Elastic wave device

Abstract

Provided is an elastic wave device that, when used in a filter device, is capable of achieving suitable filter waveforms even if the size of the elastic wave device is not increased.　An elastic wave device according to the present invention is provided with: a piezoelectric layer 14 having a first principal surface 14a and a second principal surface that are opposed to each other; at least one first electrode finger 25 that is provided on the first principal surface 14a of the piezoelectric layer 14 and that is connected to an input potential; at least one second electrode finger 26 that is provided on the first principal surface 14a of the piezoelectric layer 14 and that is connected to an output potential; and at least one third electrode finger 27 that is provided on at least one of the first principal surface 14a and the second principal surface of the piezoelectric layer 14 and that is connected to a reference potential. When viewed in an electrode finger-orthogonal direction that is orthogonal to the direction in which the first electrode finger 25 and the second electrode finger 26 extend, the first electrode finger 25 and the second electrode finger 26 are opposed to each other. In the electrode finger orthogonal direction, a region in which a first electrode finger 25 and a second electrode finger 26 adjacent to each other overlap is an opposed region F. When viewed in a principal surface-opposed direction in which the first principal surface 14a and the second principal surface of the piezoelectric layer 14 are opposed to each other, the third electrode finger 27 overlaps at least a portion of at least one opposed region F.

Description

Technical Field

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

Background Art

[0002] Conventionally, elastic wave devices have been widely used in filters for mobile phones and the like. In recent years, an elastic wave device using a bulk wave in a thickness shear mode as described in Patent Document 1 below has been proposed. In this elastic wave device, a piezoelectric layer is provided on a support. On the piezoelectric layer, opposing electrodes are provided. The opposing electrodes face each other on the piezoelectric layer and are connected to different potentials. By applying an alternating voltage between the electrodes, a bulk wave in a thickness shear mode is excited.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An elastic wave device is, for example, an elastic wave resonator and is used in, for example, a ladder-type filter. In order to obtain good characteristics in a ladder-type filter, it is necessary to increase the capacitance ratio between a plurality of elastic wave resonators. In this case, it is necessary to increase the capacitance of some of the elastic wave resonators in the ladder-type filter.

[0005] In order to increase the capacitance of the elastic wave resonator, for example, it is necessary to increase the size of the elastic wave resonator. Therefore, when the elastic wave resonator is used in a ladder-type filter, the ladder-type filter tends to become large. In particular, a ladder-type filter having an elastic wave resonator that utilizes a bulk wave in a thickness shear mode with a small capacitance becomes large.

[0006] An object of the present invention is to provide an elastic wave device capable of obtaining a suitable filter waveform without increasing the size when used in a filter device.

Means for Solving the Problems

[0007] The elastic wave device according to the present invention includes a piezoelectric layer having opposing first and second main surfaces, at least one first electrode finger provided on the first main surface of the piezoelectric layer and connected to an input potential, at least one second electrode finger provided on the first main surface of the piezoelectric layer and connected to an output potential, and at least one third electrode finger provided on at least one of the first main surface and the second main surface of the piezoelectric layer and connected to a reference potential. When viewed from a direction orthogonal to the direction in which the first electrode finger and the second electrode finger extend, the first electrode finger and the second electrode finger face each other. In the direction orthogonal to the electrode fingers, a region where adjacent first electrode fingers and second electrode fingers overlap is an opposing region. When viewed from the main surface opposing direction in which the first main surface and the second main surface of the piezoelectric layer face each other, the third electrode finger overlaps at least a part of at least one of the opposing regions.

Effects of the Invention

[0008] According to the present invention, it is possible to provide an elastic wave device capable of obtaining a suitable filter waveform without increasing the size when used in a filter device.

Brief Description of the Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the present invention will be clarified by explaining specific embodiments of the present invention with reference to the drawings.

[0011] It should be noted that each embodiment described in this specification is exemplary, and it is pointed out that partial substitution or combination of configurations is possible between different embodiments.

[0012] FIG. 1 is a schematic front cross-sectional view of an elastic wave device according to a first embodiment of the present invention. FIG. 2 is a schematic plan view showing the electrode structure of the elastic wave device according to the first embodiment.

[0013] The elastic wave device 10 shown in FIG. 1 is an elastic wave resonator configured to be able to utilize the thickness shear mode. In addition, the elastic wave device 10 is an acoustic coupling type filter. Hereinafter, the configuration of the elastic wave device 10 will be described.

[0014] The elastic wave device 10 includes a piezoelectric substrate 12 and a functional electrode 11. The piezoelectric substrate 12 includes a support member 13 and a piezoelectric layer 14. In the present embodiment, the support member 13 includes a support substrate 16 and an insulating layer 15. The insulating layer 15 is provided on the support substrate 16. The piezoelectric layer 14 is provided on the insulating layer 15. However, the support member 13 may be constituted by only the support substrate 16.

[0015] 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 face each other. Among the first main surface 14a and the second main surface 14b, the second main surface 14b is located on the support member 13 side. In the present embodiment, the functional electrode 11 is provided on the first main surface 14a of the piezoelectric layer 14. Note that, among the first main surface 14a and the second main surface 14b, the first main surface 14a may be located on the support member 13 side. In this case, the functional electrode 11 may be provided on the first main surface 14a.

[0016] As shown in FIG. 2, 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 are 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. More specifically, the first comb-shaped electrode 17 is connected to the input potential via an input terminal 28. On the other hand, the second comb-shaped electrode 18 is connected to an output potential. More specifically, the second comb-shaped electrode 18 is connected to the output potential via an output terminal 29. The input terminal 28 and the output terminal 29 may be configured as electrode pads, or may be configured as wirings.

[0017] The first comb-shaped electrode 17 is directly connected to the input terminal 28. However, the first comb-shaped electrode 17 may be indirectly connected to the input terminal 28 via other elements. The second comb-shaped electrode 18 is directly connected to the output terminal 29. However, the second comb-shaped electrode 18 may be indirectly connected to the output terminal 29 via other elements. Note that the first comb-shaped electrode 17 may be connected to the output potential and the second comb-shaped electrode 18 may be connected to the input potential.

[0018] The 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 the first bus bar 22. The 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 the second bus bar 23.

[0019] The first bus bar 22 and the second bus bar 23 face each other. In the present embodiment, the number of each of the plurality of first electrode fingers 25 and the plurality of second electrode fingers 26 is three or more. The plurality of first electrode fingers 25 and the plurality of second electrode fingers 26 are interposed with each other.

[0020] Hereinafter, the direction in which the first electrode finger 25 and the second electrode finger 26 extend is defined as the electrode finger extension direction, and the direction orthogonal to the electrode finger extension direction is defined as the electrode finger orthogonal direction. When the direction in which the first electrode finger 25 and the second electrode finger 26 face each other is defined as the electrode finger facing direction, the electrode finger facing direction and the electrode finger orthogonal direction are parallel.

[0021] Between the first comb-shaped electrode 17 and the second comb-shaped electrode 18, a plurality of opposing regions F, a plurality of first regions Ga, and a plurality of second regions Gb are formed. In FIG. 2, one opposing region F, first region Ga, and second region Gb are shown as examples.

[0022] More specifically, when viewed from the direction orthogonal to the electrode fingers, the region where the adjacent first electrode finger 25 and second electrode finger 26 overlap is the opposing region F. The region between the opposing region F and the first bus bar 22 is the first region Ga. The region between the opposing region F and the second bus bar 23 is the second region Gb. The opposing region F, the first region Ga, and the second region Gb are regions of the piezoelectric layer 14 defined based on the configuration of the functional electrode 11.

[0023] The reference potential electrode 19 has a meandering shape. Specifically, the reference potential electrode 19 includes a plurality of third electrode fingers 27 and a plurality of connection electrodes 24. The plurality of third electrode fingers 27 extend parallel to the electrode finger extending direction and are arranged parallel to the direction orthogonal to the electrode fingers. That is, when the direction in which the plurality of third electrode fingers 27 are arranged in a plan view is defined as the column direction, the column direction and the direction orthogonal to the electrode fingers are parallel. In this specification, the plan view means viewing along the lamination direction of the support member 13 and the piezoelectric layer 14 from the direction corresponding to above in FIG. 1. In FIG. 1, for example, the piezoelectric layer 14 side is above among the support substrate 16 and the piezoelectric layer 14. Further, in this specification, the plan view is considered to be synonymous with viewing from the main surface facing direction. The main surface facing direction is the direction in which the first main surface 14a and the second main surface 14b of the piezoelectric layer 14 face each other. More specifically, the main surface facing direction is, for example, the normal direction of the first main surface 14a. In the present embodiment, when viewed from the main surface facing direction, the plurality of third electrode fingers 27 are arranged in the direction orthogonal to the electrode fingers.

