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 that has a first main surface and a second main surface; an IDT electrode that is provided on at least one of the first main surface and the second main surface of the piezoelectric layer, and that includes a plurality of electrode fingers; a support member that faces the second main surface of the piezoelectric layer, and has an acoustic reflection part on the second main surface side of the piezoelectric layer; and a load film that is provided over a region overlapping at least, in a plan view from the first direction, the fourth electrode finger from one outer side to the fourth electrode finger from the other outer side in the array direction among the plurality of electrode fingers. The load film is not provided in at least a part of a region that overlaps, in the plan view, a first electrode finger among the plurality of electrode fingers that is on the outermost side in the array direction. 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 load film provided across a region of the plurality of electrode fingers that overlaps in a planar view from the first direction, from at least a fourth electrode finger from one outer side in the arrangement direction to a fourth electrode finger from the other outer side, wherein the load film is not provided in at least a portion of a region that overlaps in a planar view with a first electrode finger that is arranged outermost in the arrangement direction of the plurality of electrode fingers, and wherein, where 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.

[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 illustrating 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 illustrating an example of admittance characteristics of an elastic wave device according to a first modification of the first embodiment. FIG. 14 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to a first modification of the first embodiment. FIG. 15 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to a second modification of the first embodiment. FIG. 16 is a cross-sectional view illustrating an elastic wave device according to a second embodiment. FIG. 17 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to the second embodiment. FIG. 18 is a cross-sectional view illustrating an elastic wave device according to a third embodiment. FIG. 19 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to the third embodiment. FIG. 20 is a cross-sectional view illustrating an elastic wave device according to a fourth embodiment. FIG. 21 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to the fourth embodiment. FIG. 22 is a cross-sectional view illustrating an elastic wave device according to a fifth embodiment. FIG. 23 is an enlarged cross-sectional view illustrating region A1 illustrated in FIG. 22. FIG. 24 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a fifth embodiment. FIG. 25 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a comparative example. FIG. 26 is a cross-sectional view of an elastic wave device according to a sixth embodiment. FIG. 27 is a cross-sectional view of an elastic wave device according to a seventh embodiment. FIG. 28 is a cross-sectional view of an elastic wave device according to an eighth embodiment. FIG. 29 is a cross-sectional view of an elastic wave device according to a ninth embodiment. FIG. 30 is a cross-sectional view of an elastic wave device according to a tenth embodiment. FIG. 31 is a cross-sectional view of an elastic wave device according to an eleventh embodiment. FIG. 32 is a cross-sectional view of an elastic wave device according to a twelfth embodiment. FIG. 33 is a cross-sectional view of an elastic wave device according to a third modification of the twelfth embodiment. FIG. 34 is a circuit diagram of an elastic wave filter device according to a thirteenth embodiment. FIG. 35 is a cross-sectional view of an elastic wave device according to a fourteenth embodiment. FIG. 36 is a cross-sectional view of an elastic wave device according to a fifteenth embodiment. FIG. 37 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to a sixteenth embodiment. FIG. 38 is a diagram illustrating an example of impedance phase in a higher 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 and a load film 50 are indicated by two-dot chain lines.

[0012] 1 and 2 , an elastic wave device 10 according to the first embodiment includes a piezoelectric layer 20, an IDT electrode 30, a support substrate 11, a first protective film 41, a second protective film 42, and a load film 50. As shown in Fig. 2 , the elastic wave device 10 includes the second protective film 42, the piezoelectric layer 20, the IDT electrode 30, the first protective film 41, and the load film 50 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.

[0027] The load film 50 is provided on the first protective film 41. The load film 50 extends over at least an overlapping region from the fourth electrode finger 31 from the outside in the arrangement direction of the electrode fingers 31, 32 to the fourth electrode finger 32 from the outside on the side opposite to the first electrode finger 31 a. In the first embodiment, the load film 50 extends over an overlapping region from the outermost electrode finger 31 (hereinafter referred to as the first electrode finger 31 a) in the arrangement direction of the electrode fingers 31, 32 to the outermost electrode finger 32 (hereinafter referred to as the second electrode finger 32 a) on the side opposite to the first electrode finger 31 a.

[0028] In the following description, a portion of the load film 50 that extends from at least the fourth electrode finger 31 from the outside in the arrangement direction of the electrode fingers 31, 32 to the fourth electrode finger 32 from the outside on the opposite side to the first electrode finger 31 a may be referred to as an inner load film 51. The detailed configuration of the load film 50 will be described later with reference to FIGS.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Piezoelectric layer 20: LiNbO with Euler angles (0°, 0°, 90°) ３ Thickness of the piezoelectric layer 20: 400 nm

[0039] 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

[0040] First protective film 41, second protective film 42: silicon oxide film with a thickness of 1 μm

[0041] Support substrate 11: Si

[0042] 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.

[0043] As is clear from FIG. 5, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 refers to the region of the electrode finger 31 where it overlaps with the electrode finger 32, the region of the electrode finger 32 where it overlaps with the electrode finger 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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).

[0057] (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)

[0058] 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.

[0059] Next, the detailed configuration of the load film 50 will be described. Fig. 12 is an enlarged cross-sectional view of region A shown in Fig. 2. Fig. 12 describes a portion of the load film 50 that overlaps with the first electrode finger 31a, which is located outermost in the arrangement direction of the multiple electrode fingers 31 and 32 of the load film 50. However, the load film 50 also has an arrangement relationship that is line-symmetrical with the second electrode finger 32a, which is located outermost on the opposite side of the first electrode finger 31a. In other words, the description of the first electrode finger 31a can also be applied to the second electrode finger 32a.

[0060] 12 , the load film 50 is provided on the first protective film 41 and is provided so as to overlap a portion of the first electrode finger 31 a. That is, the load film 50 is not provided in a portion of the region overlapping with the first electrode finger 31 a. In this embodiment, the upper surface of the first protective film 41 is formed flat. Specifically, the upper surface of the first protective film 41 is formed substantially flat across the region where the electrode fingers 31 and 32 are provided and the region where the electrode fingers 31 and 32 are not provided.

[0061] The load film 50 is provided to protrude from the upper surface of the first protective film 41. A step is formed between the load film 50 and the first protective film 41 in a region overlapping with the first electrode finger 31 a. More specifically, the first main surface 20 a of the piezoelectric layer 20 has a region where the first electrode finger 31 a, the first protective film 41, and the load film 50 are stacked in this order, a region where the first electrode finger 31 a and the first protective film 41 are stacked in this order, and a region where the first protective film 41 is stacked. In the region overlapping with the first electrode finger 31 a, a step is formed between a portion where the load film 50 and the first protective film 41 are stacked and a portion where the first protective film 41 is provided but the load film 50 is not provided.

[0062] The load film 50 is provided on the inside of the first electrode finger 31a in the arrangement direction of the multiple electrode fingers 31 and 32. One side surface of the load film 50 is arranged so as to overlap the midpoint of the first electrode finger 31a in the width direction. That is, the load film 50 includes an overlapping region that overlaps with a part of the first electrode finger 31a. The width W1 of the overlapping region of the load film 50 is, for example, 0.3 μm.

[0063] In this embodiment, the thickness t4 of the load film 50 is 55 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 thickness t4 of the load film 50 and is thicker than the thickness t3 of the IDT electrode 30.

