Elastic wave device

Abstract

Provided is an elastic wave device with which it is possible to reduce the size of a filter device and to enlarge the bandwidth of a passband. This elastic wave device (10) is provided with: a piezoelectric layer (14) that contains lithium niobate; and first and second comb electrodes (17, 18) that are provided on a first main surface (14a) of the piezoelectric layer (14), have a plurality of first and second electrode fingers (25, 26) that are interleaved with each other, and are connected to input and output potentials, respectively. And a third electrode (19) connected to different potentials so as to be aligned with the first electrode finger (25) and the second electrode finger (26) in plan view, the first electrode finger (25), the third electrode finger (27), the second electrode finger (26), and the third electrode finger (27) are arranged in this order with the first electrode finger (25), the third electrode finger (27), the second electrode finger (26), and the third electrode finger (27) as one cycle, and in each of the pair of electrode fingers, 0.65 < = de / d < = 1.15 and me / pa < = 0.5, and de / d < = 0.25, or 0.7 < = de / d < = 1.5 and me / pa < = 0.15 are satisfied.

Description

Technical Field

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

[0002] Traditionally, elastic wave devices have been widely used in filters for mobile phones and other applications. In recent years, elastic wave devices utilizing thickness-shear mode bulk waves have been proposed, as described in Patent Document 1 below. This elastic wave device comprises a piezoelectric layer disposed on a support. A pair of electrodes is disposed on the piezoelectric layer. The paired electrodes are positioned opposite each other on the piezoelectric layer and connected to different potentials. By applying an AC voltage between these electrodes, thickness-shear mode bulk waves are excited.

[0003] Prior art literature

[0004] Patent Literature

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

[0006] Problems to be solved by the invention

[0007] An elastic wave device, for example, is an elastic wave resonator, used in a ladder filter. To achieve good performance in a ladder filter, it is necessary to increase the capacitance ratio between the multiple elastic wave resonators. In this case, the capacitance of some of the elastic wave resonators in the ladder filter must be increased.

[0008] To increase the capacitance of an elastic wave resonator, for example, the resonator must be larger. Therefore, when such an elastic wave resonator is used in a ladder filter, the ladder filter often becomes larger. In particular, ladder filters using elastic wave resonators with low capacitance that utilize bulk waves in the thickness shear mode tend to be larger.

[0009] The inventors of the present invention have discovered that, by configuring an elastic wave device as follows, it is possible to obtain an appropriate filter waveform without increasing the size of the filter device when the elastic wave device is used in a filter device. This configuration is a configuration in which an electrode connected to a potential different from the input and output potentials, such as a reference potential, is disposed between an electrode connected to an input potential and an electrode connected to an output potential.

[0010] However, the inventors of the present invention have also discovered that even with the above-mentioned structure alone, unnecessary waves may not be sufficiently suppressed and the passband bandwidth may not be sufficiently expanded.

[0011] An object of the present invention is to provide an elastic wave device that can contribute to miniaturization of a filter device and expand the bandwidth of a passband.

[0012] Technical solutions to solve problems

[0013] In a broad aspect of the elastic wave device according to the present invention, the device comprises: a piezoelectric film including a piezoelectric layer, the piezoelectric layer including lithium niobate and having a first main surface and a second main surface facing each other; a first comb-shaped portion provided on the first main surface of the piezoelectric layer, having a first bus bar portion and a plurality of first electrode fingers each having one end connected to the first bus bar portion, and connected to an input potential; a second comb-shaped portion provided on the first main surface of the piezoelectric layer, having a second bus bar portion and a plurality of second electrode fingers each having one end connected to the second bus bar portion, and connected to an output potential, the plurality of second electrode fingers being connected to the plurality of first electrode fingers The parts are interlaced with each other; and the third part has a plurality of third electrode fingers and a connecting portion connecting adjacent third electrode fingers to each other, which is connected to a potential different from that of the first comb-shaped portion and the second comb-shaped portion, and the plurality of third electrode fingers are respectively arranged on the first main surface of the piezoelectric layer so that when viewed from above, they are arranged side by side 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, when starting from the first electrode finger, is to place the first electrode finger , the third electrode finger portion, the second electrode finger portion, and the third electrode finger portion are set in a periodic order, the first electrode finger portion, the second electrode finger portion, and the third electrode finger portion each have at least one layer, and the at least one layer includes a layer containing a material mainly composed of Al, and three adjacent electrode fingers in the order of the first electrode finger portion, the third electrode finger portion, and the second electrode finger portion are set as a group of electrode fingers, and when the product of a value obtained by dividing the density of the at least one layer by the density of Al and the thickness of the layer in each of the group of electrode fingers is set as the Al normalized thickness of the layer, all the electrode fingers are connected. The value obtained by summing up the normalized Al thickness of the layer is the electrode finger thickness de of each of the group of electrode fingers. When the width of each of the group of electrode fingers is set as the electrode finger width me, the average of the center-to-center distance between the adjacent first electrode finger and the third electrode finger in the group of electrode fingers and the center-to-center distance between the second electrode finger and the third electrode finger is set as the average center-to-center distance pa, and the thickness of the piezoelectric film is set as d, in each of the group of electrode fingers, one of 0.65≤de / d≤1.15 and me / pa≤0.5, and de / d≤0.25 is satisfied.

[0014] In other broad aspects of the elastic wave device according to the present invention, the device comprises: a piezoelectric film including a piezoelectric layer, the piezoelectric layer including lithium niobate and having a first main surface and a second main surface facing each other; a first comb-shaped portion provided on the first main surface of the piezoelectric layer, having a first bus bar portion and a plurality of first electrode fingers each having one end connected to the first bus bar portion, and connected to an input potential; a second comb-shaped portion provided on the first main surface of the piezoelectric layer, having a second bus bar portion and a plurality of second electrode fingers each having one end connected to the second bus bar portion, and connected to an output potential, the plurality of second electrode fingers being connected to the plurality of The first electrode fingers are interlaced with each other; and the third part has a plurality of third electrode fingers and a connecting portion connecting adjacent third electrode fingers to each other, which is connected to a potential different from that of the first comb-shaped portion and the second comb-shaped portion, and the plurality of third electrode fingers are respectively arranged on the second main surface of the piezoelectric layer so that when viewed from above, they are arranged side by side 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 of arrangement of the first electrode finger, the second electrode finger and the third electrode finger, starting from the first electrode finger, The first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger are arranged in a periodic order, the first electrode finger, the second electrode finger, and the third electrode finger each having at least one layer, the at least one layer including a layer containing a material having Al as a main component, three adjacent electrode fingers in the order of the first electrode finger, the third electrode finger, and the second electrode finger are set as a group of electrode fingers, and the product of a value obtained by dividing the density of the at least one layer by the density of Al and the thickness of the layer in each of the group of electrode fingers is set as the thickness of the layer. When the Al normalized thickness of the layer is calculated, the value obtained by summing up the Al normalized thickness of all the layers is the electrode finger thickness de of each of the group of electrode fingers. When the width of each of the group of electrode fingers is set to the electrode finger width me, the average of the center-to-center distance between the first electrode finger and the third electrode finger and the center-to-center distance between the second electrode finger and the third electrode finger in the group of electrode fingers is set to the average center-to-center distance pa, and the thickness of the piezoelectric film is set to d, in each of the group of electrode fingers, 0.7≤de / d≤1.5 and me / pa≤0.15.

[0015] Effects of the Invention

[0016] According to the present invention, it is possible to provide an elastic wave device that can contribute to miniaturization of a filter device and expand the bandwidth of a passband. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1It is a schematic front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0018] Figure 2 It is a schematic plan view of the elastic wave device according to the first embodiment of the present invention.

[0019] 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.

[0020] Figure 4 It is a schematic front cross-sectional view for explaining various parameters in the functional electrode.

[0021] Figure 5 Graphs showing transmission characteristics of elastic wave devices according to the first embodiment of the present invention and a comparative example.

[0022] Figure 6 This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers for explaining the odd-numbered mode.

[0023] Figure 7 This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers for explaining the even-numbered mode.

[0024] Figure 8 It is a diagram schematically showing how a passband is formed in an acoustic coupling filter.

[0025] Figure 9 This is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers in a first modification of the first embodiment of the present invention.

[0026] Figure 10 Graphs showing transmission characteristics of elastic wave devices according to the first embodiment and the first modification of the present invention.

[0027] Figure 11 Graph showing the relationship between mg / pa and the fractional bandwidth of the -5 dB band.

[0028] Figure 12 This is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers in a second modification of the first embodiment of the present invention.

[0029] Figure 13 Graphs showing transmission characteristics of elastic wave devices according to the first embodiment and the second modification of the present invention.

[0030] Figure 14 This is a diagram showing a map of the fractional bandwidth with respect to the Euler angles (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0031] Figure 15 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.

[0032] Figure 16 It is a schematic plan view of an elastic wave device according to a second embodiment of the present invention.

[0033] Figure 17 This is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers in the second embodiment of the present invention.

[0034] Figure 18 It is a schematic plan view of an elastic wave device according to a third embodiment of the present invention.

[0035] Figure 19 This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers in the third embodiment of the present invention.

[0036] Figure 20 (a) is a schematic perspective view showing the appearance of an elastic wave device utilizing bulk waves in a thickness shear mode. Figure 20 (b) is a top view showing the electrode structure on the piezoelectric layer.

[0037] Figure 21 It is along Figure 20 (a) is a cross-sectional view of a portion taken along line AA.

[0038] Figure 22 (a) is a schematic front cross-sectional view for explaining Lamb waves propagating through a piezoelectric film of an elastic wave device. Figure 22 (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.

