Elastic wave device and elastic wave filter device

Abstract

Provided are an elastic wave device and an elastic wave filter device with which it is possible to suppress leakage of elastic waves. This elastic wave device comprises: a piezoelectric layer that has a first main surface and a second main surface; an IDT electrode that is provided to at least one of the first main surface and the second main surface of the piezoelectric layer, the IDT electrode including a plurality of electrode fingers arranged in a prescribed direction; and a support member that faces the second main surface of the piezoelectric layer and has an acoustic reflection part on the second-main-surface side of the piezoelectric layer. At least one of a first electrode finger disposed on the outermost side in the arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the inner side of the first electrode finger, among the plurality of electrode fingers, is different in terms of at least one of a dimension in a direction orthogonal to the extension direction of the plurality of electrode fingers and the center-to-center distance between the electrode finger and the electrode finger adjacent to the inner side in the arrangement direction with respect to a center electrode finger disposed on the inner side of the second electrode finger. The ratio 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 adjacent electrode fingers.

Description

Acoustic wave device and acoustic wave filter device

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

[0002] Patent Documents 1 and 2 describe acoustic wave devices.

[0003] JP-T-2022-524136 Publication U.S. Pat. No. 11,349,450

[0004] The acoustic wave devices disclosed in Patent Documents 1 and 2 have the possibility of acoustic wave leakage occurring in the arrangement direction of the electrode fingers.

[0005] An object of the present invention is to provide an acoustic wave device and an acoustic wave filter device that can suppress leakage of acoustic waves.

[0006] an IDT electrode provided on at least one of the first and second main surfaces of the piezoelectric layer and including a plurality of electrode fingers arranged in a predetermined direction; and a support member facing the second main surface of the piezoelectric layer and having an acoustic reflector on the second main surface side of the piezoelectric layer, wherein at least one of a first electrode finger arranged outermost in the arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the first electrode finger on the inside in the arrangement direction differs from a central electrode finger arranged on the inside of the second electrode finger in at least one of a dimension in a direction perpendicular to the extension direction of the plurality of electrode fingers and a center-to-center distance between the electrode finger adjacent to the first electrode finger on the inside in the arrangement direction, and 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 adjacent electrode fingers.

[0007] An acoustic wave filter device according to one aspect is a filter device including at least one resonator, wherein the resonator is the acoustic wave device described above.

[0008] According to the acoustic wave device and the acoustic wave filter device of the present invention, leakage of acoustic waves can be suppressed.

[0009] 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 a schematic cross-sectional view illustrating a bulk wave in a first-order thickness-shear mode propagating through a piezoelectric layer according to the first embodiment. FIG. 4 is a schematic cross-sectional view illustrating the amplitude direction of a bulk wave in a first-order thickness-shear mode propagating through a piezoelectric layer according to the first embodiment. FIG. 5 is a diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. FIG. 6 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. 7 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. 8 is a reference diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. FIG. 9 is an explanatory diagram showing the relationship between the fractional bandwidth and the amount of phase rotation of the spurious impedance normalized by 180 degrees, which represents the magnitude of the spurious, when a large number of elastic wave resonators are configured in the elastic wave device according to the first embodiment. FIG. 10 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the fractional bandwidth. FIG. 11 is an explanatory diagram showing a map of the fractional bandwidth versus the Euler angles (0°, θ, ψ) of LiNbO3 when d / p is set as close to 0 as possible. FIG. 12 is an enlarged cross-sectional view of region A shown in FIG. 2. FIG. 13 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the first embodiment. FIG. 14 is an explanatory diagram showing the distribution of vibration modes of the elastic wave device according to the first embodiment. FIG. 15 is an explanatory diagram showing the distribution of vibration modes of an elastic wave device according to a comparative example. FIG. 16 is a cross-sectional view of an elastic wave device according to a second embodiment. FIG. 17 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to the second embodiment. Fig. 18 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a second embodiment. Fig. 19 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a comparative example. Fig. 20 is a cross-sectional view of an elastic wave device according to a first modified example of the second embodiment. Fig. 21 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to the first modified example of the second embodiment. Fig. 22 is a cross-sectional view of an elastic wave device according to a second modified example of the second embodiment.FIG. 23 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to a second modified example of the second embodiment. FIG. 24 is a cross-sectional view of an elastic wave device according to a third modified example of the second embodiment. FIG. 25 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to a third modified example of the second embodiment. FIG. 26 is a cross-sectional view of an elastic wave device according to a third embodiment. FIG. 27 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to the third embodiment. FIG. 28 is a plan view of an elastic wave device according to a fourth embodiment. FIG. 29 is a cross-sectional view taken along line XXX-XXX' in FIG. 28. FIG. 30 is an enlarged cross-sectional view of region A1 shown in FIG. 29. FIG. 31 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to a fourth embodiment. FIG. 32 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to a fourth modified example of the fourth embodiment. FIG. 33 is a cross-sectional view of an elastic wave device according to a fifth modified example of the fourth embodiment. FIG. 34 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to a fifth modified example of the fourth embodiment. FIG. 35 is a circuit diagram illustrating an elastic wave filter device according to a fifth preferred embodiment. FIG. 36 is a cross-sectional view illustrating an elastic wave device according to a sixth preferred embodiment. FIG. 37 is a cross-sectional view illustrating an elastic wave device according to a seventh preferred embodiment. FIG. 38 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to an eighth preferred embodiment. FIG. 39 is an explanatory diagram illustrating an example of impedance phase in a higher mode. FIG. 40 is a plan view illustrating IDT electrodes of an elastic wave device according to a ninth preferred embodiment. FIG. 41 is a diagram illustrating the inter-electrode pitch p of an elastic wave device according to the ninth preferred embodiment. ｎ FIG. 42 is an explanatory diagram showing the impedance phase of an elastic wave device according to Comparative Example 1. FIG. 43 is an explanatory diagram showing the impedance phase at 5102 MHz of elastic wave devices according to the ninth embodiment and Comparative Examples 1 and 2. FIG. 44 is a plan view showing an IDT electrode of an elastic wave device according to a tenth embodiment. FIG. 45 is an explanatory diagram showing the impedance phase at 5102 MHz of an elastic wave device according to a tenth embodiment. ｎ 46 is a diagram illustrating the impedance phase at 5102 MHz of elastic wave devices according to the tenth embodiment and comparative examples 1 and 3.

[0010] Embodiments of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to these embodiments. Each embodiment described in the present disclosure is illustrative, and in the second and subsequent embodiments, descriptions of commonalities with the first embodiment will be omitted, and only differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned sequentially for each embodiment. Furthermore, in the present disclosure, when Euler angles or cut angles are expressed using the notation X°±Y°, this notation means that the angle is greater than or equal to X°-Y° and less than or equal to X°+Y°.

[0011] 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. In Fig. 1, a first protective film 41 is indicated by a two-dot chain line.

[0012] 1 and 2 , an elastic wave device 10 according to the first preferred embodiment includes a piezoelectric layer 20, an IDT electrode 30, a support substrate 11, a first protective film 41, and a second protective film 42. As shown in Fig. 2 , the elastic wave device 10 includes the second protective film 42, the piezoelectric layer 20, the IDT electrode 30, and the first protective film 41 stacked in this order on the support substrate 11.

[0013] 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. Here, 120°±10° includes the range of 120°-10° to 120°+10°, and 90°±10° includes the range of 90°-10° to 90°+10°.

[0014] 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, approximately 180 nm.

[0015] 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 electrode fingers 31 and 32 and busbar electrodes 33 and 34. The plurality of electrode fingers 31 extend in the Y direction, and one end side in the extension direction is connected to the busbar electrode 33. The plurality of electrode fingers 32 extend in the Y direction, and the other end side in the extension direction is connected to the busbar electrode 34. The plurality of electrode fingers 31 and the plurality of electrode fingers 32 are arranged alternately in the X direction with a gap therebetween. The busbar electrodes 33 and 34 each extend in the X direction and are spaced apart in the Y direction. The plurality of electrode fingers 31 and 32 are arranged between the busbar electrode 33 and the busbar electrode 34.

[0016] 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 electrode fingers 31 and 32 as the Y direction, and the arrangement direction of the electrode fingers 31 and 32 as the X direction. In the following description, a plan view refers to the positional relationship when viewed from a direction perpendicular to the first main surface 20 a of the piezoelectric layer 20.

[0017] The distance between the centers of the electrode fingers 31 and 32 adjacent to each other in the X direction in the width direction (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 electrode finger 31 in a direction perpendicular to the extension direction of the electrode finger 31 and the center of the width of the electrode finger 32 in a direction perpendicular to the extension direction of the electrode finger 31. The width of the electrode fingers 31 and 32 (hereinafter referred to as the electrode width), i.e., the dimension in the direction perpendicular to the extension direction of the electrode fingers 31 and 32, is preferably in the range of 150 nm to 1000 nm. Details of the inter-electrode pitch and electrode width of the electrode fingers 31 and 32 will be described later with reference to FIGS. 12 and 13 .

[0018] Furthermore, when there are multiple electrode fingers 31 and multiple electrode fingers 32 (when the electrode fingers 31 and the 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 electrode fingers 31 and the electrode fingers 32 refers to the average value of the center-to-center distances of adjacent electrode fingers 31 and electrode fingers 32 among the 1.5 or more pairs of electrode fingers 31 and electrode fingers 32.

[0019] Furthermore, in the first embodiment, since a Z-cut piezoelectric layer is used, the direction perpendicular to the extension direction of the electrode fingers 31 and 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 electrode fingers 31 and 32 and the polarization direction is, for example, 90°±10°).

[0020] The IDT electrode 30 (electrode fingers 31, 32 and busbar electrodes 33, 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 adhesive layer other than the Ti film may also be used.

[0021] More specifically, the IDT electrode 30 has a laminated structure of Ti / AlCu / Ti / AlCu, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm from the piezoelectric layer 20 side. The IDT electrode 30 has a total of 51 electrode fingers 31 and 32. The interelectrode pitch of the electrode fingers 31 and 32 is 2.38 μm, and the electrode width of each is 0.6 μm.

[0022] 1 is a region where the electrode fingers 31 and 32 overlap when viewed in the X direction. The length of the intersection region C is the dimension in the extension direction of the electrode fingers 31 and 32 in the intersection region C. In this embodiment, the length of the intersection region C is, for example, 40 μm.

[0023] During operation, an AC voltage is applied between the plurality of electrode fingers 31 and the plurality of electrode fingers 32. More specifically, an AC voltage is applied between the bus bar electrode 33 and the bus bar electrode 34. This makes it possible to obtain resonance characteristics using bulk waves in the first thickness-shear mode excited in the piezoelectric layer 20.

[0024] Furthermore, in elastic wave device 10, where d is the thickness of piezoelectric layer 20 and p is the inter-electrode pitch between pairs of electrode fingers 31 and 32, 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.

[0025] Because the elastic wave device 10 of the first embodiment has the above configuration, even if the number of pairs of electrode fingers 31 and 32 is reduced in an attempt to reduce the device size, the Q value is unlikely to decrease. This is because the resonator does not require reflectors on both sides, resulting in low propagation loss. Furthermore, the reason why the reflectors are not required is because the device utilizes bulk waves in the thickness-shear first-order mode.

