Elastic wave device

Abstract

Provided is an elastic wave device capable of promoting miniaturization of a filter device and capable of widening the bandwidth of a passband. An elastic wave device (10) according to the present invention is provided with: a piezoelectric film including a piezoelectric layer (14); a first comb electrode (17) that is provided on the piezoelectric layer (14), has a first bus bar (22) and a plurality of first electrode fingers (25) each having one end connected to the first bus bar (22), and is connected to an input potential; a second comb electrode (18) provided on the piezoelectric layer (14), having a second bus bar (23) and a plurality of second electrode fingers (26) each having one end connected to the second bus bar (23), and connected to the output potential, the plurality of second electrode fingers (26) and the plurality of first electrode fingers (25) being interleaved with each other; and a third electrode (19) having a plurality of third electrode fingers (27) and a third bus bar (24) that connects adjacent third electrode fingers (27) to each other, the third electrode fingers (27) being connected to a different potential from the first comb electrode (17) and the second comb electrode (18), the plurality of third electrode fingers (27) being provided on the piezoelectric layer (14) such that, in a plan view, the first electrode fingers (25) and the second electrode fingers (26) are aligned in the direction in which the first electrode fingers (25) and the second electrode fingers (26) are aligned, and the third bus bar (24) being aligned in the direction in which the first electrode fingers (25) and the second electrode fingers (26) are aligned in the direction in which the first electrode fingers (25) and the second electrode fingers (26) are aligned. The first electrode finger (25) and the second electrode finger (26) are aligned with each other. A third electrode finger (27) is disposed between the first electrode finger (25) and the second electrode finger (26) disposed at positions closest to each other. When the direction orthogonal to the direction in which the first electrode fingers (25), the second electrode fingers (26), and the third electrode fingers (27) extend is defined as the direction orthogonal to the electrode fingers, at least one type of electrode fingers among the plurality of first electrode fingers (25), the plurality of second electrode fingers (26), and the plurality of third electrode fingers (27) include two or more continuous electrode fingers arranged continuously in the direction orthogonal to the electrode fingers.

Description

Technical Field

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

[0002] In the past, elastic wave devices were widely used in filters for mobile phones and other applications. In recent years, an elastic wave device utilizing thickness-shear mode bulk waves, such as that described in Patent Document 1 below, has been proposed. This elastic wave device comprises a piezoelectric layer disposed on a support. Pairs of electrodes are 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] Elastic wave devices, such as elastic wave resonators, are used, for example, in ladder filters. To achieve good performance in ladder filters, 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-type filter, the ladder-type filter often becomes larger. In particular, ladder-type 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, a suitable filter waveform can be obtained without increasing the size of the device when the elastic wave device is used in a filter device. This configuration comprises an electrode connected to a potential different from the input and output potentials, such as a reference potential, disposed between an electrode connected to an input potential and an electrode connected to an output potential.

[0010] Furthermore, the inventors of the present invention have discovered that the bandwidth of the passband may not be sufficiently widened even with only the above-mentioned structure.

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

[0012] Technical solutions to solve problems

[0013] The elastic wave device according to the present invention comprises: a piezoelectric film including a piezoelectric layer; a first comb-shaped electrode arranged on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, and connected to an input potential; a second comb-shaped electrode arranged on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers each having one end connected to the second bus bar, and connected to an output potential, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a third electrode having a plurality of third electrode fingers and a third bus bar connecting adjacent third electrode fingers to each other, and connected to a potential different from that of the first comb-shaped electrode and the second comb-shaped electrode. The plurality of third electrode fingers are respectively arranged on the piezoelectric layer so that, when viewed from above, the third electrode fingers are arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged, and are arranged between the first electrode finger and the second electrode finger that are arranged at the closest positions to each other. When the direction orthogonal to the direction in which the first electrode finger, the second electrode finger and the third electrode finger extend is set as the electrode finger orthogonal direction, at least one type of electrode finger among the plurality of first electrode fingers, the plurality of second electrode fingers and the plurality of third electrode fingers includes two or more continuous electrode fingers continuously arranged in the electrode finger orthogonal direction.

[0014] Effects of the Invention

[0015] According to the present invention, an elastic wave device can be provided that can contribute to miniaturization of a filter device and widen the passband bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0017] Figure 2 It is a schematic plan view of the elastic wave device according to the first embodiment of the present invention.

[0018] 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.

[0019] Figure 4 1 is a schematic top view of an elastic wave device according to a reference example.

[0020] Figure 5 It is a diagram showing the transmission characteristics of the first embodiment of the present invention and a reference example.

[0021] Figure 6Schematic front cross-sectional view showing the vicinity of the first to third electrode fingers in a reference example for explaining the odd-numbered mode.

[0022] Figure 7 Schematic front cross-sectional view showing the vicinity of first to third electrode fingers in a reference example for explaining the even-numbered mode.

[0023] Figure 8 This is a diagram schematically showing the formation of a passband in an acoustic coupling filter.

[0024] Figure 9 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.

[0025] Figure 10 This is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers in a modification of the first embodiment of the present invention.

[0026] Figure 11 It is a schematic plan view of an elastic wave device according to a second embodiment of the present invention.

[0027] Figure 12 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.

[0028] Figure 13 (a) is a schematic perspective view showing the appearance of an elastic wave device utilizing bulk waves in a thickness shear mode. Figure 13 (b) is a top view showing the electrode structure on the piezoelectric layer.

[0029] Figure 14 It is along Figure 13 (a) is a cross-sectional view of a portion taken along line AA.

[0030] Figure 15 (a) is a schematic front cross-sectional view for explaining Lamb waves propagating through a piezoelectric film of an elastic wave device. Figure 15 (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.

