Elastic wave device and elastic wave filter device

Abstract

This elastic wave device comprises: a piezoelectric layer that has a first main surface and a second main surface; an IDT electrode that is provided to the first main surface and / or the second main surface of the piezoelectric layer, and that includes a plurality of electrode fingers which are arranged in a prescribed direction; and a support member that is opposite from the second main surface of the piezoelectric layer and that has an acoustic reflection part on the side toward the second main surface of the piezoelectric layer. The plurality of electrode fingers include a first electrode finger, which is positioned on the outermost side in the arrangement direction of the plurality of electrode fingers, and a second electrode finger, which is adjacent to the first electrode finger. The product of the width, height, and density of at least one of the first electrode finger and the second electrode finger is greater than the product of the width, height, and density of an electrode finger which is from among the plurality of electrode fingers, which is in a center part, and which differs from the first electrode finger and the second electrode finger. When d is defined as the thickness of the piezoelectric layer and p is defined as the distance between respective centers of adjacent electrode fingers, d / p is not more than 0.5.

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 elastic wave devices disclosed in Patent Documents 1 and 2 have the potential for ripples to occur in the admittance characteristics, resulting in increased propagation loss of elastic waves.

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

[0006] an IDT electrode provided on at least one of the first and second main surfaces of the piezoelectric layer and including a plurality of electrode fingers arranged in a predetermined direction; and a support member facing the second main surface of the piezoelectric layer and having an acoustic reflector on the second main surface side of the piezoelectric layer, wherein the plurality of electrode fingers include a first electrode finger positioned outermost in the arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the first electrode finger, and the product of the width, height, and density of at least one of the first electrode finger and the second electrode finger is greater than the product of the width, height, and density of a central electrode finger of the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger, and wherein d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers.

[0007] An elastic wave device according to one aspect includes: 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 arranged in a predetermined direction; a support member facing the second main surface of the piezoelectric layer and having an acoustic reflector on the second main surface side of the piezoelectric layer; and an outermost electrode finger of the plurality of electrode fingers in the arrangement direction of the plurality of electrode fingers is designated as a first electrode finger, and an electrode finger adjacent to the first electrode finger is designated as a second electrode finger. and an additional electrode provided in an area overlapping at least one of the first electrode finger and the second electrode finger when the number of electrode fingers is two, wherein the sum of the product of the width, height and density of at least one of the first electrode finger and the second electrode finger and the product of the width, height and density of the additional electrode is greater than the product of the width, height and density of a central electrode finger among the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger, and wherein d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers.

[0008] 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.

[0009] According to the acoustic wave device and the acoustic wave filter device of the present invention, it is possible to suppress propagation loss of acoustic waves.

[0010] 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 approaches 0 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 an example of the admittance characteristics of an elastic wave device according to a first modification of the first embodiment. FIG. 15 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to a second modification of the first embodiment. FIG. 16 is a cross-sectional view showing an elastic wave device according to a third modification of the first embodiment. Fig. 17 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to a third modified example of the first embodiment. Fig. 18 is a cross-sectional view of an elastic wave device according to a fourth modified example of the first embodiment. Fig. 19 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to the fourth modified example of the first embodiment. Fig. 20 is a cross-sectional view of an elastic wave device according to a second embodiment. Fig. 21 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to the second embodiment. Fig. 22 is a cross-sectional view of an elastic wave device according to a fifth modified example of the second embodiment.FIG. 23 is a cross-sectional view of an elastic wave device according to a sixth modified example of the second embodiment. FIG. 24 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to a sixth modified example of the second embodiment. FIG. 25 is an explanatory diagram illustrating a vibration mode distribution of an elastic wave device according to a sixth modified example of the second embodiment. FIG. 26 is an explanatory diagram illustrating a vibration mode distribution of an elastic wave device according to a comparative example. FIG. 27 is a cross-sectional view of an elastic wave device according to a seventh modified example of the second embodiment. FIG. 28 is a cross-sectional view of an elastic wave device according to an eighth modified example of the second embodiment. FIG. 29 is a circuit diagram of an elastic wave device according to the third embodiment. FIG. 30 is a cross-sectional view of an elastic wave device according to a ninth modified example. FIG. 31 is a cross-sectional view of an elastic wave device according to a tenth modified example. FIG. 32 is a plan view of an elastic wave device according to an eleventh modified example. FIG. 33 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to a twelfth modified example. FIG. 34 is an explanatory diagram illustrating an example of impedance phase in S2 mode.

[0011] 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.

[0012] 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, a first protective film 41 is indicated by a two-dot chain line for ease of viewing.

[0013] 1 and 2 , an elastic wave device 10 according to the first preferred embodiment includes a piezoelectric layer 20, an IDT electrode 30, a support substrate 11, a first protective film 41, and a second protective film 42. As shown in Fig. 2 , the elastic wave device 10 includes the second protective film 42, the piezoelectric layer 20, the IDT electrode 30, and the first protective film 41 stacked in this order on the support substrate 11.

[0014] 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.

[0015] The thickness of the piezoelectric layer 20 is not particularly limited, but is preferably 50 nm to 1000 nm 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, about 180 nm.

[0016] 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.

[0017] Of the multiple electrode fingers 31, 32, the electrode finger 31 located outermost in the arrangement direction of the multiple electrode fingers 31, 32 is referred to as the first electrode finger 31a. The electrode finger 32 adjacent to the first electrode finger 31a, i.e., the electrode finger 32 located second outermost in the arrangement direction, is referred to as the second electrode finger 32a. Furthermore, the pair of outermost electrode fingers 31, 32 on the opposite side from the first electrode finger 31a and second electrode finger 32a are referred to as the third electrode finger 31b and the fourth electrode finger 32b, respectively. Detailed configurations of the first electrode finger 31a, the second electrode finger 32a, the third electrode finger 31b, and the fourth electrode finger 32b will be described later with reference to FIGS. 12 and 13 .

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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°).

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Because the elastic wave device 10 of the first embodiment has the above configuration, even if the number of pairs of electrode fingers 31 and 32 is reduced in an attempt to reduce the device size, the Q value is unlikely to decrease. This is because the resonator does not require reflectors on both sides, resulting in low propagation loss. Furthermore, the reason why the reflectors are not required is because the device utilizes bulk waves in the thickness-shear first-order mode.

[0028] The first protective film 41 is provided on the first main surface 20a of the piezoelectric layer 20, covering the IDT electrode 30. The second protective film 42 is provided on the second main surface 20b of the piezoelectric layer 20. The first protective film 41 and the second protective film 42 are made of silicon oxide. 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 used.

[0029] The support substrate 11 (support member) is disposed opposite the second main surface 20b of the piezoelectric layer 20. The support substrate 11 has a cavity 14 (space) on the surface facing the second main surface 20b of the piezoelectric layer 20. More specifically, the support substrate 11 has a bottom 12 and a wall 13 provided in a frame shape on the upper surface of the bottom 12. The cavity 14 is formed in the space surrounded by the bottom 12 and the wall 13. The piezoelectric layer 20 is stacked on the upper surface of the wall 13 of the support substrate 11 with a second protective film 42 interposed therebetween. In this manner, the acoustic wave device 10 has a so-called membrane structure in which the cavity 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20. The support member may include the support substrate 11 and an intermediate (insulating) layer.

[0030] The cavity portion 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 portion 14. However, as described above, the second protective film 42 may not be provided. In this case, the support substrate 11 may be directly laminated 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 portion 13 and the second main surface 20b of the piezoelectric layer 20, and may not be provided in the region overlapping with the cavity portion 14. In other words, the support substrate 11 may be indirectly laminated 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.

[0031] 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.

[0032] 3 and 4 are schematic cross-sectional views illustrating a bulk wave in a first-order thickness-shear mode propagating through the piezoelectric layer of the first embodiment, respectively.

[0033] As shown in FIG. 3 , in the elastic wave device 10 of the first embodiment, vibration displacement occurs in the thickness shear direction. Therefore, waves propagate and resonate substantially in the direction connecting the first principal surface 20 a and the second principal surface 20 b of the piezoelectric layer 20, i.e., the Z direction. That is, the X direction component of the wave is significantly smaller than the Z direction component. Furthermore, since resonance characteristics are achieved through wave propagation in this Z direction, a reflector is not required. Therefore, no propagation loss occurs during propagation to the reflector. Therefore, even if the number of electrode pairs, each consisting of electrode fingers 31 and 32, is reduced in an effort to achieve miniaturization, the Q value is unlikely to decrease.

