Filter device

Abstract

Provided is a filter device capable of improving power resistance.　A filter device 1 according to the present invention has a piezoelectric substrate 2 including a piezoelectric layer 6, and includes a plurality of acoustic wave resonators each having an IDT electrode 7 provided on the piezoelectric layer 6. Each IDT electrode 7 has a plurality of electrode fingers. If the direction in which the plurality of electrode fingers extend is defined as an electrode finger extension direction and a direction orthogonal to the electrode finger extension direction is defined as an electrode finger orthogonal direction, a region in which adjacent electrode fingers overlap in the electrode finger orthogonal direction is a crossover region. The dimension of the crossover region along the electrode finger extension direction is a crossover width. The plurality of acoustic wave resonators include at least one series arm resonator S1a, S1b, S2a, S2b, S3a, S3b, S4, and at least one parallel arm resonator P1a, P1b, P2a, P2b, P3a, P3b, P4a-P4d. The crossover width of at least one series arm resonator S2a, S2b, S3a, S3b is less than the crossover widths of all the parallel arm resonators P1a, P1b, P2a, P2b, P3a, P3b, P4a-P4d.

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 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] Special Publication No. 2021-527344

[0006] In each resonator of a filter device such as that described in Patent Document 1, elastic waves such as bulk waves in thickness shear mode are excited, and heat is generated. More specifically, the regions of the piezoelectric plate where the 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, and the temperature of each IDT may become excessively high. Therefore, it is difficult to sufficiently increase the power durability of the above filter device.

[0007] An object of the present invention is to provide a filter device that can increase power durability.

[0008] A filter device according to the present invention has a piezoelectric substrate including a piezoelectric layer, and includes a plurality of elastic wave resonators each having an IDT electrode provided on the piezoelectric layer, the IDT electrode having a plurality of electrode fingers, a direction in which the plurality of electrode fingers extend is defined as an electrode finger extension direction and a direction orthogonal to the electrode finger extension direction is defined as an electrode finger orthogonal direction, a region where adjacent electrode fingers overlap in the electrode finger orthogonal direction is a crossing region, a dimension of the crossing region along the electrode finger extension direction is a crossing width, the plurality of elastic wave resonators include at least one series arm resonator and at least one parallel arm resonator, and the crossing width of at least one of the series arm resonators is narrower than the crossing widths of all of the parallel arm resonators.

[0009] According to the filter device of the present invention, it is possible to improve the power durability.

[0010] FIG. 1 is a circuit diagram of a filter device according to a first preferred embodiment of the present invention. FIG. 2 is a schematic plan view of the filter device according to the first preferred embodiment of the present invention. FIG. 3 is a schematic plan view showing an acoustic wave resonator according to the first preferred embodiment of the present invention. FIG. 4 is a circuit diagram of a filter device according to a reference example. FIG. 5 is a graph showing power consumption in a band between a resonant frequency and an anti-resonant frequency in each series arm resonator according to the reference example. FIG. 6 is a graph showing power consumption in a band between a resonant frequency and an anti-resonant frequency in each parallel arm resonator according to the reference example. FIG. 7 is a graph showing the relationship between the cross width A of an acoustic wave resonator and the temperature difference ΔT of the acoustic wave resonator before and after applying power to the acoustic wave resonator. FIG. 8 is a graph showing the relationship between the cross width A and the return loss at 4.65 GHz. FIG. 9 is a schematic cross-sectional view taken along line II in FIG. 3. FIG. 10 is a schematic front cross-sectional view of an acoustic wave resonator according to a first modified preferred embodiment of the first preferred embodiment of the present invention. FIG. 11 is a schematic front cross-sectional view of an acoustic wave resonator according to a second modified preferred embodiment of the first preferred embodiment of the present invention. FIG. 12 is a schematic plan view of an elastic wave resonator according to a third modified example of the first embodiment of the present invention. FIG. 13 is a circuit diagram of a filter device according to a second embodiment of the present invention. FIG. 14 is a schematic plan view of a filter device according to the second embodiment of the present invention. FIG. 15 is a schematic view of a filter device according to a third embodiment of the present invention. FIG. 16 is a schematic cross-sectional view taken along line II-II in FIG. 15. FIG. 17 is a schematic front cross-sectional view of a portion of a filter device according to a fourth embodiment of the present invention. FIG. 18 is a schematic view of a filter device according to a fifth embodiment of the present invention. FIG. 19 is a graph showing the relationship between d / p and the fractional bandwidth of an elastic wave resonator. FIG. 20 is a graph showing the relationship between the fractional bandwidth and the magnitude of normalized spurious signals in an elastic wave resonator. FIG. 21 is a graph showing the relationship between d / p, the metallization ratio MR, and the fractional bandwidth. FIG. 22 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.

[0011] The present invention will be clarified below by describing specific embodiments of the present invention with reference to the drawings.

[0012] 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.

[0013] FIG. 1 is a circuit diagram of a filter device according to a first embodiment of the present invention.

[0014] 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.

[0015] 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 S1a, S1b, S2a, S2b, S3a, S3b, and S4. The plurality of parallel arm resonators are specifically parallel arm resonators P1a, P1b, P2a, P2b, P3a, P3b, P4a, P4b, P4c, and P4d.

[0016] In terms of the circuit configuration, a series arm connects the first signal terminal 11A and the second signal terminal 11B. Each series arm resonator is arranged in the series arm. Meanwhile, a plurality of parallel arms connect the series arm and the ground potential. Each parallel arm resonator is arranged in the parallel arm. Note that in the present invention, the plurality of acoustic wave resonators in the filter device may include at least one series arm resonator and at least one parallel arm resonator.

[0017] A specific configuration of the filter device 1 of this embodiment will be described below.

[0018] 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.

[0019] The filter device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 is a substrate having piezoelectric properties. Specifically, the piezoelectric substrate 2 is a laminated substrate including a piezoelectric layer 6. However, the piezoelectric substrate 2 may be a substrate consisting of only the piezoelectric layer 6.

[0020] The piezoelectric layer 6 is made of, for example, LiNbO ３ Alternatively, the material may be made of lithium niobate such as LiTaO ３ In 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 impurities is contained to the extent that the electrical characteristics of the elastic wave resonator are not significantly deteriorated.

[0021] 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. 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 wiring.

[0022] A plurality of IDT electrodes 7 are provided on the first main surface 6a 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. A specific configuration of the elastic wave resonator of this embodiment is shown with reference to FIG. 3.

[0023] 3 is a schematic plan view showing an elastic wave resonator according to the first preferred embodiment, in which other elastic wave resonators are omitted.