[0031] Figure 16 Graph showing the amplitude direction of the body wave in the thickness shear mode.

[0032] Figure 17 Graphs showing resonance characteristics of an elastic wave device utilizing bulk waves in a thickness shear mode.

[0033] Figure 18Graph 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.

[0034] Figure 19 This is a top view of an elastic wave device that utilizes bulk waves in the thickness shear mode.

[0035] Figure 20 Graphs showing resonance characteristics of an elastic wave device according to a reference example in which spurious emission occurs.

[0036] Figure 21 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.

[0037] Figure 22 It is a graph showing the relationship between d / 2p and the metallization ratio MR.

[0038] Figure 23 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.

[0039] Figure 24 This is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0040] Figure 25 This is a partially cutaway perspective view for explaining an elastic wave device utilizing Lamb waves. DETAILED DESCRIPTION

[0041] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings to clarify the present invention.

[0042] 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.

[0043] 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, hatching is used to indicate each electrode. Figure 2 Similarly, in other schematic plan views, electrodes may be hatched.

[0044] Figure 1The 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.

[0045] The elastic wave device 10 includes a piezoelectric substrate 12 and a functional electrode 11. 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 serving as a piezoelectric film. The piezoelectric layer 14 is a layer including a piezoelectric body. On the other hand, in this specification, the term "piezoelectric film" refers to a film having piezoelectric properties, not necessarily a film including a piezoelectric body. However, in this embodiment, the piezoelectric film is a single-layer piezoelectric layer 14 including a piezoelectric body. Furthermore, in the present invention, the piezoelectric film may 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. Without being limited to the above, the supporting member 13 may be composed solely of the supporting substrate 16. Alternatively, the supporting member 13 may not necessarily be provided.

[0046] 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. Alternatively, the piezoelectric layer 14 may also include lithium tantalate such as LiTaO3. In this specification, the so-called "a certain component includes a certain material" includes the case where the material contains a trace amount of impurities to the extent that the electrical characteristics of the elastic wave device are not significantly deteriorated.

[0047] The functional electrode 11 is provided on the first main surface 14a of the piezoelectric layer 14. Figure 2 As shown, the functional electrode 11 includes a pair of comb-shaped electrodes and a third electrode 19. The pair of comb-shaped electrodes specifically includes 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. Furthermore, the third electrode 19 does not necessarily need to be connected to a reference potential. The third electrode 19 may 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 a reference potential.

[0048] 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.

[0049] 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.

[0050] 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 14a of the piezoelectric layer 14. The plurality of third electrode fingers 27 are electrically connected to each other via the third bus bar 24.

[0051] The plurality of third electrode fingers 27 are arranged 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, as viewed from above. Therefore, the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 are aligned in the same 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.

[0052] In this specification, the term "top view" refers to a view from the Figure 1 The direction above 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 the upper side. Furthermore, in this specification, viewing from above is synonymous with viewing from the principal surface facing direction. 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, the principal surface facing direction is, for example, the direction normal to the first principal surface 14a.

[0053] 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 extending direction, and the direction orthogonal to the electrode finger extending direction is referred to as the electrode finger orthogonal direction. When the direction in which the first electrode 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."

[0054] Figure 3This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers in the first embodiment.

[0055] Two third electrode fingers 27 are arranged between the first electrode fingers 25 and the second electrode fingers 26. In this embodiment, the third electrode fingers 27 are continuous electrode fingers. Continuous electrode fingers are defined as two or more electrode fingers arranged continuously in a direction perpendicular to the electrode fingers and connected to the same potential. Hereinafter, a group of two or more continuous electrode fingers arranged continuously in a direction perpendicular to the electrode fingers will sometimes be referred to as a group of continuous electrode fingers.

[0056] When a group of consecutive electrode fingers is considered a single electrode finger, the order in which the multiple electrode fingers are arranged, starting with first electrode finger 25, is such that 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. If "IN" represents the input potential, "OUT" represents the output potential, and "GND" represents the reference potential, and the order of the multiple electrode fingers is represented as the order of the connected potentials, then "IN", "GND", "OUT", "GND", "IN", "GND", "OUT", and so on.

[0057] In the present invention, at least one of the plurality of first electrode fingers 25, the plurality of second electrode fingers 26, and the plurality of third electrode fingers 27 may comprise continuous electrode fingers. For example, the plurality of first electrode fingers 25 may comprise continuous electrode fingers. In this case, two or more first electrode fingers 25 may be provided continuously between the third electrode fingers 27.

[0058] Alternatively, the plurality of second electrode fingers 26 may include continuous electrode fingers. In this case, two or more second electrode fingers 26 may be provided continuously between the third electrode fingers 27. In these cases, the third electrode fingers 27 may be provided between the first electrode fingers 25 and the second electrode fingers 26 that are located closest to each other.

[0059] 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. Alternatively, 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.

[0060] like Figure 2As shown, third bus bar 24, serving as a connecting electrode for third electrode 19, electrically connects third electrode fingers 27. Specifically, third bus bar 24 is located in the region between first bus bar 22 and the tips of second electrode fingers 26. First electrode fingers 25 are also located in this region. However, third bus bar 24 and first electrode fingers 25 are electrically insulated from each other by insulating film 29.

[0061] More specifically, the third bus bar 24 includes multiple first connecting electrodes 24A and one second connecting electrode 24B. Each first connecting electrode 24A connects the tips of four consecutive third electrode fingers 27 in a direction orthogonal to the electrode fingers. In other words, each first connecting electrode 24A connects the tips of two consecutive sets of electrode fingers. Furthermore, the second connecting electrode 24B connects multiple first connecting electrodes 24A. An insulating film 29 is provided between the second connecting electrode 24B and the multiple first electrode fingers 25.

