Filter device

Abstract

Provided is a filter device that can achieve an increase in heat dissipation and a reduction in size.　A filter device 1 according to the present invention comprises a plurality of elastic wave resonators (series arm resonators S1 to S6 and parallel arm resonators P1 to P6) that share a piezoelectric substrate 2 having a support member and a piezoelectric film provided on the support member, the piezoelectric film including a piezoelectric layer 6, and the plurality of elastic wave resonators each having an IDT electrode 7 provided on the piezoelectric film. In a plan view, hollow portions 2a are provided at respective positions in the support member overlapping the IDT electrodes 7. 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 with the plurality of hollow portions 2a therebetween. Each IDT electrode 7 has a plurality of electrode fingers. The direction in which the plurality of electrode fingers extend is defined as an electrode finger extending direction, and a direction orthogonal to the electrode finger extending direction is defined as an electrode finger orthogonal direction. The dimension of each hollow portion 2a along the electrode finger orthogonal direction is represented by Lx, and the dimension thereof along the electrode finger extending direction is represented by Ly. Then, the ratio Lx / Ly of the dimension Lx to the dimension Ly in each hollow portion 2a is greater than or equal to 4. The piezoelectric film has a main surface (first main surface 6a) on which the plurality of IDT electrodes 7 are provided. The main surface has a rectangular shape. The main surface has a pair of long sides 6c, 6d and a pair of short sides 6e, 6f. An angle formed by the electrode finger extending direction in the plurality of elastic wave resonators and the direction in which the short sides 6e, 6f of the main surface of the piezoelectric film extend is less than or equal to 5°.

Description

Filter Device

[0001] The present invention relates to a filter device having a plurality of acoustic wave resonators.

[0002] Conventionally, filter devices having acoustic wave resonators have been widely used in mobile phones, etc. In recent years, a filter device having multiple resonators using a horizontal shear acoustic mode has been proposed, as described in Patent Document 1 listed below. In this filter device, the multiple resonators include series arm resonators and parallel arm resonators as shunt resonators.

[0003] Each of the multiple resonators in Patent Document 1 is configured by providing an IDT (Interdigital Transducer) on a piezoelectric plate. The piezoelectric plate is provided on a substrate. More specifically, a cavity is formed in the substrate. The piezoelectric plate is suspended on the substrate so as to pass over the cavity.

[0004] The IDT has multiple fingers. Adjacent fingers are connected to different potentials. By applying an AC voltage between adjacent fingers, bulk waves in thickness-shear mode, which are horizontal shear acoustic modes, are excited.

[0005] Meanwhile, Patent Document 2 listed below discloses an example of a composite filter device. This composite filter device has a piezoelectric substrate. The piezoelectric substrate has a rectangular shape in a plan view. A plurality of IDT electrodes are provided on the piezoelectric substrate. These electrodes form a plurality of series arm resonators and a plurality of parallel arm resonators. The IDT electrodes have a plurality of electrode fingers. The plurality of electrode fingers in each series arm resonator and each parallel arm resonator extend in the direction of the long side of the piezoelectric substrate.

[0006] JP 2021-527344 A JP 2024-030509 A

[0007] In order to obtain desired electrical characteristics in the series arm resonators and parallel arm resonators described in Patent Document 1, the area of ​​the IDT needs to be increased to a certain extent. However, since miniaturization of the entire filter device is also required, the layout on the piezoelectric plate becomes important. However, even if the configuration described in Patent Document 2 is adopted as the specific arrangement of the series arm resonators and parallel arm resonators in Patent Document 1, it is difficult to sufficiently miniaturize the filter device.

[0008] In the series arm resonators and parallel arm resonators of the filter device described in Patent Document 1, heat is generated as elastic waves, such as bulk waves in thickness shear mode, are excited. More specifically, the regions of the piezoelectric plate where elastic waves are excited become heat sources. The areas near these heat sources face the cavity. This makes it difficult for the heat to be released to the outside.

[0009] An object of the present invention is to provide a filter device that can enhance heat dissipation and can be made smaller in size.

[0010] A filter device according to the present invention includes a piezoelectric substrate having a support member and a piezoelectric film provided on the support member and including a piezoelectric layer, and includes a plurality of acoustic wave resonators each having an IDT electrode provided on the piezoelectric film, wherein, in a plan view, cavities are provided in the support member at positions overlapping with the IDT electrodes, and the support member and the piezoelectric film are arranged such that a part of the support member and a part of the piezoelectric film face each other with the cavities therebetween, and the IDT electrode has a plurality of electrode fingers, and the direction in which the plurality of electrode fingers extend is defined by an electrode a finger extension direction, a direction perpendicular to the electrode finger extension direction, an electrode finger orthogonal direction, a dimension of each cavity along the electrode finger orthogonal direction, Lx, a dimension of each cavity along the electrode finger extension direction, Ly, a ratio Lx / Ly of the dimension Lx to the dimension Ly of each cavity is 4 or more, the piezoelectric film has a main surface on which a plurality of IDT electrodes are provided, the main surface is rectangular in shape, the main surface has a pair of long sides and a pair of short sides, and an angle formed between the electrode finger extension direction of the plurality of elastic wave resonators and the direction in which the short sides on the main surface of the piezoelectric film extend is 5° or less.

[0011] According to the filter device of the present invention, it is possible to improve heat dissipation properties and promote miniaturization.

