Elastic wave device

Abstract

In the present invention, when a direction orthogonal to a direction in which a plurality of electrode fingers extend is defined as an electrode finger orthogonal direction, a pair of electrode fingers located at both ends in the electrode finger orthogonal direction among the plurality of electrode fingers are a pair of end electrode fingers A, and the width of the end electrode fingers A is narrower than the average value of the widths of the plurality of electrode fingers other than the pair of end electrode fingers A. In plan view, regions respectively including the pair of end electrode fingers A are a pair of end regions B. The value of the dimension of the end region B along the electrode finger orthogonal direction is the same as the average value of the widths of the plurality of electrode fingers other than the pair of end electrode fingers A. When a direction toward the center side of an IDT electrode 8 in the electrode finger orthogonal direction is defined as an inner side and a direction toward the outer side of the IDT electrode 8 in the electrode finger orthogonal direction is defined as an outer side, the respective inner-side end edges of the end region B and the end electrode finger A overlap in plan view. A cutout 6c is provided in a piezoelectric layer 6 in a portion of the end region B overlapping the outer side of the end electrode finger A in plan view.

Description

Elastic Wave Device

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

[0002] Acoustic wave devices have been widely used in filters for mobile phones and the like. Recently, an acoustic wave device using bulk waves in thickness shear mode has been proposed, as described in Patent Document 1 below. In this acoustic wave device, a piezoelectric layer is provided on a support. A functional electrode and a dielectric layer are provided on one main surface of the piezoelectric layer. The functional electrode is embedded in the dielectric layer. A dielectric layer is also provided on the other main surface of the piezoelectric layer.

[0003] The functional electrodes include a pair of electrodes that face each other on the piezoelectric layer and are connected to different potentials, and a thickness-shear mode bulk wave is excited by applying an AC voltage between the electrodes.

[0004] U.S. Pat. No. 1,349,450

[0005] However, the acoustic wave device described in Patent Document 1 may not be able to sufficiently reduce loss.

[0006] An object of the present invention is to provide an acoustic wave device that can reduce loss.

[0007] An elastic wave device according to the present invention comprises a piezoelectric substrate including a piezoelectric layer having first and second principal surfaces opposed to each other, and an IDT electrode provided on the first principal surface of the piezoelectric layer and having a plurality of electrode fingers, wherein, when a direction orthogonal to a direction in which the plurality of electrode fingers extend is defined as an electrode finger orthogonal direction, a pair of the electrode fingers located at both ends in the electrode finger orthogonal direction among the plurality of electrode fingers is a pair of end electrode fingers, the width of at least one of the end electrode fingers is narrower than the average width of the plurality of electrode fingers other than the pair of end electrode fingers, and a region including the pair of end electrode fingers in a plan view The regions are a pair of end regions, and the dimension of the end regions along the electrode finger orthogonal direction is the same as the average width of the plurality of electrode fingers other than the pair of end electrode fingers. When the direction toward the center of the IDT electrode in the electrode finger orthogonal direction is defined as the inside and the direction toward the outside of the IDT electrode in the electrode finger orthogonal direction is defined as the outside, the inner edge portions of the end region and the end electrode finger overlap in a planar view. A cutout portion is provided in the piezoelectric layer in at least one of the end regions, at least in the portion that overlaps with the outside of the end electrode finger in a planar view.

[0008] According to an acoustic wave device according to a preferred embodiment of the present invention, loss can be reduced.

[0009] FIG. 1 is a schematic cross-sectional front 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 cross-sectional view taken along line II-II in FIG. 2 . FIG. 4 is a schematic cross-sectional front view of an elastic wave device according to a first comparative example. FIG. 5 is a graph showing admittance-frequency characteristics for the first preferred embodiment of the present invention and the first comparative example. FIG. 6 is a graph showing the relationship between the position of the IDT electrode in the direction perpendicular to the electrode fingers and the displacement near the resonance frequency for the first comparative example. FIG. 7 is a graph showing the relationship between the position of the IDT electrode in the direction perpendicular to the electrode fingers and the displacement near the resonance frequency for the first preferred embodiment of the present invention. FIGS. 8( a) to 8(d) are schematic cross-sectional front views illustrating an example of a manufacturing method for an elastic wave device according to the first preferred embodiment of the present invention, up to the step of providing an insulating layer. FIGS. 9( a) to 9(e) are schematic cross-sectional front views illustrating an example of a manufacturing method for an elastic wave device according to the first preferred embodiment of the present invention, up to the step of providing a cutout portion in the piezoelectric layer. FIG. 10 is a schematic front cross-sectional view showing the vicinity of multiple electrode fingers in the second embodiment of the present invention. FIG. 11 is a schematic front cross-sectional view showing the vicinity of one end electrode finger in the second embodiment of the present invention. FIG. 12 is a graph showing admittance-frequency characteristics in the second embodiment of the present invention when the outer side surface inclination angle is 70° and in a first comparative example. FIG. 13 is a graph showing admittance-frequency characteristics in the second embodiment of the present invention when the outer side surface inclination angle is 80° and in a first comparative example. FIG. 14 is a schematic front cross-sectional view showing the vicinity of multiple electrode fingers in a modified version of the second embodiment of the present invention. FIG. 15 is a graph showing admittance-frequency characteristics in the modified version of the second embodiment of the present invention when the outer side surface inclination angle is 100° and in a first comparative example. FIG. 16 is a graph showing admittance-frequency characteristics in the modified version of the second embodiment of the present invention when the outer side surface inclination angle is 110° and in a first comparative example. FIG. 17 is a schematic front cross-sectional view showing the vicinity of multiple electrode fingers in the third embodiment of the present invention. FIG. 18 is a graph showing admittance-frequency characteristics in the third embodiment of the present invention and in a first comparative example.FIG. 19 is a schematic front cross-sectional view showing the vicinity of one end electrode finger in the fourth preferred embodiment of the present invention. FIG. 20 is a graph showing admittance-frequency characteristics in the fourth preferred embodiment of the present invention and the first comparative example. FIG. 21 is a schematic plan view of an elastic wave device according to a fifth preferred embodiment of the present invention. FIG. 22 is a schematic front cross-sectional view showing the vicinity of multiple electrode fingers in the sixth preferred embodiment of the present invention. FIG. 23 is a graph showing admittance-frequency characteristics in the sixth preferred embodiment of the present invention and the second comparative example. FIG. 24 is a schematic front cross-sectional view showing the vicinity of one end electrode finger in the seventh preferred embodiment of the present invention. FIG. 25 is a schematic front cross-sectional view of an elastic wave device according to a third comparative example. FIG. 26 is a graph showing admittance-frequency characteristics in the seventh preferred embodiment of the present invention, the first comparative example, and the third comparative example. FIG. 27 is a schematic front cross-sectional view showing the vicinity of one end electrode finger in the eighth preferred embodiment of the present invention. FIG. 28 is a graph showing admittance-frequency characteristics in the eighth preferred embodiment of the present invention and the first comparative example. FIG. 29 is a schematic front cross-sectional view of an elastic wave device according to a ninth preferred embodiment of the present invention. Fig. 30 is a diagram showing the relationship between d / p and the fractional bandwidth of an elastic wave resonator. Fig. 31 is a diagram showing the relationship between the fractional bandwidth of an elastic wave resonator and the magnitude of normalized spurious. Fig. 32 is a diagram showing the relationship between d / p, the metallization ratio MR, and the fractional bandwidth. Fig. 33 is a diagram showing 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.

[0013] The acoustic wave device 1 includes a piezoelectric substrate 2, an IDT electrode 8, and a first dielectric film 7A. The piezoelectric substrate 2 is a substrate having piezoelectric properties. Specifically, the piezoelectric substrate 2 includes a support member 3, a piezoelectric layer 6, and a second dielectric film 7B. In this embodiment, the support member 3 includes a support substrate 4 and an insulating layer 5. The insulating layer 5 is provided on the support substrate 4. However, the support member 3 may be composed of only the support substrate 4.

[0014] A second dielectric film 7B is provided on the support member 3. A piezoelectric layer 6 is provided on the second dielectric film 7B. That is, the piezoelectric layer 6 is indirectly provided on the support member 3 via the second dielectric film 7B. This constitutes the piezoelectric substrate 2. A first dielectric film 7A is provided on the piezoelectric layer 6 of the piezoelectric substrate 2. However, the support member 3 and the second dielectric film 7B do not necessarily have to be provided. The piezoelectric substrate 2 may also be a substrate consisting of only the piezoelectric layer 6. The first dielectric film 7A does not necessarily have to be provided.

