Elastic wave device

Abstract

This elastic wave device comprises: a piezoelectric layer having a first main surface and a second main surface that face each other; an electrode provided to at least one of the first main surface and the second main surface of the piezoelectric layer; and a support member provided to the second main surface side of the piezoelectric layer and provided with a cavity part on the second main surface side of the piezoelectric layer. A membrane part that includes at least a portion of the piezoelectric layer is formed in a region that overlaps the cavity part. The support member has a first portion and a modified second portion. The second portion is disposed at a position closer to the cavity part as compared with the first portion. The membrane part has a third portion and a modified fourth portion. The fourth portion is disposed at a position closer to the cavity part as compared with the third portion.

Description

Elastic Wave Device

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

[0002] Patent Document 1 describes an acoustic wave device (called a filter device in Patent Document 1) that includes a substrate, a piezoelectric plate having parallel front and back surfaces and the back surface of which is attached to the substrate, and a conductor pattern formed on the front surface. A hollow portion (called a cavity in Patent Document 1) is formed in a region of the substrate that overlaps with a portion of the piezoelectric plate.

[0003] US Patent Application Publication No. 2020 / 0321939

[0004] In the acoustic wave device disclosed in Patent Document 1, heat generated in the excitation region of the piezoelectric plate may be trapped within the cavity, and therefore acoustic wave devices are required to have improved heat dissipation properties.

[0005] An object of the present invention is to provide an acoustic wave device that can improve heat dissipation properties.

[0006] An elastic wave device according to one embodiment comprises a piezoelectric layer having opposing first and second main surfaces, an electrode provided on at least one of the first and second main surfaces of the piezoelectric layer, and a support member provided on the second main surface side of the piezoelectric layer and having a cavity on the second main surface side of the piezoelectric layer, wherein a membrane portion including at least a portion of the piezoelectric layer is formed in a region overlapping with the cavity portion, the support member having a first portion and a modified second portion, the second portion being positioned closer to the cavity portion than the first portion, and the membrane portion having a third portion and a modified fourth portion, the fourth portion being positioned closer to the cavity portion than the third portion.

[0007] According to an acoustic wave device of the present invention, heat dissipation can be improved.

[0008] FIG. 1 is a plan view of an elastic wave device according to a first embodiment. FIG. 2 is a cross-sectional view taken along line II-II′ of FIG. 1 . FIG. 3 is an enlarged cross-sectional view of region III shown in FIG. 2 . FIG. 4 is an enlarged cross-sectional view of region IV shown in FIG. 2 . FIG. 5 is a schematic cross-sectional view illustrating a bulk wave in a thickness-shear first-order mode propagating through a piezoelectric layer according to the first embodiment. FIG. 6 is a schematic cross-sectional view illustrating the amplitude direction of a bulk wave in a thickness-shear first-order mode propagating through a piezoelectric layer according to the first embodiment. FIG. 7 is a diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. FIG. 8 is a diagram illustrating the relationship between d / 2p and the fractional bandwidth of a resonator, where p is the center-to-center distance or the average center-to-center distance between adjacent electrodes and d is the average thickness of the piezoelectric layer in the elastic wave device according to the first embodiment. FIG. 9 is a plan view illustrating an example of the elastic wave device according to the first embodiment, in which a pair of electrodes is provided. FIG. 10 is a reference diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. 11 is a diagram illustrating the relationship between the bandwidth ratio when a large number of elastic wave resonators are configured in the elastic wave device according to the first embodiment and the amount of phase rotation of the spurious impedance normalized by 180 degrees as the magnitude of the spurious. FIG. 12 is a diagram illustrating the relationship between d / 2p, the metallization ratio MR, and the bandwidth ratio. FIG. 13 is a diagram illustrating the relationship between d / p and the metallization ratio MR of LiNbO when d / p approaches 0. ３ FIG. 14 is a cross-sectional view of an elastic wave device according to a second embodiment. FIG. 15 is an enlarged cross-sectional view of region XV shown in FIG. 14. FIG. 16 is a diagram illustrating a method for manufacturing an elastic wave device according to the second embodiment. FIG. 17 is a cross-sectional view of an elastic wave device according to a third embodiment. FIG. 18 is a cross-sectional view of an elastic wave device according to a fourth embodiment. FIG. 19 is a diagram illustrating a method for manufacturing an elastic wave device according to the fourth embodiment. FIG. 20 is a cross-sectional view of an elastic wave device according to a fifth embodiment. FIG. 21 is a cross-sectional view of an elastic wave device according to a sixth embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments. Note that each embodiment described in the present disclosure is illustrative, and partial substitution or combination of configurations between different embodiments is possible. In modified examples and the second and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0010] First Embodiment Fig. 1 is a plan view showing an elastic wave device according to a first embodiment. Fig. 2 is a cross-sectional view taken along line II-II' in Fig. 1. Fig. 3 is a cross-sectional view showing an enlarged view of region III shown in Fig. 2. Fig. 4 is a cross-sectional view showing an enlarged view of region IV shown in Fig. 2.

[0011] 1 and 2 , an elastic wave device 10 according to the first embodiment includes a piezoelectric layer 20, an IDT electrode 30 (electrode), a support member 11, connection wirings 35 and 37, terminals 41, 42, 43, and 44, and connecting portions 45, 46, 47, and 48. As shown in Fig. 2 , in the elastic wave device 10, the piezoelectric layer 20, the IDT electrode 30, the terminals 41, 42, 43, and 44, and the connecting portions 45, 46, 47, and 48 are layered in this order on the support member 11.

[0012] The piezoelectric layer 20 is in the form of a flat plate having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is made of lithium niobate (LiNbO ３ Alternatively, the piezoelectric layer 20 may be made of lithium tantalate (LiTaO ３ ) may be made of LiNbO ３ and LiTaO ３ In the first embodiment, the cut angle is a Z-cut. ３ and LiTaO ３ The cut angle may be a rotated Y cut or an X cut. Preferably, the propagation direction is Y propagation or X propagation ±30°. Preferably, the piezoelectric layer 20 is made of lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ ) and is a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut.

[0013] The thickness of the piezoelectric layer 20 is not particularly limited, but is preferably 50 nm to 1000 nm inclusive in order to effectively excite the first-order thickness shear mode. The thickness of the piezoelectric layer 20 according to the first embodiment is, for example, about 400 nm (0.4 μm).