[0012] FIG. 1 is a circuit diagram of a filter device according to a first embodiment of the present invention. FIG. 2 is a schematic plan view of a filter device according to the first embodiment of the present invention. FIG. 3 is a schematic plan view showing an acoustic wave resonator according to the first embodiment of the present invention. FIG. 4 is a schematic cross-sectional view taken along line II in FIG. 3. FIG. 5 is a schematic diagram showing the positional relationship between a piezoelectric substrate and multiple acoustic wave resonators in a first comparative example. FIG. 6 is a schematic diagram showing the positional relationship between a piezoelectric substrate and multiple acoustic wave resonators in a second comparative example. FIG. 7 is a schematic plan view showing an acoustic wave resonator according to a modified example of the first embodiment of the present invention. FIG. 8 is a circuit diagram of a filter device according to a second embodiment of the present invention. FIG. 9 is a schematic plan view of a filter device according to the second embodiment of the present invention. FIG. 10 is a schematic plan view of a filter device according to a modified example of the second embodiment of the present invention. FIG. 11 is a graph showing the relationship between d / p and the relative bandwidth of an acoustic wave resonator. FIG. 12 is a graph showing the relationship between the relative bandwidth of an acoustic wave resonator and the magnitude of normalized spurious signals. 13 is a diagram showing the relationship between d / p, metallization ratio MR, and fractional bandwidth. ３ FIG. 10 is a diagram showing a map of fractional bandwidths versus Euler angles (0°, θ, ψ) of the .lambda.

[0013] The present invention will be clarified below by describing specific embodiments of the present invention with reference to the drawings.

[0014] 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.

[0015] FIG. 1 is a circuit diagram of a filter device according to a first embodiment of the present invention.

[0016] The filter device 1 is a ladder-type filter. The filter device 1 has a first signal terminal 11A, a second signal terminal 11B, and a plurality of acoustic wave resonators. In this embodiment, the second signal terminal 11B is an antenna terminal. The antenna terminal is connected to an antenna. Note that the second signal terminal 11B does not necessarily have to be an antenna terminal.

[0017] The plurality of acoustic wave resonators include a plurality of series arm resonators and a plurality of parallel arm resonators. In this embodiment, the plurality of series arm resonators are specifically series arm resonators S1, S2, S3, S4, S5, and S6. The plurality of parallel arm resonators are specifically parallel arm resonators P1, P2, P3, P4, P5, and P6.

[0018] The circuit configuration of the filter device 1 includes a series arm S, multiple parallel arms P, and multiple nodes N. In this specification, the series arm S is a path connecting the first signal terminal 11A and the second signal terminal 11B. On the other hand, each parallel arm P is a path branching from the series arm S to each ground potential. The node N is a connection point between the series arm S and the parallel arm P. Each series arm resonator is arranged in the series arm S. Each parallel arm P is arranged in the parallel arm P.

[0019] A specific configuration of the filter device 1 of this embodiment will be described below.

[0020] Fig. 2 is a schematic plan view of the filter device according to the first embodiment. In Fig. 2, an IDT electrode, which will be described later, is shown as a rectangle with two diagonal lines added. The same applies to the other schematic plan views.

[0021] The filter device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 is a substrate having piezoelectric properties. As shown in FIG. 2 , the piezoelectric substrate 2 has a piezoelectric layer 6 as a piezoelectric film. The piezoelectric layer 6 is a layer made of a piezoelectric material. On the other hand, 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.

[0022] The piezoelectric layer 6 is made of, for example, LiNbO ３ Alternatively, the material may be made of lithium niobate such as LiTaO ３In this embodiment, the piezoelectric layer 6 is made of lithium niobate. In this specification, a certain member being made of a certain material includes a case where a small amount of impurity is contained to the extent that the electrical characteristics of the elastic wave resonator are not significantly deteriorated.

[0023] 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. The first main surface 6a and the second main surface 6b of the piezoelectric layer 6 are rectangular in shape. The first main surface 6a has a pair of long sides 6c and 6d. The first main surface 6a has a pair of short sides 6e and 6f. 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. The long sides 6c and 6d and the short sides 6e and 6f of the first main surface 6a of the piezoelectric layer 6 are a pair of long sides and a pair of short sides of the first main surface of the piezoelectric film.

[0024] A first signal terminal 11A, a second signal terminal 11B, and a plurality of ground terminals 12 are provided on the first main surface 6a of the piezoelectric layer 6. The ground terminals 12 are terminals connected to a ground potential. Each of the above terminals is configured as an electrode pad. However, each of the above terminals may also be configured as a wiring.

[0025] A plurality of IDT electrodes 7 are provided on the first main surface 6 a of the piezoelectric layer 6. This forms a plurality of elastic wave resonators. That is, each of the elastic wave resonators has an IDT electrode 7. The elastic wave resonators share the same piezoelectric substrate 2 and piezoelectric layer 6. In this embodiment, each elastic wave resonator is configured to use a thickness-shear bulk wave as its main mode. However, each elastic wave resonator may also be configured to use, for example, a plate wave as its main mode. A specific configuration of an elastic wave resonator in this embodiment is shown with reference to FIG. 3 .

[0026] 3 is a schematic plan view showing an elastic wave resonator according to the first preferred embodiment, in which other elastic wave resonators and wiring are omitted.

[0027] The acoustic wave resonator shown in FIG. 3 is a series arm resonator S1. The IDT electrode 7 of the series arm resonator S1 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 ends of the plurality of first electrode fingers 18 are connected to the first bus bar 16, and one ends of the plurality of second electrode fingers 19 are 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 laminated metal film or a single-layer metal film.

[0028] 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 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.

[0029] In this embodiment, the electrode fingers of all the acoustic wave resonators extend in the same direction. The electrode finger extension direction of all the acoustic wave resonators is parallel to the direction in which the short sides 6 e and 6 f of the piezoelectric layer 6 serving as the piezoelectric film extend. That is, the angle between the electrode finger extension direction of all the acoustic wave resonators and the direction in which the short sides of the first principal surface of the piezoelectric film extend is 0°. Note that this angle may be 5° or less.

[0030] In the present invention, the electrode finger extension directions of all the acoustic wave resonators do not necessarily have to be the same, as long as the angle between the electrode finger extension direction of all the acoustic wave resonators and the direction in which the short side of the first principal surface of the piezoelectric film extends is 5° or less.

[0031] As shown in FIG. 3 , the series arm resonator S1 has a crossover region F. The crossover region F is a region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap in the orthogonal direction. The crossover region F includes a plurality of excitation regions C. More specifically, the crossover region F is a region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap in the orthogonal direction, and is a region between the centers of the adjacent first electrode fingers 18 and second electrode fingers 19. The crossover region F and the excitation regions C are regions of the piezoelectric layer 6 that are defined based on the configuration of the IDT electrode 7. Note that FIG. 3 shows only two of the multiple excitation regions C in the series arm resonator S1.