[0026] The first protective film 41 is provided on the first main surface 20a of the piezoelectric layer 20, covering the IDT electrode 30. The second protective film 42 is provided on the second main surface 20b of the piezoelectric layer 20. The first protective film 41 and the second protective film 42 are made of silicon oxide (SiO２ ). The first protective film 41 and the second protective film 42 can be formed of an appropriate insulating material such as silicon oxide, silicon nitride, or alumina. The thickness t1 of the first protective film 41 and the thickness t2 of the second protective film 42 are both 142 nm. The thickness t1 of the first protective film 41 refers to the maximum total distance from the surface of the first protective film 41 on the first main surface 20a side to the surface of the first protective film 41 on the opposite side of the first main surface 20a in the intersection region C. The thickness t2 of the second protective film 42 refers to the maximum total distance from the surface of the second protective film 42 on the second main surface 20b side to the surface of the second protective film 42 on the opposite side of the second main surface 20b in the intersection region C. It is sufficient that at least one of the first protective film 41 and the second protective film 42 is provided. For example, a configuration in which the first protective film 41 is provided but the second protective film 42 is not provided may also be used.

[0027] The support substrate 11 (support member) is disposed opposite the second main surface 20b of the piezoelectric layer 20. The support substrate 11 has a cavity 14 (space) on the surface facing the second main surface 20b of the piezoelectric layer 20. More specifically, the support substrate 11 has a bottom 12 and a wall 13 provided in a frame shape on the upper surface of the bottom 12. The cavity 14 is formed in the space surrounded by the bottom 12 and the wall 13. The piezoelectric layer 20 is stacked on the upper surface of the wall 13 of the support substrate 11 with a second protective film 42 interposed therebetween. In this manner, the acoustic wave device 10 has a so-called membrane structure in which the cavity 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20. The support member may include the support substrate 11 and an intermediate (insulating) layer. That is, the support substrate 11 may be stacked indirectly on the second main surface 2b of the piezoelectric layer 20. In this case, the support substrate 11 and the intermediate layer may have a frame-like shape, thereby forming the cavity portion 14. Alternatively, a recess may be provided in the intermediate layer, thereby forming the cavity portion 14.

[0028] The cavity 14 is provided so as not to interfere with vibration of the intersection region C of the piezoelectric layer 20. The second protective film 42 is provided to cover the opening of the cavity 14. However, as described above, the second protective film 42 does not have to be provided. In this case, the support substrate 11 can be stacked directly on the second main surface 20b of the piezoelectric layer 20. Alternatively, the second protective film 42 may be provided in the region between the upper surface of the wall 13 and the second main surface 20b of the piezoelectric layer 20, and not in the region overlapping with the cavity 14.

[0029] The support substrate 11 is made of silicon (Si). The surface of the Si facing the piezoelectric layer 20 may have a (100), (110), or (111) plane orientation. Preferably, Si has a high resistivity of 4 kΩ or more. However, the support substrate 11 may also be made of an appropriate insulating material or semiconductor material. Examples of materials that can be used for the support substrate 11 include piezoelectric materials such as aluminum oxide, 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.

[0030] 3 and 4 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.

[0031] As shown in FIG. 3 , 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 20 a and the second principal surface 20 b 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 electrode fingers 31 and 32, is reduced in an effort to achieve miniaturization, the Q value is unlikely to decrease.

[0032] As shown in FIG. 4 , 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. 4 schematically illustrates the bulk wave when a voltage is applied between the electrode fingers 31 and 32 such that the electrode finger 32 has a higher potential than the 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 the region of the intersection region C between the imaginary plane VP1 and the first main surface 20a. The second region 252 is the region of the intersection region C between the imaginary plane VP1 and the second main surface 20b.

[0033] In acoustic wave device 10, at least one pair of electrodes consisting of electrode finger 31 and electrode finger 32 is arranged, but because waves are not propagated in the X direction, the number of electrode pairs consisting of electrode finger 31 and 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.

[0034] For example, the electrode finger 31 is an electrode connected to a hot potential, and the electrode finger 32 is an electrode connected to a ground potential. However, the electrode finger 31 may be connected to the ground potential, and the 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.

[0035] 5 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.

[0036] Piezoelectric layer 20: LiNbO with Euler angles (0°, 0°, 90°) ３ Thickness of the piezoelectric layer 20: 400 nm

[0037] Length of the crossing region C: 40 μm Number of pairs of electrodes consisting of the electrode fingers 31 and 32: 21 pairs Inter-electrode pitch between the electrode fingers 31 and 32: 3 μm Width of the electrode fingers 31 and 32: 500 nm d / p: 0.133

[0038] First protective film 41, second protective film 42: silicon oxide film with a thickness of 1 μm

[0039] Support substrate 11: Si

[0040] As is clear from FIG. 5, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0041] In the first embodiment, when the thickness of the piezoelectric layer 20 is d and the interelectrode pitch between the electrode fingers 31 and 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. 6.

[0042] 6 is an explanatory diagram showing 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. 6, multiple elastic wave devices were obtained by varying d / 2p, similar to the elastic wave device having the resonance characteristics shown in FIG.

[0043] As shown in Figure 6, 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.

[0044] 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.

[0045] 7 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 electrode fingers 31 and 32 is provided on the first main surface 20a of the piezoelectric layer 20. Note that K in FIG. 7 represents the cross width. As described above, in the elastic wave device 10 according to the present disclosure, the number of electrode pairs may be one pair. Even in this case, if the d / p is 0.5 or less, a bulk wave in the thickness-shear first-order mode can be effectively excited.

[0046] In the acoustic wave device 10, it is preferable that the metallization ratio MR of the adjacent electrode fingers 31 and 32 with respect to the crossing 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. 8 and 9.

[0047] 8 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. 8, 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.

[0048] The metallization ratio MR will be explained with reference to FIG. 1 . Focusing on a pair of electrode fingers 31 and 32 in the electrode structure of FIG. 1 , assume that only this pair of electrode fingers 31 and 32 are provided. In this case, the area surrounded by the dashed line is the intersection region C. When the electrode fingers 31 and 32 are viewed in a direction perpendicular to the extension direction of the electrode fingers 31 and 32, i.e., in the opposing direction, the intersection region C includes the region where the electrode fingers 31 overlap with the electrode fingers 32, the region where the electrode fingers 32 overlap with the electrode fingers 31, and the region between the electrode fingers 31 and 32 where the electrode fingers 31 and 32 overlap. The metallization ratio MR is the ratio of the area of ​​the electrode fingers 31 and 32 within the intersection region C to the area of ​​the intersection region C. In other words, the metallization ratio MR is the ratio of the area of ​​the metallization portion to the area of ​​the intersection region C.

[0049] When multiple pairs of electrode fingers 31 and electrode fingers 32 are provided, the ratio of the metallization portion included in all the intersection regions C to the total area of ​​the intersection regions C may be defined as MR.

[0050] 9 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 piezoelectric layer 20 and the dimensions of electrode fingers 31 and 32. Also, FIG. 9 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.

[0051] In the region surrounded by ellipse J in Figure 9, the spurious is as large as 1.0. As is clear from Figure 9, 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 Figure 8, 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 electrode fingers 31 and 32.

[0052] FIG. 10 is an explanatory diagram showing the relationship between d / 2p, metallization ratio MR, and fractional bandwidth. 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 fractional bandwidth was measured. The hatched area to the right of dashed line D in FIG. 10 represents the region where the fractional bandwidth 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 fractional bandwidth is easily maintained at 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. 10 , is the region. That is, if MR≦1.75(d / p)+0.05, the fractional bandwidth can be reliably kept to 17% or less.

[0053] FIG. 11 shows the results of LiNbO when d / p approaches 0. ３ 11 is an explanatory diagram showing a map of fractional bandwidths with respect to Euler angles (0°, θ, ψ). The hatched areas in FIG. 11 are regions where fractional bandwidths of at least 5% or more can be obtained. The range of the regions can be approximated as the ranges expressed by the following formulas (1), (2), and (3).

[0054] (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)

[0055] 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.

[0056] Next, the detailed configuration of the electrode fingers 31 and 32 will be described. Fig. 12 is an enlarged cross-sectional view of region A shown in Fig. 2. Fig. 12 describes the first electrode finger 31a, which is located outermost in the arrangement direction of the multiple electrode fingers 31 and 32, and the second electrode finger 32b, which is adjacent to the first electrode finger 31a. However, the electrode fingers 31 and 32 have a configuration that is line-symmetrical with the third electrode finger 32a, which is located outermost on the opposite side of the first electrode finger 31a, and the fourth electrode finger 31b, which is adjacent to the third electrode finger 32a. The description of the first electrode finger 31a can also be applied to the third electrode finger 32a, and the description of the second electrode finger 32b can also be applied to the fourth electrode finger 31b.

[0057] In the following description, the electrode fingers of the plurality of electrode fingers 31, 32 other than the first electrode finger 31 a, the second electrode finger 32 b, the third electrode finger 32 a, and the fourth electrode finger 31 b may be referred to as central electrode fingers 31 c, 32 c. That is, the central electrode fingers 31 c, 32 c are electrode fingers located inside the first electrode finger 31 a, the second electrode finger 32 b, the third electrode finger 32 a, and the fourth electrode finger 31 b in the arrangement direction, and are the electrode fingers 31, 32 located in the center in the arrangement direction. In the following description, when it is not necessary to distinguish between the first electrode finger 31 a, the second electrode finger 32 b, the third electrode finger 32 a, the fourth electrode finger 31 b, and the central electrode fingers 31 c, 32 c, they will be simply referred to as electrode fingers 31, 32. In the following description, the inter-electrode pitch between the first electrode finger 31 a and the second electrode finger 32 b is represented as P3, the inter-electrode pitch between the second electrode finger 32 b and the adjacent central electrode finger 31 c is represented as P2, and the inter-electrode pitch between adjacent central electrode fingers 31 c, 32 c is represented as P1. In this embodiment, the inter-electrode pitches between adjacent central electrode fingers 31 c, 32 c are all equal to P1.

[0058] 12 , the electrode width of the first electrode finger 31a is smaller than that of the second electrode finger 32b and the central electrode fingers 31c, 32c. Furthermore, the inter-electrode pitch P3 is smaller than the inter-electrode pitches P1 and P2. In this embodiment, the electrode width W1 of the first electrode finger 31a is 0.3 μm, and the electrode widths of the second electrode finger 32b and the central electrode fingers 31c, 32c are 0.6 μm. Furthermore, the inter-electrode pitch P3 is 2.23 μm, and the inter-electrode pitches P1 and P2 are 2.38 μm.

[0059] In this way, by making the electrode width W1 and inter-electrode pitch P3 of the first electrode finger 31 a located at the outermost position in the arrangement direction different from the electrode width and inter-electrode pitch P1 of the central electrode fingers 31 c, 32 c, an acoustic impedance different from that of the areas overlapping with the first electrode finger 31 a is generated in the area. As a result, an acoustic reflection surface R is formed at the outer end of the plurality of electrode fingers 31, 32 of the first electrode finger 31 a in the arrangement direction.

[0060] As a result, the acoustic waves excited in the piezoelectric layer 20 are reflected by the acoustic reflecting surface R, and therefore the acoustic wave device 10 can suppress leakage of the acoustic waves in the arrangement direction of the plurality of electrode fingers 31 and 32 .

