Elastic wave device, elastic wave filter, and multiplexer

Abstract

Provided are an elastic wave element capable of reducing a ripple near a resonance frequency and adjusting a resonance bandwidth, an elastic wave filter, and a multiplexer. The elastic wave element includes an IDT electrode having comb electrode fingers and a reflection electrode having reflection electrode fingers. The comb electrode finger closest to the reflection electrode from among the comb electrode fingers is set as an nth end-side electrode finger in a direction toward the center of the IDT electrode. The center-to-center distance between adjacent electrode fingers in a first direction is set as a pitch. The pitch between the nth end-side electrode finger and an (n+1)th end-side electrode finger is set as an nth end-side pitch. An mth end-side pitch in the pitches from the first end-side electrode finger to the comb electrode finger at the center of the IDT electrode is smaller than an average pitch. In a case where a region of the IDT electrode from the first end-side electrode finger to the mth end-side electrode finger is set as an end region, the IDT electrode includes a gap-removing electrode disposed in the end region.

Description

Technical Field

[0001] This invention relates to elastic wave elements, elastic wave filters, and multiplexers. Background Technology

[0002] Patent Document 1 discloses an elastic wave element in which, in order to reduce ripple near the resonant frequency, the relationship between the spacing (nth end spacing) of the nth end electrode fingers of the IDT (Interdigital Transducer) electrode located from the end and the gap between the IDT electrode and the reflector (IDT-reflector gap) is specified.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2023 / 282328

[0006] When using the elastic wave element described in Patent Document 1 to construct a filter, in order to optimize the passband width and the steepness of the passband end, it is necessary to adjust the resonant bandwidth (the frequency difference between the resonant frequency and the anti-resonant frequency) of the elastic wave element. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] The present invention was made to solve the above-mentioned problems, and its purpose is to provide an elastic wave element, an elastic wave filter and a multiplexer that can reduce ripple near the resonant frequency and adjust the resonant bandwidth.

[0009] Technical solutions for solving the problem

[0010] One aspect of the present invention relates to an elastic wave element comprising: a piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; and a reflecting electrode disposed on the piezoelectric substrate and configured to be adjacent to the IDT electrode in a first direction. The IDT electrode has a plurality of comb-tooth electrode fingers extending in a second direction intersecting the first direction. The reflecting electrode has a plurality of reflecting electrode fingers extending in the second direction. The comb-tooth electrode finger closest to the reflecting electrode among the plurality of comb-tooth electrode fingers is designated as a first end-side electrode finger, and the comb-tooth electrode fingers in the direction from the first end-side electrode finger toward the center of the IDT electrode are sequentially designated as nth end-side electrode fingers (n is a natural number). The distance between the centers of adjacent electrode fingers in the first direction in the first direction is defined as the spacing. The spacing between the nth end-side electrode finger and the (n+1)th end-side electrode finger is defined as the nth end-side spacing. The mth end-side spacing in the spacing from the first end-side electrode finger to the comb electrode finger located at the center of the IDT electrode is less than the average spacing of the spacing of the multiple comb electrode fingers other than the mth end-side spacing. When the region from the first end-side electrode finger to the mth end-side electrode finger in the region where the IDT electrode is formed is defined as the end region, the IDT electrode includes a spaced-out electrode disposed in the end region.

[0011] Furthermore, one aspect of the present invention relates to an elastic wave filter comprising the elastic wave element described above.

[0012] Furthermore, one embodiment of the present invention relates to a multiplexer comprising: a common terminal; the elastic wave filter described above, connected to the common terminal; and a first filter, connected to the common terminal.

[0013] Invention Effects

[0014] According to the present invention, an elastic wave element, an elastic wave filter, and a multiplexer can be provided that can reduce ripple near the resonant frequency and adjust the resonant bandwidth. Attached Figure Description

[0015] Figure 1 This is a top view of the elastic wave element involved in the implementation method.

[0016] Figure 2A This is a cross-sectional view of the elastic wave element involved in the implementation method.

[0017] Figure 2B This is a cross-sectional view of an elastic wave element according to a variation of the implementation method.

[0018] Figure 3 These are graphs showing the impedance and reflection characteristics of the elastic wave elements involved in Comparative Example 1 and Comparative Example 2.

[0019] Figure 4The graphs represent the reflection characteristics of the elastic wave elements involved in Comparative Example 2, Comparative Example 3, and Example 1.

[0020] Figure 5 The graphs represent the reflection characteristics of the elastic wave elements involved in Comparative Example 4, Comparative Example 5, and Example 2.

[0021] Figure 6 These are graphs illustrating the reflection characteristics of the elastic wave elements involved in Embodiments 3 and 4.

[0022] Figure 7A This is a top view schematically showing the electrode structure of the elastic wave element involved in Embodiments 5 to 9.

[0023] Figure 7B This is a diagram showing the relationship between the narrow spacing position and reflection loss of the elastic wave elements involved in Examples 5 to 9.

[0024] Figure 8 This is a graph showing the relationship between the narrow spacing position and reflection loss of the elastic wave element involved in Comparative Example 6 and Examples 10 to 14.

[0025] Figure 9 The graphs show the impedance and reflection characteristics of the elastic wave elements involved in Comparative Example 7 and Example 15.

[0026] Figure 10A This is a top view schematically showing the electrode structure of the elastic wave element involved in Embodiments 16 to 20.

[0027] Figure 10B This is a diagram showing the relationship between the narrow spacing position and reflection loss of the elastic wave element involved in Examples 16 to 20.

[0028] Figure 11 This is a circuit diagram of the multiplexer involved in the implementation method.

[0029] Explanation of reference numerals in the attached figures

[0030] 1, 1A, 101, 102, 103, 104, 105, 111, 112, 113, 114, 115: Elastic wave elements;

[0031] 10, 151, 152, 153, 154, 155, 161, 162, 163, 164, 165: IDT electrodes;

[0032] 11a, 11b: Comb-tooth electrode fingers;

[0033] 12a, 12b: Busbar electrodes;

[0034] 20A, 20B: Reflective electrodes;

[0035] 21a, 21b: Reflective electrode references;

[0036] 50: Piezoelectric substrate;

[0037] 50A: Piezoelectric substrate;

[0038] 51: Piezoelectric layer;

[0039] 51a, 51b: Main face;

[0040] 52: Low-sound-velocity layer;

[0041] 53: Hypersonic layer;

[0042] 54: Support base plate;

[0043] 60: Insulating layer;

[0044] 70: Dielectric layer;

[0045] 200, 250: Filters;

[0046] 201, 202, 302, 303: Input / output terminals;

[0047] 211, 212, 213: Series arm resonators;

[0048] 221, 222: Parallel arm resonators;

[0049] 300: Multiplexer;

[0050] 301: Common terminal. Detailed Implementation

[0051] Hereinafter, embodiments of the present disclosure will be described in detail using the accompanying drawings. Furthermore, the embodiments described below are either general or specific examples. The numerical values, shapes, materials, constituent elements, arrangements of constituent elements, and connection methods shown in the following embodiments are examples and are not intended to limit the present invention.