[0014] The support member 11 is disposed opposite the second main surface 20b of the piezoelectric layer 20. The support member 11 has a hollow portion 16 that opens to the second main surface 20b side of the piezoelectric layer 20. More specifically, the support member 11 includes a support substrate 12 and an intermediate layer 13 laminated on the support substrate 12. A recess is formed on the surface of the intermediate layer 13 that faces the second main surface 20b of the piezoelectric layer 20, and the hollow portion 16 is formed between the intermediate layer 13 and the piezoelectric layer 20. The hollow portion 16 is also called a cavity portion or a recessed portion.

[0015] At least a portion of the piezoelectric layer 20 is disposed above the cavity 16 in a plan view. As a result, a membrane unit MEM including at least a portion of the piezoelectric layer 20 is formed in the region overlapping with the cavity 16. The membrane unit MEM is not limited to a configuration consisting of the piezoelectric layer 20, but may also include another insulating layer stacked on at least one of the first principal surface 20a and the second principal surface 20b. In this manner, the acoustic wave device 10 has a so-called membrane structure in which the cavity 16 is provided on the second principal surface 20b side of the piezoelectric layer 20.

[0016] Openings OP1 and OP2 are provided in regions of the piezoelectric layer 20 that overlap with the cavity 16. The openings OP1 and OP2 are each a through-hole that penetrates the piezoelectric layer 20. The openings OP1 and OP2 have a substantially rectangular shape in a plan view and are provided along sides of the cavity 16 that extend in the Y direction. That is, a portion of the upper surface of the support member 11 (intermediate layer 13) and a portion of the cavity 16 are disposed in the regions that overlap with the openings OP1 and OP2, respectively. The openings OP1 and OP2 are provided to remove the sacrificial layer 60 (see FIG. 16 ) to form the cavity 16, and the shape, number, position, etc. of the openings OP1 and OP2 can be changed as appropriate.

[0017] The support member 11 does not necessarily have to have the intermediate layer 13. That is, the piezoelectric layer 20 is bonded to the support substrate 12 directly or via the intermediate (insulating) layer 13. The cavity 16 may be formed in the support substrate 12. In that case, the support substrate 12 may have a frame-like shape, thereby forming the cavity 16.

[0018] The support substrate 12 is made of silicon (Si). The surface of the Si facing the piezoelectric layer 20 may have a (100), (110), or (111) plane orientation. High-resistivity Si, with a resistivity of 4 kΩ or higher, is preferred. However, the support substrate 12 may also be made of an appropriate insulating material or semiconductor material. Examples of materials that can be used for the support substrate 12 include piezoelectric materials such as lithium tantalate, lithium niobate, and quartz; various ceramics such as alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectric materials such as diamond and glass; and semiconductors such as gallium nitride.

[0019] The intermediate layer 13 is made of silicon oxide, but is not limited to silicon oxide and may be made of any suitable insulating material such as silicon nitride or alumina.

[0020] The IDT (Interdigital Transducer) electrode 30 is provided on the first main surface 20a of the piezoelectric layer 20. As shown in FIG. 1 , the IDT electrode 30 has first electrode fingers 31, second electrode fingers 32, first bus bar electrodes 33, and second bus bar electrodes 34. The first electrode fingers 31 extend in the Y direction, and one end of each electrode finger in the extension direction is connected to the first bus bar electrode 33. The second electrode fingers 32 extend in the Y direction, and the other end of each electrode finger in the extension direction is connected to the second bus bar electrode 34. The first electrode fingers 31 and the second electrode fingers 32 are alternately arranged in the X direction with a gap therebetween. The first bus bar electrodes 33 and the second bus bar electrodes 34 each extend in the X direction and are arranged opposite each other in the Y direction. A plurality of first electrode fingers 31 and a plurality of second electrode fingers 32 are arranged between the first bus bar electrode 33 and the second bus bar electrode 34 .

[0021] The IDT electrode 30 is not limited to a configuration having a plurality of first electrode fingers 31 and a plurality of second electrode fingers 32, but may also be configured to include at least one first electrode finger 31 whose base end is connected to a first busbar electrode 33 and at least one second electrode finger 32 whose base end is connected to a second busbar electrode 34.

[0022] In the following description, the thickness direction of the piezoelectric layer 20 may be referred to as the Z direction, the extension direction of the first electrode fingers 31 and the second electrode fingers 32 as the Y direction, and the arrangement direction of the first electrode fingers 31 and the second electrode fingers 32 as the X direction. In the following description, a planar view refers to the arrangement relationship when viewed from a direction perpendicular to the first main surface 20a of the piezoelectric layer 20. In the Z direction, the direction from the support member 11 toward the IDT electrode 30 on the outermost surface is referred to as up or upward, and the direction from the IDT electrode 30 toward the support member 11 is referred to as down or downward.

[0023] The center-to-center distance between the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the inter-electrode pitch) is preferably in the range of 1 μm to 10 μm. The inter-electrode pitch is the distance between the center of the width of the first electrode finger 31 in a direction perpendicular to the extension direction of the first electrode finger 31 and the center of the width of the second electrode finger 32 in a direction perpendicular to the extension direction of the second electrode finger 32. The width of the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the electrode width), i.e., the dimension in the direction perpendicular to the extension direction of the first electrode finger 31 and the second electrode finger 32, is preferably in the range of 150 nm to 1000 nm.

[0024] Furthermore, when there are multiple first electrode fingers 31 and multiple second electrode fingers 32 (when the first electrode fingers 31 and the second electrode fingers 32 are considered as a pair of electrode sets, there are 1.5 or more pairs of electrode sets), the inter-electrode pitch of the first electrode fingers 31 and the second electrode fingers 32 refers to the average value of the center-to-center distances of adjacent first electrode fingers 31 and second electrode fingers 32 among the 1.5 or more pairs of first electrode fingers 31 and second electrode fingers 32.

[0025] Furthermore, in the first embodiment, since a Z-cut piezoelectric layer is used, the direction perpendicular to the extension direction of the first electrode fingers 31 and the second electrode fingers 32 is perpendicular to the polarization direction of the piezoelectric layer 20. This does not apply when a piezoelectric material with a different cut angle is used as the piezoelectric layer 20. Here, "perpendicular" is not limited to strictly perpendicular, but may also be approximately perpendicular (the angle between the direction perpendicular to the extension direction of the first electrode fingers 31 and the second electrode fingers 32 and the polarization direction is, for example, 90°±10°).

