Elastic wave device

Abstract

The present invention addresses the problem of suppressing useless waves generated at frequencies that are lower than and near a resonance frequency in an elastic wave device using bulk waves in a thickness shear mode. In order to solve this problem, a first mass-adding film (24A) and a second mass-adding film (24B) are provided, the first mass-adding film (24A) being provided across the first edge region (E1) and the first gap region (G1), and the second mass-adding film (24B) being provided across the second edge region (E2) and the second gap region (G2). When the lengths of the gap region and the edge region of the first mass-added film (24A) and the second mass-added film (24B) are set as LG1, LE1, LG2, and LE2, respectively, at least one of LG1 not equal to LG2 and LE1 not equal to LE2 is satisfied, and the frequency at which useless waves are generated is dispersed by this configuration, thereby suppressing useless waves.

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, etc. In recent years, an elastic wave device using a thickness shear mode body wave has been proposed, as described in the following patent document 1. 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 body 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] In an elastic wave device using a thickness shear mode bulk wave as described in Patent Document 1, unnecessary waves are generated at a frequency lower than the resonance frequency and near the resonance frequency, which may deteriorate electrical characteristics.

[0008] An object of the present invention is to provide an elastic wave device capable of suppressing unnecessary waves at a frequency lower than a resonance frequency and near the resonance frequency.

[0009] Technical solutions to solve problems

[0010] The elastic wave device according to the present invention comprises: a piezoelectric substrate having a supporting member and a piezoelectric film, wherein the supporting member comprises a supporting substrate, the piezoelectric film comprises a piezoelectric layer provided on the supporting member, and an IDT electrode provided on the piezoelectric layer and having a first bus bar and a second bus bar facing each other, and a plurality of first electrode fingers and a plurality of second electrode fingers, wherein an acoustic reflection portion is formed at a position of the supporting member overlapping with the IDT electrode in a plan view along a stacking direction of the supporting member and the piezoelectric film, and the plurality of first electrode fingers of the IDT electrode One end of the electrode finger is connected to the first bus bar, one end of the plurality of second electrode fingers is connected to the second bus bar, the plurality of first electrode fingers and the plurality of second electrode fingers are interlaced with each other, when the thickness of the piezoelectric film is set to d and the center distance between the adjacent first electrode fingers and the second electrode fingers is set to p, d / p is less than 0.5, the direction in which the first electrode fingers and the second electrode fingers extend is set to the electrode finger extending direction, and the direction orthogonal to the electrode finger extending direction is set to the electrode finger orthogonal direction, when observing from the electrode finger orthogonal direction When the first electrode finger and the second electrode finger overlap each other, the region where the adjacent first electrode finger and the second electrode finger overlap each other is a cross region, the cross region has a central region and a first edge region and a second edge region that are configured to sandwich the central region in the extension direction of the electrode finger, the region between the first edge region and the first bus bar is a first gap region, and the region between the second edge region and the second bus bar is a second gap region, and the elastic wave device further comprises: a first mass additional film that is arranged throughout the first edge region and the first gap region; and a second mass additional film that is arranged over the first edge region and the first gap region; An additional film is arranged throughout the second edge region and the second gap region. When the dimensions of the first mass additional film and the second mass additional film along the extension direction of the electrode finger are set as the length of the first mass additional film and the second mass additional film, at least one of the length of the first mass additional film in the first gap region and the length of the second mass additional film in the second gap region and the length of the first mass additional film in the first edge region and the length of the second mass additional film in the second edge region are different from each other.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to provide an elastic wave device capable of suppressing unnecessary waves at a frequency lower than the resonance frequency and near the resonance frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic plan view of the elastic wave device according to the first embodiment of the present invention.

[0014] Figure 2 It is along Figure 1 Schematic cross-sectional view of line II in FIG.

[0015] Figure 3 It is a schematic plan view of an elastic wave device according to a first comparative example.

[0016] Figure 4 It is a graph showing the admittance frequency characteristics in the first embodiment and the first comparative example when the distance L1 is 100 nm.

[0017] Figure 5 It is a graph showing the admittance frequency characteristics in the first embodiment and the first comparative example when the distance L1 is 200 nm.

[0018] Figure 6 It is a graph showing the admittance frequency characteristics in the first embodiment and the first comparative example when the distance L1 is 300 nm.

[0019] Figure 7 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.

[0020] Figure 8 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.

[0021] Fig. 9 It is a schematic plan view of an elastic wave device according to a third modified example of the first embodiment of the present invention.

[0022] Fig.10 It is a schematic plan view of an elastic wave device according to a second embodiment of the present invention.

[0023] Fig.11 It is a schematic plan view of an elastic wave device according to a third embodiment of the present invention.

[0024] Fig.12 It is a schematic plan view of an elastic wave device according to a second comparative example.

[0025] Fig.13 It is a graph showing the admittance frequency characteristics in the third embodiment and the second comparative example when the distance L2 is 100 nm.

[0026] Fig.14 It is a diagram showing the admittance frequency characteristics in the third embodiment and the second comparative example when the distance L2 is 200 nm.

[0027] Fig.15 It is a diagram showing the admittance frequency characteristics in the third embodiment and the second comparative example when the distance L2 is 300 nm.

[0028] Fig.16 It is a schematic plan view of an elastic wave device according to a fourth embodiment of the present invention.

[0029] Fig.17 It is a schematic plan view of an elastic wave device according to a fifth embodiment of the present invention.

[0030] Fig.18 It is a schematic plan view of an elastic wave device according to a sixth embodiment of the present invention.

[0031] Fig.19 (a) is a schematic perspective view showing the appearance of an elastic wave device using a thickness shear mode bulk wave, Fig.19 (b) is a top view showing the electrode structure on the piezoelectric layer.

[0032] Fig. 20 It is along Fig.19 (a) is a cross-sectional view of a portion taken along line AA.

[0033] Fig.21 (a) is a schematic front cross-sectional view for explaining Lamb waves propagating through a piezoelectric film of an elastic wave device. Fig.21 (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.

[0034] Fig. 22 It is a diagram showing the amplitude direction of the body wave in the thickness shear mode.

[0035] Fig.23 FIG. 1 is a diagram showing the resonance characteristics of an elastic wave device using bulk waves in a thickness shear mode.

[0036] Fig.24 : 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.

[0037] Fig.25 This is a top view of an elastic wave device using bulk waves in a thickness shear mode.

[0038] Fig.26 FIG. 2 is a diagram showing the resonance characteristics of an elastic wave device according to a reference example in which spurious emission occurs.

