Filter device

Abstract

Provided is a filter device wherein electric power resistance can be improved.　A filter device according to the present invention comprises a plurality of elastic wave resonators (serial arm resonators S2a, S2b) that share a piezoelectric substrate 2 having a support member 3 and a piezoelectric film that is provided on said support member 3 and includes a piezoelectric layer 6, and each have a functional electrode (IDT electrode 7) that is provided on the piezoelectric film. In each of the plurality of elastic wave resonators, a cavity section 2a is provided in the support member 3 in a location that overlaps with the functional electrode in plan view. The support member 3 and the piezoelectric film are positioned such that a section of the support member 3 and a section of the piezoelectric film face each other with the cavity sections 2a interposed therebetween. The plurality of elastic wave resonators include at least one set of parallel-connected resonators, which are at least two elastic wave resonators that are connected in parallel to each other. The cavity sections 2a of the at least one set of parallel-connected resonators are separated from each other in at least one section by a partition wall 2b, which is a section of the support member 3.

Description

Filter device

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

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

[0003] Each of the multiple resonators in Patent Document 1 is constructed 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 from 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, a bulk wave of the thickness-slip mode is excited as a horizontal shear acoustic mode.

[0005] Special Publication No. 2021-527344

[0006] In each resonator of a filter device as described in Patent Document 1, elastic waves such as bulk waves in thickness-slip mode are excited, and heat is generated. More specifically, the region in the piezoelectric plate where the elastic waves are excited becomes the heat source. The area near these heat sources faces a cavity. As a result, heat is difficult to dissipate to the outside, and the temperature of each IDT may become excessively high. Therefore, it is difficult to achieve sufficiently high power withstand capability in the above-mentioned filter device.

[0007] The object of the present invention is to provide a filter device that can achieve high power resistance.

[0008] The filter device according to the present invention shares a support member and a piezoelectric substrate provided on the support member and having a piezoelectric film including a piezoelectric layer, and comprises a plurality of elastic wave resonators, each having a functional electrode provided on the piezoelectric film, wherein in each of the plurality of elastic wave resonators, a cavity is provided in the support member at a position that overlaps with the functional electrode when viewed from above, 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 cavity in between, and the plurality of elastic wave resonators include at least one pair of parallel connected resonators, which are at least two of the elastic wave resonators connected in parallel to each other, and the cavities in the at least one pair of parallel connected resonators are separated at least in part by a partition wall which is part of the support member.

[0009] The filter device according to the present invention can achieve high power handling capacity.

[0010] Figure 1 is a circuit diagram of a filter device according to a first embodiment of the present invention. Figure 2 is a schematic plan view of a filter device according to a first embodiment of the present invention. Figure 3 is a schematic plan view showing a pair of parallel-connected resonators in a first embodiment of the present invention. Figure 4 is a schematic cross-sectional view along the line I-I in Figure 3. Figure 5 is a schematic front cross-sectional view showing a pair of parallel-connected resonators in a first comparative example. Figure 6 is a schematic front cross-sectional view showing a pair of parallel-connected resonators in a second comparative example. Figure 7 is a schematic plan view showing a pair of parallel-connected resonators in a first modification of the first embodiment of the present invention. Figure 8 is a schematic plan view showing a pair of parallel-connected resonators in a second modification of the first embodiment of the present invention. Figure 9 is a schematic plan view showing a pair of parallel-connected resonators in a second embodiment of the present invention. Figure 10 is a schematic plan view showing a pair of parallel-connected resonators in a third embodiment of the present invention. Figure 11 is a schematic cross-sectional view along the line II-II in Figure 10. Figure 12 is a schematic front cross-sectional view showing a pair of parallel-connected resonators in a fourth embodiment of the present invention. Figure 13 is a diagram showing the relationship between d / p and the relative bandwidth of the elastic wave resonator. Figure 14 is a diagram showing the relationship between the relative bandwidth in the elastic wave resonator and the magnitude of the normalized spurious emission. Figure 15 is a diagram showing the relationship between d / p, the metallization ratio MR, and the relative bandwidth. Figure 16 shows LiNbO when d / p approaches 0. ３ This figure shows a map of the relative bandwidth for Euler angles (0°, θ, ψ).

[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 herein are illustrative, and that partial substitution or combination of configurations is possible between different embodiments.

[0013] Figure 1 is a circuit diagram of a filter device according to the 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 12 and a second signal terminal 13, and a plurality of elastic wave resonators. In this embodiment, the second signal terminal 13 is an antenna terminal. The antenna terminal is connected to an antenna. Note that the second signal terminal 13 does not necessarily have to be an antenna terminal.

[0015] Multiple elastic wave resonators include multiple series arm resonators and multiple parallel arm resonators. In this embodiment, the multiple series arm resonators are specifically series arm resonators S1a, S1b, S1c, S1d, S2a, S2b, S3a, S3b, S4a, and S4b. The multiple parallel arm resonators are specifically parallel arm resonators P1a, P1b, P2a, P2b, P3a, P3b, P4a, P4b, P4c, and P4d.

[0016] In the circuit configuration, a series arm connects the first signal terminal 12 and the second signal terminal 13. Each series arm resonator is positioned on the series arm. On the other hand, multiple parallel arms connect the series arm and the ground potential. Each parallel arm resonator is positioned on the parallel arm.

[0017] Multiple elastic wave resonators include multiple sets of parallel-connected resonators. In this specification, a parallel-connected resonator means at least two elastic wave resonators connected in parallel with each other. The filter device 1 of this embodiment has eight sets of parallel-connected resonators.

[0018] More specifically, the first set of parallel-connected resonators consists of series arm resonators S1a, S1b, S1c, and S1d. The second set of parallel-connected resonators consists of series arm resonators S2a and S2b. The third set of parallel-connected resonators consists of series arm resonators S3a and S3b. The fourth set of parallel-connected resonators consists of series arm resonators S4a and S4b. The fifth set of parallel-connected resonators consists of parallel arm resonators P1a and P1b. The sixth set of parallel-connected resonators consists of parallel arm resonators P2a and P2b. The seventh set of parallel-connected resonators consists of parallel arm resonators P3a and P3b. The eighth set of parallel-connected resonators consists of parallel arm resonators P4a, P4b, P4c, and P4d.

[0019] The filter device 1 only needs to have at least one pair of parallel-connected resonators. The pair of parallel-connected resonators only needs to consist of at least two elastic wave resonators.

[0020] In this embodiment, all parallel-connected resonators are, in terms of circuit configuration, at least two elastic wave resonators formed by dividing one resonator in parallel. In this specification, two elastic wave resonators formed by dividing one resonator in parallel in circuit configuration means that the following a) and b) are satisfied: a) The two elastic wave resonators are connected in parallel to each other. b) The absolute value of the difference in the resonant frequencies of the two elastic wave resonators is 3% or less with respect to the resonant frequency of either of the two elastic wave resonators.

[0021] When three or more elastic wave resonators are divided in parallel, the absolute value of the difference in resonant frequencies between any two of the elastic wave resonators satisfies condition b) above. However, in the present invention, the parallel connected resonator does not necessarily have to be multiple elastic wave resonators formed by dividing a single resonator in parallel in terms of circuit configuration.

[0022] The specific configuration of the filter device 1 of this embodiment is shown below.