[0039] Figure 23 Graph showing the amplitude direction of the body wave in the thickness shear mode.

[0040] Figure 24 Graphs showing resonance characteristics of an elastic wave device utilizing bulk waves in a thickness shear mode.

[0041] Figure 25 Graph showing the relationship between d / p and the fractional bandwidth of a 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.

[0042] Figure 26 This is a top view of an elastic wave device that utilizes bulk waves in the thickness shear mode.

[0043] Figure 27 Graphs showing the resonance characteristics of an elastic wave device according to a reference example in which spurious emission occurs.

[0044] Figure 28 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.

[0045] Figure 29 It is a graph showing the relationship between d / 2p and the metallization ratio MR.

[0046] Figure 30 This is a diagram showing a map of the fractional bandwidth with respect to the Euler angles (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0047] Figure 31 This is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0048] Figure 32 This is a partially cutaway perspective view for explaining an elastic wave device utilizing Lamb waves. DETAILED DESCRIPTION

[0049] Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the accompanying drawings.

[0050] 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.

[0051] Figure 1 It 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 top 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 the figure, the electrodes are shown by hatching. Figure 2 Similarly, in other schematic plan views, electrodes may be hatched.

[0052] 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.

[0053] The elastic wave device 10 includes a piezoelectric substrate 12 and a functional electrode 11 as a functional portion. The piezoelectric substrate 12 is a substrate having piezoelectric properties. Specifically, the piezoelectric substrate 12 includes 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 piezoelectric properties, and does not necessarily refer to a film containing a piezoelectric body. However, in this 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 this 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 solely of the supporting substrate 16. In addition, the supporting member 13 may not necessarily be provided.

[0054] The piezoelectric layer 14 has a first main surface 14a and a second main surface 14b. The first main surface 14a and the second main surface 14b are opposite to each other. Of the first main surface 14a and the second main surface 14b, the second main surface 14b is located on the side of the supporting member 13. In this embodiment, the piezoelectric layer 14 includes lithium niobate. Specifically, the piezoelectric layer 14 includes Z-cut LiNbO3. However, the piezoelectric layer 14 may also include rotated Y-cut lithium niobate. In this specification, the so-called "a certain component includes a certain material" includes the case where it contains a trace amount of impurities to the extent that the electrical characteristics of the elastic wave device will not be significantly deteriorated.

[0055] The functional electrode 11 as a functional part is provided on the first main surface 14a of the piezoelectric layer 14. The functional part in the present invention may also be composed of a laminate of a layer containing a metal and a layer containing a dielectric. However, the functional electrode 11 as a functional part in this embodiment is composed of a layer containing a metal. More specifically, as Figure 2 As shown, the functional electrode 11 includes a pair of comb-shaped electrodes and a third electrode 19. 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. In this embodiment, the third electrode 19 is connected to a reference potential. In addition, the third electrode 19 does not necessarily need to be connected to the reference potential. The third electrode 19 only needs to be connected to a potential different from that of the first comb-shaped electrode 17 and the second comb-shaped electrode 18. However, it is preferred that the third electrode 19 be connected to the reference potential.

[0056] First comb-shaped electrodes 17 and second comb-shaped electrodes 18 are provided on first principal surface 14a of piezoelectric layer 14. First comb-shaped electrode 17 includes a first bus bar 22 and a plurality of first electrode fingers 25. One end of each of the plurality of first electrode fingers 25 is connected to first bus bar 22. Second comb-shaped electrode 18 includes a second bus bar 23 and a plurality of second electrode fingers 26. One end of each of the plurality of second electrode fingers 26 is connected to second bus bar 23.

[0057] 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 interleaved with each other. The first electrode fingers 25 and the second electrode fingers 26 are alternately arranged in a direction perpendicular to the direction in which the first electrode fingers 25 and the second electrode fingers 26 extend.

[0058] The third 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 14 a of the piezoelectric layer 14 . The plurality of third electrode fingers 27 are electrically connected to each other via the third bus bar 24 .

[0059] The plurality of third electrode fingers 27 are arranged parallel to 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 arranged. Therefore, the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 are arranged in one direction. The plurality of third electrode fingers 27 extend parallel to the plurality of first electrode fingers 25 and the plurality of second electrode fingers 26.

[0060] Hereinafter, the direction in which the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 extend is referred to as the electrode finger extension direction, and the direction orthogonal to the electrode finger extension direction is referred to as the electrode finger orthogonal direction. When the direction in which the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 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 fingers 25, the second electrode fingers 26, and the third electrode fingers 27 are sometimes collectively referred to simply as "electrode fingers."

[0061] Figure 3 This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers in the first embodiment.

[0062] The order in which the multiple electrode fingers are arranged, starting with first electrode finger 25, is such that the first electrode finger 25, third electrode finger 27, second electrode finger 26, and third electrode finger 27 form a single cycle. Therefore, the order in which the multiple electrode fingers are arranged is first electrode finger 25, third electrode finger 27, second electrode finger 26, third electrode finger 27, first electrode finger 25, third electrode finger 27, second electrode finger 26, and so on. "IN" represents the input potential, "OUT" represents the output potential, and "GND" represents the reference potential. If the order of the multiple electrode fingers is represented by the order of the potentials to which they are connected, then "IN", "GND", "OUT", "GND", "IN", "GND", "OUT", and so on.

[0063] In this embodiment, in a region where multiple electrode fingers are provided, the electrode fingers located at both ends in a direction orthogonal to the electrode fingers are third electrode fingers 27. Furthermore, in this region, the electrode fingers located at the ends in a direction orthogonal to the electrode fingers may be any of the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27.

[0064] like Figure 2 As shown, third bus bar 24, serving as a connecting electrode for third electrode 19, electrically connects multiple third electrode fingers 27. Specifically, third bus bar 24 is located in the region between first bus bar 22 and the tips of multiple second electrode fingers 26. Multiple first electrode fingers 25 are also located in this region. However, third bus bar 24 and multiple first electrode fingers 25 are electrically insulated from each other by insulating film 29.

[0065] More specifically, the third bus bar 24 includes a plurality of first connecting electrodes 24A and a second connecting electrode 24B. Each first connecting electrode 24A connects the tips of two adjacent third electrode fingers 27. The first connecting electrodes 24A and the two third electrode fingers 27 form a U-shaped electrode. The second connecting electrode 24B connects the plurality of first connecting electrodes 24A. An insulating film 29 is provided between the second connecting electrode 24B and the plurality of first electrode fingers 25.

[0066] More specifically, an insulating film 29 is provided on the first principal surface 14a of the piezoelectric layer 14 so as to partially cover 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.

[0067] The insulating film 29 does not reach the first connecting electrode 24A of the third electrode 19. Furthermore, a second connecting electrode 24B is provided over the insulating film 29 and over the plurality of first connecting electrodes 24A. Specifically, the second connecting electrode 24B includes a stripe 24a and a plurality of protrusions 24b. Each protrusion 24b extends from the stripe 24a toward each first connecting electrode 24A. Each protrusion 24b is connected to each first connecting electrode 24A. Thus, the plurality of third electrode fingers 27 are electrically connected to each other through the first connecting electrode 24A and the second connecting electrode 24B.

[0068] In this embodiment, the third bus bar 24 is located in the 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 face the third bus bar 24 with gaps therebetween in the electrode finger extending direction. Meanwhile, the tips of the plurality of first electrode fingers 25 face the second bus bar 23 with gaps therebetween in the electrode finger extending direction.

[0069] Alternatively, third bus bar 24 may be located in a region between 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 face third bus bar 24 with gaps therebetween. Meanwhile, the tips of the plurality of second electrode fingers 26 face first bus bar 22 with gaps therebetween.

[0070] 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, bulk 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.

[0071] A portion of the 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 in the direction perpendicular to the electrode fingers, and are regions between the centers of adjacent first electrode fingers 25 and third electrode fingers 27. The remaining excitation regions C are regions where adjacent second electrode fingers 26 and third electrode fingers 27 overlap when viewed in the direction perpendicular 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 perpendicular to the electrode fingers.

[0072] The structure of the functional electrode 11, excluding the third electrode 19, is similar to that of an IDT (interdigital transducer) electrode. When viewed in a direction perpendicular to the electrode fingers, the area where adjacent first and second electrode fingers 25 and 26 overlap is the intersection region E. However, the intersection region E can also be considered the area where adjacent first and third electrode fingers 25 and 27, or adjacent second and third electrode fingers 26 and 27, overlap when viewed in a direction perpendicular to the electrode fingers. The intersection region E includes multiple excitation regions C. Furthermore, the intersection region E and the excitation region C are regions of the piezoelectric layer 14 defined by the structure of the functional electrode 11.

[0073] The functional electrode 11 is a functional portion in the present invention. The functional portion includes a first comb-shaped portion, a second comb-shaped portion, and a third portion. The first comb-shaped portion is the first comb-shaped electrode 17 in this embodiment. The second comb-shaped portion is the second comb-shaped electrode 18. The third portion is the third electrode 19.

[0074] The first comb-shaped portion includes a first bus bar portion and a plurality of first electrode fingers. The second comb-shaped portion includes a second bus bar portion and a plurality of second electrode fingers. The third portion includes a connecting portion and a plurality of third electrode fingers. In this embodiment, the first bus bar 22 is the first bus bar portion. The first electrode finger 25 is the first electrode finger. The second bus bar 23 is the second bus bar portion. The second electrode finger 26 is the second electrode finger. The third bus bar 24, which serves as a connecting electrode, is the connecting portion. The third electrode finger 27 is the third electrode finger. The direction in which the first electrode finger, the second electrode finger, and the third electrode finger extend is the electrode finger extending direction. Moreover, the direction orthogonal to the direction in which the first electrode finger, the second electrode finger, and the third electrode finger extend is the electrode finger orthogonal direction.

