Elastic wave device and filter device

Abstract

Provided is an elastic wave device capable of suppressing unwanted waves in a passband. The elastic wave device (10) of the present invention includes: a piezoelectric layer (4) having first and second main surfaces (4a, 4b) facing each other; a support member laminated to the piezoelectric layer (4); a functional electrode (1) provided on the first main surface (4a) of the piezoelectric layer (4) and having a first comb electrode (7), a second comb electrode (8), and a third electrode (9); and a dielectric film provided on at least one of the first main surface (4a) and the second main surface (4b) of the piezoelectric layer (4) and overlapping the functional electrode (1) in plan view. The first comb electrode (7) has a first bus bar (12) and a plurality of first electrode fingers (15) each having one end connected to the first bus bar (12). The second comb electrode (8) has a second bus bar (13) and a plurality of second electrode fingers (16) each having one end connected to the second bus bar (13) and alternately and oppositely arranged with the plurality of first electrode fingers (15). One of the first comb electrode (7) and the second comb electrode (8) is connected to an input potential, and the other of the first comb electrode (7) and the second comb electrode (8) is connected to the output potential. The third electrode (9) has a plurality of third electrode fingers (17) each provided on the first main surface (4a) of the piezoelectric layer (4), such that the third electrode finger (17) is arranged in a direction in which the first electrode fingers (15) and the second electrode fingers (16) are arranged, and a connection electrode (third bus bar (14)) connecting the plurality of third electrode fingers (17) to each other. The third electrode (9) is connected to a potential different from the first comb electrode (7) and the second comb electrode (8). Regarding the order of arrangement of the plurality of electrode fingers including the first electrode fingers (15), the second electrode fingers (16), and the third electrode fingers (17), in the case where the order starts with the first electrode finger (15), the order is such that the first electrode finger (15), the third electrode finger (17), the second electrode finger (16), and the third electrode finger (17) are one cycle. In plan view, a sound reflection portion is formed in a position in the support member overlapping the plurality of first electrode fingers (15), the plurality of second electrode fingers (16), and the plurality of third electrode fingers (17). In the case where the longest distance among a center-to-center distance of adjacent first electrode fingers (15) and third electrode fingers (17) and a center-to-center distance of adjacent second electrode fingers (16) and third electrode fingers (17) is p, and in the case where the thickness of the piezoelectric layer (4) is d, d / p is 0.5 or less. The elastic wave device further includes a mass addition film (19) provided at a position overlapping a first end portion electrode finger (A) in plan view, in the case where at least one of the plurality of electrode fingers of the functional electrode (1) located at one end portion in the direction of arrangement of the plurality of electrode fingers is the first end portion electrode finger (A).

Description

Technical Field

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

[0002] Previously, elastic wave devices were widely used in filters for portable telephones, etc. In recent years, an elastic wave device as an acoustic coupling type filter, as described in Patent Document 1 below, has been proposed. In this acoustic coupling type filter, an electrode connected to a potential different from the input and output potentials, such as a reference potential, is disposed between the electrode connected to the input potential and the electrode connected to the output potential. Based on this structure, a filter waveform can be formed even in a single acoustic coupling type filter. Therefore, by reducing the number of components, miniaturization of the filter device can be achieved.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2023-190656 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] However, in the elastic wave device of Patent Document 1, it is difficult to sufficiently suppress unwanted waves within the passband. Therefore, the filter characteristics may deteriorate.

[0008] The purpose of this invention is to provide an elastic wave device and a filter device capable of suppressing unwanted waves in the passband.

[0009] Technical solutions for solving the problem

[0010] The elastic wave device of the present invention comprises: a piezoelectric layer having a first main surface and a second main surface opposite to each other; a support member stacked on the piezoelectric layer; a functional electrode disposed on the first main surface of the piezoelectric layer, having a first comb-shaped electrode, a second comb-shaped electrode, and a third electrode; and a dielectric film disposed on at least one of the first main surface side and the second main surface side of the piezoelectric layer, overlapping the functional electrode in a top view, wherein the first comb-shaped electrode has a first busbar and a plurality of first electrode fingers, one end of which is respectively connected to the first busbar; and the second comb-shaped electrode... The third electrode has a second busbar and a plurality of second electrode fingers, each connected at one end to the second busbar and interleaved with the plurality of first electrode fingers. One of the first comb electrode and the second comb electrode is connected to an input potential, and the other of the first comb electrode and the second comb electrode is connected to an output potential. The third electrode has a plurality of third electrode fingers disposed on the first main surface of the piezoelectric layer such that they are arranged in the same direction as the first electrode fingers and the second electrode fingers. The interconnected connecting electrodes, the third electrode being connected to a potential different from the first comb electrode and the second comb electrode, the arrangement of the plurality of electrode fingers including the first electrode finger, the second electrode finger and the third electrode finger, in the case starting from the first electrode finger, the first electrode finger, the third electrode finger, the second electrode finger and the third electrode finger are arranged in a cycle, and in plan view, an acoustic reflector is formed at the position in the support member that overlaps with the plurality of first electrode fingers, the plurality of second electrode fingers and the plurality of third electrode fingers, when the longest distance between the centers of adjacent first electrode fingers and third electrode fingers and the center distance between adjacent second electrode fingers and third electrode fingers is set as p, and when the thickness of the piezoelectric layer is set as d, d / p is 0.5 or less, the elastic wave device also includes a mass-added film, when at least one electrode finger of the plurality of electrode fingers of the functional electrode located at one end in the direction of the arrangement of the plurality of electrode fingers is set as the first end electrode finger, the mass-added film is provided at the position that overlaps with the first end electrode finger in plan view.

[0011] The filter device according to the present invention includes an elastic wave device constructed according to the present invention, and an elastic wave resonator electrically connected to the elastic wave device. The mass-added film of the elastic wave device is a first mass-added film. The elastic wave resonator has a piezoelectric layer, an IDT electrode disposed on the piezoelectric layer and having a plurality of electrode fingers, and a third mass-added film. When at least one electrode finger of the plurality of electrode fingers of the IDT electrode located at one end in the direction in which the plurality of electrode fingers are arranged is designated as a third end electrode finger, the third mass-added film is disposed at a position overlapping the third end electrode finger in top view. At least one of the thickness and material of the first mass-added film and the third mass-added film are different from each other.

[0012] Invention Effects

[0013] According to the elastic wave device and filter device of the present invention, unwanted waves in the passband can be suppressed. Attached Figure Description

[0014] Figure 1 This is a schematic front sectional view of the elastic wave device according to the first embodiment of the present invention.

[0015] Figure 2 This is a schematic top view of the elastic wave device according to the first embodiment of the present invention.

[0016] Figure 3 This is a schematic front sectional view showing the vicinity of the functional electrode in the first embodiment of the present invention.

[0017] Figure 4 This is a diagram illustrating the throughput characteristics in the first embodiment and the first comparative example of the present invention.

[0018] Figure 5 It is along Figure 2 A schematic cross-sectional view of line II-II in the diagram.

[0019] Figure 6 This is a schematic front sectional view showing the vicinity of the functional electrode in a first variation of the first embodiment of the present invention.

[0020] Figure 7 This is a schematic front sectional view showing the vicinity of the functional electrode in a second variation of the first embodiment of the present invention.

[0021] Figure 8 This is a diagram illustrating the throughput characteristics in a first modified example and a first comparative example of the first embodiment of the present invention.

[0022] Figure 9 This is a diagram illustrating the throughput characteristics in a second modified example and a first comparative example of the first embodiment of the present invention.

[0023] Figure 10 This is a schematic front sectional view showing the vicinity of the first to third electrode fingers used to illustrate the odd-numbered pattern.

[0024] Figure 11 This is a schematic front sectional view showing the vicinity of the first to third electrode fingers used to illustrate the even-numbered pattern.

[0025] Figure 12 This is a schematic diagram illustrating the formation of the passband in an acoustically coupled filter.

[0026] Figure 13 This is a schematic front sectional view showing the vicinity of the functional electrode in a third variation of the first embodiment of the present invention.

[0027] Figure 14 This is a diagram illustrating the throughput characteristics in a third modified example and a first comparative example of the first embodiment of the present invention.

[0028] Figure 15 This is a diagram illustrating the throughput characteristics in the fourth modified example and the first comparative example of the first embodiment of the present invention.

[0029] Figure 16 This is a diagram illustrating the throughput characteristics in the fifth modified example and the first comparative example of the first embodiment of the present invention.

[0030] Figure 17 This is a diagram illustrating the passage characteristics in the sixth modified example and the first comparative example of the first embodiment of the present invention.

[0031] Figure 18 This is a diagram illustrating the throughput characteristics in the seventh modified example and the first comparative example of the first embodiment of the present invention.

[0032] Figure 19 This is a schematic top view of the elastic wave device according to the eighth variation of the first embodiment of the present invention.

[0033] Figure 20 This is a schematic top view of the elastic wave device according to the ninth variation of the first embodiment of the present invention.

[0034] Figure 21 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the second embodiment of the present invention.

[0035] Figure 22 This is a diagram illustrating the throughput characteristics in the second embodiment and the first comparative example of the present invention.

[0036] Figure 23This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the third embodiment of the present invention.

[0037] Figure 24 This is a diagram illustrating the throughput characteristics in the third embodiment and the first comparative example of the present invention.

[0038] Figure 25 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the fourth embodiment of the present invention.

[0039] Figure 26 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the first variation of the fourth embodiment of the present invention.

[0040] Figure 27 This is a diagram illustrating the throughput characteristics in the fourth embodiment of the present invention, its first variation, and its first comparative example.

[0041] Figure 28 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the second variation of the fourth embodiment of the present invention.

[0042] Figure 29 This is a schematic front sectional view of the elastic wave device according to the fifth embodiment of the present invention.

[0043] Figure 30 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the fifth embodiment of the present invention.

[0044] Figure 31 This is a diagram illustrating the throughput characteristics in the fifth embodiment and the second comparative example of the present invention.

[0045] Figure 32 This is a schematic top view of the elastic wave device according to the sixth embodiment of the present invention.

[0046] Figure 33 This is a diagram illustrating the piezoelectric layer, various regions, and mass-added film in the sixth embodiment of the present invention.

[0047] Figure 34 This is a schematic top view of the elastic wave device according to the first variation of the sixth embodiment of the present invention.

[0048] Figure 35 This is a schematic bottom view showing the structure of a mass-added film disposed on the second main surface of the piezoelectric layer in a second variation of the sixth embodiment of the present invention.

[0049] Figure 36 This is a schematic top view of the elastic wave device according to the second variation of the sixth embodiment of the present invention.

[0050] Figure 37 This is a schematic front sectional view of the elastic wave device according to the seventh embodiment of the present invention.

[0051] Figure 38 This is a schematic circuit diagram of a filter device according to the eighth embodiment of the present invention.

[0052] Figure 39 This is a schematic top view of the series arm resonator in the eighth embodiment of the present invention.

[0053] Figure 40 It is along Figure 39 A schematic cross-sectional view of line III-III in the diagram.

[0054] Figure 41 This is a graph showing the admittance frequency characteristics in the elastic wave resonator of the eighth embodiment and the third comparative example of the present invention.

[0055] Figure 42 This is a graph showing the relationship between d / p and the relative bandwidth of the elastic wave device in the reference example.

[0056] Figure 43 This is a graph showing the relationship between the relative bandwidth and the normalized spurious magnitude in the elastic wave device of the reference example.

[0057] Figure 44 This is a graph showing the relationship between d / p, metallization rate (MR), and relative bandwidth.

[0058] Figure 45 This is a diagram showing the mapping of the relative bandwidth to the Euler angles (0°, θ, ψ) of LiNbO3 when d / p is infinitely close to 0. Detailed Implementation

[0059] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby making the present invention clear.

[0060] Furthermore, it should be noted in advance that the embodiments described in this specification are illustrative, and partial substitutions or combinations of structures can be made between different embodiments.

[0061] Figure 1 This is a schematic front sectional view of the elastic wave device according to the first embodiment of the present invention. Figure 2 This is a schematic top view of the elastic wave device according to the first embodiment. Additionally, Figure 1 It is along Figure 2 A schematic cross-sectional view of line II in the diagram. Figure 2 In this context, the first dielectric film, described later, is omitted. Furthermore, in... Figure 2 In the diagram, shaded lines indicate the electrodes and mass-added films described later. Figure 2 In the diagram, the connection between the third electrode (described later) and the reference potential is schematically shown using the reference potential symbol. Figure 2 In other schematic top views, the electrodes and mass-addition films are sometimes similarly shaded and marked with reference potential symbols.

[0062] Figure 1 The elastic wave device 10 shown is configured to utilize a volume wave with a thickness shear mode. The elastic wave device 10 is an acoustic coupling type filter. The structure of the elastic wave device 10 will be described below.

[0063] The elastic wave device 10 includes a piezoelectric substrate 2 and a functional electrode 1. The piezoelectric substrate 2 is a substrate with piezoelectric properties. Specifically, the piezoelectric substrate 2 includes a support member 3 and a piezoelectric layer 4. In this embodiment, the support member 3 includes a support substrate 6 and an insulating layer 5. The insulating layer 5 is provided on the support substrate 6. The piezoelectric layer 4 is provided on the insulating layer 5. Not limited to the above, the support member 3 may also be composed only of the support substrate 6.

[0064] The piezoelectric layer 4 has a first main surface 4a and a second main surface 4b. The first main surface 4a and the second main surface 4b are opposite to each other. The second main surface 4b is located on the support member 3 side. A functional electrode 1 is provided on the first main surface 4a of the piezoelectric layer 4. However, in this invention, the first main surface 4a may also be located on the support member 3 side.

[0065] like Figure 2 As shown, the functional electrode 1 has a pair of comb-shaped electrodes and a third electrode 9. Specifically, the pair of comb-shaped electrodes are a first comb-shaped electrode 7 and a second comb-shaped electrode 8. The first comb-shaped electrode 7 is connected to the input potential. The second comb-shaped electrode 8 is connected to the output potential. In this embodiment, the third electrode 9 is connected to a reference potential. Therefore, in this embodiment, the third electrode 9 is a reference potential electrode.

[0066] Alternatively, the first comb electrode 7 can also be connected to the output potential. The second comb electrode 8 can also be connected to the input potential. Thus, the first comb electrode 7 can be connected to one of the input and output potentials, and the second comb electrode 8 can be connected to the other of the input and output potentials. This structure can also be applied to structures of the present invention other than those in the first embodiment.

[0067] The third electrode 9 does not necessarily need to be connected to the reference potential. The third electrode 9 can be connected to a potential different from that of the first comb electrode 7 and the second comb electrode 8. However, it is preferable that the third electrode 9 is connected to the reference potential.

[0068] The first comb-shaped electrode 7 and the second comb-shaped electrode 8 are disposed on the first main surface 4a of the piezoelectric layer 4. More specifically, the first comb-shaped electrode 7 and the second comb-shaped electrode 8 are directly disposed on the first main surface 4a. The first comb-shaped electrode 7 has a first busbar 12 and a plurality of first electrode fingers 15. One end of each of the plurality of first electrode fingers 15 is connected to the first busbar 12. On the other hand, the second comb-shaped electrode 8 has a second busbar 13 and a plurality of second electrode fingers 16. One end of each of the plurality of second electrode fingers 16 is connected to the second busbar 13.

[0069] The first busbar 12 and the second busbar 13 are opposite to each other. A plurality of first electrode fingers 15 and a plurality of second electrode fingers 16 are interleaved and interlocked. The first electrode fingers 15 and the second electrode fingers 16 are arranged alternately in a direction orthogonal to the direction in which they extend.

[0070] The third electrode 9 is disposed on the first main surface 4a of the piezoelectric layer 4. Specifically, the third electrode 9 has a third busbar 14 serving as a connecting electrode and a plurality of third electrode fingers 17. The plurality of third electrode fingers 17 are directly disposed on the first main surface 4a. The third busbar 14, except for a portion thereof, is directly disposed on the first main surface 4a. The plurality of third electrode fingers 17 are electrically connected to each other through the third busbar 14. In addition, the first comb-shaped electrode 7, the second comb-shaped electrode 8, and the third electrode 9 are electrically insulated from each other.

[0071] The plurality of third electrode fingers 17 are respectively configured to be arranged in the same direction as the first electrode fingers 15 and the second electrode fingers 16. Therefore, the first electrode fingers 15, the second electrode fingers 16, and the third electrode fingers 17 are arranged in one direction. The plurality of third electrode fingers 17 extend parallel to the plurality of first electrode fingers 15 and the plurality of second electrode fingers 16.

[0072] Hereinafter, the extending directions of the first electrode finger 15, the second electrode finger 16, and the third electrode finger 17 will be defined as the electrode finger extending direction, and the direction orthogonal to the electrode finger extending direction will be defined as the electrode finger orthogonal direction. In this embodiment, the electrode finger orthogonal direction is parallel to the extending directions of the first bus bar 12, the second bus bar 13, and the third bus bar 14. In this specification, the first electrode finger 15, the second electrode finger 16, and the third electrode finger 17 are sometimes collectively referred to as electrode fingers. The first bus bar 12, the second bus bar 13, and the third bus bar 14 are sometimes collectively referred to as bus bars.

[0073] In functional electrode 1, the structure, except for the third electrode 9, is the same as that of the IDT (Interdigital Transducer) electrode. When viewed from the orthogonal direction of the electrode fingers, the area where adjacent first electrode fingers 15 and second electrode fingers 16 overlap is the intersection region F. However, the intersection region F can also be described as the area where adjacent first electrode fingers 15 and third electrode fingers 17, or adjacent second electrode fingers 16 and third electrode fingers 17, overlap when viewed from the orthogonal direction of the electrode fingers. In this specification, the dimension of the intersection region F along the extension direction of the electrode fingers is the intersection width.

[0074] like Figure 2 As shown, the third busbar 14 of the third electrode 9 electrically connects multiple third electrode fingers 17 to each other. Specifically, the third busbar 14 is located in the region between the intersection region F and the first busbar 12. Multiple first electrode fingers 15 are also located in this region. However, the third busbar 14 and the multiple first electrode fingers 15 are electrically insulated from each other by multiple insulating layers 11.

[0075] Figure 3 This is a schematic front sectional view showing the vicinity of the functional electrode in the first embodiment.