[0064] The load film 50 is made of a material different from that of the first protective film 41. In this embodiment, the load film 50 is made of tantalum oxide (Ta ２ O ５ The first protective film 41 is made of silicon oxide (SiO ２ ). More specifically, in the load film 50 of the first modified example, unless otherwise specified, the "density" in this embodiment represents a physical property value specific to the material. Furthermore, the load film 50 and the first protective film 41 may be made of the same material, and even if the load film 50 and the first protective film 41 are made of the same material, the density of the load film 50 may be different from the density of the first protective film 41. For example, if the load film 50 is formed by vapor deposition, the actual density of the load film 50 is smaller than the density of the first protective film 41.

[0065] In this way, the load film 50 is provided so as to overlap a part of the first electrode finger 31 a, and therefore, 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 where only the first protective film 41 is laminated has a different acoustic impedance from the region where the load film 50 and the first protective film 41 are laminated. As a result, an acoustic reflection surface R is formed in the step portion between the load film 50 and the first protective film 41 (the portion overlapping with the side surface of the load film 50).

[0066] 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 .

[0067] FIG. 13 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the first embodiment. More specifically, FIG. 13 is an explanatory diagram showing the real part of the admittance, i.e., the conductance component, of the elastic wave device according to the first embodiment. The admittance characteristics shown in FIG. 13 represent simulation results of the admittance characteristics of elastic wave device 10 according to the first embodiment. FIG. 13 also shows simulation results of the admittance characteristics of an elastic wave device according to a comparative example. The comparative example is an elastic wave device in which load film 50 is not provided, unlike the first embodiment.

[0068] 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 arranging load film 50 so that it overlaps with a portion of first electrode finger 31a, 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.

[0069] The shapes, widths, thicknesses, etc. of the load film 50, the first protective film 41, and the IDT electrode 30 described above are merely examples and may be changed as appropriate. For example, the side surfaces of the load film 50 may be tapered.

[0070] 14 is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a first modification of the first embodiment. The elastic wave device according to the first modification is different from the elastic wave device 10 according to the first embodiment in that the load film 50 is made of silicon dioxide (SiOC). More specifically, the load film 50 of the second modification is made of a material with a lower density than the silicon oxide used for the first protective film 41. The thickness t4 of the load film 50 is 45 nm. The width W1 of the load film 50, the first protective film 41, the IDT electrode 30, and other configurations are the same as those of the first embodiment.

[0071] 14 , the elastic wave device according to the first modification 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, the first modification also exhibits reduced propagation loss due to the narrower peak width associated with the resonant frequency.

[0072] (Second Modification of First Embodiment) FIG. 15 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to a second modification of the first embodiment. The elastic wave device according to the second modification is different from the elastic wave device 10 according to the first embodiment in that the load film 50 is made of silicon nitride (SiN). More specifically, the load film 50 of the second modification is made of a material that is harder than the silicon oxide used for the first protective film 41. The thickness t4 of the load film 50 is 65 nm. The width W1 of the load film 50, the first protective film 41, the IDT electrode 30, and other configurations are the same as those of the first embodiment. Note that, unless otherwise specified, the term "hardness" in this embodiment refers to a physical property inherent to the material.

[0073] 15 , the elastic wave device according to the second modification exhibits reduced ripples indicated by dotted lines E1 and E2 compared to the comparative example. Furthermore, the elastic wave device according to the second modification also exhibits reduced ripples indicated by dotted line E3. Similar to elastic wave device 10 according to the first preferred embodiment, the elastic wave device according to the second modification exhibits reduced ripples and reduced propagation loss.

[0074] The materials of the load film 50 shown in the first and second modified examples are merely examples, and are not limited to these. The material of the load film 50 may be, for example, SiOC, SiO ２ , SiN, Ta ２ O ５ , AlN, Al ２ O ３ , HfO ２ , Nb ２ O ５ , WO is used.

[0075] Second Embodiment FIG. 16 is a cross-sectional view showing an elastic wave device according to a second embodiment. In the first embodiment and the first and second modifications, the load film 50 is provided on the first protective film 41 on the first main surface 20 a side of the piezoelectric layer 20. However, the present invention is not limited to this. As shown in FIG. 16 , in an elastic wave device 10A according to the second embodiment, the load film 50 is provided on the second main surface 20 b side of the piezoelectric layer 20 and on the lower surface of the second protective film 42. In other words, the load film 50 is not provided on the first main surface 20 a side of the piezoelectric layer 20, and the upper surface of the first protective film 41 is formed flat. The lower surface of the second protective film 42 is the surface of the second protective film 42 that faces the support substrate 11 (see FIG. 2 ).

[0076] The lower surface of the second protective film 42 is formed flat along the second main surface 20b of the piezoelectric layer 20. The load film 50 is provided on the lower surface of the second protective film 42 and overlaps with a portion of the first electrode finger 31a. In this embodiment, in the region overlapping with the first electrode finger 31a, the second main surface 20b of the piezoelectric layer 20 has a region where the second protective film 42 and the load film 50 are stacked, and a region where the second protective film 42 is provided but the load film 50 is not provided. As a result, a step is formed between the load film 50 and the second protective film 42 in the region overlapping with the first electrode finger 31a.

[0077] In the second embodiment, the load film 50 is made of a different material from the first protective film 41 and the second protective film 42, for example, silicon nitride (SiN). The width W2 of the overlapping region of the load film 50 is, for example, 0.3 μm. The thickness t5 of the load film 50 is 65 nm.

[0078] 1, a repeated description will be omitted. Although not shown, a load film 50 is also provided on the opposite side of the arrangement direction of the plurality of electrode fingers 31, 32 in a position overlapping with a part of the second electrode finger 32a (see FIG. 1).

[0079] FIG. 17 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. 17 , the elastic wave device 10A according to the second embodiment, even though the load film 50 is provided on the second main surface 20b of the piezoelectric layer 20, exhibits reduced ripples indicated by dotted lines E1, E2, and E3 compared to the comparative example, similar to the elastic wave device 10 according to the first embodiment. Furthermore, the peak width associated with the resonant frequency is narrowed in the second embodiment, thereby suppressing propagation loss. Furthermore, in the second embodiment, the load film 50 is not provided 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.

[0080] The second embodiment can be appropriately combined with the first and second modified examples described above. That is, the load film 50 may be provided on the lower surface of the second protective film 42, and may be made of various materials different from those of the second protective film 42. Alternatively, the load film 50 may be provided on the lower surface of the second protective film 42, and the thicknesses of the first protective film 41 and the second protective film 42 may be thinner than the thickness of the piezoelectric layer 20.

[0081] Third Embodiment Fig. 18 is a cross-sectional view showing an elastic wave device according to a third embodiment. As shown in Fig. 18 , in an elastic wave device 10B according to the third embodiment, load films 50 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 load film 50 provided on the first protective film 41 is referred to as an upper load film 50A, and the load film 50 provided on the bottom surface of the second protective film 42 is referred to as a lower load film 50B. Note that when it is not necessary to distinguish between the upper load film 50A and the lower load film 50B, they are simply referred to as load films 50.

[0082] In this embodiment, the upper load film 50A and the lower load film 50B are made of the same material, such as silicon nitride (SiN). The upper load film 50A and the lower load film 50B are provided to overlap with each other, and each overlaps with a part of the first electrode finger 31 a.