[0015] The piezoelectric layer 6 has a first main surface 6a and a second main surface 6b. The first main surface 6a and the second main surface 6b face each other. Of the first main surface 6a and the second main surface 6b, the second main surface 6b is located on the support member 3 side. Therefore, specifically, the first dielectric film 7A is provided on the first main surface 6a of the piezoelectric layer 6. On the other hand, the second dielectric film 7B is provided on the second main surface 6b of the piezoelectric layer 6.

[0016] The material of the support substrate 4 can be, for example, a semiconductor such as silicon, or a ceramic such as aluminum oxide. The material of the insulating layer 5 can be an appropriate dielectric such as silicon oxide or tantalum oxide.

[0017] In this embodiment, the piezoelectric layer 6 is made of 120° Y-cut LiNbO ３ The cut angle and material of the piezoelectric layer 6 are not limited to those described above. The piezoelectric layer 6 may be made of, for example, lithium niobate other than those described above, or LiTaO ３In this specification, a component made of a material includes a component containing a trace amount of impurities that does not significantly degrade the electrical characteristics of the acoustic wave device.

[0018] In this embodiment, silicon oxide is used as the material for the first dielectric film 7A and the second dielectric film 7B. However, the materials for the first dielectric film 7A and the second dielectric film 7B are not limited to the above. For example, silicon nitride or silicon oxynitride may also be used as the material for the first dielectric film 7A and the second dielectric film 7B. The materials for the first dielectric film 7A and the second dielectric film 7B may be different from each other.

[0019] An IDT electrode 8 is provided on the first main surface 6a of the piezoelectric layer 6. The first dielectric film 7A is provided on the first main surface 6a so as to cover the IDT electrode 8.

[0020] The elastic wave device 1 of this preferred embodiment is an elastic wave resonator configured to utilize a thickness-shear bulk wave as the main mode. However, the elastic wave device of the present invention may also be a filter device or a multiplexer having multiple elastic wave resonators.

[0021] 2 is a schematic plan view of the elastic wave device according to the first preferred embodiment. The first dielectric film 7A is omitted from FIG. 2. FIG. 1 is a schematic cross-sectional view taken along line II in FIG. 2.

[0022] The IDT electrode 8 has a pair of bus bars and a plurality of electrode fingers. The pair of bus bars is specifically a first bus bar 16 and a second bus bar 17. The first bus bar 16 and the second bus bar 17 face each other. The plurality of electrode fingers is specifically a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One end of each first electrode finger 18 is connected to the first bus bar 16. The other end of each first electrode finger 18 faces the second bus bar 17 across a gap. One end of each second electrode finger 19 is connected to the second bus bar 17. The other end of each second electrode finger 19 faces the first bus bar 16 across a gap. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interdigitated with each other. The first electrode fingers 18 and the second electrode fingers 19 are connected to different potentials.

[0023] The IDT electrode 8 is made of a laminated metal film. Specifically, in the IDT electrode 8, a Ti layer, an AlCu layer, a Ti layer, and an AlCu layer are laminated in this order from the piezoelectric layer 6 side. Note that the material of the IDT electrode 8 is not limited to the above. Alternatively, the IDT electrode 8 may be made of a single-layer metal film.

[0024] Hereinafter, the first electrode fingers 18 and the second electrode fingers 19 may be collectively referred to simply as electrode fingers. The first bus bar 16 and the second bus bar 17 may be collectively referred to simply as bus bars. The direction in which the multiple electrode fingers extend is referred to as the electrode finger extension direction, and the direction perpendicular to the electrode finger extension direction is referred to as the electrode finger orthogonal direction. In this specification, the electrode finger extension direction and the electrode finger orthogonal direction are also used for members other than the IDT electrode 8. In this specification, unless otherwise specified, the direction toward the center of the IDT electrode 8 in the electrode finger orthogonal direction is referred to as the inward direction, and the direction toward the outside of the IDT electrode 8 in the electrode finger orthogonal direction is referred to as the outward direction.

[0025] Of the multiple electrode fingers, the electrode fingers located at both ends in the direction perpendicular to the electrode fingers are end electrode fingers A. In this embodiment, one end electrode finger A is a first electrode finger 18, and the other end electrode finger A is a second electrode finger 19. Note that both end electrode fingers A may be first electrode fingers 18, or both end electrode fingers A may be second electrode fingers 19.

[0026] FIG. 3 is a schematic cross-sectional view taken along line II-II in FIG.

[0027] Each electrode finger of the IDT electrode 8 has a first surface 8a, a second surface 8b, and a side surface 8c. The first surface 8a and the second surface 8b face each other in the thickness direction. The side surface 8c connects the first surface 8a and the second surface 8b. In this embodiment, in the electrode fingers other than the pair of end electrode fingers A, both the inner and outer side surfaces 8c extend at an angle with respect to the normal direction to the second surface 8b. The inner side surface 8c of each end electrode finger A also extends at an angle with respect to the normal direction to the second surface 8b. Meanwhile, the outer side surface 8c of each end electrode finger A extends parallel to the normal direction to the second surface 8b. However, all the side surfaces 8c of all the electrode fingers may extend at an angle with respect to the normal direction to the second surface 8b, or may extend parallel to the normal direction to the second surface 8b.

[0028] The width of each pair of end electrode fingers A is narrower than the average width of the electrode fingers other than the pair of end electrode fingers A. The width of the electrode fingers is the dimension of the electrode fingers in the direction perpendicular to the electrode fingers. More specifically, in this specification, the width of the electrode fingers is the dimension of the electrode fingers in the direction perpendicular to the electrode fingers on the second surface 8 b. In this embodiment, the width of the electrode fingers other than the pair of end electrode fingers A is constant. When the width of the electrode fingers other than the pair of end electrode fingers A is w, the width of each of the pair of end electrode fingers A is 0.5w. However, it is sufficient that the width of at least one of the end electrode fingers A is narrower than the average width of the electrode fingers other than the pair of end electrode fingers A.

[0029] In this embodiment, the thickness of the first dielectric film 7A is greater than the thickness of the plurality of electrode fingers in the IDT electrode 8. Similarly, the thickness of the second dielectric film 7B is greater than the thickness of the plurality of electrode fingers in the IDT electrode 8.

[0030] The thickness of the first dielectric film 7A is the thickness of the portion of the first dielectric film 7A located between the electrode fingers. More specifically, the thickness of the first dielectric film 7A is the distance from the surface of the portion located on the piezoelectric layer 6 side to the surface opposite to the surface. The thickness of the second dielectric film 7B is the distance from the surface of the second dielectric film 7B located on the piezoelectric layer 6 side to the surface opposite to the surface.

[0031] In the present invention, a plurality of regions are defined. As shown in Fig. 2 , when viewed from the electrode finger orthogonal direction, the region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap is the intersection region F. The intersection region F includes a plurality of excitation regions C. More specifically, the excitation region C is the region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap in the electrode finger orthogonal direction and is the region between the centers of the adjacent first electrode fingers 18 and second electrode fingers 19. Note that Fig. 2 shows only two of the plurality of excitation regions C.

[0032] The elastic wave device 1 is an elastic wave resonator configured to utilize thickness-shear mode bulk waves as the main mode. By applying an AC voltage to the IDT electrode 8, thickness-shear mode bulk waves are excited in each excitation region C. More specifically, in the elastic wave device 1, where d is the thickness of the piezoelectric layer 6 and p is the center-to-center distance between adjacent electrode fingers, d / p is 0.5 or less. This allows thickness-shear mode bulk waves to be suitably excited in each excitation region C.

[0033] The elastic wave device 1 may be configured to use a plate wave as the main mode. In this case, the intersection region F is the excitation region.

[0034] In a plan view, the region including a pair of end electrode fingers A corresponds to a pair of end regions B shown in FIG. 1 . In this specification, a plan view refers to a view along the stacking direction of the support member 3 and the piezoelectric layer 6 from a direction corresponding to the top in FIG. 1 . In FIG. 1 , for example, the piezoelectric layer 6 side is the top, out of the support substrate 4 side and the piezoelectric layer 6 side. Furthermore, in this specification, a plan 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 6 a and the second principal surface 6 b of the piezoelectric layer 6 face each other. More specifically, the principal surface opposing direction is, for example, the normal direction to the first principal surface 6 a.

[0035] The dimension of the end region B in the direction perpendicular to the electrode fingers is the same as the average width of the multiple electrode fingers other than the pair of end electrode fingers A. The inner edges of the end region B and the end electrode fingers A overlap in a plan view. The end region B is a region that includes the support member 3, the piezoelectric layer 6, the first dielectric film 7A, and the second dielectric film 7B. On the other hand, the intersection region F and the excitation region C shown in FIG. 2 are regions of the piezoelectric layer 6 that are defined based on the configuration of the IDT electrode 8.

