Elastic wave device and elastic wave filter device

Abstract

Provided are an elastic wave device and an elastic wave filter device capable of suppressing leakage of an elastic wave. This elastic wave device comprises: a piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction; an IDT electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer, and including a plurality of electrode fingers arrayed in a predetermined direction; a support member facing the second main surface of the piezoelectric layer, and having an acoustic reflection part on the second main surface side of the piezoelectric layer; and a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer. In a region that overlaps, in a plan view from the first direction, with a first electrode finger among the plurality of electrode fingers that is positioned on the outermost side in the array direction of the plurality of electrode fingers, the protective film has a first-step surface where a side surface of the protective film is exposed in a direction intersecting the direction in which the first electrode finger extends. 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.

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; 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; and a protective film provided on at least one of the first and second main surfaces of the piezoelectric layer, wherein in a region overlapping in a planar view from the first direction with a first electrode finger that is positioned outermost in the arrangement direction of the plurality of electrode fingers, the protective film has a first step surface that exposes a side surface of the protective film in a direction intersecting the extension direction of the first electrode finger, 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.

[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. 9 is a diagram illustrating 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. FIG. 10 is a diagram illustrating the relationship between d / 2p, the metallization ratio MR, and the relative bandwidth. FIG. 11 is a diagram illustrating the relationship between d / p and the metallization ratio MR of LiNbO when d / p approaches 0. ３FIG. 12 is an explanatory diagram showing a map of fractional bandwidths versus Euler angles (0°, θ, ψ) in the elastic wave device according to the first embodiment. FIG. 13 is an explanatory diagram showing an example of admittance characteristics of an elastic wave device according to a first modification of the first embodiment. FIG. 14 is a cross-sectional view showing an elastic wave device according to a first modification of the first embodiment. FIG. 15 is an explanatory diagram showing a vibration mode distribution of an elastic wave device according to a first modification of the first embodiment. FIG. 16 is an explanatory diagram showing a vibration mode distribution of an elastic wave device according to a comparative example. FIG. 17 is a cross-sectional view showing an elastic wave device according to a second embodiment. FIG. 18 is an explanatory diagram showing an example of admittance characteristics of an elastic wave device according to the second embodiment. FIG. 19 is a cross-sectional view showing an elastic wave device according to a third embodiment. FIG. 20 is a cross-sectional view showing an elastic wave device according to a fourth embodiment. FIG. 21 is a cross-sectional view showing an elastic wave device according to a fifth embodiment. FIG. 22 is a cross-sectional view showing an elastic wave device according to a second modification of the fifth embodiment. FIG. 23 is a cross-sectional view showing an elastic wave device according to a sixth embodiment. FIG. 24 is a diagram illustrating an example of the admittance characteristics of an elastic wave device according to a sixth embodiment. FIG. 25 is a plan view of an elastic wave device according to a seventh embodiment. FIG. 26 is a cross-sectional view taken along line XXVI-XXVI′ of FIG. 25. FIG. 27 is an enlarged cross-sectional view of region A shown in FIG. 26. FIG. 28 is a diagram illustrating an example of the admittance characteristics of an elastic wave device according to a seventh embodiment. FIG. 29 is a cross-sectional view of an elastic wave device according to a third modified example of the seventh embodiment. FIG. 30 is a diagram illustrating an example of the admittance characteristics of an elastic wave device according to a third modified example of the seventh embodiment. FIG. 31 is a cross-sectional view of an elastic wave device according to an eighth embodiment. FIG. 32 is a circuit diagram of an elastic wave filter device according to a ninth embodiment. FIG. 33 is a cross-sectional view of an elastic wave device according to a tenth embodiment. FIG. 34 is a diagram illustrating an example of the admittance characteristics of an elastic wave device according to an eleventh embodiment. FIG. 35 is a diagram illustrating an example of an impedance phase in a higher-order mode.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. However, the present disclosure is not limited to these embodiments. Note that each embodiment described in the present disclosure is an example, and in the second and subsequent embodiments, a description of modifications in which partial substitution or combination of configurations is possible between different embodiments, and of matters common to the first embodiment will be omitted, and only differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[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 center-to-center distance between the electrode fingers 31 and 32 (hereinafter referred to as the inter-electrode pitch) is preferably in the range of 1 μm to 10 μm. The inter-electrode pitch is the distance between the center of the width of the electrode finger 31 in a direction perpendicular to the extension direction of the electrode fingers 31 and the center of the width of the electrode finger 32 in a direction perpendicular to the extension direction of the electrode fingers 32. 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.

[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 (SiO ２). 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. The detailed configurations of the first protective film 41 and the second protective film 42 will be described later with reference to FIGS.

[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 2. 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] In the first embodiment, the inter-electrode pitch of each of the electrode pairs, each consisting of the electrode finger 31 and the electrode finger 32, is set to be equal in all pairs. That is, the electrode fingers 31 and the electrode fingers 32 are arranged at equal pitches.

[0041] As is clear from FIG. 5, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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).

[0055] (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)

[0056] 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.

[0057] Next, the detailed configuration of the first protective film 41 will be described. Fig. 12 is an enlarged cross-sectional view of region A shown in Fig. 2 . Fig. 12 describes the portion of the first protective film 41 that overlaps with the first electrode finger 31a, which is located outermost in the arrangement direction of the multiple electrode fingers 31 and 32. However, the portion of the first protective film 41 (see Figs. 1 and 2 ) that overlaps with the second electrode finger 32a, which is located outermost, on the opposite side of the first electrode finger 31a also has a shape that is line-symmetrical to the portion of the first protective film 41 that overlaps with the first electrode finger 31a. The description of the first electrode finger 31a also applies to the second electrode finger 32a.

[0058] 12 , in the region overlapping with the first electrode finger 31 a, the first protective film 41 has a first step 41 a where the side surface of the first protective film 41 is exposed in the Y direction. The side surface of the protective film refers to a surface that extends in a direction intersecting with the surface of the protective film on the piezoelectric layer 2 side. In other words, the normal to the side surface of the protective film intersects with the thickness direction of the protective film. In this embodiment, the first step 41 a is a step that is lower on the inner side in the arrangement direction of the multiple electrode fingers 31, 32. Specifically, in the region overlapping with the first electrode finger 31 a, the first step 41 a is formed by a portion where the first protective film 41 is not provided and a portion where the first protective film 41 is provided, from the inner side in the arrangement direction of the multiple electrode fingers 31, 32.

[0059] 12 , in a region between the first electrode finger 31 a and the electrode finger 32 adjacent to the first electrode finger 31 a, the first protective film 41 has a surface of a second step 41 b where the side surface of the first protective film 41 is exposed in the Y direction. In this embodiment, the second step 41 b is a step that is lower on the outer side in the arrangement direction of the multiple electrode fingers 31, 32. In this embodiment, in the region between the first electrode finger 31 a and the adjacent electrode finger 32, the second step 41 b is formed by a portion where the first protective film 41 is thick and a portion where the first protective film 41 is thin, from the inner side in the arrangement direction of the multiple electrode fingers 31, 32.