[0083] The width W1 of the overlapping region of the upper load film 50A and the width W2 of the overlapping region of the lower load film 50B are each, for example, 0.3 μm. The thickness t4 of the upper load film 50A and the thickness t5 of the lower load film 50B are each 40 nm.

[0084] Although the upper load film 50A and the lower load film 50B have the same material and the same shape in the above example, the present invention is not limited to this example and may have different materials and different shapes.

[0085] 19 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to the third embodiment. As shown in FIG. 19 , in elastic wave device 10B according to the third embodiment, load films 50 are provided on both the first principal surface 20 a and the second principal surface 20 b of piezoelectric layer 20, and therefore ripples indicated by dotted lines E1, E2, and E3 are more effectively suppressed than in the comparative example. Furthermore, in the third embodiment, the peak width associated with the resonant frequency is narrowed, thereby suppressing propagation loss.

[0086] Fourth Embodiment FIG. 20 is a cross-sectional view showing an elastic wave device according to a fourth embodiment. As shown in FIG. 20 , in an elastic wave device 10C according to the fourth embodiment, load films 50 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 load film 50 provided on the first protective film 41 is referred to as an upper load film 50A, and the load film 50 provided on the bottom surface of the second protective film 42 is referred to as a lower load film 50B. Note that when there is no need to distinguish between the upper load film 50A and the lower load film 50B, they are simply referred to as load films 50. The upper load film 50A has an inner load film 51A and an outer load film 52A, and the lower load film 50B has an inner load film 51A and an outer load film 52B.

[0087] In this embodiment, the inner load films 51A and 51B are made of the same material, such as silicon nitride (SiN). The inner load films 51A and 51B are provided to overlap each other and to overlap a portion of the first electrode finger 31 a.

[0088] The width W1 of the overlapping region of the inner load film 51A and the width W2 of the overlapping region of the inner load film 51B are each, for example, 0.3 μm. The thickness t4 of the inner load film 51A and the thickness t5 of the inner load film 51B are each 30 nm.

[0089] Although the inner load films 51A and 51B have the same material and the same shape in the above example, the present invention is not limited to this. As will be described later, the upper load film 50A and the lower load film 50B may have different materials and different shapes.

[0090] The outer load films 52A and 52B are provided outside the inner load films 51A and 51B in the arrangement direction and in regions that do not overlap with the IDT electrodes 30 (electrode fingers 31 and 32). The outer load film 52A is provided on the first protective film 41 in the same layer as the inner load film 51A and is spaced apart from the inner load film 51A. Similarly, the outer load film 52B is provided below the second protective film 42 in the same layer as the inner load film 51B and is spaced apart from the inner load film 51B. The outer load films 52A and 52B are made of the same silicon nitride (SiN) as the inner load films 51A and 51B. A distance W3 between the inner load film 51A and the outer load film 52A and a distance W4 between the inner load film 51B and the inner load film 51B are 0.6 μm. The thickness of the outer load films 52A and 52B is 30 nm, the same as the thicknesses t4 and t5 of the inner load films 51A and 51B.

[0091] 20 , the first protective film 41 and the second protective film 42 have recesses on their surfaces on the load film 50 side that overlap with the region between the inner load film 51 and the outer load film 52. As a result, in the region overlapping with the first electrode finger 31 a, a step is formed between the inner load film 51A and the first protective film 41, and a step is formed between the inner load film 51B and the second protective film 42. The depths t6 and t7 of the recesses in the first protective film 41 and the second protective film 42 are 20 nm.

[0092] 21 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to the fourth embodiment. As shown in FIG. 21 , in the elastic wave device 10D according to the fourth embodiment, the load film 50 is provided on both the first principal surface 20 a and the second principal surface 20 b of the piezoelectric layer 20, and therefore, the ripples indicated by the dotted lines E1, E2, and E3 are more effectively suppressed than in the comparative example. Furthermore, in the fourth embodiment, the peak width associated with the resonant frequency is narrowed, thereby suppressing propagation loss.

[0093] Fifth Embodiment Fig. 22 is a cross-sectional view showing an elastic wave device according to a fifth embodiment. Fig. 23 is an enlarged cross-sectional view of region A1 shown in Fig. 22 . As shown in Figs. 22 and 23 , in an elastic wave device 10D according to the fifth embodiment, a load film 50 is provided spaced apart from a plurality of electrode fingers 31, 32 and a first main surface 20a. The upper surface of the first protective film 41 is formed with projections and recesses that reflect the shape of the load film 50. The load film 50 includes an inner load film 51 and an outer load film 52.

[0094] The inner load film 51 is disposed within the first protective film 41. That is, the first protective film 41 is provided between the first main surface 20 a of the piezoelectric layer 20 and the plurality of electrode fingers 31, 32 and the inner load film 51, and covers the side and top surfaces of the inner load film 51 (surfaces opposite to the piezoelectric layer 20).

[0095] The inner load film 51 is made of tantalum oxide (Ta ２ O ５ ). The width W1 of the overlapping region of the inner load film 51 is, for example, 0.3 μm. The film thickness of the inner load film 51 and the configurations of the first protective film 41, the second protective film 42, the IDT electrode 30, etc. are the same as those in the first embodiment. The distance between the inner load film 51 and the second main surface 20 b of the piezoelectric layer 20 in the direction perpendicular to the second main surface 20 b of the piezoelectric layer 20 is 320 nm.

[0096] The outer load film 52 is provided outside the inner load film 51 in the arrangement direction and in a region that does not overlap with the IDT electrode 30 (electrode fingers 31, 32). The outer load film 52 is disposed in the first protective film 41 in the same layer as the inner load film 51, and is provided spaced apart from the inner load film 51. The outer load film 52 is made of the same tantalum oxide (Ta ２ O５ ). The distance W3 between the inner load film 51 and the outer load film 52 is 0.6 μm. The thickness of the outer load film 52 is 55 nm, the same as the thickness t4 of the inner load film 51. However, the present invention is not limited to this, and the material and thickness of the outer load film 52 may be different from the material and thickness t4 of the inner load film 51.

[0097] Fig. 24 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a fifth embodiment. Fig. 25 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. 25 is configured such that load film 50 is not provided in elastic wave device 10D according to the fifth embodiment.

[0098] 24 and 25 show the distribution of the magnitude of displacement of piezoelectric layer 20 for the fifth embodiment and the comparative example, with the horizontal axis representing the X direction (the arrangement direction of electrode fingers 31 and 32) and the vertical axis representing frequency. The upper diagrams of Fig. 24 and Fig. 25 each show a schematic cross-sectional view of an elastic wave device corresponding to the X direction, and the left diagrams of Fig. 24 and Fig. 25 show the impedance characteristics of the elastic wave device.

[0099] As shown in Figure 25, 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.

[0100] In contrast, as shown in FIG. 24 , in the elastic wave device 10D according to the fifth embodiment, the X-direction dependency of the displacement (the X-direction positions of the antinodes and nodes of the displacement) does not depend on the frequency. That is, the X-direction positions at which the displacement peaks are measured 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 resonant frequency or in the frequency arrangement where ripples occur. Thus, it was demonstrated that a better excitation mode than the comparative example can be obtained simply by providing a load film 50 in a position overlapping with a portion of the first electrode fingers 31 a located at the outermost positions in the arrangement direction.

