Elastic wave device and filter device

Abstract

The purpose of the present invention is to provide an elastic wave device capable of suppressing unnecessary waves in a pass band.　This elastic wave device 10 includes: a piezoelectric layer 4 having a first main surface 4a and a second main surface 4b facing each other; a support member laminated on the piezoelectric layer 4; a functional electrode 1 having a first comb-shaped electrode 7, a second comb-shaped electrode 8, and a third electrode 9 provided on the first main surface 4a of the piezoelectric layer 4; and a dielectric film provided on the first main surface 4a side and / or the second main surface 4b side of the piezoelectric layer 4 and overlapping the functional electrode 1 in plan view. The first comb-shaped electrode 7 has a first bus bar 12 and a plurality of first electrode fingers 15, one end of each finger 15 being connected to the first bus bar 12. The second comb-shaped electrode 8 has a second bus bar 13, and a plurality of second electrode fingers 16 interdigitated with the plurality of first electrode fingers 15, one end of each finger 16 being connected to the second bus bar 13. The first comb-shaped electrode 7 or the second comb-shaped electrode 8 is connected to an input potential, and the other of the first comb-shaped electrode 7 and the second comb-shaped electrode 8 is connected to an output potential. The third electrode 9 has a plurality of third electrode fingers 17 provided on the first main surface 4a of the piezoelectric layer 4 so as to be aligned with the first electrode fingers 15 and the second electrode fingers 16 in the direction in which the first electrode fingers 15 and the second electrode fingers 16 are arranged, and a connection electrode (third bus bar 14) interconnecting the plurality of third electrode fingers 17. The third electrode 9 is connected to a potential different from that of the first comb-shaped electrode 7 and the second comb-shaped electrode 8. When the order in which the plurality of electrode fingers including the first electrode fingers 15, the second electrode fingers 16, and the third electrode fingers 17 are lined up starts from the first electrode finger 15, one first electrode finger 15, one third electrode finger 17, one second electrode finger 16, and one third electrode finger 17 constitute one cycle. In a plan view, an acoustic reflection part is formed at 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 . d / p≤0.5, where d is the thickness of the piezoelectric film in a case when p is the greatest distance among the center-to-center distances between mutually adjacent first electrode fingers 15 and third electrodes fingers 17 and the center-to-center distances between mutually adjacent second electrode fingers 16 and third electrode fingers 17. When at least one electrode finger of the plurality of electrode fingers of the functional electrode 1 positioned at one end in the direction in which the plurality of electrode fingers are arranged is defined as a first end electrode finger A, a mass addition film 19 is further provided at a position overlapping the first end electrode finger A in plan view.

Description

Elastic wave device and filter device

[0001] The present invention relates to an acoustic wave device and a filter device.

[0002] Acoustic wave devices have traditionally been widely used in filters for mobile phones and the like. Recently, an acoustic wave device has been proposed as an acoustically coupled filter, as described in Patent Document 1 below. In an acoustically coupled filter, an electrode connected to a potential different from the input potential and the output potential, such as a reference potential, is disposed between an electrode connected to an input potential and an electrode connected to an output potential. With this configuration, a filter waveform can be generated even with a single acoustically coupled filter. Therefore, by reducing the number of elements, the filter device can be made more compact.

[0003] International Publication No. 2023-190656

[0004] However, in the acoustic wave device of Patent Document 1, it is difficult to sufficiently suppress unwanted waves within the passband, which may result in degradation of filter characteristics.

[0005] An object of the present invention is to provide an acoustic wave device and a filter device that can suppress unwanted waves within a passband.

[0006] An elastic wave device according to a preferred embodiment of the present invention includes: a piezoelectric layer having a first principal surface and a second principal surface opposing each other; a support member laminated on the piezoelectric layer; a functional electrode provided on the first principal surface of the piezoelectric layer, the functional electrode including a first interdigital electrode, a second interdigital electrode, and a third electrode; and a dielectric film provided on at least one of the first principal surface side and the second principal surface side of the piezoelectric layer and overlapping the functional electrode in a planar view. The first interdigital electrode includes a first bus bar and a plurality of first electrode fingers, one end of each of which is connected to the first bus bar. the second comb electrode has a second bus bar and a plurality of second electrode fingers, one end of which is connected to the second bus bar and which are interdigitated 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; and the third electrode has a plurality of third electrodes provided on the first main surface of the piezoelectric layer so as to be aligned with the first electrode fingers and the second electrode fingers in a direction in which the first electrode fingers and the second electrode fingers are aligned. a third electrode finger and a connection electrode connecting the plurality of third electrode fingers to each other, the third electrode being connected to a potential different from that of the first comb electrode and the second comb electrode; an order in which the plurality of electrode fingers including the first electrode finger, the second electrode finger, and the third electrode finger are arranged is an order in which, starting from the first electrode finger, the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger form one period; and an acoustic reflector is formed at a position overlapping with the electrode finger, and when the longest distance among the center-to-center distance between the adjacent first electrode finger and the adjacent third electrode finger and the center-to-center distance between the adjacent second electrode finger and the adjacent third electrode finger is defined as p and the thickness of the piezoelectric layer is defined as d, d / p is 0.5 or less, and when at least one electrode finger is defined as a first end electrode finger and is located at one end in a direction in which the plurality of electrode fingers of the functional electrode are arranged, the acoustic reflector is provided at a position overlapping with the first end electrode finger in a plan view;It further comprises a mass-adding membrane.

[0007] A filter device according to the present invention comprises an elastic wave device configured according to the present invention and an elastic wave resonator electrically connected to the elastic wave device, wherein the mass-adding film of the elastic wave device is a first mass-adding film, the elastic wave resonator has a piezoelectric layer, an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, and a third mass-adding film, wherein when at least one electrode finger of the plurality of electrode fingers of the IDT electrode located at one end in a direction in which the plurality of electrode fingers are arranged is defined as a third end electrode finger, the third mass-adding film is provided at a position overlapping the third end electrode finger in a planar view, and at least one of the thickness and the material is different between the first mass-adding film and the third mass-adding film.

[0008] According to the acoustic wave device and filter device of the present invention, it is possible to suppress unwanted waves within the passband.

[0009] FIG. 1 is a schematic front cross-sectional view of an elastic wave device according to a first preferred embodiment of the present invention. FIG. 2 is a schematic plan view of an elastic wave device according to the first preferred embodiment of the present invention. FIG. 3 is a schematic front cross-sectional view showing the vicinity of a functional electrode in the first preferred embodiment of the present invention. FIG. 4 is a diagram illustrating passband characteristics in the first preferred embodiment of the present invention and a first comparative example. FIG. 5 is a schematic cross-sectional view taken along line II-II in FIG. 2. FIG. 6 is a schematic front cross-sectional view showing the vicinity of a functional electrode in a first modified example of the first preferred embodiment of the present invention. FIG. 7 is a schematic front cross-sectional view showing the vicinity of a functional electrode in a second modified example of the first preferred embodiment of the present invention. FIG. 8 is a diagram illustrating passband characteristics in the first modified example of the first preferred embodiment of the present invention and the first comparative example. FIG. 9 is a diagram illustrating passband characteristics in the second modified example of the first preferred embodiment of the present invention and the first comparative example. FIG. 10 is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers for illustrating an odd mode. FIG. 11 is a schematic front cross-sectional view showing the vicinity of first to third electrode fingers for illustrating an even mode. FIG. 12 is a diagram illustrating the formation of a passband in an acoustically coupled filter. FIG. 13 is a schematic front cross-sectional view showing the vicinity of a functional electrode in a third modified example of the first embodiment of the present invention. FIG. 14 is a diagram showing pass characteristics in a third modified example of the first embodiment of the present invention and a first comparative example. FIG. 15 is a diagram showing pass characteristics in a fourth modified example of the first embodiment of the present invention and a first comparative example. FIG. 16 is a diagram showing pass characteristics in a fifth modified example of the first embodiment of the present invention and a first comparative example. FIG. 17 is a diagram showing pass characteristics in a sixth modified example of the first embodiment of the present invention and a first comparative example. FIG. 18 is a diagram showing pass characteristics in a seventh modified example of the first embodiment of the present invention and a first comparative example. FIG. 19 is a schematic plan view of an elastic wave device according to an eighth modified example of the first embodiment of the present invention. FIG. 20 is a schematic plan view of an elastic wave device according to a ninth modified example of the first embodiment of the present invention. FIG. 21 is a schematic front cross-sectional view showing an enlarged view of the vicinity of a first end electrode finger in an elastic wave device according to a second preferred embodiment of the present invention. FIG. 22 is a diagram showing pass characteristics in the second preferred embodiment of the present invention and a first comparative example.FIG. 23 is a schematic front cross-sectional view illustrating an enlarged view of the vicinity of a first end electrode finger in an elastic wave device according to a third preferred embodiment of the present invention. FIG. 24 is a diagram illustrating transmission characteristics in the third preferred embodiment of the present invention and a first comparative example. FIG. 25 is a schematic front cross-sectional view illustrating an enlarged view of the vicinity of a first end electrode finger in an elastic wave device according to a fourth preferred embodiment of the present invention. FIG. 26 is a schematic front cross-sectional view illustrating an enlarged view of the vicinity of a first end electrode finger in an elastic wave device according to a first modified example of the fourth preferred embodiment of the present invention. FIG. 27 is a diagram illustrating transmission characteristics in the fourth preferred embodiment of the present invention, a first modified example thereof, and a first comparative example. FIG. 28 is a schematic front cross-sectional view illustrating an enlarged view of the vicinity of a first end electrode finger in an elastic wave device according to a second modified example of the fourth preferred embodiment of the present invention. FIG. 29 is a schematic front cross-sectional view of an elastic wave device according to a fifth preferred embodiment of the present invention. FIG. 30 is a schematic front cross-sectional view illustrating an enlarged view of the vicinity of a first end electrode finger in an elastic wave device according to the fifth preferred embodiment of the present invention. FIG. 31 is a diagram illustrating transmission characteristics in the fifth preferred embodiment of the present invention and a second comparative example. FIG. 32 is a schematic plan view of an elastic wave device according to a sixth preferred embodiment of the present invention. FIG. 33 is a diagram illustrating a piezoelectric layer, each region, and a mass addition film according to the sixth preferred embodiment of the present invention. FIG. 34 is a schematic plan view of an elastic wave device according to a first modified example of the sixth preferred embodiment of the present invention. FIG. 35 is a schematic bottom view illustrating the configuration of a mass addition film provided on a second main surface of a piezoelectric layer according to a second modified example of the sixth preferred embodiment of the present invention. FIG. 36 is a schematic plan view of an elastic wave device according to a second modified example of the sixth preferred embodiment of the present invention. FIG. 37 is a schematic front cross-sectional view of an elastic wave device according to a seventh preferred embodiment of the present invention. FIG. 38 is a schematic circuit diagram of a filter device according to an eighth preferred embodiment of the present invention. FIG. 39 is a schematic plan view of a series arm resonator according to the eighth preferred embodiment of the present invention. FIG. 40 is a schematic cross-sectional view taken along line III-III in FIG. 39 . FIG. 41 is a diagram illustrating admittance-frequency characteristics of elastic wave resonators according to the eighth preferred embodiment of the present invention and a third comparative example. FIG. 42 is a diagram illustrating the relationship between d / p and the fractional bandwidth of an elastic wave device according to a reference example. FIG. 43 is a graph showing the relationship between the fractional bandwidth and the magnitude of normalized spurious signals in the elastic wave device of the reference example.Fig. 44 shows the relationship between d / p, metallization ratio MR, and fractional bandwidth. Fig. 45 shows LiNbO when d / p approaches 0. ３ FIG. 10 is a diagram showing a map of fractional bandwidths versus Euler angles (0°, θ, ψ) of the .lambda.

[0010] The present invention will be clarified below by describing specific embodiments of the present invention with reference to the drawings.

[0011] It should be noted that the embodiments described in this specification are merely examples, and partial substitution or combination of configurations is possible between different embodiments.

[0012] FIG. 1 is a schematic front cross-sectional view of an elastic wave device according to a first preferred embodiment of the present invention. FIG. 2 is a schematic plan view of an elastic wave device according to the first preferred embodiment. FIG. 1 is a schematic cross-sectional view taken along line II in FIG. 2. A first dielectric film, which will be described later, is omitted from FIG. 2. Furthermore, in FIG. 2, the electrodes and mass-adding films, which will be described later, are indicated by hatching. In FIG. 2, the reference potential symbol is used to indicate that a third electrode, which will be described later, is connected to the reference potential. Similarly, in schematic plan views other than FIG. 2, the electrodes and mass-adding films may be indicated by hatching, and the reference potential symbol may be used.

[0013] 1 is configured to utilize bulk waves in thickness shear mode. The acoustic wave device 10 is an acoustically coupled filter. The configuration of the acoustic wave device 10 will be described below.

[0014] The acoustic wave device 10 includes a piezoelectric substrate 2 and a functional electrode 1. The piezoelectric substrate 2 is a substrate having 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. The support member 3 is not limited to the above, and may be composed of only the support substrate 6.

[0015] 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 face each other. Of the first main surface 4a and the second main surface 4b, 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 the present invention, of the first main surface 4a and the second main surface 4b, the first main surface 4a may be located on the support member 3 side.

[0016] As shown in Fig. 2, the functional electrode 1 has a pair of comb electrodes and a third electrode 9. Specifically, the pair of comb electrodes is a first comb electrode 7 and a second comb electrode 8. The first comb electrode 7 is connected to an input potential. The second comb electrode 8 is connected to an 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.

[0017] The first comb electrode 7 may be connected to the output potential. The second comb electrode 8 may be connected to the input potential. In this way, the first comb electrode 7 may be connected to one of the input potential and the output potential. The second comb electrode 8 may be connected to the other of the input potential and the output potential. This configuration can also be applied to configurations of the present invention other than the first embodiment.

[0018] The third electrode 9 does not necessarily have to be connected to the reference potential, but may 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 be connected to the reference potential.

[0019] The first comb electrode 7 and the second comb electrode 8 are provided on the first main surface 4a of the piezoelectric layer 4. More specifically, the first comb electrode 7 and the second comb electrode 8 are provided directly on the first main surface 4a. The first comb electrode 7 has a first bus bar 12 and a plurality of first electrode fingers 15. One ends of the plurality of first electrode fingers 15 are connected to the first bus bar 12. On the other hand, the second comb electrode 8 has a second bus bar 13 and a plurality of second electrode fingers 16. One ends of the plurality of second electrode fingers 16 are connected to the second bus bar 13.

[0020] The first bus bar 12 and the second bus bar 13 face each other. The first electrode fingers 15 and the second electrode fingers 16 are interdigitated with each other. The first electrode fingers 15 and the second electrode fingers 16 are alternately arranged in a direction perpendicular to the direction in which the first electrode fingers 15 and the second electrode fingers 16 extend.

[0021] The third electrode 9 is provided on the first main surface 4a of the piezoelectric layer 4. Specifically, the third electrode 9 has a third bus bar 14 as a connection electrode and a plurality of third electrode fingers 17. The plurality of third electrode fingers 17 are provided directly on the first main surface 4a. The third bus bar 14 is provided directly on the first main surface 4a with some exceptions. The plurality of third electrode fingers 17 are electrically connected to each other by the third bus bar 14. The first comb-shaped electrode 7, the second comb-shaped electrode 8, and the third electrode 9 are electrically insulated from each other.

[0022] A plurality of third electrode fingers 17 are provided so as to be aligned with the first electrode fingers 15 and the second electrode fingers 16 in the direction in which the first electrode fingers 15 and the second electrode fingers 16 are aligned. Thus, the first electrode fingers 15, the second electrode fingers 16, and the third electrode fingers 17 are aligned in one direction. The plurality of third electrode fingers 17 extend in parallel with the plurality of first electrode fingers 15 and the plurality of second electrode fingers 16.

[0023] Hereinafter, the direction in which the first electrode fingers 15, the second electrode fingers 16, and the third electrode fingers 17 extend will be referred to as the electrode finger extension direction, and the direction perpendicular to the electrode finger extension direction will be referred to as the electrode finger orthogonal direction. In this embodiment, the electrode finger orthogonal direction is parallel to the direction in which the first bus bar 12, the second bus bar 13, and the third bus bar 14 extend. In this specification, the first electrode fingers 15, the second electrode fingers 16, and the third electrode fingers 17 may be collectively referred to simply as electrode fingers. The first bus bar 12, the second bus bar 13, and the third bus bar 14 may be collectively referred to simply as bus bars.

[0024] The configuration of the functional electrode 1, excluding the third electrode 9, is the same as that of an IDT (Interdigital Transducer) electrode. When viewed from the electrode finger orthogonal direction, the region 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 said to be the region 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 electrode finger orthogonal direction. In this specification, the dimension of the intersection region F along the electrode finger extension direction is the intersection width.

