Filter device

Abstract

To provide a filter device which can widen a passband and can be made smaller.SOLUTION: A filter device 1 according to the present invention includes a plurality of resonators including a plurality of series arm resonators and at least one parallel arm resonator. The plurality of resonators includes a series arm resonator S23 as a first resonator having the largest band ratio value among the plurality of resonators, and at least one second resonator other than the first resonator. The plurality of series arm resonators includes a first resonator (series arm resonator S23) and a second resonator. The filter device 1 further includes a first inductor (inductor L) which is an inductor connected in series to the first resonator (series arm resonator S23). The series arm resonator which is the second resonator includes a series arm resonator not connected to the inductor.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a filter device including a ladder-type circuit.

Background Art

[0002] Conventionally, piezoelectric devices have been widely used in filters for mobile phones and the like. Patent Document 1 below describes an example of a ladder-type filter in which piezoelectric devices are used for series arm resonators and parallel arm resonators. In this ladder-type filter, five series arm resonators are connected in series between two terminals. Inductors are connected between the series arm resonators at both ends and the two terminals, respectively. The resonance frequencies of the series arm resonators at both ends are different from the resonance frequencies of the three series arm resonators other than the series arm resonators at both ends. Thereby, it is intended to expand the passband of the ladder-type filter and increase the attenuation amount outside the passband.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a ladder-type filter, a piezoelectric resonator with a small specific bandwidth value may be used to enhance the steepness at the end of the passband. On the other hand, a piezoelectric resonator with a large specific bandwidth value may be used to expand the passband. To achieve high steepness and a wide passband, both a piezoelectric resonator with a small specific bandwidth value and a piezoelectric resonator with a large specific bandwidth value are required.

[0005] Here, in order to increase the value of the specific band of the elastic wave resonator, an inductor may be connected to the elastic wave resonator. By increasing the inductance of the inductor, the value of the specific band can be increased. However, when the inductance of the inductor is increased, the inductor becomes large, and the entire filter device also tends to become large.

[0006] An object of the present invention is to provide a filter device that can widen the passband and can be miniaturized.

Means for Solving the Problems

[0007] The filter device according to the present invention includes a plurality of resonators including at least one series arm resonator and at least one parallel arm resonator, and the plurality of resonators include a first resonator having the largest value of the specific band among the plurality of resonators, and at least one second resonator other than the first resonator, and further includes an inductor connected in series to the first resonator.

Effects of the Invention

[0008] According to the filter device according to the present invention, the passband can be widened and miniaturization can be promoted.

Brief Description of the Drawings

[0009]

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MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

[0011] It should be noted that each embodiment described in this specification is exemplary, and it is pointed out that partial substitution or combination of configurations is possible between different embodiments.

[0012] FIG. 1 is a circuit diagram of a filter device according to a first embodiment of the present invention.

[0013] The filter device 1 has a first signal terminal 9A and a second signal terminal 9B, and a plurality of resonators. Specifically, the plurality of resonators includes a plurality of series-arm resonators and a plurality of parallel-arm resonators. The plurality of series-arm resonators are series-arm resonator S1, series-arm resonator S2, series-arm resonator S3, series-arm resonator S4, and series-arm resonator S5. The plurality of parallel-arm resonators are parallel-arm resonator P1, parallel-arm resonator P2, parallel-arm resonator P3, and parallel-arm resonator P4. In the present embodiment, all of the plurality of resonators are surface acoustic wave resonators. Specifically, the plurality of resonators are surface acoustic wave resonators. However, the plurality of resonators may also include bulk wave resonators.

[0014] In the present embodiment, the first signal terminal 9A is an antenna terminal. That is, the first signal terminal 9A is connected to an antenna. The first signal terminal 9A and the second signal terminal 9B may be provided as electrode pads, or may be provided as wirings.

[0015] The in-line wrist resonators S1, S2, S3, S4, and S5 are connected in series with each other between the first signal terminal 9A and the second signal terminal 9B. A parallel-arm resonator P1 is connected between the connection point between the in-line wrist resonators S1 and S2 and the ground potential. A parallel-arm resonator P2 is connected between the connection point between the in-line wrist resonators S2 and S3 and the ground potential. A parallel-arm resonator P3 is connected between the connection point between the in-line wrist resonators S3 and S4 and the ground potential. A parallel-arm resonator P4 is connected between the connection point between the in-line wrist resonators S4 and S5 and the ground potential. Note that the plurality of resonators of the filter device 1 only need to include at least one in-line wrist resonator and at least one parallel-arm resonator. The filter device 1 only needs to include a ladder-type circuit. The filter device 1 may include, for example, a vertically coupled resonator type surface acoustic wave filter.

[0016] Here, the plurality of resonators include a first resonator and a plurality of second resonators. The value of the ratio bandwidth of the first resonator is the largest among the values of the ratio bandwidths of the plurality of resonators. The second resonator is all the resonators other than the first resonator. In the present embodiment, the first resonator is the parallel-arm resonator P4. The second resonators are the in-line wrist resonators S1, S2, S3, S4, and S5, and the parallel-arm resonators P1, P2, and P3. Note that in this specification, the ratio bandwidth refers to the ratio bandwidth of each individual resonator. That is, when the ratio bandwidth is Δf, the resonance frequency is fr, and the anti-resonance frequency is fa, Δf = (|fa - fr| / fr) × 100 [%]. The ratio bandwidth of the first resonator is 5%. On the other hand, the ratio bandwidth of each second resonator is 3% respectively. However, the ratio bandwidths of the first resonator and the second resonators are not limited to the above.

[0017] The filter device 1 has a first inductor and a second inductor. The first inductor is an inductor connected in series to the first resonator. The second inductor is an inductor connected to the second resonator. Specifically, the first inductor is inductor L. The second inductor is inductor M. Inductor L is connected between the parallel arm resonator P4, which is the first resonator, and the ground potential. Note that inductor L is connected to the parallel arm resonator P4 without passing through other resonators. Inductor M is connected between the parallel arm resonator P2 and the ground potential.

[0018] Inductor L is an inductor for increasing the value of the specific band of the parallel arm resonator P4. Thereby, the passband of the filter device 1 can be widened. On the other hand, inductor M is an inductor for impedance matching.

