Acoustic wave resonator and acoustic wave filter device

Abstract

To suppress the occurrence of ripples on the frequency side lower than the resonance frequency of an elastic wave resonator.SOLUTION: An IDT electrode 11 of an acoustic wave resonator 10 includes, at an end portion 11e, a first region T1 closest to a reflector 12, a second region T2 located closer to a central portion 11d than the first region T1, and a third region T3 located closer to the central portion 11d than the second region T2. In the first region T1, a first pitch p1, which is the electrode finger pitch between the first electrode finger f1 closest to the reflector 12 and the second electrode finger f2 located adjacent to the first electrode finger f1, is smaller than the average IDT pitch Pia. A third pitch p3, which is the electrode finger pitch Pi between two adjacent electrode fingers in the third region T3, is smaller than the average IDT pitch Pia. A second pitch p2, which is the electrode finger pitch Pi between two adjacent electrode fingers in the second region T2, is larger than both the first pitch p1 and the third pitch p3.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave resonator and an acoustic wave filter device having an acoustic wave resonator. [Background technology]

[0002] Conventionally, an acoustic wave resonator including an IDT electrode and a plurality of reflectors has been known. Patent Document 1 discloses a technique for reducing ripples occurring at frequencies lower than the resonant frequency of the acoustic wave resonator by changing the pitch of electrode fingers at the ends of the IDT electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-182460 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the elastic wave resonator described in Patent Document 1, ripples may occur in a part of the frequency band on the lower frequency side than the resonant frequency of the elastic wave resonator.

[0005] The present invention provides an elastic wave resonator and the like that can suppress the occurrence of ripples on the frequency side lower than the resonant frequency of the elastic wave resonator. [Means for solving the problem]

[0006] An elastic wave resonator according to one aspect of the present invention includes a piezoelectric substrate, an IDT electrode, and a plurality of reflectors formed on a main surface of the piezoelectric substrate, wherein the IDT electrode has a plurality of electrode fingers arranged in a first direction and a second direction that are directions along the main surface of the piezoelectric substrate, and extending in the second direction that intersects the first direction, and each of the plurality of reflectors is arranged on both sides of the IDT electrode in the first direction and has a plurality of reflective electrode fingers arranged to extend in the second direction, wherein an electrode finger pitch is defined as a center-to-center distance in the first direction between electrode fingers adjacent to each other in the first direction among the plurality of electrode fingers, and an average IDT pitch is defined as a center-to-center distance in the first direction between reflective electrode fingers adjacent to each other in the first direction among the plurality of reflective electrode fingers, and When the average value of the pitches of the plurality of reflecting electrode fingers in the reflector is defined as an average reflector pitch, the average IDT pitch is smaller than the average reflector pitch, and the IDT electrode has, at an end different from the central portion, a first region closest to the reflector, a second region located closer to the central portion than the first region, and a third region located closer to the central portion than the second region, and in the first region, a first pitch which is the electrode finger pitch between a first electrode finger closest to the reflector and a second electrode finger located adjacent to the first electrode finger is smaller than the average IDT pitch, a second pitch which is the electrode finger pitch between two adjacent electrode fingers in the second region is larger than the first pitch, and a third pitch which is the electrode finger pitch between two adjacent electrode fingers in the third region is smaller than the second pitch and also smaller than the average IDT pitch.

[0007] An acoustic wave filter device according to one aspect of the present invention includes a first acoustic wave resonator and a second acoustic wave resonator arranged along the first direction, each of the first acoustic wave resonator and the second acoustic wave resonator having an IDT electrode and a plurality of reflectors, wherein a reflector of the plurality of reflectors of the first acoustic wave resonator located adjacent to the second acoustic wave resonator and a reflector of the plurality of reflectors of the second acoustic wave resonator located adjacent to the first acoustic wave resonator are shared by a single reflector, the first acoustic wave resonator is configured by the acoustic wave resonator according to claim 1 or 2, and the average IDT pitch of the first acoustic wave resonator is smaller than the electrode finger pitch of the IDT electrode of the second acoustic wave resonator and is smaller than the reflecting electrode finger pitch of the shared single reflector. [Effects of the Invention]

[0008] According to the elastic wave resonator and the like according to the present invention, it is possible to suppress the occurrence of ripples on the frequency side lower than the resonant frequency of the elastic wave resonator. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are a plan view and a cross-sectional view schematically illustrating an electrode configuration of an elastic wave resonator according to a first embodiment. [Figure 2] 2A and 2B are diagrams illustrating a first region, a second region, a third region, etc. of an IDT electrode included in an acoustic wave resonator. [Figure 3] 10A and 10B are diagrams illustrating an example of an electrode finger pitch of an IDT electrode and a reflector electrode finger pitch of a reflector. [Figure 4] FIG. 10 is a diagram showing another example of the electrode finger pitch of the IDT electrode and the reflector electrode finger pitch of the reflector. [Figure 5] FIG. 10 is a diagram showing another example of the electrode finger pitch of the IDT electrode and the reflector electrode finger pitch of the reflector. [Figure 6] FIG. 2 is a diagram showing electrode parameters of the acoustic wave resonators according to Examples 1, 2, 3, and 4. [Figure 7A]1 is a diagram showing the electrode finger pitch of acoustic wave resonators according to Comparative Example 1, Reference Example, and Example 1 (where the pitch ratio, which is the ratio of the average reflector pitch to the average IDT pitch, is set to 1.04). [Figure 7B] 10 is a diagram illustrating the reflection losses of the acoustic wave resonators of Comparative Example 1, Reference Example, and Example 1 (examples when the pitch ratio is 1.04). [Figure 8A] 10 is a diagram showing the electrode finger pitch of elastic wave resonators according to Comparative Example 1, Reference Example, and Example 2 (examples where the pitch ratio is 1.05). [Figure 8B] 10 is a diagram illustrating the reflection losses of the acoustic wave resonators of Comparative Example 1, Reference Example, and Example 2 (examples when the pitch ratio is 1.05). [Figure 9A] 10 is a diagram showing the electrode finger pitch of elastic wave resonators according to Comparative Example 1, Reference Example, and Example 3 (examples where the pitch ratio is 1.06). [Figure 9B] 10 is a diagram illustrating the reflection losses of the acoustic wave resonators of Comparative Example 1, Reference Example, and Example 3 (examples when the pitch ratio is 1.06). [Figure 10A] 10 is a diagram showing the electrode finger pitch of elastic wave resonators according to Comparative Example 1, Reference Example, and Example 4 (examples where the pitch ratio is 1.10). [Figure 10B] 10 is a diagram illustrating the reflection losses of the acoustic wave resonators of Comparative Example 1, Reference Example, and Example 4 (examples when the pitch ratio is 1.10). [Figure 11A] 10 is a diagram illustrating the electrode finger pitch of elastic wave resonators according to Comparative Example 2 and Example 4 (examples where the pitch ratio is 1.10). [Figure 11B] 10 is a diagram illustrating the reflection losses of the acoustic wave resonators of Comparative Example 2 and Example 4 (examples when the pitch ratio is 1.10). [Figure 12] FIG. 10 is a diagram illustrating a circuit configuration of an acoustic wave filter device according to a second embodiment. [Figure 13] 3A and 3B are diagrams illustrating an example of electrode finger pitches of IDT electrodes of a first acoustic wave resonator and a second acoustic wave resonator and a reflector finger pitch of a reflector included in an acoustic wave filter device. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail using diagrams and tables. Note that the examples described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component arrangements, and connection forms shown in the following examples are merely examples and are not intended to limit the present invention. Among the components in the following examples, components that are not recited in the independent claims are described as optional components. Furthermore, the sizes or size ratios of the components shown in the drawings are not necessarily strict.

