Elastic wave device and elastic wave filter device

Abstract

This elastic wave device comprises: a piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction; an IDT electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer and including a plurality of electrode fingers arrayed in a predetermined direction; a reflector disposed adjacent to the IDT electrode in the array direction of the plurality of electrode fingers; a support member facing the second main surface of the piezoelectric layer and having an acoustic reflection part on the second main surface side of the piezoelectric layer; and a load film provided in a region overlapping the reflector in plan view from the first direction. When the thickness of the piezoelectric layer is d and the distance between the centers of 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 elastic wave device according to one embodiment includes a piezoelectric layer having a first main surface and a second main surface opposite the first main surface in a first direction; an IDT electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the IDT electrode including a plurality of electrode fingers arranged in a predetermined direction; a reflector arranged adjacent to the IDT electrode in the arrangement direction of the plurality of electrode fingers; a support member facing the second main surface of the piezoelectric layer and having an acoustic reflection portion on the second main surface side of the piezoelectric layer; and a load film provided in an area that overlaps with the reflector in a planar view from the first direction, wherein d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers.

[0007] An acoustic wave filter device according to one aspect is an acoustic wave filter device including at least one resonator connected thereto, the resonator being the acoustic wave device described above.

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

[0009] FIG. 1 is a plan view of an elastic wave device according to a first embodiment. FIG. 2 is a cross-sectional view taken along line II-II′ of FIG. 1 . FIG. 3 is a schematic cross-sectional view illustrating a bulk wave in a first-order thickness-shear mode propagating through a piezoelectric layer according to the first embodiment. FIG. 4 is a schematic cross-sectional view illustrating the amplitude direction of a bulk wave in a first-order thickness-shear mode propagating through a piezoelectric layer according to the first embodiment. FIG. 5 is a diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. FIG. 6 is a diagram illustrating the relationship between d / 2p and the fractional bandwidth of a resonator, where p is the center-to-center distance or the average center-to-center distance between adjacent electrodes and d is the average thickness of the piezoelectric layer in the elastic wave device according to the first embodiment. FIG. 7 is a plan view illustrating an example of the elastic wave device according to the first embodiment, in which a pair of electrodes is provided. FIG. 8 is a reference diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. FIG. 9 is an explanatory diagram showing the relationship between the fractional bandwidth and the amount of phase rotation of the spurious impedance normalized by 180 degrees, which represents the magnitude of the spurious, when a large number of elastic wave resonators are configured in the elastic wave device according to the first embodiment. FIG. 10 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the fractional bandwidth. FIG. 11 is an explanatory diagram showing a map of the fractional bandwidth versus the Euler angles (0°, θ, ψ) of lithium niobate when d / p is set as close to 0 as possible. FIG. 12 is an enlarged cross-sectional view of region A shown in FIG. 2. FIG. 13 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the first embodiment. FIG. 14 is an explanatory diagram showing the distribution of vibration modes of the elastic wave device according to the first embodiment. FIG. 15 is an explanatory diagram showing the distribution of vibration modes of an elastic wave device according to a comparative example. FIG. 16 is a cross-sectional view of an elastic wave device according to a first modified example of the first embodiment. FIG. 17 is a cross-sectional view of an elastic wave device according to a second modified example of the first embodiment. FIG. 18 is a cross-sectional view of an elastic wave device according to a third modified example of the first embodiment. Fig. 19 is a cross-sectional view of an elastic wave device according to a fourth modified example of the first embodiment. Fig. 20 is a cross-sectional view of an elastic wave device according to a fifth modified example of the first embodiment. Fig. 21 is a cross-sectional view of an elastic wave device according to a sixth modified example of the first embodiment. Fig. 22 is a plan view of an elastic wave device according to a second preferred embodiment. Fig. 23 is a cross-sectional view taken along line XXIII-XXIII' of Fig. 22 .FIG. 24 is a cross-sectional view of an elastic wave device according to a seventh modified example of the second embodiment. FIG. 25 is a plan view of an elastic wave device according to a third preferred embodiment. FIG. 26 is a circuit diagram of an elastic wave device according to a fourth preferred embodiment. FIG. 27 is a cross-sectional view of an elastic wave device according to an eighth modified example. FIG. 28 is a cross-sectional view of an elastic wave device according to a ninth modified example. FIG. 29 is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a tenth modified example. FIG. 30 is an explanatory diagram illustrating an example of the 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. Note that in Fig. 1, the load film 50 is shown hatched to make the drawing easier to read. Also, in Fig. 1, the first protective film 41 is shown by a two-dot chain line.

[0012] 1 and 2 , an elastic wave device 10 according to the first embodiment includes a piezoelectric layer 20, an IDT electrode 30, reflectors 70 and 71, 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 and the reflectors 70 and 71, 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 flat and has a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is formed of lithium niobate. Alternatively, the piezoelectric layer 20 may be made of lithium tantalate. In the first embodiment, the cut angle of the lithium niobate or lithium tantalate is Z-cut. The cut angle of the lithium niobate or lithium tantalate may be rotated Y-cut or X-cut. Preferably, the propagation direction is Y-propagation or X-propagation ±30°. Preferably, the piezoelectric layer 20 includes lithium niobate or lithium tantalate and is 120°±10° rotated Y-cut or 90°±10° rotated Y-cut.

[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 aluminum or an aluminum-copper alloy. In the first embodiment, the IDT electrode 30 has a structure in which an aluminum film is laminated on a titanium film. Note that an adhesive layer other than the titanium film may also be used.

[0021] More specifically, the IDT electrode 30 has a laminated structure of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, 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] The elastic wave device 10 according to the first embodiment has the above configuration, and therefore is unlikely to experience a decrease in the Q value even if the number of pairs of electrode fingers 31 and electrode fingers 32 is reduced in an attempt to reduce the device size. This is because the elastic wave device 10 is a resonator that utilizes bulk waves in the first-order thickness-shear mode, and therefore has little propagation loss.

[0026] The reflectors 70 and 71 are provided on the first main surface 20a of the piezoelectric layer 20 in the same layer as the IDT electrode 30. The reflectors 70 and 71 are laminated films having the same electrode configuration as the IDT electrode 30 and are made of the same material as the IDT electrode 30. However, without being limited to this, the reflectors 70 and 71 may have a different electrode configuration and be made of a different material than the IDT electrode 30.

[0027] The reflectors 70 and 71 are arranged adjacent to the IDT electrode 30 at a distance in the arrangement direction of the electrode fingers 31 and 32. In this embodiment, the reflectors 70 and 71 each have one electrode finger and extend along the extension direction of the electrode fingers 31 and 32. The reflector 70 is adjacent to the IDT electrode 30 at a distance on one side of the arrangement direction of the electrode fingers 31 and 32 (the left side in FIGS. 1 and 2 ). The reflector 71 is adjacent to the IDT electrode 30 at a distance on the opposite side of the reflector 70 at the other side of the arrangement direction of the electrode fingers 31 and 32 (the right side in FIGS. 1 and 2 ). The IDT electrode 30 is arranged between the reflectors 70 and 71. The detailed configuration of the reflectors 70 and 71 will be described later with reference to FIG. 12 .