[0024] In the present embodiment, the number of the plurality of third electrode fingers 27 is three or more. One end portions or the other end portions of the adjacent third electrode fingers 27 are connected by the connection electrodes 24. Thereby, the shape of the reference potential electrode 19 is a meandering shape. Note that the shape of the reference potential electrode 19 is not limited to the meandering shape.

[0025] A part of the reference potential electrode 19 overlaps with the region between the first comb-shaped electrode 17 and the second comb-shaped electrode 18 in a plan view. Specifically, each third electrode finger 27 in the reference potential electrode 19 overlaps with the first region Ga, the opposing region F, and the second region Gb in a plan view. Among all the connection electrodes 24, a plurality of connection electrodes 24 overlap with the first region Ga in a plan view. These connection electrodes 24 connect the ends of adjacent third electrode fingers 27 that overlap with the first region Ga in a plan view.

[0026] The remaining plurality of connection electrodes 24 overlap with the second region Gb in a plan view. These connection electrodes 24 connect the ends of adjacent third electrode fingers 27 that overlap with the second region Gb in a plan view. The connection electrodes 24 provided in the first region Ga and the connection electrodes 24 provided in the second region Gb are arranged alternately in the column direction. The reference potential electrode 19 is provided so as to reach each opposing region F, each first region Ga, and each second region Gb.

[0027] A part of the reference potential electrode 19 overlaps with the region outside the first comb-shaped electrode 17 and the second comb-shaped electrode 18 in a plan view. This part is connected to the reference potential through, for example, other wirings, electrode pads, etc. In the following, the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 may be simply referred to as electrode fingers.

[0028] FIG. 3 is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers in the first embodiment.

[0029] A third electrode finger 27 is provided between the adjacent first electrode finger 25 and second electrode finger 26. When starting from the first electrode finger 25, the order in which the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 are arranged is such that one cycle consists of the first electrode finger 25, the third electrode finger 27, the second electrode finger 26, and the third electrode finger 27. In other words, the plurality of electrode fingers are arranged such that the potentials of the electrode fingers are in the order of input potential, reference potential, output potential, reference potential, input potential, …. Note that at least one of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 may be provided.

[0030] The first comb-shaped electrode 17, the second comb-shaped electrode 18, and the reference potential electrode 19 may all be made of a single-layer metal film or may be made of a laminated metal film.

[0031] The elastic wave device 10 is an elastic wave resonator configured to be able to utilize a thickness-slip mode bulk wave. As shown in FIG. 2, the elastic wave device 10 has a plurality of excitation regions C. In the plurality of excitation regions C, a thickness-slip mode bulk wave or an elastic wave of another mode is excited. Note that in FIG. 2, only two of the plurality of excitation regions C are shown.

[0032] Among all the excitation regions C, some of the plurality of excitation regions C are regions where the adjacent first electrode finger 25 and third electrode finger 27 overlap when viewed in the direction orthogonal to the electrode fingers, and are regions between the centers of the adjacent first electrode finger 25 and third electrode finger 27. The remaining plurality of excitation regions C are regions where the adjacent second electrode finger 26 and third electrode finger 27 overlap when viewed in the direction orthogonal to the electrode fingers, and are regions between the centers of the adjacent second electrode finger 26 and third electrode finger 27. These excitation regions C are arranged in the direction orthogonal to the electrode fingers. Note that the excitation region C is a region of the piezoelectric layer 14 defined based on the configuration of the functional electrode 11.

[0033] The features of this embodiment are as follows. 1) The first main surface 14a of the piezoelectric layer 14 is provided with a first electrode finger 25, a second electrode finger 26, and a third electrode finger 27. 2) When viewed from the main surface facing direction, the third electrode finger 27 overlaps at least a part of at least one opposing region F. Thereby, a filter waveform of the elastic wave device 10 can be preferably obtained. When the elastic wave device 10 is used as a filter device as an elastic wave resonator, a filter waveform can be preferably obtained even if the number of elastic wave resonators constituting the filter device is one or small, and the filter device can be miniaturized. This detail will be described below with reference to a comparative example.

[0034] As shown in FIG. 4, the comparative example is different from the first embodiment in that it does not have a reference potential electrode. Specifically, the elastic wave resonator 100 of the comparative example has a first comb-shaped electrode 107 and a second comb-shaped electrode 108. The IDT electrode 101 is constituted by the first comb-shaped electrode 107 and the second comb-shaped electrode 108. The excitation region C in the elastic wave resonator 100 is a region where adjacent first electrode fingers 105 and second electrode fingers 106 overlap when viewed from the direction orthogonal to the electrode fingers, and is a region between the centers of adjacent first electrode fingers 105 and second electrode fingers 106.

[0035] FIG. 5 is a diagram showing an example of the relationship between the capacitance and the area of the excitation region in the comparative example. In the example shown in FIG. 5, the thickness of the piezoelectric layer 14 is 375 nm, the center-to-center distance between adjacent first electrode fingers 105 and second electrode fingers 106 is 4.8 μm, and the width of each electrode finger is 960 nm. The width of the electrode finger is the dimension of the electrode finger along the direction orthogonal to the electrode finger.

[0036] As shown in Fig. 5, in the comparative example, it can be seen that as the capacitance in the elastic wave resonator 100 increases, the area of the excitation region C also increases. Here, when the elastic wave resonator 100 is used in a filter device, in order to preferably obtain a filter waveform, it is necessary to increase the capacitance ratio between a plurality of elastic wave resonators 100. However, by using an elastic wave resonator 100 with a large capacitance, it becomes more difficult to miniaturize the filter device.

[0037] On the other hand, in the first embodiment shown in Fig. 1, a filter waveform of the elastic wave device 10 can be preferably obtained. Therefore, when the elastic wave device 10 is used as an elastic wave resonator in a filter device, even if there is one or a small number of elastic wave resonators constituting the filter device, a filter waveform can be preferably obtained, and the miniaturization of the filter device can be promoted. Here, the passing characteristics and reflection characteristics of the elastic wave device 10 as an elastic wave resonator are shown below.

[0038] Fig. 6 is a diagram showing the passing characteristics and reflection characteristics of the elastic wave device according to the first embodiment. Note that Fig. 6 shows the results by FEM (Finite Element Method) simulation.

[0039] As shown in Fig. 6, it can be seen that a filter waveform can be preferably obtained even in one elastic wave device 10. The elastic wave device 10 is an acoustic coupling type filter. More specifically, as shown in Fig. 3, the elastic wave device 10 has an excitation region C located between the centers of adjacent first electrode fingers 25 and third electrode fingers 27, and an excitation region C located between the centers of adjacent second electrode fingers 26 and third electrode fingers 27. In these excitation regions C, elastic waves of a plurality of modes including a thickness-slip mode bulk wave are excited. By combining these modes, a filter waveform can be preferably obtained even in one elastic wave device 10.

[0040] Hereinafter, the configuration of the first embodiment will be described in more detail.

[0041] As shown in FIG. 1, the support member 13 is composed of a support substrate 16 and an insulating layer 15. The piezoelectric substrate 12 is a laminate 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 in the main surface facing direction. As the material of the support substrate 16, for example, a semiconductor such as silicon or a ceramic such as aluminum oxide can be used. As the material of the insulating layer 15, an appropriate dielectric 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 or a lithium tantalate layer such as a LiTaO3 layer.

[0042] A cavity 10a is provided in the insulating layer 15. More specifically, a recess is provided in the insulating layer 15. The piezoelectric layer 14 is provided on the insulating layer 15 so as to close the recess. Thereby, a hollow portion is formed. This hollow portion is the cavity 10a. In the present embodiment, the support member 13 and the piezoelectric layer 14 are arranged such that a part of the support member 13 and a part of the piezoelectric layer 14 sandwich the cavity 10a and face each other. However, the recess in the support member 13 may be provided across the insulating layer 15 and the support substrate 16. Alternatively, the recess provided only in the support substrate 16 may be closed by the insulating layer 15. The recess may be provided in the piezoelectric layer 14. Note that the cavity 10a may be a through hole provided in the support member 13.

