Elastic wave device

Abstract

An elastic wave device (1) comprises: a mounting substrate (90) having main surfaces (90a and 90b) opposite each other; a support substrate (10) having a main surface (10a) that faces the main surface (90a) and a main surface (10b) opposite the main surface (10a); an elastic wave resonator (30) which includes a piezoelectric layer (31) and a functional electrode and which is supported on the support substrate (10) so as to face the main surface (10a) across a gap (40); and an encapsulating member (21) disposed to cover the main surface (10b). An unevenness amount Td, which is the difference between the maximum value and the minimum value of the thickness of the encapsulating member (21) on the main surface (10b), is greater than the thickness of the piezoelectric layer (31).

Description

Elastic Wave Device

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

[0002] Patent Document 1 discloses an FBAR duplexer element (elastic wave device) that includes a film bulk acoustic resonator (FBAR) chip in which a (supporting) substrate, an air gap (void), and a piezoelectric layer are sequentially laminated, a PCB substrate (mounting substrate) on which the FBAR chip is mounted, and a molding portion (sealing member) that is arranged to cover the FBAR chip.

[0003] Japanese Patent Application Laid-Open No. 2005-110199

[0004] However, when the acoustic wave device disclosed in Patent Document 1 is subjected to a drop impact, stress generated in the piezoelectric layer of the FBAR chip may cause cracks in the piezoelectric layer.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an acoustic wave device in which the occurrence of cracks due to a drop impact is suppressed.

[0006] In order to achieve the above-mentioned object, an elastic wave device according to one embodiment of the present invention comprises a mounting substrate having a first main surface and a second main surface facing each other, a support substrate having a third main surface facing the first main surface and a fourth main surface facing the third main surface, an elastic wave resonator including a piezoelectric layer and a functional electrode and supported on the support substrate so as to face the third main surface across a gap, and a first sealing member arranged to cover the fourth main surface, wherein a first unevenness amount, which is the difference between the maximum and minimum thicknesses of the first sealing member on the fourth main surface, is greater than the thickness of the piezoelectric layer.

[0007] According to the present invention, it is possible to provide an acoustic wave device in which the occurrence of cracks due to a drop impact is suppressed.

[0008] FIG. 1 is a cross-sectional view of an elastic wave device according to an embodiment. FIG. 2A is a cross-sectional view of a portion of an elastic wave chip according to an embodiment. FIG. 2B is a plan view of a portion of an elastic wave chip according to an embodiment. FIG. 3 is a graph showing the relationship between a first unevenness amount and stress generated in a piezoelectric layer of an elastic wave device according to an embodiment. FIG. 4 is a cross-sectional view of a portion of an elastic wave chip according to a first modification of the embodiment. FIG. 5 is a cross-sectional view of a portion of an elastic wave chip according to a second modification of the embodiment. FIG. 6 is a cross-sectional view of an elastic wave device according to a third modification of the embodiment.

[0009] 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.

[0010] 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.

[0011] In the circuit configurations of the present disclosure, "connected" includes not only direct connection by connection terminals 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.

[0012] 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.

[0013] In addition, in this disclosure, 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 present in any one of single crystal, polycrystalline, and amorphous states, or in a mixture of these states.

[0014] Furthermore, in the present disclosure, "Layer A (or component A) is disposed on the main surface C of Layer B" includes not only Layer A (or component A) being disposed in contact with the main surface C of Layer B, but also Layer A (or component A) being disposed above main surface C without contacting main surface C (for example, Layer A (or component A) being stacked on another layer that is disposed in contact with main surface C).

[0015] 1 is a cross-sectional view of an elastic wave device 1 according to an embodiment. As shown in the figure, the elastic wave device 1 includes a mounting substrate 90, a support substrate 10, an elastic wave resonator 30, sealing members 21 and 22, and electrodes 11, 80, 91, and 92. The support substrate 10, the elastic wave resonator 30, and the electrode 11 form an elastic wave chip 1a.

[0016] The mounting substrate 90 has opposing main surfaces 90a (first main surface) and 90b (second main surface), and is a substrate on which the acoustic wave chip 1a is mounted.

[0017] The mounting substrate 90 may be, for example, a low temperature co-fired ceramics (LTCC) substrate having a laminated structure of multiple dielectric layers, a high temperature co-fired ceramics (HTCC) substrate, a component-embedded substrate, a substrate having a redistribution layer (RDL), or a printed circuit board.

[0018] The mounting substrate 90 includes an electrode 91 arranged on a principal surface 90a and an electrode 92 arranged on a principal surface 90b. The electrode 91 is connected to the electrode 11 of the acoustic wave chip 1a via an electrode 80. The electrode 80 is, for example, a solder bump or a gold (Au) bump. The electrode 92 is connected to an electrode on a motherboard on which the acoustic wave device 1 is mounted.

[0019] Support substrate 10 has principal surfaces 10a (third principal surface) and 10b (fourth principal surface) facing each other, and is a substrate that supports acoustic wave resonator 30. Principal surface 10a faces principal surface 90a with a space therebetween.

[0020] The support substrate 10 can be made of a material whose main component is at least one of silicon, sapphire, spinel, quartz, gallium arsenide, aluminum nitride, alumina, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, silicon oxide, sialon, silicon oxynitride, diamond, and diamond-like carbon.

[0021] The sealing member 21 is an example of a first sealing member and is arranged to cover the main surface 10b. The sealing member 21 can prevent the resin member 22 and other materials from entering the space between the main surface 10a and the main surface 90a.

[0022] When principal surfaces 10a and 90a are viewed in plan, a dam member may be provided in the outer circumferential region of the space between principal surfaces 10a and 90a. This prevents sealing member 21 from entering the space, which is advantageous for miniaturizing elastic wave device 1. The dam member may be disposed on either the principal surface 10a side of the outer circumferential region or the principal surface 90a side of the outer circumferential region.

[0023] The sealing member 22 is an example of a second sealing member, and is arranged to cover the sealing member 21. The sealing member 22 can protect the acoustic wave chip 1a from the external environment and improve moisture resistance.

[0024] Each of the sealing members 21 and 22 includes, for example, a resin. Examples of the resin included in the sealing members 21 and 22 include epoxy, acrylic, or polyimide. The sealing member 21 may include, for example, a laminating resin. Furthermore, at least one of the sealing members 21 and 22 does not have to be a resin. For example, the sealing member 21 may be an insulator or a resin, and the sealing member 22 may be a shield electrode layer.

