Acoustic wave device, high frequency filter, and filter circuit

Abstract

To provide a compact acoustic wave device which can adjust a fractional band width without causing deterioration in a Q value.SOLUTION: An acoustic wave device 1 includes: a substrate 3; an IDT electrode 10 arranged on the substrate 3; and a dielectric film 41 arranged on the substrate 3. The substrate 3 comprises a piezoelectric layer 31, a low acoustic velocity layer 32, and a high acoustic velocity layer 33 in this order. The IDT electrode 10 includes multiple electrode fingers 11a and 11b, a busbar electrode 12a connecting the multiple electrode fingers 11a, and a busbar electrode 12b connecting the multiple electrode fingers 11b. On the piezoelectric layer 31, the dielectric film 41 is arranged only in a region where the multiple electrode fingers 11a and 11b and the busbar electrodes 12a and 12b are not arranged in regions between the busbar electrode 12a and the busbar electrode 12b in a plan view of the substrate 3. A film thickness of the dielectric film 41 is smaller than that of the multiple electrode fingers 11a and 11b.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acoustic wave device, a high-frequency filter, and a filter circuit. [Background technology]

[0002] Patent Document 1 discloses a surface acoustic wave filter (acoustic wave device) having a high Q value by using a substrate formed of a laminate of a high acoustic velocity support substrate, a low acoustic velocity layer, and a piezoelectric layer. With this configuration, it is possible to realize a low loss surface acoustic wave filter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2012 / 086639 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the case of the acoustic wave device disclosed in Patent Document 1, for example, by optimizing the Euler angles of the piezoelectric layer, unwanted waves can be suppressed and degradation of the Q value can be suppressed, but the optimized Euler angles limit the relative bandwidth to a specific range, making it difficult to adjust the relative bandwidth. Also, due to the substrate formed of a laminate, the acoustic wave device must be made larger in order to ensure the capacity of an acoustic wave device having a thin piezoelectric layer.

[0005] Therefore, the present invention has been made to solve the above-mentioned problems, and has an object to provide a small-sized acoustic wave device, a high-frequency filter, and a filter circuit that enable adjustment of the relative bandwidth without degrading the Q value. [Means for solving the problem]

[0006] In order to achieve the above object, an elastic wave device according to one aspect of the present invention includes a substrate, an IDT (InterDigital Transducer) electrode arranged on the substrate, and a first dielectric film arranged on the substrate. The substrate includes a piezoelectric layer on which the IDT electrode is formed, a high acoustic velocity layer in which a bulk wave propagates faster than an elastic wave propagates through the piezoelectric layer, and a low acoustic velocity layer arranged between the piezoelectric layer and the high acoustic velocity layer in which the bulk wave propagates slower than the bulk wave propagating through the piezoelectric layer. The IDT electrode includes a plurality of first electrode fingers and a plurality of second electrode fingers arranged in parallel to each other, a first bus bar electrode configured to connect one ends of the plurality of first electrode fingers to each other, and a plurality of low acoustic velocity layers arranged between the piezoelectric layer and the high acoustic velocity layer. the first dielectric film is disposed on the piezoelectric layer only in an area between the first busbar electrode and the second busbar electrode in a planar view of the substrate where the first electrode fingers, the second electrode fingers, the first busbar electrode, and the second busbar electrode are not disposed, and the thickness of the first dielectric film is smaller than the thickness of the first electrode fingers and the second electrode fingers.

[0007] An acoustic wave device according to one aspect of the present invention includes a substrate, an IDT electrode disposed on the substrate, and a first dielectric film disposed on the substrate. The substrate includes a piezoelectric layer on which the IDT electrode is formed, a high acoustic velocity layer in which a bulk wave propagates faster than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer, and a low acoustic velocity layer disposed between the piezoelectric layer and the high acoustic velocity layer in which the bulk wave propagates slower than the bulk wave propagating through the piezoelectric layer. The IDT electrode includes a plurality of first electrode fingers and a plurality of second electrode fingers disposed in parallel to each other, a first bus bar electrode configured to connect one ends of the plurality of first electrode fingers to each other, and a plurality of second electrode fingers. the first dielectric film is disposed on the piezoelectric layer only in an area where the first electrode fingers and the second electrode fingers are not arranged in a planar view of the substrate among areas where the first electrode fingers and the second electrode fingers overlap when viewed from a direction parallel to the piezoelectric layer and perpendicular to the extension direction of the first electrode fingers and the second electrode fingers, and the thickness of the first dielectric film is smaller than the thickness of the first electrode fingers and the second electrode fingers.

