Elastic wave device and elastic wave filter device

Abstract

This elastic wave device is provided with: a piezoelectric layer having a first main surface and a second main surface; 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 reflection portion on the second main surface side of the piezoelectric layer, the plurality of electrode fingers including a first electrode finger located on the outermost side 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 fingers and the second electrode fingers is larger than the product of the width, height, and density of the electrode fingers in the center different from the first electrode fingers and the second electrode fingers among the plurality of electrode fingers. When the thickness of the piezoelectric layer is d and the distance between the centers of adjacent electrode fingers is p, d / p is 0.5 or less.

Description

Technical Field

[0001] This invention relates to elastic wave devices and elastic wave filter devices. Background Technology

[0002] Elastic wave devices are described in Patent Document 1 and Patent Document 2.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2022-524136

[0006] Patent Document 2: US Patent No. 11,349,450 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] The elastic wave devices shown in Patent Documents 1 and 2 may generate ripples in the admittance characteristics, thereby increasing the propagation loss of elastic waves.

[0009] The purpose of this invention is to provide an elastic wave device and an elastic wave filter device capable of suppressing the propagation loss of elastic waves.

[0010] Technical solutions for solving the problem

[0011] One type of elastic wave device 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 disposed on at least one of the first main surface and the second main surface of the piezoelectric layer, comprising a plurality of electrode fingers arranged in a given direction; and a support member facing the second main surface of the piezoelectric layer and having an acoustic reflection portion on the side of the second main surface of the piezoelectric layer, wherein the plurality of electrode fingers includes a first electrode finger located on the outermost side in the arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the first electrode finger, wherein 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 the electrode finger in the central portion of the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger, and wherein, when the thickness of the piezoelectric layer is d and the center-to-center distance between adjacent electrode fingers is p, d / p is 0.5 or less.

[0012] One approach to an elastic wave device 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 disposed on at least one of the first main surface and the second main surface of the piezoelectric layer, comprising a plurality of electrode fingers arranged in a given direction; a support member facing the second main surface of the piezoelectric layer and having an acoustic reflection portion on the side of the second main surface of the piezoelectric layer; and an additional electrode, wherein the outermost electrode finger among the plurality of electrode fingers in the arrangement direction of the plurality of electrode fingers is designated as the first electrode finger and the electrode finger adjacent to the first electrode finger is... When the electrode finger is designated as the second electrode finger, the additional electrode is disposed in the region overlapping with at least one of the first electrode finger and the second electrode finger. The sum of the product of the width, height, and density 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 the electrode finger at the center portion of the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger. When the thickness of the piezoelectric layer is set to d and the center-to-center distance between adjacent electrode fingers is set to p, d / p is 0.5 or less.

[0013] One approach involves an elastic wave filter device that is an elastic wave filter device formed by connecting at least one resonator, wherein,

[0014] The resonator is the elastic wave device described above.

[0015] Invention Effects

[0016] The elastic wave device and elastic wave filter device according to the present invention can suppress the propagation loss of elastic waves. Attached Figure Description

[0017] Figure 1 This is a top view showing the elastic wave device of the first embodiment.

[0018] Figure 2 yes Figure 1 Sectional view II-II'.

[0019] Figure 3 This is a schematic cross-sectional view used to illustrate the bulk wave of the thickness shear first mode propagating in the piezoelectric layer of the first embodiment.

[0020] Figure 4 This is a schematic cross-sectional view used to illustrate the amplitude direction of the bulk wave of the thickness shear first mode propagating in the piezoelectric layer of the first embodiment.

[0021] Figure 5 This is an explanatory diagram showing an example of the resonant characteristics of the elastic wave device according to the first embodiment.

[0022] Figure 6 This is an explanatory diagram showing the relationship between d / 2p and the relative bandwidth of the resonator when the center-to-center distance or the average center-to-center distance of adjacent electrodes is set as p and the average thickness of the piezoelectric layer is set as d in the elastic wave device of the first embodiment.

[0023] Figure 7 This is a top view showing an example of an elastic wave device in the first embodiment having a pair of electrodes.

[0024] Figure 8 This is a reference diagram showing an example of the resonant characteristics of the elastic wave device according to the first embodiment.

[0025] Figure 9 This is an explanatory diagram showing the relationship between the relative bandwidth and the phase rotation amount of the spur impedance, which is normalized by 180 degrees, in the case of a first embodiment of the elastic wave device comprising a plurality of elastic wave resonators.

[0026] Figure 10 This is an explanatory diagram showing the relationship between d / 2p, metallization rate (MR), and relative bandwidth.

[0027] Figure 11 This is an illustrative diagram showing the mapping of the relative bandwidth with respect to the Euler angles (0°, θ, ψ) of lithium niobate when d / p approaches 0.

[0028] Figure 12 It is Figure 2 The enlarged cross-sectional view of region A is shown below.

[0029] Figure 13 This is an explanatory diagram illustrating an example of the admittance characteristics of the elastic wave device according to the first embodiment.

[0030] Figure 14 This is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a first variation of the first embodiment.

[0031] Figure 15 This is an explanatory diagram illustrating an example of the admittance characteristics of an elastic wave device according to a second variation of the first embodiment.

[0032] Figure 16 This is a cross-sectional view showing the elastic wave device involved in the third variation of the first embodiment.

[0033] Figure 17 This is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to a third variation of the first embodiment.

[0034] Figure 18This is a cross-sectional view showing the elastic wave device involved in the fourth variation of the first embodiment.

[0035] Figure 19 This is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the fourth variation of the first embodiment.

[0036] Figure 20 This is a cross-sectional view showing the elastic wave device according to the second embodiment.

[0037] Figure 21 This is an explanatory diagram illustrating an example of the admittance characteristics of the elastic wave device according to the second embodiment.

[0038] Figure 22 This is a cross-sectional view showing the elastic wave device involved in the fifth variation of the second embodiment.

[0039] Figure 23 This is a cross-sectional view showing the elastic wave device involved in the sixth variation of the second embodiment.

[0040] Figure 24 This is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the sixth variation of the second embodiment.

[0041] Figure 25 This is an explanatory diagram showing the distribution of vibration modes of the elastic wave device according to the sixth variation of the second embodiment.

[0042] Figure 26 This is an explanatory diagram showing the distribution of vibration modes of the elastic wave device involved in the comparative example.

[0043] Figure 27 This is a cross-sectional view showing the elastic wave device involved in the seventh variation of the second embodiment.

[0044] Figure 28 This is a cross-sectional view showing the elastic wave device involved in the eighth variation of the second embodiment.

[0045] Figure 29 This is a circuit diagram showing the elastic wave device according to the third embodiment.

[0046] Figure 30 This is a cross-sectional view showing the elastic wave device involved in the 9th variation example.

[0047] Figure 31 This is a cross-sectional view showing the elastic wave device involved in the 10th variation example.

[0048] Figure 32 This is a top view showing the elastic wave device involved in the 11th variation example.

[0049] Figure 33 This is an illustrative diagram showing an example of the admittance characteristics of the elastic wave device involved in the 12th variation.

[0050] Figure 34 This is an illustrative diagram showing an example of the impedance phase in S2 mode. Detailed Implementation

[0051] Hereinafter, embodiments of the present disclosure will be described in detail based on the accompanying drawings. However, the present disclosure is not limited to these embodiments. Furthermore, the embodiments described in this disclosure are illustrative, and partial substitutions or combinations of structures are possible between different embodiments. From the modified examples and the second embodiment onwards, descriptions of matters common to the first embodiment are omitted, and only the differences are described. In particular, the same effects based on the same structure will not be mentioned repeatedly in each embodiment.

[0052] (First Embodiment)

[0053] Figure 1 This is a top view showing the elastic wave device of the first embodiment. Figure 2 yes Figure 1 Sectional view II-II'. Additionally, in Figure 1 In order to make the attached diagram easier to observe, the first protective film 41 is shown with a double-dotted line.

[0054] like Figure 1 as well as Figure 2 As shown, the elastic wave device 10 according to the first embodiment includes a piezoelectric layer 20, an IDT electrode 30, a support substrate 11, a first protective film 41, and a second protective film 42. Figure 2 As shown, the elastic wave device 10 has a second protective film 42, a piezoelectric layer 20, an IDT electrode 30, and a first protective film 41 stacked sequentially on the support substrate 11.

[0055] The piezoelectric layer 20 is 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 formed of lithium niobate. Alternatively, the piezoelectric layer 20 may also contain lithium tantalate. In the first embodiment, the lithium niobate or lithium tantalate is cut at a Z-angle. The lithium niobate or lithium tantalate may also be cut at a Y-angle or an X-angle. Preferably, the propagation orientation is ±30° for both Y and X propagation. Preferably, the piezoelectric layer 20 contains lithium niobate or lithium tantalate, and is cut at a 120°±10° Y-angle or a 90°±10° Y-angle.

[0056] The thickness of the piezoelectric layer 20 is not particularly limited, but in order to effectively excite the first-order mode of thickness shearing, it is preferably 50 nm or more and 1000 nm or less. The thickness of the piezoelectric layer 20 according to the first embodiment is, for example, about 180 nm.

[0057] The IDT (Interdigital Transducer) electrode 30 is disposed on the first main surface 20a of the piezoelectric layer 20. For example... Figure 1 As shown, the IDT electrode 30 has electrode fingers 31 and 32 and busbar electrodes 33 and 34. Multiple electrode fingers 31 extend in the Y direction, with one end connected to the busbar electrode 33 in the extending direction. Multiple electrode fingers 32 extend in the Y direction, with the other end connected to the busbar electrode 34 in the extending direction. The multiple electrode fingers 31 and 32 are arranged alternately in the X direction at intervals. The busbar electrode 33 and busbar electrode 34 extend in the X direction and are spaced apart in the Y direction. The multiple electrode fingers 31 and 32 are arranged between the busbar electrode 33 and the busbar electrode 34.

[0058] The outermost electrode finger 31 among the multiple electrode fingers 31 and 32 in the arrangement direction is designated as the first electrode finger 31a. The electrode finger 32 adjacent to the first electrode finger 31a, i.e., the second electrode finger 32 from the outermost position in the arrangement direction, is designated as the second electrode finger 32a. Furthermore, the pair of electrode fingers 31 and 32 located on the opposite side of the first electrode finger 31a and the second electrode finger 32a are designated as the third electrode finger 31b and the fourth electrode finger 32b, respectively. Detailed structures of the first electrode finger 31a, the second electrode finger 32a, the third electrode finger 31b, and the fourth electrode finger 32b are described using... Figure 12 , Figure 13 That will be described later.

[0059] In the following description, the thickness direction of the piezoelectric layer 20 will sometimes be defined 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. Furthermore, in the following description, "top view" refers to the arrangement when viewed from a direction perpendicular to the first main surface 20a of the piezoelectric layer 20.