[0025] Next, the structure of the acoustic wave chip 1a will be described. FIG. 2A is a cross-sectional view showing a portion of the acoustic wave chip 1a according to the embodiment. FIG. 2B is a plan view showing a portion of the acoustic wave chip 1a according to the embodiment. FIG. 2A is an enlarged cross-sectional view of region X in FIG. 1, and is also a cross-sectional view taken along line IIA-IIA in FIG. 2B. As shown in FIGS. 2A and 2B, the acoustic wave chip 1a includes a support substrate 10, an acoustic wave resonator 30, and intermediate layers 51 and 52.

[0026] The acoustic wave resonator 30 includes a piezoelectric layer 31 and an IDT (InterDigital Transducer) electrode 60, and is supported by the support substrate 10 so as to face the main surface 10a with a gap 40 interposed therebetween.

[0027] When the main surface 10a of the piezoelectric layer 31 is viewed from above, the ends of the piezoelectric layer 31 are supported by the intermediate layers 51 and 52 and the support substrate 10, and the center of the piezoelectric layer 31 in the above-mentioned planar view faces the main surface 10a across a gap 40. The gap 40 is an example of an acoustic reflecting portion. This structure allows the piezoelectric layer 31 to vibrate in an elastic wave manner specific to the piezoelectric layer 31.

[0028] The piezoelectric layer 31 includes, for example, at least one of lithium niobate, lithium tantalate, quartz crystal, potassium nitride, aluminum nitride, scandium aluminum nitride, zinc oxide, and magnesium zinc oxide.

[0029] The piezoelectric layer 31 may have a structure in which two piezoelectric films containing different piezoelectric materials are bonded together, or in which two piezoelectric films having different cut angles are bonded together, or in which a piezoelectric film containing a piezoelectric material is bonded together with a non-piezoelectric film such as an insulating film.

[0030] The IDT electrode 60 is included in the functional electrodes and is disposed on the principal surface of the piezoelectric layer 31 as shown in FIG. 2B. When the principal surface 10a is viewed in plan as shown in FIG. 2A, the IDT electrode 60 overlaps with the gap 40. The IDT electrode 60 has a plurality of electrode fingers 61a and a plurality of electrode fingers 61b, and busbar electrodes 62a and 62b. The plurality of electrode fingers 61a are disposed parallel to one another. The plurality of electrode fingers 61b are disposed parallel to one another. The plurality of electrode fingers 61a and the plurality of electrode fingers 61b are disposed parallel to one another so as to be interdigitated with one another.

[0031] The busbar electrode 62a is configured to connect one ends of the electrode fingers 61a to each other, and extends in a direction (x-axis direction) intersecting the extension direction of the electrode fingers 61a (y-axis direction in FIG. 2B ).

[0032] The busbar electrode 62b is configured to connect one ends of the electrode fingers 61b to each other. The busbar electrode 62b extends in a direction (x-axis direction) intersecting the extension direction of the electrode fingers 61b (y-axis direction in FIG. 2B ). The busbar electrodes 62a and 62b are arranged opposite each other with the electrode fingers 61a and 61b sandwiched between them. The other ends of the electrode fingers 61a face the busbar electrode 62b, and the other ends of the electrode fingers 61b face the busbar electrode 62a.

[0033] The reflecting electrodes 65 are arranged on both sides of the IDT electrode 60 so as to be adjacent to the IDT electrode 60 in a direction perpendicular to the extension direction of the electrode fingers 61 a and the electrode fingers 61 b ​​(x-axis direction). Note that the reflecting electrodes 65 may not be provided in the acoustic wave device 1.

[0034] A dielectric film or an insulating film may be disposed between the IDT electrode 60 and the main surface of the piezoelectric layer 31, and so as to cover the IDT electrode 60. The insulating film may contain, for example, at least one of silicon oxide, silicon nitride, and silicon oxynitride. The insulating film may also be made of a material such as tantalum pentoxide, amorphous silicon, polycrystalline silicon, aluminum oxide, aluminum nitride, or silicon carbide, or may be a laminate film of these materials.

[0035] An IDT electrode may also be disposed on the principal surface of the piezoelectric layer 31 facing the principal surface 10a.

[0036] The IDT electrode 60 and the reflective electrode 65 shown in FIG. 2B are intended to illustrate a typical structure of the acoustic wave resonator 30, and the number and length of the electrode fingers constituting the IDT electrode 60 and the reflective electrode 65 are not limited to these. For example, the IDT electrode 60 may have a piston structure. Specifically, a difference in acoustic velocity between the central portion and the tip portion of the electrode finger may be created by thickening the tip portion of the electrode finger (2D piston) or by arranging a load film at the tip portion of the electrode finger (3D piston). This makes it possible to suppress transverse mode ripples generated in the acoustic wave resonator 30. Furthermore, for example, the IDT electrode 60 may include a so-called withdrawal electrode.

[0037] The IDT electrode 60 has a layered structure of titanium (Ti), aluminum (Al), and titanium (Ti). However, the IDT electrode 60 is not limited to the above layered structure, and may be made of a material containing at least one of copper (Cu), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), and chromium (Cr), or an alloy or layered film containing some of these metals.

[0038] The intermediate layer 51 is disposed on the main surface 10a, and has a gap 40. The intermediate layer 52 is disposed on the intermediate layer 51 and is bonded to an end of the piezoelectric layer 31.

[0039] The intermediate layers 51 and 52 include, for example, at least one of silicon oxide, silicon oxynitride, glass, lithium oxide, tantalum pentoxide, silicon nitride, aluminum nitride, and aluminum oxide.

[0040] The intermediate layers 51 and 52 may be omitted. In that case, the support substrate 10 may have the gap 40 therein, and the piezoelectric layer 31 may be directly supported by the support substrate 10 .

[0041] The electrode 11 is disposed on the piezoelectric layer 31, the support substrate 10, and the intermediate layer 52, and is connected to the IDT electrode 60. The electrode 11 includes busbar electrodes 62a and 62b. The electrode 11 includes connection wiring that connects different IDT electrodes 60 together. The electrode 11 also includes connection wiring that connects the IDT electrodes 60 to electrodes 91 on the mounting substrate 90. Note that the thickness of the connection wiring in the electrode 11 may be greater than the thickness of the busbar electrodes 62a and 62b. This can reduce wiring loss of high-frequency signals.

[0042] According to the above-described configuration of the acoustic wave chip 1a, the acoustic wave resonator 30 has a membrane structure supported on the support substrate 10 with the gap 40 sandwiched therebetween, thereby constituting a laterally excited film bulk acoustic resonator (XBAR).