[0024] The acoustic wave resonator shown in FIG. 3 is a series arm resonator S1a. The IDT electrode 7 of the series arm resonator S1a 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.

[0025] 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.

[0026] The series arm resonator S1a has an intersection region F. The intersection region F is a region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap in the direction perpendicular to the electrode fingers. Hereinafter, the dimension of the intersection region F along the electrode finger extension direction is referred to as an intersection width A.

[0027] The intersection region F includes a plurality of excitation regions C. More specifically, the excitation region C is a region where the adjacent first electrode fingers 18 and second electrode fingers 19 overlap in the direction perpendicular to the electrode fingers, and is a region between the centers of the adjacent first electrode fingers 18 and second electrode fingers 19. The intersection region F and the excitation region 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 plurality of excitation regions C in the series arm resonator S1a.

[0028] The series arm resonator S1a 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 S1a, when the thickness of the piezoelectric layer 6 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.

[0029] 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. In this embodiment, the electrode fingers of all the elastic wave resonators are orthogonal to each other in the same direction. Note that the design parameters of the elastic wave resonators of the filter device 1 may be different depending on the desired characteristics.

[0030] A feature of this embodiment is that the crossover width A of at least one series arm resonator is narrower than the crossover widths A of all the parallel arm resonators, thereby improving the power durability of the filter device 1. This will be explained below with reference to a reference example.

[0031] 4 is similar to the circuit configuration of the first embodiment in that four parallel arms are connected to a series arm. First, the details of the circuit configuration of the first embodiment will be described.

[0032] As shown in Fig. 1, in the circuit configuration, a series arm connects the first signal terminal 11A and the second signal terminal 11B. Each series arm resonator is arranged in the series arm. Specifically, in the series arm, the series arm resonators S1a and S1b are connected in parallel to each other. The series arm resonators S2a and S2b are connected in parallel to each other. The series arm resonators S3a and S3b are connected in parallel to each other.

[0033] A group of resonators consisting of the series arm resonators S1a and S1b, a group of resonators consisting of the series arm resonators S2a and S2b, a group of resonators consisting of the series arm resonators S3a and S3b, and the series arm resonator S4 are connected in series with one another. In terms of the circuit configuration, the series arm resonator S1a, series arm resonator S2a, series arm resonator S3a, and series arm resonator S4 are arranged in this order from the first signal terminal 11A side.

[0034] The parallel arm resonators P1a and P1b are connected in parallel with each other between the connection point between the series arm resonators S1a and S2a and the ground potential. The parallel arm resonators P2a and P2b are connected in parallel with each other between the connection point between the series arm resonators S2a and S3a and the ground potential. The parallel arm resonators P3a and P3b are connected in parallel with each other between the connection point between the series arm resonators S3a and S4 and the ground potential. The parallel arm resonators P4a, P4b, P4c, and P4d are connected in parallel with each other between the second signal terminal 11B and the ground potential.

[0035] On the other hand, the filter device 101 of the reference example shown in Fig. 4 does not include any resonators connected in parallel. In a series arm connecting the first signal terminal 11A and the second signal terminal 11B, a series arm resonator S101, a series arm resonator S102, a series arm resonator S103, and a series arm resonator S104 are connected in series with each other. A parallel arm resonator P101 is connected between the connection point between the series arm resonator S101 and the series arm resonator S102 and ground potential. A parallel arm resonator P102 is connected between the connection point between the series arm resonator S102 and the series arm resonator S103 and ground potential. A parallel arm resonator P103 is connected between the connection point between the series arm resonator S103 and the series arm resonator S104 and ground potential. A parallel arm resonator P104 is connected between the second signal terminal 11B and ground potential.

[0036] In the reference example, all of the series arm resonators and all of the parallel arm resonators are acoustic wave resonators having IDT electrodes. However, in the reference example, all of the acoustic wave resonators have the same crossover width. Figures 5 and 6 show the power consumption of each acoustic wave resonator in the reference example within the band between the resonant frequency and the antiresonant frequency.

[0037] Fig. 5 is a diagram showing the power consumption in the band between the resonant frequency and the anti-resonant frequency of each series arm resonator of the reference example. Fig. 6 is a diagram showing the power consumption in the band between the resonant frequency and the anti-resonant frequency of each parallel arm resonator of the reference example. Note that the frequency ranges shown in Figs. 5 and 6 are all located within the band between the resonant frequency and the anti-resonant frequency of each elastic wave resonator.

[0038] As shown in Fig. 5 , each series arm resonator consumes large amounts of power within the frequency band between the resonant frequency and the antiresonant frequency. On the other hand, as shown in Fig. 6 , each parallel arm resonator consumes small amounts of power within the frequency band between the resonant frequency and the antiresonant frequency. When power is applied to an elastic wave resonator, elastic waves are excited and heat is generated. The greater the power consumption of the elastic wave resonator, the greater the amount of heat generated in the elastic wave resonator. Therefore, the results shown in Figs. 5 and 6 indicate that the amount of heat generated in the series arm resonators is greater than the amount of heat generated in the parallel arm resonators when the filter device is used.

[0039] In contrast, in the first embodiment, the cross width A of at least one series arm resonator is narrower than the cross width A of all of the parallel arm resonators. More specifically, the cross widths A of the series arm resonators S2a, S2b, S3a, and S3b shown in FIG. 2 are narrower than the cross widths A of all of the parallel arm resonators. This makes it possible to reduce the number of acoustic wave resonators that reach a high temperature when the filter device 1 is used. This will be described in detail below.

[0040] For each different cross width A of the elastic wave resonator, the temperature difference between before and after applying power to the elastic wave resonator was calculated. Hereinafter, this temperature difference is referred to as ΔT. In this study, the cross width A was 26.5 μm, 53.1 μm, or 92.8 μm. The power applied to each elastic wave resonator was 1500 mW.

[0041] FIG. 7 is a graph showing the relationship between the overlap width A of an elastic wave resonator and the temperature difference ΔT of the elastic wave resonator before and after power is applied to the elastic wave resonator.

[0042] As shown in Fig. 7, the wider the cross width A, the larger the temperature difference ΔT. In other words, the wider the cross width A, the higher the temperature of the elastic wave resonator becomes when power is applied to the elastic wave resonator. In an elastic wave resonator, if the temperature of the electrode fingers of the IDT electrode becomes excessively high, the IDT electrode may be damaged. On the other hand, if the cross width A is narrow, the temperature of the elastic wave resonator is less likely to rise. This is for the following reason.

