Acoustic wave device and communication device

Abstract

To improve frequency characteristics in an acoustic wave device.SOLUTION: An acoustic wave device includes a series resonator having a first IDT electrode, a first reflector, and a second reflector, and a parallel resonator having a second IDT electrode, a third reflector, and a fourth reflector. The number of first strip electrodes in the first reflector is smaller than the number of third strip electrodes in the third reflector. A first virtual line connecting tips of first electrode fingers of the first IDT electrode is inclined at an angle of 6° or less with respect to the wave propagation direction of the first IDT electrode, and a second virtual line connecting tips of third electrode fingers of the second IDT electrode is inclined at an angle of 6° or less with respect to the wave propagation direction of the second IDT electrode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an acoustic wave device and the like. [Background technology]

[0002] BACKGROUND ART Conventionally, acoustic wave filters having acoustic wave resonators are known. Patent Document 1 describes a ladder-type filter having inclined IDT (Inter-Digital Transducer) electrodes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 019169 Summary of the Invention [Problem to be solved by the invention]

[0004] Acoustic wave devices are required to have improved frequency characteristics. [Means for solving the problem]

[0005] An elastic wave device according to one aspect of the present disclosure includes a piezoelectric body, a support substrate, a low acoustic velocity layer located between the piezoelectric body and the support substrate, a series resonator having a first IDT electrode located on the piezoelectric body, and a parallel resonator having a second IDT electrode located on the piezoelectric body, wherein the first IDT electrode includes a first bus bar, a second bus bar, a plurality of first electrode fingers, and a plurality of second electrode fingers interdigitated with the first electrode fingers, the series resonator further includes a first reflector having a plurality of first strip electrodes and a second reflector having a plurality of second strip electrodes, and the second IDT electrode includes a third bus bar, a fourth bus bar, and a plurality of the parallel resonator further comprises a third reflector having a plurality of third strip electrodes and a fourth reflector having a plurality of fourth strip electrodes, the number of the first strip electrodes being less than the number of the third strip electrodes, a first virtual line connecting the tips of the plurality of first electrode fingers being inclined at an angle of 6° or less with respect to the propagation direction of the wave excited by the first IDT electrode, and a second virtual line connecting the tips of the plurality of third electrode fingers being inclined at an angle of 6° or less with respect to the propagation direction of the wave excited by the second IDT electrode. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, the frequency characteristics of an acoustic wave device can be improved. [Brief explanation of the drawings]

[0007] [Figure 1] 1A and 1B are diagrams schematically illustrating a configuration example of an elastic wave device according to a first embodiment of the present disclosure. [Figure 2] 1 is a plan view illustrating an example of a configuration of a series resonator included in an elastic wave device according to a first embodiment of the present disclosure. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] 1 is a plan view illustrating an example of a configuration of a parallel resonator included in an elastic wave device according to a first embodiment of the present disclosure. [Figure 5] 5 is a cross-sectional view taken along line VV in FIG. 4. [Figure 6] 1 is a plan view illustrating an example of a configuration of a series resonator included in an elastic wave device according to a first embodiment of the present disclosure. [Figure 7] 1 is a cross-sectional view of a plurality of series resonators included in an exemplary configuration of an elastic wave device according to a first embodiment of the present disclosure. [Figure 8] 10 is a graph showing an example of frequency characteristics of a series resonator. [Figure 9] 9 is a partially enlarged graph showing the relationship between frequency and phase characteristics shown in FIG. 8. [Figure 10] 10 is a graph showing an example of frequency characteristics when the elastic wave device is used as a transmission filter. [Figure 11] 10 is a graph showing an example of frequency characteristics when the elastic wave device is used as a transmission filter. [Figure 12] FIG. 10 is a diagram illustrating an example of the configuration of a duplexer according to a second embodiment. [Figure 13] FIG. 10 is a diagram illustrating a schematic configuration of a communication device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Embodiment 1] An acoustic wave device (an acoustic wave filter or an acoustic wave filter device) according to an embodiment of the present disclosure will be described in detail below with reference to the drawings. However, the following description is intended to facilitate a better understanding of the spirit of the invention and, unless otherwise specified, is not intended to limit the present disclosure. For the sake of convenience, the drawings referred to in the following description show only the main components necessary for explaining the embodiment in a simplified form, and descriptions of well-known technical matters will be omitted as appropriate for the sake of brevity.

[0009] (Elastic wave device) Fig. 1 is a diagram schematically illustrating an example of a configuration of an elastic wave device according to a first embodiment. Fig. 2 is a plan view illustrating an example of a configuration of a series resonator included in the elastic wave device according to the first embodiment. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Fig. 4 is a plan view illustrating an example of a configuration of a parallel resonator included in the elastic wave device according to the first embodiment. Fig. 5 is a cross-sectional view taken along line VV in Fig. 4.

[0010] As shown in FIGS. 1 to 5, the elastic wave device 100 of this preferred embodiment includes a piezoelectric body 2, a support substrate 98, a low acoustic velocity layer 8 located between the piezoelectric body 2 and the support substrate 98, a series resonator 1S having a first IDT electrode 3 located on the piezoelectric body 2, and a parallel resonator 1P having a second IDT electrode 5 located on the piezoelectric body 2.

[0011] In the example shown in FIG. 1 , the acoustic wave device 100 includes three series resonators 1S and two parallel resonators 1P as a plurality of acoustic wave elements (resonators). The series resonators 1S and the parallel resonators 1P are each a SAW (Surface Acoustic Wave) element. The acoustic wave device 100 may include a plurality of series resonators 1S and a plurality of parallel resonators 1P, and the numbers of the series resonators 1S and the parallel resonators 1P may be changed as appropriate. The acoustic wave device 100 may be a ladder filter in which a plurality of series resonators 1S and a plurality of parallel resonators 1P are arranged in a ladder shape.

[0012] Hereinafter, when the three series resonators 1S are to be distinguished from one another, they may be referred to as series resonators 1S-1 to 1S-3, and when the two parallel resonators 1P are to be distinguished from one another, they may be referred to as parallel resonators 1P-1 and 1P-2.