[0043] If the thickness of the piezoelectric layer 31 is Tm (see FIG. 2A ) and the electrode finger pitch of the IDT electrode 60 is p, it is desirable that the normalized thickness Tm / p be 0.5 or less. This increases the relative bandwidth of the acoustic wave resonator 30, resulting in a resonator with a high electromechanical coupling coefficient. The electrode finger pitch p is defined as (L+S), where L is the line width of the electrode fingers 61 a and 61 b, and S is the space width between adjacent electrode fingers 61 a and 61 b.

[0044] Although the elastic wave device 1 according to the present embodiment includes one elastic wave chip 1 a, the elastic wave device according to the present invention may include multiple elastic wave chips, and may have a structure in which, for example, multiple elastic wave chips 1 a are collectively sealed with sealing members 21 and 22. The elastic wave device according to the present invention may also include chips constituting circuit components such as capacitors, inductors, and ICs in addition to the elastic wave chip, and may have a structure in which, for example, the elastic wave chip 1 a and at least one of the capacitor, inductor, and IC are mounted on a mounting substrate 90 and collectively sealed with sealing members 21 and 22.

[0045] 1 , in elastic wave device 1 according to this embodiment, the thickness of sealing member 21 in the z-axis direction varies depending on the position on principal surface 10b. That is, unevenness amount Td (first unevenness amount), which is the difference between the maximum and minimum thicknesses of sealing member 21 on principal surface 10b, is greater than thickness Tm of piezoelectric layer 31.

[0046] More specifically, when the main surface 10b is viewed in plan, the sealing member 21 has a central region including the center of the main surface 10b and an outer edge region including the periphery of the main surface 10b, and the thickness of the sealing member 21 in the outer edge region is smaller than the thickness of the sealing member 21 in the central region. Furthermore, the thickness of the sealing member 21 monotonically decreases from the point where the thickness of the sealing member 21 is maximum to the point where the thickness of the sealing member 21 is minimum.

[0047] Here, an elastic wave device according to a comparative example is compared with the elastic wave device 1 according to an embodiment. The elastic wave device according to the comparative example differs from the elastic wave device 1 according to the embodiment only in the structure of the sealing member. In the elastic wave device according to the comparative example, the two sealing members covering main surface 10b each have a uniform thickness on main surface 10b.

[0048] When the elastic wave device according to the comparative example is dropped and, for example, the top surface (the exposed surface of the sealing member) of the elastic wave device comes into contact with the ground while parallel to the ground, the impact energy of the drop is transmitted from the resin member to the elastic wave resonators and converted into vibration energy of the elastic wave resonators, which then applies stress to the piezoelectric layer, causing cracks in the minute elastic wave resonators.

[0049] The inventors have found a problem in that when an elastic wave device including an elastic wave resonator having the above structure is dropped and subjected to an impact, cracks occur in the elastic wave resonator due to the structure of the elastic wave device.

[0050] In contrast, when the elastic wave device 1 according to the embodiment is dropped and, for example, the top surface of the elastic wave device 1 (the exposed surface of the sealing member 22) comes into contact with the ground, the sealing member 21 has a thickness distribution on the main surface 10b, and therefore the main surface 10b has an elastic modulus distribution. Therefore, when the elastic wave device 1 comes into contact with the ground, at least a portion of the impact energy is converted into transfer energy near the sealing members 21 and 22 of the elastic wave device 1 (warping and deflection near the top surface of the elastic wave chip 1a). As a result, the proportion of the impact energy converted into vibration energy of the elastic wave resonator 30 is lower than in the elastic wave device according to the comparative example. Therefore, when the elastic wave device 1 is dropped, the impact energy caused by the drop is prevented from being transmitted to the elastic wave resonator 30, thereby preventing cracks from occurring due to the drop impact.

[0051] 3 is a graph showing the relationship between the unevenness Td of the elastic wave device 1 according to the embodiment and the stress generated in the elastic wave resonator 30. The graph shows the results of a simulation of the relationship between the unevenness Td and the stress generated in the elastic wave resonator 30 when the elastic wave device 1 according to the embodiment is dropped from its top surface to the ground. Note that the stress (%) on the vertical axis represents a relative value when the stress generated in the elastic wave resonator of the elastic wave device according to the comparative example is set to 100%.

[0052] 3 , it can be seen that in the elastic wave device 1 according to the embodiment, as the unevenness amount Td increases, the stress decreases. In particular, when the thickness Tm of the piezoelectric layer 31 is 1 μm, the unevenness amount Td at which the stress reduction effect becomes significant is 1 μm, and the stress reduction effect is significant when the unevenness amount Td is greater than the thickness Tm of the piezoelectric layer 31.

[0053] It is desirable that sealing member 21 and sealing member 22 are made of different materials or compositions. This allows sealing members 21 and 22 to have different elastic moduli, which increases the rate at which impact energy when elastic wave device 1 comes into contact with the ground is converted into movement energy near sealing members 21 and 22. This further reduces the occurrence of cracks in elastic wave device 1 due to a drop impact.

[0054] Alternatively, the sealing member 21 may include a first base material and a first filler, and the sealing member 22 may include a second base material and a second filler. Examples of materials for the first filler and the second filler include, but are not limited to, silica and alumina.

[0055] Here, the concentration of the first filler may be different from the concentration of the second filler. Alternatively, the material of the first filler may be different from the material of the second filler. Alternatively, the particle diameter of the first filler may be different from the particle diameter of the second filler. For example, even if the material of the first base material is the same as the material of the second base material and no clear boundary surface can be observed between the sealing member 21 and the sealing member 22, it is sufficient that the filler particle diameter or the filler addition concentration gradually changes between the sealing member 21 and the sealing member 22.

[0056] Alternatively, the first substrate and the second substrate may be made of different materials. This allows the sealing members 21 and 22 to have different elastic moduli, thereby increasing the rate at which impact energy when the elastic wave device 1 comes into contact with the ground is converted into movement energy near the sealing members 21 and 22. This further reduces the risk of cracks occurring in the elastic wave device 1 due to a drop impact.

[0057] Furthermore, the second unevenness amount, which is the difference between the maximum and minimum values ​​of the total thickness of the sealing members 21 and 22 on the main surface 10 b, is smaller than the thickness of the support substrate 10 .

[0058] This makes it possible to suppress unevenness on the top surface of the elastic wave device 1 even when the elastic wave device 1 has multiple elastic wave chips 1a, thereby suppressing errors, for example, when picking up the elastic wave device 1 with a collet or suction nozzle during the manufacturing process.