[0019] The feature of this embodiment is that the inductor L as the first inductor is connected in series to the parallel arm resonator P4 as the first resonator. As described above, the value of the specific band of the first resonator is the largest among the values of the specific bands of the plurality of resonators. Therefore, the inductance of the first inductor required to increase the value of the specific band of the first resonator can be reduced. Thereby, the first inductor can be made smaller. Accordingly, the passband of the filter device 1 can be widened, and miniaturization can be effectively promoted. This will be described in detail below.

[0020] When an inductor is connected to an elastic wave resonator, while the resonance frequency decreases, the anti-resonance frequency does not change. As a result, the value of the specific bandwidth increases. Here, when inductors are connected to each of the first resonator and the second resonator, the inductances of the inductors required to lower the resonance frequency by 50 MHz were compared. In this comparison, as in the first embodiment, the specific bandwidth of the first resonator was set to 5%, and the specific bandwidth of the second resonator was set to 3%. Furthermore, while changing the width of lowering the resonance frequency in steps of 10 MHz in the range of 10 MHz or more and 100 MHz or less, the same comparison as above was performed.

[0021] FIG. 2 is a diagram showing the change in the specific bandwidth due to the connection of an inductor to the second resonator. FIG. 3 is a diagram showing the change in the specific bandwidth due to the connection of an inductor to the first resonator. FIG. 4 is a diagram showing the relationship between the inductance of the inductor and the change width of the resonance frequency when an inductor is connected to the resonator.

[0022] As shown in FIGS. 2 and 3, in each of the first resonator and the second resonator, the resonance frequency has decreased by 50 MHz. At this time, as shown in FIG. 2, the inductance of the inductor connected to the second resonator is 1.67 nH. On the other hand, as shown in FIG. 3, the inductance of the inductor connected to the first resonator is 1.18 nH. Furthermore, as shown in FIG. 4, even when the change width of the resonance frequency is other than 50 MHz, the inductance of the inductor connected to the first resonator is smaller than the inductance of the inductor connected to the second resonator. Thus, in the first resonator, the value of the specific bandwidth can be efficiently increased. The results of FIG. 4 are shown in Table 1.

[0023]

Table 1

[0024] As described above, it can be understood that in the first resonator, the inductance of the inductor required to increase the value of the specific bandwidth is smaller than the inductance of the inductor required to increase the value of the specific bandwidth in the second resonator. Therefore, when widening the passband of the filter device, the inductor connected to the first resonator can be made smaller.

[0025] In addition, in the present embodiment, the inductance of the inductor M as the second inductor is smaller than the inductance of the inductor L as the first inductor. Therefore, the miniaturization of the filter device 1 can be more surely advanced.

[0026] As shown in FIG. 1, the inductor L is preferably connected between the parallel arm resonator P4 and the ground potential. Thereby, impedance matching can be easily performed. However, the inductor L may be connected between the connection point between the series arm resonators S4 and S5 and the parallel arm resonator P4. That is, the first inductor may be connected between the connection point of the second resonators connected to the first resonator and the first resonator.

[0027] When the filter device has a plurality of first resonators, it is preferable that the first inductor is connected in series to any one of the first resonators.

[0028] Hereinafter, the details of the configuration of the filter device 1 of the present embodiment will be shown.

[0029] FIG. 5 is a plan view of the first resonator in the first embodiment.

[0030] The parallel arm resonator P4 as the first resonator has a piezoelectric substrate 2. On the piezoelectric substrate 2, an IDT electrode 3 is provided. By applying an alternating voltage to the IDT electrode 3, surface acoustic waves are excited. On both sides of the IDT electrode 3 in the elastic wave propagation direction on the piezoelectric substrate 2, a pair of reflectors 8A and 8B are provided.

[0031] The IDT electrode 3 has a first bus bar 16 and a second bus bar 17, and a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. The first bus bar 16 and the second bus bar 17 face each other. One end of each of the plurality of first electrode fingers 18 is connected to the first bus bar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second bus bar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interposed with each other. The IDT electrode 3, the reflector 8A, and the reflector 8B may be made of a single-layer metal film or a laminated metal film. In the following, the first electrode finger 18 and the second electrode finger 19 may be collectively referred to as an electrode finger.

[0032] A dielectric film may be provided on the piezoelectric substrate 2 so as to cover the IDT electrode 3. Thereby, the IDT electrode 3 is less likely to be damaged. As the material of the dielectric film, for example, silicon oxide, silicon nitride, or silicon oxynitride can be used.

[0033] FIG. 6 is a cross-sectional view taken along the line I-I in FIG. 5.

[0034] The piezoelectric substrate 2 of the present embodiment has a high-speed support substrate 5 as a high-speed material layer, a low-speed film 6, and a piezoelectric layer 7. More specifically, the low-speed film 6 is provided on the high-speed support substrate 5. The piezoelectric layer 7 is provided on the low-speed film 6. The piezoelectric layer 7 has a main surface 7a. The IDT electrode 3, the reflector 8A, and the reflector 8B are provided on the main surface 7a of the piezoelectric layer 7.

[0035] As the material of the piezoelectric layer 7, for example, lithium tantalate, lithium niobate, zinc oxide, aluminum nitride, quartz, or PZT (lead zirconate titanate) can be used.

[0036] The high acoustic velocity material layer is a relatively high acoustic velocity layer. More specifically, the acoustic velocity of the bulk wave propagating through the high acoustic velocity material layer is higher than the acoustic velocity of the elastic wave propagating through the piezoelectric layer 7. In this embodiment, the high acoustic velocity material layer is the high acoustic velocity support substrate 5. As the material of the high acoustic velocity material layer, for example, silicon, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a medium mainly composed of DLC (diamond-like carbon) film or diamond, etc. can be used.

[0037] The low acoustic velocity film 6 is a relatively low acoustic velocity film. More specifically, the acoustic velocity of the bulk wave propagating through the low acoustic velocity film 6 is lower than the acoustic velocity of the bulk wave propagating through the piezoelectric layer 7. As the material of the low acoustic velocity film 6, for example, glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum pentoxide, or a material mainly composed of a compound obtained by adding fluorine, carbon, or boron to silicon oxide can be used.