[0013] In the series resonator 1S, the first IDT electrode 3 includes a first busbar 31a, a second busbar 31b, a plurality of first electrode fingers 32a, and a plurality of second electrode fingers 32b interdigitated with the first electrode fingers 32a. The series resonator 1S includes a first reflector 4A including a plurality of first strip electrodes 40a and a second reflector 4B including a plurality of second strip electrodes 40b. In the parallel resonator 1P, the second IDT electrode 5 includes a third busbar 21A, a fourth busbar 21B, a plurality of third electrode fingers 23A, and a plurality of fourth electrode fingers 23B interdigitated with the third electrode fingers 23A. The parallel resonator 1P includes a third reflector 7A including a plurality of third strip electrodes 70A and a fourth reflector 7B including a plurality of fourth strip electrodes 70B.

[0014] In the following description, a Cartesian coordinate system (xyz coordinate system) such as that shown in FIG. 2 may be used. The x direction is the propagation direction of elastic waves propagating through the piezoelectric body 2 in the series resonator 1S and the parallel resonator 1P. In contrast, the y direction is the direction perpendicular to the x direction in a plan view. The z direction is the thickness direction of each component of the series resonator 1S and the parallel resonator 1P. In the following, the positive z direction may be referred to as the upside, and the term "top surface" may be used. The negative z direction may be referred to as the downside, and the term "bottom surface" may be used. Viewing the elastic wave device 100, the series resonator 1S, or the parallel resonator 1P from the z direction is referred to as a planar view.

[0015] 2, in the series resonator 1S, the first reflector 4A and the second reflector 4B may be positioned to sandwich the first IDT electrode 3 in the x-direction. A virtual line L1 (first virtual line) connecting the tips of the first electrode fingers 32a may be inclined at a certain angle A1 (first inclination angle) with respect to the x-axis (X-direction). Furthermore, a virtual line L2 connecting the tips of the second electrode fingers 32b may be inclined at a certain angle B1 (second inclination angle) with respect to the x-axis (X-direction).

[0016] 4, in the parallel resonator 1P, the third reflector 7A and the fourth reflector 7B may be positioned to sandwich the second IDT electrode 5 in the x-direction. A virtual line L3 (second virtual line) connecting the tips of the plurality of third electrode fingers 23A may be inclined at a certain angle A2 (third inclination angle) with respect to the x-axis (X-direction). Furthermore, a virtual line L4 connecting the tips of the plurality of fourth electrode fingers 23B may be inclined at a certain angle B2 (fourth inclination angle) with respect to the x-axis (X-direction).

[0017] In elastic wave device 100 of this preferred embodiment, the number of first strip electrodes 40a is smaller than the number of third strip electrodes 70A. A first virtual line L1 connecting the tips of the first electrode fingers 32a is inclined at an angle A1 of 6° or less with respect to the propagation direction of the wave excited by first IDT electrode 3 (X direction in FIG. 2). A second virtual line L3 connecting the tips of the third electrode fingers 23A is inclined at an angle A2 of 6° or less with respect to the propagation direction of the wave excited by second IDT electrode 5 (X direction in FIG. 4).

[0018] To facilitate understanding of the advantages of the elastic wave device 100 of this preferred embodiment, the findings of the present disclosure will be briefly outlined below.

[0019] In general, tilted IDT electrodes have the effect of reducing transverse-mode spurious (transverse-mode ripple) generated in a resonator. For example, in the technology described in Patent Document 1, when the passband of a ladder filter is wide, the spurious frequencies that may be present within the passband are shifted to a higher frequency by increasing the tilt angle of the IDT electrodes of a parallel resonator with a relatively low resonant frequency, thereby moving the frequency at which the spurious frequencies are generated away from the passband.

[0020] In elastic wave device 100 of this preferred embodiment, piezoelectric body 2 and support substrate 98 are bonded via low acoustic velocity layer 8, and low acoustic velocity layer 8 is configured so that the acoustic velocity of elastic waves propagating through low acoustic velocity layer 8 is slower than the acoustic velocity of elastic waves propagating through piezoelectric body 2. In this case, high acoustic velocity elastic waves are reflected toward piezoelectric body 2 and are less likely to leak toward support substrate 98, thereby reducing loss in the SAW element.

[0021] As a result of extensive research, the inventors have found that in a ladder-type filter composed of SAW elements having the above-described low-loss structure, when the tilt angle of the IDT electrodes of the SAW elements is relatively small (6° or less), specific spurious responses (hereinafter, for convenience of explanation, referred to as "target spurious responses") may occur on the relatively low frequency side of the passband. In particular, when the tilt angle of the IDT electrodes is 3° or less, the target spurious responses may occur significantly within the passband.

[0022] As a result of further investigation, the inventors discovered that the target spurious components can be reduced in the frequency characteristics of an acoustic wave filter by reducing the number of electrodes of a reflector in a series resonator to a relatively small number, thereby reducing transverse mode excitation of acoustic waves in the reflector, and thus arrived at the present invention.

[0023] The elastic wave device 100 of this preferred embodiment includes a series resonator 1S in which the inclination angle A1 of the first IDT electrode 3 is 6° or less and a parallel resonator 1P in which the inclination angle A2 of the second IDT electrode 5 is 6° or less. The number of first strip electrodes 40a of the first reflector 4A is smaller than the number of third strip electrodes 70A of the third reflector 7A. This reduces transverse-mode spurious emissions in a frequency band lower than the resonant frequency of the series resonator 1S. As a result, the frequency characteristics of the elastic wave filter are less likely to include target spurious emissions in the passband, effectively improving the frequency characteristics. The advantages of the elastic wave device 100 can be understood specifically with reference to the example frequency characteristics described below.

[0024] (Example of overall configuration of elastic wave device) 1, acoustic wave device 100 may be connected to an input terminal Tin and an output terminal Tout. Acoustic wave device 100 may be configured as a frequency filter that filters an electrical signal input to input terminal Tin and outputs the filtered electrical signal to output terminal Tout.

[0025] The elastic wave device 100 may include a series wiring SL that connects the multiple series resonators 1S and multiple parallel wirings PL that connect the multiple parallel resonators 1P. The elastic wave device 100 may be connected to multiple ground terminals TGND that correspond to the multiple parallel wirings PL. In the example shown in FIG. 1 , the elastic wave device 100 includes two parallel wirings PL-1 and PL-2, with the parallel wiring PL-1 connected to the ground terminal TGND-1 and the parallel wiring PL-2 connected to the ground terminal TGND-2.