[0061] FIG. 13 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the first embodiment. More specifically, FIG. 13 is an explanatory diagram showing the real part of the admittance, i.e., the conductance component, of the elastic wave device according to the first embodiment. The admittance characteristics shown in FIG. 13 represent simulation results of the admittance characteristics of elastic wave device 10 according to the first embodiment. FIG. 13 also shows simulation results of the admittance characteristics of an elastic wave device according to a comparative example. The comparative example is an elastic wave device in which the electrode widths and inter-electrode pitches of electrode fingers 31, 32 are all the same as those of the first embodiment.

[0062] As shown in FIG. 13 , in the elastic wave device according to the comparative example, ripples occur in a frequency range different from the resonant frequency. In the comparative example, particularly large ripples, as indicated by dotted lines E1 and E2, occur. In contrast, in the elastic wave device 10 according to the first embodiment, the electrode width W1 and interelectrode pitch P3 of the first electrode fingers 31 a located at the outermost positions in the arrangement direction are made different from the electrode width and interelectrode pitch P1 of the central electrode fingers 31 c and 32 c. This demonstrates that the ripples indicated by dotted lines E1 and E2 are suppressed compared to the comparative example. Because the peak width associated with the resonant frequency is narrower in the elastic wave device 10 according to the first embodiment than in the elastic wave device according to the comparative example, it can be seen that propagation loss and leakage of elastic waves are suppressed.

[0063] 12 illustrates a configuration in which the electrode width of one first electrode finger 31 a is smaller than the electrode widths of the other electrode fingers 31, 32. However, this is not limiting. Alternatively, the electrode widths of the outermost electrode fingers 31, 32 in the arrangement direction of the electrode fingers 31, 32 may be smaller than the electrode widths of the other electrode fingers 31, 32 located in the center. Similarly, the inter-electrode pitch P of the three or more outermost electrode fingers 31, 32 in the arrangement direction of the electrode fingers 31, 32 may be smaller than the inter-electrode pitch P of the other electrode fingers 31, 32 located in the center.

[0064] Fig. 14 is an explanatory diagram showing the distribution of vibration modes of the elastic wave device according to the first embodiment. Fig. 15 is an explanatory diagram showing the distribution of vibration modes of an elastic wave device according to a comparative example. The comparative example shown in Fig. 15 is configured such that the electrode widths and inter-electrode pitches of electrode fingers 31, 32 are all equal to those of elastic wave device 10 according to the first embodiment.

[0065] 14 and 15 show the distribution of the magnitude of displacement of piezoelectric layer 20 for the first embodiment and the comparative example, with the horizontal axis representing the X direction (the arrangement direction of electrode fingers 31 and 32) and the vertical axis representing frequency. The upper diagrams of Fig. 14 and Fig. 15 each show a schematic cross-sectional view of an elastic wave device corresponding to the X direction, and the left diagrams of Fig. 14 and Fig. 15 show the impedance characteristics of the elastic wave device.

[0066] As shown in Figure 15, in the elastic wave device of the comparative example, the X-direction dependence of the displacement (the X-direction positions of the antinodes and nodes of the displacement) is significantly frequency-dependent. For example, the X-direction positions indicating the peak displacement shift depending on the frequency, preventing stable excitation between the electrodes. Furthermore, at a specific X-direction position (near X = 5.0 μm), the phase is inverted at the resonant frequency of 5030 MHz and at frequencies of 4900 MHz and 5120 MHz where ripples occur. As such, the elastic wave device of the comparative example may not achieve an ideal excitation mode.

[0067] In contrast, as shown in FIG. 14 , in the elastic wave device 10 according to the first embodiment, the X-direction dependence of the displacement (the X-direction positions of the antinodes and nodes of the displacement) does not depend on frequency. That is, the X-direction positions indicating the peak displacement are constant regardless of frequency, indicating stable excitation between the electrodes. Furthermore, the magnitude (amplitude) of the displacement is also constant for each inter-electrode region, and no phase inversion occurs in the frequency arrangement where the resonant frequency and ripples occur. Thus, it was shown that a better excitation mode than the comparative example can be obtained simply by differentiating the electrode width W1 and inter-electrode pitch P3 of the first electrode fingers 31 a located at the outermost positions in the arrangement direction from the electrode width and inter-electrode pitch P1 of the central electrode fingers 31 c and 32 c.

[0068] Second Embodiment FIG. 16 is a cross-sectional view showing an elastic wave device according to a second embodiment. In the first embodiment, the electrode width of the first electrode finger 31a is smaller than the electrode width of the central electrode fingers 31c and 32c, and the inter-electrode pitch P3 between the first electrode finger 31a and the second electrode finger 32b is smaller than the inter-electrode pitch P1 between the central electrode fingers 31c and 32c. However, this is not limiting. As shown in FIG. 16 , in an elastic wave device 10A according to the second embodiment, the electrode width of the first electrode finger 31a is larger than the electrode widths of the second electrode finger 32b and the central electrode fingers 31c and 32c. Furthermore, the inter-electrode pitch P3 is larger than the inter-electrode pitches P1 and P2. In this modification, the IDT electrode 30 has a total of 51 electrode fingers 31 and 32. The configurations of the first protective film 41, the IDT electrode 30, and the like are the same as those of the first embodiment. In this embodiment, the electrode width of the first electrode finger 31 a is 1.2 μm, the electrode width of the second electrode finger 32 b and the central electrode fingers 31 c, 32 c is 0.6 μm, the inter-electrode pitch P3 is 2.9 μm, and the inter-electrode pitches P1, P2 are 2.38 μm.

[0069] Thus, even when the electrode width W1 and inter-electrode pitch P3 of the first electrode finger 31 a located at the outermost position in the arrangement direction are made larger than the electrode width and inter-electrode pitch P1 of the central electrode fingers 31 c and 32 c, an acoustic impedance different from that of the areas overlapping with the other electrode fingers occurs in the area overlapping with the first electrode finger 31 a. As a result, an acoustic reflection surface R is formed at the outer end of the first electrode finger 31 a in the arrangement direction of the plurality of electrode fingers 31 and 32.

[0070] As a result, the acoustic waves excited in the piezoelectric layer 20 are reflected by the acoustic reflecting surface R, and therefore, the acoustic wave device 10A can suppress leakage of the acoustic waves in the arrangement direction of the plurality of electrode fingers 31 and 32.

[0071] 16 illustrates a configuration in which the electrode width of one first electrode finger 31 a is larger than the electrode widths of the other electrode fingers 31, 32. However, this is not limiting. Alternatively, the electrode widths of the outermost electrode fingers 31, 32 in the arrangement direction of the electrode fingers 31, 32 may be larger than the electrode widths of the other electrode fingers 31, 32 located in the center. Similarly, the inter-electrode pitch of three or more outermost electrode fingers 31, 32 in the arrangement direction of the electrode fingers 31, 32 may be larger than the inter-electrode pitch of the other electrode fingers 31, 32 located in the center.

[0072] 17 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to the second embodiment. As shown in FIG. 17 , in elastic wave device 10A according to the second embodiment, the electrode width of first electrode finger 31 a is larger than the electrode width of central electrode fingers 31 c and 32 c, and interelectrode pitch P3 is larger than interelectrode pitches P1 and P2. However, similar to elastic wave device 10 according to the first embodiment, the ripple indicated by dotted line E2 is suppressed compared to the comparative example. Furthermore, in the second embodiment, the peak width associated with the resonant frequency is narrowed, thereby suppressing propagation loss.

[0073] Fig. 18 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a second embodiment. Fig. 19 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a comparative example. The comparative example illustrated in Fig. 19 is configured such that the electrode widths and inter-electrode pitches of electrode fingers 31, 32 are all equal to those of elastic wave device 10A according to the second embodiment.

[0074] 18 and 19 show the distribution of the magnitude of displacement of piezoelectric layer 20 for the second embodiment and the comparative example, with the horizontal axis representing the X direction (the arrangement direction of electrode fingers 31 and 32) and the vertical axis representing frequency. The upper diagrams of Fig. 18 and Fig. 19 each show a schematic cross-sectional view of an elastic wave device corresponding to the X direction, and the left diagrams of Fig. 18 and Fig. 19 show the impedance characteristics of the elastic wave device.

[0075] As shown in Figure 19, in the elastic wave device of the comparative example, the X-direction dependence of the displacement (the X-direction positions of the antinodes and nodes of the displacement) is significantly frequency-dependent. For example, the X-direction positions indicating the peak displacement shift depending on the frequency, preventing stable excitation between the electrodes. Furthermore, at a specific X-direction position (near X = 5.0 μm), the phase is inverted at the resonant frequency of 5030 MHz and at frequencies of 4900 MHz and 5120 MHz where ripples occur. As such, the elastic wave device of the comparative example may not achieve an ideal excitation mode.

[0076] In contrast, as shown in FIG. 18 , in the elastic wave device 10A according to the second embodiment, the X-direction dependence of the displacement (the X-direction positions of the antinodes and nodes of the displacement) does not depend on frequency. That is, the X-direction positions indicating the peak displacement are constant regardless of frequency, demonstrating stable excitation between the electrodes. Furthermore, the magnitude (amplitude) of the displacement is constant for each inter-electrode region, and no phase inversion occurs in the frequency arrangement where the resonant frequency and ripples occur. Thus, even when the electrode width W1 and inter-electrode pitch P3 of the first electrode fingers 31 a located at the outermost positions in the arrangement direction are made larger than the electrode width and inter-electrode pitch P1 of the central electrode fingers 31 c and 32 c, a better excitation mode than the comparative example is obtained.

[0077] (First Modification of Second Embodiment) FIG. 20 is a cross-sectional view showing an elastic wave device according to a first modification of the second embodiment. As shown in FIG. 20 , in an elastic wave device 10B according to the first modification, the electrode widths of the first electrode fingers 31 a and the second electrode fingers 32 b are larger than the electrode widths of the second electrode fingers 32 b and the central electrode fingers 31 c and 32 c. Furthermore, inter-electrode pitches P2 and P3 are different from inter-electrode pitch P1. In this modification, the IDT electrode 30 has a total of 51 electrode fingers 31 and 32. The configurations of the first protective film 41, the IDT electrode 30, and the like are the same as those of the first embodiment. In this embodiment, the electrode widths W1 and W2 of the first electrode fingers 31 a and the second electrode fingers 32 b are 0.8 μm, and the electrode width of the central electrode fingers 31 c and 32 c is 0.6 μm. The inter-electrode pitch P3 is 1.91 μm, the inter-electrode pitch P2 is 2.7 μm, and the inter-electrode pitch P1 is 2.38 μm.

[0078] 21 is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a first modification of the second embodiment. As shown in FIG. 21 , in elastic wave device 10B according to the first modification of the second embodiment, the electrode widths of first electrode fingers 31 a and second electrode fingers 32 b are larger than the electrode widths of central electrode fingers 31 c and 32 c, and interelectrode pitches P2 and P3 are different from interelectrode pitch P1. However, similar to elastic wave device 10 according to the first embodiment, the ripples indicated by dotted line E2 are suppressed compared to the comparative example. Furthermore, in the first modification of the second embodiment, the peak width associated with the resonant frequency is narrowed, thereby suppressing propagation loss.

