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

Abstract

This elastic wave filter comprises a plurality of elastic wave resonators that use bulk waves, wherein: each of the plurality of elastic wave resonators includes a piezoelectric body, an upper electrode that is provided above the piezoelectric body, a lower electrode that is provided below the piezoelectric body, and a frame electrode that is provided in a frame shape along the outer periphery of at least one of the upper electrode and the lower electrode; among the plurality of elastic wave resonators, the frame electrode of at least one elastic wave resonator includes a plurality of first portions and a plurality of second portions that have a width or a height greater than that of the plurality of first portions; and the plurality of first portions and the plurality of second portions are alternately arranged in a direction extending along the outer periphery.

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 (called a piezoelectric thin film device in Patent Document 1) in which weighted portions having a larger mass per unit area than the central portion are provided along the long sides of an upper electrode.

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

[0004] There is a demand for improved filter characteristics in an acoustic wave filter configured using a plurality of acoustic wave resonators each having a frame electrode (weighted portion in Patent Document 1) provided along the outer periphery of the electrode.

[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 elastic wave filter according to one embodiment is an elastic wave filter including a plurality of elastic wave resonators that utilize bulk waves, each of the plurality of elastic wave resonators having a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and a frame electrode provided in a frame shape along the outer periphery of at least one of the upper electrode and the lower electrode, and the frame electrode of at least one of the plurality of elastic wave resonators includes a plurality of first portions and a plurality of second portions having a width or height greater than that of the plurality of first portions, and the plurality of first portions and the plurality of second portions are arranged alternately in a direction along the outer periphery.

[0007] An elastic wave filter according to one embodiment is an elastic wave filter including a plurality of elastic wave resonators that utilize bulk waves, each of the plurality of elastic wave resonators having a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and a frame electrode for adding mass that is provided along the outer periphery of at least one of the upper electrode and the lower electrode, and the frame electrode of an elastic wave resonator among the plurality of elastic wave resonators that has a resonant frequency higher than the frequency of the low-end of the pass band includes a plurality of first portions and a plurality of second portions having a width or height greater than the first portions, and the plurality of first portions and the plurality of second portions are arranged alternately in a direction along the outer periphery.

[0008] 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.

[0009] A high-frequency front-end circuit according to one aspect includes the acoustic wave filter described above.

[0010] A high-frequency front-end circuit according to one embodiment includes the above multiplexer.

[0011] A communication device according to one aspect includes the above-described high-frequency front-end circuit.

[0012] 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.

[0013] 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 schematically 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 an enlarged portion of the upper electrode and frame electrode illustrated in FIG. 9. FIG. 11 is a plan view illustrating the configuration of an upper electrode and a frame electrode according to a first modified example. FIG. 12 is a plan view illustrating the configuration of an upper electrode and a frame electrode according to a second modified example. FIG. 13 is a plan view showing the configuration of an upper electrode and a frame electrode according to a third modified example. FIG. 14 is a cross-sectional view showing the configuration of an upper electrode and a frame electrode according to a fourth modified example. FIG. 15 is a plan view showing the configuration of a series arm resonator according to a fifth modified example. FIG. 16 is a plan view showing the configuration of an upper electrode and a frame electrode according to a sixth modified example. FIG. 17 is a cross-sectional view taken along line XVII-XVII′ of FIG. 16 . FIG. 18 is a graph showing the filter characteristics of the elastic wave filter according to Example 1-1. FIG. 19 is a graph showing the relationship between impedance and frequency of a series arm resonator included in the elastic wave filter according to Example 1-1. FIG. 20 is a graph showing the relationship between impedance and frequency of a parallel arm resonator included in the elastic wave filter according to Example 1-1. FIG. 21 is a graph showing the relationship between the real part of the impedance and frequency of a series arm resonator included in the elastic wave filter according to Example 1-1. FIG. 22 is a graph showing the relationship between the real part of the impedance and frequency of a parallel arm resonator included in the elastic wave filter according to Example 1-1. Fig. 23 is a graph showing the filter characteristics of the acoustic wave filters according to Examples 1-1 and 1-2 and Comparative Example 1. Fig. 24 is a graph showing an enlarged view of the vicinity of the band indicated by arrow A1 in Fig. 23 .FIG. 25 is a graph showing the filter characteristics of the elastic wave filters according to Examples 1-3 and Comparative Example 1, enlarging the vicinity of the pass band. FIG. 26 is a graph showing the filter characteristics of the elastic wave filters according to Examples 1-4 and Comparative Example 1, enlarging the vicinity of the pass band. FIG. 27 is a plan view showing the configuration of an elastic wave resonator according to Example 2. FIG. 28 is a graph showing the relationship between impedance and frequency for the elastic wave resonators according to Examples 2-1 and 2-2. FIG. 29 is a graph showing the relationship between the real part of the impedance and frequency for the elastic wave resonators according to Examples 2-1 and 2-2. FIG. 30 is a graph showing the relationship between impedance and frequency for the elastic wave resonator according to Example 3. FIG. 31 is a graph showing the relationship between the real part of the impedance and frequency for the elastic wave resonator according to Example 3. FIG. 32 is a graph showing the relationship between the real part of the impedance and the width ratio of the frame electrode for the elastic wave resonator according to Example 3. FIG. 33 is a graph showing the relationship between the Q value and the width ratio of the frame electrode for the elastic wave resonator according to Example 3. FIG. 34 is a graph showing the relationship between the real part of the impedance and the ratio of the length of the frame electrode for the elastic wave resonator according to Example 4. FIG. 35 is a graph showing the relationship between the Q factor and the ratio of the length of the frame electrode for the elastic wave resonator according to Example 4. FIG. 36 is a graph showing the relationship between the impedance and the frequency for the elastic wave resonators according to Examples 5 and 4-5. FIG. 37 is a graph showing the relationship between the real part of the impedance and the frequency for the elastic wave resonators according to Examples 5 and 4-5. FIG. 38 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 6-1. FIG. 39 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 6-2. FIG. 40 is a diagram showing the configuration of a communication device according to a second embodiment.

[0014] 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.

[0015] First Embodiment FIG. 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, and 67, and inductors 68A and 68B. At least one of the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, and 67 is a resonator that utilizes bulk waves in a thickness extensional vibration mode, i.e., a bulk acoustic wave (BAW) element. However, the present invention is not limited thereto, and at least one of the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, and 67 may be a resonator that utilizes bulk waves in a shear vibration mode.

[0016] 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, and 67 are connected in parallel between the signal path between the input terminal 60A and the output terminal 60B and grounds 69A, 69B, and 69C. The acoustic wave filter 50 according to the first embodiment is a so-called ladder filter.

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

[0018] The inductor 68A is connected in series to a signal path connecting the parallel arm resonator 65 and ground 69A. The inductor 68B is connected in series to a signal path connecting the parallel arm resonator 66 and ground 69B.

[0019] The acoustic wave filter 50 may include capacitors or the like as impedance elements, without being limited to the inductors 68A and 68B. Furthermore, the impedance elements, such as the inductors 68A and 68B and the capacitors, are not limited to being connected to the parallel arm resonators 65, 66, and 67, but may be connected to the series arm resonators 61, 62, 63, and 64. Furthermore, the impedance elements, such as the inductors 68A and 68B 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] Each of the series arm resonators 61, 62, 63, and 64 is configured to have two resonators s1, s2, s3, and s4 divided in series. 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, and each of the series arm resonators 61, 62, 63, and 64 may have no divisions or three or more divisions.