[0043] In an elastic wave resonator, the amount of heat generated near the center in the extension direction of the electrode fingers is particularly large. In contrast, when the cross width A is narrow, the distance between the center of the elastic wave resonator and each bus bar is short. Each bus bar is connected to other elements or the outside of the filter device via wiring. Therefore, when the cross width A is narrow, heat is easily released to the outside via each bus bar and wiring. Therefore, narrowing the cross width A can improve the heat dissipation properties of the portion where the elastic wave resonator is configured, making it possible to reduce the risk of damage to the IDT electrodes.

[0044] As described above, when the filter device is used, the amount of heat generated in the series arm resonators is greater than the amount of heat generated in the parallel arm resonators. In contrast, in the first embodiment, the cross width A of at least one series arm resonator is narrower than the cross widths A of all the parallel arm resonators. This reduces the number of acoustic wave resonators that reach a high temperature when the filter device 1 is used. This therefore increases the power durability of the filter device 1 as a whole.

[0045] In the first embodiment, the cross width A of at least one series arm resonator is narrower than the cross widths A of all the parallel arm resonators. In addition, when the center-to-center distance between adjacent electrode fingers is p, it is preferable that the cross widths A of all the series arm resonators be 4.7p or more. This effectively reduces loss in the filter device 1. This will be described in detail below.

[0046] The return loss at 4.65 GHz was measured each time the cross width A of the acoustic wave resonator was changed. Specifically, the cross width A was changed in 5 μm increments within the range of 5 μm to 50 μm. The center-to-center distance p was kept constant at 4.26 μm.

[0047] FIG. 8 is a diagram showing the relationship between the cross width A and the return loss at 4.65 GHz.

[0048] As shown in Figure 8, it can be seen that the wider the cross width A, the more the return loss is reduced. When the cross width A is 20 µm or less, the change in return loss is particularly large. Therefore, when the cross width A is less than 20 µm, the return loss increases significantly. In contrast, when the cross width A is 20 µm or more, the absolute value of the return loss can be made less than 1. In this study, the center-to-center distance p is 4.26 µm. From this, when the cross width A is 20 µm, the cross width A is 4.7 p to two significant digits.

[0049] Therefore, when the cross width A of all the series arm resonators is 4.7p or more, the return loss can be reduced in all the series arm resonators. In this case, the cross width A of the series arm resonators, which is narrower than the cross width A of all the parallel arm resonators, is 4.7p or more. Therefore, the cross width A of all the parallel arm resonators exceeds 4.7p. Therefore, the return loss can be reduced in all the parallel arm resonators as well. Therefore, the loss can be effectively reduced in the filter device 1. However, the cross width A of at least one series arm resonator may be 4.7p or more.

[0050] The configuration of the first embodiment will be described in more detail below.

[0051] FIG. 9 is a schematic cross-sectional view taken along line II in FIG.

[0052] The piezoelectric substrate 2 has a support member 3 and a piezoelectric layer 6. 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.

[0053] 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.

[0054] A recess is provided in the insulating layer 5. A piezoelectric layer 6 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 layer 6 are arranged so that a part of the support member 3 and a part of the piezoelectric layer 6 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.

[0055] 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. 9 along the stacking direction of the support member 3 and the piezoelectric layer 6. In FIG. 9, 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.

[0056] The cavity 2a is an acoustic reflecting portion in the present invention. The acoustic reflecting portion can reflect the elastic wave toward the piezoelectric layer 6. This allows the energy of the elastic wave to be effectively confined to the piezoelectric layer 6. It is preferable that the multiple excitation regions C overlap with the acoustic reflecting portion in a plan view. This allows the energy of the elastic wave to be more reliably and effectively confined to the piezoelectric layer 6.

[0057] In the first embodiment, in each of the plurality of acoustic wave resonators, an acoustic reflecting portion is provided on the support member 3 at a position that overlaps with the IDT electrode 7 in a plan view. Note that an acoustic reflecting film may be provided as the acoustic reflecting portion.

[0058] For example, in a first modified example of the first embodiment shown in Figure 10, the acoustic reflection portion is an acoustic reflection film 8. The support member 3A in this modified example is made only of a support substrate. The acoustic reflection film 8 is provided on the surface of the support member 3A. A piezoelectric layer 6 is provided on the acoustic reflection film 8. It is sufficient that the support member 3A and the piezoelectric layer 6 are arranged so that at least a portion of the support member 3A and at least a portion of the piezoelectric layer 6 face each other with the acoustic reflection film 8 between them.

[0059] Fig. 10 shows one acoustic wave resonator in the filter device of this modified example. Note that, in the filter device of this modified example, each acoustic wave resonator other than the acoustic wave resonator shown in Fig. 10 also has an acoustic reflection film 8. The acoustic reflection films 8 of a plurality of acoustic wave resonators may be provided integrally.

[0060] The acoustic reflecting film 8 is a laminate of multiple acoustic impedance layers. Specifically, the acoustic reflecting film 8 has multiple low acoustic impedance layers and multiple high acoustic impedance layers. The low acoustic impedance layers are layers with a relatively low acoustic impedance. More specifically, the low acoustic impedance layers are layers with a lower acoustic impedance than adjacent layers in the acoustic reflecting film 8. More specifically, the multiple low acoustic impedance layers in the acoustic reflecting film 8 are low acoustic impedance layer 14a, low acoustic impedance layer 14b, and low acoustic impedance layer 14c.

[0061] On the other hand, a high acoustic impedance layer is a layer with a relatively high acoustic impedance. More specifically, a high acoustic impedance layer is a layer with a higher acoustic impedance than adjacent layers in the acoustic reflecting film 8. More specifically, the multiple high acoustic impedance layers in the acoustic reflecting film 8 are high acoustic impedance layers 15a and 15b. The low acoustic impedance layers and high acoustic impedance layers are stacked alternately. Note that the low acoustic impedance layer 14a is the layer in the acoustic reflecting film 8 that is located closest to the piezoelectric layer 6.

[0062] The acoustic reflection film 8 has three low acoustic impedance layers and two high acoustic impedance layers, although it is sufficient that the acoustic reflection film 8 has at least one low acoustic impedance layer and one high acoustic impedance layer.

[0063] 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.

[0064] In this modification, as in the first embodiment, the cross width A of at least one series arm resonator is narrower than the cross widths A of all parallel arm resonators. This increases the power durability of the filter device. In addition, the provision of the acoustic reflection film 8 effectively confines the energy of the elastic waves to the piezoelectric layer 6.