[0062] 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 the region between the first bus bar 22 and the tips of the plurality of second electrode fingers 26. The insulating film 29 has a stripe shape.

[0063] 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 via the first connecting electrode 24A and the second connecting electrode 24B.

[0064] 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 across gaps in the electrode finger extending direction. Meanwhile, the tips of the plurality of first electrode fingers 25 face the second bus bar 23 across gaps in the electrode finger extending direction.

[0065] 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.

[0066] 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 the multiple excitation areas C are shown.

[0067] One edge of the excitation region C is the center, in the orthogonal direction, of the electrode fingers adjacent to a group of consecutive electrode fingers, among the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27, and connected to a different potential than the group of consecutive electrode fingers. The other edge is the center, in the orthogonal direction, of the group of consecutive electrode fingers. The distance between the two end edges of the excitation region C is denoted by p.

[0068] In this embodiment, a portion of the excitation regions C comprise the region between the center of the first electrode finger 25 in the orthogonal direction and the center of a group of consecutive electrode fingers adjacent to the first electrode finger 25 in the orthogonal direction. The remaining excitation regions C comprise the region between the center of the second electrode finger 26 in the orthogonal direction and the center of a group of consecutive electrode fingers adjacent to the second electrode finger 26 in the orthogonal direction. These excitation regions C are arranged in the orthogonal direction of the electrode fingers.

[0069] In the elastic wave device 10, the structure of the functional electrode 11, excluding the third electrode 19, is similar to that of an IDT (interdigital transducer) electrode. The region where adjacent first and second electrode fingers 25 and 26 overlap when viewed in a direction perpendicular to the electrode fingers is the intersection region E. However, the intersection region E can also be considered the region 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.

[0070] The following, such as Figure 3 As shown, among the electrode fingers connected to a different potential than the consecutive electrode fingers, the width of one electrode finger is m1, the width of the other electrode finger is m2, and the width of the consecutive electrode finger is me. In this embodiment, the width of the first electrode finger 25 is m1. The width of the second electrode finger 26 is m2. The width of the third electrode finger 27 is me. The width of an electrode finger refers to the dimension of the electrode finger along the direction perpendicular to the electrode finger.

[0071] The distance between an electrode finger adjacent to a continuous electrode finger and connected to a different potential than the continuous electrode finger is g1. The distance between adjacent continuous electrode fingers is g2. Distances g1 and g2 are the distances between the edges of the electrode fingers. The "edges" of the electrode fingers referred to here refer to the edges of the electrode fingers in a direction perpendicular to the electrode fingers when viewed from above.

[0072] In this embodiment, the distance between the edge of the first electrode finger 25 on the third electrode finger 27 side and the edge of the third electrode finger 27 on the first electrode finger 25 side is g1. Similarly, the distance between the edge of the second electrode finger 26 on the third electrode finger 27 side and the edge of the third electrode finger 27 on the second electrode finger 26 side is g1. The distance between adjacent edges of the third electrode fingers 27 that are close to each other is g2.

[0073] The center-to-center distance between the two types of electrode fingers connected to different potentials than consecutive electrode fingers and to different potentials is denoted as px. In this embodiment, the center-to-center distance between the first electrode finger 25 and the second electrode finger 26, which are located closest to each other, is px.

[0074] The first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 are made of Al. The material of the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 is not limited to Al. Alternatively, the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 may be made of, for example, a laminated metal film.

[0075] This embodiment is characterized by the following structures: 1) Third electrode fingers 27 are arranged between first electrode fingers 25 and second electrode fingers 26, which are positioned closest to each other in a plan view. 2) At least one type of electrode finger among the plurality of first electrode fingers 25, the plurality of second electrode fingers 26, and the plurality of third electrode fingers 27 comprises continuous electrode fingers. Consequently, when the elastic wave device 10 is used in a filter device, the filter device can be miniaturized and the passband bandwidth can be widened. This is illustrated below by comparing this embodiment with a reference example.

[0076] The difference between the reference example and the first embodiment is that Figure 4 As shown, the functional electrode does not have continuous electrode fingers. The elastic wave device of the reference example is an acoustic coupling filter. The transmission characteristics are compared in the first embodiment and the reference example. The design parameters of the elastic wave device 10 having the structure of the first embodiment are as follows. Here, the thickness of the piezoelectric film is d. In the first embodiment, thickness d is the thickness of the piezoelectric layer 14.

[0077] Piezoelectric layer: Material… Z-cut LiNbO3, thickness d… 400nm

[0078] Material of the 1st to 3rd electrode fingers: Al

[0079] Thickness of the first to third electrode fingers: 400 nm

[0080] Widths of the first to third electrode fingers: Width m1 of the first electrode finger: 420 nm, width m2 of the second electrode finger: 420 nm, width me of the third electrode finger: 350 nm

[0081] The distance g1 between the first electrode finger and the third electrode finger and the distance g1 between the second electrode finger and the third electrode finger are equal.

[0082] Distance g2 between adjacent third electrode fingers: 140 nm

[0083] Center-to-center distance px between the first and second electrode fingers: 2.8 μm

[0084] The design parameters of the reference example are the same as the design parameters of the first embodiment except that the distance g2 is 0.

[0085] Figure 5 : is a graph showing the passing characteristics of the first embodiment and the reference example. Figure 5 , the S21 passing characteristic is shown.

[0086] like Figure 5 As shown, the passband can be obtained in both the first embodiment and the reference example. It can be seen that the bandwidth of the passband can be made wider in the first embodiment than in the reference example.