[0021] Furthermore, each of the parallel arm resonators 65, 66, and 67 is configured to have two resonators p1, p2, and p3 divided in series. The number of divisions in each of the multiple parallel arm resonators 65, 66, and 67 is an even number. The number of divisions in each of the multiple parallel arm resonators 65, 66, and 67 is not limited to two, and may be zero or three 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, and 67 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, and 67 each having a plurality of resonators s1, s2, s3, s4, p1, p2, and p3 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, and 67 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, and 67, 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, and 67, and a plurality of terminals (an input terminal 60A, an output terminal 60B, and grounds 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 grounds 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, and 67, and the plurality of terminals (the input terminal 60A, the output terminal 60B, and the grounds 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 68A and 68B are formed on an inner layer of the module substrate 52. One end of the inductors 68A and 68B is electrically connected to the front surface side of the module substrate 52 through the connection pad 57 and the via 58A (see FIG. 4), respectively, and the other end is electrically connected to the back surface side of the module substrate 52 through the 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. 40) 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 schematically illustrating the configuration of the 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 each 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 each 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, and 67 (the multiple resonators s1, s2, s3, s4, p1, p2, and p3), they will be simply referred to as acoustic wave resonators 10. The cross-sectional structures of the other resonators are similar to that of the series arm resonator 61 shown in Fig. 8, and the description of the cross-sectional structure of the series arm resonator 61 in Fig. 8 can also be applied to 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, and 67 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 67 closest to the output terminal 60B among the multiple parallel arm resonators 65, 66, and 67 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, and 67 are divided in series, so that 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, and 67 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, 64 and the plurality of parallel arm resonators 65, 66, 67 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 two resonators s4 split in series. Alternatively, at least the parallel arm resonator 67 located closest to the output terminal 60B among the plurality of resonators has two resonators p3 split in series. This makes it possible to suppress the second 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 configuration of the upper electrode 31 and the frame electrode 33 will be described with reference to Fig. 8 to Fig. 10. Fig. 9 is a plan view showing the configuration of the upper electrode and the frame electrode. Fig. 10 is a plan view showing an enlarged portion of the upper electrode and the frame electrode shown in Fig. 9. Figs. 9 and 10 describe the configuration of one acoustic wave resonator 10.

[0057] 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 short sides extending in the X direction and long sides extending in the Y direction.

[0058] In this embodiment, the outer shape of the upper electrode 31 is defined by the frame electrode 33. That is, the length Wx1 of the upper electrode 31 in the X direction is equal to the maximum length of the frame electrode 33 in the X direction. More specifically, the length Wx1 of the upper electrode 31 in the X direction is equal to the maximum length in the X direction between the outer edges of two adjacent long sides of the frame electrode 33. Furthermore, the length Wy1 of the upper electrode 31 in the Y direction is equal to the maximum length in the Y direction of the frame electrode 33. More specifically, the length Wy1 of the upper electrode 31 in the Y direction is equal to the maximum length in the Y direction between the outer edges of two adjacent short sides of the frame electrode 33.

[0059] As shown in Figures 9 and 10, the frame electrode 33 includes multiple first portions 33a and multiple second portions 33b each having a width greater than that of the first portions 33a. The multiple first portions 33a and the multiple second portions 33b are alternately arranged in a direction along the outer periphery of the upper electrode 31. The multiple second portions 33b are provided so as to protrude more toward the inner periphery of the frame electrode 33 than the multiple first portions 33a. This allows the frame electrode 33 to have an uneven shape along the inner periphery of the frame electrode 33 in the planar direction. The outer periphery of the frame electrode 33 does not have an uneven shape in the planar direction but is formed linearly. The second portions 33b of the frame electrode 33 are not provided at corners where the long and short sides of the frame electrode 33 are connected. In other words, the corners of the frame electrode 33 are formed by connecting the first portions 33a of the long sides and the first portions 33a of the short sides.

[0060] 10 , on the long sides of the frame electrode 33, the first portion 33a has a first width FWx1 in the X direction perpendicular to the extension direction of the frame electrode 33. The second portion 33b has a second width FWx2 in the X direction that is larger than the first width FWx1. On the short sides of the frame electrode 33, the first portion 33a has a first width FWy1 in the Y direction perpendicular to the extension direction of the frame electrode 33. The second portion 33b has a second width FWy2 in the Y direction that is larger than the first width FWy1. The first widths FWx1 and FWy1 are each the length between the outer edge and the inner edge of the first portion 33a in the direction perpendicular to the extension direction of the frame electrode 33. The second widths FWx2 and FWy2 are the lengths between the outer and inner edges of the second portion 33b in a direction perpendicular to the extension direction of the frame electrode 33.

[0061] In this embodiment, the first width FWx1 of the first portion 33a on the long side of the frame electrode 33 is equal to the first width FWy1 of the first portion 33a on the short side of the frame electrode 33. In addition, the second width FWx2 of the second portion 33b on the long side of the frame electrode 33 is equal to the second width FWy2 of the second portion 33b on the short side of the frame electrode 33.

[0062] In the following description, when it is not necessary to distinguish between the first width FWx1 and the first width FWy1 of the first portion 33a, they will simply be referred to as the first width FW1. Furthermore, when it is not necessary to distinguish between the second width FWx2 and the second width FWy2 of the second portion 33b, they will simply be referred to as the second width FW2.

[0063] Furthermore, the first portion 33a has a first length FL1, and the second portion 33b has a second length FL2 in a direction parallel to the extension direction of the frame electrode 33. The first length FL1 of the first portion 33a on the long sides of the frame electrode 33 is equal to the first length FL1 of the first portion 33a on the short sides of the frame electrode 33. The second length FL2 of the second portion 33b on the long sides of the frame electrode 33 is equal to the second length FL2 of the second portion 33b on the short sides of the frame electrode 33.

[0064] In the elastic wave resonator 10, a standing wave mode (border ring mode (BRM)) standing in the frame electrode 33 may increase loss at a predetermined frequency. In this embodiment, the frame electrode 33 has a plurality of first portions 33a having a first width FW1 and a plurality of second portions 33b having a second width FW2. The frame electrode 33 has an uneven shape along the inner periphery of the frame electrode 33 in the planar direction, with the first portions 33a and the second width FW2 alternately arranged. Therefore, the standing wave mode influenced by the first portions 33a and the standing wave mode influenced by the second portions 33b are dispersed on the frequency axis, thereby suppressing loss at a predetermined frequency.

[0065] In the following description, the frame electrode 33 having the plurality of first portions 33 a and the plurality of second portions 33 b will be referred to as the "frame electrode 33 having an uneven shape in the planar direction." Additionally, the frame electrode 33 not having the plurality of first portions 33 a and the plurality of second portions 33 b will be referred to as the "frame electrode 33 having a constant width and not having an uneven shape."

[0066] 3 , in the acoustic wave filter 50 of this preferred embodiment, the frame electrodes 33 of the series arm resonators 61, 62, 63, and 64 are rectangular, have a plurality of first portions 33 a and a plurality of second portions 33 b, and have a concave-convex shape in the planar direction. The frame electrodes 33 of the parallel arm resonators 65, 66, and 67 are circular, do not have a plurality of first portions 33 a and a plurality of second portions 33 b, and have a constant width.

[0067] Detailed configuration examples of the frame electrodes 33 of the series arm resonators 61, 62, 63, and 64 and the frame electrodes 33 of the parallel arm resonators 65, 66, and 67, and the filter characteristics will be described later in Examples 1 to 5.

[0068] Although the present embodiment has been described with reference to a configuration in which the frame electrode 33 is provided on the upper electrode 31, the present invention is not limited to this. 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 descriptions of the shapes of the various parts of the frame electrode 33 in FIGS. 9 and 10 also apply 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 FIGS. 7 and 8 ), the outer shape of the upper electrode 31 can be rephrased as the outer shape of the region where the upper electrode 31 and the lower electrode 32 overlap (excitation region). Furthermore, the frame electrode 33 is not limited to a configuration having an uneven shape along the inner periphery of the frame electrode 33 in the planar direction, and may have an uneven shape along the outer periphery of the frame electrode 33.