[0038] In this embodiment, the high acoustic velocity support substrate 5 as the high acoustic velocity material layer, the low acoustic velocity film 6, and the piezoelectric layer 7 are laminated in this order. Thereby, the energy of the elastic wave can be effectively confined to the piezoelectric layer 7 side. However, the configuration of the piezoelectric substrate 2 is not limited to the above.

[0039] Other resonators also have IDT electrodes and a pair of reflectors, similar to the parallel arm resonator P4. In the filter device 1, all the resonators share the piezoelectric substrate 2. However, at least one resonator may have a piezoelectric substrate different from other resonators.

[0040] As described above, by connecting the inductor L to the parallel-arm resonator P4, the passband of the filter device 1 can be widened. This will be shown by comparing the present embodiment and the comparative example. The comparative example differs from the first embodiment in that it does not have the inductor L. The configurations of the piezoelectric substrate 2 and the IDT electrode 3 in the filter device 1, and the inductances of the inductor L and the inductor M were as follows. Each parameter in the comparative example is the same as each of the following parameters except for the inductor L.

[0041] High-speed acoustic support substrate 5; material... Si, thickness... 125 μm Low-speed acoustic film 6; material... SiO2, thickness... 670 nm Piezoelectric layer 7; material... LiTaO3, thickness... 600 nm IDT electrode 3; laminate structure... Ti layer / AlCu layer from the piezoelectric layer 7 side, thickness... 12 nm / 162 nm from the piezoelectric layer 7 side Inductor L; inductance... 3 nH Inductor M; inductance... 0.3 nH

[0042] FIG. 7 is a diagram showing the attenuation amount frequency characteristics of the first embodiment and the comparative example.

[0043] As shown in FIG. 7, it can be seen that the passband of the first embodiment is wider than that of the comparative example. The band W shown in FIG. 7 indicates the passband of Band41. Specifically, the passband of Band41 is 2496 MHz to 2690 MHz. In the filter device of the comparative example, the insertion loss is large around 2496 MHz. On the other hand, in the first embodiment, the inductor L is connected to the parallel-arm resonator P4. As a result, the passband of the filter device 1 is widened, and the insertion loss is small at 2496 MHz to 2690 MHz. Therefore, the filter device 1 can also be applied to a wide band such as Band41. Moreover, as described above, the inductor L for widening the passband can be made small, and the miniaturization of the filter device 1 can be promoted.

[0044] FIG. 8 is a schematic front sectional view of a filter device according to the first embodiment. In FIG. 8, the electrodes constituting the resonator are shown by a schematic diagram of a rectangle with two diagonals added.

[0045] The filter device 1 has a mounting substrate 10. A plurality of resonators of the filter device 1 are arranged on the mounting substrate 10. In the present embodiment, an inductor L is provided between the electrode constituting the parallel arm resonator P4, which is the first resonator, and the mounting substrate 10.

[0046] A plurality of IDT electrodes of a plurality of resonators are provided on the main surface 7a of the piezoelectric layer 7. Further, a plurality of terminals are provided on the main surface 7a. The plurality of terminals include a plurality of ground terminals 9C, the first signal terminal 9A, and the second signal terminal 9B.

[0047] Furthermore, a support member 11 is provided on the main surface 7a. The support member 11 is provided so as to cover at least a part of the plurality of terminals. The support member 11 has an opening 11a. The opening 11a surrounds the plurality of IDT electrodes of the plurality of resonators. A cover member 12 is provided so as to sandwich the support member 11 together with the piezoelectric layer 7. The cover member 12 covers the opening 11a of the support member 11. Thereby, a hollow space surrounded by the piezoelectric substrate 2, the support member 11, and the cover member 12 is provided. The plurality of IDT electrodes are arranged in the hollow space.

[0048] An inductor L as a first inductor is provided in the cover member 12. The inductor L is constituted by wiring. More specifically, the inductor L has a wiring electrode La, a wiring electrode Lb, and a via electrode Lc. The wiring electrode La and the wiring electrode Lb are connected to the via electrode Lc. Thereby, the inductor L is constituted. The second inductor is also configured in the same manner as the inductor L. Note that the shape of the routing of the wiring in each inductor is not particularly limited. The number of wiring electrodes and via electrodes of each inductor is also not particularly limited.

[0049] A plurality of first through electrodes are provided so as to penetrate the support member 11. The plurality of first through electrodes include a first through electrode 13A and a first through electrode 13B. One end of the first through electrode 13A is connected to the ground terminal 9C. The other end of the first through electrode 13A is connected to the wiring electrode La. The cover member 12 is provided with a plurality of first connection terminals 14A. The wiring electrode Lb is connected to the first connection terminal 14A. Thus, the first through electrode 13A is connected to the first connection terminal 14A via the inductor L.

[0050] On the other hand, the first through electrode 13B penetrates the cover member 12. One end of the first through electrode 13B is connected to the ground terminal 9C. The other end of the first through electrode 13B is connected to the first connection terminal 14A.

[0051] A plurality of second connection terminals 14B are provided on one main surface of the mounting substrate 10. A plurality of third connection terminals 14C are provided on the other main surface of the mounting substrate 10. Further, a plurality of second through electrodes 13C are provided so as to penetrate the mounting substrate 10. One end of the second through electrode 13C is connected to the second connection terminal 14B. The other end of the second through electrode 13C is connected to the third connection terminal 14C.

[0052] Bumps 15 are provided so as to connect the second connection terminals 14B of the mounting substrate 10 and the plurality of first connection terminals 14A on the resonator side. The parallel arm resonator P4 is connected to the ground potential via the ground terminal 9C, the first through electrode 13A, the inductor L, the first connection terminal 14A, the bump 15, the second connection terminal 14B, the second through electrode 13C, and the third connection terminal 14C. Among the plurality of second resonators, for example, the parallel arm resonator P3 is connected to the ground potential via the ground terminal 9C, the first through electrode 13B, the first connection terminal 14A, the bump 15, the second connection terminal 14B, the second through electrode 13C, and the third connection terminal 14C. As described above, the plurality of resonators of the filter device 1 have a WLP (Wafer Level Package) structure. However, the plurality of resonators are not limited to the WLP structure.

