of the substrate 20, functional electrode 34, and metal film 33 will be described. Fig. 3A is a plan view and a cross-sectional view schematically illustrating a first example of an 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 opposing comb electrodes 60a and 60b are formed on the substrate 20. The comb electrode 60a is composed of a plurality of parallel electrode fingers 61a (first electrode fingers) and a busbar electrode 62a (first busbar electrode) connecting one ends of the plurality of electrode fingers 61a. The comb electrode 60b is composed of a plurality of parallel electrode fingers 61b (second electrode fingers) 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 in a direction perpendicular to the acoustic wave propagation direction (X-axis direction). The busbar electrode 62a and the busbar electrode 62b are arranged opposite each other with the electrode fingers 61a and 61b sandwiched therebetween. The comb electrodes 60a and 60b form an IDT (InterDigital Transducer) electrode 54.

[0029] When elastic wave device 1 according to this preferred embodiment performs electromechanical transduction using IDT electrode 54, functional electrode 34 shown in Figures 1 and 2A includes a plurality of electrode fingers 61 a and a plurality of electrode fingers 61 b. Metal film 33 shown in Figures 1 and 2A includes bus bar electrodes 62 a and 62 b.

[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. 3A (b), the IDT electrode 54 has a laminated structure of, for example, an adhesive layer 540 and a main electrode layer 542.

[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 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 those described above. Furthermore, the IDT electrode 54 does not have to have the laminated structure described above. The IDT electrode 54 may be made of, for example, 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 metals or alloys. Furthermore, the protective layer 55 does not necessarily have to be formed.

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

[0035] As shown in (c) of FIG. 3A, the substrate 20 includes a support substrate 51, an intermediate layer 52, and a piezoelectric film 53, and has a structure in which the support substrate 51, the intermediate layer 52, and the piezoelectric film 53 are stacked in this order.

[0036] The piezoelectric film 53 is, for example, a θ° Y-cut X-propagation LiTaO ３ It is made of a piezoelectric single crystal or piezoelectric ceramics (a lithium tantalate single crystal or ceramic cut along a plane whose normal is an axis rotated θ degrees from the Y axis around the X axis, and through which surface acoustic waves propagate in the X axis direction). 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 support substrate 51 is a substrate that supports the intermediate layer 52, the piezoelectric film 53, and the IDT electrode 54. The support substrate 51 may further be a substrate in which the sound velocity of bulk waves within the support substrate 51 is faster than that of acoustic waves such as surface waves and boundary waves that propagate through the piezoelectric film 53. The support substrate 51 functions to confine the surface acoustic waves within the portion where the piezoelectric film 53 and the intermediate layer 52 are stacked, preventing the surface acoustic waves from leaking below the support substrate 51. Examples of materials that can be used for the 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; dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; semiconductors such as silicon; and materials containing any of the above materials as a main component. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl ２ O ４ , FeAl ２ O ４ , ZnAl ２ O ４ , MnAl ２ O ４ Examples include:

[0038] The intermediate layer 52 is, for example, a film in which the acoustic velocity of the bulk waves in the intermediate layer 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 support substrate 51. This structure and the property of the acoustic waves that the energy is concentrated in a medium with an essentially low acoustic velocity suppress the leakage of the surface acoustic wave energy outside the IDT electrodes. The material of the intermediate layer 52 can be, for example, a dielectric 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 containing any of the above materials as a main component.

[0039] The laminated structure of substrate 20 described above 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 support substrate 51 may have a laminated structure of a support substrate and a high acoustic velocity film in which the acoustic velocity of the propagating bulk waves is faster than that of elastic waves such as surface waves and boundary waves that propagate through the piezoelectric film 53. In this case, the high acoustic velocity film may be made of the same material as the support substrate 51. The support substrate may be made of, for example, 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, and forsterite; dielectric materials such as diamond and glass; semiconductors such as silicon and gallium nitride; resins; or materials containing any of the above materials as a main component.

[0041] The wavelength λ of the acoustic wave resonator 60 is determined by the repetition period of the electrode fingers 61 a or 61 b ​​constituting the IDT electrode 54 shown in FIG. 3A (b). The electrode finger pitch p is half the wavelength λ and is defined as (W+S), where W is the line width of the electrode fingers 61 a and 61 b ​​constituting the interdigital electrodes 60 a and 60 b, respectively, and S is the space width between adjacent electrode fingers 61 a and 61 b. The electrode finger duty D of the IDT electrode 54 is the line width occupancy rate of the electrode fingers 61 a and 61 b, and is the ratio of the line width to the sum of the line width W and the space width S, and is defined as W / (W+S). If the spacing between adjacent electrode fingers in the IDT electrode 54 is not constant, the electrode finger pitch p of the IDT electrode 54 is determined by the average electrode finger pitch p of the IDT electrode 54. ＡＶＥ The average electrode finger pitch p of the IDT electrode 54 is defined as ＡＶＥis defined as Di / (Ni-1), where Ni is the total number of electrode fingers 61a, 61b included in the IDT electrode 54, and Di is the center-to-center distance between the electrode finger located at one end and the electrode finger located at the other end of the IDT electrode 54 in the acoustic wave propagation direction. If the electrode finger duty D is not constant in the IDT electrode 54, the electrode finger duty D of the IDT electrode 54 is calculated by dividing the average electrode finger duty D of the IDT electrode 54 by the average electrode finger duty D of the IDT electrode 54. ＡＶＥ The average electrode finger duty D of the IDT electrode 54 is defined as ＡＶＥ The total number of electrode fingers 61a and 61b included in the IDT electrode 54 is Ni, and the total line width obtained by adding the line width W of (Ni-1) electrode fingers is W. ＡＬＬ The total space width obtained by adding up the (Ni-1) space widths S included in the IDT electrode 54 is S ＡＬＬ In this case, W ＡＬＬ / (W ＡＬＬ +S ＡＬＬ ) is defined as

[0042] The electrode finger pitch p of the comb-shaped electrodes of the IDT electrode 54 can be measured by using a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), or a transmission electron microscope (TEM) to view the main surface of the substrate on which the comb-shaped electrodes of the IDT electrode 54 are formed in a plan view and / or a cross-section perpendicular to the extension direction of the electrode fingers, and measuring the line width L and space width S.

[0043] 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 a single crystal, polycrystalline, or amorphous state, or a mixture of these.

[0044] 3B is a cross-sectional view schematically illustrating a second example of an elastic wave resonator 60 constituting elastic wave device 1 according to an embodiment. In elastic wave resonator 60 illustrated in FIG. 3A , IDT electrode 54 is formed on substrate 20 having piezoelectric film 53. However, as illustrated in FIG. 3B , the substrate on which IDT electrode 54 is formed may be a piezoelectric single crystal substrate 57 made of a single piezoelectric layer.

[0045] The piezoelectric single crystal substrate 57 is, for example, LiNbO ３ The elastic wave resonator according to this example is made of a piezoelectric single crystal of LiNbO ３ The piezoelectric transducer 50 is composed of a piezoelectric single crystal substrate 57, an IDT electrode 54, and a protective layer 58 formed on the piezoelectric single crystal substrate 57 and the IDT electrode 54.

[0046] The laminate structure, material, cut angle, and thickness of the piezoelectric film 53 and the piezoelectric single crystal substrate 57 may be changed as appropriate depending on the required transmission characteristics of the acoustic wave device 1. ３ Even if an elastic wave resonator uses a piezoelectric substrate or the like, it is possible to achieve the same effects as the elastic wave resonator 60 using the piezoelectric film 53 described above.

[0047] 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. The piezoelectric film may be, for example, LiTaO ３ The support substrate is a substrate that supports the piezoelectric film, the energy trapping layer, and the IDT electrode 54.