[0076] In this embodiment, the multiple electrode fingers are arranged in an orthogonal direction. Regarding the order of the multiple electrode fingers, starting with the first electrode finger 15, the sequence is: first electrode finger 15, third electrode finger 17, second electrode finger 16, and third electrode finger 17, forming a cycle. Therefore, the order of the multiple electrode fingers continues as follows: first electrode finger 15, third electrode finger 17, second electrode finger 16, third electrode finger 17, first electrode finger 15, third electrode finger 17, second electrode finger 16… If IN represents the input potential, OUT represents the output potential, and GND represents the reference potential, and the order of the multiple electrode fingers is represented by the order of the connected potentials, then it continues as IN, GND, OUT, GND, IN, GND, OUT…

[0077] In the region where multiple electrode fingers are provided, the electrode fingers located at both ends in the orthogonal direction of the electrode fingers are both second electrode fingers 16. Therefore, when at least one electrode finger of the multiple electrode fingers of the functional electrode 1 located at one end in the direction in which the multiple electrode fingers are arranged is designated as a first end electrode finger A, one of the first end electrode fingers A is a second electrode finger 16. Similarly, when at least one electrode finger of the multiple electrode fingers of the functional electrode 1 located at the other end in the direction in which the multiple electrode fingers are arranged is designated as a second end electrode finger B, one of the second end electrode fingers B is a second electrode finger 16.

[0078] Furthermore, in this embodiment, specifically, there are two first end electrode fingers A and two second end electrode fingers B. In this embodiment, the first end electrode finger A is the second electrode finger 16 and the third electrode finger 17. Similarly, the second end electrode finger B is the second electrode finger 16 and the third electrode finger 17. However, in the region of the functional electrode 1 where multiple electrode fingers are provided, the electrode finger located at the end in the orthogonal direction of the electrode fingers can be any type of electrode finger among the first electrode finger 15, the second electrode finger 16, and the third electrode finger 17. Therefore, the types of the first end electrode fingers A and the second end electrode fingers B are not limited to those described above.

[0079] In this embodiment, the first end electrode finger A is one of a plurality of electrode fingers. Figure 3 The electrode finger at the left end of the middle. Therefore, the outer side of the direction in which the multiple electrode fingers are arranged with respect to the first end electrode finger A is... Figure 3 The left side of the middle. Furthermore, in this embodiment, the outer side in the direction in which the multiple electrode fingers are arranged is synonymous with the outer side in the direction orthogonal to the electrode fingers.

[0080] On the other hand, the second end electrode finger B is one of multiple electrode fingers. Figure 3 The electrode finger at the right end of the middle. Therefore, the outer side of the direction in which the multiple electrode fingers are arranged for the second end electrode finger B is... Figure 3 On the right side of the middle. However, the second end electrode finger B can also be one of multiple electrode fingers. Figure 3 The electrode finger at the left end of the array. In this case, the first end electrode finger A is one of a plurality of electrode fingers. Figure 3 The electrode finger is located at the right end of the middle.

[0081] The first end electrode finger A and the second end electrode finger B each have a first surface 1a and a second surface 1b, and a first side surface 1c and a second side surface 1d. The first surface 1a and the second surface 1b are opposite to each other in the thickness direction. The first side surface 1c and the second side surface 1d connect the first surface 1a and the second surface 1b, and are opposite to each other in the orthogonal direction of the electrode fingers. In each of the first end electrode finger A and the second end electrode finger B, the first side surface 1c is located on the outer side in the direction in which the plurality of electrode fingers of the functional electrode 1 are arranged, compared to the second side surface 1d.

[0082] In this embodiment, the first side surface 1c and the second side surface 1d of the first end electrode finger A and the second end electrode finger B extend obliquely relative to the normal direction of the first main surface 4a of the piezoelectric layer 4. However, the first side surface 1c and the second side surface 1d may also extend parallel to the normal direction of the first main surface 4a.

[0083] The following will be equivalent to Figure 1The view taken from above, along the stacking direction of the support member 3 and the piezoelectric layer 4, is described as a top view. Additionally, in... Figure 1 In this context, for example, the piezoelectric layer 4 side is considered the upper side, in the case of the support substrate 6 side and the piezoelectric layer 4 side. In this specification, a top view is synonymous with a view from the main face orientation. The main face orientation refers to the direction in which the first main surface 4a and the second main surface 4b of the piezoelectric layer 4 are opposite each other. More specifically, the main face orientation is, for example, the normal direction of the first main surface 4a.

[0084] like Figure 3 As shown, the two mass-adding films 19 are configured to overlap with the two electrode fingers serving as the first end electrode fingers A when viewed from above. Similarly, the two mass-adding films 19 are configured to overlap with the two electrode fingers serving as the second end electrode fingers B when viewed from above. Specifically, one mass-adding film 19 overlaps with one first end electrode finger A or one second end electrode finger B when viewed from above. However, it is also possible for a continuously arranged mass-adding film 19 to overlap with both the first end electrode finger A and the second end electrode finger B when viewed from above. On the other hand, the electrode fingers other than the first end electrode finger A and the second end electrode finger B among the plurality of electrode fingers in the functional electrode 1 do not overlap with the mass-adding films 19 when viewed from above. Hereinafter, overlapping when viewed from above will sometimes be simply referred to as overlapping.

[0085] Furthermore, in this invention, the first end electrode finger A can be up to four consecutive electrode fingers located at one end in the direction in which the plurality of electrode fingers are arranged. Similarly, the second end electrode finger B can be up to four consecutive electrode fingers located at the other end in the direction in which the plurality of electrode fingers are arranged. Therefore, for example, if the first end electrode finger A and the second end electrode finger B are each one, the mass-adding film 19 can be configured to overlap with each of the first end electrode finger A and the second end electrode finger B.

[0086] However, the mass-addition film 19 only needs to be positioned so that it overlaps at least with the first end electrode finger A when viewed from above. In this specification, for convenience, the second end electrode finger B is assumed to be 0 when the mass-addition film 19 only overlaps with the first end electrode finger A.

[0087] In this embodiment, when viewed from above, the mass-adding film 19 overlaps with a portion of the first surface 1a and the second surface 1b of the first end electrode finger A, as well as a portion of the first side surface 1c. On the other hand, the mass-adding film 19 does not overlap with another portion of the first surface 1a and the second surface 1b of the first end electrode finger A, or the second side surface 1d. Furthermore, when viewed from above, the mass-adding film 19 overlaps with a portion of the first side surface 1c of the first end electrode finger A that is located further outward in the direction orthogonal to the electrode finger.

[0088] Thus, the mass-addition film 19 is continuously arranged in the orthogonal direction of the electrode fingers, overlapping the first end electrode finger A and the portion where the electrode finger is not provided when viewed from above. Moreover, the mass-addition film 19 is arranged to completely overlap the electrode finger extension direction of the portion of the first end electrode finger A located in the intersection region F when viewed from above.

[0089] Similarly, the mass-addition film 19, which overlaps with the second end electrode finger B when viewed from above, is also continuously configured in the orthogonal direction of the electrode fingers to overlap the second end electrode finger B and the portion where the electrode finger is not located when viewed from above. The mass-addition film 19 is configured to completely overlap the electrode finger extension direction of the portion of the second end electrode finger B located in the intersection region F when viewed from above.

[0090] When the overlap width is defined as the dimension of the portion of the mass-added film 19 that overlaps with the first end electrode finger A or the second end electrode finger B in a top view along the orthogonal direction of the electrode fingers, in this embodiment, the overlap width is narrower than the width of the first end electrode finger A or the second end electrode finger B. Furthermore, the width of an electrode finger is the dimension of the electrode finger along the orthogonal direction of the electrode fingers.

[0091] However, the configuration of the mass-addition film 19 is not limited to the above. The mass-addition film 19 may overlap with at least a portion of the first end electrode finger A when viewed from above.

[0092] Silicon oxide was used as the material for the mass-added film 19. However, the material of the mass-added film 19 is not limited to the one described above.

[0093] In the elastic wave device 10, a dielectric film is disposed on the piezoelectric layer 4. Specifically, the dielectric film includes a first dielectric film 18A and a second dielectric film 18B. The first dielectric film 18A is disposed on the first main surface 4a of the piezoelectric layer 4, thereby covering the functional electrode 1. The second dielectric film 18B is disposed on the second main surface 4b of the piezoelectric layer 4. A plurality of the aforementioned mass-addition films 19 are disposed on the first dielectric film 18A.

[0094] Alternatively, the dielectric film can be disposed on at least one of the first main surface 4a side and the second main surface 4b side of the piezoelectric layer 4. If the functional electrode 1 is not covered by the dielectric film, for example, the mass-addition film 19 can be directly disposed on the first end electrode finger A and the second end electrode finger B.

[0095] Silicon oxide was used as the material for both the first dielectric film 18A and the second dielectric film 18B. However, the materials for the first dielectric film 18A and the second dielectric film 18B are not limited to those described above.

[0096] In this embodiment, the first electrode finger 15, the second electrode finger 16, and the third electrode finger 17 comprise stacked metal films. Specifically, in each electrode finger, a Ti layer and an AlCu layer are sequentially stacked from the piezoelectric layer 4 side. Furthermore, the material of each electrode finger is not limited to the above. Alternatively, each electrode finger may also comprise a single-layer metal film.

[0097] like Figure 2 As shown, the elastic wave device 10 has multiple excitation regions C. Elastic waves are excited in the multiple excitation regions C. Furthermore, in... Figure 2 In the diagram, only two of the multiple excitation regions C are shown.

[0098] A portion of the total excitation regions C are regions where adjacent first electrode fingers 15 and third electrode fingers 17 overlap when viewed from the orthogonal direction of the electrode fingers, and are the regions between the centers of adjacent first electrode fingers 15 and third electrode fingers 17 in the orthogonal direction of the electrode fingers. The remaining excitation regions C are regions where adjacent second electrode fingers 16 and third electrode fingers 17 overlap when viewed from the orthogonal direction of the electrode fingers, and are the regions between the centers of adjacent second electrode fingers 16 and third electrode fingers 17 in the orthogonal direction of the electrode fingers. These excitation regions C are arranged in the orthogonal direction of the electrode fingers. Multiple excitation regions C are contained within the aforementioned cross region F. Furthermore, the cross region F and the excitation regions C are regions of the piezoelectric layer 4 defined based on the structure of the functional electrode 1.

[0099] The elastic wave device 10 is an acoustic coupling type filter. In the excitation region C located between the centers of adjacent first electrode fingers 15 and third electrode fingers 17, and in the excitation region C located between the centers of adjacent second electrode fingers 16 and third electrode fingers 17, multiple modes of elastic waves containing thickness shear modes of volume waves are excited. By coupling these modes, a suitable filter waveform can be obtained even within a single elastic wave device 10.

[0100] The feature of this embodiment is that a mass-addition film 19 is provided at a position overlapping the first end electrode finger A and the second end electrode finger B when viewed from above. However, the mass-addition film 19 only needs to be provided at the position overlapping the first end electrode finger A when viewed from above. As a result, unwanted waves in the passband can be suppressed. As a result, when the elastic wave device 10 is used in a filter device, the degradation of the filter characteristics of the filter device can be suppressed. This detail will be shown below by comparing this embodiment with the first comparative example.

[0101] The first comparative example differs from the first embodiment in that it does not have the mass-added membrane 19. Transmission characteristics were compared in both the first embodiment and the first comparative example. The design parameters of the elastic wave device 10 having the structure of the first embodiment are as follows. Furthermore, the design parameters of the first comparative example are set to be the same as those of the first embodiment, except for the mass-added membrane 19.

[0102] Piezoelectric layer: Material…LiNbO3, cleavage angle…120°Y, thickness…335nm

[0103] The first electrode refers to the third electrode. Layer structure…Ti layer / AlCu layer from the piezoelectric layer side, thickness…10nm / 400nm from the piezoelectric layer side, width…0.4μm

[0104] The center-to-center distance between the first and third electrode fingers is 1.38 μm.

[0105] The center-to-center distance between the second and third electrode fingers: 1.38 μm

[0106] Cross width: 40μm

[0107] Total number of first to third electrode fingers: 51

[0108] Number of first-end electrode fingers and second-end electrode fingers: 2

[0109] First dielectric film: Material…silicon oxide, thickness…75nm

[0110] Second dielectric film: Material…silicon oxide, thickness…75nm

[0111] Mass-added film: Material…silicon oxide, thickness…70nm, dimension along the orthogonal direction of the electrode…0.9μm, overlap width…0.2μm

[0112] Figure 4 This is a diagram illustrating the throughput characteristics in the first embodiment and the first comparative example. Additionally, Figure 4 The results of simulations based on the FEM (Finite Element Method) are shown. The characteristic is the frequency response of attenuation, represented by S-parameters. Figure 4 The frequency band D shown is the low-frequency band within the passband of the elastic wave device. Figure 4 The arrow H in the diagram indicates a portion of the frequency within the passband. Figure 4 The same applies to the diagram showing the characteristics other than those shown.

[0113] like Figure 4As shown, in the attenuation frequency response of the first comparative example, a significant amount of ripple was generated within the passband. Specifically, a large amount of ripple was generated in frequency band D, located on the low-frequency side of the passband. Furthermore, in... Figure 4 The frequencies near the center of the passband, indicated by arrow H, exhibit significant ripple. These ripples are caused by unwanted waves. In contrast, it can be seen that the attenuation frequency characteristics of the first embodiment suppress ripple. Thus, in the first embodiment, unwanted waves within the passband can be suppressed. The reasons for this are explained below.

[0114] In the first embodiment, the mass-added membrane 19 is disposed at a position overlapping the first end electrode A when viewed from above. The sound velocity of the bulk wave propagating in the portion where the mass-added membrane 19 is disposed is different from the sound velocity of the bulk wave propagating in the portion where the mass-added membrane 19 is not disposed. Therefore, the boundary between the portion where the mass-added membrane 19 is disposed and the portion where the mass-added membrane 19 is not disposed functions as a reflective surface for reflecting the bulk wave. As a result, the bulk wave of the thickness shear mode can be confined to the inside of the functional electrode 1. As a result, the bulk wave of the thickness shear mode can be stably excited in each excitation region C. Along with this, the excitation of unwanted waves can be suppressed.

[0115] The structure of the first embodiment will now be described in further detail.

[0116] like Figure 1 As shown, a recess is provided in the insulating layer 5. A piezoelectric layer 4 is provided on the insulating layer 5 to block the recess. This forms a hollow portion. This hollow portion is a cavity 10a. In the first embodiment, the support member 3 and the piezoelectric layer 4 are arranged such that a part of the support member 3 and a part of the piezoelectric layer 4 sandwich the cavity 10a and face each other. However, it is also possible that the recess in the support member 3 is provided throughout the insulating layer 5 and the support substrate 6. Alternatively, it is also possible that only the recess provided in the support substrate 6 is blocked by the insulating layer 5. The recess may also be provided in the piezoelectric layer 4, for example. In addition, the cavity 10a may also be a through hole provided in the support member 3.

[0117] The cavity 10a is the acoustic reflection part in this invention. The acoustic reflection part effectively confines the energy of the elastic wave to the piezoelectric layer 4. In plan view, the acoustic reflection part is positioned in the support member 3 at a location overlapping at least a portion of the functional electrode 1. More specifically, in plan view, at least a portion of each of the first electrode finger 15, the second electrode finger 16, and the third electrode finger 17 overlaps with the acoustic reflection part. In plan view, the plurality of excitation regions C preferably overlap with the acoustic reflection part.

[0118] Alternatively, the sound-reflecting part can also be a sound-reflecting membrane such as a multilayer sound-reflecting membrane, as described later. For example, a sound-reflecting membrane can also be provided on the surface of the supporting member.

[0119] In the first embodiment, the center-to-center distance between multiple pairs of adjacent first electrode fingers 15 and third electrode fingers 17 is the same as the center-to-center distance between multiple pairs of adjacent second electrode fingers 16 and third electrode fingers 17. However, the center-to-center distance between adjacent first electrode fingers 15 and third electrode fingers 17 and the center-to-center distance between adjacent second electrode fingers 16 and third electrode fingers 17 may not be fixed. In this case, the longest distance among the center-to-center distances of adjacent first electrode fingers 15 and third electrode fingers 17 and adjacent second electrode fingers 16 and third electrode fingers 17 is set as p. Alternatively, in the case where the center-to-center distance is fixed as in this embodiment, the center-to-center distance between any two adjacent electrode fingers is always p.

[0120] When the thickness of the piezoelectric layer 4 is set to d, d / p is preferably 0.5 or less, and more preferably 0.24 or less. This allows for the appropriate excitation of bulk waves in the thickness shear mode.

[0121] Figure 5 It is along Figure 2 A schematic cross-sectional view of line II-II in the diagram.

[0122] An insulating layer 11 is disposed on the first main surface 4a of the piezoelectric layer 4, thereby covering the first electrode finger 15. More specifically, in this embodiment, an insulating layer 11 covers a portion of the electrode finger extension direction of a first electrode finger 15.

[0123] More specifically, such as Figure 2 As shown, multiple insulating layers 11 are arranged along the orthogonal direction of the electrode fingers. Each insulating layer 11 is configured to cover a portion of a first electrode finger 15. A third busbar 14 is provided throughout the first main surface 4a of the piezoelectric layer 4, the multiple insulating layers 11, and the multiple third electrode fingers 17.

[0124] Thus, the plurality of first electrode fingers 15, which are part of the first comb electrode 7, intersect with the third busbar 14, which is part of the third electrode 9, on the piezoelectric layer 4, separated by an insulating layer 11. In other words, the third busbar 14 and the plurality of first electrode fingers 15 intersect three-dimensionally, separated by the insulating layer 11. As a result, the third busbar 14 and the plurality of first electrode fingers 15 are electrically insulated from each other. On the other hand, the third busbar 14 electrically connects the plurality of third electrode fingers 17.

[0125] Furthermore, the stacking order of the first electrode finger 15, the insulating layer 11, and the third busbar 14 at the stacked portions is not limited to the above. For example, they can also be stacked in the order of the third busbar 14, the insulating layer 11, and the first electrode finger 15.

