Elastic wave device

Abstract

Provided is an elastic wave device that makes it possible to suppress unnecessary waves.　The elastic wave device 1 comprises: a support member; a piezoelectric film that is provided on the support member, and includes a piezoelectric layer 6; and an IDT electrode 7 that is provided on the piezoelectric film, and has a plurality of electrode fingers (a plurality of first and second electrode fingers 18 and 19). In a plan view, an acoustic reflection portion is formed at a position of the support member overlapping the IDT electrode 7. When a direction that is orthogonal to the direction in which the plurality of electrode fingers extend is defined as an electrode finger orthogonal direction, a plurality of electrode finger formation regions E1 and E2 that include two or more electrode fingers are constituted in the portion where the IDT electrode 7 is formed. The plurality of electrode finger formation regions E1 and E2 are arranged in the electrode finger orthogonal direction. Each electrode finger formation region E1 and E2 spans from the center in the electrode finger orthogonal direction of the electrode finger at one end in the electrode finger orthogonal direction among two or more electrode fingers to the center in the electrode finger orthogonal direction of the electrode finger at the other end. When the center-to-center distance between adjacent electrode fingers is defined as an in-region center-to-center distance p, the average value of the inter-region center distance p in each of the electrode finger formation regions E1 and E2 is substantially the same between the plurality of electrode finger formation regions E1 and E2. When the thickness of the piezoelectric film is d, d / p is 0.5 or less in the plurality of electrode finger formation regions E1 and E2,. Out of the center-to-center distances between electrode fingers in one electrode finger formation region E1 and electrode fingers in the other electrode finger formation region E2 among adjacent electrode finger formation regions E1 and E2, the shortest center-to-center distance between electrode fingers that are connected to different potentials (the first and second electrode fingers 18 and 19) and the inter-region center distance p in each of the adjacent electrode finger formation regions E1 and E2 are different from each other.

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. Patent Document 1 below discloses an example of an acoustic wave device. In this acoustic wave device, a piezoelectric layer is provided on a support member. A plurality of functional electrodes are provided on the piezoelectric layer. A space is provided in the support member so as to overlap with the plurality of functional electrodes in a plan view.

[0003] Each functional electrode has multiple pairs of electrode fingers, which face each other on the piezoelectric layer and are connected to different potentials. By applying an AC voltage between the electrode fingers, thickness-shear mode bulk waves are excited.

[0004] International Publication No. 2022 / 211056

[0005] However, even if the acoustic wave device described in Patent Document 1 can sufficiently excite bulk waves in thickness shear mode, it may not be possible to sufficiently suppress unwanted waves.

[0006] An object of the present invention is to provide an acoustic wave device that can suppress unwanted waves.

[0007] An elastic wave device according to one embodiment of the present invention includes a support member, a piezoelectric film provided on the support member and including a piezoelectric layer, and an IDT electrode provided on the piezoelectric film and having a plurality of electrode fingers, wherein an acoustic reflecting portion is formed on the support member at a position overlapping with the IDT electrode in a planar view, and when a direction orthogonal to a direction in which the plurality of electrode fingers extend is defined as an electrode finger orthogonal direction, a plurality of electrode finger formation regions each including two or more of the electrode fingers are configured in the portion in which the IDT electrode is formed, the plurality of electrode finger formation regions are aligned in the electrode finger orthogonal direction, and each of the electrode finger formation regions is located between a center of one end of the two or more electrode fingers in the electrode finger orthogonal direction and a center of the other end of the two or more electrode fingers in the electrode finger orthogonal direction. The electrode finger formation region is a region extending to the center of the electrode finger in the direction perpendicular to the electrode fingers, and in each electrode finger formation region, when the center-to-center distance between adjacent electrode fingers is defined as an intra-region center-to-center distance p, the average value of the intra-region center-to-center distance p is substantially the same among the plurality of electrode finger formation regions, and when the thickness of the piezoelectric film is defined as d, in the plurality of electrode finger formation regions, d / p is 0.5 or less, and among the center-to-center distances between the electrode fingers in one electrode finger formation region and the electrode fingers in the other electrode finger formation region in adjacent electrode finger formation regions, the shortest center-to-center distance a is different from the intra-region center-to-center distance p in each of the adjacent electrode finger formation regions.

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

[0009] FIG. 1 is a schematic plan view of an elastic wave device according to a first preferred embodiment of the present invention. FIG. 2 is a schematic cross-sectional view taken along line II in FIG. 1 . FIG. 3 is a schematic plan view of an elastic wave device according to a comparative example. FIG. 4 is a graph showing admittance-frequency characteristics of the first preferred embodiment of the present invention and a comparative example. FIG. 5 is a graph showing admittance-frequency characteristics from 100 MHz to 1000 MHz of the first preferred embodiment of the present invention and a comparative example. FIGS. 6( a) to 6(c) are schematic front cross-sectional views showing the vicinity of multiple electrode fingers for illustrating that spurious waves can be suppressed in the first preferred embodiment of the present invention. FIG. 7 is a schematic plan view of an elastic wave device according to a modified preferred embodiment of the first preferred embodiment of the present invention. FIG. 8 is a graph showing admittance-frequency characteristics from 100 MHz to 1000 MHz of the first preferred embodiment of the present invention, the modified preferred embodiment, and the comparative example. FIG. 9 is a graph showing the relationship between L2 / (L1+L2) and the ratio g / p and the intensity of spurious waves. FIG. 10 is a schematic front cross-sectional view of an elastic wave device according to a second preferred embodiment of the present invention. FIG. 11 is a graph showing admittance-frequency characteristics in the second embodiment of the present invention and a comparative example. FIG. 12 is a graph showing admittance-frequency characteristics from 100 MHz to 1000 MHz in the second embodiment of the present invention and a comparative example. FIGS. 13(a) to 13(c) are schematic front cross-sectional views showing the vicinity of multiple electrode fingers, illustrating that spurious waves can be suppressed in the second embodiment of the present invention. FIG. 14 is a graph showing the relationship between L2 / (L1+L2) and the ratio g / p and the intensity of spurious waves. FIG. 15 is a schematic front cross-sectional view showing the vicinity of multiple electrode fingers in the third embodiment of the present invention. FIG. 16 is a schematic front cross-sectional view of an elastic wave device according to a fourth embodiment of the present invention. FIG. 17 is a graph showing the relationship between d / p and the fractional bandwidth of an elastic wave resonator. FIG. 18 is a graph showing the relationship between the fractional bandwidth of an elastic wave resonator and the magnitude of normalized spurious signals. FIG. 19 is a graph showing the relationship between d / p, the metallization ratio MR, and the fractional bandwidth. FIG. 20 is a graph showing the relationship between d / p and the fractional bandwidth of a LiNbO resonator 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 plan view of an elastic wave device according to a first preferred embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view taken along line II in Fig. 1.