[0075] Hereinafter, the first electrode finger, the second electrode finger, and the third electrode finger may be collectively referred to simply as "electrode finger." Each electrode finger may comprise a single-layer metal film, a stacked metal film, or a laminate comprising a metal layer and a dielectric layer.

[0076] In this embodiment, each electrode finger, serving as each electrode finger portion, comprises a single-layer metal film. Specifically, the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 comprise Al. The material of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 can be any material containing Al as a main component. Furthermore, in the present invention, it suffices that at least one layer in each electrode finger portion comprises a layer containing Al as a main component. In this specification, the term "main component" refers to a component that accounts for more than 50% by weight of the component.

[0077] Hereinafter, three adjacent electrode fingers in the order of the first electrode finger 25, the third electrode finger 27, and the second electrode finger 26 are referred to as a group of electrode fingers. Figure 4 As shown, in a group of electrode fingers, the thickness of the first electrode finger 25 is set to d1, the thickness of the second electrode finger 26 is set to d2, and the thickness of the third electrode finger 27 is set to dg. The thickness of each electrode finger in a group is collectively referred to as the electrode finger thickness de. In addition, three adjacent electrode fingers in the order of the first electrode finger, the third electrode finger, and the second electrode finger are set as a group of electrode fingers. The same symbols as the thickness of each electrode finger mentioned above are used as the thickness of each electrode finger. That is, in a group of electrode fingers, the thickness of the first electrode finger is set to d1, the thickness of the second electrode finger is set to d2, and the thickness of the third electrode finger is set to dg. The thickness of each electrode finger in a group is collectively referred to as the electrode finger thickness de.

[0078] Here, the details of the thickness de of the electrode finger are explained. Let k be an arbitrary natural number with n as the maximum value, and the electrode finger has one or more k-th layers, and the closer the layer is to the piezoelectric layer 14 side, the smaller the value of k. For example, in the case where the electrode finger is a single layer, n=1, and the electrode finger has only the first layer. On the other hand, in the case where the electrode finger is a laminate, for example, the first layer, the second layer, the third layer ... the nth layer are stacked in order from the piezoelectric layer 14 side. When the thickness of the layer of the electrode finger is t k When the actual thickness of the electrode finger becomes Σt k (1≤k≤n).

[0079] On the other hand, the electrode finger thickness de is the thickness normalized by the density of Al, that is, the Al normalized thickness. Specifically, when the density of the electrode finger layer is ρ k , let the density of Al be ρ Al , the normalized Al thickness of the electrode finger layer is set to t k-Al When t k-Al =(ρ k / ρ Al ) × t k Moreover, the electrode finger thickness de is de=Σ[(ρ k / ρ Al ) × t k ] (1≤k≤n). That is, the electrode finger thickness de is the value obtained by summing the Al-normalized thicknesses of all layers in a set of electrode fingers, where the product of the value obtained by dividing the density of at least one layer by the density of Al and the thickness of the layer is defined as the Al-normalized thickness of the layer.

[0080] However, in this embodiment, each electrode finger comprises a single-layer metal film and contains Al. Therefore, the density of each electrode finger in this embodiment is pAl , the electrode finger thickness de as the electrode finger thickness de is de=t1. In addition, when each electrode finger contains an alloy mainly composed of Al, if the density of the alloy is ρ1, then de=(ρ1 / ρ Al )×t1.

[0081] Furthermore, below, within a group of electrode fingers, the width of the first electrode finger 25 is denoted by m1, the width of the second electrode finger 26 is denoted by m2, and the width of the third electrode finger 27 is denoted by mg. The widths of the electrode fingers in a group are collectively referred to as the electrode finger width, me. The electrode finger width refers to the dimension of the electrode finger along a direction perpendicular to the electrode finger. The same symbols as those used for the widths of the electrode fingers are used to denote the widths of the electrode fingers. That is, within a group of electrode fingers, the width of the first electrode finger is denoted by m1, the width of the second electrode finger is denoted by m2, and the width of the third electrode finger is denoted by mg. The widths of the electrode fingers in a group are collectively referred to as the electrode finger width, me.

[0082] The center-to-center distance between the adjacent first electrode finger 25 and third electrode finger 27 in a set of electrode fingers is denoted by p1, and the center-to-center distance between the second electrode finger 26 and third electrode finger 27 is denoted by p2. Similarly, the center-to-center distance between the adjacent first and third electrode finger portions in a set of electrode finger portions is denoted by p1, and the center-to-center distance between the second and third electrode finger portions is denoted by p2. The average of the center-to-center distances p1 and p2 is denoted by the average center-to-center distance pa. In other words, pa = (p1 + p2) / 2. The thickness of the piezoelectric film is denoted by d. In this embodiment, thickness d is the thickness of the piezoelectric layer 14.

[0083] In a set of electrode fingers in elastic wave device 10, the electrode finger thickness de is constant, the electrode finger width me is constant, and the center-to-center distances p1 and p2 are the same. That is, d1 = d2 = dg, m1 = m2 = mg, and p1 = p2. However, the electrode finger thickness de does not need to be constant. The electrode finger width me does not need to be constant. The center-to-center distances p1 and p2 do not need to be constant.

[0084] This embodiment is characterized by the following structures: 1) In a plan view, third electrode fingers 27 of the third electrode 19 are disposed between the first electrode fingers 25 of the first comb-shaped electrode 17 and the second electrode fingers 26 of the second comb-shaped electrode 18. 2) Multiple third electrode fingers 27 are disposed on the first principal surface 14a of the piezoelectric layer 14. 3) For each of the electrode fingers in a group, one of the following conditions is satisfied: 0.65 ≤ de / d ≤ 1.15, me / pa ≤ 0.5, or de / d ≤ 0.25. Consequently, when the elastic wave device 10 is used in a filter device, the filter device can be miniaturized and the passband width can be expanded.

[0085] In this specification, the term "top view" refers to a view from the Figure 1 The upper direction in FIG is observed along the stacking direction of the support member 13 and the piezoelectric film. Figure 1 For example, between the support substrate 16 side and the piezoelectric layer 14 side, the piezoelectric layer 14 side is considered the upper side. Furthermore, in this specification, "viewed from above" is synonymous with "viewed from the direction facing the principal surfaces." The principal surface facing direction refers to the direction in which the first principal surface 14a and the second principal surface 14b of the piezoelectric layer 14 face each other. More specifically, for example, the principal surface facing direction refers to the direction normal to the first principal surface 14a.

[0086] The following describes the details of the above-described effects of the first embodiment by comparing the first embodiment and a comparative example. The difference between the comparative example and the first embodiment is that, in a set of electrode fingers, neither 0.65 ≤ de / d ≤ 1.15, me / pa ≤ 0.5, nor de / d ≤ 0.25 is satisfied. In the first embodiment involved in this comparison, 0.65 ≤ de / d ≤ 1.15 and me / pa ≤ 0.5 are satisfied. The first embodiment and the comparative example compare the pass characteristics. The design parameters of the elastic wave device 10 having the structure of the first embodiment are as follows.

[0087] Piezoelectric layer: Material: Z-cut LiNbO3, thickness d: 400 nm

[0088] Electrode fingers 1 to 3: Material: Al, electrode finger width me: m1 = m2 = mg = 420 nm, electrode finger thickness de: d1 = d2 = dg = 400 nm

[0089] The third electrode finger is located on the main surface: the first main surface of the piezoelectric layer

[0090] Average center distance pa: pa = p1 = p2 = 1400nm

[0091] In the first embodiment, de / d = 1 and me / pa = 0.3. Meanwhile, the design parameters of the comparative example are the same as those of the first embodiment, except that the electrode finger thickness de is 600 nm. In the comparative example, me / pa = 0.3, but de / d = 1.5.

[0092] Figure 5 : is a graph showing the transmission characteristics of the elastic wave device according to the first embodiment and the comparative example. Figure 5 The results of FEM (Finite Element Method) simulations are shown. The characteristics are expressed using S parameters.

[0093] like Figure 5As shown in FIG. 1 , in the comparative example, many unnecessary waves are generated and the passband is narrow. In contrast, in the first embodiment, unnecessary waves are suppressed and the passband can be expanded. Figure 5 The double-headed arrow W in represents the passband in the first embodiment. In the first embodiment, even in a single elastic wave device 10 , an appropriate filter waveform can be obtained.

[0094] 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 adjacent first and third electrode fingers 25, 27, and an excitation region C located between the centers of adjacent second and third electrode fingers 26, 27. In these excitation regions C, multiple modes of elastic waves are excited.

[0095] Figure 6 This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers for explaining the odd-numbered mode. Figure 7 This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers for explaining the even-numbered mode. Figure 8 It is a diagram schematically showing how a passband is formed in an acoustic coupling filter.

[0096] In acoustically coupled filters, Figure 6 The odd-numbered modes shown and Figure 7 The so-called odd mode is a mode in which the electrical conditions are in phase. The so-called even mode is a mode in which the electrical conditions are in opposite phase. Figure 6 Zhonghe Figure 7 The arrows in show the direction of the electric field.

[0097] like Figure 8 As shown in FIG, in an acoustic coupling filter, a passband is formed by even-numbered modes and odd-numbered modes. The even-numbered modes form the low-frequency end of the passband, while the odd-numbered modes form the high-frequency end of the passband.