[0026] The IDT electrode 30 (first electrode fingers 31, second electrode fingers 32, first bus bar electrodes 33, and second bus bar electrodes 34) is made of an appropriate metal or alloy such as Al or an AlCu alloy. In the first embodiment, the IDT electrode 30 has a structure in which an Al film is laminated on a titanium (Ti) film. Note that an adhesion layer other than the Ti film may also be used.

[0027] 1 is a region where the first electrode fingers 31 and the second electrode fingers 32 overlap when viewed in the X direction. The length of the intersection region C is the dimension in the extension direction of the first electrode fingers 31 and the second electrode fingers 32 in the intersection region C. In this embodiment, the length of the intersection region C is, for example, 40 μm.

[0028] During operation, an AC voltage is applied between the plurality of first electrode fingers 31 and the plurality of second electrode fingers 32. More specifically, the first busbar electrode 33 is connected to a terminal 41 via a connection wiring 35. The second busbar electrode 34 is connected to a terminal 42 via a connection wiring 37. One of the terminals 41 and 42 is an input terminal, and the other is an output terminal. The terminals 43 and 44 are ground terminals connected to a reference potential, such as ground potential. The terminals 41, 42, 43, and 44 are connected to an external substrate via connection portions 45, 46, 47, and 48, respectively. The connection portions 45, 46, 47, and 48 are, for example, Au bumps. This allows an AC voltage to be applied between the first busbar electrode 33 and the second busbar electrode 34. This makes it possible to obtain resonance characteristics utilizing bulk waves in a first-order thickness-shear mode excited in the piezoelectric layer 20.

[0029] Furthermore, in the elastic wave device 10, where d is the thickness of the piezoelectric layer 20 and p is the inter-electrode pitch between the first and second electrode fingers 31 and 32, the ratio d / p is set to 0.5 or less. This effectively excites the bulk waves in the thickness-shear first-order mode, resulting in good resonance characteristics. More preferably, d / p is set to 0.24 or less, which results in even better resonance characteristics.

[0030] The elastic wave device 10 according to the first embodiment has the above-described configuration, and therefore is unlikely to suffer a decrease in the Q value even if the number of pairs of the first electrode fingers 31 and the second electrode fingers 32 is reduced in an attempt to reduce the device's size. This is because the resonator does not require reflectors on either side, resulting in low propagation loss. Furthermore, the absence of the reflectors is due to the use of bulk waves in the thickness-shear first-order mode.

[0031] As shown in FIGS. 2 and 3 , the intermediate layer 13 of the support member 11 has a first portion 14 and a modified second portion 15. The second portion 15 is a portion modified by diffusing a metal into the insulating material (e.g., silicon oxide) constituting the intermediate layer 13, and has a higher metal concentration than the first portion 14. The second portion 15 is modified by diffusing zinc (Zn) and contains zinc oxide (ZnO), for example, in which zinc is oxidized. Alternatively, the second portion 15 may contain diffused zinc (Zn) in addition to zinc oxide. The second portion 15 is positioned closer to the cavity 16 than the first portion 14. More specifically, the second portion 15 is formed in a region of the intermediate layer 13 along the bottom and sidewalls of the cavity 16.

[0032] As shown in FIGS. 2 and 4 , the membrane unit MEM (the piezoelectric layer 20 in the region of the piezoelectric layer 20 overlapping with the cavity 16) includes a third portion 21 and a modified fourth portion 22. The fourth portion 22 is a portion modified by diffusing a metal into lithium niobate or lithium tantalate constituting the piezoelectric layer 20, and has a higher metal concentration than the third portion 21. The fourth portion 22 is modified by diffusing zinc (Zn) and contains zinc oxide (ZnO) formed by oxidizing the zinc. Alternatively, the fourth portion 22 may contain diffused zinc (Zn) in addition to zinc oxide. The fourth portion 22 is located closer to the cavity 16 than the third portion 21. More specifically, the fourth portion 22 is formed on the second main surface 20b side of the membrane unit MEM (piezoelectric layer 20), and the third portion 21 is formed on the first main surface 20a side.

[0033] With the above-described configuration, the IDT electrode 30 is driven, and heat generated in the membrane portion MEM is dissipated to the outside through the IDT electrode 30, the connection wirings 35, 37, and the terminals 41, 44 provided on the piezoelectric layer 20. In addition, in the region overlapping with the membrane portion MEM, a modified second portion 15 is provided in the intermediate layer 13 of the support member 11, and a modified fourth portion 22 is provided in the piezoelectric layer 20 constituting the membrane portion MEM. Here, zinc oxide (ZnO) contained in the second portion 15 and the fourth portion 22 adsorbs moisture, or zinc (Zn) reduces moisture to generate hydrogen, or other reactions occur.

[0034] When the membrane unit MEM generates heat, moisture is released from the second portion 15 and the fourth portion 22 into the cavity 16, and the thermal conductivity of the cavity 16 is improved compared to when moisture is not released. As a result, the heat generated in the membrane unit MEM is transferred from the second main surface 20b of the piezoelectric layer 20 through the cavity 16 to the intermediate layer 13 and the support substrate 12, where it is dissipated. Therefore, the elastic wave device 10 of this embodiment can efficiently dissipate the heat generated in the membrane unit MEM to both the first main surface 20a and the second main surface 20b of the piezoelectric layer 20.

[0035] 2 to 4, the second portion 15 and the fourth portion 22 are depicted as layers for ease of understanding. However, the second portion 15 and the fourth portion 22 are portions modified by metal diffusion and do not necessarily have a constant thickness. The second portion 15 is not limited to a configuration formed along the bottom and wall portions of the cavity 16, as long as it is formed on at least a portion of the bottom and wall portions of the cavity 16. Furthermore, the fourth portion 22 is not limited to a configuration formed along the surface of the membrane portion MEM facing the cavity 16 (the second main surface 20b of the piezoelectric layer 20), as long as it is formed on at least a portion of the surface of the membrane portion MEM facing the cavity 16.

[0036] The metal diffused into the second portion 15 of the intermediate layer 13 and the fourth portion 22 of the membrane unit MEM is not limited to zinc (Zn) and may include other metals such as titanium (Ti), magnesium (Mg), nickel (Ni), iron (Fe), cobalt (Co), etc. That is, the second portion 15 and the fourth portion 22 may include at least one of titanium oxide, magnesium oxide, nickel oxide, iron oxide, and cobalt oxide.