[0023] Figure 2 is a schematic plan view of the filter device according to the first embodiment. In Figure 2, the functional electrodes, which will be described later, are shown as a schematic diagram of a rectangle with two diagonals.

[0024] The filter device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 is a piezoelectric substrate. Specifically, the piezoelectric substrate 2 is a laminated substrate including a piezoelectric film. The piezoelectric film includes at least a piezoelectric layer 6. The piezoelectric layer 6 is a layer made of a piezoelectric material. On the other hand, in this specification, a piezoelectric film is a film that has 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 piezoelectric layer 6 and is a film made of a piezoelectric material. In this invention, the piezoelectric film may be a laminated film including a piezoelectric layer 6.

[0025] The piezoelectric layer 6 is, for example, LiNbO ３ It may consist of lithium niobate, or LiTaO ３ It may consist of lithium tantalate, etc. In this embodiment, the piezoelectric layer 6 is made of lithium niobate. In this specification, when a certain component is said to consist of a certain material, it includes cases where it contains trace amounts of impurities that do not significantly degrade the electrical properties of the elastic wave resonator.

[0026] 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. In this embodiment, 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.

[0027] The first main surface 6a of the piezoelectric layer 6 is provided with a first signal terminal 12, a second signal terminal 13, and a plurality of ground terminals 14. The ground terminals 14 are terminals connected to 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.

[0028] Multiple functional electrodes are provided on the first main surface 6a of the piezoelectric layer 6. This constitutes multiple elastic wave resonators. That is, each of the multiple elastic wave resonators has a functional electrode. The multiple elastic wave resonators share the same piezoelectric substrate 2. In this embodiment, the functional electrode in each elastic wave resonator is an IDT electrode 7. The specific configuration of the elastic wave resonator in this embodiment is shown with reference to Figure 3.

[0029] Figure 3 is a schematic plan view showing a pair of parallel-connected resonators in the first embodiment. Note that other elastic wave resonators are omitted in Figure 3. In Figure 3, electrodes are indicated by hatching. The same applies to other schematic plan views.

[0030] The pair of parallel-connected resonators shown in Figure 3 are a series arm resonator S2a and a series arm resonator S2b. The IDT electrode 7 of the series arm resonator S2a has a pair of busbars and a plurality of electrode fingers. The pair of busbars are specifically a first busbar 16 and a second busbar 17. The first busbar 16 and the second busbar 17 face each other. The plurality of electrode fingers are specifically a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One end of each of the plurality of first electrode fingers 18 is connected to the first busbar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second busbar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interlocked with each other. The first electrode fingers 18 and the second electrode fingers 19 are connected to different potentials. The IDT electrode 7 may consist of a multilayer metal film or a single layer metal film.

[0031] In the following, the first electrode fingers 18 and the second electrode fingers 19 may be collectively referred to simply as electrode fingers. The direction in which the multiple first electrode fingers 18 and the multiple second electrode fingers 19 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.

[0032] The series-arm resonator S2a has an intersection region F. The intersection region F is the region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap in the direction perpendicular to the electrode fingers. Hereafter, the dimension of the intersection region F along the direction of electrode finger extension will be defined as the intersection width.

[0033] The crossing region F includes multiple excitation regions C. More specifically, it is the region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap in the direction perpendicular to the electrode fingers, and the region between the centers of adjacent first electrode fingers 18 and second electrode fingers 19 is the excitation region C. The crossing region F and excitation region C are regions of the piezoelectric layer 6 defined based on the configuration of the IDT electrode 7. Note that in Figure 3, only three of the multiple excitation regions C in the series arm resonator S2a are shown.

[0034] The series arm resonator S2a is an elastic wave resonator configured to utilize the bulk wave of the thickness-slip mode as the main mode. By applying an AC voltage to the IDT electrode 7, the bulk wave of the thickness-slip mode is excited in each excitation region C. More specifically, in the series arm resonator S2a, when the thickness of the piezoelectric film is d and the distance between the centers of adjacent first electrode fingers 18 and second electrode fingers 19 is p, d / p is 0.5 or less. As a result, the bulk wave of the thickness-slip mode is suitably excited in each excitation region C. In this embodiment, the thickness d is the thickness of the piezoelectric layer 6.

[0035] The series arm resonators S2a shown in Figure 1, as well as the multiple series arm resonators and the multiple parallel arm resonators, are each elastic wave resonators configured to utilize bulk waves of the thickness-slip mode. Each of the multiple elastic wave resonators in the filter device 1 has an IDT electrode 7 and has an intersection region F and multiple excitation regions C. In addition, the design parameters of the multiple elastic wave resonators in the filter device 1 may differ depending on the desired characteristics.

[0036] Figure 4 is a schematic cross-sectional view along the line I-I in Figure 3.

[0037] The piezoelectric substrate 2 has a support member 3 and a piezoelectric layer 6 as a piezoelectric film. In the present 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 constituted only by the support substrate 4.

[0038] As the material of the support substrate 4, for example, semiconductors such as silicon, and ceramics such as aluminum oxide can be used. As the material of the insulating layer 5, an appropriate dielectric such as silicon oxide or tantalum oxide can be used.

[0039] The insulating layer 5 is provided with a plurality of recesses. On the insulating layer 5, a piezoelectric layer 6 as a piezoelectric film is provided so as to close the plurality of recesses. Thereby, a plurality of hollow portions are formed. These hollow portions are the cavity portions 2a. The support member 3 and the piezoelectric film are arranged such that a part of the support member 3 and a part of the piezoelectric film sandwich the plurality of cavity portions 2a and face each other.

[0040] One of the plurality of cavity portions 2a is provided at a position overlapping with the IDT electrode 7 of the series arm resonator S2a in plan view. Another one of the plurality of cavity portions 2a is provided at a position overlapping with the IDT electrode 7 of the series arm resonator S2b in plan view. In other words, each cavity portion 2a overlaps with the IDT electrode 7 in one of the elastic wave resonators of one set of parallel-connected resonators in plan view.

[0041] In this specification, plan view means looking along the stacking direction of the support member 3 and the piezoelectric film from the direction corresponding to above in FIG. 4. In FIG. 4, for example, of the support substrate 4 side and the piezoelectric layer 6 side, the piezoelectric layer 6 side is above. Further, in this specification, plan view is defined as synonymous with looking from the main surface facing direction. The main surface facing direction is the direction in which the first main surface 6a and the second main surface 6b of the piezoelectric layer 6 face each other. More specifically, the main surface facing direction is, for example, the normal direction of the first main surface 6a.

[0042] The series arm resonators S2a and S2b, which are a set of parallel-connected resonators, each have a cavity 2a. Similarly, the other surface acoustic wave resonators shown in FIG. 1 also have a cavity 2a. In each surface acoustic wave resonator, when viewed in plan view, the IDT electrode 7 as a functional electrode overlaps with the cavity 2a. Thereby, in each surface acoustic wave resonator, the energy of the surface acoustic wave can be effectively confined to the piezoelectric layer 6 side.

[0043] As shown in FIG. 4, a partition wall 2b is located between the cavities 2a. In the present embodiment, the partition wall 2b is a part of the insulating layer 5. However, the configuration of the partition wall 2b varies depending on the form of the cavity 2a. For example, the plurality of recesses in the support member 3 may be provided across the insulating layer 5 and the support substrate 4. In this case, the partition wall 2b is a part of the insulating layer 5 and a part of the support substrate 4. Note that the cavity 2a is not limited to a hollow portion. The cavity 2a may be, for example, a through hole in the support member 3. Also in this case, the partition wall 2b is a part of the insulating layer 5 and a part of the support substrate 4.