[0065] The configuration in this modified example in which the acoustic reflection portion is the acoustic reflection film 8 can also be applied to configurations of the present invention other than this modified example.

[0066] In the present invention, it is sufficient that at least one elastic wave resonator has an acoustic reflecting portion. However, it is preferable that all elastic wave resonators have an acoustic reflecting portion. This allows the energy of elastic waves to be effectively confined within the piezoelectric layer 6 in all elastic wave resonators. This makes it possible to more reliably reduce loss in the filter device.

[0067] In the first embodiment and its first modification, no dielectric film is provided on the first principal surface 6a or the second principal surface 6b of the piezoelectric layer 6. However, a dielectric film may be provided on at least one of the first principal surface 6a or the second principal surface 6b of the piezoelectric layer 6. For example, in a second modification of the first embodiment shown in FIG. 11 , a first dielectric film 9A is provided on the first principal surface 6a of the piezoelectric layer 6 so as to cover the IDT electrode 7. In this case, the IDT electrode 7 is protected by the first dielectric film 9A. This makes the IDT electrode 7 less likely to be damaged.

[0068] A second dielectric film 9B is provided on the second main surface 6b of the piezoelectric layer 6. The second dielectric film 9B overlaps the IDT electrode 7 in a plan view. In this modification, the piezoelectric substrate 2B includes a support substrate 4, an insulating layer 5, the second dielectric film 9B, and the piezoelectric layer 6.

[0069] The first dielectric film 9A and the second dielectric film 9B may be made of, for example, silicon oxide, silicon nitride, silicon oxynitride, etc. The materials of the first dielectric film 9A and the second dielectric film 9B may be the same or different from each other.

[0070] 11 shows one acoustic wave resonator in the filter device of this modified example. Each of the acoustic wave resonators in the filter device of this modified example, other than the acoustic wave resonator shown in FIG. 11 , also has a first dielectric film 9A and a second dielectric film 9B. The first dielectric films 9A of a plurality of acoustic wave resonators may be integrally formed. The second dielectric films 9B of a plurality of acoustic wave resonators may be integrally formed.

[0071] In this modification, as in the first embodiment, the cross width A of at least one series arm resonator is narrower than the cross widths A of all the parallel arm resonators, thereby increasing the power durability of the filter device.

[0072] The multiple elastic wave resonators may include elastic wave resonators that do not have a dielectric film on the first principal surface 6 a or the second principal surface 6 b of the piezoelectric layer 6. However, it is preferable that at least one series arm resonator has a dielectric film on at least one of the first principal surface 6 a and the second principal surface 6 b of the piezoelectric layer 6 so as to overlap with the IDT electrode 7 in a plan view. In other words, it is preferable that at least one series arm resonator has at least one of the first dielectric film 9A and the second dielectric film 9B.

[0073] Of all the series arm resonators, it is preferable that the cross width A of the series arm resonator having the largest total thickness of the first dielectric film 9A and the second dielectric film 9B be narrower than the cross widths A of all the parallel arm resonators. This can reliably increase the power durability of the filter device. This will be described in detail below.

[0074] The resonant frequency of the acoustic wave resonator can be adjusted by adjusting the thicknesses of the first dielectric film 9A and the second dielectric film 9B. Specifically, the greater the total thickness of the first dielectric film 9A and the second dielectric film 9B, the lower the resonant frequency of the acoustic wave resonator. In a filter device, a series arm resonator having the lowest resonant frequency is often used to increase the steepness near the highest frequency in the pass band. In this specification, high steepness means that the amount of change in frequency is small relative to a certain amount of change in attenuation near the highest or lowest frequency in the pass band.

[0075] The series arm resonators used to increase the steepness consume particularly large amounts of power. Therefore, the IDT electrodes 7 of the series arm resonators are likely to become excessively hot when the filter device is used. By narrowing the cross width A of the series arm resonators, the heat dissipation performance of the part where the series arm resonators are configured can be improved. This increases the power durability of the series arm resonators, and more reliably increases the power durability of the filter device.

[0076] In the first embodiment, each elastic wave resonator is configured to use a thickness-shear bulk wave as the main mode. Specifically, in each elastic wave resonator having an acoustic reflector, d / p≦0.5. Note that each elastic wave resonator may be configured to use, for example, a plate wave as the main mode.

[0077] 12, a pair of reflectors 13A and 13B are provided on the first main surface 6a of the piezoelectric layer 6. More specifically, the reflectors 13A and 13B face each other with the IDT electrode 7 interposed therebetween in the direction perpendicular to the electrode fingers.

[0078] 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.

[0079] When the thickness of the piezoelectric layer 6 is d and the center-to-center distance between the 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 the reflectors 13A and 13B can improve the resonance characteristics. When plate waves are used as the main mode, the crossing region F is the excitation region.

[0080] 12 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. 12 also has a reflector 13A and a reflector 13B. In this modified example, as in the first embodiment, the power durability of the filter device can be improved.

[0081] In the first embodiment and its modifications, the filter device is a ladder filter. However, the filter device may also include, for example, a longitudinally coupled resonator type acoustic wave filter. In this case, the filter device only needs to include at least one series arm resonator and at least one parallel arm resonator. The cross width A of at least one series arm resonator needs to be narrower than the cross widths A of all the parallel arm resonators. In the first embodiment and its modifications, all the series arm resonators and all the parallel arm resonators share the same piezoelectric substrate and piezoelectric layer. However, in the present invention, all the series arm resonators and all the parallel arm resonators do not necessarily need to share the same piezoelectric substrate.

[0082] 13 and 14 are circuit diagrams and schematic plan views of a filter device according to a second embodiment of the present invention.

[0083] As shown in Fig. 13, this embodiment differs from the first embodiment in the configuration of the series arms in the circuit configuration. As shown in Fig. 14, this embodiment also differs from the first embodiment in that the cross width A of all the series arm resonators is narrower than the cross width A of all the parallel arm resonators. Except for the above points, the filter device 21 of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0084] 13 , the filter device 21 includes a plurality of series arm resonators, namely, a series arm resonator S21a, a series arm resonator S21b, a series arm resonator S22, a series arm resonator S23, and a series arm resonator S24. In the series arm, the series arm resonators S21a and S21b are connected in parallel. In the series arm, a group of resonators consisting of the series arm resonators S21a and S21b is connected in series with the series arm resonators S22, S23, and S24. In terms of the circuit configuration, the series arm resonators S21a, S22, S23, and S24 are arranged in this order from the first signal terminal 11A side.

