Elastic wave device

Abstract

Provided is an elastic wave device in which degradation in Q characteristics is less likely to occur. An elastic wave device (1) includes a piezoelectric substrate (2) and an IDT electrode (7) provided on the piezoelectric substrate (2), the IDT electrode (7) having an overlapping region in which a first electrode finger and a second electrode finger overlap along an elastic wave propagation direction, the overlapping region having a central region and first and second low sound velocity regions on both outer sides of the central region in the extension direction of the first and second electrode fingers, the first and second bus bars (11, 12) having a plurality of openings (11a, 12a), an inner bus bar portion (11b, 12b) on one side of the opening (11a, 12a) being connected to an outer bus bar portion (11c, 12c) on the other side through a plurality of connecting portions (11d, 12d), at least one of the plurality of connecting portions (11d, 12d) being a wide connecting portion (11d1, 12d1) having a width greater than the remaining connecting portions (11d, 12d).

Description

Technical Field

[0001] The present invention relates to an elastic wave device having a first busbar and a second busbar, and having a plurality of openings provided in the first busbar and the second busbar. Background Technology

[0002] Conventionally, elastic wave devices utilizing a piston mode have been known to suppress transverse mode ripple. For example, in Patent Document 1 described below, a central region and low-velocity regions are provided on either side of the central region within the cross-region of the IDT electrodes. Furthermore, multiple openings are provided in the busbar along the propagation direction. The portion of the opening on the cross-region side of the busbar becomes the inner busbar portion, and the portion on the outer side opposite the cross-region becomes the outer busbar portion. The inner and outer busbar portions are connected by multiple thin connecting portions. Thus, the portion with the opening, together with the inner busbar portion, forms a high-velocity region.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-174595 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In the elastic wave device described in Patent Document 1, the inner busbar section and the outer busbar section are connected by multiple thin connecting parts. Therefore, there is a problem of Q-characteristic deterioration.

[0008] The purpose of this invention is to provide an elastic wave device that is difficult to generate with deteriorated Q characteristics.

[0009] means for solving problems

[0010] The elastic wave device of the present invention includes: a piezoelectric substrate; and an IDT electrode disposed on the piezoelectric substrate. The IDT electrode has a first busbar and a second busbar facing each other, a plurality of first electrode fingers extending from the first busbar toward the second busbar, and a plurality of second electrode fingers extending from the second busbar toward the first busbar. The intersection region where the first electrode fingers and the second electrode fingers coincide in the elastic wave propagation direction has a central region located at the center of the extending directions of the first electrode fingers and the second electrode fingers, and a first low-sound velocity region and a second low-sound velocity region disposed on two outer sides of the extending directions of the first electrode fingers and the second electrode fingers in the central region. The sound speed in the low-speed region is lower than that in the central region. The first busbar and the second busbar have multiple openings arranged along the direction of elastic wave propagation. The portions of the multiple openings on the intersection side of the first busbar and the second busbar are respectively the first inner busbar portion and the second inner busbar portion. The portions of the multiple openings on the opposite side from the intersection area are respectively the first outer busbar portion and the second outer busbar portion. The first inner busbar portion and the second inner busbar portion are connected to the first outer busbar portion and the second outer busbar portion through multiple connecting portions. At least one of the multiple connecting portions is a wide connecting portion with a size larger than the remaining connecting portions along the direction of elastic wave propagation.

[0011] Invention Effects

[0012] According to the present invention, it is possible to provide an elastic wave device that is difficult to produce Q-characteristic degradation. Attached Figure Description

[0013] Figure 1 This is a top view of a simplified diagram illustrating the electrode structure of the elastic wave device according to the first embodiment of the present invention.

[0014] Figure 2 This is a schematic diagram showing the electrode structure of the elastic wave device according to the first embodiment of the present invention.

[0015] Figure 3 This is a front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0016] Figure 4 This is a partial cross-sectional top view showing the main part of the IDT electrode of the elastic wave device according to the first embodiment of the present invention.

[0017] Figures 5(a) and 5(b) are... Figure 1 The enlarged view of the portion indicated by arrows A and B is shown in the top view.

[0018] Figure 6This is a graph showing the Q characteristics of Example 1 and Comparative Example 1.