[0044] Alternatively, for example, a plurality of recesses provided only in the support substrate 4 may be blocked by the insulating layer 5. In this case, the partition wall 2b is a part of the support substrate 4. The plurality of recesses may be provided, for example, in the piezoelectric layer 6. In this case, the partition wall 2b is a part of the piezoelectric layer 6.

[0045] As shown in FIG. 4, all parts between the cavities 2a in the series arm resonator S2a and the series arm resonator S2b are separated by the partition wall 2b. Note that at least some of the parts between the cavities 2a in the series arm resonator S2a and the series arm resonator S2b may be separated by the partition wall 2b.

[0046] A feature of this embodiment is that the cavities 2a of at least one pair of parallel-connected resonators are separated at least in part by a partition wall 2b, which is part of the support member 3. This allows for higher heat dissipation and higher power handling capacity in the parallel-connected resonators. Consequently, the power handling capacity of the filter device 1 as a whole can also be increased. This will be explained below with reference to the first and second comparative examples.

[0047] The first comparative example shown in Figure 5 differs from the first embodiment in that it does not have parallel-connected resonators. The circuit configuration of the first comparative example corresponds to a circuit configuration in which each pair of parallel-connected resonators in the circuit configuration of the first embodiment becomes a single resonator. As shown in Figure 5, the filter device of the first comparative example has a series arm resonator S102. In terms of circuit configuration, the series arm resonator S102 corresponds to the series arm resonators S2a and S2b in Figure 1.

[0048] In the first comparative example, the capacitance of the series arm resonator S102 is approximately the same as the sum of the capacitances of the series arm resonators S2a and S2b in the first embodiment. The number of electrode fingers in the series arm resonator S102 is the same as the sum of the number of electrode fingers in the series arm resonators S2a and S2b. Furthermore, in the series arm resonator S102, a cavity 102a is provided so as to overlap with the IDT electrode 107 in a plan view.

[0049] When power is applied to the functional electrode of an elastic wave resonator, the elastic wave is excited, and heat is generated in the excited region. Therefore, the excited region becomes a heat source. In the first comparative example, most of the portion of the piezoelectric film near the heat source faces the cavity 102a. Therefore, the heat generated in the IDT electrode 107, which is the functional electrode, is difficult to dissipate. As a result, the temperature of the IDT electrode 107 becomes excessively high, making it prone to damage. Therefore, the power handling capacity of the series arm resonator S102 is low. Consequently, the power handling capacity of the filter device as a whole in the first comparative example is also low.

[0050] The second comparative example shown in Figure 6 differs from the first embodiment in that each pair of parallel-connected resonators shares a cavity 112a. The circuit configuration of the second comparative example is the same as that of the first embodiment. As shown in Figure 6, the filter device of the second comparative example has a series arm resonator S112a and a series arm resonator S112b. The series arm resonators S112a and S112b correspond to the series arm resonators S2a and S2b in Figure 1 in terms of circuit configuration.

[0051] In the second comparative example, the IDT electrodes 7 of the series arm resonator S112a and the IDT electrodes 7 of the series arm resonator S112b are configured in the same way as the IDT electrodes 7 of the series arm resonator S2a and the IDT electrodes 7 of the series arm resonator S2b in the first embodiment. In the second comparative example, similar to the first comparative example, most of the portion of the piezoelectric film near the heat source faces the cavity 112a. As a result, the heat dissipation of the series arm resonators S112a and S112b is low. Consequently, the power handling capacity of the filter device in the second comparative example is low.

[0052] In contrast to these, in the first embodiment shown in Figure 3, the cavities 2a of the series arm resonators S2a and S2b, which are parallel connected resonators, are separated by a partition wall 2b. Therefore, the piezoelectric film is in contact with the partition wall 2b between the parallel connected resonators. This allows the heat generated in the excitation region C to be propagated to the outside through the partition wall 2b. In this way, heat dissipation can be increased in the part where the parallel connected resonators are configured. This makes it less likely for the IDT electrode 7 to be damaged and increases the power withstand capability of the filter device 1.

[0053] In addition, in the first embodiment, the piezoelectric layer 6, which is a piezoelectric film, is supported by a partition wall 2b between a pair of parallel-connected resonators, which are elastic wave resonators. This makes it difficult for cracks to occur in the piezoelectric film.

[0054] The details of the circuit configuration in the first embodiment will be described below. As shown in Figure 1, in the circuit configuration, the first signal terminal 12 and the second signal terminal 13 are connected by a series arm. In the series arm, a group of resonators that constitute the first set of parallel connected resonators, a group of resonators that constitute the second set of parallel connected resonators, a group of resonators that constitute the third set of parallel connected resonators, and a group of resonators that constitute the fourth set of parallel connected resonators are connected in series with each other.

[0055] As mentioned above, the first set of parallel-connected resonators consists of series arm resonators S1a, S1b, S1c, and S1d. The second set of parallel-connected resonators consists of series arm resonators S2a and S2b. The third set of parallel-connected resonators consists of series arm resonators S3a and S3b. The fourth set of parallel-connected resonators consists of series arm resonators S4a and S4b.

[0056] In terms of the circuit configuration, the first set of parallel-connected resonators, the second set of parallel-connected resonators, the third set of parallel-connected resonators, and the fourth set of parallel-connected resonators are arranged in this order from the first signal terminal 12 side.

[0057] A fifth pair of parallel-connected resonators, parallel arm resonators P1a and P1b, are connected between the connection point between series arm resonators S1a and S2a and the ground potential. A sixth pair of parallel-connected resonators, parallel arm resonators P2a and P2b, are connected between the connection point between series arm resonators S2a and S3a and the ground potential. A seventh pair of parallel-connected resonators, parallel arm resonators P3a and P3b, are connected between the connection point between series arm resonators S3a and S4a and the ground potential. A fifth pair of parallel-connected resonators, parallel arm resonators P4a, P4b, P4c and P4d, are connected between the second signal terminal 13 and the ground potential.

[0058] As described above, in the series arm resonators S2a and S2b, which form a pair of parallel-connected resonators as shown in Figure 3, the cavities 2a of the series arm resonators are separated by a partition wall 2b in at least a portion of the space. It is preferable that the functional electrodes 7 of at least one pair of parallel-connected resonators having such a relationship are adjacent to each other without the need for other electrodes. More specifically, it is preferable that the excitation regions C of at least one pair of parallel-connected resonators having the above-described relationship are adjacent to each other without the need for other electrodes. In this case, electrodes other than the functional electrodes have difficulty functioning as heat dissipation paths. Therefore, heat dissipation tends to be low. In contrast, in the present invention, the partition wall 2b can be used as a heat dissipation path. Therefore, in the above configuration, the present invention is preferable.

[0059] The relative positions of a pair of parallel-connected resonators are not particularly limited. For example, the functional electrodes of a pair of parallel-connected resonators do not need to be adjacent to each other. The excitation regions of a pair of parallel-connected resonators do not need to be adjacent to each other. It is sufficient that the cavities 2a of the elastic wave resonators, which are a pair of parallel-connected resonators, are separated at least in part by a partition wall 2b, which is part of the support member. However, it is preferable that the excitation regions C of a pair of parallel-connected resonators are adjacent to each other. As described above, it is even more preferable that the excitation regions C of a pair of parallel-connected resonators are adjacent to each other without other electrodes in between.