[0026] Each of the series resonators 1S-1 to 1S-3 may be connected to an input terminal Tin and an output terminal Tout via a series wiring SL. In the example shown in Fig. 1, the series resonator 1S-1 is the series resonator closest to the input terminal Tin. In contrast, the series resonator 1S-3 is the series resonator closest to the output terminal Tout (in other words, the series resonator farthest from the input terminal Tin).

[0027] In the example shown in FIG. 1 , the parallel resonator 1P-1 is the parallel resonator closest to the input terminal Tin. In contrast, the parallel resonator 1P-2 is the parallel resonator closest to the output terminal Tout. The parallel wiring PL-1 branches off from the series wiring SL between the series resonators 1S-1 and 1S-2 and is connected to the ground terminal TGND-1. The parallel wiring PL-2 branches off from the series wiring SL between the series resonators 1S-2 and 1S-3 and is connected to the ground terminal TGND-2. With the above configuration, unwanted components contained in the electrical signal can be filtered by discharging them to TGND via the parallel resonator 1P.

[0028] As shown in Figures 3 and 5, in the elastic wave device 100, the low acoustic velocity layer 8 may be located below the piezoelectric body 2 and above the support substrate 98, and the piezoelectric body 2 and the support substrate 98 may be bonded via the low acoustic velocity layer 8.

[0029] The piezoelectric body 2 may be made of a single crystal material having piezoelectric properties. For example, the material of the piezoelectric body 2 may be lithium tantalate (also referred to as LiTaO3:LT) or lithium niobate (also referred to as LiNbO3:LN). As an example, the piezoelectric body 2 may be an LT film.

[0030] The support substrate 98 is located on the lower surface 2B side of the piezoelectric body 2 and supports the respective components of the series resonator 1S and the parallel resonator 1P. The support substrate 98 may be configured so that the acoustic velocity of the elastic waves propagating through the support substrate 98 is faster than the acoustic velocity of the elastic waves propagating through the piezoelectric body 2. This configuration can improve the loss characteristics of the resonators. Examples of materials for the support substrate 98 include silicon (Si), sapphire, quartz crystal, and aluminum nitride (AlN). As an example, the support substrate 98 may be a Si substrate.

[0031] The low acoustic velocity layer 8 may be configured so that the acoustic velocity of the elastic waves propagating through the low acoustic velocity layer 8 is slower than the acoustic velocity of the elastic waves propagating through the piezoelectric body 2. This configuration can improve the loss characteristics of the resonator. An example of the material for the low acoustic velocity layer 8 is silicon oxide (SiOx). As an example, the low acoustic velocity layer 8 may be an SiO2 film.

[0032] In this specification, "low acoustic velocity" means a bulk wave acoustic velocity that is slower than the bulk wave acoustic velocity that propagates through the piezoelectric body 2. Furthermore, "high acoustic velocity" means a bulk wave acoustic velocity that is faster than the bulk wave acoustic velocity that propagates through the piezoelectric body 2. The bulk wave acoustic velocity may be compared based on any one of the acoustic velocities of longitudinal waves, fast shear waves, and slow shear waves.

[0033] (Example of a series resonator configuration) 2 and 3, the series resonator 1S has a first IDT electrode (excitation electrode) 3 located between two ports (terminals) P1 and P2 on the upper surface 2A of the piezoelectric body 2. The ports P1 and P2 may be the input port and the output port of the series resonator 1S, respectively.

[0034] The first IDT electrode 3 may have a first comb-tooth electrode 30a (comb-tooth electrode on the port P1 side) and a second comb-tooth electrode 30b (comb-tooth electrode on the port P2 side). In this specification, the first comb-tooth electrode 30a and the second comb-tooth electrode 30b may be collectively referred to as the comb-tooth electrode 30.

[0035] The first comb-tooth electrode 30a includes a first bus bar 31a. The second comb-tooth electrode 30b includes a second bus bar 31b. The first bus bar 31a and the second bus bar 31b may face each other in the y direction. The first bus bar 31a and the second bus bar 31b may each have a substantially constant width and be formed in an elongated shape extending linearly. The first bus bar 31a and the second bus bar 31b do not necessarily have a constant width.

[0036] The first comb-tooth electrode 30a is connected to the first bus bar 31a and has a plurality of first electrode fingers 32a extending toward the second bus bar 31b. The second comb-tooth electrode 30b is connected to the second bus bar 31b and has a plurality of second electrode fingers 32b extending toward the first bus bar 31a. The second electrode fingers 32b may be interdigitated with the first electrode fingers 32a. The first electrode fingers 32a and the second electrode fingers 32b may be alternately positioned on the upper surface 2A of the piezoelectric body 2 at approximately constant intervals in the x direction. In this specification, the first electrode fingers 32a and the second electrode fingers 32b may be collectively referred to as electrode fingers 32.

[0037] The inclination angle A1 of the virtual line L1 of the first electrode finger 32a and the inclination angle B1 of the virtual line L2 of the second electrode finger 32b may be set to be equal to each other or different from each other. Fig. 2 illustrates a case where the inclination angle A1 and the inclination angle B1 are equal to each other. The inclination angle A1 may be 6° or less, or may be 1° to 6°, or may be 1° to 3°. The inclination angle B1 may be 6° or less, or may be 1° to 6°, or may be 1° to 3°.

[0038] The comb-tooth electrode 30 may have a plurality of dummy electrode fingers 35. The pitch of the dummy electrode fingers 35 may be set to a value equal to the pitch of the electrode fingers 32. The dummy electrode fingers 35 include first dummy electrode fingers 35a connected to the first bus bar 31a and second dummy electrode fingers 35b connected to the second bus bar 31b. Each of the plurality of first dummy electrode fingers 35a may face a tip of each of the plurality of second electrode fingers 32b across a gap. Each of the plurality of second dummy electrode fingers 35b may face a tip of each of the plurality of first electrode fingers 32a across a gap.

[0039] As shown in FIG. 3 , in this specification, the thickness of the first IDT electrode 3 is represented as s, the electrode finger pitch of the first IDT electrode 3 as p1, the thickness of the piezoelectric body 2 as Tp, and the thickness of the low acoustic velocity layer 8 as Ti. The electrode finger pitch p1 is, for example, the pitch (repetition interval) between the centers of the electrode fingers 32 of the first IDT electrode 3 in the x direction. As an example, the electrode finger pitch p1 may be set equal to half the wavelength (λ / 2) of the acoustic wave excited by the first IDT electrode 3. In this case, the wavelength λ of the acoustic wave can be defined as twice the length of the electrode finger pitch p1. That is, λ can be defined as 2×p1.