[0034] As shown in FIG. 4 , the amplitude direction of the bulk wave in the first thickness-shear mode is opposite between a first region 251 included in the intersection region C (see FIG. 1 ) of the piezoelectric layer 20 and a second region 252 included in the intersection region C. FIG. 4 schematically illustrates the bulk wave when a voltage is applied between the electrode fingers 31 and 32 such that the electrode finger 32 has a higher potential than the electrode finger 31. Here, the imaginary plane VP1 is a plane that is perpendicular to the thickness direction of the piezoelectric layer 20 and divides the piezoelectric layer 20 in half. The first region 251 is the region of the intersection region C between the imaginary plane VP1 and the first main surface 20a. The second region 252 is the region of the intersection region C between the imaginary plane VP1 and the second main surface 20b.

[0035] In acoustic wave device 10, at least one pair of electrodes consisting of electrode finger 31 and electrode finger 32 is arranged, but because waves are not propagated in the X direction, the number of electrode pairs consisting of electrode finger 31 and electrode finger 32 does not necessarily need to be multiple. In other words, it is sufficient that at least one pair of electrodes is provided.

[0036] For example, the electrode finger 31 is an electrode connected to a hot potential, and the electrode finger 32 is an electrode connected to a ground potential. However, the electrode finger 31 may be connected to the ground potential, and the electrode finger 32 may be connected to the hot potential. In the first embodiment, at least one pair of electrodes is an electrode connected to a hot potential or an electrode connected to a ground potential, as described above, and no floating electrode is provided.

[0037] 5 is a diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. The design parameters of the elastic wave device 10 that achieved the resonance characteristics shown in FIG.

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

[0039] Length of the crossing region C: 40 μm Number of pairs of electrodes consisting of the electrode fingers 31 and 32: 21 pairs Inter-electrode pitch between the electrode fingers 31 and 32: 3 μm Width of the electrode fingers 31 and 32: 500 nm d / p: 0.133

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

[0041] Support substrate 11: silicon

[0042] In the first embodiment, the inter-electrode pitch of each of the electrode pairs, each consisting of the electrode finger 31 and the electrode finger 32, is set to be equal in all pairs. That is, the electrode fingers 31 and the electrode fingers 32 are arranged at equal pitches.

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

[0044] In the first embodiment, when the thickness of the piezoelectric layer 20 is d and the interelectrode pitch between the electrode fingers 31 and 32 is p, d / p is 0.5 or less, and more preferably 0.24 or less. This will be explained with reference to FIG. 6.

[0045] 6 is an explanatory diagram showing the relationship between d / 2p and the fractional bandwidth of a resonator in the elastic wave device according to the first embodiment, where p is the center-to-center distance or the average center-to-center distance between adjacent electrodes and d is the average thickness of the piezoelectric layer. In FIG. 6, multiple elastic wave devices were obtained by varying d / 2p, similar to the elastic wave device having the resonance characteristics shown in FIG.

[0046] As shown in Figure 6, when d / 2p exceeds 0.25, i.e., when d / p > 0.5, adjusting d / p results in a fractional bandwidth of less than 5%. In contrast, when d / 2p ≤ 0.25, i.e., when d / p ≤ 0.5, varying d / p within this range can increase the fractional bandwidth to 5% or more, thereby enabling the construction of a resonator with a high coupling coefficient. Furthermore, when d / 2p is 0.12 or less, i.e., when d / p is 0.24 or less, the fractional bandwidth can be increased to 7% or more. Furthermore, adjusting d / p within this range can result in a resonator with a wider fractional bandwidth and a higher coupling coefficient. Therefore, by setting d / p to 0.5 or less, a resonator with a high coupling coefficient can be constructed using the bulk wave in the thickness-shear primary mode.

[0047] When the piezoelectric layer 20 has thickness variations, the thickness d of the piezoelectric layer 20 may be an average value of the thickness variations.

[0048] 7 is a plan view illustrating an example in which a pair of electrodes is provided in the elastic wave device according to the first embodiment. In the elastic wave device 10, a pair of electrodes including electrode fingers 31 and 32 is provided on the first main surface 20a of the piezoelectric layer 20. Note that K in FIG. 7 represents the cross width. As described above, in the elastic wave device 10 according to the present disclosure, the number of electrode pairs may be one pair. Even in this case, if the d / p is 0.5 or less, a bulk wave in the thickness-shear first-order mode can be effectively excited.

[0049] In the acoustic wave device 10, it is preferable that the metallization ratio MR of the adjacent electrode fingers 31 and 32 with respect to the crossing region C satisfies MR≦1.75(d / p)+0.075. In this case, spurious signals can be effectively reduced. This will be described with reference to FIGS. 8 and 9.

[0050] 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.

[0051] The metallization ratio MR will be explained with reference to FIG. 1 . Focusing on a pair of electrode fingers 31 and 32 in the electrode structure of FIG. 1 , assume that only this pair of electrode fingers 31 and 32 are provided. In this case, the area surrounded by the dashed line is the intersection region C. When the electrode fingers 31 and 32 are viewed in a direction perpendicular to the extension direction of the electrode fingers 31 and 32, i.e., in the opposing direction, the intersection region C 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.

[0052] When multiple pairs of electrode fingers 31 and electrode fingers 32 are provided, the ratio of the metallization portion included in all the intersection regions C to the total area of ​​the intersection regions C may be defined as MR.

[0053] 9 is an explanatory diagram showing the relationship between the 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.

[0054] In the region surrounded by ellipse J in Figure 9, the spurious is as large as 1.0. As is clear from Figure 9, when the fractional bandwidth exceeds 0.17, i.e., 17%, large spurious signals with a spurious level of 1 or more appear within the passband, even if the parameters constituting the fractional bandwidth are changed. That is, as in the resonance characteristics shown in Figure 8, large spurious signals indicated by arrow B appear within the passband. Therefore, it is preferable that the fractional bandwidth be 17% or less. In this case, the spurious signals can be reduced by adjusting the film thickness of piezoelectric layer 20 and the dimensions of electrode fingers 31 and 32.

[0055] FIG. 10 is an explanatory diagram showing the relationship between d / 2p, metallization ratio MR, and fractional bandwidth. Various elastic wave devices 10 with different d / 2p and MR were constructed in the elastic wave device 10 according to the first embodiment, and the fractional bandwidth was measured. The hatched area to the right of dashed line D in FIG. 10 represents the region where the fractional bandwidth is 17% or less. The boundary between this hatched area and the unhatched area is represented by MR = 3.5(d / 2p) + 0.075. That is, MR = 1.75(d / p) + 0.075. Therefore, preferably, MR ≦ 1.75(d / p) + 0.075. In this case, the fractional bandwidth is easily maintained at 17% or less. More preferably, the region to the right of MR = 3.5(d / 2p) + 0.05, as indicated by dashed line D1 in FIG. 10 , is the region. That is, if MR≦1.75(d / p)+0.05, the fractional bandwidth can be reliably kept to 17% or less.

[0056] 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).

[0057] (0°±10°, 0° to 20°, any ψ) ... Equation (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50)２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3)

[0058] Therefore, in the case of the Euler angle range of the above formula (1), formula (2), or formula (3), the relative bandwidth can be made sufficiently wide, which is preferable.

[0059] Next, the detailed configuration of the IDT electrode 30 will be described. FIG. 12 is an enlarged cross-sectional view of region A shown in FIG. 2 . Note that FIG. 12 describes the first electrode finger 31a, which is located on the outermost side in the arrangement direction of the multiple electrode fingers 31 and 32, and the second electrode finger 32a, which is adjacent to the first electrode finger 31a. However, the third electrode finger 31b and the fourth electrode finger 32b (see FIGS. 1 and 2 ), which are located on the outermost side opposite the first electrode finger 31a and the second electrode finger 32a, also have an arrangement relationship that is line-symmetrical. The description of the first electrode finger 31a and the second electrode finger 32a also applies to the third electrode finger 31b and the fourth electrode finger 32b. In the following description, when it is not necessary to distinguish between the first electrode finger 31a and the second electrode finger 32a, they will simply be referred to as electrode fingers 31 and 32.

[0060] 12 , the first electrode fingers 31 a, the second electrode fingers 32 a, and the central electrode fingers 31 and 32 different from the first electrode fingers 31 a and the second electrode fingers 32 a are provided in the same layer on the first main surface 20 a of the piezoelectric layer 20. The first protective film 41 is provided to cover the first electrode fingers 31 a, the second electrode fingers 32 a, and the central electrode fingers 31 and 32. In this embodiment, the upper surface of the first protective film 41 is formed flat. The lower surface of the second protective film 42 is formed flat along the second main surface 20 b of the piezoelectric layer 20.

[0061] 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 piezoelectric layer 20 is, for example, 180 nm. The thickness t1 of the first protective film 41 is equal to the thickness t2 of the second protective film 42. The thickness t1 of the first protective film 41 is thinner than the thickness t3 of the piezoelectric layer 20 and thicker than the height H1 and Hc (thickness) of the IDT electrode 30.