[0032] The series arm resonator S1 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 7, thickness-shear mode bulk waves are excited in each excitation region C. More specifically, in the series arm resonator S1, when the thickness of the piezoelectric film is d and the center-to-center distance between the adjacent first electrode finger 18 and second electrode finger 19 is p, d / p is 0.5 or less. This allows thickness-shear mode bulk waves to be suitably excited in each excitation region C. In this embodiment, the thickness d is the thickness of the piezoelectric layer 6.

[0033] 1 are also elastic wave resonators configured to utilize thickness-shear mode bulk waves. Each of the elastic wave resonators of the filter device 1 has an IDT electrode 7, a crossing region F, and multiple excitation regions C. Note that the elastic wave resonators of the filter device 1 may have different design parameters depending on desired characteristics.

[0034] For example, when the dimension of the crossover region F of an elastic wave resonator along the direction in which the electrode fingers extend is defined as the crossover width, the capacitance of the elastic wave resonator depends on the product of the crossover width and the number of electrode fingers in the elastic wave resonator. Therefore, in order to obtain a desired capacitance in the elastic wave resonator, if the crossover width is narrowed, the number of electrode fingers must be increased. On the other hand, if the number of electrode fingers is reduced, the crossover width must be widened.

[0035] FIG. 4 is a schematic cross-sectional view taken along line II in FIG.

[0036] The piezoelectric substrate 2 has a support member 3 and a piezoelectric layer 6 as a piezoelectric film. 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. The piezoelectric layer 6 is provided on the insulating layer 5. However, the support member 3 may be composed of only the support substrate 4.

[0037] 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.

[0038] 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 this 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.

[0039] In a plan view, at least a portion of the IDT electrode 7 overlaps with the cavity 2a. In this specification, a plan view refers to a view from a direction corresponding to the top in FIG. 4 along the stacking direction of the support member 3 and the piezoelectric film. In FIG. 4, 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.

[0040] The cavity 2a allows the elastic wave to be reflected toward the piezoelectric layer 6. This allows the energy of the elastic wave to be effectively confined to the piezoelectric layer 6. As shown in FIG. 3, all of the multiple excitation regions C overlap with the cavity 2a in a plan view. This makes it difficult for the support member 3 to interfere with the excitation of the elastic wave. In addition, the energy of the elastic wave can be more reliably and effectively confined to the piezoelectric layer 6.

[0041] As shown in FIG. 2 , each of the plurality of acoustic wave resonators includes a cavity 2 a in the support member 3 at a position overlapping the IDT electrode 7 in a plan view. Hereinafter, the dimension of each cavity 2 a in the direction perpendicular to the electrode fingers is defined as Lx, and the dimension of each cavity 2 a in the direction along the electrode finger extension is defined as Ly. Therefore, the ratio of the dimension Lx to the dimension Ly of each cavity 2 a is expressed as Lx / Ly. Note that the dimension Lx of the cavity 2 a shown in FIG. 4 varies in the thickness direction. In this case, the dimension Lx of the cavity 2 a closest to the piezoelectric layer 6 is measured as the dimension Lx of the cavity 2 a. Similarly, the dimension Ly of the cavity 2 a closest to the piezoelectric layer 6 is measured as the dimension Ly of the cavity 2 a. However, in the present invention, the dimensions Lx and Ly of the cavity 2 a may be constant in the thickness direction.

[0042] This embodiment is characterized in that the ratio Lx / Ly in each cavity 2 a is 4 or greater, and the angle between the extension direction of the electrode fingers in the plurality of acoustic wave resonators and the direction in which the short side of the first principal surface of the piezoelectric film extends is 5° or less. This improves the heat dissipation of the portion in which each acoustic wave resonator is configured, and also contributes to the miniaturization of the filter device 1. This is described below.

[0043] When an AC voltage is applied to the IDT electrode 7 of the acoustic wave resonator, acoustic waves are excited and heat is generated in the excitation region C. Therefore, when the filter device 1 is used, the excitation region C serves as a heat source. More specifically, the amount of heat generated is particularly large near the center of the excitation region C in the direction in which the electrode fingers extend. In a configuration in which the cavity 2a confines the energy of acoustic waves to the piezoelectric layer 6 side, the excitation region C faces the cavity 2a. The heat generated in the excitation region C is difficult to dissipate through the cavity 2a.

[0044] In contrast, in this embodiment, the ratio Lx / Ly in the cavity 2a is 4 or more, and the dimension Ly is small. This makes it possible to shorten the distance from the center of the excitation region C in the electrode finger extension direction to the portion of the support member 3 that supports the piezoelectric layer 6. This allows this portion of the support member 3 to be suitably used as a heat dissipation path.

[0045] Additionally, in a configuration in which the cavity 2 a and the excitation region C overlap in plan view, the smaller the dimension Ly of the cavity 2 a, the narrower the crossing width. Accordingly, the dimension of the IDT electrode 7 along the electrode finger extension direction can also be reduced. More specifically, the distance between the bus bars in the electrode finger extension direction can be reduced. Therefore, the distance from the center of the excitation region C in the electrode finger extension direction to the bus bar can be reduced.

[0046] Each bus bar is connected to another element via wiring. When the filter device 1 is mounted on a mounting board or the like, each bus bar is connected to the outside of the filter device 1 via wiring. Therefore, when the ratio Lx / Ly is 4 or greater and the cross width is narrow, heat is easily released to the outside via each bus bar and wiring. In the filter device 1, the ratio Lx / Ly is 4 or greater in each acoustic wave resonator. Therefore, heat dissipation can be effectively improved in the portion where each acoustic wave resonator is configured.