[0028] The first protective film 41 is provided on the first main surface 20a of the piezoelectric layer 20, covering the IDT electrode 30 and the reflectors 70 and 71. 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. The first protective film 41 and the second protective film 42 can be made of an appropriate insulating material such as silicon oxide, silicon nitride, or alumina. The thickness of the first protective film 41 and the second protective film 42 is thicker than the thickness of the IDT electrode 30. The thickness of the first protective film 41 and the second protective film 42 is 142 nm. 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 and the second protective film 42 is not provided may be adopted.

[0029] The load film 50 is provided on the first protective film 41. The load film 50 is provided in an area overlapping with the reflectors 70 and 71. The load film 50 is not provided in an area overlapping with the plurality of electrode fingers 31 and 32 located between the reflectors 70 and 71.

[0030] A portion of the load film 50 overlapping with the reflector 70 is referred to as a first extension portion 51, and a portion of the load film 50 overlapping with the reflector 71 is referred to as a second extension portion 52. The first extension portion 51 and the second extension portion 52 are spaced apart in the arrangement direction of the electrode fingers 31, 32, and the electrode fingers 31, 32 are arranged between the first extension portion 51 and the second extension portion 52. The first extension portion 51 overlaps with a portion of the reflector 70 and extends along the extension direction of the reflector 70. The second extension portion 52 overlaps with a portion of the reflector 71 and extends along the extension direction of the reflector 71. The detailed configuration of the load film 50 will be described later with reference to FIGS. 12 and 13 .

[0031] 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.

[0032] 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.

[0033] The support substrate 11 is made of silicon. The surface of the silicon facing the piezoelectric layer 20 may have a (100), (110), or (111) plane orientation. High-resistivity silicon with a resistivity of 4 kΩ or higher is preferable. 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.

[0034] 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.

[0035] 3 , in the elastic wave device 10 according to the first embodiment, vibration displacement occurs in the thickness shear direction, and 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. This Z direction wave propagation provides the resonance characteristics.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] Piezoelectric layer 20: lithium niobate with Euler angles (0°, 0°, 90°) Thickness of piezoelectric layer 20: 400 nm

[0041] 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

[0042] First protective film 41, second protective film 42: silicon oxide film with a thickness of 1 μm

[0043] Support substrate 11: silicon

[0044] 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.

[0045] As is clear from FIG. 5, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] FIG. 8 is a reference diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. As shown in FIG. 8 , a spurious response indicated by arrow B appears between the resonance frequency and the antiresonance frequency. Note that d / p was set to 0.08, and the Euler angles of the lithium niobate were set to 0°, 0°, and 90°. The metallization ratio MR was set to 0.35.

[0053] The metallization ratio MR will be explained with reference to FIG. 1 . Focusing on a pair of electrode fingers 31 and 32 in the electrode structure of FIG. 1 , assume that only this pair of electrode fingers 31 and 32 are provided. In this case, the area surrounded by the dashed line is the intersection region C. When the electrode fingers 31 and 32 are viewed in a direction perpendicular to the extension direction of the electrode fingers 31 and 32, i.e., in the opposing direction, the intersection region C includes the region where the electrode fingers 31 overlap with the electrode fingers 32, the region where the electrode fingers 32 overlap with the electrode fingers 31, and the region between the electrode fingers 31 and 32 where the electrode fingers 31 and 32 overlap. The metallization ratio MR is the ratio of the area of ​​the electrode fingers 31 and 32 within the intersection region C to the area of ​​the intersection region C. In other words, the metallization ratio MR is the ratio of the area of ​​the metallization portion to the area of ​​the intersection region C.

[0054] 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.

[0055] 9 is an explanatory diagram showing the relationship between the bandwidth fraction 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 bandwidth fraction was adjusted by changing the film thickness of the piezoelectric layer 20 and the dimensions of the electrode fingers 31 and 32. While FIG. 9 shows the results when a piezoelectric layer 20 made of Z-cut lithium niobate is used, similar trends are observed when a piezoelectric layer 20 having a different cut angle is used.

[0056] 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.

[0057] 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.

[0058] 11 is an explanatory diagram showing a map of the fractional bandwidth versus the Euler angles (0°, θ, ψ) of lithium niobate when d / p approaches 0. The hatched area in FIG. 11 is the region where a fractional bandwidth of at least 5% or more is obtained. The range of this region can be approximated as the ranges expressed by the following formulas (1), (2), and (3).

[0059] (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)

[0060] 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.

[0061] 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 . While FIG. 12 illustrates the load film 50 (first extension portion 51) overlapping with the reflector 70 arranged on one side of the arrangement direction of the electrode fingers 31 and 32, the second extension portion 52 (see FIGS. 1 and 2 ) on the opposite side of the reflector 70 overlapping with the reflector 71 arranged on the other side of the arrangement direction of the electrode fingers 31 and 32 also has an arrangement relationship that is line-symmetrical to the first extension portion 51. The description of the first extension portion 51 also applies to the second extension portion 52. In the following description, when it is not necessary to distinguish between the first extension portion 51 and the second extension portion 52, they will simply be referred to as the load film 50.

[0062] 12 , the load film 50 is provided on the first protective film 41 and overlaps a portion of the reflector 70. In this embodiment, the load film 50 is provided in a region that does not overlap the IDT electrode 30 (the plurality of electrode fingers 31, 32). That is, the load film 50 is disposed outside the IDT electrode 30 in the arrangement direction of the plurality of electrode fingers 31, 32. 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 over the region where the electrode fingers 31, 32 and the reflector 70 are provided and the region where the electrode fingers 31, 32 and the reflector 70 are not provided.

[0063] 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 the region overlapping with the reflector 70. More specifically, on the first main surface 20a of the piezoelectric layer 20, there are a region where the reflector 70 and the first protective film 41 are stacked in this order, a region where the reflector 70, the first protective film 41 and the load film 50 are stacked in this order, and a region where the first protective film 41 and the load film 50 are stacked in this order. In the region overlapping with the reflector 70, a step is formed between a portion where the first protective film 41 is provided but the load film 50 is not provided, and a portion where the load film 50 and the first protective film 41 are stacked.

[0064] The load film 50 is provided at a position shifted outward relative to the reflector 70 in the arrangement direction of the multiple electrode fingers 31, 32. One side of the load film 50 is arranged overlapping the midpoint of the reflector 70 in the width direction, and the other side of the load film 50 is located outward relative to the reflector 70 in the arrangement direction. That is, the load film 50 includes an overlapping region that overlaps with the reflector 70 and a non-overlapping region that does not overlap with the reflector 70. The width W1 of the load film 50 is, for example, 1.2 μm. The width W1a of the overlapping region of the load film 50 is, for example, 0.6 μm. The width W1b of the non-overlapping region of the load film 50 is, for example, 0.6 μm.

