Elastic wave device

Abstract

The present invention provides an elastic wave device that improves resonance characteristics. The elastic wave device is provided with a piezoelectric layer having a first main surface and a second main surface, an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer, a dielectric layer provided on at least one of the first main surface and the second main surface of the piezoelectric layer, and a support member provided on the second main surface side of the piezoelectric layer. The electrode is an IDT electrode including a first bus bar and a second bus bar opposing each other, a plurality of first electrode fingers of which the basal ends are connected to the first bus bar, and a plurality of second electrode fingers of which the basal ends are connected to the second bus bar. Regions overlapping each other as viewed in a second direction in which adjacent first and second electrode fingers oppose each other are defined as intersection regions. Regions obtained by dividing the intersection region in each of a pair of the adjacent first and second electrode fingers are defined as partial intersection regions. In the intersection regions, there is at least one partial intersection region in which the thickness of the piezoelectric layer is different from that in another partial intersection region.

Description

Elastic Wave Device

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

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

[0003] U.S. Patent No. 11,349,450 International Publication No. 2021 / 060523

[0004] The acoustic wave devices disclosed in Patent Documents 1 and 2 have the possibility of generating unwanted waves because the thickness of the piezoelectric layer is uniform.

[0005] An object of the present invention is to provide an acoustic wave device that can improve resonance characteristics.

[0006] An elastic wave device according to one aspect includes: a piezoelectric layer having a first main surface and a second main surface opposite to the first main surface in a first direction; an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer; a dielectric layer provided on at least one of the first main surface and the second main surface of the piezoelectric layer; and a support member provided on the second main surface side of the piezoelectric layer, the support member having an acoustic reflector on the second main surface side of the piezoelectric layer, the support member including a first bus bar and a second bus bar that face each other. The IDT electrode includes a plurality of first electrode fingers whose base ends are connected to the first bus bar and a plurality of second electrode fingers whose base ends are connected to the second bus bar, and when an area where adjacent first electrode fingers and second electrode fingers overlap when viewed in a second direction in which they face each other is defined as an intersection area, and an area obtained by dividing the intersection area for each pair of adjacent first electrode fingers and second electrode fingers is defined as a partial intersection area, there is at least one partial intersection area in which the thickness of the piezoelectric layer is different from that of other partial intersection areas.

[0007] According to the acoustic wave device of the present invention, the resonance characteristics can be improved.

[0008] 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 an enlarged cross-sectional view of an intersection region CA shown in FIG. 2 . FIG. 4 is a schematic cross-sectional view illustrating a bulk wave in a thickness-shear first-order mode propagating through a piezoelectric layer according to the first embodiment. FIG. 5 is a schematic cross-sectional view illustrating the amplitude direction of a bulk wave in a thickness-shear first-order mode propagating through a piezoelectric layer according to the first embodiment. FIG. 6 is a diagram illustrating an example of the resonance characteristics of the elastic wave device according to the first embodiment. FIG. 7 is a diagram illustrating 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 distance between the centers of adjacent electrodes and d is the average thickness of the piezoelectric layer. 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 a diagram illustrating 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. 10 is a diagram showing the relationship between d / 2p, metallization ratio MR, and fractional bandwidth. ３FIG. 12 is an explanatory diagram illustrating a map of fractional bandwidths versus Euler angles (0°, θ, ψ). FIG. 12 is an enlarged cross-sectional view of an elastic wave device according to Comparative Example 1. FIG. 13A is a diagram illustrating the resonance characteristics of an elastic wave device according to an example. FIG. 13B is a diagram illustrating the resonance characteristics of an elastic wave device according to an example. FIG. 14A is a diagram illustrating the resonance characteristics of an elastic wave device according to Comparative Example 1. FIG. 14B is a diagram illustrating the resonance characteristics of an elastic wave device according to Comparative Example 1. FIG. 15A is a diagram illustrating the rd dependence of the resonance characteristics of an elastic wave device according to an example. FIG. 15B is a diagram illustrating the rd dependence of the resonance characteristics of an elastic wave device according to an example. FIG. 15C is a diagram illustrating the rd dependence of the resonance characteristics of an elastic wave device according to an example. FIG. 16 is an enlarged cross-sectional view of an elastic wave device according to Comparative Example 2. FIG. 17A is a diagram illustrating the resonance characteristics of an elastic wave device according to an example. FIG. 17B is a diagram illustrating the resonance characteristics of an elastic wave device according to an example. FIG. 17C is a diagram illustrating the resonance characteristics of an elastic wave device according to an example. FIG. 18A is a diagram illustrating the resonance characteristics of an elastic wave device according to Comparative Example 2. Fig. 18B is a diagram showing the resonance characteristics of an elastic wave device in accordance with Comparative Example 2. Fig. 18C is a diagram showing the resonance characteristics of an elastic wave device in accordance with Comparative Example 2. Fig. 19 is an enlarged cross-sectional view of an elastic wave device in accordance with a second preferred embodiment of the present invention. Fig. 20 is an enlarged cross-sectional view of an elastic wave device in accordance with a third preferred embodiment of the present invention. Fig. 21 is a cross-sectional view of an elastic wave device in accordance with a fourth preferred embodiment of the present invention.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments. Note that each embodiment described in the present disclosure is illustrative, and partial substitution or combination of configurations between different embodiments is possible. In modified examples and the second and subsequent embodiments, descriptions 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.

[0010] 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. Fig. 3 is an enlarged cross-sectional view of an intersection region CA shown in Fig. 2. Note that in Fig. 1, a first dielectric layer 41 is indicated by a two-dot chain line for ease of viewing.

[0011] 1 and 2 , the elastic wave device according to the first embodiment includes a piezoelectric layer 20, an IDT electrode 30 (electrode), a support substrate 11 (support member), a first dielectric layer 41, and a second dielectric layer 42. As shown in Fig. 2 , the elastic wave device 10 includes the second dielectric layer 42, the piezoelectric layer 20, the first dielectric layer 41, and the IDT electrode 30 stacked in this order on the support substrate 11.

[0012] The piezoelectric layer 20 is in the form of a flat plate having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is made of lithium niobate (LiNbO ３ Alternatively, the piezoelectric layer 20 may be made of lithium tantalate (LiTaO ３ ) may be made of LiNbO ３ and LiTaO ３ In the first embodiment, the cut angle is a Z-cut. ３ and LiTaO ３ The cut angle may be a rotated Y cut or an X cut. Preferably, the propagation direction is Y propagation or X propagation ±30°. Preferably, the piezoelectric layer 20 is made of lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ ) and is a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut.

[0013] In the first embodiment, the thickness of the piezoelectric layer 20 is not constant and varies depending on the position in the X direction. The thickness of the piezoelectric layer 20 will be described in detail later.

