Elastic wave resonator and elastic wave filter device

Abstract

Provided are an elastic wave resonator and an elastic wave filter device that suppress the generation of ripples on the lower frequency side than the resonant frequency of the elastic wave resonator. An IDT electrode (11) of an elastic wave resonator (10) has, in an end portion (11e), a first region (T1) closest to a reflector (12), a second region (T2) positioned closer to a center portion (11d) side than the first region, and a third region (T3) positioned closer to the center portion side than the second region. A first pitch (p1), which is an electrode finger pitch between a first electrode finger (f1) closest to the reflector in the first region and a second electrode finger (f2) located next to the first electrode finger, is smaller than an average IDT pitch (Pia). A third pitch (p3), which is an electrode finger pitch (Pi) between two adjacent electrode fingers in the third region, is smaller than the average IDT pitch. A second pitch (p2), which is an electrode finger pitch (Pi) between two adjacent electrode fingers in the second region, is larger than either the first pitch or the third pitch.

Description

Technical Field

[0001] The present invention relates to an elastic wave resonator and an elastic wave filter device having the elastic wave resonator. Background Art

[0002] Conventionally, elastic wave resonators including an IDT electrode and multiple reflectors are known. Patent Document 1 discloses a technique for reducing ripples generated at frequencies lower than the resonant frequency of the elastic wave resonator by changing the pitch of electrode fingers at the ends of the IDT electrode.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-182460

[0006] However, in the elastic wave resonator described in Patent Document 1, ripples may occur in a frequency band that is lower than the resonant frequency of the elastic wave resonator. Summary of the Invention

[0007] Problems to be solved by the invention

[0008] The present invention provides an elastic wave resonator and the like capable of suppressing the generation of ripples at a frequency lower than the resonant frequency of the elastic wave resonator.

[0009] Technical solutions to solve problems

[0010] An elastic wave resonator according to one embodiment of the present invention includes: a piezoelectric substrate; an IDT electrode; and a plurality of reflectors formed on a principal surface of the piezoelectric substrate, wherein the IDT electrode has a plurality of electrode fingers arranged in a first direction and a second direction along the principal surface of the piezoelectric substrate so as to extend in the second direction intersecting the first direction; the plurality of reflectors are arranged on both sides of the IDT electrode in the first direction and have a plurality of reflective electrode fingers arranged so as to extend in the second direction; an electrode finger pitch is defined as a distance between centers of adjacent electrode fingers in the first direction, a reflective electrode finger pitch is defined as a distance between centers of adjacent reflective electrode fingers in the first direction, and an average value of the plurality of electrode finger pitches in a central portion of the IDT electrode is defined as an average value. In the case where the average IDT pitch is set, and the average value of the multiple reflective electrode finger pitches in the reflector is set as the average reflector pitch, the average IDT pitch is smaller than the average reflector pitch, 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, the first pitch of the electrode finger pitch of the first electrode finger closest to the reflector in the first region and the second electrode finger located next to the first electrode finger is smaller than the average IDT pitch, the second pitch of the electrode finger pitch of two adjacent electrode fingers in the second region is larger than the first pitch, and the third pitch of the electrode finger pitch of two adjacent electrode fingers in the third region is smaller than the second pitch and smaller than the average IDT pitch.

[0011] An elastic wave filter device according to one embodiment of the present invention includes a first elastic wave resonator and a second elastic wave resonator arranged along a first direction. The first elastic wave resonator and the second elastic wave resonator each include an IDT electrode and a plurality of reflectors. A reflector located adjacent to the second elastic wave resonator among the plurality of reflectors of the first elastic wave resonator and a reflector located adjacent to the first elastic wave resonator among the plurality of reflectors of the second elastic wave resonator are shared as a single reflector. The first elastic wave resonator is formed of the aforementioned elastic wave resonators. The average IDT pitch of the first elastic wave resonator is smaller than the electrode finger pitch of the IDT electrode of the second elastic wave resonator and smaller than the reflective electrode finger pitch of the shared reflector.

[0012] Effects of the Invention

[0013] According to the elastic wave resonator and the like according to the present invention, it is possible to suppress the generation of ripples at a frequency lower than the resonant frequency of the elastic wave resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 1 and 2 are a plan view and a cross-sectional view schematically showing the electrode structure of the elastic wave resonator according to the first embodiment.

[0015] Figure 2 1 is a diagram illustrating a first region, a second region, a third region, and the like of an IDT electrode included in an elastic wave resonator.

[0016] Figure 3 FIG. 1 is a diagram showing an example of the electrode finger pitch of the IDT electrode and the reflective electrode finger pitch of the reflector.

[0017] Figure 4 FIG. 1 is a diagram showing another example of the electrode finger pitch of the IDT electrode and the reflective electrode finger pitch of the reflector.

[0018] Figure 5 FIG. 1 is a diagram showing another example of the electrode finger pitch of the IDT electrode and the reflective electrode finger pitch of the reflector.

[0019] Figure 6 Graphs showing electrode parameters of the elastic wave resonators of Examples 1, 2, 3, and 4.

[0020] Figure 7A Graphs showing electrode finger pitches of elastic wave resonators according to Comparative Example 1, Reference Example, and Example 1 (this example assumes a pitch ratio of the average reflector pitch to the average IDT pitch of 1.04).

[0021] Figure 7B Graphs showing the reflection losses of the elastic wave resonators of Comparative Example 1, Reference Example, and Example 1 (example when the pitch ratio is 1.04).

[0022] Figure 8A Graphs showing the electrode finger pitches of the elastic wave resonators of Comparative Example 1, Reference Example, and Example 2 (example when the pitch ratio is set to 1.05).

[0023] Figure 8B Graphs showing the reflection losses of the elastic wave resonators of Comparative Example 1, Reference Example, and Example 2 (example when the pitch ratio is 1.05).

[0024] Figure 9A Graphs showing the electrode finger pitches of the elastic wave resonators of Comparative Example 1, Reference Example, and Example 3 (example when the pitch ratio is set to 1.06).

[0025] Figure 9BGraphs showing the reflection losses of the elastic wave resonators of Comparative Example 1, Reference Example, and Example 3 (example when the pitch ratio is 1.06).

[0026] Figure 10A Graphs showing the electrode finger pitches of the elastic wave resonators of Comparative Example 1, Reference Example, and Example 4 (example when the pitch ratio is set to 1.10).