[0062] 12 , the product Xe (=W1×H1×d1) of the width W1, height H1, and density d1 of at least one of the first electrode finger 31 a and the second electrode finger 32 a is greater than the product Xc (=Wc×Hc×dc) of the width Wc, height Hc, and density dc of the central electrode finger 31, 32, which is different from the first electrode finger 31 a and the second electrode finger 32 a, among the plurality of electrode fingers 31, 32. In the following description, the products Xe and Xc are values ​​calculated for each of the electrode fingers 31, 32. In this embodiment, unless otherwise specified, "density" refers to a physical property value specific to the material. The densities of the materials used for the electrode fingers 31, 32 are as follows: Tungsten: 19.3 g / cm ３ , molybdenum: 10.22 g / cm ３ , ruthenium: 12.41 g / cm ３ , platinum: 21.45g / cm ３ , copper: 8.96g / cm ３ , Silver: 10.5g / cm ３ , chromium: 7.189 g / cm ３ , gold 19.32g / cm ３ .

[0063] In this embodiment, the product Xe (=W1×H1×d1) of the first electrode finger 31a, which is located outermost in the arrangement direction among the first electrode fingers 31a and the second electrode fingers 32a, is larger than the product Xc (=Wc×Hc×dc) of the second electrode finger 32a adjacent to the first electrode finger 31a and the central electrode fingers 31, 32. In the following description, the second electrode finger 32a adjacent to the first electrode finger 31a and the central electrode fingers 31, 32 will be referred to as the other electrode fingers 31, 32.

[0064] For example, the width W1 of the first electrode finger 31a is equal to the width Wc of each of the other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32). The width W1 and the width Wc are, for example, 0.6 μm.

[0065] Of the first electrode fingers 31a and the second electrode fingers 32a, the first electrode finger 31a located on the outermost side in the arrangement direction is made of a material with a higher density than the central electrode fingers 31 and 32. The first electrode finger 31a is made of a platinum single layer. The density d1 of the first electrode finger 31a (platinum) is 21,450 kg / m ３The other electrode fingers 31 and 32 are, as described above, laminated films of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy. The density of the aluminum-copper alloy constituting the other electrode fingers 31 and 32 is 2695 kg / m ３ and the density of titanium is 4500 kg / m ３ That is, the density d1 of the first electrode finger 31 a is greater than the density dc of the other electrode fingers 31 and 32 .

[0066] The height H1 (film thickness) of the first electrode finger 31a is 112 nm. The film thicknesses of the laminated films constituting the second electrode finger 32a are 12 nm, 70 nm, 18 nm, and 12 nm, respectively. That is, the height Hc (total film thickness) of the other electrode fingers 31 and 32 is 112 nm. In this embodiment, the height H1 of the first electrode finger 31a is equal to the height Hc of the other electrode fingers 31 and 32, and the heights H1 and Hc are each 112 nm.

[0067] As an example, the product Xe (=W1×H1×d1) of the first electrode finger 31a is Xe=0.6 (μm)×0.112 (μm)×21450 (kg / m ３ The product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 is Xc=0.6 (μm)×0.03 (μm)×4500 (kg / m ３ )+0.6(μm)×0.082(μm)×2695(kg / m ３ ) = 213.594.

[0068] FIG. 13 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the first embodiment. FIG. 13 is an explanatory diagram showing the real part of the admittance, i.e., the conductance component, of the elastic wave device 10 according to the first embodiment. The admittance characteristics shown in FIG. 13 represent simulation results of the admittance characteristics of the elastic wave device 10 according to the first embodiment. FIG. 13 also shows simulation results of the admittance characteristics of an elastic wave device according to a comparative example. The comparative example is an elastic wave device configured such that, compared to the first embodiment, the product Xe (= W1 × H1 × d1) of the first electrode finger 31a located outermost in the arrangement direction is equal to the product Xc (= Wc × Hc × dc) of each of the other electrode fingers 31 and 32. More specifically, the comparative example is an elastic wave device configured such that the first electrode finger 31a, like the other electrode fingers 31 and 32, is formed of a laminated film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy.

[0069] As shown in FIG. 13 , in the elastic wave device according to the comparative example, ripples occur in a frequency range different from the resonant frequency. In the comparative example, particularly large ripples, as indicated by dotted line E1, occur. In contrast, in the elastic wave device 10 according to the first embodiment, the product Xe of the first electrode finger 31 a is larger than the products Xc of the other electrode fingers 31 and 32, thereby suppressing the ripples indicated by dotted line E1 compared to the comparative example. Furthermore, the elastic wave device 10 according to the first embodiment exhibits reduced propagation loss in the frequency range indicated by dotted line E2 compared to the comparative example. Because the peak width associated with the resonant frequency is narrower in the elastic wave device 10 according to the first embodiment than in the elastic wave device according to the comparative example, it can be seen that propagation loss and leakage of elastic waves are suppressed.

[0070] In the first embodiment, the density d1 of the first electrode fingers 31a is greater than the density d2 of the other electrode fingers 31 and 32, and the width W1 and height H1 of the first electrode fingers 31a are equal to the width Wc and height Hc of the other electrode fingers 31 and 32. However, this is not limited thereto, and the density d1 of the first electrode fingers 31a may be equal to the density d2 of the other electrode fingers 31 and 32, and the width W1 of the first electrode fingers 31a may be greater than the width Wc of the other electrode fingers 31 and 32. Alternatively, the density d1 of the first electrode fingers 31a may be equal to the density d2 of the other electrode fingers 31 and 32, and the height H1 of the first electrode fingers 31a may be greater than the height Hc of the other electrode fingers 31 and 32. Two or more of the width W1, height H1, and density d1 of the first electrode fingers 31a may be different from the width Wc, height Hc, and density dc of the other electrode fingers 31 and 32, respectively.

[0071] The material of the electrode fingers 31, 32 of the IDT electrode 30 is merely an example and is not limited to this. The material of the electrode fingers 31, 32 of the IDT electrode 30 may be at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum.

[0072] 14 is an explanatory diagram illustrating an example of admittance characteristics of an elastic wave device according to a first modification of the first embodiment. In the first embodiment described above, the product Xe (= W1 × H1 × d1) of the first electrode finger 31 a, which is located outermost in the arrangement direction among the first electrode fingers 31 a and the second electrode fingers 32 a, is larger than the product Xc (= Wc × Hc × dc) of each of the other electrode fingers 31 and 32 (the second electrode fingers 32 a and the central electrode fingers 31 and 32). However, the present invention is not limited to this.

[0073] In the elastic wave device of the first modified example, the product Xe (= W1 × H1 × d1) of both the first electrode finger 31a and the second electrode finger 32a, i.e., the first electrode finger 31a located at the outermost position in the arrangement direction and the second electrode finger 32a adjacent to the first electrode finger 31a (the second electrode finger 32a located second from the outside in the arrangement direction), is larger than the product Xc (= Wc × Hc × dc) of each of the other electrode fingers 31, 32 (the central electrode fingers 31, 32).

[0074] In the first modification, the first electrode finger 31a and the second electrode finger 32a are configured as a single layer of platinum. The density d1 of the first electrode finger 31a and the density d1 of the second electrode finger 32a are greater than the density dc of the other electrode fingers 31 and 32. The width W1 of the first electrode finger 31a and the width W1 of the second electrode finger 32a are the same as the width Wc of the other electrode fingers 31 and 32 (the central electrode fingers 31 and 32). The height H1 of the first electrode finger 31a and the height H1 of the second electrode finger 32a are the same as the height Hc of the other electrode fingers 31 and 32 (the central electrode fingers 31 and 32).

[0075] That is, the product Xe (=W1×H1×d1) of the first electrode finger 31a and the product Xe (=W1×H1×d1) of the second electrode finger 32a in the first modification are equivalent to the product Xe (=W1×H1×d1) of the first electrode finger 31a described in the first embodiment. Moreover, the product Xc (=Wc×Hc×dc) of each of the other electrode fingers 31, 32 (the central electrode fingers 31, 32) in the first modification is equivalent to the product Xc (=Wc×Hc×dc) of each of the other electrode fingers 31, 32 (the second electrode finger 32a and the central electrode fingers 31, 32) described in the first embodiment.

[0076] 14 , in the elastic wave device according to the first modification, even if the product Xe of both the first electrode finger 31 a and the second electrode finger 32 a is larger than the product Xc of the other electrode fingers 31 and 32, the ripple indicated by the dotted line E1 is suppressed at least as compared to the comparative example, as in the first embodiment. Furthermore, in the first modification, the propagation loss is also suppressed in the frequency range indicated by the dotted line E2.

