Elastic wave device

Abstract

Provided is an elastic wave device capable of promoting miniaturization of a filter device and capable of reducing insertion loss. This elastic wave device (10) is provided with: a piezoelectric layer (14) containing lithium niobate and having Euler angles (phi, theta, psi) within the range of formula (1), formula (2), or formula (3); a first comb electrode (17) which is provided on the piezoelectric layer (14), has a first bus bar (22) and a plurality of first electrode fingers (25) each having one end connected to the first bus bar (22), and is connected to an input potential; a second comb electrode (18) provided on the piezoelectric layer (14), having a second bus bar (23) and a plurality of second electrode fingers (26) each having one end connected to the second bus bar (23), and connected to the output potential, the plurality of second electrode fingers (26) and the plurality of first electrode fingers (25) being interleaved with each other; and a reference potential electrode (19) connected to a reference potential and having a plurality of third electrode fingers (27) and connection electrodes (34) that connect adjacent third electrode fingers (27), the plurality of third electrode fingers (27) being provided on the piezoelectric layer (14) so as to be aligned with the first electrode fingers (25) and the second electrode fingers (26) in the direction in which the first electrode fingers (25) and the second electrode fingers (26) are aligned. The order in which the first electrode fingers (25), the second electrode fingers (26), and the third electrode fingers (27) are arranged is an order in which the first electrode fingers (25), the third electrode fingers (27), the second electrode fingers (26), and the third electrode fingers (27) are arranged as one cycle from the first electrode fingers (25). The total number of the first electrode fingers (25), the second electrode fingers (26), and the third electrode fingers (27) is 16 or more. (in the range of 0 DEG + / -10 DEG, 0 DEG to 25 DEG, any psi) Formula (1) (in the range of 0 DEG + / -10 DEG, 25 DEG to 100 DEG, 0 DEG to 75 DEG [(1-(theta-50) 2 / 2500)] 1 / 2 or 180 DEG to 75 DEG [(1-(theta-50) 2 / 2500)] 1 / 2-180 DEG) Formula (2) (in the range of 0 DEG + / -10 DEG, 180 DEG to 40 DEG [(1-(psi-90) 2 / 8100)] 1 / 2-180 DEG, any psi) Formula (3)

Description

Technical Field

[0001] The present invention relates to elastic wave devices. Background Art

[0002] In the past, elastic wave devices were widely used in filters of portable phones and the like. In recent years, an elastic wave device using a thickness shear mode bulk wave as described in the following patent document 1 has been proposed. In this elastic wave device, a piezoelectric layer is provided on a support. A pair of electrodes is provided on the piezoelectric layer. The paired electrodes are opposed to each other on the piezoelectric layer and are connected to different potentials. By applying an alternating voltage between the electrodes, a thickness shear mode bulk wave is excited.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: U.S. Patent No. 10491192 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] The so-called elastic wave device is, for example, an elastic wave resonator, which is used in, for example, a ladder filter. In order to obtain good characteristics in the ladder filter, it is necessary to increase the electrostatic capacitance ratio between a plurality of elastic wave resonators. In this case, it is necessary to increase the electrostatic capacitance of some elastic wave resonators in the ladder filter.

[0008] In order to increase the capacitance of the elastic wave resonator, for example, the elastic wave resonator needs to be enlarged. Therefore, when the elastic wave resonator is used in a ladder-type filter, the ladder-type filter tends to be enlarged. In particular, a ladder-type filter having an elastic wave resonator with a small capacitance and utilizing a bulk wave in a thickness shear mode tends to be enlarged.

[0009] The inventors of the present invention have found that, when the elastic wave device is used in a filter device, a suitable filter waveform can be obtained without increasing the size thereof by configuring the elastic wave device to have the following structure: the structure in which an electrode connected to a reference potential is arranged between an electrode connected to an input potential and an electrode connected to an output potential.

[0010] Furthermore, the inventors of the present invention have found that the insertion loss may not be reduced sufficiently only by using the above-mentioned structure.

[0011] An object of the present invention is to provide an elastic wave device that can promote miniaturization of a filter device and reduce insertion loss.

[0012] Technical solutions to solve problems

[0013] In a broad embodiment of the elastic wave device according to the present invention, the device comprises: a piezoelectric layer, wherein the Euler angles (φ, θ, ψ) are within the range of the following formula (1), formula (2) or formula (3), and the device comprises lithium niobate; a first comb-shaped electrode, arranged on the piezoelectric layer, comprising a first bus bar and a plurality of first electrode fingers, each of which has one end connected to the first bus bar, and is connected to an input potential; a second comb-shaped electrode, arranged on the piezoelectric layer, comprising a second bus bar and a plurality of second electrode fingers, each of which has one end connected to the second bus bar, and is connected to an output potential, wherein the plurality of second electrode fingers are interlaced with the plurality of first electrode fingers; and a reference potential electrode, comprising a plurality of third electrode fingers. The pole fingers and the connecting electrodes connecting the adjacent third electrode fingers to each other are connected to a reference potential, and the plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged, and the order in which the first electrode finger, the second electrode finger and the third electrode finger are arranged is the order of the first electrode finger, the third electrode finger, the second electrode finger and the third electrode finger as one period when starting from the first electrode finger, and the total number of the first electrode finger, the second electrode finger and the third electrode finger is more than 16.

[0014] (within the range of 0°±10°, 0°~25°, arbitrary ψ) …Formula (1)

[0015] (Within the range of 0°±10°, 25°~100°, 0°~75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2)

[0016] (0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, any ψ) …Formula (3)

[0017] In another broad form of the elastic wave device according to the present invention, the device comprises: a piezoelectric layer comprising lithium niobate; a first comb-shaped electrode arranged on the piezoelectric layer, comprising a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, connected to an input potential; a second comb-shaped electrode arranged on the piezoelectric layer, comprising a second bus bar and a plurality of second electrode fingers each having one end connected to the second bus bar, connected to an output potential, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a reference potential electrode comprising a plurality of third electrode fingers and connecting electrodes connecting adjacent third electrode fingers to each other, connected to a reference potential, the plurality of third electrode fingers being arranged on the piezoelectric layer so as to be aligned with the first electrode fingers and the second electrode fingers in the direction in which the first electrode fingers and the second electrode fingers are arranged. An electrode finger arrangement, wherein the order of arrangement of the first electrode finger, the second electrode finger, and the third electrode finger is one periodic order when starting from the first electrode finger, the direction in which the first electrode finger, the second electrode finger, and the third electrode finger extend is set as an electrode finger extension direction, when observed from a direction orthogonal to the electrode finger extension direction, an area where the first electrode finger and the second electrode finger overlap with each other is a crossing area, and when a size of the crossing area along the electrode finger extension direction is set as a crossing width Ap, and a center-to-center distance between adjacent first and third electrode fingers or a center-to-center distance between adjacent second and third electrode fingers is set as px, Ap / px≥5.

[0018] In another broad aspect of the elastic wave device according to the present invention, the device comprises: a piezoelectric layer, wherein the Euler angles (φ, θ, ψ) are within the range of the following formula (1), formula (2) or formula (3), and the device comprises lithium niobate; a first comb-shaped electrode, arranged on the piezoelectric layer, comprising a first bus bar and a plurality of first electrode fingers, each of which has one end connected to the first bus bar, and connected to an input potential; a second comb-shaped electrode, arranged on the piezoelectric layer, comprising a second bus bar and a plurality of second electrode fingers, each of which has one end connected to the second bus bar, and connected to an output potential, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a reference potential electrode, comprising a plurality of third electrode fingers and a connecting electrode for connecting adjacent third electrode fingers to each other, and connected to a reference potential, the plurality of third electrode fingers being arranged on the piezoelectric layer so as to be in contact with the first electrode fingers and the second electrode fingers in the direction in which the first electrode fingers and the second electrode fingers are arranged. The arrangement of electrode fingers, wherein the order of arrangement of the first electrode finger, the second electrode finger and the third electrode finger is such that the first electrode finger, the third electrode finger, the second electrode finger and the third electrode finger form one period when starting from the first electrode finger, and when the direction in which the first electrode finger, the second electrode finger and the third electrode finger extend is set as the electrode finger extending direction, the front ends of the plurality of first electrode fingers and the plurality of second electrode fingers are respectively opposed to electrodes connected to a potential different from that of the electrode finger and having a potential of any one of an input potential, an output potential and a reference potential, with gaps therebetween in the electrode finger extending direction, and when the dimension of each of the gaps along the electrode finger extending direction is set as a gap length G, and the center-to-center distance between adjacent first and third electrode fingers or the center-to-center distance between adjacent second and third electrode fingers is set as px, G / px≤0.5.

[0019] (within the range of 0°±10°, 0°~25°, arbitrary ψ) …Formula (1)

[0020] (Within the range of 0°±10°, 25°~100°, 0°~75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2)

[0021] (0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, any ψ) …Formula (3)

[0022] In another broad aspect of the elastic wave device according to the present invention, the device comprises: a piezoelectric layer, wherein the Euler angles (φ, θ, ψ) are within the range of the following formula (1), formula (2) or formula (3), and the device comprises lithium niobate; a first comb-shaped electrode, arranged on the piezoelectric layer, and comprising a first bus bar and a plurality of first electrode fingers, each of which has one end connected to the first bus bar; a second comb-shaped electrode, arranged on the piezoelectric layer, and comprising a second bus bar and a plurality of second electrode fingers, each of which has one end connected to the second bus bar, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a reference potential electrode, comprising a plurality of third electrode fingers and a connecting electrode for connecting adjacent third electrode fingers to each other, the plurality of third electrode fingers being connected to a reference potential, the plurality of third electrode fingers being arranged on the piezoelectric layer so as to be aligned with the first electrode fingers and the second electrode fingers in the direction in which the first electrode fingers and the second electrode fingers are arranged. The first comb-shaped electrode is connected to one of an input potential and an output potential, and the second comb-shaped electrode is connected to the other of an input potential and an output potential. The order of arrangement of the first electrode finger, the second electrode finger and the third electrode finger is in the order of the first electrode finger, the third electrode finger, the second electrode finger and the third electrode finger as one cycle when starting from the first electrode finger. The front ends of at least a part of the adjacent third electrode fingers among all adjacent third electrode fingers are connected to each other on the first bus bar side through the connecting electrode. When the distance between the connecting electrode connecting the front ends of the first bus bar sides of the adjacent third electrode fingers to each other and the first bus bar is set as the GB gap length, and the distance between the connecting electrode and the front ends of the second electrode fingers is set as the GF gap length, the GB gap length ≤ the GF gap length.

[0023] (within the range of 0°±10°, 0°~25°, arbitrary ψ) …Formula (1)

[0024] (Within the range of 0°±10°, 25°~100°, 0°~75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2)

[0025] (0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, any ψ) …Formula (3)

[0026] In another broad aspect of the elastic wave device according to the present invention, the device comprises: a piezoelectric layer including lithium niobate having Euler angles (φ, θ, ψ) within the range of (within the range of 0°±5°, within the range of -8°±14°, and within the range of 90°±5°); a first comb-shaped electrode arranged on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, connected to an input potential; a second comb-shaped electrode arranged on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers each having one end connected to the second bus bar, connected to an output potential, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and a connecting electrode connecting adjacent third electrode fingers to each other, connected to a reference potential, the plurality of third electrode fingers being arranged on the piezoelectric layer so as to be aligned with the first electrode fingers in the direction in which the first electrode fingers and the second electrode fingers are arranged. And the second electrode finger arrangement, the order of arrangement of the first electrode finger, the second electrode finger and the third electrode finger is in the order of the first electrode finger, the third electrode finger, the second electrode finger and the third electrode finger as one period when starting from the first electrode finger, when the extending direction of the first electrode finger, the second electrode finger and the third electrode finger is set as the electrode finger extending direction, the front ends of the plurality of first electrode fingers and the plurality of second electrode fingers are respectively opposite to electrodes connected to a potential different from that of the electrode finger and being any one of an input potential, an output potential and a reference potential with gaps in the electrode finger extending direction, when the dimension of each of the gaps along the electrode finger extending direction is set as the gap length G, and the center-to-center distance between adjacent first electrode fingers and third electrode fingers or the center-to-center distance between adjacent second electrode fingers and third electrode fingers is set as px, G / px≥1.

