Elastic wave device

Abstract

Provided is an elastic wave device (10) capable of suppressing degradation of filter characteristics and capable of advancing miniaturization, including a piezoelectric substrate (2) including a piezoelectric layer (7), a first IDT electrode (8A) and a second IDT electrode (8B) provided on the piezoelectric layer, a first reflector (9A) and a second reflector (9B) opposing each other with the first IDT electrode sandwiched therebetween on the piezoelectric layer, and a third reflector (9C) and a fourth reflector (9D) opposing each other with the second IDT electrode sandwiched therebetween on the piezoelectric layer. When a wavelength defined by an average center-to-center distance in the second reflector and the third reflector is set to λa and λb, respectively, λa < λb. A distance between the second reflector and the third reflector is a distance Xn in a range represented by the following Formula 1, where n is an arbitrary natural number.[Mathematical Formula 1] … Formula 1.

Description

Technical Field

[0001] This invention relates to elastic wave devices. Background Technology

[0002] Previously, elastic wave devices have been widely used in filters for portable telephones, etc. An example of an elastic wave device is disclosed in Patent Document 1 below. In this elastic wave device, multiple IDT (Interdigital Transducer) electrodes are disposed on a piezoelectric layer. This constitutes multiple elastic wave resonators. Elastic waves leak from each of the multiple elastic wave resonators. If the leaked elastic waves acoustically couple with each other, unwanted waves are amplified, and the filter characteristics sometimes deteriorate. In the elastic wave device of Patent Document 1, acoustic barriers are disposed between the elastic wave resonators to suppress acoustic coupling.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: U.S. Patent Application Publication No. 2023 / 0006125

[0006] However, in the elastic wave device described in Patent Document 1, an area is needed to set up an acoustic barrier in order to suppress the amplification of unwanted waves caused by acoustic coupling. Therefore, it becomes difficult to miniaturize the elastic wave device when it is desired to suppress acoustic coupling and thus suppress the degradation of filter characteristics. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] The purpose of this invention is to provide an elastic wave device that can suppress the degradation of filter characteristics and promote miniaturization.

[0009] Technical solutions for solving the problem

[0010] The elastic wave device of the present invention comprises: a piezoelectric substrate including a piezoelectric layer; a first IDT electrode disposed on the piezoelectric layer; a second IDT electrode disposed on the piezoelectric layer; a first reflector and a second reflector disposed on the piezoelectric layer, positioned opposite each other and sandwiching the first IDT electrode, and each having a plurality of reflector electrode fingers; and a third reflector and a fourth reflector disposed on the piezoelectric layer, positioned opposite each other and sandwiching the second IDT electrode, and each having a plurality of reflector electrode fingers, wherein the second reflector of the first reflector and the second reflector is located on the side of the second IDT electrode, and the third reflector of the third reflector and the fourth reflector is located on the side of the first IDT electrode, in a direction orthogonal to the direction in which the plurality of reflector electrode fingers of the second reflector extend. When the directions are orthogonal, the plurality of reflector electrode fingers in the second reflector and the plurality of reflector electrode fingers in the third reflector overlap each other in the orthogonal direction. In each of the second and third reflectors, when the center value of all the center-to-center distances among the center-to-center distances of the plurality of adjacent reflector electrode fingers is set as M, the average value of the center-to-center distances within the range of M ± 40% is set as the average center-to-center distance. When the wavelength defined by the average center-to-center distance in the second reflector is set as λa, and the wavelength defined by the average center-to-center distance in the third reflector is set as λb, λa < λb. When n is set as any natural number, the distance between the second reflector and the third reflector is a distance Xn within the range represented by the following Equation 1.

[0011] [Mathematical Expression 1]

[0012] …Formula 1

[0013] Invention Effects

[0014] The elastic wave device according to the present invention can suppress the degradation of filter characteristics and can promote miniaturization. Attached Figure Description

[0015] Figure 1 This is a circuit diagram of the elastic wave device according to the first embodiment of the present invention.

[0016] Figure 2 This is a schematic top view showing the first elastic wave resonator and the second elastic wave resonator in the elastic wave device according to the first embodiment of the present invention.

[0017] Figure 3 It is along Figure 2 A simplified sectional view of line II in the diagram.

[0018] Figure 4 This is a graph illustrating the frequency characteristics of attenuation in the first embodiment and the first comparative example of the present invention.

[0019] Figure 5 This is a graph showing the relationship between the distance between the second and third reflectors and the frequency at which ripples caused by acoustic coupling are generated.

[0020] Figure 6 The graph shows the attenuation frequency characteristics in the first embodiment of the present invention when the wavelength ratio λa / λb is 0.98 and the wavelength ratio λb / λa is 1.02, as well as the attenuation frequency characteristics in the first comparative example.

[0021] Figure 7 The graph shows the attenuation frequency characteristics in the case of n=3 in the first embodiment of the present invention and the attenuation frequency characteristics in the first comparative example.

[0022] Figure 8 This is a graph showing the relationship between the ratio R1 and the frequency characteristics of the attenuation.

[0023] Figure 9 This is a graph showing the relationship between the ratio R1 and the admittance frequency characteristics.

[0024] Figure 10 This is a graph showing the relationship between the ratio R1 and the magnitude of the ripple caused by acoustic coupling.

[0025] Figure 11 This is a schematic top view showing a portion of the first IDT electrode and the second reflector in the first embodiment of the present invention.

[0026] Figure 12 This is a schematic top view showing the first elastic wave resonator and the second elastic wave resonator in the elastic wave device according to the second embodiment of the present invention.

[0027] Figure 13 This is a schematic top view showing the first elastic wave resonator and the second elastic wave resonator in the elastic wave device according to the third embodiment of the present invention.

[0028] Figure 14 This is a schematic top view showing the first elastic wave resonator and the second elastic wave resonator in the elastic wave device according to the fourth embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures

[0030] 1A, 1B: First elastic wave resonator, second elastic wave resonator;

[0031] 2: Piezoelectric substrate;

[0032] 3: Supporting components;

[0033] 4: Support base plate;

[0034] 5, 6: First intermediate layer, second intermediate layer;

[0035] 7: Piezoelectric layer;

[0036] 7a~7d: Sides 1 to 4;

[0037] 8A, 8B: First IDT electrode, Second IDT electrode;

[0038] 9A~9D: Reflector 1 to Reflector 4;

[0039] 9a, 9b: Busbar for the first reflector and busbar for the second reflector;

[0040] 9c: Reflector electrode finger;

[0041] 9d, 9e: Busbar for the 3rd reflector and busbar for the 4th reflector;

[0042] 9f: Reflector electrode finger;

[0043] 10: Elastic wave device;

[0044] 12, 13: Signal terminal 1 and signal terminal 2;

[0045] 16, 17: Busbar 1 and Busbar 2;

[0046] 16a, 17a: First inner busbar section, second inner busbar section;

[0047] 16b, 17b: First outer busbar section, second outer busbar section;

[0048] 16c, 17c: First connecting part, second connecting part;

[0049] 16d, 17d: Openings;

[0050] 18, 19: First electrode finger, second electrode finger;

[0051] 20: Elastic wave device;

[0052] 23, 24: Connect the electrodes;

[0053] 30, 40: Elastic wave device;

[0054] P1a, P1b, P3, P4: Parallel arm resonators;

[0055] S1a, S1b, S2a, S3, S4a, S4b, S5a~S5c: Series arm resonators. Detailed Implementation

[0056] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.