[0014] The support substrate 11 (support member) is disposed opposite the second principal surface 20b of the piezoelectric layer 20. The support substrate 11 has a recess 14 (energy trapping portion) that opens toward the second principal surface 20b of the piezoelectric layer 20. More specifically, the support substrate 11 has a bottom 12 and a wall portion 13 that is provided in a frame shape on the upper surface of the bottom 12. The recess 14 is formed in the space surrounded by the bottom 12 and the wall portion 13. The recess 14 is also referred to as a cavity portion or hollow portion. The piezoelectric layer 20 is stacked on the upper surface of the wall portion 13 of the support substrate 11. At least a portion of the piezoelectric layer 20 is disposed on the recess 14 (energy trapping portion) in a planar view. In this manner, the acoustic wave device 10 has a so-called membrane structure in which the recess 14 is provided on the second principal surface 20b of the piezoelectric layer 20. In this embodiment, the recess 14 (energy trapping portion) is an acoustic reflecting portion. In the example of FIG. 2, the support substrate 11 is in direct contact with the second main surface 20b of the piezoelectric layer 20 at the peripheral edge portion where the recess 14 is not provided.

[0015] The support member may include a support substrate 11 and an intermediate (insulating) layer. The piezoelectric layer 20 is bonded to the support substrate 11 directly or via the intermediate (insulating) layer. The recess 14 may be formed in the intermediate (insulating) layer. In this case, the support substrate 11 and the intermediate layer may have a frame-like shape, thereby forming the recess 14. Alternatively, the recess 14 may be formed in the intermediate layer.

[0016] The support substrate 11 is made of silicon (Si). The surface of the Si facing the piezoelectric layer 20 may have a (100), (110), or (111) plane orientation. Preferably, Si has a high resistivity of 4 kΩ or more. However, the support substrate 11 may also be made of an appropriate insulating material or semiconductor material. Examples of materials that can be used for the support substrate 11 include piezoelectric materials such as aluminum oxide, lithium tantalate, lithium niobate, and quartz; various ceramics such as alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectric materials such as diamond and glass; and semiconductors such as gallium nitride.

[0017] 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 first electrode fingers 31, second electrode fingers 32, first bus bar electrodes 33, and second bus bar electrodes 34. The first electrode fingers 31 extend in the Y direction, and one end of each electrode finger in the extension direction is connected to the first bus bar electrode 33. The second electrode fingers 32 extend in the Y direction, and the other end of each electrode finger in the extension direction is connected to the second bus bar electrode 34. The first electrode fingers 31 and the second electrode fingers 32 are alternately arranged in the X direction with a gap therebetween. The first bus bar electrodes 33 and the second bus bar electrodes 34 each extend in the X direction and are arranged opposite each other in the Y direction. A plurality of first electrode fingers 31 and a plurality of second electrode fingers 32 are arranged between the first bus bar electrode 33 and the second bus bar electrode 34 .

[0018] The IDT electrode 30 is not limited to a configuration having a plurality of first electrode fingers 31 and a plurality of second electrode fingers 32, but may also be configured to include at least one first electrode finger 31 whose base end is connected to a first busbar electrode 33 and at least one second electrode finger 32 whose base end is connected to a second busbar electrode 34.

[0019] In the following description, the thickness direction of the piezoelectric layer 20 may be referred to as the Z direction or first direction, the extension direction of the first electrode fingers 31 and the second electrode fingers 32 as the Y direction, and the arrangement direction of the first electrode fingers 31 and the second electrode fingers 32 as the X direction or second 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. In the Z direction, the direction from the support substrate 11 toward the outermost IDT electrode 30 is referred to as up or upward, and the direction from the IDT electrode 30 toward the support substrate 11 is referred to as down or downward.

[0020] The center-to-center distance between the first electrode finger 31 and the second electrode finger 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 first electrode finger 31 in a direction perpendicular to the extension direction of the first electrode finger 31 and the center of the width of the second electrode finger 32 in a direction perpendicular to the extension direction of the second electrode finger 32. The widths of the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the electrode width), i.e., the dimensions in the direction perpendicular to the extension direction of the first electrode finger 31 and the second electrode finger 32, are preferably in the range of 150 nm to 1000 nm.

[0021] Furthermore, when there are multiple first electrode fingers 31 and multiple second electrode fingers 32 (when the first electrode fingers 31 and the second electrode fingers 32 are considered as a pair of electrodes, there are 1.5 or more pairs of electrodes), the inter-electrode pitch of the first electrode fingers 31 and the second electrode fingers 32 refers to the average value of the center-to-center distances of adjacent first electrode fingers 31 and second electrode fingers 32 among the 1.5 or more pairs of first electrode fingers 31 and second electrode fingers 32.

[0022] Furthermore, in the first embodiment, since a Z-cut piezoelectric layer is used, the direction perpendicular to the extension direction of the first electrode fingers 31 and the second electrode fingers 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 first electrode fingers 31 and the second electrode fingers 32 and the polarization direction is, for example, 90°±10°).

[0023] The IDT electrode 30 (first electrode fingers 31, second electrode fingers 32, first busbar electrodes 33, and second busbar electrodes 34) is made of an appropriate metal or alloy such as Al or an AlCu alloy. In the first embodiment, the IDT electrode 30 has a structure in which an Al film is laminated on a titanium (Ti) film. Note that an adhesion layer other than a Ti film may also be used.

[0024] 1 is a region where the first electrode fingers 31 and the second electrode fingers 32 overlap when viewed in the X direction. The length of the intersection region CA is the dimension in the extension direction of the first electrode fingers 31 and the second electrode fingers 32 in the intersection region CA. In this embodiment, the length of the intersection region CA is, for example, 40 μm.

[0025] During operation, an AC voltage is applied between the plurality of first electrode fingers 31 and the plurality of second electrode fingers 32. More specifically, an AC voltage is applied between the first bus bar electrode 33 and the second bus bar electrode 34. This makes it possible to obtain resonance characteristics utilizing 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 first electrode fingers 31 and second electrode fingers 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] The elastic wave device 10 according to the first embodiment has the above-described configuration, which reduces propagation loss and makes it difficult for the Q value to decrease even if the number of pairs of the first electrode fingers 31 and the second electrode fingers 32 is reduced in an attempt to reduce the device size. This is because the device utilizes bulk waves in the thickness-shear first-order mode.

[0028] 2 and 3 , the first dielectric layer 41 is provided on the first main surface 20 a of the piezoelectric layer 20. The IDT electrode 30 is provided on the first dielectric layer 41. That is, in the Z direction, the first dielectric layer 41 is provided between the first main surface 20 a of the piezoelectric layer 20 and the IDT electrode 30.

[0029] The first dielectric layer 41 is made of silicon oxide (SiO ２ ), silicon nitride (Si ３ N ４ ), aluminum nitride (AlN), aluminum oxide (Al ２ O ３ ), tantalum oxide (Ta２ O ５ ), niobium oxide (Nb ２ O ５ ) at least one of the following.

[0030] In the first embodiment, the thickness of the first dielectric layer 41 is not constant and varies depending on the position in the X direction. The thickness of the first dielectric layer 41 will be described in detail later.

[0031] As shown in FIGS. 2 and 3, the second dielectric layer 42 is provided on the second major surface 20 b of the piezoelectric layer 20 .