[0013] As shown in FIG. 1 , the acoustic wave device 1 includes a piezoelectric substrate 2 and an IDT electrode 7. The piezoelectric substrate 2 is a substrate having piezoelectric properties. As shown in FIG. 2 , the piezoelectric substrate 2 includes a support member 3 and a piezoelectric layer 6 serving as a piezoelectric film. The piezoelectric layer 6 is a layer made of a piezoelectric material. However, in this specification, a piezoelectric film refers to a film having piezoelectric properties, and does not necessarily refer to a film made of a piezoelectric material. However, in this embodiment, the piezoelectric film is a single-layer piezoelectric layer 6, which is a film made of a piezoelectric material. Note that in the present invention, the piezoelectric film may be a laminated film including the piezoelectric layer 6.

[0014] 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. A piezoelectric layer 6 is provided on the insulating layer 5. However, the support member 3 may be composed of only the support substrate 4.

[0015] The support substrate 4 may be made of a semiconductor such as silicon or a ceramic such as aluminum oxide. The insulating layer 5 may be made of an appropriate dielectric such as silicon oxide or tantalum oxide. The piezoelectric layer 6 may be made of LiNbO ３ Alternatively, the material may be made of lithium niobate such as LiTaO ３ In this embodiment, piezoelectric layer 6 is made of lithium niobate. In this specification, a certain component made of a certain material includes a component containing a trace amount of impurities that does not significantly degrade the electrical characteristics of the acoustic wave device.

[0016] 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. The first main surface 6a and the second main surface 6b of the piezoelectric layer 6 are the first main surface and the second main surface of the piezoelectric film in this embodiment.

[0017] An IDT electrode 7 is provided on the first principal surface 6 a of the piezoelectric layer 6. The elastic wave device 1 of this preferred embodiment is an elastic wave resonator configured to utilize thickness-shear mode bulk waves. However, the elastic wave device of the present invention may also be a filter device or a multiplexer having multiple elastic wave resonators.

[0018] As shown in FIG. 1 , the IDT electrode 7 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 of the plurality of first electrode fingers 18 is connected to the first bus bar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second bus bar 17. 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. The IDT electrode 7 may be made of a single-layer metal film or a laminated metal film.

[0019] Hereinafter, the first electrode fingers 18 and the second electrode fingers 19 may be collectively referred to simply as electrode fingers. The direction in which the 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 perpendicular direction.

[0020] A plurality of electrode finger formation regions are defined in the portion of the acoustic wave device 1 where the IDT electrode 7 is formed. In other words, the acoustic wave device 1 is divided into a plurality of electrode finger formation regions in the portion where the IDT electrode 7 is formed. In this embodiment, specifically, an electrode finger formation region E1 and an electrode finger formation region E2 are defined.

[0021] The electrode finger formation region in the present invention is a region including two or more electrode fingers. More specifically, the electrode finger formation region in the present invention is a region extending from the center of one of the two or more electrode fingers in the orthogonal direction to the center of the other electrode finger in the orthogonal direction. The multiple electrode finger formation regions are aligned in the orthogonal direction. However, adjacent electrode finger formation regions do not share the same electrode fingers.

[0022] In the acoustic wave device 1, two electrode finger formation regions, an electrode finger formation region E1 and an electrode finger formation region E2, are configured. Therefore, the electrode finger formation region E1 and the electrode finger formation region E2 are adjacent to each other. Note that the acoustic wave device 1 may be configured with three or more electrode finger formation regions.

[0023] In each electrode finger formation region, when the center-to-center distance between adjacent electrode fingers is defined as the intra-region center distance p, the average values ​​of the intra-region center distances p are substantially the same among the plurality of electrode finger formation regions. In this specification, the average values ​​of the intra-region center distances p being substantially the same among the plurality of electrode finger formation regions is as follows: That is, when the difference between the maximum and minimum values ​​of the average values ​​of the intra-region center distances p among the plurality of electrode finger formation regions is 25% or less of any of the average values ​​of the intra-region center distances p, the average values ​​are substantially the same among the plurality of electrode finger formation regions.

[0024] However, it is preferable that the average value of the intra-region center-to-center distance p is the same among the multiple electrode finger formation regions. In this embodiment, the average value of the intra-region center-to-center distance p in the electrode finger formation region E1 and the average value of the intra-region center-to-center distance p in the electrode finger formation region E2 are the same. Furthermore, in this embodiment, the intra-region center-to-center distance p is constant in both the electrode finger formation region E1 and the electrode finger formation region E2. Therefore, the intra-region center-to-center distance p in the electrode finger formation region E1 and the intra-region center-to-center distance p in the electrode finger formation region E2 are the same.

[0025] The electrode finger in the electrode finger formation region E1 closest to the electrode finger formation region E2 is the first electrode finger 18. The electrode finger in the electrode finger formation region E2 closest to the electrode finger formation region E1 is the second electrode finger 19. Therefore, in the adjacent electrode finger formation regions E1 and E2, adjacent electrode fingers are connected to different potentials. Hereinafter, the center-to-center distance between adjacent electrode fingers in adjacent electrode finger formation regions is referred to as the inter-region distance g.

[0026] The electrode finger formation region E1 and the electrode finger formation region E2 each include a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. The shortest center-to-center distance between the first electrode fingers 18 in the electrode finger formation region E1 and the second electrode fingers 19 in the electrode finger formation region E2 is defined as the center-to-center distance a. In other words, the shortest center-to-center distance between the electrode fingers in one electrode finger formation region E1 and the electrode fingers in the other electrode finger formation region E2 in adjacent electrode finger formation regions that are connected to different potentials is defined as a. Note that in the acoustic wave device 1, the center-to-center distance a is the same as the region-to-region distance g between adjacent electrode finger formation regions.

[0027] The acoustic wave device 1 is an acoustic wave resonator configured to utilize thickness-shear mode bulk waves as the main mode. More specifically, in the acoustic wave device 1, when the thickness of the piezoelectric film is d, the ratio d / p is 0.5 or less in the regions where the electrode fingers are formed. This allows for optimal excitation of thickness-shear mode bulk waves. In this embodiment, the thickness d is the thickness of the piezoelectric layer 6.