[0027] Figure 10B Graphs showing the reflection losses of the elastic wave resonators of Comparative Example 1, Reference Example, and Example 4 (example when the pitch ratio is 1.10).

[0028] Figure 11A Graphs showing the electrode finger pitches of the elastic wave resonators of Comparative Example 2 and Example 4 (example when the pitch ratio is set to 1.10).

[0029] Figure 11B Graphs showing the reflection losses of the elastic wave resonators of Comparative Example 2 and Example 4 (example when the pitch ratio is 1.10).

[0030] Figure 12 This is a diagram showing a circuit configuration of an elastic wave filter device according to a second embodiment.

[0031] Figure 13 This diagram shows an example of the electrode finger pitch of IDT electrodes of the first and second elastic wave resonators and the reflection electrode finger pitch of reflectors included in the elastic wave filter device.

[0032] Description of Reference Numerals

[0033] 1 Elastic wave filter device

[0034] 10 Elastic Wave Resonator

[0035] 11 IDT electrode

[0036] 11A, 11B comb-shaped electrodes

[0037] 11a, 11b electrode fingers

[0038] 11c Busbar electrode

[0039] 11d Central

[0040] 11e end

[0041] 12 Reflector

[0042] 12a Reflective electrode finger

[0043] 12c busbar electrode

[0044] 50, 60 input and output terminals

[0045] 100 Piezoelectric substrate

[0046] 100a main surface

[0047] 110 electrodes

[0048] 111 Adhesive layer

[0049] 112 main electrode layer

[0050] 113 protective film

[0051] 210 First Elastic Wave Resonator

[0052] 220 Second elastic wave resonator

[0053] d1 1st direction

[0054] d2 2nd direction

[0055] f1 Electrode finger 1

[0056] f2 2nd electrode finger

[0057] p1 1st spacing

[0058] p2 2nd spacing

[0059] p3 3rd spacing

[0060] p4 4th pitch

[0061] p5 5th pitch

[0062] Pi electrode finger pitch

[0063] Pia average IDT spacing

[0064] Pr reflective electrode finger spacing

[0065] Pra average reflector spacing

[0066] Pra / Pia spacing ratio

[0067] P10, P20, P30, P40 parallel arm resonators

[0068] S10, S20, S30, S40 series arm resonators

[0069] T1 Area 1

[0070] T2 Area 2

[0071] T3 Area 3

[0072] T4 Area 4

[0073] T5 Zone 5. DETAILED DESCRIPTION

[0074] Below, the embodiments of the present invention are described in detail using diagrams. In addition, the embodiments described below all show general or specific examples. The numerical values, shapes, materials, components, configurations of components, and connection methods shown in the following embodiments are examples, and the main purpose is not to limit the present invention. Among the components in the following embodiments, the components that are not described in the independent claims are described as arbitrary components. In addition, the sizes or size ratios of the components shown in the drawings are not necessarily strict.

[0075] (Implementation Method 1)

[0076] [Structure of elastic wave resonator]

[0077] For the structure of the elastic wave resonator 10 according to this embodiment, refer to Figures 1 to 5 To explain.

[0078] Figure 1 1 and 2 are a plan view and a cross-sectional view schematically showing the electrode structure of the elastic wave resonator 10 according to the first embodiment.

[0079] The elastic wave resonator 10 shown in this figure is formed from a piezoelectric substrate 100, an electrode 110, and a protective film 113. It includes an IDT (Interdigital Transducer) electrode 11 and multiple reflectors 12, which are formed from these components. The elastic wave resonator 10 according to this embodiment is a surface acoustic wave (SAW) resonator composed of the IDT electrode 11, multiple reflectors 12, and the piezoelectric substrate 100.

[0080] in addition, Figure 1 The elastic wave resonator 10 shown is for explaining a typical structure thereof, and the number and length of the electrode fingers constituting the electrodes are not limited thereto.

[0081] like Figure 1 As shown in the cross-sectional view of FIG, the electrode 110 constituting the IDT electrode 11 and the plurality of reflectors 12 has a laminated structure of an adhesion layer 111 and a main electrode layer 112 .

[0082] The adhesion layer 111 is a layer for improving the adhesion between the piezoelectric substrate 100 and the main electrode layer 112 , and is made of, for example, Ti.

[0083] The main electrode layer 112 is made of, for example, Al containing 1% Cu.

[0084] The protective film 113 is formed to cover the electrode 110. The protective film 113 is a layer for protecting the main electrode layer 112 from the external environment, adjusting the frequency-temperature characteristics, and improving moisture resistance, and is a film mainly composed of silicon dioxide (SiO2), for example.

[0085] The materials constituting the adhesion layer 111, main electrode layer 112, and protective film 113 are not limited to those described above. Furthermore, the electrode 110 does not necessarily have to have the aforementioned laminated structure. For example, the electrode 110 may be composed of a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd. Furthermore, it may be composed of multiple laminates composed of the aforementioned metals or alloys. Furthermore, the protective film 113 may not be formed.

[0086] As a material of the piezoelectric substrate 100 , for example, a piezoelectric body such as aluminum nitride, lithium tantalate, lithium niobate, or quartz can be used.

[0087] Alternatively, the piezoelectric substrate 100 may include a piezoelectric layer at least partially, or may have a laminated structure including the piezoelectric layer. For example, the piezoelectric substrate 100 may include a high-acoustic-velocity supporting substrate, a low-acoustic-velocity film, and a piezoelectric layer, with the high-acoustic-velocity supporting substrate, the low-acoustic-velocity film, and the piezoelectric layer being laminated in this order.

[0088] The structures of the high-acoustic-velocity supporting substrate, the low-acoustic-velocity film, and the piezoelectric layer will be described below.

[0089] The piezoelectric layer includes, for example, a θ° Y-cut X-propagating LiTaO3 piezoelectric single crystal or piezoelectric ceramic (a lithium tantalate single crystal or ceramic cut at a plane whose normal line is an axis rotated θ° from the Y-axis toward the Z-axis with the X-axis as the center axis, and a single crystal or ceramic in which surface acoustic waves propagate in the X-axis direction).

[0090] The high-acoustic-velocity supporting substrate is a substrate that supports the low-acoustic-velocity film, the piezoelectric layer, and the electrode 110. Furthermore, the high-acoustic-velocity supporting substrate is a substrate that allows the acoustic velocity of bulk waves in the high-acoustic-velocity supporting substrate to be higher than the surface waves and boundary waves propagating through the piezoelectric layer. Furthermore, the high-acoustic-velocity supporting substrate functions to confine surface acoustic waves within the stacked portion of the piezoelectric layer and the low-acoustic-velocity film, preventing them from leaking downward from the high-acoustic-velocity supporting substrate.