[0039] Fig. 27 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.

[0040] Fig.28 It is a graph showing the relationship between d / 2p and the metallization ratio MR.

[0041] Fig.29 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.

[0042] Fig.30 It is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane. DETAILED DESCRIPTION

[0043] Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the accompanying drawings.

[0044] 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.

[0045] Figure 1 It is a schematic plan view of the elastic wave device according to the first embodiment of the present invention. Figure 2 It is along Figure 1 Schematic cross-sectional view of line II in FIG.

[0046] like Figure 1 As shown in FIG. 1 , the elastic wave device 10 includes a piezoelectric substrate 12 and an IDT electrode 11. The piezoelectric substrate 12 is a substrate having piezoelectricity. Figure 2 As shown, the piezoelectric substrate 12 has a supporting member 13 and a piezoelectric layer 14 as a piezoelectric film. The piezoelectric layer 14 is a layer containing a piezoelectric body. On the other hand, in this specification, the so-called piezoelectric film is a film having piezoelectricity, and does not necessarily refer to a film containing a piezoelectric body. However, in the present embodiment, the piezoelectric film is a single-layer piezoelectric layer 14, which is a film containing a piezoelectric body. In addition, in the present invention, the piezoelectric film may also be a stacked film including the 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 disposed on the supporting substrate 16. The piezoelectric layer 14 is disposed on the insulating layer 15. However, the supporting member 13 may also be composed of only the supporting substrate 16.

[0047] 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.

[0048] As the material of the support substrate 16, for example, semiconductors such as silicon, ceramics such as aluminum oxide, etc. can be used. As the material of the insulating layer 15, appropriate dielectrics such as silicon oxide or tantalum oxide can be used. For example, the piezoelectric layer 14 may also include lithium niobate such as LiNbO3, or may also include lithium tantalate such as LiTaO3. In addition, in the present embodiment, the piezoelectric layer 14 includes lithium niobate. In this specification, a certain component includes a certain material, including a case where the component contains a trace amount of impurities to the extent that the electrical characteristics of the elastic wave device will not be significantly deteriorated.

[0049] like Figure 2 As shown, a recess is provided in the insulating layer 15. A piezoelectric layer 14 as a piezoelectric film 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 present embodiment, the supporting member 13 and the piezoelectric film are configured so that a portion of the supporting member 13 and a portion of the piezoelectric film 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. For example, 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.

[0050] IDT electrode 11 is provided on first principal surface 14a of piezoelectric layer 14. Elastic wave device 10 of the present embodiment is an elastic wave resonator capable of utilizing bulk waves in a thickness shear mode. However, the elastic wave device of the present invention may be a filter device, a multiplexer, or the like having a plurality of elastic wave resonators.

[0051] In a plan view, at least a portion of the IDT electrode 11 overlaps with the cavity 10a of the support member 13. In this specification, the term "plan view" refers to a view from a direction corresponding to the direction of the support member 13. Figure 2 The upper direction in FIG. 1 is viewed along the stacking direction of the support member 13 and the piezoelectric film. Figure 2 For example, the piezoelectric layer 14 side is the upper side of the support substrate 16 side and the piezoelectric layer 14 side. In addition, 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, for example, the main surface facing direction is the normal direction of the first main surface 14a.

[0052] like Figure 1As shown, the IDT electrode 11 has a pair of bus bars and a plurality of electrode fingers. Specifically, the pair of bus bars is a first bus bar 26 and a second bus bar 27. The first bus bar 26 and the second bus bar 27 are opposite to each other. Specifically, the plurality of electrode fingers are a plurality of first electrode fingers 28 and a plurality of second electrode fingers 29. One end of the plurality of first electrode fingers 28 is respectively connected to the first bus bar 26. One end of the plurality of second electrode fingers 29 is respectively connected to the second bus bar 27. The plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 are interlaced with each other. The IDT electrode 11 may include a single-layer metal film, or may include a stacked metal film.

[0053] Hereinafter, the first electrode finger 28 and the second electrode finger 29 are sometimes collectively and simply recorded as electrode fingers. The direction in which the plurality of electrode fingers 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. In addition, when the direction in which adjacent electrode fingers face each other is referred to as the electrode finger facing direction, the electrode finger orthogonal direction and the electrode finger facing direction are parallel.

[0054] Back to Figure 1 When viewed from the orthogonal direction of the electrode fingers, the area where the adjacent first electrode fingers 28 and second electrode fingers 29 overlap each other is the intersection area F. The intersection area F has a central area H and a pair of edge areas. Specifically, the pair of edge areas are the first edge area E1 and the second edge area E2. The first edge area E1 and the second edge area E2 are configured to sandwich the central area H in the extending direction of the electrode fingers. The first edge area E1 is located on the first bus bar 26 side. The second edge area E2 is located on the second bus bar 27 side.

[0055] The region between the intersection region F and the pair of bus bars is a pair of gap regions. Specifically, the pair of gap regions are the first gap region G1 and the second gap region G2. The first gap region G1 is located between the first bus bar 26 and the first edge region E1. The second gap region G2 is located between the second bus bar 27 and the second edge region E2.

[0056] The elastic wave device 10 is an elastic wave resonator configured to utilize a thickness shear mode bulk wave. More specifically, in the elastic wave device 10, when the thickness of the piezoelectric film is set to d and the center-to-center distance between the adjacent first electrode finger 28 and the second electrode finger 29 is set to p, d / p is less than 0.5. Thus, a thickness shear mode bulk wave is appropriately excited. In the present embodiment, the thickness d is the thickness of the piezoelectric layer 14.

[0057] When viewed from the orthogonal direction of the electrode fingers, the region where the adjacent first electrode fingers 28 and second electrode fingers 29 overlap each other and the region between the centers of the adjacent first electrode fingers 28 and second electrode fingers 29 is the excitation region. That is, the intersection region F includes a plurality of excitation regions. In each excitation region, a body wave of a thickness shear mode is excited. In addition, the intersection region F, the excitation region, and a pair of gap regions are regions of the piezoelectric layer 14 defined based on the structure of the IDT electrode 11.

[0058] Figure 2 The hollow portion 10a of the support member 13 shown is the sound reflection portion in the present invention. The sound reflection portion can effectively seal the energy of the elastic wave on the piezoelectric layer 14 side. In addition, as the sound reflection portion, an acoustic multilayer film described later may also be provided. For example, a sound reflection film may also be provided on the surface of the support member.