[0028] This embodiment is characterized in that a thickness-shear mode bulk wave can be used as the main mode, and the intra-region center-to-center distance p between adjacent electrode finger formation regions is different from the center-to-center distance a between adjacent electrode finger formation regions. Note that in this embodiment, the center-to-center distance a and the inter-region distance g are the same. Therefore, this embodiment can also be characterized in that a thickness-shear mode bulk wave can be used as the main mode, and the intra-region center-to-center distance p between adjacent electrode finger formation regions is different from the inter-region distance g between adjacent electrode finger formation regions. This makes it possible to suppress unwanted waves. Details of this will be explained below by comparing this embodiment with a comparative example.

[0029] 3 , the comparative example differs from the first embodiment in that the center-to-center distance between adjacent electrode fingers is constant throughout the entire IDT electrode 107. In the acoustic wave device of the comparative example, the portion where the IDT electrode 107 is formed is not divided into multiple electrode finger formation regions.

[0030] The admittance-frequency characteristics of the first embodiment and a comparative example were compared. The respective admittance-frequency characteristics were derived by FEM (Finite Element Method) simulation. In this comparison, in the first embodiment, the inter-region distance g was set to twice the intra-region center-to-center distance p. The inter-region distance g was the same as the center-to-center distance a. That is, in the first embodiment, g = a = 2p. The design parameters of the elastic wave device of the first embodiment for this comparison are as follows:

[0031] Piezoelectric layer: Material... LiNbO ３ , thickness... 368 nm Protective film layer: material... SiO ２ , thickness...133 nm Electrode fingers: material...Al, thickness...500 nm Intra-region center distance p: 4.26 μm Region-to-region distance g: 8.52 μm

[0032] The design parameters of the comparative example were the same as those of the first embodiment, except that the inter-region distance g and the center-to-center distance a were not defined. The center-to-center distance between adjacent electrode fingers in the comparative example was set to the same as the intra-region center-to-center distance p in the first embodiment.

[0033] Fig. 4 is a diagram showing the admittance frequency characteristics in the first embodiment and the comparative example, and Fig. 5 is a diagram showing the admittance frequency characteristics in the range of 100 MHz to 1000 MHz in the first embodiment and the comparative example.

[0034] As shown in the dashed-dotted line frame in Fig. 4 and in Fig. 5, in the comparative example, large unwanted waves are generated around 600 MHz, which is lower than the resonant frequency. In contrast, in the first embodiment, it can be seen that unwanted waves are suppressed around 600 MHz. The reason for this will be explained below, along with the details of the configuration of the first embodiment.

[0035] As shown in Fig. 1 , when viewed from the direction perpendicular to the electrode fingers, the excitation region C is a region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap and between the centers of the adjacent first electrode fingers 18 and second electrode fingers 19. The excitation region C is a region of the piezoelectric layer 6 that is defined based on the configuration of the IDT electrode 7. Fig. 1 shows only two of the multiple excitation regions C. Each of the electrode finger forming region E1 and the electrode finger forming region E2 includes multiple excitation regions C. However, it is sufficient for each electrode finger forming region to include at least one excitation region C.

[0036] By applying an AC voltage to the IDT electrode 7, thickness-shear mode bulk waves are excited in each excitation region C. The thickness-shear mode bulk waves propagate in the thickness direction of the piezoelectric layer 6. When the thickness-shear mode bulk waves are excited, unwanted waves are also excited. For example, unwanted waves originating from plate wave harmonics propagate in the direction perpendicular to the electrode fingers. In the first embodiment, such unwanted waves can be suppressed.

[0037] 6A to 6C are schematic front cross-sectional views showing the vicinity of a plurality of electrode fingers, for explaining that spurious waves can be suppressed in the first embodiment.

[0038] As shown in FIG. 6A, the inter-region distance g between the electrode finger forming regions E1 and E2 and the intra-region center-to-center distance p between the electrode finger forming regions E1 and E2 are different from each other.

[0039] The spurious waves excited in the electrode finger formation region E1 propagate in a direction perpendicular to the electrode fingers, as shown by the dashed line in Fig. 6B. The phase of the spurious waves excited in the electrode finger formation region E1 depends on the arrangement of the electrode fingers in the region.

[0040] 6B, the dashed lines indicate that the electrode fingers are virtually arranged outside the electrode finger formation region E1 at the same period as inside the region. The phase of the spurious waves excited in the electrode finger formation region E1 outside the region is based on the virtual configuration in which the electrode fingers are virtually arranged in the same manner both inside and outside the region.

[0041] 6(c) schematically shows spurious waves excited in the electrode finger formation region E2, as in Fig. 6(b). In Fig. 6(c), the dashed lines indicate that electrode fingers are also virtually arranged outside the electrode finger formation region E2 at the same period as those within the region.

[0042] 6(b) and 6(c), the phase of the unwanted wave excited in the electrode finger formation region E1 is different from the phase of the unwanted wave excited in the electrode finger formation region E2, so that the unwanted waves excited in both regions can be weakened by interference between them.

[0043] The electrode finger in the electrode finger formation region E1 closest to the electrode finger formation region E2 and the electrode finger in the electrode finger formation region E2 closest to the electrode finger formation region E1 are connected to different potentials. In this case, if the intra-region center distance p in both regions and the inter-region distance g between the two regions are the same, the phases of the spurious waves in both regions will be the same. In contrast, in the first embodiment, the intra-region center distance p in the electrode finger formation region E1 and the electrode finger formation region E2 are different from the inter-region distance g between the electrode finger formation region E1 and the electrode finger formation region E2. This makes it possible to make the phases of the spurious waves excited in both regions different from each other, thereby weakening the spurious waves.

[0044] On the other hand, the bulk wave of the thickness-shear mode used as the main mode propagates in the thickness direction of the piezoelectric layer 6. Therefore, even if multiple electrode finger formation regions are configured as in the first embodiment, the main mode is not suppressed. Therefore, the main mode can be suitably excited and unwanted waves can be suppressed.

[0045] In the present invention, it is preferable that the average value of the intra-region center-to-center distance p in each of adjacent electrode finger formation regions is different from the center-to-center distance a between adjacent electrode finger formation regions. When adjacent electrode fingers in adjacent electrode finger formation regions are connected to different potentials, it is preferable that the average value of the intra-region center-to-center distance p in each of adjacent electrode finger formation regions is different from the inter-region distance g between adjacent electrode finger formation regions. In this case, it is possible to more reliably suppress unwanted waves.