[0065] As described above, the inter-electrode pitch of the electrode fingers 31, 32 in the IDT electrode 30 is 2.38 μm, and the electrode width is 0.6 μm. The inter-electrode pitch between the outermost electrode finger 31 in the arrangement direction and the reflector 70 is 2.38 μm. The electrode width of the reflector 70 is 1.2 μm. In other words, the electrode width of the reflector 70 is larger than the electrode width of the electrode fingers 31, 32 of the IDT electrode 30. The reflector 70 and the electrode fingers 31, 32 of the IDT electrode 30 are arranged with the same inter-electrode pitch.

[0066] 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 and the thickness t5 of the reflector 70 are 112 nm. The thickness t1 of the first protective film 41 is thicker than the thickness t4 of the load film 50, and is also thicker than the thickness t3 of the IDT electrode 30 and the thickness t5 of the reflector 70.

[0067] The load film 50 is made of the same material as the first protective film 41. In this embodiment, the load film 50 and the first protective film 41 are made of silicon oxide. 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.

[0068] In this way, the load film 50 is provided overlapping the reflector 70, and therefore, in the region overlapping with the reflector 70, the region where the load film 50 and the first protective film 41 are laminated has a different acoustic impedance from the region where only the first protective film 41 is laminated without the load film 50. As a result, an acoustic reflection surface R is formed at the step between the load film 50 and the first protective film 41 (the portion overlapping with the side surface of the load film 50).

[0069] 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 .

[0070] 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 that does not have a load film 50 in comparison with the first embodiment.

[0071] 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 are generated, as indicated by dotted lines E1 and E2. In contrast, in elastic wave device 10 according to the first embodiment, the provision of load film 50 suppresses the ripples indicated by dotted lines E1 and E2 compared to the comparative example. It can be seen that elastic wave device 10 according to the first embodiment exhibits less propagation loss in the frequency range indicated by dotted line E2, which is higher than the resonant frequency, and thus suppresses leakage of elastic waves, compared to the elastic wave device according to the comparative example.

[0072] Fig. 14 is an explanatory diagram showing the distribution of vibration modes of the elastic wave device according to the first embodiment. Fig. 15 is an explanatory diagram showing the distribution of vibration modes of an elastic wave device according to a comparative example. In Figs. 14 and 15, the horizontal axis represents the X direction (the arrangement direction of electrode fingers 31 and 32) and the vertical axis represents frequency, showing the distribution of the magnitude of displacement of piezoelectric layer 20 for the first embodiment and the comparative example. The upper diagrams in Figs. 14 and 15 each show a schematic cross-sectional view of the elastic wave device corresponding to the X direction, and the left diagrams in Figs. 14 and 15 show the impedance characteristics of the elastic wave device.

[0073] As shown in Figure 15, in the elastic wave device of the comparative example, the X-direction dependence of the displacement (the X-direction positions of the antinodes and nodes of the displacement) is significantly frequency-dependent. For example, the X-direction positions indicating the peak displacement shift depending on the frequency, preventing stable excitation between the electrodes. Furthermore, at a specific X-direction position (near X = 5.0 μm), the phase is inverted at the resonant frequency of 5030 MHz and at frequencies of 4900 MHz and 5120 MHz where ripples occur. As such, the elastic wave device of the comparative example may not achieve an ideal excitation mode.

[0074] In contrast, as shown in FIG. 14 , in the elastic wave device 10 according to the first embodiment, the X-direction dependency of the displacement (the X-direction positions of the antinodes and nodes of the displacement) does not have frequency dependency. That is, the X-direction positions indicating the peak displacement are constant regardless of frequency, demonstrating stable excitation between the electrodes. Furthermore, the magnitude (amplitude) of the displacement is also constant for each region between the electrodes, and no phase inversion occurs in the frequency arrangement where the resonant frequency and ripples occur. Thus, it was demonstrated that a better excitation mode than the comparative example can be obtained simply by providing the load film 50 at a position overlapping the outermost reflectors 70 and 71 in the arrangement direction.

[0075] The shapes, widths, thicknesses, etc. of the load film 50, first protective film 41, IDT electrode 30, and reflectors 70 and 71 described above are merely examples and can be changed as appropriate. For example, the side surfaces of the load film 50 may be tapered. The first extension portion 51 and the second extension portion 52 of the load film 50 shown in FIG. 1 may have the same width and thickness. Alternatively, the first extension portion 51 and the second extension portion 52 of the load film 50 may have different widths and thicknesses due to variations in the manufacturing process, for example.

[0076] In addition, the example has been described in which the material of the load film 50 is the same as that of the first protective film 41, for example, silicon oxide. However, the present invention is not limited to this, and the load film 50 may be made of a material different from that of the first protective film 41. For example, the load film 50 may be made of a material having a higher density than the silicon oxide used in the first protective film 41, for example, tantalum oxide. Note that, unless otherwise specified, the term "density" in this embodiment refers to a physical property value specific to the material.

[0077] Alternatively, the load film 50 may be formed of a material having a lower density than the silicon oxide used in the first protective film 41, such as carbon-added silicon oxide. Alternatively, the load film 50 may be formed of a material having a harder hardness than the silicon oxide used in the first protective film 41, such as silicon nitride. In this embodiment, "hardness" refers to a physical property value specific to the material, unless otherwise specified.

[0078] The above-described materials for the load film 50 are merely examples and can be changed as appropriate. The load film 50 is formed from 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. The load film 50 is not limited to a single-layer film and may be a multilayer film. The load film 50 may be a combination of two or more of the above materials.

[0079] (First Modification of First Embodiment) FIG. 16 is a cross-sectional view showing an elastic wave device according to a first modification of the first embodiment. As shown in FIG. 16 , in an elastic wave device 10A according to the first modification, 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 bottom 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 ). 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.

[0080] In this embodiment, the upper load film 50A and the lower load film 50B are made of the same material, such as silicon oxide. The first extension 51 of the upper load film 50A and the first lower extension 54 of the lower load film 50B are provided to overlap with each other, and each overlaps with a part of the reflector 70.

[0081] The width W1 of the upper load film 50A (first extension portion 51) and the width W2 of the lower load film 50B (lower first extension portion 54) are each 1.2 μm, as in the first embodiment described above. The width W1a of the overlapping region of the upper load film 50A and the width W2a of the overlapping region of the lower load film 50B are each 0.6 μm, for example. The width W1b of the non-overlapping region of the upper load film 50A and the width W2b of the non-overlapping region of the lower load film 50B are each 0.6 μm, for example.

[0082] 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.

[0083] For example, the width W1 of the upper load film 50A may be different from the width W2 of the lower load film 50B. The width W2 of the lower load film 50B may be longer than the width W1 of the upper load film 50A. Alternatively, the width W2 of the lower load film 50B may be shorter than the width W1 of the upper load film 50A.

[0084] The thickness of the upper load film 50A may be different from the thickness of the lower load film 50B. For example, the thickness of the upper load film 50A may be thinner than the thickness of the lower load film 50B. Alternatively, the thickness of the upper load film 50A may be thicker than the thickness of the lower load film 50B.

[0085] Furthermore, the material of the upper load film 50A may be different from the material of the lower load film 50B. For example, the material of the upper load film 50A may be silicon oxide, and the material of the lower load film 50B may be carbon-doped silicon oxide. However, the present invention is not limited to this, and the materials of the upper load film 50A and the lower load film 50B may be any appropriate combination of the above-mentioned materials.