[0079] (Second Modification of Second Embodiment) FIG. 22 is a cross-sectional view showing an elastic wave device according to a second modification of the second embodiment. As shown in FIG. 22 , in an elastic wave device 10C according to the second modification, the electrode width of the second electrode finger 32b is larger than the electrode widths of the first electrode finger 31a and the central electrode fingers 31c and 32c. Furthermore, the inter-electrode pitches P2 and P3 are different from the inter-electrode pitch P1. In this modification, the IDT electrode 30 has a total of 51 electrode fingers 31 and 32. The configurations of the first protective film 41, the IDT electrode 30, and the like are the same as those of the first embodiment. In this embodiment, the electrode width W2 of the second electrode finger 32b is 1.2 μm, and the electrode widths of the first electrode finger 31a and the central electrode fingers 31c and 32c are 0.6 μm. Furthermore, the inter-electrode pitch P3 is 1.79 μm, the inter-electrode pitch P2 is 2.9 μm, and the inter-electrode pitch P1 is 2.38 μm.

[0080] 23 is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a second modification of the second embodiment. As shown in FIG. 23 , in elastic wave device 10C according to the second modification of the second embodiment, the electrode widths of first electrode fingers 31 a and second electrode fingers 32 b are larger than the electrode widths of central electrode fingers 31 c and 32 c, and interelectrode pitches P2 and P3 are different from interelectrode pitch P1. However, similar to elastic wave device 10 according to the first embodiment, the ripples indicated by dotted line E2 are suppressed compared to the comparative example. Furthermore, in the second modification of the second embodiment, the peak width associated with the resonant frequency is narrowed, thereby suppressing propagation loss.

[0081] (Third Modification of Second Embodiment) FIG. 24 is a cross-sectional view showing an elastic wave device according to a third modification of the second embodiment. As shown in FIG. 24 , in an elastic wave device 10D according to the third modification, the thicknesses of the first protective film 41 and the second protective film 42 are thinner than the thickness of the IDT electrode 30. In this modification, the IDT electrode 30 has a stacked structure of Ti / AlCu / Ti / AlCu, with respective thicknesses of 12 nm / 27 nm / 18 nm / 12 nm from the piezoelectric layer 20 side. In this modification, the IDT electrode 30 has a total of 101 electrode fingers 31 and 32. The configurations of the first protective film 41, the IDT electrode 30, and the like are the same as those of the first embodiment. Specifically, the thickness of the piezoelectric layer 20 is, for example, 360 nm. The thickness of the first protective film 41 is 30 nm. The thickness of the second protective film 42 is 30 nm.

[0082] In the third modification, the first protective film 41 is provided following the surfaces and side surfaces of the electrode fingers 31 and 32 and the first main surface 20 a of the piezoelectric layer 20. The upper surface of the first protective film 41 is formed with projections and depressions that reflect the shapes of the electrode fingers 31 and 32. The second protective film 42 is formed flat along the second main surface 20 b of the piezoelectric layer 20.

[0083] The electrode width of the first electrode finger 31a is larger than that of the second electrode finger 32b and the central electrode fingers 31c, 32c. Furthermore, the inter-electrode pitch P3 is larger than the inter-electrode pitches P1 and P2. In this embodiment, the electrode width of the first electrode finger 31a is 1.2 μm, and the electrode widths of the second electrode finger 32b and the central electrode fingers 31c, 32c are 0.6 μm. Furthermore, the inter-electrode pitch P3 is 2.9 μm, and the inter-electrode pitches P1 and P2 are 1.96 μm.

[0084] 25 is a diagram illustrating an example of the admittance characteristics of an elastic wave device according to a third modification of the second embodiment. As shown in FIG. 25 , elastic wave device 10D according to the third modification exhibits reduced ripple compared to the comparative example. Thus, even when load film 50 is provided on both first principal surface 20 a and second principal surface 20 b of piezoelectric layer 20 and first protective film 41 and second protective film 42 are thin, ripple is suppressed and propagation loss is reduced.

[0085] Although the elastic wave device 10D according to the third modification has been described with the first protective film 41 and the second protective film 42 each having a thickness smaller than that of the IDT electrode 30, the present invention is not limited to this. Either the first protective film 41 or the second protective film 42 may have a thickness smaller than that of the IDT electrode 30.

[0086] Third Embodiment FIG. 26 is a cross-sectional view showing an elastic wave device according to a third embodiment. In the first embodiment, the electrode width of the first electrode finger 31a is smaller than the electrode width of the central electrode fingers 31c and 32c, and the inter-electrode pitch P3 between the first electrode finger 31a and the second electrode finger 32b is smaller than the inter-electrode pitch P1 between the central electrode fingers 31c and 32c. However, this is not limiting. As shown in FIG. 26 , in an elastic wave device 10E according to the third embodiment, the first electrode finger 31a, the second electrode finger 32b, and the central electrode fingers 31c and 32c have the same electrode width. Furthermore, the inter-electrode pitch P3 is larger than the inter-electrode pitches P1 and P2. The configurations of the first protective film 41, the IDT electrode 30, and the like are the same as those of the first embodiment. In this embodiment, the electrode width of the first electrode finger 31a, the second electrode finger 32b, and the central electrode fingers 31c and 32c is 0.6 μm. The inter-electrode pitch P3 is 2.68 μm, and the inter-electrode pitches P1 and P2 are 2.38 μm.

[0087] In this way, even if the electrode width W1 of the first electrode finger 31 a located at the outermost position in the arrangement direction is made equal to the electrode width of the central electrode fingers 31 c, 32 c, by making the inter-electrode pitch P3 different from the electrode width and inter-electrode pitch P1 of the central electrode fingers 31 c, 32 c, an acoustic impedance different from that of the areas overlapping with the first electrode finger 31 a is generated in the area overlapping with the other electrode fingers. As a result, an acoustic reflection surface R is formed at the inner end of the first electrode finger 31 a in the arrangement direction of the plurality of electrode fingers 31, 32.

[0088] As a result, the acoustic waves excited in the piezoelectric layer 20 are reflected by the acoustic reflecting surface R, and therefore, the acoustic wave device 10E can suppress leakage of the acoustic waves in the arrangement direction of the plurality of electrode fingers 31 and 32 .

[0089] 27 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to the third embodiment. As shown in FIG. 27 , elastic wave device 10E according to the third embodiment has a configuration in which the electrode width of first electrode finger 31 a is equal to the electrode width of central electrode fingers 31 c and 32 c and interelectrode pitch P3 is larger than interelectrode pitches P1 and P2. However, similar to elastic wave device 10 according to the first embodiment, ripples are suppressed compared to the comparative example. Furthermore, in the third embodiment, the peak width associated with the resonant frequency is narrowed, which indicates that propagation loss is suppressed.

[0090] Fourth Embodiment Fig. 28 is a plan view showing an elastic wave device according to a fourth embodiment. Fig. 29 is a cross-sectional view taken along the line XXIX-XXIX' in Fig. 28. Note that in Fig. 28, load film 50 is shown hatched to make the drawing easier to read. Also, in Fig. 28, first protective film 41 is shown by a two-dot chain line.

[0091] 28 and 29 , an elastic wave device 10F according to the fourth preferred embodiment further includes a load film 50. As shown in Fig. 29 , in the elastic wave device 10F, the load film 50 is stacked on the first protective film 41.

[0092] A portion of the load film 50 overlapping with the first electrode finger 31 a is referred to as a first extension portion 51, and a portion overlapping with the third electrode finger 32 a is referred to as a second extension portion 52. The first extension portion 51 and the second extension portion 52 are spaced apart in the arrangement direction of the multiple electrode fingers 31, 32, and the multiple electrode fingers 31, 32 are arranged between the first extension portion 51 and the second extension portion 52. The first extension portion 51 overlaps with a portion of the first electrode finger 31 a and extends along the extension direction of the first electrode finger 31 a. The second extension portion 52 overlaps with a portion of the third electrode finger 32 a and extends along the extension direction of the third electrode finger 32 a.

[0093] Fig. 30 is an enlarged cross-sectional view of region A1 shown in Fig. 29. Note that Fig. 33 describes the load film 50 (first extension portion 51) overlapping the first electrode finger 31a, but the second extension portion 52 (see Figs. 28 and 29) overlapping the third electrode finger 32a also has an arrangement relationship that is line-symmetrical to the first extension portion 51. The description of the first extension portion 51 also applies to the second extension portion 52. In the following description, when it is not necessary to distinguish between the first extension portion 51 and the second extension portion 52, they will simply be referred to as the load film 50.

[0094] In this embodiment, the load film 50 is made of the same material as the first protective film 41. In this embodiment, the load film 50 and the first protective film 41 are made of silicon oxide (SiO ２ ). Even if the load film 50 and the first protective film 41 are made of the same material, the density of the load film 50 may be different from the density of the first protective film 41. For example, if the load film 50 is formed by vapor deposition, the actual density of the load film 50 is smaller than the density of the first protective film 41.

[0095] As shown in FIG. 30 , in an elastic wave device 10F according to the fourth embodiment, the electrode width of the first electrode finger 31 a, which is located on the outermost side in the arrangement direction of the multiple electrode fingers 31 and 32, is smaller than the electrode width of the electrode fingers 31 and 32 located in the center in the arrangement direction. Furthermore, the inter-electrode pitch P2 between the outermost electrodes in the arrangement direction is smaller than the inter-electrode pitch P2 and the inter-electrode pitch P1 between the central electrodes. The configurations of the first protective film 41, IDT electrode 30, and the like are the same as those of the first embodiment. In this embodiment, the electrode width W1 of the first electrode finger 31 a is 0.3 μm, and the electrode widths of the second electrode finger 32 b and the central electrode fingers 31 c and 32 c are 0.6 μm. Furthermore, the inter-electrode pitch P3 is 2.23 μm, and the inter-electrode pitches P1 and P2 are 2.38 μm.

[0096] The load film 50 is provided in a region that does not overlap with the first electrode finger 31 a. That is, the load film 50 is provided in a region that is outward in the arrangement direction of the first electrode finger 31 a, which is the outermost of the plurality of electrode fingers 31, 32 in the arrangement direction of the plurality of electrode fingers 31, 32, and does not overlap with the IDT electrode 30. The width W3 of the load film 50 is 0.6 μm. The thickness of the load film 50 is 90 nm.

[0097] FIG. 31 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to a fourth embodiment. As shown in FIG. 31 , elastic wave device 10F according to the fourth embodiment suppresses ripples indicated by dotted lines E1, E2, and E3 compared to the comparative example. Thus, even in a configuration including load film 50, ripples are suppressed, thereby suppressing propagation loss. Furthermore, elastic wave device 10F according to the fourth embodiment effectively suppresses propagation loss over a wide frequency range from 4700 MHz to 5500 MHz compared to the above-described embodiments and modifications.

[0098] The shape, width, thickness, etc. of the load film 50 described above are merely examples and can be changed as appropriate. For example, the side surface of the load film 50 may be tapered. The first extension portion 51 and the second extension portion 52 of the load film 50 shown in FIG. 28 may have the same width and thickness. Alternatively, the first extension portion 51 and the second extension portion 52 of the load film 50 may have different widths and thicknesses due to, for example, variations in the manufacturing process.