[0040] In this specification, the length of the electrode finger 32 in the x-direction is referred to as the width of the electrode finger 32. The width ws1 of each electrode finger 32 may be set appropriately, for example, depending on the electrical characteristics required of the series resonator 1S. As an example, the width ws1 may be set depending on the electrode finger pitch p1. In this specification, the ratio of the width ws1 to the electrode finger pitch p1, i.e., ws1 / p1, is referred to as the duty of the electrode finger 32. The width ws1 may be approximately constant. The width ws1 does not have to be constant throughout the y-direction for one electrode finger 32. In this case, for example, the width of the electrode finger 32 at the center of the first IDT electrode 3 can be defined as the width ws1.

[0041] As shown in FIG. 2, the width ws2 of the second dummy electrode finger 35b may be equal to the width ws1 of the electrode finger 32. The width ws2 may be set larger than the width ws1. The width ws3 of the first dummy electrode finger 35a may be equal to the width ws1 of the electrode finger 32. The width ws3 may be set larger than the width ws1. When the widths ws2 and ws3 are larger than the width ws1, the transverse-mode spurious emissions in the series resonator 1S can be further reduced. The width of the root portion (the portion connected to the first bus bar 31a or the second bus bar 31b) of the electrode finger 32 may be wider than the average width of the portions other than the root portion of the electrode finger 32. In this case, the transverse-mode spurious emissions in the series resonator 1S can be effectively reduced.

[0042] The series resonator 1S may have a pair of reflectors 4 corresponding to the first IDT electrode 3. The reflectors 4 include a first reflector 4A and a second reflector 4B. The first reflector 4A and the second reflector 4B may be located on both sides of the first IDT electrode 3 in the x direction (the acoustic wave propagation direction). The reflectors 4 include a plurality of strip electrodes extending from a pair of bus bars facing each other. The first reflector 4A includes a plurality of first strip electrodes 40a, and the second reflector 4B includes a plurality of second strip electrodes 40b. At least one of the first reflector 4A and the second reflector 4B may be inclined in the same manner as the first IDT electrode 3. Specifically, the bus bar connecting the plurality of first strip electrodes 40a or the bus bar connecting the plurality of second strip electrodes 40b may extend in the direction of the inclination angle A1 or the inclination angle B1.

[0043] As described above, the number of the first strip electrodes 40a in the series resonator 1S is smaller than the number of the third strip electrodes 70A in the third reflector 7A (see FIG. 4 ) in the parallel resonator 1P. For example, the number of the first strip electrodes 40a in the first reflector 4A may be 12 or less, or may be 10 or less. The number of the first strip electrodes 40a in the first reflector 4A may be 4 or more, or may be 8 or more. For example, if the number of first strip electrodes 40a is four, large spurious signals may be generated due to reflection between the first strip electrode 40a farthest from the first IDT electrode 3 and the space adjacent to that first strip electrode 40a. For example, if the number of first strip electrodes 40a is eight, the loss characteristics are somewhat improved compared to when the number of first strip electrodes 40a is four. Furthermore, when the number of first strip electrodes 40a is eight, the spurious response due to reflection between the first strip electrode 40a farthest from the first IDT electrode 3 and the space adjacent to that first strip electrode 40a is relatively small compared to when the number is four.

[0044] In the series resonator 1S, the number of first strip electrodes 40a in the first reflector 4A and the number of second strip electrodes 40b in the second reflector 4B may be the same as or different from each other. In the series resonator 1S, the number of the second strip electrodes 40b may be smaller than the number of the third strip electrodes 70A in the third reflector 7A (see FIG. 4) in the parallel resonator 1P. For example, the number of the second strip electrodes 40b in the second reflector 4B may be 12 or less, or may be 10 or less. Furthermore, the number of the second strip electrodes 40b in the second reflector 4B may be 4 or more, or may be 8 or more.

[0045] In the series resonator 1S, the number of the plurality of first strip electrodes 40a and the number of the plurality of second strip electrodes 40b may both be smaller than the number of the plurality of third strip electrodes 70A of the third reflector 7A in the parallel resonator 1P, and may also be smaller than the number of the plurality of fourth strip electrodes 70B of the fourth reflector 7B.

[0046] (Example of parallel resonator configuration) The parallel resonator 1P is located on the same chip as the series resonator 1S, that is, it shares the support substrate 98 with the series resonator 1S. The parallel resonator 1P may have the piezoelectric element 2 and the low acoustic velocity layer 8 in common with the series resonator 1S.

[0047] 4 and 5, the parallel resonator 1P has a second IDT electrode (excitation electrode) 5 located between two ports P3 and P4 on the upper surface 2A of the piezoelectric body 2. The ports P3 and P4 may be the input port and the output port of the parallel resonator 1P, respectively.

[0048] The second IDT electrode 5 may have a third comb-tooth electrode 13A (comb-tooth electrode on the port P3 side) and a fourth comb-tooth electrode 13B (comb-tooth electrode on the port P4 side). In this specification, the third comb-tooth electrode 13A and the fourth comb-tooth electrode 13B may be collectively referred to as comb-tooth electrode 13.

[0049] The third comb-tooth electrode 13A includes a third bus bar 21A. The fourth comb-tooth electrode 13B includes a fourth bus bar 21B. The third bus bar 21A and the fourth bus bar 21B may face each other in the y direction. The third bus bar 21A and the fourth bus bar 21B may each have a substantially constant width and be formed in an elongated shape that extends linearly. The third bus bar 21A and the fourth bus bar 21B do not necessarily have a constant width.

[0050] The third comb-tooth electrode 13A is connected to the third bus bar 21A and has a plurality of third electrode fingers 23A extending toward the fourth bus bar 21B. The fourth comb-tooth electrode 13B is connected to the fourth bus bar 21B and has a plurality of fourth electrode fingers 23B extending toward the third bus bar 21A. The plurality of fourth electrode fingers 23B may be interdigitated with the plurality of third electrode fingers 23A. The third electrode fingers 23A and the fourth electrode fingers 23B may be alternately positioned on the upper surface 2A of the piezoelectric body 2 at approximately constant intervals in the x direction. In this specification, the third electrode fingers 23A and the fourth electrode fingers 23B may be collectively referred to as electrode fingers 23.