[0027] In another broad aspect of the elastic wave device according to the present invention, the device comprises: a piezoelectric layer including lithium niobate having Euler angles (φ, θ, ψ) within the range of (within the range of 0°±5°, within the range of -8°±14°, and within the range of 90°±5°); a first comb-shaped electrode arranged on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers each connected to the first bus bar at one end; a second comb-shaped electrode arranged on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers each connected to the second bus bar at one end, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and connecting electrodes connecting adjacent third electrode fingers to each other, the plurality of third electrode fingers being connected to a reference potential, the plurality of third electrode fingers being arranged on the piezoelectric layer so as to be in contact with the first electrode fingers and the second electrode fingers in the direction in which the first electrode fingers and the second electrode fingers are arranged. The pole finger arrangement, the first comb-shaped electrode is connected to one of an input potential and an output potential, the second comb-shaped electrode is connected to the other of an input potential and an output potential, the order of arrangement of the first electrode finger, the second electrode finger and the third electrode finger is in the order of the first electrode finger, the third electrode finger, the second electrode finger and the third electrode finger as one cycle when starting from the first electrode finger, the front ends of at least a part of the adjacent third electrode fingers among all adjacent third electrode fingers on the first bus bar side are connected to each other through the connecting electrode, and when the distance between the connecting electrode connecting the front ends of the first bus bar sides of adjacent third electrode fingers to each other and the first bus bar is set as the GB gap length, and the distance between the connecting electrode and the front ends of the second electrode fingers on the first bus bar side is set as the GF gap length, the GB gap length>GF gap length.

[0028] Effects of the Invention

[0029] According to the present invention, it is possible to provide an elastic wave device that can promote miniaturization of a filter device and reduce insertion loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0031] Figure 2 It is a schematic plan view of the elastic wave device according to the first embodiment of the present invention.

[0032] Figure 3 This is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers in the first embodiment of the present invention.

[0033] Figure 4This is a diagram showing a mapping of the fractional bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0034] Figure 5 This is a diagram showing the transmission characteristics of the elastic wave device when the total number of the first to third electrode fingers is four.

[0035] Figure 6 This is a diagram showing the transmission characteristics of the elastic wave device when the total number of the first to third electrode fingers is 10.

[0036] Figure 7 This is a diagram showing the transmission characteristics of the elastic wave device when the total number of the first to third electrode fingers is 80.

[0037] Figure 8 This is a diagram showing the relationship between the total number of first to third electrode fingers and the insertion loss around 6 GHz.

[0038] Fig. 9 It is a schematic plan view of an elastic wave device according to a first modification example of the first embodiment of the present invention.

[0039] Fig.10 It is a schematic plan view of an elastic wave device according to a second modified example of the first embodiment of the present invention.

[0040] Fig.11 This is a graph showing the relationship between Ap / px and insertion loss near 6 GHz.

[0041] Fig.12 This is a graph showing the relationship between G / px and insertion loss near 6 GHz.

[0042] Fig.13 This is a graph showing the relationship between G / px and insertion loss near 6 GHz.

[0043] Fig.14 It is a schematic plan view of an elastic wave device according to a fifth embodiment of the present invention.

[0044] Fig.15 (a) is a schematic perspective view showing the appearance of an elastic wave device using a thickness shear mode bulk wave, Fig.15 (b) is a top view showing the electrode structure on the piezoelectric layer.

[0045] Fig.16 It is along Fig.15 (a) is a cross-sectional view of a portion taken along line AA.

[0046] Fig.17(a) is a schematic front cross-sectional view for explaining Lamb waves propagating through a piezoelectric film of an elastic wave device. Fig.17 (b) is a schematic front cross-sectional view for explaining a thickness shear mode bulk wave propagating through a piezoelectric film in an elastic wave device.

[0047] Fig.18 It is a diagram showing the amplitude direction of the body wave in the thickness shear mode.

[0048] Fig.19 FIG. 1 is a diagram showing the resonance characteristics of an elastic wave device using bulk waves in a thickness shear mode.

[0049] Fig. 20 : This is a diagram showing the relationship between d / p and the fractional bandwidth of the resonator when the distance between the centers of adjacent electrodes is defined as p and the thickness of the piezoelectric layer is defined as d.

[0050] Fig.21 This is a top view of an elastic wave device using bulk waves in a thickness shear mode.

[0051] Fig. 22 FIG. 2 is a diagram showing the resonance characteristics of an elastic wave device according to a reference example in which spurious emission occurs.

[0052] Fig.23 This is a diagram showing the relationship between the fractional bandwidth and the phase rotation amount of the impedance of the spurious signal normalized by 180 degrees, which is the magnitude of the spurious signal.

[0053] Fig.24 It is a graph showing the relationship between d / 2p and the metallization ratio MR.

[0054] Fig.25 This is a diagram showing a mapping of the fractional bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0055] Fig.26 It is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0056] Fig. 27 This is a partially cutaway perspective view for explaining an elastic wave device using Lamb waves. DETAILED DESCRIPTION

[0057] Below, while referring to the attached Figure 1 The present invention will be clarified by describing specific embodiments of the present invention.

[0058] In addition, it should be noted that each embodiment described in this specification is an example, and some structures can be replaced or combined among different embodiments.

[0059] Figure 1It is a schematic front cross-sectional view of the elastic wave device according to the first embodiment of the present invention. Figure 2 is a schematic plan view of the elastic wave device according to the first embodiment. Figure 1 It is along Figure 2 Schematic cross-sectional view of line II in FIG. Figure 2 In FIG. 1 , hatching is performed to indicate each electrode. Figure 2 Similarly, in other schematic plan views, electrodes may be hatched.

[0060] Figure 1 The elastic wave device 10 shown is configured to utilize the thickness shear mode. The elastic wave device 10 is an acoustic coupling filter. The structure of the elastic wave device 10 will be described below.

[0061] The elastic wave device 10 has a piezoelectric substrate 12 and a functional electrode 11. The piezoelectric substrate 12 is a substrate having piezoelectricity. Specifically, the piezoelectric substrate 12 has a supporting member 13 and a piezoelectric layer 14. In the present embodiment, the supporting member 13 includes a supporting substrate 16 and an insulating layer 15. The insulating layer 15 is provided on the supporting substrate 16. The piezoelectric layer 14 is provided on the insulating layer 15. However, the supporting member 13 may also be composed of only the supporting substrate 16. In addition, the supporting member 13 may not necessarily be provided.

[0062] The piezoelectric layer 14 has a first principal surface 14a and a second principal surface 14b. The first principal surface 14a and the second principal surface 14b face each other. Of the first principal surface 14a and the second principal surface 14b, the second principal surface 14b is located on the support member 13 side.

[0063] The functional electrode 11 is provided on the first main surface 14a of the piezoelectric layer 14. Figure 2 As shown, the functional electrode 11 includes a pair of comb-shaped electrodes and a reference potential electrode 19. The reference potential electrode 19 is connected to a reference potential. Specifically, the pair of comb-shaped electrodes is a first comb-shaped electrode 17 and a second comb-shaped electrode 18. The first comb-shaped electrode 17 is connected to an input potential. The second comb-shaped electrode 18 is connected to an output potential.

[0064] In addition, the first comb-shaped electrode 17 may be connected to the output potential. The second comb-shaped electrode 18 may be connected to the input potential. In this way, the first comb-shaped electrode 17 may be connected to one of the input potential and the output potential. The second comb-shaped electrode 18 may be connected to the other of the input potential and the output potential.

[0065] The first comb-shaped electrode 17 and the second comb-shaped electrode 18 are provided on the first main surface 14a of the piezoelectric layer 14. The first comb-shaped electrode 17 has a first bus bar 22 and a plurality of first electrode fingers 25. One ends of the plurality of first electrode fingers 25 are respectively connected to the first bus bar 22. The second comb-shaped electrode 18 has a second bus bar 23 and a plurality of second electrode fingers 26. One ends of the plurality of second electrode fingers 26 are respectively connected to the second bus bar 23.

[0066] The first bus bar 22 and the second bus bar 23 face each other. The plurality of first electrode fingers 25 and the plurality of second electrode fingers 26 are interlaced with each other. The first electrode fingers 25 and the second electrode fingers 26 are alternately arranged in a direction orthogonal to the direction in which the first electrode fingers 25 and the second electrode fingers 26 extend.

[0067] The reference potential electrode 19 includes a third bus bar 24 as a connection electrode and a plurality of third electrode fingers 27. The plurality of third electrode fingers 27 are provided on the first principal surface 14a of the piezoelectric layer 14. The plurality of third electrode fingers 27 are connected to each other by the third bus bar 24.

[0068] The third electrode fingers 27 are arranged in the direction in which the first electrode fingers 25 and the second electrode fingers 26 are arranged. Therefore, the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 are arranged in one direction. The third electrode fingers 27 extend in parallel with the first electrode fingers 25 and the second electrode fingers.

[0069] Hereinafter, the direction in which the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 extend is referred to as the electrode finger extending direction, and the direction orthogonal to the electrode finger extending direction is referred to as the electrode finger orthogonal direction. When the direction in which the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 are arranged is referred to as the electrode finger arrangement direction, the electrode finger arrangement direction is parallel to the electrode finger orthogonal direction. In this specification, the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 are sometimes collectively and simply recorded as electrode fingers. The first bus bar 22 and the second bus bar 23 are sometimes collectively and simply recorded as bus bars.

[0070] Figure 3 This is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers in the first embodiment.

[0071] The order in which the plurality of electrode fingers are arranged is the order of the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, and the third electrode finger 27 as one cycle, when starting from the first electrode finger 25. Therefore, the order in which the plurality of electrode fingers are arranged is the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, the third electrode finger 27, the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, ... and so on. If the input potential is represented by IN, the output potential is represented by OUT, and the reference potential is represented by GND, and the order of the plurality of electrode fingers is represented as the order of the potentials to which they are connected, then it is represented as IN, GND, OUT, GND, IN, GND, OUT, ... and so on.

[0072] In the present embodiment, in a region where a plurality of electrode fingers are provided, the electrode fingers located at both ends in the orthogonal direction of the electrode fingers are the third electrode fingers 27. In addition, in this region, the electrode fingers located at the ends in the orthogonal direction of the electrode fingers may be any type of electrode fingers among the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27.

[0073] like Figure 2 As shown, the third bus bar 24, which is a connection electrode of the reference potential electrode 19, electrically connects the plurality of third electrode fingers 27 to each other. Specifically, the third bus bar 24 is located in a region between the first bus bar 22 and the front ends of the plurality of second electrode fingers 26. The plurality of first electrode fingers 25 are also located in this region. However, the third bus bar 24 and the plurality of first electrode fingers 25 are electrically insulated from each other by the insulating film 29.

[0074] More specifically, the third bus bar 24 includes a plurality of first connection electrodes 24A and a second connection electrode 24B. Each first connection electrode 24A connects the front ends of two adjacent third electrode fingers 27 to each other. A U-shaped electrode is formed by the first connection electrode 24A and the two third electrode fingers 27. The second connection electrode 24B connects the plurality of first connection electrodes 24A to each other. An insulating film 29 is provided between the second connection electrode 24B and the plurality of first electrode fingers 25.

[0075] More specifically, the insulating film 29 is provided on the first main surface 14a of the piezoelectric layer 14 so as to cover a portion of the plurality of first electrode fingers 25. The insulating film 29 is provided in a region between the first bus bar 22 and the tips of the plurality of second electrode fingers 26. The insulating film 29 has a strip shape.

[0076] The insulating film 29 does not reach the first connection electrode 24A of the reference potential electrode 19. Moreover, the second connection electrode 24B is provided over the insulating film 29 and the plurality of first connection electrodes 24A. Specifically, the second connection electrode 24B has a stripe 24a and a plurality of protrusions 24b. Each protrusion 24b extends from the stripe 24a toward each first connection electrode 24A. Each protrusion 24b is connected to each first connection electrode 24A. Thus, the plurality of third electrode fingers 27 are electrically connected to each other through the first connection electrode 24A and the second connection electrode 24B.