[0043] The cavity 10a is an acoustic reflection part in the present invention. The acoustic reflection part can effectively confine the energy of the elastic wave to the piezoelectric layer 14 side. The acoustic reflection part may be provided at a position in the support member 13 that overlaps at least a part of the functional electrode 11 in a plan view. More specifically, in a plan view, at least a part of each of the first electrode finger 25 and the second electrode finger 26 may overlap the cavity 10a. In a plan view, it is preferable that at least a part of each of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 overlaps the cavity 10a. In a plan view, it is more preferable that a plurality of excitation regions C overlap the cavity 10a. As described above, in this specification, "plan view" is synonymous with "viewed from the main surface facing direction".

[0044] In the first embodiment, the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 are provided on the same main surface of the piezoelectric layer 14. However, for example, the first electrode finger 25 and the second electrode finger 26 may be provided on the first main surface 14a, and the third electrode finger 27 may be provided on the second main surface 14b. Alternatively, the first electrode finger 25 and the second electrode finger 26 may be provided on the second main surface 14b, and the third electrode finger 27 may be provided on the first main surface 14a.

[0045] Even in these cases, it is sufficient that the third electrode finger 27 overlaps at least a part of the opposing region F shown in FIG. 1 in a plan view. In these cases, the adjacent first electrode finger 25 and the third electrode finger 27 refer to the first electrode finger 25 and the third electrode finger 27 that are adjacent in a plan view. Similarly, the adjacent second electrode finger 26 and the third electrode finger 27 refer to the second electrode finger 26 and the third electrode finger 27 that are adjacent in a plan view. However, the same applies even when the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 are provided on the same main surface. The electrode fingers adjacent in a plan view are synonymous with the electrode fingers adjacent when viewed from the thickness opposing direction.

[0046] In the first embodiment, the center-to-center distance between a plurality of pairs of adjacent first electrode fingers 25 and third electrode fingers 27 in a plan view is the same as the center-to-center distance between a plurality of pairs of adjacent second electrode fingers 26 and third electrode fingers 27 in a plan view. In this case, when the thickness of the piezoelectric layer 14 is d and the center-to-center distance between adjacent electrode fingers is p, it is preferable that d / p is 0.5 or less. More preferably, d / p is 0.24 or less. Thereby, the bulk wave of the thickness-slip mode is preferably excited.

[0047] However, the center-to-center distance between the first electrode finger 25 and the third electrode finger 27 adjacent to each other in a plan view and the center-to-center distance between the second electrode finger 26 and the third electrode finger 27 adjacent to each other in a plan view do not necessarily have to be constant. In this case, it is preferable to set the longest distance among the center-to-center distance between the first electrode finger 25 and the third electrode finger 27 adjacent to each other in a plan view and the center-to-center distance between the second electrode finger 26 and the third electrode finger 27 adjacent to each other in a plan view as p. In this case, it is preferable that d / p is 0.5 or less, and more preferably, d / p is 0.24 or less. Note that the elastic wave device of the present invention does not necessarily have to be configured to be able to utilize the thickness-slip mode.

[0048] In the first embodiment, the frequency and the bandwidth can be adjusted by adjusting the center-to-center distance p between adjacent electrode fingers. This example is shown below. Specifically, the center-to-center distance p was changed, and the transmission characteristics were obtained by FEM simulation. The design parameters of the elastic wave device 10 are as follows.

[0049] Piezoelectric layer: Material... Z-cut LiNbO3, Thickness... 400 nm First to third electrode fingers: Material... Al, Thickness... 500 nm, Width... 800 nm Center-to-center distance p: 4 μm or 2 μm

[0050] FIG. 7 is a diagram showing the relationship between the center-to-center distance between adjacent electrode fingers and the transmission characteristics in the first embodiment.

[0051] As shown in FIG. 7, when the center-to-center distance p between adjacent electrode fingers is made different, the position of the passband and the bandwidth are different. Therefore, by adjusting the center-to-center distance p, it is possible to obtain pass characteristics that are the desired position of the passband and the bandwidth.

[0052] In the elastic wave device 10, a plurality of modes including a thickness-slip mode bulk wave are excited. The passband is determined by the frequency interval between different modes. And by adjusting the center-to-center distance p between adjacent electrode fingers, the position of each mode and the frequency interval between different modes can be adjusted. Thereby, the position and bandwidth of the passband can be adjusted.

[0053] Note that in the present invention, at least one of the first electrode finger 25, the second electrode finger 26, and the third electrode finger 27 may be provided. The first comb-shaped electrode 17 and the second comb-shaped electrode 18 do not necessarily have to be configured.

[0054] It is preferable that the elastic wave device 10 has a plurality of opposing regions F. In this case, at least one of the first electrode finger 25 and the second electrode finger 26 may be provided in a plurality. Thereby, it is only necessary that a plurality of opposing regions F are configured. However, it is more preferable that both the first electrode finger 25 and the second electrode finger 26 are provided in a plurality.

[0055] In the present invention, at least one third electrode finger 27 may be provided on at least one of the first main surface 14a and the second main surface 14b of the piezoelectric layer 14. And at least one third electrode finger 27 may overlap at least a part of at least one opposing region F in a plan view.

[0056] However, it is preferable that a plurality of third electrode fingers 27 are provided and the plurality of third electrode fingers 27 are arranged side by side as in the first embodiment. Specifically, it is preferable that at least two third electrode fingers 27 arranged continuously in the column direction overlap, in a plan view, with the opposing regions F that are arranged continuously in the direction orthogonal to the electrode fingers among the plurality of opposing regions F. It is more preferable that three or more third electrode fingers 27 arranged continuously in the column direction overlap, in a plan view, with the opposing regions F that are arranged continuously in the direction orthogonal to the electrode fingers among the plurality of opposing regions F. Thereby, the filter waveform of the elastic wave device 10 can be obtained more reliably. Note that it is preferable that the column direction is parallel to the direction orthogonal to the electrode fingers.

[0057] Incidentally, in the present invention, it is sufficient that at least one third electrode finger 27 is provided. For example, in a modification of the first embodiment shown in FIG. 8, the reference potential electrode 19A has one third electrode finger 27. The reference potential electrode 19A does not have a connection electrode. However, the reference potential electrode 19A has a wiring connected to the reference potential, as in the first embodiment. The third electrode finger 27 is connected to the reference potential by this wiring.

[0058] In this modification, the functional electrode 11A has a pair of first electrode fingers 25 and second electrode fingers 26. That is, the number of the first electrode fingers 25 of the first comb-shaped electrode 17A is one. Similarly, the number of the second electrode fingers 26 of the second comb-shaped electrode 18A is one. Even when the elastic wave device of this modification is used as an elastic wave resonator in a filter device, a filter waveform can be suitably obtained even if the number of elastic wave resonators constituting the filter device is one or small, as in the first embodiment. Therefore, the filter device can be made small.

[0059] FIG. 9 is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers in the second embodiment.

[0060] This embodiment is different from the first embodiment in that the reference potential electrode 19 is provided on the second main surface 14b of the piezoelectric layer 14. Except for the above point, the surface acoustic wave device 30 of this embodiment has the same configuration as the surface acoustic wave device 10 of the first embodiment.

[0061] In this embodiment, when viewed in plan view, the adjacent first electrode fingers 25 and third electrode fingers 27 overlap in the direction orthogonal to the electrode fingers, and the region between the centers of the adjacent first electrode fingers 25 and third electrode fingers 27 is the excitation region C. When viewed in plan view, the adjacent second electrode fingers 26 and third electrode fingers 27 overlap in the direction orthogonal to the electrode fingers, and the region between the centers of the adjacent second electrode fingers 26 and third electrode fingers 27 is also the excitation region C. In other words, when viewed from the main surface facing direction, the region where the adjacent first electrode fingers 25 and second electrode fingers 26 overlap directly or via the third electrode finger 27 in the direction orthogonal to the electrode fingers is the excitation region C.