[0025] 2 , the third bus bar 14 of the third electrode 9 electrically connects the plurality of third electrode fingers 17 to each other. Specifically, the third bus bar 14 is located in the region between the intersection region F and the first bus bar 12. The plurality of first electrode fingers 15 are also located in this region. However, the third bus bar 14 and the plurality of first electrode fingers 15 are electrically insulated from each other by the plurality of insulator layers 11.

[0026] FIG. 3 is a schematic front cross-sectional view showing the vicinity of the functional electrodes in the first embodiment.

[0027] In this embodiment, the direction in which the multiple electrode fingers are arranged is the direction perpendicular to the electrode fingers. The order in which the multiple electrode fingers are arranged is such that, starting from the first electrode finger 15, one period includes the first electrode finger 15, the third electrode finger 17, the second electrode finger 16, and the third electrode finger 17. Therefore, the order in which the multiple electrode fingers are arranged is the first electrode finger 15, the third electrode finger 17, the second electrode finger 16, the third electrode finger 17, the first electrode finger 15, the third electrode finger 17, the second electrode finger 16, and so on. If the input potential is represented by IN, the output potential is represented by OUT, and the reference potential is represented by GND, the order of the multiple electrode fingers is IN, GND, OUT, GND, IN, GND, OUT, and so on.

[0028] In the region where a plurality of electrode fingers are provided, the electrode fingers located at both ends in the direction perpendicular to the electrode fingers are both second electrode fingers 16. Therefore, when at least one electrode finger located at one end in the direction in which the plurality of electrode fingers are arranged among the plurality of electrode fingers of the functional electrode 1 is defined 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 located at the other end in the direction in which the plurality of electrode fingers are arranged among the plurality of electrode fingers of the functional electrode 1 is defined as a second end electrode finger B, one of the second end electrode fingers B is a second electrode finger 16.

[0029] In this embodiment, specifically, the number of first end electrode fingers A and second end electrode fingers B is two each. In this embodiment, the first end electrode fingers A are the second electrode fingers 16 and the third electrode fingers 17. Similarly, the second end electrode fingers B are the second electrode fingers 16 and the third electrode fingers 17. However, in the region where a plurality of electrode fingers are provided in the functional electrode 1, the electrode fingers located at the ends in the direction perpendicular to the electrode fingers may be any type of electrode finger among the first electrode fingers 15, the second electrode fingers 16, and the third electrode fingers 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.

[0030] In this embodiment, the first end electrode finger A is the electrode finger at the end on the left side in Fig. 3 among the plurality of electrode fingers. Therefore, for the first end electrode finger A, the outside in the direction in which the plurality of electrode fingers are arranged is the left side in Fig. 3. Note that in this embodiment, the outside in the direction in which the plurality of electrode fingers are arranged is synonymous with the outside in the direction perpendicular to the electrode fingers.

[0031] On the other hand, the second end electrode finger B is the electrode finger at the right end of the multiple electrode fingers in Fig. 3. Therefore, for the second end electrode finger B, the outer side in the direction in which the multiple electrode fingers are arranged is the right side in Fig. 3. However, the second end electrode finger B may also be the electrode finger at the left end of the multiple electrode fingers in Fig. 3. In this case, the first end electrode finger A is the electrode finger at the right end of the multiple electrode fingers in Fig. 3.

[0032] The first end electrode finger A and the second end electrode finger B each have a first surface 1 a, a second surface 1 b, and a first side surface 1 c and a second side surface 1 d. The first surface 1 a and the second surface 1 b face each other in the thickness direction. The first side surface 1 c and the second side surface 1 d connect the first surface 1 a and the second surface 1 b and face each other in the direction perpendicular to the electrode fingers. In each of the first end electrode finger A and the second end electrode finger B, the first side surface 1 c is located outward of the second side surface 1 d in the direction in which the multiple electrode fingers of the functional electrode 1 are arranged.

[0033] In this embodiment, the first side surface 1 c and the second side surface 1 d of the first end electrode finger A and the second end electrode finger B extend at an angle with respect to the normal direction of the first main surface 4 a of the piezoelectric layer 4. However, the first side surface 1 c and the second side surface 1 d may extend parallel to the normal direction of the first main surface 4 a.

[0034] Hereinafter, a view from a direction corresponding to the top in Fig. 1 along the stacking direction of the support member 3 and the piezoelectric layer 4 will be referred to as a planar view. Note that in Fig. 1, for example, of the support substrate 6 side and the piezoelectric layer 4 side, the piezoelectric layer 4 side is the top. In this specification, a planar view is synonymous with a view from the principal surface opposing direction. The principal surface opposing direction is the direction in which the first principal surface 4a and the second principal surface 4b of the piezoelectric layer 4 face each other. More specifically, the principal surface opposing direction is, for example, the normal direction of the first principal surface 4a.

[0035] As shown in FIG. 3 , two mass addition films 19 are provided so as to overlap two electrode fingers that are the first end electrode fingers A in a planar view. Similarly, two mass addition films 19 are provided so as to overlap two electrode fingers that are the second end electrode fingers B in a planar view. Specifically, one mass addition film 19 overlaps one first end electrode finger A or one second end electrode finger B in a planar view. However, one continuously provided mass addition film 19 may overlap the first end electrode finger A and the second end electrode finger B in a planar view. On the other hand, the mass addition film 19 does not overlap electrode fingers other than the first end electrode finger A and the second end electrode finger B in a planar view among the multiple electrode fingers in the functional electrode 1. Hereinafter, overlapping in a planar view may be simply referred to as overlapping.

[0036] In the present invention, the first end electrode fingers A may be four or fewer consecutive electrode fingers from the electrode finger located at one end in the direction in which the plurality of electrode fingers are arranged. Similarly, the second end electrode fingers B may be four or fewer consecutive electrode fingers from the electrode finger located at the other end in the direction in which the plurality of electrode fingers are arranged. Therefore, for example, if there is only one first end electrode finger A and one second end electrode finger B, the mass addition film 19 may be provided so as to overlap one of the first end electrode fingers A and one of the second end electrode fingers B.

[0037] However, it is sufficient that the mass adding film 19 is provided at a position where it overlaps in a plan view with at least the first end electrode finger A. When the mass adding film 19 overlaps only the first end electrode finger A, for the sake of convenience, in this specification, it is assumed that the number of second end electrode fingers B is zero.

[0038] In this embodiment, in plan view, the mass adding film 19 overlaps with parts of the first surface 1 a and the second surface 1 b and the first side surface 1 c of the first end electrode finger A. On the other hand, the mass adding film 19 does not overlap with other parts of the first surface 1 a and the second surface 1 b and the second side surface 1 d of the first end electrode finger A. Furthermore, in plan view, the mass adding film 19 overlaps with a portion of the first end electrode finger A that is further outward in the direction perpendicular to the electrode fingers than the first side surface 1 c.

[0039] In this way, the mass adding film 19 is provided continuously in the direction perpendicular to the electrode fingers so as to overlap the first end electrode fingers A and the portions where the electrode fingers are not provided in a plan view. The mass adding film 19 is provided so as to overlap the entire portion of the first end electrode fingers A located in the crossing region F in the electrode finger extension direction in a plan view.

[0040] Similarly, the mass adding film 19 overlapping the second end electrode finger B in plan view is also provided continuously in the direction perpendicular to the electrode fingers so as to overlap the second end electrode finger B and a portion where the electrode finger is not provided in plan view. The mass adding film 19 is provided so as to overlap the entire portion of the second end electrode finger B located in the crossing region F in the electrode finger extension direction in plan view.

[0041] In this embodiment, when the overlapping width is defined as the dimension of the portion of the mass addition film 19 that overlaps with the first end electrode finger A or the second end electrode finger B in a direction perpendicular to the electrode fingers in a plan view, the overlapping width is narrower than the width of the first end electrode finger A or the second end electrode finger B. The width of the electrode finger is the dimension of the electrode finger in the direction perpendicular to the electrode fingers.

[0042] However, the arrangement of the mass adding film 19 is not limited to the above. The mass adding film 19 only needs to overlap at least a part of the first end electrode finger A in a plan view.

[0043] Silicon oxide is used as the material of the mass adding film 19. However, the material of the mass adding film 19 is not limited to the above.

[0044] In the acoustic wave device 10, a dielectric film is provided 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 provided on the first main surface 4a of the piezoelectric layer 4 so as to cover the functional electrode 1. The second dielectric film 18B is provided on the second main surface 4b of the piezoelectric layer 4. A plurality of mass-adding films 19 are provided on the first dielectric film 18A.

[0045] The dielectric film may be provided on at least one of the first main surface 4 a and the second main surface 4 b of the piezoelectric layer 4. When the functional electrode 1 is not covered with a dielectric film, for example, the mass-adding film 19 may be provided directly on the first end electrode finger A and the second end electrode finger B.

[0046] Silicon oxide is used as the material of the first dielectric film 18A and the second dielectric film 18B, but the materials of the first dielectric film 18A and the second dielectric film 18B are not limited to the above.

[0047] In this embodiment, the first electrode finger 15, the second electrode finger 16, and the third electrode finger 17 are made of a laminated metal film. Specifically, in each electrode finger, a Ti layer and an AlCu layer are laminated in this order from the piezoelectric layer 4 side. Note that the material of each electrode finger is not limited to the above. Alternatively, each electrode finger may be made of a single-layer metal film.

[0048] As shown in Fig. 2, the elastic wave device 10 has a plurality of excitation regions C. Elastic waves are excited in the plurality of excitation regions C. Note that Fig. 2 shows only two of the plurality of excitation regions C.

[0049] A portion of all the excitation regions C, namely, a plurality of excitation regions C, are regions where the adjacent first electrode fingers 15 and third electrode fingers 17 overlap when viewed from the electrode finger orthogonal direction, and are regions between the centers of the adjacent first electrode fingers 15 and third electrode fingers 17 in the electrode finger orthogonal direction. The remaining excitation regions C are regions where the adjacent second electrode fingers 16 and third electrode fingers 17 overlap when viewed from the electrode finger orthogonal direction, and are regions between the centers of the adjacent second electrode fingers 16 and third electrode fingers 17 in the electrode finger orthogonal direction. These excitation regions C are lined up in the electrode finger orthogonal direction. The intersection region F includes a plurality of excitation regions C. The intersection region F and the excitation regions C are regions of the piezoelectric layer 4 defined based on the configuration of the functional electrode 1.

[0050] Acoustic wave device 10 is an acoustically coupled filter. Acoustic waves of multiple modes, including thickness-shear bulk waves, are excited in excitation region C located between the centers of adjacent first electrode finger 15 and third electrode finger 17 and excitation region C located between the centers of adjacent second electrode finger 16 and third electrode finger 17. By coupling these modes, a suitable filter waveform can be obtained even in a single acoustic wave device 10.

[0051] A feature of this embodiment is that a mass-adding film 19 is provided at a position overlapping the first end electrode finger A and the second end electrode finger B in a planar view. However, it is sufficient that the mass-adding film 19 is provided at a position overlapping the first end electrode finger A in a planar view. This makes it possible to suppress unwanted waves within the passband. Therefore, when the acoustic wave device 10 is used in a filter device, it is possible to suppress degradation of the filter characteristics of the filter device. Details of this are provided below by comparing this embodiment with a first comparative example.

[0052] The first comparative example differs from the first embodiment in that it does not have mass-adding film 19. The transmission characteristics were compared between the first embodiment and the first comparative example. The design parameters of elastic wave device 10 having the configuration of the first embodiment are as follows. Note that the design parameters of the first comparative example were the same as those of the first embodiment, except for mass-adding film 19.

[0053] Piezoelectric layer: Material... LiNbO ３ , cut angle...120°Y, thickness...335nm First to third electrode fingers: layer structure...Ti layer / AlCu layer from the piezoelectric layer side, thickness...10nm / 400nm from the piezoelectric layer side, width...0.4μm Center-to-center distance between first electrode finger and third electrode finger: 1.38μm Center-to-center distance between second electrode finger and third electrode finger: 1.38μm Cross width: 40μm Total number of first to third electrode fingers: 51 Number of first end electrode fingers and second end electrode fingers: 2 First dielectric film: material...silicon oxide, thickness...75nm Second dielectric film: material...silicon oxide, thickness...75nm Mass-addition film: material...silicon oxide, thickness...70nm, dimension along the direction orthogonal to the electrode fingers...0.9μm, overlap width...0.2μm

[0054] FIG. 4 is a diagram showing the pass characteristics in the first embodiment and the first comparative example. Note that FIG. 4 shows the results of a finite element method (FEM) simulation. The pass characteristics are attenuation-frequency characteristics indicated by S parameters. Band D shown in FIG. 4 is a band located on the low-frequency side within the pass band of the elastic wave device. Arrow H in FIG. 4 indicates a portion of the frequency within the pass band. The same applies to figures showing pass characteristics other than FIG. 4.

[0055] As shown in FIG. 4, in the attenuation frequency characteristic of the first comparative example, many ripples occur within the pass band. Specifically, many ripples occur in band D, which is located on the low-frequency side of the pass band. In addition, large ripples occur near frequencies higher than the center of the pass band, as indicated by arrow H in FIG. 4. These ripples are caused by unwanted waves. In contrast, it can be seen that ripples are suppressed in the attenuation frequency characteristic of the first embodiment. In this way, in the first embodiment, unwanted waves within the pass band can be suppressed. The reason for this will be explained below.

[0056] In the first embodiment, the mass-adding film 19 is provided at a position overlapping the first end electrode finger A in a planar view. The acoustic velocity of the bulk wave in the portion where the mass-adding film 19 is provided is different from the acoustic velocity of the bulk wave in the portion where the mass-adding film 19 is not provided. Therefore, the boundary between the portion where the mass-adding film 19 is provided and the portion where the mass-adding film 19 is not provided functions as a reflective surface that reflects the bulk wave. This allows the thickness-shear mode bulk wave to be confined inside the functional electrode 1. This allows the thickness-shear mode bulk wave to be stably excited in each excitation region C. As a result, the excitation of unwanted waves can be suppressed.

[0057] The configuration of the first embodiment will be described in further detail below.

[0058] As shown in FIG. 1 , a recess is provided in the insulating layer 5. A piezoelectric layer 4 is provided on the insulating layer 5 so as to close the recess. This forms a hollow portion. This hollow portion is the cavity 10a. In the first embodiment, the support member 3 and the piezoelectric layer 4 are arranged so that a portion of the support member 3 and a portion of the piezoelectric layer 4 face each other with the cavity 10a in between. However, the recess in the support member 3 may be provided across the insulating layer 5 and the support substrate 6. Alternatively, a recess provided only in the support substrate 6 may be closed by the insulating layer 5. The recess may be provided in the piezoelectric layer 4, for example. The cavity 10a may be a through-hole provided in the support member 3.

[0059] The cavity 10a is the acoustic reflector of the present invention. The acoustic reflector can effectively confine the energy of the elastic wave to the piezoelectric layer 4 side. The acoustic reflector may be provided at a position on the support member 3 that overlaps with at least a portion of the functional electrode 1 in a planar view. More specifically, at least a portion of each of the first electrode finger 15, the second electrode finger 16, and the third electrode finger 17 may overlap with the acoustic reflector in a planar view. It is preferable that a plurality of excitation regions C overlap with the acoustic reflector in a planar view.

[0060] The acoustic reflecting portion may be an acoustic reflecting film such as an acoustic multilayer film, which will be described later. For example, an acoustic reflecting film may be provided on the surface of the support member.

[0061] In the first embodiment, the center-to-center distance between the adjacent pairs of first electrode fingers 15 and third electrode fingers 17 is the same as the center-to-center distance between the adjacent pairs of second electrode fingers 16 and third electrode fingers 17. However, the center-to-center distance between the adjacent first electrode fingers 15 and third electrode fingers 17 and the center-to-center distance between the adjacent second electrode fingers 16 and third electrode fingers 17 do not have to be constant. In this case, the longest distance among the center-to-center distance between the adjacent first electrode fingers 15 and third electrode fingers 17 and the center-to-center distance between the adjacent second electrode fingers 16 and third electrode fingers 17 is defined as p. Note that when the center-to-center distance is constant, as in this embodiment, the center-to-center distance between any adjacent electrode fingers is distance p.

[0062] When the thickness of the piezoelectric layer 4 is d, d / p is preferably 0.5 or less, and more preferably 0.24 or less, so that bulk waves in thickness shear mode are suitably excited.

[0063] FIG. 5 is a schematic cross-sectional view taken along line II-II in FIG.

[0064] The insulator layer 11 is provided on the first main surface 4 a of the piezoelectric layer 4 so as to cover the first electrode fingers 15. More specifically, in this embodiment, one insulator layer 11 covers a part of one first electrode finger 15 in the electrode finger extension direction.