[0057] In addition, it should be noted that the embodiments described in this specification are illustrative and that partial substitutions or combinations of structures can be made between different embodiments.

[0058] Figure 1 This is a circuit diagram of the elastic wave device according to the first embodiment of the present invention.

[0059] The elastic wave device 10 is a filter device. Specifically, the elastic wave device 10 is a trapezoidal filter having multiple series-arm resonators and multiple parallel-arm resonators. More specifically, the elastic wave device 10 is a transmitting filter. However, the elastic wave device 10 is not limited to a transmitting filter. The elastic wave device 10 can also be a receiving filter, for example.

[0060] The passband of the elastic wave device 10 is the transmission band of Band 66, which is 1710MHz to 1780MHz. However, the passband of the elastic wave device 10 is not limited to the above-mentioned passband.

[0061] In this embodiment, all the series-arm resonators and all the parallel-arm resonators are elastic wave resonators. The plurality of series-arm resonators in the elastic wave device 10 includes a first elastic wave resonator 1A. The plurality of parallel-arm resonators in the elastic wave device 10 includes a second elastic wave resonator 1B. However, the first elastic wave resonator 1A can also be a parallel-arm resonator. The second elastic wave resonator 1B can also be a series-arm resonator.

[0062] Figure 2 This is a schematic top view showing the first elastic wave resonator and the second elastic wave resonator in the elastic wave device according to the first embodiment. Figure 2 In this diagram, elastic wave resonators and wiring other than the first elastic wave resonator 1A and the second elastic wave resonator 1B are omitted. Figure 2 The piezoelectric substrate described later is simplified in the diagram. These are in Figure 2 The same applies to the schematic top view.

[0063] The first elastic wave resonator 1A and the second elastic wave resonator 1B are configured adjacent to each other. The elastic wave device 10 of the present invention only needs to have at least the adjacent first elastic wave resonator 1A and the second elastic wave resonator 1B. The elastic wave device 10 of the present invention is not limited to filter devices such as transmitting filters and receiving filters. The elastic wave device 10 can also be, for example, an element used in a filter device.

[0064] Figure 3It is along Figure 2 A simplified sectional view of line II in the diagram. Figure 3 In the diagram, a simplified representation of each IDT electrode and reflector, which will be described later, is shown by adding two diagonals to a rectangle.

[0065] The elastic wave device 10 includes a piezoelectric substrate 2. The piezoelectric substrate 2 is a substrate with piezoelectric properties. The piezoelectric substrate 2 includes a support member 3 and a piezoelectric layer 7. In this embodiment, the support member 3 includes a support substrate 4, a first intermediate layer 5, and a second intermediate layer 6. The first intermediate layer 5 is disposed on the support substrate 4. The second intermediate layer 6 is disposed on the first intermediate layer 5. The piezoelectric layer 7 is disposed on the second intermediate layer 6. Thus, the piezoelectric layer 7 is indirectly disposed on the support substrate 4, separated from the first intermediate layer 5 and the second intermediate layer 6.

[0066] Alternatively, the support member 3 may consist solely of the support substrate 4. In this case, it is sufficient to directly provide the piezoelectric layer 7 on the support substrate 4. Alternatively, the piezoelectric substrate 2 may not have the support member 3 and may consist solely of the piezoelectric layer 7.

[0067] In this embodiment, the material combination of the support substrate 4, the first intermediate layer 5, the second intermediate layer 6, and the piezoelectric layer 7, which are part of the laminate, is silicon / silicon nitride / silicon oxide / lithium tantalate. However, the materials of the support substrate 4, the first intermediate layer 5, the second intermediate layer 6, and the piezoelectric layer 7 are not limited to the above-mentioned materials.

[0068] Return to Figure 2 A first IDT electrode 8A, a first reflector 9A, and a second reflector 9B are disposed on the piezoelectric layer 7 in the piezoelectric substrate 2. This constitutes a first elastic wave resonator 1A. Furthermore, a second IDT electrode 8B, a third reflector 9C, and a fourth reflector 9D are disposed on the piezoelectric layer 7. This constitutes a second elastic wave resonator 1B. Thus, the first elastic wave resonator 1A and the second elastic wave resonator 1B share the piezoelectric substrate 2 and the piezoelectric layer 7.

[0069] In the first elastic wave resonator 1A, an elastic wave is excited by applying an AC voltage to the first IDT electrode 8A. In the second elastic wave resonator 1B, an elastic wave is excited by applying an AC voltage to the second IDT electrode 8B.

[0070] The first IDT electrode 8A has a pair of busbars and a plurality of electrode fingers. Specifically, the pair of busbars is a first busbar 16 and a second busbar 17. The first busbar 16 and the second busbar 17 are opposite to each other. Specifically, the plurality of electrode fingers is a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One end of each of the plurality of first electrode fingers 18 is connected to the first busbar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second busbar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interleaved with each other. The first electrode fingers 18 and the second electrode fingers 19 are connected to different potentials. Hereinafter, the first busbar 16 and the second busbar 17 are sometimes referred to as a busbar together. The first electrode fingers 18 and the second electrode fingers 19 are sometimes referred to as electrode fingers together.

[0071] The second IDT electrode 8B, like the first IDT electrode 8A, has a pair of busbars and multiple electrode fingers. Hereinafter, the direction in which the multiple electrode fingers 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. In the elastic wave device 10, the electrode finger extension directions in the first elastic wave resonator 1A and the electrode finger extension directions in the second elastic wave resonator 1B are parallel. However, the electrode finger extension directions in the first elastic wave resonator 1A and the electrode finger extension directions in the second elastic wave resonator 1B do not necessarily have to be parallel.

[0072] The first reflector 9A and the second reflector 9B are positioned opposite each other, with their electrode fingers in the first IDT electrode 8A perpendicular to each other. The third reflector 9C and the fourth reflector 9D are positioned opposite each other, with their electrode fingers in the second IDT electrode 8B perpendicular to each other.

[0073] Of the first reflector 9A and the second reflector 9B, the second reflector 9B is located on the side of the second IDT electrode 8B. Of the third reflector 9C and the fourth reflector 9D, the third reflector 9C is located on the side of the first IDT electrode 8A. The second reflector 9B and the third reflector 9C are adjacent to each other.

[0074] The first reflector 9A has a pair of reflector busbars and a plurality of reflector electrode fingers 9c. Specifically, the pair of reflector busbars are a first reflector busbar 9a and a second reflector busbar 9b. The first reflector busbar 9a and the second reflector busbar 9b are opposite to each other. One end of each of the plurality of reflector electrode fingers 9c is connected to the first reflector busbar 9a. The other end of each of the plurality of reflector electrode fingers 9c is connected to the second reflector busbar 9b. Similarly, the second reflector 9B also has a first reflector busbar 9a, a second reflector busbar 9b, and a plurality of reflector electrode fingers 9c.

[0075] The third reflector 9C has a third reflector busbar 9d, a fourth reflector busbar 9e, and a plurality of reflector electrode fingers 9f. The third reflector busbar 9d and the fourth reflector busbar 9e are opposite to each other. One end of each of the plurality of reflector electrode fingers 9f is connected to the third reflector busbar 9d. The other end of each of the plurality of reflector electrode fingers 9f is connected to the fourth reflector busbar 9e. Similarly, the fourth reflector 9D also has a third reflector busbar 9d, a fourth reflector busbar 9e, and a plurality of reflector electrode fingers 9f.