[0053] Incidentally, when the inductor is formed of wiring, the longer the length of the wiring electrode or via electrode, the larger the inductance. Therefore, the larger the required inductance, the larger the inductor. In contrast, in the present embodiment, even if the inductance of the inductor L is small, the value of the ratio band of the parallel arm resonator P4 can be increased. Therefore, when the inductor L is formed of wiring, the present invention is suitable.

[0054] The inductor L may be provided in a portion other than the cover member 12. For example, in the first modification shown in FIG. 9, the inductor L is provided in the mounting substrate 10. The inductor L is connected to the second connection terminal 14B by the via electrode 23A. Further, the inductor L is connected to the third connection terminal 14C by the via electrode 23B. Note that the inductor L is not limited to being within the cover member 12 or the mounting substrate 10, and may be provided on the surface of the cover member 12 or the mounting substrate 10. Alternatively, the inductor L may be provided on the piezoelectric substrate 2.

[0055] In the first embodiment, the first resonator is a parallel arm resonator. However, the first resonator may be a series arm resonator. For example, in the second modification shown in FIG. 10, the value of the ratio band of the series arm resonator S23 among the plurality of resonators is the largest. That is, the series arm resonator S23 is the first resonator, and the other resonators including the parallel arm resonator P24 are a plurality of second resonators. An inductor L as a first inductor is connected between the connection point of the series arm resonator S2 and the parallel arm resonator P2 and the series arm resonator S23. The inductor L is connected in series to the series arm resonator S2. Note that the inductor L may be connected between the connection point of the series arm resonator S4 and the parallel arm resonator P3 and the series arm resonator S23. Also in this modification, as in the first embodiment, miniaturization of the filter device can be promoted.

[0056] However, it is preferable that the first resonator is a shunt arm resonator and the first inductor is connected in series to the shunt arm resonator. Thereby, deterioration of the insertion loss of the filter device is less likely to occur.

[0057] As shown in FIG. 6, in the piezoelectric substrate 2 of the present embodiment, the piezoelectric layer 7 is indirectly provided on the high acoustic velocity support substrate 5 as the high acoustic velocity material layer via the low acoustic velocity film 6. However, the configuration of the piezoelectric substrate 2 is not limited to the above. In the following, a third modification example and a fourth modification example of the first embodiment, in which only the configuration of the piezoelectric substrate is different from that of the first embodiment, will be shown. Also in the third modification example and the fourth modification example, similar to the first embodiment, the filter device can be miniaturized. In addition, similar to the first embodiment, since a laminated structure including a high acoustic velocity material layer and a piezoelectric layer is provided, the energy of the elastic wave can be effectively confined to the piezoelectric layer side.

[0058] In the third modification example shown in FIG. 11, the piezoelectric substrate 22A has the high acoustic velocity support substrate 5 and the piezoelectric layer 7. The piezoelectric layer 7 is directly provided on the high acoustic velocity support substrate 5 as the high acoustic velocity material layer.

[0059] In the fourth modification example shown in FIG. 12, the piezoelectric substrate 22B has the support substrate 24, the high acoustic velocity film 25 as the high acoustic velocity material layer, the low acoustic velocity film 6, and the piezoelectric layer 7. More specifically, the high acoustic velocity film 25 is provided on the support substrate 24. The low acoustic velocity film 6 is provided on the high acoustic velocity film 25. The piezoelectric layer 7 is provided on the low acoustic velocity film 6.

[0060] As the material of the support substrate 24, for example, piezoelectric materials such as aluminum oxide, lithium tantalate, lithium niobate, and quartz, various ceramics such as alumina, sapphire, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite, dielectrics such as diamond and glass, semiconductors such as silicon and gallium nitride, or resins can be used.

[0061] Note that the piezoelectric substrate may be a laminate of a support substrate 24, a high-velocity sound film 25, and a piezoelectric layer 7. Alternatively, the piezoelectric substrate may be a piezoelectric substrate composed only of a piezoelectric layer.

[0062] In the first embodiment and its modified example, the piezoelectric layer 7 is supported by other layers including the portion where the IDT electrode 3 is provided. However, the piezoelectric layer 7 does not necessarily have to be supported by other layers in the portion that overlaps at least a part of the IDT electrode 3 in plan view. More specifically, a cavity may be provided in the portion of the layer other than the piezoelectric layer 7 that overlaps at least a part of the IDT electrode 3 in plan view. In this case, the cavity may be open on the piezoelectric layer 7 side. The cavity may be provided in only one layer or may be provided over a plurality of layers. The cavity may be a recess or a through hole. When such a cavity is provided, it is preferable that the resonator utilizes plate waves.

[0063] Here, the IDT electrode of the first resonator is referred to as the first IDT electrode, and the IDT electrode of the second resonator is referred to as the second IDT electrode. In the following, the second to fifth embodiments are shown in which only the configuration of the first IDT electrode or the second IDT electrode is different from that of the first embodiment. Also in the second to fifth embodiments, an inductor L is connected to the first resonator in the same manner as in the first embodiment. Therefore, the passband of the filter device can be widened, and the miniaturization of the filter device can be promoted.

[0064] FIG. 13 is a plan view of the first resonator in the second embodiment. FIG. 14 is a plan view of the second resonator in the second embodiment.

[0065] As shown in FIG. 13, in this embodiment, the configuration of the first IDT electrode 33A of the first resonator is different from that of the first embodiment. The first resonator is a surface acoustic wave resonator that utilizes the piston mode. As shown in FIG. 14, in this embodiment, the configuration of the second IDT electrode 33B of the second resonator is also different from that of the first embodiment. The second IDT electrode 33B is an inclined IDT electrode. Below, the details of the configurations of the first IDT electrode 33A and the second IDT electrode 33B will be described.