[0087] The elastic wave device 10 of the first embodiment is an acoustic coupling filter. Figure 2 As shown, elastic wave device 10 includes an excitation region C located between the orthogonal center of a first electrode finger 25 and the orthogonal center of a group of consecutive electrode fingers adjacent to the first electrode finger 25. Elastic wave device 10 also includes an excitation region C located between the orthogonal center of a second electrode finger 26 and the orthogonal center of a group of consecutive electrode fingers adjacent to the second electrode finger 26. Multiple modes of elastic waves are excited in these excitation regions C.

[0088] The elastic wave device of the reference example also has multiple excitation regions. The excitation regions in the reference example are the region located between the centers of adjacent first electrode fingers 25 and third electrode fingers 27 , and the region located between the centers of adjacent second electrode fingers 26 and third electrode fingers 27 .

[0089] Figure 6 Schematic front cross-sectional view showing the vicinity of the first to third electrode fingers of a reference example for explaining the odd-numbered mode. Figure 7 Schematic front cross-sectional view showing the vicinity of the first to third electrode fingers of a reference example for explaining the even-numbered mode. Figure 8 This is a diagram schematically showing the formation of a passband in an acoustic coupling filter. Figure 6 as well as Figure 7 The arrows in show the direction of the electric field.

[0090] In acoustically coupled filters, Figure 6 The odd-numbered modes shown, and Figure 7 The even mode shown in the figure. The odd mode is the mode in which the electrical conditions are in phase. Figure 6 The figure shows the region corresponding to one wavelength of the odd-numbered mode. One wavelength of the odd-numbered mode is the distance px between the centers of adjacent first electrode fingers 25 and second electrode fingers 26. When the wavelength of the odd-numbered mode is λo, λo = px. Therefore, half the wavelength (1 / 2) λo of the odd-numbered mode is 0.5 px.

[0091] The so-called even mode is a mode in which the electrical conditions are inverted. Figure 7 The figure shows an area corresponding to half the wavelength of the even mode. Half the wavelength of the even mode is the distance px between the centers of adjacent first electrode fingers 25 and second electrode fingers 26. When the wavelength of the even mode is λe, (1 / 2)λe = px. The wavelength of the even mode λe is twice the wavelength of the odd mode λo.

[0092] 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.

[0093] Figures 6 to 8 The modes and passbands shown are based on the structure of the acoustic coupling filter of the reference example. Furthermore, in the first embodiment, as in the reference example, the passband is formed by odd and even modes. In this way, a suitable filter waveform can be obtained even with a single elastic wave device 10. When the elastic wave device 10 is used as an elastic wave resonator in a filter device, a suitable filter waveform can be obtained even if the filter device comprises only one or a small number of elastic wave resonators. This facilitates miniaturization of the filter device.

[0094] Furthermore, in the first embodiment, the functional electrode 11 has continuous electrode fingers, which enables mode control and widening of the passband.

[0095] As in the first embodiment, the third electrode fingers 27 are preferably continuous electrode fingers. This allows for obtaining suitable filter characteristics.

[0096] In more detail, Figure 7 As shown, in the reference example, mass is added by the third electrode fingers 27 in a region corresponding to half the wavelength of the even mode. The same is true in the first embodiment. However, in the first embodiment, the third electrode fingers 27 are continuous. By adjusting the arrangement and width of the plurality of third electrode fingers 27 forming a group of continuous electrode fingers, the addition of mass in a region corresponding to half the wavelength of the even mode can be easily adjusted. This allows the frequency of the even mode to be adjusted, resulting in optimal filter characteristics.

[0097] Preferably Figure 3 As shown in the first embodiment, the relationship between the distance g1 and the distance g2 is g2 ≤ g1. This can reduce the influence of the continuous electrode fingers on the odd-numbered modes, thereby making it less likely that the filter characteristics will deteriorate.

[0098] Hereinafter, the structure of this embodiment will be described in more detail.

[0099] 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.

[0100] 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.

[0101] A recess is provided in the insulating layer 15. A piezoelectric layer 14 as a piezoelectric film is provided on the insulating layer 15 so as to block the recess. Thus, a hollow portion is formed. The hollow portion is a cavity 10a. In the present embodiment, the supporting member 13 and the piezoelectric film are configured so that a portion of the supporting member 13 and a portion of the piezoelectric film are opposed to each other with the cavity 10a sandwiched therebetween. However, the recess in the supporting member 13 may 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. The recess may also be provided in the piezoelectric layer 14, for example. In addition, the cavity 10a may also be a through hole provided in the supporting member 13.

[0102] The cavity 10a is the acoustic reflector in the present invention. The acoustic reflector effectively confines the energy of elastic waves to the piezoelectric layer 14. The acoustic reflector can be positioned in a position within the support member 13 that overlaps at least a portion of the functional electrode 11 when viewed from above. More specifically, when viewed from above, at least a portion of each of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 overlaps with the acoustic reflector. Preferably, when viewed from above, the plurality of excitation regions C overlap with the acoustic reflector.

[0103] The acoustic reflective portion may be an acoustic reflective film such as an acoustic multilayer film described later. For example, an acoustic reflective film may be provided on the surface of the support member.

[0104] As described above, one end edge of the excitation region C is the center of the electrode finger in the orthogonal direction of the electrode finger that is adjacent to a group of continuous electrode fingers and connected to a potential different from that of the group of continuous electrode fingers among the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27. The other end edge is the center of the electrode finger in the orthogonal direction of the group of continuous electrode fingers. The distance between the two end edges of the excitation region C is p. In this case, when the thickness of the piezoelectric film is set to d, d / p is preferably less than 0.5, and d / p is more preferably less than 0.24. Thereby, the body wave of the thickness shear mode can be suitably excited. In addition, in the first embodiment, the thickness d is the thickness of the piezoelectric layer 14.