[0065] 2 , a plurality of insulator layers 11 are arranged in a direction perpendicular to the electrode fingers. Each insulator layer 11 is provided so as to cover a portion of one of the first electrode fingers 15. A third bus bar 14 is provided on the first main surface 4 a of the piezoelectric layer 4, the plurality of insulator layers 11, and the plurality of third electrode fingers 17.

[0066] In this manner, the plurality of first electrode fingers 15 that are part of the first comb electrode 7 and the third bus bar 14 that are part of the third electrode 9 intersect with each other on the piezoelectric layer 4 via the insulator layer 11. In other words, the third bus bar 14 and the plurality of first electrode fingers 15 intersect with each other via the insulator layer 11. As a result, the third bus bar 14 and the plurality of first electrode fingers 15 are electrically insulated from each other. On the other hand, the third bus bar 14 electrically connects the plurality of third electrode fingers 17.

[0067] The order of stacking the first electrode fingers 15, the insulator layers 11, and the third bus bars 14 is not limited to the above. For example, the third bus bars 14, the insulator layers 11, and the first electrode fingers 15 may be stacked in this order.

[0068] As described above, the number of each of the first end electrode fingers A and the second end electrode fingers B is not limited to 2. Below, first and second modified examples will be shown, which differ from the first embodiment only in the number of the first end electrode fingers A and the second end electrode fingers B.

[0069] 6, the number of each of the first end electrode finger A and the second end electrode finger B is one. Therefore, the mass addition film 19 overlaps, in plan view, one electrode finger located at one end in the direction in which the multiple electrode fingers are arranged, and one electrode finger located at the other end.

[0070] 7 , the number of each of the first end electrode fingers A and the second end electrode fingers B is four. Therefore, the mass addition film 19 overlaps, in plan view, four consecutive electrode fingers from the electrode finger located at one end in the direction in which the multiple electrode fingers are arranged and four consecutive electrode fingers from the electrode finger located at the other end.

[0071] The transmission characteristics of the first and second modified examples were derived by FEM simulation, and the results of the first comparative example shown in FIG.

[0072] 8A and 8B are diagrams illustrating pass characteristics in a first modified example of the first embodiment and a first comparative example, respectively. 9A and 9B are diagrams illustrating pass characteristics in a second modified example of the first embodiment and a first comparative example.

[0073] As shown in Fig. 8, the first modified example is more effective than the first comparative example in suppressing unwanted waves in band D and unwanted waves near the frequency indicated by arrow H. As shown in Fig. 9, the second modified example is more effective than the first comparative example in suppressing unwanted waves near the frequency indicated by arrow H.

[0074] However, as in the first embodiment, it is preferable that the number of each of the first end electrode fingers A and the second end electrode fingers B is two. As is clear from a comparison of Figures 4, 8, and 9, the first embodiment shown in Figure 4 can effectively suppress unwanted waves and reduce insertion loss. The reason for this will be explained below.

[0075] Fig. 10 is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers to explain the odd mode. Fig. 11 is a schematic front cross-sectional view showing the vicinity of the first to third electrode fingers to explain the even mode. Fig. 12 is a diagram showing the formation of a passband in an acoustically coupled filter. Note that the arrows in Figs. 10 and 11 indicate the direction of the electric field.

[0076] In an acoustically coupled filter, an odd mode shown in FIG. 10 and an even mode shown in FIG. 11 occur. The odd mode is a mode in which the electrical conditions are in phase. FIG. 10 shows a region corresponding to one wavelength of the odd mode. One wavelength of the odd mode is the center-to-center distance between adjacent first electrode fingers 15 and second electrode fingers 16.

[0077] The even mode is a mode in which the electrical conditions are in opposite phase. Fig. 11 shows a region corresponding to half the wavelength of the even mode. The half wavelength of the even mode is the distance between the centers of adjacent first electrode fingers 15 and second electrode fingers 16. The wavelength of the even mode is twice the wavelength of the odd mode.

[0078] 12, in an acoustically coupled filter, a passband is formed by an even mode and an odd mode. The even mode constitutes the lower end of the passband, and the odd mode constitutes the upper end of the passband.

[0079] 6 , there is one first end electrode finger A, and the mass addition film 19 overlaps with the one first end electrode finger A in plan view. In this case, the odd mode can be sufficiently reflected toward the center of the functional electrode 1. On the other hand, the wavelength of the even mode is twice that of the odd mode. As a result, the effect of reflecting the even mode toward the center of the functional electrode 1 is not as great as the effect of reflecting the odd mode toward the center of the functional electrode 1. The same is true for the second end electrode finger B.

[0080] In contrast, in the first embodiment shown in FIG. 3 , there are two first end electrode fingers A, and the mass addition film 19 overlaps the two first end electrode fingers A in a planar view. In this case, both the odd mode and the even mode can be sufficiently reflected toward the center of the functional electrode 1. The same is true for the second end electrode finger B. As a result, the odd mode and the even mode can be stably excited in each excitation region C. As a result, the excitation of unwanted waves can be effectively suppressed. Furthermore, since the passband can be easily configured stably, the insertion loss can be reduced on the high-frequency side of the passband.

[0081] Furthermore, by setting the number of first end electrode fingers A and second end electrode fingers B to two as in the first embodiment rather than four as in the second modified example, the odd mode and even mode can be excited more stably.

[0082] In the first embodiment and its first and second modifications, the number of first end electrode fingers A and the number of second end electrode fingers B are the same. However, this is not limited to this. For example, in a third modification of the first embodiment shown in FIG. 13 , 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 addition film 19 overlaps, in plan view, three consecutive electrode fingers from the electrode finger located at one end in the direction in which the multiple electrode fingers are arranged and two consecutive electrode fingers from the electrode finger located at the other end. The third modification can also suppress unwanted waves in the passband. This will be demonstrated below by comparing the third modification with the first comparative example.

[0083] The first comparative example differs from the third modified example in that it does not include the mass-adding film 19. The third modified example and the first comparative example were compared in terms of pass characteristics.

[0084] The design parameters of the elastic wave device according to the third modification were the same as those of the first embodiment, except that the number of first end electrode fingers A was three. The design parameters of the first comparative example were the same as those of the first embodiment, except for the mass addition film 19.

[0085] FIG. 14 is a diagram showing the pass characteristics in the third modified example of the first embodiment and the first comparative example.

[0086] 14, in the third modified example, it is possible to suppress more unwanted waves near the frequency indicated by the arrow H than in the first comparative example. In this way, in the third modified example, it is possible to suppress unwanted waves within the passband.

[0087] In the third modification, the number of first end electrode fingers A and the number of second end electrode fingers B are different from each other. In this manner, the conditions may be different between one end and the other end in the direction in which the electrode fingers of the functional electrode are arranged. For example, the mass addition film 19 provided at one end in the direction in which the electrode fingers of the functional electrode are arranged may be different from the mass addition film 19 provided at the other end in the direction in which the electrode fingers are arranged in at least one of the thickness, the dimension in the direction perpendicular to the electrode fingers, and the overlap width. In this case, as in the first embodiment and the third modification, unwanted waves in the passband can be suppressed.

[0088] In the first embodiment, the type and density of the material of the mass adding film 19 are the same as the type and density of the material of the dielectric film. More specifically, the type and density of the material of the mass adding film 19 are the same as the type and density of the material of the first dielectric film 18A and the type and density of the material of the second dielectric film 18B. However, this is not limitative.

[0089] In this specification, the expression "the type of one material and the type of the other material are the same" also includes the case where the types of elements contained in the one material and the other material are the same but the composition ratios of the one material and the other material are different from each other.

[0090] For example, in a fourth modification of the first embodiment shown in FIG. 3 , the material of the mass-adding film 19 is the same as the material of the dielectric film, and the density of the mass-adding film 19 is lower than the density of the dielectric film. More specifically, the material of the mass-adding film 19 is the same as the material of the first dielectric film 18A and the material of the second dielectric film 18B, and the density of the mass-adding film 19 is lower than the densities of the first dielectric film 18A and the second dielectric film 18B. Note that in the fourth modification, 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. The fourth modification also suppresses unwanted waves in the passband. This will be demonstrated below by comparing the fourth modification with the first comparative example.

[0091] The first comparative example differs from the fourth modified example in that the mass-adding film 19 is not provided. The transmission characteristics were compared between the fourth modified example and the first comparative example. The design parameters of the elastic wave device according to the fourth modified example are the same as those of the first embodiment, except for the density of the mass-adding film 19. The parameters related to the mass-adding film 19 in the fourth modified example are as follows. Note that the design parameters of the first comparative example are the same as those of the first embodiment, except for the mass-adding film 19.

[0092] Mass-adding film: material...silicon oxide, thickness...70 nm, dimension along the direction perpendicular to the electrode fingers...0.9 μm, overlap width...0.2 μm, density...0.9 times the density of the first dielectric film and the density of the second dielectric film

[0093] FIG. 15 is a diagram showing the pass characteristics in the fourth modified example of the first embodiment and the first comparative example.

[0094] 15, in the fourth modified example, the unwanted waves in band D and the unwanted waves near the frequency indicated by the arrow H are suppressed more than in the first comparative example. In this way, in the fourth modified example, the unwanted waves within the pass band can be suppressed. In addition, in the fourth modified example, the insertion loss can also be reduced on the high-frequency side within the pass band.

[0095] In the first embodiment, the material of the mass adding film 19 is silicon oxide. However, the material of the mass adding film 19 is not limited to silicon oxide. For example, the Young's modulus of the mass adding film 19 may be higher than that of silicon oxide.

[0096] It is preferable that the Young's modulus of the mass adding film 19 is 50 GPa or more, in which case unwanted waves within the passband can be suitably suppressed.

[0097] The material of the mass-adding film 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-adding film 19 is preferably at least one material selected from the group consisting of silicon oxycarbide, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, hafnium oxide, niobium oxide, and tungsten oxide. ２ , SiN, Ta２ O ５ , AlN, Al ２ O ３ , HfO ２ , Nb ２ O ５ and WO. In this case, unwanted waves within the passband can be suitably suppressed.

[0098] The material of the mass adding film 19 is not limited to the above, and may be, for example, silicon oxide containing fluorine (SiOF), etc. In this case as well, it is possible to suppress unwanted waves within the passband.

[0099] In the first embodiment, the material of the mass adding 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 adding film 19 may be different from the material of the first dielectric film 18A and the second dielectric film 18B. This example is shown as fifth to seventh modified examples of the first embodiment with reference to FIG. 3. In the fifth to seventh modified examples, the material of the first dielectric film 18A and the second dielectric film 18B is silicon oxide. On the other hand, the material of the mass adding film 19 in the fifth modified example is tantalum oxide. More specifically, the material of the mass adding film 19 is Ta. ２ O ５ Therefore, the density of the mass adding film 19 is higher than the density of the first dielectric film 18A and the density of the second dielectric film 18B.

[0100] In the sixth modification, the mass adding film 19 is made of fluorine-containing silicon oxide (SiOF), and the density of the mass adding film 19 is lower than the density of the first dielectric film 18A and the density of the second dielectric film 18B.

[0101] In the seventh modification, the mass adding film 19 is made of silicon nitride. More specifically, the mass adding film 19 is made of SiN. In this modification, the acoustic velocity of the bulk wave propagating through the mass adding film 19 is higher than the acoustic velocity of the bulk wave propagating through the first dielectric film 18A and the acoustic velocity of the bulk wave propagating through the second dielectric film 18B.

[0102] The transmission characteristics were compared between the fifth to seventh modified examples and the first comparative example. The first comparative example differs from the fifth to seventh modified examples in that it does not have the mass-adding film 19. The design parameters of the elastic wave devices according to the fifth to seventh modified examples were the same as those of the first embodiment, except for the material of the mass-adding film 19. The design parameters of the first comparative example were the same as those of the fifth to seventh modified examples, except for the mass-adding film 19.

[0103] Fig. 16 is a diagram showing pass characteristics in a fifth modified example of the first embodiment and a first comparative example. Fig. 17 is a diagram showing pass characteristics in a sixth modified example of the first embodiment and a first comparative example. Fig. 18 is a diagram showing pass characteristics in a seventh modified example of the first embodiment and a first comparative example.

[0104] 16 to 18, in any of the fifth to seventh modified examples, it is possible to suppress the unwanted waves near the frequency indicated by the arrow H more effectively than in the first comparative example. As such, in the fifth to seventh modified examples, it is possible to suppress the unwanted waves within the passband.

[0105] 3, the mass adding film 19 in the first embodiment has an end face 19d. Specifically, the end face 19d is a face connecting the face of the mass adding film 19 facing the piezoelectric layer 4 with the face facing the piezoelectric layer 4. The end face 19d extends at an angle with respect to the normal direction to the first main surface 4a of the piezoelectric layer 4. However, in the present invention, the end face 19d may extend parallel to the normal direction to the first main surface 4a.

[0106] In the first embodiment, the thickness of the first dielectric film 18A and the thickness of the second dielectric film 18B are the same. However, the thickness of the first dielectric film 18A and the thickness of the second dielectric film 18B may be different from each other. However, it is preferable that the difference between the thickness of the first dielectric film 18A and the thickness of the second dielectric film 18B is 10% or less of both the thickness of the first dielectric film 18A and the thickness of the second dielectric film 18B. In this case, unwanted waves can be canceled out on 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.

[0107] When comparing the thickness of the first dielectric film 18A with the thickness of other members, the thickness of the portion of the first dielectric film 18A that does not cover the electrodes should be compared with the thickness of the other members. Similarly, when comparing the thickness of the second dielectric film 18B with the thickness of other members, the thickness of the portion of the second dielectric film 18B that does not cover the electrodes should be compared with the thickness of the other members.

[0108] 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. Note that the thickness of the first dielectric film 18A and the thickness of the second dielectric film 18B may be thicker than the thickness of the piezoelectric layer 4. Even in this case, it is possible to suppress unwanted waves within the passband.

[0109] In this specification, the phrase "the dielectric film and the piezoelectric layer have different thicknesses" 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 thickness of the dielectric film and the thickness of the piezoelectric layer. When comparing the thickness of the piezoelectric layer with the thickness of another member, it is sufficient to compare the thickness of the piezoelectric layer at the portion where the excitation region is located with the thickness of the other member.

[0110] 2 , in the first embodiment, the connection electrode of the third electrode 9 in the functional electrode 1 is a third bus bar 14. The third bus bar 14 is located in the region between the intersection region F and the first bus bar 12. In other words, the third bus bar 14 is located in the region between the tips of the second electrode fingers 16 and the first bus bar 12. Therefore, the tips of the second electrode fingers 16 each face the third bus bar 14 across a gap in the electrode finger extension direction. On the other hand, the tips of the first electrode fingers 15 each face the second bus bar 13 across a gap in the electrode finger extension direction.

[0111] The third bus bar 14 may be located in a region between the tips of the first electrode fingers 15 and the second bus bar 13. In this case, the tips of the first electrode fingers 15 face the third bus bar 14 across a gap. On the other hand, the tips of the second electrode fingers 16 face the first bus bar 12 across a gap.

[0112] However, the connection electrode of the third electrode 9 does not necessarily have to be the third bus bar 14. For example, in an eighth modification of the first embodiment shown in FIG. 19 , the third electrode 9A has a meandering shape. Specifically, the third electrode 9A has a plurality of connection electrodes 14A. In this modification, the connection electrodes 14A are not third bus bars. Furthermore, in this modification, the insulator layer 11 is not provided on the piezoelectric layer 4.

[0113] More specifically, the third electrode 9A has a plurality of connection electrodes 14A located on the first bus bar 12 side and a plurality of connection electrodes 14A located on the second bus bar 13 side. Of the plurality of third electrode fingers 17, the third electrode fingers 17 other than those at both ends in the direction perpendicular to the electrode fingers have one connection electrode 14A connected to each of their tip ends on the first bus bar 12 side and the second bus bar 13 side. Each third electrode finger 17 is connected to adjacent third electrode fingers 17 on both sides by each connection electrode 14A. By repeating this structure, the third electrode 9A has a meandering shape.

[0114] In this modification, the tips of the second electrode fingers 16 face the connection electrodes 14A in the electrode finger extension direction, respectively. The tips of the first electrode fingers 15 also face the connection electrodes 14A in the electrode finger extension direction, respectively.

[0115] Similar to the first embodiment, the functional electrode 1A of this modification also has first end electrode fingers A and second end electrode fingers B. The first end electrode fingers A and second end electrode fingers B each overlap the mass adding film 19 in plan view, thereby making it possible to suppress unwanted waves within the passband.

[0116] Another example of the configuration of the third electrode is shown below as a ninth modification of the first embodiment. In the ninth modification shown in Fig. 20 , the third electrode 9B includes a meander-shaped portion and a portion connected to the meander-shaped portion. Fig. 20 shows a portion of the functional electrode 1B that is closer to the intersection region F than the first bus bar 12 and the second bus bar 13 shown in Fig. 19 and other figures.