[0046] It is preferable that adjacent electrode finger formation regions are symmetrical with respect to an axis of symmetry extending in the electrode finger extension direction. Alternatively, it is preferable that adjacent electrode finger formation regions have the same configuration. More specifically, it is preferable that the relationship between the position of each electrode finger and the width of each electrode finger, and the relationship between the position of each electrode finger and the center-to-center distance between adjacent electrode fingers, are the same in both electrode finger formation regions. In these cases, it can be said that one acoustic wave resonator is divided into regions that are equivalent in terms of electrical characteristics. This makes it possible to more reliably achieve the desired electrical characteristics of the acoustic wave device and suppress unwanted waves.

[0047] The energy of the bulk wave in the thickness shear mode can be effectively confined on the side of the piezoelectric layer 6 by an acoustic reflecting portion, which will be described later. This will be described in detail below.

[0048] As shown in FIG. 2 , a recess is provided in the insulating layer 5. A piezoelectric layer 6 serving as a piezoelectric film is provided on the insulating layer 5 so as to close the recess. This forms a hollow portion. This hollow portion is the cavity 2a. In the first embodiment, the support member 3 and the piezoelectric film are arranged so that a portion of the support member 3 and a portion of the piezoelectric film face each other with the cavity 2a 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 2a may be a through-hole provided in the support member 3.

[0049] In a plan view, at least a portion of the IDT electrode 7 overlaps the cavity 2a of the support member 3. In this specification, a plan view refers to a view from a direction corresponding to the top in FIG. 2 along the stacking direction of the support member 3 and the piezoelectric film. In FIG. 2, for example, of the support substrate 4 side and the piezoelectric layer 6 side, the piezoelectric layer 6 side is the top. 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 6a and the second principal surface 6b of the piezoelectric layer 6 face each other. More specifically, the principal surface opposing direction is, for example, the normal direction of the first principal surface 6a.

[0050] The cavity 2a of the support member 3 shown in Figure 2 is the acoustic reflecting portion in the present invention. As described above, the excited thickness-shear mode bulk waves propagate in the thickness direction of the piezoelectric layer 6. The thickness-shear mode bulk waves can be reflected toward the piezoelectric layer 6 by the acoustic reflecting portion. This allows the energy of the thickness-shear mode bulk waves to be effectively trapped toward the piezoelectric layer 6. Note that an acoustic reflecting film, which will be described later, may be provided as the acoustic reflecting portion. For example, an acoustic reflecting film may be provided on the surface of the support member.

[0051] It is preferable that the excitation regions C overlap with the acoustic reflecting portions in a plan view, so that the energy of the thickness-shear mode bulk waves can be more reliably and effectively confined on the piezoelectric layer 6 side.

[0052] In the first embodiment, two electrode finger formation regions are formed. However, three or more electrode finger formation regions may be formed. For example, in a modification of the first embodiment shown in FIG. 7 , multiple electrode finger formation regions are formed, including electrode finger formation region E1, electrode finger formation region E2, electrode finger formation region E3, and electrode finger formation region E4.

[0053] In this modification, the intra-region center-to-center distance p between adjacent electrode finger formation regions is different from the center-to-center distance a between adjacent electrode finger formation regions. That is, the intra-region center-to-center distance p between adjacent electrode finger formation regions is different from the inter-region distance g between adjacent electrode finger formation regions. This makes it possible to suppress unwanted waves.

[0054] The greater the number of electrode finger formation regions formed by dividing the acoustic wave device, the more effectively unwanted waves can be suppressed. This is demonstrated by comparing the admittance-frequency characteristics of the first embodiment, its modification, and a comparative example. The admittance-frequency characteristics of each embodiment were derived by FEM simulation.

[0055] The design parameters in the first embodiment and the comparative example for comparison were the same as those in the comparison shown in Fig. 5. The design parameters in the modified version of the first embodiment for comparison were the same as those in the first embodiment for comparison shown in Fig. 5. Therefore, in the first embodiment and its modified version, g = a = 2p. However, the number of electrode finger formation regions in the first embodiment is two, while the number of electrode finger formation regions in the modified version of the first embodiment is four.

[0056] FIG. 8 is a diagram showing admittance frequency characteristics in the range of 100 MHz to 1000 MHz in the first embodiment, its modified example, and the comparative example.

[0057] 8, in the first embodiment and its modified example, unwanted waves are suppressed more than in the comparative example. Furthermore, in the modified example of the first embodiment, unwanted waves are suppressed more than in the first embodiment.

[0058] In the following description, the dimension of one of adjacent electrode finger formation regions along the direction perpendicular to the electrode fingers is defined as length L1, and the dimension of the other electrode finger formation region along the direction perpendicular to the electrode fingers is defined as length L2. For example, in the first embodiment shown in FIG. 1 , if the dimension of electrode finger formation region E1 along the direction perpendicular to the electrode fingers is defined as length L1, the dimension of electrode finger formation region E2 along the direction perpendicular to the electrode fingers is length L2. In the first embodiment, L1 = L2.

[0059] 7 , adjacent electrode finger formation regions are electrode finger formation region E1 and electrode finger formation region E2, electrode finger formation region E2 and electrode finger formation region E3, and electrode finger formation region E3 and electrode finger formation region E4. In this modification of the first embodiment, L1=L2 in each adjacent electrode finger formation region. Note that the lengths L1 and L2 in adjacent electrode finger formation regions may be different from each other.

[0060] The intensity of spurious waves was calculated for an elastic wave device having a configuration similar to that of the first embodiment, except that L1≠L2. More specifically, the intensity of spurious waves was calculated for each of the ratios of length L1 to length L2 and the ratio of inter-region distance g to intra-region center distance p. Specifically, L1>L2 was set, and L1:L2 was set to 90:10, 80:20, 70:30, or 60:40. Each of the above conditions was expressed as L2 / (L1+L2), which is the value obtained by dividing length L2 by the sum of length L1 and length L2, and was 0.1, 0.2, 0.3, or 0.4. The ratio g / p of inter-region distance g to intra-region center distance p was varied in increments of 0.25 from 0.5 to 5.

[0061] Even under the condition where L1 = L2 and L1:L2 = 50:50, the intensity of the spurious waves was calculated for each different g / p ratio. This condition is expressed as L2 / (L1 + L2), which is 0.5. The g / p ratio was varied in increments of 0.25 between 0.5 and 5.

[0062] 9 is a diagram showing the relationship between L2 / (L1+L2) and the ratio g / p and the intensity of the spurious waves. Note that the intensities of the spurious waves shown in Fig. 9 are normalized based on the intensity of the spurious waves when L1 = L2 and g / p = 1.