[0051] The inclination angle A2 of the virtual line L3 of the third electrode finger 23A and the inclination angle B2 of the virtual line L4 of the fourth electrode finger 23B may be set to be equal to each other or different from each other. Fig. 4 illustrates a case where the inclination angle A2 and the inclination angle B2 are equal to each other. The inclination angle A2 may be 6° or less, or may be 1° or more and 6° or less, or may be 1° or more and 3° or less. The inclination angle B2 may be 6° or less, or may be 1° or more and 6° or less, or may be 1° or more and 3° or less.

[0052] Comb-tooth electrode 13 may have a plurality of dummy electrode fingers 25. The pitch of dummy electrode fingers 25 may be set to a value equal to the pitch of electrode fingers 23. Dummy electrode fingers 25 include third dummy electrode fingers 25A connected to third bus bar 21A and fourth dummy electrode fingers 25B connected to fourth bus bar 21B. Each of the plurality of third dummy electrode fingers 25A may face a tip of each of the plurality of fourth electrode fingers 23B across a gap. Each of the plurality of fourth dummy electrode fingers 25B may face a tip of each of the plurality of third electrode fingers 23A across a gap.

[0053] As shown in FIG. 5 , in this specification, the thickness of the second IDT electrode 5 is represented as s, the electrode finger pitch of the second IDT electrode 5 as p2, and the width of each electrode finger 23 as wp1. In the example of FIG. 5 , the second IDT electrode 5 has the same thickness (s) as the first IDT electrode 3. The electrode finger pitch p2 is, for example, the pitch (repetition interval) between the centers of the multiple electrode fingers 23 of the second IDT electrode 5 in the x direction. As an example, the electrode finger pitch p2 may be set equal to half the wavelength (λ / 2) of the acoustic wave excited by the second IDT electrode 5. In this case, the wavelength λ of the acoustic wave can be defined as twice the length of the electrode finger pitch p2. That is, λ can be defined as 2×p1.

[0054] The width wp1 of each electrode finger 23 may be set appropriately depending on, for example, the electrical characteristics required of the parallel resonator 1P. As an example, the width wp1 may be set depending on the electrode finger pitch p2. In this specification, the ratio of the width wp1 to the electrode finger pitch p2, i.e., wp1 / p2, is referred to as the duty of the electrode finger 23. The width wp1 may be approximately constant. The width wp1 does not have to be constant throughout the y-direction for one electrode finger 23. In this case, for example, the width of the electrode finger 23 at the center of the second IDT electrode 5 can be defined as the width wp1. The width wp2 of the fourth dummy electrode finger 25B may be equal to the width wp1 of the electrode finger 23. The width wp2 may be set larger than the width wp1. The width wp3 of the third dummy electrode finger 25A may be equal to the width wp1 of the electrode finger 32. The width wp3 may be set larger than the width wp1.

[0055] The parallel resonator 1P may have a pair of reflectors 7 corresponding to the second IDT electrode 5. The reflectors 7 include a third reflector 7A and a fourth reflector 7B. The third reflector 7A and the fourth reflector 7B may be located on both sides of the second IDT electrode 5 in the x direction (the acoustic wave propagation direction). The reflectors 7 include multiple strip electrodes extending from a pair of bus bars facing each other. The third reflector 7A includes multiple third strip electrodes 70A, and the fourth reflector 7B includes multiple fourth strip electrodes 70B. At least one of the third reflector 7A and the fourth reflector 7B may be inclined similarly to the second IDT electrode 5. Specifically, the bus bar connecting the multiple third strip electrodes 70A or the bus bar connecting the multiple fourth strip electrodes 70B may extend in the direction of inclination angle A2 or inclination angle B2.

[0056] As described above, the number of the third strip electrodes 70A in the parallel resonator 1P is greater than the number of the first strip electrodes 40a in the first reflector 4A (see FIG. 2) in the series resonator 1S. For example, the number of the third strip electrodes 70A in the third reflector 7A may be five or more, or may be ten or more. Furthermore, the number of the third strip electrodes 70A in the third reflector 7A may be twenty or less, or may be thirty or less.

[0057] In the parallel resonator 1P, the number of third strip electrodes 70A in the third reflector 7A and the number of fourth strip electrodes 70B in the fourth reflector 7B may be the same as or different from each other. In the parallel resonator 1P, the number of the plurality of fourth strip electrodes 70B may be greater than the number of the plurality of first strip electrodes 40a in the first reflector 4A (see FIG. 2 ) in the series resonator 1S. For example, the number of the plurality of fourth strip electrodes 70B in the fourth reflector 7B may be five or more, or may be ten or more. Furthermore, the number of the plurality of fourth strip electrodes 70B in the fourth reflector 7B may be 20 or less, or may be 30 or less.

[0058] In the parallel resonator 1P, the number of the plurality of third strip electrodes 70A and the number of the plurality of fourth strip electrodes 70B may both be smaller than the number of the plurality of first strip electrodes 40a of the first reflector 4A in the series resonator 1S, and may also be smaller than the number of the plurality of second strip electrodes 40b of the fourth reflector 7B.

[0059] [Another configuration example] 6(a) is a plan view showing a series resonator according to an example configuration of an elastic wave device according to Embodiment 1. FIG. 7 is a cross-sectional view of a plurality of series resonators according to an example configuration of an elastic wave device according to Embodiment 1. The diagram indicated by reference numeral 7001 in FIG. 7 is a cross-sectional view of the series resonator 1S (first series resonator) according to the example shown in FIG. 2 (see FIG. 3), and the diagram indicated by reference numeral 7002 is a cross-sectional view taken along line VII-VII in FIG. 6.

[0060] In one configuration example, the acoustic wave device 100 may further include a second series resonator 1SA having a third IDT electrode 3A located on the piezoelectric body 2. The acoustic wave device 100 may include, for example, the series resonator 1S of the example shown in FIGS. 2 and 3 as the series resonator 1S-1 (see FIG. 1), and the second series resonator 1SA of the example shown in FIG. 6 as the series resonator 1S-2 (see FIG. 1).