[0011] (Embodiment 1) [Structure of elastic wave resonator] The configuration of an acoustic wave resonator 10 according to the present embodiment will be described with reference to FIGS.

[0012] FIG. 1 is a plan view and a cross-sectional view schematically illustrating an electrode configuration of an acoustic wave resonator 10 according to a first embodiment.

[0013] The acoustic wave resonator 10 shown in the figure is formed of a piezoelectric substrate 100, an electrode 110, and a protective film 113, and includes an IDT (InterDigital Transducer) electrode 11 configured from these components, and a plurality of reflectors 12. The acoustic wave resonator 10 according to this embodiment is a surface acoustic wave (SAW) resonator configured from the IDT electrode 11, the plurality of reflectors 12, and the piezoelectric substrate 100.

[0014] It should be noted that acoustic wave resonator 10 shown in FIG. 1 is for illustrating a typical structure, and the number and length of electrode fingers constituting the electrodes are not limited to this.

[0015] The electrode 110 constituting the IDT electrode 11 and the plurality of reflectors 12 has a laminated structure of an adhesive layer 111 and a main electrode layer 112, as shown in the cross-sectional view of FIG.

[0016] The adhesive layer 111 is a layer for improving the adhesiveness between the piezoelectric substrate 100 and the main electrode layer 112, and is made of, for example, Ti.

[0017] The main electrode layer 112 is made of, for example, Al containing 1% Cu.

[0018] The protective film 113 is formed to cover the electrode 110. The protective film 113 is a layer intended to protect the main electrode layer 112 from the external environment, adjust the frequency-temperature characteristics, and increase moisture resistance, and is, for example, a film whose main component is silicon dioxide (SiO2).

[0019] The materials constituting the adhesion layer 111, the main electrode layer 112, and the protective film 113 are not limited to those mentioned above. Furthermore, the electrode 110 does not have to have the above-mentioned laminated structure. The electrode 110 may be made of, for example, a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or may be made of a laminate of multiple layers made of the above-mentioned metals or alloys. Furthermore, the protective film 113 does not have to be formed.

[0020] Examples of materials that can be used for the piezoelectric substrate 100 include piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectrics such as diamond and glass; semiconductors such as silicon and gallium nitride; resins; and materials containing any of the above materials as their main components.

[0021] The piezoelectric substrate 100 may be a substrate having a piezoelectric layer at least in a portion thereof, or may have a laminated structure having a piezoelectric layer. The piezoelectric substrate 100 may have a structure including, for example, a high acoustic speed support substrate, a low acoustic speed film, and a piezoelectric layer, with the high acoustic speed support substrate, the low acoustic speed film, and the piezoelectric layer laminated in this order.

[0022] The configurations of the high acoustic velocity support substrate, the low acoustic velocity film, and the piezoelectric layer will be described below.

[0023] The piezoelectric layer is made of, for example, a θ° Y-cut X-propagation LiTaO3 piezoelectric single crystal or piezoelectric ceramic (a lithium tantalate single crystal or ceramic cut along a plane whose normal is an axis rotated θ° from the Y-axis in the Z-axis direction around the X-axis, and in which surface acoustic waves propagate in the X-axis direction).

[0024] The high acoustic speed support substrate is a substrate that supports the low acoustic speed film, the piezoelectric layer, and the electrode 110. The high acoustic speed support substrate is also a substrate in which the acoustic speed of bulk waves in the high acoustic speed support substrate is faster than that of surface waves and boundary waves that propagate through the piezoelectric layer, and functions to confine the surface acoustic waves to the portion where the piezoelectric layer and the low acoustic speed film are laminated, preventing them from leaking below the high acoustic speed support substrate.

[0025] The high acoustic velocity support substrate is, for example, a silicon substrate. Materials for the high acoustic velocity support substrate include, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon; dielectric materials such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; semiconductors such as silicon; and materials containing the above materials as their main components. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, and the like. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0026] The low acoustic velocity film is a film in which the acoustic velocity of the bulk wave in the low acoustic velocity film is slower than the acoustic velocity of the elastic wave propagating through the piezoelectric layer, and is placed between the piezoelectric layer and the high acoustic velocity support substrate. This structure, together with the property that the energy of the elastic wave is concentrated in a medium with an essentially low acoustic velocity, suppresses the leakage of surface acoustic wave energy outside the IDT electrode.

[0027] The low acoustic velocity film is, for example, a film whose main component is silicon dioxide (SiO2). The material of the low acoustic velocity film is not limited to the above, and for example, dielectrics such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or compounds in which fluorine, carbon, or boron is added to silicon oxide, or materials whose main component is any of the above materials, can also be used.

[0028] The above-described layered structure of the piezoelectric substrate 100 makes it possible to significantly increase the Q value of the surface acoustic wave resonator at the resonant frequency and anti-resonant frequency, compared to a structure using a single layer of the piezoelectric substrate 100. In other words, a surface acoustic wave resonator with a high Q value can be configured, and therefore a filter with low insertion loss can be configured using the surface acoustic wave resonator.

[0029] The high acoustic velocity support substrate may have a laminated structure of a support substrate and a high acoustic velocity film that makes the acoustic velocity of the bulk waves that propagate through the piezoelectric layer faster than the acoustic velocity of the surface waves or boundary waves that propagate through the piezoelectric layer.

[0030] In the case of this laminated structure, the material of the support substrate can be selected from the following: piezoelectric materials such as sapphire, lithium tantalate, lithium niobate, and quartz; various ceramics such as alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectric materials such as glass; semiconductors such as silicon and gallium nitride; and resin substrates.