[0059] Note that elastic wave device 1 according to this preferred embodiment does not necessarily have to include sealing member 22. That is, elastic wave device 1 may include only one sealing member 21 as a sealing member.

[0060] With this, for example, when the top surface (exposed surface of the sealing member 21) of the elastic wave device 1 comes into contact with the ground, the sealing member 21 has a thickness distribution on the main surface 10 b, and therefore has an elastic modulus distribution on the main surface 10 b. Therefore, when the elastic wave device 1 falls, the impact energy caused by the fall is prevented from being transmitted to the elastic wave resonator 30, and cracks in the elastic wave resonator 30 due to the impact of the fall can be prevented.

[0061] In an elastic wave device according to a preferred embodiment of the present invention, the thickness distribution of sealing member 21 is not limited to a monotonically decreasing thickness distribution from the central region to the outer edge region, as in elastic wave device 1 according to the preferred embodiment. The thickness may be increasing from the central region to the outer edge region, or may have multiple maximum thickness points between the central region and the outer edge region. Furthermore, the thickness may be decreasing or increasing from one end of the outer edge region to the other.

[0062] [2 Configuration of Elastic Wave Chip 1b According to Modification 1] The elastic wave resonators included in the elastic wave device according to the present invention are not limited to XBARs and may be FBARs. The elastic wave device according to Modification 1 includes a mounting substrate 90, an elastic wave chip 1b, sealing members 21 and 22, and electrodes 80, 91, and 92. The elastic wave device according to this modification differs from the elastic wave device 1 according to the embodiment only in that the elastic wave chip 1a is replaced with an elastic wave chip 1b. Therefore, in the following, a description of the same configuration as that of the elastic wave device 1 according to the embodiment will be omitted, and only the elastic wave chip 1b, which has a different configuration, will be described.

[0063] 4 is a cross-sectional view showing a part of an acoustic wave chip 1b according to Modification 1 of the embodiment, which corresponds to an enlarged cross-sectional view of region X in FIG.

[0064] The support substrate 10 has principal surfaces 10a (third principal surface) and 10b (fourth principal surface) facing each other, and supports the acoustic wave resonator 30A. The principal surface 10a faces the principal surface 90a with a space therebetween.

[0065] As shown in FIG. 4, the acoustic wave chip 1 b includes a support substrate 10 , an acoustic wave resonator 30A, and an intermediate layer 51 .

[0066] The acoustic wave resonator 30A includes a piezoelectric layer 31A and planar electrodes 12 and 13, and is supported by the support substrate 10 so as to face the main surface 10a with a gap 40 interposed therebetween.

[0067] When the main surface 10a of the piezoelectric layer 31A is viewed from above, the ends of the piezoelectric layer 31A are supported by the intermediate layer 51 and the support substrate 10, and the center of the piezoelectric layer 31A in the above-mentioned planar view faces the main surface 10a across the gap 40. This structure allows the piezoelectric layer 31A to generate elastic wave vibrations that are specific to the piezoelectric layer 31A.

[0068] The piezoelectric layer 31A includes, for example, at least one of lithium niobate, lithium tantalate, quartz crystal, potassium nitride, aluminum nitride, scandium aluminum nitride, zinc oxide, and magnesium zinc oxide.

[0069] The piezoelectric layer 31A may have a structure in which two piezoelectric films containing different piezoelectric materials are bonded together, or in which two piezoelectric films having different cut angles are bonded together, or in which a piezoelectric film containing a piezoelectric material is bonded together with a non-piezoelectric film such as an insulating film.

[0070] The planar electrode 12 (first planar electrode) and the planar electrode 13 (second planar electrode) are included in the functional electrodes and are arranged to sandwich the piezoelectric layer 31A. The planar electrode 12, the piezoelectric layer 31A, and the planar electrode 13 are arranged in this order from the main surface 10a toward the main surface 90a.

[0071] The intermediate layer 51 is disposed on the main surface 10a, and has a gap 40. The intermediate layer 51 includes at least one of silicon oxide, silicon oxynitride, glass, lithium oxide, tantalum pentoxide, silicon nitride, aluminum nitride, and aluminum oxide, for example. The intermediate layer 51 may be omitted, in which case a gap is provided in the support substrate 10, and the piezoelectric layer 31A is directly supported by the support substrate 10.

[0072] According to the above-described configuration of the acoustic wave chip 1b, the acoustic wave resonator 30A has a membrane structure supported by the support substrate 10 with the gap 40 sandwiched therebetween, thereby constituting an FBAR.

[0073] Although the acoustic wave device according to this modification includes one acoustic wave chip 1b, the acoustic wave device according to the present invention may include multiple acoustic wave chips, and may have a structure in which, for example, multiple acoustic wave chips 1b are collectively sealed with sealing members 21 and 22. Furthermore, the acoustic wave device according to the present invention may include chips constituting circuit components such as capacitors, inductors, and ICs in addition to the acoustic wave chip, and may have a structure in which, for example, acoustic wave chip 1b and at least one of the capacitor, inductor, and IC are mounted on mounting substrate 90 and collectively sealed with sealing members 21 and 22.

[0074] In the elastic wave device according to this modification, the thickness of sealing member 21 in the z-axis direction varies depending on the position on principal surface 10b. That is, unevenness amount Td (first unevenness amount), which is the difference between the maximum and minimum thicknesses of sealing member 21 on principal surface 10b, is greater than thickness Tm of piezoelectric layer 31A.

[0075] This reduces the rate at which impact energy when the elastic wave device comes into contact with the ground is converted into vibration energy of the elastic wave resonator 30A. Therefore, if the elastic wave device falls, the impact energy caused by the fall is prevented from being transmitted to the elastic wave resonator 30A, thereby preventing cracks from occurring due to the impact of the fall.

[0076] [3 Configuration of Acoustic Wave Chip 1c According to Modification 2] Note that in an acoustic wave resonator included in an acoustic wave device according to the present invention, an acoustic multilayer film 41 may be disposed in place of the gap 40, which is an example of an acoustic reflecting portion. The acoustic wave device according to Modification 2 includes a mounting substrate 90, an acoustic wave chip 1c, sealing members 21 and 22, and electrodes 91 and 92. The acoustic wave device according to this modification differs from the acoustic wave device 1 according to the embodiment only in that the acoustic wave chip 1a is replaced with an acoustic wave chip 1c. Therefore, in the following, a description of the same configuration as that of the acoustic wave device 1 according to the embodiment will be omitted, and only the acoustic wave chip 1c, which has a different configuration, will be described.