[0059] like Figure 1 As shown, in this embodiment, the elastic wave device 10 includes a first mass addition film 24A and a second mass addition film 24B. The first mass addition film 24A is provided over the first edge region E1 and the first gap region G1. The second mass addition film 24B is provided over the second edge region E2 and the second gap region G2. The first mass addition film 24A and the second mass addition film 24B have a strip shape.

[0060] The first mass addition film 24A is provided on the first main surface 14a of the piezoelectric layer 14 so as to cover the plurality of electrode fingers. When the region between the first electrode finger 28 and the second electrode finger 29 is set as the inter-electrode finger region, the first mass addition film 24A is also provided on the portion of the first main surface 14a located in the inter-electrode finger region. That is, in a plan view, the first mass addition film 24A is continuously provided so as to overlap with the plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 and the inter-electrode finger region. In a plan view, the second mass addition film 24B is also continuously provided so as to overlap with the plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 and the inter-electrode finger region.

[0061] Hereinafter, the dimensions of the first mass added film 24A and the second mass added film 24B along the electrode finger extension direction are referred to as the lengths of the first mass added film 24A and the second mass added film 24B. The length of the first mass added film 24A in the first gap region G1 is referred to as LG1, and the length of the first mass added film 24A in the first edge region E1 is referred to as LE1. The length of the second mass added film 24B in the second gap region G2 is referred to as LG2, and the length of the second mass added film 24B in the second edge region E2 is referred to as LE2. The total length of the first mass added film 24A in the first edge region E1 and the first gap region G1 is referred to as LT1, and the total length of the second mass added film 24B in the second edge region E2 and the second gap region G2 is referred to as LT2.

[0062] In this embodiment, LT1=LT2. That is, LG1+LE1=LG2+LE2. On the other hand, LG1>LG2, LE1 <LE2。

[0063] The present embodiment is characterized in that LG1≠LG2, LE1≠LE2. That is, in the present embodiment, the length of the first mass addition film 24A in the first gap region G1 and the length of the second mass addition film 24B in the second gap region G2 are different from each other. The length of the first mass addition film 24A in the first edge region E1 and the length of the second mass addition film 24B in the second edge region E2 are different from each other. Accordingly, it is possible to suppress unnecessary waves at a frequency lower than the resonance frequency and located near the resonance frequency. This is illustrated below by comparing the present embodiment and the first comparative example.

[0064] In the first comparative example, Figure 3 As shown, the first mass adding film 104A is provided over the first edge region E1 and the first gap region G1. The second mass adding film 104B is provided over the second edge region E2 and the second gap region G2. The first comparative example differs from the first embodiment in that LG1=LG2 and LE1=LE2.

[0065] In addition, in the first embodiment and the first comparative example, the total length LT1 of the first mass added film in the first edge region E1 and the first gap region G1 is the same. In the first embodiment and the first comparative example, the total length LT2 of the second mass added film in the second edge region E2 and the second gap region G2 is also the same. The structure of the first embodiment is equivalent to a structure in which both the first mass added film 24A and the second mass added film 24B are provided at a position closer to the first bus bar 26 than in the first comparative example.

[0066] Here, the positions of the first mass added film 104A and the second mass added film 104B in the first comparative example are set as reference positions. The distance in the electrode finger extension direction from the reference position of the first mass added film 24A and the second mass added film 24B in the first embodiment is set as distance L1. As the elastic wave device 10 having the structure of the first embodiment, a plurality of elastic wave devices 10 having different distances L1 are prepared. Specifically, in the plurality of elastic wave devices 10 having the structure of the first embodiment, the distance L1 is 100 nm, 200 nm, or 300 nm, respectively. In the elastic wave devices of the first embodiment and the first comparative example, the admittance frequency characteristics are compared.

[0067] Figure 4 It is a graph showing the admittance frequency characteristics in the first embodiment and the first comparative example when the distance L1 is 100 nm. Figure 5 It is a graph showing the admittance frequency characteristics in the first embodiment and the first comparative example when the distance L1 is 200 nm. Figure 6 It is a graph showing the admittance frequency characteristics in the first embodiment and the first comparative example when the distance L1 is 300 nm.

[0068] As Figures 4 to 6 As shown by the arrow T in FIG. 1 , in the first embodiment, it can be seen that unnecessary waves lower than the resonant frequency and near the resonant frequency are suppressed. Figure 5 as well as Figure 6 As shown, when the distance L1 is 200 nm and 300 nm, it can be seen that the unnecessary waves are further suppressed. Unless otherwise specified, when the unnecessary waves are described below, the unnecessary waves refer to the unnecessary waves lower than the resonance frequency and near the resonance frequency.

[0069] In the elastic wave device 10 of the first embodiment, LG1≠LG2 and LE1≠LE2. This makes it possible to disperse the frequencies of the generated unnecessary waves and reduce the intensity of the unnecessary waves as a whole. This makes it possible to suppress the unnecessary waves.

[0070] In the present invention, at least one of the length LG1 of the first mass adding film 24A and the length LG2 of the second mass adding film 24B and the length LE1 of the first mass adding film 24A and the length LE2 of the second mass adding film 24B may be different from each other. In other words, at least one of LG1≠LG2 and LE1≠LE2 may be satisfied. In this case, the frequency of the generated unnecessary waves can be dispersed, and the unnecessary waves can be suppressed.

[0071] In the first embodiment, the sum of the lengths of the first mass addition film 24A in the first edge region E1 and the first gap region G1 is the same as the sum of the lengths of the second mass addition film 24B in the second edge region E2 and the second gap region G2. That is, LT1 = LT2. However, it is not limited thereto. Hereinafter, the first to third modified examples of the first embodiment where LT1 ≠ LT2 are shown. In the first to third modified examples, at least one of LG1 ≠ LG2 and LE1 ≠ LE2 is also satisfied. Accordingly, useless waves can be suppressed in the same manner as in the first embodiment.

[0072] In Figure 7 the first modified example shown, LE1 > LE2 and LG1 > LG2. That is, the length of the first mass addition film 24A in the first edge region E1 is longer than the length of the second mass addition film 24B in the second edge region E2. The length of the first mass addition film 24A in the first gap region G1 is longer than the length of the second mass addition film 24B in the second gap region G2. Therefore, the sum of the lengths of the first mass addition film 24A in the first edge region E1 and the first gap region G1 is different from the sum of the lengths of the second mass addition film 24B in the second edge region E2 and the second gap region G2.