[0047] Furthermore, in this embodiment, the angle between the extension direction of the electrode fingers of the plurality of acoustic wave resonators and the extension direction of the short sides 6 e and 6 f on the first main surface 6 a of the piezoelectric layer 6 is 5° or less. This not only improves heat dissipation as described above, but also facilitates miniaturization of the filter device 1. Details of this will be described with reference to a first comparative example and a second comparative example. The circuit configurations of the first comparative example and the second comparative example are the same as the circuit configuration of the first embodiment.

[0048] Fig. 5 is a schematic diagram showing the positional relationship between a piezoelectric substrate and a plurality of acoustic wave resonators in a first comparative example. Fig. 6 is a schematic diagram showing the positional relationship between a piezoelectric substrate and a plurality of acoustic wave resonators in a second comparative example. Wiring is omitted in Figs. 5 and 6. In Figs. 5 and 6, the IDT electrodes are shown as a simplified diagram of a rectangle with two diagonal lines added.

[0049] 5 , in the first comparative example, the electrode finger extension direction of each elastic wave resonator is parallel to the extension direction of the long sides 6 c and 6 d of the piezoelectric layer 6. That is, the angle between the electrode finger extension direction of each elastic wave resonator and the extension direction of the short sides 6 e and 6 f is 90°. In this case, if the ratio Lx / Ly is 4 or greater and all the elastic wave resonators are aligned in the electrode finger extension direction as in the first comparative example, the area of ​​the portion of the piezoelectric layer 6 in which no elastic wave resonators are located increases in the extension direction of the short sides 6 e and 6 f. This results in a larger piezoelectric substrate 2 and a larger filter device 101.

[0050] On the other hand, when the ratio Lx / Ly is set to 4 or more, and multiple acoustic wave resonators are arranged in the direction perpendicular to the electrode fingers, the short sides 6e and 6f of the piezoelectric layer 6 must be lengthened. Accordingly, the long sides 6c and 6d also become long. Therefore, the piezoelectric substrate 2 becomes large, and the filter device 101 becomes large.

[0051] 6 , in the second comparative example, as in the first comparative example, the angle between the extension direction of the electrode fingers in each acoustic wave resonator and the extension direction of the short sides 6 e and 6 f of the piezoelectric layer 6 is 90°. The area of ​​the piezoelectric substrate 2 in the filter device 111 is the same as the area of ​​the piezoelectric substrate 2 in the filter device 1 of the first embodiment. The capacitance of each acoustic wave resonator in the second comparative example is approximately the same as the capacitance of each acoustic wave resonator in the first embodiment.

[0052] However, in the second comparative example, the ratio Lx / Ly is smaller than 4. Therefore, in the portion where each elastic wave resonator is formed, the distance from the center of the excitation region in the electrode finger extension direction to the suitable heat dissipation path is long. Therefore, heat dissipation is poor in the portion where each elastic wave resonator is formed.

[0053] In contrast, in the first embodiment shown in Fig. 2, the angle between the extension direction of the electrode fingers in the multiple acoustic wave resonators and the extension direction of the short sides 6e and 6f on the first main surface 6a of the piezoelectric layer 6 is 5° or less. This provides a high degree of layout freedom in the direction orthogonal to the electrode fingers without increasing the area of ​​the piezoelectric substrate 2. This allows multiple acoustic wave resonators with a ratio Lx / Ly of 4 or greater and large dimensions in the direction orthogonal to the electrode fingers to be efficiently arranged on the first main surface 6a. This makes it possible to achieve both miniaturization of the filter device 1 and improved heat dissipation in the portions where the acoustic wave resonators are configured.

[0054] It is preferable that the ratio Lx / Ly is 7 or greater in at least one cavity 2a, and more preferably 7 or greater in all cavities 2a. This effectively improves the heat dissipation of the portion where the acoustic wave resonators are configured. In addition, it is more preferable that the angle between the extension direction of the electrode fingers of the plurality of acoustic wave resonators and the extension direction of the short sides 6e and 6f of the first main surface 6a of the piezoelectric layer 6 is 5° or less. Specifically, this allows for more efficient miniaturization of the filter device 1.

[0055] The configuration of the first embodiment will be described in more detail below. As shown in Fig. 1, in a series arm S connecting the first signal terminal 11A and the second signal terminal 11B, a series arm resonator S1, a series arm resonator S2, a series arm resonator S3, a series arm resonator S4, a series arm resonator S5, and a series arm resonator S6 are connected in series with each other. In terms of the circuit configuration, the series arm resonator S1, the series arm resonator S2, the series arm resonator S3, the series arm resonator S4, the series arm resonator S5, and the series arm resonator S6 are arranged in this order from the first signal terminal 11A side.

[0056] The parallel arm resonator P1 is connected between the connection point between the series arm resonators S1 and S2 and ground potential. The parallel arm resonator P2 is connected between the connection point between the series arm resonators S2 and S3 and ground potential. The parallel arm resonator P3 is connected between the connection point between the series arm resonators S3 and S4 and ground potential. The parallel arm resonator P4 is connected between the connection point between the series arm resonators S4 and S5 and ground potential. The parallel arm resonator P5 is connected between the connection point between the series arm resonators S5 and S6 and ground potential. The parallel arm resonator P6 is connected between the second signal terminal 11B and ground potential.

[0057] The circuit configuration of the filter device 1 is not limited to the above. For example, a plurality of series arm resonators may be arranged between the first signal terminal 11A and the node N, between adjacent nodes N, or between the node N and the second signal terminal 11B. Alternatively, a plurality of parallel arm resonators may be arranged in one parallel arm P.

[0058] Each elastic wave resonator of the filter device 1 is configured to use a thickness-shear bulk wave as the main mode. Specifically, d / p≦0.5 in each elastic wave resonator. However, each elastic wave resonator may be configured to use a plate wave as the main mode.

[0059] 7, a pair of reflectors 13A and 13B are provided on the first main surface 6a of the piezoelectric layer 6. Specifically, the reflectors 13A and 13B face each other with the IDT electrode 7 interposed therebetween in the direction perpendicular to the electrode fingers.