[0091] The high acoustic velocity support substrate is, for example, a silicon substrate. The material of the high acoustic velocity support substrate can also include, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, forsterite, spinel, and Sialon; dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; or semiconductors such as silicon, or materials containing the above materials as the main component. Furthermore, the spinel includes an aluminum compound containing one or more elements selected from Mg, Fe, Zn, and Mn, and oxygen. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0092] The low-acoustic-velocity membrane is a membrane that lowers the acoustic velocity of bulk waves propagating through the piezoelectric layer compared to the acoustic velocity of elastic waves propagating through the piezoelectric layer. It is positioned between the piezoelectric layer and the high-acoustic-velocity support substrate. This structure, combined with the inherent concentration of elastic wave energy within the low-acoustic-velocity medium, suppresses the leakage of surface acoustic wave energy outside the IDT electrode.

[0093] The low-acoustic-velocity film is, for example, a film primarily composed of silicon dioxide (SiO2). The material of the low-acoustic-velocity film is not limited to the above-mentioned materials. For example, dielectric materials such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or compounds containing fluorine, carbon, or boron added to silicon oxide, or materials primarily composed of the above materials, may also be used.

[0094] The stacked structure of the piezoelectric substrate 100 can significantly improve the Q value of the elastic wave resonator at both the resonant and antiresonant frequencies compared to a structure using a single piezoelectric substrate 100. This allows for the formation of a surface acoustic wave resonator with a high Q value, enabling the use of this surface acoustic wave resonator to construct a filter with low insertion loss.

[0095] Alternatively, the high-acoustic-velocity support substrate may have a structure in which a support substrate and a high-acoustic-velocity film are stacked to increase the acoustic velocity of bulk waves propagating through the piezoelectric layer compared to surface waves and boundary waves.

[0096] In the case of this stacked structure, as the material of the supporting substrate, piezoelectric materials such as sapphire, lithium tantalate, lithium niobate, quartz, various ceramics such as alumina, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, forsterite, dielectrics such as glass, semiconductors such as silicon and gallium nitride, and resin substrates can be used.

[0097] In addition, materials for the high-acoustic-velocity membrane include, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, forsterite, spinel, and sialon; dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; or semiconductors such as silicon, or materials primarily composed of the above materials. Furthermore, the spinel mentioned above includes aluminum compounds containing one or more elements selected from Mg, Fe, Zn, and Mn, and oxygen. Examples of the spinel mentioned above include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0098] The materials and the like of the respective 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 prioritized among the required high-frequency propagation characteristics.

[0099] like Figure 1 As shown in the plan view of FIG, the IDT electrode 11 includes a pair of comb-shaped electrodes 11A and 11B facing each other.

[0100] Here, a given direction along the principal surface 100a of the piezoelectric substrate 100 is referred to as a first direction d1, and a direction along the principal 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 direction of propagation of elastic waves in the elastic wave resonator 10. In this embodiment, the first direction d1 and the second direction d2 are orthogonal to each other.

[0101] The comb-shaped electrode 11A is composed of a plurality of electrode fingers 11a arranged to extend in the second direction d2, and a bus bar electrode 11c connecting one end of each of the plurality of electrode fingers 11a. The comb-shaped electrode 11B is composed of a plurality of electrode fingers 11b arranged to extend in the second direction d2, and a bus bar electrode 11c connecting one end of each of the plurality of electrode fingers 11b. The plurality of electrode fingers 11a and 11b are arranged alternately in the first direction d1.

[0102] The reflectors 12 are arranged adjacent to the IDT electrode 11 in the first direction d1. Multiple reflectors 12 are arranged on both sides of the IDT electrode 11. The multiple reflectors 12 consist of one reflector 12 located on the negative side of the first direction d1 as viewed from the IDT electrode 11, and another reflector 12 located on the positive side of the first direction d1. The reflectors 12 consist of multiple reflective electrode fingers 12a arranged to extend in the second direction d2, and a busbar electrode 12c connecting one end of the multiple reflective electrode fingers 12a.

[0103] Figure 21 is a diagram illustrating a first region T1 , a second region T2 , a third region T3 , and the like of an IDT electrode 11 included in the elastic wave resonator 10 .

[0104] The IDT electrode 11 has a central portion 11d, which comprises the majority of the center in the first direction d1, and end portions 11e, distinct from the central portion 11d. The central portion 11d comprises an area that accounts for 90% of the total number of electrode fingers 11a and 11b of the IDT electrode 11. The end portions 11e are located on either side of the central portion 11d in the first direction d1 and have one end portion and another end portion. The one end portion and the other end portion each comprise an area that accounts for 5% of the total number of electrode fingers 11a and 11b of the IDT electrode 11.

[0105] The IDT electrode 11 includes, at the end 11e of the IDT electrode 11, a first region T1 closest to the reflector 12, a second region T2 located closer to the center portion 11d than the first region T1, and a third region T3 located closer to the center portion 11d than the second region T2. Furthermore, the IDT electrode 11 includes a fourth region T4 located closer to the center portion 11d than the third region T3, and a fifth region T5 located closer to the center portion 11d than the fourth region T4. These first region T1, second region T2, third region T3, fourth region T4, and fifth region T5 may be arranged adjacent to each other in the first direction d1, or may be arranged with intervals therebetween.

[0106] Furthermore, the IDT electrode 11 includes a first electrode finger f1 closest to the reflector 12 among the plurality of electrode fingers 11a and 11b in the first direction d1, and a second electrode finger f2 second closest to the reflector 12 and located next to the first electrode finger f1.

[0107] Here, the distance between the centers of the electrode fingers 11a and 11b adjacent to each other in the first direction d1 among the multiple electrode fingers 11a and 11b is defined as the electrode finger pitch Pi, and the distance between the centers of the reflective electrode fingers 12a adjacent to each other in the first direction d1 among the multiple reflective electrode fingers 12a is defined as the reflective electrode finger pitch Pr.

[0108] exist Figure 2 , as an example, 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, are shown.