[0048] The energy trapping layer is composed of one or more layers, and the velocity of the bulk acoustic waves propagating through at least one of the layers is greater than the velocity of the acoustic waves 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 waves in the low acoustic velocity layer is slower than the acoustic velocity of the acoustic waves propagating through the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk waves in the high acoustic velocity layer is faster than the acoustic velocity of the acoustic waves propagating through the piezoelectric film. The support substrate may also be the high acoustic velocity layer.

[0049] The energy trapping layer may also be an acoustic impedance layer having a configuration in which low acoustic impedance layers with a relatively low acoustic impedance and high acoustic impedance layers with a relatively high acoustic impedance are alternately stacked.

[0050] 3C is a cross-sectional view schematically illustrating a third example of an elastic wave resonator 60 included in the elastic wave device 1 according to the embodiment. Fig. 3C illustrates a bulk elastic wave resonator as the elastic wave resonator of the elastic wave device 1. As shown in the figure, the bulk elastic wave resonator includes, for example, a support substrate 65, a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68, and is configured such that the support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are layered in this order.

[0051] The support substrate 65 is a substrate, such as a silicon substrate, for supporting the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68. The support substrate 65 has a cavity in the region that contacts the lower electrode 66. This allows the piezoelectric layer 67 to vibrate freely.

[0052] 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.

[0053] 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, and LiBO (lithium borate).

[0054] A bulk acoustic wave resonator having the above-described layered structure generates resonance by inducing bulk acoustic waves in the piezoelectric layer 67 when electrical energy is applied 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.

[0055] 1 and 2A includes a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68. Furthermore, the substrate 20 shown in FIGS. 1 and 2A may not have piezoelectricity and may include a support substrate 65.

[0056] 3D is a cross-sectional view schematically illustrating a fourth example of elastic wave resonator 60 constituting elastic wave device 1 according to an embodiment. In elastic wave device 1 of this example, substrate 20 includes support substrate 51, intermediate layer 52, void 160, and piezoelectric film 53.

[0057] In the elastic wave device 1 of this example, when the main surface 20 a is viewed in plan, a gap 160 is provided between the piezoelectric film 53 and the support substrate 51 in the region overlapping with the IDT electrode 54. Furthermore, when the thickness (in the z-axis direction) of the piezoelectric film 53 is d and the electrode finger pitch of the IDT electrode 54 is p, the normalized film thickness d / p of the piezoelectric film 53 is 0.5 or less.

[0058] The normalized thickness d / p of the piezoelectric film 53 is 0.5 or less, and the air gap 160 is provided, so that the elastic wave resonator 60 constitutes a laterally excited bulk acoustic resonator (XBAR). The normalized thickness d / p of the piezoelectric film 53 is 0.5 or less, so that the relative bandwidth of the elastic wave resonator 60 can be increased, and a resonator with a high electromechanical coupling coefficient can be constituted.

[0059] It is more desirable that the normalized thickness d / p of the piezoelectric film 53 be 0.24 or less, which allows the fractional bandwidth of the acoustic wave resonator 60 to be 7% or more.

[0060] It is desirable that the electrode finger duty D of the IDT electrode 54 and the normalized film thickness d / p satisfy the relationship of Equation 1.

[0061] D≦1.75(d / p)+0.075 (Formula 1)

[0062] This effectively reduces the spurious response of the higher-order mode of the XBAR. Specifically, the fractional bandwidth of the XBAR (the value obtained by dividing the difference frequency between the antiresonance frequency and the resonant frequency by the average frequency of the antiresonance frequency and the resonant frequency) can be set to 17% or less, thereby preventing the spurious response of the higher-order mode from being included in the passband.

[0063] It is more desirable that the electrode finger duty D of the IDT electrode 54 and the normalized film thickness d / p satisfy the relationship of Equation 2.

[0064] D≦1.75(d / p)+0.05 (Formula 2)

[0065] This ensures that the fractional bandwidth of the XBAR is 17% or less, and prevents spurious signals of higher modes from being included in the passband.

[0066] Furthermore, it is desirable that the piezoelectric film 53 is made of lithium niobate or lithium tantalate, and that the Euler angles (θ1, θ2, θ3) of the lithium niobate or lithium tantalate constituting the piezoelectric film 53 are within the range of the following formula 3, formula 4, formula 5 or formula 6.

[0067] −10°≦θ1≦10°, and 0°≦θ2≦20° (Equation 3)

[0068] -10°≦θ1≦10°, and 20°≦θ2≦80°, and 0°≦θ3≦60° (1-(θ2-50) ２ / 900) １／２ ) (Formula 4)

[0069] -10°≦θ1≦10°, and 20°≦θ2≦80°, and [180°-60°(1-(θ2-50) ２ / 900) １／２ )]≦θ3≦180° (Formula 5)

[0070] -10°≦θ1≦10°, and [180°-30°(1-(θ3-90) ２ / 8100) １／２ )]≦θ2≦180° (Formula 6)

[0071] By defining the Euler angles of piezoelectric film 53 made of lithium niobate or lithium tantalate as described above, the fractional bandwidth of elastic wave resonator 60 can be set to 5% or more.

[0072] In the fourth example of the elastic wave device 1, an energy trapping layer including a low acoustic impedance layer and a high acoustic impedance layer may be disposed instead of the gap 160. Specifically, an energy trapping layer having a configuration in which low acoustic impedance layers with relatively low acoustic impedance and high acoustic impedance layers with relatively high acoustic impedance are alternately stacked may be disposed between the piezoelectric film 53 and the support substrate 51. The energy trapping layer may have a laminated structure of a low acoustic velocity film and a high acoustic velocity film. The low acoustic velocity film is a film in which the acoustic velocity of a bulk wave in the low acoustic velocity film is slower than the acoustic velocity of a bulk acoustic wave propagating through the piezoelectric film 53. The high acoustic velocity film is a film in which the acoustic velocity of a bulk wave in the high acoustic velocity film is faster than the acoustic velocity of an elastic wave propagating through the piezoelectric film 53. Since the normalized thickness d / p of the piezoelectric film 53 is 0.5 or less and an energy trapping layer is provided, the elastic wave resonator 60 constitutes an XBAR.

[0073] [3 Bonding Structure of Substrate 10, Via Conductor 11, and Metal Films 31-33] Next, the bonding structure of substrate 10, via conductor 11, and metal films 31-33 will be described. FIG. 4 is an enlarged cross-sectional view of via conductor 11 and its surroundings in elastic wave device 1 according to an embodiment. This figure is a microscope image of region IV in FIG. 1 . As shown in the figure, via conductor 11 is formed inside substrate 10, and planar electrode 12 is bonded to the upper opening of via conductor 11 (positive z-axis direction), and metal film 31 is bonded to the lower opening of via conductor 11 (negative z-axis direction). Furthermore, metal film 32, metal film 33, and substrate 20 are bonded, in this order, to the negative z-axis side of metal film 31.

[0074] 2B , in a plan view of the main surface 10a, the region of the metal film 31 (in the upper right corner of FIG. 2B ) includes the region of the via conductor 11 (in the upper right corner of FIG. 2B ), and the area of ​​the metal film 31 (in the upper right corner of FIG. 2B ) is larger than the area of ​​the via conductor 11 (in the upper right corner of FIG. 2B ). In addition, in a plan view of the main surface 10a, the region of the metal film 32 (in the upper right corner of FIG. 2B ) includes the region of the via conductor 11 (in the upper right corner of FIG. 2B ), and the area of ​​the metal film 32 (in the upper right corner of FIG. 2B ) is larger than the area of ​​the via conductor 11 (in the upper right corner of FIG. 2B ).