[0060] The reflector 13A has a pair of reflector bus bars 13a and 13b and a plurality of reflector electrode fingers 13c. The reflector bus bars 13a and 13b face each other. One end and the other end of each of the plurality of reflector electrode fingers 13c are short-circuited by the reflector bus bars 13a and 13b. The reflector 13B has a similar configuration to the reflector 13A.

[0061] When the thickness of the piezoelectric film is d and the center-to-center distance between adjacent first electrode fingers 18 and second electrode fingers 19 is p, it is preferable that d≦2p. In this case, plate waves are suitably excited. In addition, the provision of reflectors 13A and 13B can improve resonance characteristics. When the elastic wave resonator uses plate waves as its main mode, the crossing region F of the elastic wave resonator is the excitation region.

[0062] 7 shows one acoustic wave resonator in the filter device of this modified example. Note that each acoustic wave resonator in the filter device of this modified example other than the acoustic wave resonator shown in FIG. 7 also has a reflector 13A and a reflector 13B. In this modified example, as in the first embodiment, it is possible to improve the heat dissipation performance of the portion where the multiple acoustic wave resonators are configured, and to further reduce the size of the filter device.

[0063] 1 , in the first embodiment, in terms of the circuit configuration, one series arm resonator is arranged in the section between the first signal terminal 11A and the node N and between adjacent nodes N. No series arm resonator is arranged in the section between the node N and the second signal terminal 11B. One parallel arm resonator is arranged in each parallel arm P.

[0064] However, for example, at least two series arm resonators connected in series or parallel to each other may be arranged in at least one of the sections between the first signal terminal 11A and the node N, between adjacent nodes N, and between the node N and the second signal terminal 11B. Alternatively, at least two parallel arm resonators connected in series or parallel to each other may be arranged in at least one parallel arm P. These examples are shown in the second embodiment.

[0065] The filter device of the second embodiment has the same configuration as the filter device 1 of the first embodiment except for the circuit configuration and the arrangement of the multiple acoustic wave resonators. Therefore, in the second embodiment as well, it is possible to improve the heat dissipation performance of the portion where each acoustic wave resonator is configured, and to further reduce the size of the filter device.

[0066] FIG. 8 is a circuit diagram of a filter device according to the second embodiment.

[0067] In the filter device 21, the series arm resonators S26a and S26b are connected in parallel to each other in the series arm S. In the series arm S, a group of resonators consisting of the series arm resonators S21a, S21b, S2, S3, S4, S5, and the series arm resonators S26a and S26b are connected in series to each other. In terms of the circuit configuration, the series arm resonators S21a, S21b, S2, S3, S4, S5, and S26a are arranged in this order from the first signal terminal 11A side.

[0068] The parallel arm resonator P1 is connected between the connection point between the series arm resonator S21b and the series arm resonator S2 and the ground potential. The parallel arm resonators P22a and P22b are connected in series with each other between the connection point between the series arm resonator S2 and the series arm resonator S3 and the ground potential. The parallel arm resonator P3 is connected between the connection point between the series arm resonator S3 and the series arm resonator S4 and the ground potential.

[0069] The parallel arm resonator P4 is connected between the connection point between the series arm resonators S4 and S5 and ground potential. The parallel arm resonator P5 is connected between the connection point between the series arm resonator S5 and series arm resonator S26a and ground potential. The parallel arm resonators P26a and P26b are connected in parallel with each other between the second signal terminal 11B and ground potential.

[0070] In this embodiment, the series arm resonators S21a and S21b are arranged between the first signal terminal 11A and the node N in the circuit configuration. The series arm resonators S26a and S26b are arranged in one section between adjacent nodes N. In the section between adjacent nodes N where the series arm resonators S26a and S26b are not arranged, one series arm resonator is arranged. No series arm resonator is arranged between the node N and the second signal terminal 11B.

[0071] However, in terms of the circuit configuration, two or more series arm resonators may be arranged in any section between the first signal terminal 11A and the node N, between adjacent nodes N, or between the node N and the second signal terminal 11B. These series arm resonators may be connected in series or in parallel.

[0072] In terms of the circuit configuration, the parallel arm resonators P22a and P22b are arranged in one parallel arm P. Similarly, the parallel arm resonators P26a and P26b are arranged in one parallel arm P. In each parallel arm P other than the parallel arms P in which the parallel arm resonators P22a and P22b, and the parallel arm resonators P26a and P26b are arranged, one parallel arm resonator is arranged.

[0073] However, in terms of the circuit configuration, two or more parallel arm resonators may be arranged in any of the parallel arms P. These parallel arm resonators may be connected in series or in parallel to each other.

[0074] When a plurality of elastic wave resonators connected in series are arranged in any one of the sections or one of the parallel arms P, the power consumption per elastic wave resonator is small, thereby increasing the power durability of the elastic wave resonators.

[0075] When multiple elastic wave resonators connected in parallel to one another are arranged in any of the sections or in one of the parallel arms P, the areas of the cavities in these elastic wave resonators are small, which makes it difficult for cracks to occur in the piezoelectric film and improves the power durability of these elastic wave resonators.

[0076] Hereinafter, at least one section between the first signal terminal 11A and the node, between adjacent nodes, and between the node and the second signal terminal 11B may be simply referred to as at least one section.

[0077] FIG. 9 is a schematic plan view of a filter device according to a second embodiment.

[0078] As described above, the series arm resonator S21a and the series arm resonator S21b are arranged between the first signal terminal 11A and the node, and are connected in series with each other. The series arm resonator S21a and the series arm resonator S21b are arranged on the piezoelectric substrate 2 so as to be adjacent to each other in the electrode finger extension direction. This allows multiple acoustic wave resonators to be efficiently arranged on the piezoelectric substrate 2. This facilitates miniaturization of the filter device 21.

[0079] In this embodiment, the above arrangement is in one location. However, the piezoelectric substrate 2 may be configured such that at least two series arm resonators, which are arranged in at least one section and connected in series to each other, are adjacent to each other in the direction in which the electrode fingers extend. In this case, as in this embodiment, it is easy to reduce the size of the filter device.