[0126] As described above, the number of each of the first end electrode finger A and the second end electrode finger B is not limited to two. Hereinafter, a first variation and a second variation are shown where only the number of the first end electrode finger A and the second end electrode finger B differs from the first embodiment.

[0127] exist Figure 6 In the first modified example shown, the number of first end electrode fingers A and second end electrode fingers B is one. Therefore, the mass-added film 19 overlaps with one electrode finger at one end and one electrode finger at the other end in the direction in which the plurality of electrode fingers are arranged when viewed from above.

[0128] exist Figure 7 In the second variation shown, the number of first end electrode fingers A and second end electrode fingers B are each four. Therefore, the mass-added film 19 overlaps, in top view, with four consecutive electrode fingers from one end of the electrode fingers arranged in the direction of the plurality of electrode fingers and four consecutive electrode fingers from the electrode fingers located at the other end.

[0129] The passage characteristics of the first and second modified examples were derived through FEM simulation. Additionally, the following are also shown... Figure 4 The results of the first comparative example are shown.

[0130] Figure 8 This is a diagram illustrating the throughput characteristics in a first modified example and a first comparative example of the first embodiment. Figure 9 This is a diagram illustrating the passage characteristics in a second variation of the first embodiment and a first comparative embodiment.

[0131] like Figure 8 As shown, in the first modified example, compared with the first comparative example, it is able to suppress unwanted waves in frequency band D and unwanted waves near the frequency indicated by arrow H. Figure 9 As shown, in the second modified example, compared with the first comparative example, it is able to suppress unwanted waves near the frequency indicated by arrow H.

[0132] However, as in the first embodiment, the number of each of the first end electrode finger A and the second end electrode finger B is preferably two. (Comparison) Figure 4 , Figure 8 and Figure 9 It is clear that, Figure 4 In the first embodiment shown, unwanted waves can be effectively suppressed, and insertion loss can be reduced. The reasons are explained below.

[0133] Figure 10 This is a schematic front sectional view showing the vicinity of the first to third electrode fingers used to illustrate the odd-numbered pattern. Figure 11 This is a schematic front sectional view showing the vicinity of the first to third electrode fingers used to illustrate the even-numbered pattern. Figure 12This is a schematic diagram illustrating the passband formation in an acoustically coupled filter. Additionally, Figure 10 China and Figure 11 The arrows in the diagram indicate the direction of the electric field.

[0134] In acoustically coupled filters, the generation Figure 10 The odd number pattern shown and Figure 11 The even-numbered modes are shown. Odd-numbered modes refer to modes where the electrical conditions are in phase. Figure 10 The diagram shows the region corresponding to one wavelength of the odd-numbered mode. One wavelength of the odd-numbered mode is the distance between the centers of adjacent first electrode fingers 15 and second electrode fingers 16.

[0135] Even-numbered modes refer to modes where the electrical conditions are in opposite phase. Figure 11 The diagram shows the region corresponding to half the wavelength of the even-numbered mode. The half-wavelength of the even-numbered mode is the distance between the centers of adjacent first electrode fingers 15 and second electrode fingers 16. The wavelength of the even-numbered mode is twice the wavelength of the odd-numbered mode.

[0136] like Figure 12 As shown, in an acoustically coupled filter, the passband is formed using even-numbered and odd-numbered modes. Even-numbered modes constitute the low-frequency end of the passband, while odd-numbered modes constitute the high-frequency end.

[0137] exist Figure 6 In the first variant shown, the first end electrode finger A is a single element, and the mass-added film 19 overlaps with the single first end electrode finger A when viewed from above. In this case, the odd-numbered modes can be sufficiently reflected towards the central side of the functional electrode 1. On the other hand, the wavelength of the even-numbered modes is twice the wavelength of the odd-numbered modes. For this reason, the effect of reflecting the even-numbered modes towards the central side of the functional electrode 1 is not as good as the effect of reflecting the odd-numbered modes towards the central side of the functional electrode 1. The same applies to the second end electrode finger B side.

[0138] In contrast, Figure 3 In the first embodiment shown, there are two first end electrode fingers A, and the mass-added film 19 overlaps with the two first end electrode fingers A when viewed from above. In this case, sufficient reflection can be achieved on the central side of the bidirectional functional electrodes 1 for both odd and even modes. The same applies to the side of the second end electrode finger B. Thus, in each excitation region C, both odd and even modes can be stably excited. Along with this, the excitation of unwanted waves can be effectively suppressed. Moreover, the passband can be easily and stably constructed, thereby reducing insertion loss on the high-frequency side within the passband.

[0139] Furthermore, compared to setting the number of first end electrode fingers A and second end electrode fingers B to four as in the second variation, setting them to two as in the first embodiment allows for more stable excitation of both odd and even modes.

[0140] In the first embodiment and its first and second modifications, the number of first end electrode fingers A is the same as the number of second end electrode fingers B. However, it is not limited to this. For example, in Figure 13 In the third variation of the first embodiment shown, the number of first end electrode fingers A is three, and the number of second end electrode fingers B is two. That is, the mass-added film 19 overlaps, in top view, with three consecutive electrode fingers from one end in the direction of the multiple electrode fingers arrangement and two consecutive electrode fingers from the other end. Even in the third variation, unwanted waves in the passband can be suppressed. Hereinafter, this situation will be shown by comparing the third variation with the first comparative example.

[0141] The difference between the first comparative example and the third modified example is that the mass-added membrane 19 was not provided. The throughput characteristics were compared in the third modified example and the first comparative example.

[0142] The design parameters of the elastic wave device involved in the third modification are the same as those of the first embodiment, except that the number of first end electrode fingers A is three. The design parameters of the first comparative example are the same as those of the first embodiment, except that the mass-added membrane 19 is the same.

[0143] Figure 14 This is a diagram illustrating the passage characteristics in the third variation of the first embodiment and the first comparative embodiment.

[0144] like Figure 14 As shown, in the third modified example, compared with the first comparative example, unwanted waves near the frequency indicated by arrow H can be suppressed. Thus, in the third modified example, unwanted waves within the passband can be suppressed.

[0145] In the third variation, the number of first end electrode fingers A and the number of second end electrode fingers B are different. Thus, the conditions at one end and the other end in the direction in which the multiple electrode fingers are arranged in the functional electrode can also be different. For example, the thickness, dimension along the orthogonal direction of the electrode fingers, and overlap width of the mass-added film 19 at one end and the mass-added film 19 at the other end in the direction in which the multiple electrode fingers are arranged in the functional electrode can all be different. Even in this case, as in the first embodiment and the third variation, unwanted waves in the passband can be suppressed.

[0146] In the first embodiment, the material type and density of the mass-added film 19 are the same as those of the dielectric film. More specifically, the material type and density of the mass-added film 19, the material type and density of the first dielectric film 18A, and the material type and density of the second dielectric film 18B are the same. However, this is not a limitation.

[0147] Furthermore, in this specification, the statement that "one material is the same as another material" also includes cases where one material and another material contain the same types of elements, but the composition ratios of the two materials are different.

[0148] For example, in citing Figure 3 In the fourth variation of the first embodiment shown, the material of the mass-added film 19 is the same as that of the dielectric film, and the density of the mass-added film 19 is lower than that of the dielectric film. More specifically, the material of the mass-added film 19 is the same as that of the first dielectric film 18A and the second dielectric film 18B, and the density of the mass-added film 19 is lower than that of the first dielectric film 18A and the second dielectric film 18B. Furthermore, in the fourth variation, similar to the first embodiment, the number of first end electrode fingers A is two, and the number of second end electrode fingers B is two. Even in the fourth variation, unwanted waves in the passband can be suppressed. This situation will be illustrated below by comparing the fourth variation with the first comparative example.

[0149] The difference between the first comparative example and the fourth modified example is that the mass-added membrane 19 is not provided. Transmission characteristics were compared in the fourth modified example and the first comparative example. The design parameters of the elastic wave device involved in the fourth modified example are the same as those in the first embodiment, except for the density of the mass-added membrane 19. The parameters related to the mass-added membrane 19 in the fourth modified example are described below. Furthermore, the design parameters of the first comparative example are set to be the same as those in the first embodiment, except for the mass-added membrane 19.

[0150] Mass-added film: Material…silicon oxide, thickness…70nm, dimension along the orthogonal direction of the electrodes…0.9μm, overlap width…0.2μm, density…0.9 times the density of the first dielectric film and the density of the second dielectric film.

[0151] Figure 15 This is a diagram illustrating the passage characteristics in the fourth modified example and the first comparative example of the first embodiment.

[0152] like Figure 15As shown, in the fourth modified example, compared to the first comparative example, unwanted waves in frequency band D and unwanted waves near the frequency indicated by arrow H are suppressed. Thus, in the fourth modified example, unwanted waves in the passband can be suppressed. In addition, in the fourth modified example, insertion loss on the high-frequency side of the passband can also be reduced.

[0153] In the first embodiment, the material of the mass-added film 19 is silicon oxide. However, the material of the mass-added film 19 is not limited to silicon oxide. For example, the Young's modulus of the mass-added film 19 may be higher than that of silicon oxide.

[0154] The Young's modulus of the mass-added membrane 19 is preferably 50 GPa or higher. In this case, unwanted waves in the passband can be appropriately suppressed.

[0155] The material of the mass-added coating 19 is preferably at least one material selected from the group consisting of silicon oxycarbide, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide, and tungsten oxide. Specifically, the material of the mass-added coating 19 is preferably at least one material selected from the group consisting of SiOC, SiO2, SiN, Ta2O5, AlN, Al2O3, HfO2, Nb2O5, and WO. In this case, unwanted waves in the passband can be appropriately suppressed.

[0156] Furthermore, the material of the mass-added film 19 is not limited to the above; for example, it can also be fluorine-containing silicon oxide (SiOF). Even in this case, unwanted waves in the passband can be suppressed.

[0157] In the first embodiment, the material of the mass-added film 19 is the same as the material of the first dielectric film 18A and the second dielectric film 18B. However, the material of the mass-added film 19 may also be different from the materials of the first dielectric film 18A and the second dielectric film 18B. Figure 3 The fifth to seventh modifications of the first embodiment are shown here. In the fifth to seventh modifications, the first dielectric film 18A and the second dielectric film 18B are made of silicon oxide. On the other hand, the mass-added film 19 in the fifth modification is made of tantalum oxide. More specifically, the mass-added film 19 is made of Ta₂O₅. Therefore, the density of the mass-added film 19 is higher than the density of the first dielectric film 18A and the second dielectric film 18B.

[0158] In the sixth variation, the mass-added film 19 is made of fluorine-containing silicon oxide (SiOF). In this variation, the density of the mass-added film 19 is lower than the density of the first dielectric film 18A and the density of the second dielectric film 18B.

[0159] In the seventh variation, the mass-added film 19 is made of silicon nitride. More specifically, the mass-added film 19 is made of SiN. In this variation, the sound speed of the bulk wave propagating in the mass-added film 19 is higher than the sound speed of the bulk wave propagating in the first dielectric film 18A and the second dielectric film 18B.

[0160] In the fifth to seventh modifications and the first comparative example, the throughput characteristics were compared. The first comparative example differs from the fifth to seventh modifications in that it does not have the mass-added membrane 19. The design parameters of the elastic wave devices involved in the fifth to seventh modifications are set to be the same as those of the first embodiment, except for the material of the mass-added membrane 19. The design parameters of the first comparative example are set to be the same as those of the fifth to seventh modifications, except for the mass-added membrane 19.

[0161] Figure 16 This is a diagram illustrating the passage characteristics in the fifth variation and the first comparative example of the first embodiment. Figure 17 This is a diagram illustrating the passage characteristics in the sixth variation and the first comparative example of the first embodiment. Figure 18 This is a diagram illustrating the passage characteristics in the seventh modified example and the first comparative example of the first embodiment.

[0162] like Figures 16-18 As shown, in any of the fifth to seventh modifications, compared to the first comparative example, unwanted waves near the frequency indicated by arrow H can be suppressed. Thus, in the fifth to seventh modifications, unwanted waves within the passband can be suppressed.

[0163] Furthermore, such as Figure 3 As shown, the mass-adding film 19 in the first embodiment has an end face 19d. Specifically, the end face 19d is the surface connecting the piezoelectric layer 4 side of the mass-adding film 19 and the surface opposite to it. The end face 19d extends obliquely relative to the normal direction of the first main surface 4a of the piezoelectric layer 4. However, in the present invention, the end face 19d may also extend parallel to the normal direction of the first main surface 4a.

[0164] In the first embodiment, the thickness of the first dielectric film 18A is the same as the thickness of the second dielectric film 18B. Alternatively, the thicknesses of the first dielectric film 18A and the second dielectric film 18B may differ. However, it is preferable that the difference between the thicknesses of the first dielectric film 18A and the second dielectric film 18B is 10% or less relative to the thicknesses of both films. In this case, unwanted waves can be canceled out on both the first main surface 4a side and the second main surface 4b side of the piezoelectric layer 4. Therefore, unwanted waves can be effectively suppressed.

[0165] When comparing the thickness of the first dielectric film 18A with the thickness of other components, the thickness of the portion of the first dielectric film 18A not covered by the electrode is compared with the thickness of the other components. Similarly, when comparing the thickness of the second dielectric film 18B with the thickness of other components, the thickness of the portion of the second dielectric film 18B not covered by the electrode is compared with the thickness of the other components.

[0166] In the first embodiment, the thickness of the first dielectric film 18A and the thickness of the second dielectric film 18B are thinner than the thickness of the piezoelectric layer 4. Alternatively, the thickness of the first dielectric film 18A and the thickness of the second dielectric film 18B may also be thicker than the thickness of the piezoelectric layer 4. Even in this case, unwanted waves in the passband can be suppressed.

[0167] Furthermore, in this specification, "the thicknesses of the dielectric film and the piezoelectric layer are different" means that the difference between the thickness of the dielectric film and the thickness of the piezoelectric layer is 5% or more relative to the thicknesses of the dielectric film and the piezoelectric layer. When comparing the thickness of the piezoelectric layer with the thickness of other components, the thickness of the portion of the piezoelectric layer where the excitation region is located is compared with the thickness of the other components.

[0168] like Figure 2 As shown, in the first embodiment, the connecting electrode of the third electrode 9 in the functional electrode 1 is the third busbar 14. The third busbar 14 is located in the region between the intersection region F and the first busbar 12. In other words, the third busbar 14 is located in the region between the tips of the plurality of second electrode fingers 16 and the first busbar 12. Therefore, the tips of the plurality of second electrode fingers 16 are spaced apart in the electrode finger extension direction and face the third busbar 14. On the other hand, the tips of the plurality of first electrode fingers 15 are spaced apart in the electrode finger extension direction and face the second busbar 13.

[0169] Alternatively, the third busbar 14 may be located in the region between the tips of the plurality of first electrode fingers 15 and the second busbar 13. In this case, the tips of the plurality of first electrode fingers 15 are spaced apart and opposite the third busbar 14. On the other hand, the tips of the plurality of second electrode fingers 16 are spaced apart and opposite the first busbar 12.

[0170] However, the connecting electrode in the third electrode 9 does not necessarily have to be the third busbar 14. For example, in Figure 19 In the eighth variation of the first embodiment shown, the third electrode 9A has a meandering shape. Specifically, the third electrode 9A has a plurality of connecting electrodes 14A. In this variation, the connecting electrodes 14A are not the third busbar. Furthermore, in this variation, the insulating layer 11 is not provided on the piezoelectric layer 4.

[0171] More specifically, the third electrode 9A has multiple connecting electrodes 14A located on the side of the first busbar 12 and multiple connecting electrodes 14A located on the side of the second busbar 13. Each of the multiple third electrode fingers 17, excluding the two ends in the orthogonal direction, is connected to a connecting electrode 14A at its front end on both the first busbar 12 side and the second busbar 13 side. Each third electrode finger 17 is connected to its adjacent third electrode fingers 17 via its connecting electrodes 14A. By repeating this configuration, the shape of the third electrode 9A becomes meandering.

[0172] In this modified example, the tips of the plurality of second electrode fingers 16 are respectively opposed to the plurality of connecting electrodes 14A in the electrode finger extension direction. The tips of the plurality of first electrode fingers 15 are also respectively opposed to the plurality of connecting electrodes 14A in the electrode finger extension direction.

[0173] The functional electrode 1A in this modified example also has a first end electrode finger A and a second end electrode finger B, similar to the first embodiment. Furthermore, the first end electrode finger A and the second end electrode finger B overlap with the mass-added film 19 when viewed from above. This allows for the suppression of unwanted waves within the passband.

[0174] Hereinafter, another example of the structure in the third electrode will be shown through a ninth variation of the first embodiment. Figure 20 In the ninth modified example shown, the third electrode 9B includes a meandering portion and a portion connected to that portion. Additionally, Figure 20 The functional electrode 1B is shown to have a ratio of Figure 19 The portions of the first busbar 12 and the second busbar 13 shown are located on the side of the intersection region F.

[0175] In this modified example, the connecting electrode 14B of the third electrode 9B has multiple common electrode portions 14a, multiple connecting electrode fingers 14b, and a pair of strip portions 14c. The multiple common electrode portions 14a and... Figure 19 The plurality of connecting electrodes 14A shown in the eighth modified example are similarly configured. Therefore, in this modified example, the plurality of common electrode portions 14a include portions located at the corresponding Figure 20 Multiple common electrode portions 14a on the upper side of the first busbar and located at the equivalent Figure 20 Multiple common electrode sections 14a on the lower side of the second busbar.

[0176] On the first busbar side, each of the plurality of common electrode portions 14a is connected to a connecting electrode finger 14b. The connecting electrode fingers 14b connected to these common electrode portions 14a extend from the common electrode portion 14a side toward the first busbar side along the electrode finger extension direction. Similarly, on the second busbar side, each of the plurality of common electrode portions 14a is connected to a connecting electrode finger 14b. The connecting electrode fingers 14b connected to these common electrode portions 14a extend from the common electrode portion 14a side toward the second busbar side along the electrode finger extension direction.

[0177] One of a pair of strips 14c is provided between the first busbar and the crossover region. The other strip 14c is provided between the second busbar and the crossover region. Each strip 14c extends in a direction orthogonal to the electrode fingers. However, the direction in which each strip 14c extends is not limited to the above. The strip 14c on the first busbar side and the plurality of common electrode portions 14a are connected by a plurality of connecting electrode fingers 14b. Similarly, the strip 14c on the second busbar side and the plurality of common electrode portions 14a are connected by a plurality of connecting electrode fingers 14b.