[0098] In this way, even with a single elastic wave device 10, an appropriate filter waveform can be obtained. When the elastic wave device 10 is used as an elastic wave resonator in a filter device, an appropriate filter waveform can be obtained even with a single or relatively small number of elastic wave resonators. This facilitates miniaturization of the filter device.

[0099] The inventors of the present invention have studied the conditions for suppressing unnecessary waves and widening the passband bandwidth by changing de / d and me / pa. Figure 5The comparison involves the same design parameters of the first embodiment. In addition, let m1 = m2 = mg, d1 = d2 = dg, and p1 = p2. The results of this study are shown in Table 1.

[0100] In Table 1, the conditions under which a passband can be appropriately obtained and the bandwidth of the passband can be expanded are marked as ○. The conditions under which unwanted waves cannot be suppressed and the bandwidth of the passband becomes narrow are marked as ×.

[0101] [Table 1]

[0102]

[0103] As shown in Table 1, when de / d ≤ 0.25, regardless of the value of me / pa, a passband can be appropriately obtained and the bandwidth of the passband can be expanded. On the other hand, when 0.65 ≤ de / d ≤ 1.15, when me / pa ≤ 0.5, a passband can be appropriately obtained and the bandwidth of the passband can be expanded.

[0104] In the first embodiment, each electrode finger of each electrode finger portion contains Al. However, in the present invention, each electrode finger may also contain a material mainly composed of Al. The acoustic characteristics of the material mainly composed of Al are similar to those of Al. Therefore, by satisfying the conditions of the parameters of the present invention, the bandwidth of the passband can be expanded. In addition, for example, each electrode finger portion in the present invention may also contain a laminate, which is a laminate of a layer containing a metal and a layer containing a dielectric.

[0105] In the first embodiment, the electrode finger width me is fixed. In addition, the electrode finger width me does not necessarily have to be fixed. For example, in Figure 9 In the first modification example of the first embodiment shown, m1 = m2 < mg. In this case, in each of a set of electrode fingers, it is only necessary to satisfy one of 0.65 ≤ de / d ≤ 1.15 and me / pa ≤ 0.5, and de / d ≤ 0.25. Accordingly, similar to the first embodiment, when the elastic wave device is used in a filter device, miniaturization of the filter device can be promoted and the bandwidth of the passband can be expanded.

[0106] By adjusting the width mg of the third electrode finger 27, particularly among a set of electrode fingers, the excited mode can be controlled. This will be shown below. Specifically, the transmission characteristics of the first modification example are shown. The passband in the first embodiment with m1 = m2 = mg is also shown. [[ID=2&]]

[0107] Figure 10 It is a diagram showing the transmission characteristics in the elastic wave devices of the first embodiment and the first modification example. In Figure 10, the results of the FEM simulation are shown when m1=m2=mg=420 nm and when m1=m2=420 nm and mg=700 nm.

[0108] like Figure 10 As shown, compared to the case where the electrode finger width me is fixed, increasing the width mg of the third electrode finger 27 widens the -5dB bandwidth. The so-called -5dB band refers to the frequency band where the S parameter is -5dB or greater. The -5dB bandwidth is the bandwidth of the -5dB band. The -5dB band can be considered a type of passband. The reasons for expanding the -5dB bandwidth are as follows.

[0109] When the electrode finger width me is fixed, the A1-3 mode does not contribute to the formation of the passband. In contrast, increasing the width mg of the third electrode finger 27 allows the frequency of the A1-3 mode to approach the frequency of the main mode. This allows the A1-3 mode to contribute to the formation of the passband. Consequently, the -5 dB bandwidth, which serves as the passband's bandwidth, can be expanded.

[0110] The fractional bandwidth of the -5dB band was calculated for each change in mg / Pa (me / Pa). The fractional bandwidth here refers to the fractional bandwidth of an elastic wave device with a passband. This fractional bandwidth is expressed as (|fh - fl| / fc) × 100[%], where the frequency at the high-frequency end of the passband is fh, the frequency at the low-frequency end of the passband is fl, and the center frequency of the passband is fc.

[0111] Figure 11 Graph showing the relationship between mg / pa and the fractional bandwidth of the -5 dB band.

[0112] like Figure 11 As shown in the figure, when mg / Pa is greater than 0.5, the fractional bandwidth of the -5dB band increases. Therefore, mg / Pa ≥ 0.5 is preferred. This effectively expands the -5dB bandwidth. Furthermore, when mg / Pa > 0.5, de / d ≤ 0.25 is sufficient.

[0113] In the first modification, the width mg of the third electrode finger 27 is wider than the width m1 of the first electrode finger 25 and the width m2 of the second electrode finger 26. However, the width mg of the third electrode finger 27 may be narrower than the width m1 of the first electrode finger 25 and the width m2 of the second electrode finger 26.

[0114] In addition, the electrode finger thickness de may not necessarily be constant. Figure 12In the second variation of the first embodiment shown, d1 = d2 > dg. In this case, each electrode finger in a pair only needs to satisfy one of the following: 0.65 ≤ de / d ≤ 1.15, me / pa ≤ 0.5, or de / d ≤ 0.25. Consequently, similar to the first embodiment, when the elastic wave device is used in a filter device, the filter device can be miniaturized and the passband bandwidth can be expanded.

[0115] The following shows the transmission characteristics of the second modification. The electrode finger thickness de is set to d1 = d2 = 400 nm, dg = 50 nm, and all other parameters except the electrode finger thickness de are set to me = m1 = m2 = mg = 420 nm, pa = p1 = p2 = 1400 nm, and d = 400 nm.

[0116] Under these conditions, in the first electrode finger 25, d1 / d, representing de / d, is 1, and me / pa is 0.3. Therefore, in the first electrode finger 25, 0.65 ≤ de / d ≤ 1.15 and me / pa ≤ 0.5. The same applies to the second electrode finger 26. In the third electrode finger 27, dg / d, representing de / d, is 0.125. Therefore, in the third electrode finger 27, de / d ≤ 0.25.

[0117] The transmission characteristics of the first embodiment, where d1 = d2 = dg, are also shown. The electrode finger thickness de is set to de = d1 = d2 = d = 400 nm. All parameters other than the electrode finger thickness de in the first embodiment are the same as those described above in this second variation. Therefore, for each electrode finger in a set, 0.65 ≤ de / d ≤ 1.15 and me / pa ≤ 0.5.

[0118] Figure 13 Graphs showing the transmission characteristics of the elastic wave devices according to the first embodiment and the second modification. Figure 13 , the results of FEM simulation are shown.

[0119] like Figure 13 As shown, it can be seen that by reducing the thickness dg of the third electrode finger 27 , the bandwidth on the low-frequency side of the passband is widened.

[0120] In the second modification, the thickness dg of the third electrode finger 27 is thinner than the thickness d1 of the first electrode finger 25 and the thickness d2 of the second electrode finger 26. However, the thickness dg of the third electrode finger 27 may be thicker than the thickness d1 of the first electrode finger 25 and the thickness d2 of the second electrode finger 26.

[0121] At least one of the electrode finger width me and the electrode finger thickness de may be different between the third electrode finger 27 and at least one of the first electrode finger 25 and the second electrode finger 26 in a set of electrode fingers.

[0122] The structure of the first embodiment will be described in more detail below. The first and second modified examples also have the same structure as that described below.

[0123] 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, the piezoelectric layer 14 and the support member 13 overlap when viewed from a direction in which the first principal surface 14a and the second principal surface 14b of the piezoelectric layer 14 face each other.

[0124] As a material for the support substrate 16 , for example, a semiconductor such as silicon, a ceramic such as aluminum oxide, etc. can be used. As a material for the insulating layer 15 , an appropriate dielectric such as silicon oxide or tantalum oxide can be used.

[0125] 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 first 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 interposed therebetween. However, the recess in the supporting member 13 may be provided throughout the insulating layer 15 and the supporting substrate 16. Alternatively, only the recess provided in the supporting substrate 16 may be blocked by the insulating layer 15. For example, the recess may be provided in the piezoelectric layer 14. In addition, the cavity 10a may be a through hole provided in the supporting member 13.

[0126] 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 to the piezoelectric layer 14 side. When viewed from above, the acoustic reflection portion only needs to be provided at a position in the support member 13 that overlaps with at least a portion of the functional electrode 11. More specifically, when viewed from above, it is sufficient that at least a portion of the first electrode finger 25 serving as the first electrode finger portion, the second electrode finger 26 serving as the second electrode finger portion, and the third electrode finger 27 serving as the third electrode finger portion each overlaps with the acoustic reflection portion. When viewed from above, it is preferred that multiple excitation regions C overlap with the acoustic reflection portion.

[0127] In addition, the sound reflecting portion may be a sound reflecting film such as a multi-layered film described later. For example, a sound reflecting film may be provided on the surface of the supporting member.

[0128] In the first embodiment, the center-to-center distance p1 between adjacent pairs of first and third electrode fingers 25, 27 and the center-to-center distance p2 between adjacent pairs of second and third electrode fingers 26, 27 are all the same. However, the center-to-center distance p1 between adjacent first and third electrode fingers 25, 27 and the center-to-center distance p2 between adjacent second and third electrode fingers 26, 27 do not need to be constant. In this case, the longest distance between the center-to-center distance p1 between adjacent first and third electrode fingers 25, 27 and the center-to-center distance p2 between adjacent second and third electrode fingers 26, 27 is denoted as p. Furthermore, when p1 = p2, as in the first embodiment, both the center-to-center distance p1 and the center-to-center distance p2 are equal to the distance p.

[0129] Preferably, d / p is 0.5 or less, and more preferably d / p is 0.24 or less. This allows thickness-shear mode bulk waves to be appropriately excited.