[0099] The material of the load film 50 shown in the fourth embodiment is merely an example, and is not limited to this. The material of the load film 50 may be, for example, carbon-added silicon oxide (SiOC), silicon oxide (SiO ２ ), silicon nitride (SiN), tantalum pentoxide (Ta ２ O ５ ), aluminum nitride (AlN), aluminum oxide (Al ２ O ３ ), hafnium oxide (HfO ２ ), niobium pentoxide (Nb ２ O ５ ), or tungsten oxide (WO). The load film 50 may be made of a combination of two or more of the above materials.

[0100] 30 shows a configuration in which the load film 50 is provided in a region that does not overlap with the first electrode fingers 31 a, but this is not limiting. In the fourth embodiment and the fourth modified example, the load film 50 may be provided in a region that overlaps with the first electrode fingers 31 a. Although the load film 50 is provided on the first protective film 41, this is not limiting. The fourth embodiment can be combined with the above-described embodiments and modified examples.

[0101] (Fourth Modification of Fourth Embodiment) FIG. 32 is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a fourth modification of the fourth embodiment. The elastic wave device according to the fourth modification has a different load film 50 dimension compared to elastic wave device 10F according to the fourth embodiment. More specifically, the load film 50 according to the fourth modification has a thickness of 60 nm and a width W3 of 0.8 μm. The load film 50, first protective film 41, IDT electrode 30, and other components are similar to those of the fourth embodiment. As shown in FIG. 32 , the elastic wave device according to the fourth modification of the fourth embodiment suppresses ripples indicated by dotted lines E1 and E2 compared to the comparative example. As such, even when the dimension of the load film 50 is changed, ripples are suppressed, thereby suppressing propagation loss. Furthermore, the elastic wave device according to the fourth modification of the fourth embodiment effectively suppresses propagation loss over a wide frequency range from 4700 MHz to 5500 MHz compared to the above-described embodiments and modifications.

[0102] (Fifth Modification of Fourth Embodiment) FIG. 33 is a cross-sectional view showing an elastic wave device according to a fifth modification of the fourth embodiment. As shown in FIG. 33 , in an elastic wave device 10G according to the fifth modification of the fourth embodiment, the electrode width W1 of the first electrode finger 31 a located on the outermost side in the arrangement direction of the plurality of electrode fingers 31, 32 is larger than the electrode width of the electrode fingers 31, 32 located in the center in the arrangement direction. Furthermore, the outermost inter-electrode pitch P2 in the arrangement direction is larger than the inter-electrode pitch P1 in the center. The configurations of the load film 50, first protective film 41, IDT electrode 30, etc. are the same as those of the fourth embodiment. In this example, the electrode width of the outermost first electrode finger 31 a in the arrangement direction is 1.0 μm, and the electrode width of the other plurality of centrally located electrode fingers 31, 32 is 0.6 μm. Furthermore, the outermost inter-electrode pitch P2 in the arrangement direction is 2.58 μm, and the inter-electrode pitch P1 in the center is 2.38 μm.

[0103] In the fifth modification of the fourth embodiment, the load film 50 is provided in a region overlapping with the first electrode finger 31a, which is the outermost of the plurality of electrode fingers 31, 32 in the arrangement direction of the plurality of electrode fingers 31, 32. The width W3 of the load film 50 is 0.8 μm. The thickness of the load film 50 is 15 nm. One side surface of the load film 50 is positioned shifted toward the second electrode finger 32b from the center of the first electrode finger 31a in the width direction. The width of the overlapping region of the load film 50 with the first electrode finger 31a is, for example, 0.7 μm. The width of the non-overlapping region of the load film 50 is, for example, 0.1 μm.

[0104] 34 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to a fifth modification of the fourth embodiment. As shown in FIG. 34 , elastic wave device 10G according to the fifth modification of the fourth embodiment exhibits reduced ripples, indicated by dotted line E2, compared to the comparative example. As such, even in a configuration in which the electrode width of first electrode finger 31 a is greater than the electrode widths of the other electrode fingers 31 and 32 and inter-electrode pitch P2 is greater than inter-electrode pitch P1, ripples are suppressed, thereby reducing propagation loss.

[0105] 32 shows a configuration in which the load film 50 is provided in a region overlapping with the first electrode fingers 31 a, but this is not limiting. Furthermore, the load film 50 is provided on the first protective film 41, but this is not limiting. The fifth modification of the fourth embodiment can be combined with any of the above-described embodiments and modifications.

[0106] Fifth Preferred Embodiment Fig. 35 is a circuit diagram illustrating an acoustic wave filter device according to a fifth preferred embodiment. As shown in Fig. 35, an acoustic wave filter device 10H according to the fifth preferred embodiment includes a plurality of series arm resonators 61, 62, and 63 and a plurality of parallel arm resonators 64, 65, 66, and 67. The series arm resonators 61, 62, and 63 are connected in series to a signal path between an input terminal 60A and an output terminal 60B. The parallel arm resonators 64, 65, 66, and 67 are connected in parallel between the signal path between the input terminal 60A and the output terminal 60B and ground 68. The acoustic wave filter device 10H according to the fifth preferred embodiment is a so-called ladder filter.

[0107] One terminal of each of the series-connected series arm resonators 61, 62, and 63 is electrically connected to the input terminal 60A, and the other terminal is electrically connected to the output terminal 60B. One terminal of the parallel arm resonator 64 is electrically connected to the input terminal 60A, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 65 is electrically connected to a signal path connecting the series arm resonators 61 and 62, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 66 is electrically connected to a signal path connecting the series arm resonators 62 and 63, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 67 is electrically connected to the output terminal 60B, and the other terminal is electrically connected to ground 68.

[0108] In this embodiment, electrode fingers with different configurations are employed for the plurality of series arm resonators 61, 62, and 63 and the plurality of parallel arm resonators 64, 65, 66, and 67. In this embodiment, by changing the configurations of the electrode fingers 31 and 32 for the plurality of series arm resonators 61, 62, and 63 and the plurality of parallel arm resonators 64, 65, 66, and 67, it is possible to obtain a better output waveform as a filter.

[0109] The fifth embodiment can be combined with the above-described embodiments and modifications.

[0110] 36 is a cross-sectional view of an elastic wave device according to a sixth embodiment. In the elastic wave device 10 according to the first embodiment described above, the support substrate 11 has a cavity 14, and the cavity 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20, which is a so-called membrane structure. However, the present invention is not limited to this.

[0111] 36 , in an elastic wave device 10I according to the sixth embodiment, an acoustic multilayer film 43 is laminated on the second main surface 20b of the piezoelectric layer 20. The acoustic multilayer film 43 has a laminate structure of low acoustic impedance layers 43a, 43c, and 43e, which have a relatively low acoustic impedance, and high acoustic impedance layers 43b and 43d, which have a relatively high acoustic impedance. The low acoustic impedance layers 43a, 43c, and 43e are made of, for example, SiO ２ The high acoustic impedance layers 43b and 43d are metal layers such as W or Pt, or dielectric layers such as aluminum nitride or silicon nitride. When the acoustic multilayer film 43 is used, bulk waves in the first thickness-shear mode can be confined within the piezoelectric layer 20 without using the cavity portion 14.

[0112] In acoustic wave device 10I, by setting d / p to 0.5 or less, resonance characteristics based on bulk waves in the first thickness-shear mode can be obtained. Note that the number of stacked low acoustic impedance layers 43a, 43c, and 43e and high acoustic impedance layers 43b and 43d in acoustic multilayer film 43 is not particularly limited. It is sufficient that at least one high acoustic impedance layer 43b or 43d is located farther from piezoelectric layer 20 than low acoustic impedance layers 43a, 43c, and 43e.

[0113] The low acoustic impedance layers 43a, 43c, and 43e and the high acoustic impedance layers 43b and 43d can be made of any suitable material as long as the above acoustic impedance relationship is satisfied. For example, the low acoustic impedance layers 43a, 43c, and 43e can be made of silicon oxide or silicon oxynitride. The high acoustic impedance layers 43b and 43d can be made of alumina, silicon nitride, or metal.

[0114] The sixth embodiment can be combined with the above-described embodiments and modifications.

[0115] Seventh Embodiment Fig. 37 is a cross-sectional view of an elastic wave device according to a seventh embodiment. In the elastic wave device 10 according to the first embodiment described above, the IDT electrode 30 is provided on the first main surface 20a of the piezoelectric layer 20, but this is not limiting. As shown in Fig. 37, an elastic wave device 10J according to the seventh embodiment has a first IDT electrode provided on the first main surface 20a of the piezoelectric layer 20 and a second IDT electrode provided on the second main surface 20b of the piezoelectric layer 20. The first IDT electrode and the second IDT electrode have the same configuration as the IDT electrode 30 (see Figs. 1 and 2).

[0116] The electrode fingers 36, 37 of the second IDT electrode are provided in an area overlapping the electrode fingers 31, 32 of the first IDT electrode. The electrode fingers 36, 37 of the second IDT electrode are provided with the same width and the same inter-electrode pitch as the electrode fingers 31, 32 of the first IDT electrode. In Figure 37, the first electrode finger 36a and the central electrode finger 36c are an example of the electrode finger 36, and the second electrode finger 37b and the central electrode finger 37c are an example of the electrode finger 37.

[0117] In the seventh embodiment, the first IDT electrode and the second IDT electrode are provided on the first principal surface 20a and the second principal surface 20b of the piezoelectric layer 20, respectively, so that the temperature coefficient of frequency (TCF) can be improved.

[0118] 37 shows an example in which the electrode fingers 31 and 32 shown in the first embodiment are provided, but the present invention is not limited to this. The seventh embodiment can be combined with each of the above-described embodiments and modifications.

[0119] Eighth Embodiment Fig. 38 is an explanatory diagram showing an example of admittance characteristics of an elastic wave device according to an eighth embodiment. Fig. 39 is an explanatory diagram showing an example of impedance phase in a higher mode. The elastic wave device according to the eighth embodiment shown in Fig. 38 is configured such that the first protective film 41 and the second protective film 42 have different thicknesses in elastic wave device 10 according to the first embodiment.

[0120] 38 shows frequency characteristics of the absolute value of admittance for the elastic wave device according to embodiment 8. As shown in Fig. 38 , in the elastic wave device according to embodiment 8, a higher-order mode resonance (hereinafter referred to as S2 mode) occurs in a frequency region indicated by a dashed dotted line F1 that is different from the resonant frequency.

[0121] The horizontal axis of the graph shown in Fig. 39 represents the ratio ((t1+tLN / 2) / (t2+tLN / 2)) of the sum (t1+tLN / 2) of the thickness t1 of the first protective film 41 and 1 / 2 of the thickness tLN of the piezoelectric layer 20 to the sum (t2+tLN / 2) of the thickness t2 of the second protective film 42 and 1 / 2 of the thickness tLN of the piezoelectric layer 20. The vertical axis of the graph shown in Fig. 39 corresponds to the intensity of the S2 mode.

[0122] 39, the range indicated by arrows F2 and F3 indicates the ratio (t1 + tLN / 2) / (t2 + tLN / 2) in the configuration of the acoustic resonator described in JP-T-2022-524136. In the acoustic resonator described in JP-T-2022-524136, the ratio (t1 + tLN / 2) / (t2 + tLN / 2) is 0.93 or less and 1.07 or more, and the intensity of the S2 mode is large.

