Elastic wave filter, multiplexer, high-frequency front-end circuit, and communication device

Abstract

This elastic wave filter includes a plurality of elastic wave resonators which use bulk waves in the thickness longitudinal vibration mode. The elastic wave filter comprises serial arm resonators and parallel arm resonators configured by using the elastic wave resonators. Each of the serial arm resonators and the parallel arm resonators has a piezoelectric material, an upper electrode which is provided above the piezoelectric material, a lower electrode which is provided below the piezoelectric material, and draw-out wirings which are connected to at least one of the upper electrode and the lower electrode and face each other in a first direction with the upper electrode and the lower electrode therebetween in a plan view. When the ratio between the length (Wa1) in the first direction and the length (Wb1) in a second direction perpendicular to the first direction of at least one of the upper electrode and the lower electrode is defined as an aspect ratio (Wb1 / Wa1), the aspect ratios (Wb1 / Wa1) of the serial arm resonators are greater than the aspect ratios (Wb1 / Wa1) of the parallel arm resonators.

Description

Acoustic wave filter, multiplexer, high frequency front-end circuit and communication device

[0001] The present invention relates to an acoustic wave filter, a multiplexer, a high-frequency front-end circuit, and a communication device.

[0002] Patent Document 1 describes an elastic wave resonator (referred to as a piezoelectric thin film device in Patent Document 1) having an elongated two-dimensional shape in which the longitudinal dimension of the electrode is at least twice the lateral dimension.

[0003] Japanese Patent Application Laid-Open No. 2008-042871

[0004] In an acoustic wave filter configured using a plurality of such acoustic wave resonators, there is a demand for improved filter characteristics. If the acoustic wave resonator of Patent Document 1 is applied to an acoustic wave filter as is and the electrodes of the acoustic wave resonators are made elongated, there is a possibility that the Q factor will deteriorate and the filter loss will increase.

[0005] An object of the present invention is to provide an acoustic wave filter, a multiplexer, a high-frequency front-end circuit, and a communication device that can improve filter characteristics.

[0006] An acoustic wave filter according to one aspect includes a plurality of acoustic wave resonators that utilize bulk waves in a thickness extensional vibration mode, and includes series arm resonators and parallel arm resonators configured using the acoustic wave resonators. Each of the series arm resonators and the parallel arm resonators includes a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and lead-out wiring that is connected to at least one of the upper electrode and the lower electrode and faces each other in a first direction across the upper electrode and the lower electrode in a plan view. When the aspect ratio (Wb1 / Wa1) is a ratio of a length (Wa1) of at least one of the upper electrode and the lower electrode in the first direction to a length (Wb1) of the series arm resonators in a second direction perpendicular to the first direction, the aspect ratio (Wb1 / Wa1) is greater than the aspect ratio (Wb1 / Wa1) of the parallel arm resonators.

[0007] A multiplexer according to one aspect includes a plurality of filters including the acoustic wave filter described above, and one of the input terminal and one of the output terminal of each of the plurality of filters are electrically connected to each other.

[0008] A high-frequency front-end circuit according to one aspect includes the acoustic wave filter described above.

[0009] A high-frequency front-end circuit according to one embodiment includes the above multiplexer.

[0010] A communication device according to one aspect includes the above-described high-frequency front-end circuit.

[0011] According to the acoustic wave filter, multiplexer, high-frequency front-end circuit, and communication device of the present invention, it is possible to improve the filter characteristics.

[0012] FIG. 1 is a circuit diagram illustrating an acoustic wave filter according to a first embodiment. FIG. 2 is a cross-sectional view schematically illustrating the configuration of the acoustic wave filter according to the first embodiment. FIG. 3 is a plan view schematically illustrating the configuration of a resonator chip in the acoustic wave filter according to the first embodiment. FIG. 4 is a plan view schematically illustrating the front surface of a module substrate in the acoustic wave filter according to the first embodiment. FIG. 5 is a plan view schematically illustrating inner layers of a module substrate in the acoustic wave filter according to the first embodiment. FIG. 6 is a plan view schematically illustrating the rear surface of a module substrate in the acoustic wave filter according to the first embodiment. FIG. 7 is a plan view illustrating the configuration of a series arm resonator in the acoustic wave filter according to the first embodiment. FIG. 8 is a cross-sectional view taken along line VIII-VIII′ in FIG. 7. FIG. 9 is a plan view illustrating the configuration of an upper electrode and a frame electrode. FIG. 10 is a plan view illustrating the configuration of an upper electrode and a frame electrode according to a first modified example. FIG. 11 is a plan view illustrating the configuration of an upper electrode and a frame electrode according to a second modified example. FIG. 12 is a plan view illustrating the configuration of an upper electrode and a frame electrode according to a third modified example. FIG. 13 is a cross-sectional view showing the configuration of an upper electrode and a frame electrode according to a fourth modification. FIG. 14 is a plan view showing the configuration of a series arm resonator according to a fifth modification. FIG. 15 is a graph showing the filter characteristics of the elastic wave filter according to Example 1. FIG. 16 is a graph showing the filter characteristics of the elastic wave filters according to Example 1 and Comparative Example 1. FIG. 17 is a graph showing an enlarged view of the vicinity of the band indicated by arrow A1 in FIG. 16. FIG. 18 is a graph showing the relationship between impedance and frequency for elastic wave resonators according to Examples 2-1 and 2-10. FIG. 19 is a graph showing the relationship between Q and frequency for elastic wave resonators according to Examples 2-1 and 2-10. FIG. 20 is a graph showing the relationship between Qr and the aspect ratio (Wb1 / Wa1) for the elastic wave resonator according to Example 2. FIG. 21 is a graph showing the relationship between Qa and the aspect ratio (Wb1 / Wa1) for the elastic wave resonator according to Example 2. FIG. 22 is a plan view showing the configuration of an elastic wave resonator according to Example 3. Fig. 23 is a graph showing the relationship between impedance and frequency for the elastic wave resonators according to Examples 3 and 2-10. Fig. 24 is a graph showing the relationship between Q and frequency for the elastic wave resonators according to Examples 3 and 2-10.FIG. 25 is a graph showing the relationship between impedance and frequency for the elastic wave resonator according to Example 4, for different ratios S / t. FIG. 26 is a graph showing the relationship between Q and frequency for the elastic wave resonator according to Example 4, for different ratios S / t. FIG. 27 is a graph showing the relationship between resonance resistances Zr and Qr and the ratio S / t for the elastic wave resonator according to Example 4. FIG. 28 is a graph showing the relationship between Qa and Qc and the ratio S / t for the elastic wave resonator according to Example 4. FIG. 29 is a graph showing the relationship between the Euler angles and the fractional bandwidth of the piezoelectric body using lithium niobate for the elastic wave resonator according to Example 5-1. FIG. 30 is a graph showing the relationship between the Euler angles and the fractional bandwidth of the piezoelectric body using lithium tantalate for the elastic wave resonator according to Example 5-2. FIG. 31 is a diagram showing the configuration of a communication device according to a second embodiment.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments. Note that each embodiment described in the present disclosure is illustrative, and partial substitution or combination of configurations between different embodiments is possible. In modified examples and the second and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0014] 1 is a circuit diagram illustrating an acoustic wave filter according to a first embodiment. As shown in FIG. 1 , an acoustic wave filter 50 according to the first embodiment includes a plurality of series arm resonators 61, 62, 63, and 64, a plurality of parallel arm resonators 65, 66, 67, and 68, and inductors 70A and 70B. At least one of the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, 67, and 68 is a resonator utilizing bulk waves in a thickness extensional vibration mode, i.e., a bulk acoustic wave (BAW) element.

[0015] The plurality of series arm resonators 61, 62, 63, and 64 are connected in series to a signal path between an input terminal 60A and an output terminal 60B. The plurality of parallel arm resonators 65, 66, 67, and 68 are connected in parallel between the signal path between the input terminal 60A and the output terminal 60B and grounds 69A, 69B, 69C, and 69D. The acoustic wave filter 50 according to the first embodiment is a so-called ladder filter.

[0016] One terminal of each of the series-connected series arm resonators 61, 62, 63, and 64 is electrically connected to an input terminal 60A, and the other terminal is electrically connected to an output terminal 60B. One terminal of the parallel arm resonator 65 is electrically connected to a signal path connecting the series arm resonators 61 and 62, and the other terminal is electrically connected to ground 69A via an inductor 70A. One terminal of the parallel arm resonator 66 is electrically connected to a signal path connecting the series arm resonators 62 and 63, and the other terminal is electrically connected to ground 69B.

[0017] One terminal of the parallel arm resonator 67 is electrically connected to the signal path connecting the series arm resonators 63 and 64, and the other terminal is electrically connected to ground 69C via inductor 70B. One terminal of the parallel arm resonator 68 is electrically connected to the signal path connecting the series arm resonator 64 and the output terminal 60B, and the other terminal is electrically connected to ground 69D.

[0018] The inductor 70A is connected in series to a signal path connecting the parallel arm resonator 65 and the ground 69A. The inductor 70B is connected in series to a signal path connecting the parallel arm resonator 67 and the ground 69C.