[0037] 5 and 6 are schematic cross-sectional views illustrating a bulk wave in a first-order thickness shear mode propagating through the piezoelectric layer of the first embodiment, respectively.

[0038] As shown in Figure 5, in the elastic wave device 10 of the first embodiment, vibration displacement occurs in the thickness shear direction. Therefore, waves propagate and resonate substantially in the direction connecting the first principal surface 20a and the second principal surface 20b of the piezoelectric layer 20, i.e., the Z direction. That is, the X direction component of the wave is significantly smaller than the Z direction component. Furthermore, since resonance characteristics are achieved through wave propagation in this Z direction, a reflector is not required. Therefore, no propagation loss occurs during propagation to the reflector. Therefore, even if the number of electrode pairs, each consisting of the first electrode fingers 31 and the second electrode fingers 32, is reduced in an effort to achieve miniaturization, the Q value is unlikely to decrease.

[0039] As shown in FIG. 6 , the amplitude direction of the bulk wave in the first thickness-shear mode is opposite between a first region 251 included in the intersection region C (see FIG. 1 ) of the piezoelectric layer 20 and a second region 252 included in the intersection region C. FIG. 6 schematically illustrates the bulk wave when a voltage is applied between the first electrode finger 31 and the second electrode finger 32 such that the second electrode finger 32 has a higher potential than the first electrode finger 31. Here, the imaginary plane VP1 is a plane that is perpendicular to the thickness direction of the piezoelectric layer 20 and divides the piezoelectric layer 20 in half. The first region 251 is a region of the intersection region C between the imaginary plane VP1 and the first main surface 20a. The second region 252 is a region of the intersection region C between the imaginary plane VP1 and the second main surface 20b.

[0040] In elastic wave device 10, at least one pair of electrodes each consisting of first electrode finger 31 and second electrode finger 32 is arranged, but because waves are not propagated in the X direction, the number of electrode pairs each consisting of first electrode finger 31 and second electrode finger 32 does not necessarily need to be multiple. In other words, it is sufficient that at least one pair of electrodes is provided.

[0041] For example, the first electrode finger 31 is an electrode connected to a hot potential, and the second electrode finger 32 is an electrode connected to a ground potential. However, the first electrode finger 31 may be connected to the ground potential, and the second electrode finger 32 may be connected to the hot potential. In the first embodiment, at least one pair of electrodes is an electrode connected to a hot potential or an electrode connected to a ground potential, as described above, and no floating electrode is provided.

[0042] 7 is a diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. The design parameters of the elastic wave device 10 that achieved the resonance characteristics shown in FIG.

[0043] Piezoelectric layer 20: LiNbO with Euler angles (0°, 0°, 90°) ３ Thickness of the piezoelectric layer 20: 400 nm

[0044] Length of intersection region C: 40 μm Number of pairs of electrodes consisting of first electrode fingers 31 and second electrode fingers 32: 21 pairs Inter-electrode pitch between first electrode fingers 31 and second electrode fingers 32: 3 μm Width of first electrode fingers 31 and second electrode fingers 32: 500 nm d / p: 0.133

[0045] Support substrate 12: Si

[0046] In the first embodiment, the inter-electrode pitch of each electrode pair, which is made up of the first electrode fingers 31 and the second electrode fingers 32, is set to be equal for all pairs. That is, the first electrode fingers 31 and the second electrode fingers 32 are arranged at equal pitches.

[0047] As is clear from FIG. 7, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0048] In the first embodiment, when the thickness of the piezoelectric layer 20 is d and the interelectrode pitch between the first electrode fingers 31 and the second electrode fingers 32 is p, d / p is 0.5 or less, and more preferably 0.24 or less. This will be explained with reference to FIG. 8 .

[0049] 8 is a diagram illustrating the relationship between d / 2p and the fractional bandwidth of a resonator in the elastic wave device according to the first embodiment, where p is the center-to-center distance or the average center-to-center distance between adjacent electrodes and d is the average thickness of the piezoelectric layer. In FIG. 8, multiple elastic wave devices were obtained by varying d / 2p, similar to the elastic wave device having the resonance characteristics shown in FIG.

[0050] As shown in Figure 8, when d / 2p exceeds 0.25, i.e., when d / p > 0.5, adjusting d / p results in a fractional bandwidth of less than 5%. In contrast, when d / 2p ≤ 0.25, i.e., when d / p ≤ 0.5, varying d / p within this range can increase the fractional bandwidth to 5% or more, thereby enabling the construction of a resonator with a high coupling coefficient. Furthermore, when d / 2p is 0.12 or less, i.e., when d / p is 0.24 or less, the fractional bandwidth can be increased to 7% or more. Furthermore, adjusting d / p within this range can result in a resonator with a wider fractional bandwidth and a higher coupling coefficient. Therefore, by setting d / p to 0.5 or less, a resonator with a high coupling coefficient can be constructed using the bulk wave in the thickness-shear primary mode.

[0051] When the piezoelectric layer 20 has thickness variations, the thickness d of the piezoelectric layer 20 may be an average value of the thickness variations.

[0052] 9 is a plan view illustrating an example in which a pair of electrodes is provided in the elastic wave device according to the first embodiment. In the elastic wave device 10, a pair of electrodes including a first electrode finger 31 and a second electrode finger 32 is provided on the first main surface 20a of the piezoelectric layer 20. Note that K in FIG. 9 represents the crossover width. As described above, the number of electrode pairs in the elastic wave device 10 according to the present disclosure may be one pair. Even in this case, if the d / p ratio is 0.5 or less, a bulk wave in the thickness-shear first-order mode can be effectively excited.

[0053] In the acoustic wave device 10, it is preferable that the metallization ratio MR of the adjacent first electrode fingers 31 and second electrode fingers 32 with respect to the intersection region C satisfies MR≦1.75(d / p)+0.075. In this case, spurious signals can be effectively reduced. This will be described with reference to FIGS. 10 and 11 .

[0054] 10 is a reference diagram showing an example of the resonance characteristics of the elastic wave device according to the first embodiment. As shown in FIG. 10, a spurious component indicated by an arrow B appears between the resonance frequency and the anti-resonance frequency. Note that, when d / p=0.08 and LiNbO ３ The Euler angles were (0°, 0°, 90°), and the metallization ratio was set to MR=0.35.