[0036] In one end region B, a cutout 6c is provided in the piezoelectric layer 6 in a portion that overlaps the outside of the end electrode finger A in plan view. Similarly, in the other end region B, a cutout 6c is provided in the piezoelectric layer 6 in a portion that overlaps the outside of the end electrode finger A in plan view. Note that the first dielectric film 7A and the second dielectric film 7B also have cutouts, similar to the piezoelectric layer 6. In this embodiment, the cutouts provided in the piezoelectric layer 6, the first dielectric film 7A, and the second dielectric film 7B are specifically through holes.

[0037] In this embodiment, the cutout 6c in the piezoelectric layer 6 and the end electrode finger A are not separated from each other in plan view. More specifically, the inner edge of the cutout 6c in the piezoelectric layer 6 overlaps with the outer edge of the end electrode finger A in plan view. Note that the inner edge of the cutout 6c in the piezoelectric layer 6 may be located outside the outer edge of the end electrode finger A in plan view.

[0038] As shown in FIG. 1 , the piezoelectric layer 6 has an end face facing the cutout portion 6c. The inner end face of the piezoelectric layer 6 is the inner end face 6d. The inner end face 6d of the piezoelectric layer 6 and the outer side surface 8c of the end electrode finger A are flush with each other. The inner end face 6d extends parallel to the normal direction of the second main surface 6b. That is, when the angle formed by the second main surface 6b and the inner end face 6d of the piezoelectric layer 6 is defined as the inner end face inclination angle, the inner end face inclination angle is 90°. However, the inner end face inclination angle is not limited to 90°.

[0039] Similarly, in the end electrode finger A, when the angle formed by the second surface 8 b and the outer side surface 8 c is defined as the outer side surface inclination angle, the outer side surface inclination angle is 90°, but the outer side surface inclination angle is not limited to 90°.

[0040] A feature of this embodiment is that a cutout portion 6c is provided in the piezoelectric layer 6 in at least one of the end regions B, at least in the portion that overlaps the outer side of the end electrode finger A in plan view. This makes it possible to reduce loss. Details of this will be explained below by comparing this embodiment with a first comparative example.

[0041] 4 , the first comparative example differs from the first embodiment in that no notches are provided in piezoelectric layer 106 and that the width of a pair of end electrode fingers A is the same as the average width of the electrode fingers other than the pair of end electrode fingers A. The admittance-frequency characteristics were compared between the first embodiment and the first comparative example. The design parameters of elastic wave device 1 of the first embodiment for this comparison are as follows. Here, the dimension of intersection region F along the electrode finger extension direction is defined as the intersection width.

[0042] Piezoelectric layer: Material... 120° Y-cut - LiNbO ３, thickness...180 nm, inner end face inclination angle...90° IDT electrode: layer structure...Ti layer / AlCu layer / Ti layer / AlCu layer from the piezoelectric layer side, thickness...12 nm / 70 nm / 18 nm / 12 nm from the piezoelectric layer side, center-to-center distance p: 2.38 μm, width of electrode fingers other than end electrode fingers...0.6 μm, width of end electrode fingers...0.3 μm, number of electrode fingers...51, outer side face inclination angle...90° Cross width: 39.727 μm First dielectric film: material...SiO ２ , thickness: 142 nm Second dielectric film: material: SiO ２ , thickness...142 nm

[0043] The design parameters of the first comparative example were the same as those of the first embodiment, except that the inclination angle of the inner end face of the piezoelectric layer was not defined and the width of the end electrode fingers was 0.6 μm.

[0044] 5 is a diagram showing the admittance-frequency characteristics in the first embodiment and the first comparative example. The admittance-frequency characteristics shown in FIG. 5 were derived by FEM (Finite Element Method) simulation. The same applies to the other figures showing admittance-frequency characteristics.

[0045] 5, in the vicinity of the frequency indicated by the dashed line, the admittance in the first embodiment is smaller than the admittance in the first comparative example. That is, the first embodiment can reduce the loss more than the first comparative example. The reason for this will be explained below.

[0046] In the first embodiment and the first comparative example, a bulk wave in thickness shear mode is used as the main mode. In this case, it is ideal that a bulk wave in thickness shear mode is excited in each excitation region C.

[0047] Fig. 6 is a diagram showing the relationship between the position of the IDT electrode in the direction perpendicular to the electrode fingers and the displacement near the resonance frequency in the first comparative example. Fig. 7 is a diagram showing the relationship between the position of the IDT electrode in the direction perpendicular to the electrode fingers and the displacement near the resonance frequency in the first embodiment. The scales on the horizontal axis in Fig. 6 and Fig. 7 indicate the center positions between the electrode fingers.

[0048] As shown in Fig. 6, in the first comparative example, the displacement is large in some areas where the electrode fingers are located, rather than in the areas between the electrode fingers. The change in displacement in the direction perpendicular to the electrode fingers is not a regular wave-like change, but rather disturbance occurs. Thus, in the first comparative example, the state in which thickness-shear mode bulk waves are excited is different from the ideal state.

[0049] In contrast, as shown in Figure 7, in the first embodiment, the displacement is large in the region between the electrode fingers. The change in displacement in the direction perpendicular to the electrode fingers is a regular wave-like change. In this way, in the first embodiment, the state in which thickness-shear mode bulk waves are excited can be made closer to the ideal state. This can reduce loss.

[0050] More specifically, in the first embodiment, as shown in Fig. 1, a cutout portion 6c is provided in the piezoelectric layer 6 in the edge region B. Therefore, the piezoelectric layer 6 has an inner end face 6d located in the edge region B. The inner end face 6d is the boundary between the air and the piezoelectric layer 6. This inner end face 6d serves as a reflective surface, allowing waves to be reflected inward. As a result, waves can be confined to the portion where the IDT electrode 8 is provided.

[0051] In addition, the inner end surface 6d is located in the end region B. This makes it possible to suppress the breakdown of regularity in the state where thickness-shear mode bulk waves are excited over the entire portion where the IDT electrode 8 is provided, thereby reducing loss.

[0052] The same effect as above can be obtained even when the acoustic wave device 1 uses plate waves as the main mode. That is, the waves can be confined to the portion where the IDT electrode 8 is provided, thereby reducing loss.

[0053] As in the first embodiment, it is preferable that the piezoelectric layer 6 has cutouts 6c in both end regions B, at least in the portions that overlap the outer sides of the end electrode fingers A in plan view, thereby more reliably reducing loss.

[0054] The configuration of the first embodiment will be described in more detail below.

[0055] As shown in FIG. 1 , a recess is provided in the insulating layer 5. A second dielectric film 7B and a piezoelectric layer 6 are provided on the insulating layer 5 so as to close the recess. This forms a hollow portion. This hollow portion is the cavity 1a. In the first embodiment, the support member 3 and the piezoelectric layer 6 are arranged so that a portion of the support member 3 and a portion of the piezoelectric layer 6 face each other with the cavity 1a in between. However, the recess in the support member 3 may be provided across the insulating layer 5 and the support substrate 4. Alternatively, a recess provided only in the support substrate 4 may be closed by the insulating layer 5. The recess may be provided in the piezoelectric layer 6, for example. The cavity 1a may be a through-hole provided in the support member 3.

[0056] In a plan view, at least a portion of the IDT electrode 8 overlaps with the cavity 1a of the support member 3. The cavity 1a of the support member 3 is the acoustic reflecting portion of the present invention. The acoustic reflecting portion can effectively confine the energy of the elastic wave on the piezoelectric layer 6 side. Note that an acoustic reflecting film, which will be described later, may be provided as the acoustic reflecting portion.

[0057] It is preferable that the excitation regions C overlap with the acoustic reflecting portions in a plan view, so that the energy of the elastic waves can be more reliably and effectively confined on the piezoelectric layer 6 side.

[0058] An example of a method for manufacturing the elastic wave device 1 according to the first preferred embodiment will be described below.

[0059] 8A to 8D are schematic cross-sectional front views illustrating an example of a method for manufacturing an elastic wave device according to the first embodiment, up to a step of providing an insulating layer. 9A to 9E are schematic cross-sectional front views illustrating an example of a method for manufacturing an elastic wave device according to the first embodiment, up to a step of providing a cutout portion in a piezoelectric layer.

[0060] As shown in FIG. 8( a), a piezoelectric substrate 6A is prepared. The piezoelectric substrate 6A has a third main surface 6e and a fourth main surface 6f. The third main surface 6e and the fourth main surface 6f face each other. Next, as shown in FIG. 8( b), a second dielectric film 7B is provided on the fourth main surface 6f of the piezoelectric substrate 6A. The second dielectric film 7B can be provided by, for example, sputtering or vacuum deposition.