[0076] Hereinafter, the direction in which the plurality of reflector electrode fingers 9c in the first reflector 9A and the second reflector 9B extend is defined as the first extension direction dy1, which is the extension direction in this invention. The direction orthogonal to the first extension direction dy1 is defined as the first orthogonal direction dx1, which is the orthogonal direction in this invention. The direction in which the plurality of reflector electrode fingers 9f in the third reflector 9C and the fourth reflector 9D extend is defined as the second extension direction dy2, and the direction orthogonal to the second extension direction dy2 is defined as the second orthogonal direction dx2.

[0077] The first orthogonal direction dx1 is parallel to the orthogonal direction of the electrode index of the first IDT electrode 8A. Therefore, it can also be said that the first reflector 9A and the second reflector 9B are positioned opposite each other, sandwiching the first IDT electrode 8A along the first orthogonal direction dx1. On the other hand, the second orthogonal direction dx2 is parallel to the orthogonal direction of the electrode index of the second IDT electrode 8B. Therefore, it can also be said that the third reflector 9C and the fourth reflector 9D are positioned opposite each other, sandwiching the second IDT electrode 8B along the second orthogonal direction dx2.

[0078] In the first orthogonal direction dx1, the plurality of reflector electrode fingers 9c in the second reflector 9B and the plurality of reflector electrode fingers 9f in the third reflector 9C overlap each other. In this embodiment, the first orthogonal direction dx1 and the second orthogonal direction dx2 are parallel. Therefore, in the second orthogonal direction dx2, the plurality of reflector electrode fingers 9c in the second reflector 9B and the plurality of reflector electrode fingers 9f in the third reflector 9C also overlap each other. However, the first orthogonal direction dx1 and the second orthogonal direction dx2 do not necessarily have to be parallel.

[0079] Hereinafter, the first IDT electrode 8A and the second IDT electrode 8B may be referred to together as simply IDT electrodes. The first reflector 9A, the second reflector 9B, the third reflector 9C, and the fourth reflector 9D may be referred to together as simply reflectors.

[0080] Each IDT electrode and each reflector in this embodiment comprises a stacked metal film. Specifically, in each IDT electrode and each reflector, a Ti layer and an AlCu layer are sequentially stacked from the piezoelectric layer 7 side. Furthermore, the materials of each IDT electrode and each reflector are not limited to the aforementioned materials. Alternatively, each IDT electrode and each reflector may also comprise a single-layer metal film.

[0081] In each of the first reflector 9A and the second reflector 9B of the elastic wave device 10, the center-to-center distance between adjacent reflector electrode fingers 9c in the first orthogonal direction dx1 is fixed. Similarly, in each of the third reflector 9C and the fourth reflector 9D, the center-to-center distance between adjacent reflector electrode fingers 9f in the second orthogonal direction dx2 is fixed. Hereinafter, the center-to-center distance between adjacent reflector electrode fingers 9c and adjacent reflector electrode fingers 9f will sometimes be described simply as the center-to-center distance. In this invention, the center-to-center distance in each of the first reflector 9A, the second reflector 9B, the third reflector 9C, and the fourth reflector 9D may not be fixed.

[0082] For example, the wavelength in the second reflector 9B can be defined by the center-to-center distance between adjacent reflector electrode fingers 9c in the second reflector 9B. However, when the second reflector 9B has m reflector electrode fingers 9c, the second reflector 9B has (m-1) sets of adjacent reflector electrode fingers 9c. In this case, the center-to-center distance in the second reflector 9B is the center-to-center distance between each of the (m-1) sets of adjacent reflector electrode fingers 9c.

[0083] In the second reflector 9B, when the center-to-center distance among multiple sets of adjacent reflector electrode fingers 9c is set as M, the average center-to-center distance within a range of M ± 40% is set as the average center-to-center distance. For example, when all center-to-center distances are within a range of M ± 40%, the average of all center-to-center distances is the average center-to-center distance. On the other hand, for example, when some center-to-center distances are not within a range of M ± 40%, the center-to-center distances outside the range of M ± 40% are excluded when calculating the average center-to-center distance. The wavelength defined by the average center-to-center distance in the second reflector 9B is the wavelength λa in the second reflector 9B.

[0084] Similarly, in the third reflector 9C, when the center-to-center distance among the center-to-center distances of multiple sets of adjacent reflector electrode fingers 9f is set as M, the average center-to-center distance within the range of M ± 40% is set as the average center-to-center distance. The wavelength defined by the average center-to-center distance in the third reflector 9C is the wavelength λb in the third reflector 9C.

[0085] In this invention, λa < λb. Furthermore, when the average inter-center distance in the second reflector 9B is set to pa, λa = 2pa. When the average inter-center distance in the third reflector 9C is set to pb, λb = 2pb.

[0086] In this specification, the wavelength defined by the center-to-center distance between adjacent electrode fingers of the first IDT electrode 8A is also defined by the average center-to-center distance calculated in the same manner as that of the second reflector 9B and the third reflector 9C. The same applies to the second IDT electrode 8B.

[0087] This embodiment is characterized by a structure in which, when n is set to any natural number, the distance between the second reflector 9B and the third reflector 9C is a distance Xn within the range expressed by Equation 1 below. This suppresses the degradation of the filter characteristics of the elastic wave device 10 and promotes miniaturization of the elastic wave device 10. The details of the circuit structure of the elastic wave device 10 will be described below.

[0088] [Mathematical Expression 2]

[0089] …Formula 1

[0090] like Figure 1 As shown, the elastic wave device 10 has a first signal terminal 12 and a second signal terminal 13. The first signal terminal 12 and the second signal terminal 13 can be configured as electrode pads, or they can be configured as wiring. A plurality of series arm resonators are connected in series between the first signal terminal 12 and the second signal terminal 13.

[0091] Specifically, the multiple series-arm resonators of the elastic wave device 10 are series-arm resonator S1a, series-arm resonator S1b, series-arm resonator S2a, first elastic wave resonator 1A, series-arm resonator S3, series-arm resonator S4a, series-arm resonator S4b, series-arm resonator S5a, series-arm resonator S5b, and series-arm resonator S5c. They are arranged in the following order from the first signal terminal 12 side: series-arm resonator S1a, series-arm resonator S1b, series-arm resonator S2a, first elastic wave resonator 1A, series-arm resonator S3, series-arm resonator S4a, series-arm resonator S4b, series-arm resonator S5a, series-arm resonator S5b, and series-arm resonator S5c.

[0092] In this embodiment, the plurality of series-arm resonators includes a plurality of series-arm resonators that have been split in series. Specifically, series-arm resonators S1a and S1b are two series-arm resonators obtained by splitting a single series-arm resonator in series in the circuit structure. Series-arm resonator S2a and the first elastic wave resonator 1A are two series-arm resonators obtained by splitting a single series-arm resonator in series in the circuit structure. Series-arm resonators S4a and S4b are two series-arm resonators obtained by splitting a single series-arm resonator in series in the circuit structure. Series-arm resonators S5a, S5b, and S5c are three series-arm resonators obtained by splitting a single series-arm resonator in series in the circuit structure.