[0032] The second dielectric layer 42 contains at least one of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum oxide, and niobium oxide. The material of the second dielectric layer 42 may be the same as or different from that of the first dielectric layer 41.

[0033] In the first embodiment, the thickness of the second dielectric layer 42 does not vary depending on the position in the X direction, but is constant.

[0034] 4 and 5 are schematic cross-sectional views illustrating a bulk wave in a first-order thickness-shear mode propagating through the piezoelectric layer of the first embodiment, respectively.

[0035] As shown in FIG. 4 , 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 the first electrode fingers 31 and the second electrode fingers 32, is reduced in an effort to achieve miniaturization, the Q value is unlikely to decrease.

[0036] In the first embodiment, as shown in FIG. 5 , the amplitude direction of the bulk wave in the first thickness-shear mode is substantially opposite between a first region 251 included in the intersection region CA (see FIG. 1 ) of the piezoelectric layer 20 and a second region 252 included in the intersection region CA. FIG. 5 schematically illustrates the bulk wave when a voltage is applied between the first electrode finger 31 and the second electrode finger 32 such that the second electrode finger 32 has a higher potential than the first 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 a region of the intersection region CA between the imaginary plane VP1 and the first principal surface 20a. The second region 252 is a region of the intersection region CA between the imaginary plane VP1 and the second principal surface 20b.

[0037] In acoustic wave device 10, at least one pair of electrodes consisting of first electrode finger 31 and second electrode finger 32 is arranged, but because waves are not propagated in the X direction, the number of electrode pairs consisting of first electrode finger 31 and second electrode finger 32 does not necessarily need to be multiple. In other words, it is sufficient that at least one pair of electrodes is provided.

[0038] For example, the first electrode finger 31 is an electrode connected to a hot potential, and the second electrode finger 32 is an electrode connected to a ground potential. However, the first electrode finger 31 may be connected to the ground potential, and the second electrode finger 32 may be connected to the hot potential. In the first embodiment, at least one pair of electrodes is an electrode connected to a hot potential or an electrode connected to a ground potential, as described above, and no floating electrode is provided.

[0039] 6 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. 6 are as follows.

[0040] Piezoelectric layer 20: LiNbO with Euler angles (0°, 0°, 90°) ３ Thickness of the piezoelectric layer 20: 400 nm

[0041] Length of intersection region CA: 40 μm Number of pairs of electrodes consisting of first electrode fingers 31 and second electrode fingers 32: 21 pairs Inter-electrode pitch between first electrode fingers 31 and second electrode fingers 32: 3 μm Width of first electrode fingers 31 and second electrode fingers 32: 500 nm d / p: 0.133

[0042] Support substrate 11: Si

[0043] In the first embodiment, the inter-electrode pitch of each electrode pair, which is made up of the first electrode fingers 31 and the second electrode fingers 32, is set to be equal for all pairs. That is, the first electrode fingers 31 and the second electrode fingers 32 are arranged at equal pitches.

[0044] As is clear from FIG. 6, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0045] In the first embodiment, when the thickness of the piezoelectric layer 20 is d and the average interelectrode pitch (average distance) between the first electrode fingers 31 and the second electrode fingers 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. 7 .

[0046] 7 is a graph showing 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. In FIG. 7 , multiple elastic wave devices were obtained in the same manner as the elastic wave device with the resonance characteristics shown in FIG. 6 , except that d / 2p was changed.

[0047] As shown in Figure 7, 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 an even 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.

[0048] 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.

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

[0050] 8 is a reference diagram showing an example of the resonance characteristics of the elastic wave device according to the first embodiment. As shown in FIG. 8, a spurious component indicated by an arrow B appears between the resonance frequency and the anti-resonance frequency. Note that, when d / p=0.08 and the LiNbO ３ The Euler angles were (0°, 0°, 90°), and the metallization ratio was set to MR=0.35.

[0051] The metallization ratio MR will be described with reference to Fig. 1 . Focusing on a pair of first and second electrode fingers 31 and 32 in the electrode structure of Fig. 1 , let us assume that only this pair of first and second electrode fingers 31 and 32 is provided. In this case, the area surrounded by the dashed-dotted line is a partial intersection region C. When the first and second electrode fingers 31 and 32 are viewed in a direction perpendicular to the extending direction of the first and second electrode fingers 31 and 32, i.e., in the opposing direction, this partial intersection region C refers to a region where the first electrode finger 31 overlaps with the second electrode finger 32, a region where the second electrode finger 32 overlaps with the first electrode finger 31, and a region where the first and second electrode fingers 31 and 32 overlap in the region between the first and second electrode fingers 31 and 32. The metallization ratio MR is the ratio of the area of ​​the first electrode finger 31 and the second electrode finger 32 in the partial intersection region C to the area of ​​the partial 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 partial intersection region C.

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

[0053] 9 is an explanatory diagram showing the relationship between the relative bandwidth when a large number of elastic wave resonators are configured in the elastic wave device according to the first embodiment and the amount of phase rotation of the spurious impedance normalized by 180 degrees as the magnitude of the spurious. The relative bandwidth was adjusted by changing the film thickness of piezoelectric layer 20 and the dimensions of first electrode finger 31 and second electrode finger 32. Also, FIG. 9 shows the relationship between the relative bandwidth and the spurious impedance normalized by 180 degrees as the magnitude of the spurious. ３ Although this is the result when a piezoelectric layer 20 having a cut angle of 100° is used, the same tendency is observed when a piezoelectric layer 20 having a different cut angle is used.

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

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

[0056] Fig. 11 is an explanatory diagram showing a map of the fractional bandwidth versus the Euler angles (0°, θ, ψ) of LiNbO3 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 equations (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 fractional bandwidth can be made sufficiently wide, which is preferable.

[0059] Although the elastic wave device 10 of this embodiment has been described as being capable of utilizing bulk waves in a thickness-shear first-order mode, the present invention is not limited to this. The elastic wave device 10 may also utilize plate waves. In this case, the elastic wave device 10 has reflectors provided on both sides of the IDT electrode 30 in the direction of elastic wave propagation. In the elastic wave device 10, Lamb waves as plate waves are excited by applying an AC electric field to the first electrode fingers 31 and the second electrode fingers 32 on the recesses 14. In this case, because reflectors are provided on both sides, resonance characteristics due to the Lamb waves as plate waves can be obtained.

[0060] The thicknesses of the piezoelectric layer 20, the first dielectric layer 41, and the second dielectric layer of the elastic wave device 10 according to the first preferred embodiment are described in detail below. In the following description, an adjacent pair of first electrode fingers 31 and second electrode fingers 32 is referred to as an electrode finger pair, the regions obtained by dividing the intersection region for each electrode finger pair are referred to as partial intersection regions, and the average thickness within one partial intersection region C is referred to as the thickness of the partial intersection region.

[0061] In the present disclosure, the partial intersection region C is defined in detail as follows.