[0060] In the following description, the region between the first step 41 a and the second step 41 b will be referred to as the inter-step region. The height of the step refers to the difference in height from the main surface (the first main surface 20 a or the second main surface 20 b) of the piezoelectric layer 20 between the surface on the inside and the surface on the outside of the step in the arrangement direction, and corresponds to the length of the step surface in the Z direction.

[0061] The inter-step region is positioned inward relative to the first electrode finger 31a in the arrangement direction of the multiple electrode fingers 31 and 32. The side surface of the first protective film 41 at the first step 41a is positioned overlapping the midpoint of the first electrode finger 31a in the width direction, and the side surface of the first protective film at the second step 41b is positioned more inward in the arrangement direction than the first electrode finger 31a. That is, the inter-step region includes an overlapping region that overlaps with the first electrode finger 31a and a non-overlapping region that does not overlap with the first electrode finger 31a. The width W1 of the region between the first step 41a and the second step 41b is, for example, 0.6 μm. The width W1a of the overlapping region in the inter-step region is, for example, 0.3 μm. The width W1b of the non-overlapping region in the inter-step region is, for example, 0.3 μm. In this embodiment, the top surfaces of the first electrode finger 31a and the first protective film 41 in the inter-step region are flat. Specifically, the upper surfaces of the first electrode fingers 31a and the first protective film 41 in the inter-step region are formed substantially flat across the region where the first electrode fingers 31a are provided and the region where the first electrode fingers 31a are not provided.

[0062] In this embodiment, the height t4 of the first step 41 a and the second step 41 b is 30 nm. As described above, the thickness t1 of the first protective film 41 and the thickness t2 of the second protective film 42 are 142 nm, and the thickness t3 of the IDT electrode 30 is 112 nm. The thickness t1 of the first protective film 41 is thicker than the height t4 of the first step 41 a and the second step 41 b and is also thicker than the thickness t3 of the IDT electrode 30. In this embodiment, the inter-step region includes a region where the first protective film 41 is not provided. That is, the inter-step region includes a region where the first electrode finger 31 a is exposed.

[0063] In this way, since the first step 41 a is provided so as to overlap the first electrode finger 31 a, in the region overlapping with the first electrode finger 31 a positioned outermost in the arrangement direction of the plurality of electrode fingers 31, 32, the region inside the arrangement direction of the first step 41 a does not have the first protective film 41 and has a different acoustic impedance from the region where the first protective film 41 is laminated. As a result, an acoustic reflection surface R is formed in the first step (the portion overlapping with the side surface of the first protective film 41).

[0064] 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 .

[0065] 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 the 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 that does not have the first step 41 a and the second step 41 b compared to the first embodiment.

[0066] 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 elastic wave device 10 according to the first embodiment, by providing first step 41a and second step 41b, the ripples indicated by dotted lines E1 and E2 are suppressed compared to the comparative example. It can be seen that, because the peak width associated with the resonant frequency is narrower in elastic wave device 10 according to the first embodiment than in the elastic wave device according to the comparative example, propagation loss is suppressed, and leakage of elastic waves is suppressed.

[0067] The shapes, widths, thicknesses, etc. of the first protective film 41 and the IDT electrode 30 are merely examples and can be changed as appropriate. For example, the first step 41 a and the second step 41 b may be formed in a tapered shape.

[0068] (First Modification of First Embodiment) FIG. 14 is a cross-sectional view showing an elastic wave device according to a first modification of the first embodiment. As shown in FIG. 14 , in the first modification of the first embodiment, the height of the first step 41 a is different from the height of the second step 41 b, and the thickness of the first protective film 41 in the inter-step region is thinner than the thickness of the first electrode finger 31 a. In the first modification, in the region overlapping with the first electrode finger 31 a, the first protective film 41 has a surface of the first step 41 a where the side surface of the first protective film 41 is exposed in the Y direction. The first step 41 a has a lower surface on the inner side in the arrangement direction of the electrode fingers 31 and 32. Specifically, in the region overlapping with the first electrode finger 31 a, the first step 41 a is formed by a portion where the first protective film 41 is not provided and a portion where the first protective film 41 is provided, from the inner side in the arrangement direction of the electrode fingers 31 and 32.

[0069] 14 , in a region between the first electrode finger 31 a and the electrode finger 32 adjacent to the first electrode finger 31 a, the first protective film 41 has a surface of a second step 41 b where the side surface of the first protective film 41 is exposed in the Y direction. In the first modification, the second step 41 b is a step that is lower on the outer side in the arrangement direction of the plurality of electrode fingers 31, 32. In the first modification, in the region between the first electrode finger 31 a and the adjacent electrode finger 32, the second step 41 b is formed by a portion where the first protective film 41 is thick and a portion where the first protective film 41 is thin, from the inner side in the arrangement direction of the plurality of electrode fingers 31, 32.

[0070] The inter-step region is positioned inward relative to the first electrode finger 31a in the arrangement direction of the multiple electrode fingers 31 and 32. The side surface of the first protective film 41 at the first step 41a is positioned so as to overlap the midpoint of the first electrode finger 31a in the width direction, and the side surface of the first protective film at the second step 41b is positioned more inward in the arrangement direction than the first electrode finger 31a. That is, the inter-step region includes an overlapping region that overlaps with the first electrode finger 31a and a non-overlapping region that does not overlap with the first electrode finger 31a. The width W1 of the region between the first step 41a and the second step 41b is, for example, 0.6 μm. The width W1a of the overlapping region in the inter-step region is, for example, 0.3 μm. The width W1b of the non-overlapping region in the inter-step region is, for example, 0.3 μm.

[0071] In the first modified example, the height t4 of the first step 41a is 30 nm, and the height t6 of the second step 41b is 40 nm. As described above, the thickness t1 of the first protective film 41 and the thickness t2 of the second protective film 42 are 142 nm, and the thickness t3 of the IDT electrode 30 is 112 nm. The thickness t1 of the first protective film 41 is thicker than the height t4 of the first step 41a and the height t6 of the second step 41b, and is also thicker than the thickness t3 of the IDT electrode 30.

[0072] Fig. 15 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a first modified example. Fig. 16 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. 16 is configured such that the first step 41a and the second step 41b are not provided in elastic wave device 10A according to the first modified example.

[0073] 15 and 16 show the distribution of the magnitude of displacement of piezoelectric layer 20 for the first modified example 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. 15 and Fig. 16 each show a schematic cross-sectional view of an elastic wave device corresponding to the X direction, and the left diagrams of Fig. 15 and Fig. 16 show the impedance characteristics of the elastic wave device.