[0060] The center-to-center distance between electrode fingers 31 and 32 (hereinafter referred to as the electrode spacing) is preferably in the range of 1 μm or more and 10 μm or less. Furthermore, the electrode spacing is defined as the distance connecting the center of the width dimension of electrode finger 31 in a direction orthogonal to the extension direction of electrode finger 31 and the center of the width dimension of electrode finger 32 in a direction orthogonal to the extension direction of electrode finger 32. Furthermore, the width of electrode fingers 31 and 32 (hereinafter referred to as electrode width), i.e., the dimension of electrode fingers 31 and 32 in the direction orthogonal to the extension direction, is preferably in the range of 150 nm or more and 1000 nm or less.

[0061] Furthermore, when there are multiple electrode fingers 31 and 32 (when there are 1.5 or more electrode groups when electrode fingers 31 and 32 are set as a pair of electrode groups), the electrode spacing of electrode fingers 31 and 32 refers to the average value of the center-to-center distance of adjacent electrode fingers 31 and 32 in 1.5 or more pairs of electrode fingers 31 and 32.

[0062] Furthermore, in the first embodiment, a Z-cut piezoelectric layer is used, so the direction orthogonal to the extension directions of electrode fingers 31 and 32 becomes the direction orthogonal to the polarization direction of the piezoelectric layer 20. This is not a limitation if a piezoelectric material with other cut angles is used as the piezoelectric layer 20. Here, "orthogonal" is not limited to strictly orthogonal; it can also be approximately orthogonal (the angle between the direction orthogonal to the extension directions of electrode fingers 31 and 32 and the polarization direction is, for example, 90° ± 10°).

[0063] The IDT electrodes 30 (electrodes 31, 32 and busbar electrodes 33, 34) comprise suitable metals or alloys such as aluminum or aluminum-copper alloys. In the first embodiment, the IDT electrodes 30 have a structure in which an aluminum film is laminated on a titanium film. Alternatively, a close-fitting layer other than a titanium film may be used.

[0064] More specifically, regarding the electrode structure of the IDT electrode 30, starting from the piezoelectric layer 20 side, it is a stacked film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12nm / 70nm / 18nm / 12nm. Furthermore, the IDT electrode 30 has a total of 51 electrode fingers 31 and 32. The inter-electrode spacing of electrode fingers 31 and 32 is 2.38μm, and the electrode width is 0.6μm.

[0065] Here, Figure 1 The cross region C (excitation region) shown is the area where electrode fingers 31 and 32 overlap when viewed in the X direction. The length of the cross region C is the dimension in the extending direction of electrode fingers 31 and 32 within the cross region C. In this embodiment, the length of the cross region C is, for example, 40 μm.

[0066] During driving, an alternating voltage is applied between multiple electrode fingers 31 and multiple electrode fingers 32. More specifically, an alternating voltage is applied between busbar electrodes 33 and 34. As a result, the resonant characteristics of a bulk wave utilizing the thickness shear first-order mode excited in the piezoelectric layer 20 can be obtained.

[0067] Furthermore, in the elastic wave device 10, when the thickness of the piezoelectric layer 20 is set to d and the inter-electrode spacing of the multiple pairs of electrode fingers 31 and 32 is set to p, d / p is set to 0.5 or less. Therefore, the bulk wave of the aforementioned thickness shear first mode can be effectively excited, and good resonance characteristics can be obtained. More preferably, d / p is 0.24 or less, in which case even better resonance characteristics can be obtained.

[0068] In the elastic wave device 10 of the first embodiment, the above-described structure is provided, so even if the number of pairs of electrode fingers 31 and 32 is reduced in order to achieve miniaturization, a decrease in the Q value is not easily generated. This is because it is a resonator that does not require reflectors on both sides, resulting in low propagation loss. Furthermore, the reason why the above-described reflectors are not required is because a body wave with a thickness shear first mode is utilized.

[0069] A first protective film 41 covers the IDT electrode 30 and is disposed on the first main surface 20a of the piezoelectric layer 20. A second protective film 42 is disposed on the second main surface 20b of the piezoelectric layer 20. Both the first protective film 41 and the second protective film 42 are formed of silicon oxide. In addition to silicon oxide, the first protective film 41 and the second protective film 42 can also be formed of suitable insulating materials such as silicon nitride or bauxite. The thickness of both the first protective film 41 and the second protective film 42 is greater than the thickness of the IDT electrode 30. The thicknesses of both the first protective film 41 and the second protective film 42 are 142 nm. Furthermore, it is sufficient to have at least one of the first protective film 41 and the second protective film 42. For example, a structure with the first protective film 41 but without the second protective film 42 is also possible.

[0070] The support substrate 11 (support member) is configured to face the second main surface 20b of the piezoelectric layer 20. The support substrate 11 has a cavity 14 (space portion) 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 frame-shaped wall portion 13 on the upper surface of the bottom 12. The cavity 14 is formed in the space surrounded by the bottom 12 and the wall portion 13. The piezoelectric layer 20 is laminated on the upper surface of the wall portion 13 of the support substrate 11 with a second protective film 42 in between. Thus, the elastic wave device 10 has a so-called diaphragm structure in which the cavity 14 (void portion) is provided on the side of the second main surface 20b of the piezoelectric layer 20. Alternatively, the support member may also include the support substrate 11 and an intermediate (insulating) layer.

[0071] The cavity 14 is provided so as not to interfere with the vibration of the cross region C of the piezoelectric layer 20. Furthermore, the second protective film 42 is provided to cover the opening of the cavity 14. However, as described above, the second protective film 42 may not be provided. In this case, the support substrate 11 can 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 not in the region overlapping with the cavity 14. That is, the support substrate 11 may also 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 also have a frame-like shape, thereby forming the cavity 14. Furthermore, a recess may be provided in the intermediate layer, thereby forming the cavity 14.

[0072] The support substrate 11 is formed of silicon. The orientation of the face on the side of the piezoelectric layer 20 of silicon can be (100), (110), or (111). Preferably, it is silicon with a high resistivity of 4kΩ or higher. However, the support substrate 11 can also be constructed using suitable insulating materials or semiconductor materials. For example, piezoelectric materials such as alumina, lithium tantalate, lithium niobate, and quartz, bauxite, magnesium oxide, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, and forsterite, as well as various ceramics such as diamond, glass, and semiconductors such as gallium nitride can be used.

[0073] Figure 3 This is a schematic cross-sectional view used to illustrate the bulk wave of the thickness shear first mode propagating in the piezoelectric layer of the first embodiment. Figure 4 This is a schematic cross-sectional view used to illustrate the amplitude direction of the bulk wave of the thickness shear first mode propagating in the piezoelectric layer of the first embodiment.

[0074] like Figure 3 As shown, in the elastic wave device 10 of the first embodiment, the vibration displacement is in the thickness shear direction, so the wave propagates and resonates approximately in the Z direction, which is the direction connecting the first principal surface 20a and the second principal surface 20b of the piezoelectric layer 20. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Moreover, since the resonance characteristic can be obtained through the propagation of the wave in this Z-direction, a reflector is not required. Therefore, no propagation loss occurs during propagation in the reflector. Therefore, even if the number of electrode pairs including electrode fingers 31 and 32 is reduced to promote miniaturization, a decrease in the Q value is not easily generated.

[0075] In addition, such as Figure 4 As shown, the amplitude direction of the bulk wave of the first-order thickness shear mode is in the intersection region C of the piezoelectric layer 20 (refer to...). Figure 1 The first region 251 contained in region C and the second region 252 contained in the intersection region C become opposite. Figure 4 The diagram schematically illustrates a bulk wave when a voltage is applied between electrode fingers 31 and 32, with electrode finger 32 having a higher potential than electrode finger 31. Here, the imaginary plane VP1 is a plane orthogonal to the thickness direction of the piezoelectric layer 20 and dividing the piezoelectric layer 20 into two parts. The first region 251 is the region between the imaginary plane VP1 and the first main surface 20a in the intersection region C. The second region 252 is the region between the imaginary plane VP1 and the second main surface 20b in the intersection region C.

[0076] In the elastic wave device 10, at least one pair of electrodes, including electrode fingers 31 and electrode fingers 32, is provided. However, the wave is not propagated in the X direction. Therefore, the number of electrode pairs including electrode fingers 31 and electrode fingers 32 does not necessarily have to be multiple. That is, it is sufficient to provide at least one pair of electrodes.

[0077] For example, electrode 31 is an electrode connected to a signal (hot) potential, and electrode 32 is an electrode connected to a ground potential. However, it is also possible that electrode 31 is connected to a ground potential, and electrode 32 is connected to a signal potential. In the first embodiment, as described above, at least one pair of electrodes is either an electrode connected to a signal potential or an electrode connected to a ground potential, and no floating electrode is provided.

[0078] Figure 5 This is an explanatory diagram showing an example of the resonant characteristics of the elastic wave device according to the first embodiment. (The diagram is incomplete and requires further context.) Figure 5 The design parameters of the elastic wave device 10 with the resonant characteristics shown are as follows.

[0079] Piezoelectric layer 20: Lithium niobate with Euler angles of (0°, 0°, 90°)

[0080] Thickness of piezoelectric layer 20: 400nm

[0081] Length of the cross region C: 40μm

[0082] Number of electrode pairs including electrode finger 31 and electrode finger 32: 21 pairs

[0083] Electrode spacing between electrode finger 31 and electrode finger 32: 3 μm

[0084] Width of electrode finger 31 and electrode finger 32: 500nm

[0085] d / p: 0.133

[0086] First protective film 41 and second protective film 42: silicon oxide film with a thickness of 1 μm.

[0087] Support substrate 11: Silicon

[0088] In the first embodiment, the inter-electrode spacing of the electrode pairs including electrode fingers 31 and electrode fingers 32 is set to be equal in all pairs. That is, the electrode fingers 31 and electrode fingers 32 are arranged at equal intervals.

[0089] according to Figure 5 It is clear that, despite the absence of a reflector, a good resonant characteristic with a relative bandwidth of 12.5% ​​was still achieved.

[0090] Furthermore, when the thickness of the piezoelectric layer 20 is set to d and the inter-electrode spacing between the electrode fingers 31 and 32 is set to p, in the first embodiment, d / p is 0.5 or less, more preferably 0.24 or less. (Refer to...) Figure 6 This needs to be explained.

[0091] Figure 6 This is an explanatory diagram showing the relationship between d / 2p and the relative bandwidth of the resonator when the center-to-center distance or the average center-to-center distance of adjacent electrodes is set as p and the average thickness of the piezoelectric layer is set as d in the elastic wave device of the first embodiment. Figure 6 In the middle, and obtained Figure 5 Similarly, the elastic wave device with the resonant characteristics shown is obtained by changing d / 2p, thus obtaining multiple elastic wave devices.