[0077] In the present embodiment, the third bus bar 24 is located in a region between the first bus bar 22 and the tips of the plurality of second electrode fingers 26. Therefore, the tips of the plurality of second electrode fingers 26 are opposed to the third bus bar 24 via gaps g1 in the electrode finger extending direction. On the other hand, the tips of the plurality of first electrode fingers 25 are opposed to the second bus bar 23 via gaps g2 in the electrode finger extending direction.

[0078] In addition, the third bus bar 24 may be located in a region between the second bus bar 23 and the tips of the plurality of first electrode fingers 25. In this case, the tips of the plurality of first electrode fingers 25 are opposed to the third bus bar 24 via gaps. On the other hand, the tips of the plurality of second electrode fingers 26 are opposed to the first bus bar 22 via gaps.

[0079] As described above, in the present invention, the following configuration is sufficient. The front ends of the plurality of first electrode fingers 25 may be opposed to electrodes connected to a potential different from that of the electrode finger and any one of an input potential, an output potential, and a reference potential, with gaps therebetween in the electrode finger extension direction. Similarly, the front ends of the plurality of second electrode fingers 26 may be opposed to electrodes connected to a potential different from that of the electrode finger and any one of an input potential, an output potential, and a reference potential, with gaps therebetween in the electrode finger extension direction.

[0080] The dimension of these gaps along the electrode finger extending direction is referred to as gap length. In the present embodiment, the gap length G of the gap g1 and the gap length G of the gap g2 are the same. However, the gap length G of the gap g1 and the gap length G of the gap g2 may be different from each other.

[0081] The elastic wave device 10 is an elastic wave resonator configured to utilize bulk waves in a thickness shear mode. Figure 2 As shown, the elastic wave device 10 has a plurality of excitation regions C. In the plurality of excitation regions C, body waves in the thickness shear mode and elastic waves in other modes are excited. Figure 2 In FIG, only two excitation areas C among multiple excitation areas C are shown.

[0082] A part of the plurality of excitation regions C among all the excitation regions C are regions where adjacent first electrode fingers 25 and third electrode fingers 27 overlap when viewed from the direction orthogonal to the electrode fingers, and are regions between the centers of adjacent first electrode fingers 25 and third electrode fingers 27. The remaining plurality of excitation regions C are regions where adjacent second electrode fingers 26 and third electrode fingers 27 overlap when viewed from the direction orthogonal to the electrode fingers, and are regions between the centers of adjacent second electrode fingers 26 and third electrode fingers 27. These excitation regions C are arranged in the direction orthogonal to the electrode fingers.

[0083] In the functional electrode 11, the structure other than the reference potential electrode 19 is the same as the structure of the IDT (Interdigital Transducer) electrode. When viewed from the orthogonal direction of the electrode fingers, the area where the adjacent first electrode fingers 25 and second electrode fingers 26 overlap each other is the intersection area E. However, the intersection area E can also be said to be an area where the adjacent first electrode fingers 25 and third electrode fingers 27, or the adjacent second electrode fingers 26 and third electrode fingers 27 overlap each other when viewed from the orthogonal direction of the electrode fingers. The intersection area E includes a plurality of excitation areas C. In addition, the intersection area E and the excitation area C are areas of the piezoelectric layer 14 defined based on the structure of the functional electrode 11.

[0084] Hereinafter, the dimension of the intersection region E along the electrode finger extension direction is referred to as the intersection width Ap. The center-to-center distance between adjacent first electrode fingers 25 and third electrode fingers 27, or the center-to-center distance between adjacent second electrode fingers 26 and third electrode fingers 27 is referred to as px. In the present embodiment, the center-to-center distance px between adjacent pairs of first electrode fingers 25 and third electrode fingers 27, and the center-to-center distance px between adjacent pairs of second electrode fingers 26 and third electrode fingers 27 are the same.

[0085] However, the center-to-center distance px between the adjacent first electrode fingers 25 and the third electrode fingers 27 and the center-to-center distance px between the adjacent second electrode fingers 26 and the third electrode fingers 27 may not be constant. In this case, the longest distance between the center-to-center distance px between the adjacent first electrode fingers 25 and the third electrode fingers 27 and the center-to-center distance px between the adjacent second electrode fingers 26 and the third electrode fingers 27 is set to p. In addition, when the center-to-center distance px is fixed as in the present embodiment, the center-to-center distance px between any adjacent electrode fingers is the distance p.

[0086] In the present embodiment, the piezoelectric layer 14 is a lithium niobate layer. Specifically, a rotated Y-cut LiNbO3 is used as the material of the piezoelectric layer 14. In this case, the fractional bandwidth of the elastic wave device 10 depends on the Euler angles (φ, θ, ψ) of the lithium niobate used for the piezoelectric layer 14. The so-called fractional bandwidth is represented by (|fa-fr| / fr)×100[%] when the resonant frequency is fr and the antiresonant frequency is fa.

[0087] The relationship between the fractional bandwidth of elastic wave device 10 and the Euler angles (φ, θ, ψ) of piezoelectric layer 14 was derived when d / p was made as close to 0 as possible. In addition, φ in the Euler angles was set to 0°.

[0088] Figure 4 This is a diagram showing a mapping of the fractional bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0089] Figure 4 The region R indicated by the hatching is the region where a fractional bandwidth of at least 2% can be obtained. If the range of region R is approximated, it becomes the range represented by the following equations (1), (2), and (3). In addition, when φ in the Euler angles (φ, θ, ψ) is within the range of 0°±10°, the relationship between θ and ψ and the fractional bandwidth is the same as Figure 4 When the piezoelectric layer 14 is a lithium tantalate layer, the relationship between θ and ψ in the Euler angle (in the range of 0°±10°, θ, ψ) and the fractional bandwidth is also the same as Figure 4 The relationship shown is the same.

[0090] (within the range of 0°±10°, 0°~25°, arbitrary ψ) …Formula (1)

[0091] (Within the range of 0°±10°, 25°~100°, 0°~75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2)

[0092] (0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, any ψ) …Formula (3)

[0093] The range of the Euler angles of the above-mentioned formula (1), formula (2), or formula (3) is preferably 0. This allows the fractional bandwidth to be sufficiently widened. This allows the elastic wave device 10 to be suitably used in a filter device.

[0094] The present embodiment is characterized in that it has the following structure. 1) The Euler angles (φ, θ, ψ) of the piezoelectric layer 14 are within the range of the above-mentioned formula (1), formula (2) or formula (3). 2) The third electrode finger 27 of the reference potential electrode 19 is provided between the first electrode finger 25 of the first comb-shaped electrode 17 and the second electrode finger 26 of the second comb-shaped electrode 18. 3) The total number of the first electrode finger 25, the second electrode finger 26 and the third electrode finger 27 is 16 or more. Thus, when the elastic wave device 10 is used for a filter device, the miniaturization of the filter device can be promoted and the insertion loss can be reduced. This is explained below.

[0095] The filter characteristics are compared by making the total number of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 different. The elastic wave device involved in the comparison also includes an elastic wave device in which the total number of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 is less than 16. Specifically, the total number of the plurality of electrode fingers is changed in units of 2 within a range of more than 4 and less than 80. When the total number of the plurality of electrode fingers is 4, the order of the potentials connected to the plurality of electrode fingers is set to GND, IN, GND, OUT. However, the order is essentially the same as IN, GND, OUT, GND. The design parameters of the elastic wave device involved in the comparison are as follows.

[0096] Piezoelectric layer: Material…LiNbO3, Euler angles (φ, θ, ψ)…(0°, 0°, 90°), Thickness…400nm

[0097] First electrode finger to third electrode finger: layer structure: Ti layer / AlCu layer / Ti layer from the piezoelectric layer side, thickness of each layer: 10 nm / 390 nm / 4 nm from the piezoelectric layer side

[0098] The order of the first electrode finger to the third electrode finger is represented by the connected potentials: a repeating order of IN, GND, OUT, GND, or GND, IN, GND, OUT.

[0099] The center-to-center distance px between adjacent electrode fingers is 1.4 μm.

[0100] Duty cycle of functional electrode: 0.3

[0101] Cross width Ap: 40μm

[0102] The total number of the first to third electrode fingers: changed in units of 2 within a range of 4 to 80.

[0103] Figure 5This is a diagram showing the transmission characteristics of the elastic wave device when the total number of the first to third electrode fingers is four. Figure 6 This is a diagram showing the transmission characteristics of the elastic wave device when the total number of the first to third electrode fingers is 10. Figure 7 This is a diagram showing the transmission characteristics of the elastic wave device when the total number of the first to third electrode fingers is 80.

[0104] like Figure 5 As shown in FIG. 1 , when the total number of electrode fingers is 4, a filter waveform is obtained in one elastic wave device. Figure 5 In the area around 5.5 GHz to 6 GHz surrounded by the dot-dashed line, the insertion loss is large. Figure 6 As shown in FIG. 1 , when the total number of electrode fingers is 10, the insertion loss is also large near 5.5 GHz to 6 GHz. Figure 7 As shown, it can be seen that when the total number of the plurality of electrode fingers is 80, a suitable filter waveform is obtained and the insertion loss can be reduced in the vicinity of 5.5 GHz to 6 GHz.

[0105] Figure 8 This is a diagram showing the relationship between the total number of first to third electrode fingers and the insertion loss around 6 GHz.

[0106] like Figure 8 As shown, it can be seen that when the total number of electrode fingers is less than 16, the greater the total number of electrode fingers, the smaller the insertion loss. It can be seen that when the total number of electrode fingers is more than 16, the insertion loss can be effectively reduced. Moreover, when the total number of electrode fingers is more than 16, the insertion loss does not change much.

[0107] As described above, in the elastic wave device 10 of the present embodiment, a filter waveform can be obtained appropriately. This is because the elastic wave device 10 is an acoustic coupling filter. More specifically, Figure 2 As shown, the elastic wave device 10 includes an excitation region C located between the centers of the adjacent first electrode finger 25 and the third electrode finger 27, and an excitation region C located between the centers of the adjacent second electrode finger 26 and the third electrode finger 27. Elastic waves of multiple modes including a thickness shear mode bulk wave are excited in these excitation regions C. By coupling these modes, a filter waveform can be appropriately obtained in one elastic wave device 10.

[0108] When elastic wave device 10 is used as an elastic wave resonator in a filter device, a filter waveform can be appropriately obtained even if the number of elastic wave resonators constituting the filter device is one or less, thereby promoting miniaturization of the filter device.

[0109] Furthermore, in the present embodiment, the total number of the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 is 16 or more. Figure 8 As shown, the insertion loss can be reduced.

[0110] Hereinafter, the structure of the first embodiment will be described in more detail.

[0111] like Figure 1 As shown, the support member 13 includes a support substrate 16 and an insulating layer 15. The piezoelectric substrate 12 is a stack of the support substrate 16, the insulating layer 15, and the piezoelectric layer 14. That is, when viewed from the direction in which the first principal surface 14a and the second principal surface 14b of the piezoelectric layer 14 are opposite, the piezoelectric layer 14 and the support member 13 overlap.

[0112] As a material of the support substrate 16 , for example, a semiconductor such as silicon, a ceramic such as aluminum oxide, etc. can be used. As a material of the insulating layer 15 , an appropriate dielectric such as silicon oxide or tantalum oxide can be used.

[0113] A recess is provided in the insulating layer 15. A piezoelectric layer 14 is provided on the insulating layer 15 so as to block the recess. Thus, a hollow portion is formed. The hollow portion is a cavity 10a. In the first embodiment, the supporting member 13 and the piezoelectric layer 14 are configured so that a part of the supporting member 13 and a part of the piezoelectric layer 14 are opposed to each other with the cavity 10a sandwiched therebetween. However, the recess in the supporting member 13 may also be provided throughout the insulating layer 15 and the supporting substrate 16. Alternatively, it may be that only the recess provided in the supporting substrate 16 is blocked by the insulating layer 15. The recess may also be provided in the piezoelectric layer 14. In addition, the cavity 10a may also be a through hole provided in the supporting member 13.