[0031] In addition, materials for the high acoustic velocity film can include, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon; dielectric materials such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; semiconductors such as silicon; or materials containing the above materials as their main components. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0032] The materials of the layers exemplified in the above-described laminated structure of the piezoelectric substrate 100 are merely examples, and may be changed depending on, for example, the characteristics that are to be emphasized among the required high-frequency propagation characteristics.

[0033] As shown in the plan view of FIG. 1, the IDT electrode 11 has a pair of comb-shaped electrodes 11A and 11B facing each other.

[0034] Here, a predetermined direction along the main surface 100a of the piezoelectric substrate 100 is referred to as a first direction d1, and a direction along the main surface 100a of the piezoelectric substrate 100 and intersecting the first direction d1 is referred to as a second direction d2. The first direction d1 is the acoustic wave propagation direction of the acoustic wave resonator 10. In this embodiment, the first direction d1 and the second direction d2 are orthogonal to each other.

[0035] The interdigital electrode 11A is composed of a plurality of electrode fingers 11a arranged to extend in the second direction d2 and a busbar electrode 11c connecting one ends of the electrode fingers 11a to each other. The interdigital electrode 11B is composed of a plurality of electrode fingers 11b arranged to extend in the second direction d2 and a busbar electrode 11c connecting one ends of the electrode fingers 11b to each other. The electrode fingers 11a and 11b are arranged alternately in the first direction d1.

[0036] The reflector 12 is arranged next to the IDT electrode 11 in the first direction d1. The multiple reflectors 12 are arranged on both outer sides of the IDT electrode 11. The multiple reflectors 12 are composed of one reflector 12 located on the negative side of the IDT electrode 11 in the first direction d1 and the other reflector 12 located on the positive side of the first direction d1 when viewed from the IDT electrode 11. The reflector 12 is composed of multiple reflective electrode fingers 12a arranged to extend in the second direction d2 and a bus bar electrode 12c connecting one ends of the multiple reflective electrode fingers 12a to each other.

[0037] FIG. 2 is a diagram showing a first region T1, a second region T2, a third region T3, and the like of an IDT electrode 11 included in acoustic wave resonator 10. As shown in FIG.

[0038] The IDT electrode 11 has a central portion 11d that includes most of the center in the first direction d1, and an end portion 11e that is different from the central portion 11d. The central portion 11d is a region that accounts for 90% of the total number of electrode fingers 11a, 11b of the IDT electrode 11. The end portions 11e are located on both sides of the central portion 11d in the first direction d1 and have one end and the other end. The one end and the other end are regions that each account for 5% of the total number of electrode fingers 11a, 11b of the IDT electrode 11.

[0039] At an end 11e of the IDT electrode 11, the IDT electrode 11 has a first region T1 closest to the reflector 12, a second region T2 located closer to the central region 11d than the first region T1, and a third region T3 located closer to the central region 11d than the second region T2. ​​The IDT electrode 11 also has a fourth region T4 located closer to the central region 11d than the third region T3, and a fifth region T5 located closer to the central region 11d than the fourth region T4. The first region T1, second region T2, third region T3, fourth region T4, and fifth region T5 may be arranged adjacent to each other in this order in the first direction d1, or may be arranged with an interval between them in this order.

[0040] In addition, the IDT electrode 11 has, in the first direction d1, a first electrode finger f1 which is the electrode finger closest to the reflector 12 among the multiple electrode fingers 11a, 11b, and a second electrode finger f2 which is the electrode finger second closest to the reflector 12 and is located next to the first electrode finger f1.

[0041] Here, the center-to-center distance in the first direction d1 between adjacent electrode fingers 11a, 11b among the multiple electrode fingers 11a, 11b is defined as the electrode finger pitch Pi, and the center-to-center distance in the first direction d1 between adjacent reflective electrode fingers 12a among the multiple reflective electrode fingers 12a is defined as the reflective electrode finger pitch Pr.

[0042] As an example, FIG. 2 shows a first pitch p1, a second pitch p2, a third pitch p3, a fourth pitch p4, and a fifth pitch p5 corresponding to the first region T1, the second region T2, the third region T3, the fourth region T4, and the fifth region T5, respectively.

[0043] The first pitch p1 is the electrode finger pitch Pi formed by the first electrode finger f1 and the second electrode finger f2. The second pitch p2 is the electrode finger pitch Pi formed by the third and fourth electrode fingers counting from the outermost end, the third pitch p3 is the electrode finger pitch Pi formed by the fourth and fifth electrode fingers counting from the outermost end, the fourth pitch p4 is the electrode finger pitch Pi formed by the fifth and sixth electrode fingers counting from the outermost end, and the fifth pitch p5 is the electrode finger pitch Pi formed by the seventh and eighth electrode fingers counting from the outermost end. Note that the positions of the regions and pitches shown in FIG. 2 are merely examples.

[0044] Also, the average value of a plurality of electrode finger pitches Pi in the central portion 11d of the IDT electrode 11 is defined as the average IDT pitch Pia, and the average value of a plurality of reflector electrode finger pitches Pr in the reflector 12 is defined as the average reflector pitch Pra. The average IDT pitch Pia can be obtained, for example, by dividing the distance between both ends of the central portion 11d in the first direction d1 by "the number of electrode fingers 11a and 11b in the central portion 11d - 1". Also, the average reflector pitch Pra can be obtained, for example, by dividing the distance between both ends of the plurality of reflector electrode fingers 12a in the first direction d1 by "the total number of the plurality of reflector electrode fingers 12a - 1".

[0045] Under the above definition, the surface acoustic wave resonator 10 of the present embodiment has a configuration in which the average IDT pitch Pia is smaller than the average reflector pitch Pra (Pia < Pra). Further, the surface acoustic wave resonator 10 of the present embodiment has the following configuration.

[0046] FIG. 3 is a diagram showing an example of the electrode finger pitch Pi of the IDT electrode 11 and the reflector electrode finger pitch Pr of the reflector 12.

[0047] In the figure, a diagram connecting the values of the average reflector pitch Pra, the average IDT pitch Pia, and each electrode finger pitch Pi at the end portion 11e of the IDT electrode 11 with lines is shown. The same applies to FIGS. 4 and 5.

[0048] The IDT electrode 11 has a configuration in which, in the first region T1, the first pitch p1, which is the electrode finger pitch Pi between the first electrode finger f1 and the second electrode finger f2, is smaller than the average IDT pitch Pia (p1 < Pia). For example, the first pitch p1 is 0.88 times or more and 0.96 times or less of the average IDT pitch Pia (see FIGS. 10A and 9A shown later).