[0077] 15 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to a second modification of the first embodiment. In the elastic wave device according to the second modification, the product Xe (= W1 × H1 × d1) of the first electrode finger 31 a and the second electrode finger 32 a, which are located on the outermost side in the arrangement direction, and the adjacent second electrode finger 32 a (the electrode finger 32 located second from the outside in the arrangement direction) is larger than the product Xc (= Wc × Hc × dc) of the other electrode fingers 31 and 32 (the first electrode finger 31 a and the central electrode fingers 31 and 32).

[0078] In the second modification, the first electrode finger 31a located at the outermost position in the arrangement direction is not a single layer of platinum, but the second electrode finger 32a adjacent to the first electrode finger 31a is a single layer of platinum. The density d1 of the second electrode finger 32a is greater than the density dc of the other electrode fingers 31 and 32 (the first electrode finger 31a and the central electrode fingers 31 and 32). The width W1 of the second electrode finger 32a is the same as the width Wc of the other electrode fingers 31 and 32 (the first electrode finger 31a and the central electrode fingers 31 and 32). The height H1 of the second electrode finger 32a is the same as the height Hc of the other electrode fingers 31 and 32 (the first electrode finger 31a and the central electrode fingers 31 and 32).

[0079] That is, the product Xe (= W1 × H1 × d1) of the second electrode finger 32 a in the second modification is equivalent to the product Xe (= W1 × H1 × d1) of the first electrode finger 31 a described in the first embodiment. Also, the product Xc (= Wc × Hc × dc) of each of the other electrode fingers 31 and 32 (the first electrode finger 31 a and the central electrode fingers 31 and 32) in the second modification is equivalent to the product Xc (= Wc × Hc × dc) of each of the other electrode fingers 31 and 32 (the second electrode finger 32 a and the central electrode fingers 31 and 32) described in the first embodiment.

[0080] As shown in Figure 15, even though the elastic wave device of the second modified example is configured so that the product Xe of the second electrode finger 32a located second from the outside in the arrangement direction is larger than the product Xc of the other electrode fingers 31 and 32, it was shown that, as with the first embodiment, at least the ripple shown by the dotted line E1 is suppressed compared to the comparative example.

[0081] 16 is a cross-sectional view showing an elastic wave device according to a third modification of the first embodiment. As shown in FIG. 16 , in an elastic wave device 10A according to the third modification, the thickness t1 of the first protective film 41 and the thickness t2 of the second protective film 42 are thinner than the thickness t3 of the piezoelectric layer 20. Specifically, the thickness of the piezoelectric layer 20 is, for example, 360 nm. The thickness t1 of the first protective film 41 is 30 nm. The thickness t2 of the second protective film 42 is 30 nm. Furthermore, the thickness t1 of the first protective film 41 is thinner than the thickness (heights H1 and Hc) of the IDT electrode 30.

[0082] In the third modification, the first protective film 41 is provided to follow the surfaces and side surfaces of the electrode fingers 31 and 32 and the first main surface 20 a of the piezoelectric layer 20. Since the thickness t1 of the first protective film 41 is thin, irregularities that reflect the shapes of the electrode fingers 31 and 32 are formed on the upper surface of the first protective film 41.

[0083] As in the first embodiment, the electrode configuration of the IDT electrode 30 is such that the density d1 of the first electrode fingers 31 a is greater than the density d2 of the other electrode fingers 31, 32, and the width W1 and height H1 of the first electrode fingers 31 a are equal to the width Wc and height Hc of the other electrode fingers 31, 32. However, the film thickness is different from that of the first embodiment described above.

[0084] That is, in the third modification, the first electrode finger 31a, which is located outermost in the arrangement direction, is a platinum single layer and has a height H1 (film thickness) of 69 nm. The other electrode fingers 31, 32 (the second electrode finger 32a and the central electrode fingers 31, 32) are, as described above, a laminated film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12 nm / 27 nm / 18 nm / 12 nm. The height Hc (total film thickness) of each of the other electrode fingers 31, 32 is 69 nm.

[0085] In the third variant, the product Xe (= W1 × H1 × d1) of the first electrode finger 31a located at the outermost position in the arrangement direction is larger than the product Xc (= Wc × Hc × dc) of each of the other electrode fingers 31, 32 (the second electrode finger 32a and the central electrode fingers 31, 32).

[0086] The product Xe (= W1 × H1 × d1) of the first electrode finger 31a is Xe = 0.6 (μm) × 0.069 (μm) × 21450 (kg / m ３ The product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 is Xc=0.6 (μm)×0.03 (μm)×4500 (kg / m ３ )+0.6(μm)×0.039(μm)×2695(kg / m ３ ) = 144.063.

[0087] 17 is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a third modification of Embodiment 1. The comparative example illustrated in Fig. 17 is an elastic wave device in which, in elastic wave device 10A according to the third modification, first protective film 41 and second protective film 42 have thicknesses t1 and t2 thinner than thickness t3 of piezoelectric layer 20, and first electrode finger 31a, which is located outermost in the arrangement direction, has the same electrode configuration as the other electrode fingers 31 and 32.

[0088] As shown in FIG. 17 , in the elastic wave device 10A shown in the third modified example, even when the film thicknesses t1 and t2 of the first protective film 41 and the second protective film 42 are thin, the ripples shown by the dotted lines E1 and E2 are suppressed compared to the comparative example, and the propagation loss is suppressed in the frequency range shown by the dotted line E2.

[0089] The electrode configuration of the IDT electrode 30 shown in the third modification can be combined with the first and second modifications. That is, the product Xe (= W1 × H1 × d1) of each of the first and second electrode fingers 31 a and 32 a may be larger than the product Xc (= Wc × Hc × dc) of the other electrode fingers 31 and 32 (the central electrode fingers 31 and 32). Alternatively, the product Xe (= W1 × H1 × d1) of the second outermost second electrode finger 32 a in the arrangement direction may be larger than the product Xc (= Wc × Hc × dc) of the other electrode fingers 31 and 32 (the first electrode finger 31 a and the central electrode fingers 31 and 32).

[0090] 18 is a cross-sectional view showing an elastic wave device according to a fourth modification of Embodiment 1. As shown in Fig. 18 , in elastic wave device 10B according to the fourth modification, height H1 of first electrode finger 31a located outermost in the arrangement direction is greater than height Hc of the other electrode fingers 31 and 32 (second electrode finger 32a and central electrode fingers 31 and 32).

[0091] In the fourth modification, the width W1 of the first electrode finger 31a is equal to the width Wc of the other electrode fingers 31 and 32. The density d1 of the first electrode finger 31a is equal to the density dc of the other electrode fingers 31 and 32.

[0092] Specifically, the first electrode finger 31a, which is located outermost in the arrangement direction, is a single layer of aluminum and has a height H1 (film thickness) of 100 nm. The other electrode fingers 31, 32 (the second electrode finger 32a and the central electrode fingers 31, 32) are, as described above, stacked films of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12 nm / 27 nm / 18 nm / 12 nm. The height Hc (total film thickness) of each of the other electrode fingers 31, 32 is 69 nm.

[0093] The product Xe (= W1 × H1 × d1) of the first electrode finger 31a is Xe = 0.6 (μm) × 0.100 (μm) × 2695 (kg / m ３ )=161.7 The product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 is the same as in the third modification, that is, Xc=144.063.

[0094] Thus, in the fourth modified example, the product Xe (= W1 × H1 × d1) of the first electrode finger 31a located at the outermost position in the arrangement direction is larger than the product Xc (= Wc × Hc × dc) of each of the other electrode fingers 31, 32 (the second electrode finger 32a and the central electrode fingers 31, 32).

[0095] 19 is a diagram illustrating an example of the admittance characteristics of an elastic wave device according to a fourth modification of Embodiment 1. As shown in Fig. 19 , in elastic wave device 10B according to the fourth modification, even when first protective film 41 and second protective film 42 have thin film thicknesses t1 and t2 and first electrode fingers 31a located outermost in the arrangement direction have a large height H1, at least the ripple indicated by dotted line E2 is suppressed compared to the comparative example, and propagation loss is suppressed.

[0096] The electrode configuration of the IDT electrode 30 shown in the fourth modification can be combined with the first and second modifications described above. The height H1 of each of the first and second electrode fingers 31 a and 32 a may be greater than the height Hc of each of the other electrode fingers 31 and 32 (the central electrode fingers 31 and 32). Alternatively, the height H1 of the second electrode finger 32 a positioned second from the outside in the arrangement direction may be greater than the height Hc of each of the other electrode fingers 31 and 32 (the first electrode finger 31 a and the central electrode fingers 31 and 32).

