Elastic wave device

Abstract

Provided is an elastic wave device capable of promoting miniaturization of a filter device and capable of reducing insertion loss. An elastic wave device (10) according to the present invention is provided with: a piezoelectric layer (14) containing lithium niobate; a first comb electrode (17) which is provided on the piezoelectric layer (14), has a first bus bar (22) and a plurality of first electrode fingers (25) each having one end connected to the first bus bar (22), and is connected to an input potential; a second comb electrode (18) provided on the piezoelectric layer (14), having a second bus bar (23) and a plurality of second electrode fingers (26) each having one end connected to the second bus bar (23), and connected to the output potential, the plurality of second electrode fingers (26) and the plurality of first electrode fingers (25) being interleaved with each other; and a reference potential electrode (19) connected to a reference potential, the reference potential electrode (19) having a plurality of third electrode fingers (27) provided on the piezoelectric layer (14) so as to be aligned with the first electrode fingers (25) and the second electrode fingers (26) in the direction in which the first electrode fingers (25) and the second electrode fingers (26) are arranged, and connection electrodes (third bus bars (24)) that connect adjacent third electrode fingers (27) to each other. The order in which the first electrode fingers (25), the second electrode fingers (26), and the third electrode fingers (27) are arranged is an order in which the first electrode fingers (25), the third electrode fingers (27), the second electrode fingers (26), and the third electrode fingers (27) are arranged as one cycle from the first electrode fingers (25). The piezoelectric device is further provided with a pair of reflectors (33A) and (33B) that are provided on the piezoelectric layer (14) so as to sandwich a region in which the first electrode finger (25), the second electrode finger (26), and the third electrode finger (27) are provided in the direction orthogonal to the electrode fingers, where the direction orthogonal to the direction in which the first electrode finger (25), the second electrode finger (26), and the third electrode finger (27) extend is defined as the direction orthogonal to the electrode fingers. Each of the reflector electrodes has at least one reflector electrode finger.

Description

Technical Field

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

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

[0003] Prior Art Literature

[0004] Patent Literature

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

[0006] Problem that the invention aims to solve

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

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

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

[0010] Furthermore, the inventors of the present invention have found that there is a concern that the insertion loss may not be sufficiently reduced even with the above-mentioned structure alone.

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

[0012] Technical solutions to solve problems

[0013] The elastic wave device of the present invention comprises: a piezoelectric layer comprising lithium niobate; a first comb-shaped electrode arranged on the piezoelectric layer, comprising a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, connected to an input potential; a second comb-shaped electrode arranged on the piezoelectric layer, comprising a second bus bar and a plurality of second electrode fingers each having one end connected to the second bus bar, connected to an output potential, the plurality of second electrode fingers being interlaced with the plurality of first electrode fingers; and a reference potential electrode comprising a plurality of third electrode fingers and a connecting electrode connecting adjacent third electrode fingers to each other, connected to a reference potential, the plurality of third electrode fingers being arranged on the piezoelectric layer, so that the first electrode fingers and the second electrode fingers are arranged in a manner that is close to each other. The first electrode finger, the second electrode finger and the third electrode finger are arranged in parallel with the first electrode finger and the second electrode finger in a direction, 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 an order in which the first electrode finger, the third electrode finger, the second electrode finger and the third electrode finger form one period. The elastic wave device also has a pair of reflectors. 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, the pair of reflectors are arranged on the piezoelectric layer to sandwich an area where the first electrode finger, the second electrode finger and the third electrode finger are arranged in the electrode finger orthogonal direction, and each has at least one reflector electrode finger.

[0014] Effects of the Invention

[0015] According to the present invention, it is possible to provide an elastic wave device that can promote miniaturization of a filter device and reduce insertion loss. BRIEF DESCRIPTION OF THE DRAWINGS

[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 It is a diagram showing the transmission characteristics of the elastic wave device according to the first embodiment of the present invention.

[0020] Figure 5 It is a graph showing the passage characteristics in the first embodiment of the present invention and a comparative example.

[0021] Figure 6 This is a diagram showing the relationship between the number of reflector electrode fingers of each reflector and the insertion loss near the center of the passband.

[0022] Figure 7 This is a diagram showing a map of the relative bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0023] Figure 8 It is a schematic plan view of an elastic wave device according to a modified example of the first embodiment of the present invention.

[0024] Fig. 9 It is a diagram showing the passage characteristics in the first embodiment of the present invention where p1=p2, the second embodiment where p1>p2, and a comparative example.

[0025] Fig.10 It is a diagram showing the transmission characteristics in the first embodiment of the present invention where p1=p2, the second embodiment where p1<p2, and a comparative example.

[0026] Fig.11 It is a diagram showing the passage characteristics in the first embodiment of the present invention where p1=p3, the third embodiment where p1>p3, and a comparative example.

[0027] Fig.12 It is a diagram showing the transmission characteristics in the first embodiment of the present invention where p1=p3, the third embodiment where p1<p3, and a comparative example.

[0028] Fig.13 It is a diagram showing the transmission characteristics in the first embodiment of the present invention where w1=w2, the fourth embodiment where w1>w2, and a comparative example.

[0029] Fig.14 It is a diagram showing the transmission characteristics in the first embodiment of the present invention where w1=w2, the fourth embodiment where w1<w2, and a comparative example.

[0030] Fig.15 (a) is a schematic perspective view showing the appearance of an elastic wave device using a thickness shear mode bulk wave, Fig.15 (b) is a top view showing the electrode structure on the piezoelectric layer.

[0031] Fig.16 It is along Fig.15 (a) is a cross-sectional view of a portion taken along line AA.

[0032] Fig.17 (a) is a schematic front cross-sectional view for explaining Lamb waves propagating through a piezoelectric film of an elastic wave device. Fig.17(b) is a schematic front cross-sectional view for explaining a thickness shear mode bulk wave propagating through a piezoelectric film in an elastic wave device.

[0033] Fig.18 It is a diagram showing the amplitude direction of the body wave in the thickness shear mode.

[0034] Fig.19 FIG. 1 is a diagram showing the resonance characteristics of an elastic wave device using bulk waves in a thickness shear mode.

[0035] Fig. 20 1 is a diagram showing the relationship between d / p and the relative bandwidth of the resonator when the distance between the centers of adjacent electrodes is defined as p and the thickness of the piezoelectric layer is defined as d.

[0036] Fig.21 This is a top view of an elastic wave device using bulk waves in a thickness shear mode.

[0037] Fig. 22 FIG. 2 is a diagram showing the resonance characteristics of an elastic wave device according to a reference example in which spurious emission occurs.

[0038] Fig.23 This is a diagram showing the relationship between the relative 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.

[0039] Fig.24 It is a graph showing the relationship between d / 2p and the metallization ratio MR.

[0040] Fig.25 This is a diagram showing a map of the relative bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0041] Fig.26 It is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0042] Fig. 27 This is a partially cutaway perspective view for explaining an elastic wave device using Lamb waves. DETAILED DESCRIPTION

[0043] Below, while referring to the attached Figure 1 The present invention will be clarified by describing specific embodiments of the present invention.

[0044] In addition, it should be noted that each embodiment described in this specification is an example, and some structures can be replaced or combined among different embodiments.

[0045] Figure 1 It is a schematic front cross-sectional view of the elastic wave device according to the first embodiment of the present invention. Figure 2is a schematic plan view of the elastic wave device according to the first embodiment. Figure 1 It is along Figure 2 A schematic cross-sectional view of the line I-I in FIG. Figure 2 In FIG. 1 , hatching is performed to indicate each electrode. Figure 2 Similarly, in other schematic plan views, electrodes may be hatched.

[0046] 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.

[0047] The elastic wave device 10 has a piezoelectric substrate 12 and a functional electrode 11. The piezoelectric substrate 12 is a substrate having piezoelectricity. Specifically, the piezoelectric substrate 12 has a supporting member 13 and a piezoelectric layer 14. In the present embodiment, the supporting member 13 includes a supporting substrate 16 and an insulating layer 15. The insulating layer 15 is provided on the supporting substrate 16. The piezoelectric layer 14 is provided on the insulating layer 15. However, the supporting member 13 may also be composed of only the supporting substrate 16. In addition, the supporting member 13 may not necessarily be provided.

[0048] The piezoelectric layer 14 has a first principal surface 14 a and a second principal surface 14 b. The first principal surface 14 a and the second principal surface 14 b face each other. Of the first principal surface 14 a and the second principal surface 14 b, the second principal surface 14 b is located on the support member 13 side.