[0093] In this invention, each series arm resonator obtained by series splitting is treated as an independent elastic wave resonator. Similarly, each series arm resonator obtained by parallel splitting is also treated as an independent elastic wave resonator. Likewise, each parallel arm resonator obtained by series or parallel splitting is also treated as an independent elastic wave resonator.

[0094] Specifically, the multiple parallel-arm resonators of the elastic wave device 10 are parallel-arm resonators P1a, P1b, the second elastic wave resonator 1B, P3, and P4. Parallel-arm resonators P1a and P1b are connected in series between the connection point between the series-arm resonators S1b and S2a and the ground potential. The second elastic wave resonator 1B is connected between the connection point between the first elastic wave resonator 1A and the series-arm resonator S3 and the ground potential. The parallel-arm resonator P4 is connected between the connection point between the series-arm resonators S4b and S5a and the ground potential. Furthermore, parallel-arm resonators P1b, the second elastic wave resonator 1B, and P3 are all connected to the ground potential. However, the circuit structure of the elastic wave device 10 is not limited to the above-described circuit structure.

[0095] As described above, if the elastic waves leaking from multiple elastic wave resonators undergo acoustic coupling with each other, unwanted waves may sometimes be amplified. Due to this amplification of unwanted waves, ripple may occur, for example, in the attenuation frequency characteristics of the elastic wave device, which serves as a filter. In the first embodiment, the degradation of the filter characteristics of the elastic wave device caused by ripple due to acoustic coupling can be suppressed. This will be illustrated below by comparing the first embodiment and the first comparative example.

[0096] The basic structure of the first comparative example is the same as that of the first embodiment. The difference between the first comparative example and the first embodiment is that the distance between the second reflector and the third reflector is not a distance Xn within the range expressed by Equation 1 above. The attenuation frequency characteristics were compared in the elastic wave device 10 having the structure of the first embodiment and the elastic wave device of the first comparative example. In this comparison, n=1 was set in Equation 1. The design parameters of the elastic wave device 10 are set as follows.

[0097] Support substrate: material is Si, azimuth angle is (111).

[0098] First intermediate layer: material is SiN, thickness is 300nm

[0099] Second intermediate layer: material is SiO2, thickness is 300nm

[0100] Piezoelectric layer: The material is 400 nm thick LiTaO3 cut at 42°Y.

[0101] The first IDT electrode, the second IDT electrode, the first reflector, the second reflector, the third reflector, and the fourth reflector: the material is Ti / AlCu from the piezoelectric layer side, and the thickness is 12nm / 100nm from the piezoelectric layer side.

[0102] The wavelength defined by the average intercenter distance in the first IDT electrode: 2.2498 μm

[0103] The wavelength defined by the average intercenter distance in the second IDT electrode: 2.3944 μm

[0104] The wavelength defined by the average intercenter distance in the first reflector: 2.3847 μm

[0105] The wavelength λa, defined by the average intercenter distance in the second reflector, is 2.3847 μm.

[0106] The wavelength λb, defined by the average intercenter distance in the third reflector, is 2.4184 μm.

[0107] The wavelength defined by the average intercenter distance in the fourth reflector: 2.4184 μm

[0108] The design parameters of the elastic wave device in the first comparative example are also set to be the same as those of the elastic wave device 10 in the first embodiment. However, as described above, the distance between the second reflector and the third reflector in the first comparative example differs from that in the first embodiment.

[0109] Figure 4 This is a graph showing the frequency characteristics of the attenuation in the first embodiment and the first comparative example. Figure 4The double-headed arrow B in the diagram indicates the passband in the elastic wave device of the first embodiment and the first comparative example. This passband is 1710MHz to 1780MHz.

[0110] Figure 4 Arrows C1 and C2 illustrate the ripple caused by acoustic coupling between the elastic waves leaking from the first and second elastic wave resonators. As indicated by arrow C2, in the first comparative example, ripple was generated around 1765 MHz. Therefore, in the first comparative example, ripple caused by acoustic coupling was generated within the passband. In contrast, as indicated by arrow C1, in the first embodiment, ripple was generated around 1785 MHz. Therefore, in the first embodiment, ripple caused by acoustic coupling was generated outside the passband.

[0111] In the first embodiment, ripples caused by acoustic coupling within the passband can be suppressed. Therefore, degradation of the filter characteristics of the elastic wave device 10 can be suppressed. Furthermore, in the first embodiment, as... Figure 2 As shown, the above-mentioned effects can be achieved without setting up a structure between the first elastic wave resonator 1A and the second elastic wave resonator 1B. Therefore, it is possible to promote the miniaturization of the elastic wave device 10.

[0112] Furthermore, the following illustrates that by making the distance between the second reflector 9B and the third reflector 9C a distance Xn within the range expressed by Equation 1, ripple generation in the passband can be suppressed.

[0113] [Mathematical Expression 3]

[0114] …Formula 1

[0115] An elastic wave device with a structure substantially the same as that of the first embodiment was investigated. In this study, the reference numerals used in the description of the first embodiment are cited. In this elastic wave device, the frequency at which ripples caused by acoustic coupling are generated is measured whenever the distance between the second reflector 9B and the third reflector 9C is varied. The distance between the second reflector 9B and the third reflector 9C is varied both within and outside the range shown in Equation 1. Thus, the relationship between the aforementioned distance and the frequency at which ripples caused by acoustic coupling are derived. Regarding the design parameters of this elastic wave device, in addition to the aforementioned distance, they are set to be... Figure 4 The comparison shown involves the same design parameters for the elastic wave device 10 in the first embodiment.

[0116] This study revealed that unwanted waves of multiple modes are amplified through acoustic coupling, thereby generating ripple. Furthermore, it was found that large ripples caused by acoustic coupling are periodically generated relative to the distance between the second reflector 9B and the third reflector 9C. It was further discovered that the order of unwanted waves amplified significantly through acoustic coupling varies depending on the aforementioned distance. Hereinafter, ripples amplified by acoustic coupling, for example, unwanted waves of the nth order, will sometimes be referred to only as nth-order ripples. In the following... Figure 5 The values ​​shown in the diagram represent the frequencies at which 5th, 6th, and 7th ripples are generated.

[0117] Figure 5 This is a graph showing the relationship between the distance between the second and third reflectors and the frequency at which ripples caused by acoustic coupling are generated. Figure 5 The double-headed arrow B in the figure indicates the passband of the elastic wave device involved in this study. Figure 5 The range indicated by the double-headed arrow labeled X5 in the attached figure represents the range of distance Xn when n=5 in Equation 1. Similarly, the range indicated by the double-headed arrow labeled X6 represents the range of distance Xn when n=6, and the range indicated by the double-headed arrow labeled X7 represents the range of distance Xn when n=7. Furthermore, in Figure 5 In the diagram, a shading line is applied to the range where the distance between the second reflector 9B and the third reflector 9C is within a distance X5 and the frequency is within the passband. Similarly, a shading line is also applied to the range where the distance is within a distance X6 or a distance X7 and the frequency is within the passband.