[0019] The acoustic wave filter 50 may include capacitors or the like as impedance elements, without being limited to the inductors 70A and 70B. Furthermore, the impedance elements, such as the inductors 70A and 70B and the capacitors, are not limited to being connected to the parallel arm resonators 65, 66, 67, and 68, but may be connected to the series arm resonators 61, 62, 63, and 64. Furthermore, the impedance elements, such as the inductors 70A and 70B and the capacitors, may be connected to switch elements. In this case, the acoustic wave filter 50 can vary the frequency of the filter characteristics by switching the switch elements on and off.

[0020] The series arm resonator 61 is configured to have two resonators s1 divided in series. The series arm resonators 62, 63, and 64 are configured to have four resonators s2, s3, and s4 divided in series, respectively. The number of divisions in each of the series arm resonators 61, 62, 63, and 64 is an even number. The number of divisions in each of the series arm resonators 61, 62, 63, and 64 is not limited to two or four, and may be zero, three, five, or more.

[0021] The parallel arm resonator 65 is configured to have two resonators p1 divided in series. Each of the multiple parallel arm resonators 66, 67, and 68 is configured to have four resonators p2, p3, and p4 divided in series. The number of divisions in each of the multiple parallel arm resonators 65, 66, 67, and 68 is an even number. The number of divisions in each of the multiple parallel arm resonators 65, 66, 67, and 68 is not limited to two or four, and may be zero, or may be three, five, or more. In the following description, "divided in series" refers to a configuration in which multiple resonators with the same resonant frequency are connected in series.

[0022] The detailed configurations of the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, 67, and 68 will be described later with reference to Fig. 7 and subsequent figures. The effect of the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, 67, and 68 each having a plurality of resonators s1, s2, s3, s4, p1, p2, p3, and p4 divided in series will also be described later with reference to Fig. 7 and subsequent figures.

[0023] In the acoustic wave filter 50 of this preferred embodiment, the configurations and numbers of the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, 67, and 68 can be changed as appropriate depending on the required filter characteristics. For example, the acoustic wave filter 50 may include at least one series arm resonator and at least one parallel arm resonator.

[0024] Fig. 2 is a cross-sectional view schematically illustrating the configuration of the acoustic wave filter according to the first embodiment. Fig. 3 is a plan view schematically illustrating the configuration of a resonator chip in the acoustic wave filter according to the first embodiment. Fig. 4 is a plan view schematically illustrating the front surface of a module substrate in the acoustic wave filter according to the first embodiment. Fig. 5 is a plan view schematically illustrating inner layers of the module substrate in the acoustic wave filter according to the first embodiment. Fig. 6 is a plan view schematically illustrating the rear surface of the module substrate in the acoustic wave filter according to the first embodiment.

[0025] 2, an acoustic wave filter 50 according to the first preferred embodiment includes a resonator chip 51, a module substrate 52, bumps 55, and a sealing resin 56. The resonator chip 51 is mounted on the module substrate 52 via the bumps 55. The resonator chip 51 includes a plurality of series arm resonators 61, 62, 63, and 64 and a plurality of parallel arm resonators 65, 66, 67, and 68, etc., as shown in FIG.

[0026] The module substrate 52 is a laminated substrate having a plurality of dielectric layers 53 and 54. The module substrate 52 may be, for example, a printed circuit board made of resin or a ceramic substrate such as LTCC (Low Temperature Co-fired Ceramics) or HTCC (High Temperature Co-fired Ceramics). The module substrate 52 is not limited to the two dielectric layers 53 and 54, and may have three or more dielectric layers, or may be a single-layer substrate.

[0027] 3, the resonator chip 51 has a plurality of series arm resonators 61, 62, 63, and 64, a plurality of parallel arm resonators 65, 66, 67, and 68, and a plurality of terminals (an input terminal 60A, an output terminal 60B, and ground terminals 69A, 69B, 69C, and 69D) provided on a support member 13. The input terminal 60A and the output terminal 60B are located at diagonally opposite corners of the support member 13. The ground terminals 69A, 69B, 69C, and 69D are located on the periphery of the support member 13. The connections of the plurality of series arm resonators 61, 62, 63, and 64, the plurality of parallel arm resonators 65, 66, 67, and 68, and the plurality of terminals (the input terminal 60A, the output terminal 60B, and the ground terminals 69A, 69B, 69C, and 69D) are the same as those in FIG. 1, and therefore, repeated explanations will be omitted.

[0028] 4, the module substrate 52 has a plurality of connection pads 57 and vias 58A. The plurality of connection pads 57 are electrically connected to the input terminal 60A, output terminal 60B, and grounds 69A, 69B, 69C, and 69D of the resonator chip 51 via bumps 55. The plurality of connection pads 57 are also electrically connected to the inner layer and the back surface side of the module substrate 52 via vias 58A.

[0029] 5, inductors 70A and 70B are formed on an inner layer of module substrate 52. One end of inductors 70A and 70B is electrically connected to the front surface side of module substrate 52 through connection pad 57 and via 58A (see FIG. 4), respectively, and the other end is electrically connected to the back surface side of module substrate 52 through via 58B.

[0030] 6, a plurality of connection pads 59 are provided on the back surface of the module substrate 52. The acoustic wave filter 50 is mounted on an external device such as a high-frequency front-end circuit 101 (see FIG. 31) through the plurality of connection pads 59.

[0031] Next, the detailed configuration of the series arm resonator 61 will be described. FIG. 7 is a plan view showing the configuration of a series arm resonator in the acoustic wave filter according to the first preferred embodiment. FIG. 8 is a cross-sectional view taken along line VIII-VIII′ in FIG. 7. FIGS. 7 and 8 show an enlarged view of the configuration of the series arm resonator 61 among the multiple resonators included in the resonator chip 51. That is, FIGS. 7 and 8 show the configuration of the series arm resonator 61 located on the input terminal 60A side among the multiple resonators.

[0032] In the following description, when there is no need to distinguish between the multiple series arm resonators 61, 62, 63, and 64 and the multiple parallel arm resonators 65, 66, 67, and 68 (the multiple resonators s1, s2, s3, s4, p1, p2, p3, and p4), they will be simply referred to as the acoustic wave resonator 10. The other resonators have the same configuration as the series arm resonator 61 shown in Figures 7 and 8, and the description of the configuration of the series arm resonator 61 in Figures 7 and 8 can also be applied to the configurations of the other resonators.

[0033] First, the configuration of one resonator s1 (elastic wave resonator 10) included in the series arm resonator 61 will be described. As shown in Fig. 7 and Fig. 8 , the elastic wave resonator 10 has a support member 13, a piezoelectric body 20, an upper electrode 31, a lower electrode 32, a frame electrode 33, and lead wires 34 and 35. As shown in Fig. 8 , the lower electrode 32, the piezoelectric body 20, the upper electrode 31, the lead wires 34 and 35, and the frame electrode 33 are layered in this order on the support member 13.

[0034] In the following description, the thickness direction of the piezoelectric body 20 is referred to as the Z direction, the direction perpendicular to the Z direction is referred to as the X direction, and the direction perpendicular to the Z direction and the X direction is referred to as the Y direction. The X direction and the Y direction are each parallel to the surface (first main surface 20a) of the piezoelectric body 20. In the following description, a plan view refers to the positional relationship when viewed from a direction perpendicular to the first main surface 20a of the piezoelectric body 20 (Z direction).

[0035] The support member 13 is provided opposite the second main surface 20b of the piezoelectric body 20. The support member 13 includes a support substrate 11 and an intermediate layer 12. The support substrate 11 is made of silicon (Si), quartz crystal, or the like. The intermediate layer 12 is provided between the support substrate 11 and the piezoelectric body 20. The intermediate layer 12 is formed of an insulating material such as silicon oxide. Note that the support member 13 may be configured without the intermediate layer 12, with the piezoelectric body 20 provided on the support substrate 11. In other words, the piezoelectric body 20 is bonded to the support substrate 11 directly or via the intermediate layer 12 (insulating layer).

[0036] A recess 14 (hollow portion) is formed on the surface of the support member 13 (intermediate layer 12) facing the second main surface 20b of the piezoelectric body 20. The recess 14 is provided so as to overlap, in plan view, with the excitation region of the resonator formed by overlapping the piezoelectric body 20, the upper electrode 31, and the lower electrode 32. This reduces energy loss of the bulk wave during excitation, resulting in good resonance characteristics.

[0037] The piezoelectric body 20 is in the form of a flat plate having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric body 20 is made of lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ The piezoelectric body 20 is a substrate made of a single crystal of aluminum nitride (AlN). The piezoelectric body 20 is not limited to this, and aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), etc. may also be used. The thickness of the piezoelectric body 20 is not particularly limited, but is preferably 1 μm or less. Furthermore, the piezoelectric body 20 may have a structure in which multiple layers of piezoelectric bodies with different crystal orientations are stacked.

[0038] The upper electrode 31 is provided on the top (first main surface 20a) of the piezoelectric body 20. The lower electrode 32 is provided on the bottom (second main surface 20b) of the piezoelectric body 20. As shown in Figures 7 and 8, the upper electrode 31 and the lower electrode 32 overlap in a region overlapping with the recess 14. In other words, in the region overlapping with the recess 14, the piezoelectric body 20 is disposed between the upper electrode 31 and the lower electrode 32 in the Z direction. This allows bulk waves to propagate between the upper electrode 31 and the lower electrode 32. In the following description, the region where the upper electrode 31 and the lower electrode 32 overlap in a planar view may be described as the excitation region of the resonator.