[0109] 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 counted from the outermost end, the third pitch p3 is the electrode finger pitch Pi formed by the fourth and fifth electrode fingers counted from the outermost end, the fourth pitch p4 is the electrode finger pitch Pi formed by the fifth and sixth electrode fingers counted from the outermost end, and the fifth pitch p5 is the electrode finger pitch Pi formed by the seventh and eighth electrode fingers counted from the outermost end. Additionally, Figure 2 The positions of the respective regions and pitches shown are merely examples.

[0110] Furthermore, 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 reflection electrode finger pitches Pr in the reflector 12 is defined as the average reflector pitch Pra. Additionally, the average IDT pitch Pia is obtained, for example, by dividing the distance between the two ends of the central portion 11d in the first direction d1 by "the number of the plurality of electrode fingers 11a, 11b in the central portion 11d - 1". Moreover, the average reflector pitch Pra is obtained, for example, by dividing the distance between the two ends of the plurality of reflection electrode fingers 12a in the first direction d1 by "the total number of the plurality of reflection electrode fingers 12a - 1".

[0111] Under the above definitions, in the surface acoustic wave resonator 10 of the present embodiment, it has a structure in which the average IDT pitch Pia is smaller than the average reflector pitch Pra (Pia < Pra). Additionally, the surface acoustic wave resonator 10 of the present embodiment also has the following structure.

[0112] Figure 3 It is a diagram showing an example of the electrode finger pitch Pi of the IDT electrode 11 and the reflection electrode finger pitch Pr of the reflector 12.

[0113] In this diagram, a diagram is shown in which the values of the average reflector pitch Pra, the average IDT pitch Pia, and the electrode finger pitch Pi in the end portion 11e of the IDT electrode 11 are connected by lines. In Figure 4 and Figure 5 it is the same.

[0114] The IDT electrode 11 has a structure in which the first pitch p1, which is the electrode finger pitch Pi between the first electrode finger f1 and the second electrode finger f2 in the first region T1, 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 (refer to Figure 10A and Figure 9A ) shown later.

[0115] In addition, the IDT electrode 11 has a structure in which the second pitch p2 of the electrode finger pitch Pi of two adjacent electrode fingers 11a and 11b in the second region T2 is greater than the first pitch p1 (p2 > p1). In addition, it is desirable that the second pitch p2 be 0.99 times or more and 1.01 times or less of the average IDT pitch Pia.

[0116] In addition, the IDT electrode 11 has a structure in which the third pitch p3 of the electrode finger pitch Pi of two adjacent electrode fingers 11a and 11b in the third region T3 is less than the second pitch p2 and less than the average IDT pitch Pia (p3 < p2 and p3 < Pia). For example, the third pitch p3 is 0.88 times or more and 0.97 times or less of the average IDT pitch Pia (refer to Figure 9A and Figure 7A ).

[0117] That is, the IDT electrode 11 has a pitch structure in the end portion 11e of the IDT electrode 11 in which the first pitch p1 is less than the average IDT pitch Pia, and the third pitch p3 becomes a value less than the electrode finger pitch Pi of the second pitch p2 and the central portion 11d.

[0118] According to the surface acoustic wave resonator 10 having these structures (Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia), strong excitation waves generated at the end portion 11e of the IDT electrode 11 can be suppressed. Thereby, ripples generated on the low-frequency side with respect to the resonance frequency of the surface acoustic wave resonator 10 can be suppressed.

[0119] <​​​​​​​​​​​​​The IDT electrode 11 has a structure in which the fourth pitch p4, which is the pitch Pi between two adjacent electrode fingers 11a and 11b in the fourth region T4, is greater than the third pitch p3 (p4 > p3). Additionally, it is desirable that the fourth pitch p4 be not less than 0.99 times and not more than 1.01 times the average IDT pitch Pia.

[0124] Furthermore, the IDT electrode 11 has a structure in which the fifth pitch p5, which is the pitch Pi between two adjacent electrode fingers 11a and 11b in the fifth region T5, is less than the fourth pitch p4 and less than the average IDT pitch Pia (p5 < p4 and p5 < Pia). For example, the fifth pitch p5 is not less than 0.96 times and not more than 0.98 times the average IDT pitch Pia (refer to Figure 10A and Figure 9A ).

[0125] That is to say, the IDT electrode 11 also 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 portion 11e of the IDT electrode 11.

[0126] In other words, the IDT electrode 11 has a pitch structure in which, among the three electrode finger pitches Pi arranged along the first direction d1, one electrode finger pitch Pi on the inner side between the two electrode finger pitches Pi on the outer sides becomes a value smaller than the two electrode finger pitches Pi on the outer sides. The IDT electrode 11 has a plurality of the above pitch structures at the end portion 11e of the IDT electrode 11. In Figure 5 the example shown, the third pitch p3 becomes a value smaller than the second pitch p2 and the fourth pitch p4 on the two outer sides of the third pitch p3, and the fifth pitch p5 becomes a value smaller than the fourth pitch p4 and the electrode finger pitch Pi of the central portion 11d on the two outer sides of the fifth pitch p5. According to this structure, it is possible to further suppress the generation of ripples on the low-frequency side relative to the resonance frequency of the surface acoustic wave resonator 10.

[0127] Hereinafter, Comparative Example, Reference Example, and Examples will be compared to illustrate the above structure and effects of the surface acoustic wave resonator 10.

[0128] [Comparative Example 1, Reference Example, and Examples 1, 2, 3, 4]

[0129] Comparative Example 1, Reference Example, and Examples 1, 2, 3, 4 will be described. Examples 1 to 4 are an example of Embodiment 1.

[0130] Figure 6 is a diagram showing the electrode parameters of the surface acoustic wave resonators 10 of Examples 1, 2, 3, and 4.

[0131] In this figure, regarding the wavelengths of the elastic wave resonator 10, the wavelengths of the IDT electrodes 11, one reflector 12 (on the negative side of the first direction d1), and the other reflector 12 (on the positive side of the first direction d1) are shown. Additionally, the wavelength is a value corresponding to the electrode finger pitch Pi or the reflector electrode finger pitch Pr. Further, in this figure, the crossover width of the IDT electrodes 11 is shown. Moreover, in this figure, regarding the logarithm, the logarithm of the IDT electrodes 11, the logarithm of one reflector 12, and the logarithm of the other reflector 12 are shown. The value obtained by doubling the logarithm and adding 1 becomes the total number of electrode fingers 11a, 11b. Furthermore, in this figure, regarding the duty ratio, the duty ratio of the IDT electrodes 11, the duty ratio of one reflector 12, and the duty ratio of the other reflector 12 are shown. Additionally, in this figure, regarding the electrode gap, the gap between one reflector 12 and the IDT electrodes 11 and the gap between the IDT electrodes 11 and the other reflector 12 are shown. These gaps are calculated by "(the center-to-center distance [μm] in the first direction d1 between adjacent electrode fingers and reflector electrode fingers in the first direction d1) ÷ the reflector wavelength [μm]". The resonance frequencies of the elastic wave resonators 10 in Examples 1 to 4 are 1938 MHz.