[0052] Furthermore, the figures are schematic diagrams that have been appropriately emphasized, omitted, or proportionally adjusted for the purpose of illustrating the invention, and are not necessarily strictly illustrative, sometimes differing from the actual shapes, positional relationships, and proportions. In the figures, substantially identical structures are labeled with the same reference numerals, and sometimes repeated descriptions are omitted or simplified.

[0053] In addition, terms such as "parallel" and "perpendicular" that indicate the relationship between elements, terms such as "rectangle" that indicate the shape of elements, and numerical ranges that do not only indicate a strict meaning but also imply a substantially equal range, for example, also include a degree of error of a few percent.

[0054] Furthermore, in this disclosure, the term "terminal" means the point where the conductor within an element ends. Additionally, when the impedance of the conductors between elements is sufficiently low, a terminal is not merely a single point, but can also be interpreted as any point on the conductors between elements or the entire conductor assembly.

[0055] Furthermore, in this disclosure, the passband of the filter is a portion of the spectrum transmitted by the filter, defined as the band between two frequencies that is 3 dB greater than the minimum power insertion loss.

[0056] Furthermore, in this disclosure, the term "main component of the material" refers to a component that accounts for more than 50% by weight in the material. The aforementioned main component may exist in any of the following states: single crystal, polycrystalline, and amorphous, or a mixture thereof.

[0057] Furthermore, in the layer structure disclosed herein, the term "layer A (or component A) is disposed on the main surface C of layer B" includes not only layer A (or component A) being disposed in contact with the main surface C of layer B, but also layer A (or component A) being disposed on top of the main surface C without contacting the main surface C (for example, layer A (or component A) is stacked on other layers disposed in contact with the main surface C).

[0058] (Implementation Method)

[0059] [1 Structure of elastic wave element]

[0060] The structure of the elastic wave element 1 according to this embodiment will be described.

[0061] Figure 1 This is a top view of the elastic wave element 1 according to the embodiment. Furthermore, Figure 2A This is a cross-sectional view of the elastic wave element 1 according to the embodiment. Figure 1 The electrode structure of the elastic wave element 1 is shown in (a). Figure 1 The spacing distribution of each electrode finger is shown in (b). Furthermore, Figure 2A yes Figure 1 A cross-sectional view at line II-II in (a). Additionally... Figure 1 The elastic wave element 1 shown is used to illustrate its typical structure, and the number, length, etc. of the electrode fingers constituting the electrodes are not limited thereto.

[0062] like Figure 1 as well as Figure 2A As shown, the elastic wave element 1 includes a piezoelectric substrate 50, an IDT electrode 10, and reflective electrodes 20A and 20B. The elastic wave element 1 functions as a surface acoustic wave (SAW) resonator.

[0063] The IDT electrode 10, reflective electrodes 20A and 20B are, for example, a stacked structure of a bonding layer and a main electrode layer. The bonding layer is used to improve the adhesion between the piezoelectric substrate 50 and the main electrode layer; for example, Ti can be used as the material. The main electrode layer can, for example, use Al containing 1% Cu as the material. Furthermore, although in Figure 2A Although not shown in the diagram, a protective film can also be formed to cover the IDT electrode 10, the reflective electrodes 20A and 20B. The protective film is a layer designed to protect the main electrode layer from external environmental influences, adjust frequency-temperature characteristics, and improve moisture resistance; for example, it may be a film primarily composed of silicon dioxide (SiO2). Furthermore, the materials constituting the bonding layer, the main electrode layer, and the protective film are not limited to the materials described above.

[0064] Furthermore, the IDT electrode 10, reflective electrodes 20A and 20B may not be of the above-described stacked structure. The IDT electrode 10, reflective electrodes 20A and 20B may each be made of metals or alloys such as Ti, Al, Cu, Pt, Au, Ag, and Pd. Alternatively, they may be constructed by multiple stacks of the aforementioned metals or alloys.

[0065] like Figure 2A As shown, the piezoelectric substrate 50 is piezoelectric and includes a piezoelectric body layer 51, a low-velocity layer 52, a high-velocity layer 53, and a support substrate 54.

[0066] The piezoelectric layer 51 has opposing main surfaces 51a (first main surface) and 51b (second main surface). The IDT electrode 10, reflective electrodes 20A and 20B are disposed on the main surface 51a. The piezoelectric layer 51 can be made of, for example, lithium tantalate or lithium niobate, or a material mainly composed of the above materials.

[0067] The support substrate 54 is disposed on the main surface 51b side of the piezoelectric layer 51 and is a substrate that supports the IDT electrode 10, the reflective electrodes 20A and 20B, the piezoelectric layer 51, the low-velocity layer 52, and the high-velocity layer 53. The support substrate 54 can be made of piezoelectric materials such as silicon, aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, and forsterite; dielectrics such as diamond and glass; semiconductors such as gallium nitride; or resin; or materials mainly composed of the above materials.

[0068] A low-velocity acoustic layer 52 is disposed between the piezoelectric layer 51 and the support substrate 54. The velocity of sound of the bulk waves propagating in the low-velocity acoustic layer 52 is lower than that of the bulk waves propagating in the piezoelectric layer 51 and the support substrate 54. Based on this structure and the property that elastic waves inherently concentrate energy in a low-velocity medium, leakage of surface acoustic wave energy to the outside of the IDT electrode 10 can be suppressed. The low-velocity acoustic layer 52 can be, for example, a dielectric material such as silicon oxide, glass, silicon oxynitride, lithium oxide, tantalum oxide, or a compound in which fluorine, carbon, or boron are added to silicon oxide, or a material mainly composed of the above materials.

[0069] The high-velocity sound layer 53 is disposed between the low-velocity sound layer 52 and the support substrate 54. The volume wave velocity propagating in the high-velocity sound layer 53 is higher than that propagating in the low-velocity sound layer 52. The high-velocity sound layer 53 can be made of, for example, piezoelectric materials such as silicon nitride, aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesium oxide, silicon carbide, zirconium oxide, cordierite, mullite, block talc, and forsterite; dielectrics such as diamond and glass; semiconductors such as silicon and gallium nitride; or resins; or materials mainly composed of the above materials.

[0070] Based on the above-described laminated structure of the piezoelectric substrate 50, compared with the conventional structure using a single-layer piezoelectric substrate, the resonant frequency and the Q value at the anti-resonant frequency can be significantly improved. That is, a high-Q elastic wave element can be constructed, and therefore this elastic wave element can be used to construct an elastic wave filter with low insertion loss. Furthermore, the frequency-temperature characteristics can be improved.

[0071] Alternatively, the high-velocity acoustic layer 53 and the support substrate 54 can be combined into a single high-velocity acoustic support substrate. This high-velocity acoustic support substrate is a substrate where the velocity of the bulk waves propagating in the piezoelectric layer 51 is significantly higher than that of surface waves and boundary waves, thus preventing leakage of surface acoustic waves into the portion where the piezoelectric layer 51 and the low-velocity acoustic layer 52 are stacked, preventing leakage below the high-velocity acoustic support substrate. Materials used for the high-velocity acoustic support substrate include, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; dielectric materials such as bauxite, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, forsterite, spinel, and silane; ceramics such as alumina, silicon oxynitride, DLC (diamond-like carbon), and diamond; dielectric materials such as silicon; or materials primarily composed of the aforementioned materials. Furthermore, the aforementioned spinels contain aluminum compounds containing one or more elements selected from Mg, Fe, Zn, Mn, etc., and oxygen. Examples of such spinels include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0072] Alternatively, a structure in which a support substrate, an energy sealing layer, and a piezoelectric layer are stacked sequentially can be used instead of the piezoelectric substrate 50.