[0085] The circuit configuration of this embodiment is similar to that of the first embodiment in that four groups of resonators are arranged in the series arm and in the arrangement of each parallel arm resonator.

[0086] In the filter device 21, the cross width A of all the series arm resonators is narrower than the cross width A of all the parallel arm resonators. This improves the heat dissipation of the portion where all the series arm resonators are formed, and the IDT electrodes 7 of all the series arm resonators are less likely to be damaged. This effectively improves the power durability of the filter device 21.

[0087] Fig. 15 is a schematic diagram of a filter device according to a third embodiment. Fig. 16 is a schematic cross-sectional view taken along line II-II in Fig. 15. Note that Fig. 15 shows the IDT electrodes as a rectangle with two diagonal lines added. The first dielectric film is omitted from Fig. 15. Fig. 16 also shows electrodes other than those constituting the acoustic wave resonator.

[0088] As shown in Fig. 15, this embodiment differs from the second embodiment in the circuit configuration and the arrangement of the acoustic wave resonators. This embodiment also differs from the second embodiment in that all of the series arm resonators and all of the parallel arm resonators have the first dielectric film 9A shown in Fig. 16. Except for the above points, the filter device 31 of this embodiment has the same configuration as the filter device 21 of the second embodiment.

[0089] The plurality of series arm resonators of the filter device 31 are a series arm resonator S31, a series arm resonator S32, a series arm resonator S33, and a series arm resonator S34. In terms of the circuit configuration, the series arm resonator S31, the series arm resonator S32, the series arm resonator S33, and the series arm resonator S34 are arranged in this order from the first signal terminal 11A side.

[0090] The filter device 31 includes a plurality of parallel arm resonators, namely, a parallel arm resonator P31, a parallel arm resonator P32, a parallel arm resonator P33, and a parallel arm resonator P34. The parallel arm resonator P31 is connected between the first signal terminal 11A and the ground potential. The parallel arm resonator P32 is connected between the ground potential and a connection point between the series arm resonator S31 and the series arm resonator S32. The parallel arm resonator P33 is connected between the ground potential and a connection point between the series arm resonator S32 and the series arm resonator S33. The parallel arm resonator P34 is connected between the ground potential and a connection point between the series arm resonator S33 and the series arm resonator S34.

[0091] In this embodiment, as in the second embodiment, the cross width A of all the series arm resonators is narrower than the cross width A of all the parallel arm resonators, thereby effectively increasing the power durability of the filter device 31.

[0092] 15 , all of the series arm resonators and all of the parallel arm resonators of the filter device 31 share the same piezoelectric substrate 2. The piezoelectric layer 6 of the piezoelectric substrate 2 has a first region B1 and a second region B2. Specifically, the first region B1 and the second region B2 are two regions obtained by dividing the piezoelectric layer 6 in the orthogonal direction of the electrode fingers of at least one series arm resonator. However, in this embodiment, the orthogonal direction of the electrode fingers of all of the series arm resonators and all of the parallel arm resonators is the same.

[0093] All the series arm resonators are located in the first region B1. All the parallel arm resonators are located in the second region B2. As shown in FIG. 16 , a first dielectric film 9A is provided on the first main surface 6a across the first region B1 and the second region B2 of the piezoelectric layer 6. In this embodiment, the first dielectric films 9A of all the series arm resonators and all the parallel arm resonators are integrally provided. The thickness of the first dielectric film 9A provided in the first region B1 is different from the thickness of the first dielectric film 9A provided in the second region B2. As a result, the thickness of the first dielectric film 9A in all the series arm resonators is different from the thickness of the first dielectric film 9A in all the parallel arm resonators.

[0094] More specifically, the thickness of the first dielectric film 9A provided in the first region B1 is thinner than the thickness of the first dielectric film 9A provided in the second region B2, so that the thickness of the first dielectric film 9A in all the series arm resonators is thinner than the thickness of the dielectric film in all the parallel arm resonators.

[0095] More specifically, the thickness of the first dielectric film 9A in all the series arm resonators is the same. The thickness of the first dielectric film 9A in all the parallel arm resonators is the same. On the other hand, the thickness of the first dielectric film 9A in any of the series arm resonators is thinner than the thickness of the first dielectric film 9A in all the parallel arm resonators.

[0096] In general, the series arm resonators constitute the higher band of the pass band of the filter device. The parallel arm resonators constitute the lower band of the pass band of the filter device. Therefore, the resonant frequency of the series arm resonators is higher than the resonant frequency of the parallel arm resonators. As described above, the greater the total value of the thicknesses of the first dielectric film 9A and the second dielectric film 9B shown in FIG. 11 , the lower the resonant frequency of the elastic wave resonator. In other words, the smaller this total value, the higher the resonant frequency of the elastic wave resonator. Therefore, by making this total value in the series arm resonators smaller than that in the parallel arm resonators, the resonant frequency of the series arm resonators can easily be made higher than the resonant frequency of the parallel arm resonators.

[0097] As shown in FIG. 16 , the first region B1 and the second region B2 of the piezoelectric layer 6 are regions that divide the piezoelectric layer 6 in the direction perpendicular to the electrode fingers of the acoustic wave resonators. Therefore, the thicknesses of the first dielectric films 9A in the first region B1 and the second region B2 can be easily made different from each other. Furthermore, all of the series arm resonators are provided in the first region B1, and all of the parallel arm resonators are provided in the second region B2. This allows the thicknesses of the first dielectric films 9A of all of the series arm resonators to be easily made thinner than the thicknesses of the first dielectric films 9A of all of the parallel arm resonators. This effectively improves the productivity of the filter device 31.

[0098] 11 is not provided in this embodiment. Therefore, the thickness of the second dielectric film 9B is 0. However, the second dielectric film 9B may be provided on the second main surface 6b of the piezoelectric layer 6.

[0099] 17 is a schematic front cross-sectional view showing a part of a filter device according to a fourth preferred embodiment of the present invention, which also shows electrodes other than the electrodes constituting the acoustic wave resonators.

[0100] This embodiment differs from the third embodiment in that the thickness of the first dielectric film 9A is the same in all acoustic wave resonators. This embodiment also differs from the third embodiment in that the thickness of the piezoelectric layer 6 in the first region B1 is different from the thickness of the piezoelectric layer 6 in the second region B2. Except for the above points, the filter device 41 of this embodiment has the same configuration as the filter device 31 of the third embodiment.

[0101] In this embodiment, as in the third embodiment, the cross width A of all the series arm resonators is narrower than the cross width A of all the parallel arm resonators, thereby effectively increasing the power durability of the filter device 41.