[0063] As shown in Figure 9, when L2 / (L1+L2) is 0.2 or more, the intensity of the unwanted waves can be reduced to 0.8 or less depending on the ratio g / p. For this reason, it is preferable that L1 ≥ L2 and L2 / (L1+L2) ≥ 0.2. This makes it possible to more reliably and effectively suppress unwanted waves.

[0064] When the ratio g / p is 0.65 or more and 0.9 or less, and when 1.8 or more and 2.8 or less, and when L2 / (L1+L2) is 0.3 or more, the intensity of the spurious waves can be kept to 0.8 or less. Therefore, it is more preferable that L1≧L2 and L2 / (L1+L2)≧0.3, and the relationship between the inter-region distance g and the intra-region center-to-center distance p in adjacent electrode finger formation regions is 0.65p≦g≦0.9p or 1.8p≦g≦2.8p. This makes it possible to more reliably and effectively suppress spurious waves.

[0065] Here, the average value of the intra-region center-to-center distance p in the electrode finger formation regions is defined as pa. L1≧L2, L2 / (L1+L2)≧0.3, and the relationship between the inter-region distance g and the average value pa in each of the adjacent electrode finger formation regions may be 0.65pa≦g≦0.9pa or 1.8pa≦g≦2.8pa. Even in this case, spurious waves can be more reliably and effectively suppressed. When 0.65p≦g≦0.9p or 1.8p≦g≦2.8p, or 0.65pa≦g≦0.9pa or 1.8pa≦g≦2.8pa, it is more preferable that L1≧L2 and L2 / (L1+L2) is 0.4 or greater. In this case, spurious waves can be more reliably and effectively suppressed.

[0066] Even when the acoustic wave device is divided into three or more electrode finger formation regions in the portion where the IDT electrodes are formed, it is preferable that L1≧L2 and L2 / (L1+L2)≧0.2 be satisfied in adjacent electrode finger formation regions. It is more preferable that L1≧L2 and L2 / (L1+L2)≧0.3 be satisfied, and 0.65p≦g≦0.9p or 1.8p≦g≦2.8p be satisfied in adjacent electrode finger formation regions. Alternatively, it is more preferable that L1≧L2 and L2 / (L1+L2)≧0.3 be satisfied, and 0.65pa≦g≦0.9pa or 1.8pa≦g≦2.8pa be satisfied. In each of the above conditions, it is even more preferable that L1≧L2 and L2 / (L1+L2) be 0.4 or greater.

[0067] 7, the length of electrode finger formation region E1 may be L1, the length of electrode finger formation region E2 may be L2, the length of electrode finger formation region E3 may be L1, and the length of electrode finger formation region E4 may be L2. In such a case, it is preferable that the above conditions are satisfied in each of the adjacent electrode finger formation regions.

[0068] When L1≧L2 between adjacent electrode finger formation regions, it is preferable that the electrode finger formation region having length L1 includes a portion that is symmetrical with the electrode finger formation region having length L2 about an axis of symmetry extending in the electrode finger extension direction. Alternatively, it is preferable that the electrode finger formation region having length L1 includes a portion that has the same configuration as the electrode finger formation region having length L2. In these cases, it can be said that a single acoustic wave resonator includes portions that are divided into regions that are equivalent in terms of electrical characteristics. This makes it possible to more reliably achieve the desired electrical characteristics of the acoustic wave device and suppress unwanted waves.

[0069] In the first embodiment and its modified example, adjacent electrode fingers in adjacent electrode finger formation regions are connected to different potentials. However, adjacent electrode fingers in adjacent electrode finger formation regions may also be connected to the same potential. This example is shown in the second embodiment.

[0070] FIG. 10 is a schematic front cross-sectional view of an elastic wave device according to a second preferred embodiment of the present invention.

[0071] This embodiment differs from the first embodiment in that the electrode finger in the electrode finger formation region E2 closest to the electrode finger formation region E1 is the first electrode finger 18. In this embodiment, adjacent electrode fingers in adjacent electrode finger formation regions are connected to the same potential. This embodiment also differs from the first embodiment in that the inter-region distance g and the center-to-center distance a in the electrode finger formation region E1 and the electrode finger formation region E2 are different from each other. Except for the above points, the elastic wave device 21 of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0072] The inter-region distance g between the electrode finger formation regions E1 and E2 in the acoustic wave device 21 is the center-to-center distance between the first electrode finger 18 in the electrode finger formation region E1 closest to the electrode finger formation region E2 and the first electrode finger 18 in the electrode finger formation region E2 closest to the electrode finger formation region E1. Therefore, the inter-region distance g is different from the center-to-center distance a, which is the shortest distance between the first electrode finger 18 in the electrode finger formation region E1 and the second electrode finger 19 in the electrode finger formation region E2. In addition, in the acoustic wave device 21, the intra-region center-to-center distance p in the electrode finger formation regions E1 and E2 is different from the center-to-center distance a in the electrode finger formation regions E1 and E2.

[0073] In this embodiment, as in the first embodiment, unwanted waves can be suppressed. Details of this will be shown by comparing this embodiment with a comparative example. Note that this comparative example is the same as the comparative example shown in FIG. 8 and the like.

[0074] The admittance-frequency characteristics of the second embodiment and the comparative example were compared. The respective admittance-frequency characteristics were derived by FEM simulation. In this comparison, in the second embodiment, the inter-region distance g was set to be the same as the intra-region center-to-center distance p. In this case, the center-to-center distance a was twice the intra-region center-to-center distance p. That is, in the second embodiment, g = 0.5 a = p. The design parameters of the elastic wave device of the second embodiment for this comparison are as follows:

[0075] Piezoelectric layer: Material... LiNbO ３ , thickness... 368 nm Protective film layer: material... SiO ２ , thickness...133 nm Electrode fingers: material...Al, thickness...500 nm Intra-region center distance p: 4.26 μm Region-to-region distance g: 4.26 μm

[0076] The design parameters of the comparative example were the same as those of the second embodiment, except that the inter-region distance g and the center-to-center distance a were not defined. The center-to-center distance between adjacent electrode fingers in the comparative example was set to the same as the intra-region center-to-center distance p in the second embodiment.

[0077] Fig. 11 is a diagram showing the admittance frequency characteristics in the second embodiment and the comparative example, and Fig. 12 is a diagram showing the admittance frequency characteristics in the range of 100 MHz to 1000 MHz in the second embodiment and the comparative example.

[0078] As shown in the dashed-dotted line frame in Fig. 11 and in Fig. 12, in the comparative example, large spurious waves are generated around 600 MHz, which is lower than the resonant frequency. In contrast, in the second embodiment, it can be seen that spurious waves are suppressed around 600 MHz. The reason for this will be explained below.