[0123] In contrast, in the eighth embodiment, the ratio (t1 + tLN / 2) / (t2 + tLN / 2) is in the range of 0.94 to 1.06, inclusive, and the intensity of the S2 mode is smaller than that of the acoustic resonator device described in JP-A 2022-524136. In other words, in the eighth embodiment, when the total distance from the center of the thickness of the piezoelectric layer 20 to the top surface of the first protective film 41 is A and the total distance from the center of the thickness of the piezoelectric layer 20 to the top surface of the second protective film 42 is B, it is preferable that the value of A / B be in the range of 1-0.06 to 1+0.06, inclusive.

[0124] Although the eighth embodiment has been described with reference to the elastic wave device 10 according to the first embodiment, in which the first protective film 41 and the second protective film 42 have different thicknesses, the present invention is not limited to this. The relationship between the thickness t1 of the first protective film 41, the thickness tLN of the piezoelectric layer 20, and the thickness t2 of the second protective film 42 in the eighth embodiment can be combined with any of the embodiments and modified examples described above.

[0125] 40 is a plan view showing an IDT electrode of an elastic wave device according to a ninth preferred embodiment of the present invention, where N is the number of central electrode fingers 31c and 32c.

[0126] In the ninth embodiment, as shown in FIG. 40, the inter-electrode pitch between the nth (n is an integer of 1 to N-1) central electrode finger and the (n+1)th central electrode finger counted in the X direction from the electrode finger adjacent to the second electrode finger 32b among the central electrode fingers is set to p ｎ The interelectrode pitch between the first electrode finger counted in the X direction and the adjacent electrode finger on the outside in the arrangement direction, i.e., the second electrode finger 32b, is set to p Ｌ The interelectrode pitch between the Nth electrode finger counted in the X direction and the adjacent electrode finger on the outside in the X direction, i.e., the fourth electrode finger 31b, is set to p Ｒ In this case, the change rate of the inter-electrode pitch pr ｎ , pr Ｌ , pr Ｒ is a value expressed by each of the following formulas (4) to (6). In addition, the change rate pr of the inter-electrode pitch expressed by the following formula (7) is ｎ The arithmetic mean of the average change rate of the inter-electrode pitch pr ＡIn the present disclosure, the average change rate of the inter-electrode pitch of the central electrode fingers 31c and 32c is the average change rate of the inter-electrode pitch pr Ａ The rate of change in the inter-electrode pitch of the electrode fingers (fourth electrode finger 31b, second electrode finger 32b) adjacent to the outer sides of the central electrode fingers 31c, 32c in the arrangement direction (X direction) is the rate of change in the inter-electrode pitch pr Ｌ and pr Ｒ It refers to at least one of the following. ｎ = | (p ｎ＋１ -p ｎ ) / p ｎ | ... Equation (4) pr Ｌ = (p １ -p Ｌ ) / p Ｌ ...Equation (5) pr Ｒ = (p Ｎ－１ -p Ｒ ) / p Ｒ ...Formula (6)

[0127] In the ninth embodiment, the average change rate pr of the inter-electrode pitch Ａ The change rate of the electrode pitch pr Ｌ and pr Ｒ Here, the inter-electrode pitch between the first electrode finger 31a and the second electrode finger 32b is p Ｌ and the inter-electrode pitch between the fourth electrode finger 31b and the third electrode finger 32a is equal to the inter-electrode pitch p Ｒ is equal to.

[0128] FIG. 41 shows the inter-electrode pitch p ｎ In the ninth embodiment, the total number of electrode fingers 31 and electrode fingers 32 of the IDT electrode 30 is 51. That is, in the ninth embodiment, N=47. As shown in FIG. 41 , the inter-electrode pitch p ｎ As n increases from n=1 to n closest to N / 2 (n=23), the inter-electrode pitch p ｎ is small, and the inter-electrode pitch p ｎis minimized, and as n increases from n (n=24) closest to (N+1) / 2 to n=N-1 (n=46), the inter-electrode pitch p ｎ That is, the inter-electrode pitch p between the central electrode fingers 31c and 32c according to the ninth embodiment ｎ becomes larger toward the center of the central electrode fingers 31c and 32c. Here, the average change rate pr of the inter-electrode pitch according to the ninth embodiment Ａ is 0.006. The average inter-electrode pitch of the central electrode fingers 31c and 32c according to the ninth embodiment is 2.38 μm.

[0129] In the elastic wave device according to the ninth preferred embodiment, the first electrode finger 31 a, the second electrode finger 32 b, the third electrode finger 32 a, the fourth electrode finger 31 b, and the central electrode fingers 31 c and 32 c have the same electrode width, which is 0.6 μm.

[0130] In the ninth embodiment, the electrode configuration of the IDT electrode 30 is a laminated film of Ti / AlCu / Ti / AlCu from the piezoelectric layer 20 side, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm. The configuration of the first protective film 41 and the like is the same as in the first embodiment. Specifically, the piezoelectric layer 20 has a film thickness of 181 nm. The film thickness of the first protective film 41 is 142 nm. The film thickness of the second protective film 42 is 142 nm.

[0131] Fig. 42 is an explanatory diagram showing the impedance phase of an elastic wave device according to Comparative Example 1. In Comparative Example 1 shown in Fig. 42 , the electrode widths and inter-electrode pitches of electrode fingers 31, 32 are all equal to those of the elastic wave device according to the ninth embodiment. As shown in Fig. 42 , in the elastic wave device according to Comparative Example 1, the phase is lowered at 5102 MHz, and leaky wave L is generated.

[0132] In Comparative Example 2, the change rate of the electrode pitch pr Ｌ , pr Ｒ is set to 0, that is, the inter-electrode pitch p Ｌ o p １ and the electrode pitch p Ｒ o p Ｎ－１The elastic wave device of the ninth preferred embodiment has the same configuration as that of the elastic wave device of the ninth preferred embodiment, except that the thicknesses of the elastic waves are equal to each other.

[0133] 43 is an explanatory diagram showing the impedance phase at 5102 MHz of the elastic wave devices according to the ninth embodiment and comparative examples 1 and 2. As shown in FIG. 43 , in the elastic wave device according to the ninth embodiment, the average rate of change pr Ａ When is 0.006, the change rate of the electrode pitch pr Ｌ and pr Ｒ is −0.008 or less or 0.008 or more, the phase drop at 5102 MHz is improved compared to the acoustic wave devices of Comparative Examples 1 and 2. This indicates that the average rate of change pr Ａ The change rate of the electrode pitch pr Ｌ and pr Ｒ The absolute value of the ratio (|pr Ｌ / pr Ａ | and | pr Ｒ / pr Ａ By setting the value of | to be 1.33 (=0.008 / 0.006) or greater, the influence of leaky wave L shown in FIG. 43 on the impedance phase of the elastic wave device can be suppressed.

[0134] In the above description of the ninth embodiment, the inter-electrode pitch between the first electrode finger 31 a and the second electrode finger 32 b is p Ｌ and the inter-electrode pitch between the fourth electrode finger 31b and the third electrode finger 32a is equal to the inter-electrode pitch p Ｒ However, the inter-electrode pitch between the first electrode finger 31a and the second electrode finger 32b is equal to the inter-electrode pitch p Ｌ The inter-electrode pitch between the fourth electrode finger 31b and the third electrode finger 32a may be different from the inter-electrode pitch p Ｒ may be different from.

[0135] In the above description of the ninth embodiment, the ratio of the change rate of the inter-electrode pitch pr Ｌ / pr Ａ and the ratio of the change rate of the electrode pitch pr Ｒ / pr Ａ The ratio of the change rate of the electrode pitch pr Ｌ / pr Ａand the ratio of the change rate of the electrode pitch pr Ｒ / pr Ａ In this case, the absolute value of the ratio of the change rate of the inter-electrode pitch |pr Ｌ / pr Ａ | and | pr Ｒ / pr Ａ If at least one of | is equal to or greater than 1.33, the influence of the leaky wave L described above on the impedance phase of the elastic wave device can be suppressed.

[0136] The relationship between the electrode pitches in the ninth embodiment described above can be combined with each of the above-described embodiments and modifications.

[0137] 44 is a plan view showing an IDT electrode of an elastic wave device according to a tenth preferred embodiment of the present invention. As in the ninth preferred embodiment, the number of central electrode fingers 31c and 32c is denoted as N.

[0138] In the tenth embodiment, as shown in FIG. 44, the electrode width of the nth (n is an integer of 1 to N) central electrode finger 31c, 32c counting in the X direction from the electrode finger adjacent to the second electrode finger 32b is set to w ｎ The electrode width of the electrode finger adjacent to the first electrode finger in the arrangement direction on the outside as counted in the X direction, i.e., the second electrode finger 32b, is set to w Ｌ The electrode width of the electrode finger adjacent to the Nth electrode finger on the outer side in the arrangement direction, i.e., the fourth electrode finger 31b, is set to w Ｒ In this case, the change rate of the electrode width wr ｎ , wr Ｌ , wr Ｒ is a value expressed by each of the following formulas (8) to (10). Also, the rate of change of the electrode width wr ｎ The arithmetic mean of the average change rate of the electrode width wr Ａ In the present disclosure, the average rate of change in the dimension (electrode width) of the central electrode fingers 31c and 32c in the direction perpendicular to the extending direction of the plurality of electrode fingers is the average rate of change in the electrode width wr ＡThe rate of change in the dimension (electrode width) of the electrode fingers (fourth electrode finger 31b, second electrode finger 32b) adjacent to the outer sides of the central electrode fingers 31c, 32c in the arrangement direction (X direction) is the rate of change in the electrode width wr Ｌ and wr Ｒ It refers to at least one of the following. ｎ =|(w ｎ＋１ -w ｎ ) / w ｎ | ... Equation (8) wr Ｌ = (w １ -w Ｌ ) / w Ｌ ...Equation (9) wr Ｒ = (w Ｎ -w Ｒ ) / w Ｒ ...Formula (10)

[0139] In the tenth embodiment, the average change rate of the electrode width wr Ａ The rate of change of electrode width wr Ｌ and wr Ｒ In the elastic wave device according to the tenth embodiment, the first electrode finger 31 a, the second electrode finger 32 b, and the central electrode fingers 31 c and 32 c have the same electrode width. Here, the electrode width of the first electrode finger 31 a is the electrode width w Ｌ The electrode width of the third electrode finger 32a is equal to the electrode width w Ｒ is equal to.

[0140] FIG. 45 shows the electrode width w ｎ In the tenth embodiment, the total number of electrode fingers 31 and electrode fingers 32 of the IDT electrode 30 is 51. That is, in the tenth embodiment, N=47. As shown in FIG. 45 , the electrode width w ｎ As n increases from n=1 to n=23, which is closest to (N+1) / 2, the electrode width w ｎ is increased, and the electrode width w ｎ is maximized, and as n increases from n (n=25) closest to (N+1) / 2 to n=N (n=47), the electrode width w ｎThat is, the electrode width w of the central electrode fingers 31c and 32c according to the tenth embodiment is reduced. ｎ becomes smaller toward the center of the central electrode fingers 31c and 32c. Here, the average change rate of the electrode width wr Ａ is 0.004. The average electrode width of the central electrode fingers 31c and 32c according to the tenth embodiment is 0.6 μm.