[0069] Furthermore, the phrase "arranged along the periphery" of the frame electrode 33 includes a configuration in which the frame electrode 33 is arranged in contact with the outer periphery of the upper electrode 31 or the lower electrode 32, and a configuration in which the frame electrode 33 is arranged slightly inward from and spaced a predetermined distance from the outer periphery of the upper electrode 31 or the lower electrode 32. More specifically, for example, when the area of ​​the lower electrode 32 is smaller than that of the upper electrode 31 (see FIG. 14 ), the frame electrode 33 needs to be arranged along the periphery of the lower electrode 32. Alternatively, when the area of ​​the lower electrode 32 is smaller than that of the upper electrode 31 and the frame electrode 33 is arranged on the upper electrode 31, the frame electrode 33 needs to be arranged along the portion of the upper electrode 31 that overlaps the periphery of the lower electrode 32.

[0070] 9, for ease of understanding, the frame electrode 33 has been described as having a rectangular shape, i.e., the outer shape of the upper electrode 31 is rectangular. However, this is not limiting, and the frame electrode 33 and the upper electrode 31 may have other shapes.

[0071] 11 is a plan view showing the configuration of the upper electrode and frame electrode according to the first modified example. As shown in FIG. 11, the upper electrode 31 and frame electrode 33A according to the first modified example 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 Y direction. That is, the length Wx1 of the upper electrode 31 is defined by the maximum length of the elliptical shape in the X direction. Furthermore, the length Wy1 of the upper electrode 31 is defined by the maximum length of the elliptical shape in the Y direction.

[0072] In this modification, the frame electrode 33A also has a plurality of first portions 33Aa and a plurality of second portions 33Ab. The plurality of first portions 33Aa and the plurality of second portions 33Ab are alternately arranged along the outer periphery of the upper electrode 31. As a result, the frame electrode 33A has an uneven shape along the inner periphery of the frame electrode 33A in the planar direction. The definitions of the first width FW1 of the first portions 33Aa and the second width FW2 of the plurality of second portions 33Ab of the frame electrode 33A in the second modification are the same as those in the first embodiment described above.

[0073] FIG. 12 is a plan view showing the configuration of the upper electrode and frame electrode according to the second modification. As shown in FIG. 12, the upper electrode 31 and frame electrode 33B according to the second modification are rectangular with arc-shaped corners. In other words, the portions along the long sides of the frame electrode 33B are smoothly connected to the portions along the short sides in an arc-like manner. Alternatively, the upper electrode 31 and frame electrode 33B may be oval. The definitions of the lengths Wx1 and Wy1 of the upper electrode 31, the first width FW1 of the first portion 33Ba of the frame electrode 33B, and the second width FW2 of the multiple second portions 33Bb in the second modification are the same as those in the first embodiment. Furthermore, the second portions 33Bb of the frame electrode 33B are not provided at the arc-shaped corners of the frame electrode 33. In other words, the corners of the frame electrode 33 are formed by the first portions 33Ba being curved in an arc-shaped manner.

[0074] FIG. 13 is a plan view showing the configuration of the upper electrode and frame electrode according to the third modified example. As shown in FIG. 13, the upper electrode 31 and frame electrode 33C according to the third modified example are polygonal. The first side 33Cs1, second side 33Cs2, and third side 33Cs3 of the frame electrode 33C extend in directions inclined at angles relative to the X and Y directions, respectively. In this modified example, the length Wx1 of the upper electrode 31 is also the maximum length of the frame electrode 33C in the X direction. Furthermore, the length Wy1 of the upper electrode 31 is also the maximum length of the frame electrode 33C in the Y direction.

[0075] In the third modification, each of the first side 33Cs1, the second side 33Cs2, and the third side 33Cs3 has a plurality of first portions 33Ca and a plurality of second portions 33Cb. This allows the frame electrode 33C to have an uneven shape along the inner periphery of the frame electrode 33C in the planar direction. Also in this modification, the second portions 33Cb of the frame electrode 33C are not provided at corners (connections between the first side 33Cs1, the second side 33Cs2, and the third side 33Cs3).

[0076] 14 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. 14, 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 Wy1 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 Wy1. In other words, the length Wy1 of the upper electrode 31 is the length in the Y direction of the portion of the upper electrode 31 that contacts the piezoelectric body 20 and is provided with the frame electrode 33.

[0077] The first width FW1 of the first portion 33a of the frame electrode 33 is also defined by a portion of the frame electrode 33 that overlaps the region where the upper electrode 31 and the piezoelectric body 20 are in contact (a portion where the piezoelectric body 20, the upper electrode 31, and the frame electrode 33 are laminated in this order). A portion of the frame electrode 33 that overlaps the region where the upper electrode 31 and the piezoelectric body 20 are separated (a portion where the piezoelectric body 20, the insulating layer 22, the upper electrode 31, and the frame electrode 33 are laminated in this order) is not included in the first width FW1. In other words, the first width FW1 of the first portion 33a of the frame electrode 33 is the length in the Y direction (a direction perpendicular to the extension direction of the frame electrode 33) 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.

[0078] 14 has described the length Wy1 of the upper electrode 31 in the Y direction and the first width FW1 of the frame electrode 33 in the Y direction, but the description in Fig. 14 can also be applied to the X direction. Also, while Fig. 14 has described the first width FW1 of the first portion 33a of the frame electrode 33, the same applies to the second width FW2 of the second portion 33b.

[0079] Fig. 15 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. 15, 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.

[0080] 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. 15 ) 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. 15 ) is arranged to overlap the other recess 14b. The lower electrode 32 is provided continuously across the two recesses 14a, 14b.

[0081] 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.

[0082] Fig. 16 is a plan view showing the configuration of the upper electrode and frame electrode according to the sixth modified example. Fig. 17 is a cross-sectional view taken along line XVII-XVII' in Fig. 16. In the first embodiment and each modified example described above, the frame electrode 33 has an uneven shape along the inner periphery of the frame electrode 33 in the planar direction, but the present invention is not limited to this.

[0083] 16 and 17 , a frame electrode 33D according to the sixth modification has a plurality of first portions 33Da and a plurality of second portions 33Db that are higher than the first portions 33Da. The first portions 33Da and the second portions 33Db have the same width in a plan view and are alternately arranged along the extension direction of the frame electrode 33D.

[0084] As shown in FIG. 17 , the second height FH2 of each of the second portions 33Db is greater than the first height FH1 of each of the first portions 33Da. This configuration allows the frame electrode 33D to have an uneven shape in the Z direction. The first height FH1 is the length between the bottom surface (the surface in contact with the upper electrode 31) and the top surface (the surface opposite the upper electrode 31) of each of the first portions 33Da in the Z direction (the direction perpendicular to the first main surface 20a of the piezoelectric body 20). The second height FH2 is the length between the bottom surface (the surface in contact with the upper electrode 31) and the top surface (the surface opposite the upper electrode 31) of each of the second portions 33Db in the Z direction (the direction perpendicular to the first main surface 20a of the piezoelectric body 20).

[0085] In the sixth modification, the first portions 33Da and the second portions 33Db of the frame electrode 33D have different masses per unit area, so that, similar to the first embodiment described above, the standing wave mode influenced by the first portions 33Da and the standing wave mode influenced by the second portions 33Db are dispersed along the frequency axis, thereby suppressing loss at a predetermined frequency.

[0086] Next, a description will be given of filter characteristics when the configuration of the frame electrodes 33 of the series arm resonators 61, 62, 63, and 64 is changed from the configuration of the frame electrodes 33 of the parallel arm resonators 65, 66, and 67. Furthermore, a description will be given of resonator characteristics when the shapes of the first width FW1, second width FW2, etc. of the frame electrodes 33 of the elastic wave resonators 10 constituting the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, and 67 are changed.

[0087] 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°).

[0088] 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 / 20.6 to 58.2 nm / 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 / 20.59 to 58.21 nm / 14 / 100 / 4 nm, respectively.

[0089] 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.

[0090] 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).

[0091] Furthermore, in Tables 1 to 4 and FIGS. 18 to 39 of each embodiment described below, variations in filter characteristics and variations in resonator characteristics caused by variations in processing during the manufacturing process are included.