[0105] 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.

[0106] As described above, in this embodiment, piezoelectric layer 14 comprises Z-cut LiNbO3. However, piezoelectric layer 14 may also comprise rotated Y-cut lithium niobate. In this case, the fractional bandwidth of elastic wave device 10 depends on the Euler angles (φ, θ, ψ) of the lithium niobate used in piezoelectric layer 14. The fractional bandwidth is expressed as (|fa - fr| / fr) × 100 [%], where the resonant frequency is fr and the antiresonant frequency is fa.

[0107] 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°.

[0108] Figure 9 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.

[0109] Figure 9The region R indicated by the hatching is the region where the fractional bandwidth is obtained by 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 9 The relationship shown is the same. When the piezoelectric layer 14 is a lithium tantalate layer, the relationship between θ and ψ in the Euler angle (within the range of 0°±10°, θ, ψ) and the fractional bandwidth is also the same. Figure 9 The relationship shown is the same.

[0110] (Within the range of 0°±10°, 0°~25°, arbitrary ψ) …Equation (1)

[0111] (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)

[0112] (Within the range of 0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, arbitrary ψ) …Equation (3)

[0113] The Euler angle range of the above-mentioned formula (1), formula (2), or formula (3) is preferably . This can sufficiently increase the value of the fractional bandwidth. This allows the elastic wave device 10 to be suitably used in a filter device.

[0114] In the first embodiment, two third electrode fingers 27 as continuous electrode fingers are arranged continuously in the direction perpendicular to the electrode fingers. In addition, the number of continuous electrode fingers arranged continuously in the direction perpendicular to the electrode fingers is not limited to two. For example, Figure 10 In the illustrated variation of the first embodiment, three third electrode fingers 27, which serve as continuous electrode fingers, are arranged continuously in a direction orthogonal to the electrode fingers. In this case, a set of three continuous electrode fingers consists of three third electrode fingers 27. In this variation, as in 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 widened.

[0115] Figure 11 It is a schematic plan view of an elastic wave device according to the second embodiment. Figure 12 This is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers in the second embodiment.

[0116] like Figure 11 as well as Figure 12 As shown, this embodiment differs from the first embodiment in that a third electrode 19 is provided on the second principal surface 14b of the piezoelectric layer 14. Except for the above-described features, the elastic wave device of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0117] The arrangement of the third electrode 19 in a plan view is 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 in a plan view. In a plan view, the plurality of third electrode fingers 27, which are continuous electrode fingers, are positioned between the first electrode fingers 25 and the second electrode fingers 26.

[0118] In this embodiment, similarly 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 widened.

[0119] 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 ground potential.

[0120] Figure 13 (a) is a schematic perspective view showing the appearance of an elastic wave device utilizing bulk waves in a thickness shear mode. Figure 13 (b) is a top view showing the electrode structure on the piezoelectric layer. Figure 14 It is along Figure 13 (a) is a cross-sectional view of a portion taken along line AA.

[0121] The elastic wave device 1 has a piezoelectric layer 2 including LiNbO3. The piezoelectric layer 2 may also be a piezoelectric layer including LiTaO3. The cutting angle of LiNbO3 and LiTaO3 is Z-cut, but may also be a rotated Y-cut or X-cut. The thickness of the piezoelectric layer 2 is not particularly limited, but in order to effectively excite the thickness shear mode, it is preferably greater than 40 nm and less than 1000 nm, 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 13 (a) and Figure 13In (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 the electrodes 4 have a rectangular shape and a length direction. In a direction perpendicular to the length direction, the electrode 3 and the adjacent electrode 4 are opposed to each other. The length directions of the electrodes 3 and 4, and the directions perpendicular to the length directions of the electrodes 3 and 4 are directions that intersect with the thickness direction of the piezoelectric layer 2. Therefore, the electrode 3 and the adjacent electrode 4 can also be said to be opposed to each other 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 13 (a) and Figure 13 The direction perpendicular to the length direction of electrodes 3 and 4 shown in (b) is changed. Figure 13 (a) and Figure 13 In (b), the electrodes 3 and 4 may be extended in the direction in which the first bus bar 5 and the second bus bar 6 extend. In this case, the first bus bar 5 and the second bus bar 6 are arranged in a direction in which the first bus bar 5 and the second bus bar 6 extend. Figure 13 (a) and Figure 13 (b) extends 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 are provided in a direction orthogonal to the longitudinal direction of the electrodes 3 and 4. Here, the so-called adjacent electrodes 3 and 4 do not refer to the case where the electrodes 3 and 4 are arranged in direct contact, but rather to the case where the electrodes 3 and 4 are arranged with a gap between them. 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 may also be 1.5 pairs, 2.5 pairs, etc. The center-to-center distance between the electrodes 3 and 4, i.e., 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, i.e., 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.

[0122] Furthermore, in elastic wave device 1, a Z-cut piezoelectric layer is used, so 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 using a piezoelectric layer 2 with a different cut angle. Here, the term "perpendicular" is not limited to 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°).

[0123] The support member 8 is stacked on the second main surface 2b side of the piezoelectric layer 2 via the insulating layer 7. The insulating layer 7 and the support member 8 have a frame shape. Figure 14 As shown, it has through holes 7a and 8a. Thus, a cavity 9 is formed. The cavity 9 is provided so as not to hinder the vibration of the excitation region C of the piezoelectric layer 2. Therefore, the support member 8 is stacked on the second main surface 2b via the insulating layer 7 at a position that does not overlap with the portion where at least one pair of electrodes 3 and 4 is provided. In addition, the insulating layer 7 may not be provided. Therefore, the support member 8 can be stacked directly or indirectly on the second main surface 2b of the piezoelectric layer 2.