[0060] In the following, the direction connecting the closest parts of the excitation regions of a pair of parallel-connected resonators is defined as the direction of opposing excitation regions. The dimension of the part located between these parts, along the direction of opposing excitation regions, is the shortest distance between the excitation regions. In the first embodiment shown in Figure 3, the direction of opposing excitation regions is parallel to the direction orthogonal to the electrode fingers. However, the relationship between the direction of opposing excitation regions and the direction orthogonal to the electrode fingers is not limited to the above.

[0061] In the first embodiment, the shortest distance between the excitation regions C of the series arm resonators S2a and S2b is short. In this case, the present invention is particularly suitable. This will be specifically shown below.

[0062] In a parallel-connected resonator where the cavities 2a are separated by a partition wall 2b in at least a portion of the space, let L be the dimension representing the shortest distance between the excitation regions C. In one of the parallel-connected resonators having this relationship, let W1 be the dimension along the direction of the opposing excitation regions of a single region comprising all the excitation regions C combined in one elastic wave resonator. In the other elastic wave resonator, let W2 be the dimension along the direction of the opposing excitation regions of a single region comprising all the excitation regions C combined in one elastic wave resonator. In the first embodiment, L < W1 and L < W2. Thus, the dimension L is small, and the shortest distance between the excitation regions C of the series arm resonators S2a and S2b is short.

[0063] In a pair of parallel-connected resonators, if the distance between the excitation regions is short, the distance between the heat sources is also short. Therefore, the temperature of the functional electrodes in a pair of parallel-connected resonators tends to rise. In contrast, in the present invention, heat dissipation can be increased in the portion where a pair of parallel-connected resonators are configured. Therefore, the present invention is particularly suitable when L < W1 and L < W2.

[0064] In the first embodiment, the cavities 2a in the series arm resonators S2a and S2b are separated by partition walls 2b in all parts. It is preferable that the cavities 2a in at least one pair of parallel connected resonators are separated by partition walls 2b in all parts. It is even more preferable that the cavities 2a in all parallel connected resonators are separated by partition walls 2b in all parts. This increases the area of ​​contact between the partition walls 2b and the piezoelectric film, thereby increasing the heat dissipation effect of the partition walls 2b. Thus, the power withstand capability of the filter device 1 can be effectively increased.

[0065] In the following, in the direction perpendicular to the electrode fingers, the direction toward the center of the IDT electrode 7 is defined as the inward direction, and the direction away from the center of the IDT electrode 7 is defined as the outward direction. When Ex is the dimension along the direction perpendicular to the electrode fingers from the outer edge of one end of the electrode finger to the outer edge of the other end of the electrode finger, it is preferable that Ex < 500 μm. When Ey is the dimension along the direction of electrode finger extension from the edge of the first busbar 16 on the second busbar 17 side to the edge of the second busbar 17 on the first busbar 16 side, it is preferable that Ey < 100 μm.

[0066] In this case, even if the area of ​​the cavity 2a in plan view is reduced, the configuration of the elastic wave resonator can be such that all excitation regions C and the cavity 2a overlap in plan view. Therefore, even if the area of ​​the cavity 2a in plan view is reduced, the energy of the elastic waves can be effectively confined to the piezoelectric layer 6. Furthermore, the area of ​​the piezoelectric layer 6, which acts as a piezoelectric film, that is not supported by the support member 3 can be effectively reduced. This effectively suppresses the occurrence of cracks in the piezoelectric film.

[0067] On the other hand, it is preferable that Ex > 50 μm. It is preferable that Ey > 20 μm. In this case, the IDT electrode 7 can be easily formed, and productivity can be increased.

[0068] Incidentally, when creating the cavity 2a shown in Figure 4, a sacrificial layer is used, for example. Specifically, a sacrificial layer and an insulating layer 5 are provided on the piezoelectric substrate so that the sacrificial layer is positioned within the recess of the insulating layer 5. Next, after forming a piezoelectric film by adjusting the thickness of the piezoelectric substrate, the sacrificial layer can be removed. When removing the sacrificial layer, for example, through holes can be made in the piezoelectric film, and wet etching can be performed using these through holes.

[0069] In Figure 3, the through-holes in the piezoelectric film are omitted. Examples in which through-holes are provided in the piezoelectric film are shown as the first and second modifications of the first embodiment. In the first and second modifications as well, the power withstand capability of the filter device can be increased, similar to the first embodiment.

[0070] In the first modified example shown in Figure 7, four through-holes 6c are provided in the piezoelectric layer 6, which is a piezoelectric film, so as to reach each cavity 2a in a pair of parallel connected resonators. In the series arm resonators S2a and S2b, which are a pair of parallel connected resonators, the cavities 2a are separated from each other by a partition wall 2b in at least a portion of the space.

[0071] In this modified example, two of the through-holes 6c reach the cavity 2a in the series arm resonator S2a. More specifically, these two through-holes 6c face each other, sandwiching the excitation region C of the series arm resonator S2a in the direction perpendicular to the electrode fingers. More precisely, these two through-holes 6c face each other, sandwiching the entire excitation region C of the series arm resonator S2a in the direction perpendicular to the electrode fingers. The other two through-holes 6c reach the cavity 2a in the series arm resonator S2b. These two through-holes 6c face each other, sandwiching the excitation region C of the series arm resonator S2b in the direction perpendicular to the electrode fingers. More precisely, these two through-holes 6c face each other, sandwiching the entire excitation region C of the series arm resonator S2b in the direction perpendicular to the electrode fingers.

[0072] As shown in Figure 7, two through holes 6c are provided between the excitation regions C of the series arm resonators S2a and S2b. As a result, unwanted waves generated in the excitation region C of the series arm resonator S2a are less likely to propagate to the excitation region C of the series arm resonator S2b. Similarly, unwanted waves generated in the excitation region C of the series arm resonator S2b are less likely to propagate to the excitation region C of the series arm resonator S2a. Therefore, interference and reinforcement between unwanted waves generated in the series arm resonators S2a and S2b, which act as a pair of parallel-connected resonators, can be suppressed. Consequently, unwanted waves can be suppressed in the filter device.

[0073] The piezoelectric layer 6, which serves as the piezoelectric film, may have four or more through-holes 6c. In this case as well, some of the through-holes 6c may reach the cavity 2a of the series arm resonator S2a and face each other across the excitation region C of the series arm resonator S2a. Other multiple through-holes 6c may reach the cavity 2a of the series arm resonator S2b and face each other across the excitation region C of the series arm resonator S2b.

[0074] In the present invention, at least one through-hole 6c may be provided in the piezoelectric layer 6, which is a piezoelectric film, so as to reach the cavity 2a in at least one elastic wave resonator. The piezoelectric layer 6 may also be provided with through-holes 6c so as to reach the cavity 2a in elastic wave resonators not shown in Figure 7.

[0075] However, in at least one pair of parallel-connected resonators in which the cavity portions 2a are separated by a partition wall 2b in at least a portion of the area, it is preferable that at least one through-hole 6c is provided between the excitation regions C. This makes it possible to suppress unwanted waves in the filter device, as in the modified example shown.