[0130] Furthermore, the elastic wave device of the present invention may not necessarily be configured to utilize bulk waves in 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.

[0131] As described above, in the first embodiment, the piezoelectric layer 14 comprises Z-cut LiNbO 3 . However, the piezoelectric layer 14 may also comprise rotated Y-cut lithium niobate. 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 in the piezoelectric layer 14 .

[0132] 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. Note that φ in the Euler angles was set to 0°.

[0133] Figure 14 This is a diagram showing a map of the fractional bandwidth with respect to the Euler angles (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0134] Figure 14 The region R indicated by the hatching is the region where the fractional bandwidth is obtained to be at least 2%. If the range of the region R is approximated, it becomes the range expressed 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 14 The relationship shown is the same.

[0135] (Within the range of 0°±10°, 0°~25°, arbitrary ψ)…Equation (1)

[0136] (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)

[0137] (Within the range of 0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, arbitrary ψ)…Equation (3)

[0138] The range of the Euler angles in the above-mentioned equations (1), (2), or (3) is preferably 0. This allows the fractional bandwidth to be sufficiently increased, thereby enabling the elastic wave device 10 to be suitably used in a filter device.

[0139] like Figure 2 As shown in the first embodiment, the third electrode 19 has a third bus bar 24 as a connecting electrode and a plurality of third electrode fingers 27. The third electrode 19 is a comb-shaped electrode. However, the third electrode 19 may not be a comb-shaped electrode. For example, Figure 15 In the third variation of the first embodiment shown, the third electrode 39 has a zigzag shape. In this variation, the insulating film 29 is not provided on the piezoelectric layer 14. Furthermore, the connecting electrode 34 only includes a portion corresponding to the plurality of first connecting electrodes 24A in the first embodiment. The connecting electrode 34 in this variation is not a third bus bar.

[0140] More specifically, the third electrode 39 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 tip 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. For example, each of the third electrode fingers 27 other than the ends in the orthogonal direction of the electrode fingers has a connection electrode 34 connected to both the tip end on the first bus bar 22 side and the tip end on the second bus bar 23 side. Each third electrode finger 27 is connected to the third electrode finger 27 adjacent to it on the left and right via each connection electrode 34. By repeating this structure, the shape of the third electrode 39 is formed into a zigzag shape.

[0141] In this variation, similar to the first embodiment, third electrode fingers 27 are arranged between first electrode fingers 25 and second electrode fingers 26 in a plan view. Each electrode finger in a pair satisfies one of the following conditions: 0.65 ≤ de / d ≤ 1.15, me / pa ≤ 0.5, or de / d ≤ 0.25. This allows for miniaturization of the filter device and expansion of the passband width when the elastic wave device is used in the filter device.

[0142] Alternatively, the plurality of third electrode fingers 27 may be provided on the second principal surface 14b of the piezoelectric layer 14. However, in this case, the conditions of the parameters are different from those in the case where the plurality of third electrode fingers 27 are provided on the first principal surface 14a. This example is described in the second embodiment.

[0143] Figure 16 It is a schematic plan view of an elastic wave device according to the second embodiment. Figure 17 This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers in the second embodiment.

[0144] like Figure 16 as well as Figure 17 As shown, this embodiment differs from the first embodiment in that third electrode 19 is provided on second principal surface 14b of piezoelectric layer 14. This embodiment also differs from the first embodiment in the relationship between electrode finger width me, electrode finger thickness de, thickness d of piezoelectric layer 14 (the piezoelectric film), and average center-to-center distance pa. Other than these features, the elastic wave device of this embodiment has the same structure as elastic wave device 10 of the first embodiment.

[0145] In this embodiment, the top-view arrangement of the third electrode 19 is also similar to that of the first embodiment. Therefore, the plurality of third electrode fingers 27 are provided on the second principal surface 14b of 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 when viewed from above. When viewed from above, the plurality of electrode fingers are arranged in such a sequence that, starting with the first electrode finger 25, the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, and finally the third electrode finger 27 form a single period.

[0146] This embodiment is characterized by the following structures. 1) In a plan view, third electrode fingers 27 of the third electrode 19 are disposed between the first electrode fingers 25 of the first comb-shaped electrode 17 and the second electrode fingers 26 of the second comb-shaped electrode 18. 2) Multiple third electrode fingers 27 are disposed on the second principal surface 14b of the piezoelectric layer 14. 3) For each of the electrode fingers in a group, 0.7 ≤ de / d ≤ 1.5 and me / pa ≤ 0.15. Consequently, when the elastic wave device is used in a filter device, the filter device can be miniaturized and the passband width can be expanded. This is described below.

[0147] The inventors of the present invention have studied the conditions for suppressing unnecessary waves and widening the passband bandwidth by changing de / d and me / pa. In this study, the design parameters other than de / d and me / pa were set to Figure 5 The design parameters of the first embodiment related to the comparison are the same. In addition, it is assumed that m1=m2=mg, d1=d2=dg, and p1=p2. Table 2 shows the results of this study.

[0148] In Table 2, the condition where a passband can be appropriately obtained and the bandwidth of the passband can be expanded is marked as ◯, and the condition where unnecessary waves cannot be suppressed and the bandwidth of the passband is narrowed is marked as ×.

[0149] [Table 2]

[0150]

[0151] As shown in Table 2, when 0.7≤de / d≤1.5 and me / pa≤0.15, a passband can be appropriately obtained, and the bandwidth of the passband can be expanded.

[0152] Furthermore, when multiple third electrode fingers 27 are provided on the second principal surface 14b of the piezoelectric layer 14, the electrode finger width me does not need to be constant. The electrode finger thickness de also does not need to be constant. Alternatively, at least one of the electrode finger width me and the electrode finger thickness de can be made different between the third electrode finger 27 and at least one of the first electrode finger 25 and the second electrode finger 26 within a set of electrode fingers. This allows adjustment of the passband width.

[0153] Figure 18 It is a schematic plan view of an elastic wave device according to a third embodiment. Figure 19 : is a schematic front cross-sectional view showing the vicinity of the first electrode finger portion to the third electrode finger portion in the third embodiment. Figure 18 In the figure, hatching indicates a portion including electrodes.

[0154] like Figure 18As shown, the elastic wave device 40 of this embodiment differs from the first embodiment in that the portion corresponding to the pair of comb-shaped electrodes and the third electrode is a laminate. Except for the above-described features, this embodiment has the same structure as the first embodiment.

[0155] The elastic wave device 40 includes a functional portion 41. The functional portion 41 includes a first comb-shaped portion, a second comb-shaped portion, and a third portion. The first comb-shaped portion, the second comb-shaped portion, and the third portion are each provided on the first principal surface 14a of the piezoelectric layer 14. Furthermore, the first comb-shaped portion includes a first bus bar portion and a plurality of first electrode fingers 45. The second comb-shaped portion includes a second bus bar portion and a plurality of second electrode fingers 46. The third portion includes a connecting portion and a plurality of third electrode fingers 47.

[0156] The first comb-shaped portion is connected to an input potential. The second comb-shaped portion is connected to an output potential. In this embodiment, the third portion is connected to a reference potential. Furthermore, the third portion only needs to be connected to a potential different from that of the first comb-shaped portion and the second comb-shaped portion.

[0157] The shape of the functional portion 41 in a plan view is similar to Figure 2 The functional electrodes 11 in the first embodiment shown have the same top-view shape. Specifically, one end of each of the plurality of first electrode fingers 45 is connected to a first bus bar. One end of each of the plurality of second electrode fingers is connected to a second bus bar. Adjacent third electrode fingers 47 are connected to each other via a connecting portion. The first bus bar and the second bus bar are opposed to each other. The plurality of first electrode fingers 45 and the plurality of second electrode fingers 46 are interlaced with each other.

[0158] The order in which the plurality of electrode fingers are arranged is such that, starting from the first electrode finger 45 , the first electrode finger 45 , the third electrode finger 47 , the second electrode finger 46 , and the third electrode finger 47 form one cycle.

[0159] like Figure 19 As shown, the first electrode finger portion 45 is a stacked structure comprising a first layer 45a and a second layer 45b. Specifically, the second layer 45b is provided on the first layer 45a. Similarly, the second electrode finger portion 46 is a stacked structure comprising a first layer 46a and a second layer 46b. The third electrode finger portion 47 is a stacked structure comprising a first layer 47a and a second layer 47b.

[0160] That is, in this embodiment, when an arbitrary natural number with n as the maximum value is set to k, n=2, and each electrode finger portion has two layers, a first layer and a second layer, which are the kth layers. The thickness of each layer of each electrode finger portion is t k (k=1, 2).

[0161] As described above, when the density of the electrode finger layer is set to p k, let the density of Al be ρ Al , the normalized Al thickness of the electrode finger layer is set to t k-Al When t k-Al =(ρ k / ρ Al ) × t k , the electrode finger thickness de is de=Σ[(ρ k / ρ Al ) × t k ] (1≤k≤n). In this embodiment, specifically, de=Σ[(ρ k / ρ Al ) × t k ] (1≤k≤2).

[0162] The first layer of each electrode finger contains Al. However, for example, the first layer of each electrode finger may also contain a material primarily composed of Al. In this embodiment, the second layer of each electrode finger contains silicon oxide. The acoustic properties of silicon oxide are similar to those of Al. Therefore, by satisfying the same parameter conditions as in the first embodiment, the passband bandwidth can be expanded.