[0117] In this modification, the connection electrode 14B of the third electrode 9B has a plurality of common electrode portions 14a, a plurality of connection electrode fingers 14b, and a pair of bar portions 14c. The plurality of common electrode portions 14a are configured in the same manner as the plurality of connection electrodes 14A in the eighth modification shown in Fig. 19. Therefore, in this modification, the plurality of common electrode portions 14a include a plurality of common electrode portions 14a located on the first bus bar side, which corresponds to the upper side in Fig. 20, and a plurality of common electrode portions 14a located on the second bus bar side, which corresponds to the lower side in Fig. 20.

[0118] One connecting electrode finger 14b is connected to each of the multiple common electrode portions 14a on the first bus bar side. The multiple connecting electrode fingers 14b connected to these multiple common electrode portions 14a extend in the electrode finger extension direction from the multiple common electrode portions 14a side toward the first bus bar side. Similarly, one connecting electrode finger 14b is connected to each of the multiple common electrode portions 14a on the second bus bar side. The multiple connecting electrode fingers 14b connected to these multiple common electrode portions 14a extend in the electrode finger extension direction from the multiple common electrode portions 14a side toward the second bus bar side.

[0119] One of the pair of bar portions 14c is provided between the first bus bar and the intersection region. The other of the pair of bar portions 14c is provided between the second bus bar and the intersection region. Each bar portion 14c extends in a direction perpendicular to the electrode fingers. However, the direction in which each bar portion 14c extends is not limited to the above. The bar portion 14c and the multiple common electrode portions 14a on the first bus bar side are connected by multiple connecting electrode fingers 14b. Similarly, the bar portion 14c and the multiple common electrode portions 14a on the second bus bar side are connected by multiple connecting electrode fingers 14b.

[0120] In this modification, similar to the first embodiment, the third electrode 9B is electrically insulated from the first and second comb-shaped electrodes 7B and 8B by the insulator layer 11. However, in this modification, one insulator layer 11 is provided on the first main surface 4a of the piezoelectric layer 4 so as to cover the plurality of first electrode fingers 15B. A bar portion 14c on the first bus bar side is provided on the insulator layer 11. In this manner, the plurality of first electrode fingers 15B that are part of the first comb-shaped electrode 7B and the connection electrode 14B that is part of the third electrode 9B intersect on the piezoelectric layer 4 via the insulator layer 11.

[0121] An insulator layer 11 is provided on the first main surface 4 a of the piezoelectric layer 4 so as to cover the second electrode fingers 16B. A bar portion 14 c on the second bus bar side is provided on the insulator layer 11. In this manner, the second electrode fingers 16B, which are part of the second comb-shaped electrode 8B, and the connection electrode 14B, which is part of the third electrode 9B, intersect on the piezoelectric layer 4 with the insulator layer 11 interposed therebetween.

[0122] By including the pair of bar portions 14c in the third electrode 9B, the electrical resistance of the third electrode 9B can be reduced, thereby enabling the third electrode 9B to approach the reference potential more reliably.

[0123] Similar to the first embodiment, the functional electrode 1B of this modification also has first end electrode fingers A and second end electrode fingers B. The first end electrode fingers A and second end electrode fingers B each overlap the mass adding film 19 in plan view, thereby making it possible to suppress unwanted waves within the passband.

[0124] In this modification, the width of each first electrode finger 15B is not constant. Specifically, the width of each first electrode finger 15B gradually increases toward the first bus bar. More specifically, the width of the portion of each first electrode finger 15B overlapping with the common electrode portion 14a in the electrode-finger-orthogonal direction is wider than the width of the portion of each first electrode finger 15B located in the intersection region. When viewed from the electrode-finger-orthogonal direction, the width of a portion of each first electrode finger 15B located between the common electrode portion 14a and the first bus bar is wider than the width of the portion of each first electrode finger 15B overlapping with the common electrode portion 14a in the electrode-finger-orthogonal direction.

[0125] Similarly, the width of each second electrode finger 16B is not constant. Specifically, the width of each second electrode finger 16B gradually increases toward the second bus bar. More specifically, the width of the portion of each second electrode finger 16B overlapping with the common electrode portion 14a in the electrode-finger-orthogonal direction is wider than the width of the portion of each second electrode finger 16B located in the intersection region. The width of a portion of each second electrode finger 16B located between the common electrode portion 14a and the second bus bar when viewed in the electrode-finger-orthogonal direction is wider than the width of the portion of each second electrode finger 16B overlapping with the common electrode portion 14a in the electrode-finger-orthogonal direction. Note that the width of each first electrode finger 15B and the width of each second electrode finger 16B may be constant.

[0126] Each connection electrode finger 14b in the connection electrode 14B of the third electrode 9B includes a tip portion and a base portion. The tip portion is the end located on the crossing region side. The tip portion includes the tip. The base portion is the end connected to the bar portion 14c. The tip of each connection electrode finger 14b has a curved shape in a planar view. However, the shape of the tip in a planar view is not limited to the above, and may be, for example, a linear shape, and the distance between the tip and the crossing region may be constant. The width of the base portion of each connection electrode finger 14b increases as it approaches the bar portion 14c. The width of the base portion may also be constant.

[0127] 1 , 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 support member 3 side. In the present invention, of the first main surface 4a and the second main surface 4b of the piezoelectric layer 4, the first main surface 4a may be located on the support member 3 side. In this case, for example, the functional electrode 1 is located in the cavity 10a.

[0128] FIG. 21 is a schematic enlarged front cross-sectional view illustrating the vicinity of a first end electrode finger in an elastic wave device according to a second preferred embodiment of the present invention.

[0129] This embodiment differs from the first embodiment in the arrangement of mass addition film 19 and the configuration of first end electrode finger A. Although not shown, this embodiment also differs from the first embodiment in the configuration of second end electrode finger B. Except for the above points, the elastic wave device of this embodiment has a similar configuration to elastic wave device 10 of the first embodiment.

[0130] The mass addition film 19 is provided directly on the first main surface 4a of the piezoelectric layer 4. Specifically, the mass addition film 19 is located between a part 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 that is indirectly provided on the first main surface 4a via the mass addition film 19, and a portion that is provided directly on the first main surface 4a. Therefore, the second surface 1b of the first end electrode finger A has a step portion 1f, and the first surface 1a has a step portion 1e.

[0131] More specifically, the first end electrode finger A is provided on the mass adding film 19 from a portion of the second surface 1 b between an edge portion on the first side surface 1 c side and an edge portion on the second side surface 1 d side to an edge portion on the first side surface 1 c side. Thus, the mass adding film 19 overlaps the first side surface 1 c of the first end electrode finger A in a plan view, but does not overlap the second side surface 1 d in a plan view. Note that the mass adding film 19 may overlap the entire portion of the first end electrode finger A located in the crossing region F in a plan view.

[0132] The mass addition 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. In the mass addition film 19, the 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 overlaps with a portion that is further outward in the direction perpendicular to the electrode fingers than the first side surface 1c of the first end electrode finger A in plan view.

[0133] Although not shown, a mass addition film 19 is also provided on the second end electrode finger B side in the same manner as on the first end electrode finger A side.

[0134] 21 , the mass-adding film 19, together with the functional electrodes, is covered with a first dielectric film 18A. However, the first dielectric film 18A does not necessarily have to be provided. In this case, it is sufficient that the second dielectric film 18B is provided on the second main surface 4b side of the piezoelectric layer 4.

[0135] In this embodiment, as in the first embodiment, unwanted waves in the passband can be suppressed. Details of this will be explained below by comparing this embodiment with a first comparative example. The first comparative example differs from this embodiment in that it does not have a mass-adding film 19 and that the electrode fingers corresponding to the first end electrode finger A and the second end electrode finger B do not have a step portion. This first comparative example is similar to the first comparative example compared with the first embodiment and its respective modifications.

[0136] The transmission characteristics of the second embodiment and the first comparative example were compared. The design parameters of the elastic wave device having the configuration of the second embodiment are as follows. The design parameters of the first comparative example were the same as those of the first comparative example shown in FIG. 16 and other figures.

[0137] Piezoelectric layer: Material... LiNbO ３, cut angle...120°Y, thickness...335nm First to third electrode fingers: layer structure...Ti layer / AlCu layer from the piezoelectric layer side, thickness...10nm / 400nm from the piezoelectric layer side, width...0.4μm Center-to-center distance between first electrode finger and third electrode finger: 1.38μm Center-to-center distance between second electrode finger and third electrode finger: 1.38μm Cross width: 40μm Total number of first to third electrode fingers: 51 Number of first end electrode fingers and second end electrode fingers: 2 First dielectric film: material...silicon oxide, thickness...75nm Second dielectric film: material...silicon oxide, thickness...75nm Mass-addition film: material...silicon oxide, thickness...100nm

[0138] FIG. 22 is a diagram showing the pass characteristics in the second embodiment and the first comparative example.

[0139] 22 , in the second embodiment, unwanted waves in band D and those near the frequency indicated by arrow H can be suppressed more effectively than in the first comparative example. In this way, the second embodiment can suppress unwanted waves within the passband. In addition, the second embodiment can reduce insertion loss. As a result, when the elastic wave device of the second embodiment is used in a filter device, degradation of the filter characteristics of the filter device can be effectively suppressed.

[0140] FIG. 23 is a schematic enlarged front cross-sectional view illustrating the vicinity of a first end electrode finger in an elastic wave device according to a third preferred embodiment of the present invention.

[0141] This embodiment differs from the first embodiment in the arrangement of mass-adding film 19. Except for the above points, the elastic wave device of this embodiment has the same configuration as elastic wave device 10 of the first embodiment.

[0142] The mass adding film 19 is provided on the second main surface 4b side of the piezoelectric layer 4. Specifically, a second dielectric film 18B is provided on the second main surface 4b. The mass adding film 19 is provided on the second dielectric film 18B. In other words, the mass adding film 19 is indirectly provided on the second main surface 4b via the second dielectric film 18B. On the other hand, the mass adding film 19 is not provided on the first main surface 4a side.

[0143] The mass adding film 19 overlaps, in plan view, the entire portions of the first end electrode fingers A that are located in the crossing region F. More specifically, one mass adding film 19 overlaps, in plan view, the entire portions of two first end electrode fingers A that are located in the crossing region F. Note that each mass adding film 19 may overlap, in plan view, one first end electrode finger A.

[0144] Although not shown, a mass addition film 19 is also provided on the second end electrode finger B side in the same manner as on the first end electrode finger A side.

[0145] In this embodiment, as in the first embodiment, unwanted waves within the passband can be suppressed. Details of this will be shown below by comparing this embodiment with a first comparative example. The first comparative example differs from this embodiment in that it does not have the mass-adding film 19. This first comparative example is similar to the first comparative example compared with the first and second embodiments.

[0146] The transmission characteristics were compared between the third embodiment and the first comparative example. The design parameters of the acoustic wave device having the configuration of the third embodiment are as follows. The design parameters of the first comparative example were the same as those of the third embodiment, except for mass addition film 19.

[0147] Piezoelectric layer: Material... LiNbO ３ , cut angle...120°Y, thickness...335nm First to third electrode fingers: layer structure...Ti layer / AlCu layer from the piezoelectric layer side, thickness...10nm / 400nm from the piezoelectric layer side, width...0.4μm Center-to-center distance between first electrode finger and third electrode finger: 1.38μm Center-to-center distance between second electrode finger and third electrode finger: 1.38μm Cross width: 40μm Total number of first to third electrode fingers: 51 Number of first end electrode fingers and second end electrode fingers: 2 First dielectric film: material...silicon oxide, thickness...75nm Second dielectric film: material...silicon oxide, thickness...75nm Mass-addition film: material...silicon oxide, thickness...110nm

[0148] 24 is a diagram illustrating the passband characteristics of the third preferred embodiment and the first comparative example, where arrow J indicates a portion of a frequency within the passband of the elastic wave device.

[0149] 24 , in the third embodiment, unwanted waves in band D and unwanted waves near the frequency indicated by arrow J can be suppressed more effectively than in the first comparative example. In this way, in the third embodiment, unwanted waves within the passband can be suppressed. As a result, when the elastic wave device of the third embodiment is used in a filter device, degradation of the filter characteristics of the filter device can be suppressed.

[0150] FIG. 25 is a schematic enlarged front cross-sectional view illustrating the vicinity of a first end electrode finger in an elastic wave device according to a fourth preferred embodiment of the present invention.

[0151] This embodiment differs from the first embodiment in that mass addition films 19 are provided on both the first principal surface 4 a and the second principal surface 4 b of the piezoelectric layer 4. Except for the above, the elastic wave device of this embodiment has the same configuration as the elastic wave device 10 of the first embodiment.

[0152] The mass-adding film 19 provided on the first main surface 4 a side of the piezoelectric layer 4 is provided in the same manner as in the first embodiment, while the mass-adding film 19 provided on the second main surface 4 b side of the piezoelectric layer 4 is provided in the same manner as in the third embodiment.

[0153] The mass addition film 19 provided on the first principal surface 4 a of the piezoelectric layer 4 overlaps, in plan view, a portion of the first end electrode finger A in the direction orthogonal to the electrode fingers. On the other hand, the mass addition film 19 provided on the second principal surface 4 b of the piezoelectric layer 4 overlaps the entire first end electrode finger A in the direction orthogonal to the electrode fingers. Therefore, the dimension of the mass addition film 19 provided on the first principal surface 4 a in the direction orthogonal to the electrode fingers is different from the dimension of the mass addition film 19 provided on the second principal surface 4 b in the direction orthogonal to the electrode fingers.

[0154] In this embodiment, as in the first embodiment, unwanted waves in the passband can be suppressed. As a result, when the elastic wave device of this embodiment is used in a filter device, degradation of the filter characteristics of the filter device can be suppressed.

[0155] In this embodiment, the thickness of the mass adding film 19 provided on the first main surface 4a side of the piezoelectric layer 4 is thicker than the thickness of the mass adding film 19 provided on the second main surface 4b side of the piezoelectric layer 4. However, this is not limited to this. For example, in a first modification of the fourth embodiment shown in FIG. 26, the thickness of the mass adding film 19 provided on the first main surface 4a side of the piezoelectric layer 4 is thinner than the thickness of the mass adding film 19 provided on the second main surface 4b side of the piezoelectric layer 4. This modification also makes it possible to suppress unwanted waves within the passband. This will be explained below.

[0156] When comparing the thickness of the mass adding film 19 with the thickness of the other members, it is sufficient to compare the thickness of the portion that does not overlap in plan view with the first end electrode finger A or the second end electrode finger B. However, this does not apply when the entire mass adding film 19 overlaps in plan view with the first end electrode finger A or the second end electrode finger B.

[0157] The transmission characteristics of the fourth preferred embodiment and the first modified example thereof were derived by FEM simulation. The design parameters of the acoustic wave device of the fourth preferred embodiment are as follows.

[0158] Piezoelectric layer: Material... LiNbO ３, cut angle...120°Y, thickness...335 nm First to third electrode fingers: layer structure...Ti layer / AlCu layer from the piezoelectric layer side, thickness...10 nm / 400 nm from the piezoelectric layer side, width...0.4 μm Center-to-center distance between the first electrode finger and the third electrode finger: 1.38 μm Center-to-center distance between the second electrode finger and the third electrode finger: 1.38 μm Crossing width: 40 μm Total number of first to third electrode fingers: 51 Number of first end electrode fingers and number of second end electrode fingers: 2 First dielectric film: material...silicon oxide, thickness...75 nm Second dielectric film: material...silicon oxide, thickness...75 nm Mass-adding film provided on the first main surface side of the piezoelectric layer: material...silicon oxide, thickness...70 nm, dimension in the direction perpendicular to the electrode fingers...0.9 μm, overlapping width...0.2 μm Mass-adding film provided on the second main surface side of the piezoelectric layer: Material: silicon oxide, Thickness: 20 nm

[0159] The design parameters of the elastic wave device according to the first modified example of the fourth embodiment are the same as those of the fourth embodiment, except for the thickness of each mass adding film 19. The parameters of each mass adding film 19 in the first modified example are as follows:

[0160] Mass-adding film provided on the first principal surface side of the piezoelectric layer: Material...silicon oxide, thickness...20 nm, dimension along the direction perpendicular to the electrode fingers...0.9 μm, overlap width...0.2 μm Mass-adding film provided on the second principal surface side of the piezoelectric layer: Material...silicon oxide, thickness...100 nm

[0161] 27 shows the pass characteristics of the fourth embodiment and the first modification thereof, along with the results of the first comparative example shown in FIG.

[0162] FIG. 27 is a diagram showing the pass characteristics in the fourth embodiment, the first modification thereof, and the first comparative example.