[0076] In at least one pair of parallel-connected resonators in which the cavities 2a are separated by partition walls 2b in at least a portion of the space, it is more preferable that through holes 6c are provided, as in the case shown in Figure 7. Specifically, this is as follows.

[0077] A piezoelectric layer 6, which serves as a piezoelectric film, is provided with four or more through-holes 6c. In at least one pair of parallel-connected resonators, where the cavities 2a are separated by a partition wall 2b in at least a portion of the space between them, several of the through-holes 6c reach the cavities 2a of one of the elastic wave resonators. These multiple through-holes 6c face each other across the excitation region C of the elastic wave resonator. The other multiple through-holes 6c reach the cavities 2a of the other elastic wave resonator and also face each other across the excitation region C of the elastic wave resonator. In this case, unwanted waves can be suppressed more reliably in the filter device.

[0078] In the second modified example shown in Figure 8, in a parallel connected resonator where the cavities 2a are separated by a partition wall 2b in at least a portion of the space, one through-hole 6c is provided in the piezoelectric layer 6 so as to reach both cavities 2a. More specifically, only one through-hole 6c is provided so as to reach both cavities 2a of the series arm resonators S2a and S2b. This through-hole 6c also reaches the partition wall 2b. Alternatively, multiple through-holes 6c may be provided so as to reach both cavities 2a of the series arm resonators S2a and S2b. In this case, for example, multiple through-holes 6c may be provided in the vertical direction in Figure 8.

[0079] In this modified example, as in the first modified example, unwanted waves can be suppressed in the filter device.

[0080] Furthermore, in at least one pair of parallel-connected resonators in which the cavities 2a are separated by a partition wall 2b in at least a portion of the area, it is preferable that through-holes 6c are provided, similar to the case shown in Figure 8. Specifically, in at least one pair of parallel-connected resonators in which the cavities 2a are separated by a partition wall 2b in at least a portion of the area, it is preferable that at least one through-hole 6c is provided in the piezoelectric layer 6, which is a piezoelectric film, so as to reach both cavities 2a. In this case, unwanted waves can be suppressed more reliably in the filter device.

[0081] The following describes a preferred configuration in the present invention.

[0082] Preferably, at least one pair of parallel-connected resonators is, in terms of circuit configuration, at least two elastic wave resonators formed by parallel-dividing one resonator. In this case, power is applied to the at least two elastic wave resonators. That is, the power applied to one resonator is distributed as power applied to multiple elastic wave resonators through parallel division. Therefore, the load applied to each of the multiple elastic wave resonators is small. Thus, by parallel-dividing a single resonator having the desired electrical characteristics, it is possible to obtain the desired electrical characteristics and, in addition, increase the power withstand capability of the filter device.

[0083] Furthermore, in the present invention, the power withstand capability of multiple elastic wave resonators, each formed by parallel-dividing a single resonator, can be suitably increased. Consequently, the power withstand capability of the filter device can be further enhanced.

[0084] It is more preferable that all parallel-connected resonators, in terms of circuit configuration, consist of at least two elastic wave resonators formed by the parallel division of a single resonator. In this case, the present invention is particularly suitable.

[0085] It is preferable that at least two series-arm resonators are connected in parallel with at least one pair of other resonators. Particularly high power is applied to the series-arm resonators. As a result, the temperature of the functional electrodes in the series-arm resonators tends to rise. In contrast, by having each series-arm resonator connected in parallel, the power applied to each series-arm resonator can be reduced.

[0086] As in the first embodiment, it is preferable that all elastic wave resonators are connected in parallel. This makes it possible to reduce the power applied to each elastic wave resonator. As a result, the power withstand capability of the filter device 1 can be effectively increased. In addition, the area of ​​each cavity 2a in plan view can be reduced. As a result, the piezoelectric film can be suitably supported by the support member 3. Therefore, cracks are less likely to occur in the piezoelectric film.

[0087] However, it is sufficient if at least two elastic wave resonators are connected in parallel. Even in this case, the power applied to at least two elastic wave resonators, which function as parallel resonators, can be reduced. In addition, in the portion where parallel resonators are configured, the area of ​​each cavity 2a in plan view is small. Therefore, cracks are less likely to occur in the piezoelectric film.

[0088] In all parallel-connected resonators, it is more preferable that the piezoelectric film portion located between the elastic wave resonators in each pair of parallel-connected resonators is supported by the partition wall 2b. This increases the heat dissipation path near the heat source of each elastic wave resonator. As a result, even when power is applied to each elastic wave resonator, the temperature of the functional electrode can be prevented from becoming excessively high, and damage to the functional electrode can be prevented. Therefore, the power withstand capability of the filter device can be further increased.

[0089] In the present invention, the filter device may include a longitudinally coupled resonator type elastic wave filter. In this case, the filter device may include at least two series-arm resonators or at least two parallel-arm resonators. Furthermore, the filter device may have at least one pair of parallel-connected resonators. The cavities in at least one pair of parallel-connected resonators may be separated by a partition wall in at least a portion of their respective parts.

[0090] In parallel-connected resonators, the cavities may be separated in some parts by partitions. An example of this is shown in the second embodiment.

[0091] Figure 9 is a schematic plan view showing a pair of parallel-connected resonators in the second embodiment.

[0092] This embodiment differs from the first embodiment in that the cavities 2a of the series arm resonators S2a and S2b, which are parallel connected resonators, are connected by connection holes 28. Apart from the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0093] The connection hole 28 is provided in the support member 23. Specifically, in this embodiment, the connection hole 28 is formed by a groove provided in the insulating layer 5 of the support member 23 being blocked by a piezoelectric film.

[0094] One end of the connection hole 28 is connected to the cavity 2a in the series arm resonator S2a. The other end of the connection hole 28 is connected to the cavity 2a in the series arm resonator S2b. As a result, the cavities 2a of the series arm resonators S2a and S2b, which function as parallel connected resonators, are connected by the connection hole 28. The connection hole 28 corresponds to a portion of the partition wall 2b that has been removed. Even when the connection hole 28 is provided, the partition wall 2b still functions as a heat dissipation path.

[0095] In the following, the direction perpendicular to the direction in which the connection hole 28 extends from one cavity 2a to the other cavity 2a is defined as the connection hole width direction, and the dimension along the connection hole width direction of the connection hole 28 is defined as the width of the connection hole 28. In this embodiment, the connection hole width direction is parallel to the electrode finger extension direction. Therefore, the dimension along the connection hole width direction of each excitation region C in the series arm resonator S2a corresponds to the intersection width. The same applies to the series arm resonator S2b. However, the relationship between the connection hole width direction and the electrode finger extension direction is not limited to the above.

[0096] In this embodiment, the width of the connection hole 28 is narrower than the crossover width of the series arm resonators S2a and S2b, which are parallel connected resonators connected by the connection hole 28, with the cavity portions 2a connected to each other. That is, the width of the connection hole 28 is smaller than the dimension along the connection hole width direction of either excitation region C in the parallel connected resonators. This allows the area of ​​the contact between the piezoelectric layer 6 as a piezoelectric film and the partition wall 2b to be sufficiently large. Therefore, heat dissipation can be increased in the parts where the series arm resonators S2a and S2b are configured. Consequently, the power withstand capability of the filter device can be increased, similar to the first embodiment.