[0049] The piezoelectric layer 14 includes lithium niobate. More specifically, in the present embodiment, the lithium niobate used for the piezoelectric layer 14 is LiNbO3. The Euler angles (φ, θ, ψ) of the LiNbO3 are (0°, 0°, 90°). However, the Euler angles (φ, θ, ψ) of the piezoelectric layer 14 are not limited to the above. In addition, in the present specification, the so-called component containing a certain material includes the case where a trace amount of impurities is contained to the extent that the electrical characteristics of the elastic wave device are not deteriorated.

[0050] The functional electrode 11 is provided on the first main surface 14a of the piezoelectric layer 14. Figure 2 As shown, the functional electrode 11 includes a pair of comb-shaped electrodes and a reference potential electrode 19. The reference potential electrode 19 is connected to a reference potential. The pair of comb-shaped electrodes is specifically 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.

[0051] The first comb-shaped electrode 17 and the second comb-shaped electrode 18 are provided on the first main surface 14a of the piezoelectric layer 14. The first comb-shaped electrode 17 has a first bus bar 22 and a plurality of first electrode fingers 25. One ends of the plurality of first electrode fingers 25 are respectively connected to the first bus bar 22. The second comb-shaped electrode 18 has a second bus bar 23 and a plurality of second electrode fingers 26. One ends of the plurality of second electrode fingers 26 are respectively connected to the second bus bar 23.

[0052] The first bus bar 22 and the second bus bar 23 face each other. The plurality of first electrode fingers 25 and the plurality of second electrode fingers 26 are interlaced with each other. The first electrode fingers 25 and the second electrode fingers 26 are alternately arranged in a direction orthogonal to the direction in which the first electrode fingers 25 and the second electrode fingers 26 extend.

[0053] The reference potential electrode 19 has 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 extend in parallel with the plurality of first electrode fingers 25 and the plurality of second electrode fingers. 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. In this specification, the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27 are sometimes collectively described as simply electrode fingers.

[0054] The third electrode finger 27 is arranged in parallel with the first electrode finger 25 and the second electrode finger 26 in the direction in which the first electrode finger 25 and the second electrode finger 26 are arranged. Therefore, the first electrode finger 25, the second electrode finger 26 and the third electrode finger 27 are arranged in one direction. When the direction in which the first electrode finger 25, the second electrode finger 26 and the third electrode finger 27 are arranged is set as the electrode finger arrangement direction, the electrode finger arrangement direction is parallel to the electrode finger orthogonal direction. The two third electrode fingers 27 are located at both ends in the electrode finger orthogonal direction in the area where the plurality of electrode fingers are arranged. The plurality of third electrode fingers 27 other than the above-mentioned two third electrode fingers 27 are arranged between the first electrode finger 25 and the second electrode finger 26.

[0055] Figure 3 This is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers in the first embodiment.

[0056] The order in which the plurality of electrode fingers are arranged is the order of the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, and the third electrode finger 27 as one cycle, when starting from the first electrode finger 25. Therefore, the order in which the plurality of electrode fingers are arranged is the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, the third electrode finger 27, the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, ..., and so on. If the input potential is represented by IN, the output potential is represented by OUT, and the reference potential is represented by GND, and the order of the plurality of electrode fingers is represented as the order of the potentials to be connected, then it is continuous as IN, GND, OUT, GND, IN, GND, OUT, ..., and so on.

[0057] In the present embodiment, in a region where a plurality of electrode fingers are provided, the electrode fingers located at both ends in the orthogonal direction of the electrode fingers are the third electrode fingers 27. In addition, the electrode fingers located at the ends in the orthogonal direction of the electrode fingers may be any type of electrode fingers among the first electrode fingers 25, the second electrode fingers 26, and the third electrode fingers 27.

[0058] like Figure 2 As shown, the third bus bar 24 as the connection electrode of the reference potential electrode 19 electrically connects the plurality of third electrode fingers 27 to each other. Specifically, the third bus bar 24 is located in a region between the first bus bar 22 and the front ends of the plurality of second electrode fingers 26. The plurality of first electrode fingers 25 are also located in this region. However, the third bus bar 24 and the plurality of first electrode fingers 25 are electrically insulated from each other by the insulating film 29.

[0059] More specifically, the third bus bar 24 includes a plurality of first connection electrodes 24A and a second connection electrode 24B. Each first connection electrode 24A connects the front ends of two adjacent third electrode fingers 27 to each other. A U-shaped electrode is formed by the first connection electrode 24A and the two third electrode fingers 27. The second connection electrode 24B connects the plurality of first connection electrodes 24A to each other. An insulating film 29 is provided between the second connection electrode 24B and the plurality of first electrode fingers 25.

[0060] More specifically, the insulating film 29 is provided on the first main surface 14a of the piezoelectric layer 14 so as to cover a portion of the plurality of first electrode fingers 25. The insulating film 29 is provided in a region between the first bus bar 22 and the front ends of the plurality of second electrode fingers 26. The insulating film 29 has a strip shape.

[0061] The insulating film 29 does not reach the first connection electrode 24A of the reference potential electrode 19. Moreover, the second connection electrode 24B is provided over the insulating film 29 and the plurality of first connection electrodes 24A. Specifically, the second connection electrode 24B has a stripe 24a and a plurality of protrusions 24b. Each protrusion 24b extends from the stripe 24a toward each first connection electrode 24A. Each protrusion 24b is connected to each first connection electrode 24A. Thus, the plurality of third electrode fingers 27 are electrically connected to each other through the first connection electrode 24A and the second connection electrode 24B.

[0062] In the present embodiment, the third bus bar 24 is located in a region between the first bus bar 22 and the front ends of the plurality of second electrode fingers 26. Therefore, the front ends of the plurality of second electrode fingers 26 are opposed to the third bus bar 24 with gaps therebetween in the electrode finger extending direction. On the other hand, the front ends of the plurality of first electrode fingers 25 are opposed to the second bus bar 23 with gaps therebetween in the electrode finger extending direction.

[0063] In addition, the third bus bar 24 may be located in a region between the second bus bar 23 and the front ends of the plurality of first electrode fingers 25. In this case, the front ends of the plurality of first electrode fingers 25 are opposed to the third bus bar 24 via gaps. On the other hand, the front ends of the plurality of second electrode fingers 26 are opposed to the first bus bar 22 via gaps.

[0064] The elastic wave device 10 is an elastic wave resonator configured to utilize bulk waves in a thickness shear mode. Figure 2 As shown, the elastic wave device 10 has a plurality of excitation regions C. In the plurality of excitation regions C, body waves in the thickness shear mode and elastic waves in other modes are excited. Figure 2 In FIG, only two excitation areas C among multiple excitation areas C are shown.

[0065] A part of the plurality of excitation regions C among all the excitation regions C are regions where adjacent first electrode fingers 25 and third electrode fingers 27 overlap when viewed from the direction orthogonal to the electrode fingers, and are regions between the centers of adjacent first electrode fingers 25 and third electrode fingers 27. The remaining plurality of excitation regions C are regions where adjacent second electrode fingers 26 and third electrode fingers 27 overlap when viewed from the direction orthogonal to the electrode fingers, and are regions between the centers of adjacent second electrode fingers 26 and third electrode fingers 27. These excitation regions C are arranged in the direction orthogonal to the electrode fingers.

[0066] In the functional electrode 11, the structure other than the reference potential electrode 19 is the same as the structure of the IDT (Interdigital Transducer) electrode. When viewed from the orthogonal direction of the electrode fingers, the area where the adjacent first electrode fingers 25 and second electrode fingers 26 overlap each other is the intersection area E. The intersection area E includes a plurality of excitation areas C. Hereinafter, the size of the intersection area E along the orthogonal direction of the electrode fingers is referred to as the intersection width Ap. In addition, the intersection area E and the excitation area C are areas of the piezoelectric layer 14 defined based on the structure of the functional electrode 11.

[0067] In this embodiment, in the functional electrode 11, the center distances between adjacent pairs of first electrode fingers 25 and third electrode fingers 27 are the same as the center distances between adjacent pairs of second electrode fingers 26 and third electrode fingers 27. Hereinafter, the center distance between adjacent electrode fingers of the functional electrode 11 is referred to as p1.

[0068] The present embodiment is characterized in that a pair of reflectors 33A and 33B are provided on piezoelectric layer 14 so as to sandwich a region where first electrode finger 25, second electrode finger 26, and third electrode finger 27 are provided in a direction orthogonal to the electrode fingers. Thus, when elastic wave device 10 is used in a filter device, the filter device can be miniaturized and insertion loss can be reduced. The following describes the details of this effect together with the structure of each reflector.