[0073] An energy-sealing layer comprises one or more layers, wherein the speed of bulk acoustic waves propagating in at least one layer is greater than the speed of elastic waves propagating near the piezoelectric layer. For example, the energy-sealing layer can also be a stacked structure of low-velocity and high-velocity layers. A low-velocity layer is a film in which the speed of bulk waves is low compared to the speed of elastic waves propagating in the piezoelectric layer. A high-velocity layer is a film in which the speed of bulk waves is high compared to the speed of elastic waves propagating in the piezoelectric layer. Alternatively, the supporting substrate can also be used as the high-velocity layer.

[0074] In addition, the energy sealing layer can also be an acoustic impedance layer with a structure that alternately stacks low acoustic impedance layers with relatively low acoustic impedance and high acoustic impedance layers with relatively high acoustic impedance.

[0075] Alternatively, a gap can be formed between the piezoelectric layer and the supporting substrate to replace the energy sealing layer. Thus, the elastic wave element 1 can function as a laterally excited bulk acoustic resonator (XBAR).

[0076] In addition, the piezoelectric substrate 50 may also be a piezoelectric substrate 50A containing a piezoelectric single crystal. Figure 2B This is a cross-sectional view of the elastic wave element 1A according to a modified embodiment. As shown in the figure, the elastic wave element 1A according to this modified embodiment includes a piezoelectric substrate 50A, an IDT electrode 10, reflective electrodes 20A and 20B, an insulating layer 60, and a dielectric layer 70. Compared with the elastic wave element 1 according to the embodiment, the elastic wave element 1A according to this modified embodiment differs in that a piezoelectric substrate 50A is provided instead of a piezoelectric substrate 50, and an insulating layer 60 and a dielectric layer 70 are added. Hereinafter, the description will focus on the structure that differs from the elastic wave element 1 according to the embodiment.

[0077] The piezoelectric substrate 50A is an example of a piezoelectric substrate, having a main surface 51a containing a piezoelectric single crystal. The piezoelectric substrate 50A is, for example, a single-crystal piezoelectric substrate containing lithium niobate. Alternatively, the piezoelectric substrate 50A can also be a single-crystal piezoelectric substrate containing lithium tantalate, quartz, or potassium nitride. The IDT electrode 10, and the reflective electrodes 20A and 20B are disposed on the main surface 51a.

[0078] The insulating layer 60 is configured to cover the main surface 51a, the IDT electrode 10, and the reflective electrodes 20A and 20B, and is configured to embed the IDT electrode 10. In other words, the insulating layer 60 extends from the main surface 51a to approximately the upper surface of the IDT electrode 10. The insulating layer 60 is, for example, a layer primarily composed of silicon dioxide (SiO2). Based on the configuration of the insulating layer 60, the frequency-temperature characteristics of the elastic wave element 1A can be improved.

[0079] The dielectric layer 70 is configured to cover the insulating layer 60. The dielectric layer 70 is, for example, a layer with the same material as the hypersonic layer 53 as its main component. Alternatively, the dielectric layer 70 may not be present.

[0080] [2 Electrode Finger Structure of IDT Electrode and Reflective Electrode]

[0081] Next, the electrode finger structure of IDT electrode 10, reflective electrodes 20A and 20B will be described.

[0082] like Figure 1 As shown in (a), the IDT electrode 10 is disposed on the piezoelectric substrate 50 and has a pair of comb-shaped electrodes facing each other. One of the pair of comb-shaped electrodes consists of a plurality of comb-shaped electrode fingers 11a arranged to extend in a second direction (y-axis direction) intersecting a first direction (x-axis direction) which is the direction of elastic wave propagation, and a busbar electrode 12a connecting one end of each of the plurality of comb-shaped electrode fingers 11a to each other. The other of the pair of comb-shaped electrodes consists of a plurality of comb-shaped electrode fingers 11b arranged to extend in the second direction (y-axis direction), and a busbar electrode 12b connecting one end of each of the plurality of comb-shaped electrode fingers 11b to each other. The electrode fingers of the plurality of comb-shaped electrode fingers 11a and 11b are arranged alternately in the first direction.

[0083] Reflective electrodes 20A and 20B are disposed on the piezoelectric substrate 50 and are configured to be adjacent to the IDT electrode 10 in a first direction. Reflective electrode 20A includes a plurality of reflective electrode fingers 21a configured to extend in a second direction. Reflective electrode 20B includes a plurality of reflective electrode fingers 21b configured to extend in the second direction.

[0084] The comb electrode finger closest to the reflective electrode 20A among the plurality of comb electrode fingers 11a and 11b is designated as the first end-side electrode finger, and the comb electrode fingers moving from the first end-side electrode finger toward the center of the IDT electrode 10 are sequentially designated as the nth end-side electrode finger (n is a natural number). Furthermore, the comb electrode finger closest to the reflective electrode 20B among the plurality of comb electrode fingers 11a and 11b is designated as the first end-side electrode finger, and the comb electrode fingers moving from the first end-side electrode finger toward the center of the IDT electrode 10 are sequentially designated as the nth end-side electrode finger (n is a natural number).

[0085] Furthermore, the center-to-center distance in the first direction between adjacent electrode fingers constituting IDT electrode 10, reflective electrodes 20A, and 20B is defined as the spacing, and the spacing between the nth end-side electrode finger and the (n+1)th end-side electrode finger is defined as the nth end-side spacing. Here, the mth end-side spacing among the spacings from the first end-side electrode finger to the comb-tooth electrode finger located at the center of IDT electrode 10 is less than the average spacing pA of the spacings of the multiple comb-tooth electrode fingers 11a and 11b excluding the mth end-side spacing. Hereinafter, the mth end-side spacing is denoted as the narrow spacing (=pK). In addition, the mth end-side spacing may also be the smallest among the nth end-side spacings of IDT electrode 10.

[0086] like Figure 1 As shown in (a), when viewed from above the main surface 51a, the region in the area where the IDT electrode 10 is formed, from the first end-side electrode finger to the m-th end-side electrode finger with a narrow spacing, is defined as the end region. The IDT electrode 10 has two end regions at both ends in the first direction, and the region sandwiched between these two end regions is defined as the central region.

[0087] Here, the IDT electrode 10 includes a spacer rejection electrode M disposed in the end region. The spacer rejection electrode M is further defined as follows: The spacer rejection electrode includes (1) a polarity-reversed spacer rejection electrode, (2) a floating spacer rejection electrode, and (3) a filled spacer rejection electrode.