[0092] like Figure 6 As shown, if d / 2p exceeds 0.25, i.e., if d / p > 0.5, then even if d / p is adjusted, the relative bandwidth is less than 5%. In contrast, when d / 2p ≤ 0.25, i.e., when d / p ≤ 0.5, if d / p is varied within this range, the relative bandwidth can be increased to 5% or more, i.e., a resonator with a high coupling coefficient can be constructed. Furthermore, when d / 2p is 0.12 or less, i.e., when d / p is 0.24 or less, the relative bandwidth can be increased to 7% or more. In addition, if d / p is adjusted within this range, a resonator with an even wider relative bandwidth can be obtained, achieving a resonator with a higher coupling coefficient. Therefore, it can be seen that by keeping d / p below 0.5, a resonator with a high coupling coefficient utilizing the aforementioned thickness shear first-order mode of the bulk wave can be constructed.

[0093] Furthermore, regarding the thickness d of the piezoelectric layer 20, if the piezoelectric layer 20 has a thickness deviation, it is sufficient to use a value that has been averaged over the thickness.

[0094] Figure 7 This is a top view showing an example of an elastic wave device according to the first embodiment, in which a pair of electrodes are provided. In the elastic wave device 10, a pair of electrodes having electrode fingers 31 and electrode fingers 32 are provided on the first main surface 20a of the piezoelectric layer 20. Furthermore, Figure 7 K in the figure represents the cross width. As previously mentioned, in the elastic wave device 10 of this disclosure, the number of electrode pairs can also be one. In this case, as long as the aforementioned d / p is 0.5 or less, it is possible to effectively excite a first-order thickness shear mode volume wave.

[0095] In the elastic wave device 10, preferably, the metallization rate MR of the adjacent electrode fingers 31 and 32 relative to the intersection region C best satisfies MR ≤ 1.75 (d / p) + 0.075. In this case, stray emissions can be effectively reduced. (Refer to...) Figure 8 as well as Figure 9 This needs to be explained.

[0096] Figure 8 This is a reference diagram illustrating an example of the resonant characteristics of the elastic wave device according to the first embodiment. (See diagram below.) Figure 8 As shown, spurious emissions, indicated by arrow B, appear between the resonant and anti-resonant frequencies. Furthermore, d / p = 0.08, and the Euler angles of lithium niobate are assumed to be (0°, 0°, 90°). Additionally, the metallization rate MR is assumed to be 0.35.

[0097] Reference Figure 1 The metallization rate (MR) is explained. Figure 1 In the electrode structure, considering only a pair of electrode fingers 31 and 32, it is assumed that only this pair of electrode fingers 31 and 32 are provided. In this case, the portion enclosed by the single-dotted line is called the intersection region C. This intersection region C refers to the area where electrode fingers 31 and 32 overlap when observed in a direction orthogonal to the extending direction of electrode fingers 31 and 32 (i.e., in the opposing direction), the area where electrode fingers 31 and 32 overlap, the area where electrode fingers 32 overlap with electrode fingers 31, and the area between electrode fingers 31 and 32. Furthermore, the area of ​​electrode fingers 31 and 32 within the intersection region C relative to the area of ​​the intersection region C is called the metallization rate MR. That is, the metallization rate MR is the ratio of the area of ​​the metallized portion to the area of ​​the intersection region C.

[0098] In addition, when multiple pairs of electrode fingers 31 and electrode fingers 32 are provided, it is sufficient to set the ratio of the metallized portion contained in all cross regions C to the total area of ​​the cross regions C as MR.

[0099] Figure 9This is an explanatory diagram showing the relationship between the relative bandwidth and the phase rotation amount of the stray impedance, which is normalized by 180 degrees and represents the magnitude of the stray, in the case where a plurality of elastic wave resonators are configured in the elastic wave device of the first embodiment. Furthermore, regarding the relative bandwidth, various adjustments were made to the film thickness of the piezoelectric layer 20 and the dimensions of the electrode fingers 31 and 32. In addition, although... Figure 9 This is the result when a piezoelectric layer 20 containing Z-cut lithium niobate is used, but the same tendency occurs even when a piezoelectric layer 20 with other cut angles is used.

[0100] exist Figure 9 In the region enclosed by ellipse J, the stray energy increases to 1.0. According to... Figure 9 It is clear that if the relative bandwidth exceeds 0.17, that is, if it exceeds 17%, then even if the parameters constituting the relative bandwidth are changed, large spurious signals with a spurious level greater than 1 will appear in the passband. That is, like... Figure 8 As shown in the resonance characteristics, large stray rays appear within the band, as indicated by arrow B. Therefore, the relative bandwidth is preferably 17% or less. In this case, stray rays can be reduced by adjusting the thickness of the piezoelectric layer 20, the dimensions of the electrode fingers 31 and 32, etc.

[0101] Figure 10 This is an explanatory diagram showing the relationship between d / 2p, metallization rate MR, and relative bandwidth. Various elastic wave devices 10 with different d / 2p and MR were constructed in the elastic wave device 10 of the first embodiment, and the relative bandwidth was measured. Figure 10 The area to the right of the dashed line D, indicated by the shading, represents a region with a relative bandwidth of 17% or less. The boundary between this shaded and unshaded region can be represented by MR = 3.5(d / 2p) + 0.075, i.e., MR = 1.75(d / p) + 0.075. Therefore, MR ≤ 1.75(d / p) + 0.075 is preferred. In this case, it is easier to achieve a relative bandwidth of 17% or less. More preferably... Figure 10 The region to the right of the dashed line D1 in the diagram is MR = 3.5(d / 2p) + 0.05. That is, if MR ≤ 1.75(d / p) + 0.05, the relative bandwidth can be reliably kept below 17%.

[0102] Figure 11 This is an illustrative diagram showing the mapping of the relative bandwidth with respect to the Euler angles (0°, θ, ψ) of lithium niobate when d / p approaches 0. Figure 11 The area shown by the shading is the region where a relative bandwidth of at least 5% can be obtained. If the range of the region is approximated, it becomes the range represented by the following equations (1), (2) and (3).

[0103] (0°±10°, 0°~20°, any ψ)... Equation (1)

[0104] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ]~180°)…Formula (2)

[0105] (0°±10°, [180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ~180°, any ψ)

[0106] …Formula (3)

[0107] Therefore, within the range of Euler angles in equations (1), (2), or (3) above, it is preferable to have a sufficiently wide relative bandwidth.

[0108] Next, the detailed structure of the IDT electrode 30 will be explained. Figure 12 It is Figure 2 The enlarged cross-sectional view shown is of region A. Additionally, in Figure 12 In this description, the first electrode finger 31a, located on the outermost side in the arrangement direction of the plurality of electrode fingers 31, 32, and the second electrode finger 32a adjacent to the first electrode finger 31a, are explained. However, the third electrode finger 31b and the fourth electrode finger 32b, located on the outermost side opposite to the first electrode finger 31a and the second electrode finger 32a (see reference 31a) are also described. Figure 1 , Figure 2 It also has a linearly symmetrical configuration. The description of the first electrode finger 31a and the second electrode finger 32a can also be applied to the third electrode finger 31b and the fourth electrode finger 32b. Furthermore, in the following description, unless it is necessary to distinguish between the first electrode finger 31a and the second electrode finger 32a, they will only be referred to as electrode fingers 31 and 32.

[0109] like Figure 12 As shown, the first electrode finger 31a, the second electrode finger 32a, and the central electrode fingers 31 and 32, which are different from the first electrode fingers 31a and the second electrode fingers 32a, are disposed in the same layer on the first main surface 20a of the piezoelectric layer 20. The first protective film 41 is configured to cover the first electrode fingers 31a, the second electrode fingers 32a, and the central electrode fingers 31 and 32. In this embodiment, the upper surface of the first protective film 41 is formed flat. Furthermore, the lower surface of the second protective film 42 is formed flat along the second main surface 20b of the piezoelectric layer 20.

[0110] 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. Furthermore, the thickness t1 of the first protective film 41 is thinner than the thickness t3 of the piezoelectric layer 20, and thicker than the heights H1 and Hc (film thickness) of the IDT electrode 30.

[0111] like Figure 12 As shown, the product Xe (=W1×H1×d1) of the width W1, height H1, and density d1 of at least one of the first electrode finger 31a and the second electrode finger 32a is greater than the product Xc (=Wc×Hc×dc) of the width Wc, height Hc, and density dc of the central portion of the plurality of electrode fingers 31 and 32 that is different from the first electrode finger 31a and the second electrode finger 32a. In the following description, the product Xe and the product Xc are values ​​calculated for one electrode finger 31 and 32 respectively. In addition, the term "density" in this embodiment, unless otherwise specified, refers to the inherent physical property value of the material. The densities of the materials used for the electrode fingers 31 and 32 are shown below. Tungsten: 19.3 g / cm³ 3 Molybdenum: 10.22 g / cm³ 3 Ruthenium: 12.41 g / cm³ 3 Platinum: 21.45 g / cm³ 3 Copper: 8.96 g / cm³ 3 Silver: 10.5g / cm³ 3 Chromium: 7.189 g / cm³ 3 Gold 19.32 g / cm³ 3 .

[0112] In this embodiment, the product Xe (=W1×H1×d1) of the outermost first electrode finger 31a in the arrangement direction is greater than the product Xc (=Wc×Hc×dc) of the second electrode finger 32a adjacent to the first electrode finger 31a and the electrode fingers 31 and 32 in the central part. In the following description, the second electrode finger 32a adjacent to the first electrode finger 31a and the electrode fingers 31 and 32 in the central part are referred to as other electrode fingers 31 and 32.

[0113] As an 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 widths W1 and Wc are, for example, 0.6 μm.

[0114] Furthermore, the outermost first electrode finger 31a in the arrangement direction of the first electrode finger 31a and the second electrode finger 32a is formed of a material with a higher density than the central electrode fingers 31 and 32. The first electrode finger 31a is formed of a platinum monolayer. The density d1 of the first electrode finger 31a (platinum) is 21450 kg / m³. 3 As mentioned above, the other electrodes, 31 and 32, are multilayer films of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy. The density of the aluminum-copper alloy constituting the other electrodes 31 and 32 is 2695 kg / m³. 3 Titanium has a density of 4500 kg / m³. 3 In other words, the density d1 of the first electrode finger 31a is greater than the density dc of the other electrode fingers 31 and 32.

[0115] Furthermore, the height H1 (film thickness) of the first electrode finger 31a is 112 nm. The film thicknesses of the stacked films constituting the second electrode finger 32a are 12 nm / 70 nm / 18 nm / 12 nm respectively. That is, the total height Hc (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 both height H1 and height Hc are 112 nm.