[0163] 27, in the fourth embodiment and its first modification, unwanted waves near the frequency indicated by the arrow H are suppressed more than in the first comparative example. In this way, in the fourth embodiment and its first modification, unwanted waves within the passband can be suppressed. In addition, in the fourth embodiment and its first modification, the insertion loss can also be reduced.

[0164] As in the fourth embodiment, it is preferable that the thickness of the mass adding film 19 provided on the first main surface 4a side of the piezoelectric layer 4 is thicker than the thickness of the mass adding film 19 provided on the second main surface 4b side of the piezoelectric layer 4. In this case, as in the fourth embodiment shown in Fig. 27, it is possible to suitably suppress unwanted waves in band D.

[0165] In the fourth embodiment and its first modified example, the material of the mass adding film 19 provided on the first main surface 4 a of the piezoelectric layer 4 is the same as the material of the mass adding film 19 provided on the second main surface 4 b of the piezoelectric layer 4. However, the present invention is not limited to this.

[0166] For example, in a second modification of the fourth embodiment shown in FIG. 28 , the material of the mass adding film 19 provided on the first principal surface 4 a of the piezoelectric layer 4 is different from the material of the mass adding film 19B provided on the second principal surface 4 b of the piezoelectric layer 4. Specifically, in this modification, the material of the mass adding film 19 provided on the first principal surface 4 a is silicon oxide. On the other hand, the material of the mass adding film 19B provided on the second principal surface 4 b is tantalum oxide. The thickness of the mass adding film 19 provided on the first principal surface 4 a and the thickness of the mass adding film 19B provided on the second principal surface 4 b are the same. This modification also enables suppression of unwanted waves within the passband.

[0167] Furthermore, even if the material of the mass-adding film 19 provided on the first main surface 4a and the material of the mass-adding film 19B provided on the second main surface 4b are different from each other, the thickness of the mass-adding film 19 and the thickness of the mass-adding film 19B may be different from each other.

[0168] The combination of materials for the mass adding film 19 and the mass adding film 19B shown in this modification is an example and is not limited to silicon oxide and tantalum oxide. It is preferable that the mass adding film 19 and the mass adding film 19B each contain at least one different material selected from the group consisting of, for example, silicon oxycarbide, silicon oxide, silicon nitride, tantalum oxide, aluminum nitride, aluminum oxide, hafnium oxide, niobium oxide, and tungsten oxide.

[0169] In the first to fourth embodiments and their modifications, the functional electrode is provided only on the first principal surface of the piezoelectric layer. However, this is not limiting. The fifth embodiment shows an example in which the functional electrode is provided on both the first principal surface and the second principal surface of the piezoelectric layer. Note that, hereinafter, the functional electrode provided on the first principal surface in the first embodiment and the like may be referred to as the first functional electrode.

[0170] FIG. 29 is a schematic front cross-sectional view of an elastic wave device according to a fifth preferred embodiment of the present invention.

[0171] In this embodiment, the first functional electrode 21A corresponds to the functional electrode 1 shown in FIG. 3 and other figures. The first functional electrode 21A is provided on the first main surface 4a of the piezoelectric layer 4. This embodiment differs from the first embodiment in that a second functional electrode 21B is provided on the second main surface 4b of the piezoelectric layer 4. Accordingly, this embodiment differs from the first embodiment in that a second dielectric film 18B is provided on the second main surface 4b of the piezoelectric layer 4 so as to cover the second functional electrode 21B. This embodiment also differs from the first embodiment in that a mass addition film 19 is provided on the second main surface 4b of the piezoelectric layer 4. Except for the above points, the elastic wave device of this embodiment has the same configuration as the first embodiment.

[0172] The second functional electrode 21B has a first comb-shaped electrode 27, a second comb-shaped electrode 28, and a third electrode 29, which are different from the first comb-shaped electrode 7, the second comb-shaped electrode 8, and the third electrode 9 in the first functional electrode 21A. However, the first comb-shaped electrode 27, the second comb-shaped electrode 28, and the third electrode 29 in the second functional electrode 21B are configured in the same manner as the first comb-shaped electrode 7, the second comb-shaped electrode 8, and the third electrode 9 in the first functional electrode 21A.

[0173] Specifically, the first comb electrode 27 has a first bus bar and a plurality of first electrode fingers 35. One ends of the plurality of first electrode fingers 35 are connected to the first bus bar. On the other hand, the second comb electrode 28 has a second bus bar and a plurality of second electrode fingers 36. One ends of the plurality of second electrode fingers 36 are connected to the second bus bar. The first bus bar of the first comb electrode 27 and the second bus bar of the second comb electrode 28 face each other. The plurality of first electrode fingers 35 and the plurality of second electrode fingers 36 are interdigitated with each other.

[0174] The third electrode 29 has a third bus bar as a connection electrode and a plurality of third electrode fingers 37. The plurality of third electrode fingers 37 are electrically connected to each other by the third bus bar. The plurality of third electrode fingers 37 are provided so as to be aligned with the first electrode fingers 35 and the second electrode fingers 36 in the direction in which the first electrode fingers 35 and the second electrode fingers 36 are aligned. The first comb-shaped electrode 27, the second comb-shaped electrode 28, and the third electrode 29 are electrically insulated from each other.

[0175] The order in which the multiple electrode fingers in the second functional electrode 21B are arranged is such that, starting from the first electrode finger 35, one period consists of the first electrode finger 35, the third electrode finger 37, the second electrode finger 36, and the third electrode finger 37.

[0176] The elastic wave device of this preferred embodiment has a crossing region and multiple excitation regions defined based on the configuration of the first functional electrode 21A, and a crossing region and multiple excitation regions defined based on the configuration of the second functional electrode 21B. Hereinafter, the region defined based on the configuration of the first functional electrode 21A may be referred to as the region of the first functional electrode 21A. Similarly, the region defined based on the configuration of the second functional electrode 21B may be referred to as the region of the second functional electrode 21B.

[0177] The first functional electrode 21A and the second functional electrode 21B face each other with the piezoelectric layer 4 interposed therebetween. The crossing region of the first functional electrode 21A and the crossing region of the second functional electrode 21B overlap in a planar view. The excitation regions of the first functional electrode 21A and the excitation regions of the second functional electrode 21B overlap in a planar view.

[0178] 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. The electrode fingers of the first functional electrode 21A and the electrode fingers of the second functional electrode 21B overlap with each other in a plan view.

[0179] More specifically, an electrode finger located at one end in the direction in which the plurality of electrode fingers in the first functional electrode 21A are arranged overlaps with an electrode finger located at one end in the direction in which the plurality of electrode fingers in the second functional electrode 21B are arranged in a plan view, and an electrode finger located at the other end in the direction in which the plurality of electrode fingers in the first functional electrode 21A are arranged overlaps with an electrode finger located at the other end in the direction in which the plurality of electrode fingers in the second functional electrode 21B are arranged in a plan view.

[0180] 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 in a plan view, and 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 in a plan view.

[0181] The center of the portion of each electrode finger of the first functional electrode 21A located in the crossing region overlaps with the center of the portion of each electrode finger of the second functional electrode 21B located in the crossing region in a plan view, but 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 in a plan view.

[0182] The elastic wave device of this preferred embodiment includes two acoustically coupled filters. More specifically, one acoustically coupled filter is formed by providing a first functional electrode 21A on the first principal surface 4a of the piezoelectric layer 4. Another acoustically coupled filter is formed by providing a second functional electrode 21B on the second principal surface 4b of the piezoelectric layer 4. The first functional electrode 21A and the second functional electrode 21B face each other with the piezoelectric layer 4 interposed therebetween. This allows the elastic wave device including the two acoustically coupled filters to be compact.

[0183] FIG. 30 is a schematic enlarged front cross-sectional view illustrating the vicinity of a first end electrode finger in an elastic wave device according to a fifth preferred embodiment of the present invention.

[0184] A plurality of mass adding films 19 are provided on both the first main surface 4a and the second main surface 4b of the piezoelectric layer 4. Each mass adding film 19 provided on the first main surface 4a is provided on a first dielectric film 18A. Each mass adding film 19 provided on the second main surface 4b is provided on a second dielectric film 18B.

[0185] The plurality of mass addition films 19 provided on the first main surface 4 a side of the piezoelectric layer 4 overlap both the first end electrode fingers A1 of the first functional electrode 21 A and the first end electrode fingers A2 of the second functional electrode 21 B in plan view. The plurality of mass addition films 19 provided on the second main surface 4 b side of the piezoelectric layer 4 overlap both the first end electrode fingers A1 of the first functional electrode 21 A and the first end electrode fingers A2 of the second functional electrode 21 B in plan view.

[0186] As shown in Figure 29, on the second end electrode finger B1 side, similar to the first end electrode finger A1 side, multiple mass-adding films 19 are provided on both the first main surface 4a side and the second main surface 4b side of the piezoelectric layer 4.

[0187] In this embodiment, as in the first embodiment, unwanted waves in the passband can be suppressed. Details of this will be shown below by comparing this embodiment with a second comparative example. Note that the second comparative example differs from this embodiment in that it does not have the mass-adding film 19. In the second comparative example, like this embodiment, a first functional electrode, a second functional electrode, and a first dielectric film and a second dielectric film are provided.

[0188] The transmission characteristics were compared between the fifth embodiment and the second comparative example. The design parameters of the elastic wave device having the configuration of the fifth embodiment were the same for the first functional electrode and the second functional electrode. The design parameters of the elastic wave device are as follows. The design parameters of the second comparative example were also the same as those of the fifth embodiment, except for mass-adding film 19.

[0189] Piezoelectric layer: Material... LiNbO ３ , cut angle...120°Y, thickness...335nm First to third electrode fingers: layer structure...Ti layer / AlCu layer from the piezoelectric layer side, thickness...10nm / 400nm from the piezoelectric layer side, width...0.4μm Center-to-center distance between first electrode finger and third electrode finger: 1.38μm Center-to-center distance between second electrode finger and third electrode finger: 1.38μm Cross width: 40μm Total number of first to third electrode fingers: 51 Number of first end electrode fingers and second end electrode fingers: 2 First dielectric film: material...silicon oxide, thickness...75nm Second dielectric film: material...silicon oxide, thickness...75nm Mass addition film provided on the first main surface side of the piezoelectric layer: material...silicon oxide, thickness...70nm Mass addition film provided on the second main surface side of the piezoelectric layer: material...silicon oxide, thickness...70nm

[0190] 31 is a diagram illustrating the pass characteristics of the fifth preferred embodiment and the second comparative example. Band K shown in FIG. 31 is a band located on the low-frequency side within the pass band of the elastic wave device. Arrow L in FIG. 31 indicates a portion of the frequency within the pass band.

[0191] As shown in FIG. 31 , the fifth embodiment can suppress the unwanted waves indicated in band K and the unwanted waves near the frequency indicated by the arrow L more effectively than the second comparative example. In this way, the fifth embodiment can suppress unwanted waves within the passband. In addition, the fifth embodiment can reduce insertion loss on the high-frequency side of the passband. Therefore, when the elastic wave device of the fifth embodiment is used in a filter device, degradation of the filter characteristics of the filter device can be suppressed.

[0192] 30 , in the fifth embodiment, the mass adding film 19 provided on the second principal surface 4b side of the piezoelectric layer 4 is provided on the second dielectric film 18B. The mass adding film 19 provided on the second principal surface 4b side may be located between the first end electrode finger A2 of the second functional electrode 21B and the second principal surface 4b. Similarly, the mass adding film 19 may be located between the second end electrode finger B2 of the second functional electrode 21B shown in FIG. 29 and the second principal surface 4b. In this case, unwanted waves within the passband can also be suppressed.

[0193] In the first to fifth embodiments and their modifications, the mass addition film overlaps at least the first end electrode finger in plan view, but does not overlap electrodes other than the first end electrode finger and the second end electrode finger in plan view. However, a mass addition film may be provided that overlaps electrode fingers other than the first end electrode finger and the second end electrode finger in plan view. This example is shown in the sixth embodiment. Note that in the sixth embodiment and its modifications, the mass addition film in the first embodiment and the like is considered to be the first mass addition film.

[0194] FIG. 32 is a schematic plan view of an elastic wave device according to a sixth preferred embodiment of the present invention.

[0195] In this embodiment, the first mass addition film 49A corresponds to the mass addition film 19 shown in FIG. 2 and other figures. The first mass addition film 49A overlaps with the first end electrode finger A and the second end electrode finger B in a plan view. This embodiment differs from the first embodiment in that there is only one first end electrode finger A and one second end electrode finger B. Accordingly, this embodiment also differs from the first embodiment in that there is a pair of first mass addition films 49A. Furthermore, this embodiment also differs from the first embodiment in that there is a second mass addition film 49B. Except for the above points, the elastic wave device of this embodiment has a similar configuration to the elastic wave device 10 of the first embodiment.

[0196] Hereinafter, the first mass adding film 49A and the second mass adding film 49B may be collectively referred to simply as the mass adding film.

[0197] FIG. 33 is a diagram showing a piezoelectric layer, each region, and a mass addition film in the sixth embodiment.

[0198] The intersection region F includes a pair of edge regions and a central region M. Specifically, the pair of edge regions is a first edge region E1 and a second edge region E2. The first edge region E1 is a region in which the tips of the plurality of second electrode fingers 16 shown in FIG. 32 are located and extends in the direction perpendicular to the electrode fingers. On the other hand, the second edge region E2 is a region in which the tips of the plurality of first electrode fingers 15 are located and extends in the direction perpendicular to the electrode fingers. The first edge region E1 and the second edge region E2 face each other across the central region M in the electrode finger extension direction. It should be noted that the intersection region F also includes a pair of edge regions and a central region M in other embodiments of the present invention other than the sixth embodiment.

[0199] The elastic wave device of the sixth preferred embodiment has a pair of gap regions. Specifically, the pair of gap regions is a first gap region G1 and a second gap region G2. The first gap region G1 is the region between the intersection region F and the third bus bar 14 shown in FIG. 32 . On the other hand, the second gap region G2 is the region between the intersection region F and the second bus bar 13. It should be noted that elastic wave devices of other preferred embodiments of the present invention besides the sixth preferred embodiment also have a pair of gap regions.

[0200] The elastic wave device of the sixth embodiment has a pair of second mass addition films 49B. One of the pair of second mass addition films 49B is provided across the first edge region E1 and the first gap region G1. The other second mass addition film 49B is provided across the second edge region E2 and the second gap region G2. The second mass addition film 49B is not provided in the central region M.

[0201] The second mass adding film 49B may be provided 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.

[0202] The pair of first mass adding films 49A is connected to both of the pair of second mass adding films 49B, so that the pair of first mass adding films 49A and the pair of second mass adding films 49B form a frame-shaped mass adding film.

[0203] By providing a pair of first mass-adding films 49A, similar to the first embodiment, thickness-shear mode bulk waves can be suitably confined to the functional electrode 1 side. This allows the thickness-shear mode to be stably excited in each excitation region. As a result, unwanted waves in the passband can be suppressed.

[0204] By providing a pair of second mass-adding films 49B in a pair of edge regions and a pair of gap regions, respectively, thickness-shear mode bulk waves can be suitably confined to the functional electrode 1 side even in the direction perpendicular to the electrode fingers. However, even when one second mass-adding film 49B is provided in at least one of the first edge region E1 and the first gap region G1, thickness-shear mode bulk waves can be confined to the functional electrode 1 side. Similarly, even when the other second mass-adding film 49B is provided in at least one of the second edge region E2 and the second gap region G2, thickness-shear mode bulk waves can be confined to the functional electrode 1 side.

[0205] The second mass adding film 49B may overlap the busbars in plan view. Specifically, the second mass adding film 49B on the first busbar 12 and third busbar 14 side may overlap the third busbar 14 in plan view. The second mass adding film 49B on the second busbar 13 side may overlap the second busbar 13 in plan view.

[0206] As described above, the third bus bar 14 serving as a connection electrode of the third electrode 9 may be provided between the intersection region F and the second bus bar 13. Alternatively, as in the eighth modification of the first embodiment shown in Fig. 19 , a plurality of connection electrodes 14A of the third electrode 9A may be located on both the first bus bar 12 side and the second bus bar 13 side.

[0207] Therefore, the second mass adding film 49B on the first busbar 12 side may overlap, in plan view, electrodes of the connection electrodes of the first busbar 12 and the third electrode 9, in which the tip portions of the second electrode fingers 16 face each other across a gap in the electrode finger extension direction. The second mass adding film 49B on the second busbar 13 side may overlap, in plan view, electrodes of the connection electrodes of the second busbar 13 and the third electrode 9, in which the tip portions of the first electrode fingers 15 face each other across a gap in the electrode finger extension direction.