[0049] Further, the IDT electrode 11 has a configuration in which a second pitch p2, which is the electrode finger pitch Pi between two adjacent electrode fingers 11a and 11b in the second region T2, is larger than the first pitch p1 (p2 > p1). It is desirable that the second pitch p2 be not less than 0.99 times and not more than 1.01 times the average IDT pitch Pia.

[0050] Further, the IDT electrode 11 has a configuration in which a third pitch p3, which is the electrode finger pitch Pi between two adjacent electrode fingers 11a and 11b in the third region T3, is smaller than the second pitch p2 and smaller than the average IDT pitch Pia (p3 < p2 and p3 < Pia). For example, the third pitch p3 is not less than 0.88 times and not more than 0.97 times the average IDT pitch Pia (see FIGS. 9A and 7A shown later).

[0051] That is, the IDT electrode 11 has a pitch structure in which, at the end portion 11e of the IDT electrode 11, the first pitch p1 is smaller than the average IDT pitch Pia, and the third pitch p3 is smaller than the second pitch p2 and the electrode finger pitch Pi of the central portion 11d.

[0052] According to the surface acoustic wave resonator 10 having these configurations (Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia), generation of a strong excitation wave at the end portion 11e of the IDT electrode 11 can be suppressed. Thereby, generation of a ripple on the lower frequency side than the resonance frequency of the surface acoustic wave resonator 10 can be suppressed.

[0053] FIG. 4 is a diagram showing another example of the electrode finger pitch Pi of the IDT electrode 11 and the reflection electrode finger pitch Pr of the reflector 12.

[0054] The IDT electrode 11 shown in the figure also has a configuration of “Pia < Pra, p1 < Pia, p3 < Pia, and p2 > p1, p2 > p3”. Even in the surface acoustic wave resonator 10 having this configuration, generation of a ripple on the lower frequency side than the resonance frequency of the surface acoustic wave resonator 10 can be suppressed.

[0055] Furthermore, the surface acoustic wave resonator 10 of the present embodiment may have the following configuration.

[0056] FIG. 5 is a diagram showing another example of the electrode finger pitch Pi of the IDT electrode 11 and the reflective electrode finger pitch Pr of the reflector 12.

[0057] The IDT electrode 11 has a configuration in which a fourth pitch p4, which is the electrode finger pitch Pi of two adjacent electrode fingers 11a and 11b in the fourth region T4, is larger than the third pitch p3 (p4 > p3). The fourth pitch p4 is preferably 0.99 times or more and 1.01 times or less the average IDT pitch Pia.

[0058] Also, the IDT electrode 11 has a configuration in which a fifth pitch p5, which is the electrode finger pitch Pi of two adjacent electrode fingers 11a and 11b in the fifth region T5, is smaller than the fourth pitch p4 and smaller than the average IDT pitch Pia (p5 < p4 and p5 < Pia). For example, the fifth pitch p5 is 0.96 times or more and 0.98 times or less the average IDT pitch Pia (see FIGS. 10A and 9A shown later).

[0059] That is, the IDT electrode 11 further has a pitch structure in which the value of the fifth pitch p5 between the fourth pitch p4 and the central portion 11d is small at the end 11e of the IDT electrode 11.

[0060] In other words, the IDT electrode 11 has a pitch structure in which, among three electrode finger pitches Pi arranged along the first direction d1, an inner electrode finger pitch Pi located between two outer electrode finger pitches Pi is smaller than the two outer electrode finger pitches Pi. The IDT electrode 11 has a plurality of such pitch structures at the end portion 11e of the IDT electrode 11. In the example shown in FIG. 5 , the third pitch p3 is smaller than the second pitch p2 and the fourth pitch p4 on both sides of the third pitch p3, and the fifth pitch p5 is smaller than the fourth pitch p4 on both sides of the fifth pitch p5 and the electrode finger pitch Pi in the central portion 11d. This configuration further suppresses ripples at frequencies lower than the resonant frequency of the acoustic wave resonator 10.

[0061] The above configuration and effects of acoustic wave resonator 10 will be described below by comparing a comparative example, a reference example, and an example.

[0062] [Comparative Example 1, Reference Example and Examples 1, 2, 3 and 4] A description will be given of Comparative Example 1, Reference Example, and Examples 1, 2, 3, and 4. Examples 1 to 4 are examples of the first embodiment.

[0063] FIG. 6 is a diagram showing electrode parameters of the acoustic wave resonators 10 according to the first, second, third, and fourth examples.

[0064] The figure shows the wavelengths of the IDT electrode 11, the wavelength of the reflector 12 on one side (the minus side in the first direction d1), and the wavelength of the reflector 12 on the other side (the plus side in the first direction d1) with respect to the wavelength of the elastic wave resonator 10. The wavelength is a value corresponding to the electrode finger pitch Pi or the reflective electrode finger pitch Pr. The figure also shows the intersection width of the IDT electrode 11. The figure also shows the logarithms of the IDT electrode 11, the logarithm of one reflector 12, and the logarithm of the other reflector 12 with respect to the logarithm. The value obtained by doubling the logarithm and adding 1 is the total number of electrode fingers 11a and 11b. The figure also shows the duty ratios of the IDT electrode 11, the duty ratio of one reflector 12, and the duty ratio of the other reflector 12 with respect to the duty. The figure also shows the gaps between the one reflector 12 and the IDT electrode 11, and the gap between the IDT electrode 11 and the other reflector 12 with respect to the electrode gap. These gaps are calculated by "(center-to-center distance [μm] in the first direction d1 of the electrode fingers and reflective electrode fingers adjacent in the first direction d1) ÷ reflector wavelength [μm]". The resonance frequencies of the elastic wave resonators 10 of Examples 1 to 4 are 1938 MHz.

[0065] The figure also shows the pitch ratio (= Pra / Pia), which is the ratio of the average reflector pitch Pra to the average IDT pitch Pia. In this example, examples in which the pitch ratio is changed to 1.04, 1.05, 1.06, and 1.10 are shown. The above electrode parameters are shown corresponding to each pitch ratio.

[0066] Examples 1 to 4 have the configuration of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia" shown in Embodiment 1. Examples 1 to 4 also have a pitch structure in which the electrode finger pitch Pi between both outer sides is smaller than the electrode finger pitch Pi of both outer sides at the end 11e of the IDT electrode 11.

[0067] On the other hand, in Comparative Example 1, the electrode finger pitch of the IDT electrode is the same, and the reflector's reflector electrode finger pitch is also the same. In the Reference Example, the electrode finger pitch of the first electrode finger closest to the reflector is the same as the electrode finger pitch in the central portion. In addition, the Reference Example has the above pitch structure in only one location. The resonant frequencies of the acoustic wave resonators of Comparative Example 1 and the Reference Example are the same as those of Examples 1 to 4.