[0062] Similar to the first embodiment, the filter waveform of the surface acoustic wave device 30 can be suitably obtained. Therefore, by using the surface acoustic wave device 30 as a surface acoustic wave resonator in a filter device, the number of surface acoustic wave resonators constituting the filter device can be reduced. Therefore, the filter device can be made small.

[0063] FIG. 10 is a schematic front cross-sectional view showing the vicinity of the first to fifth electrode fingers in the third embodiment. FIG. 11 is a schematic bottom view showing the electrode structure on the second main surface of the piezoelectric layer in the third embodiment.

[0064] As shown in FIG. 10, this embodiment is different from the first embodiment in that a pair of comb-shaped electrodes and a reference potential electrode are provided on both main surfaces of the piezoelectric layer 14, respectively. The functional electrode 41 includes a first comb-shaped electrode 17, a second comb-shaped electrode 18, a reference potential electrode 19, a fourth comb-shaped electrode 47, a fifth comb-shaped electrode 48, and a reference potential electrode 49. The fourth comb-shaped electrode 47 is the third comb-shaped electrode in the functional electrode 41, but for convenience, it is referred to as the fourth comb-shaped electrode 47. Except for the above points, the surface acoustic wave device 40 of this embodiment has the same configuration as the surface acoustic wave device 10 of the first embodiment.

[0065] On the first main surface 14a of the piezoelectric layer 14, a first comb-shaped electrode 17, a second comb-shaped electrode 18, and a reference potential electrode 19 are provided. The configuration of the functional electrode 41 on the first main surface 14a is the same as that of the first embodiment. On the other hand, on the second main surface 14b, a fourth comb-shaped electrode 47, a fifth comb-shaped electrode 48, and a reference potential electrode 49 are provided.

[0066] As shown in FIG. 11, the fourth comb-shaped electrode 47 includes a fourth bus bar 42 and a plurality of fourth electrode fingers 45. One end portions of the plurality of fourth electrode fingers 45 are respectively connected to the fourth bus bar 42. The fifth comb-shaped electrode 48 includes a fifth bus bar 43 and a plurality of fifth electrode fingers 46. One end portions of the plurality of fifth electrode fingers 46 are respectively connected to the fifth bus bar 43.

[0067] The fourth bus bar 42 and the fifth bus bar 43 face each other. In this embodiment, the number of the plurality of fourth electrode fingers 45 and the number of the plurality of fifth electrode fingers 46 are each three or more. The plurality of fourth electrode fingers 45 and the plurality of fifth electrode fingers 46 are interposed with each other. The fourth comb-shaped electrode 47 is connected to the input potential. On the other hand, the fifth comb-shaped electrode 48 is connected to the output potential.

[0068] In this embodiment, the fourth bus bar 42 shown in FIG. 11 and the first bus bar 22 shown by referring to FIG. 1 are electrically connected. For example, the fourth bus bar 42 and the first bus bar 22 may be connected by a through electrode passing through the piezoelectric layer 14.

[0069] Similarly, the fifth bus bar 43 shown in FIG. 11 and the second bus bar 23 shown by referring to FIG. 1 are electrically connected. For example, the fifth bus bar 43 and the second bus bar 23 may be connected by a through electrode passing through the piezoelectric layer 14.

[0070] The reference potential electrode 19 provided on the first main surface 14a of the piezoelectric layer 14 and the reference potential electrode 49 provided on the second main surface 14b, shown in FIG. 10, are provided in the same manner. That is, the reference potential electrode 49 shown in FIG. 11 has a plurality of third electrode fingers 27 and a plurality of connection electrodes 24. One end portions or the other end portions of adjacent third electrode fingers 27 are connected by the connection electrodes 24. Thereby, the shape of the reference potential electrode 49 is a meander shape. A part of the reference potential electrode 49 overlaps with the region between the fourth comb-shaped electrode 47 and the fifth comb-shaped electrode 48 in a plan view. Note that at least one of the fourth electrode finger 45, the fifth electrode finger 46, and the third electrode finger 27 of the reference potential electrode 49 may be provided.

[0071] As shown in FIG. 10, the fourth electrode finger 45 sandwiches the piezoelectric layer 14 and faces the first electrode finger 25. The fifth electrode finger 46 sandwiches the piezoelectric layer 14 and faces the second electrode finger 26. The third electrode finger 27 provided on the second main surface 14b of the piezoelectric layer 14 sandwiches the piezoelectric layer 14 and overlaps with the third electrode finger 27 provided on the first main surface 14a.

[0072] In the present embodiment, the center-to-center distance between the adjacent fourth electrode fingers 45 and the third electrode finger 27 in a plan view is the same as the center-to-center distance between the adjacent first electrode fingers 25 and the third electrode finger 27 in a plan view. The center-to-center distance between the adjacent fifth electrode fingers 46 and the third electrode finger 27 in a plan view is the same as the center-to-center distance between the adjacent second electrode fingers 26 and the third electrode finger 27 in a plan view.

[0073] Here, when viewed from the direction orthogonal to the electrode fingers, a region where the adjacent first electrode finger 25 and second electrode finger 26 overlap is defined as a first opposing region F1. The first opposing region F1 corresponds to the opposing region F in the first embodiment shown in FIG. 2. When viewed from the direction orthogonal to the electrode fingers, a region where the adjacent fourth electrode finger 45 and fifth electrode finger 46 overlap is defined as a second opposing region F2. Note that the first opposing region F1 is a region of the first main surface 14a of the piezoelectric layer 14 defined based on the configuration of the functional electrode 41. The second opposing region F2 is a region of the second main surface 14b of the piezoelectric layer 14 defined based on the configuration of the functional electrode 41.

[0074] In a plan view, the first opposing region F1 and the second opposing region F2 overlap. And each of the third electrode fingers 27 provided on the first main surface 14a and the second main surface 14b of the piezoelectric layer 14 overlaps with the first opposing region F1 and the second opposing region F2 in a plan view.

[0075] Similar to the first embodiment, the filter waveform of the elastic wave device 40 can be suitably obtained. Therefore, when the elastic wave device 40 is used as an elastic wave resonator in a filter device, the filter waveform can be suitably obtained even if there is one or a small number of elastic wave resonators constituting the filter device, and the filter device can be made small.

[0076] As shown in FIG. 10, in the present embodiment, a plurality of third electrode fingers 27 are provided on both the first main surface 14a and the second main surface 14b of the piezoelectric layer 14 so as to be continuously arranged in the column direction. And the third electrode fingers 27 provided on the first main surface 14a and the third electrode fingers 27 provided on the second main surface 14b overlap in a plan view. Therefore, any third electrode finger 27 provided on the first main surface 14a and the third electrode finger 27 adjacent thereto in a plan view are the third electrode fingers 27 provided on the first main surface 14a and the third electrode fingers 27 provided on the second main surface 14b.

[0077] The third electrode fingers 27 that overlap in a plan view are not arranged in the column direction. On the other hand, the third electrode fingers 27 that do not overlap in a plan view are arranged in the column direction. For example, in the present embodiment, it holds even if the three third electrode fingers 27 continuously arranged in the column direction are the three third electrode fingers 27 provided on the first main surface 14a. Alternatively, for example, the three third electrode fingers 27 may be two third electrode fingers 27 provided on the first main surface 14a and one third electrode finger 27 provided on the second main surface 14b. As described above, the third electrode fingers 27 continuously arranged in the column direction may include the third electrode fingers 27 provided on the first main surface 14a, or may include the third electrode fingers 27 provided on the second main surface 14b.

[0078] Note that, for example, a plurality of third electrode fingers 27 may be alternately provided on the first main surface 14a and the second main surface 14b of the piezoelectric layer 14 so as to be arranged in the column direction. In this case, any third electrode finger 27 provided on the first main surface 14a and the third electrode finger 27 adjacent thereto in a plan view are the third electrode fingers 27 provided on the second main surface 14b.

[0079] In this case, the third electrode fingers 27 continuously arranged in the column direction include both the third electrode fingers 27 provided on the first main surface 14a of the piezoelectric layer 14 and the third electrode fingers 27 provided on the second main surface 14b.