[0118] like Figure 5 As shown, when the distance between the second reflector 9B and the third reflector 9C is within the range of distance X5, a 5th-order ripple is generated. The depiction point of the 5th-order ripple is not located within the range shown by the shading. More specifically, when the aforementioned distance is within the range of distance X5, a 5th-order ripple is generated on the higher frequency side than the passband. On the other hand, when the aforementioned distance is longer than distance X5, a 5th-order ripple is generated within the passband. Therefore, when the aforementioned distance is within the range of distance X5, the generation of ripple within the passband can be suppressed.

[0119] When the distance between the second reflector 9B and the third reflector 9C is within the range of distance X6, a 6th-order ripple is generated. The plotted point showing the 6th-order ripple is not located within the range indicated by the shading. More specifically, when the aforementioned distance is within the range of distance X6, a 6th-order ripple is generated on the higher frequency side than the passband. On the other hand, when the aforementioned distance is longer than distance X6, a 6th-order ripple is generated within the passband. Therefore, when the aforementioned distance is within the range of distance X6, the generation of ripple within the passband can be suppressed.

[0120] When the distance between the second reflector 9B and the third reflector 9C is near the range of distance X7, a 7th-order ripple is generated. The plotted point showing the 7th-order ripple is not located within the range indicated by the shading. More specifically, when the aforementioned distance is within the range of distance X7, a 7th-order ripple is generated on the higher frequency side than the passband. On the other hand, when the aforementioned distance is longer than distance X7, a 7th-order ripple is generated within the passband. Therefore, when the aforementioned distance is within the range of distance X7, the generation of ripple within the passband can be suppressed.

[0121] Furthermore, when the distance between the second reflector 9B and the third reflector 9C is near the range of distance X5, not only 5th-order ripple but also 6th-order ripple is generated. However, when the distance is near the range of distance X5, ripple beyond the 5th-order is very small. Therefore, even when ripple beyond the 5th-order is generated when the distance is within the range of distance X5, the filter characteristics of the elastic wave device 10 are hardly degraded. Similarly, when the distance is within the range of distance X6, ripple beyond the 6th-order is very small. When the distance is within the range of distance X7, ripple beyond the 7th-order is very small.

[0122] As described above, large ripples are periodically generated relative to the distance between the second reflector 9B and the third reflector 9C. The number of unwanted waves amplified by acoustic coupling and generating large ripples varies depending on the aforementioned distance. This is also true when the number is beyond 5 to 7. Figure 5 The dashed lines in the diagram are imaginary lines illustrating the periodicity of the ripples relative to the aforementioned distances. Each dashed line shows the approximate frequency at which the ripples occur, for frequencies of 5 to 7 and for frequencies other than 5 to 7.

[0123] Here, the exact frequency at which the ripples are generated is shown by each plotted point. Figure 5 The dashed lines in the diagram illustrate the periodicity of the ripple. Even if a dashed line crosses the area indicated by the shadow lines, it does not necessarily mean that the filter characteristics will immediately deteriorate. As mentioned above, the points that produce large ripples are not located within the area indicated by the shadow lines.

[0124] Based on the above, by making the distance between the second reflector 9B and the third reflector 9C a distance Xn within the range expressed by Equation 1, it is possible to suppress ripple generation in the passband. This is based on the following reasons.

[0125] When the round-trip distance between the second reflector 9B and the third reflector 9C is an integer multiple of the average length of wavelengths λa and λb, ripples caused by acoustic coupling are generated near the upper end of the stopband. That is, when the distance between the second reflector 9B and the third reflector 9C is a distance Yn and Yn×2=[(λa+λb) / 2]×n or Yn=[(λa+λb) / 4]×n, the aforementioned ripples are generated near the upper end of the stopband.

[0126] In this specification, the term "stopband" refers to the frequency band determined by the period of a periodically constructed metal grating. The term "upper end of the stopband" refers to the highest frequency within the stopband. The "near the upper end of the stopband" can refer to the vicinity of the upper end of the stopband in both the first elastic wave resonator 1A and the second elastic wave resonator 1B. Generally, the vicinity of the upper end of the stopband in an elastic wave resonator used in a filter device is located at a higher frequency than the highest frequency of the filter device's passband.

[0127] If the distance between the second reflector 9B and the third reflector 9C deviates from the distance Yn, the frequency of the ripple caused by acoustic coupling shifts from near the upper end of the stopband towards the lower frequency side. However, the inventors of this invention have figured out that when the distance between the second reflector 9B and the third reflector 9C is longer than Yn×(λa / λb) and shorter than Yn×(λb / λa), the frequency of the ripple caused by acoustic coupling is generated at a higher frequency side than the passband. This range is represented by Equation 1.

[0128] [Mathematical Expression 4]

[0129] …Formula 1

[0130] By making the distance between the second reflector 9B and the third reflector 9C a distance Xn within the range expressed by Equation 1, ripple generation in the passband can be suppressed. That is, the degradation of the filter characteristics of the elastic wave device 10 can be suppressed without setting up a structure between the first elastic wave resonator 1A and the second elastic wave resonator 1B. Therefore, miniaturization of the elastic wave device 10 can be promoted.

[0131] In this invention, it is preferable that λa / λb, which is the wavelength ratio of wavelength λa to wavelength λb, and λb / λa, which is the wavelength ratio of wavelength λb to wavelength λa, are within the following ranges. That is, preferably, 0.9 ≤ (λa / λb) < 1, and 1 < (λb / λa) ≤ 1.1. This allows for more reliable suppression of ripple generation within the passband. Hereinafter, an example is shown where the wavelength ratio λa / λb is set to 0.98 and the wavelength ratio λb / λa is set to 1.02. Also shown... Figure 4 The comparison shown relates to the results of the first comparison example.

[0132] Figure 6 The graph shows the attenuation frequency characteristics when the wavelength ratio λa / λb is 0.98 and the wavelength ratio λb / λa is 1.02 in the first embodiment, as well as the attenuation frequency characteristics in the first comparative example.

[0133] like Figure 6 As shown, when the wavelength ratio λa / λb is 0.98 and the wavelength ratio λb / λa is 1.02, ripple is generated on the higher frequency side of the passband. Furthermore, as described above, in this invention, λa < λb. Therefore, (λa / λb) < 1, and (λb / λa) > 1. Thus, by making 0.9 ≤ (λa / λb) < 1 and 1 < (λb / λa) ≤ 1.1, ripple generation within the passband can be suppressed more reliably, and the degradation of filter characteristics can be suppressed. In addition, miniaturization of the elastic wave device 10 can be promoted.

[0134] Furthermore, the frequency response of the attenuation is shown when n=3. Also shown is... Figure 4 The comparison shown relates to the results of the first comparison example.

[0135] Figure 7 The graph shows the attenuation frequency characteristics in the case of n=3 in the first embodiment and the attenuation frequency characteristics in the first comparative example.

[0136] like Figure 7 As shown, when n=3, ripple is generated on the higher frequency side than the passband. In this invention, n≤3 is preferred. This allows for a shorter distance between the second reflector 9B and the third reflector 9C. Therefore, miniaturization of the elastic wave device 10 can be effectively promoted. Furthermore, ripple generation within the passband can be suppressed more reliably, and degradation of the filter characteristics of the elastic wave device 10 can be suppressed.

[0137] More preferably, n=1. As a result, the degradation of the filter characteristics of the elastic wave device 10 can be suppressed, and the miniaturization of the elastic wave device 10 can be further promoted.