[0039] The names "upper electrode 31" and "lower electrode 32" are used simply to define the respective portions, and do not limit the spatial arrangement or position of the BAW resonator. In addition, although the upper electrode 31, the lower electrode 32, and the recess 14 are each rectangular in plan view, they are not limited to this and may be circular or have other shapes.

[0040] The upper electrode 31 and the lower electrode 32 are formed of a conductive material such as aluminum (Al), platinum (Pt), gold (Au), copper (Cu), molybdenum (Mo), tungsten (W), titanium (Ti), chromium (Cr), ruthenium (Ru), tantalum (Ta), or iridium (Ir), or an alloy containing at least one of these materials. The upper electrode 31 and the lower electrode 32 may be a laminate film containing these materials. An adhesive layer such as Ti or NiCr may be provided between the upper electrode 31 and the lower electrode 32 and the support member 13 (intermediate layer 12).

[0041] In this embodiment, the series arm resonator 61 has a plurality of resonators s1 (elastic wave resonators 10) divided in series. The recess 14 is shared by two resonators s1 constituting the series arm resonator 61. In other words, one recess 14 is provided for two resonators s1.

[0042] The upper electrodes 31 of the two resonators s1 are provided on the first main surface 20a of the piezoelectric body 20 in regions overlapping with the recesses 14, and are spaced apart in the X direction. The lower electrode 32 is provided in common to the two resonators s1 and is provided on the second main surface 20b of the piezoelectric body 20 in a region overlapping with the recesses 14. In other words, one region of the lower electrode 32 in the X direction (the right-hand portion in FIG. 8 ) faces the upper electrode 31 of one resonator s1 across the piezoelectric body 20. The other region of the lower electrode 32 in the X direction (the left-hand portion in FIG. 8 ) faces the upper electrode 31 of the other resonator s1 across the piezoelectric body 20.

[0043] The lead-out wirings 34 and 35 are provided in the same layer as the upper electrode 31 and are connected to the upper electrode 31 in the X direction. More specifically, the lead-out wiring 34 is connected to the long side of the upper electrode 31 of one resonator s1 that constitutes the series arm resonator 61. The lead-out wiring 35 is connected to the long side of the upper electrode 31 of the other resonator s1 that constitutes the series arm resonator 61. The lead-out wirings 34 and 35 face each other in the X direction, sandwiching the upper electrode 31 and the lower electrode 32, in a plan view.

[0044] The lead-out wirings 34 and 35 are formed of the same material as the upper electrode 31. However, the lead-out wirings 34 and 35 may be formed of a material different from that of the upper electrode 31.

[0045] Furthermore, through holes 15 are provided in the region of the piezoelectric body 20 that overlaps with the recessed portion 14. The through holes 15 are provided for etching the sacrificial layer when forming the recessed portion 14. The positions, number, etc. of the through holes 15 are not limited to the example shown in Fig. 7 and can be changed as appropriate. Furthermore, in the following embodiments and examples, the through holes 15 may be omitted.

[0046] As described above, the acoustic wave resonator 10 included in the acoustic wave filter of this embodiment is a film bulk acoustic resonator (FBAR). That is, the recess 14 (cavity) is formed in the support member 13 (intermediate layer 12) in a portion overlapping the excitation region, and the piezoelectric body 20, upper electrode 31, and lower electrode 32 have a membrane structure. However, without being limited thereto, the acoustic wave resonator 10 may be a solidly mounted resonator (SMR) in which multiple low-impedance layers and multiple high-impedance layers are stacked instead of the recess 14 (cavity).

[0047] 1 and 3, all of the series arm resonators 61, 62, 63, and 64 and all of the parallel arm resonators 65, 66, 67, and 68 are divided in series. However, this is not limiting, and it is sufficient that at least the series arm resonator 64 closest to the output terminal 60B among the multiple series arm resonators 61, 62, 63, and 64 is divided in series. Alternatively, it is sufficient that at least the parallel arm resonator 68 closest to the output terminal 60B among the multiple parallel arm resonators 65, 66, 67, and 68 is divided in series.

[0048] In this embodiment, the plurality of series arm resonators 61, 62, 63, and 64 and the plurality of parallel arm resonators 65, 66, 67, and 68 are divided in series. Therefore, when the impedance of the resonant circuit is high, the ratio (S / t) of the area S of the upper electrode 31 to the film thickness t of the piezoelectric body 20 increases, thereby improving the Q factor. Furthermore, the plurality of series arm resonators 61, 62, 63, and 64 and the plurality of parallel arm resonators 65, 66, 67, and 68 have a reduced power density per unit area, thereby improving the power handling performance. More specifically, the area S of the upper electrode 31 indicates the area of ​​the excitation region where the upper electrode 31 and the lower electrode 32 overlap.

[0049] The plurality of series arm resonators 61, 62, 63, and 64 and the plurality of parallel arm resonators 65, 66, 67, and 68 are not limited to being divided in series, but may be divided in parallel. In this case, particularly when the impedance of the resonant circuit is low, dividing them in parallel can prevent the area of ​​the recess 14 from becoming larger, and can prevent a decrease in the mechanical strength of each resonator.

[0050] In the acoustic wave filter 50 using BAW resonators, a second harmonic spectrum may be output due to nonlinear operation of the BAW resonators. In the acoustic wave filter 50, the second harmonic spectrum of each resonator is attenuated by the output-side resonator and output from the output terminal 60B. However, the second harmonic spectrum of a resonator close to the output terminal 60B (e.g., the series arm resonator 64) may be output from the output terminal 60B with almost no attenuation.

[0051] In this embodiment, at least the series arm resonator 64 located closest to the output terminal 60B among the plurality of resonators has four resonators s4 divided in series. Alternatively, at least the parallel arm resonator 68 located closest to the output terminal 60B among the plurality of resonators has four resonators p4 divided in series. This makes it possible to suppress the 1st harmonic spectrum output from the output terminal 60B in this embodiment.

[0052] For example, if a resonator is divided into n parts in series (n is an integer), the energy density is n ２ 7 and 8, the nonlinear effect is reduced by 6 dB compared to a configuration without division.

[0053] 7 and 8 , since the series arm resonator 61 is divided into an even number of parts, the upper electrode 31 and the lead wiring 34 of the input-side resonator s1 and the upper electrode 31 and the lead wiring 35 of the output-side resonator s1 are formed in the same layer. Therefore, compared to when the series arm resonator 61 is divided into an odd number of parts, a via hole for connecting the lower electrode 32 to the first main surface 20a of the piezoelectric body 20 is not required, and manufacturing costs can be reduced.

[0054] 7 and 8 , the relationship between the voltages of the resonators s1 is indicated by arrows G1 and G2, the relationship between the polarization axes of the piezoelectric bodies 20 is indicated by arrows G3 and G4, and the direction of displacement of the piezoelectric bodies 20 is indicated by arrows G5 and G6. In this embodiment, since the number of divisions of the series arm resonator 61 is even, the relationship between the voltage and polarization axis of one resonator s1 (e.g., the right side in FIGS. 7 and 8 ) (see arrows G1 and G3) is opposite to the relationship between the voltage and polarization axis of the other resonator s1 (e.g., the left side in FIGS. 7 and 8 ) (see arrows G2 and G4). This cancels out the second-order nonlinear signal, thereby reducing the second-order harmonic spectrum.

[0055] It is preferable that the two resonators s1 of the series arm resonator 61 divided in series have the same resonant frequency and the same impedance (the same damping capacitance), so that the nonlinear signals of the series-connected resonators s1 have the same magnitude and cancel out the second-order nonlinear signals.

[0056] Next, the configurations of the upper electrode 31 and the frame electrode 33 will be described with reference to FIGS. 8 and 9 . FIG. 9 is a plan view showing the configuration of the upper electrode and the frame electrode. The configuration of one elastic wave resonator 10 will be described with reference to FIG. 9 . Furthermore, in FIG. 9 , a first direction Da indicated by an arrow indicates the direction in which the lead wiring 34 (or the lead wiring 35) is connected to the upper electrode 31. In other words, the first direction Da is a direction parallel to the surface (first main surface 20 a) of the piezoelectric body 20, and is a direction in which the lead wiring 34 and the lead wiring 35 face each other across the upper electrode 31 and the lower electrode 32 that constitute one elastic wave resonator 10. The second direction Db is a direction perpendicular to the first direction Da.

[0057] 8 and 9 , in the elastic wave resonator 10 constituting the series arm resonator 61, the first direction Da is parallel to the X direction, and the second direction Db is parallel to the Y direction. However, the orientations of the first direction Da and the second direction Db are different for the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, 67, and 68.

[0058] 3 , in the elastic wave resonator 10 (resonator s2) constituting the series arm resonator 62 and the elastic wave resonator 10 (resonator s3) constituting the series arm resonator 63, the first direction Da is parallel to the Y direction and the second direction Db is parallel to the X direction. In the elastic wave resonator 10 (resonator s4) constituting the series arm resonator 64, the first direction Da is parallel to the X direction and the second direction Db is parallel to the Y direction. In addition, in the elastic wave resonators 10 constituting the parallel arm resonators 65, 66, 67, and 68, the first direction Da is parallel to the X direction and the second direction Db is parallel to the Y direction.