[0097] In addition, when connection holes 28 are provided, sacrificial layer residue is less likely to be generated in the cavity 2a during the manufacture of the filter device. More specifically, when providing the cavity 2a as shown with reference to Figure 4, the sacrificial layer is placed in the recess of the insulating layer 5, and after forming the piezoelectric film, the sacrificial layer can be removed. When connection holes 28 are provided, grooves are provided in the insulating layer 5 to connect the recesses, and then the sacrificial layer is provided in the grooves and recesses. Alternatively, the sacrificial layer may be patterned so that the sacrificial layer is provided in each recess and groove, and then the insulating layer 5 may be formed. Next, after forming the piezoelectric film, the sacrificial layer is removed from the grooves and recesses. When removing the sacrificial layer, wet etching can be performed using the through holes of the piezoelectric film.

[0098] During wet etching, the etching solution moves through the grooves and between the recesses. This allows for a wider range of etching solution flow and a higher degree of freedom of flow. As a result, the sacrificial layer can be removed more reliably, and sacrificial layer residue is less likely to form in the cavity 2a. Therefore, it is possible to suppress problems such as the piezoelectric film becoming fixed due to sacrificial layer residue. Consequently, it is possible to suppress malfunctions in the elastic wave resonator.

[0099] In the first embodiment and this embodiment, each elastic wave resonator is configured to utilize bulk waves in thickness-slip mode as the main mode. However, each elastic wave resonator may be configured to utilize plate waves or the like as the main mode. In this case, the excitation region is the crossover region F. Even when using plate waves, as in the first embodiment and this embodiment, heat dissipation can be increased in the portion where parallel-connected resonators are configured. This increases the power handling capacity of the filter device.

[0100] In this invention, the functional electrode is not limited to an IDT electrode. An example in which the functional electrode is not an IDT electrode is shown in the third embodiment.

[0101] Figure 10 is a schematic plan view showing a pair of parallel-connected resonators in the third embodiment. Figure 11 is a schematic cross-sectional view along the line II-II in Figure 10. Note that Figure 11 shows a cross-section that does not pass through the connection hole 28 shown in Figure 10.

[0102] In this embodiment, the pair of parallel-connected resonators are BAW (Bulk Acoustic Wave) elements. The circuit configuration of the filter device according to this embodiment is the same as the circuit configuration of the first embodiment. As shown in Figure 10, the filter device of this embodiment has a series arm resonator S32a and a series arm resonator S32b. The series arm resonators S32a and S32b correspond to the series arm resonators S2a and S2b in Figure 1 in terms of circuit configuration.

[0103] As shown in Figure 11, the functional electrode 37A of the series arm resonator S32a has a first excitation electrode 37a and a second excitation electrode 37b. The first excitation electrode 37a is provided on the first main surface 6a of the piezoelectric layer 6, which serves as the first main surface of the piezoelectric film. The second excitation electrode 37b is provided on the second main surface 6b of the piezoelectric layer 6, which serves as the second main surface of the piezoelectric film. More specifically, the second excitation electrode 37b is provided on the second main surface 6b so as to face the first excitation electrode 37a across the piezoelectric layer 6.

[0104] The first excitation electrode 37a and the second excitation electrode 37b are connected to different potentials. Specifically, the first excitation electrode 37a is electrically connected to the elastic wave resonator on the input potential side. On the other hand, the second excitation electrode 37b is electrically connected to the elastic wave resonator on the output potential side. However, the first excitation electrode 37a may also be electrically connected to the elastic wave resonator on the output potential side. In this case, the second excitation electrode 37b only needs to be electrically connected to the elastic wave resonator on the input potential side.

[0105] The first excitation electrode 37a is electrically connected to another elastic wave resonator by appropriate wiring provided on the first main surface 6a of the piezoelectric layer 6, as shown in Figure 10. On the other hand, although not shown, the second excitation electrode 37b may also be connected to another elastic wave resonator by appropriate wiring provided on the second main surface 6b of the piezoelectric layer 6. A through electrode may also be provided in the piezoelectric layer 6. The second excitation electrode 37b may be electrically connected to another elastic wave resonator by appropriate wiring provided on the second main surface 6b of the piezoelectric layer 6, a through electrode, and appropriate wiring provided on the first main surface 6a.

[0106] As shown in Figure 11, the excitation region C in the series arm resonator S32a is the region in the piezoelectric layer 6 sandwiched between the first excitation electrode 37a and the second excitation electrode 37b. By applying an AC voltage to the functional electrode 37A, a bulk wave is excited in the excitation region C.

[0107] The functional electrode 37B of the series-arm resonator S32b has a first excitation electrode 37c and a second excitation electrode 37d. The first excitation electrode 37c and the second excitation electrode 37d of the functional electrode 37B are connected to different potentials.

[0108] The functional electrode 37B of the series arm resonator S32b is provided in the same manner as the functional electrode 37A of the series arm resonator S32a. The first excitation electrode 37c and the second excitation electrode 37d of the functional electrode 37B are electrically connected to other elastic wave resonators, similar to the first excitation electrode 37a and the second excitation electrode 37b of the functional electrode 37A.

[0109] The excitation region C in the series-arm resonator S32b is the region in the piezoelectric layer 6 sandwiched between the first excitation electrode 37c and the second excitation electrode 37d. By applying an AC voltage to the functional electrode 37B, a bulk wave is excited in the excitation region C.

[0110] In this embodiment, as in the first embodiment, the cavities 2a of the series arm resonators S32a and S32b, which form a pair of parallel-connected resonators, are separated by a partition wall 2b. This allows for higher heat dissipation in the portion where the parallel-connected resonators are located. Consequently, the power handling capacity of the filter device can be increased.

[0111] In the series arm resonators S32a and S32b, which are connected in parallel, there is one excitation region C. Therefore, in the series arm resonator S32a, the single region formed by combining all the excitation regions C is the excitation region C itself. The same applies to the series arm resonator S32b. Thus, in the series arm resonator S32a, the dimension of the excitation region C along the direction opposite to the excitation region is W1. In the series arm resonator S32b, the dimension of the excitation region C along the direction opposite to the excitation region is W2.

[0112] In the series arm resonators S32a and S32b, the dimension representing the shortest distance between the excitation regions C is L. In this embodiment, as in the first embodiment, L < W1 and L < W2. Therefore, a configuration in which the cavities 2a are separated by a partition wall 2b is particularly preferred.

[0113] As shown in Figure 10, in this embodiment, similar to the second embodiment, the cavities 2a of the parallel-connected resonators are connected by connection holes 28. This makes it less likely for sacrificial layer residue to be generated inside the cavities 2a during the manufacture of the filter device.

[0114] As shown in Figure 10, let M be the dimension along the width direction of the connection hole in the excitation region C. The width of the connection hole 28 is smaller than dimension M. This allows the area of ​​contact between the piezoelectric layer 6 as a piezoelectric film and the partition wall 2b to be sufficiently large. Therefore, heat dissipation can be increased in the area where the series arm resonators S32a and S32b are configured. Consequently, the power withstand capability of the filter device can be increased, similar to the second embodiment. Note that the connection hole 28 does not necessarily have to be provided.

[0115] As in this embodiment, each functional electrode in at least one pair of parallel-connected resonators may be a functional electrode having a first excitation electrode and a second excitation electrode. Alternatively, as in the first and second embodiments, each functional electrode in at least one pair of parallel-connected resonators may be an IDT electrode having multiple electrode fingers.