[0114] The cavity 10a is the acoustic reflection portion in the present invention. The acoustic reflection portion can effectively confine the energy of the elastic wave on the piezoelectric layer 14 side. The acoustic reflection portion can be provided at a position overlapping with at least a portion of the functional electrode 11 in the support member 13 when viewed from above. More specifically, when viewed from above, at least a portion of each of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 can overlap with the acoustic reflection portion. When viewed from above, it is preferred that a plurality of excitation regions C overlap with the acoustic reflection portion.

[0115] In this specification, the term "top view" refers to a view from the Figure 1 The upper direction in FIG. 1 is viewed along the stacking direction of the support member 13 and the piezoelectric layer 14. Figure 1 For example, the piezoelectric layer 14 side is the upper side of the support substrate 16 side and the piezoelectric layer 14 side. Furthermore, in this specification, looking down is synonymous with observing from the main surface facing direction. The so-called main surface facing direction is the direction in which the first main surface 14a and the second main surface 14b of the piezoelectric layer 14 are facing each other. More specifically, the main surface facing direction is, for example, the normal direction of the first main surface 14a.

[0116] In addition, the sound reflecting portion may be a sound reflecting film such as a sound multilayer film described later. For example, a sound reflecting film may be provided on the surface of the supporting member.

[0117] As described above, the longest distance between the center distance px of the adjacent first electrode finger 25 and the third electrode finger 27 and the center distance px of the adjacent second electrode finger 26 and the third electrode finger 27 is p. In this case, when the thickness of the piezoelectric layer 14 is d, preferably d / p is 0.5 or less, and more preferably d / p is 0.24 or less. Thus, the body wave of the thickness shear mode can be appropriately excited.

[0118] In addition, the elastic wave device of the present invention may not necessarily be configured to utilize the thickness shear mode. For example, the elastic wave device of the present invention may be configured to excite plate waves. In this case, the excitation region is Figure 2 The intersection area E is shown.

[0119] like Figure 2 As shown, in the first embodiment, the reference potential electrode 19 has a third bus bar 24 as a connection electrode and a plurality of third electrode fingers 27. The reference potential electrode 19 is a comb-shaped electrode. However, the reference potential electrode 19 may not be a comb-shaped electrode. This example is shown by the first modification and the second modification.

[0120] Fig. 9 FIG. 1 is a schematic plan view of an elastic wave device according to a first modification of the first embodiment. Fig. 9 In FIG. 1 , the reference potential electrode is schematically shown to be connected to the reference potential by the reference potential symbol. Fig. 9 Similarly, in other schematic plan views, the reference potential symbol may be used.

[0121] The reference potential electrode 39A of this modification has a meandering shape. In this modification, the insulating film 29 is not provided on the piezoelectric layer 14. The connection electrode 34 includes only a portion corresponding to the plurality of first connection electrodes 24A in the first embodiment. The connection electrode 34 of this modification is not a third bus bar.

[0122] More specifically, the reference potential electrode 39A includes a plurality of connection electrodes 34 located on the first bus bar 22 side and a plurality of connection electrodes 34 located on the second bus bar 23 side. The ends of two adjacent third electrode fingers 27 on the first bus bar 22 side or on the second bus bar 23 side are connected via the connection electrodes 34.

[0123] For example, the third electrode fingers 27 other than the two ends in the orthogonal direction of the electrode fingers among the plurality of third electrode fingers 27 are each connected to one connection electrode 34 at the front end on the first bus bar 22 side and the front end on the second bus bar 23 side. The third electrode finger 27 is connected to the third electrode finger 27 adjacent to the left and right through each connection electrode 34. By repeating this structure, the shape of the reference potential electrode 39A is set to a meandering shape.

[0124] In this modification, the front ends of the plurality of second electrode fingers 26 are respectively opposed to the plurality of connection electrodes 34 with a gap g1 in the electrode finger extension direction. That is, the front ends of the plurality of second electrode fingers 26 are respectively opposed to the electrode connected to a potential different from that of the electrode finger and any one of the input potential, the output potential, and the reference potential with a gap g1 in the electrode finger extension direction. Specifically, the second electrode finger 26 is connected to the output potential, and the connection electrode 34 is connected to the reference potential. The dimension of the gap g1 between the front ends of the second electrode fingers 26 and the connection electrode 34 along the electrode finger extension direction is the gap length G.

[0125] Similarly, the front ends of the plurality of first electrode fingers 25 are respectively opposed to the plurality of connection electrodes 34 with a gap g2 in the electrode finger extension direction. That is, the front ends of the plurality of first electrode fingers 25 are respectively opposed to electrodes connected to a potential different from that of the electrode finger and any one of the input potential, the output potential, and the reference potential with a gap g2 in the electrode finger extension direction. Specifically, the first electrode finger 25 is connected to the input potential, and the connection electrode 34 is connected to the reference potential. The dimension of the gap g2 between the front ends of the first electrode fingers 25 and the connection electrode 34 along the electrode finger extension direction is the gap length G.

[0126] In the present modification, the gap length G of the gap g1 and the gap length G of the gap g2 are the same. However, the gap length G of the gap g1 and the gap length G of the gap g2 may be different from each other.

[0127] The portion of the reference potential electrode 39A connected to the reference potential is a potential connection portion. Specifically, the reference potential electrode 39A has two potential connection portions. Specifically, the two potential connection portions of the reference potential electrode 39A are a first potential connection portion 36A and a second potential connection portion 36B.

[0128] The first potential connection portion 36A is located at a third electrode finger 27 at one end of the plurality of third electrode fingers 27 in the direction orthogonal to the electrode fingers. More specifically, the first potential connection portion 36A is configured as a part of the third electrode finger 27. In addition, although not shown, at least one connection wiring is provided on the first main surface 14a of the piezoelectric layer 14. The first potential connection portion 36A is connected to the connection wiring. The first potential connection portion 36A is connected to the reference potential via the connection wiring.

[0129] As described above, the first potential connection portion 36A is located at the third electrode finger 27 at one end in the orthogonal direction of the electrode fingers among the plurality of third electrode fingers 27. On the other hand, the second potential connection portion 36B is located at the third electrode finger 27 at the other end in the orthogonal direction of the electrode fingers among the plurality of third electrode fingers 27. The second potential connection portion 36B is connected to the reference potential via a connection wiring.

[0130] It is sufficient that at least one connection wiring is provided. That is, one connection wiring may be connected to both the first potential connection portion 36A and the second potential connection portion 36B. Alternatively, one of the two connection wirings may be connected to the first potential connection portion 36A. Alternatively, the other connection wiring may be connected to the second potential connection portion 36B.

[0131] In addition, in the present modification, two third electrode fingers 27 at both ends in the electrode finger orthogonal direction among the plurality of third electrode fingers 27 are located outside in the electrode finger orthogonal direction than both ends in the electrode finger orthogonal direction of the second comb-shaped electrode 18. The connection wiring connected to the first potential connection portion 36A and the second potential connection portion 36B passes outside in the electrode finger orthogonal direction than the above-mentioned both ends of the second comb-shaped electrode 18.

[0132] In this modification, the Euler angle of the piezoelectric layer 14 is the same as that of the first embodiment. The order in which the plurality of electrode fingers are arranged is such that, starting from the first electrode finger 25, the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, and the third electrode finger 27 form one cycle. Moreover, the total number of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 is 16 or more. Thus, when the elastic wave device is used for a filter device, the miniaturization of the filter device can be promoted, and the insertion loss can be reduced.

[0133] Fig.10 It is a schematic plan view of an elastic wave device according to a second modification of the first embodiment.

[0134] The reference potential electrode 39B of this modification has potential connection parts at five locations. Each potential connection part is connected to the reference potential via a connection wiring. In addition, the shape of the reference potential electrode 39B is meandering in the same manner as in the first modification. In this modification, both the first bus bar 32 and the second bus bar 33 are divided into a plurality of split bus bar parts. The connection wiring passes between the split bus bar parts.

[0135] Specifically, the first bus bar 32 of the first comb-shaped electrode 37 includes a split bus bar portion 32A, a split bus bar portion 32B, and a split bus bar portion 32C. The split bus bar portion 32A and the split bus bar portion 32B face each other with a gap in the electrode finger orthogonal direction. The split bus bar portion 32B and the split bus bar portion 32C face each other with a gap in the electrode finger orthogonal direction.

[0136] The second bus bar 33 of the second comb-shaped electrode 38 includes a divided bus bar portion 33A and a divided bus bar portion 33B. The divided bus bar portion 33A and the divided bus bar portion 33B face each other with a gap therebetween in the electrode finger orthogonal direction.

[0137] The reference potential electrode 39B has the same first potential connection portion 36A and second potential connection portion 36B as the first modification. In addition, the reference potential electrode 39B has three third potential connection portions. Specifically, the three third potential connection portions are a third potential connection portion 36C, a third potential connection portion 36D, and a third potential connection portion 36E.

[0138] The third potential connection portions at three locations are located between two third electrode fingers 27 at both ends of the electrode fingers in the orthogonal direction among the plurality of third electrode fingers of the reference potential electrode 39B. More specifically, the third potential connection portion 36C is located at the connection electrode 34 that connects the tips of the second bus bar 33 side of the adjacent third electrode fingers 27. On the other hand, the third potential connection portion 36D and the third potential connection portion 36E are located at the connection electrode 34 that connects the tips of the first bus bar 32 side of the adjacent third electrode fingers 27. The third potential connection portion 36C is located between the third potential connection portion 36D and the third potential connection portion 36E.

[0139] The connection wiring connected to the third potential connection portion 36C passes between the divided bus bar portion 33A and the divided bus bar portion 33B of the second bus bar 33. The connection wiring connected to the third potential connection portion 36D passes between the divided bus bar portion 32A and the divided bus bar portion 32B of the first bus bar 32. The connection wiring connected to the third potential connection portion 36E passes between the divided bus bar portion 32B and the divided bus bar portion 32C of the first bus bar 32.

[0140] In this modification, the reference potential electrode 39B has five potential connection portions. This can effectively shorten the length of the portion between the potential connection portions. This can effectively reduce the resistance of the reference potential electrode 39B.

[0141] Moreover, in this variation, similarly to the first embodiment and the first variation, when the elastic wave device is used for the filter device, the miniaturization of the filter device can be promoted and the insertion loss can be reduced. In addition, the number of parts and positions of the potential connection portion are not limited to the above. The number of divisions of the first bus bar 32 and the second bus bar 33 is also not limited to the above. At least one of the first bus bar 32 and the second bus bar 33 may also be divided.

[0142] The structure of the second embodiment is described below. The basic structure of the second embodiment is the same as that of the first embodiment. Therefore, in the description of the second embodiment, the drawings and reference numerals used in the description of the first embodiment are used. In addition, the difference between the second embodiment and the first embodiment is that the relationship between the cross width Ap and the center distance px between adjacent electrode fingers is limited to Ap / px≥5.

[0143] The second embodiment is characterized by having the following structure. 1) A third electrode finger 27 of a reference potential electrode 19 is provided between the first electrode finger 25 of the first comb-shaped electrode 17 and the second electrode finger 26 of the second comb-shaped electrode 18. 2) Ap / px ≥ 5. Thus, when the elastic wave device 10 is used in a filter device, the miniaturization of the filter device can be promoted and the insertion loss can be reduced. In addition, in the second embodiment, the total number of the plurality of electrode fingers and the Euler angle of the piezoelectric layer 14 are not particularly limited. The above-mentioned effects are shown below.

[0144] The insertion loss around 6 GHz was compared by varying Ap / px. The elastic wave devices involved in this comparison also include elastic wave devices with Ap / px<5. Specifically, Ap / px was varied within a range of 1.25 to 12.5. The design parameters of the elastic wave devices involved in this comparison are as follows.

[0145] Piezoelectric layer: Material…LiNbO3, Euler angles (φ, θ, ψ)…(0°, 0°, 90°), Thickness…400nm

[0146] First electrode finger to third electrode finger: layer structure: Ti layer / AlCu layer / Ti layer from the piezoelectric layer side, thickness of each layer: 10 nm / 390 nm / 4 nm from the piezoelectric layer side

[0147] The order of the first electrode finger to the third electrode finger is represented by the order of the potentials to be connected: IN, GND, OUT, GND are repeated.

[0148] The center-to-center distance px between adjacent electrode fingers is 1.4 μm.