[0062] The extension direction of the first electrode finger 31 and the second electrode finger 32 of the partial intersection region C, i.e., the range in the Y direction, is the range in which one first electrode finger 31 and one second electrode finger 32 overlap when viewed in the X direction. In the present disclosure, "a first electrode finger 31 and a second electrode finger are adjacent to each other" means that no other first electrode finger 31 or second electrode finger 32 is provided between the first electrode finger 31 and the second electrode finger 32. Therefore, in the example of FIG. 2 , the Y direction range of the partial intersection region C is the range extending from the Y direction position of the tip of the one first electrode finger 31 to the Y direction position of the tip of the one second electrode finger 32.

[0063] The range of the partial intersection region C in the opposing direction of the first electrode finger 31 and the second electrode finger 32, that is, in the X direction, is an area obtained by dividing the intersection region CA for each pair of electrode fingers.

[0064] The boundary E between the partial intersection regions C is located midway between the sets of electrode fingers. There are no particular limitations on how the boundary E is defined; for example, the boundary E may be defined as a position where the distance to the center of the width of the electrode fingers of one set of electrode fingers is equal to the distance to the center of the width of the electrode fingers of the other set of electrode fingers. Therefore, in the examples of Figures 2 and 3, the boundary E can be defined as a position that is p / 2 away from the centers of the first electrode finger 31 and the second electrode finger 32 that are adjacent to each other and that are included in different sets of electrode fingers.

[0065] Although the method for defining the X-direction ends EA and EB of the partial intersection region C at the end in the X direction, i.e., the X-direction ends EA and EB of the intersection region CA, is not particularly limited, for example, the ends EA and EB may be positioned at a distance of half the center-to-center distance between the electrode finger (first electrode finger 31 or second electrode finger 32) at the end in the X direction of the intersection region CA from the center of the width of the electrode finger at the end in the X direction. Therefore, in the examples of Figures 2 and 3, the ends EA and EB can be defined as positions p / 2 away from the center of the X-direction width of the first electrode finger 31 or second electrode finger 32 at the end in the X direction.

[0066] The intersection area CA of the elastic wave device 10 according to the first preferred embodiment includes a plurality of partial intersection areas. In the following description, as shown in FIG. 3 , the partial intersection areas C are numbered starting from 1 from the end EA on one side in the X direction of the intersection area CA as k, the total number of partial intersection areas C in the intersection area is N, the kth partial intersection area counted from the end EA on one side in the X direction of the intersection area CA is the partial intersection area Ck, and the width of the partial intersection area Ck in the X direction is L. ｋ In the first embodiment, since the inter-electrode pitches are all equal at p, the width L of the partial intersection region Ck in the X direction is ｋ are all equal to twice the inter-electrode pitch p. Also, the width L of the partial intersection region Ck in the X direction ｋ , that is, the length from the end EA to the end EB in the X direction of the intersection area CA may be referred to as L.

[0067] (Thickness of Piezoelectric Layer) The thickness of the piezoelectric layer 20 in the partial intersection region C according to the first embodiment will be described in detail below. In the following description, the average thickness of the piezoelectric layer 20 is referred to as d ａｖ The maximum thickness of the piezoelectric layer 20 for each partial intersection region Ck is d ｍａｘ The minimum thickness of the piezoelectric layer 20 for each partial intersection region Ck is d ｍｉｎ That is, the thickness of the piezoelectric layer 20 in the partial intersection region Ck is d ｋ In this case, the average thickness d ａｖ , maximum thickness d ｍａｘ , minimum thickness d ｍｉｎ is defined by the following equations (4) to (6). Therefore, the average thickness d ａｖ corresponds to the thickness d of the piezoelectric layer 20 described above. ａｖ = (d １ L １ +d ２ L ２ +...+d ｋ L ｋ +...+d Ｎ L Ｎ ) / L ... (4) d ｍａｘ = max(d １ , d ２ , ..., d ｋ , ..., d Ｎ ) ... (5) d ｍｉｎ = min(d１ , d ２ , ..., d ｋ , ..., d Ｎ ) … (6)

[0068] In the elastic wave device 10 according to the first preferred embodiment, the thickness d ｋ In other words, in the first embodiment, in the intersection region CA, the thickness of the piezoelectric layer 20 in the partial intersection region C is not constant but varies depending on the position in the X direction.

[0069] In the first embodiment, the thickness of the piezoelectric layer 20 in the partial intersection region C increases from one side to the other side in the X direction. That is, the thickness of the piezoelectric layer 20 is a minimum thickness d ｍｉｎ and the maximum thickness d ｍａｘ This becomes:

[0070] 2 and 3, the thickness of the piezoelectric layer 20 in the partial intersection region C is designed so that the thickness of the piezoelectric layer 20 in the partial intersection region C increases stepwise from an end EA on one side in the X direction of the intersection region CA to an end EB on the other side in the X direction for each partial intersection region C. More specifically, the thickness d ｋ is expressed by the following formula (7): ｋ = d ｍｉｎ + k × (d ｍａｘ -d ｍｉｎ 2 and 3, the thickness of the piezoelectric layer 20 is constant within one partial intersection region Ck. In addition, in the examples of Figures 2 and 3, the first main surface 20a of the piezoelectric layer 20 is made to be flush, and the second main surface 20b is made to be a stepped surface with a step at the boundary E, but this is merely an example and is not limiting, and the first main surface 20a may also be a stepped surface.

[0071] Here, rd ｍａｘ , rd ｍｉｎ is defined by the following equations (8) and (9). ｍａｘ , rd ｍｉｎis a parameter indicating the amount of change in thickness of the piezoelectric layer 20 in the partial intersection region C. ｍａｘ and rd ｍｉｎ and are equal, rd ｍａｘ and rd ｍｉｎ When explaining without distinguishing between , it may be explained as rd. ｍａｘ (%) = |d ｍａｘ -d ａｖ | / d ａｖ ×100...(8)rd ｍｉｎ (%) = |d ｍｉｎ -d ａｖ | / d ａｖ × 100 … (9)

[0072] rd ｍａｘ and rd ｍｉｎ is preferably 10% or less. By setting it in this range, deterioration of the main wave M can be suppressed, and the unwanted wave S2 can be suppressed. ｍａｘ and rd ｍｉｎ It is more preferable that the ratio is 6% or less. This makes it possible to further suppress unwanted waves. ｍａｘ and rd ｍｉｎ It is more preferable that the ratio is 4% or less. This makes it possible to further suppress unwanted waves.

[0073] (Thickness of First Dielectric Layer) The thickness of the first dielectric layer 41 in the partial intersection region C according to the first embodiment will be described in detail below. In the following description, the average value of the thickness of the first dielectric layer 41 in each partial intersection region Ck is referred to as t1 ａｖ The maximum thickness of the first dielectric layer 41 in each partial intersection region Ck is t1 ｍａｘ The minimum thickness of the first dielectric layer 41 for each partial intersection region Ck is t1 ｍｉｎ That is, the thickness of the first dielectric layer 41 in the partial intersection region Ck is set to t1 ｋ In this case, the average thickness t1 ａｖ , maximum thickness t1 ｍａｘ , minimum thickness t1 ｍｉｎ is defined by the following equations (10) to (12): ａｖ = (t1 １ L １ +t1 ２ L２ +...+t1 ｋ L ｋ +...+t1 Ｎ L Ｎ ) / L…(10) t1 ｍａｘ = max (t １ , t1 ２ , ..., t1 ｋ , ..., t1 Ｎ ) ... (11) t1 ｍｉｎ = min (t １ , t1 ２ , ..., t1 ｋ , ..., t1 Ｎ ) … (12)

[0074] In the elastic wave device 10 according to the first preferred embodiment, the first dielectric layer 41 has a thickness t1 ｋ In the first embodiment, in the intersection region CA, the thickness of the first dielectric layer 41 in the partial intersection region C is not constant but varies depending on the position in the X direction.