[0080] Even in this case, it is preferable that at least two third electrode fingers 27 arranged continuously in the column direction overlap, in a plan view, with the opposing regions F arranged continuously in the direction orthogonal to the electrode fingers among the plurality of opposing regions F. More preferably, three or more third electrode fingers 27 arranged continuously in the column direction overlap, in a plan view, with the opposing regions F arranged continuously in the direction orthogonal to the electrode fingers among the plurality of opposing regions F. Thereby, a filter waveform can be obtained more reliably.

[0081] FIG. 12 is a circuit diagram of an elastic wave filter device according to a fourth embodiment of the present invention.

[0082] The elastic wave filter device 50 includes a first signal terminal 52, a second signal terminal 53, an elastic wave resonator 51A, an elastic wave resonator 51B, and an elastic wave resonator 51C. The elastic wave resonator 51A is an elastic wave device according to the present invention. The elastic wave resonator 51A may have any configuration of, for example, the first to third embodiments or a modified example of the first embodiment. On the other hand, the functional electrodes in the elastic wave resonators 51B and 51C are IDT electrodes, respectively.

[0083] The first signal terminal 52 and the second signal terminal 53 may be configured as, for example, electrode pads, or may be configured as wirings. In the present embodiment, the second signal terminal 53 is an antenna terminal. The antenna terminal is connected to an antenna.

[0084] The elastic wave resonator 51A and the elastic wave resonator 51B are connected in series with each other between the first signal terminal 52 and the second signal terminal 53. The elastic wave resonator 51C is connected between the connection point between the elastic wave resonator 51A and the elastic wave resonator 51B and the reference potential.

[0085] In the elastic wave filter device 50, the elastic wave device according to the present invention is used as the elastic wave resonator 51A. As a result, a suitable filter waveform can be obtained without increasing the size of the elastic wave filter device 50. Therefore, the elastic wave filter device 50 can be made small.

[0086] Note that the circuit configuration of the elastic wave filter device 50 is not limited to the above. The elastic wave filter device 50 may be composed of, for example, only the elastic wave resonator 51A which is the elastic wave device of the present invention.

[0087] Hereinafter, the details of the thickness shear mode will be described using an example in which the functional electrode is an IDT electrode. Note that the IDT electrode does not have a third electrode finger. The "electrode" in the IDT electrode described later corresponds to the electrode finger. The support member in the following example corresponds to the support substrate in the present invention. Hereinafter, the reference potential may be described as the ground potential.

[0088] FIG. 13(a) is a schematic perspective view showing the appearance of an elastic wave device using a bulk wave of the thickness shear mode, FIG. 13(b) is a plan view showing the electrode structure on the piezoelectric layer, and FIG. 14 is a cross-sectional view of a portion taken along the line A-A in FIG. 13(a).

[0089] The elastic wave device 1 has a piezoelectric layer 2 made of LiNbO3. The piezoelectric layer 2 may be made of LiTaO3. The cut angle of LiNbO3 or LiTaO3 is Z-cut, but it may also be rotated Y-cut or X-cut. The thickness of the piezoelectric layer 2 is not particularly limited, but in order to effectively excite the thickness shear mode, it is preferably 40 nm or more and 1000 nm or less, and more preferably 50 nm or more and 1000 nm or less. The piezoelectric layer 2 has opposing first and second main surfaces 2a, 2b. An electrode 3 and an electrode 4 are provided on the first main surface 2a. Here, the electrode 3 is an example of the "first electrode", and the electrode 4 is an example of the "second electrode". In FIGS. 13(a) and 13(b), a plurality of electrodes 3 are connected to the first bus bar 5. The plurality of electrodes 4 are connected to the second bus bar 6. The plurality of electrodes 3 and the plurality of electrodes 4 are interposed with each other. The electrodes 3 and 4 have a rectangular shape and a length direction. In a direction orthogonal to this length direction, the electrode 3 and the adjacent electrode 4 face each other. Both the length direction of the electrodes 3, 4 and the direction orthogonal to the length direction of the electrodes 3, 4 are directions that cross the thickness direction of the piezoelectric layer 2. Therefore, it can also be said that the electrode 3 and the adjacent electrode 4 face each other in a direction that crosses the thickness direction of the piezoelectric layer 2. Also, the length direction of the electrodes 3, 4 may be interchanged with the direction orthogonal to the length direction of the electrodes 3, 4 shown in FIGS. 13(a) and 13(b). That is, in FIGS. 13(a) and 13(b), the electrodes 3, 4 may be extended in the direction in which the first bus bar 5 and the second bus bar 6 extend. In that case, the first bus bar 5 and the second bus bar 6 will extend in the direction in which the electrodes 3, 4 extend in FIGS. 13(a) and 13(b). And a plurality of pairs of structures in which an electrode 3 connected to one potential and an electrode 4 connected to the other potential are adjacent to each other are provided in a direction orthogonal to the length direction of the electrodes 3, 4. Here, the fact that the electrode 3 and the electrode 4 are adjacent to each other does not refer to the case where the electrode 3 and the electrode 4 are arranged so as to be in direct contact, but refers to the case where the electrode 3 and the electrode 4 are arranged with a gap therebetween. Also, when the electrode 3 and the electrode 4 are adjacent to each other, no electrode connected to a hot electrode or a ground electrode, including other electrodes 3, 4, is arranged between the electrode 3 and the electrode 4.These logarithms do not have to be integer pairs and may be 1.5 pairs, 2.5 pairs, etc. The center-to-center distance, i.e., the pitch, between the electrodes 3 and 4 is preferably in the range of 1 μm or more and 10 μm or less. Also, the width of the electrodes 3 and 4, i.e., the dimension in the facing 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. Note that the center-to-center distance between the electrodes 3 and 4 is the distance connecting the center of the dimension (width dimension) of the electrode 3 in the direction orthogonal to the length direction of the electrode 3 and the center of the dimension (width dimension) of the electrode 4 in the direction orthogonal to the length direction of the electrode 4.

[0090] Also, in the elastic wave device 1, since a Z-cut piezoelectric layer is used, the direction orthogonal to the length direction of the electrodes 3 and 4 is the direction orthogonal to the polarization direction of the piezoelectric layer 2. This is not the case when a piezoelectric body with another cut angle is used as the piezoelectric layer 2. Here, the "orthogonal" is not limited to only the case of strict orthogonality and may be approximately orthogonal (the angle formed by the direction orthogonal to the length direction of the electrodes 3 and 4 and the polarization direction is, for example, within the range of 90° ± 10°).

[0091] On the second main surface 2b side of the piezoelectric layer 2, a support member 8 is laminated via an insulating layer 7. The insulating layer 7 and the support member 8 have a frame shape and have through holes 7a and 8a as shown in FIG. 14. Thereby, a cavity 9 is formed. The cavity 9 is provided so as not to hinder the vibration of the excitation region C of the piezoelectric layer 2. Therefore, the support member 8 is laminated on the second main surface 2b via the insulating layer 7 at a position that does not overlap with at least the portion where the pair of electrodes 3 and 4 are provided. Note that the insulating layer 7 may not be provided. Therefore, the support member 8 can be laminated directly or indirectly on the second main surface 2b of the piezoelectric layer 2.

[0092] The insulating layer 7 is made of silicon oxide. However, in addition to silicon oxide, appropriate insulating materials such as silicon oxynitride and alumina can be used. The support member 8 is made of Si. The plane orientation on the surface of the Si on the piezoelectric layer 2 side may be (100) or (110), or may be (111). The Si constituting the support member 8 preferably has a high resistance with a resistivity of 4 kΩcm or more. However, the support member 8 can also be configured using an appropriate insulating material or semiconductor material.

[0093] As materials for the support member 8, for example, piezoelectric materials such as aluminum oxide, lithium tantalate, lithium niobate, and quartz, various ceramics such as alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite, dielectrics such as diamond and glass, and semiconductors such as gallium nitride can be used.

[0094] The plurality of electrodes 3, 4 and the first and second bus bars 5, 6 are made of an appropriate metal or alloy such as Al 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 Al film is laminated on a Ti film. Note that an adhesion layer other than the Ti film may be used.