[0061] Next, a sacrificial layer 13A is provided on the second dielectric film 7B. Next, the sacrificial layer 13A is appropriately patterned. At this time, for example, the sacrificial layer 13A may be patterned by forming an appropriate resist pattern and performing etching. As a result, the sacrificial layer 13 is obtained as shown in FIG. 8(c). The material of the sacrificial layer 13 may be, for example, ZnO or SiO ２ , Cu, resin, or the like can be used.

[0062] 8( d ), an insulating layer 5 is provided on the second dielectric film 7B so as to cover the sacrificial layer 13. The insulating layer 5 can be provided by, for example, a sputtering method or a vacuum deposition method. The surface of the insulating layer 5 may be flattened by performing a process such as grinding.

[0063] 9A, the support substrate 4 is bonded to the insulating layer 5. For example, an insulating layer may be separately formed on the support substrate 4, and then the insulating layer may be bonded to the insulating layer 5 covering the sacrificial layer 13.

[0064] Next, the thickness of the piezoelectric substrate 6A is adjusted by polishing or grinding the third principal surface 6e of the piezoelectric substrate 6A. Specifically, the thickness of the piezoelectric substrate 6A can be adjusted by, for example, grinding, chemical mechanical polishing (CMP), ion slicing, or etching. This results in a piezoelectric layer 6B, as shown in FIG. 9(b). The piezoelectric layer 6B has a first principal surface 6a and a second principal surface 6b. The second principal surface 6b of the piezoelectric layer 6B corresponds to the fourth principal surface 6f of the piezoelectric substrate 6A shown in FIG. 9(a).

[0065] 9(c), the IDT electrode 8A is provided on the piezoelectric layer 6B. The IDT electrode 8A can be provided by patterning a metal film using, for example, a combination of a sputtering method or a vacuum deposition method and a photolithography method. In this example of the manufacturing method, there is no difference between the multiple electrode fingers in the IDT electrode 8A.

[0066] Next, a first dielectric film 7A is provided on the piezoelectric layer 6B so as to cover the IDT electrode 8A. The first dielectric film 7A can be provided by, for example, sputtering or vacuum deposition.

[0067] 9( d ), a resist pattern 12 is provided on first dielectric film 7A so as to overlap, in plan view, all electrode fingers other than a pair of end electrode fingers A and a portion of the pair of end electrode fingers A. More specifically, half of each end electrode finger A in the direction perpendicular to the electrode fingers overlaps resist pattern 12 in plan view. The remaining half of each end electrode finger A in the direction perpendicular to the electrode fingers does not overlap resist pattern 12 in plan view.

[0068] Next, dry etching is performed to form cutouts in the piezoelectric layer 6B and remove a portion of each end electrode finger A. At the same time, cutouts are also formed in the first dielectric film 7A and the second dielectric film 7B. This results in the piezoelectric layer 6 and IDT electrode 8, as shown in FIG. 9( e). For example, argon gas or fluorine gas can be used in the dry etching.

[0069] Thereafter, an etching solution is poured into the recesses of the insulating layer 5 from the notched portions 6c of the piezoelectric layer 6, etc., to remove the sacrificial layer 13.

[0070] 3 , the inner end face inclination angle, which is the angle between the second main surface 6 b and the inner end face 6 d of the piezoelectric layer 6, is 90°. Similarly, the outer side face inclination angle, which is the angle between the second surface 8 b and the outer side face 8 c of the end electrode finger A, is 90°. When the average value of the widths of the electrode fingers other than the pair of end electrode fingers A is w, the width of the end electrode finger A is 0.5w. The outer side face 8 c of the end electrode finger A is not covered with a dielectric film. However, the configurations of the piezoelectric layer 6, the end electrode fingers A, and the dielectric film are not limited to those described above.

[0071] Second to fourth embodiments are examples of acoustic wave devices according to the present invention other than the first embodiment. In the second to fourth embodiments, similar to the first embodiment, notches are provided in the piezoelectric layer in the end region B, at least in the portions that overlap the outer sides of the end electrode fingers A in plan view. This allows loss to be reduced in the second to fourth embodiments as well.

[0072] 10 is a schematic front cross-sectional view showing the vicinity of a plurality of electrode fingers in the second embodiment, and FIG. 11 is a schematic front cross-sectional view showing the vicinity of one end electrode finger in the second embodiment.

[0073] 10 , this embodiment differs from the first embodiment in that the inclination angle of the outer side surface of the end electrode finger A and the inclination angle of the inner end surface of the piezoelectric layer 26 are not 90°. More specifically, as shown in FIG. 11 , when the inclination angle of the outer side surface of the end electrode finger A is α1, α1<90°. When the inclination angle of the inner end surface of the piezoelectric layer 26 is α2, α2<90°. Apart from the above, the elastic wave device of this embodiment has the same configuration as elastic wave device 1 of the first embodiment.

[0074] The admittance-frequency characteristics were compared between the second embodiment and the first comparative example. For the elastic wave device having the configuration of the second embodiment, the admittance-frequency characteristics were derived when the outer side surface inclination angle was set to 70° or 80°. The design parameters of the second comparative embodiment were the same as those of the first comparative embodiment shown in FIG. 5 except for the outer side surface inclination angle. Meanwhile, the first comparative example is the same as the first comparative example shown in FIG. 5 .

[0075] 12 and 13 are graphs showing the admittance-frequency characteristics of the second embodiment and the first comparative example when the outer side surface inclination angle is 70° and 80°, respectively.

[0076] In Fig. 12, the admittance in the second embodiment is smaller than that in the first comparative example near the frequency indicated by the dashed-dotted line. In Fig. 13, the admittance in the second embodiment is smaller than that in the first comparative example near the frequency indicated by the dashed-dotted line. As such, the second embodiment can reduce loss.

[0077] In the present invention, the inclination angle of the inner end face of the piezoelectric layer and the inclination angle of the outer side face of the end electrode finger A are not limited to 90° or less. In the modification of the second embodiment shown in Fig. 14, the inclination angle of the inner end face of the piezoelectric layer 26A and the inclination angle of the outer side face of the end electrode finger A are greater than 90°. In the piezoelectric layer 26A, the cutout portion 6c is provided in the end region B over a portion overlapping the outside of the end electrode finger A in plan view and over a portion overlapping the end electrode finger A in plan view.

[0078] In this modification, loss can be reduced in the same way as in the second embodiment. Details of this effect will be shown below by comparing the admittance frequency characteristics of this modification and the first comparative example.

[0079] In an acoustic wave device having a configuration according to a modification of the second embodiment, the admittance-frequency characteristics were derived each time the outer side surface inclination angle of the end electrode finger A was changed. Specifically, the outer side surface inclination angle was set to 100° or 110°. The design parameters of the modification of the second embodiment for comparison were the same as those of the first embodiment for comparison shown in FIG. 5 except for the outer side surface inclination angle. Meanwhile, the first comparative example for comparison is the same as the first comparative example shown in FIG.

[0080] 15 and 16 are graphs showing the admittance-frequency characteristics of the modified example of the second embodiment and the first comparative example when the outer side surface inclination angle is 100° and 110°, respectively.

[0081] In Fig. 15, near the frequency indicated by the dashed-dotted line, the admittance in the modified example of the second embodiment is smaller than that in the first comparative example. In Fig. 16, near the frequency indicated by the dashed-dotted line, the admittance in the modified example of the second embodiment is smaller than that in the first comparative example. As such, in the modified example of the second embodiment, loss can be reduced.

[0082] FIG. 17 is a schematic front cross-sectional view showing the vicinity of a plurality of electrode fingers in the third embodiment.

[0083] This embodiment differs from the first embodiment in that the width of the pair of end electrode fingers A is less than 0.5w, where w is the average width of the electrode fingers other than the pair of end electrode fingers A. Specifically, the width of each end electrode finger A is 0.33w. Apart from this, the elastic wave device of this embodiment has the same configuration as elastic wave device 1 of the first embodiment.

[0084] The admittance-frequency characteristics of the third embodiment and the first comparative example were compared. The design parameters of the third comparative embodiment were the same as those of the first comparative embodiment shown in FIG. 5 except for the width of the end electrode fingers A. That is, the parameters of the IDT electrodes in the elastic wave device of the third embodiment are as follows. Meanwhile, the first comparative example is the same as the first comparative example shown in FIG.

[0085] IDT electrode: Layer structure...Ti layer / AlCu layer / Ti layer / AlCu layer from the piezoelectric layer side; Thickness...12 nm / 70 nm / 18 nm / 12 nm from the piezoelectric layer side; Center-to-center distance p: 2.38 μm; Width of electrode fingers other than end electrode fingers...0.6 μm; Width of end electrode fingers...0.2 μm; Number of electrode fingers...51; Outer side surface inclination angle...90°

[0086] FIG. 18 is a diagram showing admittance frequency characteristics in the third embodiment and the first comparative example.