[0061] As shown in Figures 6 and 7, the second series resonator 1SA has a fifth reflector 4C having a plurality of fifth strip electrodes 40C. The second series resonator 1SA may have the same configuration as the series resonator 1S (first series resonator) of the example shown in Figures 2 and 3 except for the following description, and detailed description will not be repeated. As shown in Figure 7, the thickness of the third IDT electrode 3A is s, the electrode finger pitch of the third IDT electrode 3A is p3, and the width of the electrode fingers 32 is ws1. In the example of Figure 7, the third IDT electrode 3A has the same thickness (s) and width (ws1) as the first IDT electrode 3.

[0062] In the second series resonator 1SA, the number of the plurality of fifth strip electrodes 40C in the fifth reflector 4C may be greater than the number of the first strip electrodes 40a in the first reflector 4A. Furthermore, in the acoustic wave device 100, the pitch (electrode finger pitch p1) of the first IDT electrode 3 in the series resonator 1S (first series resonator) may be smaller than the pitch (electrode finger pitch p3) of the third IDT electrode 3A in the second series resonator 1SA.

[0063] Generally, increasing the electrode finger pitch of the series resonator 1S can shift the spurious frequencies toward the lower frequency side in the frequency characteristics of the acoustic wave filter, while narrowing the high frequency side of the pass band. Therefore, in one configuration example, the acoustic wave device 100 includes a second series resonator 1SA with a relatively large electrode finger pitch and a series resonator 1S (first series resonator) with a relatively small electrode finger pitch. As described above, the series resonator 1S with a relatively small electrode finger pitch is less likely to generate target spurious emissions by having a relatively small number of strip electrodes in the reflector.

[0064] The acoustic wave device 100 in this configuration example includes the second series resonator 1SA, which shifts the frequency of target spurious signals that occur on the relatively low side of the pass band to the lower side, and the series resonator 1S, which ensures that the high side of the pass band is maintained in the frequency characteristics of the acoustic wave filter while making target spurious signals less likely to occur, thereby enabling the frequency characteristics of the acoustic wave filter to be improved more effectively.

[0065] The second series resonator 1SA may include a sixth reflector 4D having a plurality of sixth strip electrodes 40D, and the fifth reflector 4C and the sixth reflector 4D may be positioned to sandwich the third IDT electrode 3A in the x-direction. The third IDT electrode 3A may have the same configuration as the above-described first IDT electrode 3. In the second series resonator 1SA, the number of fifth strip electrodes 40C in the fifth reflector 4C and the number of sixth strip electrodes 40D in the sixth reflector 4D may be the same as or different from each other.

[0066] (b) In one configuration example, the elastic wave device 100 may include a plurality of series resonators 1S and a plurality of parallel resonators 1P (see FIG. 1 ), where each of the plurality of series resonators 1S may include a first reflector 4A and a second reflector 4B, and each of the plurality of parallel resonators 1P may include a third reflector 7A and a fourth reflector 7B. In the elastic wave device 100, the number of the plurality of first strip electrodes 40a of the first reflector 4A and the number of the plurality of second strip electrodes 40b of the second reflector 4B in any of the plurality of series resonators 1S (in other words, all of the plurality of series resonators 1S) may be smaller than the smallest number of the number of the third strip electrodes 70A of the third reflector 7A and the number of the fourth strip electrodes 70B of the fourth reflector 7B in each of the plurality of parallel resonators 1P.

[0067] With the above configuration, it is possible to more reliably prevent target spurious components from occurring in the frequency characteristics of the acoustic wave filter, thereby more reliably improving the frequency characteristics of the acoustic wave filter.

[0068] (c) The inclination angles A1, B1 of the first IDT electrode 3 of the series resonator 1S or the third IDT electrode 3A of the second series resonator 1SA and the inclination angles A2, B2 of the second IDT electrode 5 of the parallel resonator 1P may be set to be equal to each other or different from each other.

[0069] (d) In one exemplary configuration of the elastic wave device 100, the series resonator 1S and / or the parallel resonator 1P may have a high acoustic velocity layer (high acoustic velocity film) located between the piezoelectric body 2 and the low acoustic velocity layer 8. The high acoustic velocity layer may be shared by the series resonator 1S and the parallel resonator 1P. The loss characteristics of the resonators can be improved by providing a high acoustic velocity layer. Examples of materials for the high acoustic velocity layer include Al2O3. The high acoustic velocity layer may be located between the low acoustic velocity layer 8 and the support substrate 98. In one exemplary configuration of the elastic wave device 100, the series resonator 1S and / or the parallel resonator 1P may have an acoustic reflection film, which has a laminated structure of a low acoustic impedance layer and a high acoustic impedance layer, located between the piezoelectric body 2 and the support substrate 98.

[0070] (Example of frequency characteristics) FIG. 8 is a graph showing an example of the frequency characteristics of a series resonator. FIG. 9 is a graph showing an enlarged portion of the graph showing the relationship between frequency and phase characteristics shown in FIG. 8. In each graph shown in FIG. 8 (and FIG. 9), a solid line indicates an example of the series resonator 1S of this embodiment, and a dashed line indicates a comparative example of a series resonator having a reflector with a larger number of strip electrodes than the series resonator 1S of this embodiment. The horizontal axis of each graph shown in FIG. 8 (and FIG. 9) represents frequency (unit: MHz). The graph indicated by reference numeral 8001 represents the impedance characteristics of each resonator, and the vertical axis of this graph represents the absolute value (magnitude) of the impedance (unit: Ohm). The graph indicated by reference numeral 8002 represents the impedance phase characteristics of each resonator, and the vertical axis of this graph represents the impedance phase (unit: degree). In the following description, the phase of the impedance will be abbreviated simply as "phase."

[0071] In the examples of Figures 8 and 9, in the embodiment (solid line in the graph), the number of first and second strip electrodes 40a and 40b in the first and second reflectors 4A and 4B is 10, respectively, and in the comparative example (dashed line in the graph), the number of strip electrodes in each of the pair of reflectors sandwiching the first IDT electrode 3 is 15.

[0072] Other design conditions were as follows: Tp (thickness of LT film as common dielectric film): 1.8 μm ·Ti (thickness of SiO2 film as a common low sound velocity layer): 0.6 μm ·Si (common support substrate) thickness: 200μm s (IDT electrode thickness): 500 nm Electrode finger pitch of each IDT electrode: 2.849 μm - Composition of each IDT electrode: Ti60Å / AlCu1400Å Intersection width: 16λ Number of electrode fingers in each IDT electrode: 400 Duty of electrode fingers in the crossing area of ​​each IDT electrode: 0.5 Tilt angle: 6° In the above design conditions, the inclination angles A1 and B1 are collectively referred to as the inclination angles.