[0075] In the first embodiment, the thickness of the first dielectric layer 41 in the partial intersection region where the thickness of the piezoelectric layer 20 is greater is smaller than the thickness of the first dielectric layer 41 in the partial intersection region where the thickness of the piezoelectric layer 20 is smaller. In other words, a first dielectric layer 41 with a smaller thickness is provided in the partial intersection region where the thickness of the piezoelectric layer 20 is greater, and a first dielectric layer 41 with a larger thickness is provided in the partial intersection region where the thickness of the piezoelectric layer 20 is smaller. Therefore, the thickness of the first dielectric layer 41 in the partial intersection region C decreases from one side to the other in the X direction, and the thickness of the first dielectric layer 41 in the partial intersection region C reaches a maximum thickness t1 in a partial intersection region C1 at one end in the X direction. ｍａｘ and the minimum thickness t1 ｍｉｎ This becomes:

[0076] 2 and 3, the thickness of the first dielectric layer 41 in the partial intersection region C is designed to decrease stepwise from an end EA on one side in the X direction of the intersection region CA to an end EB on the other side in the X direction for each partial intersection region C. More specifically, the thickness t1 of the first dielectric layer 41 in the partial intersection region Ck is ｋ is expressed by the following formula (13): ｋ = t1 ｍａｘ −k×(t ｍａｘ -t1 ｍｉｎ ) / N (13) In the examples of FIGS. 2 and 3, the thickness of the first dielectric layer 41 is made constant within one partial intersection region Ck.

[0077] Here, rt1 ｍａｘ , rt1 ｍｉｎ is defined by the following equations (14) and (15). ｍａｘ , rt1 ｍｉｎ is a parameter indicating the amount of change in thickness of the first dielectric layer 41 in the partial intersection region C. In the following description, rt1 ｍａｘ and rt1 ｍｉｎ and are equal, rt1 ｍａｘ and rt1 ｍｉｎ When explaining without distinguishing between them, it may be explained as rt1. ｍａｘ = |t1 ｍａｘ -t1 ａｖ | / d ａｖ …(14) rt1 ｍｉｎ = |t1 ｍｉｎ -t1 ａｖ | / d ａｖ …(15)

[0078] rt1 ｍａｘ and rt1 ｍｉｎ is set to r d so as to maintain the resonant frequency of the elastic wave device 10. ｍａｘ and rd ｍｉｎ It is preferable that the temperature is adjusted to

[0079] (Thickness of Second Dielectric Layer) The thickness of the second dielectric layer 42 in the partial intersection region C according to the first embodiment will be described in detail below. In the following description, the average thickness of the second dielectric layer 42 in each partial intersection region Ck is referred to as t2ａｖ The maximum thickness of the second dielectric layer 42 for each partial intersection region Ck is t2 ｍａｘ The minimum thickness of the second dielectric layer 42 for each partial intersection region Ck is t2 ｍｉｎ That is, the thickness of the second dielectric layer 42 in the partial intersection region Ck is t2 ｋ In this case, the average thickness t2 ａｖ , maximum thickness t2 ｍａｘ , minimum thickness t2 ｍｉｎ is defined by the following equations (16) to (18): ａｖ = (t2 １ L １ +t2 ２ L ２ +...+t2 ｋ L ｋ +...+t2 Ｎ L Ｎ ) / L…(16) t2 ｍａｘ = max (t １ , t2 ２ , ..., t2 ｋ , ..., t2 Ｎ ) ... (17) t2 ｍｉｎ = min (t １ , t2 ２ , ..., t2 ｋ , ..., t2 Ｎ ) … (18)

[0080] In the elastic wave device 10 according to the first preferred embodiment, the thickness t2 of the second dielectric layer 42 in the partial intersection region C is ｋ are all average thickness t2 ａｖ 2 and 3, the thickness of the second dielectric layer 42 is constant within one partial intersection region Ck.

[0081] EXAMPLES The elastic wave device 10 according to the first embodiment will be described below using examples and comparative examples. Note that the elastic wave device according to the first embodiment is not limited to the examples described below.

[0082] (First Test) In a first test, the resonance characteristics of the elastic wave devices according to the example and comparative example 1 were compared.

[0083] The elastic wave device according to the example is the elastic wave device 10 according to the first embodiment 10. That is, in the elastic wave device according to the example, the thicknesses of the piezoelectric layer 20 and the first dielectric layer 41 are varied depending on the position in the X direction, and the thickness of the second dielectric layer 42 is set to an average thickness t2 ａｖ (=54 nm). The design parameters of the elastic wave device according to the example are as follows. In the example in the first test, the thickness of the first dielectric layer 41 was set to be smaller as the thickness of the piezoelectric layer 20 increased in each partial intersection region C. Piezoelectric layer 20: LiNbO ３ (average thickness d ａｖ : 299.5 nm) First dielectric layer 41: SiO ２ (Average thickness t1 ａｖ : 42 nm) Second dielectric layer 42: SiO ２ (Average thickness t2 ａｖ :54nm) rd:0.037 rt1:0.21

[0084] In the acoustic wave device according to the example, the IDT electrode 30 has a laminated structure of Ti / AlCu / Ti / AlCu, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm from the piezoelectric layer 20 side. The IDT electrode 30 has a total of 51 first electrode fingers 31 and second electrode fingers 32. The interelectrode pitch of the first electrode fingers 31 and the second electrode fingers 32 is 4.4 μm, and the electrode width is 0.6 μm.

[0085] 12 is an enlarged cross-sectional view of an elastic wave device according to Comparative Example 1. Here, FIG. 12 is an enlarged cross-sectional view of a range corresponding to FIG. 3. As shown in FIG. 12, the elastic wave device according to Comparative Example 1 has the same configuration as the elastic wave device according to Example 1, except that the thicknesses of piezoelectric layer 20 and first dielectric layer 41 in partial intersection region C are constant and do not vary depending on the position in the X direction. In the elastic wave device according to Comparative Example 1, the thickness of piezoelectric layer 20 is an average thickness d ａｖ (=299.5 nm), and the thickness of the first dielectric layer 41 is set to an average thickness t1 ａｖ (=42 nm) and was made uniform.