[0138] like Figure 2 As shown, in the first embodiment, in the first orthogonal direction dx1, the plurality of reflector electrode fingers 9c in the second reflector 9B and the plurality of reflector electrode fingers 9f in the third reflector 9C overlap each other. Specifically, in the first orthogonal direction dx1, almost all portions of the plurality of reflector electrode fingers of the second reflector 9B and the third reflector 9C overlap each other. The details are as follows.

[0139] Define the dimensions of the plurality of reflector electrode fingers 9c in the second reflector 9B and the plurality of reflector electrode fingers 9f in the third reflector 9C as follows. Let the dimension of the plurality of reflector electrode fingers 9c in the second reflector 9B along the first extension direction dy1 be L1, and let the dimension of the plurality of reflector electrode fingers 9f in the third reflector 9C along the first extension direction dy1 be L2. Let the dimension of the portion of the plurality of reflector electrode fingers 9c in the second reflector 9B that overlaps the plurality of reflector electrode fingers 9f in the third reflector 9C in the first orthogonal direction dx1 along the first extension direction dy1 be L1x. Let the dimension of the portion of the plurality of reflector electrode fingers 9f in the third reflector 9C that overlaps the plurality of reflector electrode fingers 9c in the second reflector 9B in the first orthogonal direction dx1 along the first extension direction dy1 be L2x.

[0140] In the elastic wave device 10 of the first embodiment, L1 < L2 and L1x = L2x. Moreover, the dimension L1x is 100% of the dimension L1, and the dimension L2x is 97.3% of the dimension L2. Additionally, in the present invention, in the first orthogonal direction dx1, the plurality of reflector electrode fingers 9c in the second reflector 9B and the plurality of reflector electrode fingers 9f in the third reflector 9C do not necessarily overlap each other in almost all parts. However, preferably, the dimension L1x is 20% or more of the dimension L1, and the dimension L2x is 20% or more of the dimension L2. In this case, the ripple due to acoustic coupling is large. In contrast, in the present invention, the frequency at which this ripple is generated can be made to be outside the passband. Thus, in the above case, the present invention is particularly suitable. The details are shown below.

[0141] When the ratio of the dimension L1x to the dimension L1 is set as R1 and the ratio of the dimension L2x to the dimension L2 is set as R2, an elastic wave device having the same structure as the first embodiment except for the ratios R1 and R2 was studied. Additionally, R1 = (L1x / L1) × 100 [%]. R2 = (L2x / L2) × 100 [%]. In this elastic wave device, whenever the ratio R1 was changed, the attenuation amount frequency characteristics were measured. Specifically, the ratio R1 was changed in the range of 20% or more and 100% or less at an interval of 20%. In this elastic wave device, as the ratio R1 becomes larger, the ratio R2 also becomes larger. Thus, in this study, both the ratio R1 and the ratio R2 were changed.

[0142] Figure 8 It is a graph showing the relationship between the ratio R1 and the attenuation amount frequency characteristics.

[0143] As Figure 8 shown, even when the ratio R1 changes, the attenuation amount frequency characteristics as a whole do not change significantly. However, Figure 8The ripple in the image is enclosed by a circle with double dots and dashes, and its size varies. This ripple is caused by acoustic coupling.

[0144] Furthermore, in the aforementioned elastic wave device, the admittance frequency characteristics near the frequency at which the ripple caused by acoustic coupling is generated are measured whenever the ratio R1 is changed. Specifically, the ratio R1 is varied by an amplitude of 20% within a range of 0% to 100%.

[0145] Figure 9 This is a graph showing the relationship between the ratio R1 and the admittance frequency characteristics. Figure 10 This is a graph showing the relationship between the ratio R1 and the magnitude of the ripple caused by acoustic coupling.

[0146] like Figure 9 as well as Figure 10 As shown, the larger the ratio R1 becomes, the larger the ripple caused by acoustic coupling becomes. Furthermore, when the ratio R1 is 20% or higher, the ripple is larger compared to when the ratio R1 is 0%. Therefore, when the ratio R1 is 20% or higher and ripple caused by acoustic coupling occurs within the passband, the filter characteristics of the elastic wave device may deteriorate significantly. The same applies when the ratio R2 is 20% or higher. In contrast, in this invention, the frequency at which the ripple caused by acoustic coupling occurs is located outside the passband, thus suppressing the deterioration of the filter characteristics of the elastic wave device. Therefore, this invention is particularly suitable when both the ratio R1 and the ratio R2 are 20% or higher.

[0147] More preferably, the ratio R1 is 40% or more and the ratio R2 is 40% or more; even more preferably, the ratio R1 is 60% or more and the ratio R2 is 60% or more; and still more preferably, the ratio R1 is 80% or more and the ratio R2 is 80% or more. In these cases, the present invention is more suitable.

[0148] Furthermore, Figure 2 Each busbar of the first IDT electrode 8A shown has multiple openings. Details of this structure will be described below.

[0149] Figure 11 This is a schematic top view showing a portion of the first IDT electrode and the second reflector in the first embodiment.

[0150] The first busbar 16 in the first IDT electrode 8A has a plurality of openings 16d. The plurality of openings 16d are arranged in the orthogonal direction of the electrode.

[0151] More specifically, the first busbar 16 has a first inner busbar portion 16a, a first outer busbar portion 16b, and a plurality of first connecting portions 16c. The first inner busbar portion 16a and the first outer busbar portion 16b are opposite to each other. The first inner busbar portion 16a is located on the side of the second busbar 17. The plurality of first connecting portions 16c connect the first inner busbar portion 16a and the first outer busbar portion 16b. The plurality of openings 16d are openings surrounded by the first inner busbar portion 16a, the first outer busbar portion 16b, and the plurality of first connecting portions 16c.

[0152] Similarly, the second busbar 17 also has a second inner busbar portion 17a, a second outer busbar portion 17b, and a plurality of second connecting portions 17c. The second busbar 17 is provided with a plurality of openings 17d. The plurality of openings 17d are arranged in an orthogonal direction to the electrodes. Each of the plurality of openings 17d is surrounded by the second inner busbar portion 17a, the second outer busbar portion 17b, and the plurality of second connecting portions 17c. Furthermore, Figure 2 The busbars in the second IDT electrode 8B shown are configured in the same way as the busbars in the first IDT electrode 8A.

[0153] Furthermore, each of the first reflector busbars 9a and 9b in the first reflector 9A and the second reflector 9B also has at least one opening. The opening of the first reflector busbar 9a in the first reflector 9A and the second reflector 9B is aligned with the opening 16d of the first busbar 16 in the first IDT electrode 8A in the first orthogonal direction dx1. The opening of the second reflector busbar 9b in the first reflector 9A and the second reflector 9B is aligned with the opening 17d of the second busbar 17 in the first IDT electrode 8A in the first orthogonal direction dx1.

[0154] The third reflector busbar 9d and the fourth reflector busbar 9e in the third reflector 9C and the fourth reflector 9D are constructed in the same manner as the first reflector busbar 9a and the second reflector busbar 9b in the first reflector 9A and the second reflector 9B.

[0155] However, each busbar in the first IDT electrode 8A and the second IDT electrode 8B may also not have an opening. Similarly, the first reflector busbar 9a and the second reflector busbar 9b in the first reflector 9A and the second reflector 9B, and the third reflector busbar 9d and the fourth reflector busbar 9e in the third reflector 9C and the fourth reflector 9D may also not have an opening.