[0092] In Examples 1-1 and 1-2 and Comparative Example 1, filter characteristics will be described when the frame electrodes 33 of at least the series arm resonators 61, 62, 63, and 64 among the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, and 67 have an uneven shape in the planar direction.

[0093] First, the filter characteristics of the elastic wave filter 50 according to Example 1-1 and the resonator characteristics of each elastic wave resonator 10 constituting the elastic wave filter 50 will be described. FIG. 18 is a graph showing the filter characteristics of the elastic wave filter according to Example 1-1. FIG. 19 is a graph showing the relationship between impedance and frequency of a series arm resonator included in the elastic wave filter according to Example 1-1. FIG. 20 is a graph showing the relationship between impedance and frequency of a parallel arm resonator included in the elastic wave filter according to Example 1-1. FIG. 21 is a graph showing the relationship between the real part of the impedance and frequency of a series arm resonator included in the elastic wave filter according to Example 1-1. FIG. 22 is a graph showing the relationship between the real part of the impedance and frequency of a parallel arm resonator included in the elastic wave filter according to Example 1-1. Table 1 shows an example configuration of each resonator in the elastic wave filter according to Example 1.

[0094] In Example 1-1, the frame electrodes 33 of the series arm resonators 61, 62, 63, and 64 are rectangular with concave and convex shapes in the planar direction, and the frame electrodes 33 of the parallel arm resonators 65, 66, and 67 are circular with no concave and convex shapes (see FIG. 2).

[0095]

[0096] As shown in Table 1, in the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4), the first width FW1 (FWx1, FWy1) of the first portion 33a of the frame electrode 33 is 1.2 μm, and the second width FW2 (FWx2, FWy2) of the second portion 33b is 1.4 μm. That is, in the frame electrode 33 of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4), the second width FW2 of the second portion 33b is larger than the first width FW1 of the first portion 33a.

[0097] The width ratio RW shown in Table 1 is the ratio of the difference between the first width FW1 and the second width FW2 to the first width FW1, and is expressed by the following formula (1): RW=((FW2-FW1) / FW1)×100% (1)

[0098] In each of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4), the width ratio RW of the frame electrode 33 is 16.67%.

[0099] The length ratio RL shown in Table 1 is the ratio of the length along the periphery of the frame electrode 33 (i.e., the length of the entire circumference of the frame electrode 33) to the sum of the second lengths FL2 of the multiple second portions 33b in the direction along the periphery. When the frame electrode 33 is rectangular, the periphery length of the frame electrode 33 is (Wx1 + Wy1) ​​× 2. Furthermore, when the total number of second portions 33b is n, the sum of the second lengths FL2 is FL2 × n. In Example 1, the length ratio RL is expressed by the following formula (2). Note that the length along the periphery of the frame electrode 33 in formula (2) (Wx1 + Wy1) ​​× 2 is an example for a rectangular shape, and a different value is used depending on the shape of the frame electrode 33. RL = (FL2 × n) / ((Wx1 + Wy1) ​​× 2) × 100% (2)

[0100] In each of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4), the length ratio RL of the frame electrode 33 is 58.0.

[0101] In contrast, in the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3), the first width FW1 (FWx1, FWy1) and the second width FW2 (FWx2, FWy2) of the frame electrode 33 are both 1.2 μm. That is, in the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3), the second width FW2 of the frame electrode 33 is equal to the first width FW1, and the frame electrode 33 does not have an uneven shape. Furthermore, in the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3), the width ratio RW and length ratio RL of the frame electrode 33 are both zero.

[0102] The lengths Wx1, Wy1 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 Wx1, Wy1 and areas S of the upper electrodes 31 of the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3) are different from one another.

[0103] The material of the upper electrode 31, the lower electrode 32, and the frame electrode 33 is the same for the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) and the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3). 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, and 67 (resonators p1, p2, and p3). Furthermore, the Pt film thickness of the series arm resonators 61 and 64 (resonators s1 and s4) on the input terminal 60A side and the output terminal 60B side is thinner than the Pt film thickness of the series arm resonators 62 and 63 (resonators s2 and s3). The thickness of the Pt of the parallel arm resonators 65 and 67 (resonators p1 and p3) on the input terminal 60A side and the output terminal 60B side is thicker than the thickness of the Pt of the parallel arm resonator 66 (resonator p2).

[0104] As shown in FIG. 18, the acoustic wave filter 50 in accordance with Example 1-1 has a loss of 2.0 dB or less in the band indicated by the arrow A1 (n77 band: 3300 MHz or more and 4200 MHz or less).

[0105] The acoustic wave filter 50 according to Example 1-1 achieves an attenuation of 15 dB or more in the band indicated by arrow A2 (LTE band: 2690 MHz or less). The acoustic wave filter 50 according to Example 1-1 achieves an attenuation of 38 dB or more in the band indicated by arrow A3 (n79 band: 4400 MHz or more and 5000 MHz or less). The acoustic wave filter 50 according to Example 1-1 achieves an attenuation of 22 dB or more in the band indicated by arrow A4 (WiFi7 band: 5150 MHz or more and 7125 MHz or less).

[0106] As described above, it has been shown that the acoustic wave filter 50 in accordance with Example 1-1 has excellent filter characteristics.

[0107] 19 , the impedance of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) of the acoustic wave filter 50 varies depending on the area S of the upper electrode 31. The resonance frequencies fr of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) are higher than the low-frequency end frequency of the pass band (see arrow A1 in FIG. 18 ) of the acoustic wave filter 50. The resonance frequencies fr of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) are located within the pass band, and the anti-resonance frequencies fa are located in the attenuation band higher than the pass band.

[0108] 20 , the resonant frequencies fr of the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3) of the acoustic wave filter 50 are lower than the frequency at the low end of the pass band (see arrow A1 in FIG. 18 ) of the acoustic wave filter 50. That is, the antiresonant frequencies fa of the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3) are located within the pass band, and the resonant frequencies fr are located in an attenuation band lower than the pass band.

[0109] As shown in Fig. 21, the boundary ring mode occurs at a frequency of approximately 3500 MHz in the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4). Also, as shown in Fig. 22, the boundary ring mode occurs at a frequency of approximately 2600 MHz in the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3). Comparing the real parts of the impedance at the boundary ring mode occurrence frequencies of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) and the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3), the real part of the impedance of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) having the frame electrode 33 with a concave-convex shape is smaller.

[0110] In Example 1-1, among the multiple elastic wave resonators 10 included in the elastic wave filter 50, the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) having a resonance frequency fr higher than the frequency at the low end of the pass band include multiple first portions 33a and multiple second portions 33b, and are provided with a frame electrode 33 having an uneven shape in the planar direction. The results shown in Figures 21 and 22 indicate that in Example 1-1, the mode of a standing wave standing on the frame electrode 33 within the pass band is dispersed along the frequency axis, thereby suppressing loss within the pass band.

[0111] 21 and 22 , the real parts of the impedances of the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) at the anti-resonance frequency fa are larger than those of the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3). That is, the series arm resonators 61, 62, 63, and 64 (resonators s1, s2, s3, and s4) having frame electrodes 33 with unevenness in the planar direction leak more energy outside the frame electrodes 33 (outside the excitation region) than the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3) having frame electrodes 33 without unevenness, resulting in a lower Q at the anti-resonance frequency fa.

[0112] In other words, in Example 1-1, among the multiple elastic wave resonators 10 included in the elastic wave filter 50, the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3) whose anti-resonance frequency fa is located within the pass band include a frame electrode 33 that does not have a concave-convex shape. This improves the Q of the parallel arm resonators 65, 66, and 67 (resonators p1, p2, and p3) at the anti-resonance frequency fa. As a result, the elastic wave filter 50 can suppress loss in the pass band.