[0116] 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 / m²) 3 =1441.44. The product Xc (=Wc×Hc×dc) of the other electrodes 31 and 32 is Xc = 0.6 (μm) × 0.03 (μm) × 4500 (kg / m²). 3 )+0.6(μm)×0.082(μm)×2695(kg / m 3 =213.594.

[0117] Figure 13 This is an explanatory diagram illustrating an example of the admittance characteristics of the elastic wave device according to the first embodiment. Figure 13 This is an explanatory diagram showing the real part of the admittance, i.e., the conductivity component, of the elastic wave device 10 according to the first embodiment. Figure 13 The admittance characteristics shown illustrate simulation results of the admittance characteristics of the elastic wave device 10 according to the first embodiment. Furthermore, in Figure 13Simulation results of the admittance characteristics of the elastic wave device involved in the comparative example are also shown. Compared to the first embodiment, the comparative example is an elastic wave device with the following structure: the product Xe (=W1×H1×d1) of the first electrode finger 31a located on the outermost side 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 with the following structure: the first electrode finger 31a, like the other electrode fingers 31 and 32, is formed of a multilayer film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy.

[0118] like Figure 13 As shown, in the elastic wave device of the comparative example, ripple is generated in a frequency region different from the resonant frequency. In particular, a large ripple, indicated by dotted line E1, is generated in the comparative example. In contrast, in the elastic wave device 10 according to the first embodiment, it is shown that the product Xe of the first electrode finger 31a is greater than the product Xc of the other electrode fingers 31 and 32, thereby suppressing the ripple shown by dotted line E1 compared to the comparative example. Furthermore, the elastic wave device 10 according to the first embodiment suppresses propagation loss in the frequency range shown by dotted line E2 compared to the comparative example. It can be seen that the elastic wave device 10 according to the first embodiment has a narrower peak width related to the resonant frequency compared to the elastic wave device according to the comparative example, thus suppressing propagation loss and suppressing elastic wave leakage.

[0119] Furthermore, in the first embodiment, the density d1 of the first electrode finger 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 finger 31a are equal to the width Wc and height Hc of the other electrode fingers 31 and 32. However, this is not a limitation; the structure could also be such that the density d1 of the first electrode finger 31a is equal to the density d2 of the other electrode fingers 31 and 32, and the width W1 of the first electrode finger 31a is greater than the width Wc of the other electrode fingers 31 and 32. Alternatively, the structure could be such that the density d1 of the first electrode finger 31a is equal to the density d2 of the other electrode fingers 31 and 32, and the height H1 of the first electrode finger 31a is higher than the height Hc of the other electrode fingers 31 and 32. It is also possible that two or more of the width W1, height H1, and density d1 of the first electrode finger 31a are different from the width Wc, height Hc, and density dc of the other electrode fingers 31 and 32.

[0120] Furthermore, the materials of the multiple electrode tips 31 and 32 of the IDT electrode 30 are merely one example and are not limited thereto. For example, at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum can be used.

[0121] (First variation of the first embodiment)

[0122] Figure 14 This is an explanatory diagram illustrating an example of the admittance characteristics of the elastic wave device according to a first variation of the first embodiment. In the first embodiment described above, the structure in which the product Xe (=W1×H1×d1) of the outermost first electrode finger 31a in the arrangement direction is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32) has been described, but it is not limited to this.

[0123] In the elastic wave device involved in the first modification, the product Xe (=W1×H1×d1) of the first electrode finger 31a and the second electrode finger 32a, that is, the first electrode finger 31a located on the outermost side in the arrangement direction and the second electrode finger 32a adjacent to the first electrode finger 31a (the second second electrode finger 32a located from the outer side in the arrangement direction) is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 (the electrode fingers 31 and 32 in the central part).

[0124] In the first variation, the electrode structure of the first electrode finger 31a and the second electrode finger 32a is a platinum monolayer. 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. Furthermore, 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).

[0125] 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 equal to the product Xe (=W1×H1×d1) of the first electrode finger 31a described in the first embodiment. Furthermore, the product Xc (=Wc×Hc×dc) of each of the other electrode fingers 31 and 32 (the central electrode fingers 31 and 32) in the first modification are equal to the product Xc (=Wc×Hc×dc) of each of the other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32) described in the first embodiment.

[0126] like Figure 14As shown, in the elastic wave device according to the first modification, even if the product Xe of the first electrode finger 31a and the second electrode finger 32a is greater than the product Xc of the other electrode fingers 31 and 32, the ripple shown by the dotted line E1 can be suppressed at least compared with the comparative example, similar to the first embodiment. Furthermore, in the first modification, propagation loss can also be suppressed in the frequency range shown by the dotted line E2.

[0127] (Second variation of the first embodiment)

[0128] Figure 15 This is an explanatory diagram illustrating an example of the admittance characteristics of the elastic wave device according to the second modification of the first embodiment. In the elastic wave device according to the second modification, the product Xe (=W1×H1×d1) of the second electrode finger 32a (the second electrode finger 32 located from the outside of the first electrode finger 31a in the arrangement direction) of the first electrode finger 31a and the second electrode finger 32a is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 (the first electrode finger 31a and the central electrode fingers 31 and 32).

[0129] In the second variation, the outermost first electrode finger 31a in the arrangement direction is not a platinum monolayer, while the electrode structure of the second electrode finger 32a adjacent to the first electrode finger 31a is a platinum monolayer. 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). Furthermore, 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).

[0130] That is, the product Xe (=W1×H1×d1) of the second electrode finger 32a in the second modification is equal to the product Xe (=W1×H1×d1) of the first electrode finger 31a described in the first embodiment. Furthermore, the product Xc (=Wc×Hc×dc) of each of the other electrode fingers 31 and 32 (the first electrode finger 31a and the central electrode fingers 31 and 32) in the second modification is equal to the product Xc (=Wc×Hc×dc) of each of the other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32) described in the first embodiment.

[0131] like Figure 15As shown, in the elastic wave device involved in the second modified example, it is shown that even if the product Xe of the second electrode finger 32a located second from the outside in the arrangement direction is greater than the product Xc of the other electrode fingers 31 and 32, the ripple shown by the dotted line E1 can be suppressed at least compared with the comparative example, just like in the first embodiment.

[0132] (Third variation of the first embodiment)

[0133] Figure 16 This is a cross-sectional view showing the elastic wave device according to the third variation of the first embodiment. (See attached image.) Figure 16 As shown, in the elastic wave device 10A according to the third modification, the film thickness t1 of the first protective film 41 and the film thickness t2 of the second protective film 42 are thinner than the film thickness t3 of the piezoelectric layer 20. Specifically, the film thickness of the piezoelectric layer 20 is, for example, 360 nm. The film thickness t1 of the first protective film 41 is 30 nm. The film thickness t2 of the second protective film 42 is 30 nm. Furthermore, the film thickness t1 of the first protective film 41 is thinner than the film thickness (heights H1, Hc) of the IDT electrode 30.

[0134] In the third variation, the first protective film 41 is provided in accordance with the surface and side of the electrode fingers 31 and 32 and the first main surface 20a of the piezoelectric layer 20. Because the thickness t1 of the first protective film 41 is thin, an uneven surface reflecting the shape of the electrode fingers 31 and 32 is formed on the upper surface of the first protective film 41.

[0135] The electrode structure of the IDT electrode 30 is the same as in the first embodiment, except that the density d1 of the first electrode finger 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 finger 31a are equal to the width Wc and height Hc of the other electrode fingers 31 and 32. However, the film thickness is different from that in the first embodiment described above.

[0136] That is, in the third variation, the outermost first electrode finger 31a in the arrangement direction is a platinum monolayer with a height H1 (film thickness) of 69 nm. The other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 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 total height Hc (film thickness) of the other electrode fingers 31 and 32 is 69 nm.

[0137] In the third variation, the product Xe (=W1×H1×d1) of the outermost first electrode finger 31a in the arrangement direction is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32).

[0138] The product Xe (=W1×H1×d1) of the first electrode finger 31a is Xe=0.6 (μm)×0.069 (μm)×21450 (kg / m²) 3 =888.03. The product Xc (=Wc×Hc×dc) of the other electrodes 31 and 32 is Xc = 0.6 (μm) × 0.03 (μm) × 4500 (kg / m²). 3 )+0.6(μm)×0.039(μm)×2695(kg / m 3 =144.063.

[0139] Figure 17 This is an explanatory diagram showing an example of the admittance characteristics of an elastic wave device according to a third variation of the first embodiment. Figure 17 The comparative example shown is an elastic wave device in which the elastic wave device 10A shown in the third modified example has a structure in which the thicknesses t1 and t2 of the first protective film 41 and the second protective film 42 are thinner than the thickness t3 of the piezoelectric layer 20. The electrode structure of the first electrode finger 31a located on the outermost side in the arrangement direction is the same as the electrode structure of the other electrode fingers 31 and 32.

[0140] like Figure 17 As shown, 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 can be suppressed compared with the comparative example, and the propagation loss can also be suppressed in the frequency range shown by the dotted line E2.

[0141] The electrode structure of the IDT electrode 30 shown in the third modification example can be combined with the first and second modifications described above. That is, it can also be a structure in which the product Xe (=W1×H1×d1) of the first electrode finger 31a and the second electrode finger 32a is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 (the central electrode fingers 31 and 32). Alternatively, it can also be a structure in which the product Xe (=W1×H1×d1) of the second electrode finger 32a located second from the outside in the arrangement direction is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 (the first electrode finger 31a and the central electrode fingers 31 and 32).

[0142] (Fourth variation of the first embodiment)

[0143] Figure 18 This is a cross-sectional view showing the elastic wave device according to the fourth variation of the first embodiment. (See attached image.) Figure 18As shown, in the elastic wave device 10B according to the fourth modification, the height H1 of the first electrode finger 31a located on the outermost side in the arrangement direction is higher than the height Hc of the other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32).

[0144] In the fourth variation, 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.

[0145] Specifically, the outermost electrode 31a, located in the arrangement direction, is a single layer of aluminum with a height H1 (film thickness) of 100 nm. The other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32) are, as described above, multilayer films of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12 nm / 27 nm / 18 nm / 12 nm. The total height Hc (film thickness) of the other electrode fingers 31 and 32 is 69 nm.

[0146] The product Xe (=W1×H1×d1) of the first electrode finger 31a is Xe=0.6 (μm)×0.100 (μm)×2695 (kg / m²). 3 =161.7. The product Xc (=Wc×Hc×dc) of the other electrodes 31 and 32 is the same as that of the third variant, Xc=144.063.