[0087] 18, in the vicinity of the frequency indicated by the dashed line, the admittance in the third embodiment is smaller than the admittance in the first comparative example. In this way, the third embodiment can reduce loss.

[0088] As in the first and third embodiments, it is preferable that the width of the end electrode finger A is 0.5 times or less the average width of the electrode fingers other than the pair of end electrode fingers A. This makes it possible to more reliably reduce loss.

[0089] In the third embodiment, the value of the distance between the inner end surface 6d of the piezoelectric layer 6 and the inner edge portion of the end region B is less than 0.5 times the average value of the widths of the electrode fingers other than the pair of end electrode fingers A. This makes it possible to further reliably reduce loss.

[0090] FIG. 19 is a schematic front cross-sectional view showing the vicinity of one end electrode finger in the fourth embodiment.

[0091] This embodiment differs from the first embodiment in that a protective film 37 is provided to cover outer side surfaces 8 c of the end electrode fingers A. The outer side surfaces 8 c of the end electrode fingers A (not shown) are also covered with the protective film 37. Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0092] The protective film 37 is a dielectric film. In this embodiment, the material of the protective film 37 and the material of the first dielectric film 7A are the same. Specifically, silicon oxide is used as the material of the protective film 37 and the first dielectric film 7A. Note that the material of the protective film 37 and the material of the first dielectric film 7A may be different from each other. The material of the protective film 37 may also be, for example, silicon nitride or silicon oxynitride.

[0093] The protective film 37 is connected to the first dielectric film 7A. The protective film 37 covers not only the outer side surfaces 8c of the end electrode fingers A but also the inner end surfaces 6d of the piezoelectric layer 6. The protective film 37 is further connected to the second dielectric film 7B. However, it is sufficient that the protective film 37 covers at least the outer side surfaces 8c of the end electrode fingers A.

[0094] The thickness of the protective film 37 is thinner than the thickness of the first dielectric film 7 A. The thickness of the protective film 37 is the distance from the surface located on the outer side surface 8 c side of the end electrode finger A to the surface opposite to the surface.

[0095] The admittance-frequency characteristics were compared between the fourth embodiment and the first comparative example. The design parameters of the fourth comparative embodiment were the same as those of the first comparative embodiment shown in FIG. 5 , except for the inclusion of a protective film. The parameters of the protective film in the elastic wave device of the fourth embodiment are as follows. Meanwhile, the first comparative example is similar to the first comparative example shown in FIG. 5 .

[0096] Protective film: Material...SiO ２ , thickness...10 nm

[0097] FIG. 20 is a diagram showing admittance frequency characteristics in the fourth embodiment and the first comparative example.

[0098] 20, in the vicinity of the frequency indicated by the dashed line, the admittance in the fourth embodiment is smaller than the admittance in the first comparative example. In this way, the fourth embodiment can reduce loss.

[0099] In addition, the provision of the protective film 37 effectively prevents the end electrode fingers A from being damaged.

[0100] 21 is a schematic plan view of an elastic wave device according to a fifth preferred embodiment of the present invention, in which the first dielectric film is omitted.

[0101] This embodiment differs from the first embodiment in that through holes 46g are provided between the bus bars and the electrode fingers. Except for this, the elastic wave device of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0102] Specifically, a through hole 46g is provided in each of the portions of the piezoelectric layer 46 that overlap in plan view with the plurality of gaps between the plurality of first electrode fingers 18 and the second bus bar 17. A through hole 46g is also provided in each of the portions that overlap in plan view with the plurality of gaps between the plurality of second electrode fingers 19 and the first bus bar 16. Note that it is sufficient that a through hole 46g is provided in a portion that overlaps in plan view with at least one of the plurality of gaps between the plurality of first electrode fingers 18 and the second bus bar 17 and the plurality of gaps between the plurality of second electrode fingers 19 and the first bus bar 16.

[0103] 21, when a through hole 46g is provided in the gap between the end electrode finger A and the bus bar, the through hole 46g and the cutout portion 6c are provided integrally, although the through hole 46g and the cutout portion 6c do not necessarily have to be provided integrally.

[0104] In this embodiment, as in the first embodiment, a cutout portion 6c is provided in the piezoelectric layer 6 in the end region B in a portion that overlaps with the outer side of the end electrode finger A in a plan view, thereby reducing loss.

[0105] In addition, it is possible to suppress the leakage of acoustic waves not only in the direction perpendicular to the electrode fingers but also in the direction in which the electrode fingers extend, thereby effectively reducing loss.

[0106] The dimension of the through hole 46g in the direction perpendicular to the electrode fingers is preferably equal to or greater than the width of the electrode finger facing the through hole 46g. This makes it easier to suppress leakage of acoustic waves in the electrode finger extension direction. However, the dimension of the through hole 46g in the direction perpendicular to the electrode fingers may be smaller than the width of the electrode finger facing the through hole 46g.

[0107] FIG. 22 is a schematic front cross-sectional view showing the vicinity of a plurality of electrode fingers in the sixth embodiment.

[0108] This embodiment differs from the first embodiment in that the thickness of first dielectric film 57A is thinner than the thickness of the plurality of electrode fingers of IDT electrode 8. This embodiment also differs from the first embodiment in that the thickness of second dielectric film 57B is thinner than the thickness of the plurality of electrode fingers of IDT electrode 8. Except for the above points, the elastic wave device of this embodiment has the same configuration as elastic wave device 1 of the first embodiment.

[0109] In the sixth embodiment, as in the first embodiment, loss can be reduced. Details of this effect will be shown below by comparing the admittance-frequency characteristics of the sixth embodiment and the second comparative example. Note that the second comparative example differs from the sixth embodiment in that no notches are provided in the piezoelectric layer and that the width of a pair of end electrode fingers is the same as the average width of the multiple electrode fingers other than the pair of end electrode fingers.

[0110] The design parameters of the sixth embodiment for comparison are as follows:

[0111] Piezoelectric layer: Material... 120° Y-cut - LiNbO ３, thickness...360 nm, inner end face inclination angle...90° IDT electrode: layer structure...Ti layer / AlCu layer / Ti layer / AlCu layer from the piezoelectric layer side, thickness...12 nm / 27 nm / 18 nm / 12 nm from the piezoelectric layer side, center-to-center distance p: 1.96 μm, width of electrode fingers other than end electrode fingers...0.6 μm, width of end electrode fingers...0.3 μm, number of electrode fingers...102, outer side face inclination angle...90° Cross width: 39.727 μm First dielectric film: material...SiO ２ , thickness... 30 nm Second dielectric film: material... SiO ２ , thickness...30 nm

[0112] The design parameters of the second comparative example were the same as those of the sixth embodiment, except that the inclination angle of the inner end face of the piezoelectric layer was not defined and the width of the end electrode fingers was 0.6 μm.

[0113] FIG. 23 is a diagram showing admittance frequency characteristics in the sixth embodiment and the second comparative example.

[0114] 23, in the vicinity of the frequency indicated by the dashed line, the admittance in the sixth embodiment is smaller than the admittance in the second comparative example. In this way, the sixth embodiment can reduce loss.

[0115] Additionally, in the sixth embodiment, the value of the bandwidth ratio can be increased. The bandwidth ratio is expressed by (|fa-fr| / fr)×100[%], where fr is the resonant frequency and fa is the anti-resonant frequency.

[0116] In the first to sixth embodiments, the inner edge of the cutout in the piezoelectric layer overlaps the outer edge of the end electrode finger in a plan view. The cutout only needs to be provided in the end region at least in a portion that overlaps with the outer edge of the end electrode finger in a plan view. The seventh embodiment shows an example in which the position of the cutout is different from that of the first to sixth embodiments.

[0117] FIG. 24 is a schematic front cross-sectional view showing the vicinity of one end electrode finger in the seventh embodiment.

[0118] This embodiment differs from the first embodiment in that the inner edge of the cutout 6 c in the piezoelectric layer 66 is located outside the outer edge of the end electrode finger A. However, at least a portion of the cutout 6 c is provided in the end region B. The configuration on the end electrode finger A side (not shown) is also similar to the configuration on the end electrode finger A side shown in FIG. 24 . Apart from the above, the elastic wave device of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0119] Hereinafter, the distance between the inner edge of the cutout 6 c in the piezoelectric layer 66 and the outer edge of the end electrode finger A in a planar view is referred to as the edge-to-edge distance. In this embodiment, the value of the edge-to-edge distance is greater than 0 and less than or equal to the width of the end electrode finger A. However, the value of the edge-to-edge distance may be greater than the width of the end electrode finger A. When the inner edge of the cutout 6 c is located outside the outer edge of the end electrode finger A, it is sufficient that the sum of the edge-to-edge distance and the width of the end electrode finger A is less than the dimension of the end region B in the direction perpendicular to the electrode fingers.