[0208] A portion of the second mass adding film 49B does not have to overlap with the cavity 10a shown in Fig. 1 in plan view. In other words, the second mass adding film 49B may be provided from the portion of the piezoelectric layer 4 that overlaps with the cavity 10a in plan view to the portion that does not overlap with the cavity 10a.

[0209] It is preferable that the first mass adding film 49A and the second mass adding film 49B are made of the same material. In this case, the first mass adding film 49A and the second mass adding film 49B can be formed simultaneously, thereby improving the productivity of the acoustic wave device. However, the first mass adding film 49A and the second mass adding film 49B may be made of different materials.

[0210] It is preferable that the thickness of the first mass adding film 49A and the thickness of the second mass adding film 49B are the same. In this case, the manufacturing process of the acoustic wave device can be prevented from becoming complicated. Therefore, the productivity of the acoustic wave device can be increased. In this specification, "the thicknesses of the mass adding films are the same" means that the difference in thickness between one mass adding film and the other mass adding film is 5% or less of the thickness of both mass adding films.

[0211] The thickness of the first mass adding film 49A and the thickness of the second mass adding film 49B may be different from each other. In this specification, "the thicknesses of the mass adding films are different from each other" means that the difference between the thickness of one mass adding film and the thickness of the other mass adding film is more than 5% of the thickness of both mass adding films.

[0212] When comparing the thickness of the first mass adding film 49A with the thickness of the other member, it is sufficient to compare 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 plan view with the thickness of the other member. However, this does not apply when the entire first mass adding film 49A overlaps with the first end electrode finger A or the second end electrode finger B in a plan view. When comparing the thickness of the second mass adding film 49B with the thickness of the other member, it is sufficient to compare the thickness of the portion that does not overlap with the electrode finger in a plan view with the thickness of the other member. However, this does not apply when the entire second mass adding film 49B overlaps with the electrode finger in a plan view.

[0213] In the sixth embodiment, there is one first end electrode finger A and one second end electrode finger B. Therefore, one pair of first mass adding films 49A is provided. However, there may be, for example, two first end electrode fingers A and two second end electrode fingers B. In this case, two pairs of first mass adding films 49A are provided. The two pairs of first mass adding films 49A may be connected to the second mass adding films 49B.

[0214] It is not necessary for the first mass adding film 49A and the second mass adding film 49B to form a frame-shaped mass adding film. For example, in a first modification of the sixth embodiment shown in Fig. 34, both of the pair of first mass adding films 49A are connected to one of the pair of second mass adding films 49B. Specifically, the second mass adding film 49B on the second bus bar 13 side is connected to the pair of first mass adding films 49A. The other second mass adding film 49B is not connected to the first mass adding film 49A.

[0215] In this modification, similarly to the sixth embodiment, thickness-shear mode bulk waves can be confined to the functional electrode 1 side in both the electrode finger perpendicular direction and the electrode finger extension direction, thereby suppressing unwanted waves in the passband.

[0216] The mass-adding film in this modification and the sixth embodiment can be formed, for example, by using a lift-off method. In this case, a dielectric layer is provided on a resist pattern, and then the resist pattern is peeled off to pattern the mass-adding film. The resist pattern is a pattern consisting of a portion where a resist layer is provided and a portion where a resist layer is not provided.

[0217] 33, the mass-adding film is formed in a frame shape. In this case, the portion of the resist pattern where the resist layer is not provided is frame-shaped. Therefore, in the resist pattern, the resist layer inside the frame is separated from the resist layer outside the frame.

[0218] On the other hand, when forming the mass addition film of this modified example shown in FIG. 34 , the mass addition film is formed so as not to be frame-shaped. Specifically, the second mass addition film 49B on the third bus bar 14 side and the pair of first mass addition films 49A are formed with a gap between them. In this case, the portion of the resist pattern where the resist layer is not provided does not have a frame shape. Therefore, the resist layer is integrated in the resist pattern. As a result, when the resist pattern is peeled off, residue of the resist pattern is unlikely to be left. This can suppress defects in the acoustic wave device.

[0219] In the sixth embodiment and its first modification, the first mass addition film 49A and the second mass addition film 49B are provided on the first main surface 4a of the piezoelectric layer 4. However, this is not limited to this. In a second modification of the sixth embodiment shown in FIGS. 35 and 36, a pair of first mass addition films 49A are provided on both the first main surface 4a and the second main surface 4b of the piezoelectric layer 4. Note that FIG. 35 is a schematic bottom view showing the second main surface 4b side. Therefore, FIG. 35 is inverted left and right with respect to the schematic plan view showing the first main surface 4a as shown in FIG. 36.

[0220] 35, a pair of second mass adding films 49B are provided on the second main surface 4b of the piezoelectric layer 4. The pair of second mass adding films 49B overlap in plan view with the first edge region E1 and first gap region G1, and the second edge region E2 and second gap region G2, respectively, which are shown with reference to FIG.

[0221] The pair of first mass adding films 49A provided on the second main surface 4b of the piezoelectric layer 4 is connected to both of the pair of second mass adding films 49B. The pair of first mass adding films 49A provided on the second main surface 4b overlaps with the first end electrode fingers A and the second end electrode fingers B in plan view.

[0222] 36, a pair of first mass adding films 49A provided on the first main surface 4a of the piezoelectric layer 4 overlaps, in plan view, the first end electrode finger A and the second end electrode finger B. In this modification, the second mass adding film 49B shown in FIG. 35 is not provided on the first main surface 4a.

[0223] In this modification, similarly to the sixth embodiment, thickness-shear mode bulk waves can be confined to the functional electrode 1 side in both the electrode finger perpendicular direction and the electrode finger extension direction, thereby suppressing unwanted waves in the passband.

[0224] 35, the pair of first mass addition films 49A and the pair of second mass addition films 49B provided on the second main surface 4b of the piezoelectric layer 4 are preferably made of silicon oxide. In this case, the first mass addition films 49A and the second mass addition films 49B tend to shrink toward the functional electrode 1. This tends to make the shape of the piezoelectric layer 4 convex toward the outside of the first main surface 4a, out of the outside of the first main surface 4a and the outside of the second main surface 4b in the normal direction of the first main surface 4a. This makes it possible to suppress sticking of the piezoelectric layer 4.

[0225] 1 and the like, making it difficult for the piezoelectric layer 4 to separate from the support member 3. In this modified example, when the second dielectric film 18B is provided as in the first embodiment, the sticking of the piezoelectric layer 4 occurs when the piezoelectric layer 4 indirectly contacts the support member 3 via the second dielectric film 18B.

[0226] In contrast, in this modification, the shape of the piezoelectric layer 4 tends to be convex outward from the first main surface 4a in 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, sticking of the piezoelectric layer 4 can be suppressed.

[0227] 35 , in this modification, one second mass adding film 49B overlaps with the third bus bar 14 in a plan view. The other second mass adding film 49B overlaps with the second bus bar 13 in a plan view. Note that the second mass adding film 49B does not have to overlap with the bus bar in a plan view.

[0228] 32 , in the sixth embodiment, the tips of the second electrode fingers 16 face the third bus bar 14, which serves as a connection electrode for the third electrode 9, across a gap in the electrode finger extension direction. A first gap region G1 shown in FIG. 33 is a region between the third bus bar 14 and the intersection region F. However, for example, if the third bus bar 14 is provided between the intersection region F and the second bus bar 13, the tips of the second electrode fingers 16 face the first bus bar 12 across a gap in the electrode finger extension direction. In this case, the first gap region G1 is a region between the first bus bar 12 and the intersection region F.

[0229] In the present invention, the first gap region G1 may be a region between the first bus bar 12 and the third electrode 9, among the connecting electrodes, in which the tips of the multiple second electrode fingers 16 face each other across a gap in the electrode finger extension direction, and the intersection region F.

[0230] On the other hand, in the sixth embodiment, the tips of the plurality of first electrode fingers 15 face the second bus bar 13 across a gap in the electrode finger extension direction. The second gap region G2 is the region between the second bus bar 13 and the intersection region F. However, for example, if a third bus bar 14 serving as a connection electrode for the third electrode 9 is provided between the intersection region F and the second bus bar 13, the tips of the plurality of first electrode fingers 15 face the third bus bar 14 across a gap in the electrode finger extension direction. In this case, the second gap region G2 is the region between the third bus bar 14 and the intersection region F.

[0231] In the present invention, the second gap region G2 may be a region between the connection electrodes of the second bus bar 13 and the third electrode 9, in which the tips of the multiple first electrode fingers 15 face each other across a gap in the electrode finger extension direction, and the intersection region F.

[0232] 19 , the first gap region G1 is a region between the multiple connection electrodes 14A on the first bus bar 12 side and the intersection region F. The second gap region G2 is a region between the multiple connection electrodes 14A on the second bus bar 13 side and the intersection region F.

[0233] In the first to sixth embodiments and their modifications, the acoustic reflector is a cavity in the piezoelectric substrate. However, the acoustic reflector may be an acoustic reflecting film. This example is shown in the seventh embodiment.

[0234] FIG. 37 is a schematic front cross-sectional view of an elastic wave device according to a seventh preferred embodiment of the present invention.

[0235] This embodiment differs from the first embodiment in that the acoustic reflection portion is an acoustic reflection film 58. This embodiment also differs from the first embodiment in that the support member 53 is formed only from a support substrate. Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 10 of the first embodiment.

[0236] An acoustic reflection film 58 is provided on the surface of the support member 53. A second dielectric film 18B is provided on the acoustic reflection film 58. A piezoelectric layer 4 is provided on the second dielectric film 18B. That is, the piezoelectric layer 4 is indirectly provided on the acoustic reflection film 58 via the second dielectric film 18B. It is sufficient that the support member 53 and the piezoelectric layer 4 are arranged so that at least a portion of the support member 53 and at least a portion of the piezoelectric layer 4 face each other with the acoustic reflection film 58 in between.

[0237] The acoustic reflecting film 58 is a laminate of multiple acoustic impedance layers. Specifically, the acoustic reflecting film 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 reflecting film 58 are low acoustic impedance layer 55a, low acoustic impedance layer 55b, and low acoustic impedance layer 55c.

[0238] On the other hand, the high acoustic impedance layer is a layer with a relatively high acoustic impedance. More specifically, the multiple high acoustic impedance layers of the acoustic reflecting film 58 are the high acoustic impedance layer 56a and the high acoustic impedance layer 56b. The low acoustic impedance layers and the high acoustic impedance layers are alternately stacked. The low acoustic impedance layer 55a is the layer of the acoustic reflecting film 58 that is located closest to the piezoelectric layer 4.

[0239] The acoustic reflection film 58 has three low acoustic impedance layers and two high acoustic impedance layers, although it is sufficient that the acoustic reflection film 58 has at least one low acoustic impedance layer and one high acoustic impedance layer.

[0240] The low acoustic impedance layer may be made of, for example, silicon oxide or aluminum, while the high acoustic impedance layer may be made of, for example, a metal such as platinum or tungsten, or a dielectric such as aluminum nitride, silicon nitride or hafnium oxide.

[0241] In this embodiment, as in the first embodiment, thickness-shear mode bulk waves can be suitably confined to the functional electrode 1 side. This allows for stable excitation of thickness-shear mode in each excitation region. This also allows for suppression of unwanted waves within the passband. Additionally, the provision of the acoustic reflection film 58 allows for effective confinement of the energy of the elastic waves to the piezoelectric layer 4 side.

[0242] The configuration in this embodiment in which the acoustic reflecting portion is the acoustic reflecting film 58 can be applied to configurations of the present invention other than this embodiment.

[0243] The acoustic wave device of the present invention can be used, for example, in a filter device, as will be described below.

[0244] 38 is a schematic circuit diagram of a filter device according to an eighth preferred embodiment of the present invention, illustrating an acoustic wave device in block form.

[0245] The filter device 60 is a ladder filter. The filter device 60 includes an input terminal 62, an output terminal 63, a plurality of series arm resonators, a plurality of parallel arm resonators, and the elastic wave device 10. The elastic wave device 10 is the elastic wave device according to the first preferred embodiment. Note that the filter device 60 may include an elastic wave device according to an aspect of the present invention other than the first preferred embodiment, instead of the elastic wave device 10.

[0246] The input terminal 62 and the output terminal 63 may be configured as, for example, electrode pads or wiring. All of the series arm resonators and all of the parallel arm resonators in the filter device 60 are elastic wave resonators. Each of the elastic wave resonators in the filter device 60 uses a bulk wave in thickness shear mode as its main mode. Note that it is sufficient that at least one series arm resonator or at least one parallel arm resonator is an elastic wave resonator that uses a bulk wave in thickness shear mode as its main mode.

[0247] In this embodiment, each series arm resonator is a series trap. In this embodiment, each parallel arm resonator is a parallel trap. However, the series arm resonators do not necessarily have to be series traps. The parallel arm resonators do not necessarily have to be parallel traps.

[0248] Specifically, the multiple series arm resonators are series arm resonators S1 and S2. The series arm resonator S1, the elastic wave device 10, and the series arm resonator S2 are connected in series between the input terminal 62 and the output terminal 63, in this order from the input terminal 62 side. Note that the first bus bar 12 shown in FIG. 2 is connected to the series arm resonator S1. The second bus bar 13 is connected to the series arm resonator S2. On the other hand, the third bus bar 14 is connected to ground potential.

[0249] Specifically, the multiple parallel arm resonators are parallel arm resonators P1 and P2. The parallel arm resonator P1 is connected between a connection point between the series arm resonator S1 and the elastic wave device 10 and ground potential. The parallel arm resonator P2 is connected between a connection point between the elastic wave device 10 and the series arm resonator S2 and ground potential. The circuit configuration of the filter device 60 is not limited to the above. The filter device 60 may include 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.

[0250] A specific configuration of an acoustic wave resonator in a filter device according to the present invention will be described below.

[0251] Fig. 39 is a schematic plan view of a series arm resonator according to the eighth embodiment, in which a third dielectric film, which will be described later, is omitted.

[0252] The series arm resonator S1 has a piezoelectric substrate 2. The piezoelectric substrate 2 includes a piezoelectric layer 4. In this preferred embodiment, the multiple series arm resonators, the multiple parallel arm resonators, and the elastic wave device 10 shown in FIG. 38 share the same piezoelectric substrate 2 and the same piezoelectric layer 4. However, each series arm resonator, each parallel arm resonator, and the elastic wave device 10 may have a separate piezoelectric substrate 2. Each series arm resonator, each parallel arm resonator, and the elastic wave device 10 may have a separate piezoelectric layer 4.

[0253] An IDT electrode 64 is provided on the piezoelectric layer 4 of the series arm resonator S1. Specifically, the IDT electrode 64 is provided 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 is a first comb-shaped electrode 7C and a second comb-shaped electrode 8C.

[0254] The first interdigital transducer 7C and the second interdigital transducer 8C are configured in the same manner as the first interdigital transducer 7 and the second interdigital transducer 8 shown in FIG. 2 in the acoustic wave device 10, which is an acoustically coupled filter. Thus, the IDT electrode 64 has a plurality of first electrode fingers 15C and a plurality of second electrode fingers 16C. In the IDT electrode 64, as in the functional electrode 1 in the acoustically coupled filter, the direction in which the plurality of electrode fingers extend is the electrode finger extension direction, and the direction perpendicular to the electrode finger extension direction is the electrode finger orthogonal direction.

[0255] The series arm resonator S1 has a crossover region F and a plurality of excitation regions C defined by the configuration of the IDT electrode 64. More specifically, the region where adjacent first electrode fingers 15C and second electrode fingers 16C overlap when viewed from the electrode finger orthogonal direction is the crossover region F in the series arm resonator S1. The crossover region F includes a plurality of excitation regions C. The excitation region C of the series arm resonator S1 is the region where adjacent first electrode fingers 15C and second electrode fingers 16C overlap when viewed from the electrode finger orthogonal direction, and is also the region between the centers of the adjacent first electrode fingers 15C and second electrode fingers 16C in the electrode finger orthogonal direction.

[0256] Of the multiple electrode fingers of the IDT electrode 64, at least one electrode finger located at one end in the direction in which the multiple electrode fingers are arranged is defined as a third end electrode finger N. At least one electrode finger located at the other end is defined as a fourth end electrode finger O. In this embodiment, there are two third end electrode fingers N and two fourth end electrode fingers O.

[0257] FIG. 40 is a schematic cross-sectional view taken along line III-III in FIG.

[0258] The third end electrode finger N and the fourth end electrode finger O of the IDT electrode 64 each have a third surface 64 a, a fourth surface 64 b, and a third side surface 64 c, and a fourth side surface 64 d. ​​The third surface 64 a and the fourth surface 64 b face each other in the thickness direction. The third side surface 64 c and the fourth side surface 64 d connect the third surface 64 a and the fourth surface 64 b and face each other in the direction perpendicular to the electrode fingers. In each of the third end electrode finger N and the fourth end electrode finger O, the third side surface 64 c is located outward of the fourth side surface 64 d in the direction in which the multiple electrode fingers of the IDT electrode 64 are arranged.