[0178] In this modified example, similar to the first embodiment, the third electrode 9B is electrically insulated from the first comb electrode 7B and the second comb electrode 8B by the insulating layer 11. However, in this modified example, an insulating layer 11 is provided on the first main surface 4a of the piezoelectric layer 4, covering a plurality of first electrode fingers 15B. A strip portion 14c on the first busbar side is provided on this insulating layer 11. Thus, the plurality of first electrode fingers 15B, which are part of the first comb electrode 7B, and the connecting electrode 14B, which is part of the third electrode 9B, intersect on the piezoelectric layer 4 across the insulating layer 11.

[0179] An insulating layer 11 is provided on the first main surface 4a of the piezoelectric layer 4, covering a plurality of second electrode fingers 16B. A strip portion 14c on the second busbar side is provided on the insulating layer 11. Thus, the plurality of second electrode fingers 16B, which are part of the second comb electrode 8B, and the connecting electrode 14B, which are part of the third electrode 9B, intersect on the piezoelectric layer 4 across the insulating layer 11.

[0180] By including a pair of strips 14c in the third electrode 9B, the resistance of the third electrode 9B can be reduced. This allows the third electrode 9B to more reliably approach the reference potential.

[0181] The functional electrode 1B in this modified example also has a first end electrode finger A and a second end electrode finger B, similar to the first embodiment. Furthermore, the first end electrode finger A and the second end electrode finger B overlap with the mass-added film 19 when viewed from above. This allows for the suppression of unwanted waves within the passband.

[0182] Furthermore, in this modified example, the width of each first electrode finger 15B is not fixed. Specifically, the width of the first electrode finger 15B gradually increases towards the first busbar side. More specifically, the width of the portion of the first electrode finger 15B that overlaps with the common electrode portion 14a in the orthogonal direction of the electrode fingers is wider than the width of the portion of the first electrode finger 15B located in the intersection region. The width of a portion of the first electrode finger 15B located between the common electrode portion 14a and the first busbar when viewed from the orthogonal direction of the electrode fingers is wider than the width of the portion of the first electrode finger 15B that overlaps with the common electrode portion 14a in the orthogonal direction of the electrode fingers.

[0183] Similarly, the width of each second electrode finger 16B is not fixed. Specifically, the width of the second electrode finger 16B gradually increases towards the second busbar side. More specifically, the width of the portion of the second electrode finger 16B that overlaps with the common electrode portion 14a in the orthogonal direction of the electrode fingers is wider than the width of the portion of the second electrode finger 16B located in the intersection region. The width of a portion of the second electrode finger 16B located between the common electrode portion 14a and the second busbar when viewed from the orthogonal direction of the electrode fingers is wider than the width of the portion of the second electrode finger 16B that overlaps with the common electrode portion 14a in the orthogonal direction of the electrode fingers. Furthermore, the widths of each first electrode finger 15B and each second electrode finger 16B can also be fixed.

[0184] Each connecting electrode finger 14b in the connecting electrode 14B of the third electrode 9B includes a front end and a base end. The front end is the end located on the side of the intersection region. The front end includes a front tip. The base end is the end that connects to the strip 14c. The top view of the front tip of each connecting electrode finger 14b is curved. However, the top view shape of the front tip is not limited to the above; for example, it may be a straight shape, and the distance between the front tip and the intersection region is fixed. The width of the base end of each connecting electrode finger 14b increases as it approaches the strip 14c. Alternatively, the width of the base end may be fixed.

[0185] like Figure 1 As shown, of the first main surface 4a and the second main surface 4b of the piezoelectric layer 4, the second main surface 4b is located on the side of the support member 3. Alternatively, in this invention, the first main surface 4a of the piezoelectric layer 4 may also be located on the side of the support member 3. In this case, for example, the functional electrode 1 is located within the cavity 10a.

[0186] Figure 21 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the second embodiment.

[0187] The difference between this embodiment and the first embodiment lies in the arrangement of the mass-added membrane 19 and the structure of the first end electrode pointing to A. Although not shown, this embodiment also differs from the first embodiment in that the structure of the second end electrode pointing to B is different. Apart from the above points, the elastic wave device of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0188] The mass-added film 19 is directly disposed on the first main surface 4a of the piezoelectric layer 4. Specifically, the mass-added film 19 is located between a portion of the second surface 1b of the first end electrode finger A and the first main surface 4a of the piezoelectric layer 4. The first end electrode finger A has a portion indirectly disposed on the first main surface 4a through the mass-added film 19, and a portion directly disposed on the first main surface 4a. Therefore, the second surface 1b of the first end electrode finger A has a stepped portion 1f. The first surface 1a has a stepped portion 1e.

[0189] More specifically, the first end electrode finger A is disposed on the mass-adding film 19 from the portion between the end edge of the first side surface 1c and the end edge of the second side surface 1d in the second surface 1b to the end edge of the first side surface 1c. Therefore, the mass-adding film 19 overlaps with the first side surface 1c of the first end electrode finger A when viewed from above, but does not overlap with the second side surface 1d when viewed from above. Alternatively, the mass-adding film 19 may also completely overlap with the portion of the first end electrode finger A located in the intersection region F when viewed from above.

[0190] The mass-added film 19 has a portion located between the second surface 1b of the first end electrode finger A and the first main surface 4a of the piezoelectric layer 4, and a portion not located between the second surface 1b of the first end electrode finger A and the first main surface 4a of the piezoelectric layer 4. The portion of the mass-added film 19 not located between the second surface 1b of the first end electrode finger A and the first main surface 4a of the piezoelectric layer 4 overlaps, when viewed from above, with the portion located on the outer side of the first side surface 1c of the first end electrode finger A in the direction orthogonal to the electrode finger.

[0191] Although not shown in the figure, a mass-added film 19 is provided on the side of the second end electrode (B) in the same manner as on the side of the first end electrode (A).

[0192] like Figure 21 As shown, the mass-added film 19 is covered by the first dielectric film 18A together with the functional electrode. However, it is not necessary to provide the first dielectric film 18A. In this case, the second dielectric film 18B can be provided on the second main surface 4b side of the piezoelectric layer 4.

[0193] Even in this embodiment, as in the first embodiment, unwanted waves in the passband can be suppressed. Hereinafter, this detail will be shown by comparing this embodiment with the first comparative example. The first comparative example differs from this embodiment in that it does not have the mass-added film 19; and each electrode finger corresponding to the first end electrode finger A and the second end electrode finger B does not have a stepped portion. This first comparative example is the same as the first comparative example compared with the first embodiment and its various modifications.

[0194] In the second embodiment and the first comparative example, the transmission characteristics were compared. The design parameters of the elastic wave device having the structure of the second embodiment are as follows. Furthermore, the design parameters of the first comparative example are set to be... Figure 16 The design parameters of the first comparative example shown are the same.

[0195] Piezoelectric layer: Material…LiNbO3, cleavage angle…120°Y, thickness…335nm

[0196] The first electrode refers to the third electrode. Layer structure…Ti layer / AlCu layer from the piezoelectric layer side, thickness…10nm / 400nm from the piezoelectric layer side, width…0.4μm

[0197] The center-to-center distance between the first and third electrode fingers is 1.38 μm.

[0198] The center-to-center distance between the second and third electrode fingers: 1.38 μm

[0199] Cross width: 40μm

[0200] Total number of first to third electrode fingers: 51

[0201] The number of first and second end electrode fingers: two.

[0202] First dielectric film: Material…silicon oxide, thickness…75nm

[0203] Second dielectric film: Material…silicon oxide, thickness…75nm

[0204] Mass-added film: Material…silicon oxide, thickness…100nm

[0205] Figure 22 This is a diagram illustrating the throughput characteristics in the second embodiment and the first comparative example.

[0206] like Figure 22As shown, in the second embodiment, compared to the first comparative example, unwanted waves in frequency band D and unwanted waves near the frequency indicated by arrow H can be suppressed. Thus, in the second embodiment, unwanted waves within the passband can be suppressed. Furthermore, in the second embodiment, insertion loss can be reduced. Therefore, when the elastic wave device of the second embodiment is used in a filter device, the degradation of the filter characteristics of the filter device can be effectively suppressed.

[0207] Figure 23 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the third embodiment.

[0208] The difference between this embodiment and the first embodiment lies in the arrangement of the mass-added membrane 19. Apart from the points mentioned above, the elastic wave device of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0209] The mass-added film 19 is disposed on the second main surface 4b side of the piezoelectric layer 4. Specifically, a second dielectric film 18B is disposed on the second main surface 4b. The mass-added film 19 is disposed on the second dielectric film 18B. That is, the mass-added film 19 is indirectly disposed on the second main surface 4b through the second dielectric film 18B. On the other hand, the mass-added film 19 is not disposed on the first main surface 4a side.

[0210] The mass-adding film 19, when viewed from above, completely overlaps with the portion of the first end electrode finger A located in the intersection region F. More specifically, one mass-adding film 19, when viewed from above, completely overlaps with the portions of the two first end electrode fingers A located in the intersection region F. Alternatively, one mass-adding film 19 may overlap with one first end electrode finger A, respectively, when viewed from above.

[0211] Although not shown in the figure, a mass-added film 19 is provided on the side of the second end electrode (B) in the same manner as on the side of the first end electrode (A).

[0212] Even in this embodiment, unwanted waves in the passband can be suppressed in the same way as in the first embodiment. Hereinafter, this detail will be shown by comparing this embodiment with the first comparative example. The first comparative example differs from this embodiment in that it does not have the mass-added film 19. This first comparative example is the same as the first comparative example compared with the first and second embodiments.

[0213] In the third embodiment and the first comparative example, the transmission characteristics were compared. The design parameters of the elastic wave device having the structure of the third embodiment are as follows. In addition, the design parameters of the first comparative example are set to be the same as those of the third embodiment, except for the mass-added membrane 19.

[0214] Piezoelectric layer: Material…LiNbO3, cleavage angle…120°Y, thickness…335nm

[0215] The first electrode refers to the third electrode. Layer structure…Ti layer / AlCu layer from the piezoelectric layer side, thickness…10nm / 400nm from the piezoelectric layer side, width…0.4μm

[0216] The center-to-center distance between the first and third electrode fingers is 1.38 μm.

[0217] The center-to-center distance between the second and third electrode fingers: 1.38 μm

[0218] Cross width: 40μm

[0219] Total number of first to third electrode fingers: 51

[0220] The number of first and second end electrode fingers: two.

[0221] First dielectric film: Material…silicon oxide, thickness…75nm

[0222] Second dielectric film: Material…silicon oxide, thickness…75nm

[0223] Mass-added film: Material…silicon oxide, thickness…110nm

[0224] Figure 24 This is a diagram illustrating the throughput characteristics in the third embodiment and the first comparative example. Additionally, Figure 24 Arrow J in the diagram indicates a portion of the frequency within the passband of the elastic wave device.

[0225] like Figure 24 As shown, in the third embodiment, compared to the first comparative example, unwanted waves in frequency band D and unwanted waves near the frequency indicated by arrow J can be suppressed. Thus, in the third embodiment, unwanted waves within the passband can be suppressed. Consequently, when the elastic wave device of the third embodiment is used in a filter device, the degradation of the filter characteristics of the filter device can be suppressed.

[0226] Figure 25 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the fourth embodiment.

[0227] The difference between this embodiment and the first embodiment is that the mass-added film 19 is disposed on both the first main surface 4a side and the second main surface 4b side of the piezoelectric layer 4. Apart from the above, the elastic wave device of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0228] The mass-added film 19 disposed on the first main surface 4a side of the piezoelectric layer 4 is disposed in the same manner as in the first embodiment. On the other hand, the mass-added film 19 disposed on the second main surface 4b side of the piezoelectric layer 4 is disposed in the same manner as in the third embodiment.

[0229] Viewed from above, the mass-added film 19 disposed on the first main surface 4a side of the piezoelectric layer 4 partially overlaps with a portion of the first end electrode finger A in the direction orthogonal to the electrode fingers. Conversely, the mass-added film 19 disposed on the second main surface 4b side of the piezoelectric layer 4 completely overlaps with the first end electrode finger A in the direction orthogonal to the electrode fingers. Therefore, the dimensions of the mass-added film 19 disposed on the first main surface 4a side along the direction orthogonal to the electrode fingers are different from those of the mass-added film 19 disposed on the second main surface 4b side.

[0230] Even in this embodiment, unwanted waves in the passband can be suppressed in the same way as in the first embodiment. Therefore, when the elastic wave device of this embodiment is used in a filter device, the degradation of the filter characteristics of the filter device can be suppressed.

[0231] Furthermore, in this embodiment, the thickness of the mass-added film 19 disposed on the first main surface 4a side of the piezoelectric layer 4 is greater than the thickness of the mass-added film 19 disposed on the second main surface 4b side of the piezoelectric layer 4. However, this is not a limitation. For example, in Figure 26 In the first variation of the fourth embodiment shown, the thickness of the mass-added film 19 disposed on the first main surface 4a side of the piezoelectric layer 4 is thinner than the thickness of the mass-added film 19 disposed on the second main surface 4b side of the piezoelectric layer 4. Even in this variation, unwanted waves in the passband can be suppressed. This situation is shown below.

[0232] Furthermore, when comparing the thickness of the mass-added film 19 with the thickness of other components, the thickness of the portion that does not overlap with the first end electrode finger A or the second end electrode finger B in a top view can be compared with the thickness of other components. However, this is not limited to cases where the entire mass-added film 19 overlaps with the first end electrode finger A or the second end electrode finger B in a top view.

[0233] The transmission characteristics of the fourth embodiment and its first variation were derived through FEM simulation. The design parameters of the elastic wave device of the fourth embodiment are as follows.

[0234] Piezoelectric layer: Material…LiNbO3, cleavage angle…120°Y, thickness…335nm

[0235] The first electrode refers to the third electrode. Layer structure…Ti layer / AlCu layer from the piezoelectric layer side, thickness…10nm / 400nm from the piezoelectric layer side, width…0.4μm

[0236] The center-to-center distance between the first and third electrode fingers is 1.38 μm.

[0237] The center-to-center distance between the second and third electrode fingers: 1.38 μm

[0238] Cross width: 40μm

[0239] Total number of first to third electrode fingers: 51

[0240] The number of first and second end electrode fingers: two.

[0241] First dielectric film: Material…silicon oxide, thickness…75nm

[0242] Second dielectric film: Material…silicon oxide, thickness…75nm

[0243] Mass-added film disposed on the first main surface side of the piezoelectric layer: material…silicon oxide, thickness…70nm, dimension along the orthogonal direction of the electrode fingers…0.9μm, overlap width…0.2μm

[0244] Mass-added film disposed on the second principal surface side of the piezoelectric layer: material…silicon oxide, thickness…20nm

[0245] The design parameters of the elastic wave device involved in the first modification of the fourth embodiment are the same as those in the fourth embodiment, except for the thickness of each mass-added membrane 19. The parameters related to each mass-added membrane 19 in the first modification are described below.

[0246] Mass-added film disposed on the first main surface side of the piezoelectric layer: material…silicon oxide, thickness…20nm, dimension along the orthogonal direction of the electrode…0.9μm, overlap width…0.2μm

[0247] Mass-added film disposed on the second principal surface side of the piezoelectric layer: material…silicon oxide, thickness…100nm

[0248] pass Figure 27 The passage characteristics of the fourth embodiment and its first variation are shown here. Additionally, the passage characteristics of the fourth embodiment and its first variation are also shown here. Figure 24 The results of the first comparative example are shown.

[0249] Figure 27 This is a diagram illustrating the passage characteristics in the fourth embodiment, its first variation, and the first comparative example.

[0250] like Figure 27As shown, in the fourth embodiment and its first modification, unwanted waves near the frequency indicated by arrow H are suppressed compared to the first comparative example. Thus, in the fourth embodiment and its first modification, unwanted waves within the passband can be suppressed. Furthermore, in the fourth embodiment and its first modification, insertion loss can also be reduced.

[0251] Furthermore, it is preferable that the thickness of the mass-added film 19 disposed on the first main surface 4a side of the piezoelectric layer 4, as in the fourth embodiment, is greater than the thickness of the mass-added film 19 disposed on the second main surface 4b side of the piezoelectric layer 4. In this case, as... Figure 27 As shown in the fourth embodiment, unwanted waves in frequency band D can be appropriately suppressed.

[0252] Furthermore, in the fourth embodiment and its first variation, the material of the mass-added film 19 disposed on the first main surface 4a of the piezoelectric layer 4 is the same as the material of the mass-added film 19 disposed on the second main surface 4b of the piezoelectric layer 4. However, it is not limited to this.

[0253] For example, in Figure 28 In the second variation of the fourth embodiment shown, the materials of the mass-added film 19 disposed on the first main surface 4a of the piezoelectric layer 4 and the mass-added film 19B disposed on the second main surface 4b of the piezoelectric layer 4 are different. Specifically, in this variation, the material of the mass-added film 19 disposed on the first main surface 4a is silicon oxide. On the other hand, the material of the mass-added film 19B disposed on the second main surface 4b is tantalum oxide. The thickness of the mass-added film 19 disposed on the first main surface 4a is the same as the thickness of the mass-added film 19B disposed on the second main surface 4b. Even in this variation, unwanted waves in the passband can be suppressed.

[0254] Alternatively, if the material of the mass-addition film 19 disposed on the first main surface 4a is different from the material of the mass-addition film 19B disposed on the second main surface 4b, the thickness of the mass-addition film 19 and the thickness of the mass-addition film 19B may also be different.

[0255] The combination of materials for mass-added films 19 and 19B shown in this variation is an example and is not limited to silicon oxide and tantalum oxide. Mass-added films 19 and 19B preferably contain, for example, at least one different material selected from the group consisting of silicon carbide, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide, and tungsten oxide.

[0256] In the first to fourth embodiments and their variations, the functional electrode is provided only on the first main surface of the piezoelectric layer. However, this is not a limitation. The fifth embodiment illustrates an example in which the functional electrode is provided on both the first and second main surfaces of the piezoelectric layer. Furthermore, hereafter, the functional electrode provided on the first main surface in the first embodiment, etc., will sometimes be referred to as the first functional electrode.