[0069] The reflector 33A includes a first reflector bus bar 33a and a second reflector bus bar 33b, and a plurality of reflector electrode fingers 33c. The first reflector bus bar 33a and the second reflector bus bar 33b are opposite to each other. One end of the plurality of reflector electrode fingers 33c is connected to the first reflector bus bar 33a, respectively. The other ends of the plurality of reflector electrode fingers 33c are connected to the second reflector bus bar 33b, respectively. Similarly, the reflector 33B also includes a first reflector bus bar 33d and a second reflector bus bar 33e, and a plurality of reflector electrode fingers 33f.

[0070] The direction in which the reflector electrode fingers of each reflector extend is parallel to the electrode finger extending direction. In this embodiment, the number of reflector electrode fingers of each reflector is 8 or more. In addition, each reflector in the elastic wave device of the present invention only needs to have at least one reflector electrode finger.

[0071] Each electrode finger of the functional electrode 11 and each reflector electrode finger of each reflector include a stacked metal film. Specifically, in each electrode finger and each reflector electrode finger, a Ti layer, an AlCu layer, and a Ti layer are stacked in sequence from the piezoelectric layer 14 side. In addition, the materials of each electrode finger and each reflector electrode finger are not limited to the above. Alternatively, each electrode finger and each reflector electrode finger may also include a single-layer metal film.

[0072] The potential to which the reflectors 33A and 33B are connected is not particularly limited. For example, each reflector may be connected to a reference potential. Each reflector may be connected to an input potential or an output potential. Alternatively, each reflector may be a floating electrode. A floating electrode is an electrode that is not connected to an input potential, an output potential, or a reference potential.

[0073] In this embodiment, a filter waveform can be obtained in one elastic wave device 10. Therefore, when the elastic wave device 10 is used as an elastic wave resonator in a filter device, a filter waveform can be obtained appropriately even if the elastic wave resonator constituting the filter device is one or a small number. Therefore, the miniaturization of the filter device can be promoted.

[0074] An example of the transmission characteristics of the elastic wave device 10 is shown below. The design parameters of the elastic wave device 10 are as follows.

[0075] Piezoelectric layer: Material…LiNbO3, Euler angles (φ, θ, ψ)…(0°, 0°, 90°), Thickness…400nm

[0076] First to third electrode fingers: layer structure: Ti layer / AlCu layer / Ti layer from the piezoelectric layer side, thickness of each layer: 10 nm / 390 nm / 4 nm from the piezoelectric layer side

[0077] The order of the first to third electrode fingers is represented by the order of the potentials to be connected: IN, GND, OUT, GND are repeated.

[0078] The center-to-center distance between adjacent electrode fingers p1: 1.4 μm

[0079] Duty cycle of functional electrode: 0.3

[0080] Cross width Ap: 40μm

[0081] Total number of first to third electrode fingers: 81

[0082] Number of reflector electrode fingers of each reflector: 8

[0083] Figure 4 It is a diagram showing the transmission characteristics of the elastic wave device according to the first embodiment.

[0084] like Figure 4 As shown in FIG. 1 , it can be seen that a filter waveform can be appropriately obtained in one elastic wave device 10. The elastic wave device 10 is an acoustic coupling type filter. In more detail, Figure 2 As shown, the elastic wave device 10 includes an excitation region C located between the centers of the adjacent first electrode fingers 25 and third electrode fingers 27, and an excitation region C located between the centers of the adjacent second electrode fingers 26 and third electrode fingers 27. Elastic waves of multiple modes including a body wave of a thickness shear mode are excited in these excitation regions C. By combining these modes, a filter waveform can be appropriately obtained in one elastic wave device 10.

[0085] Furthermore, in this embodiment, insertion loss can also be reduced. This will be described below by comparing this embodiment with a comparative example.

[0086] The difference between the comparative example and the first embodiment is that the comparative example does not have a reflector. The transmission characteristics of the first embodiment and the comparative example are compared. In addition, the design parameters of the elastic wave device 10 of the first embodiment and the comparative example are compared. Figure 4 The design parameters of the elastic wave device in the comparative example are the same as those in the example shown. Figure 4 The design parameters in the example shown are the same.

[0087] Figure 5 It is a diagram showing the passage characteristics in the first embodiment and the comparative example.

[0088] Figure 5 The frequency band surrounded by the double-dashed line in is the frequency band near the center of the passband. It can be seen that in the first embodiment, the insertion loss near the center of the passband is smaller than that in the comparative example. This is because, Figure 2 The elastic wave device 10 according to the first embodiment shown includes a reflector 33A and a reflector 33B.

[0089] Furthermore, the insertion loss near the center of the passband was measured each time the number of reflector electrode fingers in each reflector was changed. Specifically, the number of reflector electrode fingers in each reflector was changed in units of 2 within a range of 0 to 30. Figure 5 The design parameters in the example shown are the same.

[0090] Figure 6 This is a diagram showing the relationship between the number of reflector electrode fingers of each reflector and the insertion loss near the center of the passband.

[0091] like Figure 6As shown, it can be seen that when the number of reflector electrode fingers is less than 8, the more the number of reflector electrode fingers is, the smaller the insertion loss is. It can be seen that when the number of reflector electrode fingers is more than 8, the insertion loss can be effectively reduced. Based on this, each reflector preferably has more than 8 reflector electrode fingers.

[0092] Hereinafter, the structure of the first embodiment will be described in more detail.

[0093] like Figure 1 As shown, the support member 13 includes a support substrate 16 and an insulating layer 15. The piezoelectric substrate 12 is a stack of the support substrate 16, the insulating layer 15, and the piezoelectric layer 14. That is, when viewed from the direction in which the first principal surface 14a and the second principal surface 14b of the piezoelectric layer 14 are opposite, the piezoelectric layer 14 and the support member 13 overlap.

[0094] As the material of the support substrate 16, for example, semiconductors such as silicon, ceramics such as aluminum oxide, etc. can be used. As the material of the insulating layer 15, appropriate dielectrics such as silicon oxide or tantalum oxide can be used. The piezoelectric layer 14 is, for example, a lithium niobate layer such as a LiNbO3 layer.

[0095] A recess is provided in the insulating layer 15. A piezoelectric layer 14 is provided on the insulating layer 15 so as to block the recess. Thus, a hollow portion is formed. The hollow portion is a cavity 10a. In the first embodiment, the supporting member 13 and the piezoelectric layer 14 are arranged so that a part of the supporting member 13 and a part of the piezoelectric layer 14 are opposite to each other with the cavity 10a sandwiched therebetween. However, the recess in the supporting member 13 may also be provided throughout the insulating layer 15 and the supporting substrate 16. Alternatively, 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. In addition, the cavity 10a may also be a through hole provided in the supporting member 13.

[0096] The cavity 10a is the acoustic reflection portion in the present invention. The acoustic reflection portion can effectively confine the energy of the elastic wave on the piezoelectric layer 14 side. The acoustic reflection portion can be provided at a position overlapping at least a portion of the functional electrode 11 in the support member 13 when viewed from above. More specifically, when viewed from above, at least a portion of each of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 can overlap with the acoustic reflection portion. When viewed from above, it is preferred that a plurality of excitation regions C overlap with the acoustic reflection portion.

[0097] In this specification, the term "top view" refers to a view from the Figure 1 The upper direction in FIG. 1 is viewed along the stacking direction of the support member 13 and the piezoelectric layer 14. Figure 1In the embodiment of the present invention, for example, the piezoelectric layer 14 side is the upper side of the support substrate 16 side and the piezoelectric layer 14 side. Furthermore, in this specification, looking down is synonymous with observing from the main surface opposite direction. The so-called main surface opposite direction is the direction in which the first main surface 14a and the second main surface 14b of the piezoelectric layer 14 are opposite to each other. More specifically, the main surface opposite direction is, for example, the normal direction of the first main surface 14a.

[0098] In addition, the sound reflecting portion may be a sound reflecting film such as a sound multilayer film described later. For example, a sound reflecting film may be provided on the surface of the supporting member.

[0099] exist Figure 2 In the functional electrode 11 shown, the center-to-center distance p1 of adjacent electrode fingers is fixed. However, the center-to-center distance p1 of the adjacent first electrode fingers 25 and the third electrode fingers 27 and the center-to-center distance p1 of the adjacent second electrode fingers 26 and the third electrode fingers 27 may not be fixed. In this case, the longest distance among the center-to-center distance p1 of the adjacent first electrode fingers 25 and the third electrode fingers 27 and the center-to-center distance p1 of the adjacent second electrode fingers 26 and the third electrode fingers 27 is set to p. In this case, when the thickness of the piezoelectric layer 14 is set to d, it is preferred that d / p is less than 0.5, and more preferably d / p is less than 0.24. Thus, the body wave of the thickness shear mode can be appropriately excited.