[0074] As shown in Figure 16, 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.

[0075] In contrast, as shown in FIG. 15 , in the elastic wave device 10A according to the first modification, the X-direction dependence of the displacement (the X-direction positions of the antinodes and nodes of the displacement) does not have frequency dependence. 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 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 demonstrated that a better excitation mode than the comparative example can be obtained simply by providing the first step 41 a at a position overlapping with a portion of the first electrode finger 31 a positioned at the outermost position in the arrangement direction.

[0076] Second Embodiment Fig. 17 is a cross-sectional view showing an elastic wave device according to a second embodiment. In the first embodiment and the first modified example, the first step 41a and the second step 41b are provided on the first protective film 41 on the first main surface 20a side of the piezoelectric layer 20. However, this is not limiting. As shown in Fig. 17, in an elastic wave device 10B according to the second embodiment, the first step 42a and the second step 42b are provided on the second protective film 42 on the second main surface 20b side of the piezoelectric layer 20. In other words, the step region is not on the first main surface 20a side of the piezoelectric layer 20, and the top surface of the first protective film 41 is formed flat.

[0077] 17 , in the region overlapping with the first electrode finger 31 a, the second protective film 42 has a first step 42 a where the side surface of the second protective film 42 is exposed in the Y direction. In the present embodiment, the first step 42 a is a step that is lower on the inner side in the arrangement direction of the plurality of electrode fingers 31, 32. Specifically, in the region overlapping with the first electrode finger 31 a, the first step 42 a is formed by a portion where the second protective film 42 is thin and a portion where the second protective film 42 is thick, from the inner side in the arrangement direction of the plurality of electrode fingers 31, 32.

[0078] 17 , in the region between the first electrode finger 31 a and the electrode finger 32 adjacent to the first electrode finger 31 a, the second protective film 42 has a second step 42 b where the side surface of the second protective film 42 is exposed in the Y direction. In this embodiment, the second step 42 b is a step that is lower on the outer side in the arrangement direction of the multiple electrode fingers 31, 32. The configuration of the IDT electrode 30 and the like is the same as in the first embodiment. In this embodiment, in the region between the first electrode finger 31 a and the adjacent electrode finger 32, the second step 41 b is formed by a thick portion of the second protective film 42 and a thin portion of the second protective film 42, from the inner side in the arrangement direction of the multiple electrode fingers 31, 32.

[0079] In the following description, the region between the first step 42a and the second step 42b will be referred to as the inter-step region. The inter-step region is located inwardly of the first electrode finger 31a in the arrangement direction of the multiple electrode fingers 31 and 32. The side surface of the second protective film 42 at the first step 42a is positioned so as to overlap the midpoint of the first electrode finger 31a in the width direction, and the side surface of the second protective film 42 at the second step 42b is located more inward than the first electrode finger 31a in the arrangement direction. That is, the inter-step region includes an overlapping region that overlaps with the first electrode finger 31a and a non-overlapping region that does not overlap with the first electrode finger 31a. The width W2 of the region between the first step 42a and the second step 42b is, for example, 0.6 μm. The width W2a of the overlapping region in the inter-step region is, for example, 0.3 μm. The width W2b of the non-overlapping region in the inter-step region is, for example, 0.3 μm. In this embodiment, the lower surface of the second protective film 42 in the inter-step region is formed flat. Specifically, the lower surface of the second protective film 42 in the inter-step region is formed substantially flat across the region where the first electrode fingers 31 a are provided and the region where the first electrode fingers 31 a are not provided. The lower surface of the second protective film 42 refers to the surface of the second protective film 42 that faces the support substrate 11 (see FIG. 2 ).

[0080] 1, a first step 42a is also provided on the opposite side of the arrangement direction of the plurality of electrode fingers 31, 32 at a position overlapping with a part of the second electrode finger 32a (see FIG. 1), although this is not shown in the drawings.

[0081] FIG. 18 is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to the second embodiment. As shown in FIG. 18 , the elastic wave device 10B according to the second embodiment, even though the first step 42 a is provided on the second main surface 20 b side of the piezoelectric layer 20, exhibits reduced ripples indicated by dotted lines E1 and E2 compared to the comparative example, similar to the elastic wave device 10 according to the first embodiment. Furthermore, the second embodiment also exhibits a narrower peak width associated with the resonant frequency, thereby suppressing propagation loss. Furthermore, the second embodiment does not include a first step on the first protective film 41, unlike the first embodiment. Therefore, the resonant frequency can be easily adjusted by changing the film thickness of the first protective film 41.

[0082] Third Embodiment FIG. 19 is a cross-sectional view of an elastic wave device according to a third embodiment. As shown in FIG. 19 , in an elastic wave device 10C according to the third embodiment, a first step and a second step are provided on the top of the first protective film 41 and on the bottom surface of the second protective film 42 (the surface facing the support substrate 11 (see FIG. 2 )). In the following description, the region between the first steps 41 a, 42 a and the second steps 41 b, 42 b is referred to as an inter-step region. The configuration of the IDT electrode 30 and other components is the same as in the first embodiment. In this embodiment, the top surfaces of the first electrode fingers 31 a and the first protective film 41 in the inter-step region are flat. Specifically, the top surfaces of the first electrode fingers 31 a and the first protective film 41 in the inter-step region are substantially flat across the region where the first electrode fingers 31 a are provided and the region where the first electrode fingers 31 a are not provided. In this embodiment, the bottom surface of the second protective film 42 in the inter-step region is flat. Specifically, the lower surface of the second protective film 42 in the inter-step region is formed to be substantially flat across the region where the first electrode fingers 31a are provided and the region where the first electrode fingers 31a are not provided.

[0083] The inter-step regions are provided to overlap with portions of the first electrode fingers 31a. The width W1 of the step region of the first protective film 41 and the width W2 of the step region of the second protective film are each 0.8 μm. The width W1a of the overlapping region of the step region of the first protective film 41 and the width W2a of the overlapping region of the step region of the second protective film are each 0.5 μm, for example. The width W1b of the non-overlapping region of the step region of the first protective film 41 and the width W2b of the non-overlapping region of the step region of the second protective film are each 0.3 μm, for example. The height t4 of the first step 41a and the second step 41b and the height t5 of the first step 42a and the second step 42b are 40 nm. In this embodiment, the inter-step regions of the first protective film 41 include regions where the first protective film 41 is not provided. That is, the inter-step regions of the first protective film 41 include regions where the first electrode fingers 31a are exposed.

[0084] Although the first protective film 41 and the second protective film 42 have the same shape in the above example, the first protective film 41 and the second protective film 42 may have different shapes.