[0132] Moreover, in this figure, the pitch ratio (= Pra / Pia) as the ratio of the average reflector pitch Pra to the average IDT pitch Pia is shown. In this example, examples where the pitch ratio is changed to 1.04, 1.05, 1.06, and 1.10 are shown. The above-mentioned electrode parameters are shown corresponding to each pitch ratio.

[0133] Examples 1 to 4 have the structure of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia" shown in Embodiment 1. Additionally, in Examples 1 to 4, in the end portion 11e of the IDT electrodes 11, there is a pitch structure in which the electrode finger pitch Pi between the two outer sides becomes a value smaller than the electrode finger pitch Pi of the two outer sides.

[0134] On the other hand, the electrode finger pitches of the IDT electrodes in Comparative Example 1 are the same, and moreover, the reflector electrode finger pitches of the reflectors are the same. The pitch of the first electrode finger closest to the reflector in the Reference Example is the same as the electrode finger pitch in the central portion. Additionally, there is only one such pitch structure in the Reference Example. The resonance frequencies of the elastic wave resonators in Comparative Example 1 and the Reference Example are the same as those in Examples 1 to 4.

[0135] First, in Examples 1, 2, 3, and 4, refer to Figures 7A to 10BThe following describes examples in which the pitch ratio (=Pra / Pia) is set to 1.04, 1.05, 1.06, and 1.10. In addition, regarding the pitch ratio (=Pra / Pia) in the comparative example and the reference example, the pitch ratio is changed in the same manner as in Examples 1, 2, 3, and 4. For example, Figure 7A as well as Figure 7B Set the spacing ratio to 1.04 in Figure 8A as well as Figure 8B Set the spacing ratio to 1.05 in Figure 9A as well as Figure 9B In the example, the spacing ratio is set to 1.06. Figure 10A as well as Figure 10B Set the spacing ratio to 1.10. Figure 7A 、 Figure 8A 、 Figure 9A 、 Figure 10A In the description, the end portion 11 e located next to one reflector 12 among the two end portions 11 e of the IDT electrode 11 is taken as an example, but the end portion 11 e located next to the other reflector 12 also has the same structure.

[0136] Figure 7A Graphs showing electrode finger pitches of elastic wave resonators according to Comparative Example 1, Reference Example, and Example 1 (this example assumes a pitch ratio of the average reflector pitch to the average IDT pitch of 1.04).

[0137] exist Figure 7A The vertical axis shows the size (magnification) of each pitch when the average IDT pitch Pia is used as a reference (Pia=1). Figure 7A The horizontal axis of shows the electrode fingers at the end 11e of the IDT electrode 11. Figure 7A In the graph, the electrode finger pitch Pi of two adjacent electrodes is connected in sequence by a line, and the change of the electrode finger pitch Pi is shown in a broken line graph. The electrode fingers 11a and 11b in the end portion 11e are sequentially referred to as the kth electrode finger (where k is an integer greater than 1) from the electrode finger closest to the reflector 12 toward the central portion 11d. Figure 7A The horizontal axis of is marked as "kth". Figure 8A 、 Figure 9A 、 Figure 10A 、 Figure 11A Same in Chinese.

[0138] As shown in the figure, the electrode finger pitch of the IDT electrode and the reflective electrode finger pitch of the reflector are the same in Comparative Example 1. In the reference example, the first electrode finger pitch closest to the reflector is the same as the electrode finger pitch in the center.

[0139] The first pitch p1 of Example 1 is the pitch between the first electrode finger and the second electrode finger, the second pitch p2 is the pitch between the third electrode finger and the fourth electrode finger, the third pitch p3 is the pitch between the seventh electrode finger and the eighth electrode finger, the fourth pitch p4 is the pitch between the eighth electrode finger and the ninth electrode finger, and the fifth pitch p5 is the pitch between the tenth electrode finger and the eleventh electrode finger.

[0140] Example 1 has a structure of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia". In addition, Example 1 has a pitch structure in the end portion 11e of the IDT electrode 11 where the pitch Pi between the two outer sides becomes a value smaller than the pitch Pi of the two outer sides. Specifically, the third pitch p3 becomes a value smaller than the second pitch p2 and the fourth pitch p4 respectively, and the fifth pitch p5 becomes a value smaller than the fourth pitch p4 and the pitch Pi of the central portion 11d respectively. In this example, the third pitch p3 and the fifth pitch p5 respectively become minimum points.

[0141] Figure 7B It is a diagram showing the reflection loss of the surface acoustic wave resonators of Comparative Example 1, Reference Example, and Example 1 (example when the pitch ratio is set to 1.04).

[0142] On Figure 7B the vertical axis, the reflection loss becomes larger as it goes closer to the lower side of the vertical axis. Hereinafter, the same applies to Figure 8B , Figure 9B , Figure 10B , Figure 11B .

[0143] As Figure 7B shown, in Comparative Example 1, large ripples occurred on the low-frequency side of the resonance frequency of the surface acoustic wave resonator. In contrast, in Example 1, the generation of ripples was suppressed on the low-frequency side of the resonance frequency of the surface acoustic wave resonator. In addition, the Reference Example also suppressed the generation of ripples.

[0144] Figure 8A It is a diagram showing the electrode finger pitches of the surface acoustic wave resonators of Comparative Example 1, Reference Example, and Example 2 (example when the pitch ratio is set to 1.05).

[0145] Comparative Example 1 and the Reference Example are the same as Figure 7A .

[0146] The first pitch p1 of Example 2 is the pitch between the first electrode finger and the second electrode finger, the second pitch p2 is the pitch between the second electrode finger and the third electrode finger, the third pitch p3 is the pitch between the fourth electrode finger and the fifth electrode finger, the fourth pitch p4 is the pitch between the fifth electrode finger and the sixth electrode finger, and the fifth pitch p5 is the pitch between the seventh electrode finger and the eighth electrode finger.