[0101] Sixth Embodiment Fig. 26 is a cross-sectional view showing an elastic wave device according to a sixth embodiment. As shown in Fig. 26, in an elastic wave device 10E according to the sixth embodiment, the load film 50 is provided on the second main surface 20b side of the piezoelectric layer 20. More specifically, the load film 50 faces the second main surface 20b of the piezoelectric layer 20 and is spaced apart from the second main surface 20b. The lower surface of the second protective film 42 is formed with irregularities that reflect the shape of the load film 50. The load film 50 includes an inner load film 51 and an outer load film 52.

[0102] The inner load film 51 is disposed within the second protective film 42. That is, the second protective film 42 is provided between the second main surface 20b of the piezoelectric layer 20 and the inner load film 51, and covers the side and bottom surfaces of the inner load film 51 (surfaces opposite to the piezoelectric layer 20).

[0103] The inner load film 51 is made of tantalum oxide (Ta ２ O ５ ). The width W2 of the overlapping region of the inner load film 51 is, for example, 0.3 μm. The film thickness of the inner load film 51 and the configurations of the first protective film 41, the second protective film 42, the IDT electrode 30, etc. are the same as those in the first embodiment. The distance between the inner load film 51 and the second main surface 20 b of the piezoelectric layer 20 in the direction perpendicular to the second main surface 20 b of the piezoelectric layer 20 is 50 nm.

[0104] The outer load film 52 is provided outside the inner load film 51 in the arrangement direction and in a region that does not overlap with the IDT electrode 30 (electrode fingers 31, 32). The outer load film 52 is provided in the second protective film 42 in the same layer as the inner load film 51, and is provided spaced apart from the inner load film 51. The outer load film 52 is made of the same tantalum oxide (Ta ２ O ５ ). The distance W4 between the inner load film 51 and the outer load film 52 is 0.6 μm. The thickness of the outer load film 52 is 55 nm, the same as the thickness t5 of the inner load film 51. However, the present invention is not limited to this, and the material and thickness of the outer load film 52 may be different from the material and thickness t4 of the inner load film 51.

[0105] Seventh Embodiment FIG. 27 is a cross-sectional view showing an elastic wave device according to a seventh embodiment. As shown in FIG. 27 , in an elastic wave device 10F according to the seventh embodiment, a load film 50 is provided on each of the first main surface 20 a of the piezoelectric layer 20 and the second main surface 20 b of the piezoelectric layer 20. In the following description, the load film 50 provided on the first protective film 41 is referred to as an upper load film 50A, and the load film 50 provided on the lower surface of the second protective film 42 is referred to as a lower load film 50B. Note that when there is no need to distinguish between the upper load film 50A and the lower load film 50B, they are simply referred to as load films 50. The upper load film 50A is provided spaced apart from the plurality of electrode fingers 31, 32 and the first main surface 20 a, and the lower load film 50B faces the second main surface 20 b of the piezoelectric layer 20 and is provided spaced apart from the second main surface 20 b. The upper load film 50A has an inner load film 51A and an outer load film 52A, and the lower load film 50B has an inner load film 51A and an outer load film 52B.

[0106] The inner load film 51A is disposed within the first protective film 41. The inner load film 51B is disposed within the second protective film 42. That is, the first protective film 41 is provided between the first main surface 20a of the piezoelectric layer 20 and the plurality of electrode fingers 31, 32 and the inner load film 51, and covers the side and top surfaces (surfaces opposite the piezoelectric layer 20) of the inner load film 51. The second protective film 42 is provided between the second main surface 20b of the piezoelectric layer 20 and the inner load film 51, and covers the side and bottom surfaces (surfaces opposite the piezoelectric layer 20) of the inner load film 51. The top surface of the first protective film 41 has irregularities that reflect the shape of the inner load film 51A. The top surface of the second protective film 42 has irregularities that reflect the shape of the inner load film 51B.

[0107] The inner load film 51A and the inner load film 51B are made of the same material, tantalum oxide (Ta), as in the first embodiment. ２ O ５ ). The width W1 of the overlapping region of the inner load film 51A and the width W2 of the overlapping region of the inner load film 51B are each, for example, 0.3 μm. The film thickness of the inner load film 51 and the configurations of the first protective film 41, the second protective film 42, the IDT electrode 30, etc. are the same as those in the first embodiment. In the direction perpendicular to the second main surface 20 b of the piezoelectric layer 20, the distance between the inner load film 51A and the first main surface 20 a of the piezoelectric layer 20 and the distance between the inner load film 51B and the second main surface 20 b of the piezoelectric layer 20 are 50 nm.

[0108] Although the inner load membranes 51A and 51B have the same material and the same shape in the above example, the present invention is not limited to this example and the inner load membranes 51A and 51B may have different materials and different shapes.

[0109] The outer load film 52A is disposed in the first protective film 41 in the same layer as the inner load film 51A, and is spaced apart from the inner load film 51A. Similarly, the outer load film 52B is disposed in the second protective film 42 in the same layer as the inner load film 51B, and is spaced apart from the inner load film 51B. The outer load films 52A and 52B are made of the same tantalum oxide (TaO) as the inner load films 51A and 51B. ２ O ５). The distance W3 between the inner load film 51A and the outer load film 52A and the distance W4 between the inner load film 51B and the inner load film 51B are 0.6 μm. The thicknesses of the outer load films 52A and 52B are 55 nm, the same as the thicknesses t4 and t5 of the inner load films 51A and 51B. However, the present invention is not limited to this, and the material and thickness of the outer load film 52 may be different from the material and thickness t4 of the inner load film 51.

[0110] 28 is a cross-sectional view of an elastic wave device according to embodiment 8. As shown in FIG. 28 , in an elastic wave device 10G according to embodiment 8, a load film 50 is provided at a distance from a plurality of electrode fingers 31, 32 and a first main surface 20 a.

[0111] The load film 50 is disposed within the first protective film 41. That is, the first protective film 41 is provided between the first main surface 20 a of the piezoelectric layer 20 and the plurality of electrode fingers 31, 32 and the load film 50, and covers the side and top surfaces (surfaces opposite the piezoelectric layer 20) of the load film 50. In this embodiment, the top surface of the first protective film 41 is formed flat. Specifically, the top surface of the first protective film 41 is formed substantially flat across the region where the load film 50 is provided and the region where the load film 50 is not provided. The load film 50 includes an inner load film 51 and an outer load film 52.

[0112] The inner load film 51 is made of tantalum oxide (Ta ２ O ５ ). The width W1 of the overlapping region of the inner load film 51 is, for example, 0.3 μm. The film thickness of the inner load film 51 and the configurations of the first protective film 41, the second protective film 42, the IDT electrode 30, etc. are the same as those in the first embodiment. The distance between the inner load film 51 and the second main surface 20 b of the piezoelectric layer 20 in the direction perpendicular to the second main surface 20 b of the piezoelectric layer 20 is 320 nm.

[0113] The outer load film 52 is provided outside the inner load film 51 in the arrangement direction and in a region that does not overlap with the IDT electrode 30 (electrode fingers 31, 32). The outer load film 52 is disposed in the first protective film 41 in the same layer as the inner load film 51, and is provided spaced apart from the inner load film 51. The outer load film 52 is made of the same tantalum oxide (Ta ２ O ５The distance W3 between the inner load film 51 and the outer load film 52 is 0.6 μm. The thickness of the outer load film 52 is 55 nm, which is the same as the thickness t5 of the inner load film 51.