[0097] Second Embodiment Fig. 20 is a cross-sectional view of an elastic wave device according to a second embodiment. As shown in Fig. 20, an elastic wave device 10C according to the second embodiment includes an additional electrode 35. The additional electrode 35 is provided in a region overlapping at least one of the first electrode finger 31a and the second electrode finger 32a, which are located outermost in the arrangement direction of the electrode fingers 31 and 32, among the plurality of electrode fingers 31 and 32. In the second embodiment, the additional electrode 35 is provided on and in direct contact with the first electrode finger 31a, which is located outermost in the arrangement direction. Furthermore, in the second embodiment, the additional electrode 35 is not provided on the second electrode finger 32a, which is located second from the outside in the arrangement direction.

[0098] The first electrode finger 31a is a laminated film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm. The height H1 (total film thickness) of the first electrode finger 31a is 112 nm. The additional electrode 35 is an aluminum-copper alloy, with a height H2 (film thickness) of 110 nm. The height (total of height H1 and height H2) of the laminated film of the first electrode finger 31a and the additional electrode 35 is 222 nm.

[0099] The width W2 of the additional electrode 35 is equal to the width W1 of the first electrode finger 31a, 0.6 μm, and the density d2 of the additional electrode 35 (aluminum-copper alloy) is equal to the density of part of the first electrode finger 31a (aluminum-copper alloy).

[0100] The other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32) are, as described above, a laminated film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm. The height Hc (total film thickness) of each of the other electrode fingers 31 and 32 is 112 nm.

[0101] In this embodiment, the sum (Xe1 + Xe2) of the product Xe1 of the width W1, height H1, and density d1 of the first electrode finger 31a and the product Xe2 of the width W2, height H2, and density d2 of the additional electrode 35 is greater than the product Xc of the width Wc, height Hc, and density dc of the other electrode fingers (the second electrode finger 32a and the central electrode fingers 31, 32) among the multiple electrode fingers 31, 32.

[0102] The sum (Xe1 + Xe2) of the area Xe1 (= W1 × H1 × d1) of the first electrode finger 31a and the area Xe2 (= W2 × H2 × d2) of the additional electrode 35 is: Xe1 + Xe2 = 0.6 (μm) × 0.03 (μm) × 4500 (kg / m ３ )+0.6(μm)×0.192(μm)×2695(kg / m ３ The product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 is Xc=0.6 (μm)×0.03 (μm)×4500 (kg / m ３ )+0.6(μm)×0.082(μm)×2695(kg / m ３ ) = 213.594.

[0103] 21 is a diagram illustrating an example of admittance characteristics of an elastic wave device according to the second embodiment. The comparative example shown in FIG. 21 is an elastic wave device in which the additional electrode 35 is not provided in elastic wave device 10C according to the second embodiment.

[0104] 21 , in elastic wave device 10C according to the second embodiment, additional electrodes 35 are provided on first electrode fingers 31a that are located outermost in the arrangement direction, and therefore, at least the ripple indicated by dotted line E1 is suppressed compared to the comparative example. Furthermore, in elastic wave device 10C according to the second embodiment, propagation loss is suppressed in the frequency range indicated by dotted line E2.

[0105] In the second embodiment, the additional electrode 35 is provided on the first electrode finger 31 a located outermost in the arrangement direction, but this is not limited to this. For example, a plurality of additional electrodes 35 may be provided on each of the first electrode fingers 31 a and the second electrode fingers 32 a. Alternatively, the additional electrode 35 may not be provided on the first electrode finger 31 a located outermost in the arrangement direction, but may be provided on the second electrode finger 32 a adjacent to the first electrode finger 31 a.

[0106] 20, the additional electrode 35 is provided to protrude from the upper surface of the first protective film 41, but this is not limited to this. The first protective film 41 may be provided to cover the additional electrode 35. The film thickness t1 of the first protective film 41 may be thicker than the height (the sum of the heights H1 and H2) of the stacked film of the first electrode fingers 31a and the additional electrode 35. The material of the additional electrode 35 is not limited to an aluminum-copper alloy, and may be, for example, at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum.

[0107] Fifth Modification of Second Embodiment FIG. 22 is a cross-sectional view showing an elastic wave device according to a fifth modification of the second embodiment. As shown in FIG. 22 , in an elastic wave device 10D according to the fifth modification, the additional electrode 35 is provided on the first protective film 41 in a region overlapping with the first electrode finger 31 a positioned outermost in the array direction. In other words, the first protective film 41 is provided between the first electrode finger 31 a and the additional electrode 35 in a direction perpendicular to the first main surface 20 a of the piezoelectric layer 20. The first electrode finger 31 a and the additional electrode 35 are electrically isolated by the first protective film 41. The top surface of the first protective film 41 is flat across the regions overlapping with the electrode fingers 31 and 32 and the regions not overlapping with the electrode fingers 31 and 32. The additional electrode 35 is provided to protrude from the top surface of the first protective film 41.

[0108] In the fifth modification, the electrode configuration and material of each of the first electrode fingers 31 a and the additional electrodes 35 are the same as those in the fourth modification. Even in a configuration in which the first electrode fingers 31 a and the additional electrodes 35 are spaced apart, the sum (Xe1 + Xe2) of the product Xe1 (= W1 × H1 × d1) of the first electrode fingers 31 a and the product Xe2 (= W2 × H2 × d2) of the additional electrodes 35 is larger than the product Xc (= Wc × Hc × dc) of the other electrode fingers (the second electrode fingers 32 a and the central electrode fingers 31 and 32) among the multiple electrode fingers 31 and 32.

[0109] In the fifth modification, the additional electrode 35 is provided on the first protective film 41 in a region overlapping with the first electrode finger 31 a located outermost in the arrangement direction, but this is not limiting. For example, a plurality of additional electrodes 35 may be provided on the first protective film 41 in regions overlapping with both the first electrode finger 31 a and the second electrode finger 32 a. Alternatively, the additional electrode 35 may not be provided in a region overlapping with the first electrode finger 31 a located outermost in the arrangement direction, but may be provided on the first protective film 41 in a region overlapping with the second electrode finger 32 a adjacent to the first electrode finger 31 a.

[0110] 23 is a cross-sectional view showing an elastic wave device according to a sixth modification of the second embodiment. As shown in FIG. 23 , in elastic wave device 10E according to the sixth modification, additional electrode 35 is provided on second main surface 20b of piezoelectric layer 20 in a region overlapping with first electrode fingers 31a located outermost in the arrangement direction. A second protective film 42 is provided on second main surface 20b of piezoelectric layer 20 to cover additional electrode 35. Additional electrode 35 is not provided on first main surface 20a of piezoelectric layer 20, and the upper surface of first protective film 41 is formed flat.

[0111] The first electrode fingers 31a are laminated films of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm. The height H1 (total film thickness) of the first electrode fingers 31a is 112 nm. The additional electrode 35 is a laminated film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm from the second main surface 20b side of the piezoelectric layer 20. The height H2 (film thickness) of the additional electrode 35 is 112 nm.

[0112] The width W2 of the additional electrode 35 is larger than the width W1 of the first electrode finger 31a. The width W1 of the first electrode finger 31a is 0.6 μm. The width W2 of the additional electrode 35 is 1.2 μm. The deviation Wx between the center in the width direction of the first electrode finger 31a (electrode center) and the center in the width direction of the additional electrode 35 (electrode center) is 0.2 μm. The density d2 of the additional electrode 35 is equal to the density d1 of the first electrode finger 31a.

[0113] The electrode configuration (width Wc, height Hc, density dc) of the other electrode fingers 31, 32 (second electrode finger 32a and central electrode fingers 31, 32) is the same as that of the first electrode finger 31a.

[0114] In the sixth modified example, even in a configuration in which the first electrode finger 31a is provided on the first main surface 20a of the piezoelectric layer 20 and the additional electrode 35 is provided on the second main surface 20b of the piezoelectric layer 20, the sum (Xe1 + Xe2) of the product Xe1 (= W1 × H1 × d1) of the first electrode finger 31a and the product Xe2 (= W2 × H2 × d2) of the additional electrode 35 is greater than the product Xc (= Wc × Hc × dc) of the other electrode fingers (the second electrode finger 32a and the central electrode fingers 31, 32) among the multiple electrode fingers 31, 32.

[0115] The sum (Xe1 + Xe2) of the area Xe1 (= W1 × H1 × d1) of the first electrode finger 31a and the area Xe2 (= W2 × H2 × d2) of the additional electrode 35 is: Xe1 + Xe2 = 0.6 (μm) × 0.03 (μm) × 4500 (kg / m ３ )+0.6(μm)×0.082(μm)×2695(kg / m ３ )+1.2(μm)×0.03(μm)×4500(kg / m ３ )+1.2(μm)×0.082(μm)×2695(kg / m ３ The product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 is Xc=0.6 (μm)×0.03 (μm)×4500 (kg / m ３ )+0.6(μm)×0.082(μm)×2695(kg / m ３ ) = 213.594.