[0120] On the other hand, for example, in the first embodiment shown in FIG. 1, the distance between the edges of the piezoelectric layer 6 and the end electrode fingers A is zero.

[0121] In the seventh embodiment, loss can be reduced in the same way as in the first embodiment. Details of this effect will be shown below by comparing the admittance frequency characteristics in the seventh embodiment, the first comparative example, and the third comparative example.

[0122] The first comparative example is the first comparative example shown in Fig. 4 above. On the other hand, the third comparative example shown in Fig. 25 differs from the seventh embodiment in that notches are provided in the piezoelectric layer 116, the first dielectric film, and the second dielectric film only outside the end region B. The third comparative example also differs from the seventh embodiment in that the width of a pair of end electrode fingers A is the same as the average width of the multiple electrode fingers other than the pair of end electrode fingers A.

[0123] More specifically, in the third comparative example, the inner edge of the cutout 6 c is located at the boundary between the end region B and the region outside the end region B. That is, the value of the distance between the edges of the piezoelectric layer 116 and the end electrode fingers A is 0. Therefore, in the third comparative example, the sum of the distance between the edges and the width of the end electrode fingers A is not less than the value of the dimension in the direction perpendicular to the electrode fingers in the end region B. Therefore, as described above, the cutouts in the piezoelectric layer 116, the first dielectric film, and the second dielectric film are provided only outside the end region B.

[0124] The design parameters of the seventh comparative embodiment are as follows: The design parameters of the seventh comparative embodiment are the same as those of the first comparative embodiment shown in FIG. 5 except for the distance between the edges of the piezoelectric layer and the end electrode fingers.

[0125] Piezoelectric layer: Material... 120° Y-cut - LiNbO ３ , thickness...180 nm, inner end face inclination angle...90° IDT electrode: layer structure...Ti layer / AlCu layer / Ti layer / AlCu layer from the piezoelectric layer side, thickness...12 nm / 70 nm / 18 nm / 12 nm from the piezoelectric layer side, center-to-center distance p: 2.38 μm, width of electrode fingers other than end electrode fingers...0.6 μm, width of end electrode fingers...0.3 μm, number of electrode fingers...51, outer side face inclination angle...90° Cross width: 39.727 μm First dielectric film: material...SiO ２ , thickness: 142 nm Second dielectric film: material: SiO ２ , thickness: 142 nm Distance between the edges of the piezoelectric layer and the electrode fingers: 0.1 μm

[0126] The design parameters of the first comparative example were the same as those of the seventh embodiment, except that the inner end face inclination angle and the distance between the edges of the piezoelectric layer were not defined and the width of the end electrode fingers was 0.6 μm. The design parameters of the third comparative example were the same as those of the seventh embodiment, except that the width of the end electrode fingers was 0.6 μm and the distance between the edges of the piezoelectric layer and the end electrode fingers was 0.

[0127] FIG. 26 is a diagram showing admittance frequency characteristics in the seventh embodiment, the first comparative example, and the third comparative example.

[0128] 26, in the vicinity of the frequency indicated by the dashed line, the admittance in the seventh embodiment is smaller than the admittance in the first and third comparative examples. In this way, the seventh embodiment can reduce loss.

[0129] In the seventh embodiment, the inner end surface 6d of the piezoelectric layer 66 is located in the end region B. This makes it possible to suppress the breakdown of regularity when bulk waves in thickness-shear mode are excited in the entire area where the IDT electrode 8 is provided, thereby reducing loss.

[0130] FIG. 27 is a schematic front cross-sectional view showing the vicinity of one end electrode finger in the eighth embodiment.

[0131] This embodiment differs from the first embodiment in that an inner end surface 76d of a piezoelectric layer 76 has a step portion 76h. This embodiment also differs from the first embodiment in that the portion of the inner end surface 76d connected to the first main surface 6a and the portion of the inner end surface 76d connected to the second main surface 6b do not overlap in a plan view. The configuration of the end electrode finger A side (not shown) is also the same as the configuration of the end electrode finger A side shown in FIG. 27 . Apart from the above, the elastic wave device of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0132] More specifically, the step portion 76h of the inner end surface 76d of the piezoelectric layer 76 is a portion that connects portions where the inner end surface inclination angle changes. In this embodiment, the inner end surface inclination angle is 90° in the portion of the inner end surface 76d from the portion connected to the first main surface 6a to the step portion 76h. The inner end surface inclination angle is 0° in the step portion 76h. The inner end surface inclination angle is 90° in the portion of the inner end surface 76d from the step portion 76h to the portion connected to the second main surface 6b.

[0133] In this embodiment, the dimension of the step portion 76h of the inner end surface 76d of the piezoelectric layer 76 along the direction perpendicular to the electrode fingers is greater than 0 and is equal to or less than the width of the end electrode fingers A.

[0134] In this embodiment, loss can be reduced in the same way as in the first embodiment. Details of this effect will be shown below by comparing the admittance frequency characteristics of this embodiment and the first comparative example.

[0135] The design parameters of the eighth comparative embodiment were the same as those of the first comparative embodiment shown in Fig. 5 , except for the parameters related to the step portion on the inner end surface of the piezoelectric layer. That is, the parameters of the piezoelectric layer in the elastic wave device of the eighth embodiment are as follows. Meanwhile, the first comparative example is the same as the first comparative example shown in Fig. 5 .

[0136] Piezoelectric layer: Material... 120° Y-cut - LiNbO ３ , thickness: 180 nm, inner end face inclination angle: 90°, distance in the thickness direction between the first main surface and the step portion: 90 nm, dimension of the step portion along the direction perpendicular to the electrode fingers: 0.1 μm

[0137] FIG. 28 is a diagram showing admittance frequency characteristics in the eighth embodiment and the first comparative example.

[0138] 28, in the vicinity of the frequency indicated by the dashed line, the admittance in the eighth embodiment is smaller than the admittance in the first comparative example. In this way, the eighth embodiment is able to reduce loss.

[0139] FIG. 29 is a schematic front cross-sectional view of an elastic wave device according to a ninth preferred embodiment of the present invention.

[0140] This embodiment differs from the first embodiment in that the acoustic reflection portion is an acoustic reflection film 84. This embodiment also differs from the first embodiment in that the support member 83 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 1 of the first embodiment.

[0141] An acoustic reflection film 84 is provided on the surface of the support member 83. A piezoelectric layer 6 is provided on the acoustic reflection film 84. More specifically, the piezoelectric layer 6 is indirectly provided on the acoustic reflection film 84 via a second dielectric film 7B. The support member 83 and the piezoelectric layer 6 may be arranged such that at least a portion of the support member 83 and at least a portion of the piezoelectric layer 6 face each other with the acoustic reflection film 84 sandwiched between them.

[0142] The acoustic reflecting film 84 is a laminate of multiple acoustic impedance layers. Specifically, the acoustic reflecting film 84 has multiple low acoustic impedance layers and multiple high acoustic impedance layers. The low acoustic impedance layers are layers with a relatively low acoustic impedance. More specifically, the low acoustic impedance layers are layers with a lower acoustic impedance than the adjacent layers in the acoustic reflecting film 84. More specifically, the multiple low acoustic impedance layers in the acoustic reflecting film 84 are low acoustic impedance layer 87a, low acoustic impedance layer 87b, and low acoustic impedance layer 87c.

[0143] On the other hand, a high acoustic impedance layer is a layer with a relatively high acoustic impedance. More specifically, a high acoustic impedance layer is a layer with a higher acoustic impedance than the adjacent layers in the acoustic reflecting film 84. More specifically, the multiple high acoustic impedance layers in the acoustic reflecting film 84 are high acoustic impedance layers 88a and 88b. The low acoustic impedance layers and high acoustic impedance layers are stacked alternately. Note that the low acoustic impedance layer 87a is the acoustic impedance layer located closest to the piezoelectric layer 6 in the acoustic reflecting film 84.

[0144] The acoustic reflection film 84 has three low acoustic impedance layers and two high acoustic impedance layers, although it is sufficient that the acoustic reflection film 84 has at least one low acoustic impedance layer and one high acoustic impedance layer.

[0145] The low acoustic impedance layer may be made of a dielectric material such as silicon oxide or a metal such as aluminum or titanium, while the high acoustic impedance layer may be made of a dielectric material such as aluminum nitride, silicon nitride, or hafnium oxide or a metal such as platinum or tungsten.