[0073] In Figure 8 the second modified example shown, LE1 = LE2 and LG1 > LG2. That is, the length of the first mass addition film 24A in the first edge region E1 is the same as the length of the second mass addition film 24B in the second edge region E2. The length of the first mass addition film 24A in the first gap region G1 is longer than the length of the second mass addition film 24B in the second gap region G2.

[0074] In Fig. 9 the third modified example shown, LE1 < LE2 and LG1 = LG2. That is, the length of the first mass addition film 24A in the first edge region E1 is shorter than the length of the second mass addition film 24B in the second edge region E2. The length of the first mass addition film 24A in the first gap region G1 is the same as the length of the second mass addition film 24B in the second gap region G2.

[0075] Returning to Figure 1 , in a plan view, the first mass addition film 24A and the second mass addition film 24B only need to overlap with a plurality of electrode fingers, and may not overlap with all the electrode fingers. However, in a plan view, the first mass addition film 24A and the second mass addition film 24B preferably overlap with all the electrode fingers. Accordingly, useless waves can be more reliably suppressed.

[0076] As the material of the first mass additional film 24A and the second mass additional film 24B, at least one dielectric selected from the group consisting of silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, and hafnium oxide is preferably used. This makes it possible to more reliably suppress unnecessary waves.

[0077] In the first embodiment, in the portion where the first mass added film 24A and the first electrode finger 28 are stacked, the piezoelectric layer 14, the first electrode finger 28, and the first mass added film 24A are stacked in sequence. In the portion where the second mass added film 24B and the first electrode finger 28 are stacked, the piezoelectric layer 14, the first electrode finger 28, and the second mass added film 24B are stacked in sequence. The same is true in the portion where the first mass added film 24A and the second electrode finger 29 are stacked, and in the portion where the second mass added film 24B and the second electrode finger 29 are stacked. However, the stacking order of the first mass added film 24A, the second mass added film 24B, and the electrode fingers is not limited to the above.

[0078] Fig.10 It is a schematic plan view of an elastic wave device according to a second embodiment.

[0079] This embodiment differs from the first embodiment in that a first mass added film 24A and a second mass added film 24B are provided between the piezoelectric layer 14 and the IDT electrode 11. Except for the above point, the elastic wave device of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0080] In the portion where the first mass added film 24A and the first electrode finger 28 are stacked, the piezoelectric layer 14, the first mass added film 24A, and the first electrode finger 28 are stacked in this order. In the portion where the second mass added film 24B and the first electrode finger 28 are stacked, the piezoelectric layer 14, the second mass added film 24B, and the first electrode finger 28 are stacked in this order. The same is true in the portion where the first mass added film 24A and the second electrode finger 29 are stacked, and in the portion where the second mass added film 24B and the second electrode finger 29 are stacked.

[0081] In this embodiment, similarly to the first embodiment, at least one of LG1≠LG2 and LE1≠LE2 is satisfied. Specifically, LG1≠LG2 and LE1≠LE2 are satisfied. This makes it possible to suppress unnecessary waves.

[0082] In the first and second embodiments, the first mass adding film 24A and the second mass adding film 24B are continuously provided so as to overlap with the plurality of electrode fingers and the region between the electrode fingers in a plan view. In addition, in a plan view, one first mass adding film 24A and one second mass adding film 24B may not overlap with the plurality of electrode fingers, respectively. This example is shown in the third embodiment.

[0083] Fig.11 It is a schematic plan view of an elastic wave device according to a third embodiment.

[0084] The present embodiment is different from the first embodiment in that a plurality of first mass addition films 34A are provided throughout the first edge region E1 and the first gap region G1. The present embodiment is also different from the first embodiment in that a plurality of second mass addition films 34B are provided throughout the second edge region E2 and the second gap region G2. Except for the above, the elastic wave device of the present embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0085] The plurality of first mass additional films 34A are arranged in a direction orthogonal to the electrode fingers. In a plan view, each first mass additional film 34A overlaps with one first electrode finger 28 or one second electrode finger 29. Specifically, each first mass additional film 34A is provided over the first main surface 14a of the piezoelectric layer 14 and one electrode finger. Each first mass additional film 34A is not provided over a plurality of electrode fingers.

[0086] The plurality of second mass addition films 34B are arranged in a direction orthogonal to the electrode fingers. In a plan view, each second mass addition film 34B overlaps with one first electrode finger 28 or one second electrode finger 29. Specifically, each second mass addition film 34B is provided over the first main surface 14a of the piezoelectric layer 14 and one electrode finger. Each second mass addition film 34B is not provided over a plurality of electrode fingers.

[0087] In this embodiment, as in the first embodiment, at least one of LG1≠LG2 and LE1≠LE2 is satisfied. Specifically, LG1≠LG2 and LE1≠LE2 are satisfied. This makes it possible to suppress unnecessary waves. This is shown by comparing this embodiment with the second comparative example.

[0088] In the second comparative example, Fig.12 As shown, a plurality of first mass adding films 114A are provided over the first edge region E1 and the first gap region G1. A plurality of second mass adding films 114B are provided over the second edge region E2 and the second gap region G2. The second comparative example differs from the third embodiment in that LG1=LG2 and LE1=LE2.

[0089] In addition, in the third embodiment and the second comparative example, the total length of the first mass addition film in the first edge region E1 and the first gap region G1 is the same. In the third embodiment and the second comparative example, the total length of the second mass addition film in the second edge region E2 and the second gap region G2 is also the same. The structure of the third embodiment is equivalent to a structure in which both the first mass addition film 34A and the second mass addition film 34B are provided at a position closer to the first bus bar 26 than in the second comparative example.

[0090] Here, the positions of the first mass added film 114A and the second mass added film 114B in the second comparative example are set as reference positions. The distance in the electrode finger extension direction from the reference position of the first mass added film 34A and the second mass added film 34B in the third embodiment is set as distance L2. As elastic wave devices having the structure of the third embodiment, a plurality of elastic wave devices having different distances L2 are prepared. Specifically, in the plurality of elastic wave devices having the structure of the third embodiment, the distance L2 is 100 nm, 200 nm, or 300 nm, respectively. In the elastic wave devices of the third embodiment and the second comparative example, the admittance frequency characteristics are compared.

[0091] Fig.13 It is a graph showing the admittance frequency characteristics in the third embodiment and the second comparative example when the distance L2 is 100 nm. Fig.14 It is a graph showing the admittance frequency characteristics in the third embodiment and the second comparative example when the distance L2 is 200 nm. Fig.15 It is a diagram showing the admittance frequency characteristics in the third embodiment and the second comparative example when the distance L2 is 300 nm.