[0163] This embodiment is characterized by the following structures: 1) In plan view, a third electrode finger 47 is provided between the first electrode finger 45 and the second electrode finger 46. 2) Multiple third electrode fingers 47 are provided on the first principal surface 14a of the piezoelectric layer 14. 3) Each of the electrode fingers in a set satisfies one of the following conditions: 0.65 ≤ de / d ≤ 1.15, me / pa ≤ 0.5, or de / d ≤ 0.25. Consequently, similar to the first embodiment, when the elastic wave device is used in a filter device, the filter device can be miniaturized and the passband width can be expanded.

[0164] The material of the second layer of each electrode finger is not limited to silicon oxide. For example, a metal or alloy different from that of the first layer, or a dielectric, may be used as the material of the second layer of each electrode finger. Table 3 shows examples of materials for the second layer. Table 3 also shows the density of each material [g / cm 3 ], longitudinal wave speed [m / s], shear wave speed [m / s], longitudinal wave acoustic impedance [×10 6 kg / (m 2 ·s)] and shear wave acoustic impedance [×10 6 kg / (m 2 ·s)]. In addition, the above parameters of Al are also shown in Table 3.

[0165] [Table 3]

[0166]

[0167] The number of layers in each electrode finger is not limited to one or two. In the present invention, each electrode finger only needs to have at least one layer. At least one layer in each electrode finger only needs to include a layer containing a material primarily composed of Al. The materials listed in Table 3 can also be used for layers other than the second layer, for example, when each electrode finger has three or more layers.

[0168] A plurality of third electrode fingers 47 can also be provided on the second principal surface 14b of the piezoelectric layer 14. In this case, for each of the electrode fingers, 0.7 ≤ de / d ≤ 1.5 and me / pa ≤ 0.15 are sufficient. Thus, similar to the second embodiment, when the elastic wave device is used in a filter device, the filter device can be miniaturized and the passband width can be expanded.

[0169] The following describes the details of the thickness shear mode using an example in which the functional electrode is an IDT electrode. Note that the IDT electrode does not have a third electrode. The "electrode" in the IDT electrode described below corresponds to the electrode finger. The supporting member in the following examples corresponds to the supporting substrate in the present invention. The reference potential may also be described as the ground potential.

[0170] Figure 20 (a) is a schematic perspective view showing the appearance of an elastic wave device utilizing bulk waves in a thickness shear mode. Figure 20 (b) is a top view showing the electrode structure on the piezoelectric layer. Figure 21 It is along Figure 20 (a) is a cross-sectional view of a portion taken along line AA.

[0171] 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 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 40 nm and less than 1000 nm, and more preferably greater than 50 nm and less than 1000 nm. The piezoelectric layer 2 has a first main surface 2a and a second main surface 2b facing each other. An electrode 3 and an electrode 4 are provided on the first main surface 2a. Here, the electrode 3 is an example of a "first electrode" and the electrode 4 is an example of a "second electrode". In Figure 20 (a) and Figure 20In (b), a plurality of electrodes 3 are connected to the first bus bar 5. A plurality of electrodes 4 are 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 perpendicular 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 perpendicular to the length directions of the electrodes 3 and 4 are all directions that intersect 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 that intersects 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. Figure 20 (a) and Figure 20 The longitudinal directions of the electrodes 3 and 4 shown in (b) are switched orthogonally. Figure 20 (a) and Figure 20 In (b), the electrodes 3 and 4 may be extended along 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 Figure 20 (a) and Figure 20 (b) becomes extended in the direction in which the electrodes 3 and 4 extend. Moreover, a pair of adjacent structures of an electrode 3 connected to one potential and an electrode 4 connected to another potential is provided in a direction orthogonal to the longitudinal direction of the electrodes 3 and 4. Here, the so-called adjacent electrodes 3 and 4 refer to the situation where the electrodes 3 and 4 are arranged with a gap between them, rather than the situation where the electrodes 3 and 4 are arranged in direct contact. In addition, when the electrodes 3 and 4 are adjacent, no electrodes connected to the signal electrode or the ground electrode, including other electrodes 3 and 4, are arranged between the electrodes 3 and 4. The number of pairs does not need to be an integer number of pairs, 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 dimension of the electrodes 3 and 4 in the opposing direction, 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. In addition, the so-called center-to-center distance between electrodes 3 and 4 is the distance connecting the center of the size (width dimension) of electrode 3 in a direction perpendicular to the length direction of electrode 3 and the center of the size (width dimension) of electrode 4 in a direction perpendicular to the length direction of electrode 4.

[0172] Furthermore, in elastic wave device 1, since a Z-cut piezoelectric layer is used, the direction perpendicular to the longitudinal direction of electrodes 3 and 4 is perpendicular to the polarization direction of piezoelectric layer 2. This is not the case when a piezoelectric layer 2 is formed using a piezoelectric body with a different cut angle. Here, "perpendicular" is not limited to being strictly perpendicular; it may also be substantially perpendicular (for example, the angle formed by the direction perpendicular to the longitudinal direction of electrodes 3 and 4 and the polarization direction is within the range of 90°±10°).

[0173] On the second main surface 2b side of the piezoelectric layer 2, a support member 8 is stacked via an insulating layer 7. The insulating layer 7 and the support member 8 have a frame shape. Figure 21 As shown, it has 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 laminated 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 laminated directly or indirectly on the second main surface 2b of the piezoelectric layer 2.

[0174] The insulating layer 7 comprises silicon oxide. However, in addition to silicon oxide, suitable insulating materials such as silicon oxynitride and alumina can be used. The support member 8 comprises Si. The plane orientation of the Si surface on the piezoelectric layer 2 side can be (100), (110), or (111). The Si constituting the support member 8 is preferably a high resistance with a resistivity of 4 kΩcm or more. However, the support member 8 can also be composed of a suitable insulating material or semiconductor material.

[0175] As the material of the supporting member 8, for example, piezoelectric bodies 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.

[0176] The plurality of electrodes 3, 4 and first and second bus bars 5, 6 are made of a suitable metal or alloy, such as aluminum or an AlCu alloy. In elastic wave device 1, electrodes 3, 4 and first and second bus bars 5, 6 have a structure in which an aluminum film is laminated on a titanium film. Alternatively, an adhesive layer other than a titanium film may be used.

[0177] During driving, an AC voltage is applied between the multiple electrodes 3 and the multiple electrodes 4. More specifically, an AC voltage is applied between the first bus bar 5 and the second bus bar 6. This allows for resonance characteristics that utilize bulk waves in the thickness-shear mode excited in the piezoelectric layer 2. Furthermore, in the elastic wave device 1, when the thickness of the piezoelectric layer 2 is denoted as d and the center-to-center distance between any adjacent pairs of electrodes 3 and 4 is denoted as p, d / p is set to be less than 0.5. Consequently, bulk waves in the thickness-shear mode described above can be effectively excited, resulting in excellent resonance characteristics. More preferably, d / p is less than 0.24, in which case even better resonance characteristics can be achieved.

[0178] In the elastic wave device 1, because 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 unlikely to decrease. This is because even if the number of electrode fingers in the reflectors on both sides is reduced, the propagation loss is reduced. In addition, the reduction in the number of electrode fingers is possible because the bulk wave of the thickness shear mode is utilized. Figure 22 (a) and Figure 22 (b) illustrates the difference between Lamb waves used in elastic wave devices and the bulk waves of the thickness shear mode described above.

[0179] Figure 22 (a) is a schematic front cross-sectional view for explaining the Lamb wave propagating through the piezoelectric film of the elastic wave device described in Japanese Patent Application Publication 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 main surface 201a and the second main surface 201b are opposite to each other, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the Z direction. The X direction is the direction in which the electrode fingers of the IDT electrode are arranged. Figure 22 As shown in (a), Lamb waves propagate in the X direction as shown. Since these are plate waves, the piezoelectric film 201 vibrates as a whole, but the waves propagate in the X direction. Therefore, the placement of reflectors on both sides creates a resonant characteristic. This results in wave propagation loss, and when miniaturization is achieved, that is, when the number of electrode finger pairs is reduced, the Q value decreases.

[0180] In contrast, Figure 22 As shown in (b), in elastic wave device 1, because the vibration displacement occurs in the thickness shear direction, the wave propagates and resonates primarily in the direction connecting the first principal surface 2a and the second principal surface 2b of piezoelectric layer 2, that is, the Z direction. In other words, the X-direction component of the wave is significantly smaller than the Z-direction component. Furthermore, because the resonant characteristics are achieved through the propagation of the wave in the Z direction, propagation loss is less likely to occur even when the number of electrode fingers in the reflector is reduced. Furthermore, even when the number of electrode pairs, including electrodes 3 and 4, is reduced to promote miniaturization, a decrease in the Q value is less likely to occur.

[0181] In addition, if Figure 23 As shown, the amplitude directions of the bulk 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. Figure 23, schematically illustrates a bulk wave generated when a voltage is applied between electrodes 3 and 4 such that electrode 4 has a higher potential than electrode 3. A first region 451 is a region within the excitation region C between the first principal surface 2a and an imaginary plane VP1, which is perpendicular to the thickness direction of the piezoelectric layer 2 and divides the piezoelectric layer 2 into two parts. A second region 452 is a region within the excitation region C between the imaginary plane VP1 and the second principal surface 2b.

[0182] As described above, elastic wave device 1 includes at least one pair of electrodes, namely, electrode 3 and electrode 4. However, since waves are not propagated in the X direction, the number of pairs of electrodes 3 and 4 does not need to be large. In other words, at least one pair of electrodes is sufficient.

[0183] For example, electrode 3 is connected to a signal potential, and electrode 4 is connected to a ground potential. However, electrode 3 may be connected to a ground potential, and electrode 4 may be connected to a signal potential. In elastic wave device 1, as described above, at least one pair of electrodes is connected to a signal potential or to a ground potential, and no floating electrode is provided.