[0008] A high-frequency filter according to one aspect of the present invention includes the above-described acoustic wave device.

[0009] Moreover, a filter circuit according to one embodiment of the present invention includes a plurality of the above-described high-frequency filters, the plurality of high-frequency filters sharing a single substrate, and a first dielectric film of a first high-frequency filter of the plurality of high-frequency filters and a first dielectric film of a second high-frequency filter of the plurality of high-frequency filters having different thicknesses, materials, or compositions. Effect of the Invention

[0010] According to the present invention, it is possible to provide a small-sized acoustic wave device, a high-frequency filter, and a filter circuit that are capable of adjusting the relative bandwidth without degrading the Q value. [Brief description of the drawings]

[0011] [Figure 1]1A and 1B are a plan view and a cross-sectional view of an elastic wave device in accordance with a first embodiment. [Diagram 2] 1A and 1B are a plan view and a cross-sectional view of an elastic wave device according to a comparative example. [Figure 3A] 13 is a graph showing the relationship between the thickness of a dielectric film and the rate of change in relative bandwidth of elastic wave devices according to Example 1 and a comparative example. [Figure 3B] 13 is a graph showing the relationship between the thickness of a dielectric film and the rate of change of Qmax in elastic wave devices according to Example 1 and a comparative example. [Figure 3C] 13 is a graph showing the relationship between the rate of change in Qmax and the rate of change in fractional bandwidth in elastic wave devices according to Example 1 and a comparative example. [Figure 4A] 11 is a graph showing a relationship between the film thickness of a first dielectric film and the rate of change in relative bandwidth when the relative dielectric constant of the first dielectric film is changed in the elastic wave device in accordance with Example 1. [Figure 4B] 13 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of Qmax when the first dielectric film has a relative dielectric constant of 3.75 in an elastic wave device in accordance with Example 1. [Figure 4C] 13 is a graph showing the relationship between the relative dielectric constant and the rate of decrease in the relative bandwidth when the rate of change in Qmax is 80% in the elastic wave device in accordance with Example 1. [Figure 5A] 1 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of the relative bandwidth when the first dielectric film is silicon nitride or silicon oxide. [Figure 5B] 11 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of the relative bandwidth when the first dielectric film is made of yttrium oxide or silicon oxide. [Figure 5C] 11 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of the relative bandwidth when the first dielectric film is made of aluminum oxide or silicon oxide. [Figure 5D] 11 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of the relative bandwidth when the first dielectric film is made of tantalum oxide or silicon oxide. [Figure 5E] 11 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of a relative bandwidth when the first dielectric film is titanium oxide or silicon oxide. [Figure 5F] 11 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of a relative bandwidth when the first dielectric film is hafnium oxide or silicon oxide. [Figure 5G] 11 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of a relative bandwidth when the first dielectric film is made of zirconium oxide or silicon oxide. [Figure 5H] 1 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change of a relative bandwidth when the first dielectric film is made of sialon or silicon oxide. [Figure 6] 11 is a graph showing the relationship between the film thickness of a first dielectric film and the rate of change in the relative bandwidth when the piezoelectric layer of the elastic wave device in accordance with Example 1 is made of lithium niobate. [Figure 7A] FIG. 11 is a plan view of an elastic wave device in accordance with a first modification. [Figure 7B] 11 is a plan view of an elastic wave device in accordance with a second modification. FIG. [Figure 8] 11A and 11B are a plan view and a cross-sectional view of an elastic wave device in accordance with a second embodiment. [Figure 9A] 1A and 1B are diagrams illustrating an electrode configuration of an elastic wave resonator according to an embodiment and a diagram illustrating an elastic wave resonator; [Figure 9B] 1A and 1B are diagrams each showing a schematic electrode configuration of a longitudinally coupled resonator according to an embodiment, and a diagram showing a longitudinally coupled resonator. [Figure 10A] 1 is a circuit configuration diagram of a ladder-type high-frequency filter according to an embodiment of the present invention; [Figure 10B] 1 is a circuit diagram of a high-frequency filter including a longitudinally coupled resonator according to an embodiment; [Figure 10C] 1 is a circuit configuration diagram of a high-frequency filter including a plurality of longitudinally coupled resonators according to an embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangements and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present invention. Among the components in the following embodiments, components that are not described in the independent claims are described as optional components. Also, the size or size ratio of the components shown in the drawings is not necessarily strict.