[0075] 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

[0076] If the regions of metal films 31 and 32 were included in the region of via conductor 11 in a plan view of principal surface 10a, all of the compressive stress of metal films 31 and 32 would be applied to via conductor 11, which could result in deformation of via conductor 11 or peeling of via conductor 11 from substrate 10. In contrast, with the above-described configuration of elastic wave device 1 according to the present embodiment, the region of via conductor 11 is included in the regions of metal films 31 and 32 in a plan view of principal surface 10a, and the area of ​​metal film 31 is larger than the area of ​​via conductor 11, and the area of ​​metal film 32 is larger than the area of ​​via conductor 11. As a result, the substrate 10 adjacent to via conductor 11 in the x-axis direction is bonded to metal film 31, and therefore the substrate 10 bonded to metal film 31 absorbs the compressive stress of metal films 31 and 32, thereby suppressing deformation and peeling of via conductor 11. In other words, fixation of via conductor 11 can be promoted. Furthermore, since metal film 32 is bonded to metal film 33, and metal film 33 is bonded to substrate 20, the compressive stress generated in metal films 31 and 32 can be dispersed to substrate 20. This makes it possible to provide elastic wave device 1 with improved bonding strength of via conductors 11.

[0077] In this specification, when region A includes region B, it is defined that the entire area of ​​region B is disposed within region A.

[0078] Next, the bonding state between via conductor 11 and substrate 10 will be described. Fig. 10A is a cross-sectional schematic diagram showing the interface between via conductor 11 and substrate 10 in elastic wave device 1 according to the embodiment. Fig. 10B is an SEM image showing the interface between via conductor 11 and substrate 10 in elastic wave device 1 according to the embodiment. Fig. 10A is a cross-sectional view schematically enlarging region X in Fig. 4 .

[0079] Due to the process of forming a cylindrical cavity in the substrate 10 made of Si for filling the via conductors 11 in the substrate 10, a shell-shaped uneven structure called a scallop is generated on the inner wall of the cylindrical cavity in the substrate 10. If the tips of the protrusions in the scallop uneven structure are sharp, the electrical resistance at the tips of the uneven structure increases, making them more susceptible to heat generation, and reducing the bonding strength of the via conductors 11.

[0080] In elastic wave device 1 according to this embodiment, the PV (Peak to Valley) value of the scalloped uneven structure is preferably 100 μm or less. The PV value is defined as the difference in height between the highest point at the tip of the convex portion of the uneven structure and the lowest point at the valley of the concave portion. In elastic wave device 1 according to this embodiment, the tips of the convex portions of the scalloped uneven structure are flattened, as shown in FIGS. 10A and 10B . This reduces electrical resistance at the tips of the uneven structure, suppressing heat generation. Furthermore, it 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.

[0081] 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 that constitute the elastic wave device 1 according to an embodiment. This figure is a cross-sectional view that schematically enlarges region V in Fig. 4.

[0082] 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.

[0083] The intermediate layer 313 (first intermediate layer) and the intermediate layer 316 are metal layers containing, for example, Ti (titanium) as a main component, and function as diffusion prevention layers.

[0084] The intermediate layers 312 and 315 are metal layers containing, for example, platinum (Pt) as a main component, and function as diffusion prevention layers together with the intermediate layers 313 and 316 .

[0085] The main electrode layer 314 is an example of a first main electrode layer, and is a metal layer whose main components are, for example, Al (aluminum) and Cu (copper), and functions as the main medium of the metal film 31 for transmitting high-frequency signals.

[0086] The bonding layer 311 is an example of a first bonding layer, and is a metal layer containing, for example, Au (gold) as a main component, and has the function of forming a good electrical and mechanical bond with the metal film 32 .

[0087] In the metal film 31 according to this embodiment, the intermediate layers 312 and 315 may be omitted. Furthermore, the metal film 31 may be composed of only the main electrode layer 314.

[0088] As shown in FIG. 5, the metal film 32 has, from the main surface 10a side, a bonding layer 321, an intermediate layer 322, an intermediate layer 323, a main electrode layer 324, and an intermediate layer 325.

[0089] The bonding layer 321 is an example of a second bonding layer, and is a metal layer containing, for example, Au (gold) as a main component, and has the function of forming a good electrical and mechanical bond with the metal film 31 .

[0090] The intermediate layer 322 is a metal layer containing, for example, platinum (Pt) as a main component, and functions as a diffusion prevention layer together with the intermediate layer 323 .

[0091] The intermediate layer 323 (second intermediate layer) and the intermediate layer 325 are metal layers containing, for example, Ti (titanium) as a main component, and function as diffusion prevention layers.

[0092] The main electrode layer 324 is an example of a second main electrode layer, and is a metal layer whose main components are, for example, Al (aluminum) and Cu (copper), and functions as the main medium of the metal film 32 for transmitting high-frequency signals.

[0093] The metal film 32 according to this embodiment may not have the intermediate layer 322. Furthermore, the metal film 32 may be composed of only the main electrode layer 324.

[0094] 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.

[0095] The intermediate layers 331 and 333 are metal layers containing, for example, Ti (titanium) as a main component, and function as diffusion prevention layers.

[0096] The main electrode layer 332 is a metal layer containing, for example, aluminum (Al) and copper (Cu) as its main components, and functions as the main medium of the metal film 33 for transmitting high-frequency signals.

[0097] In the metal film 33 according to this embodiment, the intermediate layers 331 and 333 may be omitted, and the metal film 33 may be composed of only the main electrode layer 332 .

[0098] The main electrode layer 332 in FIG. 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 adhesive layer 540 in FIG. 3A.

[0099] The relationship in size between the areas (and lengths) of the metal layers constituting each metal film is not limited to the relationship in size between the areas (and lengths) of the metal layers shown in Fig. 5. The relationship in size between the areas (and lengths) of the metal layers will be described with reference to Fig. 6.

[0100] Also, as shown in FIG. 2B , in a plan view of the main surface 10 a, the region of the metal film 31 (at the upper right of FIG. 2B ) includes the region of the metal film 32 (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 metal film 32 (at the upper right of FIG. 2B ).

[0101] 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 is greater than.

[0102] In this way, the shape of the end of the metal film 31 is not deformed by bonding the metal film 32, and therefore, the bonding between the substrate 10 and the metal film 31 can promote a reduction in the compressive stress acting on the via conductor 11.

[0103] Furthermore, the hardness of the metal film 32 is higher than the hardness of the metal film 31 .

[0104] When joining two metal films, if the metal film with the smaller area has a lower hardness, the metal film with the smaller area will be crushed during pressure joining and will protrude to the edge of the joining interface. The metal film protruding to the edge will cause local heat generation at the joint, deteriorating the joint, and the metal film protruding to the edge will become unwanted particles.

[0105] In contrast, in elastic wave device 1 according to the present embodiment, when principal surface 10a is viewed in plan, the hardness of small-area metal film 32 is greater than the hardness of large-area metal film 31. Therefore, when metal films 31 and 32 are pressure-bonded together, crushing of small-area metal film 32 can be prevented, and bonding in which large-area metal film 31 envelops small-area metal film 32 can be achieved. Therefore, localized heat generation and generation of unwanted particles at the end of the bonding interface can be suppressed, and elastic wave device 1 with improved bonding strength of the support portion can be provided.

[0106] As shown in FIGS. 2A and 2B, in plan view of the main surface 20 a , 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 .

[0107] 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 20a (z-axis direction) and passes through the via conductor 11, the length L ３３ is the length L of the metal film 32 ３２ is greater than.

[0108] This allows the metal film 32 to avoid restricting the area of ​​the functional electrodes 34 and the metal film 33 on the main surface 20a, and prioritizes the layout of the functional electrodes 34 and the metal film 33.

[0109] Moreover, it is desirable that the hardness of the metal film 33 be higher than the hardness of the metal film 31 .

[0110] This allows for a bonding configuration in which metal film 31 encases metal films 32 and 33. This makes it possible to suppress localized heat generation and generation of unwanted particles at the end of the bonding interface, thereby providing elastic wave device 1 with improved bonding strength at the support portion.

[0111] Furthermore, it is desirable that the element with the highest weight ratio among the metal elements constituting bonding layer 321 is the same as the element with the highest weight ratio among the metal elements constituting bonding layer 311. In this embodiment, each of bonding layers 311 and 321 is a metal layer containing, for example, Au as a main component. The element with the highest weight ratio (Au) in bonding layer 321 is the same as the element with the highest weight ratio (Au) in bonding layer 311.