[0085] Fourth Embodiment FIG. 20 is a cross-sectional view of an elastic wave device according to a fourth embodiment. As shown in FIG. 20 , in an elastic wave device 10D according to the fourth embodiment, the heights of the first and second steps provided on the upper surface of the first protective film 41 are smaller than the heights of the first and second steps provided on the lower surface of the second protective film 42 (the surface facing the support substrate 11 (see FIG. 2 )). In the following description, the region between the first steps 41 a, 42 a and the second steps 41 b, 42 b is referred to as an inter-step region. In this embodiment, the upper surfaces of the first electrode fingers 31 a and the first protective film 41 in the inter-step region are flat. Specifically, the upper surface of the first protective film 41 in the inter-step region is substantially flat across the region where the first electrode fingers 31 a are provided and the region where the first electrode fingers 31 a are not provided. The configuration of the IDT electrode 30 and the like is the same as in the first embodiment. In this embodiment, the lower surface of the second protective film 42 in the inter-step region is formed flat. Specifically, the lower surface of the second protective film 42 in the inter-step region is formed substantially flat across the region where the first electrode fingers 31 a are provided and the region where the first electrode fingers 31 a are not provided.

[0086] The inter-step regions are provided to overlap with portions of the first electrode fingers 31a. The width W1 of the step region of the first protective film 41 and the width W2 of the step region of the second protective film are each 0.8 μm. The width W1a of the overlapping region of the step region of the first protective film 41 and the width W2a of the overlapping region of the step region of the second protective film are each 0.5 μm, for example. The width W1b of the non-overlapping region of the step region of the first protective film 41 and the width W2b of the non-overlapping region of the step region of the second protective film are each 0.3 μm, for example. The height t4 of the first step 41a and the second step 41b is 20 nm, and the height t5 of the first step 42a and the second step 42b is 40 nm. In this embodiment, there is no region in the inter-step region of the first protective film 41 where the first electrode fingers 31a are exposed.

[0087] Fifth Embodiment Fig. 21 is a cross-sectional view of an elastic wave device according to a fifth embodiment. As shown in Fig. 21 , in an elastic wave device 10E according to the fifth embodiment, a step is formed in the first protective film 41 outside the inter-step region between the first step 41a and the second step 41b. The configuration of the IDT electrode 30 and the like is the same as in the first embodiment. In this embodiment, the top surfaces of the first electrode fingers 31a and the first protective film 41 in the inter-step region are flat. Specifically, the top surface of the first protective film 41 in the inter-step region is substantially flat across the region where the first electrode fingers 31a are provided and the region where the first electrode fingers 31a are not provided.

[0088] The inter-step region is provided so as to overlap a portion of the first electrode finger 31a. The width W1 of the step region of the first protective film 41 is 0.6 μm. The width W1a of the overlapping region of the step region of the first protective film 41 is, for example, 0.3 μm. The width W1b of the non-overlapping region of the step region of the first protective film 41 is, for example, 0.3 μm. The height t4 of the first step 41a and the second step 41b is 30 nm.

[0089] As shown in FIG. 21 , in this embodiment, a third step 41c and a fourth step are formed in the first protective film 41 in an outer region in the arrangement direction of the electrode fingers 31, 32. In this embodiment, the third step 41c is a step that is lower on the inner side in the arrangement direction of the electrode fingers 31, 32. In this embodiment, the fourth step 41d is a step that is lower on the outer side in the arrangement direction of the electrode fingers 31, 32. The third step 41c is provided outside the fourth step 41d in the arrangement direction of the electrode fingers 31, 32. A width W3 of the region between the third step 41c and the fourth step 41d is, for example, 0.6 μm. In this embodiment, the upper surface of the first protective film 41 in the region between the third step 41c and the fourth step 41d is formed flat. In this embodiment, the height t7 of the third step 41c and the fourth step 41d is 30 nm, which is the same as the height t4 of the first step 41a and the second step 41b. However, without being limited to this, the height t7 of the third step 41c and the fourth step 41d may be different from the height t4 of the first step 41a and the second step 41b.

[0090] Second Modification of Fifth Embodiment FIG. 22 is a cross-sectional view showing an elastic wave device according to a second modification of the fifth embodiment. As shown in FIG. 22 , in an elastic wave device 10F according to the second modification, a first step and a second step are provided on the top of the first protective film 41 and on the bottom surface of the second protective film 42 (the surface facing the support substrate 11 (see FIG. 2 )). In this embodiment, the top surfaces of the first electrode fingers 31 a and the first protective film 41 in the inter-step region are flat. Specifically, the top surface of the first protective film 41 in the inter-step region is substantially flat across the region where the first electrode fingers 31 a are provided and the region where the first electrode fingers 31 a are not provided. The configuration of the IDT electrode 30 and the like is the same as in the first embodiment. In this example, the bottom surface of the second protective film 42 in the inter-step region is flat. Specifically, the lower surface of the second protective film 42 in the inter-step region is formed to be substantially flat across the region where the first electrode fingers 31a are provided and the region where the first electrode fingers 31a are not provided.

[0091] The inter-step regions are provided to overlap with portions of the first electrode fingers 31a. The width W1 of the step region of the first protective film 41 and the width W2 of the step region of the second protective film are each 0.8 μm. The width W1a of the overlapping region of the step region of the first protective film 41 and the width W2a of the overlapping region of the step region of the second protective film are each 0.3 μm, for example. The width W1b of the non-overlapping region of the step region of the first protective film 41 and the width W2b of the non-overlapping region of the step region of the second protective film are each 0.3 μm, for example. The height t4 of the first step 41a and the second step 41b is 20 nm, and the height t5 of the first step 42a and the second step 42b is 30 nm. In this embodiment, there is no region in the inter-step region of the first protective film 41 where the first electrode fingers 31a are exposed.

[0092] 22 , in this embodiment, the first protective film 41 and the second protective film 42 form third steps 41c, 42c and fourth steps 41d, 42d in regions outside the arrangement direction of the electrode fingers 31, 32 relative to the first protective film 41 and the second protective film 42. In this embodiment, the third steps 41c, 42c are lower on the inner side in the arrangement direction of the electrode fingers 31, 32. In this embodiment, the fourth steps 41d, 42d are lower on the outer side in the arrangement direction of the electrode fingers 31, 32. The third steps 41c, 42c are provided outside the fourth steps 41d, 42d in the arrangement direction of the electrode fingers 31, 32. A width W3 of the region between the third step 41c and the fourth step 41d and a width W4 of the region between the third step 42c and the fourth step 42d are, for example, 0.6 μm. In this embodiment, the upper surface of the first protective film 41 in the region between the third step 41c and the fourth step 41d and the lower surface of the second protective film 42 in the region between the third step 42c and the fourth step 42d are formed flat. In this embodiment, the heights t7 and t8 of the third step 41c, 42c and the fourth step 41d, 42d are 30 nm, the same as the heights of the first step 41a, 42a and the second step 41b, 42b. However, this is not limited thereto, and the heights t7 and t8 of the third step 41c, 42c and the fourth step 41d, 42d may be different from the heights t4 and t5 of the first step 41a, 42a and the second step 41b, 42b.