[0124] The insulating layer 7 includes silicon oxide. However, in addition to silicon oxide, suitable insulating materials such as silicon oxynitride and alumina can also be used. The support member 8 includes Si. The plane orientation of the Si surface on the piezoelectric layer 2 side can be (100), (110), or (111). It is desirable that the Si constituting the support member 8 has 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.

[0125] 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.

[0126] The plurality of electrodes 3, 4 and the first and second bus bars 5, 6 are made of a suitable metal or alloy, such as aluminum or an AlCu alloy. In the elastic wave device 1, the electrodes 3, 4 and the 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.

[0127] During driving, an AC voltage is applied between the plurality of electrodes 3 and the plurality of electrodes 4. More specifically, an AC voltage is applied between the first bus bar 5 and the second bus bar 6. 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.

[0128] 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 in order 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 number of electrode fingers can be reduced because the body waves of the thickness shear mode are utilized. Figure 15 (a) and Figure 15 (b) illustrates the difference between the Lamb wave used in the elastic wave device and the bulk wave of the thickness shear mode described above.

[0129] Figure 15 (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 15 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. However, since the waves propagate in the X direction, reflectors are placed on both sides, resulting in resonant characteristics. This results in wave propagation loss, and when miniaturization is pursued, that is, when the number of electrode finger pairs is reduced, the Q value decreases.

[0130] In contrast, Figure 15As shown in (b), in elastic wave device 1, the vibration displacement is in the thickness shear direction, so the wave propagates and resonates primarily in the Z direction, connecting the first principal surface 2a and the second principal surface 2b of piezoelectric layer 2. 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.

[0131] In addition, if Figure 16 As shown in FIG. 1 , 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 16 , schematically illustrates a bulk wave generated when a voltage is applied between electrodes 3 and 4, causing electrode 4 to have a higher potential than electrode 3. A first region 451 is a region in 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 in the excitation region C between the imaginary plane VP1 and the second principal surface 2b.

[0132] As described above, elastic wave device 1 includes at least one pair of electrodes, including electrodes 3 and 4. However, since waves are not propagated in the X direction, there does not need to be a plurality of pairs of electrodes, including electrodes 3 and 4. In other words, at least one pair of electrodes is sufficient.

[0133] 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, at least one pair of electrodes is connected to a signal potential or to a ground potential, as described above, and no floating electrode is provided.

[0134] Figure 17 It shows Figure 14 The resonance characteristics of the elastic wave device are shown in FIG. The design parameters of the elastic wave device 1 that obtain the resonance characteristics are as follows.

[0135] Piezoelectric layer 2: LiNbO3 with Euler angles (0°, 0°, 90°), thickness = 400 nm.

[0136] 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, i.e., the excitation area C, is 40 μm, the number of pairs of electrodes including electrodes 3 and 4 is 21 pairs, the center distance between electrodes is 3 μm, the width of electrodes 3 and 4 is 500 nm, and d / p is 0.133.

[0137] Insulating layer 7: a silicon oxide film with a thickness of 1 μm.

[0138] Support member 8: Si.

[0139] 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 .

[0140] In elastic wave device 1 , the inter-electrode distances of the electrode pairs including electrodes 3 and 4 are all equal among a plurality of pairs. In other words, electrodes 3 and electrodes 4 are arranged at equal intervals.

[0141] according to Figure 17 It is clear that even without a reflector, a good resonance characteristic with a fractional bandwidth of 12.5% ​​can be obtained.

[0142] 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 18 Explain this.

[0143] and got Figure 17 The elastic wave devices having the same resonant characteristics as shown above were obtained by varying d / p. Figure 18 3 is a graph showing the relationship between d / p and the fractional bandwidth of a resonator as an elastic wave device.

[0144] according to Figure 18 It is clear that if d / p>0.5, then 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. Furthermore, when d / p is less than 0.24, the fractional bandwidth can be increased to greater than 7%. Furthermore, if d / p is adjusted within this range, a resonator with an even wider fractional bandwidth can be obtained, enabling a resonator with an even higher coupling coefficient to be realized. Therefore, it can be seen that by making d / p 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.

[0145] Figure 19 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 19K in represents 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.

[0146] In the elastic wave device 1 , it is desirable that the metallization ratio MR of the excitation region C, where adjacent electrodes 3 and 4 overlap when viewed in opposing directions, satisfies MR ≤ 1.75 (d / p) + 0.075. In this case, spurious emission can be effectively reduced. Figure 20 as well as Figure 21 Explain this. Figure 20 This 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. Furthermore, 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.

[0147] Reference Figure 13 (b) is used to illustrate the metallization ratio MR. Figure 13 In the electrode structure of (b), when focusing on a pair of electrodes 3 and 4, it is assumed that only the pair of electrodes 3 and 4 is provided. In this case, the portion surrounded by the single-dot chain line becomes the excitation region C. This excitation region C is the region of electrode 3 that overlaps with electrode 4, the region of electrode 4 that overlaps with electrode 3, and the region between electrodes 3 and 4 that overlaps with electrode 3, when observing electrodes 3 and 4 in a direction perpendicular to the longitudinal direction of electrodes 3 and 4, that is, in the opposing direction. Furthermore, the area of ​​electrodes 3 and 4 within the excitation region C relative to the area of ​​this 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.

[0148] 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.