[0147] Example 2 also has a structure of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2, and p3 < Pia". In addition, Example 2 also has a pitch structure in the end portion 11e of the IDT electrode 11, that is, a pitch structure in which the pitch Pi between the two outer sides becomes a value smaller than the pitch Pi between the two outer sides. In this example, the third pitch p3 and the fifth pitch p5 also become minimum points respectively.

[0148] Figure 8B It is a diagram showing the reflection loss of the surface acoustic wave resonators of Comparative Example 1, Reference Example, and Example 2 (an example when the pitch ratio is 1.05).

[0149] As Figure 8B shown, in Comparative Example 1, large ripples occurred on the low-frequency side of the resonance frequency of the surface acoustic wave resonator. In contrast, in Example 2, the generation of ripples was suppressed on the low-frequency side of the resonance frequency of the surface acoustic wave resonator. In addition, the Reference Example also suppressed the generation of ripples to some extent.

[0150] Figure 9A It is a diagram showing the electrode finger pitches of the surface acoustic wave resonators of Comparative Example 1, Reference Example, and Example 3 (an example when the pitch ratio is 1.06).

[0151] Comparative Example 1 and the Reference Example are the same as Figure 7A the same.

[0152] The first pitch p1 of Example 3 is the pitch between the first electrode finger and the second electrode finger, the second pitch p2 is the pitch between the third electrode finger and the fourth electrode finger, the third pitch p3 is the pitch between the fourth electrode finger and the fifth electrode finger, the fourth pitch p4 is the pitch between the fifth electrode finger and the sixth electrode finger, and the fifth pitch p5 is the pitch between the seventh electrode finger and the eighth electrode finger.

[0153] Embodiment 3 also has a structure of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia". In addition, Embodiment 3 also has two pitch structures in the end portion 11e of the IDT electrode 11, that is, a pitch structure in which the electrode finger pitch Pi between the two outer sides becomes a value smaller than the electrode finger pitch Pi of the two outer sides. In this example, the third pitch p3 and the fifth pitch p5 also respectively become minimum points.

[0154] Figure 9B FIG. is a diagram showing the reflection loss of the surface acoustic wave resonators of Comparative Example 1, Reference Example, and Embodiment 3 (example when the pitch ratio is set to 1.06).

[0155] As Figure 9B shown, in Comparative Example 1, large ripples occurred on the low-frequency side of the resonance frequency of the surface acoustic wave resonator. The Reference Example also had small ripples on the low-frequency side of the resonance frequency of the surface acoustic wave resonator. In contrast, in Embodiment 3, the generation of ripples was suppressed on the low-frequency side of the resonance frequency of the surface acoustic wave resonator.

[0156] Figure 10A FIG. is a diagram showing the electrode finger pitch of the surface acoustic wave resonators of Comparative Example 1, Reference Example, and Embodiment 4 (example when the pitch ratio is set to 1.10).

[0157] Comparative Example 1 and the Reference Example are the same as Figure 7A the same.

[0158] The first pitch p1 of Embodiment 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.

[0159] Embodiment 4 also has a structure of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia". In addition, Embodiment 4 has three pitch structures in the end portion 11e of the IDT electrode 11, that is, a pitch structure in which the electrode finger pitch Pi between the two outer sides becomes a value smaller than the electrode finger pitch Pi of the two outer sides. In this example, the third pitch p3 and the fifth pitch p5 respectively become minimum points, and the pitch between the tenth electrode finger and the eleventh electrode finger becomes a minimum point.

[0160] Figure 10B FIG. is a diagram showing the reflection loss of the surface acoustic wave resonators of Comparative Example 1, Reference Example, and Embodiment 4 (example when the pitch ratio is set to 1.10).

[0161] like Figure 10B As shown, in Comparative Example 1, large ripples were generated at frequencies lower than the resonant frequency of the elastic wave resonator. The reference example also generated ripples at frequencies lower than the resonant frequency of the elastic wave resonator. In contrast, in Example 4, the generation of ripples at frequencies lower than the resonant frequency of the elastic wave resonator was suppressed compared to Comparative Example 1 and the reference example.

[0162] Next, a case where the electrode finger pitch of the first electrode finger closest to the reflector is the same as the electrode finger pitch in the center portion will be described as Comparative Example 2.

[0163] Figure 11A Graphs showing the electrode finger pitches of the elastic wave resonators of Comparative Example 2 and Example 4 (example when the pitch ratio is set to 1.10).

[0164] Comparative Example 2 is an example in which the first electrode finger pitch closest to the reflector is equal to the electrode finger pitch in the center. In other words, in Comparative Example 2, the first pitch p1 = the average IDT pitch Pia. Figure 10A The structure shown is the same.

[0165] Figure 11B Graphs showing the reflection losses of the elastic wave resonators of Comparative Example 2 and Example 4 (example when the pitch ratio is 1.10).

[0166] like Figure 11B As shown, in Comparative Example 2, where the first pitch p1 equals the average IDT pitch Pia, ripples occur at frequencies lower than the resonant frequency of the elastic wave resonator. In contrast, in Example 4, the generation of ripples at frequencies lower than the resonant frequency of the elastic wave resonator is suppressed compared to Comparative Example 2.

[0167] As described above, the elastic wave resonator 10 of the present embodiment has the following structures (1) to (4).

[0168] (1) Average IDT spacing Pia < average reflector spacing Pra

[0169] (2) The first pitch p1 < the average IDT pitch Pia

[0170] (3) The second spacing p2> the first spacing p1

[0171] (4) The third pitch p3 < the second pitch p2 and the third pitch p3 < the average IDT pitch Pia

[0172] With the above-described configuration, it is possible to suppress the generation of ripples at frequencies lower than the resonant frequency of elastic wave resonator 10 .

[0173] In order to suppress the generation of ripples, it is desirable that the relationship between the average IDT pitch Pia and the average reflector pitch Pra has the following relationship (see Figures 7A to 10B ).

[0174] For example, the average reflector pitch Pra is preferably 1.04 times or more and 1.1 times or less of the average IDT pitch Pia. Alternatively, the average reflector pitch Pra is preferably greater than 1.05 times or more and 1.1 times or less of the average IDT pitch Pia. Alternatively, the average reflector pitch Pra is preferably 1.06 times or more and 1.1 times or less of the average IDT pitch Pia.

[0175] (Implementation Method 2)

[0176] In embodiment 2, referring to Figure 12 as well as Figure 13 Next, an elastic wave filter device 1 including the elastic wave resonator 10 according to the first embodiment will be described.