[0257] Figure 29 This is a schematic front sectional view of the elastic wave device according to the fifth embodiment.

[0258] In this embodiment, the first functional electrode 21A is equivalent to Figure 3 The functional electrode 1 is shown in the figure. The first functional electrode 21A is disposed on the first main surface 4a of the piezoelectric layer 4. The difference between this embodiment and the first embodiment is that a second functional electrode 21B is disposed on the second main surface 4b of the piezoelectric layer 4. Also, the difference between this embodiment and the first embodiment is that a second dielectric film 18B is disposed on the second main surface 4b of the piezoelectric layer 4, covering the second functional electrode 21B. Furthermore, the difference between this embodiment and the first embodiment is that a mass-adding film 19 is disposed on the second main surface 4b side of the piezoelectric layer 4. Apart from the above points, the elastic wave device of this embodiment has the same structure as the first embodiment.

[0259] The second functional electrode 21B has a first comb electrode 27, a second comb electrode 28, and a third electrode 29 that are different from the first comb electrode 7, the second comb electrode 8, and the third electrode 9 in the first functional electrode 21A. However, the first comb electrode 27, the second comb electrode 28, and the third electrode 29 in the second functional electrode 21B are constructed in the same way as the first comb electrode 7, the second comb electrode 8, and the third electrode 9 in the first functional electrode 21A.

[0260] Specifically, the first comb electrode 27 has a first busbar and a plurality of first electrode fingers 35. One end of each of the plurality of first electrode fingers 35 is connected to the first busbar. On the other hand, the second comb electrode 28 has a second busbar and a plurality of second electrode fingers 36. One end of each of the plurality of second electrode fingers 36 is connected to the second busbar. The first busbar in the first comb electrode 27 and the second busbar in the second comb electrode 28 are opposite to each other. The plurality of first electrode fingers 35 and the plurality of second electrode fingers 36 are interleaved and interlocked.

[0261] The third electrode 29 has a third busbar serving as a connecting electrode and a plurality of third electrode fingers 37. The plurality of third electrode fingers 37 are electrically connected to each other through the third busbar. The plurality of third electrode fingers 37 are respectively arranged in the same direction as the first electrode fingers 35 and the second electrode fingers 36. In addition, the first comb electrode 27, the second comb electrode 28 and the third electrode 29 are electrically insulated from each other.

[0262] Regarding the order of the multiple electrode fingers in the second functional electrode 21B, when starting from the first electrode finger 35, the first electrode finger 35, the third electrode finger 37, the second electrode finger 36, and the third electrode finger 37 are arranged in a cycle.

[0263] The elastic wave device of this embodiment has a cross-region and multiple excitation regions defined based on the structure of the first functional electrode 21A, and a cross-region and multiple excitation regions defined based on the structure of the second functional electrode 21B. Hereinafter, the region defined based on the structure of the first functional electrode 21A will sometimes be referred to as the region of the first functional electrode 21A. Similarly, the region defined based on the structure of the second functional electrode 21B will sometimes be referred to as the region of the second functional electrode 21B.

[0264] The first functional electrode 21A and the second functional electrode 21B are positioned opposite each other, sandwiching the piezoelectric layer 4. Furthermore, the intersection regions of the first functional electrode 21A and the second functional electrode 21B overlap when viewed from above. The excitation regions of the first functional electrode 21A and the excitation regions of the second functional electrode 21B also overlap when viewed from above.

[0265] In this embodiment, the number of electrode fingers of the first functional electrode 21A is the same as the number of electrode fingers of the second functional electrode 21B. Moreover, each electrode finger of the first functional electrode 21A overlaps with each electrode finger of the second functional electrode 21B when viewed from above.

[0266] More specifically, the electrode finger at one end of the first functional electrode 21A in the direction of the arrangement of multiple electrode fingers overlaps with the electrode finger at one end of the second functional electrode 21B in the direction of the arrangement of multiple electrode fingers when viewed from above. The electrode finger at the other end of the first functional electrode 21A in the direction of the arrangement of multiple electrode fingers overlaps with the electrode finger at the other end of the second functional electrode 21B in the direction of the arrangement of multiple electrode fingers when viewed from above.

[0267] Therefore, the first end electrode finger A1 of the first functional electrode 21A and the first end electrode finger A2 of the second functional electrode 21B overlap when viewed from above. The second end electrode finger B1 of the first functional electrode 21A and the second end electrode finger B2 of the second functional electrode 21B overlap when viewed from above.

[0268] Furthermore, the center of the portion of each electrode finger of the first functional electrode 21A located in the intersection region overlaps with the center of the portion of each electrode finger of the second functional electrode 21B located in the intersection region when viewed from above. However, it is sufficient that at least a portion of each electrode finger of the first functional electrode 21A overlaps with at least a portion of each electrode finger of the second functional electrode 21B when viewed from above.

[0269] The elastic wave device of this embodiment includes two acoustic coupling type filters. More specifically, an acoustic coupling type filter is formed by providing a first functional electrode 21A on the first main surface 4a of the piezoelectric layer 4. Another acoustic coupling type filter is formed by providing a second functional electrode 21B on the second main surface 4b of the piezoelectric layer 4. Furthermore, the first functional electrode 21A and the second functional electrode 21B are positioned opposite each other, sandwiching the piezoelectric layer 4. As a result, the elastic wave device including two acoustic coupling type filters can be made smaller.

[0270] Figure 30 This is a schematic front sectional view showing the vicinity of the first end electrode finger in the elastic wave device according to the fifth embodiment.

[0271] Multiple mass-added films 19 are disposed on both the first main surface 4a side and the second main surface 4b side of the piezoelectric layer 4. Each mass-added film 19 disposed on the first main surface 4a side is disposed on the first dielectric film 18A. Each mass-added film 19 disposed on the second main surface 4b side is disposed on the second dielectric film 18B.

[0272] The plurality of mass-added films 19 disposed on the first main surface 4a side of the piezoelectric layer 4 overlap with the first end electrode finger A1 of the first functional electrode 21A and the first end electrode finger A2 of the second functional electrode 21B when viewed from above. The plurality of mass-added films 19 disposed on the second main surface 4b side of the piezoelectric layer 4 overlap with the first end electrode finger A1 of the first functional electrode 21A and the first end electrode finger A2 of the second functional electrode 21B when viewed from above.

[0273] like Figure 29 As shown, on the side of the second end electrode (B1), similarly to the side of the first end electrode (A1), multiple mass-added films 19 are provided on both the first main surface 4a side and the second main surface 4b side of the piezoelectric layer 4.

[0274] Even in this embodiment, as in the first embodiment, unwanted waves in the passband can be suppressed. This detail will be shown below by comparing this embodiment and the second comparative example. Furthermore, the second comparative example differs from this embodiment in that it does not have the mass-added film 19. In the second comparative example, the first functional electrode and the second functional electrode, as well as the first dielectric film and the second dielectric film, are provided in the same manner as in this embodiment.

[0275] In the fifth embodiment and the second comparative example, the transmission characteristics were compared. In the design parameters of the elastic wave device having the structure of the fifth embodiment, the parameters related to the first functional electrode and the parameters related to the second functional electrode were set to be the same. The design parameters of this elastic wave device are described below. Furthermore, the design parameters of the second comparative example were also set to be the same as those of the fifth embodiment, except for the mass-added membrane 19.

[0276] Piezoelectric layer: Material…LiNbO3, cleavage angle…120°Y, thickness…335nm

[0277] The first electrode refers to the third electrode. Layer structure…Ti layer / AlCu layer from the piezoelectric layer side, thickness…10nm / 400nm from the piezoelectric layer side, width…0.4μm

[0278] The center-to-center distance between the first and third electrode fingers is 1.38 μm.

[0279] The center-to-center distance between the second and third electrode fingers: 1.38 μm

[0280] Cross width: 40μm

[0281] Total number of first to third electrode fingers: 51

[0282] The number of first and second end electrode fingers: two.

[0283] First dielectric film: Material…silicon oxide, thickness…75nm

[0284] Second dielectric film: Material…silicon oxide, thickness…75nm

[0285] Mass-added film disposed on the first principal surface side of the piezoelectric layer: material…silicon oxide, thickness…70nm

[0286] Mass-added film disposed on the second principal surface side of the piezoelectric layer: material…silicon oxide, thickness…70nm

[0287] Figure 31 This is a diagram illustrating the throughput characteristics in the fifth embodiment and the second comparative example. Figure 31 The frequency band K shown is the low-frequency band within the passband of the elastic wave device. Figure 31 The arrow L in the diagram indicates a portion of the frequency within the passband.

[0288] like Figure 31As shown, in the fifth embodiment, compared to the second comparative example, unwanted waves shown in frequency band K and unwanted waves near the frequency indicated by arrow L can be suppressed. Thus, in the fifth embodiment, unwanted waves within the passband can be suppressed. Furthermore, in the fifth embodiment, insertion loss on the high-frequency side within the passband can be reduced. Therefore, when the elastic wave device of the fifth embodiment is used in a filter device, the degradation of the filter characteristics of the filter device can be suppressed.

[0289] like Figure 30 As shown, in the fifth embodiment, a mass-added film 19 disposed on the second main surface 4b side of the piezoelectric layer 4 is disposed on the second dielectric film 18B. Alternatively, the mass-added film 19 disposed on the second main surface 4b side may also be located between the first end electrode finger A2 in the second functional electrode 21B and the second main surface 4b. Similarly, the mass-added film 19 may also be located... Figure 29 The second end electrode in the second functional electrode 21B shown refers to the area between B2 and the second main surface 4b. Even in this case, unwanted waves in the passband can be suppressed.

[0290] In the first to fifth embodiments and their variations, the mass-adding film overlaps at least with the first end electrode finger when viewed from above, and does not overlap with electrodes other than the first and second end electrode fingers when viewed from above. However, it is also possible to provide a mass-adding film that overlaps with electrode fingers other than the first and second end electrode fingers when viewed from above. This example is shown through the sixth embodiment. Furthermore, in the sixth embodiment and its variations, the mass-adding film in the first embodiment, etc., is assumed to be the first mass-adding film.

[0291] Figure 32 This is a schematic top view of the elastic wave device according to the sixth embodiment.

[0292] In this embodiment, the first mass-added membrane 49A is equivalent to Figure 2 The mass-adding membrane 19 is shown. The first mass-adding membrane 49A overlaps with the first end electrode finger A and the second end electrode finger B when viewed from above. Furthermore, this embodiment differs from the first embodiment in that the first end electrode finger A and the second end electrode finger B are each a single piece. Also, this embodiment differs from the first embodiment in that the first mass-adding membrane 49A is a pair. Furthermore, this embodiment differs from the first embodiment in that a second mass-adding membrane 49B is provided. Apart from the above points, the elastic wave device of this embodiment has the same structure as the elastic wave device 10 of the first embodiment.

[0293] Hereinafter, the first mass-adding membrane 49A and the second mass-adding membrane 49B will sometimes be referred to simply as mass-adding membranes.

[0294] Figure 33 This is a diagram showing the piezoelectric layer, each region, and the mass-added film in the sixth embodiment.

[0295] The intersection region F comprises a pair of edge regions and a central region M. Specifically, the pair of edge regions are a first edge region E1 and a second edge region E2. The first edge region E1 is... Figure 32 The region shown is the area where the front ends of the plurality of second electrode fingers 16 are located, extending in the orthogonal direction of the electrode fingers. On the other hand, the second edge region E2 is the region where the front ends of the plurality of first electrode fingers 15 are located, extending in the orthogonal direction of the electrode fingers. The first edge region E1 and the second edge region E2 are opposite each other, sandwiching the central region M in the direction of electrode finger extension. In addition, it should be noted in advance that even in other embodiments of the present invention besides the sixth embodiment, the intersection region F also includes a pair of edge regions and a central region M.

[0296] The elastic wave device of the sixth embodiment has a pair of gap regions. Specifically, the pair of gap regions are a first gap region G1 and a second gap region G2. The first gap region G1 is the intersection region F and... Figure 32 The region between the third busbar 14 is shown. On the other hand, the second gap region G2 is the region between the cross region F and the second busbar 13. Furthermore, it should be noted in advance that elastic wave devices of other embodiments of the present invention besides the sixth embodiment also have a pair of gap regions.

[0297] The elastic wave device of the sixth embodiment has a pair of second mass-added membranes 49B. One of the second mass-added membranes 49B is disposed in the first edge region E1 and the first gap region G1. The other second mass-added membrane 49B is disposed in the second edge region E2 and the second gap region G2. The second mass-added membrane 49B is not disposed in the central region M.

[0298] In addition, the second mass-adding membrane 49B may be disposed in at least one of the first edge region E1 and the first gap region G1 and at least one of the second edge region E2 and the second gap region G2.

[0299] A pair of first mass-adding membranes 49A and a pair of second mass-adding membranes 49B are connected to each other. Thus, a frame-shaped mass-adding membrane is formed by the pair of first mass-adding membranes 49A and the pair of second mass-adding membranes 49B.

[0300] By providing a pair of first mass-added films 49A, similar to the first embodiment, the bulk wave of the thickness shear mode can be appropriately confined to the functional electrode 1 side. This allows for stable excitation of the thickness shear mode in each excitation region. In addition, unwanted waves in the passband can be suppressed.

[0301] By disposing a pair of second mass-adding films 49B on a pair of edge regions and a pair of gap regions respectively, the bulk wave of the thickness shear mode can be appropriately confined to the functional electrode 1 side even in the orthogonal direction of the electrodes. However, even if one second mass-adding film 49B is disposed on at least one of the first edge region E1 and the first gap region G1, the bulk wave of the thickness shear mode can still be confined to the functional electrode 1 side. Similarly, even if the other second mass-adding film 49B is disposed on at least one of the second edge region E2 and the second gap region G2, the bulk wave of the thickness shear mode can still be confined to the functional electrode 1 side.

[0302] Additionally, the second mass-adding membrane 49B can also overlap with the busbars when viewed from above. Specifically, the second mass-adding membrane 49B on the side of the first busbar 12 and the third busbar 14 can also overlap with the third busbar 14 when viewed from above. The second mass-adding membrane 49B on the side of the second busbar 13 can also overlap with the second busbar 13 when viewed from above.

[0303] As described above, the third busbar 14, which serves as a connecting electrode in the third electrode 9, can also be disposed between the cross region F and the second busbar 13. Alternatively, it can be as follows: Figure 19 As shown in the eighth variation of the first embodiment, the plurality of connecting electrodes 14A of the third electrode 9A are located on both the side of the first busbar 12 and the side of the second busbar 13.

[0304] Therefore, the second mass-addition membrane 49B on the side of the first busbar 12 can also overlap, when viewed from above, with the electrodes in the connecting electrodes of the first busbar 12 and the third electrode 9, where the front ends of a plurality of second electrode fingers 16 are spaced apart in the electrode finger extension direction. The second mass-addition membrane 49B on the side of the second busbar 13 can also overlap, when viewed from above, with the electrodes in the connecting electrodes of the second busbar 13 and the third electrode, where the front ends of a plurality of first electrode fingers 15 are spaced apart in the electrode finger extension direction.

[0305] A portion of the second mass additional membrane 49B can also be seen from above and referenced. Figure 1 The void portions 10a shown do not overlap. That is, the second mass-added film 49B can also be provided from the portion of the piezoelectric layer 4 that overlaps with the void portion 10a in top view to the non-overlapping portion.

[0306] Preferably, the material of the first mass-adding membrane 49A is the same as the material of the second mass-adding membrane 49B. In this case, both the first mass-adding membrane 49A and the second mass-adding membrane 49B can be formed simultaneously. This improves the productivity of the elastic wave device. Alternatively, the materials of the first mass-adding membrane 49A and the second mass-adding membrane 49B can be different.

[0307] Preferably, the thickness of the first mass-adding film 49A is the same as the thickness of the second mass-adding film 49B. In this case, it is possible to prevent the manufacturing process from becoming complicated during the production of the elastic wave device. Therefore, the productivity of the elastic wave device can be improved. In addition, in this specification, "the same thickness of the mass-adding films" means that the difference between the thickness of one mass-adding film and the thickness of the other mass-adding film is 5% or less relative to the thickness of both mass-adding films.

[0308] Furthermore, the thickness of the first mass-adding film 49A and the thickness of the second mass-adding film 49B may also be different. In this specification, "different thicknesses of the mass-adding films" means that the difference between the thickness of one mass-adding film and the thickness of the other mass-adding film exceeds 5% relative to the total thickness of both mass-adding films.

[0309] When comparing the thickness of the first mass-adding film 49A with the thickness of other components, the thickness of the portion that does not overlap with the first end electrode finger A or the second end electrode finger B in a top view is compared with the thickness of the other components. However, this is not limited to cases where the entire first mass-adding film 49A overlaps with the first end electrode finger A or the second end electrode finger B in a top view. When comparing the thickness of the second mass-adding film 49B with the thickness of other components, the thickness of the portion that does not overlap with the electrode finger in a top view is compared with the thickness of the other components. However, this is not limited to cases where the entire second mass-adding film 49B overlaps with the electrode finger in a top view.

[0310] In the sixth embodiment, the first end electrode finger A and the second end electrode finger B are each one. Therefore, a pair of first mass-adding films 49A are provided. However, the first end electrode finger A and the second end electrode finger B may also be two each. In this case, the structure becomes one in which two pairs of first mass-adding films 49A are provided. Moreover, the two pairs of first mass-adding films 49A may also be connected to the second mass-adding film 49B.

[0311] Alternatively, it is not necessary to provide a frame-shaped mass-adding membrane through the first mass-adding membrane 49A and the second mass-adding membrane 49B. For example, in Figure 34 In the first variation of the sixth embodiment shown, both sides of the pair of first mass-adding membranes 49A are connected to one of the pair of second mass-adding membranes 49B. Specifically, the second mass-adding membrane 49B on the second busbar 13 side is connected to the pair of first mass-adding membranes 49A. The other second mass-adding membrane 49B is not connected to the first mass-adding membrane 49A.