[0184] Figure 24 It shows Figure 21 The resonance characteristics of the elastic wave device are shown in FIG. The design parameters of the elastic wave device 1 for obtaining the resonance characteristics are as follows.

[0185] Piezoelectric layer 2: LiNbO3 with Euler angles (0°, 0°, 90°), thickness = 400 nm.

[0186] When observed in a direction perpendicular 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.

[0187] Insulating layer 7: a silicon oxide film with a thickness of 1 μm.

[0188] Support member 8: Si.

[0189] The length of the excitation region C refers to the dimension of the excitation region C along the longitudinal direction of the electrodes 3 and 4 .

[0190] In elastic wave device 1 , the inter-electrode distances of the electrode pairs including electrodes 3 and 4 are set equal among all pairs. In other words, electrodes 3 and electrodes 4 are arranged at equal intervals.

[0191] Depend on Figure 24 It can be seen that, despite the absence of a reflector, a good resonance characteristic with a fractional bandwidth of 12.5% ​​is obtained.

[0192] Furthermore, 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. Figure 25 Explain this.

[0193] and get Figure 24 The elastic wave devices having the same resonant characteristics as shown above were obtained by varying d / p. Figure 25 3 is a graph showing the relationship between d / p and the fractional bandwidth of a resonator as an elastic wave device.

[0194] Depend on Figure 25 It 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 varied 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 bulk wave of the thickness shear mode described above can be constructed.

[0195] Figure 26 This is a top view of an elastic wave device utilizing bulk waves in a thickness shear mode. 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. Figure 26 K in is the crossover width. As described above, in the elastic wave device of the present invention, the number of electrode pairs may be one. In this case, if d / p is 0.5 or less, bulk waves in the thickness shear mode can be effectively excited.

[0196] In the elastic wave device 1, it is preferred that the metallization ratio MR of any adjacent electrodes 3 and 4 relative to the excitation region C satisfies MR ≤ 1.75(d / p) + 0.075. This excitation region C is the region where the adjacent electrodes 3 and 4 overlap when viewed in opposing directions. In this case, spurious emission can be effectively reduced. Figure 27 as well as Figure 28 Explain this. Figure 27This is a reference graph showing an example of the resonance characteristics of the elastic wave device 1. Spurious signals, indicated by arrow B, appear between the resonant frequency and the antiresonant frequency. d / p is assumed to be 0.08, and the Euler angles of LiNbO3 are assumed to be (0°, 0°, 90°). Furthermore, the metallization ratio MR is assumed to be 0.35.

[0197] Reference Figure 20 (b) is used to illustrate the metallization ratio MR. Figure 20 In the electrode structure of (b), when focusing on the 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 of electrode 3 overlapping with electrode 4, the region of electrode 4 overlapping with electrode 3, and the region between electrodes 3 and 4 where electrodes 3 and 4 overlap when viewing electrodes 3 and 4 in a direction perpendicular to the longitudinal direction of electrodes 3 and 4, that is, in the opposing direction. The area of ​​electrodes 3 and 4 within the excitation region C relative to the area of ​​the excitation region C is the metallization ratio MR. In other words, the metallization ratio MR is the ratio of the area of ​​the metallized portion to the area of ​​the excitation region C.

[0198] Furthermore, when a plurality of pairs of electrodes are provided, the ratio of the metallized portions included in all the excitation regions to the total area of ​​the excitation regions may be defined as MR.

[0199] Figure 28 This graph shows the relationship between the fractional bandwidth and the phase rotation of the impedance of the spurious signal normalized by 180 degrees, which is the magnitude of the spurious signal, when a large number of spurious wave resonators are formed according to the structure of the spurious wave device 1. The fractional bandwidth was adjusted by making various changes to the thickness of the piezoelectric layer and the dimensions of the electrodes. Figure 28 These are the results obtained when a piezoelectric layer containing Z-cut LiNbO 3 is used, but the same tendency is observed when piezoelectric layers having other cut angles are used.

[0200] exist Figure 28 In the area surrounded by ellipse J, the spurious signal becomes as large as 1.0. Figure 28 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 signals with a spurious level of 1 or more will appear in the passband. Figure 27 As shown in the resonance characteristics, large spurious signals appear within the frequency band, as indicated by arrow B. Therefore, the fractional bandwidth is preferably 17% or less. In this case, spurious signals can be reduced by adjusting the thickness of the piezoelectric layer 2, the dimensions of the electrodes 3 and 4, and the like.

[0201] Figure 29Graph showing the relationship between d / 2p, metallization ratio MR, and fractional bandwidth. Various elastic wave devices having different d / 2p and MR were constructed in the aforementioned elastic wave devices, and the fractional bandwidths were measured. Figure 29 The hatched portion to the right 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 preferable 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, Figure 29 The region to the right of MR=3.5(d / 2p)+0.05 indicated by the dashed line D1 in FIG. That is, if MR≤1.75(d / p)+0.05, the fractional bandwidth can be reliably set to 17% or less.

[0202] Figure 30 This is a diagram showing a map of the fractional bandwidth with respect to the Euler angles (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible. Figure 30 The multiple regions R shown with hatching are regions where a fractional bandwidth of 2% or more can be obtained. In addition, when φ in the Euler angles (φ, θ, ψ) is within the range of 0°±5°, the relationship between θ and ψ and the fractional bandwidth is the same as Figure 30 When the piezoelectric layer contains lithium tantalate (LiTaO3), the relationship between θ and ψ in the Euler angle (within the range of 0°±5°, θ, ψ) and BW is also the same as Figure 30 The relationship shown is the same.

[0203] Therefore, if the Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of 0°±5°, θ and φ are within the range of Figure 30 The fractional bandwidth can be sufficiently expanded within the range of any of the plurality of regions R shown, which is preferable.

[0204] Figure 31 This is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0205] In the elastic wave device 81, an acoustic multilayer film 82 is laminated on the second principal surface 2b of the piezoelectric layer 2. The acoustic multilayer film 82 has a laminated structure comprising low-acoustic impedance layers 82a, 82c, and 82e, each with relatively low acoustic impedance, and high-acoustic impedance layers 82b and 82d, each with relatively high acoustic impedance. The use of the acoustic multilayer film 82 allows bulk waves in the thickness-shear mode to be confined within the piezoelectric layer 2, even without utilizing the cavity 9 in the elastic wave device 1. In the elastic wave device 81, by setting the d / p ratio to 0.5 or less, resonance characteristics based on bulk waves in the thickness-shear mode can be achieved. Furthermore, the number of low-acoustic impedance layers 82a, 82c, and 82e and high-acoustic impedance layers 82b and 82d laminated in the acoustic multilayer film 82 is not particularly limited. It suffices to arrange at least one high-acoustic impedance layer 82b or 82d farther from the piezoelectric layer 2 than the low-acoustic impedance layers 82a, 82c, and 82e.

[0206] The low-acoustic-impedance layers 82a, 82c, 82e and the high-acoustic-impedance layers 82b, 82d can be made of any suitable material, as long as the above-mentioned acoustic impedance relationship is satisfied. For example, silicon oxide or silicon oxynitride can be used as the material for the low-acoustic-impedance layers 82a, 82c, and 82e. Furthermore, alumina, silicon nitride, or metal can be used as the material for the high-acoustic-impedance layers 82b and 82d.

[0207] Figure 32 This is a partially cutaway perspective view for explaining an elastic wave device utilizing Lamb waves.

[0208] The elastic wave device 91 has a supporting substrate 92. A recessed portion is provided on the upper surface of the supporting substrate 92. A piezoelectric layer 93 is stacked on the supporting 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 the elastic wave. Figure 32 In the figure, the outer periphery of cavity 9 is indicated by a dotted line. Here, IDT electrode 94 includes 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 first bus bar 94a. The plurality of second electrode fingers 94d are connected to second bus bar 94b. The plurality of first electrode fingers 94c and the plurality of second electrode fingers 94d are interlaced with each other.

[0209] In elastic wave device 91, Lamb waves, which are plate waves, are excited by applying an AC electric field to IDT electrode 94 on cavity 9. Furthermore, since reflectors 95 and 96 are provided on both sides, resonance characteristics based on the Lamb waves can be obtained.

[0210] Thus, the elastic wave device of the present invention may also be an elastic wave device utilizing plate waves. Figure 32 In the example shown, the Figure 1 The first principal surface 14a of the piezoelectric layer 14 shown in FIG. 1 is provided with an IDT electrode 94, a reflector 95, and a reflector 96. Meanwhile, in the elastic wave device of the present invention, a pair of comb-shaped electrodes is provided on the first principal surface 14a, and a plurality of third electrode fingers are provided on the first principal surface 14a or the second principal surface 14b, or a structure equivalent thereto. If the elastic wave device of the present invention is an elastic wave device utilizing plate waves, it suffices to provide the reflectors 95 and 96 described above on the first principal surface 14a of the piezoelectric layer 14 in the first to third embodiments and their respective modifications. In this case, in a plan view, the reflectors 95 and 96 suffice to sandwich the pair of comb-shaped electrodes and the plurality of third electrode fingers, or portions equivalent thereto, in a direction orthogonal to the electrode fingers.

[0211] In the elastic wave devices of the first to third embodiments and their modifications, for example, an acoustic reflection film may be provided between the support member and the piezoelectric layer as the piezoelectric film. Figure 31 The acoustic multilayer film 82 shown. Specifically, the support member and the piezoelectric film can be arranged so that at least a portion of the support member and at least a portion of the piezoelectric film face each other with the acoustic multilayer film 82 sandwiched therebetween. In this case, low-acoustic-impedance layers and high-acoustic-impedance layers can be alternately stacked in the acoustic multilayer film 82. The acoustic multilayer film 82 can also serve as an acoustic reflector in an elastic wave device.