[0116] Figure 12 is a schematic front cross-sectional view showing a pair of parallel-connected resonators in the fourth embodiment.

[0117] This embodiment differs from the first embodiment in that a metal film 45 is provided on the second main surface 6b of the piezoelectric layer 6 in each of the series arm resonators S42a and S42b, which are a pair of parallel connected resonators. The metal film 45 is provided so as to overlap with each IDT electrode 7 in a plan view. Except for the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0118] Similar to the first embodiment, the piezoelectric film is a single-layer piezoelectric layer 6. Therefore, the first main surface and the second main surface of the piezoelectric film are the first main surface 6a and the second main surface 6b of the piezoelectric layer 6.

[0119] The metal film 45 is a floating electrode. A floating electrode is an electrode that is not connected to the signal potential or the ground potential.

[0120] In this embodiment, the metal film 45 can be used as a heat dissipation path. Therefore, the heat dissipation can be further improved in the portion where the parallel-connected resonators are configured. Consequently, the power withstand capability of the filter device can be effectively increased.

[0121] Furthermore, it is sufficient that at least one pair of parallel-connected resonators each have an IDT electrode 7 provided on the first main surface of the piezoelectric film and a metal film 45 provided on the second main surface. For example, all parallel-connected resonators may each have an IDT electrode 7 provided on the first main surface of the piezoelectric film and a metal film 45 provided on the second main surface.

[0122] Each elastic wave resonator in this embodiment is configured to utilize bulk waves in thickness-slip mode as its main mode. However, each elastic wave resonator may also be configured to utilize plate waves.

[0123] In the following, preferred configurations of the elastic wave resonator in the present invention will be described with reference to Figure 3. However, the preferred configurations shown below can also be applied to configurations of elastic wave resonators that utilize the thickness-slip mode as the main mode, other than the first embodiment of the present invention.

[0124] In the first embodiment, when the thickness of the piezoelectric film is d and the distance between the centers of adjacent electrode fingers is p, d / p is 0.5 or less. Preferably, d / p is 0.24 or less. This allows the bulk wave of the thickness-slip mode to be more suitably excited in each excitation region C, and the relative bandwidth of the elastic wave resonator can be made sufficiently large. The relative bandwidth is expressed as (|fa - fr| / fr) × 100 [%], where fr is the resonant frequency and fa is the anti-resonant frequency.

[0125] Figure 13 shows the relationship between d / p and the specific bandwidth of an elastic wave resonator.

[0126] As is clear from Figure 13, when d / p > 0.5, the relative bandwidth is less than 5%. In contrast, when d / p ≤ 0.5, the relative bandwidth can be increased to 5% or more. Therefore, the electromechanical coupling coefficient of the bulk wave in the thickness-slip mode can be increased. When d / p ≤ 0.24, the relative bandwidth can be increased to 7% or more. Therefore, the electromechanical coupling coefficient of the bulk wave in the thickness-slip mode can be effectively increased. Note that d / p ≤ 0.5 may also be the case for each of at least one pair of parallel-connected resonators. d / p ≤ 0.24 may also be the case for each of at least one pair of parallel-connected resonators.

[0127] When the metallization ratio of the electrode finger with respect to the excitation region C is denoted as MR, it is preferable that MR ≤ 1.75 (d / p) + 0.075 is satisfied. In this case, the ratio bandwidth value of the elastic wave resonator does not become too large, and the generation of spurious signals between the resonant frequency and the anti-resonant frequency can be suppressed. The details are shown below.

[0128] In this specification, the metallization ratio MR of the electrode fingers with respect to the excitation region C is the proportion of the excitation region C occupied by the portion of the piezoelectric layer 6 that is covered by the metal constituting the electrode fingers, when viewed from above. Specifically, the metallization ratio MR is the ratio of the area of ​​the first electrode fingers 18 and the second electrode fingers 19 within the excitation region C to the area of ​​the excitation region C when viewed from above. If the width of the electrode fingers located within the excitation region C is constant, the metallization ratio MR can also be calculated by dividing the sum of the widths of the electrode fingers located within the excitation region C by the dimension along the direction perpendicular to the electrode fingers in the excitation region C.

[0129] Figure 14 shows the relationship between the relative bandwidth and the normalized spurious amplitude in an elastic wave resonator. Figure 14 shows the results of measuring the phase rotation of the spurious amplitude for each change in the relative bandwidth, achieved by varying the thickness of the piezoelectric layer and the dimensions of the electrode fingers. Specifically, the normalized spurious amplitude in Figure 14 is the value of the spurious impedance phase rotation normalized by 180°. The results shown in Figure 14 are for Z-cut LiNbO ３ The results shown are for the case where a piezoelectric layer consisting of [specific material] is used, but a similar trend is observed when piezoelectric layers with other cut angles are used.

[0130] In the region enclosed by ellipse A in Figure 14, the normalized spurious magnitude between the resonant frequency and the anti-resonant frequency is 1.0. When the relative bandwidth of the elastic wave resonator exceeds 17%, the normalized spurious magnitude may be 1.0 or greater. For this reason, it is preferable that the relative bandwidth be 17% or less. This allows for the suppression of spurious emissions between the resonant frequency and the anti-resonant frequency.

[0131] Figure 15 shows the relationship between d / p, metallization ratio MR, and ratio bandwidth. Figure 15 shows the results of calculating the ratio bandwidth for each different d / p and metallization ratio MR.

[0132] In Figure 15, the hatched area represents the region with a relative bandwidth of 17% or less. The boundary between this hatched region and the unhatched region is roughly represented by the dashed line B. The dashed line B is represented by MR = 1.75(d / p) + 0.075. It is preferable that MR ≤ 1.75(d / p) + 0.075 for each of at least one pair of parallel-connected resonators in the filter device. It is even more preferable that MR ≤ 1.75(d / p) + 0.075 for each of all parallel-connected resonators. In this case, it is easier to achieve a relative bandwidth of 17% or less for each elastic wave resonator.

[0133] On the other hand, the dashed line B1 in Figure 15 indicates the boundary where the slope of the change in the metallization ratio MR with respect to the change in d / p is the same as the slope of the dashed line B, and the relative bandwidth is 17% or less in the entire range. The dashed line B1 is represented by MR = 1.75(d / p) + 0.05. Furthermore, it is more preferable that MR ≤ 1.75(d / p) + 0.05 for each of at least one pair of parallel-connected resonators in the filter device. It is even more preferable that MR ≤ 1.75(d / p) + 0.05 for each of all parallel-connected resonators. In this case, the relative bandwidth can be more reliably reduced to 17% or less for each elastic wave resonator.

[0134] Figure 16 shows LiNbO when d / p approaches 0. ３ This figure shows a map of the relative bandwidth for the Euler angle (0°, θ, ψ). The hatched area in Figure 16 is the region where a relative bandwidth of at least 5% is obtained, and the range of this region can be approximated by the following equations (1), (2), and (3).

[0135] (0°±10°, 0°~20°, any ψ) ...Equation (1) (0°±10°, 20°~80°, 0°~60° (1-(θ-50)) ２ / 900)１／２ ), or (0° ± 10°, 20° to 80°, [180° - 60°(1 - (θ - 50) ２ / 900) １／２ to 180°)... Equation (2) (0° ± 10°, [180° - 30°(1 - (ψ - 90) ２ / 8100) １／２ to 180°, any ψ)... Equation (3)

[0136] It is preferable that the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer are within the ranges of the above Equation (1), Equation (2), or Equation (3). Thereby, the specific bandwidth of the elastic wave resonator can be made sufficiently wide.