[0149] Duty cycle of functional electrode: 0.3

[0150] Ap / px: Changed within the range of 1.25 or more and 12.5 or less.

[0151] Fig.11 This is a graph showing the relationship between Ap / px and insertion loss near 6 GHz.

[0152] like Fig.11 As shown, it can be seen that the larger the Ap / px, the smaller the insertion loss. It can be seen that the slopes of the change in insertion loss relative to the change in Ap / px are very different in the case of Ap / px <5 and in the case of Ap / px ≥5. Specifically, the above slope in the case of Ap / px <5 is greater than the above slope in the case of Ap / px ≥5. In the case of Ap / px <5, the closer Ap / px is to 5, the more significantly the insertion loss decreases. Moreover, in the case of Ap / px ≥5 as in the second embodiment, the insertion loss can be effectively reduced.

[0153] In the second embodiment, similarly to the first embodiment, when the elastic wave device 10 is used as an elastic wave resonator in a filter device, a filter waveform can be obtained appropriately even if the number of elastic wave resonators constituting the filter device is one or less, thereby promoting miniaturization of the filter device.

[0154] In the second embodiment, the total number of the plurality of electrode fingers is preferably 16 or more. This can more reliably and effectively reduce the insertion loss. The Euler angles (φ, θ, ψ) of the piezoelectric layer 14 are preferably in the range represented by the above-mentioned equations (1), (2), and (3). This can more reliably increase the value of the fractional bandwidth.

[0155] The structures of the third and fourth embodiments are described below. The basic structures of the third and fourth embodiments are the same as those of the first embodiment. Therefore, in the description of the third and fourth embodiments, the drawings and figure numerals used in the description of the first embodiment are used. In addition, the third embodiment differs from the first embodiment in that the relationship between the gap length G and the center-to-center distance px between adjacent electrode fingers is limited to G / px≥1, and in the range of the Euler angle of the piezoelectric layer 14. The fourth embodiment differs from the first embodiment in that it is limited to G / px≤0.5.

[0156] In the third embodiment and the fourth embodiment, the gap length G of the gap g1 and the gap length G of the gap g2 are the same. However, the gap length G of the gap g1 and the gap length G of the gap g2 may be different from each other.

[0157] The third embodiment is characterized by having the following structure. 1) The Euler angles (φ, θ, ψ) of the piezoelectric layer 14 are (within the range of 0°±5°, within the range of -8°±14°, within the range of 90°±5°). 2) The third electrode finger 27 of the reference potential electrode 19 is provided between the first electrode finger 25 of the first comb-shaped electrode 17 and the second electrode finger 26 of the second comb-shaped electrode 18. 3) The relationship between the center distance px and the gap length G of adjacent electrode fingers is G / px≥1. Thus, when the elastic wave device 10 is used for a filter device, the miniaturization of the filter device can be promoted and the insertion loss can be reduced. This is illustrated below. In addition, in the third embodiment, the total number of the plurality of electrode fingers is not particularly limited.

[0158] The insertion loss around 6 GHz was compared by varying G / px. The elastic wave devices involved in this comparison also include elastic wave devices with 0.5<G / px<1. Specifically, Ap / px was varied within the range of 0.625 to 2.5. The design parameters of the elastic wave devices involved in this comparison are as follows.

[0159] Piezoelectric layer: Material…LiNbO3, Euler angles (φ, θ, ψ)…(0°, 0°, 90°), Thickness…400nm

[0160] First electrode finger to third electrode finger: layer structure: Ti layer / AlCu layer / Ti layer from the piezoelectric layer side, thickness of each layer: 10 nm / 390 nm / 4 nm from the piezoelectric layer side

[0161] The order of the first electrode finger to the third electrode finger is represented by the order of the potentials to be connected: IN, GND, OUT, GND are repeated.

[0162] The center-to-center distance px between adjacent electrode fingers is 1.4 μm.

[0163] Duty cycle of functional electrode: 0.3

[0164] G / px: Changed within the range of 0.625 to 2.5.

[0165] Fig.12 This is a graph showing the relationship between G / px and insertion loss near 6 GHz.

[0166] like Fig.12As shown, it can be seen that, in the case of 0.5<G / px<1, the closer G / px is to 1, the more the insertion loss decreases. Furthermore, it can be seen that, in the case of G / px≥1, the insertion loss can be effectively reduced.

[0167] In the third embodiment, similarly to the first embodiment, when the elastic wave device 10 is used as an elastic wave resonator in a filter device, a filter waveform can be obtained appropriately even if the number of elastic wave resonators constituting the filter device is one or less, thereby promoting miniaturization of the filter device.

[0168] In the third embodiment, the total number of the plurality of electrode fingers is preferably equal to or greater than 16. This makes it possible to more reliably and effectively reduce the insertion loss.

[0169] exist Fig.12 , the insertion loss when the Euler angle (φ, θ, ψ) of the piezoelectric layer 14 is (0°, 0°, 90°) in the third embodiment is shown. However, the Euler angle (φ, θ, ψ) of the piezoelectric layer 14 may be (within the range of 0°±5°, within the range of -8°±14°, within the range of 90°±5°). In this case, by setting G / px≥1, the insertion loss can be reduced.

[0170] The fourth embodiment is characterized by having the following structure. 1) The Euler angles (φ, θ, ψ) of the piezoelectric layer 14 are within the range of the above-mentioned formula (1), formula (2) or formula (3). 2) The third electrode finger 27 of the reference potential electrode 19 is provided between the first electrode finger 25 of the first comb-shaped electrode 17 and the second electrode finger 26 of the second comb-shaped electrode 18. 3) The relationship between the center distance px and the gap length G of adjacent electrode fingers is G / px≤0.5. Thus, when the elastic wave device 10 is used for a filter device, the miniaturization of the filter device can be promoted and the insertion loss can be reduced. This is illustrated below. In addition, in the fourth embodiment, the total number of multiple electrode fingers is not particularly limited.

[0171] The insertion loss around 6 GHz was compared by varying G / px. The elastic wave devices involved in this comparison also include elastic wave devices with 0.5<G / px. Specifically, G / px was varied within a range of 0.125 to 1.25. The design parameters of the elastic wave devices involved in this comparison are as follows.

[0172] Piezoelectric layer: Material…LiNbO3, Euler angles (φ, θ, ψ)…(0°, 127.5°, 0°), thickness…400nm

[0173] First electrode finger to third electrode finger: layer structure: Ti layer / AlCu layer / Ti layer from the piezoelectric layer side, thickness of each layer: 10 nm / 390 nm / 4 nm from the piezoelectric layer side

[0174] The order of the first electrode finger to the third electrode finger is represented by the order of the potentials to be connected: IN, GND, OUT, GND are repeated.

[0175] The center-to-center distance px between adjacent electrode fingers is 1.4 μm.

[0176] Duty cycle of functional electrode: 0.3

[0177] G / px: Changed within the range of 0.125 to 1.25.

[0178] Fig.13 This is a graph showing the relationship between G / px and insertion loss near 6 GHz.

[0179] like Fig.13 As shown, it can be seen that when 0.5≤G / px, the insertion loss can be effectively reduced.

[0180] Moreover, in the fourth embodiment, the filter device can be miniaturized as in the first embodiment. In the fourth embodiment, the total number of the plurality of electrode fingers is preferably 16 or more. This can more reliably and effectively reduce the insertion loss.

[0181] exist Fig.13 , the insertion loss when the Euler angle (φ, θ, ψ) of the piezoelectric layer 14 is (0°, 127.5°, 0°) in the fourth embodiment is shown. However, in the case where the piezoelectric layer 14 includes rotated Y-cut lithium niobate, the insertion loss can be reduced by setting G / px≤0.5. Moreover, as in the present embodiment, when the Euler angle (φ, θ, ψ) of the piezoelectric layer 14 is within the range of the above-mentioned formula (1), formula (2) or formula (3), the value of the fractional bandwidth can be increased more reliably.

[0182] In the second to fourth embodiments, if the Figure 2 As shown in the figure, the connection electrode is the third bus bar 24. The reference potential electrode 19 is a comb-shaped electrode. However, in the second to fourth embodiments, it is also possible to use Fig. 9 The reference potential electrode 39A shown, Fig.10 The reference potential electrode 39B shown. In the second to fourth embodiments, the reference potential electrode may have a meandering shape.

[0183] Hereinafter, further examples in which the reference potential electrode has a meandering shape will be described with reference to the fifth and sixth embodiments.

[0184] Fig.14 FIG. 1 is a schematic top view of an elastic wave device according to a fifth embodiment. Fig.14 In the figure, the GB gap length described later is represented by the reference symbol GB. The GF gap length is represented by the reference symbol GF.

[0185] This embodiment is different from the first embodiment in the structure of the first bus bar 32, the second bus bar 33 and the reference potential electrode 39B. In addition, the basic structure of the first bus bar 32, the second bus bar 33 and the reference potential electrode 39B is the same as the second variant of the first embodiment. However, in this embodiment, the distance between the connecting electrode 34 and the front end of the electrode finger and the bus bar is limited. Except for the above aspects, the elastic wave device of the fifth embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0186] Hereinafter, the distance between the connection electrode 34 and the first bus bar 32 connecting the first bus bar 32 side tips of adjacent third electrode fingers 27 is referred to as the GB gap length. The distance between the connection electrode 34 and the tips of the second electrode fingers 26 is referred to as the GF gap length.

[0187] The present embodiment is characterized in that it has the following structure. 1) The Euler angles (φ, θ, ψ) of the piezoelectric layer 14 are within the range of the above-mentioned formula (1), formula (2) or formula (3). 2) The third electrode finger 27 of the reference potential electrode 19 is provided between the first electrode finger 25 of the first comb-shaped electrode 17 and the second electrode finger 26 of the second comb-shaped electrode 18. 3) The GB gap length ≤ the GF gap length. Thus, when the elastic wave device is used in a filter device, the miniaturization of the filter device can be promoted and the insertion loss can be reduced.

[0188] In the present embodiment, the total number of the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 is not particularly limited. However, the total number of the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 is preferably 16 or more. This can more reliably and effectively reduce the insertion loss.

[0189] In the present embodiment, the first comb-shaped electrode 37 is connected to the input potential. The second comb-shaped electrode 38 is connected to the output potential. Therefore, the GB gap length is the distance between the connection electrode 34 connected to the reference potential and the first bus bar 32 connected to the input potential. The GF gap length is the distance between the connection electrode 34 connected to the reference potential and the tip of the second electrode finger 26 connected to the output potential.

[0190] However, the first comb-shaped electrode 37 may be connected to the output potential, and the second comb-shaped electrode 38 may be connected to the input potential. In this case, the GB gap length is the distance between the connection electrode 34 connected to the reference potential and the first bus bar 32 connected to the output potential. The GF gap length is the distance between the connection electrode 34 connected to the reference potential and the tip of the second electrode finger 26 connected to the input potential.

[0191] Alternatively, the GB gap length may be set to the distance between the connection electrode 34 and the second bus bar 33 that connect the second bus bar 33-side tips of the adjacent third electrode fingers 27. In this case, the GF gap length is set to the distance between the connection electrode 34 and the tips of the first electrode fingers 25.

[0192] The structure of the sixth embodiment is described below. The structure of the sixth embodiment is basically the same as that of the fifth embodiment. Therefore, the drawings and reference numerals used in the description of the fifth embodiment are used in the description of the sixth embodiment. In addition, the sixth embodiment is different from the fifth embodiment in that the GB gap length is greater than the GF gap length and in the range of the Euler angle of the piezoelectric layer 14.

[0193] The sixth embodiment is characterized in that it has the following structure. 1) The Euler angles (φ, θ, ψ) of the piezoelectric layer 14 are (within the range of 0°±5°, within the range of -8°±14°, and within the range of 90°±5°). 2) The third electrode finger 27 of the reference potential electrode 19 is provided between the first electrode finger 25 of the first comb-shaped electrode 17 and the second electrode finger 26 of the second comb-shaped electrode 18. 3) The GB gap length is greater than the GF gap length. Thus, when the elastic wave device is used in a filter device, the filter device can be miniaturized and the insertion loss can be reduced.

[0194] In the sixth embodiment, the total number of the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 is not particularly limited. However, the total number of the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 is preferably 16 or more. This can more reliably and effectively reduce the insertion loss.