[0055] The metallization ratio MR will be described with reference to FIG. 1 . Focusing on a pair of first and second electrode fingers 31 and 32 in the electrode structure of FIG. 1 , assume that only this pair of first and second electrode fingers 31 and 32 is provided. In this case, the area surrounded by the dashed line is the intersection region C. When the first and second electrode fingers 31 and 32 are viewed in a direction perpendicular to the extension direction of the first and second electrode fingers 31 and 32, i.e., in the opposing direction, the intersection region C includes the region of the first electrode finger 31 overlapping with the second electrode finger 32, the region of the second electrode finger 32 overlapping with the first electrode finger 31, and the region between the first and second electrode fingers 31 and 32 where the first and second electrode fingers 31 and 32 overlap. The ratio of the area of ​​the first and second electrode fingers 31 and 32 within the intersection region C to the area of ​​the intersection region C is the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of ​​the metallization portion to the area of ​​the intersection region C.

[0056] When multiple pairs of first electrode fingers 31 and second electrode fingers 32 are provided, the ratio of the metallization portion included in all intersection regions C to the total area of ​​the intersection regions C may be defined as MR.

[0057] 11 is an explanatory diagram showing the relationship between the relative bandwidth when a large number of elastic wave resonators are configured in the elastic wave device according to the first embodiment and the amount of phase rotation of the spurious impedance normalized by 180 degrees as the magnitude of the spurious. The relative bandwidth was adjusted by changing the film thickness of the piezoelectric layer 20 and the dimensions of the first electrode fingers 31 and the second electrode fingers 32. Also, FIG. 11 shows the relationship between the relative bandwidth and the spurious impedance normalized by 180 degrees as the magnitude of the spurious. ３ Although this is the result when a piezoelectric layer 20 having a cut angle of 100° is used, the same tendency is observed when a piezoelectric layer 20 having a different cut angle is used.

[0058] In the region surrounded by ellipse J in Fig. 11, the spurious is as large as 1.0. As is clear from Fig. 11, when the fractional bandwidth exceeds 0.17, i.e., 17%, large spurious signals with a spurious level of 1 or more appear within the passband, even if the parameters constituting the fractional bandwidth are changed. That is, as in the resonance characteristics shown in Fig. 10, large spurious signals indicated by arrow B appear within the passband. Therefore, it is preferable that the fractional bandwidth be 17% or less. In this case, the spurious signals can be reduced by adjusting the film thickness of piezoelectric layer 20 and the dimensions of first electrode fingers 31 and second electrode fingers 32, etc.

[0059] FIG. 12 is an explanatory diagram showing the relationship between d / 2p, metallization ratio MR, and bandwidth fraction. Various elastic wave devices 10 with different d / 2p and MR were constructed in the elastic wave device 10 according to the first embodiment, and the bandwidth fraction was measured. The hatched area to the right of dashed line D in FIG. 12 represents the region where the bandwidth fraction is 17% or less. The boundary between this hatched area and the unhatched area is represented by MR = 3.5(d / 2p) + 0.075. That is, MR = 1.75(d / p) + 0.075. Therefore, preferably, MR ≦ 1.75(d / p) + 0.075. In this case, the bandwidth fraction is easily reduced to 17% or less. More preferably, the region to the right of MR = 3.5(d / 2p) + 0.05, as indicated by dashed line D1 in FIG. 12 , is the region. That is, if MR≦1.75(d / p)+0.05, the fractional bandwidth can be reliably kept to 17% or less.

[0060] Fig. 13 is an explanatory diagram showing a map of the fractional bandwidth versus the Euler angles (0°, θ, ψ) of LiNbO3 when d / p approaches 0. The hatched area in Fig. 13 is the region where a fractional bandwidth of at least 5% or more is obtained. The range of this region can be approximated as the ranges expressed by the following formulas (1), (2), and (3).

[0061] (0°±10°, 0° to 20°, any ψ) ... Equation (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3)

[0062] Therefore, in the case of the Euler angle range of the above formula (1), formula (2), or formula (3), the relative bandwidth can be made sufficiently wide, which is preferable.

[0063] Although the elastic wave device 10 of this embodiment has been described as being capable of utilizing bulk waves in a thickness-shear first-order mode, the present invention is not limited to this. The elastic wave device 10 may also utilize plate waves. In this case, the elastic wave device 10 has reflectors provided on both sides of the IDT electrode 30 in the direction of propagation of the elastic waves. In the elastic wave device 10, Lamb waves as plate waves are excited by applying an AC electric field to the first electrode fingers 31 and the second electrode fingers 32 above the cavity 16. In this case, because reflectors are provided on both sides, resonance characteristics due to the Lamb waves as plate waves can be obtained.

[0064] Second Embodiment Fig. 14 is a cross-sectional view showing an elastic wave device according to a second embodiment. Fig. 15 is an enlarged cross-sectional view of region XV shown in Fig. 14. As shown in Fig. 14, an elastic wave device 10A according to the second embodiment has a different configuration from the first embodiment described above in that it includes an insulating layer 50.

[0065] In the second embodiment, the insulating layer 50 is provided on the second main surface 20b of the piezoelectric layer 20. In other words, the insulating layer 50 is provided between the piezoelectric layer 20 and the support member 11 (intermediate layer 13). In this embodiment, the membrane unit MEM is made of the piezoelectric layer 20 and the insulating layer 50. The insulating layer 50 is made of, for example, silicon oxide (SiO ２ ) or other insulating materials.

[0066] In this embodiment, the resonant frequency of the resonator including the IDT electrode 30 and the piezoelectric layer 20 can be adjusted by changing the film thickness of the insulating layer 50. That is, the insulating layer 50 is a frequency adjustment layer. The insulating layer 50 is also provided on the flat surface (second principal surface 20b) of the piezoelectric layer 20 opposite the IDT electrode 30. Therefore, the thickness of the insulating layer 50 in the elastic wave device 10A can be easily adjusted, and changes in the capacitance of the IDT electrode 30 can be suppressed even when the thickness of the insulating layer 50 is changed.