[0177] Figure 12 This is a diagram showing a circuit configuration of an elastic wave filter device 1 according to a second embodiment.

[0178] like Figure 12 As shown, the elastic 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 and second input / output terminals 50 and 60; and a plurality of parallel-arm resonators P10, P20, P30, and P40 connected to nodes on the path connecting the first and second input / output terminals 50 and 60 and to ground. Thus, the elastic 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.

[0179] Figure 13 1 is a diagram illustrating an example of the electrode finger pitch Pi of the IDT electrodes 11 and the reflection electrode finger pitch Pr of the reflectors 12 of the first and second elastic wave resonators 210 and 220 included in the elastic wave filter device 1 .

[0180] like Figure 13 As shown, elastic wave filter device 1 includes a first elastic wave resonator 210 and a second elastic wave resonator 220 arranged along a first direction d1. At least one of the plurality of series-arm resonators S10 to S40 is formed by first elastic wave resonator 210, and at least one of the plurality of parallel-arm resonators P10 to P40 is formed by second elastic wave resonator 220.

[0181] Each of the first elastic wave resonator 210 and the second elastic wave resonator 220 includes an IDT electrode 11 and a plurality of reflectors 12 .

[0182] The reflector (the other reflector) located next to the second elastic wave resonator 220 among the multiple reflectors 12 of the first elastic wave resonator 210 and the reflector located next to the first elastic wave resonator 210 among the multiple reflectors 12 of the second elastic wave resonator 220 are shared as a single reflector 12. In other words, a single reflector 12 is disposed between the IDT electrode 11 of the first elastic wave resonator 210 and the IDT electrode of the second elastic wave resonator 220, rather than two reflectors. The reflection electrode finger pitch Pr of the shared reflector 12 is, for example, not less than 0.99 times and not more than 1.01 times the electrode finger pitch Pi of the IDT electrode 11 of the second elastic wave resonator 220.

[0183] First elastic wave resonator 210 is formed of elastic wave resonator 10 described in Embodiment 1. Average IDT pitch Pia of first elastic wave resonator 210 is smaller than electrode finger pitch Pi of IDT electrode 11 of second elastic wave resonator 220 and smaller than reflection electrode finger pitch Pr of a single shared reflector 12 .

[0184] According to this configuration, the first elastic wave resonator 210 and the second elastic wave resonator 220 arranged along the first direction d1 can share one reflector 12. This allows the elastic wave filter device 1 to be miniaturized.

[0185] (Summarize)

[0186] The elastic wave resonator and the like according to the present invention are exemplified.

[0187] The elastic wave resonator 10 of Example 1 includes a piezoelectric substrate 100, an IDT electrode 11 formed on a principal surface 100a of the piezoelectric substrate 100, and a plurality of reflectors 12. The IDT electrode 11 includes a plurality of electrode fingers 11a and 11b arranged in a first direction d1 and a second direction d2, which extend along the principal surface 100a of the piezoelectric substrate 100, and extending in a second direction d2 that intersects the first direction d1. The plurality of reflectors 12 are arranged on either side of the IDT electrode 11 in the first direction d1 and include a plurality of reflective electrode fingers 12a extending in the second direction d2.

[0188] When the center-to-center distance in the first direction d1 between adjacent electrode fingers 11a and 11b among the plurality of electrode fingers 11a and 11b is defined as the electrode finger pitch Pi, the center-to-center distance in the first direction d1 between adjacent reflector electrode fingers 12a among the plurality of reflector electrode fingers 12a is defined as the reflector electrode finger pitch Pr, the average value of the plurality of electrode finger pitches Pi in the central portion 11d of the IDT electrode 11 is set as the average IDT pitch Pia, and the average value of the plurality of reflector electrode finger pitches Pr in the reflector 12 is set as the average reflector pitch Pra, the average IDT pitch Pia is smaller than the average reflector pitch Pra.

[0189] In an end portion 11e different from the central portion 11d of the IDT electrode 11, there are a first region T1 closest to the reflector 12, a second region T2 located closer to the central portion 11d side than the first region T1, and a third region T3 located closer to the central portion 11d side than the second region T2.

[0190] A first pitch p1 of the electrode finger pitch between the first electrode finger f1 closest to the reflector 12 and the second electrode finger f2 located beside the first electrode finger f1 in the first region T1 is smaller than the average IDT pitch Pia. A second pitch p2 of the electrode finger pitch Pi between two adjacent electrode fingers in the second region T2 is larger than the first pitch p1. A third pitch p3 of the electrode finger pitch Pi between two adjacent electrode fingers in the third region T3 is smaller than the second pitch p2 and smaller than the average IDT pitch Pia.

[0191] In this way, by the elastic wave resonator 10 having a structure of "Pia < Pra, p1 < Pia, p2 > p1, p3 < p2 and p3 < Pia", it is possible to suppress the generation of ripples on the low-frequency side compared to the resonance frequency of the elastic wave resonator 10.

[0192] In the elastic wave resonator 10 of Example 2, in the elastic wave resonator described in Example 1, the second pitch p2 may be 0.99 times or more and 1.0 times or less of the average IDT pitch Pia.

[0193] In this way, by setting the second pitch p2 to be 0.99 times or more and 1.0 times or less of the average IDT pitch Pia, it is possible to suppress the generation of ripples on the low-frequency side compared to the resonance frequency of the elastic wave resonator 10.

[0194] The elastic wave resonator 10 of Example 3, among the elastic wave resonators described in Example 1 or 2, further has a fourth region T4 located closer to the central portion 11d side than the third region T3, and a fifth region T5 located closer to the central portion 11d side than the fourth region T4. It is also possible that the fourth pitch p4, which is the pitch Pi of two adjacent electrode fingers in the fourth region T4, is greater than the third pitch p3, the fifth pitch p5, which is the pitch Pi of two adjacent electrode fingers in the fifth region T5, is less than the fourth pitch p4, and is less than the average IDT pitch Pia.

[0195] In this way, by setting "p4 > p3, p5 < p4 and p5 < Pia", it is possible to suppress the generation of ripples on the low-frequency side relative to the resonance frequency of the elastic wave resonator 10.