[0195] The fifth and sixth embodiments show examples of defining the GB gap length and the GF gap length when the reference potential electrode has a meandering shape. Figure 2In the reference potential electrode 19 as the comb-shaped electrode shown, the GB gap length and the GF gap length can also be defined. Specifically, the GB gap length is the distance between the third bus bar 24 and the first bus bar 22. The GF gap length corresponds to the gap length G in the gap g1.

[0196] When the reference potential electrode 19 is a comb-shaped electrode, GB gap length ≤ GF gap length may be satisfied as in the fifth embodiment. Alternatively, GB gap length > GF gap length may be satisfied as in the sixth embodiment.

[0197] The following describes the details of the thickness shear mode using an example in which the functional electrode is an IDT electrode. In addition, the IDT electrode does not have a third electrode finger. The "electrode" in the IDT electrode described later is equivalent to the electrode finger. The supporting member in the following example is equivalent to the supporting substrate in the present invention. In the following, the reference potential is sometimes recorded as the ground potential.

[0198] Fig.15 (a) is a schematic perspective view showing the appearance of an elastic wave device using a thickness shear mode bulk wave, Fig.15 (b) is a top view showing the electrode structure on the piezoelectric layer. Fig.16 It is along Fig.15 (a) is a cross-sectional view of a portion taken along line AA.

[0199] The elastic wave device 1 has a piezoelectric layer 2 containing LiNbO3. The piezoelectric layer 2 may also contain LiTaO3. The cutting angle of LiNbO3 and LiTaO3 is Z-cut, but it may also be a rotated Y-cut or X-cut. The thickness of the piezoelectric layer 2 is not particularly limited, but in order to effectively excite the thickness shear mode, it is preferably greater than 40nm and less than 1000nm, and more preferably greater than 50nm and less than 1000nm. The piezoelectric layer 2 has a first principal surface 2a and a second principal surface 2b facing each other. An electrode 3 and an electrode 4 are provided on the first principal surface 2a. Here, electrode 3 is an example of a "first electrode", and electrode 4 is an example of a "second electrode". In Fig.15 (a) and Fig.15 In (b), a plurality of electrodes 3 are connected to a first bus bar 5. A plurality of electrodes 4 are connected to a second bus bar 6. The plurality of electrodes 3 and the plurality of electrodes 4 are interlaced with each other. The electrodes 3 and 4 have a rectangular shape and a length direction. In a direction perpendicular to the length direction, the electrode 3 and the adjacent electrode 4 are opposed to each other. The length directions of the electrodes 3 and 4, and the directions perpendicular to the length directions of the electrodes 3 and 4 are all directions intersecting with the thickness direction of the piezoelectric layer 2. Therefore, it can also be said that the electrode 3 and the adjacent electrode 4 are opposed to each other in a direction intersecting with the thickness direction of the piezoelectric layer 2. In addition, the length directions of the electrodes 3 and 4 can also be perpendicular to the length directions of the electrodes 3 and 4. Fig.15 (a) and Fig.15 The direction perpendicular to the length direction of the electrodes 3 and 4 shown in (b) is changed. Fig.15 (a) and Fig.15 In (b), the electrodes 3 and 4 may be extended in the direction in which the first bus bar 5 and the second bus bar 6 extend. In this case, the first bus bar 5 and the second bus bar 6 are Fig.15 (a) and Fig.15 (b) becomes extended in the direction in which electrodes 3 and 4 extend. Moreover, a pair of structures in which an electrode 3 connected to one potential and an electrode 4 connected to another potential are adjacent are provided with multiple pairs in a direction orthogonal to the length direction of the electrodes 3 and 4. Here, the so-called electrode 3 and electrode 4 are adjacent does not mean that the electrodes 3 and electrode 4 are arranged in direct contact, but refers to the case where the electrodes 3 and electrode 4 are arranged with a gap. In addition, when the electrode 3 and electrode 4 are adjacent, no electrode connected to the signal electrode and the ground electrode, including other electrodes 3 and 4, is arranged between the electrode 3 and the electrode 4. The number of pairs does not need to be an integer pair, and can also be 1.5 pairs, 2.5 pairs, etc. The center-to-center distance between the electrodes 3 and 4, that is, the spacing, is preferably in the range of 1 μm or more and 10 μm or less. In addition, the width of the electrodes 3 and 4, that is, the size of the opposing direction of the electrodes 3 and 4, is preferably in the range of 50 nm or more and 1000 nm or less, and more preferably in the range of 150 nm or more and 1000 nm or less. The center-to-center distance between electrodes 3 and 4 is the distance connecting the center of the dimension (width dimension) of electrode 3 in a direction perpendicular to the length direction of electrode 3 and the center of the dimension (width dimension) of electrode 4 in a direction perpendicular to the length direction of electrode 4.

[0200] In addition, in the elastic wave device 1, since a Z-cut piezoelectric layer is used, the direction perpendicular to the length direction of the electrodes 3 and 4 becomes a direction perpendicular to the polarization direction of the piezoelectric layer 2. In the case where a piezoelectric body with another cutting angle is used as the piezoelectric layer 2, this is not limited to this. Here, the so-called "orthogonal" is not limited to the case of being strictly orthogonal, and can also be approximately orthogonal (the angle formed by the direction perpendicular to the length direction of the electrodes 3 and 4 and the polarization direction is, for example, within the range of 90°±10°).

[0201] A support member 8 is stacked on the second main surface 2b side of the piezoelectric layer 2 via an insulating layer 7. The insulating layer 7 and the support member 8 have a frame-like shape. Fig.16As shown, there are through holes 7a and 8a. Thus, a cavity 9 is formed. The cavity 9 is provided so as not to hinder the vibration of the excitation region C of the piezoelectric layer 2. Therefore, the support member 8 is stacked on the second main surface 2b via the insulating layer 7 at a position that does not overlap with the portion where at least one pair of electrodes 3 and 4 is provided. In addition, the insulating layer 7 may not be provided. Therefore, the support member 8 may be directly or indirectly stacked on the second main surface 2b of the piezoelectric layer 2.

[0202] The insulating layer 7 includes silicon oxide. However, in addition to silicon oxide, suitable insulating materials such as silicon nitride oxide and alumina can also be used. The supporting member 8 includes Si. The surface orientation of Si in the surface on the side of the piezoelectric layer 2 can be (100), (110), or (111). It is preferred that the Si constituting the supporting member 8 has a high resistance with a resistivity of more than 4 kΩcm. However, the supporting member 8 can also be composed of suitable insulating materials or semiconductor materials.

[0203] As the material of the supporting member 8, for example, piezoelectrics such as aluminum oxide, lithium tantalate, lithium niobate, and quartz, various ceramics such as alumina, magnesium oxide, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, and forsterite, dielectrics such as diamond and glass, and semiconductors such as gallium nitride can be used.

[0204] The plurality of electrodes 3, 4 and the first bus bar 5 and the second bus bar 6 include a suitable metal or alloy such as Al or AlCu alloy. In the elastic wave device 1, the electrodes 3, 4 and the first bus bar 5 and the second bus bar 6 have a structure in which an Al film is stacked on a Ti film. Alternatively, a bonding layer other than a Ti film may be used.

[0205] During driving, an AC voltage is applied between the plurality of electrodes 3 and the plurality of electrodes 4. More specifically, an AC voltage is applied between the first bus bar 5 and the second bus bar 6. Thus, it is possible to obtain a resonance characteristic of a body wave utilizing a thickness shear mode excited in the piezoelectric layer 2. In addition, in the elastic wave device 1, when the thickness of the piezoelectric layer 2 is set to d and the center distance between any adjacent electrodes 3 and 4 among the plurality of pairs of electrodes 3 and 4 is set to p, d / p is set to be less than 0.5. Therefore, the body wave of the thickness shear mode can be effectively excited, and a good resonance characteristic can be obtained. More preferably, d / p is less than 0.24, in which case, a better resonance characteristic can be obtained.

[0206] In the elastic wave device 1, since it has the above-mentioned structure, even if the number of pairs of electrodes 3 and 4 is reduced in order to achieve miniaturization, the Q value is not likely to decrease. This is because even if the number of electrode fingers in the reflectors on both sides is reduced, the propagation loss is small. In addition, the number of electrode fingers can be reduced because the body wave of the thickness shear mode is utilized. Fig.17 (a) and Fig.17 (b) explains the difference between the Lamb wave used in the elastic wave device and the body wave of the thickness shear mode.

[0207] Fig.17 (a) is a schematic front cross-sectional view for explaining Lamb waves propagating in a piezoelectric film of an elastic wave device as described in Japanese Patent Gazette No. 2012-257019. Here, the wave propagates in the piezoelectric film 201 as indicated by the arrow. Here, in the piezoelectric film 201, the first principal surface 201a and the second principal surface 201b are opposed to each other, and the thickness direction connecting the first principal surface 201a and the second principal surface 201b is the Z direction. The X direction is the direction in which the electrode fingers of the IDT electrode are arranged. Fig.17 As shown in (a), for Lamb waves, the waves propagate in the X direction as shown in the figure. Since it is a plate wave, although the piezoelectric film 201 vibrates as a whole, the waves propagate in the X direction, so reflectors are arranged on both sides to obtain resonance characteristics. Therefore, wave propagation loss occurs, and when miniaturization is sought, that is, when the number of pairs of electrode fingers is reduced, the Q value decreases.

[0208] In contrast, Fig.17 As shown in (b), in the elastic wave device 1, the vibration displacement is in the thickness shear direction, so the wave generally propagates in the direction connecting the first main surface 2a and the second main surface 2b of the piezoelectric layer 2, that is, the Z direction, and resonates. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Moreover, the resonance characteristics can be obtained by the propagation of the wave in the Z direction, so even if the number of electrode fingers of the reflector is reduced, it is not easy to cause propagation loss. Furthermore, even if the number of pairs of electrode pairs including electrodes 3 and 4 is reduced in order to promote miniaturization, it is not easy to cause a decrease in the Q value.

[0209] In addition, if Fig.18 As shown in FIG. 1 , the amplitude directions of the thickness shear mode body wave are opposite in the first region 451 included in the excitation region C of the piezoelectric layer 2 and in the second region 452 included in the excitation region C. Fig.18 , a body wave is schematically shown when a voltage is applied between the electrode 3 and the electrode 4 so that the electrode 4 has a higher potential than the electrode 3. The first region 451 is a region between the first principal surface 2a and the imaginary plane VP1 which is orthogonal to the thickness direction of the piezoelectric layer 2 and divides the piezoelectric layer 2 into two parts in the excitation region C. The second region 452 is a region between the imaginary plane VP1 and the second principal surface 2b in the excitation region C.

[0210] As described above, elastic wave device 1 includes at least one pair of electrodes including electrode 3 and electrode 4 , but since waves are not propagated in the X direction, there is no need to have more than one pair of electrodes including electrode 3 and electrode 4 . In other words, at least one pair of electrodes is sufficient.

[0211] For example, the electrode 3 is an electrode connected to the signal potential, and the electrode 4 is an electrode connected to the ground potential. However, the electrode 3 may be connected to the ground potential, and the electrode 4 may be connected to the signal potential. In the elastic wave device 1, at least one pair of electrodes is an electrode connected to the signal potential or an electrode connected to the ground potential as described above, and no floating electrode is provided.

[0212] Fig.19 It is shown Fig.16 The resonance characteristics of the elastic wave device are shown in FIG. 1. The design parameters of the elastic wave device 1 that obtain the resonance characteristics are as follows.

[0213] Piezoelectric layer 2: LiNbO3 with Euler angles (0°, 0°, 90°), thickness = 400nm.

[0214] When observed in a direction orthogonal to the length direction of electrode 3 and electrode 4, the length of the overlapping area of ​​electrode 3 and electrode 4, i.e., the excitation area C, is 40 μm, the number of pairs of electrodes including electrodes 3 and 4 is 21 pairs, the center distance between electrodes is 3 μm, the width of electrodes 3 and 4 is 500 nm, and d / p is 0.133.

[0215] Insulating layer 7: a silicon oxide film having a thickness of 1 μm.

[0216] Supporting member 8: Si.