[0068] First, examples in which the pitch ratio (= Pra / Pia) is 1.04, 1.05, 1.06, and 1.10 in Examples 1, 2, 3, and 4 will be described with reference to FIGS. 7A to 10B. The pitch ratio (= Pra / Pia) in the comparative example and reference example is also changed in the same way as in Examples 1, 2, 3, and 4. For example, the pitch ratio is 1.04 in FIGS. 7A and 7B, 1.05 in FIGS. 8A and 8B, 1.06 in FIGS. 9A and 9B, and 1.10 in FIGS. 10A and 10B. In FIGS. 7A, 8A, 9A, and 10A, the end 11e of the IDT electrode 11 adjacent to one of the reflectors 12 will be described as an example. However, the end 11e adjacent to the other reflector 12 also has a similar configuration.

[0069] FIG. 7A is a diagram showing the electrode finger pitch of the acoustic wave resonators of Comparative Example 1, Reference Example, and Example 1 (where the pitch ratio, which is the ratio of the average reflector pitch to the average IDT pitch, is 1.04).

[0070] The vertical axis of FIG. 7A indicates the magnitude (magnification) of each pitch when the average IDT pitch Pia is used as the reference (Pia=1). The horizontal axis of FIG. 7A indicates the electrode fingers at the end 11e of the IDT electrode 11. In FIG. 7A, two adjacent electrode finger pitches Pi are connected by a line, and the change in the electrode finger pitch Pi is shown as a line graph. Each of the electrode fingers 11a and 11b at the end 11e is referred to as the kth electrode finger (where k is an integer greater than or equal to 1) from the electrode finger closest to the reflector 12 toward the center 11d, and the "kth" is written sequentially on the horizontal axis of FIG. 7A. The same applies to FIGS. 8A, 9A, 10A, and 11A.

[0071] As shown in the figure, in Comparative Example 1, the electrode finger pitch of the IDT electrode and the reflection electrode finger pitch of the reflector are the same. In the reference example, the first electrode finger pitch closest to the reflector is the same as the electrode finger pitch at the center.

[0072] The first pitch p1 of Example 1 is the electrode finger pitch formed by the first electrode finger and the second electrode finger, the second pitch p2 is the electrode finger pitch formed by the third electrode finger and the fourth electrode finger, the third pitch p3 is the electrode finger pitch formed by the seventh electrode finger and the eighth electrode finger, the fourth pitch p4 is the electrode finger pitch formed by the eighth electrode finger and the ninth electrode finger, and the fifth pitch p5 is the electrode finger pitch formed by the tenth electrode finger and the eleventh electrode finger.

[0073] Example 1 has a configuration of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia". Also, in Example 1, at the end 11e of the IDT electrode 11, there are two pitch structures in which the electrode finger pitch Pi between the two outer sides is smaller than the electrode finger pitch Pi of the two outer sides. Specifically, the third pitch p3 is smaller than each of the second pitch p2 and the fourth pitch p4, and the fifth pitch p5 is smaller than each of the fourth pitch p4 and the electrode finger pitch Pi of the central portion 11d. In this example, each of the third pitch p3 and the fifth pitch p5 is a minimum point.

[0074] FIG. 7B is a diagram showing the reflection loss of the surface acoustic wave resonators of Comparative Example 1, the reference example, and Example 1 (example when the pitch ratio is 1.04).

[0075] On the vertical axis of FIG. 7B, the reflection loss increases as it goes downward on the vertical axis. The same applies to FIGS. 8B, 9B, 10B, and 11B below.

[0076] As shown in FIG. 7B, in Comparative Example 1, large ripples occur on the lower frequency side than the resonance frequency of the elastic wave resonator. On the other hand, in Example 1, the occurrence of ripples is suppressed on the lower frequency side than the resonance frequency of the elastic wave resonator. Note that the occurrence of ripples is also suppressed in the reference example.

[0077] FIG. 8A is a diagram showing the electrode finger pitch of the elastic wave resonators of Comparative Example 1, the reference example, and Example 2 (example when the pitch ratio is 1.05).

[0078] Comparative Example 1 and the reference example are the same as in FIG. 7A.

[0079] The first pitch p1 of Example 2 is the electrode finger pitch formed by the first electrode finger and the second electrode finger, the second pitch p2 is the electrode finger pitch formed by the second electrode finger and the third electrode finger, the third pitch p3 is the electrode finger pitch formed by the fourth electrode finger and the fifth electrode finger, the fourth pitch p4 is the electrode finger pitch formed by the fifth electrode finger and the sixth electrode finger, and the fifth pitch p5 is the electrode finger pitch formed by the seventh electrode finger and the eighth electrode finger.

[0080] Example 2 also has a configuration of "Pia <Pra, p1 <Pia, p2> p1, p3 <p2 and p3 <Pia". Also, Example 2 also has two pitch structures in which at the end 11e of the IDT electrode 11, the electrode finger pitch Pi between both outer sides becomes a value smaller than the electrode finger pitch Pi of both outer sides. In this example as well, each of the third pitch p3 and the fifth pitch p5 is a minimum point.

[0081] FIG. 8B is a diagram showing the reflection loss of the elastic wave resonators of Comparative Example 1, the reference example, and Example 2 (example when the pitch ratio is 1.05).

[0082] As shown in FIG. 8B, in Comparative Example 1, large ripples occur on the lower frequency side than the resonance frequency of the elastic wave resonator. On the other hand, in Example 2, the occurrence of ripples is suppressed on the lower frequency side than the resonance frequency of the elastic wave resonator. Note that the occurrence of ripples is also suppressed to some extent in the reference example.

[0083] FIG. 9A is a diagram showing the electrode finger pitch of the elastic wave resonators of Comparative Example 1, the reference example, and Example 3 (example when the pitch ratio is 1.06).

[0084] Comparative Example 1 and the reference example are the same as in FIG. 7A.

[0085] The first pitch p1 of Example 3 is the electrode finger pitch formed by the first electrode finger and the second electrode finger, the second pitch p2 is the electrode finger pitch formed by the third electrode finger and the fourth electrode finger, the third pitch p3 is the electrode finger pitch formed by the fourth electrode finger and the fifth electrode finger, the fourth pitch p4 is the electrode finger pitch formed by the fifth electrode finger and the sixth electrode finger, and the fifth pitch p5 is the electrode finger pitch formed by the seventh electrode finger and the eighth electrode finger.