[0147] In this way, in the fourth variation, the product Xe (=W1×H1×d1) of the outermost first electrode finger 31a in the arrangement direction is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32).

[0148] Figure 19 This is an explanatory diagram illustrating an example of the admittance characteristics of the elastic wave device according to the fourth modification of the first embodiment. (See diagram below.) Figure 19 As shown, in the elastic wave device 10B shown in the fourth modified example, even when the thicknesses t1 and t2 of the first protective film 41 and the second protective film 42 are thin and the height H1 of the first electrode finger 31a located on the outermost side in the arrangement direction is high, the ripple shown by the dotted line E2 can be suppressed at least compared with the comparative example, and the propagation loss can be suppressed.

[0149] The electrode structure of the IDT electrode 30 shown in the fourth modification example can be combined with the first and second modifications described above. Alternatively, the structure may have a height H1 greater than the height Hc of the other electrode fingers 31 and 32 (the central electrode fingers 31 and 32). Or, the structure may have a height H1 greater than the height Hc of the second electrode finger 32a, which is the second one from the outside in the arrangement direction.

[0150] (Second Implementation)

[0151] Figure 20 This is a cross-sectional view showing the elastic wave device according to the second embodiment. (As shown) Figure 20 As shown, the elastic wave device 10C according to the second embodiment has an additional electrode 35. The additional electrode 35 is disposed in a region overlapping with at least one of the first electrode finger 31a and the second electrode finger 32a, which are located on the outermost side of the plurality of electrode fingers 31, 32 in the arrangement direction of the plurality of electrode fingers 31, 32. In the second embodiment, the additional electrode 35 is disposed directly on the first electrode finger 31a located on the outermost side in the arrangement direction. Furthermore, in the second embodiment, the additional electrode 35 is not disposed on the second electrode finger 32a located on the second side from the outside in the arrangement direction.

[0152] The first electrode, 31a, is a multilayer film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12nm / 70nm / 18nm / 12nm. The height H1 (total film thickness) of the first electrode, 31a, is 112nm. The additional electrode, 35, is an aluminum-copper alloy with a height H2 (film thickness) of 110nm. The total height of the multilayer film of the first electrode, 31a, and the additional electrode, 35 (the sum of height H1 and height H2), is 222nm.

[0153] The width W2 of the additional electrode 35 is equal to the width W1 of the first electrode finger 31a, both being 0.6 μm. Furthermore, the density d2 of the additional electrode 35 (aluminum-copper alloy) is equal to the density of a portion of the first electrode finger 31a (aluminum-copper alloy).

[0154] The other electrodes, 31 and 32 (the second electrode is 32a and the central electrodes are 31 and 32), are, as described above, titanium / aluminum-copper alloy / titanium / aluminum-copper alloy laminated films, with respective film thicknesses of 12nm / 70nm / 18nm / 12nm. The height Hc (total film thickness) of each of the other electrodes, 31 and 32, is 112nm.

[0155] In this embodiment, the sum 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 (Xe1+Xe2) 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 and 32) among the plurality of electrode fingers 31 and 32.

[0156] The total of the product Xe1 (=W1×H1×d1) of the first electrode 31a and the product Xe2 (=W2×H2×d2) of the additional electrode 35 (Xe1+Xe2) is Xe1+Xe2=0.6 (μm)×0.03 (μm)×4500 (kg / m²). 3 )+0.6(μm)×0.192(μm)×2695(kg / m 3 =391.464. The product Xc (=Wc×Hc×dc) of the other electrodes 31 and 32 is Xc = 0.6 (μm) × 0.03 (μm) × 4500 (kg / m²). 3 )+0.6(μm)×0.082(μm)×2695(kg / m 3 =213.594.

[0157] Figure 21 This is an explanatory diagram illustrating an example of the admittance characteristics of the elastic wave device according to the second embodiment. Figure 21 The comparative example shown is an elastic wave device without an additional electrode 35 in the elastic wave device 10C shown in the second embodiment.

[0158] like Figure 21 As shown, the elastic wave device 10C according to the second embodiment has an additional electrode 35 provided on the outermost first electrode finger 31a in the arrangement direction, thus suppressing at least the ripple shown by dotted line E1 compared to the comparative example. Furthermore, the elastic wave device 10C shown in the second embodiment can suppress propagation loss in the frequency range shown by dotted line E2.

[0159] In addition, in the second embodiment, the additional electrode 35 is disposed on the outermost first electrode finger 31a in the arrangement direction, but it is not limited to this. For example, it is also possible to have a plurality of additional electrodes 35, which are disposed on each of the first electrode finger 31a and the second electrode finger 32a. Alternatively, the additional electrode 35 may not be disposed on the outermost first electrode finger 31a in the arrangement direction, but on the second electrode finger 32a adjacent to the first electrode finger 31a.

[0160] In addition, Figure 20In this configuration, the additional electrode 35 is configured to protrude from the upper surface of the first protective film 41, but is not limited thereto. The first protective film 41 may also be configured to cover the additional electrode 35. The film thickness t1 of the first protective film 41 may also be thicker than the height (the sum of height H1 and height H2) of the laminated film of the first electrode finger 31a and the additional electrode 35. The material of the additional electrode 35 is not limited to an aluminum-copper alloy; for example, at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum may be used.

[0161] (Fifth variation of the second embodiment)

[0162] Figure 22 This is a cross-sectional view showing the elastic wave device according to the fifth variation of the second embodiment. (See attached image.) Figure 22 As shown, in the elastic wave device 10D according to the fifth modification, the additional electrode 35 is disposed on the first protective film 41 in the region overlapping with the first electrode finger 31a located on the outermost side in the arrangement direction. In other words, the first protective film 41 is disposed between the first electrode finger 31a and the additional electrode 35 in a direction perpendicular to the first main surface 20a of the piezoelectric layer 20. The first electrode finger 31a and the additional electrode 35 are electrically isolated by the first protective film 41. The upper surface of the first protective film 41 is formed flatly, spanning the region overlapping with the electrode fingers 31 and 32 and the region not overlapping with the electrode fingers 31 and 32. The additional electrode 35 is configured to protrude from the upper surface of the first protective film 41.

[0163] In the fifth modification, the electrode structure and material of the first electrode finger 31a and the additional electrode 35 are the same as those in the fourth modification described above. Even in the structure where the first electrode finger 31a and the additional electrode 35 are arranged separately, the sum 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 (Xe1+Xe2) is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers among the plurality of electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32).

[0164] Furthermore, in the fifth modification, the additional electrode 35 is disposed on the first protective film 41 in a region overlapping with the outermost first electrode finger 31a in the arrangement direction, but this is not a limitation. For example, it is also possible to have multiple additional electrodes 35, which are disposed on the first protective film 41 and in regions overlapping with both the first electrode finger 31a and the second electrode finger 32a. Alternatively, the additional electrode 35 may not be disposed in the region overlapping with the outermost first electrode finger 31a in the arrangement direction, but rather in the region overlapping with the second electrode finger 32a adjacent to the first electrode finger 31a on the first protective film 41.

[0165] (Sixth variation of the second embodiment)

[0166] Figure 23 This is a cross-sectional view showing the elastic wave device according to the sixth variation of the second embodiment. (See attached image.) Figure 23 As shown, in the elastic wave device 10E according to the sixth modification, the additional electrode 35 is disposed on the second main surface 20b of the piezoelectric layer 20 in a region overlapping with the first electrode finger 31a located on the outermost side in the arrangement direction. The second protective film 42 covers the additional electrode 35 and is disposed on the second main surface 20b of the piezoelectric layer 20. The additional electrode 35 is not disposed on the side of the first main surface 20a of the piezoelectric layer 20, and the upper surface of the first protective film 41 is formed flat.

[0167] The first electrode 31a is a multilayer film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy, with respective film thicknesses of 12nm / 70nm / 18nm / 12nm. The height H1 (total film thickness) of the first electrode 31a is 112nm. The additional electrode 35 is a multilayer film of titanium / aluminum-copper alloy / titanium / aluminum-copper alloy sequentially stacked from the second main surface 20b side of the piezoelectric layer 20, with respective film thicknesses of 12nm / 70nm / 18nm / 12nm. The height H2 (film thickness) of the additional electrode 35 is 112nm.

[0168] The width W2 of the additional electrode 35 is greater 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 offset Wx between the center (electrode center) of the first electrode finger 31a and the center (electrode center) of the additional electrode 35 in the width direction is 0.2 μm. Furthermore, the density d2 of the additional electrode 35 is equal to the density d1 of the first electrode finger 31a.

[0169] The electrode structures (width Wc, height Hc, density dc) of the other electrode fingers 31 and 32 (the second electrode finger 32a and the central electrode fingers 31 and 32) are the same as those of the first electrode finger 31a.

[0170] In the sixth variation, even if the first electrode finger 31a is disposed on the first main surface 20a of the piezoelectric layer 20 and the additional electrode 35 is disposed on the second main surface 20b of the piezoelectric layer 20, the sum 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 (Xe1+Xe2) is greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers (the second electrode finger 32a and the electrode fingers 31 and 32 in the central part) among the multiple electrode fingers 31 and 32.

[0171] The total of the product Xe1 (=W1×H1×d1) of the first electrode 31a and the product Xe2 (=W2×H2×d2) of the additional electrode 35 (Xe1+Xe2) is Xe1+Xe2=0.6 (μm)×0.03 (μm)×4500 (kg / m²). 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 =640.782. The product Xc (=Wc×Hc×dc) of the other electrodes 31 and 32 is Xc = 0.6 (μm) × 0.03 (μm) × 4500 (kg / m²). 3 )+0.6(μm)×0.082(μm)×2695(kg / m 3 =213.594.

[0172] Figure 24 This is an explanatory diagram illustrating an example of the admittance characteristics of the elastic wave device according to the sixth modification of the second embodiment. (See diagram below.) Figure 24 As shown, even with the structure of adding an electrode 35 to the second main surface 20b of the piezoelectric layer 20, the elastic wave device 10E according to the sixth modification can at least suppress the ripple shown by dotted line E1 compared to the comparative example. Furthermore, the elastic wave device 10E according to the sixth modification can suppress propagation loss in the frequency range shown by dotted line E2. In addition, in this embodiment, the upper surface of the first protective film 41 is formed flat, thus allowing for easy adjustment of the resonant frequency by changing the thickness of the first protective film 41.

[0173] In addition, in the sixth variation, the additional electrode 35 is disposed on the second main surface 20b of the piezoelectric layer 20 in a region overlapping with the outermost first electrode finger 31a in the arrangement direction, but this is not a limitation. For example, it is also possible to have multiple additional electrodes 35, which are disposed on the second main surface 20b of the piezoelectric layer 20 and in regions that overlap with both the first electrode finger 31a and the second electrode finger 32a. Alternatively, the additional electrode 35 may not be disposed in the region overlapping with the outermost first electrode finger 31a in the arrangement direction, but rather in the region overlapping with the second electrode finger 32a adjacent to the first electrode finger 31a on the second main surface 20b of the piezoelectric layer 20.