[0100] On the other hand, as in the first embodiment, when the center-to-center distance p1 is fixed, the center-to-center distance p1 between any adjacent electrode fingers is p1 = p. In this case, d / p is preferably less than 0.5, and more preferably less than 0.24. In addition, the elastic wave device of the present invention may not necessarily be configured to utilize the thickness shear mode.

[0101] The elastic wave device according to the present invention may also be configured to utilize plate waves. In this case, the excitation region is Figure 2 The intersection region E shown. In the present invention, a pair of reflectors is provided. Thus, even when plate waves are used, the resonance characteristics can be suitably improved.

[0102] In the first embodiment, the piezoelectric layer 14 is a LiNbO3 layer. In this case, the relative bandwidth of the elastic wave device 10 depends on the Euler angles (φ, θ, ψ) of lithium niobate used for the piezoelectric layer 14. The relative bandwidth is represented by (|fa-fr| / fr)×100 [%] when the resonant frequency is fr and the antiresonant frequency is fa.

[0103] The relationship between the relative bandwidth of elastic wave device 10 and the Euler angles (φ, θ, ψ) of piezoelectric layer 14 was derived when d / p was made as close to 0 as possible. In addition, φ in the Euler angles was set to 0°.

[0104] Figure 7 This is a diagram showing a map of the relative bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0105] Figure 7 The region R indicated by the hatching is the region where a relative bandwidth of at least 2% can be obtained. 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 relative bandwidth is the same as Fig. 9 When the piezoelectric layer 14 is a lithium tantalate layer, and when φ is in the range of 0°±10°, the relationship between θ and ψ and the relative bandwidth is also the same as Fig. 9 The relationship shown is the same. If the range of the region R is approximated, it becomes a range expressed by the following formula (1), formula (2) and formula (3).

[0106] (within the range of 0°±10°, 0°~25°, arbitrary ψ) …Formula (1)

[0107] (Within the range of 0°±10°, 25°~100°, 75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2)

[0108] (Within the range of 0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, any ψ) …Formula (3)

[0109] The range of the Euler angles of the above-mentioned formula (1), formula (2), or formula (3) is preferably 0. This can sufficiently expand the relative bandwidth. This allows the elastic wave device 10 to be suitably used in a filter device.

[0110] like Figure 2 As shown in the first embodiment, the reference potential electrode 19 has a third bus bar 24 as a connection electrode and a plurality of third electrode fingers 27. The reference potential electrode 19 is a comb-shaped electrode. However, the reference potential electrode 19 may not be a comb-shaped electrode. For example, Figure 8 In the modification of the first embodiment shown, the reference potential electrode 39 has a meandering shape. In this modification, the insulating film 29 is not provided on the piezoelectric layer 14. Moreover, the connection electrode 35 includes only a portion corresponding to the plurality of first connection electrodes 24A in the first embodiment. The connection electrode 35 of this modification is not a third bus bar.

[0111] More specifically, the reference potential electrode 39 includes a plurality of connection electrodes 35 located on the first bus bar 22 side and a plurality of connection electrodes 35 located on the second bus bar 23 side. The front end portions 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 35. For example, the third electrode fingers 27 other than the two ends in the orthogonal direction of the electrode fingers among the plurality of third electrode fingers 27 are connected to one connection electrode 35 at each of the front end portions on the first bus bar 22 side and the front end portions on the second bus bar 23 side. The third electrode finger 27 is connected to the third electrode finger 27 adjacent to the left and right via each connection electrode 35. By repeating this structure, the shape of the reference potential electrode 39 is set to be a zigzag shape.

[0112] In this modification, the order in which the plurality of electrode fingers are arranged is such that, starting from first electrode finger 25, first electrode finger 25, third electrode finger 27, second electrode finger 26, and third electrode finger 27 form one cycle. Furthermore, the elastic wave device includes a pair of reflectors 33A and 33B. Thus, as in the first embodiment, the filter device can be miniaturized and the insertion loss can be reduced.

[0113] return Figure 2 , hereinafter, the center-to-center distance between the electrode finger located outermost in the orthogonal direction of the electrode fingers among the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 and the reflector electrode finger located innermost in the orthogonal direction of the electrode fingers is set as p2. The center-to-center distance between adjacent reflector electrode fingers is set as p3. In the first embodiment, p1=p2=p3. However, this is not limited to this. hereinafter, examples of the case where p1≠p2 and the case where p1≠p3 are shown through the second embodiment and the third embodiment.

[0114] The basic structure of the elastic wave device involved in the second embodiment and the third embodiment is the same as that of the first embodiment. Therefore, in the description of the second embodiment and the third embodiment, the drawings and reference numerals used in the description of the first embodiment are used. In addition, in the second embodiment and the third embodiment, a pair of reflectors are provided, as in the first embodiment. Thus, when the elastic wave device is used in a filter device, the miniaturization of the filter device can be promoted, and the insertion loss can be reduced.

[0115] In the second embodiment, p1≠p2. In the second embodiment, the center-to-center distance p1 between adjacent electrode fingers in the functional electrode 11 is constant.

[0116] The second embodiment and the comparative example compare the transmission characteristics. The elastic wave device of the comparative example is different from the second embodiment in that it does not have a reflector. Therefore, the elastic wave device of the comparative example does not have Figure 2 The center-to-center distance p2 and the center-to-center distance p3 between adjacent reflector electrode fingers are shown in FIG. This comparison is performed in two cases: the center-to-center distance p1 and the center-to-center distance p2 in the second embodiment are set to p1>p2, and the center-to-center distance p1<p2. The design parameters of the elastic wave device having the structure of the second embodiment are as follows.

[0117] Piezoelectric layer: Material…LiNbO3, Euler angles (φ, θ, ψ)…(0°, 0°, 90°), Thickness…400nm

[0118] First to third electrode fingers: layer structure: Ti layer / AlCu layer / Ti layer from the piezoelectric layer side, thickness of each layer: 10 nm / 390 nm / 4 nm from the piezoelectric layer side

[0119] The order of the first to third electrode fingers is represented by the order of the potentials to be connected: IN, GND, OUT, GND are repeated.

[0120] The center-to-center distance between adjacent electrode fingers p1: 1.4 μm

[0121] Duty cycle of functional electrode: 0.3

[0122] Number of reflector electrode fingers of each reflector: 8

[0123] The results of the first embodiment with p1=p2 are also shown. Design parameters of the elastic wave devices of the first embodiment and the comparative example are shown in FIG. Figure 5 The design parameters in the comparison shown are the same.

[0124] Fig. 9 It is a diagram showing the passage characteristics in the first embodiment where p1=p2, the second embodiment where p1>p2, and a comparative example. Fig.10 It is a diagram showing the passage characteristics in the first embodiment where p1=p2, the second embodiment where p1<p2, and a comparative example.

[0125] Fig. 9 The frequency band surrounded by the double-dashed line in is the frequency band on the low-frequency side of the passband. In the second embodiment, the ripple is smaller on the low-frequency side of the passband than in the first embodiment. This is because, in the second embodiment, Figure 2The reflectors 33A and 33B shown in the figure are arranged such that p1>p2. In the second embodiment, as in the first embodiment, the insertion loss is reduced near the center of the passband compared to the comparative example. In this way, in the case of p1>p2, the insertion loss can be reduced as in the case of p1=p2.

[0126] like Fig.10 As shown, in the case of p1<p2, the peak loss becomes smaller than that of the comparative example on the low-frequency side in the passband.

[0127] By adjusting the center distance p2 between the outermost electrode finger and the innermost reflector electrode finger in the orthogonal direction of the electrode fingers, the position of the mode can be finely adjusted. Thus, when p1>p2 or p1<p2 is set, the above-mentioned respective effects can be obtained.

[0128] In the third embodiment, the center-to-center distance p1 between adjacent electrode fingers and the center-to-center distance p3 between adjacent reflector electrode fingers are different from each other. In the third embodiment, the center-to-center distance p1 is constant.

[0129] The third embodiment and the comparative example compare the transmission characteristics. The elastic wave device of the comparative example is different from the third embodiment in that it does not have a reflector. Therefore, the elastic wave device of the comparative example does not have Figure 2 The center-to-center distance p2 and center-to-center distance p3 are shown in the figure. This comparison is performed in two cases: the center-to-center distance p1 and center-to-center distance p3 in the third embodiment are set to p1>p3, and the case is set to p1<p3. In addition, the results of the first embodiment with p1=p3 are also shown. The design parameters and comparison of the elastic wave devices of the first embodiment, the third embodiment, and the comparative example Fig. 9 as well as Fig.10 The design parameters in the comparison shown are the same.