[0116] 24 is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a sixth modified example of the second embodiment. As shown in FIG. 24 , elastic wave device 10E according to the sixth modified example has a configuration in which additional electrode 35 is provided on second main surface 20 b of piezoelectric layer 20, and yet at least the ripple indicated by dotted line E1 is suppressed compared to the comparative example. Furthermore, elastic wave device 10E according to the sixth modified example has suppressed propagation loss in the frequency range indicated by dotted line E2. Furthermore, in this embodiment, the top surface of first protective film 41 is formed flat, and thus the resonant frequency can be easily adjusted by changing the film thickness of first protective film 41.

[0117] In the sixth modification, the additional electrode 35 is provided on the second main surface 20b of the piezoelectric layer 20 in a region overlapping with the first electrode finger 31a located outermost in the arrangement direction, but this is not limiting. For example, a plurality of additional electrodes 35 may be provided on the second main surface 20b of the piezoelectric layer 20 in regions overlapping with both the first electrode finger 31a and the second electrode finger 32a. Alternatively, the additional electrode 35 may not be provided in a region overlapping with the first electrode finger 31a located outermost in the arrangement direction, but may be provided on the second main surface 20b of the piezoelectric layer 20 in a region overlapping with the second electrode finger 32a adjacent to the first electrode finger 31a.

[0118] The electrode configuration (width W2, height H2, density d2) of the additional electrode 35 and the offset Wx from the first electrode finger 31a are merely examples and can be changed as appropriate. For example, the additional electrode 35 is not limited to a configuration in which the width W2 is larger than the width W1 of the first electrode finger 31a. The width W2, height H2, and density d2 of the additional electrode 35 may be equal to the width W1, height H1, and density d1 of the first electrode finger 31a. Alternatively, the offset Wx between the additional electrode 35 and the first electrode finger 31a may be 0 (zero). The additional electrode 35 is not limited to a laminated film and may be a multilayer film, or may be formed of a material having a density different from that of the first electrode finger 31a.

[0119] Fig. 25 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a sixth modified example of the second embodiment. Fig. 26 is a diagram illustrating the distribution of vibration modes of an elastic wave device according to a comparative example. The comparative example shown in Fig. 26 is configured such that additional electrode 35 is not provided in elastic wave device 10E according to the sixth modified example.

[0120] 25 and 26 show the distribution of the magnitude of displacement of piezoelectric layer 20 for the sixth modification and the comparative example, with the horizontal axis representing the X direction (the arrangement direction of electrode fingers 31 and 32) and the vertical axis representing frequency. The upper diagrams of Fig. 25 and Fig. 26 each show a schematic cross-sectional view of an elastic wave device corresponding to the X direction, and the left diagrams of Fig. 25 and Fig. 26 show the impedance characteristics of the elastic wave device.

[0121] As shown in Figure 26, 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.

[0122] In contrast, as shown in FIG. 25 , in the elastic wave device 10E according to the sixth modification, the X-direction dependence of the displacement (the X-direction positions of the antinodes and nodes of the displacement) does not depend on the frequency. That is, the X-direction positions indicating the peak displacement are constant regardless of frequency, indicating stable excitation between the electrodes. Furthermore, the magnitude (amplitude) of the displacement is also constant for each region between the electrodes, and no phase inversion occurs in the frequency arrangement where the resonant frequency and ripples occur. Thus, by providing the additional electrodes 35 in the regions overlapping with the first electrode fingers 31 a positioned at the outermost positions in the arrangement direction, a better excitation mode can be obtained than in the comparative example.

[0123] 27 is a cross-sectional view showing an elastic wave device according to a seventh modification of the second embodiment. As shown in FIG. 27 , in elastic wave device 10F according to the seventh modification, additional electrode 35 is provided on the second main surface 20b of piezoelectric layer 20 in a region overlapping with first electrode fingers 31a positioned outermost in the arrangement direction. More specifically, additional electrode 35 faces second main surface 20b of piezoelectric layer 20 and is provided at a distance from second main surface 20b.

[0124] The additional electrode 35 is disposed in the second protective film 42. That is, the second protective film 42 is provided between the second main surface 20b of the piezoelectric layer 20 and the additional electrode 35, and covers the side and bottom surfaces of the additional electrode 35 (surfaces opposite to the piezoelectric layer 20).

[0125] In the seventh modification, the electrode configuration of the first electrode finger 31 a and the additional electrode 35 can be the same as that of the sixth modification. That is, also in the seventh modification, the sum (Xe1 + Xe2) of the product Xe1 (= W1 × H1 × d1) of the first electrode finger 31 a and the product Xe2 (= W2 × H2 × d2) of the additional electrode 35 is larger than the product Xc (= Wc × Hc × dc) of the other electrode fingers (the second electrode finger 32 a and the central electrode fingers 31 and 32) among the multiple electrode fingers 31 and 32.

[0126] 28 is a cross-sectional view showing an elastic wave device according to an eighth modification of the second embodiment. As shown in FIG. 28 , in elastic wave device 10G according to the eighth modification, additional electrode 35 is provided on the lower surface of second protective film 42 in a region overlapping with first electrode fingers 31 a positioned outermost in the array direction. The lower surface of second protective film 42 is formed flat along second main surface 20 b of piezoelectric layer 20. Additional electrode 35 is provided to protrude from the lower surface of second protective film 42. The lower surface of second protective film 42 refers to the surface of second protective film 42 that faces support substrate 11 (see FIG. 2 ).

[0127] In the eighth modification, the electrode configuration of the first electrode finger 31 a and the additional electrode 35 can be the same as that of the sixth and seventh modifications. That is, also in the eighth modification, the sum (Xe1 + Xe2) of the product Xe1 (= W1 × H1 × d1) of the first electrode finger 31 a and the product Xe2 (= W2 × H2 × d2) of the additional electrode 35 is larger than the product Xc (= Wc × Hc × dc) of the other electrode fingers (the second electrode finger 32 a and the central electrode fingers 31, 32) among the multiple electrode fingers 31, 32.

[0128] In the seventh and eighth modifications, the additional electrode 35 is provided in a region overlapping with the first electrode finger 31 a located outermost in the arrangement direction, but this is not limiting. For example, a plurality of additional electrodes 35 may be provided in the second protective film 42 or on the lower surface of the second protective film 42 in regions overlapping with the first electrode finger 31 a and the second electrode finger 32 a. Alternatively, the additional electrode 35 may not be provided in a region overlapping with the first electrode finger 31 a located outermost in the arrangement direction, but may be provided in the second protective film 42 or on the lower surface of the second protective film 42 in a region overlapping with the second electrode finger 32 a adjacent to the first electrode finger 31 a.

[0129] In the seventh and eighth modifications, the electrode configuration (width W2, height H2, density d2) of the additional electrode 35, the offset Wx from the first electrode finger 31a, and the like are merely examples and can be changed as appropriate. For example, the configuration is not limited to one in which the width W2 of the additional electrode 35 is larger than the width W1 of the first electrode finger 31a. The width W2, height H2, and density d2 of the additional electrode 35 may be equal to the width W1, height H1, and density d1 of the first electrode finger 31a. Alternatively, the additional electrode 35 is not limited to a laminated film and may be a multilayer film. Alternatively, the additional electrode 35 may be formed of a material having a density different from that of the first electrode finger 31a.

[0130] Third Embodiment Fig. 29 is a circuit diagram showing an elastic wave device according to a third embodiment. As shown in Fig. 29, an elastic wave device 10H according to the third embodiment includes multiple series arm resonators 61, 62, and 63 and multiple parallel arm resonators 64, 65, 66, and 67. The multiple 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 multiple 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. An elastic wave device 10H according to the ninth embodiment is a so-called ladder filter.

[0131] 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.

[0132] In this embodiment, different electrode configurations are employed for the first electrode fingers 31 a and second electrode fingers 32 a located on the outside in the arrangement direction between the plurality of series arm resonators 61, 62, and 63 and the plurality of parallel arm resonators 64, 65, 66, and 67. For example, the plurality of series arm resonators 61, 62, and 63 have the first electrode fingers 31 a 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.

[0133] On the other hand, the parallel arm resonators 64, 65, 66, and 67 have the first electrode fingers 31a and the additional electrodes 35 shown in the second embodiment (see FIGS. 20 and 21). The admittance characteristics of the parallel arm resonators 64, 65, 66, and 67 are the same as those shown in FIG. 21, and therefore repeated description will be omitted.

[0134] In this embodiment, by changing the configurations of the first electrode fingers 31 a, the second electrode fingers 32 a, and the additional electrodes 35 between the multiple series arm resonators 61, 62, and 63 and the multiple parallel arm resonators 64, 65, 66, and 67, it is possible to obtain a better output waveform as a filter.