[0093] Although the first protective film 41 and the second protective film 42 have the same shape in the above example, the first protective film 41 and the second protective film 42 may have different shapes.

[0094] Sixth Embodiment Fig. 23 is a cross-sectional view showing an elastic wave device according to a sixth embodiment. As shown in Fig. 23, in an elastic wave device 10G according to the sixth embodiment, the film thickness of the first protective film 41 and the film thickness of the second protective film 42 are thinner than the film thickness of the piezoelectric layer 20. Specifically, the film thickness of the piezoelectric layer 20 is, for example, 360 nm. The film thickness of the first protective film 41 is 30 nm. The film thickness of the second protective film 42 is 30 nm. The configuration of the IDT electrode 30 and the like is the same as in the first embodiment.

[0095] The width W1 of the inter-step region of the first protective film 41 is, for example, 0.5 μm. The width W1a of the overlapping region of the inter-step region of the first protective film 41 is, for example, 0.3 μm. The width W1b of the non-overlapping region of the inter-step region of the first protective film 41 is, for example, 0.2 μm. The width W2 of the inter-step region of the second protective film 42 is, for example, 0.5 μm. The width W2a of the overlapping region of the inter-step region of the second protective film 42 is, for example, 0.3 μm. The width W2b of the non-overlapping region of the inter-step region of the second protective film 42 is, for example, 0.2 μm.

[0096] In the sixth embodiment, the first protective film 41, excluding the inter-step regions, is provided to follow 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, excluding the inter-step regions, is formed with projections and depressions that reflect the shapes of the electrode fingers 31 and 32. The second protective film 42, excluding the inter-step regions, is formed flat along the second main surface 20 b of the piezoelectric layer 20.

[0097] The inter-step regions of the first protective film 41 are provided on the first protective film 41 and more inward in the arrangement direction than the first electrode fingers 31a. The inter-step regions of the second protective film 42 are formed flat along the second main surface 20b of the piezoelectric layer 20. In this embodiment, the first protective film 41 and the second protective film 42 are not provided in the inter-step regions of the first protective film 41 and the second protective film 42. That is, the first electrode fingers 31a and the first main surface 20a are exposed in the inter-step regions of the first protective film 41. The second main surface 20b is exposed in the inter-step regions of the second protective film 42.

[0098] 24 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to the sixth embodiment. As shown in FIG. 24 , elastic wave device 10G according to the sixth embodiment, even though the first step 42 a is provided on the second main surface 20 b side of the piezoelectric layer 20, exhibits reduced ripples indicated by dotted line E2 compared to the comparative example, similar to elastic wave device 10 according to the first embodiment. Furthermore, in the sixth embodiment, the peak width associated with the resonant frequency is narrowed, thereby suppressing propagation loss.

[0099] Seventh Embodiment FIG. 25 is a plan view showing an elastic wave device according to a seventh embodiment. FIG. 26 is a cross-sectional view taken along line XXVI-XXVI′ in FIG. 25 . FIG. 27 is an enlarged cross-sectional view showing region A1 shown in FIG. 26 . As shown in FIGS. 25 to 27 , in an elastic wave device 10H according to the seventh embodiment, first steps 41c are provided at the outer ends of first electrode fingers 31a in the arrangement direction of electrode fingers 31 and 32, and the outer sides of the arrangement direction of electrode fingers 31 and 32 are low steps. Specifically, the first steps 41c are formed from the inner side in the arrangement direction of electrode fingers 31 and 32 by a portion where first electrode finger 31a and first protective film 41 are provided and a portion where first main surface 20a is exposed. In this embodiment, as shown in FIGS. 25 to 27 , the first electrode fingers 31a and second electrode fingers 32a have shorter electrode widths than the other electrode fingers of the electrode fingers 31 and 32. The electrode width of the first electrode finger 31a and the second electrode finger 32a is, for example, 0.3 μm.

[0100] 27 , in an outer region in the arrangement direction of the electrode fingers 31, 32, the first protective film 41 has a surface of a second step 41 d where the side surface of the first protective film 41 is exposed in the Y direction. In this embodiment, the second step 41 d is a step that is lower on the inner side in the arrangement direction of the electrode fingers 31, 32. In this embodiment, in a region between the first electrode finger 31 a and the adjacent electrode finger 32, the second step 41 d is formed from the inner side in the arrangement direction of the electrode fingers 31, 32 by a portion where the first protective film 41 is not provided and a portion where the first protective film 41 is provided.

[0101] The inter-step region is located at the outer end of the first electrode finger 31a in the arrangement direction of the electrode fingers 31 and 32. The side surface of the first protective film 41 at the first step 41c is arranged to overlap the outer end of the electrode fingers 31 and 32 in the arrangement direction, and the side surface of the first protective film at the second step 41d is located outward of the first step 41c in the arrangement direction. In other words, the inter-step region does not overlap with the first electrode finger 31a. The width W1 of the inter-step region is, for example, 0.6 μm. In this embodiment, the first electrode finger 31a and the first protective film 41 are not provided in the inter-step region, and the first main surface 20a is exposed.

[0102] In this way, since the first step 41 c is provided so as to overlap the first electrode finger 31 a, in the region overlapping with the first electrode finger 31 a positioned outermost in the arrangement direction of the plurality of electrode fingers 31, 32, the region inside the arrangement direction of the first step 41 c does not have the first protective film 41 and has a different acoustic impedance from the region where the first protective film 41 is laminated. As a result, an acoustic reflection surface R is formed in the first step (the portion overlapping with the side surface of the first protective film 41).

[0103] 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 .

[0104] FIG. 28 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to a seventh embodiment. As shown in FIG. 28 , 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 are generated, as indicated by dotted lines E1 and E2. In contrast, in elastic wave device 10H according to the seventh embodiment, the provision of first step 41 a and second step 41 b suppresses the ripples indicated by dotted lines E1 and E2 compared to the comparative example. Elastic wave device 10H according to the seventh embodiment has a narrower peak width associated with the resonant frequency than the elastic wave device according to the comparative example, which indicates that propagation loss and leakage of elastic waves are suppressed.