[0130] Fig.11 It is a diagram showing the passage characteristics in the first embodiment where p1=p3, the third embodiment where p1>p3, and a comparative example. Fig.12 It is a diagram showing the passage characteristics in the first embodiment where p1=p3, the third embodiment where p1<p3, and a comparative example.

[0131] Fig.11 The frequency band surrounded by the double-dashed line in is the frequency band on the low-frequency side of the passband. In the third embodiment, the ripple is smaller on the low-frequency side of the passband than in the first embodiment. This is because, in the third embodiment, Figure 2The reflectors 33A and 33B shown in the figure are arranged such that p1>p3. In the third embodiment, as in the first embodiment, the insertion loss is reduced near the center of the passband compared to the comparative example. In this way, in the case of p1>p3, the insertion loss can be reduced as in the case of p1=p3.

[0132] Fig.12 The frequency band surrounded by the two-dot chain line in is a frequency band on the high frequency side in the passband. In the case of p1<p3, the insertion loss can be effectively reduced on the high frequency side in the passband.

[0133] By adjusting the distance p3 between the centers of adjacent reflector electrode fingers, the position of the mode can be finely adjusted. Therefore, when p1>p3 or p1<p3 is set, the above-mentioned respective effects can be obtained.

[0134] In the first to third embodiments, when the width of the electrode finger of the functional electrode 11 is set to w1 and the width of the reflector electrode finger is set to w2, w1=w2. In addition, the width w1 of the electrode finger is the dimension of the electrode finger along the direction orthogonal to the electrode finger. Similarly, the width w2 of the reflector electrode finger is the dimension of the reflector electrode finger along the direction orthogonal to the direction in which the reflector electrode finger extends. However, w1≠w2 may also be satisfied. This example is shown in the fourth embodiment.

[0135] The basic structure of the elastic wave device of the fourth embodiment is the same as that of the first embodiment. Therefore, in the description of the fourth embodiment, the drawings and reference numerals used in the description of the first embodiment are used. In addition, in the fourth embodiment, a pair of reflectors is provided, as in the first embodiment. Thus, when the elastic wave device is used in a filter device, the miniaturization of the filter device can be promoted, and the insertion loss can be reduced.

[0136] In the fourth embodiment, w1≠w2. In the fourth embodiment and the comparative example, the pass characteristics are compared. The elastic wave device of the comparative example differs from the fourth embodiment in that it does not have a reflector. Therefore, the elastic wave device of the comparative example does not have a parameter such as the width w2 of the reflector electrode finger. The comparison is performed in two cases: the width w1 of the electrode finger and the width w2 of the reflector electrode finger in the fourth embodiment are set to w1>w2, and the width w1<w2 is set to w1. The design parameters of the elastic wave device having the structure of the fourth embodiment are as follows.

[0137] Piezoelectric layer: Material…LiNbO3, Euler angles (φ, θ, ψ)…(0°, 0°, 90°), Thickness…400nm

[0138] First to third electrode fingers: layer structure: Ti layer / AlCu layer / Ti layer from the piezoelectric layer side, thickness of each layer: 10 nm / 390 nm / 4 nm from the piezoelectric layer side

[0139] The order of the first to third electrode fingers is represented by the order of the potentials to be connected: IN, GND, OUT, GND are repeated.

[0140] The center-to-center distance between adjacent electrode fingers p1: 1.4 μm

[0141] Duty cycle of functional electrode: 0.3

[0142] Number of reflector electrode fingers of each reflector: 8

[0143] The results of the first embodiment when w1=w2 are also shown. Design parameters of the elastic wave devices of the first embodiment and the comparative example are shown in FIG. Figure 5 The design parameters in the comparison shown are the same.

[0144] Fig.13 It is a diagram showing the passage characteristics in the first embodiment where w1=w2, the fourth embodiment where w1>w2, and a comparative example. Fig.14 It is a diagram showing the passage characteristics in the first embodiment where w1=w2, the fourth embodiment where w1<w2, and a comparative example.

[0145] Fig.13 The frequency band surrounded by the double-dashed line in is the frequency band on the low-frequency side of the passband. In the fourth embodiment, the ripple is smaller on the low-frequency side of the passband than in the first embodiment. This is because, in the fourth embodiment, Figure 2 The reflector 33A and the reflector 33B shown in the figure are provided, and w1>w2. In the fourth embodiment, as in the first embodiment, the insertion loss is reduced near the center of the passband compared to the comparative example. In this way, in the case of w1>w2, the insertion loss can be reduced as in the case of w1=w2.

[0146] like Fig.14 As shown, in the case of w1<w2, the peak loss becomes smaller on the low-frequency side in the passband than in the comparative example.

[0147] In the present invention, at least one of p1≠p2, p1≠p3, and w1≠w2 may be satisfied. For example, a plurality of p1≠p2, p1≠p3, and w1≠w2 may be satisfied.

[0148] The following describes the details of the thickness shear mode using an example in which the functional electrode is an IDT electrode. In addition, the IDT electrode does not have a third electrode finger. The "electrode" in the IDT electrode described later is equivalent to the electrode finger. The supporting member in the following example is equivalent to the supporting substrate in the present invention. In the following, the reference potential is sometimes recorded as the ground potential.

[0149] Fig.15 (a) is a schematic perspective view showing the appearance of an elastic wave device using a thickness shear mode bulk wave, Fig.15 (b) is a top view showing the electrode structure on the piezoelectric layer. Fig.16 It is along Fig.15 (a) is a cross-sectional view of a portion taken along line AA.

[0150] The elastic wave device 1 has a piezoelectric layer 2 containing LiNbO3. The piezoelectric layer 2 may also contain LiTaO3. The cutting angle of LiNbO3 and LiTaO3 is Z-cut, but it may also be a rotated Y-cut or X-cut. The thickness of the piezoelectric layer 2 is not particularly limited, but in order to effectively excite the thickness shear mode, it is preferably greater than 40nm and less than 1000nm, and more preferably greater than 50nm and less than 1000nm. The piezoelectric layer 2 has a first principal surface 2a and a second principal surface 2b facing each other. An electrode 3 and an electrode 4 are provided on the first principal surface 2a. Here, electrode 3 is an example of a "first electrode", and electrode 4 is an example of a "second electrode". In Fig.15 (a) and Fig.15 In (b), a plurality of electrodes 3 are connected to a first bus bar 5. A plurality of electrodes 4 are connected to a second bus bar 6. The plurality of electrodes 3 and the plurality of electrodes 4 are interlaced with each other. The electrodes 3 and the electrodes 4 have a rectangular shape and a length direction. In a direction orthogonal 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 orthogonal to the length directions of the electrodes 3 and 4 are directions intersecting with the thickness direction of the piezoelectric layer 2. Therefore, it can also be said that the electrode 3 and the adjacent electrode 4 are opposed to each other in a direction intersecting with the thickness direction of the piezoelectric layer 2. In addition, the length directions of the electrodes 3 and 4 can also be orthogonal to the length directions of the electrodes 3 and 4. Fig.15 (a) and Fig.15 The direction perpendicular to the length direction of the electrodes 3 and 4 shown in (b) is changed. Fig.15 (a) and Fig.15 In (b), the electrodes 3 and 4 may be extended in the direction in which the first bus bar 5 and the second bus bar 6 extend. In this case, the first bus bar 5 and the second bus bar 6 are Fig.15 (a) and Fig.15(b) becomes extended in the direction in which electrodes 3 and 4 extend. Moreover, a pair of structures in which an electrode 3 connected to one potential and an electrode 4 connected to another potential are adjacent are provided with multiple pairs in a direction orthogonal to the length direction of the electrodes 3 and 4. Here, the so-called electrode 3 and electrode 4 are adjacent does not mean that the electrodes 3 and electrode 4 are arranged in direct contact, but refers to the case where the electrodes 3 and electrode 4 are arranged with a gap. In addition, when the electrode 3 and electrode 4 are adjacent, no electrode connected to the signal electrode and the ground electrode, including other electrodes 3 and 4, is arranged between the electrode 3 and the electrode 4. The number of pairs does not need to be an integer pair, and can also be 1.5 pairs, 2.5 pairs, etc. The center-to-center distance between the electrodes 3 and 4, that is, the spacing, is preferably in the range of 1 μm or more and 10 μm or less. In addition, the width of the electrodes 3 and 4, that is, the size of the opposing direction of the electrodes 3 and 4, is preferably in the range of 50 nm or more and 1000 nm or less, and more preferably in the range of 150 nm or more and 1000 nm or less. The center-to-center distance between electrodes 3 and 4 is the distance connecting the center of the dimension (width dimension) of electrode 3 in a direction perpendicular to the length direction of electrode 3 and the center of the dimension (width dimension) of electrode 4 in a direction perpendicular to the length direction of electrode 4.