[0114] Ninth Embodiment Fig. 29 is a cross-sectional view showing an elastic wave device according to a ninth embodiment. As shown in Fig. 29, in an elastic wave device 10H according to the ninth embodiment, a load film 50 is provided on the outermost first electrode finger 31a. More specifically, the load film 50 is provided over the top and side surfaces of the first electrode finger 31a and over the first main surface 20a of the piezoelectric layer 20 in a portion where the electrode fingers 31 and 32 are not provided. The load film 50 is provided to follow the steps formed by the piezoelectric layer 20 and the first electrode finger 31a. The load film 50 includes an inner load film 51 and an outer load film 52.

[0115] The inner load film 51 is made of tantalum oxide (Ta ２ O ５ ). The width W1 of the overlapping region of the inner load film 51 is, for example, 0.3 μm. The film thickness of the inner load film 51 is 55 nm. As in the first embodiment described above, the film thickness of the first protective film 41 and the film thickness of the second protective film 42 are 142 nm, and the film thickness of the IDT electrode 30 is 112 nm. In this embodiment, the upper surface of the first protective film 41 is formed flat. Specifically, the upper surface of the first protective film 41 is formed substantially flat across the region where the inner load film 51 is provided and the region where the inner load film 51 is not provided.

[0116] The first protective film 41 is provided on the first main surface 20a of the piezoelectric layer 20, covering the inner load film 51 and the IDT electrode 30. In this embodiment, the upper surface of the inner load film 51 is covered with the first protective film 41. In addition, the region overlapping with the first electrode finger 31a has a portion where the inner load film 51 and the first protective film 41 are provided, and a portion where the first protective film 41 is provided but the inner load film 51 is not provided.

[0117] The outer load film 52 is provided outside the inner load film 51 in the arrangement direction and in a region that does not overlap with the IDT electrode 30 (electrode fingers 31, 32). The outer load film 52 is provided in the same layer as the inner load film 51 across the first main surface 20a and is provided spaced apart from the inner load film 51. The outer load film 52 is made of the same tantalum oxide (TaO ２ O ５ The distance W3 between the inner load film 51 and the outer load film 52 is 0.6 μm. The thickness of the outer load film 52 is 55 nm, which is the same as the thickness t5 of the inner load film 51.

[0118] Tenth Embodiment FIG. 30 is a cross-sectional view showing an elastic wave device according to a tenth embodiment. As shown in FIG. 30 , in an elastic wave device 10I according to the tenth embodiment, a load film 50 is provided on the first main surface 20a of the piezoelectric layer 20. A first protective film 41 and first electrode fingers 31a are provided on the first main surface 20a of the piezoelectric layer 20, covering the load film 50. The upper surface of the first protective film 41 is flat across a region that overlaps with the load film 50 and a region that does not overlap with the load film 50. In this embodiment, the load film 50 is not provided on the second main surface 20b of the piezoelectric layer 20, and the lower surface of the second protective film 42 is flat. The load film 50 includes an inner load film 51 and an outer load film 52.

[0119] The inner load film 51 is provided so as to overlap a part of the first electrode finger 31 a. In the tenth embodiment, the inner load film 51 is made of a material different from that of the first protective film 41 and the second protective film 42, for example, tantalum oxide (Ta ２ O ５ The width W2 of the overlapping region of the inner load film 51 is, for example, 0.3 μm. The thickness t5 of the inner load film 51 is 55 nm.

[0120] The outer load film 52 is provided outside the inner load film 51 in the arrangement direction and in a region that does not overlap with the IDT electrode 30 (electrode fingers 31, 32). The outer load film 52 is provided in the same layer as the inner load film 51 across the first main surface 20a and is provided spaced apart from the inner load film 51. The outer load film 52 is made of the same tantalum oxide (TaO ２ O ５The distance W3 between the inner load film 51 and the outer load film 52 is 0.6 μm. The thickness of the outer load film 52 is 55 nm, which is the same as the thickness t5 of the inner load film 51.

[0121] Eleventh Embodiment Fig. 31 is a cross-sectional view showing an elastic wave device according to an eleventh embodiment. As shown in Fig. 31 , in an elastic wave device 10J according to the eleventh embodiment, a load film 50 is provided on the second main surface 20b of the piezoelectric layer 20. A second protective film 42 is provided on the second main surface 20b of the piezoelectric layer 20, covering the load film 50. The lower surface of the second protective film 42 is formed with irregularities that reflect the shape of the load film 50. Furthermore, in this embodiment, the load film 50 is not provided on the first main surface 20a of the piezoelectric layer 20, and the upper surface of the first protective film 41 is formed flat. The load film 50 includes an inner load film 51 and an outer load film 52.

[0122] The inner load film 51 is provided so as to overlap a part of the first electrode finger 31 a. In the eleventh embodiment, the inner load film 51 is made of a material different from that of the first protective film 41 and the second protective film 42, for example, tantalum oxide (Ta ２ O ５ The width W2 of the overlapping region of the inner load film 51 is, for example, 0.3 μm. The thickness t5 of the inner load film 51 is 55 nm.

[0123] The outer load film 52 is provided outside the inner load film 51 in the arrangement direction and in a region that does not overlap with the IDT electrode 30 (electrode fingers 31, 32). The outer load film 52 is provided in the same layer as the inner load film 51, extending across the second main surface 20b, and is provided spaced apart from the inner load film 51. The outer load film 52 is made of the same tantalum oxide (Ta ２ O ５ The distance W4 between the inner load film 51 and the outer load film 52 is 0.6 μm. The thickness of the outer load film 52 is 55 nm, which is the same as the thickness t5 of the inner load film 51.

[0124] 32 is a cross-sectional view of an elastic wave device according to a twelfth embodiment. As shown in FIG. 32 , in an elastic wave device 10K according to the twelfth embodiment, a load film 50 is provided at a distance from a plurality of electrode fingers 31, 32 and a first main surface 20 a.

[0125] The load film 50 is disposed within the first protective film 41. That is, the first protective film 41 is provided between the first main surface 20 a of the piezoelectric layer 20 and the plurality of electrode fingers 31, 32 and the load film 50, and covers the side and top surfaces (the surfaces opposite the piezoelectric layer 20) of the load film 50. In the example of FIG. 32 , the top surface of the first protective film 41 has irregularities that reflect the shape of the load film 50. In this embodiment, the load film 50 is not provided on the second main surface 20 b side of the piezoelectric layer 20, and the bottom surface of the second protective film 42 is formed flat. The load film 50 includes an inner load film 51, an outer load film 52, and an overlying load film 53.

[0126] The inner load film 51 is made of tantalum oxide (Ta ２ O ５ ). The width W1 of the overlapping region of the inner load film 51 is, for example, 0.3 μm. The film thickness of the inner load film 51 and the configurations of the first protective film 41, the second protective film 42, the IDT electrode 30, etc. are the same as those in the first embodiment. The distance between the inner load film 51 and the second main surface 20 b of the piezoelectric layer 20 in the direction perpendicular to the second main surface 20 b of the piezoelectric layer 20 is 320 nm.