[0059] As shown in Fig. 8, the frame electrode 33 is in contact with the upper electrode 31 and is provided on the upper surface of the upper electrode 31 (the surface opposite the piezoelectric body 20). As shown in Fig. 9, the frame electrode 33 is provided in a frame shape along the outer periphery of the upper electrode 31. The frame electrode 33 is rectangular and has a first portion 33a extending in a first direction Da and a second portion 33b extending in a second direction Db.

[0060] In this embodiment, the outer shape of the upper electrode 31 is defined by the frame electrode 33. That is, the length Wa1 of the upper electrode 31 in the first direction Da is equal to the maximum length of the frame electrode 33 in the first direction Da. More specifically, the length Wa1 of the upper electrode 31 in the first direction Da is equal to the maximum length in the first direction Da between the outer edges of two adjacent second portions 33b of the frame electrode 33. Furthermore, the length Wb1 of the upper electrode 31 in the second direction Db is equal to the maximum length in the second direction Db of the frame electrode 33. More specifically, the length Wb1 of the upper electrode 31 in the second direction Db is equal to the maximum length in the second direction Db between the outer edges of two adjacent first portions 33a of the frame electrode 33.

[0061] Furthermore, the width Wa2 in the first direction Da of the second portion 33b of the frame electrode 33 extending in the second direction Db is equal to the width Wb2 in the second direction Db of the first portion 33a of the frame electrode 33 extending in the first direction Da. In other words, the frame electrode 33 has equal widths Wa2 and Wb2 along the circumferential direction. However, this is not limitative, and the widths Wa2 and Wb2 of the frame electrode 33 may be different.

[0062] 9 , in the elastic wave resonator 10 constituting the series arm resonator 61, the upper electrode 31 and the frame electrode 33 are rectangular and have a longitudinal direction that is perpendicular to the connection direction (first direction Da) of the lead-out wirings 34, 35 (second direction Db). That is, the length Wb1 of the upper electrode 31 in the second direction Db is longer than the length Wa1 of the upper electrode 31 in the first direction Da. The aspect ratio (Wb1 / Wa1), which is the ratio of the length Wa1 of the upper electrode 31 in the first direction Da to the length Wb1 of the upper electrode 31 in the second direction Db, is greater than 1.

[0063] 3 , in the acoustic wave filter 50 of this preferred embodiment, the aspect ratio (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 is larger than the aspect ratio (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68. Specifically, the upper electrode 31 of each of the series arm resonators 61, 62, 63, and 64 has a rectangular shape with its longitudinal direction aligned along the second direction Db. The upper electrode 31 of each of the parallel arm resonators 65, 66, 67, and 68 has a circular shape with a length Wa1 in the first direction Da and a length Wb1 in the second direction Db that are equal to each other.

[0064] As a result, the acoustic wave filter 50 of this preferred embodiment can suppress filter loss more effectively than a configuration in which the aspect ratios (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 are the same as the aspect ratios (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68, or a configuration in which the aspect ratios (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 are smaller than the aspect ratios (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68.

[0065] Detailed configuration examples regarding the aspect ratio (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 and the aspect ratio (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68, and filter characteristics will be described later in Examples 1 to 5.

[0066] Although the present embodiment has been described with respect to the outer shape of the upper electrode 31, the outer shape of the lower electrode 32 may also have a similar configuration. That is, the length Wb1 of the lower electrode 32 of the series arm resonator 61 shown in FIGS. 8 and 9 in the second direction Db is longer than the length Wa1 of the lower electrode 32 in the first direction Da. Furthermore, the aspect ratio (Wb1 / Wa1) of the lower electrodes 32 of the series arm resonators 61, 62, 63, and 64 is greater than the aspect ratio (Wb1 / Wa1) of the lower electrodes 32 of the parallel arm resonators 65, 66, 67, and 68. Furthermore, while the configuration in which the frame electrode 33 is provided on the upper electrode 31 has been described, this is not limiting. The frame electrode 33 may be provided on the lower electrode 32, or on both the upper electrode 31 and the lower electrode 32. In this case, the description of the shape of each part of the frame electrode 33 in FIG. 9 also applies to the frame electrode 33 provided on the lower electrode 32. Furthermore, when the shapes of the upper electrode 31 and the lower electrode 32 are different (see Figures 7 and 8), the outer shape of the upper electrode 31 can be rephrased as the outer shape of the area where the upper electrode 31 and the lower electrode 32 overlap (excitation area).

[0067] 9, for ease of understanding, the case where the frame electrode 33 has a rectangular shape, that is, the case where the outer shape of the upper electrode 31 is rectangular, has been described. However, this is not limiting, and the shapes of the frame electrode 33 and the upper electrode 31 may be other shapes.

[0068] 10 is a plan view showing the configuration of the upper electrode and frame electrode according to the first modification. As shown in FIG. 10, the upper electrode 31 and frame electrode 33A according to the first modification have an elliptical shape. More specifically, the upper electrode 31 and frame electrode 33A have an elliptical shape with their major axes oriented along the second direction Db perpendicular to the connection direction of the lead-out wirings 34 and 35. That is, the length Wa1 of the upper electrode 31 is defined by the maximum length of the elliptical shape in the first direction Da. Furthermore, the length Wb1 of the upper electrode 31 is defined by the maximum length of the elliptical shape in the second direction Db.

[0069] Also, in this modified example, the width Wa2 in the first direction Da of the portion of the frame electrode 33A extending along the second direction Db (the portion intersecting with the short axis direction) is equal to the width Wb2 in the second direction Db of the portion of the frame electrode 33A extending along the first direction Da (the portion intersecting with the long axis direction).

[0070] 11 is a plan view showing the configuration of the upper electrode and frame electrode according to the second modification. As shown in FIG. 11 , the upper electrode 31 and frame electrode 33B according to the second modification are rectangular with arc-shaped corners. In other words, the first portion 33Ba and the second portion 33Bb of the frame electrode 33B are smoothly connected in an arc-like manner. Alternatively, the upper electrode 31 and frame electrode 33B may be elliptical. The definitions of the lengths Wa1 and Wb1 of the upper electrode 31 and the aspect ratio (Wb1 / Wa1) of the frame electrode 33B in the second modification, and the width Wa2 in the first direction Da and the width Wb2 in the second direction Db of the frame electrode 33B are the same as those in the first embodiment.

[0071] 12 is a plan view showing the configuration of the upper electrode and frame electrode according to the third modification. As shown in FIG. 12, the upper electrode 31 and frame electrode 33C according to the third modification are polygonal. The first portion 33Ca, the second portion 33Cb, and the third portion 33Cc of the frame electrode 33C each extend in a direction inclined at an angle relative to the connection direction (first direction Da) of the lead-out wirings 34 and 35. In this modification, the length Wa1 of the upper electrode 31 is also the maximum length of the frame electrode 33C in the first direction Da. Furthermore, the length Wb1 of the upper electrode 31 is also the maximum length of the frame electrode 33C in the second direction Db.

[0072] In the third modified example, the width Wa2 of the frame electrode 33C in the first direction Da is the width Wa2 in the first direction Da of a portion of the first portion 33Ca, the second portion 33Cb, and the third portion 33Cc that extends along the second direction Db (e.g., the second portion 33Cb that forms the smallest angle with the second direction Db). Also, the width Wb2 of the frame electrode 33C in the second direction Db is the width Wb2 in the second direction Db of a portion of the first portion 33Ca, the second portion 33Cb, and the third portion 33Cc that extends along the first direction Da (e.g., the first portion 33Ca that forms the smallest angle with the first direction Da).

[0073] 13 is a cross-sectional view showing the configuration of an upper electrode and a frame electrode according to a fourth modified example. As shown in FIG. 13, the peripheral edge of the upper electrode 31 according to the fourth modified example is spaced apart from the piezoelectric body 20 via an insulating layer 22. In this case, the length Wb1 of the upper electrode 31 is determined by the portion of the upper electrode 31 that contacts the piezoelectric body 20 and is provided with the frame electrode 33 (the portion in which the piezoelectric body 20, the upper electrode 31, and the frame electrode 33 are stacked in this order). The portion of the upper electrode 31 that is spaced apart from the piezoelectric body 20 (the portion in which the piezoelectric body 20, the insulating layer 22, the upper electrode 31, and the frame electrode 33 are stacked in this order) is not included in the length Wb1. In other words, the length Wb1 of the upper electrode 31 is the length of the portion of the upper electrode 31 that contacts the piezoelectric body 20 and is provided with the frame electrode 33 in the second direction Db.

[0074] The width Wb2 of the frame electrode 33 in the second direction Db is also determined by the portion of the frame electrode 33 that overlaps the region where the upper electrode 31 and the piezoelectric body 20 are in contact (the portion where the piezoelectric body 20, the upper electrode 31, and the frame electrode 33 are stacked in this order). The width Wb2 does not include the portion of the frame electrode 33 that overlaps the region where the upper electrode 31 and the piezoelectric body 20 are separated (the portion where the piezoelectric body 20, the insulating layer 22, the upper electrode 31, and the frame electrode 33 are stacked in this order). In other words, the width Wb2 of the frame electrode 33 in the second direction Db is the length in the second direction Db of the portion of the frame electrode 33 that overlaps the region where the upper electrode 31 and the piezoelectric body 20 are in contact. Note that while FIG. 13 has described the length Wb1 of the upper electrode 31 in the second direction Db and the width Wb2 of the frame electrode 33 in the second direction Db, the description of FIG. 13 can also be applied to the first direction Da.