[0174] Furthermore, the electrode structure (width W2, height H2, density d2) of the additional electrode 35 and its offset Wx from the first electrode finger 31a are merely examples and can be appropriately modified. For example, it is not limited to a structure where the width W2 of the additional electrode 35 is greater than the width W1 of the first electrode finger 31a. The width W2, height H2, and density d2 of the additional electrode 35 can also 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 can also be 0 (zero). Furthermore, the additional electrode 35 is not limited to a laminated film; it can also be a multilayer film, or it can be formed of a material having a different density than the first electrode finger 31a.

[0175] Figure 25 This is an explanatory diagram showing the distribution of vibration modes of the elastic wave device according to the sixth variation of the second embodiment. Figure 26 This is an explanatory diagram showing the distribution of vibration modes of the elastic wave device involved in the comparative example. Figure 26 The comparative example shown is a structure in which the additional electrode 35 is not provided, compared to the elastic wave device 10E involved in the sixth modified example.

[0176] exist Figure 25 as well as Figure 26 In the sixth modified example and comparative example, the horizontal axis is set to the X direction (the arrangement direction of electrodes 31 and 32), and the vertical axis is set to the frequency, thus showing the distribution of the magnitude of the displacement of the piezoelectric layer 20. Figure 25 as well as Figure 26 The figures above schematically show cross-sectional views of the elastic wave device corresponding to the X-direction. Figure 25 as well as Figure 26 The left figure shows the impedance characteristics of the elastic wave device.

[0177] like Figure 26 As shown, in the elastic wave device of the comparative example, the X-direction dependence of the displacement (the X-direction position of the displacement's belly and node) has a large frequency dependence. For example, the X-direction position of the peak displacement is shown to shift with frequency, indicating that the device is not stably excited between the electrodes. Furthermore, if a given X position (around X = 5.0 μm) is of interest, phase reversal occurs at the resonant frequency of 5030 MHz and at frequencies of 4900 MHz and 5120 MHz where ripples are generated. Thus, in the elastic wave device of the comparative example, an ideal excitation mode is sometimes not obtained.

[0178] In contrast, such as Figure 25As shown, in the elastic wave device 10E according to the sixth modification, the X-direction dependence of the displacement (the X-direction position of the displacement's belly and node) is not frequency-dependent. That is, it is shown that the X-direction position of the peak displacement is fixed regardless of the frequency, and is stably excited between the electrodes. Furthermore, the magnitude (amplitude) of the displacement also becomes fixed for each region between the electrodes, and no phase reversal occurs at the resonant frequency and the frequency arrangement that generates ripples. In this way, it is shown that by providing an additional electrode 35 in the region overlapping with the outermost first electrode finger 31a located in the arrangement direction, a better excitation mode can be obtained compared to the comparative example.

[0179] (Seventh variation of the second embodiment)

[0180] Figure 27 This is a cross-sectional view showing the elastic wave device according to the seventh modification of the second embodiment. (See attached image.) Figure 27 As shown, in the elastic wave device 10F according to the seventh modification, the additional electrode 35 is disposed on the second main surface 20b side of the piezoelectric layer 20 in a region overlapping with the first electrode finger 31a located on the outermost side in the arrangement direction. More specifically, the additional electrode 35 is configured to be opposite to and spaced apart from the second main surface 20b of the piezoelectric layer 20.

[0181] The additional electrode 35 is disposed within the second protective film 42. That is, the second protective film 42 is disposed between the second main surface 20b of the piezoelectric layer 20 and the additional electrode 35, and covers the side surface and the lower surface (the side opposite to the piezoelectric layer 20) of the additional electrode 35.

[0182] In the seventh modification, the electrode structure of the first electrode finger 31a and the additional electrode 35 can be set to the same structure as in the sixth modification. That is, in the seventh modification, the sum 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 (Xe1+Xe2) is also greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers (the second electrode finger 32a and the central electrode fingers 31 and 32) among the plurality of electrode fingers 31 and 32.

[0183] (Eighth variation of the second embodiment)

[0184] Figure 28 This is a cross-sectional view showing the elastic wave device according to the eighth variation of the second embodiment. (See attached image.) Figure 28As shown, in the elastic wave device 10G according to the eighth modification, an additional electrode 35 is disposed on the lower surface of the second protective film 42 in a region overlapping with the first electrode finger 31a located on the outermost side in the arrangement direction. The lower surface of the second protective film 42 is formed flatly along the second main surface 20b of the piezoelectric layer 20. The additional electrode 35 is configured to protrude from the lower surface of the second protective film 42. Furthermore, the so-called lower surface of the second protective film 42 is the surface of the second protective film 42 that meets the support substrate 11 (see reference 10G). Figure 2 Opposite face.

[0185] In the eighth modification, the electrode structure of the first electrode finger 31a and the additional electrode 35 can be set to the same structure as in the sixth and seventh modifications. That is, in the eighth modification, the sum 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 (Xe1+Xe2) is also greater than the product Xc (=Wc×Hc×dc) of the other electrode fingers (the second electrode finger 32a and the central electrode fingers 31 and 32) among the plurality of electrode fingers 31 and 32.

[0186] Furthermore, in the seventh and eighth modifications, the additional electrode 35 is disposed in the region overlapping with the outermost first electrode finger 31a in the arrangement direction, but this is not a limitation. For example, multiple additional electrodes 35 may be provided, and these multiple additional electrodes 35 may be disposed in the second protective film 42 or on the lower surface of the second protective film 42 in the regions overlapping with the first electrode finger 31a and the second electrode finger 32a, respectively. Alternatively, the additional electrode 35 may not be disposed in the region overlapping with the outermost first electrode finger 31a in the arrangement direction, but may be disposed in the second protective film 42 or on the lower surface of the second protective film 42 in the region overlapping with the second electrode finger 32a adjacent to the first electrode finger 31a.

[0187] In the seventh and eighth modifications, the electrode structure (width W2, height H2, density d2) and offset Wx of the additional electrode 35 relative to the first electrode finger 31a are merely examples and can be appropriately modified. For example, it is not limited to a structure where the width W2 of the additional electrode 35 is greater than the width W1 of the first electrode finger 31a. The width W2, height H2, and density d2 of the additional electrode 35 may also 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 also be formed of a material having a different density than the first electrode finger 31a.

[0188] (Third implementation)

[0189] Figure 29This is a circuit diagram illustrating the elastic wave device according to the third embodiment. Figure 29 As shown, the elastic wave device 10H according to the third embodiment includes a plurality of series arm resonators 61, 62, 63 and a plurality of parallel arm resonators 64, 65, 66, 67. The plurality of series arm resonators 61, 62, 63 are connected in series in the signal path between the input terminal 60A and the output terminal 60B. The plurality of parallel arm resonators 64, 65, 66, 67 are connected in parallel between the signal path between the input terminal 60A and the output terminal 60B and ground 68. The elastic wave device 10H according to the ninth embodiment is a so-called trapezoidal filter.

[0190] One terminal of each of the series-connected series-arm resonators 61, 62, and 63 is electrically connected to input terminal 60A, and the other terminal is electrically connected to output terminal 60B. One terminal of the parallel-arm resonator 64 is electrically connected to 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 the signal path connecting 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 the signal path connecting 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 output terminal 60B, and the other terminal is electrically connected to ground 68.

[0191] In this embodiment, different electrode structures are used for the first electrode finger 31a and the second electrode finger 32a located on the outer side of the arrangement direction in the plurality of series arm resonators 61, 62, 63 and the plurality of parallel arm resonators 64, 65, 66, 67. For example, the plurality of series arm resonators 61, 62, 63 have the first embodiment (see the first embodiment). Figure 12 , Figure 13 The first electrode shown is 31a. The admittance characteristics of the multiple series-arm resonators 61, 62, and 63 are... Figure 13 Same, repeated descriptions omitted.

[0192] On the other hand, the multiple parallel arm resonators 64, 65, 66, and 67 have a second embodiment (see reference). Figure 20 , Figure 21 The first electrode shown is 31a, and the additional electrode is 35. The admittance characteristics of the multiple parallel arm resonators 64, 65, 66, and 67 are... Figure 21 Same, repeated descriptions omitted.

[0193] In this embodiment, by changing the structure of the first electrode finger 31a, the second electrode finger 32a, and the additional electrode 35 in multiple series arm resonators 61, 62, 63 and multiple parallel arm resonators 64, 65, 66, 67, a better output waveform can be obtained as a filter.

[0194] In the elastic wave device 10H according to the third embodiment, an example is shown that combines with the electrode structure of the first electrode finger 31a and the second electrode finger 32a shown in the first embodiment and the electrode structure of the additional electrode 35 shown in the second embodiment, but it is not limited thereto. The third embodiment can be combined with the above-described embodiments and modifications.

[0195] (9th variation)

[0196] Figure 30 This is a cross-sectional view showing the elastic wave device involved in the 9th modified example. In the elastic wave device 10 of the first embodiment described above, a so-called diaphragm structure in which the support substrate 11 has a cavity 14 and the cavity 14 (hole portion) is provided on the second main surface 20b side of the piezoelectric layer 20 has been described, but it is not limited to this.

[0197] like Figure 30 As shown, in the elastic wave device 10I according to the 9th modification, an acoustic multilayer film 43 is stacked on the second main surface 20b of the piezoelectric layer 20. The acoustic multilayer film 43 has a stacked structure of low acoustic impedance layers 43a, 43c, and 43e with relatively low acoustic impedance and high acoustic impedance layers 43b and 43d with relatively high acoustic impedance. The low acoustic impedance layers 43a, 43c, and 43e are, for example, layers of silicon oxide, and the high acoustic impedance layers 43b and 43d are, for example, metal layers of tungsten, platinum, etc., or dielectric layers of aluminum nitride, silicon nitride, etc. When the acoustic multilayer film 43 is used, even without using the cavity 14, the bulk wave of the thickness shear first mode can be contained within the piezoelectric layer 20.

[0198] In the elastic wave device 10I, the resonant characteristics of a bulk wave based on the thickness shear first mode can also be obtained by setting the aforementioned d / p to 0.5 or less. Furthermore, in the acoustic multilayer film 43, the number of layers of the low acoustic impedance layers 43a, 43c, 43e and the high acoustic impedance layers 43b, 43d is not particularly limited. It is sufficient that at least one high acoustic impedance layer 43b, 43d is disposed on the side further away from the piezoelectric layer 20 than the low acoustic impedance layers 43a, 43c, 43e.