[0086] Example 3 also has the configuration of "Pia <Pra, p1 <Pia, p2> p1, p3 <p2 and p3 <Pia". Also, Example 3 also has two pitch structures in which the electrode finger pitch Pi between both outer sides is smaller than the electrode finger pitch Pi of both outer sides at the end 11e of the IDT electrode 11. In this example as well, each of the third pitch p3 and the fifth pitch p5 is a minimum point.

[0087] FIG. 9B is a diagram showing the reflection loss of the elastic wave resonators of Comparative Example 1, the reference example, and Example 3 (example when the pitch ratio is 1.06).

[0088] As shown in FIG. 9B, in Comparative Example 1, large ripples occur on the lower frequency side than the resonance frequency of the elastic wave resonator. In the reference example, small ripples also occur on the lower frequency side than the resonance frequency of the elastic wave resonator. In contrast, in Example 3, the occurrence of ripples is suppressed on the lower frequency side than the resonance frequency of the elastic wave resonator.

[0089] FIG. 10A is a diagram showing the electrode finger pitches of the elastic wave resonators of Comparative Example 1, the reference example, and Example 4 (an example when the pitch ratio is 1.10).

[0090] Comparative Example 1 and the reference example are the same as in FIG. 7A.

[0091] The first pitch p1 of Example 4 is the electrode finger pitch formed by the first electrode finger and the second electrode finger, the second pitch p2 is the electrode finger pitch formed by the third electrode finger and the fourth electrode finger, the third pitch p3 is the electrode finger pitch formed by the fourth electrode finger and the fifth electrode finger, the fourth pitch p4 is the electrode finger pitch formed by the fifth electrode finger and the sixth electrode finger, and the fifth pitch p5 is the electrode finger pitch formed by the sixth electrode finger and the seventh electrode finger.

[0092] Example 4 also has a configuration of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia". Further, Example 4 has three pitch structures in which the electrode finger pitch Pi between both outer sides is smaller than the electrode finger pitch Pi between both outer sides at the end 11e of the IDT electrode 11. In this example, each of the third pitch p3 and the fifth pitch p5 becomes a minimum point, and further, the pitch between the tenth electrode finger and the eleventh electrode finger becomes a minimum point.

[0093] FIG. 10B is a diagram showing the reflection loss of the elastic wave resonators of Comparative Example 1, the reference example, and Example 4 (an example when the pitch ratio is 1.10).

[0094] 10B, in Comparative Example 1, large ripples occur on the frequency side lower than the resonant frequency of the elastic wave resonator. In the Reference Example, ripples also occur on the frequency side lower than the resonant frequency of the elastic wave resonator. In contrast, in Example 4, ripples are suppressed on the frequency side lower than the resonant frequency of the elastic wave resonator compared to Comparative Example 1 and the Reference Example.

[0095] Next, an example in which the electrode finger pitch of the first electrode finger closest to the reflector is the same as the electrode finger pitch in the central portion will be described as Comparative Example 2.

[0096] FIG. 11A is a diagram showing the electrode finger pitches of the acoustic wave resonators of Comparative Example 2 and Example 4 (examples where the pitch ratio is 1.10).

[0097] In Comparative Example 2, the pitch of the first electrode finger closest to the reflector is the same as the pitch of the electrode fingers in the central portion. That is, in Comparative Example 2, the first pitch p1 is equal to the average IDT pitch Pia. Example 4 has the same configuration as that shown in FIG. 10A.

[0098] FIG. 11B is a diagram showing the reflection losses of the acoustic wave resonators of Comparative Example 2 and Example 4 (when the pitch ratio is 1.10).

[0099] 11B, in Comparative Example 2 where the first pitch p1=the average IDT pitch Pia, ripples occur on the frequency side lower than the resonant frequency of the elastic wave resonator. In contrast, in Example 4, the occurrence of ripples on the frequency side lower than the resonant frequency of the elastic wave resonator is suppressed compared to Comparative Example 2.

[0100] As described above, acoustic wave resonator 10 of the present embodiment has the following configurations (1) to (4). (1) Average IDT pitch Pia < Average reflector pitch Pra (2) First pitch p1<average IDT pitch Pia (3) Second pitch p2 > First pitch p1 (4) Third pitch p3<second pitch p2 and third pitch p3<average IDT pitch Pia

[0101] With the above configuration, it is possible to suppress the occurrence of ripples on the frequency side lower than the resonance frequency of acoustic wave resonator 10.

[0102] In order to suppress the occurrence of ripples, it is desirable that the relationship between the average IDT pitch Pia and the average reflector pitch Pra satisfy the following relationship (see FIGS. 7A to 10B).

[0103] For example, the average reflector pitch Pra is preferably 1.04 times or more and 1.1 times or less the average IDT pitch Pia. Alternatively, the average reflector pitch Pra is preferably more than 1.05 times or more and 1.1 times or less the average IDT pitch Pia. Alternatively, the average reflector pitch Pra is preferably 1.06 times or more and 1.1 times or less the average IDT pitch Pia.

[0104] (Embodiment 2) In the second embodiment, an acoustic wave filter device 1 including an acoustic wave resonator 10 according to the first embodiment will be described with reference to FIGS.

[0105] FIG. 12 is a diagram illustrating a circuit configuration of an acoustic wave filter device 1 according to a second embodiment.

[0106] 12, the acoustic wave filter device 1 includes a first input / output terminal 50 and a second input / output terminal 60, a plurality of series arm resonators S10, S20, S30, and S40 connected between the first input / output terminal 50 and the second input / output terminal 60, and a plurality of parallel arm resonators P10, P20, P30, and P40 connected to a node on a path connecting the first input / output terminal 50 and the second input / output terminal 60 and to ground. In this way, the acoustic wave filter device 1 has a ladder structure including the plurality of series arm resonators S10 to S40 and the plurality of parallel arm resonators P10 to P40.

[0107] FIG. 13 is a diagram illustrating an example of the electrode finger pitch Pi of the IDT electrode 11 and the reflector finger pitch Pr of the reflector 12 of the first acoustic wave resonator 210 and the second acoustic wave resonator 220 included in the acoustic wave filter device 1.

[0108] 13, the acoustic wave filter device 1 includes a first acoustic wave resonator 210 and a second acoustic wave resonator 220 arranged along a first direction d1. At least one of the plurality of series arm resonators S10 to S40 is configured by the first acoustic wave resonator 210, and at least one of the plurality of parallel arm resonators P10 to P40 is configured by the second acoustic wave resonator 220.

[0109] Each of the first acoustic wave resonator 210 and the second acoustic wave resonator 220 includes an IDT electrode 11 and a plurality of reflectors 12 .