[0019] Figure 7 It is Figure 6 The Q characteristic plot is shown in magnified form.

[0020] Figure 8 This is a top view showing a simplified diagram of the electrode structure of the elastic wave device according to the second embodiment of the present invention.

[0021] Figure 9 This is a diagram showing the Q characteristics of the elastic wave devices of Examples 1 to 4.

[0022] Figure 10 It is Figure 9 A portion of the image is shown in enlarged form.

[0023] Figure 11 This is a partial cross-sectional top view showing the electrode structure of the elastic wave device according to the third embodiment of the present invention.

[0024] Figure 12 This is a front cross-sectional view of the elastic wave device according to the fourth embodiment of the present invention.

[0025] Figure 13 This is a front cross-sectional view of the elastic wave device according to the fifth embodiment of the present invention. Detailed Implementation

[0026] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby making the present invention clear.

[0027] It should be noted that the embodiments described in this specification are illustrative, and it is indicated in advance that partial substitutions or combinations of structures can be made between different embodiments.

[0028] Figure 3 This is a front cross-sectional view of the elastic wave device according to the first embodiment of the present invention. The elastic wave device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 has a piezoelectric film 3, a low-velocity sound material layer 4, a high-velocity sound material layer 5, and a support substrate 6. IDT electrodes 7 and reflectors 8 and 9 are disposed on the piezoelectric substrate 2. Figure 2 As shown in the schematic diagram, the electrode structure of the elastic wave device 1 includes an IDT electrode 7 and reflectors 8 and 9 disposed on both sides of the elastic wave propagation direction of the IDT electrode 7. Thus, a single-port type elastic wave resonator is formed.

[0029] The elastic wave device 1 is characterized by the specific electrode structure of the IDT electrode 7. (Refer to...) Figure 1 , Figure 4 Figures 5(a) and 5(b) provide a detailed description of the electrode structure.

[0030] Figure 1 This is a top view showing a simplified diagram of the electrode structure of the elastic wave device 1. The IDT electrode 7 has a first busbar 11 and a second busbar 12 that are opposite each other. Figure 4 The detailed structure of the IDT electrode 7 is shown in a partial cross-sectional top view. Multiple first electrode fingers 13 are connected to the first busbar 11. The first electrode fingers 13 extend from the first busbar 11 toward the second busbar 12. Multiple second electrode fingers 14 are connected to the second busbar 12. The second electrode fingers 14 extend from the second busbar 12 toward the first busbar 11. The area where the first electrode fingers 13 and second electrode fingers 14 overlap when viewed along the elastic wave propagation direction is the intersection region K. The intersection region K has a central region C, and two outer regions, a first low-sound velocity region D1 and a second low-sound velocity region D2, located in the central region C in the direction in which the first electrode fingers 13 and second electrode fingers 14 extend. It should be noted that other regions may also exist outside the first low-sound velocity region D1 and the second low-sound velocity region D2.

[0031] The IDT electrode 7 comprises a suitable metal or alloy. In the first low-sound velocity region D1 and the second low-sound velocity region D2, as shown by the shaded lines, mass-addition films 13a and 14a are disposed on the first electrode finger 13 and the second electrode finger 14. The mass-addition films 13a and 14a comprise a metal or a dielectric. By providing the mass-addition films 13a and 14a, as... Figure 4 As shown on the right, the sound speed V2 in the first low-sound speed region D1 and the second low-sound speed region D2 is lower than the sound speed V1 in the central region C.

[0032] It should be noted that the mass-added films 13a and 14a can also be stacked on the lower surface side of the first electrode finger 13 and the second electrode finger 14.

[0033] It should be noted that, in Figure 4 In this process, although mass-added films 13a and 14a are stacked on the first electrode finger 13 and the second electrode finger 14, in the case of including a dielectric film, the mass-added film may also be formed to reach the region between the first electrode finger 13 and the second electrode finger 14.