[0013] In addition, each figure is a schematic diagram in which emphasis, omission, or adjustment of the ratio is appropriately performed in order to illustrate the present invention, and is not necessarily a strict illustration, and may differ from the actual shape, positional relationship, and ratio. In each figure, the same reference numerals are given to substantially the same configurations, and duplicated explanations may be omitted or simplified.

[0014] In the circuit configuration of the present disclosure, "connected" includes not only direct connection by a connection terminal and / or a wiring conductor, but also electrical connection via matching elements such as inductors and capacitors, and switch circuits. "Connected between A and B" means connected to both A and B between A and B.

[0015] In addition, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of an element, such as "rectangle," and numerical ranges do not only indicate the strict meaning, but also include a substantially equivalent range, for example, an error of about a few percent.

[0016] In the following embodiments, the passband of a filter is defined as a frequency band between two frequencies that are 3 dB higher than the minimum value of the insertion loss in the passband.

[0017] (Embodiment) [1. Configuration of Elastic Wave Device 1 in accordance with First Embodiment] 1A and 1B are a plan view and a cross-sectional view of an elastic wave device 1 in accordance with a first embodiment. As shown in the figure, the elastic wave device 1 includes a substrate 3, an IDT electrode 10, a reflective electrode 20, and a dielectric film 41. Note that the elastic wave device 1 shown in FIG. 1 is intended to illustrate a typical structure of an elastic wave resonator constituting the elastic wave device 1, and the number and length of electrode fingers constituting the IDT electrode 10 are not limited thereto. As shown in FIG. 1A, the IDT electrode 10 and the reflective electrode 20 are disposed on the substrate 3.

[0018] The substrate 3 has piezoelectric properties and includes a piezoelectric layer 31, a low acoustic velocity layer 32, a high acoustic velocity layer 33, and a support substrate .

[0019] The IDT electrode 10 and the reflective electrode 20 are disposed on one surface of the piezoelectric layer 31. For example, lithium tantalate, lithium niobate, or a material containing the above materials as a main component can be used for the piezoelectric layer 31. The thickness of the piezoelectric layer 31 is, for example, 400 nm.

[0020] The high acoustic velocity layer 33 is disposed on the other side of the piezoelectric layer 31, and the acoustic velocity of the bulk wave propagating through the high acoustic velocity layer 33 is faster than the acoustic velocity of the elastic wave propagating through the piezoelectric layer 31. For example, the high acoustic velocity layer 33 can be made of a piezoelectric material such as silicon nitride, aluminum nitride, lithium tantalate, lithium niobate, or quartz, a ceramic material such as alumina, sapphire, magnesia, silicon carbide, zirconia, cordierite, mullite, steatite, or forsterite, a dielectric material such as diamond or glass, a semiconductor material such as silicon or gallium nitride, or a resin, or a material mainly composed of the above materials. The thickness of the high acoustic velocity layer 33 is, for example, 300 nm.