[0135] In the elastic wave device 10H according to the third embodiment, the electrode configuration of the first electrode fingers 31 a and the second electrode fingers 32 a shown in the first embodiment and the electrode configuration of the additional electrode 35 shown in the second embodiment are combined, but the present invention is not limited to this. The third embodiment can be combined with the above-described embodiments and modified examples.

[0136] 30 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 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.

[0137] 30 , in an elastic wave device 10I according to the ninth modification, an acoustic multilayer film 43 is laminated on the second principal surface 20b of a piezoelectric layer 20. The acoustic multilayer film 43 has a laminate structure of 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 portion 14.

[0138] In acoustic wave device 10I, by setting d / p to 0.5 or less, resonance characteristics based on bulk waves in the first thickness-shear mode can be obtained. Note that the number of stacked low acoustic impedance layers 43a, 43c, and 43e and high acoustic impedance layers 43b and 43d in acoustic multilayer film 43 is not particularly limited. It is sufficient that at least one high acoustic impedance layer 43b or 43d is located farther from piezoelectric layer 20 than low acoustic impedance layers 43a, 43c, and 43e.

[0139] 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.

[0140] 30 can be combined with the electrode configuration of the first electrode fingers 31 a shown in the first embodiment. However, without being limited to this, the ninth modification can be combined with each of the above-described embodiments and modifications.

[0141] 31 is a cross-sectional view of an elastic wave device according to a tenth 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, the present invention is not limited to this. As shown in FIG. 31 , an elastic wave device 10J according to the tenth 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 ).

[0142] The electrode fingers 36 and 37 of the second IDT electrode 30B are provided in an area overlapping the electrode fingers 31 and 32 of the first IDT electrode 30A. The electrode fingers 36 and 37 of the second IDT electrode 30B are provided with the same width and the same inter-electrode pitch as the electrode fingers 31 and 32 of the first IDT electrode 30A. Also, in the tenth modification, as in the first embodiment, at least one of the first electrode fingers 31 a and the second electrode fingers 32 a of the first IDT electrode 30A is formed of a material with a higher density than the other central electrode fingers 31 and 32. At least one of the first electrode fingers 36 a and the second electrode fingers 37 a of the second IDT electrode 30B is formed of a material with a higher density than the other central electrode fingers 36 and 37.

[0143] In the tenth modification, the first IDT electrode 30A and the second IDT electrode 30B are provided on the first principal surface 20a and the second principal surface 20b of the piezoelectric layer 20, respectively, so that the temperature coefficient of frequency (TCF) can be improved.

[0144] The tenth modification can be combined with the above-described embodiments and modifications. For example, in the tenth modification, an additional electrode 35 may be provided on at least one of the first main surface 20 a and the second main surface 20 b of the piezoelectric layer 20.

[0145] 32 is a plan view illustrating an elastic wave device according to an eleventh modification. Elastic wave device 10K according to the eleventh modification differs from the first embodiment in that, in at least a portion of the extension direction of first electrode fingers 31 a, the product Xe (= W1 × H1 × d1) of width W1, height H1, and density d1 is larger than the product Xc (= Wc × Hc × dc) of width Wc, height Hc, and density dc of central electrode fingers 31, 32 that are different from first electrode fingers 31 a and second electrode fingers 32 a among multiple electrode fingers 31, 32. Even in this case, as with the first embodiment, ripple in the admittance characteristics can be suppressed compared to the comparative example.

[0146] More specifically, the first electrode finger 31a includes a first portion 31aA and a second portion 31aB. The second portion 31aB is connected to an end of the first portion 31aA in the extending direction.

[0147] The product Xe (= W1 × H1 × d1) of the width W1, height H1, and density d1 of the first portion 31aA of the first electrode finger 31a is greater than the product Xc (= Wc × Hc × dc) of the width Wc, height Hc, and density dc of the central electrode finger 31, 32, which is different from the first electrode finger 31a and the second electrode finger 32a, among the multiple electrode fingers 31, 32.

[0148] The width W1 of the second portion 31aB is smaller than the width W1 of the first portion 31aA. Furthermore, the product Xe (=W1×H1×d1) of the width W1, height H1, and density d1 of the second portion 31aB is smaller than the product Xe (=W1×H1×d1) of the width W1, height H1, and density d1 of the first portion 31aA.

[0149] Similarly, the fourth electrode finger 32b, which is located on the opposite side of the first electrode finger 31a in the arrangement direction of the electrode fingers 31 and 32, also includes a first portion 32bA and a second portion 32bB. That is, in at least a part (first portion 32bA) of the fourth electrode finger 32b in the extension direction, the product Xe (=W1×H1×d1) of the width W1, the height H1, and the density d1 is larger than the product Xc (=Wc×Hc×dc) of the width Wc, the height Hc, and the density dc of the central electrode finger 31 and 32, which is different from the third electrode finger 31b and the fourth electrode finger 32d, among the electrode fingers 31 and 32.

[0150] (Twelfth Modification) Fig. 33 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to a twelfth modification. Fig. 34 is an explanatory diagram showing an example of the impedance phase in S2 mode. The elastic wave device according to the twelfth modification shown in Fig. 33 has a configuration in which the first protective film 41 and the second protective film 42 have different thicknesses in elastic wave device 10 according to the first embodiment.

[0151] 33 shows the frequency characteristics of the absolute value of admittance for the elastic wave device according to Modification 12. As shown in Fig. 33 , in the elastic wave device according to Modification 12, a higher-order mode of resonance (hereinafter referred to as "S2 mode") occurs in a frequency region indicated by a dashed dotted line F1 that is different from the resonant frequency.

[0152] The horizontal axis of the graph shown in Fig. 34 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. 34 corresponds to the intensity of the S2 mode.

[0153] 34, the range indicated by arrows F2 and F3 indicates the ratio (t1 + tLN / 2) / (t2 + tLN / 2) in the configuration of the acoustic resonator described in JP-T-2022-524136. In the acoustic resonator described in JP-T-2022-524136, the ratio (t1 + tLN / 2) / (t2 + tLN / 2) is 0.93 or less and 1.07 or more, and the intensity of the S2 mode is large.

[0154] In contrast, in the twelfth 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, when the total distance from the center of the thickness of the piezoelectric layer 20 to the top surface of the first protective film 41 is A and the total distance from the center of the thickness of the piezoelectric layer 20 to the top surface of the second protective film 42 is B, it is preferable that the value of A / B be in the range of 1-0.06 to 1+0.06, inclusive.

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

[0156] 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.

[0157] The present disclosure may also have the following configurations.