[0199] The aforementioned low acoustic impedance layers 43a, 43c, and 43e, and high acoustic impedance layers 43b and 43d, can be constructed from suitable materials as long as the acoustic impedance relationship described above is satisfied. For example, silicon oxide or silicon oxynitride can be used as materials for the low acoustic impedance layers 43a, 43c, and 43e. Furthermore, bauxite, silicon nitride, or metals can be used as materials for the high acoustic impedance layers 43b and 43d.

[0200] exist Figure 30 In this embodiment, it can be combined with the electrode structure of the first electrode finger 31a shown in the first embodiment. However, it is not limited to this, and the ninth modification can be combined with each of the above embodiments and modifications.

[0201] (Example 10)

[0202] Figure 31 This is a cross-sectional view showing the elastic wave device according to the 10th modified example. In the elastic wave device 10 of the first embodiment described above, the structure of the IDT electrode 30 provided on the first main surface 20a of the piezoelectric layer 20 has been described, but it is not limited thereto. Figure 31 As shown, the elastic wave device 10J according to the 10th modification example has a first IDT electrode 30A disposed on the first main surface 20a of the piezoelectric layer 20 and a second IDT electrode 30B disposed on the second main surface 20b of the piezoelectric layer 20. The first IDT electrode 30A and the second IDT electrode 30B have a connection with the IDT electrode 30 (refer to...) Figure 1 , Figure 2 (The same structure)

[0203] The electrode fingers 36 and 37 of the second IDT electrode 30B are disposed in the region overlapping with 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 configured to have the same width and the same inter-electrode spacing as the electrode fingers 31 and 32 of the first IDT electrode 30A. Furthermore, in the tenth variation, similarly to the first embodiment, at least one of the first electrode fingers 31a and 32a 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 36a and 37a of the second IDT electrode 30B is formed of a material with a higher density than the other central electrode fingers 36 and 37.

[0204] In the 10th modified example, a first IDT electrode 30A and a second IDT electrode 30B are respectively provided on the first main surface 20a and the second main surface 20b of the piezoelectric layer 20, thereby improving the temperature coefficient of frequency (TCF).

[0205] The 10th modification can be combined with the above-described embodiments and modifications. For example, in the 10th modification, an additional electrode 35 may be provided on at least one of the first main surface 20a side and the second main surface 20b side of the piezoelectric layer 20.

[0206] (Example 11)

[0207] Figure 32 This is a top view showing the elastic wave device according to the 11th modification. The elastic wave device 10K according to the 11th modification differs from the first embodiment described above in the following structure: in at least a portion of the extension direction of the first electrode finger 31a, the product Xe (=W1×H1×d1) of the width W1, height H1, and density d1 is greater than the product Xc (=Wc×Hc×dc) of the width Wc, height Hc, and density dc of the central portion of the plurality of electrode fingers 31, 32 that is different from the first electrode finger 31a and the second electrode finger 32a. In this case, similarly to the first embodiment, ripple in the admittance characteristics can be suppressed compared to the comparative example.

[0208] More specifically, the first electrode 31a includes a first portion 31aA and a second portion 31aB. The second portion 31aB is connected to the end of the first portion 31aA in the extending direction.

[0209] The product of width W1, height H1, and density d1 Xe (=W1×H1×d1) in the first part 31aA of the first electrode finger 31a is greater than the product of width Wc, height Hc, and density dc Xc (=Wc×Hc×dc) of the central part of the multiple electrode fingers 31 and 32 that are different from the first electrode finger 31a and the second electrode finger 32a.

[0210] The width W1 in Part 2 31aB is smaller than the width W1 in Part 1 31aA. In addition, the product Xe (=W1×H1×d1) of the width W1, height H1 and density d1 in Part 2 31aB is smaller than the product Xe (=W1×H1×d1) of the width W1, height H1 and density d1 in Part 1 31aA.

[0211] Similarly, the fourth electrode finger 32b, located on the opposite side of the first electrode finger 31a in the arrangement direction of the plurality of electrode fingers 31, 32, also includes a first portion 32bA and a second portion 32bB. That is, in at least a portion (the first portion 32bA) in the extending direction of the fourth electrode finger 32b, the product Xe (=W1×H1×d1) of the width W1, height H1, and density d1 is greater than the product Xc (=Wc×Hc×dc) of the width Wc, height Hc, and density dc of the central portion of the electrode fingers 31, 32 that is different from the third electrode finger 31b and the fourth electrode finger 32d.

[0212] (Example 12)

[0213] Figure 33 This is an illustrative diagram showing an example of the admittance characteristics of the elastic wave device involved in the 12th variation. Figure 34 This is an illustrative diagram showing an example of the impedance phase in S2 mode. Regarding... Figure 33 The elastic wave device according to the 12th variation shown will be described in terms of the structure in the elastic wave device 10 according to the first embodiment described above, in which the thickness of the first protective film 41 and the second protective film 42 are different.

[0214] Figure 33 The frequency characteristics of the absolute value of the admittance of the elastic wave device involved in the 12th variation are shown. For example... Figure 33 As shown, in the elastic wave device involved in the 12th variation, a higher-order mode resonance (hereinafter referred to as "S2 mode") is generated in the frequency region indicated by the single-dotted line F1, which is different from the resonant frequency.

[0215] Figure 34 The horizontal axis of the graph shows the ratio of (t1+tLN / 2) to the total of the thickness t1 of the first protective film 41 and half of the thickness tLN of the piezoelectric layer 20 (t1+tLN / 2) and the total of the thickness t2 of the second protective film 42 and half of the thickness tLN of the piezoelectric layer 20 (t2+tLN / 2) (t1+tLN / 2). Figure 34 The vertical axis of the graph shown corresponds to the intensity of the S2 mode.

[0216] exist Figure 34 In the diagram, the ranges indicated by arrows F2 and F3 represent the ratio (t1+tLN / 2) / (t2+tLN / 2) in the structure of the acoustic resonator described in Japanese Patent Publication No. 2022-524136. In the acoustic resonator described in Japanese Patent Publication No. 2022-524136, the intensity of the S2 mode is high when the ratio (t1+tLN / 2) / (t2+tLN / 2) is between 0.93 and 1.07.

[0217] In contrast, in the 12th modification, the ratio (t1+tLN / 2) / (t2+tLN / 2) is in the range of 0.94 or more and 1.06 or less, which is lower than the intensity of the S2 mode compared to the acoustic resonant device disclosed in Japanese Patent Application Publication No. 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 set as 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 set as B, it is preferable that the value of A / B is 1-0.06 or more and 1+0.06 or less.

[0218] Furthermore, in the 12th variation, a case was described in which the thicknesses of the first protective film 41 and the second protective film 42 are different in the elastic wave device 10 according to the first embodiment, but it 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 12th variation can be combined with the above-described embodiments and variations.

[0219] Furthermore, the above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the scope of the invention. The present invention can be modified / improved without departing from its spirit, and the present invention also includes its equivalents.

[0220] In addition, this disclosure can also adopt the following structure.

[0221] (1) An elastic wave device, comprising:

[0222] A piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction;

[0223] An IDT electrode, disposed on at least one of the first main surface and the second main surface of the piezoelectric layer, includes a plurality of electrode fingers arranged in a given direction; and

[0224] A support member is positioned opposite the second main surface of the piezoelectric layer and has an acoustic reflection portion on the second main surface side of the piezoelectric layer.

[0225] The plurality of electrode fingers includes a first electrode finger located on the outermost side in the arrangement direction of the plurality of electrode fingers and a second electrode finger adjacent to the first electrode finger.

[0226] 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 the central portion of the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger.

[0227] When the thickness of the piezoelectric layer is set to d and the center-to-center distance between adjacent electrodes is set to p, d / p is 0.5 or less.

[0228] (2) The elastic wave device according to (1), wherein,

[0229] It has: a protective film disposed on at least one of the first main surface and the second main surface of the piezoelectric layer.

[0230] (3) The elastic wave device according to (1) or (2), wherein,

[0231] At least one of the first electrode finger and the second electrode finger is formed of a material with a higher density than the electrode finger in the central portion.

[0232] (4) The elastic wave device according to (1) or (2), wherein,

[0233] The height of at least one of the first electrode finger and the second electrode finger is higher than the height of the electrode finger in the central portion.

[0234] (5) An elastic wave device, comprising:

[0235] A piezoelectric layer having a first main surface and a second main surface facing the first main surface in a first direction;

[0236] An IDT electrode, disposed on at least one of the first main surface and the second main surface of the piezoelectric layer, comprises a plurality of electrode fingers arranged in a given direction;

[0237] A support member, facing the second main surface of the piezoelectric layer, and having an acoustic reflection portion on the second main surface side of the piezoelectric layer; and

[0238] An additional electrode is provided in a region overlapping at least one of the first and second electrode fingers when the outermost electrode finger in the arrangement direction of the plurality of electrode fingers is designated as the first electrode finger and the electrode finger adjacent to the first electrode finger is designated as the second electrode finger.

[0239] 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 the central portion of the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger.

[0240] When the thickness of the piezoelectric layer is set to d and the center-to-center distance between adjacent electrodes is set to p, d / p is 0.5 or less.

[0241] (6) The elastic wave device according to (5), wherein,

[0242] It has: a protective film disposed on at least one of the first main surface and the second main surface of the piezoelectric layer.

[0243] (7) The elastic wave device according to (5) or (6), wherein,

[0244] The additional electrode is disposed on at least one of the first electrode finger and the second electrode finger.

[0245] (8) The elastic wave device according to (6), wherein,

[0246] The protective film has: a first protective film covering the IDT electrode and disposed on the first main surface of the piezoelectric layer;

[0247] The additional electrode is disposed on the first protective film in an area overlapping with at least one of the first electrode finger and the second electrode finger.

[0248] (9) The elastic wave device according to (5), wherein,

[0249] The additional electrode is disposed 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.

[0250] (10) The elastic wave device according to any one of (1) to (9), wherein,

[0251] The plurality of electrodes of the IDT electrode refer to materials that use at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum.

[0252] (11) The elastic wave device according to any one of (5) to (9), wherein,

[0253] The material of the additional electrode is at least one of tungsten, molybdenum, ruthenium, platinum, copper, silver, chromium, gold, titanium, and aluminum.

[0254] (12) The elastic wave device according to (2) or (6), wherein,

[0255] The protective film is thinner than the films of the plurality of electrodes.

[0256] (13) The elastic wave device according to any one of (1) to (12), wherein,

[0257] The IDT electrode is provided on either the first main surface or the second main surface of the piezoelectric layer.

[0258] (14) An elastic wave filter device, comprising connecting at least one resonator, wherein,

[0259] The resonator is any one of the elastic wave devices described in (1) to (4).