[0146] In this embodiment, as in the first embodiment, a cutout portion 6c is provided in the piezoelectric layer 6 in the end region B in a portion that overlaps with the outer side of the end electrode finger A in a plan view, thereby reducing loss.

[0147] The first dielectric film 7A and the second dielectric film 7B have cutouts similar to those of the piezoelectric layer 6. On the other hand, no cutouts are provided in the acoustic reflection film 84. However, a cutout similar to that of the piezoelectric layer 6 may be provided in at least one acoustic impedance layer from the piezoelectric layer 6 side of the acoustic reflection film 84. For example, a cutout similar to that of the piezoelectric layer 6 may be provided in all of the low acoustic impedance layers and all of the high acoustic impedance layers of the acoustic reflection film 84.

[0148] The configuration in this embodiment in which the acoustic reflecting portion is the acoustic reflecting film 84 can also be applied to configurations of the present invention other than this embodiment.

[0149] A preferred configuration of the present invention will be described below with reference to Fig. 1. However, the following preferred configuration can also be applied to configurations of the present invention other than the first embodiment.

[0150] In the first embodiment, when the thickness of the piezoelectric layer is d and the center-to-center distance between adjacent electrode fingers is p, d / p is 0.5 or less. Preferably, d / p is 0.24 or less. This allows thickness-shear mode bulk waves to be more effectively excited and enables the value of the bandwidth fraction of the elastic wave resonator to be sufficiently large.

[0151] FIG. 30 is a graph showing the relationship between d / p and the bandwidth fraction of an elastic wave resonator.

[0152] As is clear from Figure 30, 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.

[0153] 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 resonator 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.

[0154] In this specification, the metallization ratio MR of the electrode fingers to the excitation region C is the ratio of the portion of the piezoelectric layer 6 that is covered with the metal constituting the electrode fingers to the excitation region C in a plan view. Specifically, the metallization ratio MR is the ratio of the area of ​​the first electrode fingers 18 and the second electrode fingers 19 in the excitation region C to the area of ​​the excitation region C in a plan view. When the width of the electrode fingers located in 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 in the excitation region C by the dimension of the excitation region C in the direction perpendicular to the electrode fingers. The width of the electrode fingers is the dimension of the electrode fingers in the direction perpendicular to the electrode fingers.

[0155] Fig. 31 is a diagram showing the relationship between the bandwidth ratio and the normalized magnitude of spurious in an elastic wave resonator. Fig. 31 shows the results of measuring the amount of phase rotation of spurious every time the bandwidth ratio is changed by changing the thickness of the piezoelectric layer and the dimensions of the electrode fingers. The normalized magnitude of spurious in Fig. 31 is specifically the value obtained by normalizing the amount of phase rotation of the spurious impedance by 180°. The results shown in Fig. 31 are for a Z-cut LiNbO ３Although 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.

[0156] In the region surrounded by ellipse D in Figure 31, 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.

[0157] 32 is a diagram showing the relationship between d / p, metallization ratio MR, and bandwidth fraction, which shows the results of calculating bandwidth fraction for different d / p and metallization ratio MR.

[0158] In Figure 32, the hatched area is the area where the fractional bandwidth is 17% or less. The boundary between this hatched area and the non-hatched area is roughly represented by dashed line E. Dashed line E is represented by MR = 1.75(d / p) + 0.075. It is preferable that MR ≤ 1.75(d / p) + 0.075. In this case, it is easy to keep the fractional bandwidth at 17% or less.

[0159] On the other hand, the dashed-dotted line E1 in Figure 32 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 E, and where the fractional bandwidth is 17% or less over the entire range. The dashed-dotted line E1 is represented by MR = 1.75(d / p) + 0.05. It is more preferable that MR ≤ 1.75(d / p) + 0.05. In this case, the fractional bandwidth can be more reliably kept at 17% or less.

[0160] FIG. 33 shows the LiNbO ３ 33 is a diagram showing a map of fractional bandwidths with respect to Euler angles (0°, θ, ψ) of the frequency band of the optical fiber 100. The hatched area in FIG. 33 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).

[0161] (0°±10°, 0° to 20°, any ψ) ... Equation (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3)

[0162] It is preferable that the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer are within the range of the above formula (1), formula (2), or formula (3). This allows the relative bandwidth of the elastic wave resonator to be sufficiently wide. The same applies when the piezoelectric layer is made of lithium tantalate.

[0163] Examples of embodiments of the acoustic wave device according to the present invention will be described below.

[0164] <1> A piezoelectric substrate including a piezoelectric layer having a first main surface and a second main surface facing each other, and an IDT electrode provided on the first main surface of the piezoelectric layer and having a plurality of electrode fingers, wherein, when a direction orthogonal to a direction in which the plurality of electrode fingers extend is defined as an electrode finger orthogonal direction, a pair of the electrode fingers located at both ends in the electrode finger orthogonal direction among the plurality of electrode fingers is a pair of end electrode fingers, and a width of at least one of the end electrode fingers is narrower than an average value of widths of the plurality of electrode fingers other than the pair of end electrode fingers, and a region including the pair of end electrode fingers is a pair of end regions in a plan view. an elastic wave device in which the dimension of the end region along the electrode finger orthogonal direction is the same as the average width of the plurality of electrode fingers other than a pair of the end electrode fingers, the inner edge portions of the end region and the end electrode fingers overlap in a planar view when the direction toward the center of the IDT electrode in the electrode finger orthogonal direction is defined as the inside and the direction toward the outside of the IDT electrode in the electrode finger orthogonal direction is defined as the outside, and a cutout portion is provided in the piezoelectric layer in at least one of the end regions, at least in the portion that overlaps with the outside of the end electrode fingers in a planar view.

[0165] <2> An elastic wave device as described in <1>, wherein the width of both of the end electrode fingers is narrower than the average width of the plurality of electrode fingers other than the end electrode fingers, and a cutout portion is provided in the piezoelectric layer in both of the end regions, at least in the portion that overlaps with the outside of the end electrode fingers when viewed in a plane.

[0166] <3> The elastic wave device according to <1> or <2>, wherein the inner edge of the cutout portion in the piezoelectric layer and the outer edge of the end electrode finger overlap in a planar view.

[0167] <4> The elastic wave device according to <1> or <2>, wherein the inner edge of the cutout portion of the piezoelectric layer is positioned further outward than the outer edge of the end electrode finger.

[0168] <5> An elastic wave device described in any one of <1> to <4>, wherein the piezoelectric layer has an end face facing the cutout portion, the inner end face is an inner end face, and the inner end face is inclined with respect to the normal direction of the second main surface of the piezoelectric layer.

[0169] <6> The acoustic wave device according to <5>, wherein the angle formed between the second main surface and the inner end surface of the piezoelectric layer is smaller than 90°.

[0170] <7> An elastic wave device as described in <5>, wherein the angle between the second main surface and the inner end surface of the piezoelectric layer is greater than 90°, and the cutout portion is provided over the portion of the end region that overlaps with the outer side of the end electrode finger when viewed in a plane, and the portion that overlaps with the end electrode finger when viewed in a plane.

[0171] <8> An elastic wave device described in any one of <1> to <4>, wherein the piezoelectric layer has an end face facing the cutout portion, the inner end face is an inner end face, the inner end face has a step portion, and a portion of the inner end face connected to the first main surface and a portion of the inner end face connected to the second main surface do not overlap in a planar view.

[0172] <9> The acoustic wave device according to any one of <1> to <8>, wherein the width of the end electrode finger is 0.5 times or less the average width of the plurality of electrode fingers other than the end electrode finger.

[0173] <10> An elastic wave device described in any one of <1> to <9>, wherein the end electrode fingers have a first surface and a second surface facing each other in the thickness direction, and a side surface connecting the first surface and the second surface, and further comprising a first dielectric film on the first main surface of the piezoelectric layer so as to cover at least the plurality of electrode fingers other than the end electrode fingers, as well as the first surface and the inner side surface of the end electrode fingers.

[0174] <11> The acoustic wave device according to <10>, wherein the thickness of the first dielectric film is thinner than the thickness of the plurality of electrode fingers.

[0175] <12> The acoustic wave device according to <10> or <11>, further comprising a protective film provided to cover the outer side surfaces of the end electrode fingers.

[0176] <13> The acoustic wave device according to any one of <1> to <12>, further comprising a second dielectric film provided on the second main surface of the piezoelectric layer.

[0177] <14> The elastic wave device according to any one of <1> to <13>, wherein the plurality of electrode fingers are a plurality of first electrode fingers and a plurality of second electrode fingers, the IDT electrode has a first bus bar and a second bus bar, one end of each of the first electrode fingers is connected to the first bus bar and the other end of each of the first electrode fingers faces the second bus bar across a gap, one end of each of the second electrode fingers is connected to the second bus bar and the other end of each of the second electrode fingers faces the first bus bar across a gap, the plurality of first electrode fingers and the plurality of second electrode fingers are interdigitated with each other, and a through hole is provided in the piezoelectric layer in a portion that overlaps in plan view with at least one of the gaps between the plurality of first electrode fingers and the second bus bar and the gaps between the plurality of second electrode fingers and the first bus bar.