[0158] (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; and a support member facing the second main surface of the piezoelectric layer and having an acoustic reflector on the second main surface side of the piezoelectric layer, wherein the plurality of electrode fingers include a first electrode finger positioned outermost in the arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the first electrode finger; a product of a width, a height, and a density of at least one of the first electrode finger and the second electrode finger is greater than a product of a width, a height, and a density of a central electrode finger of the plurality of electrode fingers different from the first electrode finger and the second electrode finger; and wherein d / p is 0.5 or less, where d is a thickness of the piezoelectric layer and p is a center-to-center distance between adjacent electrode fingers. (2) The elastic wave device according to (1), further comprising a protective film provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer. (3) The elastic wave device according to (1) or (2), wherein at least one of the first electrode fingers and the second electrode fingers is formed of a material having a higher density than the central electrode fingers. (4) The elastic wave device according to (1) or (2), wherein the height of at least one of the first electrode fingers and the second electrode fingers is greater than the height of the central electrode fingers.(5) A piezoelectric element comprising: a piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction; an IDT electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer, the IDT electrode including a plurality of electrode fingers arranged in a predetermined direction; a support member facing the second main surface of the piezoelectric layer and having an acoustic reflector on the second main surface side of the piezoelectric layer; and an additional electrode provided in an area overlapping at least one of the first electrode finger and the second electrode finger, when the electrode finger located outermost in the arrangement direction of the plurality of electrode fingers is defined as a first electrode finger and the electrode finger adjacent to the first electrode finger is defined as a second electrode finger, wherein the sum of the product of the width, height and density of at least one of the first electrode finger and the second electrode finger and the product of the width, height and density of the additional electrode is greater than the product of the width, height and density of a central electrode finger of the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger, An acoustic wave device in which 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. (6) The acoustic wave device according to (5), which includes a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer. (7) The acoustic wave device according to (5) or (6), in which the additional electrode is provided in contact with at least one of the first electrode finger and the second electrode finger. (8) The acoustic wave device according to (6), in which 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 additional electrode is provided on the first protective film in a region overlapping with at least one of the first electrode finger and the second electrode finger. (9) The acoustic wave device according to (5), in which the additional electrode is provided on the second main surface of the piezoelectric layer in a region overlapping with at least one of the first electrode finger and the second electrode finger. (10) The acoustic wave device according to any one of (1) to (9), wherein the material of the electrode fingers of the IDT electrode is at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum. (11) The acoustic wave device according to any one of (5) to (9), wherein the material of the additional electrode is at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum.(12) The elastic wave device according to (2) or (6), wherein the protective film has a thickness smaller than that of the plurality of electrode fingers. (13) The elastic wave device according to any one of (1) to (12), wherein the IDT electrodes are provided on both the first principal surface and the second principal surface of the piezoelectric layer. (14) An elastic wave filter device including at least one resonator connected thereto, wherein the resonator is the elastic wave device according to any one of (1) to (4). (15) The elastic wave filter device according to (14), comprising: an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting a node of the series arm and ground, 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 a material of at least one of the first electrode finger and the second electrode finger of the series arm resonator is different from a material of at least one of the first electrode finger and the second electrode finger of the parallel arm resonator. (16) An elastic wave filter device including at least one resonator connected, wherein the resonator is the elastic wave device according to any one of (5) to (9). (17) The elastic wave filter device according to (16), comprising an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting a node of the series arm and ground, wherein the at least one resonator is a plurality of resonators including a series arm resonator provided in the series arm and a parallel arm resonator provided in the parallel arm, and the additional electrode of the series arm resonator has a different configuration from the additional electrode of the parallel arm resonator. (18) The elastic wave device according to (2) or (6), wherein the protective film is formed of silicon oxide. (19) The elastic wave device according to any one of (1) to (13) and (18), wherein the piezoelectric layer includes lithium niobate or lithium tantalate and has a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut. (20) The elastic wave device according to (2) or (6), wherein the protective film includes a first protective film provided on the first main surface of the piezoelectric layer and covering the IDT electrode, and a second protective film provided on the second main surface of the piezoelectric layer.(21) The elastic wave device according to (2) or (6), 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), in which, 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, a value of A / B is 1-0.06 or more and 1+0.06 or less. (23) The elastic wave device according to (20) or (22), in which the top surface of the first protective film and the bottom surface of the second protective film are formed flat. (24) The elastic wave device according to any one of (1) to (13) and (18) to (23), in which d / p is 0.24 or less. (25) The acoustic wave device according to any one of (1) to (13) and (18) to (24), wherein an excitation region is a region where adjacent electrode fingers overlap each other when viewed in the electrode finger orthogonal direction and a region between the centers of the adjacent electrode fingers in the electrode finger orthogonal direction, and wherein MR≦1.75(d / p)+0.075 is satisfied, where MR is a metallization ratio of the electrode fingers to the excitation region. (26) The acoustic wave device according to any one of (1) to (13) and (18) to (25), wherein the piezoelectric layer is made of lithium tantalate or lithium niobate. (27) The acoustic wave device according to any one of (1) to (13) and (18) to (26), wherein 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) ...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) (28) The elastic wave device according to any one of (1) to (13) and (18) to (27), wherein the acoustic reflecting portion is a cavity, and the support member and the piezoelectric layer are arranged so that a part of the support member and a part of the piezoelectric layer face each other with the cavity in between. (29) The elastic wave device according to any one of (1) to (13) and (18) to (28), wherein the acoustic reflecting portion is an acoustic reflecting film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged so that at least a part of the support member and at least a part of the piezoelectric layer face each other with the acoustic reflecting film in between.

[0159] REFERENCE SIGNS LIST 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10I, 10J Acoustic wave device 11 Support substrate 12 Bottom portion 13 Wall portion 14 Cavity portion 20, 201 Piezoelectric layer 20a, 201a First principal surface 20b, 201b Second principal surface 30 IDT electrodes 31, 32 Electrode fingers 31a First electrode finger 31b Third electrode finger 32a Second electrode finger 32b Fourth electrode finger 33, 34 Bus bar electrodes 35 Additional electrode 41 First protective film 42 Second protective film

Claims

1. An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction; an IDT electrode provided on at least one of the first and second main surfaces of the piezoelectric layer, the IDT electrode including a plurality of electrode fingers arranged in a predetermined direction; and a support member facing the second main surface of the piezoelectric layer and having an acoustic reflecting portion on the second main surface side of the piezoelectric layer, the plurality of electrode fingers including a first electrode finger positioned outermost in the arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the first electrode finger, the product of the width, height and density of at least one of the first electrode finger and the second electrode finger is greater than the product of the width, height and density of a central electrode finger of the plurality of electrode fingers different from the first electrode finger and the second electrode finger, and where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers, d / p is 0.5 or less.

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

3. An elastic wave device according to claim 1 or 2, wherein at least one of the first electrode finger and the second electrode finger is formed from a material having a higher density than the central electrode finger.

4. The elastic wave device according to claim 1 or 2, wherein the height of at least one of the first electrode finger and the second electrode finger is greater than the height of the electrode finger in the central portion.

5. A piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction; an IDT electrode provided on at least one of the first and second main surfaces of the piezoelectric layer, the IDT electrode including a plurality of electrode fingers arranged in a predetermined direction; a support member facing the second main surface of the piezoelectric layer and having an acoustic reflector on the second main surface side of the piezoelectric layer; and an additional electrode provided in an area overlapping at least one of the first and second electrode fingers, when the electrode finger located outermost in the arrangement direction of the plurality of electrode fingers is defined as a first electrode finger and the electrode finger adjacent to the first electrode finger is defined as a second electrode finger, wherein the sum of the product of the width, height and density of at least one of the first and second electrode fingers and the product of the width, height and density of the additional electrode is greater than the product of the width, height and density of a central electrode finger different from the first and second electrode fingers among the plurality of electrode fingers, The acoustic wave device, 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.

6. The acoustic wave device according to claim 5, further comprising a protective film provided on at least one of the first main surface and the second main surface of the piezoelectric layer.

7. The acoustic wave device according to claim 5 or 6, wherein the additional electrode is provided on and in contact with at least one of the first electrode fingers and the second electrode fingers.

8. The elastic wave device of claim 6, 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 additional electrode is provided on the first protective film in a region overlapping at least one of the first electrode fingers and the second electrode fingers.

9. The acoustic wave device according to claim 5, wherein the additional electrode is provided on the second main surface of the piezoelectric layer in a region overlapping with at least one of the first electrode fingers and the second electrode fingers.

10. The elastic wave device according to any one of claims 1 to 9, wherein the material of the plurality of electrode fingers of the IDT electrode is at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum.

11. The elastic wave device according to any one of claims 5 to 9, wherein the additional electrode is made of at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum.

12. The acoustic wave device according to claim 2 or 6, wherein the protective film has a thickness smaller than a thickness of the plurality of electrode fingers.

13. 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.

14. An elastic wave filter device comprising at least one connected resonator, the resonator being an elastic wave device according to any one of claims 1 to 4.

15. An elastic wave filter device as described in claim 14, comprising an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting a node of the series arm and ground, wherein the at least one resonator is a plurality of resonators including a series arm resonator provided in the series arm and a parallel arm resonator provided in the parallel arm, and a material of at least one of the first electrode fingers and the second electrode fingers of the series arm resonator is different from a material of at least one of the first electrode fingers and the second electrode fingers of the parallel arm resonator.

16. 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 5 to 9.

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

18. The acoustic wave device according to claim 2 or claim 6, wherein the protective film is made of silicon oxide.

19. The elastic wave device according to any one of claims 1 to 13 and claim 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 or claim 6, 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 or 6, 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 or 22, 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 13 and claims 18 to 23, wherein d / p is 0.24 or less.

25. An elastic wave device as claimed in any one of claims 1 to 13 and claims 18 to 24, wherein, when viewed from the electrode finger orthogonal direction, the region where adjacent electrode fingers overlap each other and the region between the centers of adjacent electrode fingers in the electrode finger orthogonal direction is an excitation region, and when the metallization ratio of the electrode fingers to the excitation region is MR, MR satisfies MR≦1.75(d / p)+0.

075.

26. The elastic wave device according to any one of claims 1 to 13 and claims 18 to 25, wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.

27. The elastic wave device according to any one of claims 1 to 13 and claims 18 to 26, wherein the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3): (0°±10°, 0° to 20°, any ψ) ... formula (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60°(1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] ~ 180°, any ψ) ... Equation (3) 28. An elastic wave device as claimed in any one of claims 1 to 13 and claims 18 to 27, wherein the acoustic reflection portion is a hollow portion, and the support member and the piezoelectric layer are arranged so that a part of the support member and a part of the piezoelectric layer face each other across the hollow portion.

29. An elastic wave device as claimed in any one of claims 1 to 13 and claims 18 to 28, wherein the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged 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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