[0196] The elastic wave resonator 10 of Example 4, among the elastic wave resonators described in Example 1 or 2, it is also possible that the IDT electrode 11 has a pitch structure in which one pitch Pi located inside between the two outer pitches Pi of the three pitches Pi arranged along the first direction d1 becomes a value smaller than the two outer pitches Pi, and in the end portion 11e of the IDT electrode 11, there are a plurality of the above pitch structures.

[0197] In this way, by having a plurality of the above pitch structures in the end portion 11e of the IDT electrode 11, it is possible to suppress the generation of ripples on the low-frequency side relative to the resonance frequency of the elastic wave resonator 10.

[0198] The elastic wave filter device 1 of Example 5 includes a first elastic wave resonator 210 and a second elastic wave resonator 220 arranged along the first direction d1. The first elastic wave resonator 210 and the second elastic wave resonator 220 each have an IDT electrode 11 and a plurality of reflectors 12. Among the plurality of reflectors 12 of the first elastic wave resonator 210, the reflector 12 located next to the second elastic wave resonator 220, and among the plurality of reflectors 12 of the second elastic wave resonator 220, the reflector 12 located next to the first elastic wave resonator 210 are shared as one reflector 12. The first elastic wave resonator 210 is constituted by the above elastic wave resonator 10. The average IDT pitch Pia of the first elastic wave resonator 210 is less than the pitch Pi of the IDT electrode 11 of the second elastic wave resonator 220, and is less than the pitch Pr of the reflective electrode fingers of the shared one reflector 12.

[0199] According to this structure, it is possible to share one reflector 12 in the first elastic wave resonator 210 and the second elastic wave resonator 220 arranged along the first direction d1. Thereby, it is possible to miniaturize the elastic wave filter device 1.

[0200] The elastic wave filter device 1 of Example 6, in the elastic wave filter device described in Example 5, 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 a first elastic wave resonator 210, and at least one of the plurality of parallel arm resonators P10 to P40 may be a second elastic wave resonator 220.

[0201] According to this configuration, the series arm resonator and the parallel arm resonator can share one reflector 12. This allows the elastic wave filter device 1 to be miniaturized.

[0202] In the elastic wave filter device 1 of Example 7, in the elastic wave filter device 1 described in Example 5 or 6, the reflection electrode finger pitch Pr of the shared reflector may be greater than or equal to 0.99 times and less than or equal to 1.01 times the electrode finger pitch Pi of the IDT electrode 11 of the second elastic wave resonator 220 .

[0203] According to this configuration, one reflector 12 can be shared by first elastic wave resonator 210 and second elastic wave resonator 220. This allows for miniaturization of elastic wave filter device 1.

[0204] (Other implementations, etc.)

[0205] While the elastic wave resonator and elastic wave filter device according to the embodiments of the present invention have been described above by way of examples and embodiments, the elastic wave resonator and elastic wave filter device according to the present invention are not limited to the aforementioned embodiments and embodiments. The present invention also encompasses other embodiments realized by combining any of the components described in the aforementioned embodiments and embodiments, embodiments resulting from various modifications of the aforementioned embodiments that would occur to those skilled in the art without departing from the spirit of the present invention, and various devices incorporating the elastic wave resonator and elastic wave filter device according to the present invention.

[0206] Industrial applicability

[0207] The present invention can be widely used in communication devices such as mobile phones as a low-loss and compact elastic wave resonator and elastic wave filter device.

Claims

1. An elastic wave resonator comprising: a piezoelectric substrate; and IDT electrodes and a plurality of reflectors are formed on the main surface of the piezoelectric substrate. The IDT electrode has a plurality of electrode fingers arranged in a first direction and a second direction along the principal surface of the piezoelectric substrate so as to extend in the second direction intersecting the first direction. The plurality of reflectors are respectively arranged on both outer sides of the IDT electrode in the first direction and have a plurality of reflective electrode fingers arranged to extend in the second direction. In the case where the center-to-center distance in the first direction of electrode fingers adjacent to each other in the first direction among the plurality of electrode fingers is defined as an electrode finger pitch, the center-to-center distance in the first direction of reflective electrode fingers adjacent to each other in the first direction among the plurality of reflective electrode fingers is defined as a reflective electrode finger pitch, the average value of the plurality of electrode finger pitches in the central portion of the IDT electrode is defined as an average IDT pitch, and the average value of the plurality of reflective electrode finger pitches in the reflector is defined as an average reflector pitch, the average IDT pitch is smaller than the average reflector pitch. The IDT electrode includes, 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. A first pitch, which is the electrode finger pitch between a first electrode finger closest to the reflector in the first region and a second electrode finger located next 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 smaller than the average IDT pitch.

2. The elastic wave resonator according to claim 1, wherein The second pitch is not less than 0.99 times and not more than 1.01 times the average IDT pitch.

3. The elastic wave resonator according to claim 1 or 2, wherein: The elastic wave resonator further includes a fourth region located closer to the center portion than the third region, and a fifth region located closer to the center 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 smaller than the average IDT pitch.

4. The elastic wave resonator according to claim 1 or 2, wherein: The IDT electrode has a pitch structure in which, among the three electrode finger pitches arranged along the first direction, an inner electrode finger pitch between two outer electrode finger pitches is smaller than the two outer electrode finger pitches. The end portion of the IDT electrode has a plurality of the pitch structures.

5. The elastic wave resonator according to claim 1 or 2, wherein: The piezoelectric substrate has a laminated structure including a piezoelectric layer.

6. An elastic wave filter device comprising a first elastic wave resonator and a second elastic wave resonator arranged along a first direction, The first elastic wave resonator and the second elastic wave resonator each include an IDT electrode and a plurality of reflectors. A reflector located next to the second elastic wave resonator among the plurality of reflectors of the first elastic wave resonator and a reflector located next to the first elastic wave resonator among the plurality of reflectors of the second elastic wave resonator are shared as one reflector. The first elastic wave resonator is formed of the elastic wave resonator according to any one of claims 1 to 5. The average IDT pitch of the first elastic wave resonator is smaller than the electrode finger pitch of the IDT electrode of the second elastic wave resonator and smaller than the reflective electrode finger pitch of the one shared reflector.

7. The elastic wave filter device according to claim 6, wherein The elastic 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 formed of the first elastic wave resonator. At least one of the plurality of parallel arm resonators is formed of the second elastic wave resonator.

8. The elastic wave filter device according to claim 6 or 7, wherein: The reflective electrode finger pitch of the one shared reflector is not less than 0.99 times and not more than 1.01 times the electrode finger pitch of the IDT electrode of the second elastic wave resonator.

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