[0127] The superimposed load film 53 is provided outside the inner load film 51 in the arrangement direction and in a region overlapping a part of the first electrode finger 31 a. The superimposed load film 53 is disposed in the first protective film 41 in the same layer as the inner load film 51, and is provided spaced apart from the inner load film 51. The outer load film 52 is made of the same tantalum oxide (Ta ２ O ５ ). The width W1 of the overlapping region of the overlapping load film 53 is, for example, 0.3 μm. The distance W3 between the inner load film 51 and the overlapping load film 53 is 0.6 μm. The thickness of the overlapping load film 53 is 55 nm, the same as the thickness t4 of the inner load film 51.

[0128] The outer load film 52 is provided outside the inner load film 51 and the superimposed load film 53 in the arrangement direction, in a region that does not overlap with the IDT electrode 30 (electrode fingers 31, 32). The outer load film 52 is disposed in the first protective film 41 in the same layer as the inner load film 51, and is provided separated from the superimposed load film 53. The outer load film 52 is made of the same tantalum oxide (Ta ２ O ５The distance W5 between the inner load film 51 and the outer load film 52 is 0.6 μm. The thickness of the outer load film 52 is 55 nm, which is the same as the thickness t4 of the inner load film 51.

[0129] 33 is a cross-sectional view showing an elastic wave device according to a third modification of Embodiment 12. As shown in Fig. 33 , in an elastic wave device 10L according to Embodiment 12, a load film 50 is provided at a distance from a plurality of electrode fingers 31, 32 and a first main surface 20a.

[0130] The load film 50 is disposed within the first protective film 41. That is, the first protective film 41 is provided between the first main surface 20 a of the piezoelectric layer 20 and the plurality of electrode fingers 31, 32 and the load film 50, and covers the side and top surfaces (the surfaces opposite the piezoelectric layer 20) of the load film 50. In the example of FIG. 33 , the top surface of the first protective film 41 is formed flat. Specifically, the top surface of the first protective film 41 is formed substantially flat across the region where the load film 50 is provided and the region where the load film 50 is not provided. Furthermore, in this embodiment, the load film 50 is not provided on the second main surface 20 b side of the piezoelectric layer 20, and the bottom surface of the second protective film 42 is formed flat. The load film 50 includes an inner load film 51, an outer load film 52, and an overlapping load film 53.

[0131] The inner load film 51 is made of tantalum oxide (Ta ２ O ５ ). The width W1 of the overlapping region of the inner load film 51 is, for example, 0.3 μm. The film thickness of the inner load film 51 and the configurations of the first protective film 41, the second protective film 42, the IDT electrode 30, etc. are the same as those in the first embodiment. The distance between the inner load film 51 and the second main surface 20 b of the piezoelectric layer 20 in the direction perpendicular to the second main surface 20 b of the piezoelectric layer 20 is 320 nm.

[0132] In an elastic wave device 10L according to a third modification of the twelfth embodiment, the outer load film 52 is provided outside the inner load film 51 in the arrangement direction and in a region overlapping with a part of the first electrode fingers 31 a. The overlying load film 53 is disposed in the first protective film 41 in the same layer as the inner load film 51 and is provided at a distance from the inner load film 51. The outer load film 52 is made of the same tantalum oxide (Ta ２ O ５). The width W1 of the overlapping region of the overlapping load film 53 is, for example, 0.3 μm. The distance W3 between the inner load film 51 and the overlapping load film 53 is 0.6 μm. The thickness of the overlapping load film 53 is 55 nm, the same as the thickness t4 of the inner load film 51.

[0133] The outer load film 52 is provided outside the inner load film 51 in the arrangement direction and in a region that does not overlap with the IDT electrode 30 (electrode fingers 31, 32).

[0134] The outer load film 52 is disposed in the first protective film 41 in the same layer as the inner load film 51, and is provided apart from the superimposed load film 53. The outer load film 52 is made of the same tantalum oxide (Ta ２ O ５ The distance W5 between the inner load film 51 and the outer load film 52 is 0.6 μm. The thickness of the outer load film 52 is 55 nm, which is the same as the thickness t4 of the inner load film 51.

[0135] 34 is a circuit diagram illustrating an acoustic wave filter device according to a thirteenth embodiment. As illustrated in FIG. 34 , an acoustic wave filter device 10M according to the thirteenth 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 10M according to the thirteenth embodiment is a so-called ladder filter.

[0136] 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.

[0137] In this embodiment, the plurality of series arm resonators 61, 62, and 63 and the plurality of parallel arm resonators 64, 65, 66, and 67 employ load films 50 having different configurations. For example, the plurality of series arm resonators 61, 62, and 63 have the load films 50 shown in the first modified example (see FIGS. 12 and 13 ). The admittance characteristics of the plurality of series arm resonators 61, 62, and 63 are similar to those shown in FIG. 15 , and therefore, repeated description will be omitted.

[0138] On the other hand, the parallel arm resonators 64, 65, 66, and 67 have the load film 50 shown in the second modified example (see FIGS. 12 and 13). The admittance characteristics of the parallel arm resonators 64, 65, 66, and 67 are the same as those in FIG. 14, and therefore repeated description will be omitted.

[0139] In this embodiment, by changing the configuration of the load film 50 between the plurality of series arm resonators 61, 62, and 63 and the plurality of parallel arm resonators 64, 65, 66, and 67, it is possible to obtain a better output waveform as a filter.

[0140] Although the elastic wave device 10M according to the thirteenth embodiment is combined with the load film 50 shown in the first and second modified examples, the present invention is not limited to this. The thirteenth embodiment can be combined with the above-described embodiments and modified examples.

[0141] 35 is a cross-sectional view of an elastic wave device according to a fourth embodiment. In the elastic wave device 10 according to the first embodiment described above, the support substrate 11 has the cavity 14, and the second main surface 20 b of the piezoelectric layer 20 has the cavity 14 (hollow portion), which is a so-called membrane structure. However, the present invention is not limited to this.

[0142] 35 , in an elastic wave device 10N according to the fourteenth embodiment, an acoustic multilayer film 43 is laminated on the second main surface 20b of the piezoelectric layer 20. The acoustic multilayer film 43 has a laminate structure of low acoustic impedance layers 43a, 43c, and 43e, which have a relatively low acoustic impedance, and high acoustic impedance layers 43b and 43d, which have a relatively high acoustic impedance. The low acoustic impedance layers 43a, 43c, and 43e are made of, for example, SiO ２ The high acoustic impedance layers 43b and 43d are metal layers such as W or Pt, or dielectric layers such as aluminum nitride or silicon nitride. When the acoustic multilayer film 43 is used, bulk waves in the first thickness-shear mode can be confined within the piezoelectric layer 20 without using the cavity portion 14.

[0143] In acoustic wave device 10N, 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.

[0144] 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.

[0145] 35 shows an example in which the load film 50 shown in the first embodiment is provided, but the present invention is not limited to this. The fourteenth embodiment can be combined with each of the above-described embodiments and modifications.

[0146] Fifteenth Embodiment Fig. 36 is a cross-sectional view of an elastic wave device according to a fifteenth 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. 36, an elastic wave device 10O according to the fifteenth 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 ).

[0147] The electrode fingers 36, 37 of the second IDT electrode are provided in an area overlapping with the electrode fingers 31, 32 of the first IDT electrode. The electrode fingers 36, 37 of the second IDT electrode are provided with the same width and the same inter-electrode pitch as the electrode fingers 31, 32 of the first IDT electrode. In addition, the load film 50 is provided in an area overlapping with the first electrode finger 31 a of the first IDT electrode and the first electrode finger 36 a of the second IDT electrode.