[0092] As Figure 13 to Figure 15 As shown by the arrow T in FIG. 1 , in the third embodiment, it can be seen that unnecessary waves lower than the resonant frequency and near the resonant frequency are suppressed. Fig.14 as well as Fig.15 As shown in FIG. 1 , when the distance L2 is 200 nm and 300 nm, it can be seen that the unnecessary waves are further suppressed.

[0093] In the third embodiment, in the portion where the first mass added film 34A and the electrode fingers are stacked, the piezoelectric layer 14, the electrode fingers, and the first mass added film 34A are stacked in this order. In the portion where the second mass added film 34B and the electrode fingers are stacked, the piezoelectric layer 14, the electrode fingers, and the second mass added film 34B are stacked in this order.

[0094] However, similarly to the second embodiment, in the portion where the first mass added film 34A and the electrode fingers are stacked, the piezoelectric layer 14, the first mass added film 34A, and the electrode fingers may be stacked in sequence. In the portion where the second mass added film 34B and the electrode fingers are stacked, the piezoelectric layer 14, the second mass added film 34B, and the electrode fingers may be stacked in sequence.

[0095] Each first mass added film 34A is in contact with only the first electrode finger 28 or the second electrode finger 29. In this case, the first mass added film 34A may include metal. The second mass added film 34B may also include metal.

[0096] Fig.16 It is a schematic plan view of an elastic wave device according to a fourth embodiment.

[0097] The present embodiment is different from the first embodiment in the structure of a plurality of first electrode fingers 48 and a plurality of second electrode fingers 49. Except for the above-described points, the elastic wave device of the present embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0098] Each of the plurality of first electrode fingers 48 has a wide portion 48b. The width of the wide portion of the electrode finger is wider than the width of the electrode finger in the central region H. The width of the electrode finger is the dimension of the electrode finger along the direction orthogonal to the electrode finger. Specifically, the wide portion 48b of the first electrode finger 48 is located in the second edge region E2.

[0099] Each of the plurality of second electrode fingers 49 has a wide portion 49 a . Specifically, the wide portion 49 a of the second electrode finger 49 is located in the first edge region E1 .

[0100] In this embodiment, as in the first embodiment, at least one of LG1≠LG2 and LE1≠LE2 is satisfied. Specifically, LG1≠LG2 and LE1≠LE2. Moreover, as described above, each electrode finger has a wide portion. Thus, the frequency of generating unnecessary waves can be effectively dispersed. Thus, unnecessary waves can be effectively suppressed.

[0101] The width of the first electrode finger 48 in the first edge region E1 is the same as the width of the electrode finger in the central region H. However, each of the plurality of first electrode fingers 48 may have a wide portion located in the first edge region E1.

[0102] The width of the second electrode finger 49 in the second edge region E2 is the same as the width of the electrode finger in the central region H. However, each of the plurality of second electrode fingers 49 may have a wide portion located in the second edge region E2.

[0103] Even when the first electrode fingers 48 and the second electrode fingers 49 have wide portions, Fig.11 Similarly to the third embodiment shown, a plurality of first mass adding films 34A and a plurality of second mass adding films 34B may be provided.

[0104] In the first to fourth embodiments, the first mass added film and the second mass added film are directly provided on the plurality of electrode fingers and the piezoelectric layer 14. However, the first mass added film and the second mass added film may be indirectly provided on the plurality of electrode fingers and the piezoelectric layer 14 via a dielectric film. This example is shown in the fifth embodiment.

[0105] Fig.17 It is a schematic plan view of an elastic wave device according to a fifth embodiment.

[0106] The present embodiment is different from the first embodiment in that a dielectric film 53 is provided on the first principal surface 14a of the piezoelectric layer 14 so as to cover the IDT electrode 11. The present embodiment is also different from the first embodiment in that the first mass added film 54A and the second mass added film 54B contain metal. Except for the above-mentioned points, the elastic wave device of the present embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0107] A first mass addition film 54A and a second mass addition film 54B are provided on the dielectric film 53. As in the first embodiment, the first mass addition film 54A is provided over the first edge region E1 and the first gap region G1. In a plan view, the first mass addition film 54A is continuously provided to overlap with the plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 and the inter-electrode finger region.

[0108] Similar to the first embodiment, the second mass addition film 54B is provided over the second edge region E2 and the second gap region G2. In a plan view, the second mass addition film 54B is provided continuously to overlap with the plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 and the inter-electrode finger region.

[0109] In this embodiment, the dielectric film 53 includes silicon oxide. In addition, the material of the dielectric film 53 is not limited to the above. As the material of the dielectric film 53, for example, silicon nitride or silicon nitride oxide can also be used.

[0110] The first mass added film 54A and the second mass added film 54B include an appropriate metal. However, the first mass added film 54A and the second mass added film 54B may also include an appropriate dielectric. In this case, as the material of the first mass added film 54A and the second mass added film 54B, at least one dielectric selected from the group consisting of silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, and hafnium oxide is preferably used.

[0111] In this embodiment, as in the first embodiment, at least one of LG1≠LG2 and LE1≠LE2 is satisfied. Specifically, LG1≠LG2 and LE1≠LE2 are satisfied. This makes it possible to suppress unnecessary waves.

[0112] Furthermore, IDT electrode 11 is protected by dielectric film 53. Thus, IDT electrode 11 is not easily damaged. Furthermore, by adjusting the thickness of dielectric film 53, the frequency of the elastic wave device can be easily adjusted.

[0113] In the present embodiment, the piezoelectric layer 14, the dielectric film 53, and the first mass adding film 54A are stacked in sequence. Similarly, the piezoelectric layer 14, the dielectric film 53, and the second mass adding film 54B are stacked in sequence. However, in the case where the first mass adding film 54A includes a dielectric, the order of the piezoelectric layer 14, the dielectric film 53, and the first mass adding film 54A is not limited to the above. Similarly, the order of the piezoelectric layer 14, the dielectric film 53, and the second mass adding film 54B is not limited to the above.

[0114] Fig.18 It is a schematic plan view of an elastic wave device according to the sixth embodiment.

[0115] The present embodiment differs from the fifth embodiment in that the first mass added film 24A and the second mass added film 24B include a dielectric. The present embodiment also differs from the fifth embodiment in that the dielectric film 53 is provided on the first principal surface 14a of the piezoelectric layer 14 so as to cover the IDT electrode 11, the first mass added film 24A, and the second mass added film 24B. Except for the above, the elastic wave device of the present embodiment has the same structure as the elastic wave device of the fifth embodiment.