[0079] In the second embodiment, as in the first embodiment, when bulk waves in the thickness-shear mode, which is the main mode, are excited, unwanted waves are also excited. For example, unwanted waves originating from plate wave harmonics propagate in the direction perpendicular to the electrode fingers. In the second embodiment, such unwanted waves can be suppressed.

[0080] 13A to 13C are schematic front cross-sectional views showing the vicinity of a plurality of electrode fingers, for explaining that spurious waves can be suppressed in the second embodiment.

[0081] As shown in FIG. 13A, the inter-region distance g between the electrode finger forming regions E1 and E2 is the same as the intra-region center-to-center distance p between the electrode finger forming regions E1 and E2.

[0082] 13B schematically shows spurious waves excited in the electrode finger formation region E1. In FIG. 13B, dashed lines virtually indicate that electrode fingers are also arranged outside the electrode finger formation region E1 at the same period as within the region. The phase of the spurious waves excited in the electrode finger formation region E1 outside the region is based on a virtual configuration in which electrode fingers are arranged in the same manner both inside and outside the region.

[0083] 13(c) schematically shows spurious waves excited in the electrode finger formation region E2, as in Fig. 13(b). In Fig. 13(c), dashed lines virtually indicate that electrode fingers are also arranged outside the electrode finger formation region E2 at the same period as within the region.

[0084] 13(b) and 13(c), the phase of the unwanted waves excited in the electrode finger formation region E1 is different from the phase of the unwanted waves excited in the electrode finger formation region E2. As a result, the unwanted waves excited in both regions interfere with each other, weakening each other. This makes it possible to suppress the unwanted waves.

[0085] When adjacent electrode fingers in adjacent electrode finger formation regions are connected to the same potential, it is preferable that the relationship between the length L1 and the length L2, and the relationship between the inter-region distance g and the intra-region center-to-center distance p, satisfy the following ranges. That is, it is preferable that L1≧L2, L2 / (L1+L2)≧0.3, and that the relationship between the inter-region distance g and the intra-region center-to-center distance p in each of the adjacent electrode finger formation regions satisfy 1.6p≦g≦1.8p. This makes it possible to more reliably suppress unwanted waves. Details of this are provided below.

[0086] The intensity of unwanted waves was calculated for an elastic wave device having a configuration similar to that of the second embodiment, except that L1≠L2. More specifically, the intensity of unwanted waves was calculated for each of the ratios of length L1 to length L2 and the ratio of inter-region distance g to intra-region center distance p. Specifically, L1>L2 was set, and L1:L2 was set to 90:10, 80:20, 70:30, or 60:40. Each of the above conditions was expressed as L2 / (L1+L2), which is the value obtained by dividing length L2 by the sum of length L1 and length L2, and was 0.1, 0.2, 0.3, or 0.4. The ratio g / p of inter-region distance g to intra-region center distance p was varied in increments of 0.25 from 0.5 to 5.

[0087] Even under the condition where L1 = L2 and L1:L2 = 50:50, the intensity of the spurious waves was calculated for each different g / p ratio. This condition is expressed as L2 / (L1 + L2), which is 0.5. The g / p ratio was varied in increments of 0.25 between 0.5 and 5.

[0088] Fig. 14 is a diagram showing the relationship between L2 / (L1+L2) and the ratio g / p and the intensity of the spurious waves. Note that the intensities of the spurious waves shown in Fig. 14 are normalized based on the intensity of the spurious waves when L1=L2 and g / p=1.

[0089] As shown in Figure 14, when L2 / (L1+L2) is 0.2 or more, the intensity of the unwanted waves can be reduced to 0.8 or less depending on the ratio g / p. For this reason, it is preferable that L1 ≥ L2 and L2 / (L1+L2) ≥ 0.2. This makes it possible to more reliably and effectively suppress unwanted waves.

[0090] When the ratio g / p is 1.6 or more and 1.8 or less, and L2 / (L1+L2) is 0.3 or more, the intensity of the spurious waves can be kept to 0.8 or less. Therefore, it is more preferable that L1≧L2 and L2 / (L1+L2)≧0.3, and the relationship between the inter-region distance g and the intra-region center-to-center distance p in adjacent electrode finger formation regions satisfies 1.6p≦g≦1.8p. This makes it possible to more reliably and effectively suppress spurious waves.

[0091] When the average value of the intra-region center-to-center distance p in the electrode finger formation regions is pa, L1≧L2 and L2 / (L1+L2)≧0.3 may be satisfied, and the relationship between the region distance g and the average value pa in each of the adjacent electrode finger formation regions may be 1.6pa≦g≦1.8pa. Even in this case, unwanted waves can be suppressed more reliably and effectively.

[0092] Even when the acoustic wave device is divided into three or more electrode finger formation regions in the portion where the IDT electrodes are formed, it is preferable that L1≧L2 and L2 / (L1+L2)≧0.2 be satisfied in adjacent electrode finger formation regions. It is more preferable that L1≧L2, L2 / (L1+L2)≧0.3, and 1.6p≦g≦1.8p be satisfied in adjacent electrode finger formation regions. Alternatively, it is more preferable that L1≧L2, L2 / (L1+L2)≧0.3, and 1.6pa≦g≦1.8pa be satisfied.

[0093] FIG. 15 is a schematic front cross-sectional view showing the vicinity of a plurality of electrode fingers in the third embodiment.

[0094] This embodiment differs from the first embodiment in that a metal film 38 is provided on the second main surface 6b of the piezoelectric layer 6. The metal film 38 is provided so as to overlap the IDT electrode 7 in a plan view. Except for the above points, the elastic wave device 31 of this embodiment has a similar configuration to the elastic wave device 1 of the first embodiment.

[0095] As in the first embodiment, the piezoelectric film is a single piezoelectric layer 6. Therefore, the first and second principal surfaces of the piezoelectric film are the first and second principal surfaces 6a and 6b of the piezoelectric layer 6.

[0096] The metal film 38 is a floating electrode, which is an electrode that is not connected to the signal potential or the reference potential.

[0097] The acoustic wave device 31 is configured to utilize thickness-shear bulk waves as the main mode. The arrangement of the electrode fingers in this embodiment is the same as that in the first embodiment. Therefore, the intra-region center-to-center distance p in adjacent electrode finger formation regions is different from the center-to-center distance a between adjacent electrode finger formation regions. Furthermore, the intra-region center-to-center distance p in adjacent electrode finger formation regions is different from the inter-region distance g between adjacent electrode finger formation regions. This allows for suppression of unwanted waves.