[0066] As shown in FIG. 13, when viewed from the elastic wave propagation direction, the region where the adjacent first electrode finger 18 and second electrode finger 19 overlap is the crossover region A. The crossover region A has a central region C, a first edge region E1, and a second edge region E2. Here, the direction in which the plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 extend is defined as the electrode finger extension direction. In this embodiment, the electrode finger extension direction and the elastic wave propagation direction are orthogonal. The central region C is the region located on the central side in the electrode finger extension direction in the crossover region A. On the other hand, the first edge region E1 and the second edge region E2 are arranged so as to sandwich the central region C in the electrode finger extension direction. The first edge region E1 is located on the side of the first bus bar 16. The second edge region E2 is located on the side of the second bus bar 17. Furthermore, the first IDT electrode 33A has a first gap region G1 and a second gap region G2. The first gap region G1 is located between the first edge region E1 and the first bus bar 16. The second gap region G2 is located between the second edge region E2 and the second bus bar 17.

[0067] The speed of sound in the first edge region E1 and the second edge region E2 is lower than the speed of sound in the central region C. On the other hand, the speed of sound in the first gap region G1 and the second gap region G2 is higher than the speed of sound in the central region C. Thereby, the piston mode is established and the transverse mode is suppressed.

[0068] More specifically, in the first IDT electrode 33A of the present embodiment, in the first edge region E1, a mass addition film 35A is provided on the plurality of first electrode fingers 18 and on the plurality of second electrode fingers 19. Similarly, in the second edge region E2, a mass addition film 35B is provided on the plurality of first electrode fingers 18 and on the second electrode fingers 19. The mass addition film 35A and the mass addition film 35B are made of an appropriate dielectric.

[0069] The mass addition film 35A and the mass addition film 35B have a strip shape. Thereby, the mass addition film 35A is provided over the plurality of first electrode fingers 18, the plurality of second electrode fingers 19, and the portions located between the electrode fingers on the piezoelectric substrate 2. The same applies to the mass addition film 35B. Thereby, the sound velocity in the first edge region E1 and the second edge region E2 is lowered.

[0070] In the present embodiment, in the portion where the plurality of electrode fingers and the mass addition film 35A are laminated, they are laminated in the order of the piezoelectric substrate 2, the plurality of electrode fingers, and the mass addition film 35A. Note that the mass addition film 35A may be provided between the piezoelectric substrate 2 and the plurality of first electrode fingers 18 and the plurality of second electrode fingers 19. That is, in the portion where the plurality of electrode fingers and the mass addition film 35A are laminated, they may be laminated in the order of the piezoelectric substrate 2, the mass addition film 35A, and the plurality of electrode fingers. The same applies to the mass addition film 35B.

[0071] Note that the mass addition films 35A and 35B do not necessarily need to be provided across a plurality of electrode fingers. A plurality of mass addition films 35A and a plurality of mass addition films 35B may be laminated with each of the first electrode fingers 18 and each of the second electrode fingers 19. In this case, the plurality of mass addition films 35A and the plurality of mass addition films 35B may be made of metal or may be made of a dielectric. The mass addition film 35A or the mass addition film 35B only needs to be laminated with at least one electrode finger among the plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 in at least one of the first edge region E1 and the second edge region E2. However, it is preferable that the mass addition films 35A and 35B are laminated with a plurality of electrode fingers in both the first edge region E1 and the second edge region E2.

[0072] In the first gap region G1, only a plurality of the first electrode fingers 18 among the plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are provided. Therefore, the sound velocity in the first gap region G1 is high. Similarly, in the second gap region G2, only a plurality of the second electrode fingers 19 among the plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are provided. Therefore, the sound velocity in the second gap region G2 is high.

[0073] When the sound velocity in the central region C is V1, the sound velocity in the first edge region E1 and the second edge region E2 is V2, and the sound velocity in the first gap region G1 and the second gap region G2 is V3, V2 < V1 < V3. The relationship between the sound velocities as described above is shown in FIG. 13. In the portion showing the relationship between the sound velocities in FIG. 13, as indicated by the arrow V, the line indicating the height of each sound velocity indicates that the sound velocity is higher as the line is located on the left side.

[0074] In this embodiment, since the first IDT electrode 33A has the above-described configuration, in the first resonator, the ratio of the ratio band to the capacitance can be increased. Therefore, without making the first resonator large, the value of the ratio band can be further increased. And the inductance of the first inductor for further increasing the value of the ratio band of the first resonator can be made even smaller. Accordingly, the passband of the filter device can be widened, and the miniaturization of the filter device can be further advanced.

[0075] On the other hand, as shown in FIG. 14, the second IDT electrode 33B is an inclined IDT electrode. More specifically, when a virtual line formed by connecting the tips of the plurality of first electrode fingers 18 is defined as the first envelope B1, the first envelope B1 is inclined with respect to the elastic wave propagation direction. Similarly, when a virtual line formed by connecting the tips of the plurality of second electrode fingers 19 is defined as the second envelope B2, the second envelope B2 is inclined with respect to the elastic wave propagation direction. Thereby, spurious due to the transverse mode can be suppressed.

[0076] Note that in the second IDT electrode 33B, the first bus bar 36 and the second bus bar 37 extend inclined with respect to the elastic wave propagation direction. However, it is not limited thereto.

[0077] FIG. 15 is a plan view of the first IDT electrode in a modification of the second embodiment.

[0078] Also in this modification, similar to the second embodiment, the first resonator utilizes the piston mode. More specifically, the plurality of first electrode fingers 48 of the first IDT electrode 43A have a wide portion 48a located in the first edge region E1. Further, the plurality of first electrode fingers 48 have a wide portion 48b located in the second edge region E2. The widths of the wide portions 48a and 48b of the first electrode finger 48 are wider than the width of the central region C of the first electrode finger 48. Note that the width of the electrode finger is a dimension along the elastic wave propagation direction of the electrode finger. Similarly, the plurality of second electrode fingers 49 have a wide portion 49a in the first edge region E1. The plurality of second electrode fingers 49 have a wide portion 49b in the second edge region E2. Thereby, the sound velocity in the first edge region E1 and the second edge region E2 can be reduced. However, at least one of the plurality of first electrode fingers 48 and the plurality of second electrode fingers 49 only needs to have a wide portion in at least one of the first edge region E1 and the second edge region E2.