[0067] As shown in FIGS. 14 and 15 , the membrane unit MEM, which is composed of the piezoelectric layer 20 and the insulating layer 50, includes the insulating layer 50. The insulating layer 50 has a third portion 51 and a modified fourth portion 52. The fourth portion 52 is a portion modified by diffusing metal into the insulating material (e.g., silicon oxide) constituting the insulating layer 50, and has a higher metal concentration than the third portion 51. The fourth portion 52 is modified by diffusing zinc (Zn) to include zinc oxide (ZnO), which is oxidized zinc. Alternatively, the fourth portion 52 may include diffused zinc (Zn) in addition to zinc oxide. The fourth portion 52 is positioned closer to the cavity 16 than the third portion 51. The piezoelectric layer 20 is positioned on the third portion 51. That is, the fourth portion 52 is formed on the cavity 16 side of the membrane unit MEM (the piezoelectric layer 20 and the insulating layer 50), and the third portion 51 is formed on the second main surface 20b side of the piezoelectric layer 20.

[0068] In the second embodiment, the insulating layer 50 has the modified fourth portion 52, and therefore, similar to the first embodiment described above, heat generated in the membrane portion MEM is conducted from the piezoelectric layer 20 and the insulating layer 50 through the cavity 16 to the intermediate layer 13 and the support substrate 12, where it is dissipated. Therefore, the elastic wave device 10A of this embodiment can efficiently dissipate heat generated in the membrane portion MEM to the surrounding area.

[0069] The metal diffused into the fourth portion 52 of the membrane portion MEM is not limited to zinc (Zn) and may include other metals such as titanium (Ti), magnesium (Mg), nickel (Ni), iron (Fe), and cobalt (Co).

[0070] 16 is an explanatory diagram illustrating a method for manufacturing an elastic wave device according to the second embodiment. As shown in FIG. 16 , in the method for manufacturing elastic wave device 10A according to the second embodiment, first, piezoelectric layer 20 is bonded to the main surface of transfer substrate 100 (step S11). Piezoelectric layer 20 is ground to a predetermined thickness.

[0071] Next, the insulating layer 50 is formed on the second main surface 20b of the piezoelectric layer 20, and the sacrificial layer 60 is formed to cover a part of the insulating layer 50 (step S12). The sacrificial layer 60 is made of, for example, zinc oxide.

[0072] Next, an insulator is formed to cover the insulating layer 50 and the sacrificial layer 60, and the surface opposite to the piezoelectric layer 20 is planarized and smoothed to form the intermediate layer 13 made of the insulator (step S13).

[0073] Next, the insulating layer 50, the piezoelectric layer 20, etc. are bonded to the support substrate 12 via the intermediate layer 13 (step S14). After that, the transfer substrate 100 is removed from the piezoelectric layer 20 (step S15).

[0074] Next, the IDT electrode 30 and various wirings are formed on the first main surface 20a of the piezoelectric layer 20 (step S16). In this embodiment, the IDT electrode 30 and various wirings are formed by, for example, lift-off. After the IDT electrode 30 is formed, a layer made of an insulator such as a protective film may be formed as necessary.

[0075] Next, openings OP1 and OP2 are formed in the piezoelectric layer 20 and the insulating layer 50 in areas that overlap with the sacrificial layer 60 (step S17). The openings OP1 and OP2 are formed by forming a resist pattern on the piezoelectric layer 20 and performing dry etching.

[0076] An etching gas or an etching liquid is introduced into the openings OP1 and OP2 to remove the sacrificial layer 60, thereby forming the cavity 16 (step S18).

[0077] In the manufacturing method of this embodiment, heat treatment may be performed in the process from the formation of the intermediate layer 13 covering the sacrificial layer 60 (step S13) until the removal of the sacrificial layer 60 (for example, the process of removing the transfer substrate 100 in step S15). As a result, part of the metal of the sacrificial layer 60 diffuses into the intermediate layer 13 and the insulating layer 50, forming the second portion 15 of the intermediate layer 13 (see FIG. 4) and the fourth portion 52 of the insulating layer 50 (see FIG. 15).

[0078] The elastic wave device 10A according to this embodiment can be manufactured through the above-described steps. Note that the steps described above are merely schematic and can be modified as appropriate. Furthermore, while the method for manufacturing the elastic wave device 10A according to the second embodiment has been described with reference to FIG. 16 , the method for manufacturing the elastic wave device 10 according to the first embodiment is similar to the steps shown in FIG. 16 , except that the deposition of the insulating layer 50 is omitted.

[0079] 17 is a cross-sectional view of an elastic wave device according to a third preferred embodiment of the present invention. Unlike the cross-sectional views shown in FIGS. 2 and 14 , Fig. 17 illustrates a cross-sectional view of an elastic wave device 10B according to the third preferred embodiment taken along the Y direction.

[0080] 17 , the elastic wave device 10B according to the third preferred embodiment differs from the first and second preferred embodiments in that a void 17 is formed in the intermediate layer 13 of the support member 11. The void 17 is formed by connecting the sidewall of the cavity 16 to the surface of the intermediate layer 13 that contacts the support substrate 12.

[0081] In the third embodiment, as in the first embodiment described above, the intermediate layer 13 of the support member 11 has a first portion 14 and a modified second portion 15. The second portion 15 is modified by metal diffusion and has a higher metal concentration than the first portion 14. The piezoelectric layer 20 also has a third portion 21 and a modified fourth portion 22. The fourth portion 22 is modified by metal diffusion and has a higher metal concentration than the third portion 21.

[0082] In the third embodiment, the metal is further diffused and modified in the region along the gap 17, forming a modified portion similar to the second portion 15. As a result, when the membrane portion MEM generates heat, moisture is released into the cavity 16 from the modified portion along the gap 17 in addition to the second portion 15 and the fourth portion 22. In this embodiment, the thermal conductivity of the cavity 16 is effectively improved, and the heat generated by the membrane portion MEM can be efficiently dissipated to the surrounding area.

[0083] 18 is a cross-sectional view of an elastic wave device according to a fourth preferred embodiment of the present invention. As shown in FIG. 18 , an elastic wave device 10C according to the fourth preferred embodiment of the present invention has a different configuration from the third preferred embodiment of the present invention in that it includes an insulating layer 50.

[0084] In the fourth embodiment, as in the second embodiment described above, the intermediate layer 13 of the support member 11 has a first portion 14 and a modified second portion 15. The second portion 15 is modified by metal diffusion and has a higher metal concentration than the first portion 14. The insulating layer 50 of the membrane unit MEM has a third portion 51 and a modified fourth portion 52. The fourth portion 52 is modified by metal diffusion and has a higher metal concentration than the third portion 51.