[0137] 1... Filter device 2... Piezoelectric substrate 2a... Cavity 2b... Partition wall 3... Support member 4... Support substrate 5... Insulating layer 6... Piezoelectric layer 6a, 6b... First and second main surfaces 6c... Through hole 7... IDT electrode 12, 13... First and second signal terminals 14... Ground terminal 16, 17... First and second bus bars 18, 19... First and second electrode fingers 23... Support member 28... Connection hole 37A, 37B... Functional electrodes 37a, 37b... First and second excitation electrodes 37c, 37d... First and second excitation electrodes 45... Metal film 102a... Cavity 107... IDT electrode 112a... Cavity C... Excitation region F... Crossing region P1a, P1b, P2a, P2b, P3a, P3b, P4a to P4d... Parallel arm resonators S1a to S1d, S2a, S2b, S3a, S3b, S4a, S4b, S32a, S32b, S42a, S42b, S102, S112a, S112b... Series arm resonators

Claims

1. A filter device comprising a plurality of elastic wave resonators, each having a functional electrode provided on the piezoelectric film, and sharing a support member and a piezoelectric substrate provided on the support member, the piezoelectric film having a piezoelectric layer, and each of the plurality of elastic wave resonators having a functional electrode provided on the piezoelectric film, wherein in each of the plurality of elastic wave resonators, a cavity is provided in the support member at a position that overlaps with the functional electrode when viewed from above, 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 cavity in between, and the plurality of elastic wave resonators include at least one pair of parallel connected resonators, which are at least two of the elastic wave resonators connected in parallel with each other, and the cavities in at least one pair of the parallel connected resonators are separated at least in part by a partition wall which is part of the support member.

2. The filter device according to claim 1, wherein at least one pair of parallel connected resonators, whose cavities are separated by the partition wall in at least a portion of the area, are, in terms of circuit configuration, at least two elastic wave resonators formed by parallel division of one resonator.

3. The filter device according to claim 1 or 2, wherein each elastic wave resonator has an excitation region in which an elastic wave is excited, the cavities of at least one pair of parallel connected resonators are separated by a partition wall in at least a portion of the space, the functional electrodes of at least one pair of parallel connected resonators are adjacent to each other without other electrodes in between, the direction connecting the closest portions of the excitation regions of the parallel connected resonators is defined as the direction of opposing excitation regions, L is the dimension of the shortest distance between the excitation regions of the parallel connected resonators, W1 is the dimension of one region formed by combining all the excitation regions of one of the parallel connected resonators along the direction of opposing excitation regions, and W2 is the dimension of one region formed by combining all the excitation regions of the other along the direction of opposing excitation regions, such that L < W1 and L < W2.

4. The filter device according to claim 3, wherein at least one through-hole is provided in the piezoelectric film so as to reach the cavity in at least one of the elastic wave resonators, and in at least one pair of parallel connected resonators, the cavities are separated from each other by the partition wall in at least a portion of the area, at least one through-hole is provided between the excitation regions.

5. The filter device according to claim 4, wherein the piezoelectric film is provided with four or more through holes, and the cavities are separated from each other by a partition wall in at least a portion of the pair of parallel connected resonators, wherein a plurality of the through holes reach the cavity in one of the elastic wave resonators and face each other across the excitation region of the elastic wave resonator, and the other plurality of through holes reach the cavity in the other elastic wave resonator and face each other across the excitation region of the elastic wave resonator.

6. The filter device according to claim 4, wherein in at least one pair of parallel connected resonators, the cavities of which are separated by the partition wall in at least a portion of each other, at least one through-hole is provided in the piezoelectric film so as to reach both cavities.

7. The filter device according to any one of claims 1 to 3, wherein the cavities in at least one pair of parallel connected resonators are separated in all parts by the partition wall.

8. The filter device according to any one of claims 1 to 7, wherein each elastic wave resonator has an excitation region in which an elastic wave is excited, and is provided with a connection hole connecting the cavities of at least one pair of parallel connected resonators, and when the direction perpendicular to the direction in which the connection hole extends from one cavity to the other cavity is defined as the width direction of the connection hole, the dimension of the connection hole along the width direction of the connection hole is smaller than the dimension of the excitation region along the width direction of the connection hole in both of the parallel connected resonators whose cavities are connected by the connection hole.

9. The filter device according to any one of claims 1 to 8, wherein each of the functional electrodes in at least one set of parallel connected resonators is an IDT electrode having a plurality of electrode fingers.

10. The filter device according to claim 9, wherein, when the thickness of the piezoelectric layer is d and the distance between the centers of adjacent electrode fingers is p, d / p is 0.5 or less in each of at least one pair of parallel connected resonators.

11. The filter device according to claim 10, wherein the d / p is 0.24 or less in each of at least one pair of parallel-connected resonators.

12. The filter device according to claim 10 or 11, wherein when the direction perpendicular to the direction in which the plurality of electrode fingers extend is defined as the electrode finger orthogonal direction, the region in which adjacent electrode fingers overlap in the electrode finger orthogonal direction, and the region between the centers of adjacent electrode fingers is the excitation region, and when the metallization ratio of the electrode fingers with respect to the excitation region is defined as MR, at least one pair of parallel connected resonators satisfies MR ≤ 1.75 (d / p) + 0.

075.

13. The filter device according to any one of claims 9 to 12, wherein the piezoelectric film has a first main surface and a second main surface facing each other, and at least one pair of parallel connected resonators each have an IDT electrode provided on the first main surface of the piezoelectric film and a metal film provided on the second main surface so as to overlap with the IDT electrode in a plan view, and the metal film is not connected to the signal potential and the ground potential.

14. The IDT electrode has a first busbar and a second busbar facing each other, the plurality of electrode fingers are a plurality of first electrode fingers and a plurality of second electrode fingers, one end of each of the plurality of first electrode fingers is connected to the first busbar, one end of each of the plurality of second electrode fingers is connected to the second busbar, the plurality of first electrode fingers and the plurality of second electrode fingers are interlocked with each other, and when the direction in which the plurality of first electrode fingers and the plurality of second 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, when the dimension along the electrode finger orthogonal direction from the outer edge of one end of the IDT electrode in the electrode finger orthogonal direction to the outer edge of the other end of the IDT electrode is defined as Ex, then 50 μm < Ex < 500 μm. The filter device according to any one of claims 9 to 13, wherein when Ey is the dimension along the electrode finger extension direction from the end edge of the first busbar on the second busbar side to the end edge of the second busbar on the first busbar side, 20 μm < Ey < 100 μm.

15. A filter device according to any one of claims 1 to 14, wherein the piezoelectric layer is made of lithium niobate, and the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer are within the range of the following equations (1), (2), or (3): (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°~80°, [180°-60°(1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ ( / 8100) １／２ ] ~180°, any ψ) ...Equation (3) 16. The filter device according to any one of claims 1 to 15, wherein the plurality of elastic wave resonators include at least two series arm resonators, and at least two of the series arm resonators are at least one pair of the parallel connected resonators.

17. The filter device according to any one of claims 1 to 16, wherein all of the elastic wave resonators are parallel connected resonators.

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