[0312] Even in this modified example, similar to the sixth embodiment, the bulk wave of the thickness shear mode can be contained to the functional electrode 1 side in both the orthogonal direction of the electrode fingers and the extension direction of the electrode fingers. In addition, unwanted waves in the passband can be suppressed.

[0313] In this modified example, the sixth embodiment, and the like, the mass-added film can be formed, for example, using a peel-off method. In this case, a dielectric layer is provided on the resist pattern, and then the resist pattern is peeled off, thereby patterning the mass-added film. Furthermore, the resist pattern is a pattern composed of portions where a resist layer is provided and portions where no resist layer is provided.

[0314] In formation Figure 33 When the mass-added film of the sixth embodiment is shown, it is formed into a frame shape. In this case, the portion of the resist pattern where no resist layer is provided becomes a frame shape. Therefore, in the resist pattern, the resist layer inside the frame is separated from the resist layer outside the frame.

[0315] On the other hand, in the formation Figure 34 In the modified example shown, the mass-added film is formed in a non-frame shape. Specifically, the second mass-added film 49B on the third busbar 14 side is formed with a gap between it and a pair of first mass-added films 49A. In this case, the portion of the resist pattern where the resist layer is not provided is not frame-shaped. Therefore, the resist layer is integral in the resist pattern. As a result, it is difficult to generate resist pattern residue when the resist pattern is peeled off. As a result, defects in the elastic wave generating device can be suppressed.

[0316] In the sixth embodiment and its first variation, the first mass-added film 49A and the second mass-added film 49B are disposed on the first main surface 4a side of the piezoelectric layer 4. However, it is not limited to this. Figure 35 and Figure 36 In the second variation of the sixth embodiment shown, a pair of first mass-added films 49A are provided on both the first main surface 4a and the second main surface 4b of the piezoelectric layer 4. Furthermore, Figure 35 This is a schematic bottom view showing the second main surface 4b. Therefore, Figure 35 Compared to Figure 36 That shows a schematic top view of the first main surface 4a, which is reversed left and right.

[0317] like Figure 35 As shown, a pair of second mass-added films 49B are disposed on the second main surface 4b of the piezoelectric layer 4. The pair of second mass-added films 49B, viewed from above, are in conjunction with... Figure 33 The first edge region E1 and the first gap region G1, as well as the second edge region E2 and the second gap region G2 shown, overlap.

[0318] A pair of first mass-added films 49A and a pair of second mass-added films 49B disposed on the second main surface 4b of the piezoelectric layer 4 are connected to each other. Moreover, the pair of first mass-added films 49A disposed on the second main surface 4b overlaps with the first end electrode finger A and the second end electrode finger B when viewed from above.

[0319] like Figure 36 As shown, a pair of first mass-added films 49A disposed on the first main surface 4a of the piezoelectric layer 4 overlap with the first end electrode finger A and the second end electrode finger B when viewed from above. In this modified example, Figure 35 The second mass-addition membrane 49B shown is not disposed on the first main surface 4a.

[0320] Even in this modified example, similar to the sixth embodiment, the bulk wave of the thickness shear mode can be contained to the functional electrode 1 side in both the orthogonal direction of the electrode fingers and the extension direction of the electrode fingers. In addition, unwanted waves in the passband can be suppressed.

[0321] As Figure 35 The material of the pair of first mass-added films 49A and the pair of second mass-added films 49B disposed on the second main surface 4b of the piezoelectric layer 4, as shown, can be silicon oxide. In this case, the first mass-added films 49A and the second mass-added films 49B tend to shrink towards the functional electrode 1. As a result, the shape of the piezoelectric layer 4 tends to be such that the outer side of the first main surface 4a is convex in the direction normal to the first main surface 4a and the outer side of the second main surface 4b. As a result, adhesion of the piezoelectric layer 4 can be suppressed.

[0322] The adhesion of the piezoelectric layer 4 mentioned here refers to the direct or indirect adhesion of the piezoelectric layer 4 to... Figure 1 When the piezoelectric layer 4 contacts the support member 3 as shown, it is difficult to separate from the support member 3. In addition, as in this modified example, when the second dielectric film 18B is provided in the same way as in the first embodiment, the adhesion of the piezoelectric layer 4 is generated by the piezoelectric layer 4 indirectly contacting the support member 3 through the second dielectric film 18B.

[0323] In contrast, in this modified example, the piezoelectric layer 4 is more likely to have a convex shape that extends outward from the normal direction of the first main surface 4a. In this case, even when a force is applied to the piezoelectric layer 4 from the outside, the piezoelectric layer 4 is less likely to come into contact with the support member 3. Therefore, adhesion of the piezoelectric layer 4 can be suppressed.

[0324] like Figure 35As shown, in this modified example, one second mass-attached membrane 49B overlaps with the third busbar 14 in top view. Another second mass-attached membrane 49B overlaps with the second busbar 13 in top view. Alternatively, the second mass-attached membrane 49B may not overlap with the busbar in top view.

[0325] Return to Figure 32 In the sixth embodiment, the leading ends of the plurality of second electrode fingers 16 are spaced apart in the extending direction of the electrode fingers and face the third busbar 14, which serves as the connecting electrode of the third electrode 9. Furthermore, Figure 33 The first gap region G1 shown is the region between the third busbar 14 and the crossover region F. However, for example, when the third busbar 14 is disposed between the crossover region F and the second busbar 13, the leading ends of the plurality of second electrode fingers 16 are spaced apart in the electrode finger extension direction and face the first busbar 12. In this case, the first gap region G1 is the region between the first busbar 12 and the crossover region F.

[0326] In this invention, the first gap region G1 is the region between the front ends of the plurality of second electrode fingers 16 of the connecting electrodes of the first busbar 12 and the third electrode 9, which are separated by gaps in the electrode finger extension direction, and the intersection region F.

[0327] On the other hand, in the sixth embodiment, the leading ends of the plurality of first electrode fingers 15 are spaced apart in the electrode finger extension direction and face the second busbar 13. Furthermore, the second gap region G2 is the region between the second busbar 13 and the intersection region F. However, for example, when the third busbar 14, which serves as the connecting electrode of the third electrode 9, is provided between the intersection region F and the second busbar 13, the leading ends of the plurality of first electrode fingers 15 are spaced apart in the electrode finger extension direction and face the third busbar 14. In this case, the second gap region G2 is the region between the third busbar 14 and the intersection region F.

[0328] In this invention, the second gap region G2 is the region between the front ends of the plurality of first electrode fingers 15 of the connecting electrodes of the second busbar 13 and the third electrode 9, which are separated by gaps in the electrode finger extension direction, and the intersection region F.

[0329] For example, in Figure 19 In the eighth variation of the first embodiment shown, the first gap region G1 is the region between the plurality of connecting electrodes 14A on the first busbar 12 side and the crossover region F. The second gap region G2 is the region between the plurality of connecting electrodes 14A on the second busbar 13 side and the crossover region F.

[0330] In the first to sixth embodiments and various modifications, the acoustic reflective portion is a void in the piezoelectric substrate. Alternatively, the acoustic reflective portion may also be an acoustic reflective film. This example is illustrated by the seventh embodiment.

[0331] Figure 37 This is a schematic front sectional view of the elastic wave device according to the seventh embodiment.

[0332] The difference between this embodiment and the first embodiment is that the acoustic reflecting part is an acoustic reflecting membrane 58. Another difference is that the support member 53 only includes a support substrate. Apart from the above points, the elastic wave device of this embodiment is constructed in the same way as the elastic wave device 10 of the first embodiment.

[0333] An acoustic reflective membrane 58 is provided on the surface of the support member 53. A second dielectric membrane 18B is provided on the acoustic reflective membrane 58. A piezoelectric layer 4 is provided on the second dielectric membrane 18B. That is, the piezoelectric layer 4 is indirectly provided on the acoustic reflective membrane 58 through the second dielectric membrane 18B. In addition, the support member 53 and the piezoelectric layer 4 are arranged such that at least a portion of the support member 53 and at least a portion of the piezoelectric layer 4 sandwich the acoustic reflective membrane 58 and are placed opposite each other.

[0334] The acoustic reflector 58 is a stack of multiple acoustic impedance layers. Specifically, the acoustic reflector 58 has multiple low acoustic impedance layers and multiple high acoustic impedance layers. The low acoustic impedance layers are layers with relatively low acoustic impedance. More specifically, the multiple low acoustic impedance layers of the acoustic reflector 58 are low acoustic impedance layer 55a, low acoustic impedance layer 55b, and low acoustic impedance layer 55c.

[0335] On the other hand, the high acoustic impedance layer is a layer with relatively high acoustic impedance. More specifically, the multiple high acoustic impedance layers of the acoustic reflector 58 are high acoustic impedance layer 56a and high acoustic impedance layer 56b. Low acoustic impedance layers and high acoustic impedance layers are stacked alternately. In addition, the low acoustic impedance layer 55a is the layer located on the side closest to the piezoelectric layer 4 in the acoustic reflector 58.

[0336] The acoustic reflector 58 has three low acoustic impedance layers and two high acoustic impedance layers. However, the acoustic reflector 58 may have at least one low acoustic impedance layer and one high acoustic impedance layer.

[0337] Materials used as low acoustic impedance layers include, for example, silicon oxide or aluminum. Materials used as high acoustic impedance layers include, for example, metals such as platinum or tungsten, and dielectrics such as aluminum nitride, silicon nitride, or hafnium oxide.

[0338] Even in this embodiment, similar to the first embodiment, the bulk wave of the thickness shear mode can be appropriately confined to the functional electrode 1 side. This allows for stable excitation of the thickness shear mode in each excitation region. In conjunction with this, unwanted waves within the passband can be suppressed. Furthermore, by providing the acoustic reflector 58, the energy of the elastic wave can be effectively confined to the piezoelectric layer 4 side.

[0339] The acoustic reflector in this embodiment is an acoustic reflective membrane 58, and the structure of this invention can be applied to structures other than those in this embodiment.

[0340] The elastic wave device of the present invention can be used, for example, in a filter device. An example is shown below.

[0341] Figure 38 This is a schematic circuit diagram of a filter device according to the eighth embodiment of the present invention. Figure 38 The elastic wave device is illustrated in a block diagram.

[0342] The filter device 60 is a trapezoidal filter. The filter device 60 includes an input terminal 62 and an output terminal 63, multiple series-arm resonators and multiple parallel-arm resonators, and an elastic wave device 10. The elastic wave device 10 is the elastic wave device according to the first embodiment. Alternatively, the filter device 60 may replace the elastic wave device 10 with an elastic wave device according to the present invention other than the first embodiment.

[0343] Input terminal 62 and output terminal 63 can be configured as electrode pads or wiring, for example. All series arm resonators and all parallel arm resonators in the filter device 60 are elastic wave resonators. Each elastic wave resonator in the filter device 60 utilizes the thickness shear mode volume wave as the dominant mode. Alternatively, at least one series arm resonator or at least one parallel arm resonator may be an elastic wave resonator that utilizes the thickness shear mode volume wave as the dominant mode.

[0344] In this embodiment, each series-arm resonator is a series notch filter. Each parallel-arm resonator is a parallel notch filter. However, the series-arm resonators do not necessarily have to be series notch filters, and the parallel-arm resonators do not necessarily have to be parallel notch filters.

[0345] Specifically, the multiple series-arm resonators are series-arm resonator S1 and series-arm resonator S2. Between the input terminal 62 and the output terminal 63, starting from the input terminal 62 side, the series-arm resonator S1, the elastic wave device 10, and the series-arm resonator S2 are connected in series with each other. Furthermore, Figure 2 The first busbar 12 shown is connected to the series arm resonator S1. The second busbar 13 is connected to the series arm resonator S2. On the other hand, the third busbar 14 is connected to the ground potential.

[0346] Specifically, the multiple parallel-arm resonators are parallel-arm resonators P1 and P2. A parallel-arm resonator P1 is connected between the connection point between the series-arm resonator S1 and the elastic wave device 10 and the ground potential. A parallel-arm resonator P2 is connected between the connection point between the elastic wave device 10 and the series-arm resonator S2 and the ground potential. Furthermore, the circuit structure of the filter device 60 is not limited to the above. The filter device 60 may have at least one elastic wave device according to the present invention, and at least one elastic wave resonator electrically connected to the elastic wave device.

[0347] The following shows the specific structure of the elastic wave resonator in the filter device of the present invention.

[0348] Figure 39 This is a schematic top view of the series arm resonator in the eighth embodiment. Additionally, in Figure 39 The third dielectric film, which will be described later, is omitted in the text.

[0349] The series arm resonator S1 has a piezoelectric substrate 2. The piezoelectric substrate 2 includes a piezoelectric layer 4. Furthermore, in this embodiment, Figure 38 The multiple series-arm resonators, multiple parallel-arm resonators, and elastic wave devices 10 shown share the same piezoelectric substrate 2 and the same piezoelectric layer 4. However, each series-arm resonator, each parallel-arm resonator, and each elastic wave device 10 may also have a separate piezoelectric substrate 2. Each series-arm resonator, each parallel-arm resonator, and each elastic wave device 10 may also have a separate piezoelectric layer 4.

[0350] An IDT electrode 64 is disposed on the piezoelectric layer 4 of the series arm resonator S1. Specifically, the IDT electrode 64 is disposed on the first main surface 4a of the piezoelectric layer 4. The IDT electrode 64 has a pair of comb-shaped electrodes. Specifically, the pair of comb-shaped electrodes are a first comb-shaped electrode 7C and a second comb-shaped electrode 8C.

[0351] The first comb electrode 7C and the second comb electrode 8C, together with the elastic wave device 10 which serves as an acoustic coupling filter, Figure 2 The first comb electrode 7 and the second comb electrode 8 shown are configured similarly. Therefore, the IDT electrode 64 has a plurality of first electrode fingers 15C and a plurality of second electrode fingers 16C. Even in the IDT electrode 64, similar to the functional electrode 1 in the acoustic coupling filter, the direction in which the plurality of electrode fingers extend is set as the electrode finger extension direction, and the direction orthogonal to the electrode finger extension direction is set as the electrode finger orthogonal direction.

[0352] The series arm resonator S1 has a cross region F defined by the structure of the IDT electrodes 64 and multiple excitation regions C. More specifically, the area where adjacent first electrode fingers 15C and second electrode fingers 16C overlap when viewed from the orthogonal direction of the electrode fingers is the cross region F in the series arm resonator S1. The cross region F contains multiple excitation regions C. The excitation regions C of the series arm resonator S1 are the areas where adjacent first electrode fingers 15C and second electrode fingers 16C overlap when viewed from the orthogonal direction of the electrode fingers, and are the areas between the centers of adjacent first electrode fingers 15C and second electrode fingers 16C in the orthogonal direction of the electrode fingers.

[0353] At least one electrode finger located at one end of the plurality of electrode fingers of the IDT electrode 64 in the direction in which the plurality of electrode fingers are arranged is designated as the third end electrode finger N. At least one electrode finger located at the other end is designated as the fourth end electrode finger O. In this embodiment, there are two third end electrode fingers N and two fourth end electrode fingers O.

[0354] Figure 40 It is along Figure 39 A schematic cross-sectional view of line III-III in the diagram.

[0355] The third end electrode finger N and the fourth end electrode finger O in the IDT electrode 64 have a third surface 64a and a fourth surface 64b, and a third side surface 64c and a fourth side surface 64d, respectively. The third surface 64a and the fourth surface 64b are opposite to each other in the thickness direction. The third side surface 64c and the fourth side surface 64d connect the third surface 64a and the fourth surface 64b and are opposite to each other in the orthogonal direction of the electrode fingers. In each of the third end electrode finger N and the fourth end electrode finger O, the third side surface 64c is located on the outer side in the direction in which the multiple electrode fingers of the IDT electrode 64 are arranged, compared to the fourth side surface 64d.

[0356] In this embodiment, the third side surface 64c and the fourth side surface 64d of the third end electrode finger N and the fourth end electrode finger O extend obliquely relative to the normal direction of the first main surface 4a of the piezoelectric layer 4. Alternatively, the third side surface 64c and the fourth side surface 64d may extend parallel to the normal direction of the first main surface 4a.

[0357] The series arm resonator S1 has a plurality of third mass additional films 69. Specifically, two third mass additional films 69 are provided such that, in top view, they overlap with the two electrode fingers that serve as the third end electrode finger N. Similarly, two third mass additional films 69 are provided such that, in top view, they overlap with the two electrode fingers that serve as the fourth end electrode finger O. More specifically, one third mass additional film 69 overlaps with one third end electrode finger N or one fourth end electrode finger O in top view. However, it is also possible that a continuously arranged third mass additional film 69 overlaps with both the third end electrode finger N and the fourth end electrode finger O in top view. On the other hand, the third mass additional films 69 do not overlap with any of the electrode fingers other than the third end electrode finger N and the fourth end electrode finger O among the plurality of electrode fingers in the IDT electrode 64.

[0358] Furthermore, in this invention, the third end electrode finger N can be up to four consecutive electrode fingers located at one end in the direction in which the plurality of electrode fingers are arranged. Similarly, the fourth end electrode finger O can be up to four consecutive electrode fingers located at the other end in the direction in which the plurality of electrode fingers are arranged. Therefore, for example, if the third end electrode finger N and the fourth end electrode finger O are each one, the plurality of third mass-adding films 69 can be arranged to overlap with each of the electrode fingers that are the third end electrode finger N and the fourth end electrode finger O.

[0359] However, the third mass-addition film 69 only needs to be positioned so that it overlaps at least with the third end electrode finger N when viewed from above. In this specification, for convenience, the fourth end electrode finger O is assumed to be 0 when the third mass-addition film 69 only overlaps with the third end electrode finger N.

[0360] In this embodiment, when viewed from above, the third mass-adding film 69 overlaps with a portion of the third surface 64a and the fourth surface 64b, as well as the third side surface 64c, of the third end electrode finger N. On the other hand, the third mass-adding film 69 does not overlap with another portion of the third surface 64a and the fourth surface 64b, as well as the fourth side surface 64d, of the third end electrode finger N. Furthermore, when viewed from above, the third mass-adding film 69 overlaps with the portion of the third side surface 64c of the third end electrode finger N that is located on the outer side in the orthogonal direction of the electrode finger.