[0075] Fig. 14 is a plan view showing the configuration of a series arm resonator according to a fifth modification. In the examples shown in Figs. 7 and 8, one recess 14 is formed in each of the two series-divided resonators s1 of the series arm resonator 61, but this is not limiting. As shown in Fig. 14, in a series arm resonator 61A according to the fifth modification, recesses 14a and 14b are provided in each of the two series-divided resonators s1.

[0076] The two recesses 14a, 14b are spaced apart in the X direction. The upper electrode 31 of one resonator s1 of the series arm resonator 61A (e.g., on the right side in FIG. 14 ) is arranged to overlap one recess 14a. The upper electrode 31 of the other resonator s1 of the series arm resonator 61A (e.g., on the left side in FIG. 14 ) is arranged to overlap the other recess 14b. The lower electrode 32 is provided continuously across the two recesses 14a, 14b.

[0077] In the fifth modification, the portion of the lower electrode 32 located between the two recesses 14 a and 14 b contacts the support member 13 (intermediate layer 12). Therefore, in the fifth modification, the heat dissipation effect from the lower electrode 32 to the support member 13 is improved, and the power resistance performance can be improved.

[0078] Next, a description will be given of filter characteristics when the aspect ratios (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 and the aspect ratios (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68 are changed. Also, a description will be given of resonator characteristics when the aspect ratios (Wb1 / Wa1) and other electrode shapes of the elastic wave resonators 10 constituting the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, 67, and 68 are changed.

[0079] In the following examples and comparative examples, a single crystal of lithium niobate was used as the material of the piezoelectric body 20. The Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric body 20 were (φ, θ, ψ) = (0°, 126°, 0°).

[0080] The upper electrode 31 was formed by laminating Ti / Pt / Ti / Al / Ti in this order from the first main surface 20a of the piezoelectric body 20. The film thicknesses of Ti / Pt / Ti / Al / Ti were 4 / 11.3 to 39.3 / 14 / 100 / 4 nm, respectively. The lower electrode 32 was formed by laminating Ti / Pt / Ti / Al / Ti in this order from the second main surface 20b of the piezoelectric body 20. The film thicknesses of Ti / Pt / Ti / Al / Ti were 4 / 11.3 to 39.3 / 14 / 100 / 4 nm, respectively.

[0081] The frame electrode 33 was formed by laminating Ti / Pt / Ti in this order on the surface of the upper electrode 31. The film thicknesses of Ti / Pt / Ti were 4 / 30 / 4 nm, respectively.

[0082] In the support member 13, the intermediate layer 12 is made of silicon oxide (SiO ２ ), and the support substrate 11 is made of silicon (Si).

[0083] Furthermore, in Tables 1 to 3 and FIGS. 15 to 30 of each example described below, variations in filter characteristics and variations in resonator characteristics caused by variations in processing during the manufacturing process are included.

[0084] Example 1 In Example 1 and Comparative Example 1, filter characteristics will be described when the aspect ratio (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 is set larger than the aspect ratio (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68. FIG. 15 is a graph showing the filter characteristics of the elastic wave filter according to Example 1. FIG. 16 is a graph showing the filter characteristics of the elastic wave filters according to Example 1 and Comparative Example 1. FIG. 17 is a graph showing an enlarged view of the vicinity of the band indicated by arrow A1 in FIG. 16. Table 1 shows configuration examples of each resonator in the elastic wave filters according to Example 1 and Comparative Example 1.

[0085] In the first embodiment, the upper electrodes 31 of the series arm resonators 61, 62, 63, and 64 are rectangular, and the upper electrodes 31 of the parallel arm resonators 65, 66, 67, and 68 are circular (see FIG. 3).

[0086]

[0087] As shown in Table 1, the aspect ratio (Wb1 / Wa1) of each of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) is 4.0. The aspect ratio (Wb1 / Wa1) of each of the parallel arm resonators 65, 66, 67, and 68 (resonators p1, p2, p3, and p4) is 1.0.

[0088] The lengths Wa1, Wb1 and areas S of the upper electrodes 31 of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) are different from one another. The lengths Wa1, Wb1 and areas S of the upper electrodes 31 of the parallel arm resonators 65, 66, 67, and 68 (resonators p1, p2, p3, and p4) are also different from one another.

[0089] The upper electrode 31, the lower electrode 32, and the frame electrode 33 are made of the same material as the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) and the parallel arm resonators 65, 66, 67, and 68 (resonators p1, p2, p3, and p4). However, the Pt film thickness of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) is thinner than the Pt film thickness of the parallel arm resonators 65, 66, 67, and 68 (resonators p1, p2, p3, and p4). The Pt film thickness of the series arm resonator 61 (resonator s1) on the input terminal 60A side is thicker than the Pt film thickness of the series arm resonators 62, 63, and 64 (resonators s2, s3, and s4) on the output terminal 60B side. The thickness of the Pt film of the parallel arm resonators 67 and 68 (resonators p3 and p4) on the output terminal 60B side is thicker than the thickness of the Pt film of the parallel arm resonators 65 and 66 (resonators p1 and p2) on the input terminal 60A side.

[0090] As shown in FIG. 15, the acoustic wave filter 50 in accordance with the first embodiment has a loss of 2.1 dB or less in the band indicated by the arrow A1 (n79 band: 4400 MHz or more and 5000 MHz or less).

[0091] The acoustic wave filter 50 according to the first embodiment achieves attenuation of 25 dB or more in the band indicated by arrow A2 (LTE band: 2690 MHz or less). The acoustic wave filter 50 according to the first embodiment achieves attenuation of 30 dB or more in the band indicated by arrow A3 (n77 band: 3300 MHz or more and 4200 MHz or less). The acoustic wave filter 50 according to the first embodiment achieves attenuation of 25 dB or more in the band indicated by arrow A4 (WiFi7 band: 5150 MHz or more and 7125 MHz or less).

[0092] As described above, it has been shown that the acoustic wave filter 50 in accordance with the first embodiment has excellent filter characteristics.

[0093] 16 and 17, the aspect ratios of the elastic wave filter according to Comparative Example 1 are opposite to those of Example 1. That is, in the elastic wave filter according to Comparative Example 1, the aspect ratios (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) are all 1.0. The aspect ratios (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68 (resonators p1, p2, p3, and p4) are all 4.0.

[0094] 16 and 17 , the acoustic wave filter 50 according to Example 1 exhibited loss in the n79 band indicated by arrow A1 that was approximately 0.3 dB smaller than that of Comparative Example 1. Furthermore, Example 1 and Comparative Example 1 exhibited equivalent amounts of attenuation in each of the bands indicated by arrows A2 to A4 (LTE band, n77 band, and WiFi7 band).

[0095] From the above results, it can be seen that the acoustic wave filter 50 in accordance with the first embodiment can reduce loss in the filter characteristics by making the aspect ratio (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 larger than the aspect ratio (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68.

[0096] Second Example In a second example, the resonator characteristics of elastic wave resonator 10 including series arm resonators 61, 62, 63, and 64 and parallel arm resonators 65, 66, 67, and 68 will be described when the aspect ratio (Wb1 / Wa1) of upper electrode 31 is changed.

[0097] Fig. 18 is a graph showing the relationship between impedance and frequency for the elastic wave resonators according to Examples 2-1 and 2-10. Fig. 19 is a graph showing the relationship between Q and frequency for the elastic wave resonators according to Examples 2-1 and 2-10. Fig. 20 is a graph showing the relationship between Qr and the aspect ratio (Wb1 / Wa1) for the elastic wave resonator according to Example 2. Fig. 21 is a graph showing the relationship between Qa and the aspect ratio (Wb1 / Wa1) for the elastic wave resonator according to Example 2.

[0098] Table 2 shows the relationship between the aspect ratio, length, and area of ​​the upper electrode and Q of the elastic wave resonator according to Example 2. In Table 2 and Fig. 20, Qr represents Q at the resonant frequency fr. Also, in Table 2 and Fig. 21, Qa represents Q at the anti-resonant frequency fa.

[0099]

[0100] As shown in Table 2, the elastic wave resonators 10 according to Examples 2-1 to 2-13 have aspect ratios (Wb1 / Wa1) that vary from 4.00 to 0.40. The upper electrodes 31 in Examples 2-1 to 2-13 all have a rectangular (quadrilateral) shape. Furthermore, the area S of the upper electrodes 31 is constant in Examples 2-1 to 2-13. That is, the impedance of the elastic wave resonators 10 according to Examples 2-1 to 2-13 is a constant value.

[0101] More specifically, in Examples 2-1 to 2-9, the aspect ratio (Wb1 / Wa1) is greater than 1.00. That is, the upper electrodes 31 in Examples 2-1 to 2-9 are rectangular with their longitudinal direction along the second direction Db. In Example 2-10, the aspect ratio (Wb1 / Wa1) is 1.00. That is, the upper electrodes 31 in Example 2-10 are square. In Examples 2-11 to 2-13, the aspect ratio (Wb1 / Wa1) is less than 1.00. That is, the upper electrodes 31 in Examples 2-11 to 2-13 are rectangular with their longitudinal direction along the first direction Da.

[0102] 18, the frequency characteristics of impedance in Example 2-1 are almost the same as those in Example 2-10. However, since Example 2-1 (Wb1 / Wa1=4.0) has a larger aspect ratio than Example 2-10 (Wb1 / Wa1=1.0), the absolute value of the impedance is slightly smaller.