[0113] Fig. 23 is a graph showing the filter characteristics of the acoustic wave filters according to Examples 1-1 and 1-2 and Comparative Example 1. Fig. 24 is a graph showing an enlarged view of the vicinity of the band indicated by arrow A1 in Fig. 23. In the acoustic wave filter 50 according to Example 1-2 shown in Figs. 23 and 24, the frame electrodes 33 of all of the acoustic wave resonators 10 (i.e., the series arm resonators 61, 62, 63, and 64 and the parallel arm resonators 65, 66, and 67) have an uneven shape in the planar direction. In the acoustic wave filter according to Comparative Example 1, the frame electrodes of all of the acoustic wave resonators (i.e., all of the series arm resonators and parallel arm resonators) do not have an uneven shape but are formed with a constant width.

[0114] 23 and 24 , the acoustic wave filters 50 according to Examples 1-1 and 1-2 have smaller losses at the lower end of the pass band (the n77 band (3300 MHz) indicated by arrow A1) than Comparative Example 1. The acoustic wave filter according to Example 1-1 has even smaller losses than Example 1-2. Specifically, in the n77 band (3300 MHz), Example 1-1 exhibits a loss of 1.804 dB, Example 1-2 exhibits a loss of 1.908 dB, and Comparative Example 1 exhibits a loss of 2.035 dB.

[0115] The above results demonstrate that in the elastic wave resonator 10 (e.g., the series arm resonators 61, 62, 63, and 64) having a resonant frequency fr higher than the frequency at the low-frequency end of the pass band (see arrow A1 in FIGS. 18 and 23 ) of the elastic wave filter 50, by providing the frame electrode 33 having an uneven shape in the planar direction, it is possible to suppress loss at the low-frequency end of the pass band.

[0116] Furthermore, by using frame electrodes 33 having a concave-convex shape in the planar direction for the series arm resonators 61, 62, 63, and 64 and frame electrodes 33 having no concave-convex shape for the parallel arm resonators 65, 66, and 67, it was shown that loss at the low-frequency end of the pass band can be effectively suppressed in all of the elastic wave resonators 10 compared to the case where frame electrodes 33 having a constant width and no concave-convex shape in the planar direction are used.

[0117] In the above-described Example 1-1, all of the series arm resonators 61, 62, 63, and 64 use frame electrodes 33 having a concave-convex shape in the planar direction, and in the above-described Example 1-2, all of the elastic wave resonators 10 use frame electrodes 33 having a concave-convex shape in the planar direction, but this is not limitative. At least one of the elastic wave resonators 10 included in the elastic wave filter 50 may use a frame electrode 33 having a concave-convex shape in the planar direction.

[0118] Fig. 25 is a graph illustrating the filter characteristics of the acoustic wave filters according to Examples 1 to 3 and Comparative Example 1, with enlarged views of the vicinity of the pass band. Fig. 26 is a graph illustrating the filter characteristics of the acoustic wave filters according to Examples 1 to 4 and Comparative Example 1, with enlarged views of the vicinity of the pass band.

[0119] 25 , an elastic wave filter 50 according to Example 1-3 is provided with a frame electrode 33 having a concave-convex shape in a planar direction on the series arm resonator 62 (resonator s2, see FIG. 19 ), which has the highest impedance among the series arm resonators 61, 62, 63, and 64. The other series arm resonators 61, 63, and 64 and the parallel arm resonators 65, 66, and 67 are provided with frame electrodes 33 having a constant width and no concave-convex shape.

[0120] 26 , an acoustic wave filter 50 according to Example 1-4 is provided with a frame electrode 33 having a concave-convex shape in a planar direction on the series arm resonator 61 (resonator s1, see FIG. 19 ), which has the lowest impedance among the series arm resonators 61, 62, 63, and 64. The other series arm resonators 62, 63, and 64 and the parallel arm resonators 65, 66, and 67 are provided with frame electrodes 33 having a constant width and no concave-convex shape.

[0121] 25 and 26 , the acoustic wave filters 50 according to Examples 1-3 and 1-4 have smaller losses at the low-frequency end of the passband than Comparative Example 1. Specifically, in the n77 band (3300 MHz), Example 1-3 exhibits a loss of 1.922 dB, Example 1-4 exhibits a loss of 2.027 dB, and Comparative Example 1 exhibits a loss of 2.035 dB. This demonstrates that the acoustic wave filter 50 can reduce loss even when one of the series arm resonators 62 (or the series arm resonator 61) among the multiple acoustic wave resonators 10 is provided with a frame electrode 33 having an uneven shape in the planar direction.

[0122] Furthermore, a comparison between Examples 1-3 and 1-4 shows that using the frame electrode 33 having an uneven shape in the planar direction for the series arm resonator 62 (resonator s2), which has the highest impedance among the series arm resonators 61, 62, 63, and 64, is effective in reducing loss.

[0123] 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, and 67 when frame electrode 33 having a concave-convex shape in the planar direction is provided will be described.

[0124] Fig. 27 is a plan view showing the configuration of an elastic wave resonator in accordance with Example 2. Fig. 28 is a graph showing the relationship between impedance and frequency for the elastic wave resonators in accordance with Examples 2-1 and 2-2. Fig. 29 is a graph showing the relationship between the real part of impedance and frequency for the elastic wave resonators in accordance with Examples 2-1 and 2-2. Table 2 shows an example configuration of the elastic wave resonator in accordance with Example 2-1. Note that Figs. 28 and 29 include variations in resonator characteristics due to variations in processing during the manufacturing process.

[0125]

[0126] 27 and Table 2, the upper electrodes 31 of the elastic wave resonators 10 according to Examples 2-1 and 2-2 are both circular. The lengths Wx1, Wy1 and area S of the upper electrode 31 according to Example 2-1 are equal to the lengths Wx1, Wy1 and area S of the upper electrode 31 according to Example 2-2.

[0127] In the elastic wave resonator 10 in accordance with Example 2-1, the first width FW1 (FWx1, FWy1) of the first portion 33a of the frame electrode 33 is 1.20 μm. The second width FW2 (FWx2, FWy2) of the second portion 33b of the frame electrode 33 is 1.40 μm. The width ratio RW of each of the frame electrodes 33 is 16.67%, and the length ratio RL of each of the frame electrodes 33 is 58.0.

[0128] In the elastic wave resonator 10 in accordance with Example 2-2, the frame electrode 33 does not have an uneven shape. That is, in the elastic wave resonator 10 in accordance with Example 2-2, the second width FW2 of the frame electrode 33 is equal to the first width FW1, and the width ratio RW and length ratio RL of the frame electrode 33 are both zero.

[0129] 28, the impedances of the elastic wave resonators 10 according to Examples 2-1 and 2-2 are substantially the same. However, the elastic wave resonator 10 according to Example 2-1, which uses a frame electrode 33 having an uneven shape in the planar direction, has a smaller impedance near the anti-resonance frequency fa than that of Example 2-2, and the anti-resonance frequency fa is shifted to the higher frequency side.

[0130] 29 , the elastic wave resonator 10 according to Example 2-1 has a smaller real part of the impedance (resistance component) than Example 2-2 in a frequency band lower than the resonance frequency fr (approximately 0.8 fr to fr) where the boundary ring mode occurs. In particular, the real part of the impedance of Example 2-2 is larger than that of Example 2-1 in a band lower than the resonance frequency fr. Specifically, in Example 2-1, Re(Z) is 2.49Ω at a frequency of 0.8 fr, which is 0.8 times the resonance frequency fr (fr = 3903 MHz), and Re(Z) is 1.01Ω at a frequency of 0.9 fr, which is 0.9 times the resonance frequency fr. In Example 2-2, at a frequency of 0.8 fr that is 0.8 times the resonance frequency fr (fr=3903 MHz), Re(Z)=5.36Ω, and at a frequency of 0.9 fr that is 0.9 times the resonance frequency fr, Re(Z)=2.84Ω.