[0105] (Third Modification of Seventh Embodiment) FIG. 29 is a plan view illustrating an elastic wave device according to a third modification of the seventh embodiment. As shown in FIG. 29 , in an elastic wave device 10I according to the third modification of the seventh embodiment, first steps 41c and 42c are provided at outer ends of first electrode finger 31a in the arrangement direction of multiple electrode fingers 31 and 32, and the outer steps are lower in the arrangement direction of multiple electrode fingers 31 and 32. Specifically, from the inside in the arrangement direction of multiple electrode fingers 31 and 32, the first step 41c is formed between a portion where first electrode finger 31a and first protective film 41 are provided and a portion where first main surface 20a is exposed, and the first step 42c is formed between a portion where second protective film 42 is provided and a portion where second main surface 20b is exposed. The configuration of the IDT electrode is the same as the configuration described above in FIG. 27 .

[0106] 29 , in an outer region in the arrangement direction of the electrode fingers 31, 32, a second step 41 d is formed in the first protective film 41, and a second step 42 d is formed in the second protective film 42. In this embodiment, the second steps 41 d, 42 d are lower on the inner side in the arrangement direction of the electrode fingers 31, 32. In this embodiment, in a region between the first electrode finger 31 a and the adjacent electrode finger 32, from the inner side in the arrangement direction of the electrode fingers 31, 32, the second step 41 d is formed between a portion where the first protective film 41 is not provided and a portion where the first protective film 41 is provided, and the second step 42 d is formed between a portion where the second protective film 42 is not provided and a portion where the second protective film 42 is provided.

[0107] The inter-step region is located at the outer end of the first electrode finger 31a in the arrangement direction of the electrode fingers 31 and 32. The side surface of the first protective film 41 at the first step 41c and the side surface of the second protective film 42 at the first step 42c are arranged to overlap the outer ends of the electrode fingers 31 and 32 in the arrangement direction, while the side surface of the first protective film 41 at the second step 41d and the side surface of the second protective film 42 at the second step 42d are located outside the first steps 41c and 42c in the arrangement direction. In other words, the inter-step region does not overlap with the first electrode finger 31a. The widths W1 and W2 of the inter-step region are, for example, 0.6 μm. In this embodiment, the first electrode finger 31a and the first protective film 41 are not provided in the inter-step region, and the first main surface 20a is exposed. The second protective film 42 is not provided in the inter-step region, and the second main surface 20b is exposed.

[0108] Although the first protective film 41 and the second protective film 42 have the same shape in the above example, the first protective film 41 and the second protective film 42 may have different shapes.

[0109] FIG. 30 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the third modification. As shown in FIG. 30 , 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 are generated, as indicated by dotted lines E1 and E2. In contrast, in elastic wave device 10 according to the third modification, the provision of first steps 41 c, 42 c and second steps 41 d, 42 d suppresses the ripples indicated by dotted lines E1 and E2 compared to the comparative example. Elastic wave device 10 according to the third modification has a narrower peak width associated with the resonant frequency than the elastic wave device according to the comparative example, which indicates that propagation loss and leakage of elastic waves are suppressed.

[0110] Eighth Embodiment Fig. 31 is a cross-sectional view showing an elastic wave device according to an eighth 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. 31 , an elastic wave device 10J according to the eighth 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 ).

[0111] 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. The inter-step area is located in an area overlapping the first electrode finger 31 a of the first IDT electrode and the first electrode finger 36 a of the second IDT electrode.

[0112] In the eighth 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.

[0113] 31 shows an example in which the first step 41 a and the second step 41 b shown in the first embodiment are provided, but the present invention is not limited to this. The fifteenth embodiment can be combined with each of the above-described embodiments and modifications.

[0114] Ninth Embodiment Fig. 32 is a circuit diagram illustrating an acoustic wave filter device according to a ninth embodiment. As shown in Fig. 32, an acoustic wave filter device 10K according to the ninth 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 10K according to the ninth embodiment is a so-called ladder filter.

[0115] 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.

[0116] In this embodiment, protective films with different configurations are used for the plurality of series arm resonators 61, 62, and 63 and the plurality of parallel arm resonators 64, 65, 66, and 67. This makes it possible to obtain a better output waveform as a filter.

[0117] Although the acoustic wave filter device 10K according to the ninth preferred embodiment is combined with the first and second steps shown in the first and second modified examples, the present invention is not limited to this example and can be combined with the above-described embodiments and modified examples.

[0118] 33 is a cross-sectional view of an elastic wave device according to a tenth embodiment. In the elastic wave device 10 of the first embodiment described above, the support substrate 11 has a cavity portion 14, and the second main surface 20 b of the piezoelectric layer 20 has a cavity portion 14 (hollow portion), which is a so-called membrane structure. However, the present invention is not limited to this.

[0119] 33 , in an elastic wave device 10L according to the tenth 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 AlN or SiN. 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.

[0120] In acoustic wave device 10L, 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.

[0121] 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.

[0122] 33 shows an example in which the first step 41 a and the second step 41 b shown in the first embodiment are provided, but the present invention is not limited to this. The tenth embodiment can be combined with each of the above-described embodiments and modifications.

[0123] Eleventh Embodiment Fig. 34 is an explanatory diagram showing an example of admittance characteristics of an elastic wave device according to an eleventh embodiment. Fig. 35 is an explanatory diagram showing an example of impedance phase in a higher mode. The elastic wave device according to the eleventh embodiment shown in Fig. 34 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.

[0124] 34 shows frequency characteristics of the absolute value of admittance for the elastic wave device according to embodiment 11. As shown in Fig. 34, in the elastic wave device according to embodiment 11, a higher-order mode of 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.

[0125] The horizontal axis of the graph shown in Fig. 35 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. 35 corresponds to the intensity of the S2 mode.

[0126] 35, 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.

[0127] In contrast, in the eleventh 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 eleventh 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.

[0128] Although the eleventh embodiment has been described with reference to the case where the first protective film 41 and the second protective film 42 have different thicknesses in the elastic wave device 10 according to the first embodiment, 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 eleventh embodiment can be combined with any of the embodiments and modified examples described above.

[0129] The shapes, widths, thicknesses, etc. of the first protective film 41, the second protective film 42, 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 first protective film 41 and the second protective film 42 may be tapered. The first step and the second step may have the same height, and the inter-step region may have the same width. Alternatively, the first step overlapping the first electrode finger 31 a and the second electrode finger 32 a may have different widths and thicknesses due to, for example, variations in the manufacturing process, and may have a different height from the second step. Furthermore, the first step and the second step may be tapered.

[0130] The first step 41 a and the second step 42 b shown in the above-described embodiments and modifications are merely examples and can be modified as appropriate. At least one of the first step 41 a and the second step 42 b may be provided in a region overlapping two electrode fingers (the first electrode finger 31 a and the electrode finger 32) or three electrode fingers (the first electrode finger 31 a, the electrode finger 32, and the electrode finger 31) located on the outer sides in the arrangement direction.

[0131] 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.

[0132] The present disclosure may also have the following configurations.