[0156] like Figure 2As shown, the piezoelectric layer 7 has a rectangular shape when viewed from above. In this specification, "view from above" refers to a view equivalent to... Figure 3 The view is taken from the upper direction along the stacking direction of the support member 3 and the piezoelectric layer 7. Additionally, in... Figure 3 In the example, the piezoelectric layer 7 side is the upper side among the support substrate 4 side and the piezoelectric layer 7 side.

[0157] Return to Figure 2 The piezoelectric layer 7 has four sides when viewed from above. Specifically, the four sides are side 1 7a, side 2 7b, side 3 7c, and side 4 7d. Side 1 7a and side 3 7c are opposite each other. Side 2 7b and side 4 7d are opposite each other.

[0158] Although Figure 2 The above is a simplification, but for example, elastic wave resonators other than the first elastic wave resonator 1A and the second elastic wave resonator 1B are constructed between the first elastic wave resonator 1A and the second side 7b, and between the first elastic wave resonator 1A and the fourth side 7d. This is also the case in other embodiments described later.

[0159] The first orthogonal direction dx1 is parallel to the direction in which a portion of the edges of the piezoelectric layer 7 extends. Specifically, the first orthogonal direction dx1 is parallel to the direction in which the second edge 7b and the fourth edge 7d of the piezoelectric layer 7 extend. Similarly, the second orthogonal direction dx2 is parallel to the direction in which the second edge 7b and the fourth edge 7d of the piezoelectric layer 7 extend. However, in this invention, at least one of the first orthogonal direction dx1 and the second orthogonal direction dx2 may not be parallel to the direction in which the second edge 7b or the fourth edge 7d extends.

[0160] The following shows Figure 3 Examples of materials for each layer in the piezoelectric substrate 2 are shown. In this specification, the term "main component" refers to a component that accounts for more than 50 wt% of the composition. The material of the aforementioned main component may exist in any of the following states: single crystal, polycrystalline, and amorphous, or a mixture thereof.

[0161] As the material for the support substrate 4, for example, aluminum nitride, lithium tantalate, lithium niobate, piezoelectric materials such as quartz, bauxite, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, forsterite, spinel, siliconium, ceramics such as siliconium oxide, alumina, silicon oxynitride, DLC (diamond-like carbon), diamond, dielectrics such as diamond, or semiconductors such as silicon, or materials with the above materials as the main component can also be used. The spinel contains an aluminum compound containing one or more elements selected from Mg, Fe, Zn, Mn, etc., and oxygen. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4. The same applies to the spinels listed later as examples of materials for the first intermediate layer 5. In the first embodiment, the support substrate 4 is a silicon support substrate.

[0162] In the first embodiment, the first intermediate layer 5 is a hypersonic film. A hypersonic film is a film in which the speed of sound propagating from a bulk wave is relatively high. More specifically, the speed of sound propagating from a bulk wave in a hypersonic film is higher than the speed of sound propagating from an elastic wave in the piezoelectric layer 7. The material used for the first intermediate layer 5 of the hypersonic film can be, for example, ceramics such as aluminum nitride, lithium tantalate, lithium niobate, quartz, alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, forsterite, spinel, siliconium, alumina, silicon oxynitride, DLC (diamond-like carbon), diamond, or semiconductors such as silicon, or materials with the above materials as the main component. In the first embodiment, the first intermediate layer 5 is a silicon nitride layer.

[0163] On the other hand, the second intermediate layer 6 is a low-velocity sound film. A low-velocity sound film is a film in which the speed of sound propagating from a bulk wave is relatively low. More specifically, the speed of sound propagating from a low-velocity sound film is lower than the speed of sound propagating from a bulk wave propagating from a piezoelectric layer 7. The material for the second intermediate layer 6 of the low-velocity sound film can be, for example, glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a dielectric material such as a compound containing fluorine, carbon, or boron, or a material mainly composed of the aforementioned materials. In the first embodiment, the second intermediate layer 6 is a silicon oxide layer.

[0164] For example, lithium tantalate, lithium niobate, zinc oxide, aluminum nitride, quartz, or PZT (lead zirconate titanate) can be used as the material for the piezoelectric layer 7. In particular, lithium tantalate or lithium niobate is preferred as the material for the piezoelectric layer 7. In the first embodiment, lithium tantalate cut at 42° Y was used as the material for the piezoelectric layer 7. However, the cutting angle of the piezoelectric layer 7 is not limited to the aforementioned cutting angle.

[0165] In the elastic wave device 10, a first intermediate layer 5 serving as a high-velocity sound membrane, a second intermediate layer 6 serving as a low-velocity sound membrane, and a piezoelectric layer 7 are stacked sequentially. This allows the energy of the elastic wave to be effectively contained within the piezoelectric layer 7. Furthermore, the support member 3 does not necessarily need to include the first intermediate layer 5 and the second intermediate layer 6.

[0166] In this invention, a dielectric film may also be provided on the piezoelectric layer 7 to cover the first IDT electrode 8A, the first reflector 9A, and the second reflector 9B. Similarly, a dielectric film may be provided on the piezoelectric layer 7 to cover the second IDT electrode 8B, the third reflector 9C, and the fourth reflector 9D. This makes each IDT electrode and each reflector less prone to damage. For example, silicon oxide, silicon nitride, or silicon oxynitride can be used as the material for the dielectric film.

[0167] Figure 12 This is a schematic top view showing the first elastic wave resonator and the second elastic wave resonator in the elastic wave device according to the second embodiment.

[0168] The difference between this embodiment and the first embodiment is that the second reflector 9B and the third reflector 9C are electrically connected. Apart from the aspects described above, the elastic wave device 20 of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0169] A connecting electrode 23 and a connecting electrode 24 are provided on the piezoelectric layer 7. The connecting electrode 23 and the connecting electrode 24 electrically connect the second reflector 9B and the third reflector 9C. Specifically, the connecting electrode 23 connects the first reflector busbar 9a in the second reflector 9B and the third reflector busbar 9d in the third reflector 9C. The connecting electrode 24 connects the second reflector busbar 9b in the second reflector 9B and the fourth reflector busbar 9e in the third reflector 9C.

[0170] Even in this embodiment, similar to the first embodiment, it is possible to suppress the deterioration of the filter characteristics of the elastic wave device 20 and to promote the miniaturization of the elastic wave device 20.

[0171] In the elastic wave devices of the first embodiment, second embodiment, etc., the first orthogonal direction dx1 and the second orthogonal direction dx2 are parallel. However, the first orthogonal direction dx1 and the second orthogonal direction dx2 do not necessarily have to be parallel. An example of the non-parallel arrangement of the first orthogonal direction dx1 and the second orthogonal direction dx2 in the first elastic wave resonator and the second elastic wave resonator is shown by the third embodiment.

[0172] Figure 13This is a schematic top view showing the first elastic wave resonator and the second elastic wave resonator in the elastic wave device according to the third embodiment.