[0148] In the fifteenth 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.

[0149] 36 shows an example in which the load film 50 shown in the first embodiment is 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.

[0150] Sixteenth Embodiment Fig. 37 is an explanatory diagram showing an example of admittance characteristics of an elastic wave device according to a sixteenth embodiment. Fig. 38 is an explanatory diagram showing an example of impedance phase in a higher mode. The elastic wave device according to the sixteenth embodiment shown in Fig. 37 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.

[0151] 37 shows frequency characteristics of the absolute value of admittance for the elastic wave device according to embodiment 16. As shown in Fig. 37, in the elastic wave device according to embodiment 16, 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.

[0152] The horizontal axis of the graph shown in Fig. 38 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. 38 corresponds to the intensity of the S2 mode.

[0153] 38, 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.

[0154] In contrast, in the sixteenth 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 sixteenth 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.

[0155] Although the sixteenth embodiment has been described with reference to the elastic wave device 10 according to the first embodiment, in which the first protective film 41 and the second protective film 42 have different thicknesses, the present invention is not limited to this. The relationship between the thickness t1 of the first protective film 41, the thickness tLN of the piezoelectric layer 20, and the thickness t2 of the second protective film 42 in the sixteenth embodiment can be combined with any of the embodiments and modified examples described above.

[0156] The shapes, widths, thicknesses, etc. of the load film 50, 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 may be modified as appropriate. For example, the side surfaces of the load film 50, the first protective film 41, and the second protective film 42 may be tapered. The outer load film 52 and the overlaid load film 53 overlapping the first electrode finger 31 a and the second electrode finger 32 a may have the same width and thickness. Alternatively, the outer load film 52 and the overlaid load film 53 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, or may have a different thickness from the inner load film 51. Furthermore, the first protective film 41 and the second protective film 42 may not be provided.

[0157] The load film 50 shown in each of the above-described embodiments and modifications is merely an example and may be modified as appropriate. The load film 50 may be provided in a region that does not overlap with the two electrode fingers (the first electrode finger 31 a and the electrode finger 32) or the 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.

[0158] The materials of the load film 50 shown in the above-described embodiments and modifications are merely examples and can be changed as appropriate. The load film 50 may be made of, for example, carbon-doped silicon oxide (SiOC), silicon oxide (SiO ２ ), silicon nitride (SiN), tantalum oxide (Ta ２ O ５ ), aluminum nitride (AlN), aluminum oxide (Al ２ O ３ ), hafnium oxide (HfO ２ ), niobium oxide (Nb ２ O ５The load film 50 is formed from at least one of the following materials: silicon dioxide (SiO 2 ), tungsten oxide (WO 3 ). The load film 50 is not limited to a single layer film, but may be a laminated film. The load film 50 may be formed from a combination of two or more of the above materials.

[0159] 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.

[0160] The present disclosure may also have the following configurations.

[0161] 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; a protective film on at least one of the first main surface and the second main surface of the piezoelectric layer; and a load film provided over a region overlapping in a plan view from the first direction, from at least a fourth electrode finger from one side in an arrangement direction of the plurality of electrode fingers to a fourth electrode finger from the other side in the arrangement direction, wherein the load film is not provided in at least a part of a region overlapping in a plan view with a first electrode finger that is arranged outermost in the arrangement direction of the plurality of electrode fingers, and wherein, where 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 according to (1), further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer. (3) The elastic wave device according to (1) or (2), further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film including a first protective film covering the IDT electrodes and provided on the first main surface of the piezoelectric layer, and the load film being provided on the first protective film. (4) The elastic wave device according to any one of (1) to (3), further comprising a load film provided at a position that does not overlap with the outside of the IDT electrodes in the arrangement direction. (5) The elastic wave device according to any one of (1) to (4), further comprising: a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer; the protective film including a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer; and a second protective film provided on the second main surface of the piezoelectric layer; and the load film is provided on a surface of the second protective film facing the support member.(6) The elastic wave device according to any one of (1) to (4), further comprising: a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer; the protective film including a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer; and a second protective film provided on the second main surface of the piezoelectric layer; and the load film including an upper load film provided on the first protective film and a lower load film provided on a surface of the second protective film facing the support member. (7) The elastic wave device according to any one of (1) to (6), further comprising: a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, wherein the protective film comprises a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer, the load film is provided on the first protective film, and in a region overlapping with the first electrode finger, a step is formed between a portion where the first protective film is provided but the load film is not provided, and a portion where the load film and the first protective film are laminated. (8) The elastic wave device according to (1), further comprising: a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, 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 the load film is provided inside the first protective film. (9) The elastic wave device according to (8), 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 step is formed in a region overlapping the first electrode finger between a portion where the first protective film is provided but the load film is not provided and a portion where the load film and the first protective film are laminated. (10) The elastic wave device according to (8) or (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, and the load film is provided inside the second protective film.(11) The elastic wave device according to (8) or (9), 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 the load film includes an upper load film provided inside the first protective film and a lower load film provided inside the second protective film. (12) The elastic wave device according to any one of (8) to (11), 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 an upper surface of the first protective film and a lower surface of the second protective film are formed flat. (13) The elastic wave device according to any one of (8) to (12), wherein the load film is provided on the first electrode fingers. (14) The elastic wave device according to any one of (8) to (13), wherein the load film is provided between the first main surface of the piezoelectric layer and the first electrode fingers in a direction perpendicular to the first main surface of the piezoelectric layer. (15) The elastic wave device according to any one of (8) to (14), 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 load film is provided on the second main surface of the piezoelectric layer, and the second protective film covers the load film. (16) The elastic wave device according to any one of (1) to (15), wherein the protective film is provided on at least one of the first main surface and the second main surface of the piezoelectric layer, and the load film is made of a material having a higher density than the protective film. (17) The elastic wave device according to any one of (1) to (15), further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, wherein the load film is made of a material having a lower density than the protective film. (18) The elastic wave device according to any one of (1) to (15), further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, wherein the load film is made of a material having a harder density than the protective film.(19) The elastic wave device according to any one of (1) to (18), further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film being made of silicon oxide. (20) The elastic wave device according to any one of (1) to (19), further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film having a thickness smaller than a thickness of the piezoelectric layer. (21) An elastic wave filter device including at least one resonator, the resonator being the elastic wave device according to any one of (1) to (20). (22) The acoustic wave filter device according to (21), 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; each of the series arm resonator and the parallel arm resonator has the load film; and the load film of the series arm resonator has a different configuration from the load film of the parallel arm resonator. (23) The elastic wave filter device according to (21), 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 series arm resonator and the parallel arm resonator each have the load film, and a thickness of the load film of the series arm resonator is different from a thickness of the load film of the parallel arm resonator. (24) The elastic wave device according to any one of (1) to (20), wherein the piezoelectric layer includes lithium niobate or lithium tantalate, and is a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut. (25) The elastic wave device according to any one of (1) to (20) and (24), further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, wherein the protective film includes 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.(26) The elastic wave device according to any one of (1) to (20), (24), and (25), further comprising a protective film provided on at least one of the first and second main surfaces of the piezoelectric layer, wherein the protective film has a thickness greater than the thickness of the IDT electrode. (27) The elastic wave device according to any one of (1) to (20), (24), and (26), further comprising a protective film provided on at least one of the first and second main surfaces of the piezoelectric layer, 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, wherein a value of A / B is 1-0.06 or more and 1+0.06 or less, where A is the sum of distances from a center of thickness of the piezoelectric layer to a top surface of the first protective film and B is the sum of distances from a center of thickness of the piezoelectric layer to a top surface of the second protective film. (28) The elastic wave device according to any one of (1) to (20) and (24) to (27), wherein the IDT electrodes are provided on both the first principal surface and the second principal surface of the piezoelectric layer. (29) The elastic wave device according to any one of (1) to (20) and (24) to (28), wherein the material of the load film is at least one of carbon-doped silicon oxide, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide, and tungsten oxide. (30) The elastic wave device according to any one of (1) to (20) and (24) to (29), wherein d / p is 0.24 or less. (31) The acoustic wave device according to any one of (1) to (20) and (24) to (30), wherein, when viewed in the electrode finger orthogonal direction, an excitation region is a region where adjacent electrode fingers overlap each other and a region between centers of the adjacent electrode fingers in the electrode finger orthogonal direction, and wherein, when a metallization ratio of the electrode fingers to the excitation region is MR, MR≦1.75(d / p)+0.075 is satisfied. (32) The acoustic wave device according to any one of (1) to (20) and (24) to (31), wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.(33) The elastic wave device according to (32), 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) (34) The elastic wave device according to any one of (1) to (20) and (24) to (33), wherein the acoustic reflecting portion is a cavity, and the support member and the piezoelectric layer are arranged such that a part of the support member and a part of the piezoelectric layer face each other with the cavity in between. (35) The elastic wave device according to any one of (1) to (20) and (24) to (34), 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 such 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.