[0034] In the first busbar 11, a plurality of openings 11a are provided along the direction of elastic wave propagation. An inner busbar portion 11b is provided on the side of the intersection region K of the openings 11a in the first busbar 11. An outer busbar portion 11c is provided in the region on the outside of the openings 11a opposite to the intersection region K. In the first busbar 11, the inner busbar portion 11b and the outer busbar portion 11c are connected by a plurality of connecting portions 11d. Although not particularly limited, the connecting portions 11d extend in a direction orthogonal to the direction of elastic wave propagation; in this embodiment, they are provided at the position after the first electrode finger 13 has been extended. It should be noted that the inner busbar portion 11b is the first inner busbar portion in this invention, and the outer busbar portion 11c is the first outer busbar portion in this invention.

[0035] The second busbar 12 is constructed similarly. That is, the second busbar 12 has multiple openings 12a. Furthermore, an inner busbar portion 12b is provided on the side of the intersection region K of the openings 12a. An outer busbar portion 12c is provided on the outer side of the openings 12a, opposite to the intersection region K. The inner busbar portion 12b and the outer busbar portion 12c are connected by multiple connecting portions 12d. It should be noted that the inner busbar portion 12b is the second inner busbar portion in this invention, and the outer busbar portion 12c is the second outer busbar portion in this invention.

[0036] Because the IDT electrode 7 has the structure described above, the sound velocity in the region outside the first low-sound velocity region D1 and the second low-sound velocity region D2 becomes Figure 4 V10, V11, V12, and V13 are shown. That is, the high-sound-speed regions shown by V10, V11, and V12 are located outside the direction in which the first electrode finger 13 and the second electrode finger 14 extend in the first low-sound-speed region D1 and the second low-sound-speed region D2. Therefore, transverse mode ripples can be effectively blocked.

[0037] Figure 5(a) shows the... Figure 4 The main part of the IDT electrode 7 shown is... Figure 1 The portion indicated by arrow A is shown in a magnified top view. Figure 5(b) is a partial top view of the area indicated by arrow A. Figure 1 The portion indicated by arrow B is shown in an enlarged top view.

[0038] The first busbar 11 has a wide connecting portion 11d1. The width of the wide connecting portion 11d1 along the direction of elastic wave propagation is larger than that of the remaining connecting portion 11d (Fig. 5(a)). In Fig. 5(b), the boundary between the outer busbar portion 11c and the wide connecting portion 11d1 is shown by dashed line X1. In addition, the boundary between the wide connecting portion 11d1 and the inner busbar portion 11b is shown by dashed line X2.

[0039] The width of the wide connecting portion 11d1 is larger than the width of the remaining connecting portion 11d. Therefore, in the first busbar 11, the resistance between the outer busbar portion 11c and the inner busbar portion 11b can be reduced. Thus, the degradation of Q characteristics can be suppressed.

[0040] Especially Figure 1 As shown, in this embodiment, a pair of wide-width connectors 11d1, 11d1 are spaced apart in the elastic wave propagation direction of the first busbar 11. In the second busbar 12, wide-width connectors 12d1, 12d1 are also spaced apart in the elastic wave propagation direction. Because multiple wide-width connectors 11d1, 11d1 or wide-width connectors 12d1, 12d1 are provided, the electrical connection resistance between the outer busbar sections 11c, 12c and the inner busbar sections 11b, 12b can be further reduced. Therefore, the degradation of Q characteristics can be suppressed more effectively.

[0041] It should be noted that, in this invention, the wide connecting portion can be provided at least on at least one of the first busbar 11 and the second busbar 12. Therefore, the wide connecting portion 11d1 may also be provided only on the first busbar 11.

[0042] Preferably, wide connecting portions are provided on both sides of the first busbar 11 and the second busbar 12. Furthermore, as in this embodiment, it is more preferable that multiple wide connecting portions 11d1, 11d1, 12d1, 12d1 are provided on both sides of the first busbar and the second busbars 11 and 12.

[0043] like Figure 1 As shown, a pair of wide-width connecting portions 11d1, 11d1 are provided at both ends of the elastic wave propagation direction of the first busbar 11. In the second busbar 12, a pair of wide-width connecting portions 12d1, 12d1 are also provided at both ends of the elastic wave propagation direction. Therefore, the leakage of elastic wave energy is reduced, and in this embodiment, it is even more difficult to cause Q-value degradation. Therefore, it is more preferable that at least one of the first busbar and the second busbar 11, 12 has wide-width connecting portions 11d1, 11d1 or wide-width connecting portions 12d1, 12d1 provided at both ends of the elastic wave propagation direction.