[0086] 17 is a cross-sectional view of an elastic wave device according to a second modification of the first embodiment. In the first embodiment described above, the load film 50 is provided on the first protective film 41 on the first main surface 20a side of the piezoelectric layer 20. However, the present invention is not limited to this. As shown in FIG. 17 , in an elastic wave device 10B according to the second modification, the load film 50 (lower first extension 54) is provided on the second main surface 20b side of the piezoelectric layer 20, 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 20a side of the piezoelectric layer 20, and the upper surface of the first protective film 41 is formed flat.

[0087] 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 reflector 70. The load film 50 is provided to protrude from the lower surface of the second protective film 42. In this embodiment, in the region overlapping with the reflector 70, the second main surface 20b of the piezoelectric layer 20 has a region where the second protective film 42 is provided but the load film 50 is not provided, and a region where the second protective film 42 and the load film 50 are laminated. As a result, a step is formed between the load film 50 and the second protective film 42 in the region overlapping with the reflector 70.

[0088] In the second modification, the load film 50 is made of the same material as the first protective film 41 and the second protective film 42, for example, silicon oxide. The width W2 of the load film 50 is, for example, 1.2 μm. The width W2a of the overlapping region of the load film 50 is, for example, 0.6 μm. The width W2b of the non-overlapping region of the load film 50 is, for example, 0.6 μm.

[0089] The configuration of the lower first extension portion 54 in plan view is the same as that of the first extension portion 51 (see FIG. 1 ), and therefore a repeated description will be omitted. Although not shown, a lower second extension portion is also provided on the opposite side of the lower first extension portion 54 in the arrangement direction of the plurality of electrode fingers 31, 32 at a position overlapping with the reflector 71 (see FIG. 1 ).

[0090] In the second variant, unlike the first embodiment and the first variant, a load film 50 is not provided on the first protective film 41, so the resonant frequency can be easily adjusted by changing the film thickness of the first protective film 41.

[0091] 18 is a cross-sectional view of an elastic wave device according to a third modification of the first embodiment. In the first embodiment, the first modification, and the second modification described above, the load film 50 is provided on at least one of the top surface of the first protective film 41 and the bottom surface of the second protective film 42. However, the present invention is not limited to this.

[0092] 18 , in an elastic wave device 10C according to the third modification, the load film 50 is provided on the second main surface 20b of the piezoelectric layer 20. The 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 provided flat across an area that overlaps with the load film 50 and an area that does not overlap with the load film 50. In this modification, 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.

[0093] The load film 50 is provided so as to overlap a portion of the reflector 70. In the third modification, the load film 50 is made of a material different from that of the first protective film 41 and the second protective film 42, for example, tantalum oxide. However, the load film 50 is not limited to this, and may be made of the above-mentioned materials such as carbon-added silicon oxide or silicon nitride.

[0094] 19 is a cross-sectional view showing an elastic wave device according to a fourth modification of the first embodiment. As shown in FIG. 19 , in an elastic wave device 10D according to the fourth modification, a load film 50 is provided on a reflector 70. More specifically, the load film 50 is provided over the top and side surfaces of the reflector 70 and across the first main surface 20a of the piezoelectric layer 20 in a portion where the reflector 70 is not provided. The load film 50 is provided to follow the steps formed by the piezoelectric layer 20 and the reflector 70.

[0095] The load film 50 is made of tantalum oxide. However, the load film 50 is not limited to this, and the above-mentioned materials such as carbon-doped silicon oxide and silicon nitride can be used. The widths W1, W1a, and W1b of the load film 50 are formed to be the same as those of the first embodiment. The thickness of the load film 50 is thinner than that of the first embodiment. Furthermore, the total thickness of the load film 50 and the reflector 70 is thinner than the thickness of the first protective film 41.

[0096] The first protective film 41 is provided on the first main surface 20a of the piezoelectric layer 20, covering the load film 50, the reflector 70, and the IDT electrode 30. That is, in the region overlapping with the reflector 70, there is a portion where the load film 50 and the first protective film 41 are laminated in this order, and a portion where the first protective film 41 is provided but the load film 50 is not provided. The top surface of the first protective film 41 is formed flat over the region overlapping with the load film 50, the reflector 70, and the IDT electrode 30, and over the region where the load film 50, the reflector 70, and the IDT electrode 30 are not provided.

[0097] In the fourth modified example, the upper surface of the load film 50 and the upper surface of the reflector 70 are covered with the first protective film 41. However, the present invention is not limited to this. For example, the upper surface of the load film 50 may be provided in the same plane as the upper surface of the first protective film 41. In this case, the thickness of the load film 50 and the thickness of the first protective film 41 are equal in the region overlapping with the reflector 70.

[0098] 20 is a cross-sectional view showing an elastic wave device according to a fifth modification of the first embodiment. As shown in FIG. 20 , in an elastic wave device 10E according to the fifth modification, a load film 50 is provided on the first main surface 20 a of a piezoelectric layer 20. A reflector 70 covers a portion of the load film 50 and is provided on the first main surface 20 a of the piezoelectric layer 20. That is, the load film 50 is provided between the first main surface 20 a of the piezoelectric layer 20 and the reflector 70 in the direction perpendicular to the first main surface 20 a of the piezoelectric layer 20.

[0099] The first protective film 41 is provided on the first main surface 20a of the piezoelectric layer 20, covering the load film 50, the reflector 70, and the IDT electrode 30. That is, in this embodiment, the first main surface 20a of the piezoelectric layer 20 has a region where the reflector 70 and the first protective film 41 are stacked in this order, a region where the load film 50, the reflector 70, and the first protective film 41 are stacked in this order, and a region where the load film 50 and the first protective film 41 are stacked in this order. The top surface of the first protective film 41 is formed flat over the regions overlapping with the load film 50, the reflector 70, and the IDT electrode 30, and over the regions where the load film 50, the reflector 70, and the IDT electrode 30 are not provided.

[0100] The load film 50 is made of silicon oxide. However, the load film 50 is not limited to this, and the above-mentioned materials such as tantalum oxide, carbon-added silicon oxide, and silicon nitride can be used. Also in this modification, the total film thickness of the load film 50 and the reflector 70 is thinner than the film thickness of the first protective film 41.

[0101] 21 is a cross-sectional view showing an elastic wave device according to a sixth modification of the first embodiment. As shown in FIG. 21 , in elastic wave device 10F according to the sixth modification of the first embodiment, load film 50 has first extension portions 51 that overlap with reflectors 70, and outer load film 53 that is provided in a region that is outward of first extension portions 51 in the arrangement direction and does not overlap with reflectors 70 or IDT electrodes 30 (electrode fingers 31, 32).

[0102] The outer load film 53 is provided on the first protective film 41 in the same layer as the first extension portion 51, and is provided spaced apart from the first extension portion 51. The outer load film 53 is made of the same silicon oxide as the first extension portion 51. The thickness t6 of the outer load film 53 is the same as the thickness t4 of the first extension portion 51. The width W3 of the outer load film 53 is the same as the width W1 of the first extension portion 51. However, without being limited thereto, the shape of the outer load film 53 (thickness t5 and width W3) may be different from the shape of the first extension portion 51 (thickness t4 and width W1).