[0079] Also in this case, in the first resonator using the first IDT electrode 43A, the ratio of the ratio band to the capacitance can be increased. However, the ratio of the resonator using the first IDT electrode 33A shown in FIG. 13 is larger than the above ratio of the resonator using the first IDT electrode 43A of this modification. Therefore, it is preferable to use the first IDT electrode 33A for the first resonator.

[0080] FIG. 16 is a plan view of the second IDT electrode in the third embodiment.

[0081] This embodiment is different from the second embodiment in that the cross region A of the second IDT electrode 53B is weighted. Except for the above point, the filter device of this embodiment has the same configuration as the filter device of the second embodiment. The first resonator of this embodiment has the first IDT electrode 33A shown in FIG. 13.

[0082] The second IDT electrode 53B has a plurality of first dummy electrode fingers 58 and a plurality of second dummy electrode fingers 59. One end of each of the plurality of first dummy electrode fingers 58 is connected to the first bus bar 56. The other end of each of the plurality of first dummy electrode fingers 58 faces a plurality of second electrode fingers 19. One end of each of the plurality of second dummy electrode fingers 59 is connected to the second bus bar 57. The other end of each of the plurality of second dummy electrode fingers 59 faces a plurality of first electrode fingers 18.

[0083] Here, let the dimension along the electrode finger extension direction of the crossover region A be the crossover width D. In the second IDT electrode 53B, the crossover width D changes in the elastic wave propagation direction. More specifically, the crossover width D becomes narrower as it goes from the center to the outside in the elastic wave propagation direction of the second IDT electrode 53B. In the present embodiment, in a plan view, the crossover region A has a substantially rhombus shape.

[0084] However, the shape of the crossover region A in a plan view is not limited to the above. For example, the edge portion of the crossover region A in the electrode finger extension direction may include a curved shape. Alternatively, for example, the crossover width D may change periodically in the elastic wave propagation direction. More specifically, it may have a plurality of portions where the crossover width D becomes wider and a plurality of portions where the crossover width D becomes narrower as it goes from one side to the other side in the elastic wave propagation direction.

[0085] Note that the crossover region A of the second IDT electrode 53B only needs to have a portion where the crossover width D changes in the elastic wave propagation direction. For example, the second IDT electrode 53B may have a portion where the crossover width is constant in the elastic wave propagation direction.

[0086] In the present embodiment, the first bus bar 56 and the second bus bar 57 have portions that extend obliquely with respect to the elastic wave propagation direction. The first bus bar 56 has a bent portion 56a. The second bus bar 57 has a bent portion 57a. However, the shapes of the first bus bar 56 and the second bus bar 57 are not limited to the above. For example, the first bus bar 56 and the second bus bar 57 may have a linear shape extending parallel to the elastic wave propagation direction. In this case, as long as the lengths of the plurality of first electrode fingers 18, the plurality of second electrode fingers 19, the plurality of first dummy electrode fingers 58, and the plurality of second dummy electrode fingers 59 change in the elastic wave propagation direction, so that the crossing width D changes in that direction. Note that the length of the electrode finger is the dimension along the electrode finger extension direction of the electrode finger.

[0087] As described above, in the third embodiment, the first resonator has the same first IDT electrode 33A as in the second embodiment. The ratio of the bandwidth to the capacitance in the resonator using the first IDT electrode 33A is larger than the ratio of the bandwidth to the capacitance in the resonator using the second IDT electrode 53B. Therefore, similar to the second embodiment, the first inductor for widening the passband of the filter device can be miniaturized, and the miniaturization of the filter device can be promoted.

[0088] The fourth embodiment is different from the second embodiment in that the second IDT electrode has the same configuration as the first IDT electrode 43A shown in FIG. 15. Except for the above points, the filter device of the present embodiment has the same configuration as the filter device of the second embodiment. The first resonator of the present embodiment has the first IDT electrode 33A shown in FIG. 13. In the present embodiment, both the first resonator and the second resonator utilize the piston mode.

[0089] As described above, the ratio of the ratio bandwidth to the capacitance in the resonator using the first IDT electrode 33A is larger than the ratio of the ratio bandwidth to the capacitance in the resonator using the first IDT electrode 43A. Therefore, similar to the second embodiment, the first inductor for widening the passband of the filter device can be made smaller, and the miniaturization of the filter device can be promoted.

[0090] FIG. 17 is a plan view of the second IDT electrode in the fifth embodiment.

[0091] In this embodiment, the configuration of the second IDT electrode 63B is different from that of the first embodiment. Except for the above points, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0092] In this embodiment, the crossover region has a first portion A1 and a second portion A2. In the first portion A1, the first electrode fingers 18 and the second electrode fingers 19 are arranged alternately. That is, in the first portion A1, one ends of adjacent electrode fingers are connected to different bus bars. In this embodiment, in the first portion A1, the electrode finger pitch is constant. The electrode finger pitch is the center-to-center distance between adjacent electrode fingers. Note that the first IDT electrode and the second IDT electrode in each of the above embodiments are composed only of the first portion A1.

[0093] Here, in the first portion A1, the center-to-center distance between the outermost electrode fingers among three consecutive electrode fingers is set to 1λ. For example, in the portion arranged in the order of the first electrode finger 18, the second electrode finger 19, and the first electrode finger 18, the center-to-center distance between the first electrode fingers 18 is 1λ. On the other hand, in the second portion A2, the three consecutive electrode fingers are arranged in the order of the first electrode finger 18, the second electrode finger 19, and the second electrode finger 19. Alternatively, in the second portion A2, all three consecutive electrode fingers are the second electrode finger 19. Thus, in the second portion A2, within a range of a distance of 1λ along the elastic wave propagation direction, the first electrode finger 18 and the second electrode finger 19 are not alternately arranged three or more times. That is, within the above range, the number of adjacent electrode fingers whose one ends are connected to different bus bars and are continuously arranged is two or less.

[0094] In the present embodiment, in the second portion A2, three consecutive second electrode fingers 19 are arranged along the elastic wave propagation direction. However, in the second portion A2, it is sufficient that one ends of two or more electrode fingers consecutive in the elastic wave propagation direction are connected to the same bus bar. The second portion A2 may be arranged periodically.