[0073] The graph indicated by the symbol 9001 in Figure 9 is an enlarged view of the portion of the graph indicated by the symbol 8002 in Figure 8 where the phase characteristics are from 70° to 90°, and the graph indicated by the symbol 9002 in Figure 9 is an enlarged view of the portion of the graph indicated by the symbol 8002 in Figure 8 where the phase characteristics are from -90° to -80° and the frequency is from 650 MHz to 690 MHz.

[0074] As shown in the graph indicated by the reference numeral 9002 in FIG. 9, in the series resonator 1S of the embodiment, the transverse mode excitation of the acoustic wave in the reflector is reduced compared to the series resonator of the comparative example, and therefore the magnitude of the unwanted peaks occurring in the stop band on the lower frequency side than the main resonant frequency is smaller.

[0075] Fig. 10 is a graph showing an example of frequency characteristics when an elastic wave device is used as a transmission filter. In each graph shown in Fig. 10, a working example of an elastic wave device 100 including a series resonator 1S of this preferred embodiment is indicated by a solid line, and a comparative example of an elastic wave device including a series resonator with a greater number of strip electrodes in the reflector than the series resonator 1S of this preferred embodiment is indicated by a dashed line. In each graph shown in Fig. 10, the horizontal axis represents frequency (unit: MHz), and the vertical axis represents insertion loss (unit: dB). Insertion loss can also be referred to as attenuation or transmission.

[0076] 10, in the example (solid line in the graph), the number of first and second strip electrodes 40a and 40b of the first and second reflectors 4A and 4B in each of the multiple series resonators 1S is set to 10. In the comparative example (dashed line in the graph), the number of strip electrodes of the pair of reflectors sandwiching the first IDT electrode 3 in each of the multiple series resonators is set to 15.

[0077] The graph designated by reference numeral 1002 in Fig. 10 is an enlarged view of the portion of the graph designated by reference numeral 1001 in Fig. 10 where the insertion loss is 0 to 5 dB. As shown by the graph designated by reference numeral 1002 in Fig. 10, it can be seen that the target spurious emissions occurring at frequencies around 665 MHz within the passband are more effectively reduced in elastic wave device 100 of the example than in the elastic wave device of the comparative example.

[0078] Fig. 11, like Fig. 10, is a graph showing an example of frequency characteristics when the acoustic wave device is used as a transmit filter. The graph in Fig. 11 differs from Fig. 10 in that it shows an example of frequency characteristics of an acoustic wave device 100 including a series resonator 1S in which the number of first and second strip electrodes 40a and 40b is 12, 8, or 4. In the graph in Fig. 11, the solid line shows an example of frequency characteristics when the number of first and second strip electrodes 40a and 40b of the first and second reflectors 4A and 4B of the series resonator 1S is 12, the dotted line shows an example of frequency characteristics when the number of first and second strip electrodes 40a and 40b is 8, and the dashed line shows an example of frequency characteristics when the number of first and second strip electrodes 40a and 40b is 4.

[0079] [Embodiment 2] FIG. 12 illustrates an exemplary configuration of a duplexer 101 according to the second embodiment. A duplexer is also referred to as a multiplexer. As illustrated in FIG. 12, the duplexer 101 may include multiple acoustic wave devices 100. In the example illustrated in FIG. 12, the duplexer 101 includes four acoustic wave devices 100 (e.g., ladder filters). The duplexer 101 in FIG. 12 is an example of a quadplexer. In the following description, the four acoustic wave devices 100 are referred to as a first filter 100A, a second filter 100B, a third filter 100C, and a fourth filter 100D, respectively.

[0080] As shown in Fig. 12, at least two of the multiple acoustic wave filters may be connected to a common input terminal TCin. As an example, the input terminal TCin may be an antenna terminal (see also the third embodiment described later). In the example of Fig. 12, the first filter 100A to the fourth filter 100D are connected to the input terminal TCin. In this manner, all of the multiple acoustic wave filters may be connected to the input terminal TCin.

[0081] Input terminal TCin may be connected to ground terminal TGND via reactor 99. First filter 100A to fourth filter 100D may be connected to individual output terminals, respectively. First filter 100A to fourth filter 100D may be connected to output terminals Tout-1 to Tout-4, respectively.

[0082] The first filter 100A to the fourth filter 100D may be located on the same chip. In this case, the resonators of the first filter 100A to the fourth filter 100D may have a common support substrate 98. Therefore, the thickness of the support substrate 98 may be the same for each resonator. In addition, each resonator may have a common piezoelectric body 2 and low acoustic velocity layer 8. Each resonator may be formed, for example, by a common film formation process.

[0083] [Embodiment 3] FIG. 13 is a diagram illustrating a schematic configuration of a communication device 151 according to a third embodiment. The communication device 151 is an application example of an acoustic wave device according to an aspect of the present disclosure, and performs wireless communication using radio waves. The communication device 151 may include the above-described duplexer 101. The communication device 151 in the example of FIG. 13 may include one duplexer 101 as a transmit filter 109 and another duplexer 101 as a receive filter 111.

[0084] In the communication device 151, a transmission information signal TIS containing information to be transmitted may be modulated and frequency-raised (converted into a high-frequency signal having a carrier frequency) by an RF-IC (Radio Frequency-Integrated Circuit) 153, and converted into a transmission signal TS. A bandpass filter 155 may remove unwanted components from the transmission signal TS that are outside the transmission passband. Next, the transmission signal TS after removing the unwanted components may be amplified by an amplifier 157 and input to the transmission filter 109.

[0085] The transmission filter 109 may remove unnecessary components outside the transmission passband from the input transmission signal TS. The transmission filter 109 may output the transmission signal TS after removing the unnecessary components to the antenna 159 via an antenna terminal (for example, the above-mentioned TCin). The antenna 159 may convert the transmission signal TS, which is an electrical signal input thereto, into radio waves as a wireless signal and transmit the radio waves to the outside of the communication device 151.