[0162] REFERENCE SIGNS LIST 10, 10A to 10L, 10N, 10O Acoustic wave device 10M Acoustic wave filter device 11 Support substrate 12 Bottom 13 Wall 14 Cavity 20 Piezoelectric layer 20a First principal surface 20b Second principal surface 30 IDT electrode 31, 32, 36, 37 Electrode fingers 31a, 36a First electrode finger 32a Second electrode finger 33, 34 Bus bar electrode 41 First protective film 42 Second protective film 50 Load film 50A Upper load film 50B Lower load film 51, 51A, 51B Inner load film 52, 52A, 52B Outer load film 53 Superimposed load film

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 load film provided over a region that overlaps in a planar view from the first direction, from at least a fourth electrode finger from one outside in an arrangement direction of the plurality of electrode fingers to a fourth electrode finger from the other outside in the arrangement direction, the load film being absent in at least a part of a region that overlaps in a planar view with a first electrode finger that is arranged outermost in the arrangement direction of the plurality of electrode fingers, wherein, where 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 acoustic wave device according to claim 1, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer.

3. An elastic wave device as described in claim 1 or 2, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film comprising a first protective film provided on the first main surface of the piezoelectric layer and covering the IDT electrode, and the load film being provided on the first protective film.

4. The elastic wave device according to claim 1, wherein the load film is provided at a position that does not overlap with the outside of the IDT electrodes in the arrangement direction.

5. An elastic wave device as claimed in any one of claims 1 to 4, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film comprising a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer, and a second protective film provided on the second main surface of the piezoelectric layer, and the load film is provided on the surface of the second protective film facing the support member.

6. An elastic wave device as claimed in any one of claims 1 to 4, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film comprising a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer, and a second protective film provided on the second main surface of the piezoelectric layer, and the load film including an upper load film provided on the first protective film and a lower load film provided on a surface of the second protective film facing the support member.

7. An elastic wave device as claimed in any one of claims 1 to 6, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film comprising a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer, the load film being provided on the first protective film, and a step being formed in a region overlapping with the first electrode finger between a portion where the first protective film is provided but the load film is not provided and a portion where the load film and the first protective film are laminated.

8. The elastic wave device according to claim 1, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film comprising a first protective film provided on the first main surface of the piezoelectric layer and covering the IDT electrode, and the load film being provided inside the first protective film.

9. The elastic wave device of claim 8, wherein the protective film has a first protective film provided on the first main surface of the piezoelectric layer covering the IDT electrode, and in a region overlapping with the first electrode finger, a step is formed between a portion where the first protective film is provided but the load film is not provided, and a portion where the load film and the first protective film are laminated.

10. The elastic wave device according to claim 8 or 9, 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 the load film is provided inside the second protective film.

11. The elastic wave device of claim 8 or 9, 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 the load film includes an upper load film provided inside the first protective film and a lower load film provided inside the second protective film.

12. The elastic wave device according to any one of claims 8 to 11, 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.

13. The acoustic wave device according to claim 8, wherein the load film is provided on the first electrode finger.

14. The elastic wave device according to claim 8, wherein the load film is provided between the first main surface of the piezoelectric layer and the first electrode finger in a direction perpendicular to the first main surface of the piezoelectric layer.

15. An elastic wave device as claimed in any one of claims 8 to 14, 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, the load film is provided on the second main surface of the piezoelectric layer, and the second protective film covers the load film.

16. An elastic wave device according to any one of claims 1 to 15, further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer, and the load film is formed from a material having a higher density than the protective film.

17. An elastic wave device according to any one of claims 1 to 15, further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer, and the load film is formed from a material having a lower density than the protective film.

18. The elastic wave device according to any one of claims 1 to 15, further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer, and the load film is formed from a material harder than the protective film.

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

20. An elastic wave device according to any one of claims 1 to 19, further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer, the thickness of the protective film being thinner than the thickness of the piezoelectric layer.

21. 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 20.

22. The elastic wave filter device according to claim 21, 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 series arm resonator and the parallel arm resonator each have the load film, and the load film of the series arm resonator has a different configuration from the load film of the parallel arm resonator.

23. The elastic wave filter device according to claim 21, 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 series arm resonator and the parallel arm resonator each have the load film, and a thickness of the load film of the series arm resonator is different from a thickness of the load film of the parallel arm resonator.

24. 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.

25. An elastic wave device as claimed in any one of claims 1 to 20 and 24, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film comprising a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer, and a second protective film provided on the second main surface of the piezoelectric layer.

26. The elastic wave device according to any one of claims 1 to 20, 24 and 25, further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer, the thickness of the protective film being thicker than the thickness of the IDT electrode.

27. The elastic wave device according to any one of claims 1 to 20 and 24 to 26, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the protective film comprising a first protective film covering the IDT electrode and provided on the first main surface of the piezoelectric layer, and a second protective film provided on the second main surface of the piezoelectric layer, 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.

28. 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.

29. The elastic wave device according to any one of claims 1 to 20 and 24 to 28, wherein the material of the load film is at least one of carbon-doped silicon oxide, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide, and tungsten oxide.

30. The elastic wave device according to any one of claims 1 to 20 and 24 to 29, wherein d / p is 0.24 or less.

31. An elastic wave device according to any one of claims 1 to 20 and 24 to 30, 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.

32. The acoustic wave device according to any one of claims 1 to 20 and 24 to 31, wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.

33. The elastic wave device according to claim 32, 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) 34. An elastic wave device according to any one of claims 1 to 20 and 24 to 33, 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.

35. An elastic wave device described in any one of claims 1 to 20 and 24 to 34, 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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