[0260] (15) The elastic wave filter device according to (14), wherein,

[0261] It has an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting the node of the series arm to ground.

[0262] The at least one resonator is a plurality of resonators, including a series arm resonator disposed in the series arm and a parallel arm resonator disposed in the parallel arm.

[0263] The material of at least one of the first electrode fingers and the second electrode fingers of the series arm resonator is different from the material of at least one of the first electrode fingers and the second electrode fingers of the parallel arm resonator.

[0264] (16) An elastic wave filter device, comprising connecting at least one resonator, wherein,

[0265] The resonator is an elastic wave device as described in any one of (5) to (9).

[0266] (17) The elastic wave filter device according to (16), wherein,

[0267] It has an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting the node of the series arm to ground.

[0268] The at least one resonator is a plurality of resonators, including a series arm resonator disposed in the series arm and a parallel arm resonator disposed in the parallel arm.

[0269] The additional electrode of the series arm resonator has a different structure than the additional electrode of the parallel arm resonator.

[0270] (18) The elastic wave device according to (2) or (6), wherein,

[0271] The protective film is formed of silicon oxide.

[0272] (19) The elastic wave device according to any one of (1) to (13) and (18), wherein,

[0273] The piezoelectric layer comprises lithium niobate or lithium tantalate, and is cut by 120°±10° rotation Y-cut or 90°±10° rotation Y-cut.

[0274] (20) The elastic wave device according to (2) or (6), wherein,

[0275] The protective film has: a first protective film covering the IDT electrode and disposed on the first main surface of the piezoelectric layer; and a second protective film disposed on the second main surface of the piezoelectric layer.

[0276] (21) The elastic wave device according to (2) or (6), wherein,

[0277] The protective film is thicker than the IDT electrode.

[0278] (22) The elastic wave device according to (20), wherein,

[0279] When the total distance from the center of the piezoelectric layer to the top surface of the first protective film is set as A, and the total distance from the center of the piezoelectric layer to the top surface of the second protective film is set as B, the value of A / B is greater than or equal to 1-0.06 and less than or equal to 1+0.06.

[0280] (23) The elastic wave device according to (20) or (22), wherein,

[0281] The upper surface of the first protective film and the lower surface of the second protective film are formed in a flat manner.

[0282] (24) The elastic wave device according to any one of (1) to (13) and (18) to (23), wherein,

[0283] d / p is below 0.24.

[0284] (25) The elastic wave device according to any one of (1) to (13) and (18) to (24), wherein,

[0285] When viewed from the orthogonal direction of the electrode fingers, the region where adjacent electrode fingers overlap and the area between the centers of adjacent electrode fingers in the orthogonal direction of the electrode fingers is the excitation region.

[0286] When the metallization rate of the electrode finger relative to the excitation region is set as MR, MR ≤ 1.75 (d / p) + 0.075 is satisfied.

[0287] (26) The elastic wave device according to any one of (1) to (13) and (18) to (25), wherein,

[0288] The piezoelectric layer contains lithium tantalate or lithium niobate.

[0289] (27) The elastic wave device according to any one of (1) to (13) and (18) to (26), wherein,

[0290] The Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following equations (1), (2), or (3).

[0291] (0°±10°, 0°~20°, any ψ)... Equation (1)

[0292] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ]~180°)…Formula (2)

[0293] (0°±10°, [180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ~180°, any ψ)

[0294] …Formula (3)

[0295] (28) The elastic wave device according to any one of (1) to (13) and (18) to (27), wherein,

[0296] The sound-reflecting part is a hollow part.

[0297] The support member and the piezoelectric layer are configured such that a portion of the support member and a portion of the piezoelectric layer sandwich the cavity and are opposite to each other.

[0298] (29) The elastic wave device according to any one of (1) to (13) and (18) to (28), wherein,

[0299] The acoustic reflector is an acoustic reflector film comprising a high acoustic impedance layer with relatively high acoustic impedance and a low acoustic impedance layer with relatively low acoustic impedance.

[0300] The support member and the piezoelectric layer are configured such that at least a portion of the support member and at least a portion of the piezoelectric layer sandwich the acoustic reflective membrane and are opposite to each other.

[0301] Explanation of reference numerals in the attached figures

[0302] 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10I, 10J: Elastic wave devices;

[0303] 11: Support base plate;

[0304] 12: Bottom;

[0305] 13: Wall;

[0306] 14: Cavity;

[0307] 20, 201: Piezoelectric layers;

[0308] 20a, 201a: 1st main surface;

[0309] 20b, 201b: Second main face;

[0310] 30: IDT electrode;

[0311] 31, 32: Electrode fingers;

[0312] 31a: First electrode indicator;

[0313] 31b: Third electrode;

[0314] 32a: Second electrode;

[0315] 32b: Fourth electrode finger;

[0316] 33, 34: Busbar electrodes;

[0317] 35: Additional electrodes;

[0318] 41: First protective film;

[0319] 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, disposed on at least one of the first main surface and the second main surface of the piezoelectric layer, comprises a plurality of electrode fingers arranged in a given direction; as well as A support member is positioned opposite the second main surface of the piezoelectric layer and has an acoustic reflection portion on the second main surface side of the piezoelectric layer. The plurality of electrode fingers includes a first electrode finger located on the outermost side 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 the central portion of the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger. When the thickness of the piezoelectric layer is set to d and the center-to-center distance between adjacent electrodes is set to p, d / p is 0.5 or less.

2. The elastic wave device according to claim 1, wherein, It has: a protective film disposed on at least one of the first main surface and the second main surface of the piezoelectric layer.

3. The elastic wave device according to claim 1 or claim 2, wherein, At least one of the first electrode finger and the second electrode finger is formed of a material with a higher density than the electrode finger in the central portion.

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

5. 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, disposed on at least one of the first main surface and the second main surface of the piezoelectric layer, comprises a plurality of electrode fingers arranged in a given direction; A support member is positioned opposite the second main surface of the piezoelectric layer and has an acoustic reflection portion on the second main surface side of the piezoelectric layer; as well as An additional electrode is provided in a region overlapping at least one of the first and second electrode fingers when the outermost electrode finger in the arrangement direction of the plurality of electrode fingers is designated as the first electrode finger and the electrode finger adjacent to the first electrode finger is designated as the second electrode finger. 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 the central portion of the plurality of electrode fingers that is different from the first electrode finger and the second electrode finger. When the thickness of the piezoelectric layer is set to d and the center-to-center distance between adjacent electrodes is set to p, d / p is 0.5 or less.

6. The elastic wave device according to claim 5, wherein, It has: a protective film disposed on at least one of the first main surface and the second main surface of the piezoelectric layer.

7. The elastic wave device according to claim 5 or claim 6, wherein, The additional electrode is disposed on at least one of the first electrode finger and the second electrode finger.

8. The elastic wave device according to claim 6, wherein, The protective film has: a first protective film covering the IDT electrode and disposed on the first main surface of the piezoelectric layer; The additional electrode is disposed on the first protective film in an area overlapping with at least one of the first electrode finger and the second electrode finger.

9. The elastic wave device according to claim 5, wherein, The additional electrode is disposed 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 elastic wave device according to any one of claims 1 to 9, wherein, The plurality of electrodes of the IDT electrode refer to materials that use 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 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 claim 2 or claim 6, wherein, The protective film is thinner than the films of the plurality of electrodes.

13. The elastic wave device according to any one of claims 1 to 12, wherein, The IDT electrode is provided on either the first main surface or the second main surface of the piezoelectric layer.

14. An elastic wave filter device, comprising connecting at least one resonator, wherein, The resonator is the elastic wave device according to any one of claims 1 to 4.

15. The elastic wave filter device according to claim 14, wherein, It has an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting the node of the series arm to ground. The at least one resonator is a plurality of resonators, including a series arm resonator disposed in the series arm and a parallel arm resonator disposed in the parallel arm. The material of at least one of the first electrode fingers and the second electrode fingers of the series arm resonator is different from the 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 connecting at least one resonator, wherein, The resonator is the elastic wave device according to any one of claims 5 to 9.

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

18. The elastic wave device according to claim 2 or claim 6, wherein, The protective film is formed of silicon oxide.

19. The elastic wave device according to any one of claims 1 to 13 and claim 18, wherein, The piezoelectric layer comprises lithium niobate or lithium tantalate, and is cut by 120°±10° rotation Y-cut or 90°±10° rotation Y-cut.

20. The elastic wave device according to claim 2 or claim 6, wherein, The protective film has: a first protective film covering the IDT electrode and disposed on the first main surface of the piezoelectric layer; And a second protective film, disposed on the second main surface of the piezoelectric layer.

21. The elastic wave device according to claim 2 or claim 6, wherein, The protective film is thicker than the IDT electrode.

22. The elastic wave device according to claim 20, wherein, When the total distance from the center of the piezoelectric layer to the top surface of the first protective film is set as A, and the total distance from the center of the piezoelectric layer to the top surface of the second protective film is set as B, the value of A / B is greater than or equal to 1-0.06 and less than or equal to 1+0.

06.

23. The elastic wave device according to claim 20 or claim 22, wherein, The upper surface of the first protective film and the lower surface of the second protective film are formed in a flat manner.

24. The elastic wave device according to any one of claims 1 to 13 and claims 18 to 23, wherein, d / p is below 0.

24.

25. The elastic wave device according to any one of claims 1 to 13 and claims 18 to 24, wherein, When viewed from the orthogonal direction of the electrode fingers, the region where adjacent electrode fingers overlap and the area between the centers of adjacent electrode fingers in the orthogonal direction of the electrode fingers is the excitation region. When the metallization rate of the electrode finger relative to the excitation region is set as MR, MR ≤ 1.75 (d / p) + 0.075 is satisfied.

26. The elastic wave device according to any one of claims 1 to 13 and claims 18 to 25, wherein, The piezoelectric layer contains 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 equations (1), (2), or (3). (0°±10°, 0°~20°, any ψ)... Equation (1) (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ]~180°)…Formula (2) (0°±10°, [180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ~180°, any ψ) …Formula (3).

28. The elastic wave device according to any one of claims 1 to 13 and claims 18 to 27, wherein, The sound-reflecting part is a hollow part. The support member and the piezoelectric layer are configured such that a portion of the support member and a portion of the piezoelectric layer sandwich the cavity and are opposite to each other.

29. The elastic wave device according to any one of claims 1 to 13 and claims 18 to 28, wherein, The acoustic reflector is an acoustic reflector film comprising a high acoustic impedance layer with relatively high acoustic impedance and a low acoustic impedance layer with relatively low acoustic impedance. The support member and the piezoelectric layer are configured such that at least a portion of the support member and at least a portion of the piezoelectric layer sandwich the acoustic reflective membrane and are opposite to each other.

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