[0361] Thus, a third mass-addition film 69 is continuously configured in the orthogonal direction of the electrode fingers, overlapping the third end electrode finger N and the portion where the electrode finger is not provided when viewed from above. This third mass-addition film 69 is configured to completely overlap the electrode finger extension direction of the portion of the third end electrode finger N located in the intersection region F when viewed from above.

[0362] Similarly, the third mass-addition film 69, which overlaps with the fourth end electrode finger O when viewed from above, is also continuously arranged in the orthogonal direction of the electrode fingers, overlapping the fourth end electrode finger O and the portion where the electrode finger is not provided when viewed from above. The third mass-addition film 69 is arranged to completely overlap with the electrode finger extension direction of the portion of the fourth end electrode finger O located in the intersection region F when viewed from above.

[0363] When the dimension along the orthogonal direction of the electrode fingers of the portion of the third mass-addition film 69 that overlaps with the third end electrode finger N or the fourth end electrode finger O in a top view is set as the overlap width, in this embodiment, the overlap width is narrower than the width of the third end electrode finger N or the fourth end electrode finger O.

[0364] The material of the third mass-adding film 69 is silicon oxide. However, the material of the third mass-adding film 69 is not limited to the above.

[0365] like Figure 40 As shown, the series arm resonator S1 has a dielectric film. Specifically, the dielectric film includes a third dielectric film 68A and a fourth dielectric film 68B. The third dielectric film 68A is disposed on the first main surface 4a of the piezoelectric layer 4, such that it covers the IDT electrode 64. The fourth dielectric film 68B is disposed on the second main surface 4b of the piezoelectric layer 4. A plurality of third mass-addition films 69 are disposed on the third dielectric film 68A.

[0366] In this embodiment, the materials of the third dielectric film 68A and the fourth dielectric film 68B are silicon oxide. However, the materials of the third dielectric film 68A and the fourth dielectric film 68B are not limited to those described above.

[0367] Figure 38 The series arm resonator S2, parallel arm resonator P1, and parallel arm resonator P2 also have IDT electrodes 64, a third dielectric film 68A, a fourth dielectric film 68B, and a third mass-added film 69, and have a crossover region F and multiple excitation regions C. In this embodiment, each elastic wave resonator overlaps with the third mass-added film 69 in top view through the third end electrode finger N and the fourth end electrode finger O, thereby effectively suppressing unwanted waves.

[0368] However, in Figure 40 In the series arm resonator S1 shown, the configuration of the third mass-addition film 69 is not limited to that described above. The third mass-addition film 69 may overlap at least a portion of the third end electrode finger N when viewed from above. Even in this case, unwanted waves can be suppressed. The same applies to elastic wave resonators other than the series arm resonator S1.

[0369] In the series arm resonator S1, the dielectric film can be disposed on at least one of the first main surface 4a side and the second main surface 4b side of the piezoelectric layer 4. If the IDT electrode 64 is not covered by the dielectric film, for example, the third mass-addition film 69 can also be directly disposed on the third end electrode finger N and the fourth end electrode finger O. The same applies to elastic wave resonators other than the series arm resonator S1.

[0370] In the filter device 60, the thicknesses of the mass-added membrane 19 in the elastic wave device 10 and the third mass-added membrane 69 in each elastic wave resonator are different. However, it is sufficient that at least one of the thickness and material of the mass-added membrane 19 and the third mass-added membrane 69 is different. This allows both the condition for suppressing unwanted waves in the passband in the elastic wave device 10, which is an acoustic coupling type filter, and the condition for suppressing unwanted waves in each elastic wave resonator to coexist. Therefore, the degradation of the filter characteristics of the filter device 60 can be effectively suppressed.

[0371] As stated above, in this specification, "different thicknesses of the mass-added films" means that the difference between the thickness of one mass-added film and the thickness of another mass-added film exceeds 5% relative to the thicknesses of both mass-added films. This can also be applied when comparing the thickness of the third mass-added film 69 with the thickness of the mass-added film 19.

[0372] When comparing the thickness of the third mass-adding membrane 69 with the thicknesses of other components, the thickness of the portion that does not overlap with the third end electrode finger N or the fourth end electrode finger O in a top view is compared with the thickness of the other components. However, this is not limited to cases where the entire third mass-adding membrane 69 overlaps with the third end electrode finger N or the fourth end electrode finger O in a top view.

[0373] The elastic wave device 10 of the filter device 60 is the elastic wave device according to the first embodiment. Therefore, the elastic wave device 10 can suppress unwanted waves in the passband, such as... Figure 4 As shown. Hereinafter, by comparing the elastic wave resonator of this embodiment with the elastic wave resonator of the third comparative example, it will be shown that unwanted waves can also be suppressed in the elastic wave resonator of this embodiment. In addition, the elastic wave resonator of the third comparative example differs from the elastic wave resonator of this embodiment in that the third mass-addition membrane 69 is not provided.

[0374] The admittance frequency characteristics were compared between the elastic wave resonator of the eighth embodiment and the elastic wave resonator of the third comparative example. The design parameters of the elastic wave resonator in the eighth embodiment are as follows. Furthermore, the design parameters of the third comparative example are the same as those of the eighth embodiment, except for the third mass-added membrane 69. Hereinafter, the center-to-center distance between adjacent electrode fingers is defined as the electrode finger spacing.

[0375] Piezoelectric layer: Material…LiNbO3, cleavage angle…120°Y, thickness…335nm

[0376] First electrode refers to the first electrode, second electrode refers to the layer structure... Ti layer / AlCu layer from the piezoelectric layer side, thickness... 10nm / 400nm from the piezoelectric layer side, width... 0.8μm

[0377] Electrode finger spacing: 2.5μm

[0378] Cross width: 40μm

[0379] Total number of first electrode fingers and second electrode fingers: 80

[0380] The number of third and fourth end electrode fingers: two.

[0381] Third dielectric film: Material…silicon oxide, thickness…130nm

[0382] Fourth dielectric film: Material…silicon oxide, thickness…130nm

[0383] Third mass-added film: Material…silicon oxide, thickness…55nm, dimension along the orthogonal direction of the electrode…0.7μm, overlap width…0.4μm

[0384] Figure 41 This is a graph showing the admittance frequency characteristics in the elastic wave resonator of the eighth embodiment and the third comparative example. Figure 41 The arrow Q in the diagram indicates the resonant frequency.

[0385] like Figure 41 As shown, in the third comparative example, multiple unwanted waves were generated on the lower frequency side than the resonant frequency. In the third comparative example, multiple unwanted waves were also generated on the higher frequency side than the resonant frequency. In contrast, in the elastic wave resonator of the eighth embodiment, unwanted waves can be suppressed on both the lower and higher frequency sides than the resonant frequency.

[0386] In each elastic wave resonator of the filter device 60, unwanted waves can be suppressed. Moreover, even in the elastic wave device 10, which is an acoustic coupling type filter, unwanted waves in the passband can be suppressed. Therefore, unwanted waves in the passband of the filter device 60 can be effectively suppressed, and the degradation of filter characteristics can be effectively suppressed.

[0387] The following uses Figure 39 The example of an elastic wave resonator with IDT electrode 64 shown illustrates a preferred structure in the present invention. Hereinafter, this elastic wave resonator will be used as a reference example of an elastic wave device. In describing the structure of the reference example elastic wave device, references are made to... Figure 39 .

[0388] The elastic wave device of the reference example utilizes the thickness shear mode volume wave as the dominant mode. In this case, the portion connected to different potentials and provided with an adjacent pair of electrode fingers functions as a resonator. Therefore, the structure of the elastic wave device utilizing the thickness shear mode volume wave is equivalent to a structure in which multiple resonators are connected in parallel. In this respect, even acoustic coupling type filters such as those in the first to seventh embodiments are the same. Therefore, it can be said that the following structure in the elastic wave device of the reference example is a preferred structure even in the first to seventh embodiments.

[0389] In this invention, when the thickness of the piezoelectric layer is set as d and the center-to-center distance between adjacent electrodes is set as p, d / p is preferably 0.5 or less, and more preferably 0.24 or less. This allows for appropriate excitation of the thickness shear mode bulk wave and sufficiently increases the relative bandwidth of the elastic wave device. When the resonant frequency is set as fr and the anti-resonant frequency is set as fa, the relative bandwidth is represented by (|fa-fr| / fr)×100[%].

[0390] Figure 42 This is a graph showing the relationship between d / p and the relative bandwidth of the elastic wave device in the reference example.

[0391] according to Figure 42 It is clear that when d / p > 0.5, the relative bandwidth is less than 5%. Conversely, when d / p ≤ 0.5, the relative bandwidth can be increased to 5% or more. Therefore, the electromechanical coupling coefficient of the bulk wave in the thickness shear mode can be increased. When d / p ≤ 0.24 or less, the relative bandwidth can be increased to 7% or more. Therefore, the electromechanical coupling coefficient of the bulk wave in the thickness shear mode can be effectively increased.

[0392] When the metallization rate of the electrode fingers relative to the excitation region C is set as MR, it is preferable to satisfy MR ≤ 1.75 (d / p) + 0.075. In this case, the relative bandwidth of the elastic wave device will not become too large, and spurious emissions between the resonant frequency and the anti-resonant frequency can be suppressed. The details are shown below.

[0393] In this specification, the metallization rate MR of the electrode finger relative to the excitation region C is the proportion of the piezoelectric layer 4 covered by the metal constituting the electrode finger in the excitation region C when viewed from above. (In reference...) Figure 39 In the illustrated reference example, the ratio of the area of ​​the first electrode finger 15C and the second electrode finger 16C within the excitation region C, viewed from above, to the area of ​​the excitation region C, is called the metallization rate MR. On the other hand, in Figure 2In the first embodiment of the present invention shown, the ratio of the area of ​​the first electrode finger 15 and the third electrode finger 17 to the excitation region C, and the ratio of the area of ​​the second electrode finger 16 and the third electrode finger 17 to the excitation region C, are called the metallization rate MR.

[0394] Furthermore, with the width of the electrode fingers located within the excitation region C fixed, the metallization rate MR can also be calculated by dividing the total width of the electrode fingers located within the excitation region C by the dimension of the excitation region C along the orthogonal direction of the electrode fingers.

[0395] Figure 43 This is a graph showing the relationship between the relative bandwidth and the normalized spurious magnitude in the elastic wave apparatus of the reference example. Figure 43 The diagram shows the results obtained by measuring the stray phase rotation whenever the relative bandwidth changes by varying the thickness of the piezoelectric layer and the size of the electrode fingers. Specifically, Figure 43 The normalized spurious magnitude is the value of the spurious impedance phase rotation normalized by 180°. Figure 43 The results shown are for the case where a piezoelectric layer containing Z-cut LiNbO3 was used, but the same trend is observed even when piezoelectric layers with other cut angles are used.

[0396] exist Figure 43 In the region enclosed by the ellipse R, the normalized spurious signal between the resonant frequency and the anti-resonant frequency is 1.0. When the relative bandwidth of the elastic wave resonator exceeds 17%, the normalized spurious signal may become greater than 1.0. Therefore, the relative bandwidth is preferably less than 17%. This suppresses the spurious signal between the resonant frequency and the anti-resonant frequency.

[0397] Figure 44 This is a graph showing the relationship between d / p, metallization ratio (MR), and relative bandwidth. Figure 44 The figure shows the results of calculating the relative bandwidth whenever the d / p and metallization rate MR are different.

[0398] exist Figure 44 In the diagram, the shaded area represents the region with a relative bandwidth of 17% or less. The boundary between the shaded and unshaded areas is approximately represented by a dashed line T. The dashed line T is represented by MR = 1.75 (d / p) + 0.075. Furthermore, in the reference example, when MR ≤ 1.75 (d / p) + 0.075, it is easy to achieve a relative bandwidth of 17% or less, making it easier to suppress spurious emissions. Therefore, in this invention, MR ≤ 1.75 (d / p) + 0.075 is preferred. This facilitates the suppression of spurious emissions.

[0399] On the other hand, through Figure 44The dashed line T1 in the diagram represents the slope of the change in metallization rate MR relative to the change in d / p, which is the same as the slope of the dashed line T, and the boundary where the relative bandwidth is 17% or less over the entire range. The dashed line T1 is represented by MR = 1.75(d / p) + 0.05. Moreover, when MR ≤ 1.75(d / p) + 0.05, the relative bandwidth can be made to be 17% or less more reliably, and spurious emissions can be suppressed more reliably. Therefore, in this invention, MR ≤ 1.75(d / p) + 0.075 is more preferable. As a result, spurious emissions can be suppressed more reliably.

[0400] Here, in the structure of the first embodiment, the relationship between the relative bandwidth of the elastic wave device 10 and the Euler angles (φ, θ, ψ) in the piezoelectric layer 4 is derived when d / p is infinitely close to 0. Furthermore, φ in the Euler angles is set to 0°.

[0401] Figure 45 This is a diagram showing the mapping of the relative bandwidth to the Euler angles (0°, θ, ψ) of LiNbO3 when d / p is infinitely close to 0. Figure 45 The shaded area indicates the region where at least 5% relative bandwidth can be obtained. If the range of this region is approximated, it becomes the range represented by the following equations (1), (2) and (3).

[0402] (Within the range of 0°±10°, 0°~25°, any ψ) … Equation (1)

[0403] (Within the range of 0°±10°, 25°~100°, 0°~75° [(1-(θ-50)]) 2 / 2500)] 1 / 2 Or 180°-75° [(1-(θ-50)] 2 / 2500)] 1 / 2 ~180°) …Equation (2)

[0404] (Within the range of 0°±10°, 180°-40° [(1-(ψ-90)]) 2 / 8100)] 1 / 2 ~180°, any ψ) …Equation (3)

[0405] In this invention, the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer are preferably within the ranges of Equations (1), (2), or (3) above. This allows for a sufficiently widened relative bandwidth of the elastic wave device. The same applies when the piezoelectric layer comprises lithium tantalate.

[0406] The following is a summary of examples of the elastic wave device and filter device described in this invention.

[0407] <1> An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface facing each other; a support member stacked on the piezoelectric layer; a functional electrode disposed on the first main surface of the piezoelectric layer, having a first comb-shaped electrode, a second comb-shaped electrode, and a third electrode; and a dielectric film disposed on at least one of the first main surface side and the second main surface side of the piezoelectric layer, overlapping the functional electrode in a top view, wherein the first comb-shaped electrode has a first busbar and a plurality of first electrode fingers with one end respectively connected to the first busbar, and the second comb-shaped electrode has... The device includes a second busbar and a plurality of second electrode fingers, each connected at one end to the second busbar and interleaved with the plurality of first electrode fingers. One of the first comb electrode and the second comb electrode is connected to the input potential, and the other of the first comb electrode and the second comb electrode is connected to the output potential. The third electrode has a plurality of third electrode fingers disposed on the first main surface of the piezoelectric layer such that they are arranged in the same direction as the first electrode fingers and the second electrode fingers. The interconnected connecting electrodes, the third electrode being connected to a potential different from the first comb electrode and the second comb electrode, the arrangement of the plurality of electrode fingers including the first electrode finger, the second electrode finger and the third electrode finger, in the case starting from the first electrode finger, the first electrode finger, the third electrode finger, the second electrode finger and the third electrode finger are arranged in a cycle, and in plan view, an acoustic reflector is formed at the position in the support member that overlaps with the plurality of first electrode fingers, the plurality of second electrode fingers and the plurality of third electrode fingers, when the longest distance between the centers of adjacent first electrode fingers and third electrode fingers and the center distance between adjacent second electrode fingers and third electrode fingers is set as p, and when the thickness of the piezoelectric layer is set as d, d / p is 0.5 or less, the elastic wave device also includes a mass-added film, when at least one electrode finger of the plurality of electrode fingers of the functional electrode located at one end in the direction of the arrangement of the plurality of electrode fingers is set as the first end electrode finger, the mass-added film is provided at the position that overlaps with the first end electrode finger in plan view.

[0408] <2> According to the elastic wave device described in <1>, wherein,

[0409] When at least one of the plurality of electrode fingers of the functional electrode is located at one end in the direction of the arrangement of the plurality of electrode fingers and is designated as the first end electrode finger, and at least one electrode finger located at the other end is designated as the second end electrode finger, the mass-added film overlaps with both the first end electrode finger and the second end electrode finger when viewed from above.

[0410] <3> According to the elastic wave device described in <2>, wherein,

[0411] The number of the first end electrode finger and the number of the second end electrode finger are two each.

[0412] <4> According to any one of <1> to <3>, the elastic wave device, wherein,

[0413] The first end electrode finger has a first surface and a second surface that are opposed to each other in the thickness direction, and a first side surface and a second side surface that connect the first surface and the second surface and are opposed to each other in a direction orthogonal to the direction in which the plurality of electrode fingers of the functional electrode extend. In the first end electrode finger, the first side surface is located outside the direction in which the plurality of electrode fingers of the functional electrode are arranged compared to the second side surface. The first surface, the second surface and the first side surface of the first end electrode finger overlap with the mass-added film when viewed from above, and the second side surface does not overlap with the mass-added film when viewed from above.

[0414] <5> According to any one of <1> to <4>, the elastic wave device, wherein,

[0415] The dielectric film is disposed on the first main surface of the piezoelectric layer to cover the functional electrode, and the mass-added film is disposed on the dielectric film.

[0416] <6> According to any one of <1> to <4>, the elastic wave device, wherein,

[0417] The mass-added film is located between the first end electrode finger and the first main surface of the piezoelectric layer.

[0418] <7> According to any one of <1> to <6>, the elastic wave device, wherein,

[0419] The mass-added film is disposed on both the first main surface side and the second main surface side of the piezoelectric layer.

[0420] <8> According to the elastic wave device described in <7>, wherein,

[0421] The thickness of the mass-added film disposed on the first main surface side of the piezoelectric layer is greater than the thickness of the mass-added film disposed on the second main surface side of the piezoelectric layer.

[0422] <9> According to the elastic wave device described in <7> or <8>, wherein,

[0423] The material of the mass-added film disposed on the first main surface side of the piezoelectric layer is different from the material of the mass-added film disposed on the second main surface side of the piezoelectric layer.

[0424] <10> An elastic wave device according to any one of <1> to <9>, wherein,

[0425] The material of the mass-added membrane is different from the material of the dielectric membrane.