[0103] The sixth modification can be combined with the first to fifth modifications described above. That is, the first extension portion 51 and the outer load film 53 may be provided on both the top of the first protective film 41 and the bottom of the second protective film 42, respectively, or may be provided on the bottom of the second protective film 42 without being provided on the first protective film 41. Alternatively, the first extension portion 51 and the outer load film 53 may be provided on the first main surface 20 a or the second main surface 20 b of the piezoelectric layer 20.

[0104] In the first to sixth modified examples, the simulation results of the admittance characteristics are omitted. In all of the first to sixth modified examples, a load film 50 is provided in the region overlapping with the reflectors 70 and 71. Therefore, in the first to sixth modified examples, similar to the elastic wave device 10 according to the first embodiment, at least one of the ripples indicated by the dotted lines E1, E2, and E3 (see FIG. 13 ) is suppressed compared to the comparative example. Furthermore, in all of the first to sixth modified examples, the propagation loss is suppressed compared to the comparative example.

[0105] Second Embodiment Fig. 22 is a plan view showing an elastic wave device according to a second embodiment. As shown in Fig. 22 , in an elastic wave device 10G according to the second embodiment, a reflector 70A has a plurality of reflective electrode fingers 72, 73 and a plurality of reflective busbar electrodes 74, 75. The reflective electrode fingers 72, 73 are arranged adjacent to each other in the X direction with a gap therebetween. The reflective busbar electrodes 74, 75 extend in the X direction and are spaced apart from each other in the Y direction.

[0106] More specifically, the reflective electrode fingers 72, 73 are arranged in the arrangement direction of the electrode fingers 31, 32 of the IDT electrode 30, and extend along the extension direction of the electrode fingers 31, 32. One end side of the reflective electrode fingers 72, 73 in the extension direction is connected to a reflective busbar electrode 74. The other end side of the reflective electrode fingers 72, 73 in the extension direction is connected to a reflective busbar electrode 75.

[0107] The reflector 71A has a plurality of reflective electrode fingers 76, 77 and a plurality of reflective bus bar electrodes 78, 79. The configuration of the reflector 71A is similar to that of the reflector 70A, and a repeated description will be omitted.

[0108] The reflector 70A has two reflective electrode fingers 72 and 73, and the reflector 71A has two reflective electrode fingers 76 and 77. However, the present invention is not limited to this, and each of the reflectors 70A and 71A may have three or more reflective electrode fingers.

[0109] Fig. 23 is a cross-sectional view taken along line XXIII-XXIII' in Fig. 22. Note that Fig. 23 describes the load film 50 (first extension portions 51a, 51b) provided in the region overlapping with the reflector 70A, but the load film 50 (second extension portions 52a, 52b) provided in the region overlapping with the reflector 71A on the opposite side of the reflector 70A also has an arrangement relationship that is line-symmetrical to the first extension portions 51a, 51b. The description of the first extension portions 51a, 51b can also be applied to the second extension portions 52a, 52b.

[0110] 23 , a plurality of load films 50 are provided for each of the reflective electrode fingers 72, 73. More specifically, each of the load films 50 has two first extension portions 51 a, 51 b. The first extension portions 51 a, 51 b of the load films 50 are provided on the first protective film 41. The first extension portion 51 a is provided in a region overlapping with the reflective electrode finger 72 located outermost in the arrangement direction, and extends along the extension direction of the reflective electrode finger 72. The first extension portion 51 b is provided in a region overlapping with the reflective electrode finger 73 adjacent to the reflective electrode finger 72, and extends along the extension direction of the reflective electrode finger 73. The load film 50 (first extension portion 51 a) overlapping the reflective electrode finger 72 and the load film 50 (first extension portion 51 b) overlapping the reflective electrode finger 73 are arranged apart from each other.

[0111] In the second embodiment, the material and shape of the first extension portions 51a, 51b of the multiple load films 50 are the same as those of the load films 50 in the first embodiment. That is, the load films 50 are formed of silicon oxide, as in the first embodiment. The film thickness t4 of the first extension portions 51a, 51b of the load film 50 is 55 nm. The width W1 of the first extension portions 51a, 51b of the load film 50 is, for example, 1.2 μm. The width W1a of the overlapping region of the first extension portions 51a, 51b of the load film 50 is, for example, 0.6 μm. The width W1b of the non-overlapping region of the first extension portions 51a, 51b of the load film 50 is, for example, 0.6 μm.

[0112] The widths W1, W1a, and W1b of the first extension portions 51a and 51b are merely examples and can be changed as appropriate. The width W1 and thickness t4 of the first extension portion 51a of the load film 50 may be different from the width W1 and thickness t4 of the first extension portion 51b. The material of the load film 50 is not limited to silicon oxide, and the first extension portions 51a and 51b of the load film 50 are formed from at least one of carbon-added silicon oxide, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide, and tungsten oxide.

[0113] 24 is a cross-sectional view of an elastic wave device according to a seventh modification of Embodiment 2. As shown in FIG. 24 , in an elastic wave device 10H according to the seventh modification, the load film 50 is provided in a region overlapping with the reflective electrode finger 72 of a reflector 70A and the reflective electrode finger 73 adjacent to the reflective electrode finger 72.

[0114] The load film 50 is provided continuously across the two reflective electrode fingers 72 and 73. One side surface of the load film 50 is arranged so as to overlap the midpoint of the reflective electrode finger 73 in the width direction, and the other side surface of the load film 50 is positioned outward of the reflective electrode finger 72 in the arrangement direction.

[0115] The load film 50 is made of silicon oxide, as in the second embodiment, but is not limited thereto, and may be made of at least one of carbon-added silicon oxide, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide, and tungsten oxide.

[0116] In the second embodiment and the seventh modification, the configuration in which the load film 50 (first extension portions 51, 51a, 51b) is provided on the first protective film 41 has been described. However, the second embodiment and the seventh modification can be combined with the first to sixth modifications described above. That is, the load film 50 may be provided on both the first protective film 41 and the lower surface of the second protective film 42, or may be provided on the lower surface of the second protective film 42 without being provided on the first protective film 41. Alternatively, the load film 50 may be provided on the first main surface 20a or the second main surface 20b of the piezoelectric layer 20. Alternatively, the load film 50 may have an outer load film 53 provided in a region that is outward of the first extension portions 51, 51a, 51b in the arrangement direction and does not overlap with the reflectors 70A and the IDT electrode 30 (electrode fingers 31, 32).

[0117] In the second embodiment and the seventh modification, the simulation results of the admittance characteristics are omitted. In both the second embodiment and the seventh modification, a load film 50 is provided in the region overlapping with reflectors 70A and 71A. Therefore, in the second embodiment and the seventh modification, similar to the elastic wave device 10 according to the first embodiment, at least one of the ripples indicated by dotted lines E1, E2, and E3 (see FIG. 13 ) is suppressed compared to the comparative example. Furthermore, in both the second embodiment and the seventh modification, the propagation loss is suppressed compared to the comparative example.