[0085] In this embodiment as well, a void 17 is formed in the intermediate layer 13 of the support member 11. The void 17 is formed by connecting the sidewall of the cavity 16 and the surface of the intermediate layer 13 that contacts the support substrate 12. The metal is also diffused into the region along the void 17 to modify it, and a modified portion similar to the second portion 15 is formed.

[0086] 19 is an explanatory diagram illustrating a manufacturing method of an elastic wave device according to the fourth embodiment. As shown in FIG. 19 , after the piezoelectric layer 20 is bonded to the main surface of the transfer substrate 100, an insulating layer 50 is formed on the second main surface 20b of the piezoelectric layer 20, and a sacrificial layer 60 is formed to cover a portion of the insulating layer 50 (step S21). The sacrificial layer 60 is made of, for example, zinc oxide.

[0087] An insulator that will become intermediate layer 13 is formed so as to cover insulating layer 50 and sacrificial layer 60 (step S22). A convex shape that conforms to the shape of sacrificial layer 60 is formed on the upper surface of intermediate layer 13. The formation of the convex shape on intermediate layer 13 generates stress between the convex portion and the flat portion without the convex shape, and forms void portion 17 that connects the portion where intermediate layer 13 and the side surface of sacrificial layer 60 contact with each other and the upper surface of intermediate layer 13.

[0088] Next, the convex shape formed on the surface of the intermediate layer 13 opposite to the piezoelectric layer 20 is flattened and smoothed (step S23).

[0089] Next, the insulating layer 50, the piezoelectric layer 20, and the like are bonded to the support substrate 12 via the intermediate layer 13, and then the transfer substrate 100 is removed from the piezoelectric layer 20 (step S24).

[0090] After the transfer substrate 100 is removed, a heat treatment is performed (step S25). In the heat treatment process, a portion of the metal of the sacrificial layer 60 diffuses into the intermediate layer 13 and the insulating layer 50, and also diffuses into the region along the void 17. As a result, the second portion 15 of the intermediate layer 13 (see FIG. 4) and the fourth portion 52 of the insulating layer 50 (see FIG. 15) are formed, and modified portions are also formed in the region along the void 17.

[0091] 20 is a cross-sectional view of an elastic wave device according to a fifth embodiment. As shown in FIG. 20 , an elastic wave device 10D according to the fifth embodiment differs from the above-described embodiments in that an electrode 30A includes an upper electrode 38 and a lower electrode 39.

[0092] Specifically, the upper electrode 38 is provided on the first main surface 20a of the piezoelectric layer 20. The lower electrode 39 is provided on the second main surface 20b of the piezoelectric layer 20. The upper electrode 38 and the lower electrode 39 overlap in a region overlapping with the cavity 16. In other words, in the region overlapping with the cavity 16, the piezoelectric layer 20 is disposed between the upper electrode 38 and the lower electrode 39 in the Z direction. This allows bulk waves to propagate between the upper electrode 38 and the lower electrode 39.

[0093] The upper electrode 38 and the lower electrode 39 are formed of a metal such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), molybdenum (Mo), or ruthenium (Ru), or an alloy containing at least one of these materials.

[0094] In the fifth embodiment, as in the above-described embodiments, at least the intermediate layer 13 of the support member 11 has a first portion 14 and a modified second portion 15. Also, the region of the membrane portion MEM (piezoelectric layer 20) where the lower electrode 39 is not provided has a third portion 21 and a modified fourth portion 22. As a result, in this embodiment as well, the thermal conductivity of the cavity 16 is improved, and heat generated by the membrane portion MEM can be efficiently dissipated to the surrounding area.

[0095] 21 is a cross-sectional view of an elastic wave device according to a sixth embodiment. As shown in Fig. 21 , an elastic wave device 10E according to the sixth embodiment has a different configuration from the fifth embodiment described above in that it includes an insulating layer 50.

[0096] The insulating layer 50 is provided on the second main surface 20b of the piezoelectric layer 20, covering the lower electrode 39. In the sixth embodiment, the membrane portion MEM is made up of the piezoelectric layer 20 and the insulating layer 50. In the same manner as in the second embodiment, the insulating layer 50 in the sixth embodiment has a third portion 51 and a modified fourth portion 52. As a result, in the present embodiment as well, the thermal conductivity of the cavity 16 is improved, and heat generated by the membrane portion MEM can be efficiently dissipated to the surroundings.

[0097] The above-described embodiment is intended to facilitate understanding of the present invention, and is not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the present invention, and equivalents thereof are also included in the present invention.

[0098] The present disclosure may also have the following configurations.

[0099] (1) An elastic wave device comprising: a piezoelectric layer having first and second principal surfaces opposing each other; an electrode provided on at least one of the first and second principal surfaces of the piezoelectric layer; and a support member provided on the second principal surface side of the piezoelectric layer and having a cavity provided on the second principal surface side of the piezoelectric layer, wherein a membrane portion including at least a part of the piezoelectric layer is formed in a region overlapping with the cavity portion, the support member having a first portion and a modified second portion, the second portion being located closer to the cavity than the first portion, the membrane portion having a third portion and a modified fourth portion, the fourth portion being located closer to the cavity than the third portion. (2) The elastic wave device according to (1), wherein the second portion is a region modified by diffusing a metal, and the second portion has a higher concentration of the metal than the first portion. (3) The elastic wave device according to (1) or (2), wherein the fourth portion is a region modified by diffusing a metal, and the fourth portion has a higher concentration of the metal than the third portion. (4) The elastic wave device according to any one of (1) to (3), wherein the membrane portion is made of the piezoelectric layer, the second main surface of the piezoelectric layer is in contact with the support member, and the piezoelectric layer has the third portion and the modified fourth portion in a region overlapping with the cavity. (5) The elastic wave device according to any one of (1) to (3), wherein the membrane portion includes an insulating layer provided between the piezoelectric layer and the support member, the membrane portion being made of the piezoelectric layer and the insulating layer, and the insulating layer has the third portion and the modified fourth portion in a region overlapping with the cavity. (6) The elastic wave device according to any one of (1) to (4), wherein the second portion and the fourth portion contain zinc oxide (ZnO). (7) The elastic wave device according to (6), wherein the second portion and the fourth portion contain zinc (Zn). (8) The elastic wave device according to any one of (1) to (7), wherein the electrode is an IDT electrode including a first bus bar and a second bus bar facing each other, at least one first electrode finger having a base end connected to the first bus bar, and at least one second electrode finger having a base end connected to the second bus bar.(9) The elastic wave device according to any one of (1) to (7), wherein the electrodes include an upper electrode provided on the first main surface of the piezoelectric layer and a lower electrode provided on the second main surface. (10) The elastic wave device according to any one of (1) to (9), wherein the support member includes a support substrate and an intermediate layer laminated on the support substrate. (11) The elastic wave device according to any one of (1) to (9), wherein the support member includes a support substrate and an intermediate layer laminated on the support substrate, and the cavity is a recess in the intermediate layer that opens to the piezoelectric layer side. (12) The elastic wave device according to (8), wherein d / p is 0.5 or less, where d is the film thickness of the piezoelectric layer and p is the center-to-center distance between the first electrode finger and the second electrode finger adjacent to each other. (13) The elastic wave device according to (12), wherein d / p is 0.24 or less. (14) The elastic wave device according to any one of (1) to (13), wherein the piezoelectric layer contains lithium niobate or lithium tantalate. (15) The elastic wave device according to (14), wherein the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3): (0°±10°, 0° to 20°, any ψ) ... formula (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50). ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２] to 180°, any ψ) ...Equation (3) (16) The elastic wave device according to (8), wherein d is a film thickness of the piezoelectric layer, p is a center-to-center distance between adjacent first electrode fingers and second electrode fingers, and an excitation region is an area where adjacent first electrode fingers and second electrode fingers overlap as viewed in an opposing direction. The metallization ratio MR of the first electrode fingers and the second electrode fingers to the excitation region satisfies MR≦1.75(d / p)+0.075. (17) The elastic wave device according to any one of (1) to (16), which is configured to enable use of thickness-shear mode bulk waves. (18) The elastic wave device according to any one of (1) to (16), which is configured to enable use of plate waves. (19) The elastic wave device according to any one of (1) to (18), wherein the second portion and the fourth portion include at least one of titanium oxide, magnesium oxide, nickel oxide, iron oxide, and cobalt oxide.