[0131] As described above, in Example 2-2, the frame electrode 33 having a constant width and no concave-convex shape is provided, so that standing waves existing in the planar direction are concentrated at a predetermined frequency, resulting in loss. In contrast, in Example 2-1, the frame electrode 33 having a concave-convex shape is provided, so that standing waves existing in the planar direction are dispersed on the frequency axis, thereby suppressing loss.

[0132] Furthermore, the Qa, which is the Q at the anti-resonance frequency fa, of the elastic wave resonator 10 in accordance with Example 2-1 is Qa=263. Furthermore, the Qc, which is the Q at the center frequency fc between the resonant frequency fr and the anti-resonant frequency fa, of the elastic wave resonator 10 in accordance with Example 2-1 is Qc=317. The Qa of the elastic wave resonator 10 in accordance with Example 2-2 is Qa=298. Furthermore, the Qc of the elastic wave resonator 10 in accordance with Example 2-2 is Qc=362.

[0133] The elastic wave resonator 10 according to Example 2-2 is provided with a frame electrode 33 that has a constant width and does not have a concave-convex shape, and therefore can confine energy better within the excitation region than Example 2-1, which is provided with a frame electrode 33 that has a concave-convex shape. As a result, the elastic wave resonator 10 according to Example 2-2, which is provided with a frame electrode 33 that does not have a concave-convex shape, has a larger Qa at the antiresonance frequency fa and a larger Qc at the center frequency fc than Example 2-1.

[0134] From the above results, it is preferable that, among the elastic wave resonators 10 constituting the elastic wave filter 50, the series arm resonators 61, 62, 63, and 64 are provided with frame electrodes 33 having a concave-convex shape in the planar direction, and the parallel arm resonators 65, 66, and 67 are provided with frame electrodes 33 having no concave-convex shape. This enables the elastic wave filter 50 to suppress loss below the pass band and improve Qa at the anti-resonance frequency fa.

[0135] Third Embodiment In a third embodiment, the resonator characteristics of elastic wave resonator 10 including series arm resonators 61, 62, 63, and 64 and parallel arm resonators 65, 66, and 67 will be described when the width ratio RW (see equation (1)) of frame electrode 33 is changed.

[0136] Fig. 30 is a graph showing the relationship between impedance and frequency for the elastic wave resonator in accordance with Example 3. Fig. 31 is a graph showing the relationship between the real part of impedance and frequency for the elastic wave resonator in accordance with Example 3. Fig. 32 is a graph showing the relationship between the real part of impedance and the width ratio of the frame electrode for the elastic wave resonator in accordance with Example 3. Fig. 33 is a graph showing the relationship between Q and the width ratio of the frame electrode for the elastic wave resonator in accordance with Example 3. Note that Figs. 30 to 33 include variations in resonator characteristics due to variations in processing during the manufacturing process.

[0137] Table 3 shows the first width FW1 (FWx1, FWy1), second width FW2 (FWx2, FWy2), width difference (FW2-FW1), width ratio RW, length ratio RL, real part of impedance Re(Z), and Qr, Qc, and Qa of the frame electrodes of the elastic wave resonator in accordance with Example 3. In Table 3, Qr represents Q at the resonant frequency fr.

[0138]

[0139] As shown in Table 3, elastic wave resonator 10 in accordance with Example 3-1 is provided with frame electrode 33 that does not have a concave-convex shape and has a constant width. That is, in Example 3-1, the first width FW1 and second width FW2 are both 1.20 μm, and the width ratio RW and length ratio RL are both 0.

[0140] In elastic wave resonators 10 according to Examples 3-2 to 3-7, the first width FW1 of the first portion 33a of the frame electrode 33 is constant at 1.20 μm, and the second width FW2 of the second portion 33b is varied from 1.25 μm to 2.00 μm. In Examples 3-2 to 3-7, the width ratio RW is varied from 4.2% to 66.7%, respectively. Furthermore, in Examples 3-2 to 3-7, the length ratio RL is constant at 64.5%.

[0141] In the graphs shown in FIGS. 30 and 31, in order to make the drawings easier to see, among Examples 3-1 to 3-7, Examples 3-1 and Examples 3-4 to 3-7 are shown.

[0142] 30 , the impedances of the elastic wave resonators 10 according to Examples 3-1 and 3-4 to 3-7 are substantially the same. However, the elastic wave resonators 10 according to Examples 3-4 to 3-7, which are provided with frame electrodes 33 having concave and convex shapes in the planar direction, have slightly smaller impedances near the antiresonance frequency fa than Example 3-1, and the antiresonance frequency fa is shifted to the higher frequency side.

[0143] As shown in Figure 31, in the band lower than the resonant frequency fr, Example 3-1, in which a frame electrode 33 without an uneven shape is provided, has a larger real part of the impedance than Examples 3-4 to 3-7, in which a frame electrode 33 with an uneven shape in the planar direction is provided.

[0144] 32, when the width ratio RW of the frame electrode 33 is changed, the real part Re(Z) of the impedance changes at frequencies lower than the resonant frequency fr (frequencies 0.7 fr and 0.9 fr). The real part Re(Z) of the impedance is at its minimum when the width ratio RW is 16.7% (Example 3-4). Furthermore, the real part Re(Z) of the impedance tends to increase when the width ratio RW is smaller than 16.7% or larger than 16.7%.

[0145] As shown in Figure 33, Qr at the resonant frequency fr remains almost constant even when the width ratio RW changes. Qc at the center frequency fc and Qa at the antiresonant frequency fa decrease as the width ratio RW increases. The slope (amount of change) of Qc and Qa increases in the range where the width ratio RW is 16.7% or less, and decreases in the range where the width ratio RW is 33.3% or more. That is, as shown in Figures 32 and 33, the real part of the impedance Re(Z) and Qc and Qa exhibit opposite trends when the width ratio RW is greater than 16.7%.

[0146] As shown in Fig. 32, when the width ratio R is in the range of 4.2% to 66.7%, the real part of the impedance Re(Z) at a frequency of 0.9 fr can be suppressed to 2Ω or less. Furthermore, as shown in Fig. 33, when the width ratio R is in the range of 50.0% or less, the Qc and Qa can be suppressed to be 0.8 times or more the Qc and Qa of Example 3-1, which used frame electrode 33 without a concave-convex shape. Therefore, as can be seen from Figs. 32 and 33, the width ratio R of frame electrode 33 of elastic wave resonator 10 is preferably in the range of 4.2% to 50%.

[0147] Fourth Embodiment In a fourth embodiment, the resonator characteristics of elastic wave resonator 10 including series arm resonators 61, 62, 63, and 64 and parallel arm resonators 65, 66, and 67 will be described when the length ratio RL (see equation (2)) of frame electrode 33 is changed.

[0148] Fig. 34 is a graph showing the relationship between the real part of the impedance and the ratio of the length of the frame electrode for the elastic wave resonator in accordance with Example 4. Fig. 35 is a graph showing the relationship between the Q value and the ratio of the length of the frame electrode for the elastic wave resonator in accordance with Example 4. Note that Figs. 34 and 35 include variations in the resonator characteristics due to variations in processing during the manufacturing process.

[0149] Table 4 shows the first width FW1 (FWx1, FWy1), second width FW2 (FWx2, FWy2), width difference (FW2-FW1), width ratio RW, length ratio RL, real part of impedance Re(Z), and Qr, Qc, and Qa of the frame electrodes of the elastic wave resonator according to Example 4.

[0150]

[0151] As shown in Table 4, in elastic wave resonators 10 according to Examples 4-1 to 4-8, the first width FW1 of frame electrode 33 is constant at 1.20 μm, and the second width FW2 is constant at 1.40 μm. That is, in Examples 4-1 to 4-8, the width difference (FW2-FW1) is constant at 0.20 μm, and the width ratio RW is constant at RW = 16.7%. In Examples 4-1 to 4-8, the length ratio RL is varied from 0.0% to 100%.