[0088] A polarity-reversed interval rejection electrode is a comb electrode finger connected to the same bus electrode as the bus electrode connected to adjacent comb electrode fingers on both sides. The interval rejection rate in a given region of an IDT electrode with a polarity-reversed interval rejection electrode is defined as follows. The interval rejection rate of a given region is expressed by Equation 1, where X is the number of polarity-reversed interval rejection electrodes in the given region, one pair of adjacent comb electrode fingers 11a and 11b is defined as a pair of electrode fingers, and W is the logarithm of the given region consisting only of repetitions of comb electrode fingers 11a and 11b without polarity-reversed interval rejection electrodes. Furthermore, when calculating the interval rejection rate, three comb electrode fingers, including the polarity-reversed comb electrode finger and the comb electrode fingers adjacent to it on both sides, are considered as one interval rejection electrode.

[0089] Interval rejection rate = X / {2(WX) + 1} (Equation 1)

[0090] A floating interval rejection electrode is a comb electrode finger that is not connected to either of the opposing busbar electrodes 12a and 12b. The interval rejection rate in a given region of an IDT electrode with a floating interval rejection electrode is defined as follows. Let X be the number of floating interval rejection electrodes in the given region, let one pair of adjacent comb electrode fingers 11a and 11b be considered a pair of electrode fingers, and let W be the logarithm of the given region consisting only of repetitions of comb electrode fingers 11a and 11b without floating interval rejection electrodes. Then, Equation 1 represents the interval rejection rate of that given region. Furthermore, when calculating the interval rejection rate, three comb electrode fingers, including a comb electrode finger not connected to either of the busbar electrodes 12a and 12b and three comb electrode fingers adjacent to each other on both sides, are considered as one interval rejection electrode.

[0091] The fill-in interval rejection electrode is the electrode finger with the largest electrode finger width in the IDT electrode 10, and is a comb electrode finger with an electrode finger width that is more than twice the average electrode finger width among the comb electrode fingers other than the fill-in interval rejection electrode. The interval rejection rate in a given region of an IDT electrode with a fill-in interval rejection electrode is defined as follows. Let X be the number of fill-in interval rejection electrodes in the given region, and let W be the number of adjacent comb electrode fingers 11a and 11b as a pair of electrode fingers. The interval rejection rate of the given region is expressed by Equation 1. Furthermore, when calculating the interval rejection rate, the comb electrode finger with the largest electrode finger width is considered as one interval rejection electrode.

[0092] Furthermore, in the boundary region between the IDT electrode 10 and the reflective electrode 20A (or 20B), the distance in the first direction between the center of the comb electrode finger closest to the reflective electrode 20A (or 20B) among the plurality of comb electrode fingers 11a and 11b and the center of the reflective electrode finger closest to the IDT electrode 10 among the plurality of reflective electrode fingers 21a (or 21b) is defined as the IDT-reflective electrode gap (hereinafter referred to as IRGAP).

[0093] Here, the wavelength λ and the spacing p are defined.

[0094] The wavelength λ of the IDT electrode 10 is a unit of length defined by the repetition period of the comb electrode fingers 11a (or 11b). Furthermore, the electrode finger spacing p of the IDT electrode 10 is half the wavelength λ. Additionally, the spacing p of the reflective electrodes 20A (or 20B) is a unit of length defined by the repetition period of the reflective electrode fingers 21a (or 21b).

[0095] Furthermore, in the IDT electrode 10, when the spacing between adjacent comb electrode fingers is not fixed, the wavelength λ of the IDT electrode 10 is defined by the average wavelength λA of the IDT electrode 10. If the total number of comb electrode fingers 11a and 11b included in the IDT electrode 10 is set to Ni, and the center-to-center distance between the comb electrode fingers at one end in the first direction and the comb electrode fingers at the other end of the IDT electrode 10 is set to Di, then the average wavelength λA of the IDT electrode 10 is defined as 2×Di / (Ni-1). However, the total number of fingers Ni is the number excluding the m-th end electrode finger, and the center-to-center distance Di is set to the value after subtracting the spacing at the m-th end. In addition, the average spacing pA of the IDT electrode 10 is half of the average wavelength λA.

[0096] In addition, when the IDT electrode 10 includes a spaced-out electrode, when calculating the average wavelength λA, the number of spaced-out electrodes is removed as the total number of electrode fingers Ni, the linewidth L of the spaced-out electrode is removed as the center-to-center distance Di, and one of the two spaces (space width S) adjacent to the spaced-out electrode is removed.

[0097] Furthermore, when the IDT electrode 10 has a so-called 2D piston structure and the width of the electrode finger at the tip of the comb-tooth electrode finger is wider than that at the center of the electrode finger, the wavelength λ is defined as the wavelength of the center of the comb-tooth electrode finger. Furthermore, when it is a 2D piston structure but the width of the electrode finger at the tip of the comb-tooth electrode finger cannot be said to be wider than that at the center of the comb-tooth electrode finger, the wavelength λ is defined as the average wavelength of the cross-width region within the comb-tooth electrode finger, excluding the two ends. Furthermore, when the width of the electrode finger changes periodically in the cross-width direction of the comb-tooth electrode finger, the wavelength λ is defined as the average wavelength of the cross-width region within the comb-tooth electrode finger.

[0098] Furthermore, in the reflective electrode 20A (or 20B), when the spacing between adjacent reflective electrode fingers is not fixed, the spacing p of the reflective electrode 20A (or 20B) is defined by the average spacing pR of the reflective electrode 20A (or 20B). If the total number of reflective electrode fingers 21a (or 21b) included in the reflective electrode 20A (or 20B) is set to Ni, and the distance between the centers of the reflective electrode fingers at one end of the reflective electrode 20A (or 20B) in the first direction and the reflective electrode fingers at the other end is set to Di, then the average spacing pR of the reflective electrode 20A (or 20B) is defined as 2×Di / (Ni-1).

[0099] In addition, the wavelength λ and spacing p of the IDT electrode 10 and the spacing p of the reflective electrodes 20A and 20B can be measured by viewing the main surface 51a of the piezoelectric layer 51 from above using a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), or a transmission electron microscope (TEM), and / or by viewing a cross-section perpendicular to the extension direction (second direction) of each electrode finger and measuring its length.

[0100] [3 Reflection characteristics of elastic wave elements according to embodiments and comparative examples]

[0101] While comparing the reflection and impedance characteristics of the elastic wave elements involved in the embodiments and comparative examples, the appropriate electrode finger structure of the elastic wave element 1 involved in this embodiment will be described.

[0102] Table 1 shows the main electrode parameters of the elastic wave elements involved in Comparative Examples 1 to 7. Furthermore, Table 2 shows the main electrode parameters of the elastic wave elements involved in Examples 1 to 15. Additionally, in Tables 1 and 2, λ... IDT The wavelength λ of IDT electrode 10 is represented by λ. REF The wavelength λ represents the wavelengths of reflective electrodes 20A and 20B.

[0103] [Table 1]

[0104]

[0105] [Table 2]

[0106]

[0107] Figure 3 These are graphs showing the impedance and reflection characteristics of the elastic wave elements involved in Comparative Example 1 and Comparative Example 2. In the elastic wave element involved in Comparative Example 1, the IDT electrodes do not include a narrow spacing and do not include a gap-removing electrode. Furthermore, in the elastic wave element involved in Comparative Example 2, the IDT electrodes include a narrow spacing (m=7, pK=0.9pA) and do not include a gap-removing electrode.