[0112] According to this, the bonding strength between the metal film 31 and the metal film 32 can be increased by Au diffusion bonding, and therefore the strength of the support portion can be increased.

[0113] It is also desirable that the size of the crystal grains in bonding layer 311 and the size of the crystal grains in bonding layer 321 are approximately the same.

[0114] If the crystal grains of bonding layers 311 and 321 are different, the hardness of metal films 31 and 32 will be different, which will deform the metal film with the lower hardness during compression bonding, resulting in insufficient bonding strength. In contrast, if the crystal grains are the same, the hardness of the metal layer at the bonding interface will be the same, so sufficient bonding strength can be obtained without deforming the metal film during compression bonding.

[0115] The crystal grain size of the metal layer can be classified, for example, according to the international standard ASTM E112-13. Each metal layer is assigned a grain size number based on the average grain size specified by the international standard. Metal layers having the same grain size number are considered to have the same crystal grain size.

[0116] Furthermore, it is desirable that the surface roughness Ra of the bonding interface between the bonding layers 311 and 321 is 10 nm or less.

[0117] This makes it possible to eliminate voids at the bonding interface between the bonding layers 311 and 321, thereby enabling the bonding strength of the bonding layers 311 and 321 to be further increased.

[0118] Next, conditions for improving the bonding strength of each metal film constituting the support portion will be described. FIG. 6 is an enlarged cross-sectional view of the bonding interface between metal films 31 and 32 of elastic wave device 1 according to an embodiment. This figure is an enlarged microscope image of region VI in FIG. 4 . In the layered structure of each metal film shown in FIG. 6 , intermediate layers 313 and 312 are shown as a single layer (referred to as intermediate layer 313 (312)), and intermediate layers 323 and 322 are shown as a single layer (referred to as intermediate layer 323 (322)). Note that intermediate layers 312 and 322 may be omitted.

[0119] First, as described above, in a plan view of the main surface 10a, the region of the metal film 31 includes the region of the metal film 32, and the area of ​​the metal film 31 is larger than the area of ​​the metal film 32. Also, as shown in FIG. 6, in a plan view of the main surface 10a, the region of the intermediate layer 323 (322) includes the region of the bonding layer 321, and the area of ​​the intermediate layer 323 (322) is larger than the area of ​​the bonding layer 321. Also, in a plan view of the main surface 10a, the region of the main electrode layer 324 includes the region of the intermediate layer 323 (322), and the area of ​​the main electrode layer 324 is larger than the area of ​​the intermediate layer 323 (322). In other words, as shown in FIG. 6, in a cross section (cross section II in FIGS. 2A to 2C) perpendicular to the main surface 10a and passing through the metal films 31 to 33, the length L of the intermediate layer 323 (322) is ３２３ is the length L of the bonding layer 321 ３２１ is greater than the length L of the main electrode layer 324 ３２４ is the length L of the intermediate layer 323 (322) ３２３ is greater than.

[0120] Furthermore, the linear expansion coefficient of the bonding layer 321 is greater than that of the intermediate layer 323 ( 322 ), and the linear expansion coefficient of the main electrode layer 324 is greater than that of the bonding layer 321 .

[0121] According to the above-described stacking relationship of the metal layers constituting the metal films 31 and 32, when the metal films 31 and 32 are heated during compression bonding, the main electrode layer 324, which has a relatively large linear expansion coefficient, has a larger area than the intermediate layer 323 (322) and the bonding layer 321. Therefore, at the ends of the main electrode layer 324 and the intermediate layer 323 (322), the main electrode layer 324 and the intermediate layer 323 (322) have a bimetal structure, and the main electrode layer 324 and the intermediate layer 323 (322) tend to expand toward the bonding layer 321 (positive direction of the z-axis) at the ends. As a result, both ends of the main electrode layer 324 are pushed up toward the metal film 31 (positive direction of the z-axis), thereby achieving good bonding at the bonding ends of the metal film 32.

[0122] The method for measuring the hardness of the metal films 31 to 33 will now be described.

[0123] The hardness of the metal films 31-33 can be measured using, for example, nanoindentation. Nanoindentation (NI) is a method for measuring hardness by pressing a microindenter into a test object and determining the load-displacement curve of the test object. Figure 9 is a cross-sectional view of a support showing hardness measurement points. As shown in the figure, the microindenter is pressed into the hardness measurement points on the side of the metal films 31-33. Table 1 shows an example of hardness measurement data. The equipment used was a TriboIndenter TI980 manufactured by Bruker Japan. The measurement mode (load time-hold time-unload time) was standard (5 sec-2 sec-5 sec), the indenter load was 400 μN, and five measurements were taken for each metal film.

[0124]

[0125] Table 1 shows that the hardness of metal film 32 is higher than that of metal film 31, and the hardness of metal film 33 is higher than that of metal film 31, as a result of measuring the hardness of metal films 31 to 33 of elastic wave device 1 using the NI method.

[0126] The configuration of the support portion included in the elastic wave device 1 according to this preferred embodiment is not limited to the configuration shown in FIG. 1, and may have the configurations shown in the following FIGS. 11A to 11D.

[0127] 11A is a cross-sectional view of an elastic wave device according to a second modification of the embodiment. This figure illustrates a cross-sectional view of the elastic wave device according to the second modification, including a portion of substrate 10, a portion of substrate 20, and support portions 71 and 72. As shown in the figure, the elastic wave device according to the second modification includes substrates 10 and 20, via conductor 11, and support portions 71 and 72. Support portion 71 includes a metal film 31 disposed on principal surface 10a and not in contact with via conductor 11, a metal film 33 disposed on principal surface 20a, and a metal film 32 disposed between metal films 31 and 33. Support portion 72 includes a metal film 31 disposed on principal surface 10a and in contact with via conductor 11, a metal film 33 disposed on principal surface 20a, and a metal film 32 disposed between metal films 31 and 33. In this modified example, the metal film 31 of the support portion 71 is separated from the metal film 31 of the support portion 72, the metal film 32 of the support portion 71 is separated from the metal film 32 of the support portion 72, and the metal film 33 of the support portion 71 is integrated with the metal film 33 of the support portion 72.

[0128] In this case, metal film 33 is shared by supporting portions 71 and 72, which simplifies the manufacturing process of the acoustic wave device.

[0129] 11B is a cross-sectional view of an elastic wave device according to a third modification of the embodiment. This figure illustrates a cross-sectional view of the elastic wave device according to the third modification, including a portion of substrate 10, a portion of substrate 20, and support portions 71 and 72. As shown in the figure, the elastic wave device according to the third modification includes substrates 10 and 20, via conductor 11, and support portions 71 and 72. Support portion 71 includes a metal film 31 disposed on principal surface 10a and not in contact with via conductor 11, a metal film 33 disposed on principal surface 20a, and a metal film 32 disposed between metal films 31 and 33. Support portion 72 includes a metal film 31 disposed on principal surface 10a and in contact with via conductor 11, a metal film 33 disposed on principal surface 20a, and a metal film 32 disposed between metal films 31 and 33. In this modified example, the metal film 31 of the support portion 71 and the metal film 31 of the support portion 72 are separated, the metal film 32 of the support portion 71 and the metal film 32 of the support portion 72 are integrated, and the metal film 33 of the support portion 71 and the metal film 33 of the support portion 72 are integrated.

[0130] In this case, metal film 32 is shared by supporting portions 71 and 72, and metal film 33 is shared by supporting portions 71 and 72, which simplifies the manufacturing process of the acoustic wave device.