[0152] In Example 4-1, the length ratio RL is 0.0%, i.e., the frame electrode 33 has no concave-convex shape and a constant first width FW1 (=1.20 μm) along the outer periphery. In Example 4-8, the length ratio RL is 100.0%, i.e., the frame electrode 33 has no concave-convex shape and a constant second width FW2 (=1.40 μm) along the outer periphery.

[0153] 34 , when the length ratio RL of the frame electrode 33 is changed, the real part Re(Z) of the impedance changes at frequencies lower than the resonant frequency fr (frequencies 0.7 fr and 0.9 fr). The real part Re(Z) of the impedance is at its minimum when the length ratio RL is 64.5% (Example 4-5). Furthermore, the real part Re(Z) of the impedance tends to increase when the length ratio RL is smaller than 64.5% or larger than 64.5%.

[0154] When the length ratio RL is in the range of 20% to 85%, the real part of the impedance Re(Z) at a frequency of 0.9 fr can be suppressed to 2 Ω or less. Therefore, the length ratio RL of the frame electrode 33 of the elastic wave resonator 10 is preferably in the range of 20% to 85%.

[0155] As shown in Figure 35, Qr at the resonant frequency fr remains almost constant even when the length ratio RL changes. Qc at the center frequency fc and Qa at the antiresonant frequency fa decrease as the length ratio RL increases. That is, as shown in Figures 34 and 35, the real part of the impedance Re(Z), Qc, and Qa show opposite trends when the length ratio RL is greater than RL = 64.5%.

[0156] 35, when the length ratio RL is in the range of 65% or less, the Qc and Qa can be suppressed to be, for example, 0.8 times or more of the Qc and Qa of Example 4-1 in which frame electrode 33 having a constant width and no unevenness is provided. Therefore, as can be seen from FIGS. 34 and 35, it is more preferable that the length ratio RL of frame electrode 33 of elastic wave resonator 10 be 20% or more and 65% or less.

[0157] In the first embodiment and each example described above, the frame electrode 33 has two portions, the first portion 33 a and the second portion 33 b, which have different widths. However, the present invention is not limited to this. The frame electrode 33 may have three or more portions with different widths.

[0158] Fig. 36 is a graph showing the relationship between impedance and frequency for the elastic wave resonators according to Examples 5 and 4-5. Fig. 37 is a graph showing the relationship between the real part of impedance and frequency for the elastic wave resonators according to Examples 5 and 4-5.

[0159] In the elastic wave resonator 10 according to the fifth embodiment, the frame electrode 33 includes a first portion 33a having a first width FW1, a second portion 33b having a second width FW2, a third portion having a third width FW3, and a fourth portion having a fourth width FW4. The first width FW1 is 1.2 μm, the second width FW2 is 1.4 μm, the third width FW3 is 1.6 μm, and the fourth width FW4 is 1.8 μm. The length ratio RL is 64.5%.

[0160] In Example 5, the first portion 33a, the second portion 33b, the first portion 33a, the third portion, the first portion 33a, the fourth portion, the first portion 33a, the second portion 33b, the first portion 33a, the third portion, etc. are periodically repeated along the outer circumferential direction of the frame electrode 33.

[0161] 36 and 37 also show the resonator characteristics of the elastic wave resonator 10 according to Example 4-5 for comparison. In Example 4-5, the first width FW1 was 1.20 μm, the second width FW2 was 1.40 μm, the width ratio RW was 16.7%, and the length ratio RL was 64.5%.

[0162] As shown in FIG. 36, the acoustic wave resonator 10 in accordance with the fifth embodiment has impedance substantially equal to that of the fourth and fifth embodiments.

[0163] 37 , the real part of the impedance of the elastic wave resonator 10 according to Example 5 is smaller at a frequency lower than the resonance frequency fr than those of Examples 4-5. Specifically, the real part of the impedance of the elastic wave resonator 10 according to Example 5 at a frequency of 0.8 fr is 2.23Ω. The real part of the impedance of the elastic wave resonator 10 according to Examples 4-5 at a frequency of 0.8 fr is 2.49Ω.

[0164] In the fifth embodiment, an example in which multiple portions having different widths are periodically and repeatedly arranged has been described. However, this is not a limitation, and the multiple portions having different widths may be arranged in any manner. For example, the multiple portions having different widths may be periodically and repeatedly arranged along the circumferential direction of the frame electrode 33 in the order of first portion 33a, second portion 33b, third portion, fourth portion, first portion 33a, second portion 33b, third portion, etc. Alternatively, the multiple portions may be arranged such that the order of arrangement of the first portion 33a to fourth portion is random. Furthermore, the number of multiple portions having different widths is not limited to two or four, and may be three, five, or more.

[0165] Example 6 In Example 6, the fractional bandwidth ΔfR and the piezoelectric constant are described when the Euler angles of lithium niobate or lithium tantalate used in the piezoelectric body 20 are varied. Fig. 38 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 6-1. In the elastic wave resonator 10 in accordance with Example 6-1, lithium niobate was used as the piezoelectric body 20.

[0166] The fractional bandwidth ΔfR shown in FIG. 38 is expressed as ΔfR=(fa−fr) / fr, where fr is the resonant frequency of the elastic wave resonator 10, fa is the antiresonant frequency, and (fa−fr) is the frequency difference between the resonant frequency and the antiresonant frequency.

[0167] The horizontal axis of the graph shown in Fig. 38 represents the Euler angle θ of lithium niobate. As indicated by arrow B1 in Fig. 38, 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 6-1 can achieve a wide fractional bandwidth ΔfR of 10% or more.

[0168] 38 , 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 6-1 can reduce unwanted waves due to shear waves.

[0169] 39 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 6-2. In elastic wave resonator 10 according to Example 6-2, lithium tantalate was used for piezoelectric body 20.

[0170] The horizontal axis of the graph shown in Fig. 39 represents the Euler angle θ of the lithium tantalate. As indicated by arrow C1 in Fig. 39, 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 6-2 to have a wide fractional bandwidth ΔfR of 3% or more.

[0171] 39, it is preferable that the Euler angles (φ, θ, ψ) of the lithium tantalate 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 6-2 can reduce unwanted waves due to shear waves.

[0172] In Example 6-1, 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 6-2, 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 6-1 and 6-2, 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.

[0173] The configurations of the above-described embodiments can be combined as appropriate. The specific configurations and numerical values ​​of the embodiments (e.g., the shape of the upper electrode 31, the first width FW1 and second width FW2 of the frame electrode 33, the area S of each electrode, etc.) are merely examples and are not intended to be limiting.

[0174] (Second embodiment) Figure 40 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.

[0175] As shown in FIG. 40, a 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] The high frequency transmission signal that has passed through the transmission filter 113 a or 113 b is fed to the antenna 102 .

[0182] 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.

[0183] 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.

[0184] 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.

[0185] Note that the configuration of the communication device 100 shown in Figure 40 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.

[0186] 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.

[0187] The present disclosure may also have the following configurations.