[0108] like Figure 3As shown in (a), in the elastic wave element involved in Comparative Example 1, ripple caused by the longitudinal mode (hereinafter, sometimes referred to as longitudinal mode ripple) is generated in the low-frequency band near the resonant frequency, and ripple generated at the high-frequency end of the stopband (hereinafter, sometimes referred to as stopband ripple) is generated in the high-frequency band near the anti-resonant frequency. In contrast, as Figure 3 As shown in (b), in the elastic wave element of Comparative Example 2, the longitudinal mode ripple and stopband ripple are reduced due to the narrow spacing. However, in the elastic wave elements of Comparative Examples 1 and 2, since the spaced-out electrodes are not provided, the fractional bandwidth (the value obtained by dividing the difference frequency between the anti-resonant frequency and the resonant frequency by the resonant frequency) does not change. In other words, simply configuring a narrow spacing reduces the ripple near the resonant band, but it does not allow for adjustment of the fractional bandwidth.

[0109] Figure 4 This is a graph showing the reflection characteristics of the elastic wave elements according to Comparative Example 2, Comparative Example 3, and Example 1. In the elastic wave element according to Comparative Example 2, the IDT electrodes have a narrow spacing (m=7, pK=0.9pA) and do not include interval rejection electrodes. Furthermore, in the elastic wave element according to Comparative Example 3, the IDT electrodes have a narrow spacing (m=7, pK=0.9pA) and include interval rejection electrodes (non-periodic, interval rejection rate 4%). Furthermore, in the elastic wave element according to Example 1, the IDT electrodes have a narrow spacing (m=7, pK=0.9pA) and include interval rejection electrodes (end region configuration, interval rejection rate 4%).

[0110] Compare Figure 4 In (a) and (b), in the elastic wave element of Comparative Example 3, compared with the elastic wave element of Comparative Example 2, the fractional bandwidth is reduced by configuring the spaced-out electrodes, but the ripple near the resonant frequency band is not reduced. In contrast, as... Figure 4 As shown in (c), in the elastic wave element according to Example 1, compared with the elastic wave element according to Comparative Example 3, the ripple near the resonant frequency band is reduced by configuring the spaced-out electrode in the end region. Furthermore, although not shown, the fractional bandwidth of the elastic wave elements according to Comparative Example 3 and Example 1 is smaller than that of the elastic wave element according to Comparative Example 2.

[0111] Figure 5This is a graph showing the reflection characteristics of the elastic wave elements according to Comparative Example 4, Comparative Example 5, and Example 2. In the elastic wave element according to Comparative Example 4, the IDT electrodes have a narrow spacing (m=21, pK=0.96pA) and do not include interval rejection electrodes. Furthermore, in the elastic wave element according to Comparative Example 5, the IDT electrodes have a narrow spacing (m=21, pK=0.96pA) and include interval rejection electrodes (non-periodic, interval rejection rate 4%). Furthermore, in the elastic wave element according to Example 2, the IDT electrodes have a narrow spacing (m=21, pK=0.96pA) and include interval rejection electrodes (end region configuration, interval rejection rate 4%). Figure 5 The elastic wave elements shown in Comparative Examples 4, 5, and 2 are relative to... Figure 4 The elastic wave elements shown in Comparative Examples 2, 3 and Example 1 have a narrow pitch that is positioned further centrally towards the IDT electrode, increasing the narrow pitch pK and reducing IRGAP.

[0112] Compare Figure 5 In (a) and (b), in the elastic wave element of Comparative Example 5, compared with the elastic wave element of Comparative Example 4, the fractional bandwidth is reduced by configuring the spaced-out electrodes, but the ripple near the resonant frequency band is not reduced. In contrast, as... Figure 5 As shown in (c), in the elastic wave element according to Example 2, compared with the elastic wave element according to Comparative Example 4, the ripple near the resonant frequency band is reduced by configuring the spaced-out electrode in the end region. Furthermore, although not shown, the fractional bandwidth of the elastic wave elements according to Comparative Example 5 and Example 2 is smaller than that of the elastic wave element according to Comparative Example 4.

[0113] According to the elastic wave element of Embodiment 2, by configuring the spaced-out electrode in the end region of the IDT electrode, it is possible to reduce ripple near the resonant band (resonant frequency) and adjust the fractional bandwidth (resonant bandwidth).

[0114] Figure 6 These are graphs illustrating the reflection characteristics of the elastic wave elements according to Embodiments 3 and 4. In the elastic wave element according to Embodiment 3, the IDT electrode includes two narrow-pitched electrodes (m=21 and m=24, pK=0.96pA) on one side and includes spaced-out electrodes (two in the end region). Additionally, in the elastic wave element according to Embodiment 3, the IDT electrode does not include spaced-out electrodes in the central region. Furthermore, in the elastic wave element according to Embodiment 4, the IDT electrode includes one narrow-pitched electrode (m=21, pK=0.96pA) on one side and includes spaced-out electrodes (one in the end region and one in the central region).

[0115] like Figure 6 As shown in (b), in the elastic wave element of Embodiment 4, compared to the case where only one spaced-out electrode is arranged in the end region, the ripple on the low-frequency side of the resonant band is not improved. In contrast, as Figure 6 As shown in (a), in the elastic wave element of Embodiment 3, the ripple on the low-frequency side of the resonant band can be improved and the fractional bandwidth adjusted to the same extent as in the case where a spaced-out electrode is arranged in the end region.

[0116] According to the elastic wave element of Embodiments 3 and 4, by concentrating the interval removal electrodes in the end region and not in the central region, it is possible to further reduce the ripple near the resonant frequency band and adjust the fractional bandwidth (resonant bandwidth).

[0117] Alternatively, in the elastic wave element of this embodiment, the IDT electrode 10 may include a plurality of spaced-out electrodes disposed in the end region and one or more spaced-out electrodes disposed in the central region, and the spaced-out rate in the end region is higher than the spaced-out rate in the central region.

[0118] Therefore, the interval removal electrode is more concentrated in the end region compared to the central region, thus further reducing ripple near the resonant frequency band and adjusting the fractional bandwidth (resonant bandwidth).

[0119] Furthermore, the elastic wave element 1 involved in this embodiment may also include multiple narrow gaps in one end region, as in the elastic wave element involved in Embodiment 3.

[0120] Figure 7A This is a top view schematically showing the electrode structure of the elastic wave elements 101-105 according to Embodiments 5-9. In the elastic wave elements 101-105 according to Embodiments 5-9, each of the IDT electrodes 151-155 includes three spaced-out rejection electrodes disposed on one side of the end region. Furthermore, here, a polarity-reversed spaced-out rejection electrode is illustrated, but three comb electrode fingers including a polarity-reversed comb electrode finger and comb electrode fingers adjacent to it on both sides are defined as one spaced-out rejection electrode.