[0133] (1) An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction; 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; 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; and a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, wherein in a region overlapping in a planar view from the first direction with a first electrode finger that is positioned outermost in the arrangement direction of the plurality of electrode fingers, the protective film has a first stepped surface that exposes a side surface of the protective film in a direction intersecting with the extension direction of the first electrode finger, 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), wherein in a region between the first electrode finger and an electrode finger adjacent to the first electrode finger, the protective film has a second step surface where a side surface of the protective film is exposed in a direction intersecting a direction in which the first electrode fingers extend, the first step is a step that is lower on the inside of the arrangement direction, and the second step is a step that is lower on the outside of the arrangement direction. (3) The elastic wave device according to (2), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode, wherein the first protective film has a first stepped surface at which a side surface of the protective film is exposed in a direction intersecting with the extension direction of the first electrode finger in a region overlapping with a first electrode finger that is located outermost in an arrangement direction of the plurality of electrode fingers, among the plurality of electrode fingers, and wherein the first protective film has a second stepped surface at which a side surface of the protective film is exposed in a direction intersecting with the extension direction of the first electrode finger in a region between the first electrode finger and an electrode finger adjacent to the first electrode finger.(4) The elastic wave device according to (2), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode and a second protective film provided on the second main surface of the piezoelectric layer, wherein in a region overlapping with a first electrode finger that is located outermost in an arrangement direction of the plurality of electrode fingers, the second protective film has a first stepped surface that exposes a side surface of the protective film in a direction intersecting with the extension direction of the first electrode finger, and in a region between the first electrode finger and an electrode finger adjacent to the first electrode finger, the second protective film has a second stepped surface that exposes a side surface of the protective film in a direction intersecting with the extension direction of the first electrode finger. (5) The elastic wave device according to (2), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode and a second protective film provided on the second main surface of the piezoelectric layer, wherein in a region overlapping with a first electrode finger that is outermost in an arrangement direction of the plurality of electrode fingers, the first protective film and the second protective film have a first step surface where a side surface of the protective film is exposed in a direction intersecting with the extension direction of the first electrode finger, and in a region between the first electrode finger and an electrode finger adjacent to the first electrode finger, the first protective film and the second protective film have a second step surface where a side surface of the protective film is exposed in a direction intersecting with the extension direction of the first electrode finger. (6) The elastic wave device according to (5), wherein heights of the first and second steps formed by the first protective film are smaller than heights of the first and second steps formed by the second protective film. (7) The elastic wave device according to any one of (1) to (6), wherein the protective film further forms a third step in a region that is outward of the first electrode fingers in the arrangement direction and does not overlap with the IDT electrodes. (8) The elastic wave device according to any one of (1) to (7), wherein the protective film has a thickness smaller than a thickness of the piezoelectric layer. (9) The elastic wave device according to (1), wherein the protective film has a second step surface that exposes a side surface of the protective film in a direction intersecting with the extension direction of the first electrode fingers in a region that is outward of the first electrode fingers in the arrangement direction and does not overlap with the IDT electrodes, the first step is a step that is lower on the outer side of the arrangement direction, and the second step is a step that is lower on the inner side of the arrangement direction.(10) The elastic wave device according to (9), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode, and at an outer end of a first electrode finger among the plurality of electrode fingers that is located outermost in the arrangement direction of the plurality of electrode fingers, the first protective film has a first stepped surface that exposes a side surface of the protective film in a direction intersecting the extension direction of the first electrode finger, and in a region that is outward of the first electrode fingers in the arrangement direction and does not overlap with the IDT electrode, the first protective film has a second stepped surface that exposes a side surface of the protective film in a direction intersecting the extension direction of the first electrode finger. (11) The elastic wave device according to (9), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode and a second protective film provided on the second main surface of the piezoelectric layer, wherein at an outer end of a first electrode finger among the plurality of electrode fingers that is located outermost in the arrangement direction of the plurality of electrode fingers, the first protective film and the second protective film have a first step surface at which a side surface of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger, and wherein in a region that is outward of the first electrode finger in the arrangement direction and does not overlap with the IDT electrode, the first protective film and the second protective film have a second step surface at which a side surface of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger. (12) The elastic wave device according to any one of (1) to (11), wherein the IDT electrode is provided on both the first main surface and the second main surface of the piezoelectric layer. (13) The protective film is made of silicon oxide (SiO. ２(14) An elastic wave filter device according to any one of (1) to (12), wherein the resonator is the elastic wave device according to (1) to (13). (15) The elastic wave filter device according to (14), 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, the at least one resonator being a plurality of resonators including a series arm resonator provided in the series arm and a parallel arm resonator provided in the parallel arm, the series arm resonator and the parallel arm resonator each having a first step formed by the protective film, and a height of the first step formed by the protective film of the series arm resonator being different from a height of the first step formed by the protective film of the parallel arm resonator. (16) The elastic wave filter device according to (14), 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 protective film of the series arm resonator has a different configuration from the protective film of the parallel arm resonator. (17) The elastic wave device according to any one of (1) to (13), wherein the piezoelectric layer includes lithium niobate or lithium tantalate and has a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut. (18) The elastic wave device according to any one of (1) to (13) and (17), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer. (19) The acoustic wave device according to any one of (1) to (13), (17), and (18), wherein the protective film has a thickness greater than that of the IDT electrode.(20) The elastic wave device according to any one of (1) to (13) and (17) to (19), wherein the protective film includes 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, wherein a value of A / B is 1-0.06 or more and 1+0.06 or less, where A is a total distance from a center of thickness of the piezoelectric layer to a top surface of the first protective film and B is a total distance from the center of thickness of the piezoelectric layer to a top surface of the second protective film. (21) The elastic wave device according to any one of (1) to (13) and (17) to (20), wherein the protective film includes 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, and wherein an upper surface of the first protective film and a lower surface of the second protective film are formed flat. (22) The elastic wave device according to any one of (1) to (13) and (17) to (21), wherein d / p is 0.24 or less. (23) The elastic wave device according to any one of (1) to (13) and (17) to (22), wherein, when viewed in the electrode finger orthogonal direction, a region where adjacent electrode fingers overlap each other and a region between centers of adjacent electrode fingers in the electrode finger orthogonal direction is an excitation region, and wherein MR satisfies MR≦1.75(d / p)+0.075, where MR is a metallization ratio of the electrode fingers to the excitation region. (24) The elastic wave device according to any one of (1) to (13) and (17) to (23), wherein the piezoelectric layer is made of lithium tantalate or lithium niobate. (25) The elastic wave device according to (24), 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) (26) The elastic wave device according to any one of (1) to (13) and (17) to (25), 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. (27) The elastic wave device according to any one of (1) to (13) and (17) to (25), 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.