[0141] In the elastic wave device according to the tenth embodiment, the first electrode finger 31 a, the second electrode finger 32 b, the third electrode finger 32 a, the fourth electrode finger 31 b, and the central electrode fingers 31 c and 32 c have the same inter-electrode pitch with their adjacent inner electrodes in the arrangement direction. The inter-electrode pitch with their adjacent inner electrodes in the arrangement direction with their adjacent first electrode finger 31 a, the second electrode finger 32 b, the third electrode finger 32 a, the fourth electrode finger 31 b, and the central electrode fingers 31 c and 32 c is 2.38 μm.

[0142] In the tenth embodiment, the electrode configuration of the IDT electrode 30 is a laminated film of Ti / AlCu / Ti / AlCu from the piezoelectric layer 20 side, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm. The configuration of the first protective film 41 and the like is the same as in the first embodiment. Specifically, the piezoelectric layer 20 has a film thickness of 181 nm. The film thickness of the first protective film 41 is 142 nm. The film thickness of the second protective film 42 is 142 nm.

[0143] In Comparative Example 1, the electrode pitch and electrode width of the electrode fingers 31 and 32 are all equal to those of the elastic wave device according to the tenth embodiment. Comparative Example 1 has the same configuration as Comparative Example 1 shown in FIG. 42 described in the ninth embodiment.

[0144] In Comparative Example 3, the change rate of the electrode width wr Ｌ , wr Ｒ is set to 0, that is, the electrode width w Ｌ Wow １ and the electrode width w Ｒ Wow Ｎ The elastic wave device according to the tenth preferred embodiment has the same configuration as that of the elastic wave device according to the tenth preferred embodiment, except that the thicknesses of the elastic waves are equal to each other.

[0145] 46 is an explanatory diagram showing the impedance phase at 5102 MHz of the elastic wave devices according to the tenth embodiment and comparative examples 1 and 3. As shown in FIG. 46 , in the elastic wave device according to the tenth embodiment, the average rate of change wr Ａ When is 0.004, the change rate of the electrode width wr Ｌ and wr Ｒ is less than −0.01 or more than 0.01, the phase drop at 5102 MHz is improved compared to the acoustic wave devices of Comparative Examples 1 and 3. This indicates that the average rate of change in electrode width wr Ａ The rate of change of electrode width wr Ｌ and wr Ｒ The absolute value of the ratio (|wr Ｌ / wr Ａ | and | wr Ｒ / wr Ａ By setting | to 2.5 (=0.01 / 0.004) or greater, the influence of leaky wave L shown in FIG. 42 on the impedance phase of the elastic wave device can be suppressed.

[0146] In the above description of the tenth embodiment, the electrode width between the first electrode finger 31a and the first electrode finger 31b is the electrode width w Ｌ The electrode width of the third electrode finger 32a is equal to the electrode width w Ｒ However, the electrode width of the first electrode finger 31a is equal to the electrode width w Ｌ The electrode width of the third electrode finger 32 a may be different from the electrode width w Ｒ may be different from.

[0147] In the above description of the tenth embodiment, the ratio of the change rate of the electrode width wr Ｌ / wr Ａ and the ratio of the electrode width change rate wr Ｒ / wr Ａ The ratio of the electrode width change rate wr Ｌ / wr Ａ and the ratio of the electrode width change rate wr Ｒ / wr Ａ In this case, the absolute value of the ratio of the change rates of the electrode widths |wr Ｌ / wr Ａ | and | wr Ｒ / wr ＡIf at least one of | is 2.5 or greater, the influence of the leaky wave L described above on the impedance phase of the elastic wave device can be suppressed.

[0148] The relationship between the electrode widths in the tenth embodiment described above can be combined with each of the above-described embodiments and modifications.

[0149] The shapes, widths, thicknesses, etc. of the first protective film 41 and the IDT electrode 30 in the above-described embodiments and modifications are merely examples and can be changed as appropriate. For example, the side surfaces of the IDT electrode 30 may be tapered. The electrode fingers 31 and 32 shown in FIG. 1 may have the same thickness. Alternatively, the electrode fingers 31 and 32 may have different thicknesses due to, for example, variations in the manufacturing process. Furthermore, the central electrode fingers 31c and 32c shown in FIG. 2 may have the same width. Alternatively, the central electrode fingers 31c and 32c may have different widths due to, for example, variations in the manufacturing process.

[0150] In the above-described embodiments and modifications, the electrode width of one or two outermost electrode fingers 31, 32 is different from that of the other electrode fingers 31, 32. However, this is not limiting. The electrode width of at least one of the three outermost electrode fingers 31, 32 in the arrangement direction of the electrode fingers 31, 32 may be different from that of the other central electrode fingers 31, 32. Similarly, the inter-electrode pitch P between at least one of the three outermost electrode fingers 31, 32 in the arrangement direction of the electrode fingers 31, 32 and the electrode finger adjacent to the outermost electrode finger in the arrangement direction of the electrode fingers 31, 32 may be different from the inter-electrode pitch P between the other central electrode fingers 31, 32.

[0151] Furthermore, in a configuration in which all of the electrode fingers 31, 32 have the same electrode width and all of the central electrode fingers 31c, 32c have the same inter-electrode pitch P, the inter-electrode pitch P between at least one of the one or two outermost electrode fingers 31, 32 and the electrode finger adjacent to the outermost electrode finger in the arrangement direction of the multiple electrode fingers 31, 32 may be different from the inter-electrode pitch P between the other central electrode fingers 31, 32.

[0152] Furthermore, in a configuration in which the inter-electrode pitch P between all of the multiple electrode fingers 31, 32 is the same and the electrode widths of all of the other electrode fingers 31, 32 located in the central portion are the same, the electrode width of at least one of the one or two electrode fingers 31, 32 located on the outermost sides may be different from the electrode width of the other electrode fingers 31, 32 located in the central portion.

[0153] 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.

[0154] The present disclosure may also have the following configurations.

[0155] (1) An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; an IDT electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the IDT electrode including a plurality of electrode fingers arranged in a predetermined direction; and a support member facing the second main surface of the piezoelectric layer and having an acoustic reflector on the second main surface side of the piezoelectric layer, wherein at least one of a first electrode finger arranged outermost in an arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the first electrode finger on the inside in the arrangement direction differs from a central electrode finger arranged on the inside of the second electrode finger in at least one of a dimension in a direction perpendicular to the extension direction of the plurality of electrode fingers and a center-to-center distance between the electrode finger adjacent to the first electrode finger on the inside in the arrangement direction, and wherein d / p is 0.5 or less, where d is a thickness of the piezoelectric layer and p is a center-to-center distance between adjacent electrode fingers. (2) The elastic wave device according to (1), further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer. (3) The elastic wave device according to (1) or (2), wherein the first electrode finger differs from the central electrode finger in at least one of a dimension in a direction orthogonal to the extension direction of the plurality of electrode fingers and a center-to-center distance between the first electrode finger and an adjacent electrode finger on the inside in the arrangement direction. (4) The elastic wave device according to any one of (1) to (3), wherein the second electrode finger differs from the central electrode finger in at least one of a dimension in a direction orthogonal to the extension direction of the plurality of electrode fingers and a center-to-center distance between the second electrode finger and an adjacent electrode finger on the inside in the arrangement direction. (5) The elastic wave device according to any one of (1) to (4), wherein at least one of the first electrode finger and the second electrode finger is smaller than the central electrode finger in at least one of a dimension in a direction orthogonal to the extension direction of the plurality of electrode fingers and a center-to-center distance between the second electrode finger and an adjacent electrode finger on the inside in the arrangement direction. (6) The elastic wave device according to any one of (1) to (5), wherein at least one of the first electrode finger and the second electrode finger is larger than the central electrode finger in at least one of a dimension in a direction perpendicular to the extension direction of the plurality of electrode fingers and a center-to-center distance between the central electrode finger and an adjacent electrode finger on the inside in the arrangement direction.(7) The elastic wave device according to (1), wherein the first electrode finger, the second electrode finger, and the central electrode finger have the same dimension in a direction orthogonal to the extension direction of the plurality of electrode fingers, and at least one of the first electrode finger and the second electrode finger has a larger center-to-center distance between the central electrode finger and its adjacent electrode finger on the inside in the arrangement direction. (8) The elastic wave device according to (1), wherein the first electrode finger, the second electrode finger, and the central electrode finger have the same dimension in a direction orthogonal to the extension direction of the plurality of electrode fingers, and the central electrode finger has the same center-to-center distance between the central electrode finger and its adjacent electrode finger on the inside in the arrangement direction, and at least one of the first electrode finger and the second electrode finger has a different center-to-center distance between the central electrode finger and its adjacent electrode finger on the inside in the arrangement direction. (9) The elastic wave device according to (1), wherein the first electrode finger, the second electrode finger, and the central electrode finger have equal dimensions in a direction perpendicular to the extension direction of the plurality of electrode fingers; the central electrode finger has a different center-to-center distance from its adjacent electrode finger on the inside in the arrangement direction; the first electrode finger and the second electrode finger have a different center-to-center distance from their adjacent electrode finger on the inside in the arrangement direction relative to the central electrode finger; and the absolute value of the ratio of the rate of change in the inter-electrode pitch of the electrode finger adjacent to the outer side of the central electrode finger in the arrangement direction to the average rate of change in the inter-electrode pitch of the central electrode finger is 1.33 or more. (10) The elastic wave device according to (1), wherein the first electrode finger, the second electrode finger, and the central electrode finger have the same center-to-center distance with respect to the electrode finger adjacent to the inner side in the arrangement direction, the central electrode finger has the same dimension in a direction perpendicular to the extension direction of the plurality of electrode fingers, and at least one of the first electrode finger and the second electrode finger has a dimension different from that of the central electrode finger in a direction perpendicular to the extension direction of the plurality of electrode fingers.(11) The elastic wave device according to (1), wherein the first electrode finger, the second electrode finger, and the central electrode finger have equal center-to-center distances with respect to the electrode finger adjacent thereto on the inside in the arrangement direction, the central electrode finger has a different dimension in a direction orthogonal to the extension direction of the plurality of electrode fingers, at least one of the first electrode finger and the second electrode finger has a different dimension in the direction orthogonal to the extension direction of the plurality of electrode fingers than the central electrode finger, and an absolute value of a ratio of a rate of change in dimension of the electrode finger adjacent thereto on the outside in the arrangement direction to an average rate of change in dimension of the central electrode finger in the direction orthogonal to the extension direction of the plurality of electrode fingers is 2.5 or more. (12) The elastic wave device according to any one of (1) to (11), further comprising a load film provided in a region overlapping with a first electrode finger that is outermost among the plurality of electrode fingers in the arrangement direction of the plurality of electrode fingers. (13) The elastic wave device according to (12), wherein the load film is made of at least one of carbon-doped silicon oxide, silicon oxide, silicon nitride, tantalum pentoxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium pentoxide, and tungsten oxide. (14) The elastic wave device according to any one of (1) to (13), wherein the piezoelectric layer has a protective film provided on at least one of the first main surface and the second main surface, the protective film being made of silicon oxide. (15) The elastic wave device according to any one of (1) to (14), wherein the IDT electrode is provided on both the first main surface and the second main surface of the piezoelectric layer. (16) An elastic wave filter device including at least one resonator, wherein the resonator is the elastic wave device according to any one of (1) to (15). (17) The acoustic wave filter device according to (16), comprising: an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal; and a parallel arm connecting a node of the series arm and ground; wherein the at least one resonator is a plurality of resonators including a series arm resonator provided in the series arm and a parallel arm resonator provided in the parallel arm; and wherein the plurality of electrode fingers of the series arm resonator have a different configuration from the plurality of electrode fingers of the parallel arm resonator.(18) The elastic wave device according to any one of (1) to (15), wherein the piezoelectric layer contains lithium niobate or lithium tantalate and has a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut. (19) The elastic wave device according to any one of (1) to (15) and (18), wherein the piezoelectric layer includes a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film including a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer, and a second protective film provided on the second main surface of the piezoelectric layer. (20) The elastic wave device according to (19), wherein, where A is the sum of distances from a thickness center of the piezoelectric layer to a top surface of the first protective film and B is the sum of distances from a thickness center of the piezoelectric layer to the top surface of the second protective film, a value of A / B is 1-0.06 or more and 1+0.06 or less. (21) The elastic wave device according to (19) or (20), wherein an upper surface of the first protective film and a lower surface of the second protective film are flat. (22) The elastic wave device according to any one of (1) to (15) and (18) to (21), wherein a protective film is provided on at least one of the first main surface and the second main surface of the piezoelectric layer, and a thickness of the protective film is thinner than a thickness of the IDT electrode. (23) The elastic wave device according to any one of (1) to (15) and (18) to (22), wherein a protective film is provided on at least one of the first main surface and the second main surface of the piezoelectric layer, and a thickness of the protective film is thicker than a thickness of the IDT electrode. (24) The elastic wave device according to any one of (1) to (15) and (18) to (23), wherein d / p is 0.24 or less. (25) The acoustic wave device according to any one of (1) to (15) and (18) to (24), wherein, when viewed in the electrode finger orthogonal direction, an excitation region is a region where adjacent electrode fingers overlap each other and a region between centers of the adjacent electrode fingers in the electrode finger orthogonal direction, and wherein, when a metallization ratio of the electrode fingers to the excitation region is MR, MR≦1.75(d / p)+0.075 is satisfied. (26) The acoustic wave device according to any one of (1) to (15) and (18) to (25), wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.(27) The acoustic wave device according to (26), 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) (28) The elastic wave device according to any one of (1) to (15) and (18) to (27), wherein the acoustic reflecting portion is a cavity, and the support member and the piezoelectric layer are arranged so that a part of the support member and a part of the piezoelectric layer face each other with the cavity in between. (29) The elastic wave device according to any one of (1) to (15) and (18) to (28), wherein the acoustic reflecting portion is an acoustic reflecting film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged so that at least a part of the support member and at least a part of the piezoelectric layer face each other with the acoustic reflecting film in between.