[0151] In addition, in the elastic wave device 1, since a Z-cut piezoelectric layer is used, the direction perpendicular to the length direction of the electrodes 3 and 4 becomes a direction perpendicular to the polarization direction of the piezoelectric layer 2. When a piezoelectric body with another cutting angle is used as the piezoelectric layer 2, this is not limited to this. Here, the so-called "orthogonal" is not limited to the case of being strictly orthogonal, and can also be approximately orthogonal (the angle formed by the direction perpendicular to the length direction of the electrodes 3 and 4 and the polarization direction is, for example, within the range of 90°±10°).

[0152] A support member 8 is stacked on the second main surface 2b side of the piezoelectric layer 2 via an insulating layer 7. The insulating layer 7 and the support member 8 have a frame-like shape. Fig.16 As shown, there are through holes 7a and 8a. Thus, a cavity 9 is formed. The cavity 9 is provided so as not to hinder the vibration of the excitation region C of the piezoelectric layer 2. Therefore, the support member 8 is stacked on the second main surface 2b via the insulating layer 7 at a position that does not overlap with the portion where at least one pair of electrodes 3 and 4 is provided. In addition, the insulating layer 7 may not be provided. Therefore, the support member 8 may be directly or indirectly stacked on the second main surface 2b of the piezoelectric layer 2.

[0153] The insulating layer 7 includes silicon oxide. However, in addition to silicon oxide, suitable insulating materials such as silicon nitride oxide and alumina can also be used. The supporting member 8 includes Si. The surface orientation of the surface of Si on the side of the piezoelectric layer 2 can be (100), (110), or (111). It is preferred that the Si constituting the supporting member 8 has a high resistance with a resistivity of more than 4 kΩcm. However, the supporting member 8 can also be composed of suitable insulating materials or semiconductor materials.

[0154] As the material of the supporting member 8, for example, piezoelectrics such as aluminum oxide, lithium tantalate, lithium niobate, and quartz, various ceramics such as alumina, magnesium oxide, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, and forsterite, dielectrics such as diamond and glass, and semiconductors such as gallium nitride can be used.

[0155] The plurality of electrodes 3, 4 and the first bus bar 5 and the second bus bar 6 include a suitable metal or alloy such as Al or AlCu alloy. In the elastic wave device 1, the electrodes 3, 4 and the first bus bar 5 and the second bus bar 6 have a structure in which an Al film is stacked on a Ti film. Alternatively, a bonding layer other than a Ti film may be used.

[0156] During driving, an AC voltage is applied between the plurality of electrodes 3 and the plurality of electrodes 4. More specifically, an AC voltage is applied between the first bus bar 5 and the second bus bar 6. Thus, it is possible to obtain the resonance characteristics of the bulk wave utilizing the thickness shear mode excited in the piezoelectric layer 2. In addition, in the elastic wave device 1, when the thickness of the piezoelectric layer 2 is set to d and the center-to-center distance between any adjacent electrodes 3 and 4 among the plurality of pairs of electrodes 3 and 4 is set to p, d / p is set to be less than 0.5. Therefore, the bulk wave of the thickness shear mode is effectively excited, and good resonance characteristics can be obtained. More preferably, d / p is less than 0.24, in which case, even better resonance characteristics can be obtained.

[0157] In the elastic wave device 1, since it has the above-mentioned structure, even if the number of pairs of electrodes 3 and 4 is reduced in order to achieve miniaturization, the Q value is not likely to decrease. This is because even if the number of electrode fingers in the reflectors on both sides is reduced, the propagation loss is small. In addition, the number of electrode fingers can be reduced because the body wave of the thickness shear mode is utilized. Fig.17 (a) and Fig.17 (b) explains the difference between the Lamb wave used in the elastic wave device and the body wave of the thickness shear mode.

[0158] Fig.17(a) is a schematic front cross-sectional view for explaining the Lamb wave propagating in the piezoelectric film of the elastic wave device described in the Japanese Patent Gazette JP 2012-257019. Here, the wave propagates in the piezoelectric film 201 as shown 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. Fig.17 As shown in (a), for Lamb waves, the waves propagate in the X direction as shown in the figure. Since it is a plate wave, although the piezoelectric film 201 vibrates as a whole, since the wave propagates in the X direction, reflectors are arranged on both sides to obtain resonance characteristics. Therefore, wave propagation loss occurs, and when miniaturization is sought, that is, when the number of pairs of electrode fingers is reduced, the Q value decreases.

[0159] In contrast, Fig.17 As shown in (b), in the elastic wave device 1, the vibration displacement is in the thickness shear direction, so the wave generally propagates and resonates in the direction connecting the first main surface 2a and the second main surface 2b of the piezoelectric layer 2, that is, the Z direction. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Moreover, the resonance characteristics can be obtained by the propagation of the wave in the Z direction, so even if the number of electrode fingers of the reflector is reduced, it is not easy to cause propagation loss. Furthermore, even if the number of pairs of electrode pairs including electrodes 3 and 4 is reduced in order to promote miniaturization, it is not easy to cause a decrease in the Q value.

[0160] In addition, if Fig.18 As shown in FIG. 1 , the amplitude directions of the thickness shear mode body wave are opposite in the first region 451 included in the excitation region C of the piezoelectric layer 2 and in the second region 452 included in the excitation region C. Fig.18 , a body wave is schematically shown when a voltage is applied between the electrode 3 and the electrode 4 so that the electrode 4 has a higher potential than the electrode 3. The first region 451 is a region between the first principal surface 2a and a virtual plane VP1 that is orthogonal to the thickness direction of the piezoelectric layer 2 and divides the piezoelectric layer 2 into two parts in the excitation region C. The second region 452 is a region between the virtual plane VP1 and the second principal surface 2b in the excitation region C.

[0161] As described above, elastic wave device 1 includes at least one pair of electrodes including electrode 3 and electrode 4 , but since waves are not propagated in the X direction, there is no need to have more than one pair of electrodes including electrode 3 and electrode 4 . In other words, at least one pair of electrodes is sufficient.

[0162] For example, the electrode 3 is an electrode connected to the signal potential, and the electrode 4 is an electrode connected to the ground potential. However, the electrode 3 may be connected to the ground potential, and the electrode 4 may be connected to the signal potential. In the elastic wave device 1, at least one pair of electrodes is an electrode connected to the signal potential or an electrode connected to the ground potential as described above, and no floating electrode is provided.

[0163] Fig.19 It is shown Fig.16 The resonance characteristics of the elastic wave device are shown in FIG. 1. The design parameters of the elastic wave device 1 that obtain the resonance characteristics are as follows.

[0164] Piezoelectric layer 2: LiNbO3 with Euler angles (0°, 0°, 90°), thickness = 400 nm.

[0165] When observed in a direction orthogonal to the length direction of electrode 3 and electrode 4, the length of the overlapping area of ​​electrode 3 and electrode 4, that is, the length of the excitation area C = 40μm, the number of pairs of electrodes including electrodes 3 and 4 = 21 pairs, the center distance between electrodes = 3μm, the width of electrodes 3 and 4 = 500nm, and d / p = 0.133.

[0166] Insulating layer 7: a silicon oxide film having a thickness of 1 μm.

[0167] Supporting member 8: Si.

[0168] The length of the excitation region C refers to the dimension of the excitation region C along the length direction of the electrodes 3 and 4 .

[0169] In elastic wave device 1 , the inter-electrode distances of the electrode pairs including electrodes 3 and 4 are set equal in a plurality of pairs. In other words, electrodes 3 and electrodes 4 are arranged at equal intervals.

[0170] according to Fig.19 It is clear that good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained even though there is no reflector.

[0171] When the thickness of the piezoelectric layer 2 is d and the center-to-center distance between the electrodes 3 and 4 is p, as described above, in the elastic wave device 1, d / p is 0.5 or less, and more preferably 0.24 or less. Fig. 20 This is explained.

[0172] and got Fig.19 A plurality of elastic wave devices are obtained by changing d / p in the same manner as the elastic wave devices having the resonance characteristics shown. Fig. 20 3 is a diagram showing the relationship between d / p and the relative bandwidth of a resonator as an elastic wave device.

[0173] according to Fig. 20It is clear that if d / p>0.5, even if d / p is adjusted, the relative bandwidth is less than 5%. In contrast, when d / p≤0.5, if d / p is changed within this range, the relative 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 relative bandwidth can be increased to more than 7%. Moreover, if d / p is adjusted within this range, a resonator with a wider relative bandwidth can be obtained, and a resonator with a higher coupling coefficient can be realized. Therefore, it can be seen that by setting d / p to less than 0.5, a resonator with a high coupling coefficient that utilizes the body wave of the thickness shear mode mentioned above can be constructed.