[0077] 5 is a cross-sectional view showing a part of an acoustic wave chip 1c according to Modification 2 of the embodiment, which corresponds to an enlarged cross-sectional view of region X in FIG.

[0078] The support substrate 10 is a substrate that supports the acoustic wave resonator 30C. The main surface 10a faces the main surface 90a with a space therebetween.

[0079] 5, the acoustic wave chip 1c includes a support substrate 10, an acoustic wave resonator 30C, and an electrode 11. The acoustic wave chip 1c according to this modification differs from the acoustic wave chip 1a according to the embodiment only in that the gap 40 is replaced with an acoustic multilayer film 41. Therefore, in the following, a description of the same components as those of the acoustic wave chip 1a according to the embodiment will be omitted, and only the acoustic multilayer film 41, which is a different component, will be described.

[0080] The elastic wave resonator 30C includes a piezoelectric layer 31 and an IDT electrode 60, and is supported by the support substrate 10 so as to face the main surface 10a with the acoustic multilayer film 41 interposed therebetween.

[0081] When the main surface 10a of the piezoelectric layer 31 is viewed in a plane, the ends of the piezoelectric layer 31 are supported by the intermediate layers 51, 52 and the support substrate 10, and the central portion of the piezoelectric layer 31 in the above plane view faces the main surface 10a across the acoustic multilayer film 41.

[0082] The acoustic multilayer film 41 is an example of an acoustic reflecting portion, and has a structure in which low acoustic impedance layers 41 a and high acoustic impedance layers 41 b are alternately stacked. With this structure, the acoustic wave resonator 30C constitutes an SMR (Solidly Mounted Resonator) type surface acoustic wave resonator, and utilizes Bragg reflection by the acoustic multilayer film 41 to confine surface acoustic waves below the acoustic multilayer film 41 (in the negative z-axis direction).

[0083] This reduces the rate at which impact energy when the elastic wave device comes into contact with the ground is converted into vibration energy of the elastic wave resonator 30C. Therefore, if the elastic wave device is dropped, the impact energy caused by the drop is prevented from being transmitted to the elastic wave resonator 30C, thereby preventing cracks from occurring due to the drop impact.

[0084] 6 is a cross-sectional view of an elastic wave device 2 according to Modification 3 of the embodiment. As shown in the figure, the elastic wave device 2 includes a mounting substrate 90, a support substrate 10, an elastic wave resonator 30, sealing members 21A and 22A, and electrodes 11, 80, 91, and 92. The support substrate 10, the elastic wave resonator 30, and the electrode 11 form an elastic wave chip 1a. The elastic wave device 2 according to this modification differs from the elastic wave device 1 according to the embodiment only in the configurations of the sealing members 21A and 22A. Therefore, the following description of the elastic wave device 2 according to this modification will omit a description of the same configuration as the elastic wave device 1 according to the embodiment and will focus on the different configurations, i.e., the sealing members 21A and 22A.

[0085] The sealing member 22A is an example of a first sealing member in this modification, and is arranged to cover the main surface 10b. The sealing member 22A can protect the acoustic wave chip 1a from the external environment and improve moisture resistance.

[0086] The sealing member 21A is an example of a second sealing member in this modification, and is disposed between the main surface 10b and the sealing member 22A. The sealing member 21A can prevent the resin member 22A and other materials from entering the space sandwiched between the main surface 10a and the main surface 90a.

[0087] When the principal surfaces 10a and 90a are viewed in plan, a dam member may be provided in the outer circumferential region of the space between the principal surfaces 10a and 90a. This prevents the sealing member 21A from entering the space, which is advantageous for miniaturizing the elastic wave device 2. The dam member may be disposed on either the principal surface 10a side of the outer circumferential region or the principal surface 90a side of the outer circumferential region.

[0088] Each of the sealing members 21A and 22A includes, for example, a resin. Examples of the resin included in the sealing members 21A and 22A include epoxy, acrylic, or polyimide. The sealing member 21A may include, for example, a laminating resin. Furthermore, at least one of the sealing members 21A and 22A does not have to be a resin. For example, the sealing member 21A may be an insulator or a resin, and the sealing member 22A may be a shield electrode layer.

[0089] 6 , in the elastic wave device 2 according to this modification, the thickness of the sealing member 22A in the z-axis direction varies depending on the position on the principal surface 10b. That is, the unevenness amount Td (first unevenness amount), which is the difference between the maximum and minimum thicknesses of the sealing member 22A on the principal surface 10b, is greater than the thickness Tm of the piezoelectric layer 31.

[0090] More specifically, when the main surface 10b is viewed in plan, the sealing member 22A has a central region including the center of the main surface 10b and an outer edge region including the periphery of the main surface 10b, and the thickness of the sealing member 22A in the outer edge region is smaller than the thickness of the sealing member 22A in the central region. Furthermore, the thickness of the sealing member 22A monotonically decreases from the point where the thickness of the sealing member 22A is maximum to the point where the thickness of the sealing member 22A is minimum.

[0091] Here, the elastic wave device according to the comparative example is compared with the elastic wave device 2 according to this modification. If the elastic wave device according to the comparative example is dropped and, for example, the top surface (the exposed surface of the sealing member) of the elastic wave device comes into contact with the ground while parallel to the ground, the impact energy of the drop is transmitted from the resin member to the elastic wave resonator and converted into vibration energy of the elastic wave resonator having the above-described structure. This vibration energy applies stress to the piezoelectric layer. This stress can cause cracks in the minute elastic wave resonators.

[0092] In contrast, when the elastic wave device 2 according to this modification is dropped and, for example, the top surface of the elastic wave device 2 (the exposed surface of the sealing member 22A) comes into contact with the ground, the sealing member 22A has a thickness distribution on the main surface 10b, and therefore a modulus of elasticity distribution on the main surface 10b. Therefore, the impact energy generated when the elastic wave device 2 comes into contact with the ground is at least partially converted into transfer energy (warping and bending near the top surface of the elastic wave chip 1a) near the sealing members 21A and 22A of the elastic wave device 2. As a result, the proportion of the impact energy converted into vibration energy of the elastic wave resonator 30 is lower than in the elastic wave device according to the comparative example. Therefore, when the elastic wave device 2 is dropped, the impact energy caused by the drop is prevented from being transmitted to the elastic wave resonator 30, thereby preventing cracks from occurring in the elastic wave resonator 30 due to the drop impact.

[0093] In the elastic wave device 2 according to this modification, the unevenness amount Td is greater than the thickness Tm of the piezoelectric layer 31. This increases the effect of reducing stress in the elastic wave resonator 30.