[0118] 25 is a plan view illustrating an elastic wave device according to a third preferred embodiment. As illustrated in FIG. 25 , in an elastic wave device 10I according to the third preferred embodiment, the load film 50 is formed in a frame shape. Specifically, the load film 50 includes a first extension portion 51, a second extension portion 52, a third extension portion 55, and a fourth extension portion 56.

[0119] The first extending portion 51 is provided in an area overlapping with a reflector 70 (first reflector) located outside the IDT electrode 30 in the arrangement direction of the plurality of electrode fingers 31, 32, and extends along the extension direction of the reflector 70. The second extending portion 52 is provided in an area overlapping with a reflector 71 (second reflector) located outside the IDT electrode 30 on the opposite side of the reflector 70 in the arrangement direction of the plurality of electrode fingers 31, 32, and extends along the extension direction of the reflector 71.

[0120] The third extending portion 55 is connected to one end of the first extending portion 51 and the second extending portion 52 in the extension direction, and extends in the arrangement direction of the multiple electrode fingers 31, 32. The third extending portion 55 extends while overlapping with the ends of the multiple electrode fingers 31 in the extension direction. The fourth extending portion 56 is connected to the other end of the first extending portion 51 and the second extending portion 52 in the extension direction, and extends in the arrangement direction of the multiple electrode fingers 31, 32. The fourth extending portion 56 extends while overlapping with the ends of the multiple electrode fingers 32 in the extension direction.

[0121] As described above, in elastic wave device 10I according to the third embodiment, load film 50 is formed continuously in a frame shape. As a result, acoustic reflecting surfaces R (see FIG. 12 ) are formed along first extension portion 51, second extension portion 52, third extension portion 55, and fourth extension portion 56. Therefore, elastic wave device 10I can suppress leakage of elastic waves in the arrangement direction of multiple electrode fingers 31, 32, and also suppress leakage of elastic waves in the extension direction of multiple electrode fingers 31, 32.

[0122] The third extension portion 55 and the fourth extension portion 56 are provided in the same layer as the first extension portion 51 and the second extension portion 52 shown in the first embodiment (see FIG. 12 ), and are formed of the same material and with the same film thickness. This allows the third extension portion 55 and the fourth extension portion 56 to be formed in the same process as the first extension portion 51 and the second extension portion 52, thereby reducing manufacturing costs.

[0123] In the third embodiment, the load film 50 is provided on the first protective film 41, similarly to the first embodiment (see FIG. 12 ). However, without being limited thereto, the load film 50 of the third embodiment can be combined with each of the above-described embodiments and modified examples.

[0124] 25 has been described as a configuration in which the load film 50 has a continuous frame shape and the first extension portion 51, the second extension portion 52, the third extension portion 55, and the fourth extension portion 56 are connected. However, this is not limited to this, and a slit may be formed in a part of the load film 50, and at least one of the first extension portion 51, the second extension portion 52, the third extension portion 55, and the fourth extension portion 56 may be provided separated from the other portions. For example, at least one of the third extension portion 55 and the fourth extension portion 56 may be configured to be disposed separated from the first extension portion 51 and the second extension portion 52.

[0125] 25 illustrates a configuration in which the first extension portion 51, the second extension portion 52, the third extension portion 55, and the fourth extension portion 56 have the same width. However, this is not limited to this, and at least one of the first extension portion 51, the second extension portion 52, the third extension portion 55, and the fourth extension portion 56 may have a width (length in a direction perpendicular to the extension direction) different from the other portions. For example, the width (length in a direction perpendicular to the extension direction) of the third extension portion 55 and the fourth extension portion 56 may be greater than the width (length in a direction perpendicular to the extension direction) of the first extension portion 51 and the second extension portion 52.

[0126] 26 is a circuit diagram illustrating an elastic wave device according to a fourth embodiment. As shown in FIG. 26 , an elastic wave device 10J according to the fourth 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 plurality of 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 plurality of 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 elastic wave device 10J according to the fourth embodiment is a so-called ladder filter.

[0127] 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.

[0128] 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 embodiment (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. 13, and therefore repeated description will be omitted.

[0129] On the other hand, the parallel arm resonators 64, 65, 66, and 67 have the load film 50 shown in the second embodiment, which is different from the first embodiment, for example.

[0130] 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.

[0131] Although the elastic wave device 10J according to the fourth preferred embodiment is combined with the load film 50 shown in the first and second preferred embodiments, the present invention is not limited to this. The fourth preferred embodiment can be combined with the above-described preferred embodiments and modified examples.

[0132] 27 is a cross-sectional view of an elastic wave device according to Modification 8. In the elastic wave device 10 according to the first embodiment described above, the support substrate 11 has the cavity 14, and the cavity 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20, which is a so-called membrane structure. However, the present invention is not limited to this.

[0133] 27 , in an elastic wave device 10K according to an eighth modification, an acoustic multilayer film 43 is laminated on the second principal surface 20b of the piezoelectric layer 20. The acoustic multilayer film 43 has a laminate structure including low acoustic impedance layers 43a, 43c, and 43e, each having a relatively low acoustic impedance, and high acoustic impedance layers 43b and 43d, each having a relatively high acoustic impedance. The low acoustic impedance layers 43a, 43c, and 43e are, for example, silicon oxide layers, and the high acoustic impedance layers 43b and 43d are, for example, metal layers such as tungsten or platinum, 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 a cavity 14.

[0134] In acoustic wave device 10K, 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.

[0135] 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.

[0136] 27 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 eighth modification can be combined with each of the above-described embodiments and modifications.

[0137] 28 is a cross-sectional view of an elastic wave device according to a ninth modification. In the elastic wave device 10 according to the first embodiment described above, the IDT electrode 30 is provided on the first main surface 20 a of the piezoelectric layer 20. However, this is not limiting. As shown in FIG. 28 , an elastic wave device 10L according to the ninth modification has a first IDT electrode 30A provided on the first main surface 20 a of the piezoelectric layer 20 and a second IDT electrode 30B provided on the second main surface 20 b of the piezoelectric layer 20. The first IDT electrode 30A and the second IDT electrode 30B have the same configuration as the IDT electrode 30 (see FIGS. 1 and 2 ).

[0138] The plurality of electrode fingers 36 (only one is shown in FIG. 28 ) of the second IDT electrode 30B are provided in a region overlapping the plurality of electrode fingers 31 of the first IDT electrode 30A. The electrode fingers 36 of the second IDT electrode 30B are provided with the same width and the same inter-electrode pitch as the electrode fingers 31 of the first IDT electrode 30A.

[0139] An elastic wave device 10L in accordance with the ninth modification includes an upper reflector 70B provided on the first main surface 20a of the piezoelectric layer 20 and a lower reflector 70C provided on the second main surface 20b of the piezoelectric layer 20. The upper reflector 70B is provided on the same layer as the first IDT electrode 30A, and the lower reflector 70C is provided on the same layer as the second IDT electrode 30B. The upper reflector 70B and the lower reflector 70C have the same configuration as the reflectors 70 and 71 of the first embodiment.