[0021] The low acoustic velocity layer 32 is disposed between the other main surface of the piezoelectric layer 31 and one main surface of the high acoustic velocity layer 33, and the acoustic velocity of the bulk wave propagating through the low acoustic velocity layer 32 is lower than that of the bulk wave propagating through the piezoelectric layer 31. This structure and the property of the acoustic wave concentrating energy in a medium with an essentially low acoustic velocity suppress leakage of the surface acoustic wave energy outside the IDT electrode. The low acoustic velocity layer 32 can be made of, 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 is added to silicon oxide, or a material mainly composed of the above materials. The film thickness of the low acoustic velocity layer 32 is, for example, 300 nm.

[0022] The support substrate 34 is disposed on the other main surface of the high acoustic velocity layer 33, and is a substrate that supports the IDT electrode 10, the piezoelectric layer 31, the low acoustic velocity layer 32, and the high acoustic velocity layer 33. For the support substrate 34, for example, a piezoelectric material such as silicon, aluminum nitride, lithium tantalate, lithium niobate, or quartz, a ceramic material such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, or forsterite, a dielectric material such as diamond or glass, a semiconductor material such as gallium nitride, or a resin, or a material mainly composed of any of the above materials can be used.

[0023] The laminated structure of substrate 3 makes it possible to significantly increase the Q value at the resonant frequency and anti-resonant frequency, compared to a conventional structure using a single layer of piezoelectric substrate. In other words, an elastic wave resonator with a high Q value can be configured, and therefore, using this elastic wave resonator, it is possible to configure a high frequency filter with low insertion loss.

[0024] The high acoustic velocity layer 33 and the support substrate 34 may be combined to form one high acoustic velocity support substrate. The high acoustic velocity support substrate is a substrate that supports the IDT electrode 10, the piezoelectric layer 31, and the low acoustic velocity layer 32. The high acoustic velocity support substrate is a substrate in which the acoustic velocity of the bulk waves in the high acoustic velocity support substrate is faster than that of the surface waves and boundary waves propagating through the piezoelectric layer 31, and functions to confine the surface acoustic waves in the portion where the piezoelectric layer 31 and the low acoustic velocity layer 32 are laminated, and to prevent leakage below the high acoustic velocity support substrate. Examples of materials that can be used for the high acoustic velocity support substrate include piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon, dielectric materials such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond, semiconductors such as silicon, and materials mainly composed of the above materials. The spinel includes an aluminum compound containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0025] In this specification, the term "major component of a material" refers to a component that accounts for more than 50% by weight of the material. The major component may be in any of the following states: single crystal, polycrystalline, or amorphous, or a mixture of these.

[0026] Alternatively, instead of the substrate 3, a support substrate, an energy trapping layer, and a piezoelectric layer may be laminated in this order. The IDT electrode 10 and the reflective electrode 20 are formed on the piezoelectric layer. For example, a LiTaO3 piezoelectric single crystal or a piezoelectric ceramic is used for the piezoelectric layer. The support substrate is a substrate that supports the piezoelectric layer, the energy trapping layer, and the IDT electrode 10.

[0027] The energy trapping layer is composed of one or more layers, and the speed of the bulk acoustic wave propagating through at least one of the layers is greater than the speed of the acoustic wave propagating near the piezoelectric layer. For example, the energy trapping layer may have a laminated structure of a low acoustic velocity layer and a high acoustic velocity layer. The low acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the low acoustic velocity layer is slower than the acoustic velocity of the acoustic wave propagating through the piezoelectric layer. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the high acoustic velocity layer is faster than the acoustic velocity of the acoustic wave propagating through the piezoelectric layer. The support substrate may be the high acoustic velocity layer.

[0028] The energy trapping layer may be an acoustic impedance layer having a configuration in which low acoustic impedance layers having a relatively low acoustic impedance and high acoustic impedance layers having a relatively high acoustic impedance are alternately laminated.

[0029] As shown in FIG. 1(a), the IDT electrode 10 has a plurality of electrode fingers 11a and a plurality of electrode fingers 11b, and bus bar electrodes 12a and 12b.