[0044] The widths of the aforementioned wide-width connecting portions 11d1 and 12d1 are preferably larger than those of the remaining connecting portions 11d and 12d, but are preferably 10 μm or more and 30 μm or less. Furthermore, when the wavelength determined by the distance between the first electrode finger 13 and the second electrode finger 14 is set as λ, the widths of the aforementioned wide-width connecting portions 11d1 and 12d1 are preferably 1λ or more and 10λ or less. If the width is 1λ or more, the decrease in the Q value can be suppressed more effectively. Furthermore, if the width is 10λ or less, transverse mode ripple can be suppressed more effectively.

[0045] In reflectors 8 and 9, the two ends of multiple electrodes are short-circuited through a pair of busbars. That is, reflectors 8 and 9 are grating-type reflectors, and their construction is not particularly limited.

[0046] like Figure 3 As shown, the piezoelectric substrate 2 has a structure obtained by sequentially stacking a high-velocity material layer 5, a low-velocity material layer 4, and a piezoelectric film 3 on a support substrate 6. The support substrate 6 includes suitable semiconductor or dielectric materials such as Si or bauxite.

[0047] As the piezoelectric film 3, piezoelectric single crystals such as LiTaO3 can be used. The low-velocity material layer 4 includes a low-velocity material. A low-velocity material is a material in which the velocity of a bulk wave propagating in a low-velocity material is lower than the velocity of a bulk wave propagating in the piezoelectric film 3. Examples of such low-velocity materials include those mainly composed of glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum pentoxide, or compounds obtained by adding fluorine, carbon, or boron to silicon oxide.

[0048] The hypersonic material layer 5 includes a hypersonic material in which the velocity of the bulk wave propagating in the hypersonic material layer 5 is higher than the velocity of the elastic wave propagating in the piezoelectric film 3. Examples of such hypersonic materials include silicon, alumina, silicon carbide, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, DLC (diamond-like carbon) film, or diamond, as well as media with the above materials as the main component.

[0049] It should be noted that the low-velocity material layer 4 can also be omitted.

[0050] In the piezoelectric substrate 2 described above, due to the aforementioned laminated structure, the energy of elastic waves can be effectively blocked to the piezoelectric film 3.

[0051] Next, the effects of this embodiment will become clear by showing the Q characteristics of Example 1 and Comparative Example 1 of the first embodiment.

[0052] The design parameters for Example 1 are as follows.

[0053] The material of IDT electrode 7 and reflectors 8 and 9 is Al.

[0054] The wavelength λ, determined by the distance between the electrode fingers, is 2.12 μm. The electrode film thickness is 0.047λ.

[0055] The dimension of the intersection region K is 23.58λ. The length of the central region C is 21.77λ. The lengths of the first low-sound region D1 and the second low-sound region D2 are 0.90λ.

[0056] The width of the inner busbar sections 11b and 12b (the dimension in the extension direction of the first electrode index 13 and the second electrode index 14) is 0.20λ. The dimension of the openings 11a and 12a along the elastic wave propagation direction is 2.00λ. The dimension in the extension direction of the first electrode index 13 and the second electrode index 14 is 0.43λ. The width of the connecting sections 11d and 12d is 1.13λ. The width of the wide connecting sections 11d1 and 12d1 is 100.46λ.

[0057] The width of the outer busbar sections 11c and 12c (the dimension in the extension direction of the first electrode finger 13 and the second electrode finger 14) = 5.66λ.

[0058] The number of electrode fingers is 100.

[0059] The piezoelectric film is LiTaO3 with a thickness of 3 = 0.19λ.

[0060] Low-velocity material layer 4: SiN, thickness 0.14λ.

[0061] High-velocity material layer 5: SiO2, thickness 0.14λ.

[0062] Support substrate 6: Si.

[0063] In Comparative Example 1, the portion having remaining connecting portions 11d and 12d without the aforementioned wide connecting portions 11d1, 11d1, 12d1, 12d1 is constructed in the same manner. Regarding other structures, Comparative Example 1 is the same as Example 1.