[0103] As shown in Fig. 19, Example 2-1 and Example 2-10 have different frequency characteristics of Q. In the vicinity of the resonant frequency fr, the Qr of Example 2-1 (Wb1 / Wa1 = 4.0) is larger than the Qr of Example 2-10 (Wb1 / Wa1 = 1.0). On the other hand, in the vicinity of the anti-resonant frequency fa, the Qa of Example 2-10 is larger than the Qa of Example 2-1. Note that Figs. 18 and 19 include variations in resonator characteristics due to variations in processing during the manufacturing process.

[0104] 20, as the aspect ratio (Wb1 / Wa1) of the upper electrode 31 increases, Qr increases. Furthermore, Qr decreases sharply when the aspect ratio (Wb1 / Wa1) is 1.6 or less. That is, the slope of Qr in the region where the aspect ratio (Wb1 / Wa1) is 1.6 or less is larger than the slope of Qr in the region where the aspect ratio (Wb1 / Wa1) is 1.6 or more.

[0105] In the elastic wave filter 50 having a ladder circuit (see FIGS. 1 and 3 ), the resonant frequencies fr of the series arm resonators 61, 62, 63, and 64 are located within the passband, and the antiresonant frequencies fa are located in the attenuation band higher than the passband. Therefore, the elastic wave resonators 10 constituting the series arm resonators 61, 62, 63, and 64 must have a high Qr. The graph in FIG. 20 shows that the Qr at the resonant frequency increases when the aspect ratio (Wb1 / Wa1) of the series arm resonators 61, 62, 63, and 64 is set to 1.6 or greater. This enables the elastic wave filter 50 to reduce loss.

[0106] 21, when the aspect ratio (Wb1 / Wa1) of the upper electrode 31 is 1 (Example 2-10), Qa peaks. When the aspect ratio (Wb1 / Wa1) changes (i.e., when the aspect ratio (Wb1 / Wa1) becomes smaller than 1 or larger than 1), Qa tends to decrease.

[0107] Here, the anti-resonance frequency fa of the parallel arm resonators 65, 66, 67, and 68 is located within the passband, and the resonant frequency fr is located in the attenuation band lower than the passband. Therefore, the acoustic wave resonator 10 comprising the parallel arm resonators 65, 66, 67, and 68 needs to have a high Qa. The graph shown in FIG. 21 reveals that the Qa at the anti-resonance frequency increases when the aspect ratio (Wb1 / Wa1) of the parallel arm resonators 65, 66, 67, and 68 is set to be 0.6 or greater and 1.8 or less. More specifically, when the aspect ratio (Wb1 / Wa1) is set to be 0.6 or greater and 1.8 or less, the Qa is 230 or greater, which is equivalent to the maximum Qa value (Qa = 236). This enables the acoustic wave filter 50 to reduce loss.

[0108] Third Example In a third example, the resonator characteristics of an elastic wave resonator 10A including series arm resonators 61, 62, 63, and 64 and parallel arm resonators 65, 66, 67, and 68 will be described when the shape of the upper electrode 31 is changed.

[0109] Fig. 22 is a plan view showing the configuration of an elastic wave resonator in accordance with Example 3. Fig. 23 is a graph showing the relationship between impedance and frequency for the elastic wave resonators in accordance with Examples 3 and 2-10. Fig. 24 is a graph showing the relationship between Q and frequency for the elastic wave resonators in accordance with Examples 3 and 2-10.

[0110] As shown in FIG. 22 , in an elastic wave resonator 10A according to the third embodiment, the upper electrode 31 has a circular shape. The length Wa1 of the upper electrode 31 in the first direction Da is equal to the length Wb1 of the upper electrode 31 in the second direction Db. The aspect ratio (Wb1 / Wa1) of the upper electrode 31 in the third embodiment is 1.0. The frame electrode 33 provided on the outer periphery of the upper electrode 31 also has a circular shape. The width of the frame electrode 33 is constant along the circumferential direction. That is, the width Wa2 of the frame electrode 33 in the first direction Da is equal to the width Wb2 of the frame electrode 33 in the second direction Db.

[0111] As in the first embodiment (see FIGS. 7 and 8 ), the lower electrode 32 is provided in common to two adjacent acoustic wave resonators 10A. The lower electrode 32 has an oval shape with its longitudinal direction aligned with the first direction Da. One region of the lower electrode 32 in the first direction Da (the left portion in FIG. 22 ) faces the upper electrode 31 of one acoustic wave resonator 10A with the piezoelectric body 20 interposed therebetween. The other region of the lower electrode 32 in the first direction Da (the left portion in FIG. 22 ) faces the upper electrode 31 of the other acoustic wave resonator 10A with the piezoelectric body 20 interposed therebetween.

[0112] 23 and 24 show the resonator characteristics of Example 2-10 for comparison with the elastic wave resonator 10A of Example 3. The upper electrode 31 in Example 2-10 has a rectangular (quadrilateral) shape. The aspect ratio (Wb1 / Wa1) of the upper electrode 31 in Example 2-10 is 1.0, and in this case, the upper electrode 31 has a square shape. Note that FIGS. 23 and 24 include variations in the resonator characteristics due to variations in processing during the manufacturing process.

[0113] As shown in Fig. 23, the elastic wave resonator 10A according to Example 3 has impedance frequency characteristics that are substantially the same as those of Example 2-10. As shown in Fig. 24, the elastic wave resonator 10A according to Example 3 exhibits a larger Q than Example 2-10 in the band between the anti-resonance frequency and the resonance frequency. That is, the elastic wave resonator 10A according to Example 3 has larger Qr and Qa than Example 2-10. As a result, the elastic wave filter 50 using the elastic wave resonator 10A according to Example 3 can reduce loss.

[0114] The upper electrode 31 in Example 3 is circular, and the frame electrode 33 has a uniform width in the circumferential direction. That is, the rectangular frame electrode 33 in Examples 2-10 has corners, and the width at the corners is different from the width of other portions. On the other hand, the frame electrode 33 in Example 3 has no corners. Therefore, the elastic wave resonator 10A in Example 3 can effectively suppress leakage of bulk wave energy outside the excitation region for various modes of standing waves that exist in the planar direction in the region surrounded by the frame electrode 33, including a standing wave mode in the first direction Da and a standing wave mode in a direction tilted (for example, a direction tilted by 45°) with respect to the first direction Da.

[0115] Although an example in which the upper electrode 31 has a circular shape has been described in FIG. 22, the shape is not limited to this, and the upper electrode 31 may have an elliptical shape.

[0116] Example 4 describes the resonator characteristics of the elastic wave resonator 10 when the aspect ratio (Wb1 / Wa1) of the upper electrode 31 is fixed and the area S and ratio S / t of the upper electrode 31 are varied. More specifically, the area S of the upper electrode 31 indicates the area of ​​the region where the upper electrode 31 and the lower electrode 32 overlap.

[0117] Fig. 25 is a graph showing the relationship between impedance and frequency for the elastic wave resonator in accordance with Example 4 for different ratios S / t. Fig. 26 is a graph showing the relationship between Q and frequency for the elastic wave resonator in accordance with Example 4 for different ratios S / t. Fig. 27 is a graph showing the relationship between resonance resistances Zr and Qr and the ratio S / t for the elastic wave resonator in accordance with Example 4. Fig. 28 is a graph showing the relationship between Qa and Qc and the ratio S / t for the elastic wave resonator in accordance with Example 4. Note that Figs. 25 and 26 include variations in resonator characteristics due to variations in processing during the manufacturing process.

[0118] Table 3 shows the relationship between the area of ​​the upper electrode, the thickness of the piezoelectric body, and the ratio S / t of the elastic wave resonator according to Example 4 and the resonant resistance Zr and Q. In Table 3, Qr represents the Q at the resonant frequency fr, Qa represents the Q at the antiresonant frequency fa, and Qc represents the Q at the center frequency fc between the resonant frequency fr and the antiresonant frequency fa.

[0119]

[0120] As shown in Table 3, in Examples 4-1 to 4-11, the film thickness t of the piezoelectric body 20 was kept constant, and the area S of the upper electrode 31 was set to 500 μm ２ to 16,000 μm ２In Examples 4-1 and 4-2, when the area of ​​the upper electrode 31 is S and the film thickness of the piezoelectric body 20 is t, the ratio S / t of the area S to the film thickness t is smaller than 2000 μm. In Examples 4-3 to 4-11, the ratio S / t of the area of ​​the upper electrode 31 to the film thickness of the piezoelectric body 20 is larger than 2000 μm. The layer structure and film thickness of the upper electrode 31 and the frame electrode 33 are the same as those in Example 2 described above.

[0121] 25 and 26 show the impedance frequency characteristics of elastic wave resonators 10 according to Examples 4-3, 4-5, 4-7, 4-9, and 4-11 among Examples 4-1 to 4-11 shown in Table 3. As shown in Fig. 25, the impedance decreases as the area S of upper electrode 31 increases, that is, as the ratio S / t increases.

[0122] 26, the frequency characteristics of Q show different trends for different ratios S / t. In the vicinity of the resonant frequency fr, the smaller the ratio S / t, the larger the Q. In the vicinity of the antiresonant frequency fa, the larger the ratio S / t, the larger the Q.