[0131] 11C is a cross-sectional view of an elastic wave device according to a fourth modification of the embodiment. This figure illustrates a cross-sectional view of the elastic wave device according to this modification, including a portion of substrate 10, a portion of substrate 20, and support portions 71 and 72. As shown in the figure, the elastic wave device according to this modification includes substrates 10 and 20, via conductor 11, and support portions 71 and 72. Support portion 71 includes metal film 31 disposed on principal surface 10a, metal film 33 disposed on principal surface 20a, and metal film 32 disposed between metal films 31 and 33. Support portion 72 includes metal film 31 disposed on principal surface 10a and in contact with via conductor 11, metal film 33 disposed on principal surface 20a, and metal film 32 disposed between metal films 31 and 33. In this modified example, the metal film 31 of the support portion 71 and the metal film 31 of the support portion 72 are integrated, the metal film 32 of the support portion 71 and the metal film 32 of the support portion 72 are integrated, and the metal film 33 of the support portion 71 and the metal film 33 of the support portion 72 are integrated.

[0132] This allows metal film 31 to be shared by support portions 71 and 72, metal film 32 to be shared by support portions 71 and 72, and metal film 33 to be shared by support portions 71 and 72, thereby simplifying the manufacturing process of the acoustic wave device.

[0133] 11D is a cross-sectional view of an elastic wave device according to a fifth modification of the embodiment. This figure illustrates a cross-sectional view of the elastic wave device according to this modification, including a portion of substrate 10, a portion of substrate 20, and support portions 71 and 72. As shown in the figure, the elastic wave device according to this modification includes substrates 10 and 20, via conductor 11, and support portions 71 and 72. Support portion 71 includes metal film 31 disposed on principal surface 10a, metal film 33 disposed on principal surface 20a, and metal film 32 disposed between metal films 31 and 33. Support portion 72 includes metal film 31 disposed on principal surface 10a and in contact with via conductor 11, metal film 33 disposed on principal surface 20a, and metal film 32 disposed between metal films 31 and 33. In this modified example, the metal film 31 of the support portion 71 and the metal film 31 of the support portion 72 are integrated, the metal film 32 of the support portion 71 and the metal film 32 of the support portion 72 are separated, and the metal film 33 of the support portion 71 and the metal film 33 of the support portion 72 are separated.

[0134] In this case, metal film 31 is shared by supporting portions 71 and 72, which simplifies the manufacturing process of the acoustic wave device.

[0135] [4 Structure of Elastic Wave Device 1A According to Modification] FIG. 7 is a cross-sectional view of elastic wave device 1A according to Modification 1 of the embodiment. FIG. 8 is a first plan view of elastic wave device 1A according to Modification 1 of the embodiment. FIG. 8 is a plan view (perspective) 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 (perspective) 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. 7 is a cross-sectional view taken along line VII-VII in FIG. 8 .

[0136] 7 and 8 , elastic wave device 1A includes substrates 10 and 20, metal films 31, 32, and 33, a functional electrode 34, via conductors 11, insulating films 13 and 23, a planar electrode 12, and a bump electrode 40. Elastic wave device 1A according to this modification differs from elastic wave device 1 according to the embodiment in the relative positions of via conductor 11 and metal films 31, 32, and 33. The following description of elastic wave device 1A according to this modification will focus on the different configuration and omit a description of the same configuration as elastic wave device 1 according to the embodiment.

[0137] 7, the metal film 31 is an example of a first metal film, and is a planar electrode that is 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.

[0138] 7, the metal film 32 is an example of a second metal film, and is a planar electrode in contact with the metal film 31. The metal film 32 is, for example, a laminate of a plurality of metal layers.

[0139] 7 and 8, the metal film 33 is an example of a third metal film, and is a planar electrode that is 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.

[0140] The functional electrode 34 is disposed on the main surface 20 a and performs electromechanical transduction with the substrate 20 .

[0141] As shown in FIG. 7, metal films 31, 32, and 33 form a support portion and are stacked in this order between main surface 10a and main surface 20a, so as to provide a space between main surface 10a and main surface 20a.

[0142] In FIG. 7, the right-hand via conductor 11 of the two via conductors 11 does not overlap with the functional electrode 34 when the principal surfaces 10a and 20a are viewed in plan view.

[0143] [5. Layer Structure of Metal Films in Elastic Wave Device According to Modification 6] The elastic wave device according to Modification 6 differs from the elastic wave device 1 according to the embodiment only in the layer structure of the metal films that form the support section. Therefore, the following description of the elastic wave device according to Modification 6, including the same components as those in the elastic wave device 1 according to the embodiment, will be omitted, and the layer structure of the support section that differs from that of the elastic wave device 1 according to the embodiment will be described.

[0144] 12 is a cross-sectional view showing the layered structure of metal films 31A to 33A constituting an elastic wave device according to Modification 6. This figure corresponds to a schematic enlarged cross-sectional view of region V in FIG.

[0145] As shown in FIG. 12, the support portion has a metal film 31A disposed on the main surface 10a, a metal film 33A disposed on the main surface 20a, and a metal film 32A disposed between the metal films 31A and 33A.

[0146] The metal film 31A has, from the main surface 10a side, an intermediate layer 316, an intermediate layer 315, a main electrode layer 314A, an intermediate layer 313A, an intermediate layer 312, and a bonding layer 311.

[0147] The intermediate layer 313A and the intermediate layer 316 are metal layers containing, for example, Ti (titanium) as a main component, and function as first diffusion prevention layers.

[0148] Intermediate layers 312 and 315 are metal layers containing, for example, platinum (Pt) as a main component, and function as diffusion prevention layers together with intermediate layers 313A and 316.

[0149] The main electrode layer 314A is an example of a first main electrode layer, and is a metal layer whose main components are, for example, Al (aluminum) and Cu (copper), and functions as the main medium for transmitting high-frequency signals within the metal film 31A.

[0150] The bonding layer 311 is an example of a first bonding layer, and is a metal layer containing, for example, Au (gold) as a main component, and has the function of forming a good electrical and mechanical bond with the metal film 32A.

[0151] In the metal film 31A according to this modification, the intermediate layers 312 and 315 may be omitted.

[0152] As shown in FIG. 12, the metal film 32A has, from the main surface 10a side, a bonding layer 321, an intermediate layer 322, an intermediate layer 323A, a main electrode layer 324A, and an intermediate layer 325.

[0153] The bonding layer 321 is an example of a second bonding layer, and is a metal layer containing, for example, Au (gold) as a main component, and has the function of forming a good electrical and mechanical bond with the metal film 31A.

[0154] The intermediate layer 322 is a metal layer containing, for example, platinum (Pt) as a main component, and functions as a second diffusion prevention layer together with the intermediate layer 323A.

[0155] The intermediate layer 323A (second intermediate layer) and the intermediate layer 325 are metal layers containing, for example, Ti (titanium) as a main component, and function as diffusion prevention layers.

[0156] The main electrode layer 324A is an example of a second main electrode layer, and is a metal layer whose main components are, for example, Al (aluminum) and Cu (copper), and functions as the main medium for transmitting high-frequency signals within the metal film 32A.

[0157] In the metal film 32A according to this modification, the intermediate layer 322 may be omitted.

[0158] As shown in FIG. 12, 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.

[0159] The intermediate layers 331 and 333 are metal layers containing, for example, Ti (titanium) as a main component, and function as diffusion prevention layers.

[0160] The main electrode layer 332 is a metal layer containing, for example, aluminum (Al) and copper (Cu) as its main components, and functions as the main medium of the metal film 33 for transmitting high-frequency signals.

[0161] In the metal film 33A according to this modification, the intermediate layers 331 and 333 may be omitted, and the metal film 33A may be composed of only the main electrode layer 332.

[0162] In the metal film 31A, the angle θ2 formed between the side surface of the intermediate layer 313A and a first plane parallel to the major surface 10a is smaller than the angle θ1 formed between the side surface of the main electrode layer 314A and the first plane.

[0163] This increases the exposed area of ​​the side surface of the intermediate layer 313A, thereby preventing the metal components of the bonding layer 311 and the metal components of the main electrode layer 314A from connecting through the side surface of the intermediate layer 313A and alloying (migration).