[0217] The length of the excitation region C refers to the dimension of the excitation region C along the length direction of the electrodes 3 and 4 .

[0218] In elastic wave device 1 , the inter-electrode distances of the electrode pairs including electrodes 3 and 4 are set equal in a plurality of pairs. In other words, electrodes 3 and electrodes 4 are arranged at equal intervals.

[0219] according to Fig.19 It is clear that good resonance characteristics with a fractional bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0220] When the thickness of the piezoelectric layer 2 is d and the center-to-center distance between the electrodes 3 and 4 is p, as described above, in the elastic wave device 1, d / p is 0.5 or less, and more preferably 0.24 or less. Fig. 20 This is explained.

[0221] and got Fig.19A plurality of elastic wave devices are obtained by changing d / p in the same manner as the elastic wave devices having the resonance characteristics shown. Fig. 20 3 is a diagram showing the relationship between d / p and the fractional bandwidth of a resonator as an elastic wave device.

[0222] according to Fig. 20 It is clear that if d / p>0.5, even if d / p is adjusted, the fractional bandwidth is less than 5%. In contrast, when d / p≤0.5, if d / p is changed within this range, the fractional bandwidth can be made greater than 5%, that is, a resonator with a high coupling coefficient can be constructed. In addition, when d / p is less than 0.24, the fractional bandwidth can be increased to more than 7%. In addition, if d / p is adjusted within this range, a resonator with a wider fractional bandwidth can be obtained, and a resonator with a higher coupling coefficient can be realized. Therefore, it can be seen that by setting d / p to less than 0.5, a resonator with a high coupling coefficient that utilizes the body wave of the thickness shear mode mentioned above can be constructed.

[0223] Fig.21 1 is a top view of an elastic wave device using a thickness shear mode bulk wave. In the elastic wave device 80, a pair of electrodes including an electrode 3 and an electrode 4 are provided on the first principal surface 2a of the piezoelectric layer 2. Fig.21 K in is the crossing width. As described above, in the elastic wave device of the present invention, the number of pairs of electrodes may be 1 pair. In this case, as long as the above d / p is 0.5 or less, a thickness shear mode body wave can be effectively excited.

[0224] In the elastic wave device 1, it is preferable that the metallization ratio MR of the excitation region C, which is an area where any adjacent electrodes 3 and 4 overlap when viewed in the opposite direction relative to the adjacent electrodes 3 and 4, satisfies MR≤1.75(d / p)+0.075. In this case, the stray can be effectively reduced. Fig. 22 as well as Fig.23 Let me explain this. Fig. 22 : is a reference diagram showing an example of the resonance characteristics of the elastic wave device 1. Spurious signals indicated by arrow B appear between the resonance frequency and the antiresonance frequency. In addition, d / p=0.08 is assumed, and the Euler angles of LiNbO3 are assumed to be (0°, 0°, 90°). In addition, the metallization ratio MR is assumed to be 0.35.

[0225] Reference Fig.15 (b) will explain the metallization ratio MR. Fig.15In the electrode structure of (b), when focusing on a pair of electrodes 3 and 4, it is assumed that only the pair of electrodes 3 and 4 are provided. In this case, the portion surrounded by the single-dot chain line becomes the excitation region C. The so-called excitation region C refers to the region where the electrode 3 overlaps with the electrode 4, the region where the electrode 4 overlaps with the electrode 3, and the region between the electrode 3 and the electrode 4 where the electrode 3 overlaps with the electrode 4 when the electrode 3 and the electrode 4 are observed in the direction perpendicular to the length direction of the electrodes 3 and 4, that is, in the opposite direction. Moreover, the area of ​​the electrodes 3 and 4 in the excitation region C relative to the area of ​​the excitation region C becomes the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of ​​the metallized portion to the area of ​​the excitation region C.

[0226] When a plurality of pairs of electrodes are provided, the ratio of the total area of ​​the metallized portions included in all the excitation regions to the area of ​​the excitation regions may be defined as MR.

[0227] Fig.23 This is a diagram showing the relationship between the fractional bandwidth and the phase rotation amount of the impedance of the spurious signal normalized by 180 degrees when a plurality of spurious wave resonators are formed according to the structure of the spurious wave device 1. In addition, the film thickness of the piezoelectric layer and the size of the electrode were variously changed to adjust the fractional bandwidth. In addition, Fig.23 These are the results obtained when a piezoelectric layer including Z-cut LiNbO 3 is used, but the same tendency is observed when a piezoelectric layer having other cut angles is used.

[0228] exist Fig.23 In the area surrounded by ellipse J in , the spurious signal increases to 1.0. Fig.23 It is clear that if the fractional bandwidth exceeds 0.17, that is, if it exceeds 17%, even if the parameters constituting the fractional bandwidth are changed, large spurs with a spurious level of 1 or more will appear in the passband. Fig. 22 As shown in the resonance characteristics, large spurious signals indicated by arrow B appear in the frequency band. Therefore, the fractional bandwidth is preferably 17% or less. In this case, spurious signals can be reduced by adjusting the film thickness of the piezoelectric layer 2, the dimensions of the electrodes 3 and 4, and the like.

[0229] Fig.24 : is a graph showing the relationship between d / 2p, metallization ratio MR, and fractional bandwidth. In the above-mentioned elastic wave device, various elastic wave devices having different d / 2p and MR were constructed, and the fractional bandwidths were measured. Fig.24The hatched portion on the right side of the dotted line D is an area where the fractional bandwidth is less than 17%. The boundary between the hatched area and the unhatched area is represented by MR=3.5(d / 2p)+0.075. That is, MR=1.75(d / p)+0.075. Therefore, it is preferred that MR≤1.75(d / p)+0.075. In this case, it is easy to make the fractional bandwidth less than 17%. More preferably, Fig.24 The region to the right of MR=3.5(d / 2p)+0.05 is indicated by the dashed line D1 in FIG. That is, as long as MR≤1.75(d / p)+0.05, the fractional bandwidth can be reliably set to 17% or less.

[0230] Fig.25 This is a diagram showing a mapping of the fractional bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible. Fig.25 The multiple regions R shown in the figure and indicated by hatching are regions where a fractional bandwidth of 2% or more can be obtained. In addition, when φ among the Euler angles (φ, θ, ψ) is within the range of 0°±5°, the relationship between θ and ψ and the fractional bandwidth is Fig.25 When the piezoelectric layer contains lithium tantalate (LiTaO3), the relationship between θ and ψ in the Euler angle (in the range of 0°±5°, θ, ψ) and BW is also the same as Fig.25 The relationship shown is the same.

[0231] Therefore, as long as the Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of 0°±5°, and θ and φ are Fig.25 The fractional bandwidth can be sufficiently expanded within the range of any of the plurality of regions R shown, which is preferable.

[0232] Fig.26 It is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0233] In the elastic wave device 81, an acoustic multilayer film 82 is stacked on the second main surface 2b of the piezoelectric layer 2. The acoustic multilayer film 82 has a stacked structure of low acoustic impedance layers 82a, 82c, 82e having relatively low acoustic impedance and high acoustic impedance layers 82b, 82d having relatively high acoustic impedance. When the acoustic multilayer film 82 is used, the bulk wave of the thickness shear mode can be confined in the piezoelectric layer 2 even without using the cavity 9 in the elastic wave device 1. In the elastic wave device 81, by making the above-mentioned d / p less than 0.5, the resonance characteristics of the bulk wave based on the thickness shear mode can be obtained. In addition, in the acoustic multilayer film 82, the number of stacked low acoustic impedance layers 82a, 82c, 82e and high acoustic impedance layers 82b, 82d is not particularly limited. It is sufficient as long as at least one high acoustic impedance layer 82b, 82d is arranged on the side away from the piezoelectric layer 2 compared with the low acoustic impedance layers 82a, 82c, 82e.

[0234] The low acoustic impedance layers 82a, 82c, 82e and the high acoustic impedance layers 82b, 82d can be made of appropriate materials as long as the above-mentioned acoustic impedance relationship is satisfied. For example, silicon oxide or silicon oxynitride can be used as the material of the low acoustic impedance layers 82a, 82c, 82e. In addition, alumina, silicon nitride or metal can be used as the material of the high acoustic impedance layers 82b, 82d.

[0235] Fig. 27 This is a partially cutaway perspective view for explaining an elastic wave device using Lamb waves.

[0236] The elastic wave device 91 has a support substrate 92. A recessed portion opened on the upper surface is provided on the support substrate 92. A piezoelectric layer 93 is stacked on the support substrate 92. Thus, a cavity 9 is formed. An IDT electrode 94 is provided on the piezoelectric layer 93 above the cavity 9. Reflectors 95 and 96 are provided on both sides of the IDT electrode 94 in the direction of propagation of elastic waves. Fig. 27 In the figure, the outer periphery of the cavity 9 is shown by a dotted line. Here, the IDT electrode 94 has a first bus bar 94a, a second bus bar 94b, a plurality of first electrode fingers 94c, and a plurality of second electrode fingers 94d. The plurality of first electrode fingers 94c are connected to the first bus bar 94a. The plurality of second electrode fingers 94d are connected to the second bus bar 94b. The plurality of first electrode fingers 94c and the plurality of second electrode fingers 94d are interlaced with each other.

[0237] In the elastic wave device 91, Lamb waves as plate waves are excited by applying an alternating electric field to the IDT electrode 94 on the cavity 9. Furthermore, since the reflectors 95 and 96 are provided on both sides, resonance characteristics based on the Lamb waves can be obtained.

[0238] As described above, the elastic wave device of the present invention can also utilize plate waves. Fig. 27In the example shown, the Figure 1 The main surface of the first main surface 14a of the piezoelectric layer 14 shown in the figure is provided with an IDT electrode 94, a reflector 95, and a reflector 96. On the other hand, in the elastic wave device of the present invention, a pair of comb-shaped electrodes and a plurality of third electrode fingers are provided on the first main surface 14a. In the case where the elastic wave device of the present invention uses plate waves, a pair of comb-shaped electrodes and a plurality of third electrode fingers, and the above-mentioned reflectors 95 and 96 are provided on the first main surface 14a of the piezoelectric layer 14 in the first to sixth embodiments and each modified example. In this case, the reflectors 95 and 96 only need to sandwich a pair of comb-shaped electrodes and a plurality of third electrode fingers in the direction orthogonal to the electrode fingers.

[0239] In the elastic wave devices of the first to sixth embodiments and their respective modifications, for example, an acoustic reflection film may be provided between the support member and the piezoelectric layer. Fig.26 The acoustic multilayer membrane 82 shown. Specifically, the supporting member and the piezoelectric layer may be arranged so that at least a portion of the supporting member and at least a portion of the piezoelectric layer are opposed to each other with the acoustic multilayer membrane 82 sandwiched therebetween. In this case, in the acoustic multilayer membrane 82, it is sufficient to alternately stack low acoustic impedance layers and high acoustic impedance layers. The acoustic multilayer membrane 82 may also be an acoustic reflection portion in an elastic wave device.

[0240] In the elastic wave devices of the first to sixth embodiments and their modifications that utilize bulk waves in the thickness shear mode, as described above, d / p is preferably 0.5 or less, and more preferably 0.24 or less. This can provide better resonance characteristics.

[0241] Furthermore, in the excitation region of the elastic wave device in the first to sixth embodiments and each modified example using the body wave in the thickness shear mode, as described above, MR ≤ 1.75 (d / p) + 0.075 is preferably satisfied. More specifically, when the metallization ratio of the first electrode finger and the third electrode finger, and the second electrode finger and the third electrode finger with respect to the excitation region is MR, MR ≤ 1.75 (d / p) + 0.075 is preferably satisfied. In this case, spurious emission can be suppressed more reliably.