[0134] REFERENCE SIGNS LIST 10, 10A to 10J, 10L Acoustic wave device 10K Acoustic wave filter device 11 Support substrate 12 Bottom portion 13 Wall portion 14 Cavity portion 20 Piezoelectric layer 20a First main surface 20b Second main surface 30 IDT electrode 31, 32, 36, 37 Electrode fingers 31a First electrode finger 32a Second electrode finger 33, 34 Bus bar electrodes 41 First protective film 42 Second protective film 41a, 42a First step 41b, 42b Second step 41c, 42c Third step 41d, 42d Fourth step

Claims

1. An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction; 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; 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; and a protective film provided on at least one of the first and second main surfaces of the piezoelectric layer, wherein in a region overlapping in a planar view from the first direction with a first electrode finger that is positioned outermost in the arrangement direction of the plurality of electrode fingers among the plurality of electrode fingers, the protective film has a first step surface where a side surface of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger, wherein d is a thickness of the piezoelectric layer and p is a center-to-center distance between adjacent electrode fingers, d / p is 0.5 or less.

2. The elastic wave device of claim 1, wherein in a region between the first electrode finger and an electrode finger adjacent to the first electrode finger, the protective film has a second step surface where a side surface of the protective film is exposed in a direction intersecting the direction in which the first electrode fingers extend, the first step is a step that is lower on the inside of the arrangement direction, and the second step is a step that is lower on the outside of the arrangement direction.

3. The elastic wave device of claim 2, wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode, and in a region overlapping with a first electrode finger among the plurality of electrode fingers that is located outermost in an arrangement direction of the plurality of electrode fingers, the first protective film has a first stepped surface at which a side surface of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger, and in a region between the first electrode finger and an electrode finger adjacent to the first electrode finger, the first protective film has a second stepped surface at which a side surface of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger.

4. The elastic wave device of claim 2, wherein the protective film comprises a first protective film provided on the first main surface of the piezoelectric layer and covering the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer, wherein in a region overlapping with a first electrode finger among the plurality of electrode fingers that is located outermost in an arrangement direction of the plurality of electrode fingers, the second protective film has a first stepped surface at which a side surface of the protective film is exposed in a direction intersecting with the extension direction of the first electrode finger, and wherein in a region between the first electrode finger and an electrode finger adjacent to the first electrode finger, the second protective film has a second stepped surface at which a side surface of the protective film is exposed in a direction intersecting with the extension direction of the first electrode finger.

5. The elastic wave device of claim 2, wherein the protective film comprises a first protective film provided on the first main surface of the piezoelectric layer covering the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer, wherein in a region overlapping with a first electrode finger among the plurality of electrode fingers that is located outermost in an arrangement direction of the plurality of electrode fingers, the first protective film and the second protective film have a first stepped surface at which a side surface of the protective film is exposed in a direction intersecting with the extension direction of the first electrode finger, and wherein in a region between the first electrode finger and an electrode finger adjacent to the first electrode finger, the first protective film and the second protective film have a second stepped surface at which a side surface of the protective film is exposed in a direction intersecting with the extension direction of the first electrode finger.

6. The acoustic wave device according to claim 5, wherein the height of the first step and the second step formed by the first protective film are smaller than the height of the first step and the second step formed by the second protective film.

7. The elastic wave device according to claim 1, wherein a third step is further formed in the protective film in a region that is outside the first electrode fingers in the arrangement direction and does not overlap with the IDT electrode.

8. The elastic wave device according to claim 1, wherein the protective film has a thickness smaller than a thickness of the piezoelectric layer.

9. The elastic wave device of claim 1, wherein in a region outside the first electrode fingers in the arrangement direction and not overlapping with the IDT electrode, the protective film has a second step surface where a side surface of the protective film is exposed in a direction intersecting the direction in which the first electrode fingers extend, the first step being a lower step on the outside of the arrangement direction, and the second step being a lower step on the inside of the arrangement direction.

10. The elastic wave device of claim 9, wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode, and at an outer end of a first electrode finger among the plurality of electrode fingers that is located outermost in the arrangement direction of the plurality of electrode fingers, the first protective film has a first step surface at which a side of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger, and in a region that is outer than the first electrode fingers in the arrangement direction and does not overlap with the IDT electrode, the first protective film has a second step surface at which a side of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger.

11. The elastic wave device of claim 9, wherein the protective film comprises a first protective film provided on the first main surface of the piezoelectric layer and covering the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer, and at an outer end of a first electrode finger among the plurality of electrode fingers that is located outermost in the arrangement direction of the plurality of electrode fingers, the first protective film and the second protective film have a first step surface at which a side surface of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger, and in a region that is outer than the first electrode finger in the arrangement direction and does not overlap with the IDT electrode, the first protective film and the second protective film have a second step surface at which a side surface of the protective film is exposed in a direction intersecting the extension direction of the first electrode finger.

12. 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.

13. The protective film is made of silicon oxide (SiO ２ The acoustic wave device according to claim 1 , wherein the first insulating layer 14 is made of a ferroelectric material.

14. 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 13.

15. The elastic wave filter device according to claim 14, 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, wherein the first step is formed by the protective film of each of the series arm resonator and the parallel arm resonator, and a height of the first step formed by the protective film of the series arm resonator is different from a height of the first step formed by the protective film of the parallel arm resonator.

16. The elastic wave filter device according to claim 14, 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 protective film of the series arm resonator has a different configuration from the protective film of the parallel arm resonator.

17. The elastic wave device according to claim 1, 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.

18. The elastic wave device according to any one of claims 1 to 13 and 17, wherein the protective film comprises a first protective film provided on the first main surface of the piezoelectric layer and covering the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer.

19. The acoustic wave device according to claim 1, wherein the protective film has a thickness greater than a thickness of the IDT electrode.

20. The elastic wave device according to any one of claims 1 to 13 and 17 to 19, wherein the protective film includes 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, wherein the value of A / B is 1-0.06 or more and 1+0.06 or less, where A is the total distance from the center of the thickness of the piezoelectric layer to the top surface of the first protective film and B is the total distance from the center of the thickness of the piezoelectric layer to the top surface of the second protective film.

21. An elastic wave device according to any one of claims 1 to 13 and 17 to 20, wherein the protective film comprises 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, and an upper surface of the first protective film and a lower surface of the second protective film are formed flat.

22. The elastic wave device according to any one of claims 1 to 13 and 17 to 21, wherein d / p is 0.24 or less.

23. An elastic wave device as claimed in any one of claims 1 to 13 and 17 to 22, 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.

24. The acoustic wave device according to any one of claims 1 to 13 and 17 to 23, wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.

25. The elastic wave device according to claim 24, 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) 26. An elastic wave device according to any one of claims 1 to 13 and 17 to 25, 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.

27. An elastic wave device described in any one of claims 1 to 13 and 17 to 25, 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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