[0095] On the other hand, the first resonator has an IDT electrode 3 as the first IDT electrode shown in FIG. 5. In the crossing region A of the IDT electrode 3, one ends of adjacent electrode fingers are connected to different bus bars.

[0096] The ratio of the bandwidth to the capacitance in the resonator using the first IDT electrode 3A is larger than the ratio of the bandwidth to the capacitance in the resonator using the second IDT electrode 63B. Therefore, similar to the first embodiment, the first inductor for widening the passband of the filter device can be made small, and the miniaturization of the filter device can be advanced. Thus, when both the IDT electrode having the configuration shown in FIG. 5 and the IDT electrode having the configuration shown in FIG. 17 are provided, it is preferable to adopt the configuration shown in FIG. 5 for the first IDT electrode.

[0097] Note that in the second portion A2 of the second IDT electrode 63B, electrode fingers connected to the same bus bar do not necessarily have to be arranged continuously. In a modification of the fifth embodiment shown in FIG. 18, the width of the second electrode finger 69 in the second portion A2 is wider than the width of the second electrode finger 19 in the first portion A1. More specifically, the second electrode finger 69 corresponds to an electrode finger formed by integrating two second electrode fingers 19 in the fifth embodiment. The portion where this single second electrode finger 69 and a single first electrode finger 18 are arranged side by side corresponds to the portion where three electrode fingers are arranged side by side in the first portion A1. Therefore, in the second portion A2, the electrode fingers arranged within a distance of 1λ along the elastic wave propagation direction are only a single first electrode finger 18 and a single second electrode finger 69. Thus, within the above range, the number of adjacent electrode fingers whose one ends are connected to different bus bars and are arranged continuously is two or less.

[0098] As described above, in this modification, the second electrode finger 69 corresponds to an electrode finger formed by integrating two second electrode fingers 19. Therefore, the width of the second electrode finger 69 in the second portion A2 corresponds to twice the width of the second electrode finger 19 in the first portion A1 plus the width of the portion between the electrode fingers. Thus, the width of the second electrode finger 69 in the second portion A2 is wider than twice the width of the second electrode finger 19 in the first portion A1. Note that the second electrode finger 69 may correspond to an electrode finger formed by integrating three or more continuous second electrode fingers 19. Also in this modification, as in the fifth embodiment, miniaturization of the filter device can be promoted.

[0099] FIG. 19 is a front cross-sectional view of the first resonator and the second resonator in the sixth embodiment.

[0100] This embodiment is different from the first embodiment in that the first resonator has a dielectric film 78A and the second resonator has a dielectric film 78B. In FIG. 19, a parallel-arm resonator P74 as the first resonator and a parallel-arm resonator P73 as the second resonator are shown. Except for the above points, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment. Note that the IDT electrode of the first resonator is the first IDT electrode 3A, and the IDT electrode of the second resonator is the second IDT electrode 3B.

[0101] The dielectric film 78A is provided between the piezoelectric substrate 2 and the first IDT electrode 3A. The dielectric film 78B is provided between the piezoelectric substrate 2 and the second IDT electrode 3B. In this embodiment, the thickness of the dielectric film 78A is thinner than the thickness of the dielectric film 78B. In this case, the value of the specific bandwidth of the first resonator can be increased. Therefore, similar to the above embodiments, the passband of the filter device can be more reliably widened, and the miniaturization of the filter device can be more reliably advanced.

[0102] In this embodiment, the dielectric film 78A and the dielectric film 78B are provided integrally and have different thicknesses from each other. However, the dielectric film 78A and the dielectric film 78B may be provided separately.

Explanation of Reference Numerals

[0103] 1... Filter device 2... Piezoelectric substrate 3... IDT electrode 3A, 3B... First and second IDT electrodes 5... High-velocity support substrate 6... Low-velocity film 7... Piezoelectric layer 7a... Main surface 8A, 8B... Reflectors 9A, 9B... First and second signal terminals 9C... Ground terminal 10... Mounting substrate 11... Support member 11a... Opening 12... Cover member 13A, 13B… First through electrode 13C… Second through electrode 14A, 14B, 14C… First, second, and third connection terminals 15… Bump 16, 17… First and second bus bars 18, 19… First and second electrode fingers 22A, 22B… Piezoelectric substrate 23A, 23B… Via electrode 24… Support substrate 25… High-speed film 33A, 33B… First and second IDT electrodes 35A, 35B… Mass addition film 36, 37… First and second bus bars 43A… First IDT electrode 48, 49… First and second electrode fingers 48a, 48b, 49a, 49b… Wide portions 53B… Second IDT electrode 56, 57… First and second bus bars 56a, 57a… Bent portions 58, 59… First and second dummy electrode fingers 63B… Second IDT electrode 69… Second electrode finger 78A, 78B… Dielectric film A… Crossing region A1, A2… First and second portions C… Central region E1, E2… First and second edge regions G1, G2… First and second gap regions L… Inductor La, Lb… Wiring electrodes Lc… Via electrode M… Inductor P1~P4, P24, P73, P74… Parallel arm resonators S1~S5, S23… Series arm resonators

Claims

1. A filter device comprising a plurality of resonators including a plurality of series-arm resonators and at least one parallel-arm resonator, wherein the plurality of resonators includes a first resonator having the largest ratio-band value among the plurality of resonators and at least one second resonator other than the first resonator, the plurality of series-arm resonators includes the first resonator and the second resonator, further comprising a first inductor which is an inductor connected in series to the first resonator, wherein the series-arm resonator which is the second resonator includes the series-arm resonator not connected to an inductor.

2. further comprising at least one second inductor connected to the at least one second resonator among the plurality of resonators, the filter device according to Claim 1, wherein an inductance of the second inductor is smaller than an inductance of the first inductor.