[0116] The piezoelectric layer 14 , the first mass adding film 24A, and the dielectric film 53 are stacked in this order. Similarly, the piezoelectric layer 14 , the second mass adding film 24B, and the dielectric film 53 are stacked in this order.

[0117] In this embodiment, as in the fifth embodiment, at least one of LG1≠LG2 and LE1≠LE2 is satisfied. Specifically, LG1≠LG2 and LE1≠LE2 are satisfied. This makes it possible to suppress unnecessary waves.

[0118] The thickness shear mode will be described in detail below. In addition, the "electrode" in the IDT electrode described below corresponds to the electrode finger in the present invention. The support member in the following example corresponds to the support substrate in the present invention.

[0119] Fig.19 (a) is a schematic perspective view showing the appearance of an elastic wave device using a thickness shear mode bulk wave, Fig.19 (b) is a top view showing the electrode structure on the piezoelectric layer. Fig. 20 It is along Fig.19 (a) is a cross-sectional view of a portion taken along line AA.

[0120] The elastic wave device 1 has a piezoelectric layer 2 containing LiNbO3. The piezoelectric layer 2 may also be a piezoelectric layer containing 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.19 (a) and Fig.19 In (b), the plurality of electrodes 3 are a plurality of first electrode fingers connected to the first bus bar 5. The plurality of electrodes 4 are a plurality of second electrode fingers connected to the 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 orthogonal to the length direction, the electrode 3 is opposed to the adjacent electrode 4. The length directions of the electrodes 3 and 4, and the directions orthogonal 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 is opposed to the adjacent electrode 4 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 opposed to each other in a direction intersecting with the thickness direction of the piezoelectric layer 2. Fig.19 (a) and Fig.19 The lengthwise directions of the electrodes 3 and 4 shown in (b) are reversed. Fig.19 (a) and Fig.19 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.19 (a) and Fig.19(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 refers to the situation in which the electrode 3 and the electrode 4 are arranged with a gap, rather than the situation in which the electrode 3 and the electrode 4 are arranged in direct contact. In addition, when the electrode 3 and the electrode 4 are adjacent, between the electrode 3 and the electrode 4, no electrode including other electrodes 3 and 4 connected to the signal electrode and the ground electrode is arranged. 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.

[0121] In addition, in the elastic wave device 1, since a Z-cut piezoelectric layer is used, the direction orthogonal to the length direction of the electrodes 3 and 4 becomes a direction orthogonal 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 only being strictly orthogonal, and can also be approximately orthogonal (the angle formed by the direction orthogonal to the length direction of the electrodes 3 and 4 and the polarization direction is, for example, within the range of 90°±10°).

[0122] 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. 20 As shown, there are through holes 7a and 8a. Accordingly, 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 a pair of electrodes 3 and 4 are 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.

[0123] The insulating layer 7 includes silicon oxide. However, in addition to silicon oxide, suitable insulating materials such as silicon nitride oxide and alumina can be used. The supporting member 8 includes Si. The plane orientation of the Si on the side of the piezoelectric layer 2 can be (100), (110), or (111). It is preferable that the Si constituting the supporting member 8 has a high resistance with a resistivity of 4 kΩcm or more. However, the supporting member 8 can also be composed of a suitable insulating material or semiconductor material.

[0124] 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.

[0125] The plurality of electrodes 3, 4 and the first bus bar 5 and the second bus bar 6 include appropriate metals or alloys such as Al and AlCu alloy. In the present embodiment, 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.

[0126] 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. Accordingly, it is possible to obtain the resonance characteristics of the bulk wave utilizing the 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-to-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, it is possible to effectively excite the bulk wave of the thickness shear mode and obtain good resonance characteristics. More preferably, d / p is less than 0.24, in which case, further good resonance characteristics can be obtained.

[0127] 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 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.21 (a) and Fig.21 (b) is used to illustrate the difference between the Lamb wave used in the elastic wave device and the body wave of the thickness shear mode mentioned above.

[0128] Fig.21(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 opposite 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.21 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 achieved, that is, when the number of pairs of electrode fingers is reduced, the Q value decreases.

[0129] In contrast, Fig.21 As shown in (b), in the elastic wave device 1, since the vibration displacement is in the thickness shear direction, the wave propagates and resonates almost 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. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Moreover, since the resonance characteristic is obtained by the propagation of the wave in the Z direction, it is not easy to generate propagation loss even if the number of electrode fingers of the reflector is reduced. Moreover, even if the number of pairs of electrode pairs including electrodes 3 and 4 is reduced to promote miniaturization, it is not easy to reduce the Q value.

[0130] In addition, if Fig. 22 As shown, the amplitude directions of the body waves in the thickness shear mode are opposite in the first region 451 included in the excitation region C of the piezoelectric layer 2 and the second region 452 included in the excitation region C. Fig. 22 , 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.

[0131] As described above, elastic wave device 1 includes at least one pair of electrodes 3 and 4 , but since waves are not propagated in the X direction, there is no need to have more than one pair of electrodes 3 and 4 . In other words, at least one pair of electrodes is sufficient.

[0132] 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 this embodiment, as described above, at least one pair of electrodes is an electrode connected to the signal potential or an electrode connected to the ground potential, and no floating electrode is provided.

[0133] Fig.23 It is shown Fig. 20 The resonance characteristics of the elastic wave device are shown in FIG. 1. The design parameters of the elastic wave device 1 for obtaining the resonance characteristics are as follows.

[0134] Piezoelectric layer 2: LiNbO3 with Euler angles (0°, 0°, 90°), thickness = 400nm.

[0135] 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, that is, the length of the excitation area C = 40μm, the number of pairs of electrodes including electrodes 3 and 4 = 21 pairs, the center distance between electrodes = 3μm, the width of electrodes 3 and 4 = 500nm, and d / p = 0.133.

[0136] Insulating layer 7: a silicon oxide film having a thickness of 1 μm.

[0137] Supporting member 8: Si.

[0138] 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 .

[0139] In the present embodiment, the inter-electrode distances of the electrode pairs including the electrodes 3 and 4 are set equal in all the pairs. That is, the electrodes 3 and the electrodes 4 are arranged at equal intervals.

[0140] Depend on Fig.23 It can be seen that, despite the absence of a reflector, a good resonance characteristic with a fractional bandwidth of 12.5% ​​is obtained.

[0141] In addition, 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 present embodiment, d / p is 0.5 or less, and more preferably 0.24 or less. Fig.24 This is explained.