[0164] It is desirable that a portion of the side surface of the main electrode layer 314A is covered with the intermediate layer 313A. This can further suppress the metal component of the bonding layer 311 and the metal component of the main electrode layer 314A from bonding and forming an alloy (migration). It is desirable that a portion of the side surface of the main electrode layer 314A is covered with the intermediate layer 313A, and the other portion of the side surface of the main electrode layer 314A is exposed and not covered with the intermediate layer 313A. This can suppress the main electrode layer 314A from being damaged by cracks caused by bonding stress with the intermediate layer 313A.

[0165] The area of ​​the bonding interface between the main electrode layer 314A and the intermediate layer 313A is larger than the area of ​​the bonding interface between the bonding layer 321 and the intermediate layer 313A.

[0166] In the metal film 32A, the angle θ4 formed between the side surface of the intermediate layer 323A and the first plane is smaller than the angle θ3 formed between the side surface of the main electrode layer 324A and the first plane.

[0167] This increases the exposed area of ​​the side surface of the intermediate layer 323A, thereby preventing the metal components of the bonding layer 321 and the metal components of the main electrode layer 324A from connecting through the side surface of the intermediate layer 323A and alloying (migration).

[0168] It is desirable that a portion of the side surface of the main electrode layer 324A be covered with the intermediate layer 323A. This can further suppress the metal components of the bonding layer 321 and the main electrode layer 324A from bonding and forming an alloy (migration). It is desirable that a portion of the side surface of the main electrode layer 324A be covered with the intermediate layer 323A, and the other portion of the side surface of the main electrode layer 324A be exposed and not covered with the intermediate layer 323A. This can suppress the main electrode layer 324A from being damaged by cracks caused by bonding stress with the intermediate layer 323A.

[0169] The area of ​​the bonding interface between the main electrode layer 324A and the intermediate layer 323A is larger than the area of ​​the bonding interface between the bonding layer 321 and the intermediate layer 323A.

[0170] 13 is a cross-sectional view showing a layered structure of metal films 531A, 532A, and 33A constituting an elastic wave device according to a comparative example. The elastic wave device according to this comparative example differs from the elastic wave device according to Modification 6 only in that metal films 531A and 532A are provided instead of metal films 31A and 32A.

[0171] The metal film 531A has, from the main surface 10a side, an intermediate layer 316, an intermediate layer 315, a main electrode layer 314A, intermediate layers 3131 and 3132, an intermediate layer 312, and a bonding layer 311.

[0172] The intermediate layers 3131, 3132 and the intermediate layer 316 are metal layers whose main component is, for example, Ti (titanium).

[0173] As shown in FIG. 13, the metal film 532A has, from the main surface 10a side, a bonding layer 321, an intermediate layer 322, intermediate layers 3231 and 3232, a main electrode layer 324A, and an intermediate layer 325.

[0174] The intermediate layers 3231, 3232 and the intermediate layer 325 are metal layers whose main component is, for example, Ti (titanium).

[0175] In metal film 531A, intermediate layers 3131 and 3132 are formed in two stages as diffusion prevention films to suppress alloying (migration) between the metal component of bonding layer 311 and the metal component of main electrode layer 314A. By making the film formation area of ​​intermediate layer 3132 smaller than the film formation area of ​​intermediate layer 3131, steps are formed on the side surfaces of intermediate layers 3131 and 3132, suppressing alloying (migration) between the metal component of bonding layer 311 and the metal component of main electrode layer 314A.

[0176] Similarly, in metal film 532A, intermediate layers 3231 and 3232 are formed in two stages as diffusion prevention films to suppress alloying (migration) between the metal component of bonding layer 321 and the metal component of main electrode layer 324A. By making the film formation area of ​​intermediate layer 3231 smaller than the film formation area of ​​intermediate layer 3232, steps are formed on the side surfaces of intermediate layers 3131 and 3132, thereby suppressing alloying (migration) between the metal component of bonding layer 321 and the metal component of main electrode layer 324A. However, in the acoustic wave device according to the comparative example, intermediate layers 3131 and 3132 must be formed using different film formation processes, and intermediate layers 3231 and 3232 must be formed using different film formation processes, which complicates the manufacturing process.

[0177] In contrast, in the acoustic wave device according to Modification 6, intermediate layer 313A can be formed in a single film-forming process, and intermediate layer 323A can be formed in a single film-forming process, thereby simplifying the manufacturing process.

[0178] In the elastic wave device according to this modified example, it is not necessary for both metal films 31A and 32A to have the above-mentioned angles θ2 and θ4, respectively; it is sufficient that at least one of metal films 31A and 32A has the above-mentioned angles θ2 and θ4.

[0179] 6. Effects, etc. As described above, elastic wave device 1 according to the present embodiment includes substrate 10 having principal surfaces 10a and 10b opposing each other, substrate 20 having principal surface 20a facing principal surface 10a, functional electrode 34 arranged on principal surface 20a, support portion arranged between principal surfaces 10a and 20a such that a space is provided between principal surfaces 10a and 20a, and via conductors 11 arranged on substrate 10 from principal surface 10a to principal surface 10b, wherein support portion includes metal film 31 arranged on principal surface 10a and in contact with via conductor 11, and metal film 32 arranged on the opposite side of via conductor 11 with metal film 31 interposed therebetween, wherein the region of metal film 31 includes the region of metal film 32 in a plan view of principal surface 10a, the area of ​​metal film 31 is larger than the area of ​​metal film 32, and the hardness of metal film 32 is greater than the hardness of metal film 31.

[0180] This prevents the smaller-area metal film 32 from being crushed when the metal films 31 and 32 are pressure-bonded together, enabling bonding in which the larger-area metal film 31 envelops the smaller-area metal film 32. This prevents localized heat generation and unwanted particle generation at the end of the bonding interface, and provides an elastic wave device 1 with improved bonding strength at the support portion.

[0181] For example, in the elastic wave device 1, the support portion further includes a metal film 33 arranged on the main surface 20a, connected to the functional electrode 34, and in contact with the metal film 32, and the hardness of the metal film 33 is higher than the hardness of the metal film 31.

[0182] This allows for a bonding configuration in which metal film 31 encases metal films 32 and 33. This makes it possible to suppress localized heat generation and generation of unwanted particles at the end of the bonding interface, thereby providing elastic wave device 1 with improved bonding strength at the support portion.

[0183] For example, in the elastic wave device 1, the metal film 31 has, in order from the main 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 main surface 10a side, a bonding layer 321, an intermediate layer 323, and a main electrode layer 324.

[0184] According to this, since each of the metal films 31 and 32 is made up of a plurality of metal layers having different functions, good bonding between the metal films 31 and 32 can be achieved.

[0185] In the elastic wave device according to Modification 6, the angle θ2 between the side surface of intermediate layer 313A and the first plane parallel to principal surface 10a is smaller than the angle θ1 between the side surface of main electrode layer 314A and the first plane.

[0186] This increases the exposed area of ​​the side surface of the intermediate layer 313A, thereby preventing the metal components of the bonding layer 311 and the metal components of the main electrode layer 314A from connecting through the side surface of the intermediate layer 313A and alloying (migration).

[0187] Furthermore, for example, in the acoustic wave device according to Modification 6, part of the side surface of main electrode layer 314A is covered with intermediate layer 313A.

[0188] This can further prevent the metal component of the bonding layer 311 and the metal component of the main electrode layer 314A from bonding and forming an alloy (migration).

[0189] Furthermore, for example, in the elastic wave device according to Modification 6, the area of ​​the bonding interface between main electrode layer 314A and intermediate layer 313A is larger than the area of ​​the bonding interface between bonding layer 311 and intermediate layer 313A.

[0190] Furthermore, for example, in the acoustic wave device according to Modification 6, intermediate layer 313A contains titanium.

[0191] Furthermore, for example, in the elastic wave device according to Modification 6, the angle θ4 formed between the side surface of intermediate layer 323A and the first plane is smaller than the angle θ3 formed between the side surface of main electrode layer 324A and the first plane.