[0188] (1) An elastic wave filter including a plurality of elastic wave resonators that utilize bulk waves, wherein each of the plurality of elastic wave resonators has a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and a frame electrode provided in a frame shape along an outer periphery of at least one of the upper electrode and the lower electrode, wherein the frame electrode of at least one elastic wave resonator among the plurality of elastic wave resonators includes a plurality of first portions and a plurality of second portions having a width or height greater than that of the plurality of first portions, and the plurality of first portions and the plurality of second portions are arranged alternately in a direction along the outer periphery. (2) The elastic wave filter according to (1), wherein an elastic wave resonator among the plurality of elastic wave resonators that has a resonant frequency higher than a frequency at the low end of a pass band has the frame electrode including the plurality of first portions and the plurality of second portions. (3) The elastic wave filter according to (1) or (2), including series arm resonators and parallel arm resonators configured using the elastic wave resonators, wherein the frame electrode of the series arm resonator includes the plurality of first portions and the plurality of second portions, and the frame electrode of the parallel arm resonator does not include the plurality of first portions or the plurality of second portions and has a constant width or a constant height along the outer periphery. (4) The elastic wave filter according to any one of (1) to (3), including a plurality of series arm resonators configured using the elastic wave resonators, and wherein the series arm resonator having the highest impedance among the plurality of series arm resonators has the frame electrode including the plurality of first portions and the plurality of second portions. (5) The elastic wave filter according to any one of (1) to (4), wherein in the frame electrode of the at least one elastic wave resonator, the plurality of first portions have a first width (FW1), and the plurality of second portions have a second width (FW2) larger than the first width, and when a ratio of a difference between the first width and the second width to the first width is defined as a width ratio (RW), the width ratio (RW) is expressed as RW = ((FW2 - FW1) / FW1) × 100%, and the width ratio (RW) is 4.2% or more and 50% or less.(6) The acoustic wave filter according to any one of (1) to (5), wherein, when a ratio of a total length of the frame electrode along the outer periphery to a total length of the plurality of second portions in a direction along the outer periphery is defined as a length ratio, the length ratio is 20% or more and 85% or less. (7) The acoustic wave filter according to any one of (1) to (6), further including a plurality of third portions having widths or heights larger than the plurality of second portions, wherein the plurality of first portions, the plurality of second portions, and the plurality of third portions are periodically arranged along the outer periphery. (8) The acoustic wave filter according to any one of (1) to (7), wherein, in the frame electrode of the at least one acoustic wave resonator, the plurality of first portions have a first width, the plurality of second portions have a second width larger than the first width, the plurality of second portions are provided to protrude toward an inner periphery of the frame electrode beyond the plurality of first portions, and the frame electrode has an uneven shape along the inner periphery of the frame electrode in a planar direction. (9) The acoustic wave filter according to any one of (1) to (8), wherein the piezoelectric body includes lithium niobate or lithium tantalate. (10) The acoustic wave filter according to any one of (1) to (8), wherein the piezoelectric body includes lithium niobate, and wherein the 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°). (11) The acoustic wave filter according to any one of (1) to (8), wherein the piezoelectric body includes lithium niobate, and wherein 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°). (12) The acoustic wave filter according to any one of (1) to (8), 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°). (13) The acoustic wave filter according to any one of (1) to (8), 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°).(14) An acoustic wave filter including a plurality of acoustic wave resonators that utilize bulk waves, wherein each of the plurality of acoustic wave resonators has a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and a frame electrode for adding mass that is provided along the outer periphery of at least one of the upper electrode and the lower electrode, wherein the frame electrode of an acoustic wave resonator among the plurality of acoustic wave resonators that has a resonant frequency higher than the frequency of the low-frequency end of a pass band includes a plurality of first portions and a plurality of second portions having a width or height larger than that of the first portions, and the plurality of first portions and the plurality of second portions are arranged alternately in a direction along the outer periphery. (15) An acoustic wave filter including a plurality of filters each including the acoustic wave filter according to any one of (1) to (14), wherein one of the input terminal and one of the output terminals of each of the plurality of filters are electrically connected to each other. (16) A high-frequency front-end circuit including the acoustic wave filter according to any one of (1) to (14). (17) A high-frequency front-end circuit comprising the multiplexer according to (15). (18) A communication device comprising the high-frequency front-end circuit according to (16) or (17).

[0189] REFERENCE SIGNS LIST 10 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, 33D Frame electrode 33a, 33Aa, 33Ba, 33Ca, 33Da First portion 33b, 33Ab, 33Bb, 33Cb, 33Db Second portion 34, 35 Lead wiring 50 Acoustic wave filter 51 Resonator chip 52 Module substrate 61, 61A, 62, 63, 64 Series arm resonator 65, 66, 67 Parallel arm resonator 100 Communication device 101 High frequency front end circuit Wx1, Wy1 Length FW1, FWx1, FWy1 First width FW2, FWx2, FWy2 Second width FH1 First height FH2 Second height FL1 First length FL2 Second length

Claims

1. An elastic wave filter including a plurality of elastic wave resonators that utilize bulk waves, wherein each of the plurality of elastic wave resonators has a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and a frame electrode provided in a frame shape along the outer periphery of at least one of the upper electrode and the lower electrode, wherein the frame electrode of at least one of the plurality of elastic wave resonators includes a plurality of first portions and a plurality of second portions having a width or height greater than that of the plurality of first portions, and the plurality of first portions and the plurality of second portions are arranged alternately in a direction along the outer periphery.

2. The acoustic wave filter according to claim 1, wherein, of the plurality of acoustic wave resonators, an acoustic wave resonator having a resonance frequency higher than the frequency at the low-frequency end of the pass band has the frame electrode including the plurality of first portions and the plurality of second portions.

3. The elastic wave filter according to claim 1 or 2, comprising a series arm resonator and a parallel arm resonator configured using the elastic wave resonators, wherein the frame electrode of the series arm resonator includes the plurality of first portions and the plurality of second portions, and the frame electrode of the parallel arm resonator does not include the plurality of first portions or the plurality of second portions, and has a constant width or a constant height along the outer periphery.

4. The acoustic wave filter according to any one of claims 1 to 3, comprising a plurality of series arm resonators configured using the acoustic wave resonators, wherein the series arm resonator having the highest impedance among the plurality of series arm resonators has the frame electrode including the plurality of first portions and the plurality of second portions.

5. The acoustic wave filter according to any one of claims 1 to 4, wherein in the frame electrode of the at least one acoustic wave resonator, the plurality of first portions have a first width (FW1), and the plurality of second portions have a second width (FW2) larger than the first width, and when a ratio of a difference between the first width and the second width to the first width is defined as a width ratio (RW), the width ratio (RW) is expressed as RW = ((FW2 - FW1) / FW1) × 100%, and the width ratio (RW) is 4.2% or more and 50% or less.

6. The acoustic wave filter according to any one of claims 1 to 5, wherein, when the ratio of the total length of the frame electrode along the outer periphery to the total length of the plurality of second portions in a direction along the outer periphery is defined as a length ratio, the length ratio is not less than 20% and not more than 85%.

7. The acoustic wave filter according to any one of claims 1 to 6, further comprising a plurality of third portions each having a width or height greater than the plurality of second portions, wherein the plurality of first portions, the plurality of second portions, and the plurality of third portions are periodically arranged along the outer periphery.

8. The elastic wave filter according to any one of claims 1 to 7, wherein in the frame electrode of the at least one elastic wave resonator, the plurality of first portions have a first width, the plurality of second portions have a second width greater than the first width, the plurality of second portions are provided so as to protrude further toward the inner periphery of the frame electrode than the plurality of first portions, and the frame electrode has an uneven shape along the inner periphery of the frame electrode in a planar direction.

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

10. The acoustic wave filter according to any one of claims 1 to 8, 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°).

11. The acoustic wave filter according to any one of claims 1 to 8, 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°).

12. The acoustic wave filter according to any one of claims 1 to 8, 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°).

13. The acoustic wave filter according to any one of claims 1 to 8, 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°).

14. An elastic wave filter including a plurality of elastic wave resonators that utilize bulk waves, wherein each of the plurality of elastic wave resonators has a piezoelectric body, an upper electrode provided on the piezoelectric body, a lower electrode provided below the piezoelectric body, and a frame electrode for adding mass that is provided along the outer periphery of at least one of the upper electrode and the lower electrode, wherein the frame electrode of an elastic wave resonator among the plurality of elastic wave resonators that has a resonance frequency higher than the frequency of the low-frequency end of the pass band includes a plurality of first portions and a plurality of second portions having a width or height larger than the first portions, and the plurality of first portions and the plurality of second portions are arranged alternately in a direction along the outer periphery.

15. A multiplexer comprising a plurality of filters, each including an acoustic wave filter according to any one of claims 1 to 14, 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.

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

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

18. A communication device comprising the high-frequency front-end circuit according to claim 16 or 17.

Images