[0142] and get Fig.23 The elastic wave devices having the same resonant characteristics as shown above are obtained by changing d / p. Fig.24 3 is a graph showing the relationship between d / p and the fractional bandwidth of a resonator as an elastic wave device.

[0143] Depend on Fig.24It can be seen that when 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.

[0144] Fig.25 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.25 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, if the above d / p is 0.5 or less, a thickness shear mode bulk wave can be effectively excited.

[0145] In the elastic wave device 1, it is preferred that the metallization ratio MR of any adjacent electrodes 3 and 4 in the plurality of electrodes 3 and 4 with respect to the excitation region C satisfies MR≤1.75(d / p)+0.075, and the excitation region C is a region where the adjacent electrodes 3 and 4 overlap when viewed in opposite directions. In this case, the stray light can be effectively reduced. Fig.26 as well as Fig. 27 This is explained. Fig.26 : 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 set, and the Euler angles of LiNbO3 are set to (0°, 0°, 90°). In addition, the metallization ratio MR is set to 0.35.

[0146] Reference Fig.19 (b) is used to illustrate the metallization ratio MR. Fig.19In 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 is 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 longitudinal 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.

[0147] 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.

[0148] Fig. 27 This is a graph showing the relationship between the fractional bandwidth and the phase rotation amount of the impedance of the spurious signal normalized by 180 degrees when many elastic wave resonators are formed according to the present embodiment. In addition, the film thickness of the piezoelectric layer and the size of the electrode are variously changed to adjust the fractional bandwidth. In addition, Fig. 27 These are the results obtained when a piezoelectric layer including Z-cut LiNbO 3 is used; however, the same tendency is observed when a piezoelectric layer having other cut angles is used.

[0149] exist Fig. 27 In the area surrounded by ellipse J, the spurious signal becomes larger and becomes 1.0. Fig. 27 It can be seen 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 spurious with a spurious level of 1 or more will appear in the passband. Fig.26 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.

[0150] Fig.28 : 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 bandwidth was measured. Fig.28The 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 set the fractional bandwidth to less than 17%. More preferably, Fig.28 The region to the right of MR=3.5(d / 2p)+0.05 indicated by the dashed line D1 in FIG. 1 is shown in FIG. 1. That is, if MR≤1.75(d / p)+0.05, the fractional bandwidth can be reliably set to 17% or less.

[0151] Fig.29 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.29 The hatched portion of is a region where a fractional bandwidth of at least 5% can be obtained. If the range of this region is approximated, it becomes a range represented by the following equations (1), (2), and (3).

[0152] (0°±10°, 0°~20°, arbitrary ψ)…Formula (1)

[0153] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50) 2 / 900) 1 / 2 ]~180°)…Formula (2)

[0154] (0°±10°, [180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~180°, any ψ)…Formula (3)

[0155] Therefore, in the case of the Euler angle range of the above-mentioned formula (1), formula (2) or formula (3), the fractional bandwidth can be sufficiently widened, which is preferable. The same is true when the piezoelectric layer 2 is a lithium tantalate layer.

[0156] Fig.30 It is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0157] 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 with relatively low acoustic impedance and high acoustic impedance layers 82b, 82d with 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 setting the above-mentioned d / p to 0.5 or less, 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 layers of the low acoustic impedance layers 82a, 82c, 82e and the 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.

[0158] 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.

[0159] 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.30 The acoustic multilayer film 82 shown. Specifically, the support member and the piezoelectric film may be configured so that at least a portion of the support member and at least a portion of the piezoelectric film as the piezoelectric film are opposed to each other with the acoustic multilayer film 82 sandwiched therebetween. In this case, it is sufficient to alternately stack low acoustic impedance layers and high acoustic impedance layers in the acoustic multilayer film 82. The acoustic multilayer film 82 may also be an acoustic reflection portion in an elastic wave device.

[0160] In the elastic wave devices of the first to sixth embodiments and their variants that utilize body waves in a thickness shear mode, as described above, d / p is preferably less than or equal to 0.5, and more preferably less than or equal to 0.24. This allows for even better resonance characteristics. Furthermore, in the crossover region of the elastic wave devices of the first to sixth embodiments and their variants that utilize body waves in a thickness shear mode, MR ≤ 1.75 (d / p) + 0.075 is preferably satisfied as described above. In this case, spurious emission can be more reliably suppressed.

[0161] The piezoelectric layer in the elastic wave device of the first to sixth embodiments and each modified example using the body wave of the thickness shear mode is preferably a lithium niobate layer or a lithium tantalate layer. Furthermore, the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are preferably within the range of the above formula (1), formula (2) or formula (3). In this case, the fractional bandwidth can be fully expanded.

[0162] Description of Reference Numerals

[0163] 1…Elastic wave device

[0164] 2…Piezoelectric layer

[0165] 2a, 2b...1st main surface, 2nd main surface

[0166] 3, 4…Electrode

[0167] 5, 6…1st bus bar, 2nd bus bar

[0168] 7…Insulation layer

[0169] 7a…Through hole

[0170] 8…Supporting member

[0171] 8a…Through hole

[0172] 9…Hollow

[0173] 10…Elastic wave device

[0174] 10a…Cavity

[0175] 11…IDT electrode

[0176] 12…Piezoelectric substrate

[0177] 13…Supporting member

[0178] 14…Piezoelectric layer

[0179] 14a, 14b…1st main surface, 2nd main surface

[0180] 15…Insulation layer

[0181] 16…Support base plate

[0182] 24A, 24B ... 1st mass additional film, 2nd mass additional film

[0183] 26, 27…1st bus bar, 2nd bus bar

[0184] 28, 29…1st electrode finger, 2nd electrode finger

[0185] 34A, 34B ... 1st mass additional film, 2nd mass additional film

[0186] 48…1st electrode finger

[0187] 48b…Wide width

[0188] 49…2nd electrode finger

[0189] 49a…Wide width

[0190] 53…Dielectric film

[0191] 54A, 54B ... first mass additional film, second mass additional film

[0192] 80, 81…Elastic wave device

[0193] 82…Acoustic multilayer film

[0194] 82a, 82c, 82e…low acoustic impedance layer

[0195] 82b, 82d…high acoustic impedance layer

[0196] 104A, 104B ... first mass additional film, second mass additional film

[0197] 114A, 114B ... first mass additional film, second mass additional film

[0198] 201…Piezoelectric film

[0199] 201a, 201b…1st main surface, 2nd main surface

[0200] 451, 452…1st area, 2nd area

[0201] C…Incentive Area

[0202] E1, E2…1st edge area, 2nd edge area

[0203] F…Intersection area

[0204] G1, G2...1st gap area, 2nd gap area

[0205] H…Central area

[0206] VP1…imaginary plane.