[0095] During driving, an alternating voltage is applied between the plurality of electrodes 3 and the plurality of electrodes 4. More specifically, an alternating voltage is applied between the first bus bar 5 and the second bus bar 6. Thereby, it is possible to obtain resonance characteristics by utilizing the thickness shear mode bulk wave excited in the piezoelectric layer 2. In the elastic wave device 1, when the thickness of the piezoelectric layer 2 is d and the center-to-center distance between any adjacent electrodes 3, 4 of the plurality of pairs of electrodes 3, 4 is p, d / p is set to 0.5 or less. Therefore, the thickness shear mode bulk wave is effectively excited, and good resonance characteristics can be obtained. More preferably, d / p is 0.24 or less, and in that case, even better resonance characteristics can be obtained.

[0096] In the elastic wave device 1, since it has the above configuration, even if the number of pairs of the electrodes 3 and 4 is reduced in an attempt to miniaturize the device, a decrease in the Q value is less likely to occur. This is because even if the number of electrode fingers in the reflectors on both sides is reduced, the propagation loss is small. Also, the reason why the number of the electrode fingers can be reduced is that the bulk wave in the thickness shear mode is utilized. The difference between the Lamb wave used in the elastic wave device and the bulk wave in the thickness shear mode will be described with reference to FIGS. 15(a) and 15(b).

[0097] FIG. 15(a) is a schematic front cross-sectional view for explaining a Lamb wave propagating through a piezoelectric film of an elastic wave device as described in Japanese Patent Application Laid-Open No. 2012-257019. Here, a wave propagates through the piezoelectric film 201 as indicated by an arrow. Here, in the piezoelectric film 201, a first main surface 201a and a second main surface 201b face 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. As shown in FIG. 15(a), in the Lamb wave, the wave propagates in the X direction as shown in the figure. Since it is a plate wave, although the piezoelectric film 201 vibrates as a whole, the wave propagates in the X direction, so reflectors are arranged on both sides to obtain resonance characteristics. Therefore, a propagation loss of the wave occurs, and when miniaturization is attempted, that is, when the number of pairs of electrode fingers is reduced, the Q value decreases.

[0098] On the other hand, as shown in FIG. 15(b), in the elastic wave device 1, since the vibration displacement is in the thickness shear direction, the wave substantially 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. And since the resonance characteristics are obtained by the propagation of the wave in the Z direction, even if the number of electrode fingers of the reflector is reduced, a propagation loss is less likely to occur. Further, even if the number of pairs of the electrode pair composed of the electrodes 3 and 4 is reduced in an attempt to further miniaturize the device, a decrease in the Q value is less likely to occur.

[0099] Incidentally, as shown in FIG. 16, the amplitude directions of the bulk waves in the thickness-sliding mode are opposite between the first region 451 included in the excitation region C of the piezoelectric layer 2 and the second region 452 included in the excitation region C. FIG. 16 schematically shows bulk waves when a voltage is applied such that the electrode 4 has a higher potential than the electrode 3 between the electrode 3 and the electrode 4. The first region 451 is a region between the virtual plane VP1 that is orthogonal to the thickness direction of the piezoelectric layer 2 and bisects the piezoelectric layer 2 and the first main surface 2a within the excitation region C. The second region 452 is a region between the virtual plane VP1 and the second main surface 2b within the excitation region C.

[0100] As described above, in the elastic wave device 1, at least one pair of electrodes composed of the electrode 3 and the electrode 4 is arranged. However, since it does not propagate waves in the X direction, there is no need for a plurality of pairs of the electrode pair composed of the electrodes 3 and 4. That is, it is sufficient if at least one pair of electrodes is provided.

[0101] For example, the electrode 3 is an electrode connected to the hot 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 hot potential. In the elastic wave device 1, at least one pair of electrodes is an electrode connected to the hot potential or an electrode connected to the ground potential as described above, and no floating electrode is provided.

[0102] FIG. 17 is a diagram showing the resonance characteristics of the elastic wave device shown in FIG. 14. The design parameters of the elastic wave device 1 for obtaining this resonance characteristic are as follows.

[0103] Piezoelectric layer 2: LiNbO3 with Euler angles (0°, 0°, 90°), thickness = 400 nm. When viewed in a direction orthogonal to the length direction of the electrodes 3 and 4, the region where the electrodes 3 and 4 overlap, that is, the length of the excitation region C = 40 μm, the number of pairs of electrodes composed of the electrodes 3 and 4 = 21 pairs, the center distance between the electrodes = 3 μm, the widths of the electrodes 3 and 4 = 500 nm, d / p = 0.133. Insulating layer 7: Silicon oxide film with a thickness of 1 μm. Supporting member 8: Si.

[0104] Note that the length of the excitation region C is the dimension along the length direction of the electrodes 3 and 4 in the excitation region C.

[0105] In the elastic wave device 1, the electrode distance between the electrode pair composed of the electrodes 3 and 4 is made equal in all of the plurality of pairs. That is, the electrodes 3 and 4 are arranged at an equal pitch.

[0106] As is clear from FIG. 17, good resonance characteristics with a fractional bandwidth of 12.5% are obtained despite not having a reflector.

[0107] Incidentally, when the thickness of the piezoelectric layer 2 is d and the center distance between the electrodes of the electrodes 3 and 4 is p, as described above, in the elastic wave device 1, d / p is 0.5 or less, more preferably 0.24 or less. This will be described with reference to FIG. 18.

[0108] Similar to the elastic wave device that obtained the resonance characteristics shown in FIG. 17, a plurality of elastic wave devices were obtained by changing d / p. FIG. 18 is a diagram showing the relationship between this d / p and the fractional bandwidth of the resonator of the elastic wave device.

[0109] As is clear from FIG. 18, when d / p > 0.5, even if d / p is adjusted, the fractional bandwidth is less than 5%. On the other hand, when d / p ≤ 0.5, if d / p is changed within that range, the fractional bandwidth can be made 5% or more, that is, a resonator having a high coupling coefficient can be configured. Further, when d / p is 0.24 or less, the fractional bandwidth can be increased to 7% or more. In addition, if d / p is adjusted within this range, a resonator with an even wider fractional bandwidth can be obtained, and a resonator with an even higher coupling coefficient can be realized. Therefore, it can be understood that by setting d / p to 0.5 or less, a resonator having a high coupling coefficient using the thickness-slip mode bulk wave can be configured.

[0110] FIG. 19 is a plan view of an elastic wave device that utilizes a thickness-shear mode bulk wave. In the elastic wave device 80, a pair of electrodes having electrodes 3 and 4 are provided on the first main surface 2a of the piezoelectric layer 2. Note that K in FIG. 19 is the crossing width. As described above, in the elastic wave device of the present invention, the number of pairs of electrodes may be one pair. Even in this case, if the above d / p is 0.5 or less, a thickness-shear mode bulk wave can be effectively excited.

[0111] In the elastic wave device 1, preferably, in the plurality of electrodes 3 and 4, the metallization ratio MR of the adjacent electrodes 3 and 4 with respect to the excitation region C, which is a region where the adjacent electrodes 3 and 4 overlap when viewed in the direction in which they face each other, preferably satisfies MR ≦ 1.75(d / p) + 0.075. In that case, spurious can be effectively reduced. This will be described with reference to FIGS. 20 and 21. FIG. 20 is a reference diagram showing an example of the resonance characteristics of the elastic wave device 1. Spurious indicated by the arrow B appears between the resonance frequency and the anti-resonance frequency. Note that d / p = 0.08 and the Euler angle of LiNbO3 is (0°, 0°, 90°). Also, the metallization ratio MR = 0.35.

[0112] The metallization ratio MR will be described with reference to FIG. 13(b). In the electrode structure of FIG. 13(b), when focusing on a pair of electrodes 3 and 4, it is assumed that only this pair of electrodes 3 and 4 are provided. In this case, the portion surrounded by the dashed-dotted line becomes the excitation region C. This excitation region C is a region where electrode 3 overlaps electrode 4 in electrode 3, electrode 4 overlaps electrode 3 in electrode 4, and electrodes 3 and 4 overlap in the region between electrode 3 and electrode 4 when viewed in the direction orthogonal to the length direction of electrodes 3 and 4, that is, the facing direction. And the area of electrodes 3 and 4 in the excitation region C with respect to the area of the excitation region C is the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of the metallization portion to the area of the excitation region C.

[0113] In addition, when a plurality of pairs of electrodes are provided, the ratio MR of the metallization portion included in the entire excitation region to the total area of the excitation regions may be used.