[0123] The horizontal axis of the graph shown in Fig. 27 represents the ratio S / t of the area S of the upper electrode 31 to the film thickness t of the piezoelectric body 20. The vertical axis represents the resonance resistance Zr (right vertical axis) which is correlated with the series resistance of the elastic wave resonator 10, and Qr (left vertical axis) at the resonance frequency fr. The horizontal axis of the graph shown in Fig. 28 represents the ratio S / t, and the vertical axis represents Qc at the center frequency fc and Qa at the anti-resonance frequency fa.

[0124] As shown in Figure 27, as the ratio S / t increases, the resonant resistance Zr decreases. When the ratio S / t becomes smaller than 2000 μm (Examples 4-1 and 4-2), the resonant resistance Zr increases rapidly. As shown in Figure 27, Qr peaks when the ratio S / t is 2028 μm (Example 4-3). When the ratio S / t changes (when the ratio S / t becomes smaller or larger than 2000 μm), Qr tends to decrease.

[0125] As shown in Figure 28, as the ratio S / t increases, Qa increases. Furthermore, Qc peaks when the ratio S / t is 8114 μm (Example 4-7). As the ratio S / t changes, Qc tends to decrease. In particular, when the ratio S / t becomes smaller than 2000 μm, Qc decreases rapidly.

[0126] Here, the resonant frequencies fr of the series arm resonators 61, 62, 63, and 64 are located within the pass band, and the antiresonant frequencies fa are located in the attenuation band higher than the pass band. The center frequency fc is near the high-frequency end of the pass band. Therefore, the series arm resonators 61, 62, 63, and 64 are required to have a small resistance component near the resonant frequency fr and a large Qc at the center frequency fc.

[0127] The anti-resonance frequencies fa of the parallel arm resonators 65, 66, 67, and 68 are located within the pass band, and the resonant frequencies fr are located in the attenuation band lower than the pass band. The center frequencies fc are near the lower end of the pass band. Therefore, the parallel arm resonators 65, 66, 67, and 68 are required to have high Qa at the anti-resonance frequency fa and high Qc at the center frequency fc.

[0128] 27 and 28 show that in the elastic wave resonator 10 comprising the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, 67, and 68, by setting the ratio S / t of the area S of the upper electrode 31 to the film thickness t of the piezoelectric body 20 to be 2000 μm or greater, it is possible to suppress an increase in the resonance resistance Zr and to increase the Qa at the antiresonance frequency fa and the Qc at the center frequency fc. As a result, the elastic wave filter 50 can reduce loss.

[0129] Example 5 describes the fractional bandwidth ΔfR and the piezoelectric constant when the Euler angles of lithium niobate or lithium tantalate used in the piezoelectric body 20 are varied. Fig. 29 is a graph showing the relationship between the Euler angles and the fractional bandwidth of a piezoelectric body using lithium niobate in an elastic wave resonator in accordance with Example 5-1. In the elastic wave resonator 10 in accordance with Example 5-1, lithium niobate was used as the piezoelectric body 20.

[0130] The fractional bandwidth ΔfR shown in FIG. 29 is expressed as ΔfR=(fa−fr) / fr, where fr is the resonant frequency of elastic wave resonator 10, fa is the antiresonant frequency, and (fa−fr) is the frequency difference between the resonant frequency and the antiresonant frequency.

[0131] The horizontal axis of the graph shown in Fig. 29 represents the Euler angle θ of lithium niobate. As indicated by arrow B1 in Fig. 29, the Euler angles (φ, θ, ψ) of the lithium niobate constituting piezoelectric body 20 are preferably in the range of (φ, θ, ψ) = (0°, 107 to 140°, 0°). As a result, elastic wave resonator 10 in accordance with Example 5-1 can achieve a wide fractional bandwidth ΔfR of 10% or more.

[0132] 29, it is preferable that the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric body 20 are in the range of (φ, θ, ψ) = (0°, 123 to 139°, 0°). In this range, the fractional bandwidth ΔfR of the shear wave (in the planar direction) is 0.5% or less, and the elastic wave resonator 10 in accordance with Example 5-1 can reduce unwanted waves due to shear waves.

[0133] 30 is a graph showing the relationship between the Euler angles and the fractional bandwidth of the piezoelectric body using lithium tantalate in the elastic wave resonator according to Example 5-2. In elastic wave resonator 10 according to Example 5-2, lithium tantalate was used for piezoelectric body 20.

[0134] The horizontal axis of the graph shown in Fig. 30 represents the Euler angle θ of the lithium tantalate. As indicated by arrow C1 in Fig. 30, it is preferable that the Euler angles (φ, θ, ψ) of the lithium tantalate constituting piezoelectric body 20 be in the range of (φ, θ, ψ) = (0°, 101 to 134°, 0°). This allows elastic wave resonator 10 in accordance with Example 5-2 to have a wide fractional bandwidth ΔfR of 3% or more.

[0135] 30 , it is preferable that the Euler angles (φ, θ, ψ) of the lithium tantalate constituting the piezoelectric body 20 be in the range of (φ, θ, ψ) = (0°, 123 to 139°, 0°). In this range, the fractional bandwidth ΔfR of the shear wave (in the planar direction) is 0.5% or less, and the elastic wave resonator 10 in accordance with Example 5-2 can reduce unwanted waves due to shear waves.

[0136] In Example 5-1, when lithium niobate (longitudinal wave) in a thickness longitudinal vibration mode is used as the piezoelectric body 20, the piezoelectric constant e ３３ In Example 5-2, when lithium tantalate (longitudinal wave) in a thickness extensional vibration mode is used as the piezoelectric body 20, the piezoelectric constant e ３３ Here, unlike Examples 5-1 and 5-2, in elastic wave resonator 10 using aluminum nitride (AlN) as the material of piezoelectric body 20, longitudinal waves are generally used as the fundamental mode, and the longitudinal piezoelectric constant e ３３ Therefore, the longitudinal piezoelectric constant e of the elastic wave resonator 10 using AlN is ３３ On the other hand, the longitudinal piezoelectric constant e of the elastic wave resonator 10 using lithium niobate or lithium tantalate is ３３ is sufficiently large, a wideband resonator can be obtained.

[0137] The configurations of the above-described embodiments can be combined as appropriate. The specific configurations and numerical values ​​of the embodiments (e.g., the lengths Wa1 and Wb1 of the upper electrode 31, the widths Wa2 and Wb2 of the frame electrode 33, the area S of each electrode, etc.) are merely examples and are not intended to be limiting.

[0138] (Second embodiment) Fig. 31 is a diagram showing the configuration of a communication device according to the second embodiment. The communication device 100 according to the second embodiment is, for example, a mobile terminal such as a mobile phone, a smartphone, or a tablet terminal, or a personal computer equipped with a communication function. Alternatively, the communication device 100 may be a backhaul communication device that performs communication between base stations and communication between a base station and a core network.

[0139] As shown in FIG. 31, the communication device 100 includes a high-frequency front-end circuit 101, an antenna 102, an RF-IC (Radio Frequency Integrated Circuit) 104, and a BB-IC (Baseband Integrated Circuit) 105.

[0140] The BB-IC 105 constitutes a baseband signal processing circuit and supplies a baseband signal to the RF-IC 104. The RF-IC 104 performs high-frequency signal processing of transmission and reception signals.

[0141] The high-frequency front-end circuit 101 is connected between the antenna 102 and the RF-IC 104. In the communication device 100, a high-frequency transmission signal is output from the high-frequency front-end circuit 101 to the antenna 102, and a high-frequency reception signal from the antenna 102 can be received by the high-frequency front-end circuit 101.

[0142] Specifically, the high-frequency front-end circuit 101 includes a switch SW, power amplifiers 111a and 111b, matching circuits 112a and 112b, transmit filters 113a and 113b, a multiplexer 114, matching circuits 115a and 115b, and low-noise amplifiers 116a and 116b.

[0143] When transmitting a high-frequency signal, the switch SW is switched to the side of the transmission filter 113a or the transmission filter 113b. The high-frequency transmission signal output from the RF-IC 104 is amplified by the power amplifier 111a or the power amplifier 111b, and input to the transmission filter 113a or the transmission filter 113b through the matching circuits 112a, 112b.

[0144] The band of the transmit filter 113a is, for example, n77 of the 5G NR (New Radio) standard. The frequency range of n77 of 5G NR is 3.3 GHz or higher and 4.2 GHz or lower. The band of the transmit filter 113b is, for example, n79 of the 5G NR standard. The frequency range of n79 of 5G NR is 4.4 GHz or higher and 5.0 GHz or lower.

[0145] The high frequency transmission signal that has passed through the transmission filter 113 a or 113 b is fed to the antenna 102 .

[0146] When receiving a high-frequency signal, the switch SW is switched to the side of the multiplexer 114. The multiplexer 114 includes receive filters 117a and 117b and a matching circuit 118. In the multiplexer 114, the input terminals of the plurality of receive filters 117a and 117b are electrically connected via the matching circuit 118. The band of the receive filter 117a is, for example, n77 of the 5G NR standard. The band of the receive filter 117b is, for example, n79 of the 5G NR standard.

[0147] A received signal from the antenna 102 passes through the receiving filter 117a or 117b via the matching circuit 118. The high-frequency received signal that has passed through the receiving filter 117a or 117b is transmitted to the RF-IC 104 via the matching circuits 115a, 115b and the low-noise amplifier 116a or 116b.