[0192] This increases the exposed area of ​​the side surface of the intermediate layer 323A, thereby preventing the metal components of the bonding layer 321 and the metal components of the main electrode layer 324A from connecting through the side surface of the intermediate layer 323A and alloying (migration).

[0193] Furthermore, for example, in the acoustic wave device according to Modification 6, part of the side surface of main electrode layer 324A is covered with intermediate layer 323A.

[0194] This can further prevent the metal component of the bonding layer 321 and the metal component of the main electrode layer 324A from bonding and forming an alloy (migration).

[0195] Furthermore, for example, in the elastic wave device according to Modification 6, the area of ​​the bonding interface between main electrode layer 324A and intermediate layer 323A is larger than the area of ​​the bonding interface between bonding layer 321 and intermediate layer 323A.

[0196] Furthermore, for example, in the acoustic wave device according to Modification 6, intermediate layer 323A contains titanium.

[0197] Furthermore, for example, in elastic wave device 1, the element with the highest weight ratio among the metal elements constituting bonding layer 321 is the same as the element with the highest weight ratio among the metal elements constituting bonding layer 311.

[0198] This increases the bonding strength between the metal film 32 and the metal film 33, thereby increasing the strength of the support portion.

[0199] For example, in the elastic wave device 1, in a planar view of the main surface 10a, the region of the metal film 31 includes the region of the metal film 32, the region of the intermediate layer 323 includes the region of the bonding layer 321, and the area of ​​the intermediate layer 323 is larger than the area of ​​the bonding layer 321, the region of the main electrode layer 324 includes the region of the intermediate layer 323, and the area of ​​the main electrode layer 324 is larger than the area of ​​the intermediate layer 323, the linear expansion coefficient of the bonding layer 321 is larger than the linear expansion coefficient of the intermediate layer 323, and the linear expansion coefficient of the main electrode layer 324 is larger than the linear expansion coefficient of the bonding layer 321.

[0200] According to this, when the metal films 31 and 32 are heated during compression bonding, the main electrode layer 324, which has a relatively large linear expansion coefficient, has a larger area than the intermediate layer 323 and the bonding layer 321, and therefore the main electrode layer 324 and the intermediate layer 323 have a bimetal structure at their ends. As a result, the main electrode layer 324 and the intermediate layer 323 tend to expand toward the bonding layer 321 at their ends, and both ends of the main electrode layer 324 are pushed up toward the metal film 31, thereby achieving good bonding at the bonding ends of the metal film 32.

[0201] 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.

[0202] This makes it possible to provide a surface acoustic wave device or an XBAR device with improved bonding strength of the support portion.

[0203] For example, in the elastic wave device 1, the substrate 20 has a piezoelectric film 53 including the main surface 20a and a support substrate 51, and when the thickness of the piezoelectric film 53 is d and the electrode finger pitch of the IDT electrode 54 is p, d / p is 0.5 or less.

[0204] This makes it possible to provide an XBAR device with improved bonding strength of the support portion.

[0205] For example, in the elastic wave device 1, the support portion further includes a metal film 33 arranged on the main surface 20a, connected to the functional electrode 34, and in contact with the metal film 32, the metal film 33 including busbar electrodes 62a and 62b, and the hardness of the metal film 33 is higher than the hardness of the metal film 31.

[0206] This allows for a bonding configuration in which metal film 31 encases metal films 32 and 33. This makes it possible to suppress localized heat generation and generation of unwanted particles at the end of the bonding interface, thereby providing elastic wave device 1 with improved bonding strength at the support portion.

[0207] Furthermore, for example, in the acoustic wave device 1, the functional electrode 34 includes, in order from the principal surface 20a, a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68.

[0208] This makes it possible to provide a bulk acoustic wave device with improved bonding strength of the support portion.

[0209] Furthermore, in the acoustic wave device 1, the substrate 10 includes silicon, for example.

[0210] This improves the processing accuracy of the substrate 10 .

[0211] For example, in the elastic wave device 1, 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, and 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.

[0212] 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.

[0213] Furthermore, in the elastic wave device 1 , for example, the region of the metal film 33 includes the region of the metal film 32 in a plan view of the main surface 20 a , and the area of ​​the metal film 33 is larger than the area of ​​the metal film 32 .

[0214] This allows the metal film 32 to avoid restricting the area where the functional electrodes 34 and the metal film 33 are disposed on the main surface 20 a, and prioritizes the layout of the functional electrodes 34 and the metal film 33 .

[0215] While the elastic wave device according to the present invention has been described above with reference to exemplary embodiments, the present invention is not limited to the exemplary embodiments. The present invention also includes various modifications that can be made to the exemplary embodiments without departing from the spirit of the present invention, which modifications would occur to those skilled in the art, as well as various devices incorporating an elastic wave device according to the present invention.

[0216] The features of the acoustic wave device described based on the above embodiment will be described below.

[0217] <1> An elastic wave device comprising: a first substrate having first and second main surfaces opposing each other; a second substrate having a third main surface facing the first main surface; a functional electrode arranged on the third main surface; a support portion arranged between the first main surface and the third main surface such that a space is provided between the first main surface and the third main surface; and via conductors arranged on the first substrate from the first main surface to the second main surface, wherein the support portion has: a first metal film arranged on the first main surface 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; 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; and a hardness of the second metal film is higher than a hardness of the first metal film.

[0218] <2> The acoustic wave device according to <1>, wherein the support portion further includes a third metal film disposed on the third principal surface, connected to the functional electrode, and in contact with the second metal film, and wherein the hardness of the third metal film is higher than the hardness of the first metal film.

[0219] <3> The elastic wave device according to <1> or <2>, wherein the first metal film has, in order from the first main surface side, a first main electrode layer, a first diffusion prevention layer, and a first bonding layer; and the second metal film has, in order from the first main surface side, a second bonding layer, a second diffusion prevention layer, and a second main electrode layer, and the first bonding layer and the second bonding layer are bonded to each other.

[0220] <4> The elastic wave device according to <3>, wherein an angle formed between a side surface of the first diffusion prevention layer and a first plane parallel to the first principal surface is smaller than an angle formed between a side surface of the first main electrode layer and the first plane.

[0221] <5> The acoustic wave device according to <4>, wherein a portion of a side surface of the first main electrode layer is covered with the first diffusion prevention layer.

[0222] <6> The elastic wave device according to <4> or <5>, wherein an area of ​​a bonding interface between the first main electrode layer and the first diffusion prevention layer is larger than an area of ​​a bonding interface between the first bonding layer and the first diffusion prevention layer.

[0223] <7> The acoustic wave device according to any one of <4> to <6>, wherein the first anti-diffusion layer contains titanium.

[0224] <8> The elastic wave device according to any one of <3> to <7>, wherein an angle formed between a side surface of the second diffusion prevention layer and a first plane parallel to the first principal surface is smaller than an angle formed between a side surface of the second main electrode layer and the first plane.

[0225] <9> The acoustic wave device according to <8>, wherein a portion of a side surface of the second main electrode layer is covered with the second diffusion prevention layer.

[0226] <10> The elastic wave device according to <8> or <9>, wherein an area of ​​a bonding interface between the second main electrode layer and the second diffusion prevention layer is larger than an area of ​​a bonding interface between the second bonding layer and the second diffusion prevention layer.

[0227] <11> The acoustic wave device according to any one of <8> to <10>, wherein the second anti-diffusion layer contains titanium.

[0228] <12> The elastic wave device according to any one of <3> to <11>, wherein the element having the highest weight ratio among the metal elements constituting the second bonding layer is the same as the element having the highest weight ratio among the metal elements constituting the first bonding layer.