[0102] Here, the thinner the piezoelectric layer 6, the higher the resonant frequency of the elastic wave resonator. Therefore, by making the thickness of the piezoelectric layer 6 in the series arm resonator thinner than the thickness of the piezoelectric layer 6 in the parallel arm resonator, the resonant frequency of the series arm resonator can be easily made higher than the resonant frequency of the parallel arm resonator.

[0103] The first region B1 and the second region B2 of the piezoelectric layer 6 are regions obtained by dividing the piezoelectric layer 6 in the direction perpendicular to the electrode fingers of the acoustic wave resonators. Therefore, the thicknesses of the piezoelectric layer 6 can be easily made different in the first region B1 and the second region B2. All of the series arm resonators and all of the parallel arm resonators share the same piezoelectric substrate 2 and piezoelectric layer 6. Specifically, all of the series arm resonators are configured in the first region B1, and all of the parallel arm resonators are configured in the second region B2. This allows the thicknesses of the piezoelectric layers 6 of all of the series arm resonators to be easily made thinner than the thicknesses of the piezoelectric layers 6 of all of the parallel arm resonators. This effectively improves the productivity of the filter device 41.

[0104] In this embodiment, the thickness of the first dielectric films 9A is the same in all the series arm resonators and all the parallel arm resonators. However, the thicknesses of the piezoelectric layers 6 and the first dielectric films 9A may be different in all the series arm resonators and all the parallel arm resonators.

[0105] In the present invention, all of the series arm resonators and all of the parallel arm resonators do not necessarily have to share the same piezoelectric substrate. An example in which all of the series arm resonators and all of the parallel arm resonators do not share the same piezoelectric substrate is shown in the fifth embodiment.

[0106] Fig. 18 is a schematic diagram of a filter device according to a fifth embodiment. In Fig. 18, the IDT electrodes are shown as a rectangle with two diagonal lines added. The first dielectric film is omitted in Fig. 18.

[0107] This embodiment differs from the fourth embodiment in that the piezoelectric substrate 52A shared by all the series arm resonators and the piezoelectric substrate 52B shared by all the parallel arm resonators are different substrates. In this embodiment, the piezoelectric layer 56A shared by all the series arm resonators and the piezoelectric layer 56B shared by all the parallel arm resonators are different layers. Except for the above points, the filter device 51 of this embodiment has the same configuration as the filter device 41 of the fourth embodiment.

[0108] The circuit configuration of the filter device 51 is similar to that of the third and fourth embodiments. However, as shown in Fig. 18 , the plurality of series arm resonators of the filter device 51 are a series arm resonator S51, a series arm resonator S52, a series arm resonator S53, and a series arm resonator S54. In terms of the circuit configuration, the series arm resonator S51, the series arm resonator S52, the series arm resonator S53, and the series arm resonator S54 are arranged in this order from the first signal terminal 11A side.

[0109] The filter device 51 includes a plurality of parallel arm resonators, namely, a parallel arm resonator P51, a parallel arm resonator P52, a parallel arm resonator P53, and a parallel arm resonator P54. The parallel arm resonator P51 is connected between the first signal terminal 11A and the ground potential. The parallel arm resonator P52 is connected between the ground potential and a connection point between the series arm resonator S51 and the series arm resonator S52. The parallel arm resonator P53 is connected between the ground potential and a connection point between the series arm resonator S52 and the series arm resonator S53. The parallel arm resonator P54 is connected between the ground potential and a connection point between the series arm resonator S53 and the series arm resonator S54.

[0110] In this embodiment, as in the fourth embodiment, the cross width A of all the series arm resonators is narrower than the cross width A of all the parallel arm resonators, thereby effectively increasing the power durability of the filter device 51.

[0111] In the filter device 51, the thickness of the piezoelectric layer 56A is different from the thickness of the piezoelectric layer 56B. Specifically, the thickness of the piezoelectric layer 56A shared by all the series arm resonators is thinner than the thickness of the piezoelectric layer 56B shared by all the parallel arm resonators. This makes the resonant frequency of the series arm resonators higher than the resonant frequency of the parallel arm resonators.

[0112] The piezoelectric layer 56A and the piezoelectric layer 56B are different layers, so that the thicknesses of the piezoelectric layer 56A and the piezoelectric layer 56B can be easily made different from each other, thereby effectively increasing the productivity of the filter device 51.

[0113] In addition, the materials of the piezoelectric layer 56A and the piezoelectric layer 56B may be different from each other. Alternatively, the Euler angles (φ, θ, ψ) of the material constituting the piezoelectric layer 56A may be different from the Euler angles (φ, θ, ψ) of the material constituting the piezoelectric layer 56B. Even in these cases, since the piezoelectric layer 56A and the piezoelectric layer 56B are different layers, the filter device 51 can be easily manufactured. Therefore, the desired electrical characteristics of the filter device 51 can be easily and reliably obtained, and productivity is less likely to decrease. However, the thicknesses, materials, Euler angles, etc. of the piezoelectric layer 56A and the piezoelectric layer 56B do not necessarily have to be different from each other.

[0114] 18, the thickness of the first dielectric film provided on the first main surface of the piezoelectric layer 56A may be different from the thickness of the first dielectric film provided on the first main surface of the piezoelectric layer 56B. That is, similar to the third embodiment shown in FIG. 16, the thickness of the first dielectric films 9A in all the series arm resonators may be different from the thickness of the first dielectric films 9A in all the parallel arm resonators.

[0115] In this embodiment, the piezoelectric substrate 52A shared by all the series arm resonators and the piezoelectric substrate 52B shared by all the parallel arm resonators are different substrates. The layered structure of the piezoelectric substrates 52A and 52B is the same as the layered structure of the piezoelectric substrate 2 shown in Figures 16 and 17. Although not shown, in this embodiment, the piezoelectric substrate 52A shared by all the series arm resonators and the piezoelectric substrate 52B shared by all the parallel arm resonators are mounted on the same package substrate.

[0116] 18, the wiring connecting the series arm resonators and the parallel arm resonators is provided on the piezoelectric substrate 52A, the package substrate, and the piezoelectric substrate 52B. The package substrate may be made of, for example, an appropriate ceramic or glass epoxy resin.

[0117] For example, the piezoelectric substrates 52A and 52B may have different layer structures. For example, the acoustic reflection portion of one of the piezoelectric substrates 52A and 52B may be a cavity, and the acoustic reflection portion of the other may be an acoustic reflection film. When manufacturing the filter device 51, the piezoelectric substrates 52A and 52B may be formed separately. This makes it possible to easily and reliably obtain the desired electrical characteristics of the filter device 51, and reduces the likelihood of a decrease in productivity.