[0094] It is desirable that sealing member 21A and sealing member 22A be made of different materials or compositions. This allows sealing members 21A and 22A to have different elastic moduli, which increases the rate at which impact energy when elastic wave device 2 comes into contact with the ground is converted into movement energy near sealing members 21A and 22A. This further reduces the occurrence of cracks in elastic wave device 2 due to the impact of being dropped.

[0095] Alternatively, the sealing member 21A may include a second base material and a second filler, and the sealing member 22A may include a first base material and a first filler. Examples of materials for the first filler and the second filler include, but are not limited to, silica and alumina.

[0096] Here, the concentration of the first filler may be different from the concentration of the second filler. Alternatively, the material of the first filler may be different from the material of the second filler. Alternatively, the particle diameter of the first filler may be different from the particle diameter of the second filler. For example, even if the material of the first base material is the same as the material of the second base material and no clear boundary surface can be observed between the sealing member 22A and the sealing member 21A, it is sufficient that the filler particle diameter or the filler addition concentration gradually changes between the sealing member 22A and the sealing member 21A.

[0097] Alternatively, the first substrate and the second substrate may be made of different materials. This allows the sealing members 22A and 21A to have different elastic moduli, thereby increasing the rate at which impact energy when the elastic wave device 2 comes into contact with the ground is converted into movement energy near the sealing members 22A and 21A. This further reduces the risk of cracks occurring in the elastic wave device 2 due to a drop impact.

[0098] Furthermore, a second unevenness amount, which is the difference between the maximum and minimum values ​​of the total thickness of the sealing member 21A and the sealing member 22A on the main surface 10b, is smaller than the thickness of the support substrate 10.

[0099] This makes it possible to suppress unevenness on the top surface of the elastic wave device 2 even when the elastic wave device 2 has multiple elastic wave chips 1a, thereby suppressing errors, for example, when picking up the elastic wave device 2 with a collet or suction nozzle during the manufacturing process.

[0100] Note that the sealing member 21A does not necessarily have to be provided in the elastic wave device 2 according to this modification. That is, the elastic wave device 2 may include only one sealing member 22A.

[0101] With this, for example, when the top surface (exposed surface of the sealing member 22A) of the elastic wave device 2 comes into contact with the ground, the sealing member 22A has a thickness distribution on the main surface 10b, and therefore has an elastic modulus distribution on the main surface 10b. Therefore, when the elastic wave device 2 falls, the impact energy caused by the fall is prevented from being transmitted to the elastic wave resonator 30, and cracks caused by the fall impact can be prevented.

[0102] In an elastic wave device according to a preferred embodiment of the present invention, the thickness distribution of sealing member 22A is not limited to a monotonically decreasing thickness distribution from the central region to the outer edge region, as in elastic wave device 2 according to this modified example. The thickness may be increasing from the central region to the outer edge region, or may have multiple maximum thickness points between the central region and the outer edge region. Furthermore, the thickness may be decreasing or increasing from one end of the outer edge region to the other.

[0103] Although the elastic wave device 2 according to this modification includes one elastic wave chip 1 a, the elastic wave device according to the present invention may include multiple elastic wave chips, for example, multiple elastic wave chips 1 a may be collectively sealed with sealing members 21 A and 22 A. The elastic wave device according to the present invention may also include chips constituting circuit components such as capacitors, inductors, and ICs in addition to the elastic wave chip, for example, the elastic wave chip 1 a and at least one of the capacitor, inductor, and IC may be mounted on a mounting substrate 90 and collectively sealed with sealing members 21 A and 22 A.

[0104] In the elastic wave device 2 according to this modification, the elastic wave chip 1b according to the first modification may be disposed in place of the elastic wave chip 1a.

[0105] [5. Effects, etc.] As described above, the elastic wave device 1 according to the embodiment includes the mounting substrate 90 having principal surfaces 90a and 90b facing each other, the support substrate 10 having the principal surface 10a facing the principal surface 90a and the principal surface 10b facing the principal surface 10a, the elastic wave resonator 30 including the piezoelectric layer 31 and the functional electrode and supported on the support substrate 10 so as to face the principal surface 10a across the acoustic reflector, and the sealing member 21 arranged to cover the principal surface 10b, in which the unevenness amount Td (first unevenness amount), which is the difference between the maximum and minimum thicknesses of the sealing member 21 on the principal surface 10b, is greater than the thickness of the piezoelectric layer 31.

[0106] This configuration converts at least a portion of the impact energy generated when the elastic wave device 1 falls and hits the ground into movement energy near the top surface of the elastic wave device 1. This reduces the proportion of the impact energy that is converted into vibration energy of the elastic wave resonator 30. Therefore, when the elastic wave device 1 falls, the impact energy generated by the fall is prevented from being transmitted to the elastic wave resonator 30, thereby preventing cracks from occurring due to the impact of the fall.

[0107] In addition, for example, in the elastic wave device 1 , the acoustic reflecting portion is the gap 40 .

[0108] This prevents the impact energy from being transmitted to the acoustic wave resonator 30 when the acoustic wave device 1 is dropped, thereby preventing cracks from occurring due to the impact of the drop.

[0109] Furthermore, for example, in the acoustic wave device according to the second modification, the acoustic reflecting portion is an acoustic multilayer film 41 .

[0110] This prevents the impact energy from being transmitted to the acoustic wave resonator 30C when the acoustic wave device according to the second modification is dropped, thereby preventing cracks from occurring due to the drop impact.

[0111] For example, the elastic wave device 1 according to the embodiment further includes a sealing member 22 arranged to cover the sealing member 21 .

[0112] According to this, by disposing the sealing member 22 that is different from the sealing member 21, it is possible to increase the elastic modulus distribution in the vicinity of the main surface 10b of the acoustic wave chip 1a.

[0113] For example, the elastic wave device 2 according to variant example 3 includes a mounting substrate 90, a support substrate 10, an elastic wave resonator 30 including a piezoelectric layer 31 and a functional electrode, and supported on the support substrate 10 so as to face the main surface 10a across an acoustic reflection portion, a sealing member 22A arranged to cover the main surface 10b, and a sealing member 21A arranged between the main surface 10b and the sealing member 22A, and the unevenness amount Td (first unevenness amount), which is the difference between the maximum and minimum thicknesses of the sealing member 22A on the main surface 10b, is greater than the thickness of the piezoelectric layer 31.