[0064] Figure 6 This is a graph showing the Q characteristics of Embodiment 1 and Comparative Example 1, which are embodiments of the elastic wave device 1 as the first implementation. The solid line represents the results of Embodiment 1, and the dashed line represents the results of Comparative Example 1. Figure 7 It is Figure 6 A portion of the image is shown in enlarged form. According to... Figure 6 and Figure 7 It can be seen that near 1900MHz, where the Q value is highest, Example 1 can effectively improve the Q value compared to Comparative Example 1. That is, it can be seen that compared to Comparative Example 1, it is difficult to cause a deterioration in Q characteristics.

[0065] Figure 8 This is a top view showing a simplified diagram of the electrode structure of the elastic wave device according to the second embodiment of the present invention. In the elastic wave device 21, the positions of the wide-width connecting portions 11d1 and 12d1 along the elastic wave propagation direction in the IDT electrode 7 are changed. Regarding other structures, the elastic wave device 21 is the same as the elastic wave device 1.

[0066] like Figure 8As shown, the wide-width connecting portions 11d1, 11d1 are located inside the ends of the first busbar 11 in the elastic wave propagation direction. More specifically, when the distance between one end of the first busbar 11 in the elastic wave propagation direction and the wide-width connecting portion 11d1 is set to L, L>0. The wide-width connecting portion 12d1 in the second busbar 12 is also configured in the same way.

[0067] In the elastic wave device 21, as described above, the wide-width connecting portions 11d1 and 12d1 are located inside the ends of the first busbar and the second busbar 11 and 12 in the elastic wave propagation direction. Thus, the wide-width connecting portions 11d1 and 12d1 can also be located inside the ends of the first busbar and the second busbar 11 and 12 in the elastic wave propagation direction. In this case, the degradation of the Q characteristic can also be suppressed by reducing the resistance.

[0068] Apart from the distance L, the elastic wave devices of Examples 2 to 4 are constructed using the same design parameters as the elastic wave device of Example 1 described above.

[0069] Example 2: L = 10 μm = 4.7λ.

[0070] Example 3: L = 20 μm = 9.4λ.

[0071] Example 4: L = 30 μm = 14.1λ.

[0072] Figure 9 The Q-characteristics of the elastic wave devices of Embodiments 1 and 2-4 are shown. Additionally, in Figure 10 Enlarged view Figure 9 Part of it. Figure 10 In the diagram, solid lines represent the results of Example 1, dashed lines represent the results of Example 2, single-dotted lines represent the results of Example 3, and double-dotted lines represent the results of Example 4. According to... Figure 10 It can be seen that, compared with Examples 2-4, Example 1 is less likely to cause degradation of the Q characteristic, and is therefore more preferred. Furthermore, as shown in Examples 2-4, a smaller L value can suppress the degradation of the Q characteristic. Therefore, L less than 20 μm is more preferred, and L less than 9.4λ is even more preferred.

[0073] Figure 11This is a partial cross-sectional top view illustrating the electrode structure of the elastic wave device according to the third embodiment of the present invention. In the third embodiment, the first electrode finger 13 and the second electrode finger 14 have thick portions 13b and 14b. The regions where these thick portions 13b and 14b are provided become low-sound-velocity regions. Regarding other structures, the elastic wave device 31 of the third embodiment is configured similarly to the elastic wave device 1 of the first embodiment. Thus, in the present invention, a first low-sound-velocity region and a second low-sound-velocity region can be formed by making a portion of the first electrode finger 13 and a portion of the second electrode finger 14 the thick portions 13b and 14b without providing a mass-addition membrane.

[0074] Figure 12 This is a front cross-sectional view of the elastic wave device according to the fourth embodiment of the present invention. In the elastic wave device 41, the piezoelectric substrate 2 has a high-velocity acoustic support substrate 5A. The high-velocity acoustic support substrate 5A includes the aforementioned high-velocity acoustic material. In this case, instead of Figure 3 The support substrate 6 shown is replaced by a high-velocity support substrate 5A. Therefore, it is possible to omit the support substrate 6. Figure 3 The hypersonic material layer 5 is shown.

[0075] Figure 13 This is a front cross-sectional view of the elastic wave device according to the fifth embodiment of the present invention. In the elastic wave device 51, a piezoelectric substrate 52 is used as a piezoelectric substrate. The piezoelectric substrate 52 includes a single crystal such as LiNbO3 or LiTaO3. In the present invention, the piezoelectric substrate may also include a single piezoelectric single crystal substrate.