[0121] like Figure 7A As shown in (a), in Example 5, no comb-tooth electrode fingers are arranged between the reflective electrode 20A and the three spaced-out removal electrodes, while comb-tooth electrode fingers are arranged between the reflective electrode 20B and the three spaced-out removal electrodes. Figure 7A As shown in (b), in Example 6, a comb-tooth electrode finger is disposed between the reflective electrode 20A and the three spaced-out removal electrodes, and a comb-tooth electrode finger is disposed between the reflective electrode 20B and the three spaced-out removal electrodes. Figure 7AAs shown in (c), in Embodiment 7, two comb-tooth electrode fingers are arranged between the reflective electrode 20A and the three spaced-out removal electrodes, and two comb-tooth electrode fingers are arranged between the reflective electrode 20B and the three spaced-out removal electrodes. Figure 7A As shown in (d), in Example 8, three comb-tooth electrode fingers are arranged between the reflective electrode 20A and the three spaced-out removal electrodes, and three comb-tooth electrode fingers are also arranged between the reflective electrode 20B and the three spaced-out removal electrodes. Figure 7A As shown in (e), in embodiment 9, four comb-tooth electrode fingers are arranged between the reflective electrode 20A and the three spaced-out removal electrodes, and four comb-tooth electrode fingers are arranged between the reflective electrode 20B and the three spaced-out removal electrodes.

[0122] Figure 7B This is a graph showing the relationship between the narrow-pitch position m of the elastic wave element involved in Examples 5 to 9 and the reflection loss (return loss RL). Additionally, in Figure 7B In (a) to (e), the worst value of RL represents the minimum value of the return loss (RL) of the longitudinal mode ripple generated near the low-frequency side of the resonant band (the maximum value of the reflection loss).

[0123] like Figure 7B As shown, in the narrow-pitch position m≥23, the worst value of RL tends to decrease as it changes from elastic wave element 101 to elastic wave element 105. In other words, in the narrow-pitch position m≥23, the more comb-tooth electrodes arranged between the reflective electrode 20A (or 20B) and the three spaced-out removal electrodes, the smaller the worst value of RL becomes.

[0124] When constructing an elastic wave filter and multiplexer that include elastic wave elements, the reflection loss of the elastic wave elements is preferably 0.3 dB or less (RL ≥ -0.3 dB). Based on this viewpoint, in the elastic wave elements of Examples 5 to 8, there exists a narrow-pitch position m that satisfies RL ≥ -0.3 dB. That is, the number of comb-tooth electrode fingers disposed between the reflecting electrode 20A (or 20B) and the spacing removal electrode is preferably 0 or more and 3 or less. This further suppresses longitudinal mode ripple.

[0125] Furthermore, even in the end region, if the multiple spacer rejection electrodes are biased towards the area near the reflective electrode 20A (or 20B), longitudinal mode ripple can be suppressed. That is, when the end region is divided into a first end region near the reflective electrode 20A (or 20B) and a second end region near the center of each of the IDT electrodes 151-155, it is preferable that the spacer rejection rate of the first end region is higher than that of the second end region. This further suppresses longitudinal mode ripple.

[0126] Figure 8 This is a graph showing the relationship between the narrow spacing position m and the reflection loss (return loss RL) of the elastic wave elements involved in Comparative Example 6 and Examples 10 to 14. Additionally, in Figure 8 In this context, the worst value of RL represents the minimum return loss (maximum reflection loss) of the longitudinal mode ripple generated near the low-frequency side of the resonant band.

[0127] like Figure 8 As shown in (a), in the elastic wave element involved in Comparative Example 6, the IDT electrodes include a narrow spacing (pK = 0.90 pA) and do not include a spacing removal electrode. Figure 8 As shown in (b), in the elastic wave element of Embodiment 10, the IDT electrodes include a narrow spacing (pK = 0.90 pA) and include a spaced-out electrode (one in one end region). Figure 8 As shown in (c), in the elastic wave element according to Embodiment 11, the IDT electrodes include a narrow spacing (pK = 0.97 pA) and include spaced-out electrodes (two in one end region). Figure 8 As shown in (d), in the elastic wave element of Embodiment 12, the IDT electrodes include a narrow spacing (pK = 0.98 pA) and include spaced-out electrodes (3 in one end region). Figure 8 As shown in (e), in the elastic wave element of Embodiment 13, the IDT electrodes include a narrow spacing (pK = 0.98 pA) and include spaced-out electrodes (four in one end region). Figure 8 As shown in (f), in the elastic wave element involved in Embodiment 14, the IDT electrodes include a narrow pitch (pK=0.98pA) and include spaced-out electrodes (5 in one end region).

[0128] In the elastic wave elements according to Examples 10 to 13, there is a narrow-pitch position m that satisfies RL ≥ -0.3dB. That is, the number of spaced-out electrodes disposed in an end region is preferably one or more and four or less. As a result, longitudinal mode ripple can be further suppressed.

[0129] Furthermore, in the elastic wave element according to Embodiment 12, the range of narrow-pitch positions m that satisfy RL≥-0.3dB is m≤29, and in the elastic wave element according to Embodiment 13, the range of narrow-pitch positions m that satisfy RL≥-0.3dB is m≤32. That is to say, when the number of spaced-out electrodes arranged in an end region is 3 or 4, the degree of freedom in arranging the narrow-pitch positions is increased.

[0130] Figure 9This is a graph showing the impedance and reflection characteristics of the elastic wave elements according to Comparative Example 7 and Example 15. In the elastic wave element according to Comparative Example 7, the IDT electrodes have a narrow spacing (m=6, pK=0.92pA) and do not include spaced-out electrodes. Furthermore, in the elastic wave element according to Example 15, the IDT electrodes have a narrow spacing (m=26, pK=0.97pA) and include spaced-out electrodes (4 in one end region).

[0131] like Figure 9 As shown in (a), in the elastic wave element according to Example 15, compared with the elastic wave element according to Comparative Example 7, the longitudinal mode ripple is reduced and the fractional bandwidth is smaller on the low-frequency side near the resonant frequency band. Furthermore, on the high-frequency side near the resonant frequency band ( Figure 9 (within the dashed box of (b)) the stopband ripple is reduced.

[0132] Therefore, by configuring four spaced-out elimination electrodes in one end region and adjusting the narrow-pitch position m, the wavelength λ of the reflective electrodes 20A and 20B, and the IRGAP, it is possible to reduce the longitudinal mode ripple and stopband ripple near the resonant frequency band and adjust the fractional bandwidth.

[0133] In addition, IRGAP is preferably less than 0.45 × λ. REF This allows for a further reduction in stopband ripple on the high-frequency side near the resonant frequency band.

[0134] Figure 10A This is a top view schematically illustrating the electrode structure of the elastic wave elements 111-115 according to Embodiments 16-20. In the elastic wave elements 111-115 according to Embodiments 16-20, each of the IDT electrodes 161-165 includes four spaced-out electrodes in the end region on one side. Furthermore, a polarity-reversed spaced-out electrode is illustrated here, but three comb electrode fingers, including a polarity-reversed comb electrode finger and three comb electrode fingers adjacent to it on both sides, are defined as one spaced-out electrode.