[0086] Furthermore, the antenna 159 may convert the received external radio waves into a received signal RS, which is an electrical signal, and input the received signal RS to the receiving filter 111 via the antenna terminal. The receiving filter 111 may remove unwanted components outside the receiving passband from the input received signal RS. The receiving filter 111 may output the received signal RS after the unwanted components have been removed to the amplifier 161. The output received signal RS may be amplified by the amplifier 161. The bandpass filter 163 may remove unwanted components outside the receiving passband from the amplified received signal RS. The received signal RS after the unwanted components have been removed may be frequency-downgraded and demodulated by the RF-IC 153, and converted into a received information signal RIS.

[0087] The transmit information signal TIS and the receive information signal RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, the transmit information signal TIS and the receive information signal RIS may be analog audio signals or digitized audio signals. The passband of the radio signals may be set appropriately and may comply with various known standards.

[0088] 〔summary〕 An elastic wave device according to a first aspect of the present disclosure includes a piezoelectric body, a support substrate, a low acoustic velocity layer located between the piezoelectric body and the support substrate, a series resonator having a first IDT electrode located on the piezoelectric body, and a parallel resonator having a second IDT electrode located on the piezoelectric body, wherein the first IDT electrode includes a first bus bar, a second bus bar, a plurality of first electrode fingers, and a plurality of second electrode fingers interdigitated with the first electrode fingers, the series resonator further includes a first reflector including a plurality of first strip electrodes and a second reflector including a plurality of second strip electrodes, and the second IDT electrode includes a third bus bar, a fourth bus bar, and a plurality of the parallel resonator further comprises a third reflector having a plurality of third strip electrodes and a fourth reflector having a plurality of fourth strip electrodes, the number of the first strip electrodes being less than the number of the third strip electrodes, a first virtual line connecting the tips of the plurality of first electrode fingers being inclined at an angle of 6° or less with respect to the propagation direction of the wave excited by the first IDT electrode, and a second virtual line connecting the tips of the plurality of third electrode fingers being inclined at an angle of 6° or less with respect to the propagation direction of the wave excited by the second IDT electrode.

[0089] In the acoustic wave device according to a second aspect of the present disclosure, in addition to the first aspect, the number of the first strip electrodes of the first reflector is 12 or less.

[0090] In the acoustic wave device according to a third aspect of the present disclosure, in addition to the first or second aspect, the number of the first strip electrodes of the first reflector is four or more.

[0091] In an elastic wave device according to a fourth aspect of the present disclosure, in any one of the first to third aspects, the device further includes a second series resonator having a third IDT electrode located on the piezoelectric body, the second series resonator having a fifth reflector having a plurality of fifth strip electrodes, the number of the fifth strip electrodes in the fifth reflector being greater than the number of the first strip electrodes in the first reflector, and the pitch of the first IDT electrodes being smaller than the pitch of the third IDT electrodes.

[0092] An elastic wave device in aspect 5 of the present disclosure is any one of aspects 1 to 4, and includes a plurality of series resonators each having the first reflector and the second reflector, and a plurality of parallel resonators each having the third reflector and the fourth reflector, and the number of the first strip electrodes and the number of the second strip electrodes of all of the plurality of series resonators are smaller than the smallest number of the third strip electrodes and the number of the fourth strip electrodes of each of the plurality of parallel resonators.

[0093] A communication device according to a sixth aspect of the present disclosure includes the acoustic wave device according to any one of the first to fifth aspects.

[0094] [Additional Notes] The invention according to the present disclosure has been described above based on the drawings and embodiments. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art can easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure. [Explanation of symbols]

[0095] 1S series resonator 1P parallel resonator 2. Piezoelectric 3 First IDT electrode 4A 1st reflector 4B 2nd reflector 5 2nd IDT electrode 7A 3rd reflector 7B 4th reflector 8 Low sound speed layer 21A 3rd bus bar 21B 4th bus bar 23A 3rd electrode finger 23B 4th electrode finger 31a 1st bus bar 31b Second bus bar 32a 1st electrode finger 32b 2nd electrode finger 40a First strip electrode 40b Second strip electrode 70A 3rd strip electrode 70B 4th strip electrode 98 Support substrate 100 Elastic Wave Device 100A~100D 1st filter~4th filter (elastic wave device) 151 Communication equipment

Claims

1. A piezoelectric body; A support substrate; a low acoustic velocity layer located between the piezoelectric body and the support substrate; a series resonator having a first IDT electrode located on the piezoelectric body; a parallel resonator having a second IDT electrode located on the piezoelectric body, the first IDT electrode includes a first bus bar, a second bus bar, a plurality of first electrode fingers, and a plurality of second electrode fingers interdigitated with the first electrode fingers; the series resonator further includes a first reflector having a plurality of first strip electrodes and a second reflector having a plurality of second strip electrodes; the second IDT electrode includes a third bus bar, a fourth bus bar, a plurality of third electrode fingers, and a plurality of fourth electrode fingers interdigitated with the third electrode fingers; the parallel resonator further includes a third reflector having a plurality of third strip electrodes and a fourth reflector having a plurality of fourth strip electrodes; the number of the first strip electrodes is less than the number of the third strip electrodes; a first imaginary line connecting tips of the first electrode fingers is inclined at an angle of 6° or less with respect to the propagation direction of a wave excited by the first IDT electrode, an elastic wave device, wherein a second imaginary line connecting tips of the third electrode fingers is inclined at an angle of 6° or less with respect to the propagation direction of a wave excited by the second IDT electrode;

2. The acoustic wave device according to claim 1 , wherein the number of the first strip electrodes of the first reflector is 12 or less.

3. The acoustic wave device according to claim 1 , wherein the number of the first strip electrodes of the first reflector is four or more.

4. a second series resonator having a third IDT electrode located on the piezoelectric body; The second series resonator is a fifth reflector having a plurality of fifth strip electrodes; the number of the fifth strip electrodes in the fifth reflector is greater than the number of the first strip electrodes in the first reflector; The acoustic wave device according to claim 1 , wherein the pitch of the first IDT electrode is smaller than the pitch of the third IDT electrode.

5. a plurality of series resonators each having the first reflector and the second reflector; a plurality of parallel resonators, each of which has the third reflector and the fourth reflector; 2. The elastic wave device according to claim 1, wherein the number of the first strip electrodes and the number of the second strip electrodes of all of the plurality of series resonators are smaller than the smallest number among the number of the third strip electrodes and the number of the fourth strip electrodes of each of the plurality of parallel resonators.

6. A communication device comprising the acoustic wave device according to claim 1 .

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