[0076] Explanation of reference numerals in the attached figures

[0077] 1…elastic wave device;

[0078] 2…piezoelectric substrate;

[0079] 3…piezoelectric film;

[0080] 4…Low-velocity material layer;

[0081] 5…High-speed acoustic material layer;

[0082] 5A…high-speed acoustic support substrate;

[0083] 6...support base plate;

[0084] 7…IDT electrode;

[0085] 8, 9... reflectors;

[0086] 11, 12… First busbar, Second busbar;

[0087] 11a, 12a… openings;

[0088] 11b, 12b… inner busbar section;

[0089] 11c, 12c… outer busbar section;

[0090] 11d, 12d… connecting parts;

[0091] 11d1, 12d1… Wide-width connecting parts;

[0092] 13, 14… First electrode finger, second electrode finger;

[0093] 13a, 14a… quality-added membrane;

[0094] 13b, 14b… Bold section;

[0095] 21, 31, 41, 51… elastic wave devices;

[0096] 52… Piezoelectric substrate.

Claims

1. An elastic wave device comprising: a piezoelectric substrate; and an IDT electrode provided on the piezoelectric substrate, the IDT electrode having first and second bus bars facing each other, a plurality of first electrode fingers extending from the first bus bar toward the second bus bar, and a plurality of second electrode fingers extending from the second bus bar toward the first bus bar, an intersection region where the first electrode fingers and the second electrode fingers overlap each other in an elastic wave propagation direction having a central region located at a center of extension directions of the first electrode fingers and the second electrode fingers, and first and second low-velocity regions disposed at both outer sides of the extension directions of the first electrode fingers and the second electrode fingers from the central region, the first and second low-velocity regions having a lower velocity than the central region, the first and second bus bars having a plurality of openings provided along the elastic wave propagation direction, portions of the first and second bus bars on a side of the intersection region of the plurality of openings being first and second inner bus bar portions, respectively, portions of the first and second bus bar portions on a side opposite to the intersection region of the plurality of openings being first and second outer bus bar portions, respectively, the first and second inner bus bar portions being connected to the first and second outer bus bar portions by a plurality of connection portions, and at least one of the connection portions having a larger width than the remaining connection portions in a dimension along the elastic wave propagation direction.

2. The elastic wave device according to claim 1, wherein a plurality of the wide connection portions are provided in each of the first and second bus bars.

3. The elastic wave device according to claim 2, wherein one pair of the wide connection portions is provided in at least one of the first and second bus bars.

4. The elastic wave device according to claim 3, wherein the one pair of the wide connection portions are located at both ends in the elastic wave propagation direction in at least one of the first and second bus bars.

5. The elastic wave device according to any one of claims 1 to 4, wherein a dimension of the wide connection portion along the elastic wave propagation direction is in a range of 1λ or more and 10λ or less, when a wavelength determined by an electrode finger pitch of the first and second electrode fingers of the IDT electrode is λ.

6. The elastic wave device according to any one of claims 1 to 4, wherein a mass adding film is provided in the first and second low-velocity regions on the first and second electrode fingers.

7. The elastic wave device according to any one of claims 1 to 4, wherein a width of the first and second electrode fingers in the first and second low-velocity regions is larger than a width of the first and second electrode fingers in the central region.

8. The elastic wave device according to any one of claims 1 to 4, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The piezoelectric substrate has a piezoelectric film and a high acoustic velocity material layer including a high acoustic velocity material whose acoustic velocity of a bulk wave propagating in the high acoustic velocity material layer is higher than an acoustic velocity of an elastic wave propagating in the piezoelectric film.

9. The elastic wave device according to claim 8, wherein The elastic wave device further has a low acoustic velocity material layer laminated between the high acoustic velocity material layer and the piezoelectric film, and including a low acoustic velocity material whose acoustic velocity of a bulk wave propagating in the low acoustic velocity material layer is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film.

10. The elastic wave device according to claim 8, wherein The high acoustic velocity material layer is a high acoustic velocity support substrate including the high acoustic velocity material.

11. The elastic wave device according to any one of claims 1 to 4, wherein The piezoelectric substrate is a piezoelectric substrate including a piezoelectric single crystal.

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