[0135] like Figure 10A As shown in (a), in Example 16, a plurality of comb-tooth electrode fingers are arranged between the reflective electrode 20A and the four spaced-out removal electrodes, and a plurality of comb-tooth electrode fingers are arranged between the reflective electrode 20B and the four spaced-out removal electrodes. Figure 10A As shown in (b), in Example 17, a plurality of comb-tooth electrode fingers are arranged between the first spaced-out removal electrode from the outermost side and the second spaced-out removal electrode from the outermost side. Figure 10A As shown in (c), in Example 18, a plurality of comb-tooth electrode fingers are arranged between the second spaced-out removal electrode from the outermost side and the third spaced-out removal electrode from the outermost side. Figure 10AAs shown in (d), in Example 19, a plurality of comb-tooth electrode fingers are arranged between the third spaced-out removal electrode from the outermost side and the fourth spaced-out removal electrode from the outermost side. Figure 10A As shown in (e), in embodiment 20, a plurality of comb-tooth electrode fingers are arranged on the central side of the IDT electrode 165, which is closer to the outermost fourth interval removal electrode.

[0136] Figure 10B This is a graph showing the relationship between the narrow spacing position m of the elastic wave elements 111-115 according to Embodiments 16-20 and the reflection loss (return loss RL). Additionally, in Figure 10B In (a) to (e), the worst value of RL represents the minimum value of the return loss (RL) of the longitudinal mode ripple generated near the low-frequency side of the resonant band (the maximum value of the reflection loss).

[0137] In the elastic wave elements 114 and 115 of Embodiments 19 and 20, there are narrow-pitch positions m that satisfy RL ≥ -0.3dB. That is, even in the end regions, where multiple space-canceling electrodes are biased towards the region near the reflective electrode 20A (or 20B), longitudinal mode ripple can be suppressed. Specifically, when the end region is divided into a first end region near the reflective electrode 20A (or 20B) and a second end region near the center of each of the IDT electrodes 161-165, it is preferable that the space-canceling rate of the first end region is higher than that of the second end region. This further suppresses longitudinal mode ripple.

[0138] Furthermore, in the elastic wave elements described in Examples 1 to 20, the spacing of the comb electrode fingers of the IDT electrode can also be random. Random spacing means that the spacing is arranged in an irregular increasing or decreasing manner. That is, multiple comb electrode fingers 11a and 11b are arranged randomly, such that the spacing between adjacent comb electrode fingers 11a and 11b varies irregularly. Irregular variation refers to a variation that includes random changes rather than fixed states, proportional changes, or periodic changes. In this case, the spacing at the m-th end is the smallest among the n-th end-side spacings (n is a natural number) of the IDT electrode. By applying random spacing to the arrangement of the comb electrode fingers of the IDT electrode, stopband ripple in the high-frequency side near the resonant frequency band can be further reduced.

[0139] [4. Structure of elastic wave filter and multiplexer]

[0140] Next, an example of the circuit structure of the elastic wave filter 200 and the multiplexer 300 using the elastic wave element 1 according to the embodiment will be described. Figure 11This is a circuit diagram of the multiplexer 300 according to the embodiment. As shown in the figure, the multiplexer 300 includes filters 200 and 250, a common terminal 301, and input / output terminals 302 and 303. The common terminal 301 is connected to an antenna, for example.

[0141] Filter 200 is an example of an elastic wave filter, connected between common terminal 301 and input / output terminal 302. It is a trapezoidal bandpass filter having series arm resonators 211, 212, and 213, parallel arm resonators 221 and 222, and input / output terminals 201 and 202. At least one of the series arm resonators 211-213 and the parallel arm resonators 221 and 222 is the elastic wave element 1 according to the embodiment. Furthermore, filter 200 can be any elastic wave filter having the elastic wave element 1 according to the embodiment; it does not have to be a trapezoidal bandpass filter, for example, it can be an elastic wave filter with longitudinally coupled resonators.

[0142] Filter 250 is an example of the first filter, connected between common terminal 301 and input / output terminal 303. Filter 250 can also be an elastic wave filter, or it can be an LC filter, dielectric filter, etc., and the filter construction is arbitrary.

[0143] Based on the above-described structure of the filter 200, since it is equipped with the elastic wave element 1 according to the embodiment, a low-loss elastic wave filter that can reduce ripple near the passband and adjust the passband width can be provided.

[0144] Furthermore, based on the above-described structure of the multiplexer 300, since it includes a filter 200 containing an elastic wave element 1, it is possible to provide a multiplexer 300 that can adjust the passband width of the filter 200 and reduce the insertion loss in the passband of the filter 250.

[0145] In addition, the number of filters constituting the multiplexer 300 only needs to be two or more.

[0146] [5. Effects, etc.]

[0147] As described above, the elastic wave element 1 according to the embodiment includes: a piezoelectric substrate 50; an IDT electrode 10 disposed on the piezoelectric substrate 50; and reflective electrodes 20A and 20B disposed on the piezoelectric substrate 50 and arranged adjacent to the IDT electrode 10 in a first direction. The IDT electrode 10 has a plurality of comb-tooth electrode fingers 11a and 11b extending in a second direction intersecting the first direction. The reflective electrodes 20A and 20B have a plurality of reflective electrode fingers 21a and 21b extending in the second direction. The comb-tooth electrode finger closest to the reflective electrode 20A (or 20B) among the plurality of comb-tooth electrode fingers 11a and 11b is designated as the first end-side electrode finger, and the comb-tooth electrode fingers in the direction from the first end-side electrode finger toward the center of the IDT electrode 10 are sequentially designated as the nth end-side electrode fingers. Electrode fingers (n is a natural number), the center-to-center distance between adjacent electrode fingers in the first direction in the first direction of each of the plurality of comb electrode fingers 11a and 11b and the plurality of reflective electrode fingers 21a and 21b is defined as the spacing, the spacing between the nth end-side electrode finger and the (n+1)th end-side electrode finger is defined as the nth end-side spacing, the mth end-side spacing of the spacing from the first end-side electrode finger to the comb electrode finger located at the center of the IDT electrode 10 is less than the average spacing of the plurality of comb electrode fingers 11a and 11b other than the mth end-side spacing, when the region from the first end-side electrode finger to the mth end-side electrode finger in the region where the IDT electrode 10 is formed is defined as the end region, the IDT electrode 10 includes a spaced-out removal electrode disposed in the end region.

[0148] Therefore, by configuring the interval removal electrode in the end region of the IDT electrode 10, it is possible to reduce ripple near the resonant frequency band and adjust the fractional bandwidth (resonant bandwidth).

[0149] Furthermore, for example, in the elastic wave element 1, the number of comb electrode fingers disposed between the reflective electrode 20A (or 20B) and the spaced-out electrode is 0 or more and 3 or less.

[0150] This allows for further suppression of longitudinal mode ripple.

[0151] For example, in the elastic wave element 1, the IDT electrode 10 includes a plurality of spaced-out electrodes disposed in the end region, the end region being divided into a first end region near the reflective electrode 20A (or 20B) and a second end region near the center of the IDT electrode 10, the spaced-out rate of the first end region being higher than that of the second end region.

[0152] This allows for further suppression of longitudinal mode ripple.

[0153] Furthermore, for example, in the elastic wave element 1, one or more but no more than four spaced-out removal electrodes are arranged in the end region.