[0110] One reflector 12 is shared between the reflector (the other reflector) located adjacent to the second acoustic wave resonator 220 among the multiple reflectors 12 of the first acoustic wave resonator 210 and the reflector located adjacent to the first acoustic wave resonator 210 among the multiple reflectors 12 of the second acoustic wave resonator 220. In other words, one reflector 12, rather than two reflectors, is disposed between the IDT electrode 11 of the first acoustic wave resonator 210 and the IDT electrode of the second acoustic wave resonator 220. The reflecting electrode finger pitch Pr of the shared reflector 12 is, for example, 0.99 to 1.01 times the electrode finger pitch Pi of the IDT electrode 11 of the second acoustic wave resonator 220.

[0111] The first acoustic wave resonator 210 is configured by the acoustic wave resonator 10 described in the first embodiment. The average IDT pitch Pia of the first acoustic wave resonator 210 is smaller than the electrode finger pitch Pi of the IDT electrode 11 of the second acoustic wave resonator 220 and is also smaller than the reflector finger pitch Pr of the single shared reflector 12.

[0112] According to this configuration, the first acoustic wave resonator 210 and the second acoustic wave resonator 220 arranged along the first direction d1 can share one reflector 12. This makes it possible to reduce the size of the acoustic wave filter device 1.

[0113] (summary) An example of an elastic wave resonator of the present invention will be described below.

[0114] An acoustic wave resonator 10 of Example 1 includes a piezoelectric substrate 100, and an IDT electrode 11 and a plurality of reflectors 12 formed on a main surface 100a of the piezoelectric substrate 100. The IDT electrode 11 has a plurality of electrode fingers 11a, 11b arranged in a first direction d1 and a second direction d2 that are directions along the main surface 100a of the piezoelectric substrate 100, and extending in a second direction d2 that intersects the first direction d1. Each of the plurality of reflectors 12 is arranged on both outer sides of the IDT electrode 11 in the first direction d1, and has a plurality of reflecting electrode fingers 12a arranged to extend in the second direction d2.

[0115] The center-to-center distance in the first direction d1 between adjacent electrode fingers 11a, 11b among the plurality of electrode fingers 11a, 11b is defined as the electrode finger pitch Pi, and the center-to-center distance in the first direction d1 between adjacent reflective electrode fingers 12a among the plurality of reflective electrode fingers 12a is defined as the reflective electrode finger pitch Pr. If the average value of the plurality of electrode finger pitches Pi in the central portion 11d of the IDT electrode 11 is defined as the average IDT pitch Pia, and the average value of the plurality of reflective electrode finger pitches Pr in the reflector 12 is defined as the average reflector pitch Pra, the average IDT pitch Pia is smaller than the average reflector pitch Pra.

[0116] The IDT electrode 11 has, at an end 11e different from the central portion 11d, a first region T1 closest to the reflector 12, a second region T2 located closer to the central portion 11d than the first region T1, and a third region T3 located closer to the central portion 11d than the second region T2.

[0117] In the first region T1, the first pitch p1, which is the electrode finger pitch between the first electrode finger f1 closest to the reflector 12 and the second electrode finger f2 located next to the first electrode finger f1, is smaller than the average IDT pitch Pia. The second pitch p2, which is the electrode finger pitch Pi between two adjacent electrode fingers in the second region T2, is larger than the first pitch p1. The third pitch p3, which is the electrode finger pitch Pi between two adjacent electrode fingers in the third region T3, is smaller than the second pitch p2 and also smaller than the average IDT pitch Pia.

[0118] In this way, by having the surface acoustic wave resonator 10 configured as "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia", it is possible to suppress the occurrence of ripples on the lower frequency side than the resonance frequency of the surface acoustic wave resonator 10.

[0119] The surface acoustic wave resonator 10 of Example 2 is the surface acoustic wave resonator described in Example 1, and the second pitch p2 may be 0.99 times or more and 1.01 times or less of the average IDT pitch Pia.

[0120] In this way, by setting the second pitch p2 to be 0.99 times or more and 1.01 times or less of the average IDT pitch Pia, it is possible to suppress the occurrence of ripples on the lower frequency side than the resonance frequency of the surface acoustic wave resonator 10.

[0121] The surface acoustic wave resonator 10 of Example 3 is the surface acoustic wave resonator described in Example 1 or 2, and further has a fourth region T4 located closer to the central portion 11d than the third region T3, and a fifth region T5 located closer to the central portion 11d than the fourth region T4. The fourth pitch p4, which is the electrode finger pitch Pi between two adjacent electrode fingers in the fourth region T4, is larger than the third pitch p3, and the fifth pitch p5, which is the electrode finger pitch Pi between two adjacent electrode fingers in the fifth region T5, may be smaller than the fourth pitch p4 and also smaller than the average IDT pitch Pia.

[0122] In this way, by setting "p4 > p3, p5 < p4 and p5 < Pia", it is possible to suppress the occurrence of ripples on the lower frequency side than the resonance frequency of the surface acoustic wave resonator 10.

[0123] An elastic wave resonator 10 of Example 4 is the elastic wave resonator described in Example 1 or 2, in which the IDT electrode 11 has a pitch structure in which, among three electrode finger pitches Pi arranged along the first direction d1, one inner electrode finger pitch Pi located between two outer electrode finger pitches Pi has a smaller value than the two outer electrode finger pitches Pi, and the IDT electrode 11 may have a plurality of the above pitch structures at an end 11e.

[0124] In this way, by providing a plurality of the above-described pitch structures at end portion 11e of IDT electrode 11, it is possible to suppress the occurrence of ripples on the frequency side lower than the resonance frequency of acoustic wave resonator 10.

[0125] The acoustic wave filter device 1 of Example 5 includes a first acoustic wave resonator 210 and a second acoustic wave resonator 220 arranged along a first direction d1. Each of the first acoustic wave resonator 210 and the second acoustic wave resonator 220 includes an IDT electrode 11 and a plurality of reflectors 12. One reflector 12 is shared between the reflector 12 of the first acoustic wave resonator 210 that is adjacent to the second acoustic wave resonator 220 and the reflector 12 of the second acoustic wave resonator 220 that is adjacent to the first acoustic wave resonator 210. The first acoustic wave resonator 210 is configured using the acoustic wave resonator 10 described above. The average IDT pitch Pia of the first acoustic wave resonator 210 is smaller than the electrode finger pitch Pi of the IDT electrode 11 of the second acoustic wave resonator 220 and is smaller than the reflector finger pitch Pr of the shared reflector 12.

[0126] According to this configuration, the first acoustic wave resonator 210 and the second acoustic wave resonator 220 arranged along the first direction d1 can share one reflector 12. This allows the acoustic wave filter device 1 to be miniaturized.