[0156] 10, 10A to 10G, 10I, 10J Acoustic wave device 10H Acoustic wave filter device 11 Support substrate 12 Bottom 13 Wall 14 Cavity 20 Piezoelectric layer 20a First main surface 20b Second main surface 30 IDT electrode 31, 32, 36, 37 Electrode fingers 31a, 36a First electrode fingers 32b, 37b Second electrode fingers 32a Third electrode fingers 31b Fourth electrode fingers 31c, 32c, 36c, 37c Central electrode fingers 33, 34 Busbar electrode 41 First protective film 42 Second protective film 50 Load film 51 First extending portion 52 Second extending portion

Claims

1. An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; an IDT electrode provided on at least one of the first and second main surfaces of the piezoelectric layer, the IDT electrode including a plurality of electrode fingers arranged in a predetermined direction; and a support member facing the second main surface of the piezoelectric layer and having an acoustic reflecting portion on the second main surface side of the piezoelectric layer, wherein at least one of a first electrode finger arranged on the outermost side in the arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the inside in the arrangement direction of the first electrode finger differs from a central electrode finger arranged on the inside in the arrangement direction with respect to the second electrode finger in at least one of a dimension in a direction perpendicular to the extension direction of the plurality of electrode fingers and a center-to-center distance between the electrode finger adjacent to the inside in the arrangement direction, and wherein, when the thickness of the piezoelectric layer is d and the center-to-center distance between adjacent electrode fingers is p, d / p is 0.5 or less.

2. The acoustic wave device according to claim 1, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer.

3. An elastic wave device as described in claim 1 or 2, wherein the first electrode finger differs from the central electrode finger in at least one of the dimension in a direction perpendicular to the extension direction of the multiple electrode fingers and the center-to-center distance between the first electrode finger and the adjacent electrode finger on the inside in the arrangement direction.

4. An elastic wave device described in any one of claims 1 to 3, wherein the second electrode finger differs from the central electrode finger in at least one of the dimension in a direction perpendicular to the extension direction of the multiple electrode fingers and the center-to-center distance between the second electrode finger and the adjacent electrode finger on the inside in the arrangement direction.

5. An elastic wave device described in any one of claims 1 to 4, wherein at least one of the first electrode finger and the second electrode finger is smaller than the central electrode finger in at least one of the dimension in a direction perpendicular to the extension direction of the multiple electrode fingers and the center-to-center distance between the electrode finger and the adjacent electrode finger on the inside in the arrangement direction.

6. An elastic wave device described in any one of claims 1 to 5, wherein at least one of the first electrode finger and the second electrode finger has at least one of a dimension in a direction perpendicular to the extension direction of the multiple electrode fingers and a center-to-center distance between the electrode finger and an adjacent electrode finger on the inside in the arrangement direction that is larger than that of the central electrode finger.

7. The elastic wave device of claim 1, wherein the first electrode finger, the second electrode finger, and the central electrode finger have equal dimensions in a direction perpendicular to the extension direction of the multiple electrode fingers, and at least one of the first electrode finger and the second electrode finger has a larger center-to-center distance between the central electrode finger and the adjacent electrode finger on the inside in the arrangement direction.

8. The elastic wave device of claim 1, wherein the first electrode finger, the second electrode finger, and the central electrode finger have equal dimensions in a direction perpendicular to the extension direction of the multiple electrode fingers, the central electrode finger has an equal center-to-center distance with its adjacent electrode finger on the inside in the arrangement direction, and at least one of the first electrode finger and the second electrode finger has a different center-to-center distance with respect to the central electrode finger and its adjacent electrode finger on the inside in the arrangement direction.

9. The elastic wave device of claim 1, wherein the first electrode finger, the second electrode finger, and the central electrode finger have equal dimensions in a direction perpendicular to the extension direction of the multiple electrode fingers, the central electrode finger has a different center-to-center distance from its adjacent electrode finger on the inside in the arrangement direction, the first electrode finger and the second electrode finger have a different center-to-center distance from their adjacent electrode finger on the inside in the arrangement direction relative to the central electrode finger, and an absolute value of a ratio of the rate of change of the interelectrode pitch of the electrode finger adjacent to the outside of the central electrode finger in the arrangement direction to the average rate of change of the interelectrode pitch of the central electrode finger is 1.33 or more.

10. The elastic wave device of claim 1, wherein the first electrode finger, the second electrode finger, and the central electrode finger have the same center-to-center distance with the adjacent electrode finger on the inside in the arrangement direction, the central electrode finger has the same dimension in a direction perpendicular to the extension direction of the multiple electrode fingers, and at least one of the first electrode finger and the second electrode finger has a different dimension than the central electrode finger in a direction perpendicular to the extension direction of the multiple electrode fingers.

11. The elastic wave device of claim 1, wherein the first electrode finger, the second electrode finger, and the central electrode finger have equal center-to-center distances with respect to the electrode finger adjacent to the inner side in the arrangement direction, the central electrode finger has a different dimension in a direction perpendicular to the extension direction of the multiple electrode fingers, at least one of the first electrode finger and the second electrode finger has a different dimension in a direction perpendicular to the extension direction of the multiple electrode fingers compared to the central electrode finger, and the absolute value of the ratio of the rate of change in the dimension of the electrode finger adjacent to the outer side of the central electrode finger in the arrangement direction in the direction perpendicular to the extension direction of the multiple electrode fingers to the average rate of change in the dimension of the central electrode finger in the direction perpendicular to the extension direction of the multiple electrode fingers is 2.5 or more.

12. An elastic wave device according to any one of claims 1 to 11, further comprising a load film provided in an area overlapping with a first electrode finger that is located outermost in the arrangement direction of the plurality of electrode fingers, among the plurality of electrode fingers.

13. The acoustic wave device according to claim 12, wherein the material of the load film is at least one of carbon-doped silicon oxide, silicon oxide, silicon nitride, tantalum pentoxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium pentoxide, and tungsten oxide.

14. The elastic wave device according to claim 1, further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer, the protective film being made of silicon oxide.

15. The acoustic wave device according to claim 1, wherein the IDT electrodes are provided on both the first principal surface and the second principal surface of the piezoelectric layer.

16. An elastic wave filter device comprising at least one resonator, the resonator being an elastic wave device according to any one of claims 1 to 15.

17. The elastic wave filter device according to claim 16, comprising: an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting a node of the series arm and ground, wherein the at least one resonator is a plurality of resonators including a series arm resonator provided in the series arm and a parallel arm resonator provided in the parallel arm, and the plurality of electrode fingers of the series arm resonator have a different configuration from the plurality of electrode fingers of the parallel arm resonator.

18. The elastic wave device according to any one of claims 1 to 15, wherein the piezoelectric layer contains lithium niobate or lithium tantalate and is a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut.

19. An elastic wave device as described in any one of claims 1 to 15 and 18, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film comprising a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer, and a second protective film provided on the second main surface of the piezoelectric layer.

20. The elastic wave device of claim 19, wherein the sum of the distances from the center of the thickness of the piezoelectric layer to the top surface of the first protective film is A and the sum of the distances from the center of the thickness of the piezoelectric layer to the top surface of the second protective film is B, where A / B is a value not less than 1-0.06 and not more than 1+0.

06.

21. The acoustic wave device according to claim 19, wherein an upper surface of the first protective film and a lower surface of the second protective film are flat.

22. The elastic wave device according to any one of claims 1 to 15 and 18 to 21, further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer, the thickness of the protective film being thinner than the thickness of the IDT electrode.

23. The elastic wave device according to any one of claims 1 to 15 and 18 to 22, further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer, the thickness of the protective film being thicker than the thickness of the IDT electrode.

24. The elastic wave device according to any one of claims 1 to 15 and 18 to 23, wherein d / p is 0.24 or less.

25. An elastic wave device as claimed in any one of claims 1 to 15 and 18 to 24, wherein when viewed from the electrode finger orthogonal direction, the region where adjacent electrode fingers overlap each other and the region between the centers of adjacent electrode fingers in the electrode finger orthogonal direction is an excitation region, and when the metallization ratio of the electrode fingers to the excitation region is MR, MR satisfies MR≦1.75(d / p)+0.

075.

26. The acoustic wave device according to any one of claims 1 to 15 and 18 to 25, wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.

27. The elastic wave device according to claim 26, 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°~80°, [180°-60°(1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] ~ 180°, any ψ) ... Equation (3) 28. An elastic wave device according to any one of claims 1 to 15 and 18 to 27, wherein the acoustic reflection portion is a hollow portion, and the support member and the piezoelectric layer are arranged so that a portion of the support member and a portion of the piezoelectric layer face each other across the hollow portion.

29. An elastic wave device described in any one of claims 1 to 15 and 18 to 28, wherein the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged so that at least a portion of the support member and at least a portion of the piezoelectric layer face each other with the acoustic reflection film in between.

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