[0114] FIG. 21 is a diagram showing the relationship between the specific band and the phase rotation amount of the impedance of the spurious normalized by 180 degrees as the magnitude of the spurious when a large number of elastic wave resonators are configured according to the configuration of the elastic wave device 1. Regarding the specific band, the film thickness of the piezoelectric layer and the dimensions of the electrodes were variously changed and adjusted. Further, FIG. 21 shows the results when a piezoelectric layer made of Z-cut LiNbO3 is used, but the same tendency is obtained even when a piezoelectric layer with another cut angle is used.

[0115] In the region surrounded by the ellipse J in FIG. 21, the spurious is as large as 1.0. As is clear from FIG. 21, when the specific band exceeds 0.17, that is, exceeds 17%, a large spurious with a spurious level of 1 or more appears in the passband even if the parameters constituting the specific band are changed. That is, like the resonance characteristics shown in FIG. 20, a large spurious indicated by the arrow B appears in the band. Therefore, the specific band is preferably 17% or less. In this case, the spurious can be reduced by adjusting the film thickness of the piezoelectric layer 2 and the dimensions of the electrodes 3 and 4.

[0116] FIG. 22 is a diagram showing the relationship between d / 2p, the metallization ratio MR, and the specific bandwidth. In the above-described elastic wave device, various elastic wave devices with different d / 2p and MR were configured, and the specific bandwidth was measured. The portion shown with hatching on the right side of the broken line D in FIG. 22 is the region where the specific bandwidth is 17% or less. The boundary between the hatched region and the non-hatched region is represented by MR = 3.5(d / 2p) + 0.075. That is, MR = 1.75(d / p) + 0.075. Therefore, preferably, MR ≦ 1.75(d / p) + 0.075. In that case, it is easy to make the specific bandwidth 17% or less. More preferably, it is the region on the right side of MR = 3.5(d / 2p) + 0.05 indicated by the dashed-dotted line D1 in FIG. 22. That is, if MR ≦ 1.75(d / p) + 0.05, the specific bandwidth can surely be made 17% or less.

[0117] FIG. 23 is a diagram showing a map of the specific bandwidth with respect to the Euler angles (0°, θ, ψ) of LiNbO3 when d / p approaches 0 as much as possible. The portion shown with hatching in FIG. 23 is the region where at least a specific bandwidth of 5% or more can be obtained, and when approximating the range of the region, it becomes the range represented by the following formulas (1), (2), and (3).

[0118] (0° ± 10°, 0° to 20°, arbitrary ψ) … Formula (1) (0° ± 10°, 20° to 80°, 0° to 60°(1 - (θ - 50) 2 / 900) 1 / 2 ) or (0° ± 10°, 20° to 80°, [180° - 60°(1 - (θ - 50) 2 / 900) 1 / 2 ) ~ 180°) … Formula (2) (0° ± 10°, [180° - 30°(1 - (ψ - 90) 2 / 8100) 1 / 2 ) ~ 180°, arbitrary ψ) … Formula (3)

[0119] Therefore, in the case of the Euler angle range of the above formulas (1), (2), or (3), the specific bandwidth can be made sufficiently wide, which is preferable. The same applies when the piezoelectric layer 2 is a lithium tantalate layer.

[0120] FIG. 24 is a partial cutaway perspective view for explaining an elastic wave device using Lamb waves.

[0121] The elastic wave device 81 has a support substrate 82. A recess is provided on the upper surface of the support substrate 82. A piezoelectric layer 83 is laminated on the support substrate 82. Thereby, a cavity 9 is formed. An IDT electrode 84 is provided on the piezoelectric layer 83 above the cavity 9. Reflectors 85 and 86 are provided on both sides of the IDT electrode 84 in the elastic wave propagation direction. In FIG. 24, the outer peripheral edge of the cavity 9 is indicated by a broken line. Here, the IDT electrode 84 has first and second bus bars 84a and 84b, a plurality of first electrode fingers 84c, and a plurality of second electrode fingers 84d. The plurality of first electrode fingers 84c are connected to the first bus bar 84a. The plurality of second electrode fingers 84d are connected to the second bus bar 84b. The plurality of first electrode fingers 84c and the plurality of second electrode fingers 84d are interdigitated.

[0122] In the elastic wave device 81, by applying an alternating electric field to the IDT electrode 84 on the cavity 9, Lamb waves as plate waves are excited. And since the reflectors 85 and 86 are provided on both sides, resonance characteristics due to the above Lamb waves can be obtained.

[0123] Thus, the elastic wave device of the present invention may utilize plate waves. In the example shown in FIG. 24, an IDT electrode 84, a reflector 85, and a reflector 86 are provided on the main surface corresponding to the first main surface 14a of the piezoelectric layer 14 shown in FIG. 1 and the like. When the elastic wave device of the present invention utilizes plate waves, for example, a functional electrode, and the reflectors 85 and 86 shown in FIG. 24 may be provided on the first main surface 14a of the piezoelectric layer 14 in the elastic wave device of the first embodiment or the second embodiment. Alternatively, for example, a functional electrode 41, and the reflectors 85 and 86 shown in FIG. 24 may be provided on the first main surface 14a and the second main surface 14b of the piezoelectric layer 14 in the elastic wave device 40 of the third embodiment.

[0124] In the elastic wave devices of the first to third embodiments or modified examples that utilize the bulk wave in the thickness shear mode, as described above, it is preferable that d / p is 0.5 or less, and more preferably 0.24 or less. Thereby, even better resonance characteristics can be obtained.

[0125] Note that the center-to-center distance p between adjacent first electrode fingers and second electrode fingers of the IDT electrode corresponds to the center-to-center distance between adjacent first electrode fingers and third electrode fingers in the first embodiment or the like, or the center-to-center distance between adjacent second electrode fingers and third electrode fingers. Specifically, among the center-to-center distance between adjacent first electrode fingers and third electrode fingers, and the center-to-center distance between adjacent second electrode fingers and third electrode fingers, the longest distance corresponds to the center-to-center distance p between adjacent first electrode fingers and second electrode fingers of the IDT electrode. When the center-to-center distance between adjacent first electrode fingers and third electrode fingers, and the center-to-center distance between adjacent second electrode fingers and third electrode fingers are the same, any of these distances corresponds to the center-to-center distance p between adjacent first electrode fingers and second electrode fingers of the IDT electrode.

[0126] Furthermore, in the excitation region of the elastic wave devices of the first to third embodiments or modified examples that utilize the bulk wave in the thickness shear mode, as described above, it is preferable to satisfy MR ≦ 1.75(d / p) + 0.075. Note that the metallization ratios of the first electrode fingers and the second electrode fingers of the IDT electrode correspond to the metallization ratios of the first electrode fingers and the third electrode fingers, and the second electrode fingers and the third electrode fingers in the first embodiment or the like. Therefore, when the metallization ratios of the first electrode fingers and the third electrode fingers, and the second electrode fingers and the third electrode fingers with respect to the excitation region are defined as MR, it is preferable to satisfy MR ≦ 1.75(d / p) + 0.075. In this case, spurious can be more reliably suppressed.

[0127] In the elastic wave device according to the first to third embodiments or modified examples that utilize the bulk wave in the thickness-slip mode, the piezoelectric layer is preferably a lithium niobate layer or a lithium tantalate layer. And it is preferable that the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the ranges of the above formulas (1), (2), or (3). In this case, the specific bandwidth can be made sufficiently wide.