[0173] The difference between this embodiment and the first embodiment is that the electrode fingers of the first IDT electrode 8A and the electrode fingers of the second IDT electrode 8B are not parallel in their orthogonal directions. Another difference is that the first orthogonal direction dx1 of the first reflector 9A and the second reflector 9B, and the second orthogonal direction dx2 of the third reflector 9C and the fourth reflector 9D are not parallel. Apart from the above aspects, the elastic wave device 30 of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0174] The first orthogonal direction dx1 is orthogonal to the directions in which the first side 7a and the third side 7c extend in the piezoelectric layer 7. Furthermore, the first orthogonal direction dx1 is parallel to the directions in which the second side 7b and the fourth side 7d extend in the piezoelectric layer 7. Therefore, the minimum angle between the first orthogonal direction dx1 and the direction in which the sides of the piezoelectric layer 7 extend is 0°. On the other hand, the second orthogonal direction dx2 is not parallel to the direction in which either side of the piezoelectric layer 7 extends. Therefore, the minimum angle between the second orthogonal direction dx2 and the direction in which the sides of the piezoelectric layer 7 extend is greater than 0°. Therefore, in this embodiment, the direction with the smaller minimum angle between the first orthogonal direction dx1 and the direction in which the sides of the piezoelectric layer 7 extend is the first orthogonal direction dx1.

[0175] Here, the distance between the second reflector 9B and the third reflector 9C is defined as follows: Specifically, this distance is defined as the distance between the second reflector 9B and the third reflector 9C in the direction smaller of the angles formed by the first orthogonal direction dx1 and the direction in which the piezoelectric layer 7 extends from its edge, and in the direction smaller than the angle formed by the first orthogonal direction dx2. In this embodiment, the distance between the second reflector 9B and the third reflector 9C is the distance between the second reflector 9B and the third reflector 9C in the first orthogonal direction dx1.

[0176] However, the distance between the second reflector 9B and the third reflector 9C in the elastic wave device 30 is not fixed. In this case, the shortest distance between the second reflector 9B and the third reflector 9C is set as Amin, and the longest distance between the second reflector 9B and the third reflector 9C is set as Amax. The average of these two distances (i.e., (Amin + Amax) / 2) is set as the distance between the second reflector 9B and the third reflector 9C. Based on the above, in this embodiment, the average of the shortest distance Amin and the longest distance Amax between the second reflector 9B and the third reflector 9C in the first orthogonal direction dx1 is the distance between the second reflector 9B and the third reflector 9C.

[0177] In the elastic wave device 30, when n is set to any natural number, (Amin+Amax) / 2, which is the distance between the second reflector 9B and the third reflector 9C, is the distance Xn within the range expressed by Equation 1. Thus, similar to the first embodiment, it is possible to suppress the deterioration of the filter characteristics of the elastic wave device 30 and to promote the miniaturization of the elastic wave device 30.

[0178] The angle between the first orthogonal direction dx1 and the second orthogonal direction dx2 is preferably 15° or less. In this case, large ripples caused by acoustic coupling are easily generated. In contrast, in the present invention, the frequency at which such ripples are generated is located outside the passband. Therefore, the present invention is particularly suitable in the above-described case.

[0179] Furthermore, an example of a different arrangement of the first and second elastic wave resonators from the above is shown through a fourth embodiment.

[0180] Figure 14 This is a schematic top view showing the first elastic wave resonator and the second elastic wave resonator in the elastic wave device according to the fourth embodiment.

[0181] This embodiment differs from the first embodiment in the angle formed by the orthogonal direction of the electrode fingers in the first IDT electrode 8A and the orthogonal direction of the electrode fingers in the second IDT electrode 8B, and the direction in which the edge of the piezoelectric layer 7 extends. This embodiment also differs from the first embodiment in the angle formed by the first orthogonal direction dx1 in the first reflector 9A and the second reflector 9B, and the direction in which the edge of the piezoelectric layer 7 extends. Furthermore, this embodiment differs from the first embodiment in the angle formed by the second orthogonal direction dx2 in the third reflector 9C and the fourth reflector 9D, and the direction in which the edge of the piezoelectric layer 7 extends. Apart from the aspects described above, the elastic wave device 40 of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0182] In this embodiment, the first orthogonal direction dx1 and the second orthogonal direction dx2 are parallel. Therefore, the distance between the second reflector 9B and the third reflector 9C is the distance between the second reflector 9B and the third reflector 9C along the first orthogonal direction dx1 and the second orthogonal direction dx2.

[0183] In this embodiment, similar to the first embodiment, the degradation of the filter characteristics of the elastic wave device 40 can be suppressed, and the miniaturization of the elastic wave device 40 can be promoted.

Claims

1. An elastic wave device, comprising: A piezoelectric substrate, comprising a piezoelectric layer; The first IDT electrode is disposed on the piezoelectric layer; The second IDT electrode is disposed on the piezoelectric layer; The first and second reflectors are configured on the piezoelectric layer to sandwich the first IDT electrode and are positioned opposite each other, each having multiple reflector electrode fingers; and The third and fourth reflectors are positioned opposite each other on the piezoelectric layer, sandwiching the second IDT electrode, and each has multiple reflector electrode fingers. The second reflector, one of the first reflectors and the second reflector, is located on the side of the second IDT electrode, and the third reflector, one of the third reflectors and the fourth reflector, is located on the side of the first IDT electrode. When a direction orthogonal to the extending direction of the plurality of reflector electrode fingers in the second reflector is defined as the orthogonal direction, the plurality of reflector electrode fingers in the second reflector and the plurality of reflector electrode fingers in the third reflector overlap each other in the orthogonal direction. In both the second and third reflectors, when M is defined as the median value of all the center-to-center distances among the center-to-center distances of multiple sets of adjacent reflector electrodes, the average value of the center-to-center distances within the range of M ± 40% is defined as the average center-to-center distance. When λa is defined as the wavelength defined by the average center-to-center distance in the second reflector, and λb is defined as the wavelength defined by the average center-to-center distance in the third reflector, λa < λb. When n is set to any natural number, the distance between the second reflector and the third reflector is a distance Xn within the range expressed by Equation 1 below. [Mathematical Expression 1] …Formula 1.

2. The elastic wave device according to claim 1, wherein, 0.9≤(λa / λb)<1, 1 < (λb / λa) ≤ 1.

1.

3. The elastic wave device according to claim 1 or 2, wherein, n≤3。 4. The elastic wave device according to claim 3, wherein, n=1。 5. The elastic wave device according to any one of claims 1 to 4, wherein, It also includes: connecting electrodes to electrically connect the second reflector and the third reflector.

6. The elastic wave device according to any one of claims 1 to 5, wherein, When the direction in which the plurality of reflector electrode fingers in the second reflector extend is defined as the extension direction, the dimension of the plurality of reflector electrode fingers in the second reflector along the extension direction is defined as L1, and the dimension of the portion of the plurality of reflector electrode fingers in the second reflector overlapping with the plurality of reflector electrode fingers in the third reflector in the orthogonal direction along the extension direction is defined as L1x, the dimension L1x is at least 20% of the dimension L1. When the dimension of the plurality of reflector electrode fingers in the third reflector along the extension direction is set as L2, and the dimension of the portion of the plurality of reflector electrode fingers in the third reflector that overlaps with the plurality of reflector electrode fingers in the second reflector in the orthogonal direction along the extension direction is set as L2x, the dimension L2x is more than 20% of the dimension L2.

7. The elastic wave device according to any one of claims 1 to 6, wherein, The piezoelectric substrate includes a support substrate. The piezoelectric layer is disposed directly or indirectly on the support substrate.

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