[0080] The parallel arm resonator P22a and the parallel arm resonator P22b are connected in series to each other in one parallel arm. The parallel arm resonator P22a and the parallel arm resonator P22b are configured on the piezoelectric substrate 2 so as to be adjacent to each other in the electrode finger extension direction. This allows a plurality of acoustic wave resonators to be efficiently arranged on the piezoelectric substrate 2. This facilitates miniaturization of the filter device 21.

[0081] However, at least two parallel arm resonators, which are arranged in at least one parallel arm and connected in series to each other, may be configured adjacent to each other in the electrode finger extension direction on the piezoelectric substrate 2. In this case, similar to the present embodiment, it is easy to reduce the size of the filter device.

[0082] The series arm resonator S26a and the series arm resonator S26b are arranged between adjacent nodes and connected in parallel to each other. The series arm resonator S26a and the series arm resonator S26b are arranged on the piezoelectric substrate 2 so as to be adjacent to each other in the direction perpendicular to the electrode fingers. This allows a plurality of acoustic wave resonators to be efficiently arranged on the piezoelectric substrate 2. This facilitates miniaturization of the filter device 21.

[0083] At least two series arm resonators, which are arranged in at least one section and connected in parallel to each other, may be arranged adjacent to each other in the direction perpendicular to the electrode fingers on the piezoelectric substrate 2. In this case, similar to the present embodiment, it is easy to reduce the size of the filter device.

[0084] The parallel arm resonator P26a and the parallel arm resonator P26b are connected in parallel to each other in one parallel arm. The parallel arm resonator P26a and the parallel arm resonator P26b are configured on the piezoelectric substrate 2 so as to be adjacent to each other in the direction perpendicular to the electrode fingers. This allows a plurality of acoustic wave resonators to be efficiently arranged on the piezoelectric substrate 2. This facilitates miniaturization of the filter device 21.

[0085] However, at least two parallel arm resonators, which are arranged in at least one parallel arm and connected in parallel to each other, may be configured on the piezoelectric substrate 2 so as to be adjacent to each other in the direction perpendicular to the electrode fingers. In this case, similar to the present embodiment, it is easy to reduce the size of the filter device.

[0086] Another example of the arrangement of elastic wave resonators is shown as a modification of the second embodiment. As shown in Fig. 10, a series arm resonator S21a and a series arm resonator S21b connected to each other in series are arranged on the piezoelectric substrate 2 so as to be adjacent to each other in the direction perpendicular to the electrode fingers. This allows a plurality of elastic wave resonators to be arranged efficiently on the piezoelectric substrate 2. This facilitates miniaturization of the filter device 21A.

[0087] In this modification, the above arrangement is in one location. However, the piezoelectric substrate 2 may be configured such that at least two series arm resonators, which are arranged in at least one section and connected in series to each other, are adjacent to each other in the direction perpendicular to the electrode fingers. In this case, as in this modification, it is easy to further reduce the size of the filter device.

[0088] The parallel arm resonator P22a and the parallel arm resonator P22b, which are connected to each other in series, are configured adjacent to each other in the direction perpendicular to the electrode fingers on the piezoelectric substrate 2. This allows a plurality of acoustic wave resonators to be efficiently arranged on the piezoelectric substrate 2. This facilitates miniaturization of the filter device 21A.

[0089] However, at least two parallel arm resonators, which are arranged in at least one parallel arm and connected in series to each other, may be configured on the piezoelectric substrate 2 so as to be adjacent to each other in the direction perpendicular to the electrode fingers. In this case, as in this modification, it is easy to reduce the size of the filter device.

[0090] The series arm resonator S26a and the series arm resonator S26b, which are connected in parallel with each other, are configured adjacent to each other in the electrode finger extension direction on the piezoelectric substrate 2. This allows a plurality of acoustic wave resonators to be efficiently arranged on the piezoelectric substrate 2. This facilitates miniaturization of the filter device 21A.

[0091] Alternatively, at least two series arm resonators arranged in at least one section and connected in parallel to each other may be configured adjacent to each other in the electrode finger extension direction on the piezoelectric substrate 2. In this case, similar to the present modification, it is easy to reduce the size of the filter device.

[0092] The parallel arm resonator P26a and the parallel arm resonator P26b, which are connected in parallel to each other, are configured adjacent to each other in the electrode finger extension direction on the piezoelectric substrate 2. This allows a plurality of acoustic wave resonators to be efficiently arranged on the piezoelectric substrate 2. This facilitates miniaturization of the filter device 21A.

[0093] However, at least two parallel arm resonators, which are arranged in at least one parallel arm and connected in parallel to each other, may be configured adjacent to each other in the electrode finger extension direction on the piezoelectric substrate 2. In this case, similar to this modification, it is easy to reduce the size of the filter device.

[0094] A preferred configuration of an elastic wave resonator according to the present invention will be described below with reference to Fig. 3. However, the preferred configuration described below can also be applied to the configuration of an elastic wave resonator according to the present invention that uses thickness shear mode as the main mode, other than the first embodiment.

[0095] In the first embodiment, where d is the thickness of the piezoelectric film and p is the center-to-center distance between adjacent electrode fingers, d / p is 0.5 or less in each elastic wave resonator. It is preferable that d / p is 0.24 or less in each elastic wave resonator. This allows thickness-shear mode bulk waves to be more effectively excited in each excitation region C, and enables the value of the fractional bandwidth of the elastic wave resonator to be sufficiently large. The fractional bandwidth is expressed as (|fa-fr| / fr)×100[%], where fr is the resonant frequency and fa is the antiresonant frequency.

[0096] FIG. 11 is a graph showing the relationship between d / p and the bandwidth ratio of an elastic wave resonator.

[0097] As is clear from FIG. 11, 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.

[0098] However, in the filter device of the present invention, at least one of the acoustic wave resonators may be configured to utilize bulk waves in thickness-shear mode, and therefore, at least one of the acoustic wave resonators may satisfy d / p≦0.5, or at least one of the acoustic wave resonators may satisfy d / p≦0.24.