[0100] 10, 10A, 10B, 10C, 10D, 10E Acoustic wave device 11 Support member 12 Support substrate 13 Intermediate layer 14 First portion 15 Second portion 16 Cavity 17 Gap 20 Piezoelectric layer 20a First principal surface 20b Second principal surface 21, 51 Third portion 22, 52 Fourth portion 30 IDT electrode 30A Electrode 31 First electrode finger 32 Second electrode finger 33 First bus bar electrode 34 Second bus bar electrode 38 Upper electrode 39 Lower electrode 50 Insulating layer 60 Sacrificial layer 100 Transfer substrate

Claims

1. An elastic wave device comprising: a piezoelectric layer having opposing first and second principal surfaces; an electrode provided on at least one of the first and second principal surfaces of the piezoelectric layer; and a support member provided on the second principal surface side of the piezoelectric layer, the support member having a cavity on the second principal surface side of the piezoelectric layer, wherein a membrane portion including at least a part of the piezoelectric layer is formed in a region overlapping with the cavity portion; the support member having a first portion and a modified second portion, the second portion being positioned closer to the cavity portion than the first portion; and the membrane portion having a third portion and a modified fourth portion, the fourth portion being positioned closer to the cavity portion than the third portion.

2. The acoustic wave device according to claim 1, wherein the second portion is a region modified by diffusing a metal, and the second portion has a higher concentration of the metal than the first portion.

3. The elastic wave device according to claim 1 or 2, wherein the fourth portion is a region modified by diffusing a metal, and the fourth portion has a higher concentration of the metal than the third portion.

4. An elastic wave device according to any one of claims 1 to 3, wherein the membrane portion is made of the piezoelectric layer, the second main surface of the piezoelectric layer is in contact with the support member, and the piezoelectric layer has the third portion and the modified fourth portion in a region overlapping with the cavity portion.

5. An elastic wave device according to any one of claims 1 to 3, further comprising an insulating layer provided between the piezoelectric layer and the support member, the membrane portion consisting of the piezoelectric layer and the insulating layer, and the insulating layer having the third portion and the modified fourth portion in a region overlapping with the cavity portion.

6. The acoustic wave device according to any one of claims 1 to 4, wherein the second portion and the fourth portion contain zinc oxide.

7. The acoustic wave device according to claim 6, wherein the second portion and the fourth portion contain zinc.

8. The elastic wave device according to any one of claims 1 to 7, wherein the electrode is an IDT electrode including a first bus bar and a second bus bar facing each other, at least one first electrode finger having a base end connected to the first bus bar, and at least one second electrode finger having a base end connected to the second bus bar.

9. The acoustic wave device according to any one of claims 1 to 7, wherein the electrodes include an upper electrode provided on the first principal surface of the piezoelectric layer and a lower electrode provided on the second principal surface.

10. The acoustic wave device according to any one of claims 1 to 9, wherein the support member comprises a support substrate and an intermediate layer laminated on the support substrate.

11. An elastic wave device according to any one of claims 1 to 9, wherein the support member comprises a support substrate and an intermediate layer laminated on the support substrate, and the cavity is a recess that opens to the piezoelectric layer side of the intermediate layer.

12. The acoustic wave device according to claim 8, wherein d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between the adjacent first electrode fingers and second electrode fingers.

13. The acoustic wave device according to claim 12, wherein the ratio d / p is 0.24 or less.

14. The acoustic wave device according to any one of claims 1 to 13, wherein the piezoelectric layer contains lithium niobate or lithium tantalate.

15. The elastic wave device according to claim 14, wherein the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3): (0°±10°, 0° to 20°, any ψ) ... formula (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3) 16. The elastic wave device according to claim 8, wherein, when the film thickness of the piezoelectric layer is d, the center-to-center distance between adjacent first electrode fingers and second electrode fingers is p, and the region where adjacent first electrode fingers and second electrode fingers overlap when viewed in the opposing direction is defined as an excitation region, the metallization ratio MR of the plurality of first electrode fingers and second electrode fingers with respect to the excitation region satisfies MR≦1.75(d / p)+0.

075.

17. The elastic wave device according to any one of claims 1 to 16, which is configured to be capable of utilizing bulk waves in thickness shear mode.

18. The elastic wave device according to any one of claims 1 to 16, which is configured to be able to use plate waves.

19. The acoustic wave device according to any one of claims 1 to 18, wherein the second portion and the fourth portion contain at least one of titanium oxide, magnesium oxide, nickel oxide, iron oxide, and cobalt oxide.

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