[0242] Description of Reference Numerals

[0243] 1…Elastic wave device

[0244] 2…Piezoelectric layer

[0245] 2a, 2b...1st main surface, 2nd main surface

[0246] 3, 4…Electrode

[0247] 5, 6…1st bus bar, 2nd bus bar

[0248] 7…Insulation layer

[0249] 7a…Through hole

[0250] 8…Supporting member

[0251] 8a…Through hole

[0252] 9…Hollow

[0253] 10…Elastic wave device

[0254] 10a…Cavity

[0255] 11…Functional electrode

[0256] 12…Piezoelectric substrate

[0257] 13…Supporting member

[0258] 14…Piezoelectric layer

[0259] 14a, 14b…1st main surface, 2nd main surface

[0260] 15…Insulation layer

[0261] 16…Support base plate

[0262] 17, 18…1st comb-shaped electrode, 2nd comb-shaped electrode

[0263] 19…Reference potential electrode

[0264] 22-24…1st bus bar to 3rd bus bar

[0265] 24A, 24B ... first connecting electrode, second connecting electrode

[0266] 24a…Article

[0267] 24b…protrusion

[0268] 25 to 27…1st electrode finger to 3rd electrode finger

[0269] 29…Insulation film

[0270] 32…Bus bar 1

[0271] 32A~32C…Divided bus bar section

[0272] 33…Bus 2

[0273] 33A, 33B...divided bus bar portion

[0274] 34…Connecting electrodes

[0275] 36A, 36B ... first potential connection portion, second potential connection portion

[0276] 36C~36E…Third potential connection part

[0277] 37, 38…1st comb-shaped electrode, 2nd comb-shaped electrode

[0278] 39A, 39B…reference potential electrodes

[0279] 80, 81…Elastic wave device

[0280] 82…Acoustic multilayer film

[0281] 82a, 82c, 82e…low acoustic impedance layer

[0282] 82b, 82d…high acoustic impedance layer

[0283] 91…Elastic wave device

[0284] 92…Support base plate

[0285] 93…Piezoelectric layer

[0286] 94…IDT electrode

[0287] 94a, 94b…1st bus bar, 2nd bus bar

[0288] 94c, 94d ... first electrode finger, second electrode finger

[0289] 95, 96…Reflector

[0290] 201…Piezoelectric film

[0291] 201a, 201b…1st main surface, 2nd main surface

[0292] 451, 452…1st area, 2nd area

[0293] C…Incentive Area

[0294] E…Intersection Area

[0295] g1, g2…gap

[0296] R…Region

[0297] VP1…imaginary plane.

Claims

1. An elastic wave device comprising: The piezoelectric layer has an Euler angle (φ, θ, ψ) within the range of the following formula (1), formula (2) or formula (3), and includes lithium niobate; a first comb-shaped electrode, disposed on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, and connected to an input potential; A second comb-shaped electrode, disposed on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers, one end of each of which is connected to the second bus bar, connected to an output potential, wherein the plurality of second electrode fingers are interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and a connection electrode for connecting adjacent third electrode fingers to each other, connected to a reference potential, wherein the plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged, The first electrode finger, the second electrode finger, and the third electrode finger are arranged in the order of the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger forming one cycle, starting from the first electrode finger. The total number of the first electrode fingers, the second electrode fingers, and the third electrode fingers is 16 or more, (within the range of 0°±10°, 0°~25°, arbitrary ψ) …Formula (1) (Within the range of 0°±10°, 25°~100°, 0°~75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2) (0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, arbitrary ψ) …Equation (3).

2. An elastic wave device comprising: a piezoelectric layer comprising lithium niobate; a first comb-shaped electrode, disposed on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, and connected to an input potential; A second comb-shaped electrode, disposed on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers, one end of each of which is connected to the second bus bar, connected to an output potential, wherein the plurality of second electrode fingers are interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and a connection electrode for connecting adjacent third electrode fingers to each other, connected to a reference potential, wherein the plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged, The first electrode finger, the second electrode finger, and the third electrode finger are arranged in the order of the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger forming one cycle, starting from the first electrode finger. The direction in which the first electrode finger, the second electrode finger, and the third electrode finger extend is defined as an electrode finger extending direction, and when viewed from a direction orthogonal to the electrode finger extending direction, a region where the first electrode finger and the second electrode finger overlap each other is defined as a crossing region, When a dimension of the intersection region along the extending direction of the electrode fingers is defined as an intersection width Ap, and a center-to-center distance between adjacent first and third electrode fingers or a center-to-center distance between adjacent second and third electrode fingers is defined as px, Ap / px≥5.

3. An elastic wave device comprising: The piezoelectric layer has an Euler angle (φ, θ, ψ) within the range of the following formula (1), formula (2) or formula (3), and includes lithium niobate; a first comb-shaped electrode, disposed on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, and connected to an input potential; A second comb-shaped electrode, disposed on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers, one end of each of which is connected to the second bus bar, connected to an output potential, wherein the plurality of second electrode fingers are interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and a connection electrode for connecting adjacent third electrode fingers to each other, connected to a reference potential, wherein the plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged, The first electrode finger, the second electrode finger, and the third electrode finger are arranged in the order of the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger forming one cycle, starting from the first electrode finger. When the direction in which the first electrode finger, the second electrode finger, and the third electrode finger extend is set as the electrode finger extension direction, the front ends of the plurality of first electrode fingers and the plurality of second electrode fingers are respectively opposed to electrodes connected to a potential different from that of the electrode finger and having a potential of any one of an input potential, an output potential, and a reference potential, with gaps therebetween in the electrode finger extension direction. When the dimension of each gap along the extending direction of the electrode finger is set as a gap length G, and the center distance between the adjacent first electrode finger and the third electrode finger or the center distance between the adjacent second electrode finger and the third electrode finger is set as px, G / px≤0.5, (within the range of 0°±10°, 0°~25°, arbitrary ψ) …Formula (1) (Within the range of 0°±10°, 25°~100°, 0°~75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2) (0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, arbitrary ψ) …Equation (3).

4. An elastic wave device comprising: The piezoelectric layer has an Euler angle (φ, θ, ψ) within the range of the following formula (1), formula (2) or formula (3), and includes lithium niobate; a first comb-shaped electrode, disposed on the piezoelectric layer, comprising a first bus bar and a plurality of first electrode fingers, one end of each of which is connected to the first bus bar; a second comb-shaped electrode, disposed on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers, one end of each of which is connected to the second bus bar, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and a connection electrode for connecting adjacent third electrode fingers to each other, connected to a reference potential, wherein the plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged, The first comb-shaped electrode is connected to one of an input potential and an output potential, and the second comb-shaped electrode is connected to the other of the input potential and the output potential. The first electrode finger, the second electrode finger, and the third electrode finger are arranged in the order of the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger forming one cycle, starting from the first electrode finger. The tips of at least a portion of the third electrode fingers adjacent to each other among all the third electrode fingers adjacent to each other on the first bus bar side are connected to each other by the connection electrode. When the distance between the connection electrode and the first bus bar at which the tips of the adjacent third electrode fingers on the first bus bar side are connected is set as GB gap length, and the distance between the connection electrode and the tips of the second electrode fingers is set as GF gap length, GB gap length ≤ GF gap length, (within the range of 0°±10°, 0°~25°, arbitrary ψ) …Formula (1) (Within the range of 0°±10°, 25°~100°, 0°~75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2) (0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, arbitrary ψ) …Equation (3).

5. An elastic wave device comprising: A piezoelectric layer comprising lithium niobate having Euler angles (φ, θ, ψ) within a range of (0°±5°, within a range of -8°±14°, and within a range of 90°±5°); a first comb-shaped electrode, disposed on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, and connected to an input potential; A second comb-shaped electrode, disposed on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers, one end of each of which is connected to the second bus bar, connected to an output potential, wherein the plurality of second electrode fingers are interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and a connection electrode for connecting adjacent third electrode fingers to each other, connected to a reference potential, wherein the plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged, The first electrode finger, the second electrode finger, and the third electrode finger are arranged in the order of the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger forming one cycle, starting from the first electrode finger. When the direction in which the first electrode finger, the second electrode finger, and the third electrode finger extend is set as the electrode finger extension direction, the front ends of the plurality of first electrode fingers and the plurality of second electrode fingers are respectively opposed to electrodes connected to a potential different from that of the electrode finger and having a potential of any one of an input potential, an output potential, and a reference potential, with gaps therebetween in the electrode finger extension direction. When the dimension of each gap along the extending direction of the electrode fingers is defined as a gap length G, and the center distance between adjacent first and third electrode fingers or the center distance between adjacent second and third electrode fingers is defined as px, G / px≥1.

6. An elastic wave device comprising: A piezoelectric layer comprising lithium niobate having Euler angles (φ, θ, ψ) within a range of (0°±5°, within a range of -8°±14°, and within a range of 90°±5°); a first comb-shaped electrode, disposed on the piezoelectric layer, comprising a first bus bar and a plurality of first electrode fingers, one end of each of which is connected to the first bus bar; a second comb-shaped electrode, disposed on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers, one end of each of which is connected to the second bus bar, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and a connection electrode for connecting adjacent third electrode fingers to each other, connected to a reference potential, wherein the plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged, The first comb-shaped electrode is connected to one of an input potential and an output potential, and the second comb-shaped electrode is connected to the other of the input potential and the output potential. The first electrode finger, the second electrode finger, and the third electrode finger are arranged in the order of the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger forming one cycle, starting from the first electrode finger. The tips of at least a portion of the third electrode fingers adjacent to each other among all the third electrode fingers adjacent to each other on the first bus bar side are connected to each other by the connection electrode. When the distance between the connecting electrode connecting the front ends of the adjacent third electrode fingers on the first bus bar side to each other and the first bus bar is set as the GB gap length, and the distance between the connecting electrode and the front end of the second electrode finger on the first bus bar side is set as the GF gap length, the GB gap length>GF gap length.

7. The elastic wave device according to any one of claims 1 to 6, wherein: The elastic wave device is configured to utilize plate waves.

8. The elastic wave device according to any one of claims 1 to 6, wherein: The elastic wave device is configured to utilize thickness shear mode body waves.

9. The elastic wave device according to any one of claims 1 to 6, wherein: The elastic wave device further includes a supporting member stacked on the piezoelectric layer. In a plan view along the stacking direction of the support member and the piezoelectric layer, an acoustic reflection portion is formed at a position of the support member overlapping with the plurality of first electrode fingers, the plurality of second electrode fingers, and the plurality of third electrode fingers, When the longest distance between the centers of the adjacent first and third electrode fingers and the center distance between the adjacent second and third electrode fingers is represented by p, and the thickness of the piezoelectric layer is represented by d, d / p is equal to or less than 0.

5.

10. The elastic wave device according to claim 9, wherein: When the longest distance between the centers of the adjacent first and third electrode fingers and the center distance between the adjacent second and third electrode fingers is defined as p, and the thickness of the piezoelectric layer is defined as d, d / p is equal to or less than 0.

24.

11. The elastic wave device according to claim 9 or 10, wherein: When a direction orthogonal to the direction in which the first electrode finger, the second electrode finger, and the third electrode finger extend is set as the electrode finger orthogonal direction, an area where adjacent first electrode fingers and third electrode fingers overlap with each other in the electrode finger orthogonal direction and an area between the centers of adjacent first electrode fingers and third electrode fingers, and an area where adjacent second electrode fingers and third electrode fingers overlap with each other in the electrode finger orthogonal direction and an area between the centers of adjacent second electrode fingers and third electrode fingers are excitation areas, When the longest distance between the centers of the adjacent first electrode finger and the third electrode finger and the longest distance between the centers of the adjacent second electrode finger and the third electrode finger is set to p, when the thickness of the piezoelectric layer is set to d, and the metallization ratios of the first electrode finger and the third electrode finger and the second electrode finger and the third electrode finger relative to the excitation region are set to MR, MR≤1.75(d / p)+0.075 is satisfied.

12. The elastic wave device according to any one of claims 9 to 11, wherein: The sound reflecting portion is a cavity portion, and the supporting member and the piezoelectric layer are arranged so that a portion of the supporting member and a portion of the piezoelectric layer face each other with the cavity portion interposed therebetween.

13. The elastic wave device according to any one of claims 9 to 11, wherein: The acoustic reflection portion is an acoustic reflection membrane including a high acoustic impedance layer with relatively high acoustic impedance and a low acoustic impedance layer with relatively low acoustic impedance, and the supporting member and the piezoelectric layer are configured so that at least a portion of the supporting member and at least a portion of the piezoelectric layer are opposite to each other with the acoustic reflection membrane sandwiched therebetween.

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