[0426] <11> According to any one of <1> to <9>, the elastic wave device, wherein,

[0427] The material of the mass-added membrane is the same as the material of the dielectric membrane.

[0428] The density of the mass-added film is lower than the density of the dielectric film.

[0429] <12> According to any one of <1> to <11>, the elastic wave device, wherein,

[0430] The material of the mass-added film is at least one material selected from the group consisting of silicon oxycarbonate, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide and tungsten oxide.

[0431] <13> According to any one of <1> to <12>, the elastic wave device, wherein,

[0432] The dielectric film is made of silicon oxide.

[0433] <14> According to any one of <1> to <13>, the elastic wave device, wherein,

[0434] The functional electrode is a first functional electrode. The elastic wave device also includes a second functional electrode disposed on the second main surface of the piezoelectric layer. The second functional electrode has a first comb electrode, a second comb electrode, and a third electrode that are different from the first comb electrode, the second comb electrode, and the third electrode in the first functional electrode. The first functional electrode and the second functional electrode are positioned opposite each other, sandwiching the piezoelectric layer.

[0435] <15> According to the elastic wave device described in <14>, wherein,

[0436] The dielectric film is disposed on the second main surface of the piezoelectric layer to cover the second functional electrode, and the mass-added film is disposed on the dielectric film.

[0437] <16> According to any one of <1> to <15>, the elastic wave device, wherein,

[0438] The dielectric film includes a first dielectric film disposed on the first main surface side of the piezoelectric layer and a second dielectric film disposed on the second main surface side, wherein the difference between the thickness of the first dielectric film and the thickness of the second dielectric film is less than 10% relative to the thickness of both the first dielectric film and the second dielectric film.

[0439] <17> According to any one of <1> to <16>, the elastic wave device, wherein,

[0440] The mass-added film is a first mass-added film. When at least one electrode finger located at one end in the direction of the plurality of electrode fingers of the functional electrode is a first end electrode finger, and at least one electrode finger located at the other end is designated as a second end electrode finger, the first mass-added film includes at least one pair of first mass-added films overlapping the first end electrode finger and the second end electrode finger in a top view. The direction in which the plurality of electrode fingers of the functional electrode extend is designated as the electrode finger extension direction, and the direction orthogonal to the electrode finger extension direction is designated as the electrode finger orthogonal direction. When viewed from the electrode finger orthogonal direction, the overlapping area of ​​adjacent first electrode fingers and second electrode fingers is an intersection region. The intersection region has a first end located at the front end of the plurality of second electrode fingers extending in the electrode finger orthogonal direction. The edge region, and the second edge region extending in the orthogonal direction of the electrode fingers where the front ends of the plurality of first electrode fingers are located, the region between the electrodes facing each other with a gap in the extension direction of the electrode fingers and the intersection region in the first busbar and the connecting electrode is the first gap region, the region between the electrodes facing each other with a gap in the extension direction of the electrode fingers and the intersection region in the second busbar and the connecting electrode is the second gap region, the elastic wave device further includes a pair of second mass-adding films, the pair of second mass-adding films being disposed in at least one of the first edge region and the first gap region, and at least one of the second edge region and the second gap region, the pair of first mass-adding films and the pair of second mass-adding films being connected to each other.

[0441] <18> According to any one of <1> to <16>, the elastic wave device, wherein,

[0442] The mass-added film is a first mass-added film. When at least one electrode finger located at one end in the direction of the plurality of electrode fingers of the functional electrode is the first end electrode finger, and at least one electrode finger located at the other end is designated as the second end electrode finger, the first mass-added film includes at least one pair of first mass-added films overlapping the first end electrode finger and the second end electrode finger in a top view. The direction in which the plurality of electrode fingers of the functional electrode extend is designated as the electrode finger extension direction, and the direction orthogonal to the electrode finger extension direction is designated as the electrode finger orthogonal direction. When viewed from the electrode finger orthogonal direction, the overlapping area of ​​adjacent first electrode fingers and second electrode fingers is an intersection region. The intersection region has a first side located at the front end of the plurality of second electrode fingers, extending in the electrode finger orthogonal direction. The first gap region is the area between the electrodes facing each other in the extension direction of the first electrode fingers and the cross region, where the front ends of the first electrode fingers of the first busbar and the connecting electrode are located. The second gap region is the area between the electrodes facing each other in the extension direction of the electrode fingers and the cross region, where the front ends of the first electrode fingers of the second busbar and the connecting electrode are located. The elastic wave device also includes a pair of second mass-adding films, which are disposed in at least one of the first edge region and the first gap region, and at least one of the second edge region and the second gap region. The pair of first mass-adding films is connected to one of the pair of second mass-adding films.

[0443] <19> According to any one of <1> to <18>, the elastic wave device, wherein,

[0444] The piezoelectric layer comprises lithium niobate or lithium tantalate.

[0445] The Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following equations (1), (2), or (3).

[0446] (Within the range of 0°±10°, 0°~25°, any ψ) … Equation (1)

[0447] (Within the range of 0°±10°, 25°~100°, 0°~75° [(1-(θ-50)]) 2 / 2500)] 1 / 2 Or 180°-75° [(1-(θ-50)] 2 / 2500)] 1 / 2 ~180°) …Equation (2)

[0448] (Within the range of 0°±10°, 180°-40° [(1-(ψ-90)]) 2 / 8100)] 1 / 2 ~180°, any ψ) …Equation (3)

[0449] <20> A filter device comprising an elastic wave device described in any one of <1> to <19>, and an elastic wave resonator electrically connected to the elastic wave device, wherein the mass-added film of the elastic wave device is a first mass-added film, the elastic wave resonator having a piezoelectric layer, an IDT electrode disposed on the piezoelectric layer and having a plurality of electrode fingers, and a third mass-added film, wherein when at least one electrode finger of the plurality of electrode fingers of the IDT electrode located at one end in the direction in which the plurality of electrode fingers are arranged is designated as a third end electrode finger, the third mass-added film is disposed at a position overlapping the third end electrode finger in plan view, and at least one of the thickness and material of the first mass-added film and the third mass-added film are different from each other.

[0450] Explanation of reference numerals in the attached figures

[0451] 1, 1A, 1B… Functional electrodes;

[0452] 1a, 1b... First page, second page;

[0453] 1c, 1d… First side view, second side view;

[0454] 1e, 1f…step section;

[0455] 2…piezoelectric substrate;

[0456] 3…supporting components;

[0457] 4…piezoelectric layer;

[0458] 4a, 4b... First main face, second main face;

[0459] 5…Insulation layer;

[0460] 6...support base plate;

[0461] 7, 7B, 7C… First comb-shaped electrodes;

[0462] 8, 8B, 8C… Second comb-shaped electrodes;

[0463] 9, 9A, 9B… Third electrode;

[0464] 10…elastic wave device;

[0465] 10a…cavity section;

[0466] 11…Insulating layer;

[0467] 12~14…First busbar to third busbar;

[0468] 14A, 14B… connect electrodes;

[0469] 14a…Common electrode section;

[0470] 14b…Electrode pointer for connection;

[0471] 14c…section;

[0472] 15, 15B, 15C… First electrode refers to;

[0473] 16, 16B, 16C… Second electrode refers to;

[0474] 17… Third electrode refers to;

[0475] 18A, 18B… First dielectric film, second dielectric film;

[0476] 19, 19B… quality supplementary film;

[0477] 19d…end face;

[0478] 21A, 21B… First functional electrode, second functional electrode;

[0479] 27, 28… First comb-shaped electrode, second comb-shaped electrode;

[0480] 29…Third electrode;

[0481] 35~37… First electrode fingers~Third electrode fingers;

[0482] 49A, 49B... First mass additional membrane, second mass additional membrane;

[0483] 53…supporting components;

[0484] 55a~55c…low acoustic impedance layer;

[0485] 56a, 56b… high acoustic impedance layers;

[0486] 58…acoustic reflective membrane;

[0487] 60… filter device;

[0488] 62…input terminals;

[0489] 63… Output terminals;

[0490] 64…IDT electrode;

[0491] 64a, 64b... Third page, fourth page;

[0492] 64c, 64d… third side view, fourth side view;

[0493] 68A, 68B… third dielectric film, fourth dielectric film;

[0494] 69…Third mass additional membrane;

[0495] A, A1, A2… First end electrode refers to;

[0496] B, B1, B2… Second end electrode refers to;

[0497] C…incentive region;

[0498] D…band;

[0499] E1, E2... First edge region, second edge region;

[0500] F…intersection area;

[0501] G1, G2... First gap region, second gap region;

[0502] M…Central area;

[0503] N, O… third end electrode fingers, fourth end electrode fingers;

[0504] P1, P2... parallel arm resonator;

[0505] S1, S2... series arm resonators.

Claims

1. An elastic wave device, comprising: The piezoelectric layer has a first main surface and a second main surface that are opposite to each other; Supporting components are stacked on the piezoelectric layer; A functional electrode, disposed on the first main surface of the piezoelectric layer, has a first comb-shaped electrode, a second comb-shaped electrode, and a third electrode; and A dielectric film, disposed on at least one of the first main surface side and the second main surface side of the piezoelectric layer, overlaps with the functional electrode when viewed from above. The first comb-shaped electrode has a first busbar and a plurality of first electrode fingers, one end of which is connected to the first busbar. The second comb-shaped electrode has a second busbar and a plurality of second electrode fingers, one end of which is connected to the second busbar and interleaved with the plurality of first electrode fingers. One of the first comb electrode and the second comb electrode is connected to the input potential, and the other of the first comb electrode and the second comb electrode is connected to the output potential. The third electrode has a plurality of third electrode fingers respectively disposed on the first main surface of the piezoelectric layer such that they are arranged in the same direction as the first electrode fingers and the second electrode fingers, and a connecting electrode connecting the plurality of third electrode fingers to each other. The third electrode is connected to a potential different from that of the first comb electrode and the second comb electrode. Regarding the order of the plurality of electrode fingers, including the first electrode finger, the second electrode finger, and the third electrode finger, when starting from the first electrode finger, the order is that the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger are arranged as a cycle. From a top view, an acoustic reflector is formed at the position in the support member where it overlaps with the plurality of first electrode fingers, the plurality of second electrode fingers, and the plurality of third electrode fingers. When p is defined as the longest of the center-to-center distances between adjacent first and third electrode fingers and between adjacent second and third electrode fingers, and when d is defined as the thickness of the piezoelectric layer, d / p is 0.5 or less. The elastic wave device further comprises a mass-addition membrane, wherein when at least one of the plurality of electrode fingers of the functional electrode located at one end in the direction in which the plurality of electrode fingers are arranged is designated as a first end electrode finger, the mass-addition membrane is disposed at a position overlapping the first end electrode finger in a top view.

2. The elastic wave device according to claim 1, wherein, When at least one of the plurality of electrode fingers of the functional electrode is located at one end in the direction of the arrangement of the plurality of electrode fingers and is designated as the first end electrode finger, and at least one electrode finger located at the other end is designated as the second end electrode finger, the mass-added film overlaps with both the first end electrode finger and the second end electrode finger when viewed from above.

3. The elastic wave device according to claim 2, wherein, The number of the first end electrode finger and the number of the second end electrode finger are two each.

4. The elastic wave device according to any one of claims 1 to 3, wherein, The first end electrode finger has a first surface and a second surface that are opposed to each other in the thickness direction, and a first side surface and a second side surface that connect the first surface and the second surface and are opposed to each other in a direction orthogonal to the extending direction of the plurality of electrode fingers of the functional electrode. In the first end electrode finger, the first side is located on the outer side compared to the second side in the direction in which the plurality of electrode fingers of the functional electrode are arranged. The first surface, the second surface, and the first side surface of the first end electrode finger overlap with the mass-added film when viewed from above, while the second side surface does not overlap with the mass-added film when viewed from above.

5. The elastic wave device according to any one of claims 1 to 4, wherein, The dielectric film is disposed on the first main surface of the piezoelectric layer to cover the functional electrode, and the mass-added film is disposed on the dielectric film.

6. The elastic wave device according to any one of claims 1 to 4, wherein, The mass-added film is located between the first end electrode finger and the first main surface of the piezoelectric layer.

7. The elastic wave device according to any one of claims 1 to 6, wherein, The mass-added film is disposed on both the first main surface side and the second main surface side of the piezoelectric layer.

8. The elastic wave device according to claim 7, wherein, The thickness of the mass-added film disposed on the first main surface side of the piezoelectric layer is greater than the thickness of the mass-added film disposed on the second main surface side of the piezoelectric layer.

9. The elastic wave device according to claim 7 or 8, wherein, The material of the mass-added film disposed on the first main surface side of the piezoelectric layer is different from the material of the mass-added film disposed on the second main surface side of the piezoelectric layer.

10. The elastic wave device according to any one of claims 1 to 9, wherein, The material of the mass-added membrane is different from the material of the dielectric membrane.

11. The elastic wave device according to any one of claims 1 to 9, wherein, The material of the mass-added membrane is the same as the material of the dielectric membrane. The density of the mass-added film is lower than the density of the dielectric film.

12. The elastic wave device according to any one of claims 1 to 11, wherein, The material of the mass-added film is at least one material selected from the group consisting of silicon oxycarbonate, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide and tungsten oxide.

13. The elastic wave device according to any one of claims 1 to 12, wherein, The dielectric film is made of silicon oxide.

14. The elastic wave device according to any one of claims 1 to 13, wherein, The functional electrode is the first functional electrode. The elastic wave device also includes a second functional electrode disposed on the second main surface of the piezoelectric layer. The second functional electrode has a first comb-shaped electrode, a second comb-shaped electrode, and a third electrode that are different from the first comb-shaped electrode, the second comb-shaped electrode, and the third electrode in the first functional electrode. The first functional electrode and the second functional electrode are positioned opposite each other, sandwiching the piezoelectric layer.

15. The elastic wave device according to claim 14, wherein, The dielectric film is disposed on the second main surface of the piezoelectric layer to cover the second functional electrode, and the mass-added film is disposed on the dielectric film.

16. The elastic wave device according to any one of claims 1 to 15, wherein, The dielectric film includes a first dielectric film disposed on the first main surface side of the piezoelectric layer and a second dielectric film disposed on the second main surface side. The difference between the thickness of the first dielectric film and the thickness of the second dielectric film is less than 10% relative to the thickness of both the first dielectric film and the thickness of the second dielectric film.

17. The elastic wave device according to any one of claims 1 to 16, wherein, The mass-added film is the first mass-added film. When at least one electrode finger located at one end in the direction of the plurality of electrode fingers of the functional electrode is the first end electrode finger, and at least one electrode finger located at the other end is designated as the second end electrode finger, the first mass-adding film includes at least one pair of first mass-adding films that overlap with the first end electrode finger and the second end electrode finger in a top view. The direction in which the plurality of electrode fingers of the functional electrode 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 viewed from the electrode finger orthogonal direction, the overlapping area of ​​adjacent first electrode fingers and second electrode fingers is the intersection area. The intersection region includes a first edge region extending in the orthogonal direction of the electrode fingers, located at the tip of the plurality of second electrode fingers, and a second edge region extending in the orthogonal direction of the electrode fingers, located at the tip of the plurality of first electrode fingers. The area between the electrodes facing each other with gaps in the extension direction of the first busbar and the connecting electrodes, and the intersection area, is a first gap area. The area between the electrodes facing each other with gaps in the extension direction of the first electrode fingers, and the intersection area, is a second gap area. The elastic wave device further comprises: a pair of second mass-added membranes disposed in at least one of the first edge region and the first gap region, and at least one of the second edge region and the second gap region. A pair of first mass-added membranes and a pair of second mass-added membranes are connected to each other.

18. The elastic wave device according to any one of claims 1 to 16, wherein, The mass-added film is the first mass-added film. When at least one electrode finger located at one end in the direction of the plurality of electrode fingers of the functional electrode is the first end electrode finger, and at least one electrode finger located at the other end is designated as the second end electrode finger, the first mass-adding film includes at least one pair of first mass-adding films that overlap with the first end electrode finger and the second end electrode finger in a top view. The direction in which the plurality of electrode fingers of the functional electrode 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 viewed from the electrode finger orthogonal direction, the overlapping area of ​​adjacent first electrode fingers and second electrode fingers is the intersection area. The intersection region includes a first edge region extending in the orthogonal direction of the electrode fingers, located at the tip of the plurality of second electrode fingers, and a second edge region extending in the orthogonal direction of the electrode fingers, located at the tip of the plurality of first electrode fingers. The area between the electrodes facing each other with gaps in the extension direction of the first busbar and the connecting electrodes, and the intersection area, is a first gap area. The area between the electrodes facing each other with gaps in the extension direction of the first electrode fingers, and the intersection area, is a second gap area. The elastic wave device further comprises: a pair of second mass-added membranes disposed in at least one of the first edge region and the first gap region, and at least one of the second edge region and the second gap region. A pair of first mass-added membranes are connected to one of a pair of second mass-added membranes.

19. The elastic wave device according to any one of claims 1 to 18, wherein, The piezoelectric layer comprises lithium niobate or lithium tantalate. The Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following equations (1), (2), or (3). (Within the range of 0°±10°, 0°~25°, any ψ) … Equation (1) (Within the range of 0°±10°, 25°~100°, 0°~75° [(1-(θ-50)]) 2 / 2500)] 1 / 2 Or 180°-75° [(1-(θ-50)] 2 / 2500)] 1 / 2 ~180°) …Equation (2) (Within the range of 0°±10°, 180°-40° [(1-(ψ-90)]) 2 / 8100)] 1 / 2 ~180°, any ψ) … Equation (3).

20. A filter device comprising: The elastic wave device according to any one of claims 1 to 19; and An elastic wave resonator is electrically connected to the elastic wave device. The mass-added membrane of the elastic wave device is a first mass-added membrane. The elastic wave resonator has a piezoelectric layer, an IDT electrode disposed on the piezoelectric layer and having multiple electrode fingers, and a third mass-added film. When at least one of the plurality of electrode fingers of the IDT electrode, located at one end in the direction in which the plurality of electrode fingers are arranged, is designated as the third end electrode finger, the third mass-added film is disposed at the position overlapping the third end electrode finger in a top view. Between the first mass-added film and the third mass-added film, at least one of their thickness and material is different.

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