[0178] <15> The elastic wave device according to any one of <1> to <14>, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, an acoustic reflection portion is provided on the support member at a position overlapping the IDT electrode in a planar view, and d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers.

[0179] <16> The acoustic wave device according to <15>, wherein d / p is 0.24 or less.

[0180] <17> An elastic wave device according to <15> or <16>, wherein the region where adjacent electrode fingers overlap in the direction perpendicular to the electrode fingers, the region between the centers of adjacent electrode fingers is an excitation region, and when the metallization ratio of the electrode fingers to the excitation region is MR, MR≦1.75(d / p)+0.075 is satisfied.

[0181] <18> The elastic wave device according to any one of <1> to <17>, 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):

[0182] (0°±10°, 0° to 20°, any ψ) ... Equation (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3)

[0183] <19> An elastic wave device according to any one of <1> to <18>, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, an acoustic reflection portion is provided on the support member at a position overlapping the IDT electrode in a planar view, the acoustic reflection portion is a cavity, and the support member and the piezoelectric layer are arranged such that a portion of the support member and a portion of the piezoelectric layer face each other with the cavity between them.

[0184] <20> The elastic wave device according to any one of <1> to <18>, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, an acoustic reflection portion is provided on the support member at a position overlapping the IDT electrode in a planar view, the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged such that at least a portion of the support member and at least a portion of the piezoelectric layer face each other with the acoustic reflection film sandwiched therebetween.

[0185] REFERENCE SIGNS LIST 1...acoustic wave device 1a...cavity 2...piezoelectric substrate 3...support member 4...support substrate 5...insulating layer 6...piezoelectric layer 6A...piezoelectric substrate 6B...piezoelectric layer 6a, 6b...first and second principal surfaces 6c...cutout portion 6d...inner end face 6e, 6f...third and fourth principal surfaces 7A, 7B...first and second dielectric films 8, 8A...IDT electrodes 8a, 8b...first and second surfaces 8c...side surface 12...resist pattern 13, 13A...sacrificial layer 16, 17...first and second bus bars 18, 19...first and second electrode fingers 26, 26A...piezoelectric layer 37...protective film 46...piezoelectric layer 46g...through hole 57A, 57B...first and second dielectric films 66, 76...piezoelectric layer 76d...inner end surface 76h...step portion 83...support member 84...acoustic reflection film 87a to 87c...low acoustic impedance layers 88a, 88b...high acoustic impedance layers 106, 116...piezoelectric layers A...end electrode finger B...end region C...excitation region F...crossing region

Claims

1. A piezoelectric substrate including a piezoelectric layer having first and second principal surfaces facing each other; and an IDT electrode provided on the first principal surface of the piezoelectric layer and having a plurality of electrode fingers, wherein, when a direction perpendicular to the direction in which the plurality of electrode fingers extend is defined as an electrode finger perpendicular direction, a pair of the plurality of electrode fingers located at both ends in the electrode finger perpendicular direction is a pair of end electrode fingers, the width of at least one of the end electrode fingers is narrower than the average value of the widths of the plurality of electrode fingers other than the pair of end electrode fingers, when viewed in a plane, a region including the pair of end electrode fingers is a pair of end regions, and the value of the dimension of the end region along the electrode finger perpendicular direction is the same as the average value of the widths of the plurality of electrode fingers other than the pair of end electrode fingers, an elastic wave device in which, when the direction toward the center of the IDT electrode in the direction perpendicular to the electrode fingers is defined as the inward direction and the direction toward the outside of the IDT electrode in the direction perpendicular to the electrode fingers is defined as the outward direction, the inner edge portions of the end region and the end electrode finger overlap in a planar view, and a cutout portion is provided in the piezoelectric layer in at least one of the end regions, at least in a portion that overlaps with the outside of the end electrode finger in a planar view.

2. An elastic wave device as described in claim 1, wherein the width of both of the end electrode fingers is narrower than the average width of the plurality of electrode fingers other than the end electrode fingers, and wherein cutout portions are provided in the piezoelectric layer in both of the end regions, at least in the portions that overlap with the outer sides of the end electrode fingers when viewed in a plane.

3. The acoustic wave device according to claim 1 or 2, wherein the inner edge of the cutout in the piezoelectric layer and the outer edge of the end electrode finger overlap in a plan view.

4. The acoustic wave device according to claim 1, wherein the inner edge of the cutout of the piezoelectric layer is located further outward than the outer edge of the end electrode finger.

5. An elastic wave device according to any one of claims 1 to 4, wherein the piezoelectric layer has an end face facing the cutout portion, the inner end face being an inner end face, and the inner end face being inclined with respect to the normal direction of the second main surface of the piezoelectric layer.

6. The acoustic wave device according to claim 5, wherein the angle formed between the second main surface and the inner end surface of the piezoelectric layer is smaller than 90°.

7. An elastic wave device as described in claim 5, wherein the angle between the second main surface and the inner end surface of the piezoelectric layer is greater than 90°, and the cutout portion is provided over the portion of the end region that overlaps with the outer side of the end electrode finger when viewed in a plane and the portion that overlaps with the end electrode finger when viewed in a plane.

8. The elastic wave device according to any one of claims 1 to 4, wherein the piezoelectric layer has an end face facing the cutout portion, the inner end face is an inner end face, the inner end face has a step portion, and the portion of the inner end face that is connected to the first main surface and the portion of the inner end face that is connected to the second main surface do not overlap in a planar view.

9. The acoustic wave device according to claim 1, wherein the width of the end electrode finger is 0.5 times or less the average width of the plurality of electrode fingers other than the end electrode finger.

10. An elastic wave device according to any one of claims 1 to 9, wherein the end electrode fingers have a first surface and a second surface that face each other in the thickness direction, and a side surface that connects the first surface and the second surface, and further comprising a first dielectric film provided on the first main surface of the piezoelectric layer so as to cover at least the plurality of electrode fingers other than the end electrode fingers, as well as the first surface and the inner side surface of the end electrode fingers.

11. The acoustic wave device according to claim 10, wherein the thickness of the first dielectric film is thinner than the thickness of the plurality of electrode fingers.

12. The acoustic wave device according to claim 10, further comprising a protective film provided to cover the outer side surfaces of the end electrode fingers.

13. The acoustic wave device according to claim 1, further comprising a second dielectric film provided on the second main surface of the piezoelectric layer.

14. The elastic wave device according to any one of claims 1 to 13, wherein the plurality of electrode fingers are a plurality of first electrode fingers and a plurality of second electrode fingers, the IDT electrode has a first bus bar and a second bus bar, one end of each of the first electrode fingers is connected to the first bus bar and the other end of each of the first electrode fingers faces the second bus bar across a gap, one end of each of the second electrode fingers is connected to the second bus bar and the other end of each of the second electrode fingers faces the first bus bar across a gap, the plurality of first electrode fingers and the plurality of second electrode fingers are interdigitated with each other, and a through hole is provided in the piezoelectric layer in a portion that overlaps in plan view with at least one of the gaps between the plurality of first electrode fingers and the second bus bar and the plurality of gaps between the plurality of second electrode fingers and the first bus bar.

15. The elastic wave device according to any one of claims 1 to 14, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, an acoustic reflection portion is provided on the support member at a position overlapping the IDT electrode in a planar view, and d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers.

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

17. The elastic wave device according to claim 15 or 16, wherein the region where adjacent electrode fingers overlap in the direction perpendicular to the electrode fingers and the region between the centers of adjacent electrode fingers is an excitation region, and when MR is the metallization ratio of the electrode fingers to the excitation region, MR≦1.75(d / p)+0.075 is satisfied.

18. The acoustic wave device according to any one of claims 1 to 17, 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): (0°±10°, 0° to 20°, any ψ) ... formula (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3) 19. An elastic wave device according to any one of claims 1 to 18, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, an acoustic reflection portion is provided on the support member at a position overlapping the IDT electrode in a planar view, the acoustic reflection portion is a cavity, and the support member and the piezoelectric layer are arranged so that a portion of the support member and a portion of the piezoelectric layer face each other with the cavity between them.

20. An elastic wave device according to any one of claims 1 to 18, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, an acoustic reflection portion is provided on the support member at a position overlapping the IDT electrode in a planar view, the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged so that at least a portion of the support member and at least a portion of the piezoelectric layer face each other with the acoustic reflection film in between.

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