[0140] The lower reflector 70C is provided in an area overlapping with the upper reflector 70B. The load film 50 is provided on the first protective film 41, and is provided in an area overlapping with the upper reflector 70B and the lower reflector 70C.

[0141] In the ninth modification, the first IDT electrode 30A and the upper reflector 70B are provided on the first main surface 20a of the piezoelectric layer 20, and the second IDT electrode 30B and the lower reflector 70C are provided on the second main surface 20b of the piezoelectric layer 20, thereby improving the temperature coefficient of frequency (TCF).

[0142] 28 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 ninth modification can be combined with each of the above-described embodiments and modifications.

[0143] 29 is a diagram illustrating an example of the admittance characteristics of an elastic wave device according to a tenth modification. FIG. 30 is a diagram illustrating an example of the impedance phase in a higher mode. The elastic wave device according to the tenth modification shown in FIG. 29 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.

[0144] 29 shows frequency characteristics of the absolute value of admittance for the elastic wave device according to Modification 10. As shown in Fig. 29, in the elastic wave device according to Modification 10, 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.

[0145] The horizontal axis of the graph shown in Fig. 30 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. 30 corresponds to the intensity of the S2 mode.

[0146] 30, 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-A-2022-524136. In the acoustic resonator described in JP-A-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.

[0147] In contrast, in the tenth modification, 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 tenth modification, 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.

[0148] Although the tenth modification 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 tenth modification can be combined with any of the embodiments and modifications described above.

[0149] 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.

[0150] The present disclosure may also have the following configurations.

[0151] (1) An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction; an IDT electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the IDT electrode including a plurality of electrode fingers arranged in a predetermined direction; a reflector arranged adjacent to the IDT electrode in the arrangement direction of the plurality of electrode fingers; a support member facing the second main surface of the piezoelectric layer and having an acoustic reflecting portion on the second main surface side of the piezoelectric layer; and a load film provided in a region overlapping with the reflector in a planar view from the first direction, wherein d / p is 0.5 or less, where d is a thickness of the piezoelectric layer and p is a center-to-center distance between adjacent electrode fingers. (2) The elastic wave device according to (1), further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer. (3) The elastic wave device according to (2), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode and the reflector, and the load film is provided on the first protective film. (4) The elastic wave device according to (3), wherein in a region overlapping the reflector, 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 stacked. (5) The elastic wave device according to (1), wherein the load film is provided between the first main surface of the piezoelectric layer and the reflector in the first direction of the piezoelectric layer. (6) The elastic wave device according to (2), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer, and the load film is provided on a surface of the second protective film that faces the support member. (7) The elastic wave device according to (2), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode and a second protective film provided on the second main surface of the piezoelectric layer, the load film is provided on the second main surface of the piezoelectric layer, and the second protective film covers the load film. (8) The elastic wave device according to (2), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer to cover the IDT electrode and the reflector, the load film is provided on the reflector, and the first protective film covers the load film and the reflector.(9) The elastic wave device according to any one of (1) to (8), wherein the reflectors have a plurality of reflective electrode fingers arranged in the arrangement direction, the plurality of reflective electrode fingers extending along the extension direction of the electrode fingers of the IDT electrode, and the load film is provided in a region overlapping with the plurality of reflective electrode fingers. (10) The elastic wave device according to any one of (1) to (9), wherein the load film has a first extension portion provided in a region overlapping with the reflectors, and an outer load film provided in a region that is outward of the first extension portion in the arrangement direction and does not overlap with the reflectors and the IDT electrode. (11) The elastic wave device according to (2), wherein the thickness of the protective film is thinner than the thickness of the piezoelectric layer. (12) The elastic wave device according to any one of (1) to (11), wherein the IDT electrode is provided on both the first main surface and the second main surface of the piezoelectric layer. (13) An acoustic wave filter device including at least one resonator connected to the filter, the resonator being the acoustic wave device according to any one of (1) to (12). (14) The acoustic wave filter device according to (13), comprising: an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting a node of the series arm and ground, the at least one resonator being a plurality of resonators including a series arm resonator provided in the series arm and a parallel arm resonator provided in the parallel arm, and the load film of the series arm resonator has a different configuration from the load film of the parallel arm resonator. (15) The elastic wave device according to any one of (1) to (12), wherein the load film includes a first extension portion, a second extension portion, a third extension portion, and a fourth extension portion, wherein the first extension portion is provided in a region overlapping with a first reflector located outermost in the arrangement direction and extends along the extension direction of the first reflector, the second extension portion is provided in a region overlapping with a second reflector located outermost on the opposite side of the arrangement direction and extends along the extension direction of the second reflector, the third extension portion is connected to one end side of the extension direction of the first extension portion and the second extension portion and extends in the arrangement direction, and the fourth extension portion is connected to the other end side of the extension direction of the first extension portion and the second extension portion and extends in the arrangement direction.(16) The elastic wave device according to any one of (1) to (12), wherein the load film includes a first extension portion, a second extension portion, a third extension portion, and a fourth extension portion, wherein the first extension portion is provided in a region overlapping with a first reflector located outermost in the arrangement direction and extends along the extension direction of the first reflector, the second extension portion is provided in a region overlapping with a second reflector located outermost on the opposite side of the arrangement direction and extends along the extension direction of the second reflector, the third extension portion is located at one end side of the extension direction of the first extension portion and the second extension portion and extends in the arrangement direction, the fourth extension portion is located at the other end side of the extension direction of the first extension portion and the second extension portion and extends in the arrangement direction, and at least one of the third extension portion and the fourth extension portion is located spaced apart from the first extension portion and the second extension portion. (17) The elastic wave device according to (2), in which the load film and the protective film are formed of the same material, and the density of the load film is different from the density of the protective film. (18) The elastic wave device according to (2), in which the protective film is formed of silicon oxide. (19) The elastic wave device according to any one of (1) to (12) and (15) to (18), in which the piezoelectric layer contains lithium niobate or lithium tantalate and has a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut. (20) The elastic wave device according to (2), in which the protective film includes a first protective film provided on the first main surface of the piezoelectric layer and covers the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer. (21) The elastic wave device according to (2), in which the thickness of the protective film is thicker than the thickness of the IDT electrode. (22) The elastic wave device according to (20), wherein a value of A / B is equal to or greater than 1-0.06 and equal to or less than 1+0.06, 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. (23) The elastic wave device according to (20), wherein an upper surface of the first protective film and a lower surface of the second protective film are formed flat.(24) The elastic wave device according to any one of (1) to (11) and (15) to (23), 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. (25) The elastic wave device according to any one of (1) to (11) and (15) to (24), wherein d / p is 0.24 or less. (26) The elastic wave device according to any one of (1) to (11) and (15) to (25), wherein, when viewed in the electrode finger orthogonal direction, a region where adjacent electrode fingers overlap and a region between centers of the adjacent electrode fingers in the electrode finger orthogonal direction are excitation regions, and wherein MR satisfies MR≦1.75(d / p)+0.075, where MR is a metallization ratio of the electrode fingers to the excitation region. (27) The elastic wave device according to any one of (1) to (11) and (15) to (26), wherein the piezoelectric layer is made of lithium tantalate or lithium niobate. (28) The elastic wave device according to any one of (1) to (11) and (15) to (27), 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) (29) The elastic wave device according to any one of (1) to (11) and (15) to (28), 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. (30) The elastic wave device according to any one of (1) to (11) and (15) to (28), wherein the acoustic reflecting portion is an acoustic reflecting film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged 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.