[0259] 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 at an angle with respect to the normal direction to the first main surface 4a of the piezoelectric layer 4. Note that the third side surface 64c and the fourth side surface 64d may extend parallel to the normal direction to the first main surface 4a.

[0260] The series arm resonator S1 has a plurality of third mass addition films 69. Specifically, two third mass addition films 69 are provided so as to overlap two electrode fingers that are the third end electrode fingers N in a plan view. Similarly, two third mass addition films 69 are provided so as to overlap two electrode fingers that are the fourth end electrode fingers O in a plan view. More specifically, one third mass addition film 69 overlaps one third end electrode finger N or one fourth end electrode finger O in a plan view. However, one continuous third mass addition film 69 may overlap the third end electrode finger N and the fourth end electrode finger O in a plan view. On the other hand, the third mass addition film 69 does not overlap any of the electrode fingers in the IDT electrode 64 other than the third end electrode finger N and the fourth end electrode finger O.

[0261] In the present invention, the third end electrode finger N may be four or fewer consecutive electrode fingers from the electrode finger located at one end in the direction in which the plurality of electrode fingers are arranged. Similarly, the fourth end electrode finger O may be four or fewer consecutive electrode fingers from the electrode finger located at the other end in the direction in which the plurality of electrode fingers are arranged. Therefore, for example, if there is one third end electrode finger N and one fourth end electrode finger O, the plurality of third mass addition films 69 may be arranged so as to overlap one of the third end electrode finger N and one of the fourth end electrode fingers O.

[0262] However, it is sufficient that the third mass adding film 69 is provided at a position that overlaps in a plan view with at least the third end electrode finger N. When the third mass adding film 69 overlaps only the third end electrode finger N, for the sake of convenience, in this specification, it is assumed that the number of the fourth end electrode finger O is zero.

[0263] In this embodiment, in plan view, the third mass adding film 69 overlaps with parts of the third surface 64 a and the fourth surface 64 b and the third side surface 64 c of the third end electrode finger N. On the other hand, the third mass adding film 69 does not overlap with other parts of the third surface 64 a and the fourth surface 64 b and the fourth side surface 64 d of the third end electrode finger N. Furthermore, in plan view, the third mass adding film 69 overlaps with a portion of the third end electrode finger N that is further outward in the direction perpendicular to the electrode fingers than the third side surface 64 c.

[0264] In this way, one third mass adding film 69 is provided continuously in the direction perpendicular to the electrode fingers so as to overlap the third end electrode fingers N and the portions where the electrode fingers are not provided in a plan view. The third mass adding film 69 is provided so as to overlap the entire portions of the third end electrode fingers N located in the crossing regions F in the electrode finger extension direction in a plan view.

[0265] Similarly, the third mass adding film 69 overlapping the fourth end electrode finger O in plan view is also provided continuously in the direction perpendicular to the electrode fingers so as to overlap the fourth end electrode finger O and a portion where the electrode finger is not provided in plan view. The third mass adding film 69 is provided so as to overlap the entire portion of the fourth end electrode finger O located in the crossing region F in the electrode finger extension direction in plan view.

[0266] In a planar view, when the dimension of the portion of the third mass-adding film 69 that overlaps with the third end electrode finger N or the fourth end electrode finger O in the direction perpendicular to the electrode fingers is taken 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.

[0267] The material of the third mass adding film 69 is silicon oxide, although the material of the third mass adding film 69 is not limited to the above.

[0268] 40 , 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 provided on the first main surface 4a of the piezoelectric layer 4 so as to cover the IDT electrode 64. The fourth dielectric film 68B is provided on the second main surface 4b of the piezoelectric layer 4. A plurality of third mass addition films 69 are provided on the third dielectric film 68A.

[0269] In this embodiment, the material of the third dielectric film 68A and the material of the fourth dielectric film 68B are silicon oxide, but the materials of the third dielectric film 68A and the fourth dielectric film 68B are not limited to the above.

[0270] 38 also include an IDT electrode 64, a third dielectric film 68A, a fourth dielectric film 68B, and a third mass adding film 69, and also include a crossing region F and a plurality of excitation regions C. In each of the acoustic wave resonators of this embodiment, the third end electrode finger N and the fourth end electrode finger O overlap with the third mass adding film 69 in a plan view, thereby enabling effective suppression of unwanted waves.

[0271] 40, the arrangement of the third mass adding film 69 is not limited to the above. The third mass adding film 69 only needs to overlap at least a portion of the third end electrode finger N in a plan view. In this case, it is possible to suppress unwanted waves. The same applies to each of the acoustic wave resonators other than the series arm resonator S1.

[0272] In the series arm resonator S1, the dielectric film may be provided on at least one of the first principal surface 4a and the second principal surface 4b of the piezoelectric layer 4. When the IDT electrode 64 is not covered with a dielectric film, for example, the third mass adding film 69 may be provided directly on the third end electrode finger N and the fourth end electrode finger O. The same applies to each of the acoustic wave resonators other than the series arm resonator S1.

[0273] In the filter device 60, the mass addition film 19 in the acoustic wave device 10 and the third mass addition film 69 of each acoustic wave resonator have different thicknesses. However, it is sufficient that at least one of the thickness and the material be different between the mass addition film 19 and the third mass addition film 69. This allows the acoustic wave device 10, which is an acoustically coupled filter, to satisfy both the conditions for suppressing unwanted waves in the passband and the conditions for suppressing unwanted waves in each acoustic wave resonator. Therefore, degradation of the filter characteristics of the filter device 60 can be effectively suppressed.

[0274] As described above, in this specification, the term "the thicknesses of the mass adding films are different from each other" means that the difference between the thickness of one mass adding film and the thickness of the other mass adding film is more than 5% of the thickness of both mass adding films. This also applies when comparing the thickness of the third mass adding film 69 and the thickness of the mass adding film 19.

[0275] When comparing the thickness of the third mass adding film 69 with the thickness of the other members, it is sufficient to compare the thickness of the portion that does not overlap in plan view with the third end electrode finger N or the fourth end electrode finger O. However, this does not apply when the entire third mass adding film 69 overlaps in plan view with the third end electrode finger N or the fourth end electrode finger O.

[0276] The elastic wave device 10 of the filter device 60 is the elastic wave device according to the first preferred embodiment. Therefore, as shown in FIG. 4 , the elastic wave device 10 can suppress unwanted waves within the passband. Below, we will demonstrate that the elastic wave resonator of this preferred embodiment can also suppress unwanted waves by comparing the elastic wave resonator of this preferred embodiment with the elastic wave resonator of a third comparative example. The elastic wave resonator of the third comparative example differs from the elastic wave resonator of this preferred embodiment in that it does not include the third mass-adding film 69.

[0277] 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 of the eighth embodiment are as follows. Note that the design parameters of the third comparative example were the same as those of the eighth embodiment, except for the third mass adding film 69. Hereinafter, the center-to-center distance between adjacent electrode fingers is referred to as the electrode finger pitch.

[0278] Piezoelectric layer: Material... LiNbO ３ , cut angle...120°Y, thickness 335 nm First and second electrode fingers: layer structure...Ti layer / AlCu layer from the piezoelectric layer side, thickness...10 nm / 400 nm from the piezoelectric layer side, width...0.8 μm Electrode finger pitch: 2.5 μm Intersection width: 40 μm Total number of first and second electrode fingers: 80 Number of third end electrode fingers and fourth end electrode fingers: 2 Third dielectric film: material...silicon oxide, thickness...130 nm Fourth dielectric film: material...silicon oxide, thickness...130 nm Third mass-addition film: material...silicon oxide, thickness...55 nm, dimension along the direction orthogonal to the electrode fingers...0.7 μm, overlap width...0.4 μm

[0279] 41 is a diagram illustrating admittance-frequency characteristics of elastic wave resonators according to the eighth preferred embodiment and the third comparative example, where an arrow Q indicates a resonant frequency.

[0280] 41 , it can be seen that in the third comparative example, a plurality of unwanted waves are generated on the lower frequency side than the resonance frequency. In the third comparative example, a plurality of unwanted waves are also generated on the higher frequency side than the resonance frequency. In contrast, in the elastic wave resonator according to the eighth embodiment, unwanted waves can be suppressed both on the lower frequency side and the higher frequency side than the resonance frequency.

[0281] Unwanted waves can be suppressed in each elastic wave resonator in filter device 60. Furthermore, unwanted waves within the passband can also be suppressed in elastic wave device 10, which is an acoustically coupled filter. Therefore, unwanted waves within the passband of filter device 60 can be effectively suppressed, and degradation of the filter characteristics can be effectively prevented.

[0282] A preferred configuration of the present invention will be described below using an example of an elastic wave resonator having an IDT electrode 64 as shown in Fig. 39 . In the following, this elastic wave resonator will be referred to as an elastic wave device of a reference example. Fig. 39 will be used to explain the configuration of the elastic wave device of the reference example.

[0283] The elastic wave device of the reference example utilizes thickness-shear mode bulk waves as the main mode. In this case, a portion where a pair of adjacent electrode fingers connected to different potentials functions as a single resonator. Therefore, the configuration of an elastic wave device utilizing thickness-shear mode bulk waves is equivalent to a configuration in which multiple resonators are connected in parallel. This is also true for acoustically coupled filters such as those of the first to seventh embodiments. Therefore, the following configuration of the elastic wave device of the reference example can be said to be a preferred configuration for the first to seventh embodiments as well.

[0284] In the present invention, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers, d / p is preferably 0.5 or less, and more preferably 0.24 or less. This allows thickness-shear mode bulk waves to be suitably excited and enables the elastic wave device to have a sufficiently large fractional bandwidth. The fractional bandwidth is expressed as (|fa-fr| / fr) x 100 [%], where fr is the resonant frequency and fa is the antiresonant frequency.

[0285] FIG. 42 is a graph showing the relationship between d / p and the fractional bandwidth of an elastic wave device according to a reference example.

[0286] As is clear from Figure 42, when d / p > 0.5, the fractional bandwidth is less than 5%. In contrast, when d / p ≤ 0.5, the fractional bandwidth can be increased to 5% or more. This increases the electromechanical coupling coefficient of the thickness-shear mode bulk wave. When d / p ≤ 0.24, the fractional bandwidth can be increased to 7% or more. This effectively increases the electromechanical coupling coefficient of the thickness-shear mode bulk wave.

[0287] When the metallization ratio of the electrode fingers to the excitation region C is MR, it is preferable to satisfy MR≦1.75(d / p)+0.075. In this case, the value of the fractional bandwidth of the acoustic wave device does not become too large, and spurious emissions between the resonant frequency and the antiresonant frequency can be suppressed. Details of this are described below.

[0288] In this specification, the metallization ratio MR of the electrode fingers to the excitation region C is the proportion of the portion of the piezoelectric layer 4 that is covered with the metal constituting the electrode fingers in the excitation region C in a plan view. In a reference example shown with reference to Fig. 39 , the metallization ratio MR is the ratio of the area of ​​the first electrode fingers 15C and the second electrode fingers 16C in the excitation region C to the area of ​​the excitation region C in a plan view. On the other hand, in the first embodiment of the present invention shown in Fig. 2 and the like, the metallization ratio MR is the ratio of the area of ​​the first electrode fingers 15 and the third electrode fingers 17 and the ratio of the area of ​​the second electrode fingers 16 and the third electrode fingers 17 to the excitation region C.

[0289] In addition, when the width of the electrode fingers located within the excitation region C is constant, the metallization ratio MR can also be calculated by dividing the sum of the widths of the electrode fingers located within the excitation region C by the dimension of the excitation region C along the direction perpendicular to the electrode fingers.

[0290] Fig. 43 is a diagram showing the relationship between the relative bandwidth and the normalized magnitude of spurious signals in the elastic wave device of the reference example. Fig. 43 shows the results of measuring the amount of phase rotation of spurious signals each time the relative bandwidth is changed by changing the thickness of the piezoelectric layer and the dimensions of the electrode fingers. Note that the normalized magnitude of spurious signals in Fig. 43 is specifically the value obtained by normalizing the amount of phase rotation of the spurious impedance by 180°. The results shown in Fig. 43 are for a Z-cut LiNbO ３ Although this is the result when a piezoelectric layer made of this material was used, the same tendency is observed when a piezoelectric layer having another cut angle is used.

[0291] In the region surrounded by the ellipse R in Figure 43, the normalized magnitude of the spurious response between the resonant frequency and the anti-resonant frequency is 1.0. If the bandwidth fraction of the elastic wave resonator exceeds 17%, the normalized magnitude of the spurious response may be 1.0 or more. For this reason, it is preferable that the bandwidth fraction be 17% or less. This makes it possible to suppress the spurious response between the resonant frequency and the anti-resonant frequency.

[0292] 44 is a diagram showing the relationship between d / p, metallization ratio MR, and bandwidth fraction, in which the bandwidth fraction is calculated for each of different d / p and metallization ratio MR.

[0293] In FIG. 44 , the hatched portion is the region where the fractional bandwidth is 17% or less. The boundary between this hatched region and the non-hatched region is roughly represented by dashed line T. Dashed line T is represented by MR = 1.75(d / p) + 0.075. When MR≦1.75(d / p) + 0.075, it is easy to keep the fractional bandwidth at 17% or less in the reference example, and it is easy to suppress spurious signals. For this reason, in the present invention, it is preferable that MR≦1.75(d / p) + 0.075. This makes it easy to suppress spurious signals.

[0294] On the other hand, the dashed-dotted line T1 in Figure 44 indicates the boundary where the slope of the change in metallization ratio MR with respect to the change in d / p is the same as that of the dashed line T, and where the fractional bandwidth is 17% or less over the entire range. The dashed-dotted line T1 is represented by MR = 1.75(d / p) + 0.05. When MR ≤ 1.75(d / p) + 0.05, the fractional bandwidth can be more reliably kept to 17% or less, and spurious emissions can be more reliably suppressed. For this reason, in the present invention, it is more preferable that MR ≤ 1.75(d / p) + 0.075. This more reliably suppresses spurious emissions.

[0295] Here, the relationship between the bandwidth fraction of elastic wave device 10 and the Euler angles (φ, θ, ψ) of piezoelectric layer 4 when d / p is set as close to 0 as possible in the configuration of the first preferred embodiment was derived. Note that φ in the Euler angles was set to 0°.

[0296] FIG. 45 shows the LiNbO ３ 45 is a diagram showing a map of fractional bandwidths with respect to Euler angles (0°, θ, ψ) of the frequency domain. The hatched area in FIG. 45 is a region where a fractional bandwidth of at least 5% or more can be obtained, and the range of this region can be approximated to the ranges expressed by the following formulas (1), (2), and (3).

[0297] (within the range of 0°±10°, 0° to 25°, any ψ) ... Equation (1) (within the range of 0°±10°, 25° to 100°, 0° to 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)

[0298] In the present invention, the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer are preferably within the range of the above formula (1), formula (2), or formula (3). This allows the relative bandwidth of the acoustic wave device to be sufficiently wide. The same applies when the piezoelectric layer is made of lithium tantalate.

[0299] The following describes examples of acoustic wave devices and filter devices according to the present invention.

[0300] <1> A piezoelectric element comprising: a piezoelectric layer having a first principal surface and a second principal surface opposed to each other; a support member laminated on the piezoelectric layer; a functional electrode provided on the first principal surface of the piezoelectric layer, the functional electrode including a first comb electrode, a second comb electrode, and a third electrode; and a dielectric film provided on at least one of the first principal surface side and the second principal surface side of the piezoelectric layer and overlapping the functional electrode in a planar view, wherein the first comb electrode has a first bus bar and a plurality of first electrode fingers, one end of each of which is connected to the first bus bar; the comb electrode has a second bus bar and a plurality of second electrode fingers, one end of which is connected to the second bus bar and which are interdigitated 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, and the third electrode has a plurality of third electrode fingers respectively provided on the first main surface of the piezoelectric layer so as to be aligned with the first electrode fingers and the second electrode fingers in a direction in which the first electrode fingers and the second electrode fingers are aligned, a connection electrode connecting the plurality of third electrode fingers to each other, the third electrode being connected to a potential different from that of the first comb electrode and the second comb electrode, the order in which the plurality of electrode fingers including the first electrode finger, the second electrode finger, and the third electrode finger are arranged is an order in which, starting from the first electrode finger, the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger form one period, and sound waves are provided on the support member at positions overlapping with the plurality of first electrode fingers, the plurality of second electrode fingers, and the plurality of third electrode fingers in a plan view. a mass-adding film provided on the functional electrode, the mass-adding film being arranged at a position overlapping with a first end electrode finger in a plan view, the mass-adding film being arranged at a position overlapping with the ...Elastic wave device.