[0149] Figure 21 This graph shows the relationship between the fractional bandwidth and the phase rotation of the spurious impedance normalized by 180 degrees, which represents the magnitude of the spurious signal, when a large number of spurious wave resonators are configured according to the structure of the spurious wave device 1. The fractional bandwidth was adjusted by variously changing the thickness of the piezoelectric layer and the dimensions of the electrodes. Figure 21 These are the results obtained when a piezoelectric layer including Z-cut LiNbO 3 is used, but the same tendency is observed when piezoelectric layers having other cut angles are used.

[0150] exist Figure 21 In the area surrounded by ellipse J, the spurious value increases to 1.0. Figure 21 It is clear that if the fractional bandwidth exceeds 0.17, that is, if it exceeds 17%, even if the parameters constituting the fractional bandwidth are changed, large spurious signals with a spurious level of 1 or more will appear in the passband. Figure 20 As shown in the resonance characteristics, large spurious signals indicated by arrow B appear within the frequency band. 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 and the dimensions of the electrodes 3 and 4.

[0151] Figure 22 Graph showing the relationship between d / 2p, metallization ratio MR, and fractional bandwidth. In the above-mentioned elastic wave device, various elastic wave devices having different d / 2p and MR were constructed, and the fractional bandwidths were measured. Figure 22 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 this hatched area and the unhatched area is represented by MR = 3.5 (d / 2p) + 0.075. In other words, MR = 1.75 (d / p) + 0.075. Therefore, MR ≤ 1.75 (d / p) + 0.075 is preferred. In this case, it is easy to make the fractional bandwidth less than 17%. More preferably, Figure 22 The region to the right of MR=3.5(d / 2p)+0.05 indicated by the dashed line D1 in FIG. In other words, if MR≤1.75(d / p)+0.05, the fractional bandwidth can be reliably set to 17% or less.

[0152] Figure 23 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 23 The multiple regions R shown in the figure and hatched are regions where a fractional bandwidth of 2% or more is 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 23 In the case where the piezoelectric layer includes 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 23 The relationship shown is the same.

[0153] 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 23 If the fractional bandwidth is within any range of the plurality of regions R shown, it is possible to sufficiently widen the fractional bandwidth, which is preferable.

[0154] Figure 24 This is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0155] In elastic wave device 81, an acoustic multilayer film 82 is laminated on the second principal surface 2b of piezoelectric layer 2. Acoustic multilayer film 82 has a laminated structure consisting of 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. Using acoustic multilayer film 82 allows bulk waves in the thickness-shear mode to be confined within piezoelectric layer 2, even without the cavity 9 of elastic wave device 1. In 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 acoustic multilayer film 82 is not particularly limited. It suffices that at least one high-acoustic-impedance layer 82b or 82d is positioned farther from piezoelectric layer 2 than the low-acoustic-impedance layers 82a, 82c, and 82e.

[0156] The low-acoustic-impedance layers 82a, 82c, and 82e and the high-acoustic-impedance layers 82b and 82d can be made of any suitable material, as long as the above-mentioned acoustic impedance relationship is satisfied. For example, the low-acoustic-impedance layers 82a, 82c, and 82e can be made of silicon oxide or silicon oxynitride. The high-acoustic-impedance layers 82b and 82d can be made of alumina, silicon nitride, or metal.

[0157] Figure 25 This is a partially cutaway perspective view for explaining an elastic wave device utilizing Lamb waves.

[0158] The elastic wave device 91 has a supporting substrate 92. The supporting substrate 92 has a recessed portion formed on its upper surface. A piezoelectric layer 93 is stacked on the supporting substrate 92. This forms a cavity 9. 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 25 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.

[0159] 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.

[0160] As described above, the elastic wave device of the present invention may also be an elastic wave device utilizing plate waves. Figure 25 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 are 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. If the elastic wave device of the present invention utilizes plate waves, the reflectors 95 and 96 described above may be provided on the first principal surface 14a of the piezoelectric layer 14 in the first embodiment, the second embodiment, and the modified example. In this case, the reflectors 95 and 96 may sandwich the pair of comb-shaped electrodes and the plurality of third electrode fingers in a direction orthogonal to the electrode fingers when viewed from above.

[0161] In the elastic wave devices of the first embodiment, the second embodiment, and the modified examples, for example, an acoustic reflection film may be provided between the support member and the piezoelectric layer as the piezoelectric film. Figure 24 The acoustic multilayer film 82 is shown. Specifically, the support member and the piezoelectric film may be arranged so that at least a portion of the support member and at least a portion of the piezoelectric film face each other, sandwiching the acoustic multilayer film 82. In this case, the acoustic multilayer film 82 may be composed of alternating layers of low acoustic impedance and high acoustic impedance. The acoustic multilayer film 82 may also serve as an acoustic reflector in an elastic wave device.

[0162] In the elastic wave devices of the first embodiment, the second embodiment, and the modified examples 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 to be obtained.

[0163] Furthermore, in the excitation region of the elastic wave devices of the first and second embodiments and their variations, which utilize bulk waves in the thickness shear mode, it is preferable to satisfy MR ≤ 1.75(d / p) + 0.075, as described above. More specifically, when the metallization ratio of the first, second, and third electrode fingers, other than the continuous electrode fingers, and the continuous electrode fingers relative to the excitation region, is defined as MR, it is preferable to satisfy MR ≤ 1.75(d / p) + 0.075. This allows for more reliable suppression of spurious emissions.