[0152] 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10I, 10J, 10K, 10L Acoustic wave device 11 Support substrate 12 Bottom part 13 Wall part 14 Cavity part 20, 201 Piezoelectric layer 20a, 201a First main surface 20b, 201b Second main surface 30 IDT electrodes 31, 32 Electrode fingers 33, 34 Busbar electrode 41 First protective film 42 Second protective film 50 Load film 50A Upper load film 50B Lower load film 51, 51a, 51b First extension part 52, 52a, 52b Second extension part 53 Outer load film 54 Lower first extension part 70, 70A, 71, 71A reflector 72, 73, 76, 77 Reflective electrode fingers 74, 75, 78, 79 Reflective busbar electrodes

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 reflector arranged adjacent to the IDT electrode in the arrangement direction of the plurality of electrode fingers; a support member facing the second main surface of the piezoelectric layer and having an acoustic reflection portion on the second main surface side of the piezoelectric layer; and a load film provided in a region overlapping with the reflector in a planar view from the first direction, wherein d is a thickness of the piezoelectric layer and p is a center-to-center distance between adjacent electrode fingers, and 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. The elastic wave device according to claim 2, wherein the protective film comprises a first protective film provided on the first main surface of the piezoelectric layer, covering the IDT electrode and the reflector, and the load film is provided on the first protective film.

4. The elastic wave device according to claim 3, wherein in a region overlapping with the reflector, 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.

5. The acoustic wave device according to claim 1, wherein the load film is provided between the first main surface of the piezoelectric layer and the reflector in the first direction of the piezoelectric layer.

6. The elastic wave device according to claim 2, 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 on the surface of the second protective film facing the support member.

7. The elastic wave device of claim 2, wherein the protective film comprises a first protective film provided on the first main surface of the piezoelectric layer and covering the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer, the load film is provided on the second main surface of the piezoelectric layer, and the second protective film covers the load film.

8. The elastic wave device of claim 2, wherein the protective film has a first protective film provided on the first main surface of the piezoelectric layer, covering the IDT electrode and the reflector, the load film is provided on the reflector, and the first protective film covers the load film and the reflector.

9. An elastic wave device as claimed in any one of claims 1 to 8, wherein the reflector has a plurality of reflective electrode fingers arranged in the arrangement direction, the plurality of reflective electrode fingers each extending along the extension direction of the electrode fingers of the IDT electrode, and the load film is provided in an area overlapping with the plurality of reflective electrode fingers.

10. An elastic wave device as claimed in any one of claims 1 to 9, wherein the load film has a first extension portion provided in a region overlapping with the reflector, and an outer load film provided in a region that is outside the first extension portion in the arrangement direction and does not overlap with the reflector and the IDT electrode.

11. The acoustic wave device according to claim 2, wherein the protective film has a thickness smaller than a thickness of the piezoelectric layer.

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

13. An elastic wave filter device comprising at least one connected resonator, the resonator being an elastic wave device as defined in any one of claims 1 to 12.

14. An elastic wave filter device as claimed in claim 13, comprising: an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting a node of the series arm and ground, wherein the at least one resonator is a plurality of resonators including a series arm resonator provided in the series arm and a parallel arm resonator provided in the parallel arm, and the load film of the series arm resonator has a different configuration from the load film of the parallel arm resonator.

15. The elastic wave device according to any one of claims 1 to 12, wherein the load film includes a first extension portion, a second extension portion, a third extension portion, and a fourth extension portion, wherein the first extension portion is provided in a region overlapping with a first reflector located outermost in the arrangement direction and extends along the extension direction of the first reflector, the second extension portion is provided in a region overlapping with a second reflector located outermost on the opposite side of the arrangement direction and extends along the extension direction of the second reflector, the third extension portion is connected to one end side of the extension direction of the first extension portion and the second extension portion and extends in the arrangement direction, and the fourth extension portion is connected to the other end side of the extension direction of the first extension portion and the second extension portion and extends in the arrangement direction.

16. The elastic wave device according to any one of claims 1 to 12, wherein the load film includes a first extension portion, a second extension portion, a third extension portion, and a fourth extension portion, wherein the first extension portion is provided in a region overlapping with a first reflector located outermost in the arrangement direction and extends along the extension direction of the first reflector, the second extension portion is provided in a region overlapping with a second reflector located outermost on the opposite side of the arrangement direction and extends along the extension direction of the second reflector, the third extension portion is disposed at one end side of the extension direction of the first extension portion and the second extension portion and extends in the arrangement direction, the fourth extension portion is disposed at the other end side of the extension direction of the first extension portion and the second extension portion and extends in the arrangement direction, and at least one of the third extension portion and the fourth extension portion is disposed spaced apart from the first extension portion and the second extension portion.

17. The acoustic wave device according to claim 2, wherein the load film and the protective film are formed of the same material, and the density of the load film is different from the density of the protective film.

18. The acoustic wave device according to claim 2, wherein the protective film is made of silicon oxide.

19. The elastic wave device according to any one of claims 1 to 12 and claims 15 to 18, 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.

20. The elastic wave device according to claim 2, wherein the protective film comprises a first protective film provided on the first main surface of the piezoelectric layer and covering the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer.

21. The acoustic wave device according to claim 2, wherein the protective film has a thickness greater than a thickness of the IDT electrode.

22. The elastic wave device according to claim 20, wherein the sum of the distances from the center of the thickness of the piezoelectric layer to the top surface of the first protective film is A and the sum of the distances from the center of the thickness of the piezoelectric layer to the top surface of the second protective film is B, in which the value of A / B is 1-0.06 or more and 1+0.06 or less.

23. The acoustic wave device according to claim 20, wherein an upper surface of the first protective film and a lower surface of the second protective film are formed flat.

24. The elastic wave device according to any one of claims 1 to 11 and claims 15 to 23, 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.

25. The elastic wave device according to any one of claims 1 to 11 and claims 15 to 24, wherein d / p is 0.24 or less.

26. An elastic wave device as claimed in any one of claims 1 to 11 and claims 15 to 25, 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.

27. The acoustic wave device according to any one of claims 1 to 11 and claims 15 to 26, wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.

28. The elastic wave device according to any one of claims 1 to 11 and claims 15 to 27, 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 ] ~ 180°, any ψ) ... Equation (3) 29. An elastic wave device as claimed in any one of claims 1 to 11 and claims 15 to 28, 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.

30. An elastic wave device as claimed in any one of claims 1 to 11 and claims 15 to 28, wherein the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged such that at least a portion of the support member and at least a portion of the piezoelectric layer face each other across the acoustic reflection film.

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