Explanation of Reference Numerals

[0128] 1…Elastic wave device 2…Piezoelectric layer 2a, 2b…First and second main surfaces 3, 4…Electrodes 5, 6…First and second bus bars 7…Insulating layer 7a…Through hole 8…Supporting member 8a…Through hole 9…Hollow portion 10…Elastic wave device 10a…Hollow portion 11, 11A…Functional electrodes 12…Piezoelectric substrate 13…Supporting member 14…Piezoelectric layer 14a, 14b…First and second main surfaces 15…Insulating layer 16…Supporting substrate 17, 18…First and second comb-shaped electrodes 17A, 18A…First and second comb-shaped electrodes 19, 19A…Reference potential electrodes 22, 23…First and second bus bars 24…Connecting electrode 25~27…First to third electrode fingers 28…Input terminal 29…Output terminal 30, 40…Elastic wave device 41…Functional electrode 42, 43…Fourth and fifth bus bars 45, 46…Fourth and fifth electrode fingers 47, 48…Fourth and fifth comb-shaped electrodes 49…Reference potential electrode 50…Elastic wave filter device 51A, 51B, 51C…Elastic wave resonator 80, 81…Elastic wave device 82…Support substrate 83…Piezoelectric layer 84…IDT electrode 84a, 84b…First and second bus bars 84c, 84d…First and second electrode fingers 85, 86…Reflector 100…Elastic wave resonator 101…IDT electrode 105, 106…First and second electrode fingers 107, 108…First and second comb-shaped electrodes 201…Piezoelectric film 201a, 201b…First and second main surfaces 451, 452…First and second regions C…Excitation region F…Opposing region F1, F2…First and second opposing regions Ga, Gb…First and second regions VP1…Virtual plane

Claims

1. A piezoelectric layer having a first main surface and a second main surface facing each other, At least one first electrode finger provided on the first main surface of the piezoelectric layer and connected to an input potential, At least one second electrode finger provided on the first main surface of the piezoelectric layer and connected to an output potential, At least one third electrode finger provided on at least one of the first main surface and the second main surface of the piezoelectric layer and connected to a reference potential, Comprising, When viewed from the electrode finger orthogonal direction orthogonal to the direction in which the first electrode finger and the second electrode finger extend, the first electrode finger and the second electrode finger face each other, In the electrode finger orthogonal direction, a region where adjacent first electrode fingers and second electrode fingers overlap is an opposing region, When viewed from the main surface facing direction in which the first main surface and the second main surface of the piezoelectric layer face each other, the third electrode finger overlaps at least a part of at least one of the opposing regions, When viewed from the main surface facing direction, the order in which the first electrode finger, the second electrode finger, and the third electrode finger are arranged is, when starting from the first electrode finger, the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger in a cycle order, a surface acoustic wave device.

2. A piezoelectric layer having a first main surface and a second main surface facing each other, At least one first electrode finger provided on the first main surface of the piezoelectric layer and connected to an input potential, At least one second electrode finger provided on the first main surface of the piezoelectric layer and connected to an output potential, At least one third electrode finger provided on at least one of the first main surface and the second main surface of the piezoelectric layer and connected to a reference potential, Comprising, When viewed from the electrode finger orthogonal direction orthogonal to the direction in which the first electrode finger and the second electrode finger extend, the first electrode finger and the second electrode finger face each other, In the electrode finger orthogonal direction, a region where adjacent first electrode fingers and second electrode fingers overlap is an opposing region, When viewed from the main surface facing direction in which the first main surface and the second main surface of the piezoelectric layer face each other, the third electrode finger overlaps at least a part of at least one of the opposing regions, A plurality of the third electrode fingers are provided, A first bus bar to which one end of the first electrode finger is connected, A second bus bar to which one end of the second electrode finger is connected; A connection electrode that connects one ends or the other ends of adjacent third electrode fingers; further comprising: A region between the opposing region and the first bus bar is a first region, and a region between the opposing region and the second bus bar is a second region. A surface acoustic wave device, wherein when viewed from the main surface facing direction, the connection electrode overlaps at least one of the first region and the second region.

3. A piezoelectric layer having opposing first and second main surfaces, At least one first electrode finger provided on the first main surface of the piezoelectric layer and connected to an input potential; At least one second electrode finger provided on the first main surface of the piezoelectric layer and connected to an output potential; At least one third electrode finger provided on at least one of the first main surface and the second main surface of the piezoelectric layer and connected to a reference potential; comprising: When viewed from the electrode finger orthogonal direction orthogonal to the direction in which the first electrode finger and the second electrode finger extend, the first electrode finger and the second electrode finger face each other. In the electrode finger orthogonal direction, a region where adjacent first electrode fingers and second electrode fingers overlap is an opposing region. When viewed from the main surface facing direction in which the first main surface and the second main surface of the piezoelectric layer face each other, the third electrode finger overlaps at least a part of at least one of the opposing regions. A plurality of the first electrode fingers are provided. A plurality of the second electrode fingers are provided. In the surface acoustic wave device, the plurality of first electrode fingers and the plurality of second electrode fingers are interposed with each other.

4. The surface acoustic wave device according to any one of claims 1 to 3, wherein at least one of the third electrode fingers is provided on the first main surface of the piezoelectric layer.

5. The surface acoustic wave device according to any one of claims 1 to 3, wherein at least one of the third electrode fingers is provided on the second main surface of the piezoelectric layer.

6. The surface acoustic wave device according to any one of claims 1 to 3, further comprising a support member that overlaps the piezoelectric layer when viewed from the main surface facing direction.

7. The surface acoustic wave device according to claim 6, wherein the support member has a cavity portion, and when viewed from the main surface facing direction, at least a part of each of the first electrode finger and the second electrode finger overlaps the cavity portion.

8. The elastic wave device according to claim 7, wherein the support member is composed of a support substrate and an insulating layer, and the cavity portion is provided in the insulating layer.

9. The elastic wave device according to claim 1 or 2, wherein at least one of the first electrode fingers and the second electrode fingers is provided in plural, and a plurality of the facing regions are formed.

10. Both the first electrode fingers and the second electrode fingers are provided in plural, and a plurality of the facing regions are formed. A first bus bar connecting the plurality of first electrode fingers; A second bus bar connecting the plurality of second electrode fingers; further comprising: The plurality of first electrode fingers and the first bus bar constitute a first comb-shaped electrode, the plurality of second electrode fingers and the second bus bar constitute a second comb-shaped electrode, and the plurality of first electrode fingers and the plurality of second electrode fingers are interposed with each other. The elastic wave device according to any one of claims 1 to 3.

11. A plurality of the third electrode fingers are provided. The elastic wave device according to claim 9, wherein when viewed from the main surface facing direction, the plurality of third electrode fingers are arranged in the direction orthogonal to the electrode fingers.

12. At least two of the third electrode fingers arranged continuously in the direction orthogonal to the electrode fingers overlap, when viewed from the main surface facing direction, with a facing region arranged continuously in the direction orthogonal to the electrode fingers among the plurality of facing regions. The elastic wave device according to claim 11.

13. Three or more of the third electrode fingers arranged continuously in the direction orthogonal to the electrode fingers overlap, when viewed from the main surface facing direction, with a facing region arranged continuously in the direction orthogonal to the electrode fingers among the plurality of facing regions. The elastic wave device according to claim 12.

14. The elastic wave device according to any one of claims 1 to 3, which is configured to be able to utilize a thickness-shear mode bulk wave.

15. When the longest distance among the center distances between adjacent first electrode fingers and third electrode fingers and the center distances between adjacent second electrode fingers and third electrode fingers when viewed from the main surface facing direction is p, and the thickness of the piezoelectric layer is d, d / p is 0.5 or less. The elastic wave device according to any one of claims 1 to 3.

16. The elastic wave device according to claim 15, wherein d / p is 0.24 or less.

17. When viewed from the main surface facing direction, a region where the adjacent first electrode fingers and the second electrode fingers overlap in the direction orthogonal to the electrode fingers, either directly or via the third electrode fingers, is a vibration region, The elastic wave device according to claim 14, wherein when the metallization ratios of the first electrode fingers and the third electrode fingers, and the second electrode fingers and the third electrode fingers with respect to the vibration region are MR, MR ≦ 1.75(d / p) + 0.075 is satisfied.

18. The elastic wave device according to any one of claims 1 to 3, wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.

19. The piezoelectric layer is made of lithium tantalate or lithium niobate, The elastic wave device according to claim 14, wherein the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are in the range of the following formula (1), formula (2), or formula (3). (0° ± 10°, 0° to 20°, any ψ) … formula (1) (0° ± 10°, 20° to 80°, 0° to 60°(1 - (θ - 50) ２ / 900)) １／２ ) or (0° ± 10°, 20° to 80°, [180° - 60°(1 - (θ - 50) ２ / 900)) １／２ ] to 180°)... Equation (2) (0° ± 10°, [180° - 30°(1 - (ψ - 90) ２ / 8100) １／２ ] ~ 180°, any ψ) … Equation (3)

20. An elastic wave filter device having at least one elastic wave device according to any one of claims 1 to 3.

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