[0118] 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.

[0119] In the first embodiment, when the thickness of the piezoelectric layer 6 is d and the center-to-center distance between adjacent electrode fingers is p, the d / p ratio is 0.5 or less in the elastic wave resonator having an acoustic reflector. It is preferable that the d / p ratio is 0.24 or less in the elastic wave resonator having an acoustic reflector. 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 by (|fa-fr| / fr)×100[%], where fr is the resonant frequency and fa is the antiresonant frequency.

[0120] FIG. 19 is a graph showing the relationship between d / p and the bandwidth fraction of an elastic wave resonator.

[0121] As is clear from FIG. 19, 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.

[0122] 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.

[0123] 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.

[0124] Fig. 20 is a diagram showing the relationship between the relative bandwidth and the normalized magnitude of spurious in an elastic wave resonator. Fig. 20 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. 20 is specifically the value obtained by normalizing the amount of phase rotation of the spurious impedance by 180°. The results shown in Fig. 20 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.

[0125] In the region surrounded by ellipse D in Figure 20, 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.

[0126] 21 is a diagram showing the relationship between d / p, metallization ratio MR, and bandwidth fraction, in which the bandwidth fraction is calculated for each of different d / p and metallization ratio MR.

[0127] In FIG. 21 , 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 E. Dashed line E 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.

[0128] On the other hand, the dashed-dotted line E1 in FIG. 21 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 E, and the fractional bandwidth is 17% or less across the entire range. The dashed-dotted line E1 is represented by MR = 1.75(d / p) + 0.05. It is more preferable that MR ≦ 1.75(d / p) + 0.05 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.

[0129] FIG. 22 shows the LiNbO ３ 22 is a diagram showing a map of fractional bandwidths with respect to Euler angles (0°, θ, ψ) of the frequency band of the optical fiber 100. The hatched area in FIG. 22 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).

[0130] (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)

[0131] It is preferable that the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer be within the range of the above formula (1), formula (2), or formula (3). This allows the fractional bandwidth of the elastic wave resonator to be sufficiently wide. The same applies when the piezoelectric layer is made of lithium tantalate. Furthermore, the same applies when the piezoelectric layer 56A and the piezoelectric layer 56B are different layers, as in the fifth embodiment shown in FIG. 18. Specifically, it is preferable that the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting both piezoelectric layers be within the range of the above formula (1), formula (2), or formula (3). This allows the fractional bandwidth of each series arm resonator and each parallel arm resonator to be sufficiently wide.

[0132] Examples of the configuration of the filter device according to the present invention will be summarized below.

[0133] <1> A filter device having a piezoelectric substrate including a piezoelectric layer, comprising: a plurality of elastic wave resonators each having an IDT electrode provided on the piezoelectric layer, the IDT electrode having a plurality of electrode fingers, a direction in which the plurality of electrode fingers extend is defined as an electrode finger extension direction and a direction orthogonal to the electrode finger extension direction is defined as an electrode finger orthogonal direction, a region where adjacent electrode fingers overlap in the electrode finger orthogonal direction is a crossing region, a dimension of the crossing region along the electrode finger extension direction is a crossing width, the plurality of elastic wave resonators include at least one series arm resonator and at least one parallel arm resonator, and the crossing width of at least one of the series arm resonators is narrower than the crossing widths of all of the parallel arm resonators.

[0134] <2> The filter device according to <1>, wherein the cross widths of all the series arm resonators are narrower than the cross widths of all the parallel arm resonators.

[0135] <3> The filter device according to <1> or <2>, wherein the piezoelectric layer has a first main surface and a second main surface facing each other, at least one of the series arm resonators has a dielectric film provided on at least one of the first main surface and the second main surface of the piezoelectric layer so as to overlap with the IDT electrode in a planar view, and the series arm resonator having the largest total thickness of the dielectric films provided on the first main surface and the second main surface of the piezoelectric layer among all the series arm resonators has a cross width narrower than the cross widths of all the parallel arm resonators.

[0136] <4> The filter device according to any one of <1> to <3>, wherein the cross width of all the series arm resonators is 4.7p or more, where p is the center-to-center distance between the adjacent electrode fingers.

[0137] <5> The filter device according to any one of <1> to <4>, wherein all the series arm resonators and all the parallel arm resonators share the same piezoelectric substrate and the same piezoelectric layer, and when the piezoelectric layer is divided into a first region and a second region in the electrode finger orthogonal direction of at least one of the series arm resonators, all the series arm resonators are located in the first region and all the parallel arm resonators are located in the second region.

[0138] <6> The filter device according to <5>, wherein the piezoelectric layer has a first main surface and a second main surface facing each other, all of the series arm resonators and all of the parallel arm resonators have a dielectric film provided on the first main surface of the piezoelectric layer so as to cover the IDT electrode, and the thickness of the dielectric film in all of the series arm resonators is different from the thickness of the dielectric film in all of the parallel arm resonators.

[0139] <7> The filter device according to <5> or <6>, wherein the thickness of the piezoelectric layer in the first region and the thickness of the piezoelectric layer in the second region are different from each other.

[0140] <8> The filter device according to any one of <1> to <4>, wherein all the series arm resonators share the same piezoelectric substrate, all the parallel arm resonators share the same piezoelectric substrate, and the piezoelectric substrate shared by all the series arm resonators and the piezoelectric substrate shared by all the parallel arm resonators are different substrates.

[0141] <9> The filter device according to any one of <1> to <8>, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, and at least one of the elastic wave resonators has an acoustic reflection portion provided on the support member at a position that overlaps with the IDT electrode in a planar view, and wherein, when the thickness of the piezoelectric layer is d and the center-to-center distance between adjacent electrode fingers is p, in the elastic wave resonator having the acoustic reflection portion, d / p is 0.5 or less.

[0142] <10> The filter device according to <9>, wherein in the elastic wave resonator having d / p of 0.5 or less, a region where adjacent electrode fingers overlap in the direction perpendicular to the electrode fingers and a region between the centers of the adjacent electrode fingers is an excitation region of the elastic wave resonator, and when a metallization ratio of the electrode fingers to the excitation region is MR, at least one of the elastic wave resonators having d / p of 0.5 or less satisfies MR≦1.75(d / p)+0.075.

[0143] <11> The filter device according to <9> or <10>, wherein in the elastic wave resonator having the acoustic reflecting portion, d / p is 0.24 or less.