[0114] According to this, when the acoustic wave device 2 falls and hits the ground, the impact energy is at least partially converted into movement energy near the top surface of the acoustic wave device 2. This reduces the rate at which the impact energy is converted into vibration energy of the acoustic wave resonator 30. Therefore, when the acoustic wave device 2 falls, the impact energy caused by the fall is prevented from being transmitted to the acoustic wave resonator 30, thereby preventing cracks from occurring due to the impact of the fall. Furthermore, by disposing the sealing member 21A, which is different from the sealing member 22A, it is possible to increase the elastic modulus distribution near the main surface 10b of the acoustic wave chip 1a.

[0115] For example, in the elastic wave device 1 (2), when the main surface 10b is viewed in a plane, the sealing member 21 (22A) has a central region including the center of the main surface 10b and an outer edge region including the outer periphery of the main surface 10b, and the thickness of the sealing member 21 (22A) in the outer edge region is smaller than the thickness of the sealing member 21 (22A) in the central region.

[0116] This allows the elastic modulus distribution near the main surface 10b of the elastic wave chip 1a to be increased, so that when the elastic wave device 1 (2) is dropped, the impact energy caused by the drop is prevented from being transmitted to the elastic wave resonator 30, thereby preventing cracks from occurring due to the drop impact.

[0117] Furthermore, for example, in the elastic wave device 1 (2), the sealing member 21 (22A) and the sealing member 22 (21A) are made of different materials or have different compositions.

[0118] This allows sealing member 21 (22A) and sealing member 22 (21A) to have different elastic moduli, thereby preventing cracks from occurring due to the impact of dropping elastic wave device 1 (2).

[0119] Furthermore, for example, in the elastic wave device 1 (2), the sealing member 21 (22A) includes a first base material and a first filler, and the sealing member 22 (21A) includes a second base material and a second filler.

[0120] In addition, for example, in the elastic wave device 1 (2), the concentration of the first filler is different from the concentration of the second filler, the material of the first filler is different from the material of the second filler, and the material of the first base material is different from the material of the second base material.

[0121] This allows the elastic modulus of sealing member 21 (22A) and sealing member 22 (21A) to be different, thereby further suppressing the occurrence of cracks due to the impact of dropping elastic wave device 1 (2).

[0122] For example, in the elastic wave device 1 (2), the second unevenness amount, which is the difference between the maximum and minimum values ​​of the total thickness of the sealing member 21 (22A) and the sealing member 22 (21A) on the main surface 10b, is smaller than the thickness of the support substrate 10.

[0123] This makes it possible to suppress unevenness on the top surface of the elastic wave device 1 (2) even when the elastic wave device 1 (2) has multiple elastic wave chips 1a, thereby suppressing errors, for example, when picking up the elastic wave device 1 (2) with a collet or suction nozzle during the manufacturing process.

[0124] Furthermore, for example, in the elastic wave device 1 (2), the sealing member 21 (22A) and the sealing member 22 (21A) each contain a resin.

[0125] This increases the elastic modulus of the acoustic wave device 1 (2), thereby suppressing the occurrence of cracks due to the impact of being dropped.

[0126] In addition, for example, in the acoustic wave device 1 (2), the piezoelectric layer 31 (31A) includes at least one of lithium niobate, lithium tantalate, quartz crystal, potassium nitride, aluminum nitride, scandium aluminum nitride, zinc oxide, and magnesium zinc oxide.

[0127] Also, for example, in the elastic wave device 1 (2), the support substrate 10 includes at least one of silicon, sapphire, spinel, quartz crystal, gallium arsenide, aluminum nitride, alumina, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, silicon oxide, sialon, silicon oxynitride, diamond, and diamond-like carbon.

[0128] Furthermore, for example, in the acoustic wave device 1 ( 2 ), the functional electrodes include an IDT electrode 60 disposed on the piezoelectric layer 31 , and the IDT electrode 60 overlaps with the gap 40 when the main surface 10 a is viewed in plan.

[0129] This provides a membrane structure in which acoustic wave resonator 30 is supported by support substrate 10 with gap 40 sandwiched therebetween, thereby providing acoustic wave device 1 (2) having an XBAR.

[0130] Furthermore, for example, in the acoustic wave device according to the second modification, the functional electrodes include an IDT electrode 60 disposed on the piezoelectric layer 31, and when the main surface 10a is viewed in plan, the IDT electrode 60 overlaps with the acoustic multilayer film 41.

[0131] According to this, since the acoustic wave resonator 30C has a structure in which the acoustic multilayer film 41 is sandwiched between the acoustic wave resonator 30C and the support substrate 10, an acoustic wave device having an SMR type surface acoustic wave resonator can be provided.

[0132] For example, in the elastic wave device 1 (2), the functional electrodes include planar electrodes 12 and 13 arranged on either side of the piezoelectric layer 31A, and the planar electrode 12, the piezoelectric layer 31A, and the planar electrode 13 are arranged in this order from the main surface 10a toward the main surface 90a.

[0133] This structure has elastic wave resonator 30A supported by support substrate 10 with an acoustic reflector sandwiched therebetween, making it possible to provide elastic wave device 1 (2) having an FBAR.

[0134] While the elastic wave device according to the present invention has been described above with reference to exemplary embodiments and modifications thereof, the present invention is not limited to the exemplary embodiments and modifications thereof. The present invention also includes other embodiments realized by combining any of the components in the exemplary embodiments and modifications thereof, as well as modifications obtained by applying various modifications to the exemplary embodiments and modifications thereof that would occur to those skilled in the art without departing from the spirit of the present invention.

[0135] The features of the acoustic wave devices described based on the above-described embodiment and modifications will be described below.

[0136] <1> An elastic wave device comprising: a mounting substrate having a first main surface and a second main surface opposing each other; a support substrate having a third main surface opposing the first main surface and a fourth main surface opposing the third main surface; an elastic wave resonator including a piezoelectric layer and a functional electrode, the elastic wave resonator being supported by the support substrate so as to face the third main surface with a gap therebetween; and a first sealing member arranged to cover the fourth main surface, wherein a first unevenness amount, which is the difference between the maximum and minimum thicknesses of the first sealing member on the fourth main surface, is greater than the thickness of the piezoelectric layer.

[0137] <2> The acoustic wave device according to <1>, further comprising a second sealing member arranged to cover the first sealing member.

[0138] <3> The acoustic wave device according to <1>, further including a second sealing member disposed between the fourth main surface and the first sealing member.

[0139] <4> The elastic wave device according to <2> or <3>, wherein, when the fourth main surface is viewed in a plane, the first sealing member has a central region that includes a center of the fourth main surface and an outer edge region that includes an outer periphery of the fourth main surface, and a thickness of the first sealing member in the outer edge region is smaller than a thickness of the first sealing member in the central region.