[0229] <13> The elastic wave device according to any one of <3> to <12>, wherein, in a plan view of the first principal surface, the region of the first metal film includes the region of the second metal film; the region of the second diffusion prevention layer includes the region of the second bonding layer, and the area of ​​the second diffusion prevention layer is larger than the area of ​​the second bonding layer; the region of the second main electrode layer includes the region of the second diffusion prevention layer, and the area of ​​the second main electrode layer is larger than the area of ​​the second diffusion prevention layer; the linear expansion coefficient of the second diffusion prevention layer is larger than the linear expansion coefficient of the second bonding layer; and the linear expansion coefficient of the second main electrode layer is larger than the linear expansion coefficient of the second diffusion prevention layer.

[0230] <14> The elastic wave device according to <1>, wherein the second substrate is piezoelectric; an IDT electrode is arranged on the third main surface; the IDT electrode has: 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 plurality of first electrode fingers; and a second bus bar electrode configured to connect one ends of the plurality of second electrode fingers and arranged to face the first bus bar electrode with the plurality of first electrode fingers and the plurality of second electrode fingers interposed therebetween; and the functional electrode includes the plurality of first electrode fingers and the plurality of second electrode fingers.

[0231] <15> The elastic wave device according to <14>, wherein the second substrate has: a piezoelectric film including the third main surface; and a support substrate; and wherein, where d is a thickness of the piezoelectric film and p is an electrode finger pitch of the IDT electrode, d / p is 0.5 or less.

[0232] <16> The elastic wave device according to <14>, wherein the support portion further includes a third metal film disposed on the third principal surface, connected to the functional electrode, and in contact with the second metal film, the third metal film including the first bus bar electrode and the second bus bar electrode, and the third metal film has a higher hardness than the first metal film.

[0233] <17> The acoustic wave device according to any one of <1> to <13>, wherein the functional electrode includes, in order from the third principal surface, a first planar electrode, a piezoelectric thin film, and a second planar electrode.

[0234] <18> The acoustic wave device according to any one of <1> to <17>, wherein the first substrate includes silicon.

[0235] <19> The elastic wave device according to any one of <1> to <18>, wherein, in a planar view of the first main surface, a region of the first metal film includes a region of the via conductor, and the 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 the area of ​​the second metal film is larger than an area of ​​the via conductor.

[0236] <20> The acoustic wave device according to <2>, wherein, 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.

[0237] The present invention can be widely used as a small-sized acoustic wave device in communication devices such as mobile phones.

[0238] REFERENCE SIGNS LIST 1, 1A Acoustic wave device 10, 20 Substrate 10a, 10b, 20a, 20b Main surface 11 Via conductor 12 Planar electrode 13, 23 Insulating film 31, 31A, 32, 32A, 33, 33A, 531A, 532A Metal film 34 Functional electrode 40 Bump electrode 51 Support substrate 52 Intermediate layer 53 Piezoelectric film 54 IDT electrode 55, 58 Protective layer 57 Piezoelectric single crystal substrate 60 Acoustic wave resonator 60a, 60b Interdigital electrodes 61a, 61b Electrode fingers 62a, 62b Busbar electrodes 65 Support substrate 66 Lower electrode 67 Piezoelectric layer 68 Upper electrode 71, 72 Support portion 160 Gap 311, 321 Bonding layer 312, 313, 313A, 315, 316, 322, 323, 323A, 325, 331, 333, 3131, 3132, 3231, 3232 Intermediate layer 314, 314A, 324, 324A, 332, 542 Main electrode layer 540 Adhesion layer

Claims

1. An elastic wave device comprising: a first substrate having first and second substrates opposed to each other; a second substrate having a third substrate facing the first substrate; a functional electrode disposed on the third substrate; a support portion disposed between the first substrate and the third substrate such that a space is provided between the first substrate and the third substrate; and a via conductor disposed on the first substrate from the first substrate to the second substrate, wherein the support portion has: a first metal film disposed on the first substrate and in contact with the via conductor; and a second metal film disposed 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 second metal film, the area of ​​the first metal film is larger than the area of ​​the second metal film, and the hardness of the second metal film is greater than the hardness of the first metal film.

2. The elastic wave device according to claim 1, wherein 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 hardness of the third metal film being greater than the hardness of the first metal film.

3. An elastic wave device as described in claim 1 or 2, wherein the first metal film has, in order from the first main surface side, a first main electrode layer, a first diffusion prevention layer, and a first bonding layer; and the second metal film has, in order from the first main surface side, a second bonding layer, a second diffusion prevention layer, and a second main electrode layer, and the first bonding layer and the second bonding layer are bonded to each other.

4. The elastic wave device according to claim 3, wherein an angle between a side of the first diffusion prevention layer and a first plane parallel to the first principal surface is smaller than an angle between a side of the first main electrode layer and the first plane.

5. The acoustic wave device according to claim 4, wherein a portion of a side surface of the first main electrode layer is covered with the first diffusion prevention layer.

6. The elastic wave device according to claim 4 or 5, wherein an area of ​​a bonding interface between the first main electrode layer and the first diffusion prevention layer is larger than an area of ​​a bonding interface between the first bonding layer and the first diffusion prevention layer.

7. The acoustic wave device according to claim 4, wherein the first anti-diffusion layer contains titanium.

8. An elastic wave device according to any one of claims 3 to 7, wherein an angle between a side of the second diffusion prevention layer and a first plane parallel to the first principal surface is smaller than an angle between a side of the second main electrode layer and the first plane.

9. The acoustic wave device according to claim 8, wherein a portion of a side surface of the second main electrode layer is covered with the second diffusion prevention layer.

10. The elastic wave device according to claim 8 or 9, wherein an area of ​​a bonding interface between the second main electrode layer and the second diffusion prevention layer is larger than an area of ​​a bonding interface between the second bonding layer and the second diffusion prevention layer.

11. The acoustic wave device according to claim 8, wherein the second anti-diffusion layer contains titanium.

12. An elastic wave device according to any one of claims 3 to 11, wherein the element having the highest weight ratio among the metal elements constituting the second bonding layer is the same as the element having the highest weight ratio among the metal elements constituting the first bonding layer.

13. The elastic wave device according to any one of claims 3 to 12, wherein, in a planar view of the first principal surface, the region of the first metal film includes the region of the second metal film, the region of the second diffusion prevention layer includes the region of the second bonding layer, and the area of ​​the second diffusion prevention layer is larger than the area of ​​the second bonding layer, the region of the second main electrode layer includes the region of the second diffusion prevention layer, and the area of ​​the second main electrode layer is larger than the area of ​​the second diffusion prevention layer, the linear expansion coefficient of the second bonding layer is larger than the linear expansion coefficient of the second diffusion prevention layer, and the linear expansion coefficient of the second main electrode layer is larger than the linear expansion coefficient of the second bonding layer.

14. The elastic wave device of claim 1, wherein the second substrate is piezoelectric, an IDT electrode is arranged on the third main surface, the IDT electrode having: a plurality of first electrode fingers and a plurality of second electrode fingers arranged parallel to each other; a first busbar electrode configured to connect one ends of the plurality of first electrode fingers; and a second busbar electrode configured to connect one ends of the plurality of second electrode fingers and arranged opposite the first busbar electrode across the plurality of first electrode fingers and the plurality of second electrode fingers, and the functional electrode includes the plurality of first electrode fingers and the plurality of second electrode fingers.

15. The elastic wave device according to claim 14, wherein the second substrate has a piezoelectric film including the third main surface and a support substrate, and wherein d / p is 0.5 or less, where d is a thickness of the piezoelectric film and p is an electrode finger pitch of the IDT electrode.

16. The elastic wave device of claim 14, wherein 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 including the first bus bar electrode and the second bus bar electrode, and the hardness of the third metal film is higher than the hardness of the first metal film.

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

18. The acoustic wave device according to any one of claims 1 to 17, wherein the first substrate includes silicon.

19. An elastic wave device as described in any one of claims 1 to 18, wherein, in a planar 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, 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.

20. The elastic wave device according to claim 2, wherein, in a planar view of the third principal 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.

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