[0301] <2> The elastic wave device described in <1>, wherein, among the plurality of electrode fingers of the functional electrode, at least one electrode finger located at one end in the direction in which the plurality of electrode fingers are arranged is the first end electrode finger, and at least one electrode finger located at the other end is the second end electrode finger, and the mass-adding film overlaps with both the first end electrode finger and the second end electrode finger in a planar view.

[0302] <3> The acoustic wave device according to <2>, wherein the number of the first end electrode fingers and the number of the second end electrode fingers are each two.

[0303] <4> The elastic wave device according to any one of <1> to <3>, wherein the first end electrode finger has a first surface and a second surface that are opposed to each other in a thickness direction, and a first side surface and a second side surface that connect the first surface and the second surface and that are opposed to each other in a direction perpendicular to an extension direction of the plurality of electrode fingers of the functional electrode, the first side surface of the first end electrode finger is located outward from the second side surface 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 addition film in a planar view, and the second side surface does not overlap with the mass addition film in a planar view.

[0304] <5> An elastic wave device described in any one of <1> to <4>, wherein the dielectric film is provided on the first main surface of the piezoelectric layer so as to cover the functional electrode, and the mass-adding film is provided on the dielectric film.

[0305] <6> The elastic wave device according to any one of <1> to <4>, wherein the mass-adding film is located between the first end electrode finger and the first main surface of the piezoelectric layer.

[0306] <7> The elastic wave device according to any one of <1> to <6>, wherein the mass-adding film is provided on both the first principal surface side and the second principal surface side of the piezoelectric layer.

[0307] <8> The elastic wave device described in <7>, wherein the thickness of the mass-adding film provided on the first main surface side of the piezoelectric layer is thicker than the thickness of the mass-adding film provided on the second main surface side of the piezoelectric layer.

[0308] <9> The elastic wave device described in <7> or <8>, wherein the material of the mass-adding film provided on the first main surface side of the piezoelectric layer is different from the material of the mass-adding film provided on the second main surface side of the piezoelectric layer.

[0309] <10> The acoustic wave device according to any one of <1> to <9>, wherein the mass-adding film and the dielectric film are made of different materials.

[0310] <11> The elastic wave device according to any one of <1> to <9>, wherein the type of material of the mass-adding film is the same as the type of material of the dielectric film, and the density of the mass-adding film is lower than the density of the dielectric film.

[0311] <12> The acoustic wave device according to any one of <1> to <11>, wherein the material of the mass-adding film is 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.

[0312] <13> The acoustic wave device according to any one of <1> to <12>, wherein the dielectric film is made of silicon oxide.

[0313] <14> The elastic wave device according to any one of <1> to <13>, wherein the functional electrode is a first functional electrode, and further includes a second functional electrode provided on the second main surface of the piezoelectric layer, the second functional electrode having 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 of the first functional electrode, and the first functional electrode and the second functional electrode are opposed to each other with the piezoelectric layer sandwiched therebetween.

[0314] <15> The elastic wave device described in <14>, wherein the dielectric film is provided on the second main surface of the piezoelectric layer so as to cover the second functional electrode, and the mass-adding film is provided on the dielectric film.

[0315] <16> The elastic wave device according to any one of <1> to <15>, wherein the dielectric film includes a first dielectric film provided on the first main surface side of the piezoelectric layer and a second dielectric film provided on the second main surface side, and the difference between the thickness of the first dielectric film and the thickness of the second dielectric film is 10% or less with respect to both the thickness of the first dielectric film and the thickness of the second dielectric film.

[0316] <17> The mass addition film is a first mass addition film, and is located at one end of the plurality of electrode fingers of the functional electrode in a direction in which the plurality of electrode fingers are arranged, at least one electrode finger is the first end electrode finger and is located at the other end, and at least one electrode finger is a second end electrode finger, the first mass addition film includes at least one pair of the first mass addition films overlapping the first end electrode finger and the second end electrode finger in a plan view, the direction in which the plurality of electrode fingers of the functional electrode extend is an electrode finger extension direction, and a direction perpendicular to the electrode finger extension direction is an electrode finger perpendicular direction, and a region in which the adjacent first electrode finger and the second electrode finger overlap when viewed from the electrode finger perpendicular direction is an intersection region, and the intersection region is a region in which tips of the plurality of second electrode fingers are located, and the intersection region is a region in which tips of the plurality of second electrode fingers are located, the region including first edge regions extending in the electrode finger perpendicular direction, and the plurality of first a second edge region in which tips of the electrode fingers are located and extending in a direction perpendicular to the electrode fingers; a first gap region is a region between the first bus bar and the connection electrode, where the tips of the second electrode fingers face each other across a gap in the electrode finger extension direction, and the crossing region; a second gap region is a region between the second bus bar and the connection electrode, where the tips of the first electrode fingers face each other across a gap in the electrode finger extension direction, and the crossing region; and a pair of second mass-adding films provided 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, wherein one pair of first mass-adding films is connected to both of the pair of second mass-adding films.

[0317] <18> The mass addition film is a first mass addition film, and is located at one end of the plurality of electrode fingers of the functional electrode in a direction in which the plurality of electrode fingers are arranged, at least one electrode finger is the first end electrode finger and is located at the other end, and at least one electrode finger is a second end electrode finger, the first mass addition film includes at least one pair of first mass addition films overlapping the first end electrode finger and the second end electrode finger in a plan view, the direction in which the plurality of electrode fingers of the functional electrode extend is an electrode finger extension direction, and a direction perpendicular to the electrode finger extension direction is an electrode finger perpendicular direction, and a region where adjacent first electrode fingers and second electrode fingers overlap when viewed from the electrode finger perpendicular direction is an intersection region, and the intersection region is a region in which tips of the plurality of second electrode fingers are located, and extends in the electrode finger perpendicular direction, a second edge region in which tips of the electrode fingers are located and extending in a direction perpendicular to the electrode fingers; a first gap region is a region between the first bus bar and the connection electrode, where the tips of the second electrode fingers face each other across a gap in the electrode finger extension direction, and the crossing region; a second gap region is a region between the second bus bar and the connection electrode, where the tips of the first electrode fingers face each other across a gap in the electrode finger extension direction, and the crossing region; and a pair of second mass-adding films provided 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, wherein one of the pair of first mass-adding films is connected to one of the pair of second mass-adding films.

[0318] <19> The elastic wave device according to any one of <1> to <18>, wherein the piezoelectric layer is made of lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3): (within a range of 0°±10°, 0° to 25°, any ψ) ... formula (1) (within a range of 0°±10°, 25° to 100°, 0° to 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)

[0319] <20> A filter device comprising: the elastic wave device according to any one of <1> to <19>; and an elastic wave resonator electrically connected to the elastic wave device, wherein the mass-adding film of the elastic wave device is a first mass-adding film; the elastic wave resonator has a piezoelectric layer, an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, and a third mass-adding film; when at least one electrode finger of the plurality of electrode fingers of the IDT electrode located at one end in a direction in which the plurality of electrode fingers are arranged is defined as a third end electrode finger, the third mass-adding film is provided at a position overlapping the third end electrode finger in a planar view; and at least one of the thickness and the material of the first mass-adding film and the third mass-adding film is different from each other.

[0320] REFERENCE SIGNS LIST 1, 1A, 1B...functional electrodes 1a, 1b...first and second surfaces 1c, 1d...first and second side surfaces 1e, 1f...stepped portion 2...piezoelectric substrate 3...support member 4...piezoelectric layer 4a, 4b...first and second main surfaces 5...insulating layer 6...support substrate 7, 7B, 7C...first interdigital electrode 8, 8B, 8C...second interdigital electrode 9, 9A, 9B...third electrode 10...acoustic wave device 10a...cavity 11...insulating layer 12-14...first to third bus bars 14A, 14B...connecting electrodes 14a...common electrode portion 14b...connecting electrode fingers 14c...bar portion 15, 15B, 15C...first electrode fingers 16, 16B, 16C...second electrode fingers 17...Third electrode finger 18A, 18B...First and second dielectric films 19, 19B...Mass adding film 19d...End surface 21A, 21B...First and second functional electrodes 27, 28...First and second interdigital electrodes 29...Third electrode 35-37...First to third electrode fingers 49A, 49B...First and second mass adding films 53...Support member 55a-55c...Low acoustic impedance layers 56a, 56b...High acoustic impedance layers 58...Acoustic reflecting film 60...Filter device 62...Input terminal 63...Output terminal 64...IDT electrode 64a, 64b...Third and fourth surfaces 64c, 64d...Third and fourth side surfaces 68A, 68B...Third and fourth dielectric films 69...Third mass adding film A, A1, A2...first end electrode finger B, B1, B2...second end electrode finger C...excitation region D...band E1, E2...first and second edge regions F...crossing region G1, G2...first and second gap regions M...central region N, O...third and fourth end electrode fingers P1, P2...parallel arm resonators S1, S2...series arm resonators

Claims

1. A piezoelectric element comprising: a piezoelectric layer having a first main surface and a second main surface opposing each other; a support member laminated on the piezoelectric layer; a functional electrode provided on the first main surface of the piezoelectric layer, the functional electrode having a first comb electrode, a second comb electrode, and a third electrode; and a dielectric film provided on at least one of the first main surface side and the second main surface side of the piezoelectric layer and overlapping the functional electrode in a planar view; wherein the first comb electrode has a first bus bar and a plurality of first electrode fingers, one end of which is connected to the first bus bar; the second comb electrode has a second bus bar and a plurality of second electrode fingers, one end of which is connected to the second bus bar and interdigitated 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 provided on the first main surface of the piezoelectric layer so as to be aligned with the first electrode fingers and the second electrode fingers in a direction in which the first electrode fingers and the second electrode fingers are aligned, and a connection electrode connecting the plurality of third electrode fingers to each other, the third electrode being connected to a potential different from that of the first comb-shaped electrode and the second comb-shaped electrode; the order in which the plurality of electrode fingers including the first electrode finger, the second electrode finger, and the third electrode finger are aligned is an order in which, starting from the first electrode finger, the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger form one period; and an acoustic reflecting portion is formed on the support member at a position overlapping with the plurality of first electrode fingers, the plurality of second electrode fingers, and the plurality of third electrode fingers in a plan view; the longest distance among the center-to-center distance between the adjacent first electrode finger and the adjacent third electrode finger and the center-to-center distance between the adjacent second electrode finger and the adjacent third electrode finger is denoted by p, and the thickness of the piezoelectric layer is denoted by d, d / p is 0.5 or less;an elastic wave device further comprising: a mass-adding film that is provided in a position that overlaps with a first end electrode finger in a planar view when at least one electrode finger of the plurality of electrode fingers of the functional electrode that is located at one end in a direction in which the plurality of electrode fingers are arranged is defined as a first end electrode finger.

2. The elastic wave device according to claim 1, wherein, of the plurality of electrode fingers of the functional electrode, at least one electrode finger located at one end in the direction in which the plurality of electrode fingers are arranged is the first end electrode finger, and at least one electrode finger located at the other end is a second end electrode finger, and the mass-adding film overlaps with both the first end electrode finger and the second end electrode finger in a planar view.

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

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 that are opposed to each other in a direction perpendicular to the extension direction of the plurality of electrode fingers of the functional electrode, wherein the first side surface of the first end electrode finger is located outward from the second side surface in the direction in which the plurality of electrode fingers of the functional electrode are arranged, and wherein the first surface, the second surface, and the first side surface of the first end electrode finger overlap with the mass addition film in a planar view, and the second side surface does not overlap with the mass addition film in a planar view.

5. An elastic wave device according to any one of claims 1 to 4, wherein the dielectric film is provided on the first main surface of the piezoelectric layer so as to cover the functional electrode, and the mass-adding film is provided on the dielectric film.

6. The acoustic wave device according to any one of claims 1 to 4, wherein the mass-adding 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-adding film is provided on both the first principal surface side and the second principal surface side of the piezoelectric layer.

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

9. An elastic wave device as described in claim 7 or 8, wherein the material of the mass-adding film provided on the first main surface side of the piezoelectric layer is different from the material of the mass-adding film provided on the second main surface side of the piezoelectric layer.

10. The acoustic wave device according to any one of claims 1 to 9, wherein the mass-adding film and the dielectric film are made of different materials.

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

12. The acoustic wave device according to any one of claims 1 to 11, wherein the material of the mass-addition film is 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.

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

14. The elastic wave device according to any one of claims 1 to 13, wherein the functional electrode is a first functional electrode, and further comprises a second functional electrode provided on the second main surface of the piezoelectric layer, the second functional electrode having 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 of the first functional electrode, and the first functional electrode and the second functional electrode face each other with the piezoelectric layer sandwiched therebetween.

15. The elastic wave device according to claim 14, wherein the dielectric film is provided on the second main surface of the piezoelectric layer so as to cover the second functional electrode, and the mass-adding film is provided 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 provided on the first main surface side of the piezoelectric layer and a second dielectric film provided on the second main surface side, and the difference between the thickness of the first dielectric film and the thickness of the second dielectric film is 10% or less of both the thickness of the first dielectric film and the thickness of the second dielectric film.

17. The mass-adding film is a first mass-adding film, and when at least one electrode finger of the plurality of electrode fingers of the functional electrode located at one end in a direction in which the plurality of electrode fingers are arranged is the first end electrode finger and at least one electrode finger located at the other end is a second end electrode finger, the first mass-adding film includes at least one pair of first mass-adding films overlapping with the first end electrode finger and the second end electrode finger in a plan view, the direction in which the plurality of electrode fingers of the functional electrode extend is defined as an electrode finger extension direction, a direction perpendicular to the electrode finger extension direction is defined as an electrode finger perpendicular direction, and a region in which the adjacent first electrode finger and second electrode finger overlap when viewed from the electrode finger perpendicular direction is a crossing region, the intersection region has a first edge region in which tips of the plurality of second electrode fingers are located and extending in the direction perpendicular to the electrode fingers, and a second edge region in which tips of the plurality of first electrode fingers are located and extending in the direction perpendicular to the electrode fingers, a first gap region is a region between the first bus bar and the connection electrode, which electrodes are opposed to each other across a gap in the electrode finger extension direction by the tips of the plurality of second electrode fingers, and the intersection region, and a second gap region is a region between the second bus bar and the connection electrode, which electrodes are opposed to each other across a gap in the electrode finger extension direction by the tips of the plurality of first electrode fingers, and the intersection region, and the electronic device further comprises a pair of second mass-adding films provided 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 acoustic wave device according to claim 1, wherein each of the pair of first mass addition films is connected to both of the pair of second mass addition films.

18. The mass addition film is a first mass addition film, and when at least one electrode finger of the plurality of electrode fingers of the functional electrode located at one end in a direction in which the plurality of electrode fingers are arranged is the first end electrode finger and at least one electrode finger located at the other end is a second end electrode finger, the first mass addition film includes at least one pair of the first mass addition films overlapping with the first end electrode finger and the second end electrode finger in a plan view, the direction in which the plurality of electrode fingers of the functional electrode extend is defined as an electrode finger extension direction, a direction perpendicular to the electrode finger extension direction is defined as an electrode finger perpendicular direction, and a region in which the adjacent first electrode finger and second electrode finger overlap when viewed from the electrode finger perpendicular direction is a crossing region, the intersection region has a first edge region in which tips of the plurality of second electrode fingers are located and extending in the direction perpendicular to the electrode fingers, and a second edge region in which tips of the plurality of first electrode fingers are located and extending in the direction perpendicular to the electrode fingers, a first gap region is a region between the first bus bar and the connection electrode, which electrodes are opposed to each other across a gap in the electrode finger extension direction by the tips of the plurality of second electrode fingers, and the intersection region, and a second gap region is a region between the second bus bar and the connection electrode, which electrodes are opposed to each other across a gap in the electrode finger extension direction by the tips of the plurality of first electrode fingers, and the intersection region, and the electronic device further comprises a pair of second mass-adding films provided 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 acoustic wave device according to claim 1, wherein one of the pair of first mass addition films is connected to one of the pair of second mass addition films.

19. The acoustic wave device according to any one of claims 1 to 18, wherein the piezoelectric layer is made of lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3): (within a range of 0°±10°, 0° to 25°, any ψ) ... formula (1) (within a range of 0°±10°, 25° to 100°, 0° to 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: an elastic wave device according to any one of claims 1 to 19; and an elastic wave resonator electrically connected to the elastic wave device, wherein the mass addition film of the elastic wave device is a first mass addition film; the elastic wave resonator has a piezoelectric layer, an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, and a third mass addition film; wherein, when at least one electrode finger of the plurality of electrode fingers of the IDT electrode located at one end in a direction in which the plurality of electrode fingers are arranged is defined as a third end electrode finger, the third mass addition film is provided at a position overlapping the third end electrode finger in a plan view; and at least one of the thickness and material is different between the first mass addition film and the third mass addition film.

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