[0148] In the communication device 100 of this embodiment, at least one of the transmit filters 113a and 113b is the above-described acoustic wave filter 50. In addition, in the multiplexer 114, at least one of the receive filters 117a and 117b is the above-described acoustic wave filter 50. The high-frequency front-end circuit 101 includes the transmit filters 113a and 113b and at least one of the receive filters 117a and 117b of the multiplexer 114. In addition, the communication device 100 includes the high-frequency front-end circuit 101.

[0149] Note that the configuration of the communication device 100 shown in Figure 31 is merely a schematic diagram and can be modified as appropriate. Furthermore, the bands of the transmit filters 113a and 113b and the receive filters 117a and 117b are merely examples, and other communication standards can also be applied. The configuration of the multiplexer 114 is merely an example and can be modified as appropriate. For example, the output terminals of the multiple filters included in the multiplexer 114 may be electrically connected to each other depending on the device in which it is installed.

[0150] The above-described embodiment is intended to facilitate understanding of the present invention, and is not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the present invention, and equivalents thereof are also included in the present invention.

[0151] The present disclosure may also have the following configurations.

[0152] (1) An elastic wave filter including a plurality of elastic wave resonators utilizing bulk waves in a thickness extensional vibration mode, the elastic wave filter comprising: series arm resonators and parallel arm resonators configured using the elastic wave resonators, wherein the series arm resonators and the parallel arm resonators each have a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and lead-out wiring connected to at least one of the upper electrode and the lower electrode and facing each other in a first direction across the upper electrode and the lower electrode in a plan view, wherein when the ratio of a length (Wa1) of at least one of the upper electrode and the lower electrode in the first direction to a length (Wb1) of the series arm resonators in a second direction perpendicular to the first direction is defined as an aspect ratio (Wb1 / Wa1), the aspect ratio (Wb1 / Wa1) of the series arm resonators is greater than the aspect ratio (Wb1 / Wa1) of the parallel arm resonators. (2) The elastic wave filter according to (1), wherein the aspect ratio (Wb1 / Wa1) of the series arm resonator is 1.6 or greater. (3) The elastic wave filter according to (1) or (2), wherein the aspect ratio (Wb1 / Wa1) of the parallel arm resonator is 0.6 or greater and 1.8 or less. (4) The elastic wave filter according to any one of (1) to (3), wherein at least one of the upper electrode and the lower electrode of the parallel arm resonator has a circular or elliptical shape. (5) The elastic wave filter according to any one of (1) to (4), comprising an input terminal, an output terminal, a plurality of the series arm resonators connected between the input terminal and the output terminal, and a plurality of the parallel arm resonators, wherein the series arm resonator closest to the output terminal among the plurality of series arm resonators is configured by being divided in series, and the number of divisions of the series arm resonator is an even number. (6) The acoustic wave filter according to any one of (1) to (5), including an input terminal, an output terminal, a plurality of the series arm resonators connected between the input terminal and the output terminal, and a plurality of the parallel arm resonators, wherein the parallel arm resonator closest to the output terminal among the plurality of parallel arm resonators is configured by being divided in series, and the number of divisions of the parallel arm resonator is an even number.(7) The acoustic wave filter according to any one of (1) to (6), wherein a ratio (S / t) of an area (S) of an overlapping region of the upper electrode and the lower electrode to a film thickness (t) of the piezoelectric body is 2000 μm or more. (8) The acoustic wave filter according to any one of (1) to (7), wherein the piezoelectric body contains lithium niobate or lithium tantalate. (9) The acoustic wave filter according to any one of (1) to (7), wherein the piezoelectric body contains lithium niobate, and wherein Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric body are in the ranges of (φ, θ, ψ) = (0°, 107 to 140°, 0°). (10) The acoustic wave filter according to any one of (1) to (7), wherein the piezoelectric body includes lithium niobate, and the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric body are in the ranges of (φ, θ, ψ) = (0°, 123 to 139°, 0°). (11) The acoustic wave filter according to any one of (1) to (7), wherein the piezoelectric body includes lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium tantalate constituting the piezoelectric body are in the ranges of (φ, θ, ψ) = (0°, 101 to 134°, 0°). (12) The acoustic wave filter according to any one of (1) to (7), wherein the piezoelectric body includes lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium tantalate constituting the piezoelectric body are in the ranges of (φ, θ, ψ) = (0°, 123 to 134°, 0°). (13) A multiplexer having a plurality of filters including the acoustic wave filter according to any one of (1) to (12), wherein one of the input terminal and one of the output terminal of each of the plurality of filters are electrically connected to each other. (14) A high-frequency front-end circuit comprising the acoustic wave filter according to any one of (1) to (12). (15) A high-frequency front-end circuit comprising the multiplexer according to (13). (16) A communication device comprising the high-frequency front-end circuit according to (14) or (15).

[0153] REFERENCE SIGNS LIST 10, 10A Acoustic wave resonator 11 Support substrate 12 Intermediate layer 13 Support member 14, 14a, 14b Recess 20 Piezoelectric body 20a First main surface 20b Second main surface 31 Upper electrode 32 Lower electrode 33, 33A, 33B, 33C Frame electrode 33a, 33Ba, 33Ca First portion 33b, 33Bb, 33Cb Second portion 33Cc Third portion 34, 35 Lead wiring 50 Acoustic wave filter 51 Resonator chip 52 Module substrate 53, 54 Dielectric layer 55 Bump 56 Sealing resin 61, 61A, 62, 63, 64 Series arm resonator 65, 66, 67, 68 Parallel arm resonator 100 Communication device 101 High frequency front-end circuit Wa1, Wb1: Length Wa2, Wb2: Width

Claims

1. An elastic wave filter including a plurality of elastic wave resonators utilizing bulk waves in a thickness extensional vibration mode, comprising: series arm resonators and parallel arm resonators configured using the elastic wave resonators, each of the series arm resonators and the parallel arm resonators having a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and lead-out wiring connected to at least one of the upper electrode and the lower electrode and facing each other in a first direction across the upper electrode and the lower electrode in a plan view, wherein when the ratio of the length (Wa1) of at least one of the upper electrode and the lower electrode in the first direction to the length (Wb1) of the second direction perpendicular to the first direction is defined as an aspect ratio (Wb1 / Wa1), the aspect ratio (Wb1 / Wa1) of the series arm resonators is greater than the aspect ratio (Wb1 / Wa1) of the parallel arm resonators.

2. The acoustic wave filter according to claim 1, wherein the aspect ratio (Wb1 / Wa1) of the series arm resonator is 1.6 or greater.

3. The acoustic wave filter according to claim 1 or 2, wherein the aspect ratio (Wb1 / Wa1) of the parallel arm resonator is 0.6 or more and 1.8 or less.

4. The acoustic wave filter according to claim 1, wherein at least one of the upper electrode and the lower electrode of the parallel arm resonator has a circular or elliptical shape.

5. The acoustic wave filter according to any one of claims 1 to 4, comprising an input terminal, an output terminal, a plurality of the series arm resonators connected between the input terminal and the output terminal, and a plurality of the parallel arm resonators, wherein the series arm resonator closest to the output terminal among the plurality of series arm resonators is configured by being divided in series, and the number of divisions of the series arm resonator is an even number.

6. An acoustic wave filter according to any one of claims 1 to 5, comprising an input terminal, an output terminal, a plurality of the series arm resonators connected between the input terminal and the output terminal, and a plurality of the parallel arm resonators, wherein the parallel arm resonator closest to the output terminal among the plurality of parallel arm resonators is configured by being divided in series, and the number of divisions of the parallel arm resonator is an even number.

7. The acoustic wave filter according to any one of claims 1 to 6, wherein the ratio (S / t) of the area (S) of the region where the upper electrode and the lower electrode overlap to the film thickness (t) of the piezoelectric body is 2000 μm or more.

8. The acoustic wave filter according to any one of claims 1 to 7, wherein the piezoelectric element includes lithium niobate or lithium tantalate.

9. The acoustic wave filter according to any one of claims 1 to 7, wherein the piezoelectric body contains lithium niobate, and the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric body are in the range of (φ, θ, ψ) = (0°, 107 to 140°, 0°).

10. The acoustic wave filter according to any one of claims 1 to 7, wherein the piezoelectric body contains lithium niobate, and the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric body are in the range of (φ, θ, ψ) = (0°, 123 to 139°, 0°).

11. The acoustic wave filter according to any one of claims 1 to 7, wherein the piezoelectric element contains lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium tantalate constituting the piezoelectric element are in the range of (φ, θ, ψ) = (0°, 101 to 134°, 0°).

12. The acoustic wave filter according to any one of claims 1 to 7, wherein the piezoelectric element contains lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium tantalate constituting the piezoelectric element are in the range of (φ, θ, ψ) = (0°, 123 to 134°, 0°).

13. A multiplexer comprising a plurality of filters, each including an acoustic wave filter according to any one of claims 1 to 12, wherein one of the input terminals and one of the output terminals of each of the plurality of filters are electrically connected to each other.

14. A high-frequency front-end circuit comprising an acoustic wave filter according to any one of claims 1 to 12.

15. A high frequency front-end circuit comprising the multiplexer according to claim 13.

16. A communication device comprising the high-frequency front-end circuit according to claim 14 or 15.

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