[0174] Fig.21 1 is a top view of an elastic wave device using a thickness shear mode bulk wave. In the elastic wave device 80, a pair of electrodes including an electrode 3 and an electrode 4 are provided on the first principal surface 2a of the piezoelectric layer 2. Fig.21 K in is the crossing width. As described above, in the elastic wave device of the present invention, the number of pairs of electrodes may be 1 pair. In this case, as long as the above d / p is 0.5 or less, a thickness shear mode body wave can be effectively excited.

[0175] In the elastic wave device 1, it is preferable that the metallization ratio MR of the excitation region C, which is an area where any adjacent electrodes 3 and 4 overlap when viewed in the opposite direction relative to the adjacent electrodes 3 and 4, satisfies MR≤1.75(d / p)+0.075. In this case, the stray emission can be effectively reduced. Fig. 22 as well as Fig.23 Let's explain this. Fig. 22 : is a reference diagram showing an example of the resonance characteristics of the elastic wave device 1. Spurious signals indicated by arrow B appear between the resonance frequency and the antiresonance frequency. In addition, d / p=0.08 is assumed, and the Euler angles of LiNbO3 are assumed to be (0°, 0°, 90°). In addition, the metallization ratio MR is assumed to be 0.35.

[0176] Reference Fig.15 (b) will explain the metallization ratio MR. Fig.15In the electrode structure of (b), when focusing on a pair of electrodes 3 and 4, it is assumed that only the pair of electrodes 3 and 4 are provided. In this case, the portion surrounded by the single-dot chain line becomes the excitation region C. The so-called excitation region C refers to the region where the electrode 3 overlaps with the electrode 4, the region where the electrode 4 overlaps with the electrode 3, and the region between the electrode 3 and the electrode 4 where the electrode 3 overlaps with the electrode 4 when the electrode 3 and the electrode 4 are observed in the direction perpendicular to the length direction of the electrodes 3 and 4, that is, in the opposite direction. Moreover, the area of ​​the electrodes 3 and 4 in the excitation region C relative to the area of ​​the excitation region C becomes the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of ​​the metallized portion to the area of ​​the excitation region C.

[0177] When a plurality of pairs of electrodes are provided, the ratio of the total area of ​​the metallized portions included in all the excitation regions to the area of ​​the excitation regions may be defined as MR.

[0178] Fig.23 This is a diagram showing the relationship between the relative bandwidth and the phase rotation amount of the impedance of the stray normalized by 180 degrees when a plurality of elastic wave resonators are formed according to the structure of the elastic wave device 1. In addition, the relative bandwidth was adjusted by making various changes to the film thickness of the piezoelectric layer and the size of the electrode. In addition, Fig.23 These are the results obtained when a piezoelectric layer including Z-cut LiNbO 3 is used, but the same tendency is observed when a piezoelectric layer having other cut angles is used.

[0179] exist Fig.23 In the area surrounded by ellipse J in , the spurious signal increases to 1.0. Fig.23 It is clear that if the relative bandwidth exceeds 0.17, that is, if it exceeds 17%, even if the parameters constituting the relative bandwidth are changed, large spurious with a spurious level of 1 or more will appear in the passband. Fig. 22 As shown in the resonance characteristics, large spurious signals indicated by arrow B appear in the frequency band. Therefore, the relative bandwidth is preferably 17% or less. In this case, spurious signals can be reduced by adjusting the film thickness of the piezoelectric layer 2, the dimensions of the electrodes 3 and 4, and the like.

[0180] Fig.24 : is a graph showing the relationship between d / 2p, metallization ratio MR, and relative bandwidth. In the above-mentioned elastic wave device, various elastic wave devices having different d / 2p and MR were constructed, and the relative bandwidth was measured. Fig.24The hatched portion on the right side of the dotted line D is an area where the relative bandwidth is less than 17%. The boundary between the hatched area and the unhatched area is represented by MR=3.5(d / 2p)+0.075. That is, MR=1.75(d / p)+0.075. Therefore, it is preferred that MR≤1.75(d / p)+0.075. In this case, it is easy to make the relative bandwidth less than 17%. More preferably, Fig.24 The region to the right of MR=3.5(d / 2p)+0.05 is indicated by the dashed line D1 in FIG. That is, as long as MR≤1.75(d / p)+0.05, the relative bandwidth can be reliably made 17% or less.

[0181] Fig.25 This is a diagram showing a map of the relative bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible. Fig.25 The multiple regions R shown in the figure with hatching are regions where a relative bandwidth of 2% or more can be obtained. In addition, when φ among the Euler angles (φ, θ, ψ) is within the range of 0°±5°, the relationship between θ and ψ and the relative bandwidth is the same as Fig.25 When the piezoelectric layer contains lithium tantalate (LiTaO3), the relationship between θ and ψ in the Euler angle (in the range of 0°±5°, θ, ψ) and BW is also the same as Fig.25 The relationship shown is the same.

[0182] Therefore, as long as the Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of 0°±5°, and θ and φ are Fig.25 The relative bandwidth can be sufficiently expanded within any of the multiple regions R shown, which is preferred.

[0183] Fig.26 It is a front cross-sectional view of an elastic wave device having an acoustic multilayer membrane.

[0184] In the elastic wave device 81, an acoustic multilayer film 82 is stacked on the second main surface 2b of the piezoelectric layer 2. The acoustic multilayer film 82 has a stacked structure of low acoustic impedance layers 82a, 82c, 82e having relatively low acoustic impedance and high acoustic impedance layers 82b, 82d having relatively high acoustic impedance. When the acoustic multilayer film 82 is used, the bulk wave of the thickness shear mode can be confined in the piezoelectric layer 2 even without using the cavity 9 in the elastic wave device 1. In the elastic wave device 81, by making the above-mentioned d / p less than 0.5, the resonance characteristics of the bulk wave based on the thickness shear mode can be obtained. In addition, in the acoustic multilayer film 82, the number of stacked low acoustic impedance layers 82a, 82c, 82e and high acoustic impedance layers 82b, 82d is not particularly limited. It is sufficient as long as at least one high acoustic impedance layer 82b, 82d is arranged on the side away from the piezoelectric layer 2 compared with the low acoustic impedance layers 82a, 82c, 82e.

[0185] The low acoustic impedance layers 82a, 82c, 82e and the high acoustic impedance layers 82b, 82d can be made of appropriate materials as long as the above-mentioned acoustic impedance relationship is satisfied. For example, silicon oxide or silicon oxynitride can be used as the material of the low acoustic impedance layers 82a, 82c, 82e. In addition, alumina, silicon nitride or metal can be used as the material of the high acoustic impedance layers 82b, 82d.

[0186] Fig. 27 This is a partially cutaway perspective view for explaining an elastic wave device using Lamb waves.

[0187] The elastic wave device 91 has a support substrate 92. The support substrate 92 is provided with a recessed portion opened on the upper surface. A piezoelectric layer 93 is stacked on the support substrate 92. Thus, a cavity 9 is formed. An IDT electrode 94 is provided on the piezoelectric layer 93 above the cavity 9. Reflectors 95 and 96 are provided on both sides of the IDT electrode 94 in the direction of propagation of the elastic wave. Fig. 27 In the figure, the outer periphery of the cavity 9 is shown by a dotted line. Here, the IDT electrode 94 has a first bus bar 94a, a second bus bar 94b, a plurality of first electrode fingers 94c, and a plurality of second electrode fingers 94d. The plurality of first electrode fingers 94c are connected to the first bus bar 94a. The plurality of second electrode fingers 94d are connected to the second bus bar 94b. The plurality of first electrode fingers 94c and the plurality of second electrode fingers 94d are interlaced with each other.

[0188] In the elastic wave device 91, Lamb waves as plate waves are excited by applying an alternating electric field to the IDT electrode 94 on the cavity 9. Furthermore, since the reflectors 95 and 96 are provided on both sides, resonance characteristics based on the Lamb waves can be obtained.

[0189] In the elastic wave devices of the first to fourth embodiments and the modified examples, for example, an acoustic reflection film may be provided between the support member and the piezoelectric layer. Fig.26 The acoustic multilayer membrane 82 shown. Specifically, the supporting member and the piezoelectric layer may be arranged so that at least a portion of the supporting member and at least a portion of the piezoelectric layer are opposed to each other with the acoustic multilayer membrane 82 sandwiched therebetween. In this case, in the acoustic multilayer membrane 82, it is sufficient to alternately stack low acoustic impedance layers and high acoustic impedance layers. The acoustic multilayer membrane 82 may also be an acoustic reflection portion in an elastic wave device.