[0140] <5> The acoustic wave device according to <2> or <3>, wherein the first sealing member and the second sealing member are made of different materials or compositions.

[0141] <6> The acoustic wave device according to <2> or <3>, wherein the first sealing member includes a first base material and a first filler, and the second sealing member includes a second base material and a second filler.

[0142] <7> The acoustic wave device according to <6>, wherein the first filler and the second filler are added at different concentrations.

[0143] <8> The acoustic wave device according to <6>, wherein the first filler and the second filler are made of different materials.

[0144] <9> The acoustic wave device according to <6>, wherein the first substrate and the second substrate are made of different materials.

[0145] <10> The elastic wave device according to any one of <2> to <9>, wherein a second unevenness amount, which is a difference between a maximum value and a minimum value of a total thickness of the first sealing member and the second sealing member on the fourth main surface, is smaller than a thickness of the support substrate.

[0146] <11> The acoustic wave device according to any one of <2> to <10>, wherein the first sealing member and the second sealing member each contain a resin.

[0147] <12> The acoustic wave device according to any one of <1> to <11>, wherein the piezoelectric layer contains at least one of lithium niobate, lithium tantalate, quartz crystal, potassium nitride, aluminum nitride, scandium aluminum nitride, zinc oxide, and magnesium zinc oxide.

[0148] <13> The acoustic wave device according to any one of <1> to <12>, wherein the support substrate includes at least one of silicon, sapphire, spinel, quartz crystal, gallium arsenide, aluminum nitride, alumina, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, silicon oxide, sialon, silicon oxynitride, diamond, and diamond-like carbon.

[0149] <14> The acoustic wave device according to any one of <1> to <13>, wherein the functional electrode includes an IDT electrode disposed on the piezoelectric layer, and the IDT electrode overlaps the gap when the third principal surface is viewed in a plan view.

[0150] <15> The elastic wave device according to any one of <1> to <13>, wherein the functional electrodes include a first planar electrode and a second planar electrode arranged to sandwich the piezoelectric layer, and the first planar electrode, the piezoelectric layer, and the second planar electrode are arranged in this order from the third principal surface toward the first principal surface.

[0151] INDUSTRIAL APPLICABILITY The present invention can be widely used as an acoustic wave device disposed in a front end portion of communication devices such as mobile phones.

[0152] REFERENCE SIGNS LIST 1, 2 Acoustic wave device 1a, 1b, 1c Acoustic wave chip 10 Support substrate 10a, 10b, 90a, 90b Main surface 11, 80, 91, 92 Electrode 12, 13 Planar electrode 21, 21A, 22, 22A Sealing member 30, 30A, 30C Acoustic wave resonator 31, 31A Piezoelectric layer 40 Gap 41 Acoustic multilayer film 41a Low acoustic impedance layer 41b High acoustic impedance layer 51, 52 Intermediate layer 60 IDT electrode 61a, 61b Electrode fingers 62a, 62b Bus bar electrode 65 Reflecting electrode 90 Mounting substrate

Claims

1. An elastic wave device comprising: a mounting substrate having first and second principal surfaces opposing each other; a support substrate having a third principal surface facing the first principal surface and a fourth principal surface facing the third principal surface; an elastic wave resonator including a piezoelectric layer and a functional electrode, the elastic wave resonator being supported by the support substrate so as to face the third principal surface across an acoustic reflector; and a first sealing member disposed to cover the fourth principal surface, wherein a first unevenness amount, which is the difference between the maximum and minimum thicknesses of the first sealing member on the fourth principal surface, is greater than the thickness of the piezoelectric layer.

2. The acoustic wave device according to claim 1, wherein the acoustic reflecting portion is a gap.

3. The acoustic wave device according to claim 1, wherein the acoustic reflecting portion is an acoustic multilayer film.

4. The acoustic wave device according to any one of claims 1 to 3, further comprising a second sealing member arranged to cover the first sealing member.

5. The elastic wave device according to any one of claims 1 to 3, further comprising a second sealing member disposed between the fourth main surface and the first sealing member.

6. The elastic wave device according to claim 4 or 5, wherein, when the fourth main surface is viewed in a plane, the first sealing member has a central region that includes the center of the fourth main surface and an outer edge region that includes the periphery of the fourth main surface, and the thickness of the first sealing member in the outer edge region is smaller than the thickness of the first sealing member in the central region.

7. The acoustic wave device according to claim 4 or 5, wherein the first sealing member and the second sealing member are made of different materials or compositions.

8. The acoustic wave device according to claim 4 or 5, wherein the first sealing member includes a first base material and a first filler, and the second sealing member includes a second base material and a second filler.

9. The acoustic wave device according to claim 8, wherein the concentration of the first filler is different from the concentration of the second filler.

10. The acoustic wave device according to claim 8, wherein the first filler and the second filler are made of different materials.

11. The acoustic wave device according to claim 8, wherein the first substrate and the second substrate are made of different materials.

12. The elastic wave device according to any one of claims 4 to 11, wherein a second unevenness amount, which is the difference between the maximum and minimum values ​​of the total thickness of the first sealing member and the second sealing member on the fourth main surface, is smaller than the thickness of the support substrate.

13. The acoustic wave device according to any one of claims 4 to 12, wherein the first sealing member and the second sealing member each contain a resin.

14. The acoustic wave device according to any one of claims 1 to 13, wherein the piezoelectric layer contains at least one of lithium niobate, lithium tantalate, quartz crystal, potassium nitride, aluminum nitride, scandium aluminum nitride, zinc oxide, and magnesium zinc oxide.

15. The acoustic wave device according to any one of claims 1 to 14, wherein the support substrate includes at least one of silicon, sapphire, spinel, quartz crystal, gallium arsenide, aluminum nitride, alumina, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, silicon oxide, sialon, silicon oxynitride, diamond, and diamond-like carbon.

16. The elastic wave device according to any one of claims 1 to 15, wherein the functional electrode includes an IDT (InterDigital Transducer) electrode disposed on the piezoelectric layer, and when the third principal surface is viewed in a plan view, the IDT electrode overlaps the acoustic reflector.

17. The elastic wave device according to any one of claims 1 to 15, wherein the functional electrodes include a first planar electrode and a second planar electrode arranged to sandwich the piezoelectric layer, and the first planar electrode, the piezoelectric layer, and the second planar electrode are arranged in this order from the third principal surface toward the first principal surface.

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