[0099] 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.

[0100] In this specification, the metallization ratio MR of the electrode fingers to the excitation region C is the proportion of the portion of the piezoelectric layer 6 that is covered with the metal that constitutes the electrode fingers in the excitation region C when viewed 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 when viewed 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.

[0101] Fig. 12 is a diagram showing the relationship between the bandwidth ratio and the normalized magnitude of spurious in an elastic wave resonator. Fig. 12 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. 12 is specifically the value obtained by normalizing the amount of phase rotation of the spurious impedance by 180°. The results shown in Fig. 12 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.

[0102] In the region surrounded by ellipse A in Fig. 12, the normalized magnitude of the spurious response between the resonant frequency and the antiresonant 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 antiresonant frequency.

[0103] 13 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.

[0104] In FIG. 13 , the hatched portion represents the region where the fractional bandwidth is 17% or less. The boundary between the hatched region and the non-hatched region is roughly represented by dashed line B. Dashed line B is represented by MR = 1.75(d / p) + 0.075. Preferably, in at least one acoustic wave resonator in the filter device where d / p is 0.5 or less, MR ≦ 1.75(d / p) + 0.075. More preferably, in each of all acoustic wave resonators where d / p is 0.5 or less, MR ≦ 1.75(d / p) + 0.075. In this case, it is easy to achieve a fractional bandwidth of 17% or less in an acoustic wave resonator that uses a thickness-shear bulk wave as the main mode.

[0105] On the other hand, the dashed-dotted line B1 in FIG. 13 indicates the boundary where the slope of the change in metallization ratio MR with respect to d / p is the same as that of the dashed line B, and where the fractional bandwidth is 17% or less across 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 be satisfied for at least one acoustic wave resonator in the filter device having a d / p of 0.5 or less. It is even more preferable that MR ≦ 1.75(d / p) + 0.05 be satisfied for each of all acoustic wave resonators having a d / p of 0.5 or less. In this case, the fractional bandwidth can be more reliably maintained at 17% or less in an acoustic wave resonator that uses a thickness-shear bulk wave as the main mode.

[0106] FIG. 14 shows the results of LiNbO when d / p approaches 0. ３ 14 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. 14 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 as the ranges expressed by the following formulas (1), (2), and (3).

[0107] (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)

[0108] 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.

[0109] Examples of the configuration of the filter device according to the present invention will be summarized below.

[0110] <1> A piezoelectric substrate including a support member and a piezoelectric film provided on the support member and including a piezoelectric layer, the piezoelectric substrate including a plurality of elastic wave resonators each having an IDT electrode provided on the piezoelectric film, wherein, in a plan view, a cavity is provided in the support member at a position overlapping with each of the IDT electrodes, the support member and the piezoelectric film are arranged such that a part of the support member and a part of the piezoelectric film face each other with the plurality of cavity portions interposed therebetween, the IDT electrode has a plurality of electrode fingers, and a direction in which the plurality of electrode fingers extend is referred to as an electrode finger extension direction, a filter device in which, when a direction orthogonal to the electrode finger extension direction is defined as an electrode finger orthogonal direction, a dimension of each of the hollow portions along the electrode finger orthogonal direction is defined as Lx, and a dimension of each of the hollow portions along the electrode finger extension direction is defined as Ly, a ratio Lx / Ly of the dimension Lx to the dimension Ly of each of the hollow portions is 4 or more, the piezoelectric film has a main surface on which a plurality of the IDT electrodes are provided, the main surface is rectangular in shape, the main surface has a pair of long sides and a pair of short sides, and an angle formed between the electrode finger extension direction of the plurality of elastic wave resonators and the extension direction of the short sides of the main surface of the piezoelectric film is 5° or less.

[0111] <2> The filter device according to <1>, wherein the ratio Lx / Ly is 7 or more in at least one of the cavities.

[0112] <3> The filter device according to <1> or <2>, further comprising a first signal terminal and a second signal terminal, wherein the plurality of acoustic wave resonators include a plurality of series arm resonators and a plurality of parallel arm resonators, wherein a path connecting the first signal terminal and the second signal terminal is a series arm, a path branching from the series arm to a ground potential is a parallel arm, a connection point between the series arm and the parallel arm is a node, wherein a plurality of the parallel arms and a plurality of the nodes are arranged in a circuit configuration, and at least two of the series arm resonators connected in series or in parallel to each other are arranged in at least one section between the first signal terminal and the node, between adjacent nodes, and between the node and the second signal terminal.

[0113] <4> The filter device described in <3>, wherein the at least two series arm resonators are arranged in at least one section between the first signal terminal and the node, between adjacent nodes, and between the node and the second signal terminal, and are connected to each other in series or parallel, and are configured on the piezoelectric substrate so as to be adjacent to each other in the electrode finger orthogonal direction.

[0114] <5> The filter device described in <3> or <4>, wherein the at least two series arm resonators are arranged in at least one section between the first signal terminal and the node, between adjacent nodes, and between the node and the second signal terminal, and are connected to each other in series or parallel, and are configured on the piezoelectric substrate so as to be adjacent in the electrode finger extension direction.

[0115] <6> The filter device according to any one of <1> to <5>, further comprising a first signal terminal and a second signal terminal, wherein the plurality of elastic wave resonators include a plurality of series arm resonators and a plurality of parallel arm resonators, wherein a path connecting the first signal terminal and the second signal terminal is a series arm, a path branching from the series arm to a ground potential is a parallel arm, a connection point between the series arm and the parallel arm is a node, wherein a plurality of the parallel arms and a plurality of the nodes are arranged in a circuit configuration, and wherein at least two of the parallel arm resonators connected in series or in parallel to each other are arranged in at least one of the parallel arms.

[0116] <7> The filter device according to <6>, wherein the at least two parallel arm resonators arranged in at least one of the parallel arms and connected to each other in series or parallel are configured on the piezoelectric substrate so as to be adjacent to each other in the electrode finger orthogonal direction.