[0086] The results of the first test are shown in FIGS. 13A , 13B , 14A , and 14B . FIGS. 13A and 13B are diagrams illustrating the resonance characteristics of the elastic wave device according to the example. More specifically, FIGS. 13A and 13B are diagrams illustrating the absolute value (|Y|) and real part (ReY) of the admittance of the elastic wave device according to the example. FIGS. 14A and 14B are diagrams illustrating the resonance characteristics of the elastic wave device according to Comparative Example 1. More specifically, FIGS. 14A and 14B are diagrams illustrating the absolute value (|Y|) and real part (ReY) of the admittance of the elastic wave device according to Comparative Example 1.

[0087] 13A , 13B , 14A, and 14B , in the elastic wave devices of the example and comparative example 1, a main wave M and unwanted waves S1 and S2 appeared. As shown in FIGS. 13A , 13B , 14A, and 14B , in the elastic wave device of the example, no degradation of the main wave M was observed and the unwanted wave S2 was smaller compared to the elastic wave device of the comparative example. This shows that by varying the thicknesses of piezoelectric layer 20 and first dielectric layer 41 in the X direction in partial intersection region C, it is possible to suppress the unwanted wave S2 while suppressing degradation of the main wave, thereby improving the resonance characteristics.

[0088] (Second Test) In the second test, the rd of the elastic wave device according to the example was changed to examine the rd dependence of the resonance characteristics of the elastic wave device according to the example. The elastic wave device according to the example of the second test was the same as the elastic wave device according to the example of the first test, except for the rd being changed. That is, in the second test, the thickness of the first dielectric layer was adjusted to decrease as the thickness of the piezoelectric layer increased.

[0089] The results of the second test are shown in Figures 15A to 15C. Figures 15A to 15C are graphs showing the rd dependence of the resonance characteristics of the elastic wave device according to the example. More specifically, Figures 15A to 15C show the rd dependence of the real part of the admittance (ReY) of the elastic wave device according to the example, and Figures 15B and 15C are enlarged graphs of Figures 15A and 15B, respectively.

[0090] As shown in Fig. 15A, it can be seen that by setting rd to 10% or less, deterioration of the main wave M can be suppressed and the unwanted wave S2 can be suppressed. Also, as shown in Fig. 15B, it can be seen that by setting rd to 6% or less, the unwanted wave S2 can be further suppressed. Also, as shown in Fig. 15C, it can be seen that by setting rd to 4% or less, the unwanted wave S1 can be suppressed.

[0091] (Third Test) In a third test, the resonance characteristics of the elastic wave device according to the example and comparative example 2 were compared, and the rt1 was changed to examine the rt1 dependency of the resonance characteristics of the elastic wave device according to the example.

[0092] The elastic wave device according to the third test example was the same as the elastic wave device according to the first test example except for changing rt1. That is, in the third test, the thickness of the piezoelectric layer was adjusted to decrease as the thickness of the first dielectric layer increased.

[0093] 16 is an enlarged cross-sectional view of an elastic wave device according to Comparative Example 2. Here, FIG. 16 is an enlarged cross-sectional view of a range corresponding to FIG. 3. As shown in FIG. 16, the elastic wave device according to Comparative Example 2 has the same configuration as the elastic wave device according to the above-described Example, except that the thickness of piezoelectric layer 20 in partial intersection region C is constant and does not vary depending on the position in the X direction. In the elastic wave device according to Comparative Example 1, the thickness of piezoelectric layer 20 is an average thickness d ａｖ (=299.5 nm), but the thickness of the first dielectric layer 41 in the partial intersection region C varies depending on the position in the X direction, as in the example.

[0094] 17A to 17C are diagrams illustrating the resonance characteristics of an elastic wave device according to an example. More specifically, FIG. 17A is a diagram illustrating the frequency dependence of the absolute value of admittance (|Y|) when rt1 is 21%, and FIGS. 17B and 17C are diagrams illustrating the rt1 dependence of the absolute value of admittance (|Y|) and real part (ReY). FIGS. 18A to 18C are diagrams illustrating the resonance characteristics of an elastic wave device according to Comparative Example 2. More specifically, FIG. 18A is a diagram illustrating the frequency dependence of the absolute value of admittance (|Y|) when rt1 is 21%, and FIGS. 18B and 18C are diagrams illustrating the rt1 dependence of the absolute value of admittance (|Y|) and real part (ReY).

[0095] As shown in FIG. 17A , degradation of the main wave M is suppressed in the elastic wave device according to the example. On the other hand, as shown in FIG. 18A , degradation of the main wave M is observed in the elastic wave device according to Comparative Example 2. Furthermore, as shown in FIGS. 17B and 17C , degradation of the main wave is suppressed even when rt1 increases in the elastic wave device according to the example. However, as shown in FIGS. 18B and 18C , in the elastic wave device according to Comparative Example 2, the main wave M rapidly deteriorates as rt1 increases. Therefore, it can be seen that varying the thickness in the partial intersection region C in the X direction not only of first dielectric layer 41 but also of piezoelectric layer 20 can suppress undesired waves S1 and S2 while suppressing degradation of the main wave M.

[0096] Second Embodiment Fig. 19 is an enlarged cross-sectional view showing an elastic wave device according to a second embodiment. Here, Fig. 19 is an enlarged cross-sectional view of a range corresponding to Fig. 3. As shown in Fig. 19, the elastic wave device according to the second embodiment differs in configuration from the first embodiment described above in that the thickness of the second dielectric layer 42 in the partial intersection region C also varies in the X direction. That is, the thickness of the second dielectric layer 42 in the partial intersection region C is not constant in the X direction but varies depending on the position in the X direction.

[0097] 19, the thickness of the second dielectric layer 42 in the partial intersection region C is designed so that the thickness of the second dielectric layer 42 in the partial intersection region C increases stepwise from an end EA on one side in the X direction of the intersection region CA to an end EB on the other side in the X direction for each partial intersection region C. More specifically, the thickness t2 of the second dielectric layer 42 in the partial intersection region C in the partial intersection region Ck is ｋ is expressed by the following formula (19): ｋ = t2 ｍａｘ −k×(t ｍａｘ -t2 ｍｉｎ ) / N (19) In the example of FIG. 19, the thickness of the second dielectric layer 42 is made constant within one partial intersection region Ck.

[0098] In the second embodiment, the sum of the thickness of the first dielectric layer 41 and the thickness of the second dielectric layer 42 is the same in all partial intersection regions C. That is, in the example of FIG. 19 , it can be said that the formula (20) holds in all partial intersection regions Ck. As a result, the thickness t1 of the first dielectric layer 41 in the partial intersection region C ｋ By varying the length t1 in the X direction, it is possible to suppress the effect on the resonance characteristics of the acoustic wave device. １ +t2 １ = t1 ２ +t2 ２ = ... = t1 ｋ +t2 ｋ = ... = t1 Ｎ +t2 Ｎ …(20)

[0099] Third Embodiment Fig. 20 is an enlarged cross-sectional view of an elastic wave device according to a third embodiment. Here, Fig. 20 is an enlarged cross-sectional view of a range corresponding to Fig. 3. As shown in Fig. 20, the elastic wave device according to the third embodiment differs from the first embodiment in that the thicknesses of the piezoelectric layer 20 and the first dielectric layer 41 vary continuously in the X direction.