[0154] This allows for further suppression of longitudinal mode ripple.

[0155] Furthermore, for example, in the elastic wave element 1, the region where the IDT electrode 10 is formed includes two end regions located at both ends of the IDT electrode 10 in the first direction, and a central region sandwiched between the two end regions. The IDT electrode 10 includes a plurality of spaced-out electrodes disposed in the end regions and one or more spaced-out electrodes disposed in the central region. The spaced-out rate of the end regions is higher than that of the central region.

[0156] Therefore, the interval removal electrode is more concentrated in the end region than in the central region, thus further reducing ripple near the resonant frequency band and adjusting the fractional bandwidth (resonant bandwidth).

[0157] Furthermore, for example, in the elastic wave element 1, no spaced-out removal electrode is provided in the central region.

[0158] Therefore, by concentrating the interval removal electrodes in the end region, it is possible to further reduce ripple near the resonant band (resonant frequency) and adjust the fractional bandwidth (resonant bandwidth).

[0159] For example, in the elastic wave element 1, the piezoelectric substrate 50 includes: a piezoelectric layer 51 having opposing main surfaces 51a and 51b; a support substrate 54 disposed on the main surface 51b side of the piezoelectric layer 51; a low-velocity layer 52 disposed between the piezoelectric layer 51 and the support substrate 54, having a volume wave velocity lower than that of the piezoelectric layer 51 and the support substrate 54; and a high-velocity layer 53 disposed between the low-velocity layer 52 and the support substrate 54, having a volume wave velocity higher than that of the low-velocity layer 52.

[0160] This allows for a significant increase in the Q value at both the resonant and anti-resonant frequencies. In other words, it enables the construction of elastic wave elements with high Q values, thus allowing the use of these elements to construct elastic wave filters with low insertion loss.

[0161] Furthermore, for example, in the modified example of the elastic wave element 1A, the piezoelectric substrate is a single crystal piezoelectric substrate 50A containing lithium niobate, and the elastic wave element 1A also includes: an insulating layer 60 disposed on the piezoelectric substrate 50A and configured to embed an IDT electrode 10.

[0162] Therefore, it is possible to provide an elastic wave element 1A with improved frequency-temperature characteristics.

[0163] Furthermore, the filter 200 according to the embodiment includes an elastic wave element 1.

[0164] Therefore, it is possible to provide a low-loss elastic wave filter that can reduce ripple near the passband and adjust the passband width.

[0165] Furthermore, the multiplexer 300 according to the embodiment includes: a common terminal 301; a filter 200 connected to the common terminal 301; and a filter 250 connected to the common terminal 301.

[0166] Therefore, the passband width of filter 200 can be adjusted, and the insertion loss in the passband of filter 250 can be reduced.

[0167] (Other variations, etc.)

[0168] The above description illustrates the elastic wave element, elastic wave filter, and multiplexer through examples; however, the elastic wave element, elastic wave filter, and multiplexer of the present invention are not limited to the above embodiments. Other embodiments implemented by combining any of the constituent elements in the above embodiments, variations of the above embodiments that can be conceived by those skilled in the art by implementing various modifications to the above embodiments without departing from the spirit of the present invention, and various devices incorporating the elastic wave element, elastic wave filter, and multiplexer involved in the above embodiments are also included in the present invention.

[0169] Industrial availability

[0170] This invention, as a low-loss and high-attenuation elastic wave filter and multiplexer applicable to multi-band frequency standards, can be widely used in communication devices such as portable telephones.

Claims

1. An elastic wave element, comprising: piezoelectric substrate; Interdigitated transducers, i.e., IDT electrodes, are disposed on the piezoelectric substrate; and A reflective electrode is disposed on the piezoelectric substrate and configured to be adjacent to the IDT electrode in the first direction. The IDT electrode has a plurality of comb-tooth electrode fingers extending in a second direction intersecting the first direction. The reflective electrode has a plurality of reflective electrode fingers extending in the second direction. The comb electrode finger closest to the reflective electrode among the plurality of comb electrode fingers is designated as the first end-side electrode finger, and the comb electrode fingers moving from the first end-side electrode finger toward the center of the IDT electrode are sequentially designated as the nth end-side electrode finger, wherein... n is a natural number. The center-to-center distance between adjacent electrode fingers in the first direction is defined as the spacing, and the spacing between the nth end-side electrode finger and the (n+1)th end-side electrode finger is defined as the nth end-side spacing. The distance from the first end-side electrode finger to the comb-tooth electrode finger located at the center of the IDT electrode, in the distance between the m-th end-side electrode finger and the comb-tooth electrode finger, is less than the average distance of the distances between the plurality of comb-tooth electrode fingers excluding the m-th end-side electrode finger. When the region from the first end-side electrode to the mth end-side electrode in the region where the IDT electrode is formed is defined as the end region, the IDT electrode includes an interval removal electrode disposed in the end region.

2. The elastic wave element according to claim 1, wherein, The number of comb-tooth electrode fingers disposed between the reflective electrode and the spaced-out electrode is more than 0 and less than 3.

3. The elastic wave element according to claim 1 or 2, wherein, The IDT electrode includes a plurality of spaced-out rejection electrodes disposed in the end region. The end region is divided into a first end region near the reflective electrode and a second end region near the center of the IDT electrode. The interval removal rate of the first end region is higher than that of the second end region.

4. The elastic wave element according to any one of claims 1 to 3, wherein, In the end region, one or more but no more than four spaced rejection electrodes are provided.

5. The elastic wave element according to any one of claims 1 to 4, wherein, The region where the IDT electrode is formed includes two end regions located at both ends of the IDT electrode in the first direction, and a central region sandwiched between the two end regions. The IDT electrode includes a plurality of spaced-out rejection electrodes disposed in the end region and one or more spaced-out rejection electrodes disposed in the central region. The interval rejection rate in the end region is higher than that in the central region.

6. The elastic wave element according to any one of claims 1 to 4, wherein, The IDT electrode includes two end regions located at both ends of the IDT electrode in the first direction, and a central region sandwiched between the two end regions. No interval removal electrodes are configured in the central region.

7. The elastic wave element according to any one of claims 1 to 6, wherein, The piezoelectric substrate comprises: The piezoelectric layer has a first principal surface and a second principal surface that are opposite to each other; A support substrate is disposed on the second main surface side of the piezoelectric layer; A low-velocity sound layer is disposed between the piezoelectric layer and the support substrate, and has a volume wave velocity lower than that of the piezoelectric layer and the support substrate. and A high-velocity layer is disposed between the low-velocity layer and the support substrate, and has a volume wave velocity higher than that of the low-velocity layer.

8. The elastic wave element according to any one of claims 1 to 6, wherein, The piezoelectric substrate is a single-crystal piezoelectric substrate containing lithium niobate. The elastic wave element further comprises: an insulating layer disposed on the piezoelectric substrate and configured to embed the IDT electrode.

9. An elastic wave filter comprising the elastic wave element according to any one of claims 1 to 8.

10. A multiplexer, comprising: Common terminal; The elastic wave filter of claim 9 is connected to the common terminal; and The first filter is connected to the common terminal.

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