[0098] FIG. 16 is a schematic front cross-sectional view of an elastic wave device according to a fourth preferred embodiment of the present invention.

[0099] This embodiment differs from the first embodiment in that the acoustic reflection portion is an acoustic reflection film 48. This embodiment also differs from the first embodiment in that the support member 43 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.

[0100] An acoustic reflection film 48 is provided on the surface of the support member 43. A piezoelectric layer 6 serving as a piezoelectric film is provided on the acoustic reflection film 48. The support member 43 and the piezoelectric film may be arranged such that at least a portion of the support member 43 and at least a portion of the piezoelectric film face each other with the acoustic reflection film 48 sandwiched therebetween.

[0101] The acoustic reflecting film 48 is a laminate of multiple acoustic impedance layers. Specifically, the acoustic reflecting film 48 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 in the acoustic reflecting film 48 are low acoustic impedance layer 45a, low acoustic impedance layer 45b, and low acoustic impedance layer 45c.

[0102] 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 in the acoustic reflecting film 48 are the high acoustic impedance layer 46a and the high acoustic impedance layer 46b. The low acoustic impedance layers and the high acoustic impedance layers are alternately stacked. The low acoustic impedance layer 45a is the layer in the acoustic reflecting film 48 that is located closest to the piezoelectric layer 6.

[0103] The acoustic reflection film 48 has three low acoustic impedance layers and two high acoustic impedance layers, although it is sufficient that the acoustic reflection film 48 has at least one low acoustic impedance layer and one high acoustic impedance layer.

[0104] 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.

[0105] In this embodiment, it is possible to suppress unwanted waves as in the first embodiment. In addition, by providing the acoustic reflection film 48, it is possible to effectively confine the energy of bulk waves in the thickness shear mode, which is the main mode, to the piezoelectric layer 6 side.

[0106] The configuration in this embodiment in which the acoustic reflecting portion is the acoustic reflecting film 48 can also be applied to configurations of the present invention other than this embodiment.

[0107] 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.

[0108] In the first embodiment, when the thickness of the piezoelectric film is d, the ratio d / p is 0.5 or less in the multiple electrode finger forming regions. It is preferable that the ratio d / p is 0.24 or less in the multiple electrode finger forming regions. 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. The bandwidth fraction is expressed as (|fa-fr| / fr) x 100 [%], where fr is the resonant frequency and fa is the antiresonant frequency.

[0109] FIG. 17 is a graph showing the relationship between d / p and the fractional bandwidth of an elastic wave resonator.

[0110] As is clear from FIG. 17, 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.

[0111] When the metallization ratio of the electrode fingers in each electrode finger formation region 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.

[0112] 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.

[0113] Fig. 18 is a diagram showing the relationship between the relative bandwidth and the normalized magnitude of spurious in an elastic wave resonator. Fig. 18 shows the results of measuring the amount of phase rotation of spurious every time the relative bandwidth is changed by changing the thickness of the piezoelectric layer and the dimensions of the electrode fingers. The normalized magnitude of spurious in Fig. 18 is specifically the value obtained by normalizing the amount of phase rotation of the spurious impedance by 180°. The results shown in Fig. 18 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.

[0114] In the region surrounded by ellipse A in Fig. 18, 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.

[0115] 19 is a diagram showing the relationship between d / p, metallization ratio MR, and fractional bandwidth, in which the results of calculating fractional bandwidth for different d / p and metallization ratio MR are shown.

[0116] In Figure 19, 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 B. Dashed line B 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.

[0117] On the other hand, the dashed-dotted line B1 in Figure 19 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 B, and where the fractional bandwidth is 17% or less over the entire range. The dashed-dotted line B1 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.

[0118] FIG. 20 shows the results of LiNbO when d / p approaches 0. ３ 20 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 10. The hatched area in FIG. 20 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).

[0119] (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)

[0120] 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.

[0121] Examples of embodiments of the acoustic wave device according to the present invention will be described below.

[0122] <1> A piezoelectric element comprising: a support member; a piezoelectric film provided on the support member and including a piezoelectric layer; and an IDT electrode provided on the piezoelectric film and having a plurality of electrode fingers, wherein an acoustic reflecting portion is formed on the support member at a position overlapping with the IDT electrode in a plan view; when a direction orthogonal to a direction in which the plurality of electrode fingers extend is defined as an electrode finger orthogonal direction, a plurality of electrode finger forming regions each including two or more of the electrode fingers are configured in a portion where the IDT electrode is formed, the plurality of electrode finger forming regions are arranged in the electrode finger orthogonal direction, and each of the electrode finger forming regions is located between a center of one end of the two or more electrode fingers in the electrode finger orthogonal direction and an electrode finger of the other end of the two or more electrode fingers in the electrode finger orthogonal direction. an elastic wave device in which, when the center-to-center distance between adjacent electrode fingers in each electrode finger formation region is defined as an intra-region center-to-center distance p, the average value of the intra-region center-to-center distance p is substantially the same in the plurality of electrode finger formation regions; when the thickness of the piezoelectric film is defined as d, d / p is 0.5 or less in the plurality of electrode finger formation regions; and, among the center-to-center distances between the electrode fingers in one electrode finger formation region and the electrode fingers in the other electrode finger formation region in the adjacent electrode finger formation regions, the shortest center-to-center distance a is different from the intra-region center-to-center distance p in the adjacent electrode finger formation regions, among the center-to-center distances between the electrode fingers connected to different potentials.

[0123] <2> An elastic wave device described in <1>, in which adjacent electrode fingers in adjacent electrode finger forming regions are connected to different potentials, and when the dimension of one of the adjacent electrode finger forming regions along the electrode finger orthogonal direction is length L1 and the dimension of the other adjacent electrode finger forming region along the electrode finger orthogonal direction is length L2, L1≧L2 and L2 / (L1+L2)≧0.2.

[0124] <3> The elastic wave device according to <2>, wherein L2 / (L1+L2)≧0.3, and when the center-to-center distance between adjacent electrode fingers in adjacent electrode finger forming regions is defined as an inter-region distance g, the relationship between the inter-region distance g and the intra-region center distance p in each of the adjacent electrode finger forming regions is 0.65p≦g≦0.9p or 1.8p≦g≦2.8p.

[0125] <4> The acoustic wave device according to <1>, wherein the adjacent electrode fingers in the adjacent electrode finger formation regions are connected to the same potential.