[0100] In the example of FIG. 20 , the thickness of the piezoelectric layer 20 continuously increases from an end EA on one side of the X direction of the intersection region CA toward an end EB on the other side of the X direction. This allows the thickness of the piezoelectric layer 20 to change in the X direction without providing a step in the piezoelectric layer 20 for changing the layer thickness, thereby improving the manufacturability of the elastic wave device. More specifically, if the distance in the X direction from the end EA of the intersection region CA is x, the thickness d(x) of the piezoelectric layer 20 in the range 0≦x≦L is expressed by the following equation (21): d(x)=d(0)+(d(L)−d(0))x / L (21) In the example of FIG. 20 , since the thickness of the piezoelectric layer 20 changes linearly as shown in equation (21), the thickness d ｋ is equal to the thickness of the piezoelectric layer at the center of the partial intersection region Ck in the X direction. Furthermore, the thickness d of the piezoelectric layer 20 described above indicates the average value of the thickness d(x), and can be calculated using the following equation (22).

[0101] 20 , the thickness of the first dielectric layer 41 is designed to continuously decrease from an end EA on one side in the X direction of the intersection region CA to an end EB on the other side in the X direction. This allows the thickness to be changed in the X direction without providing a step in the first dielectric layer 41 for changing the layer thickness, thereby improving the manufacturability of the elastic wave device. More specifically, the thickness t1(x) of the first dielectric layer 41 in the range 0≦x≦L is expressed by the following equation (23): t1(x)=t1(0)−(t1(0)−t1(L))x / L (23) Note that in the example of FIG. 20 , the thickness of the first dielectric layer 41 changes linearly as shown in equation (22), and therefore the thickness t1 ｋ is equal to the thickness of the piezoelectric layer at the center of the partial intersection region Ck in the X direction.

[0102] In the example of Fig. 20, the second main surface 20b has a tapered shape extending in a direction intersecting the X direction and the Z direction. This improves manufacturability. Note that in the example of Fig. 20, the first main surface 20a extends in a direction parallel to the X direction, and the second main surface 20b extends in a direction intersecting the X direction and the Z direction. However, this is not limited thereto, and the first main surface 20a may extend in a direction intersecting the X direction and the Z direction, or both the first main surface 20a and the second main surface 20b may extend in a direction intersecting the X direction and the Z direction.

[0103] The configuration of the third embodiment can be combined with the first and second embodiments described above.

[0104] 21 is a cross-sectional view showing an elastic wave device according to a fourth embodiment. In the above-described embodiments, a so-called membrane structure has been described in which the support substrate 11 has the recess 14 and the recess 14 is provided on the second main surface 20b of the piezoelectric layer 20. However, the present invention is not limited to this.

[0105] 21 , in an elastic wave device 10A according to the fourth embodiment, an acoustic multilayer film 43 is laminated on a second main 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, which have a relatively low acoustic impedance, and high acoustic impedance layers 43b and 43d, which have a relatively high acoustic impedance. The low acoustic impedance layers 43a, 43c, and 43e are made of, for example, silicon oxide (SiO ２ ), and the high acoustic impedance layers 43b and 43d are made of, for example, silicon nitride (SiN) or aluminum oxide (Ai ２ O ３ ), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ When the acoustic multilayer film 43 is used, bulk waves in the first thickness-shear mode can be confined within the piezoelectric layer 20 without using the recesses 14.

[0106] Furthermore, the materials of the low acoustic impedance layers 43a, 43c, and 43e and the high acoustic impedance layers 43b and 43d have a lower dielectric constant than the piezoelectric layer 20 and the first dielectric layer 41. That is, the low acoustic impedance layers 43a, 43c, and 43e and the high acoustic impedance layers 43b and 43d are formed of a different material from the first dielectric layer 41.

[0107] There is no particular limitation on the number of stacked low acoustic impedance layers 43a, 43c, 43e and high acoustic impedance layers 43b, 43d in the acoustic multilayer film 43. It is sufficient that at least one of the high acoustic impedance layers 43b, 43d is disposed farther from the piezoelectric layer 20 than the low acoustic impedance layers 43a, 43c, 43e.

[0108] The low acoustic impedance layers 43 a, 43 c, and 43 e and the high acoustic impedance layers 43 b and 43 d can be made of any suitable material as long as the above acoustic impedance relationship is satisfied. For example, the high acoustic impedance layers 43 b and 43 d can be made of aluminum nitride (AlN) or metals such as tungsten (W) and platinum (Pt).

[0109] The configuration of the fourth embodiment can be combined with the first to third embodiments described above.

[0110] The above-described embodiments are provided to facilitate understanding of the present invention and are 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.

[0111] For example, the second dielectric layer 42 may not be provided in the elastic wave devices according to the first to fourth embodiments. Alternatively, the thickness of the second dielectric layer may vary depending on the position in the X direction, and the thickness of the first dielectric layer may be constant. Alternatively, the thickness of the second dielectric layer may vary depending on the position in the X direction, and the first dielectric layer may not be provided. Furthermore, the IDT electrodes may be provided on both the first principal surface 20 a and the second principal surface 20 b, or may be provided only on the second principal surface 20 b.

[0112] The present disclosure may also have the following configurations.