Claims

1. An elastic wave device comprising: A piezoelectric substrate comprises a supporting member and a piezoelectric film, wherein the supporting member comprises a supporting substrate, and the piezoelectric film comprises a piezoelectric layer provided on the supporting member, and The IDT electrode is provided on the piezoelectric layer and includes a first bus bar and a second bus bar facing each other, and a plurality of first electrode fingers and a plurality of second electrode fingers. In a plan view along the stacking direction of the support member and the piezoelectric film, an acoustic reflection portion is formed at a position of the support member overlapping with the IDT electrode. One end of the plurality of first electrode fingers of the IDT electrode is connected to the first bus bar, one end of the plurality of second electrode fingers is connected to the second bus bar, and the plurality of first electrode fingers and the plurality of second electrode fingers are interlaced with each other. When the thickness of the piezoelectric film is d and the center-to-center distance between the adjacent first electrode fingers and the second electrode fingers is p, d / p is equal to or less than 0.

5. The direction in which the first electrode finger and the second electrode finger extend is set as the electrode finger extending direction, and the direction orthogonal to the electrode finger extending direction is set as the electrode finger orthogonal direction. When observed from the electrode finger orthogonal direction, the region where the adjacent first electrode finger and the second electrode finger overlap each other is a crossing region, and the crossing region has a central region and a first edge region and a second edge region configured to sandwich the central region in the electrode finger extending direction. The area between the first edge area and the first bus bar is a first gap area, and the area between the second edge area and the second bus bar is a second gap area. The elastic wave device further comprises: a first mass added film provided over the first edge region and the first gap region; and The second mass-added film is provided over the second edge region and the second gap region. When the dimensions of the first mass added film and the second mass added film along the extending direction of the electrode fingers are set as the lengths of the first mass added film and the second mass added film, at least one of the length of the first mass added film in the first gap region and the length of the second mass added film in the second gap region and the length of the first mass added film in the first edge region and the length of the second mass added film in the second edge region are different from each other.

2. The elastic wave device according to claim 1, wherein: When a region between the first electrode fingers and the second electrode fingers is defined as an inter-electrode-finger region, the first mass added film is provided continuously to overlap the plurality of first electrode fingers, the plurality of second electrode fingers, and the inter-electrode-finger region in a plan view.

3. The elastic wave device according to claim 1, wherein: A plurality of the first mass adding films are provided over the first edge region and the first gap region, and the plurality of the first mass adding films are arranged in a direction orthogonal to the electrode fingers.

4. The elastic wave device according to claim 3, wherein: Each of the first mass added films is stacked on one of the plurality of first electrode fingers and the plurality of second electrode fingers.

5. The elastic wave device according to any one of claims 1 to 4, wherein: A total length of the first mass adding film in the first edge region and the first gap region and a total length of the second mass adding film in the second edge region and the second gap region are different from each other.

6. The elastic wave device according to any one of claims 1 to 4, wherein: A total length of the first mass adding film in the first edge region and the first gap region is equal to a total length of the second mass adding film in the second edge region and the second gap region.

7. The elastic wave device according to any one of claims 1 to 6, wherein: In a portion where the first mass added film and the first electrode fingers are stacked, the piezoelectric layer, the first electrode fingers, and the first mass added film are stacked in this order.

8. The elastic wave device according to any one of claims 1 to 6, wherein: In a portion where the first mass addition film and the first electrode fingers are stacked, the piezoelectric layer, the first mass addition film, and the first electrode fingers are stacked in this order.

9. The elastic wave device according to any one of claims 1 to 8, wherein: The plurality of first electrode fingers have a wide portion located in the second edge region, and a width of the first electrode finger in the wide portion is wider than a width of the first electrode finger in the central region.

10. The elastic wave device according to any one of claims 1 to 9, wherein: A dielectric film is provided on the piezoelectric layer so as to cover the IDT electrode, and the piezoelectric layer, the dielectric film, and the first mass added film are stacked.

11. The elastic wave device according to claim 10, wherein: The dielectric film includes silicon oxide.

12. The elastic wave device according to claim 10 or 11, wherein: The piezoelectric layer, the dielectric film, and the first mass added film are stacked in this order, The first mass added film includes metal.

13. The elastic wave device according to any one of claims 1 to 11, wherein: The first mass added film and the second mass added film include at least one material selected from the group consisting of silicon oxide, tantalum oxide, niobium oxide, tungsten oxide, and hafnium oxide.

14. The elastic wave device according to any one of claims 1 to 13, wherein: d / p is 0.24 or less.

15. The elastic wave device according to any one of claims 1 to 14, wherein: When viewed from the orthogonal direction of the electrode fingers, the region where the adjacent first electrode fingers and the second electrode fingers overlap each other and the region between the centers of the adjacent first electrode fingers and the second electrode fingers in the orthogonal direction of the electrode fingers is the excitation region. When a metallization ratio of the plurality of electrode fingers to the excitation region is defined as MR, MR≦1.75(d / p)+0.075 is satisfied.

16. The elastic wave device according to any one of claims 1 to 15, wherein: The piezoelectric layer includes lithium niobate.

17. The elastic wave device according to claim 16, wherein: The Euler angles (φ, θ, ψ) of lithium niobate constituting the piezoelectric layer are within the range of the following formula (1), formula (2) or formula (3), (0°±10°, 0°~20°, arbitrary ψ)…Formula (1) (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50) 2 / 900) 1 / 2 ]~180°)…Formula (2) (0°±10°, [180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~180°, arbitrary ψ)…Formula (3).

18. The elastic wave device according to any one of claims 1 to 17, wherein: The sound reflecting portion is a cavity portion, and the support member and the piezoelectric film are arranged so that a portion of the support member and a portion of the piezoelectric film face each other with the cavity portion interposed therebetween.

19. The elastic wave device according to any one of claims 1 to 17, wherein: The acoustic reflection portion is an acoustic reflection membrane including a high acoustic impedance layer having relatively high acoustic impedance and a low acoustic impedance layer having relatively low acoustic impedance, and the supporting member and the piezoelectric membrane are configured so that at least a portion of the supporting member and at least a portion of the piezoelectric membrane are opposed to each other with the acoustic reflection membrane sandwiched therebetween.

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