[0190] In the elastic wave devices of the first to fourth embodiments and the modified examples using bulk waves in the thickness shear mode, as described above, d / p is preferably 0.5 or less, and more preferably 0.24 or less. This can provide better resonance characteristics.

[0191] Furthermore, in the excitation region of the elastic wave device in the first to fourth embodiments and the modified examples using the thickness shear mode body wave, as described above, MR ≤ 1.75 (d / p) + 0.075 is preferably satisfied. More specifically, when the metallization ratio of the first electrode finger and the third electrode finger, and the second electrode finger and the third electrode finger with respect to the excitation region is MR, MR ≤ 1.75 (d / p) + 0.075 is preferably satisfied. In this case, spurious emission can be suppressed more reliably.

[0192] Description of Reference Numerals

[0193] 1…Elastic wave device

[0194] 2…Piezoelectric layer

[0195] 2a, 2b…1st and 2nd main surfaces

[0196] 3, 4…Electrode

[0197] 5, 6…1st and 2nd bus bars

[0198] 7…Insulation layer

[0199] 7a…Through hole

[0200] 8…Supporting member

[0201] 8a…Through hole

[0202] 9…Hollow

[0203] 10…Elastic wave device

[0204] 10a…Cavity

[0205] 11…Functional electrode

[0206] 12…Piezoelectric substrate

[0207] 13…Supporting member

[0208] 14…Piezoelectric layer

[0209] 14a, 14b…1st, 2nd main surface

[0210] 15…Insulation layer

[0211] 16...Support base plate

[0212] 17, 18…1st and 2nd comb-shaped electrodes

[0213] 19…Reference potential electrode

[0214] 22-24…1st to 3rd bus bars

[0215] 24A, 24B ... 1st and 2nd connecting electrodes

[0216] 24a…Article

[0217] 24b…protrusion

[0218] 25-27…1st to 3rd electrode fingers

[0219] 29…Insulation film

[0220] 33A, 33B…Reflector

[0221] 33a, 33b ... 1st and 2nd reflector bus bars

[0222] 33c…Reflector electrode finger

[0223] 33d, 33e…1st and 2nd reflector bus bars

[0224] 33f…Reflector electrode finger

[0225] 35…Connect the electrodes

[0226] 39…Reference potential electrode

[0227] 80, 81…Elastic wave device

[0228] 82…Acoustic multilayer film

[0229] 82a, 82c, 82e…low acoustic impedance layer

[0230] 82b, 82d…high acoustic impedance layer

[0231] 91…Elastic wave device

[0232] 92…Support base plate

[0233] 93…Piezoelectric layer

[0234] 94…IDT electrode

[0235] 94a, 94b…1st and 2nd bus bars

[0236] 94c, 94d ... first and second electrode fingers

[0237] 95, 96…Reflector

[0238] 201…Piezoelectric film

[0239] 201a, 201b ... first and second main surfaces

[0240] 451, 452…1st and 2nd areas

[0241] C…Incentive Area

[0242] E…Intersection Area

[0243] R…Region

[0244] VP1…Virtual Plane.

Claims

1. An elastic wave device comprising: a piezoelectric layer comprising lithium niobate; a first comb-shaped electrode, disposed on the piezoelectric layer, having a first bus bar and a plurality of first electrode fingers each having one end connected to the first bus bar, and connected to an input potential; A second comb-shaped electrode, disposed on the piezoelectric layer, having a second bus bar and a plurality of second electrode fingers, one end of each of which is connected to the second bus bar, connected to an output potential, wherein the plurality of second electrode fingers are interlaced with the plurality of first electrode fingers; and a reference potential electrode having a plurality of third electrode fingers and a connection electrode for connecting adjacent third electrode fingers to each other, connected to a reference potential, wherein the plurality of third electrode fingers are respectively arranged on the piezoelectric layer so as to be arranged 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, The first electrode finger, the second electrode finger, and the third electrode finger are arranged in an order starting from the first electrode finger, such that the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger form one cycle. The elastic wave device also has a pair of reflectors. When a direction orthogonal to the directions in which the first electrode finger, the second electrode finger, and the third electrode finger extend is set as an electrode finger orthogonal direction, the pair of reflectors are arranged on the piezoelectric layer to sandwich an area where the first electrode finger, the second electrode finger, and the third electrode finger are arranged in the electrode finger orthogonal direction, and each has at least one reflector electrode finger.

2. The elastic wave device according to claim 1, wherein: Each of the reflectors has eight or more reflector electrode fingers.

3. The elastic wave device according to claim 1 or 2, wherein: The distance between the centers of the adjacent first electrode fingers and the third electrode fingers, and the distance between the centers of the adjacent second electrode fingers and the third electrode fingers are constant. When the center-to-center distance between the adjacent first electrode finger and the third electrode finger, and the center-to-center distance between the adjacent second electrode finger and the third electrode finger are set to p1, and the center-to-center distance between the outermost electrode finger in the orthogonal direction of the electrode fingers among the first electrode finger, the second electrode finger, and the third electrode finger and the innermost reflector electrode finger in the orthogonal direction of the electrode fingers is set to p2, p1≠p2.

4. The elastic wave device according to any one of claims 1 to 3, wherein: The pair of reflectors each has a plurality of reflector electrode fingers, The distance between the centers of the adjacent first electrode fingers and the third electrode fingers, and the distance between the centers of the adjacent second electrode fingers and the third electrode fingers are constant. When the center-to-center distance between the adjacent first electrode fingers and the third electrode fingers and the center-to-center distance between the adjacent second electrode fingers and the third electrode fingers are denoted as p1, and the center-to-center distance between the adjacent reflector electrode fingers is denoted as p3, p1≠p3.

5. The elastic wave device according to any one of claims 1 to 4, wherein: The plurality of first electrode fingers, the plurality of second electrode fingers, and the plurality of third electrode fingers have the same width, When the width of each of the first electrode finger, the second electrode finger, and the third electrode finger is w1, and the width of the reflector electrode finger is w2, w1≠w2.

6. The elastic wave device according to any one of claims 1 to 5, wherein: The reflector is connected to any one of an output potential, an input potential, and a reference potential.

7. The elastic wave device according to any one of claims 1 to 5, wherein: The reflector is not connected to the output potential, the input potential and the reference potential.

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

9. The elastic wave device according to any one of claims 1 to 7, wherein: The elastic wave device is configured to utilize thickness shear mode body waves.

10. The elastic wave device according to any one of claims 1 to 7, wherein: The elastic wave device further includes a supporting member stacked on the piezoelectric layer. In a plan view along the stacking direction of the support member and the piezoelectric layer, an acoustic reflection portion is formed at a position of the support member overlapping with the plurality of first electrode fingers, the plurality of second electrode fingers, and the plurality of third electrode fingers, When the longest distance between the centers of the adjacent first and third electrode fingers and the center distance between the adjacent second and third electrode fingers is represented by p, and the thickness of the piezoelectric layer is represented by d, d / p is less than or equal to 0.

5.

11. The elastic wave device according to claim 10, wherein: d / p is less than 0.

24.

12. The elastic wave device according to claim 10 or 11, wherein: The sound reflecting portion is a cavity portion, and the supporting member and the piezoelectric layer are arranged so that a portion of the supporting member and a portion of the piezoelectric layer face each other with the cavity portion interposed therebetween.

13. The elastic wave device according to claim 10 or 11, 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 layer are configured so that at least a portion of the supporting member and at least a portion of the piezoelectric layer are opposite to each other with the acoustic reflection membrane sandwiched therebetween.

14. The elastic wave device according to any one of claims 10 to 13, wherein: The region where the adjacent first electrode finger and the adjacent third electrode finger overlap each other in the orthogonal direction of the electrode fingers and the region between the centers of the adjacent first electrode finger and the adjacent third electrode finger, and the region where the adjacent second electrode finger and the adjacent third electrode finger overlap each other in the orthogonal direction of the electrode fingers and the region between the centers of the adjacent second electrode finger and the adjacent third electrode finger are excitation regions. When the metallization ratio of the first electrode finger and the third electrode finger, and the second electrode finger and the third electrode finger with respect to the excitation region is MR, MR≦1.75(d / p)+0.075 is satisfied.

15. The elastic wave device according to any one of claims 1 to 14, 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°, arbitrary ψ) …Formula (1) (Within the range of 0°±10°, 25°~100°, 75°[(1-(θ-50) 2 / 2500)] 1 / 2 or 180°-75°[(1-(θ-50) 2 / 2500)] 1 / 2 ~180°) …Formula (2) (Within the range of 0°±10°, 180°-40°[(1-(ψ-90) 2 / 8100)] 1 / 2 ~180°, arbitrary ψ) …Equation (3).

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