[0113] <1> A piezoelectric element comprising: a piezoelectric layer having a first main surface and a second main surface opposite to the first main surface in a first direction; an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer; a dielectric layer provided on at least one of the first main surface and the second main surface of the piezoelectric layer; and a support member provided on the second main surface side of the piezoelectric layer, the support member having an acoustic reflector on the second main surface side of the piezoelectric layer, wherein the electrodes are IDT electrodes including a first bus bar and a second bus bar facing each other, a plurality of first electrode fingers having base ends connected to the first bus bar, and a plurality of second electrode fingers having base ends connected to the second bus bar, The elastic wave device according to the present invention is characterized in that, when an area where the adjacent first electrode finger and the adjacent second electrode finger overlap as viewed in the opposing second direction is defined as an intersection area, and when areas obtained by dividing the intersection area for each pair of the first electrode finger and the adjacent second electrode finger are defined as partial intersection areas, the intersection area includes at least one partial intersection area in which the thickness of the piezoelectric layer is different from that of the other partial intersection areas.<2> The elastic wave device according to the present invention is characterized in that the thickness of the dielectric layer in the partial intersection area where the piezoelectric layer is thicker is smaller than the thickness of the dielectric layer in the partial intersection area where the piezoelectric layer is thin.<3> The elastic wave device according to the present invention is characterized in that the average thickness of the piezoelectric layer in each partial intersection area is defined as d ａｖ The maximum thickness of the piezoelectric layer for each partial intersection region is d ｍａｘ The minimum thickness of the piezoelectric layer for each partial intersection region is d ｍｉｎ In this case, rd represented by equation (1) ｍａｘ is 10% or less, and rd represented by formula (2) ｍｉｎ rd is 10% or less. ｍａｘ (%) = |d ｍａｘ -d ａｖ | / d ａｖ ×100...(1)rd ｍｉｎ (%) = |d ｍｉｎ -d ａｖ | / d ａｖ ×100...(2) <4> Said rd ｍａｘ is 6% or less, and ｍｉｎ <5> The acoustic wave device according to <3>, wherein r d ｍａｘis 4% or less, and ｍｉｎThe elastic wave device according to <3>, wherein the difference in thickness between the first and second dielectric layers is 4% or less. <6> The elastic wave device according to any one of <1> to <5>, wherein the dielectric layer is provided on the first main surface or the second main surface of the piezoelectric layer, and the intersection region includes at least one partial intersection region in which the thickness of the dielectric layer is different from that of other partial intersection regions. <7> The elastic wave device according to any one of <1> to <6>, wherein the dielectric layer includes a first dielectric layer provided on the first main surface and a second dielectric layer provided on the second main surface, and the intersection region includes at least one partial intersection region in which the thickness of at least one of the first dielectric layer and the second dielectric layer is different from that of other partial intersection regions. <8> The elastic wave device according to <7>, wherein the intersection region includes at least one partial intersection region in which the thickness of the first dielectric layer is different from that of other partial intersection regions, and the thickness of the second dielectric layer is the same in all partial intersection regions. <9> The elastic wave device according to <7>, wherein the intersection region includes at least one partial intersection region in which the first dielectric layer is different from the other partial intersection regions, and the intersection region includes at least one partial intersection region in which the second dielectric layer is different from the other partial intersection regions. <10> The elastic wave device according to <9>, wherein the sum of the thickness of the first dielectric layer and the thickness of the second dielectric layer is the same in all partial intersection regions. <11> The elastic wave device according to any one of <1> to <10>, wherein the thickness of the piezoelectric layer in a partial intersection region on one side in the second direction is equal to or less than the thickness of the piezoelectric layer in a partial intersection region on the other side in the second direction. <12> The elastic wave device according to <11>, wherein the thickness of the piezoelectric layer continuously increases from one end of the intersection region in the second direction to the other end of the intersection region in the second direction. <13> The elastic wave device according to any one of <1> to <12>, wherein the dielectric layer contains at least one of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum oxide, and niobium oxide. <14> The elastic wave device according to any one of <1> to <13>, wherein the acoustic reflection portion is a recessed portion of the support member that is open to the piezoelectric layer side.<15> The elastic wave device according to any one of <1> to <13>, 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 with the acoustic reflection film in between.

[0114] REFERENCE SIGNS LIST 10, 10A Acoustic wave device 11 Support substrate 14 Recess 20 Piezoelectric layer 20a First principal surface 20b Second principal surface 30 IDT electrode 31 First electrode finger 32 Second electrode finger 33 First bus bar electrode 34 Second bus bar electrode 41 First dielectric layer 42 Second dielectric layer 43 Acoustic multilayer film

Claims

1. A piezoelectric element comprising: a piezoelectric layer having a first main surface and a second main surface opposite to the first main surface in a first direction; an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer; a dielectric layer provided on at least one of the first main surface and the second main surface of the piezoelectric layer; and a support member provided on the second main surface side of the piezoelectric layer, the support member having an acoustic reflector on the second main surface side of the piezoelectric layer, wherein the electrode is an IDT electrode including a first bus bar and a second bus bar facing each other, a plurality of first electrode fingers having base ends connected to the first bus bar, and a plurality of second electrode fingers having base ends connected to the second bus bar, An elastic wave device in which, when an area where adjacent first electrode fingers and second electrode fingers overlap when viewed in a second direction in which they face each other is defined as an intersection area, and an area obtained by dividing the intersection area for each pair of adjacent first electrode fingers and second electrode fingers is defined as a partial intersection area, the intersection area has at least one partial intersection area in which the thickness of the piezoelectric layer is different from that of other partial intersection areas.

2. The elastic wave device according to claim 1, wherein the thickness of the dielectric layer in the partial intersection region where the thickness of the piezoelectric layer is greater is smaller than the thickness of the dielectric layer in the partial intersection region where the thickness of the piezoelectric layer is smaller.

3. The average thickness of the piezoelectric layer for each partial intersection region is d ａｖ The maximum thickness of the piezoelectric layer for each partial intersection region is d ｍａｘ The minimum thickness of the piezoelectric layer for each partial intersection region is d ｍｉｎ In this case, rd represented by equation (1) ｍａｘ is 10% or less, and rd represented by formula (2) ｍｉｎ 3. The acoustic wave device according to claim 1, wherein rd is 10% or less. ｍａｘ (%) = |d ｍａｘ -d ａｖ | / d ａｖ ×100...(1)rd ｍｉｎ (%) = |d ｍｉｎ -d ａｖ | / d ａｖ × 100 … (2) 4. Said rd ｍａｘ is 6% or less, and ｍｉｎ The acoustic wave device according to claim 3 , wherein the coefficient of friction is 6% or less.

5. Said rd ｍａｘ is 4% or less, and ｍｉｎ The acoustic wave device according to claim 3 , wherein the coefficient of friction is 4% or less.

6. An elastic wave device according to any one of claims 1 to 5, wherein the dielectric layer is provided on the first principal surface or the second principal surface of the piezoelectric layer, and the intersection region includes at least one partial intersection region in which the thickness of the dielectric layer is different from that of other partial intersection regions.

7. An elastic wave device according to any one of claims 1 to 6, wherein the dielectric layer comprises a first dielectric layer provided on the first principal surface and a second dielectric layer provided on the second principal surface, and the intersection region includes at least one partial intersection region in which the thickness of at least one of the first dielectric layer and the second dielectric layer is different from that of other partial intersection regions.

8. The elastic wave device according to claim 7, wherein the intersection region includes at least one partial intersection region in which the thickness of the first dielectric layer is different from that of the other partial intersection regions, and the thickness of the second dielectric layer is the same in all partial intersection regions.

9. The elastic wave device according to claim 7, wherein the intersection region includes at least one partial intersection region in which the first dielectric layer is different from other partial intersection regions, and the intersection region includes at least one partial intersection region in which the second dielectric layer is different from other partial intersection regions.

10. The acoustic wave device according to claim 9, wherein the sum of the thickness of the first dielectric layer and the thickness of the second dielectric layer is the same in all partial intersection regions.

11. An elastic wave device according to any one of claims 1 to 10, wherein the thickness of the piezoelectric layer in a partial intersection region on one side of the second direction is equal to or less than the thickness of the piezoelectric layer in a partial intersection region on the other side of the second direction.

12. The acoustic wave device according to claim 11, wherein the thickness of the piezoelectric layer increases continuously from one end of the intersection region in the second direction to the other end of the intersection region in the second direction.

13. The acoustic wave device according to any one of claims 1 to 12, wherein the dielectric layer contains at least one of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum oxide, and niobium oxide.

14. The elastic wave device according to any one of claims 1 to 13, wherein the acoustic reflection portion is a recess in the support member that is open to the piezoelectric layer side.

15. An elastic wave device according to any one of claims 1 to 13, wherein the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer with a relatively high acoustic impedance and a low acoustic impedance layer with a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged so that at least a portion of the support member and at least a portion of the piezoelectric layer face each other with the acoustic reflection film in between.

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