[0212] In the elastic wave devices of the first to third embodiments and their modifications utilizing thickness shear mode bulk waves, as described above, d / p is preferably 0.5 or less, and more preferably 0.24 or less. This allows for even better resonance characteristics.

[0213] Furthermore, in the excitation region of the elastic wave devices in the first and second embodiments and their variations, which utilize bulk waves in the thickness shear mode, MR ≤ 1.75(d / p) + 0.075 is preferably satisfied, as described above. More specifically, when the metallization ratios of the first and third electrode fingers and the second and third electrode fingers relative to the excitation region are defined as MR, MR ≤ 1.75(d / p) + 0.075 is preferably satisfied. This allows for more reliable suppression of spurious emissions.

[0214] In the third embodiment utilizing bulk waves in the thickness shear mode, the metallization ratio (MR) of each first layer of each electrode finger is defined similarly to the above. Furthermore, when the metallization ratios of the first layers of the first and third electrode fingers, and the first layers of the second and third electrode fingers, are defined as MR, it is preferred that MR ≤ 1.75 (d / p) + 0.075 be satisfied. This allows for more reliable suppression of spurious emissions.

[0215] Description of Reference Numerals

[0216] 1…Elastic wave device

[0217] 2…Piezoelectric layer

[0218] 2a, 2b…1st main surface, 2nd main surface

[0219] 3, 4...Electrodes

[0220] 5, 6…Bus bar 1, bus bar 2

[0221] 7…Insulation layer

[0222] 7a…Through hole

[0223] 8…Supporting member

[0224] 8a…Through hole

[0225] 9…Cavity

[0226] 10…Elastic wave device

[0227] 10a…cavity

[0228] 11…Functional electrode

[0229] 12…Piezoelectric substrate

[0230] 13…Supporting member

[0231] 14…Piezoelectric layer

[0232] 14a, 14b…1st main surface, 2nd main surface

[0233] 15…Insulation layer

[0234] 16…Support base plate

[0235] 17, 18…1st comb-shaped electrode, 2nd comb-shaped electrode

[0236] 19…3rd electrode

[0237] 22-24…Bus bars 1 to 3

[0238] 24A, 24B...1st connecting electrode, 2nd connecting electrode

[0239] 24a...Section

[0240] 24b…protrusion

[0241] 25-27…1st electrode finger to 3rd electrode finger

[0242] 29…Insulation film

[0243] 34…Connecting electrodes

[0244] 39…3rd electrode

[0245] 40…Elastic wave device

[0246] 41…Functional Department

[0247] 45-47...1st electrode finger portion to 3rd electrode finger portion

[0248] 45a~47a…1st floor

[0249] 45b~47b…2nd floor

[0250] 80, 81… elastic wave device

[0251] 82…Acoustic multilayer film

[0252] 82a, 82c, 82e…low acoustic impedance layer

[0253] 82b, 82d…high acoustic impedance layer

[0254] 91…Elastic wave device

[0255] 92…Support base plate

[0256] 93…Piezoelectric layer

[0257] 94…IDT electrode

[0258] 94a, 94b…1st bus bar, 2nd bus bar

[0259] 94c, 94d...first electrode finger, second electrode finger

[0260] 95, 96…reflectors

[0261] 201…Piezoelectric film

[0262] 201a, 201b…1st main surface, 2nd main surface

[0263] 451, 452…Area 1, Area 2

[0264] C…Incentive Area

[0265] E…Intersection area

[0266] R…Region

[0267] VP1…imaginary plane.

Claims

1. An elastic wave device comprising: A piezoelectric film including a piezoelectric layer, wherein the piezoelectric layer includes lithium niobate and has a first main surface and a second main surface facing each other; a first comb-shaped portion, provided on the first main surface of the piezoelectric layer, having a first bus bar portion and a plurality of first electrode fingers each having one end connected to the first bus bar portion, and connected to an input potential; a second comb-shaped portion, disposed on the first main surface of the piezoelectric layer, having a second bus bar portion and a plurality of second electrode fingers each having one end connected to the second bus bar portion, connected to an output potential, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and The third portion has a plurality of third electrode fingers and a connection portion connecting adjacent third electrode fingers to each other, and is connected to a potential different from that of the first comb-shaped portion and the second comb-shaped portion, wherein the plurality of third electrode fingers are respectively arranged on the first main surface of the piezoelectric layer so as to be arranged side by side 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 when viewed from above. The order in which the first electrode finger portion, the second electrode finger portion, and the third electrode finger portion are arranged is, when starting from the first electrode finger portion, an order in which the first electrode finger portion, the third electrode finger portion, the second electrode finger portion, and the third electrode finger portion are set as one cycle, The first electrode finger portion, the second electrode finger portion, and the third electrode finger portion each include at least one layer, and the at least one layer includes a layer containing a material containing Al as a main component. Three adjacent electrode fingers in the order of the first electrode finger, the third electrode finger, and the second electrode finger are set as a group of electrode fingers, and when the product of a value obtained by dividing the density of the at least one layer by the density of Al and the thickness of the layer in each of the group of electrode fingers is set as the Al normalized thickness of the layer, the value obtained by adding up the Al normalized thicknesses of all the layers is the electrode finger thickness de of each of the group of electrode fingers, When the width of each of the group of electrode fingers is set to the electrode finger width me, the average of the center-to-center distance between the first electrode finger and the third electrode finger adjacent to each other in the group of electrode fingers and the center-to-center distance between the second electrode finger and the third electrode finger is set to the average center-to-center distance pa, and the thickness of the piezoelectric film is set to d, in each of the group of electrode fingers, one of 0.65≤de / d≤1.15 and me / pa≤0.5, and de / d≤0.25 is satisfied.

2. An elastic wave device comprising: A piezoelectric film including a piezoelectric layer, wherein the piezoelectric layer includes lithium niobate and has a first main surface and a second main surface facing each other; a first comb-shaped portion, provided on the first main surface of the piezoelectric layer, having a first bus bar portion and a plurality of first electrode fingers each having one end connected to the first bus bar portion, and connected to an input potential; a second comb-shaped portion, disposed on the first main surface of the piezoelectric layer, having a second bus bar portion and a plurality of second electrode fingers each having one end connected to the second bus bar portion, connected to an output potential, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and The third portion has a plurality of third electrode fingers and a connecting portion connecting adjacent third electrode fingers to each other, and is connected to a potential different from that of the first comb-shaped portion and the second comb-shaped portion, wherein the plurality of third electrode fingers are respectively arranged on the second main surface of the piezoelectric layer so as to be arranged side by side 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 when viewed from above. The order in which the first electrode finger portion, the second electrode finger portion, and the third electrode finger portion are arranged is, when starting from the first electrode finger portion, an order in which the first electrode finger portion, the third electrode finger portion, the second electrode finger portion, and the third electrode finger portion are set as one cycle, The first electrode finger portion, the second electrode finger portion, and the third electrode finger portion each include at least one layer, and the at least one layer includes a layer containing a material containing Al as a main component. Three adjacent electrode fingers in the order of the first electrode finger, the third electrode finger, and the second electrode finger are set as a group of electrode fingers, and when the product of a value obtained by dividing the density of the at least one layer by the density of Al and the thickness of the layer in each of the group of electrode fingers is set as the Al normalized thickness of the layer, the value obtained by adding up the Al normalized thicknesses of all the layers is the electrode finger thickness de of each of the group of electrode fingers, When the width of each of the group of electrode fingers is set to the electrode finger width me, the average of the center-to-center distance between the first electrode finger and the third electrode finger adjacent to each other in the group of electrode fingers and the center-to-center distance between the second electrode finger and the third electrode finger is set to the average center-to-center distance pa, and the thickness of the piezoelectric film is set to d, in each of the group of electrode fingers, 0.7≤de / d≤1.5 and me / pa≤0.

15.

3. The elastic wave device according to claim 1, wherein: When the electrode finger width of the third electrode finger in the group of electrode fingers is denoted as mg, mg / pa≥0.

5.

4. The elastic wave device according to any one of claims 1 to 3, wherein: At least one of the electrode finger width and the electrode finger thickness is different between the third electrode finger and at least one of the first electrode finger and the second electrode finger in the set of electrode fingers.

5. The elastic wave device according to any one of claims 1 to 4, wherein: The elastic wave device is configured to utilize thickness shear mode body waves.

6. The elastic wave device according to any one of claims 1 to 4, wherein: The elastic wave device further includes a supporting member stacked on the piezoelectric film. 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 overlapping 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 electrode finger portion and the third electrode finger portion and the centers of the adjacent second electrode finger portion and the third electrode finger portion is represented by p, d / p is equal to or less than 0.

5.

7. The elastic wave device according to claim 6, wherein: d / p is less than 0.

24.

8. The elastic wave device according to claim 6 or 7, wherein: The sound reflecting portion is a cavity portion, and the supporting member and the piezoelectric film are arranged so that a portion of the supporting member and a portion of the piezoelectric film face each other with the cavity portion interposed therebetween.

9. The elastic wave device according to claim 6 or 7, 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.

10. The elastic wave device according to any one of claims 6 to 9, 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 an 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 metallization ratios 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 are denoted as MR, MR≦1.75(d / p)+0.075 is satisfied.

11. The elastic wave device according to any one of claims 1 to 10, 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), (within the range of 0°±10°, 0°~25°, any 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).

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