[0126] <5> The elastic wave device described in <4>, wherein when the dimension of one of the adjacent electrode finger forming regions along the electrode finger orthogonal direction is length L1 and the dimension of the other of the adjacent electrode finger forming regions along the electrode finger orthogonal direction is length L2, L1≧L2 and L2 / (L1+L2)≧0.3, and when the center-to-center distance between adjacent electrode fingers in adjacent electrode finger forming regions is region-to-region distance g, the relationship between the region-to-region distance g and the intra-region center-to-center distance p in each of the adjacent electrode finger forming regions is 1.6p≦g≦1.8p.

[0127] <6> An elastic wave device described in any one of <1> to <5>, wherein the piezoelectric film has a first main surface and a second main surface facing each other, the IDT electrode is provided on the first main surface, and a metal film is provided on the second main surface so as to overlap the IDT electrode in a planar view, and the metal film is not connected to a signal potential or a reference potential.

[0128] <7> The acoustic wave device according to any one of <1> to <6>, wherein d / p is 0.24 or less in the plurality of electrode finger forming regions.

[0129] <8> An elastic wave device described in any one of <1> to <7>, wherein the acoustic reflection portion is a hollow portion, and the support member and the piezoelectric film are arranged so that a portion of the support member and a portion of the piezoelectric film face each other across the hollow portion.

[0130] <9> An elastic wave device described in any one of <1> to <7>, wherein 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 film are arranged so that at least a portion of the support member and at least a portion of the piezoelectric film face each other with the acoustic reflection film in between.

[0131] <10> An elastic wave device according to any one of <1> to <9>, wherein in each electrode finger forming region, 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 the metallization ratio of the electrode fingers to the excitation region is MR, MR≦1.75(d / p)+0.075 is satisfied.

[0132] <11> The acoustic wave device according to any one of <1> to <10>, 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)

[0133] REFERENCE SIGNS LIST 1...acoustic wave device 2...piezoelectric substrate 2a...cavity 3...support member 4...support substrate 5...insulating layer 6...piezoelectric layer 6a, 6b...first and second principal surfaces 7...IDT electrode 16, 17...first and second bus bars 18, 19...first and second electrode fingers 21, 31...acoustic wave device 38...metal film 43...support member 45a to 45c...low acoustic impedance layer 46a, 46b...high acoustic impedance layer 48...acoustic reflection film 107...IDT electrode C...excitation region E1 to E4...electrode finger forming region

Claims

1. A piezoelectric element comprising: a support member; a piezoelectric film provided on the support member and including a piezoelectric layer; and an IDT electrode provided on the piezoelectric film and having a plurality of electrode fingers, wherein an acoustic reflecting portion is formed on the support member at a position overlapping the IDT electrode in a planar view; when a direction perpendicular to the direction in which the plurality of electrode fingers extend is defined as an electrode finger orthogonal direction, a plurality of electrode finger formation regions each including two or more of the electrode fingers are configured in the portion where the IDT electrode is formed, the plurality of electrode finger formation regions are aligned in the electrode finger orthogonal direction, and each of the electrode finger formation regions is a region from the center of the electrode finger at one end in the electrode finger orthogonal direction of the two or more electrode fingers to the center of the electrode finger at the other end in the electrode finger orthogonal direction, when the center-to-center distance between the electrode fingers adjacent to each other in each of the electrode finger formation regions is defined as an intra-region center-to-center distance p, the average value of the intra-region center-to-center distance p is substantially the same among the plurality of electrode finger formation regions, an elastic wave device in which, when the thickness of the piezoelectric film is d, d / p is 0.5 or less in the plurality of electrode finger formation regions; and among the center-to-center distances between the electrode fingers in one electrode finger formation region and the electrode fingers in the other electrode finger formation region in adjacent electrode finger formation regions, a smallest center-to-center distance a is different from the intra-region center-to-center distance p in each of the adjacent electrode finger formation regions, among the center-to-center distances between the electrode fingers in one electrode finger formation region and the electrode fingers in the other electrode finger formation region that are connected to different potentials.

2. The elastic wave device according to claim 1, wherein adjacent electrode fingers in adjacent electrode finger forming regions are connected to different potentials, and when the dimension of one of the adjacent electrode finger forming regions along the electrode finger orthogonal direction is length L1 and the dimension of the other of the adjacent electrode finger forming regions along the electrode finger orthogonal direction is length L2, L1 ≧ L2 and L2 / (L1 + L2) ≧ 0.

2.

3. The elastic wave device according to claim 2, wherein L2 / (L1+L2)≧0.3, and when the center-to-center distance between adjacent electrode fingers in adjacent electrode finger formation regions is defined as an inter-region distance g, the relationship between the inter-region distance g and the intra-region center distance p in each of the adjacent electrode finger formation regions is 0.65p≦g≦0.9p or 1.8p≦g≦2.8p.

4. The acoustic wave device according to claim 1, wherein adjacent electrode fingers in adjacent electrode finger forming regions are connected to the same potential.

5. The elastic wave device according to claim 4, wherein, when the dimension of one of the adjacent electrode finger formation regions along the electrode finger orthogonal direction is length L1 and the dimension of the other of the adjacent electrode finger formation regions along the electrode finger orthogonal direction is length L2, L1≧L2 and L2 / (L1+L2)≧0.3; and when the center-to-center distance between adjacent electrode fingers in adjacent electrode finger formation regions is region-to-region distance g, the relationship between region-to-region distance g and the intra-region center-to-center distance p in each of the adjacent electrode finger formation regions is 1.6p≦g≦1.8p.

6. The elastic wave device according to any one of claims 1 to 5, wherein the piezoelectric film has a first principal surface and a second principal surface that face each other, the IDT electrode is provided on the first principal surface, and a metal film is provided on the second principal surface so as to overlap the IDT electrode in a planar view, and the metal film is not connected to a signal potential or a reference potential.

7. The acoustic wave device according to claim 1, wherein d / p is 0.24 or less in the plurality of electrode finger forming regions.

8. An elastic wave device according to any one of claims 1 to 7, wherein the acoustic reflection portion is a hollow portion, and the support member and the piezoelectric film are arranged so that a portion of the support member and a portion of the piezoelectric film face each other across the hollow portion.

9. An elastic wave device according to any one of claims 1 to 7, wherein the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer with a relatively high acoustic impedance and a low acoustic impedance layer with a relatively low acoustic impedance, and the support member and the piezoelectric film are arranged so that at least a portion of the support member and at least a portion of the piezoelectric film face each other with the acoustic reflection film in between.

10. An elastic wave device according to any one of claims 1 to 9, wherein in each electrode finger formation region, 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.

11. The acoustic wave device according to any one of claims 1 to 10, 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)

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