[0117] <8> The filter device according to <6> or <7>, wherein the at least two parallel arm resonators arranged in at least one of the parallel arms and connected to each other in series or parallel are configured on the piezoelectric substrate so as to be adjacent to each other in the electrode finger extension direction.

[0118] <9> A filter device described in any one of <1> to <8>, wherein, when the thickness of the piezoelectric film is d and the center-to-center distance between adjacent electrode fingers is p, in at least one of the elastic wave resonators, d / p is 0.5 or less.

[0119] <10> The filter device according to <9>, wherein d / p is 0.24 or less in at least one of the acoustic wave resonators.

[0120] <11> The filter device according to <9> or <10>, wherein the region where adjacent electrode fingers overlap each other 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, at least one of the elastic wave resonators has d / p of 0.5 or less and satisfies MR≦1.75(d / p)+0.075.

[0121] <12> The filter device according to any one of <1> to <11>, 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)

[0122] REFERENCE SIGNS LIST 1...filter 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 6c, 6d...long sides 6e, 6f...short sides 7...IDT electrode 11A, 11B...first and second signal terminals 12...ground terminal 13A, 13B...reflector 13a, 13b...reflector bus bar 13c...reflector electrode fingers 16, 17...first and second bus bars 18, 19...first and second electrode fingers 21, 21A, 101, 111...filter device C...excitation region F...crossing region N...node P...parallel arm P1 to P6, P22a, P22b, P26a, P26b...parallel arm resonator S...series arm S1 to S6, S21a, S21b, S26a, S26b...series arm resonators

Claims

1. A piezoelectric resonator comprising a plurality of acoustic wave resonators each having an IDT electrode provided on the piezoelectric film, the acoustic wave resonators sharing a piezoelectric substrate having a support member and a piezoelectric film provided on the support member and including a piezoelectric layer, wherein, in a plan view, cavities are provided in the support member at positions overlapping with each of the IDT electrodes, 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 with the cavities interposed therebetween, the IDT electrode has a plurality of electrode fingers, and when the direction in which the plurality of electrode fingers extend is the electrode finger extension direction and the direction perpendicular to the electrode finger extension direction is the electrode finger perpendicular direction, and the dimension of each cavity along the electrode finger perpendicular direction is Lx and the dimension along the electrode finger extension direction is Ly, the ratio Lx / Ly of the dimension Lx to the dimension Ly in each cavity is 4 or more, a filter device, wherein the piezoelectric film has a main surface on which a plurality of the IDT electrodes are provided, the main surface is rectangular in shape, the main surface has a pair of long sides and a pair of short sides, and an angle formed between the extension direction of the electrode fingers of the plurality of elastic wave resonators and the extension direction of the short sides on the main surface of the piezoelectric film is 5° or less.

2. The filter device according to claim 1, wherein the ratio Lx / Ly is 7 or greater in at least one of said cavities.

3. The filter device according to claim 2, wherein the ratio Lx / Ly is 7 or more in all of the cavities.

4. The filter device according to any one of claims 1 to 3, further comprising a first signal terminal and a second signal terminal, wherein the plurality of elastic wave resonators include a plurality of series arm resonators and a plurality of parallel arm resonators, wherein a path connecting the first signal terminal and the second signal terminal is a series arm, a path branching from the series arm to ground potential is a parallel arm, and a connection point between the series arm and the parallel arm is a node, wherein a plurality of the parallel arms and a plurality of the nodes are arranged in a circuit configuration, and wherein at least two of the series arm resonators connected in series or in parallel to each other are arranged in at least one section between the first signal terminal and the node, between adjacent nodes, and between the node and the second signal terminal.

5. A filter device as described in claim 4, wherein the at least two series arm resonators connected in series or parallel to each other are arranged in at least one section between the first signal terminal and the node, between adjacent nodes, and between the node and the second signal terminal, and are configured on the piezoelectric substrate so as to be adjacent in the direction perpendicular to the electrode fingers.

6. A filter device according to claim 4 or 5, wherein the at least two series arm resonators connected in series or parallel to each other are arranged in at least one section selected from the sections between the first signal terminal and the node, between adjacent nodes, and between the node and the second signal terminal, and are configured on the piezoelectric substrate so as to be adjacent to each other in the electrode finger extension direction.

7. The filter device according to any one of claims 1 to 6, further comprising a first signal terminal and a second signal terminal, wherein the plurality of elastic wave resonators include a plurality of series arm resonators and a plurality of parallel arm resonators, wherein a path connecting the first signal terminal and the second signal terminal is a series arm, a path branching from the series arm to ground potential is a parallel arm, and a connection point between the series arm and the parallel arm is a node, wherein a plurality of the parallel arms and a plurality of the nodes are arranged in a circuit configuration, and wherein at least two of the parallel arm resonators connected to each other in series or in parallel are arranged in at least one of the parallel arms.

8. The filter device according to claim 7, wherein the at least two parallel arm resonators arranged in at least one of the parallel arms and connected to each other in series or parallel are configured on the piezoelectric substrate so as to be adjacent to each other in the orthogonal direction of the electrode fingers.

9. A filter device according to claim 7 or 8, wherein the at least two parallel arm resonators arranged in at least one of the parallel arms and connected to each other in series or parallel are configured on the piezoelectric substrate so as to be adjacent to each other in the direction in which the electrode fingers extend.

10. A filter device according to any one of claims 1 to 9, wherein, when the thickness of the piezoelectric film is d and the center-to-center distance between adjacent electrode fingers is p, in at least one of the elastic wave resonators, d / p is 0.5 or less.

11. The filter device according to claim 10, wherein d / p is 0.24 or less in at least one of the acoustic wave resonators.

12. A filter device according to claim 10 or 11, 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 of the elastic wave resonator, and wherein, when the metallization ratio of the electrode fingers to the excitation region is MR, at least one of the elastic wave resonators has d / p of 0.5 or less, and satisfies MR≦1.75(d / p)+0.

075.

13. A filter device according to any one of claims 1 to 12, 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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