3. the first resonator has a first IDT electrode, the second resonator has a second IDT electrode, and the first IDT electrode and the second IDT electrode each include a pair of bus bars and a plurality of electrode fingers, in the first IDT electrode, a region where adjacent electrode fingers overlap when viewed from the elastic wave propagation direction is a crossing region, and the crossing region includes a central region located at the center in the direction in which the plurality of electrode fingers extend and a pair of edge regions arranged so as to sandwich the central region in the direction in which the plurality of electrode fingers extend, the first IDT electrode has a configuration in which a mass addition film is provided so as to overlap at least one of the plurality of electrode fingers in each of the pair of edge regions of the first IDT electrode when viewed in plan view, and a width of at least one of the plurality of electrode fingers in one of the pair of edge regions is wider than a width in the central region, and a width of at least one of the plurality of electrode fingers in the other of the pair of edge regions is wider than a width in the central region, having one of the configurations. In the second IDT electrode, when a pair of virtual lines formed by connecting the other ends of the plurality of electrode fingers, one end of which is connected to one of the bus bars, and a virtual line formed by connecting the other ends of the plurality of electrode fingers, one end of which is connected to the other bus bar, are used as a pair of envelope lines, the pair of envelope lines is inclined with respect to the elastic wave propagation direction. The filter device according to claim 1 or 2.

4. The first resonator has a first IDT electrode, the second resonator has a second IDT electrode, and the first IDT electrode and the second IDT electrode each include a pair of bus bars and a plurality of electrode fingers. In each of the first IDT electrode and the second IDT electrode, a region where adjacent electrode fingers overlap when viewed from the elastic wave propagation direction is an intersection region. In the first IDT electrode, the intersection region includes a central region located at the center in the direction in which the plurality of electrode fingers extend, and a pair of edge regions arranged so as to sandwich the central region in the direction in which the plurality of electrode fingers extend. The first IDT electrode has a configuration in which a mass addition film is provided so as to overlap at least one of the plurality of electrode fingers in a plan view in each of the pair of edge regions of the first IDT electrode, and at least one of the plurality of electrode fingers of the first IDT electrode has a width in one of the pair of edge regions that is wider than the width in the central region, and at least one of the plurality of electrode fingers has a width in the other of the pair of edge regions that is wider than the width in the central region. It has one of the configurations. In the second IDT electrode, when the dimension along the direction in which the plurality of electrode fingers in the intersection region extend is defined as the intersection width, the intersection region has a portion where the intersection width changes in the elastic wave propagation direction. The filter device according to claim 1 or 2.

5. The first resonator has a first IDT electrode, the second resonator has a second IDT electrode, and the first IDT electrode and the second IDT electrode each include a pair of bus bars and a plurality of electrode fingers. In each of the first IDT electrode and the second IDT electrode, a region where adjacent electrode fingers overlap when viewed from the elastic wave propagation direction is a crossing region, and each of the crossing regions includes a central region located at the center in the direction in which the plurality of electrode fingers extend, and a pair of edge regions arranged so as to sandwich the central region in the direction in which the plurality of electrode fingers extend. In each of the pair of edge regions of the first IDT electrode, a mass addition film is provided so as to overlap at least one of the plurality of electrode fingers when viewed in plan view. The filter device according to claim 1 or 2, wherein, in at least one of the plurality of electrode fingers of the second IDT electrode, the width in one of the pair of edge regions is wider than the width in the central region, and in at least one of the plurality of electrode fingers of the second IDT electrode, the width in the other of the pair of edge regions is wider than the width in the central region.

6. The first resonator has a first IDT electrode, the second resonator has a second IDT electrode, and the first IDT electrode and the second IDT electrode each include a pair of bus bars and a plurality of electrode fingers. In each of the first IDT electrode and the second IDT electrode, a region where adjacent electrode fingers overlap when viewed from the elastic wave propagation direction is a crossing region. In the crossing region of the first IDT electrode, one end of each of the adjacent electrode fingers is connected to different ones of the bus bars. The crossing region of the second IDT electrode has a first portion in which one end of each of the adjacent electrode fingers is connected to different ones of the bus bars. The filter device according to claim 1 or 2, further having a second portion, wherein, in the first portion, when the center-to-center distance between the electrode fingers at both ends of three consecutive electrode fingers is set to 1λ, in the crossing region of the second IDT electrode, within a range of a distance of 1λ along the elastic wave propagation direction, the number of adjacent electrode fingers whose one ends are connected to different bus bars and are continuously arranged is 2 or less.

7. The first resonator and the second resonator each include a piezoelectric layer, an IDT electrode provided on the piezoelectric layer, and a dielectric film provided between the piezoelectric layer and the IDT electrode. The filter device according to any one of claims 1 to 6, wherein the thickness of the dielectric film of the first resonator is thinner than the thickness of the dielectric film of the second resonator.

8. The plurality of resonators include a high-velocity material layer, a piezoelectric layer provided on the high-velocity material layer, and an IDT electrode provided on the piezoelectric layer. The filter device according to any one of claims 1 to 7, wherein the sound velocity of the bulk wave propagating through the high-velocity material layer is higher than the sound velocity of the elastic wave propagating through the piezoelectric layer.

9. The filter device according to claim 8, wherein the high-velocity material layer is a high-velocity support substrate.

10. Further comprising a support substrate, The filter device according to claim 8, wherein the high-velocity material layer is a high-velocity film provided on the support substrate.

11. Further comprising a low-velocity film provided between the high-velocity material layer and the piezoelectric layer, The filter device according to any one of claims 8 to 10, wherein the sound velocity of the bulk wave propagating through the low-velocity film is lower than the sound velocity of the bulk wave propagating through the piezoelectric layer.

12. The filter device according to any one of claims 1 to 11, wherein the first inductor is constituted by wiring and has at least one wiring electrode.

13. The filter device according to claim 12, wherein the first inductor has a plurality of the wiring electrodes and via electrodes connecting the wiring electrodes to each other.

14. The plurality of resonators include a piezoelectric layer, an IDT electrode provided on the piezoelectric layer, a support member provided on the piezoelectric layer and having an opening surrounding each of the IDT electrodes, and a cover member provided on the support member so as to cover the opening. The filter device according to claim 12 or 13, wherein the first inductor is provided on the cover member.

15. Further comprising a mounting substrate on which the plurality of resonators are arranged, The filter device according to claim 12 or 13, wherein the first inductor is provided on the mounting substrate.

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