[0164] Description of Reference Numerals

[0165] 1…Elastic wave device

[0166] 2…Piezoelectric layer

[0167] 2a, 2b…1st main surface, 2nd main surface

[0168] 3, 4...Electrodes

[0169] 5, 6…Bus bar 1, bus bar 2

[0170] 7…Insulation layer

[0171] 7a…Through hole

[0172] 8…Supporting member

[0173] 8a…Through hole

[0174] 9…Cavity

[0175] 10…Elastic wave device

[0176] 10a…cavity

[0177] 11…Functional electrode

[0178] 12…Piezoelectric substrate

[0179] 13…Supporting member

[0180] 14…Piezoelectric layer

[0181] 14a, 14b…1st main surface, 2nd main surface

[0182] 15…Insulation layer

[0183] 16…Support base plate

[0184] 17, 18…1st comb-shaped electrode, 2nd comb-shaped electrode

[0185] 19…3rd electrode

[0186] 22-24…Bus bars 1 to 3

[0187] 24A, 24B...1st connecting electrode, 2nd connecting electrode

[0188] 24a...Section

[0189] 24b…protrusion

[0190] 25-27…1st electrode finger to 3rd electrode finger

[0191] 29…Insulation film

[0192] 80, 81… elastic wave device

[0193] 82…Acoustic multilayer film

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

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

[0196] 91…Elastic wave device

[0197] 92...Support base plate

[0198] 93…Piezoelectric layer

[0199] 94…IDT electrode

[0200] 94a, 94b…1st bus bar, 2nd bus bar

[0201] 94c, 94d...first electrode finger, second electrode finger

[0202] 95, 96…reflectors

[0203] 201…Piezoelectric film

[0204] 201a, 201b…1st main surface, 2nd main surface

[0205] 451, 452…Area 1, Area 2

[0206] C…Incentive Area

[0207] E…Intersection area

[0208] R…Region

[0209] VP1…imaginary plane.

Claims

1. An elastic wave device comprising: A piezoelectric film, including a piezoelectric layer; a first comb-shaped electrode, disposed on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers, one end of each of which is connected to the first bus bar, and connected to an input potential; A second comb-shaped electrode, disposed on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers, one end of each of which is connected to the second bus bar, connected to an output potential, wherein the plurality of second electrode fingers are interlaced with the plurality of first electrode fingers; and The third electrode has a plurality of third electrode fingers and a third bus bar connecting adjacent third electrode fingers to each other, and is connected to a potential different from that of the first comb-shaped electrode and the second comb-shaped electrode. The plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged with the first electrode finger and the second electrode finger in the direction in which the first electrode finger and the second electrode finger are arranged when viewed from above. The third electrode finger is arranged between the first electrode finger and the second electrode finger which are arranged at positions closest to each other. When a direction orthogonal to the direction in which the first electrode finger, the second electrode finger, and the third electrode finger extend is set as the electrode finger orthogonal direction, at least one type of electrode finger among the plurality of first electrode fingers, the plurality of second electrode fingers, and the plurality of third electrode fingers includes two or more continuous electrode fingers continuously arranged in the electrode finger orthogonal direction.

2. The elastic wave device according to claim 1, wherein: The plurality of third electrode fingers include two or more of the continuous electrode fingers.

3. The elastic wave device according to claim 1 or 2, wherein: When the distance between the continuous electrode finger and the electrode finger adjacent to the continuous electrode finger and connected to a potential different from that of the continuous electrode finger among the first electrode finger, the second electrode finger and the third electrode finger is set to g1, and the distance between adjacent continuous electrode fingers is set to g2, g2≤g1.

4. The elastic wave device according to any one of claims 1 to 3, wherein: The elastic wave device is configured to utilize thickness shear mode bulk waves.

5. The elastic wave device according to any one of claims 1 to 3, 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 of the support member overlapping with the plurality of first electrode fingers, the plurality of second electrode fingers, and the plurality of third electrode fingers, When two or more continuous electrode fingers arranged continuously in an orthogonal direction to the electrode fingers are set as a group of continuous electrode fingers, the distance between the center of the electrode fingers in the orthogonal direction of the electrode fingers among the first electrode finger, the second electrode finger, and the third electrode finger which are adjacent to the group of continuous electrode fingers and connected to a potential different from that of the group of continuous electrode fingers and the center of the electrode fingers in the orthogonal direction of the group of continuous electrode fingers is set to p, and the thickness of the piezoelectric film is set to d, d / p is less than 0.

5.

6. The elastic wave device according to claim 5, wherein: d / p is less than 0.

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7. The elastic wave device according to claim 5 or 6, wherein: The sound reflecting portion is a cavity portion, and the supporting member and the piezoelectric film are arranged such that a portion of the supporting member and a portion of the piezoelectric film face each other with the cavity portion interposed therebetween.

8. The elastic wave device according to claim 5 or 6, wherein: The sound reflecting portion is an acoustic reflecting film 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 film are configured so that at least a portion of the supporting member and at least a portion of the piezoelectric film are opposite to each other with the acoustic reflecting film sandwiched therebetween.

9. The elastic wave device according to any one of claims 5 to 8, wherein: The region between the center of the electrode finger in the orthogonal direction of the electrode finger adjacent to the one group of continuous electrode fingers and connected to a potential different from that of the one group of continuous electrode fingers among the first electrode finger, the second electrode finger and the third electrode finger and the center of the electrode finger in the orthogonal direction of the one group of continuous electrode fingers is the excitation region, When the metallization ratio of the electrode fingers other than the continuous electrode fingers among the first electrode fingers, the second electrode fingers, and the third electrode fingers and the continuous electrode fingers with respect to the excitation region is MR, MR≦1.75(d / p)+0.075 is satisfied.

10. The elastic wave device according to any one of claims 1 to 9, wherein: The piezoelectric layer includes lithium niobate, 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°, arbitrary ψ) …Formula (1) (Within the range of 0°±10°, 25°~100°, 0°~75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2) (0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, arbitrary ψ) …Equation (3).

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