[0144] <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)

[0145] <13> A filter device according to any one of <1> to <12>, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, at least one of the elastic wave resonators has an acoustic reflection portion provided on the support member at a position overlapping the IDT electrode in a planar view, the acoustic reflection portion is a cavity, and the support member and the piezoelectric layer are arranged such that a part of the support member and a part of the piezoelectric layer face each other with the cavity between them.

[0146] <14> A filter device according to any one of <1> to <12>, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, at least one of the elastic wave resonators has an acoustic reflection portion provided on the support member at a position overlapping the IDT electrode in a planar view, the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged so that at least a portion of the support member and at least a portion of the piezoelectric layer face each other with the acoustic reflection film sandwiched therebetween.

[0147] REFERENCE SIGNS LIST 1...Filter device 2, 2B...Piezoelectric substrate 2a...Cavity 3, 3A...Support member 4...Support substrate 5...Insulating layer 6...Piezoelectric layer 6a, 6b...First and second principal surfaces 7...IDT electrode 8...Acoustic reflection film 9A, 9B...First and second dielectric films 11A, 11B...First and second signal terminals 12...Ground terminal 13A, 13B...Reflector 13a, 13b...Reflector bus bar 13c...Reflector electrode fingers 14a to 14c...Low acoustic impedance layer 15a, 15b...High acoustic impedance layer 16, 17...First and second bus bars 18, 19...First and second electrode fingers 21, 31, 41, 51...Filter device 52A, 52B...Piezoelectric substrate 56A, 56B...Piezoelectric layer 101...Filter device B1, B2...first, second area C...excitation area F...crossing area P1a, P1b, P2a, P2b, P3a, P3b, P4a~P4d, P31~P34, P51~P54, P101~P104...parallel arm resonator S1a, S1b, S2a, S2b, S3a, S3b, S4, S21a, S21b, S22 to S24, S31 to S34, S51 to S54, S101 to S104...Series arm resonator

Claims

1. A filter device having a piezoelectric substrate including a piezoelectric layer, comprising a plurality of elastic wave resonators each having an IDT electrode provided on the piezoelectric layer, wherein the IDT electrode has a plurality of electrode fingers, and when the direction in which the plurality of electrode fingers extend is defined as the electrode finger extension direction and the direction perpendicular to the electrode finger extension direction is defined as the electrode finger orthogonal direction, a region where adjacent electrode fingers overlap in the electrode finger orthogonal direction is a crossing region, and the dimension of the crossing region along the electrode finger extension direction is a crossing width, the plurality of elastic wave resonators include at least one series arm resonator and at least one parallel arm resonator, and the crossing width of at least one of the series arm resonators is narrower than the crossing widths of all of the parallel arm resonators.

2. The filter device according to claim 1, wherein the cross width of all of the series arm resonators is narrower than the cross width of all of the parallel arm resonators.

3. A filter device according to claim 1 or 2, wherein the piezoelectric layer has a first main surface and a second main surface facing each other, at least one of the series arm resonators has a dielectric film provided on at least one of the first main surface and the second main surface of the piezoelectric layer so as to overlap the IDT electrode in a planar view, and the series arm resonator having the largest total thickness of the dielectric films provided on the first main surface and the second main surface of the piezoelectric layer among all the series arm resonators has a cross width narrower than the cross widths of all the parallel arm resonators.

4. The filter device according to any one of claims 1 to 3, wherein the cross width of all the series arm resonators is 4.7p or more, where p is the center-to-center distance between adjacent electrode fingers.

5. A filter device according to any one of claims 1 to 4, wherein all of the series arm resonators and all of the parallel arm resonators share the same piezoelectric substrate and piezoelectric layer, and when the piezoelectric layer is divided into a first region and a second region in the direction perpendicular to the electrode fingers of at least one of the series arm resonators, all of the series arm resonators are located in the first region, and all of the parallel arm resonators are located in the second region.

6. The filter device according to claim 5, wherein the piezoelectric layer has a first main surface and a second main surface facing each other, all of the series arm resonators and all of the parallel arm resonators have a dielectric film provided on the first main surface of the piezoelectric layer so as to cover the IDT electrodes, and the thickness of the dielectric film in all of the series arm resonators is different from the thickness of the dielectric film in all of the parallel arm resonators.

7. The filter device according to claim 5 or 6, wherein the thickness of the piezoelectric layer in the first region and the thickness of the piezoelectric layer in the second region are different from each other.

8. The filter device according to any one of claims 1 to 4, wherein all of the series arm resonators share the same piezoelectric substrate, all of the parallel arm resonators share the same piezoelectric substrate, and the piezoelectric substrate shared by all of the series arm resonators and the piezoelectric substrate shared by all of the parallel arm resonators are mutually different substrates.

9. A filter device according to any one of claims 1 to 8, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, and at least one of the elastic wave resonators has an acoustic reflection portion provided on the support member at a position that overlaps with the IDT electrode in a planar view, and wherein, when the thickness of the piezoelectric layer is d and the center-to-center distance between adjacent electrode fingers is p, in the elastic wave resonator having the acoustic reflection portion, d / p is 0.5 or less.

10. The filter device according to claim 9, wherein in the elastic wave resonator having d / p of 0.5 or less, a region where adjacent electrode fingers overlap in the direction perpendicular to the electrode fingers and a region between the centers of adjacent electrode fingers is an excitation region of the elastic wave resonator, and when the metallization ratio of the electrode fingers to the excitation region is MR, in at least one of the elastic wave resonators having d / p of 0.5 or less, MR≦1.75(d / p)+0.075 is satisfied.

11. The filter device according to claim 9 or 10, wherein in the elastic wave resonator having the acoustic reflecting portion, d / p is 0.24 or less.

12. A filter device according to any one of claims 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) 13. A filter device according to any one of claims 1 to 12, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, and at least one of the acoustic wave resonators has an acoustic reflection portion provided on the support member at a position that overlaps with the IDT electrode in a plan view, the acoustic reflection portion being a cavity, and the support member and the piezoelectric layer are arranged so that a part of the support member and a part of the piezoelectric layer face each other with the cavity between them.

14. A filter device according to any one of claims 1 to 12, wherein the piezoelectric substrate includes a support member, the piezoelectric layer is provided on the support member, at least one of the elastic wave resonators has an acoustic reflection portion provided on the support member at a position overlapping the IDT electrode in a planar view, the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged so that at least a portion of the support member and at least a portion of the piezoelectric layer face each other with the acoustic reflection film in between.

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