[0127] An acoustic wave filter device 1 of Example 6 is the acoustic wave filter device according to Example 5, and has a ladder structure including a plurality of series arm resonators S10 to S40 and a plurality of parallel arm resonators P10 to P40. At least one of the plurality of series arm resonators S10 to S40 may be formed by a first acoustic wave resonator 210, and at least one of the plurality of parallel arm resonators P10 to P40 may be formed by a second acoustic wave resonator 220.

[0128] According to this configuration, one reflector 12 can be shared by the series arm resonators and the parallel arm resonators, thereby enabling the acoustic wave filter device 1 to be miniaturized.

[0129] The acoustic wave filter device 1 of Example 7 is the acoustic wave filter device 1 of Example 5 or 6, and the reflecting electrode finger pitch Pr of the shared reflector may be 0.99 to 1.01 times the electrode finger pitch Pi of the IDT electrode 11 of the second acoustic wave resonator 220.

[0130] This configuration allows the first acoustic wave resonator 210 and the second acoustic wave resonator 220 to share one reflector 12. This allows the acoustic wave filter device 1 to be miniaturized.

[0131] (Other embodiments, etc.) Although the acoustic wave resonators and acoustic wave filter devices according to the embodiments of the present invention have been described above with reference to the embodiments and examples, the acoustic wave resonators and acoustic wave filter devices of the present invention are not limited to the above embodiments and examples. The present invention also includes other embodiments realized by combining any of the components in the above embodiments and examples, examples obtained by applying various modifications to the above embodiments that would occur to those skilled in the art without departing from the spirit of the present invention, and various devices incorporating the acoustic wave resonators and acoustic wave filter devices of the present invention. [Industrial Applicability]

[0132] INDUSTRIAL APPLICABILITY The present invention can be widely used as a low-loss, small-sized acoustic wave resonator and acoustic wave filter device in communication devices such as mobile phones. [Explanation of symbols]

[0133] 1. Elastic wave filter device 10. Elastic wave resonator 11 IDT electrode 11A, 11B comb-shaped electrode 11a, 11b electrode fingers 11c Busbar electrode 11d central part 11e End 12 reflector 12a Reflector electrode finger 12c Busbar electrode 50, 60 input / output terminals 100 Piezoelectric substrate 100a main surface 110 electrodes 111 Adhesion layer 112 Main electrode layer 113 Protective film 210 First acoustic wave resonator 220 Second acoustic wave resonator d1 1st direction d2 2nd direction f1 1st electrode finger f2 2nd electrode finger p1 First pitch p2 2nd pitch p3 3rd pitch p4 4th pitch p5 5th pitch Pi electrode finger pitch Pia Average IDT pitch Pr Reflector finger pitch Pra mean reflector pitch Pra / Pia pitch ratio P10, P20, P30, P40 parallel arm resonators S10, S20, S30, S40 series arm resonators T1 1st area T2 2nd area T3 3rd area T4 4th Domain T5 The 5th Domain

Claims

1. a piezoelectric substrate; an IDT electrode and a plurality of reflectors formed on a main surface of the piezoelectric substrate; Equipped with the IDT electrode has a plurality of electrode fingers arranged in a first direction and a second direction that are directions along a main surface of the piezoelectric substrate, so as to extend in the second direction that intersects the first direction; each of the plurality of reflectors is disposed on both outer sides of the IDT electrode in the first direction and has a plurality of reflecting electrode fingers disposed to extend in the second direction; a center-to-center distance in the first direction between adjacent electrode fingers of the plurality of electrode fingers is defined as an electrode finger pitch; a center-to-center distance in the first direction between adjacent reflective electrode fingers of the plurality of reflective electrode fingers is defined as a reflective electrode finger pitch; When the average value of the pitches of the plurality of electrode fingers at the center of the IDT electrode is defined as an average IDT pitch, and the average value of the pitches of the plurality of reflecting electrode fingers in the reflector is defined as an average reflector pitch, the average IDT pitch is smaller than the average reflector pitch; the IDT electrode has, at an end portion different from the central portion, a first region closest to the reflector, a second region located closer to the central portion than the first region, and a third region located closer to the central portion than the second region; in the first region, a first pitch, which is the electrode finger pitch between a first electrode finger closest to the reflector and a second electrode finger positioned adjacent to the first electrode finger, is smaller than the average IDT pitch; a second pitch, which is the electrode finger pitch between two adjacent electrode fingers in the second region, is larger than the first pitch; a third pitch, which is the electrode finger pitch between two adjacent electrode fingers in the third region, is smaller than the second pitch and is also smaller than the average IDT pitch; Elastic wave resonator.

2. The second pitch is 0.99 to 1.01 times the average IDT pitch. The elastic wave resonator according to claim 1 .

3. Further, the optical fiber 100 has a fourth region located closer to the central portion than the third region, and a fifth region located closer to the central portion than the fourth region, a fourth pitch, which is the electrode finger pitch between two adjacent electrode fingers in the fourth region, is larger than the third pitch; A fifth pitch, which is the electrode finger pitch between two adjacent electrode fingers in the fifth region, is smaller than the fourth pitch and is also smaller than the average IDT pitch.

3. The elastic wave resonator according to claim 1.

4. the IDT electrode has a pitch structure in which, among the three electrode finger pitches arranged along the first direction, one inner electrode finger pitch located between two outer electrode finger pitches has a smaller value than the two outer electrode finger pitches, At the end of the IDT electrode, a plurality of the pitch structures are provided.

3. The elastic wave resonator according to claim 1.

5. a first acoustic wave resonator and a second acoustic wave resonator arranged along the first direction, each of the first acoustic wave resonator and the second acoustic wave resonator includes an IDT electrode and a plurality of reflectors; a reflector of the first acoustic wave resonator adjacent to the second acoustic wave resonator and a reflector of the second acoustic wave resonator adjacent to the first acoustic wave resonator are shared by a single reflector; the first acoustic wave resonator is configured by the acoustic wave resonator according to claim 1 or 2, The average IDT pitch of the first acoustic wave resonator is smaller than the electrode finger pitch of the IDT electrode of the second acoustic wave resonator and is also smaller than the reflector finger pitch of the shared reflector. Acoustic wave filter device.

6. the acoustic wave filter device has a ladder structure including a plurality of series arm resonators and a plurality of parallel arm resonators; at least one of the plurality of series arm resonators is configured by the first acoustic wave resonator; At least one of the plurality of parallel arm resonators is configured by the second acoustic wave resonator. The acoustic wave filter device according to claim 5 .

7. The reflecting electrode finger pitch of the shared reflector is 0.99 to 1.01 times the electrode finger pitch of the IDT electrode of the second acoustic wave resonator. The acoustic wave filter device according to claim 5 .

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