[0030] The multiple electrode fingers 11a are an example of multiple first electrode fingers and are arranged parallel to each other. The multiple electrode fingers 11b are an example of multiple second electrode fingers and are arranged parallel to each other. The multiple electrode fingers 11a and the multiple electrode fingers 11b are arranged parallel to each other so as to be interdigitated with each other.

[0031] The busbar electrode 12a is an example of a first busbar electrode and is configured to connect one ends of the electrode fingers 11a to each other. The busbar electrode 12a extends in a direction (x-axis direction) intersecting with the extension direction of the electrode fingers 11a (y-axis direction in FIG. 1).

[0032] Busbar electrode 12b is an example of a second busbar electrode, and is configured to connect one ends of the electrode fingers 11b to each other. Busbar electrode 12b extends in a direction (x-axis direction) intersecting with the extension direction of the electrode fingers 11b (y-axis direction in FIG. 1). Busbar electrode 12a and busbar electrode 12b are arranged opposite each other with the electrode fingers 11a and the electrode fingers 11b interposed therebetween. The other ends of the electrode fingers 11a face busbar electrode 12b, and the other ends of the electrode fingers 11b face busbar electrode 12a.

[0033] The reflective electrodes 20 are arranged on both sides of the IDT electrode 10 so as to be adjacent to the IDT electrode 10 in a direction (x-axis direction) perpendicular to the extension direction of the electrode fingers 11a and the electrode fingers 11b. The reflective electrodes 20 are configured to confine within the IDT electrode 10 a predetermined high-frequency signal that resonates in the IDT electrode 10. The reflective electrode 20 has a plurality of electrode fingers 21 and busbar electrodes 22a and 22b. The electrode fingers 21 are an example of a plurality of third electrode fingers, and are arranged parallel to the electrode fingers 11a and the electrode fingers 11b. The busbar electrode 22a is an example of a third busbar electrode, and is configured to connect one ends of the electrode fingers 21 to each other. The busbar electrode 22b is an example of a fourth busbar electrode, and is configured to connect the other ends of the electrode fingers 21 to each other. The busbar electrodes 22a and 22b are arranged opposite to each other with the electrode fingers 21 interposed therebetween. In the acoustic wave device 1 according to this preferred embodiment, the reflecting electrode 20 is not essential.

[0034] As shown in FIG. 1(b), the IDT electrode 10 and the reflective electrode 20 have a laminated structure of, for example, an adhesive layer and a main electrode layer.

[0035] The main electrode layer is mainly composed of aluminum (Al) and has a thickness of, for example, 100 nm. The adhesion layer is disposed between the main electrode layer and the piezoelectric layer 31 and is configured to improve adhesion of the main electrode layer to the substrate 3. The adhesion layer is made of titanium (Ti) and has a thickness of, for example, 10 nm. The IDT electrode 10 and the reflective electrode 20 are not limited to the above-mentioned laminated structure and may be made of, for example, a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or may be made of a plurality of laminated bodies made of the above-mentioned metals or alloys.

[0036] In order to optimize the propagation characteristics of the surface acoustic wave, it is necessary to optimally set the (density x film thickness) of the IDT electrode 10. By using aluminum, which has a low density and low resistance compared to high-density electrode materials, the film thickness of the IDT electrode 10 can be set large, making it possible to form a low-resistance IDT electrode 10. Furthermore, due to the relationship of the lattice constant, the IDT electrode 10 can be epitaxially grown by forming an adhesion layer (Ti) and a main electrode layer (Al) without sandwiching an amorphous dielectric film between the piezoelectric layer 31 and the IDT electrode 10. This makes it possible to realize a high-performance high-frequency filter with excellent power durability using the acoustic wave device 1.

[0037] 1A, the dielectric film 41 is an example of a first dielectric film, and is disposed on the substrate 3. As shown in FIG. 1A, the dielectric film 41 is disposed only in a region between the busbar electrodes 12a and 12b in a plan view of the substrate 3 where the electrode fingers 11a, the electrode fingers 11b, and the busbar electrodes 12a and 12b are not disposed, and is disposed only in a region between the busbar electrodes 22a and 22b in a plan view of the substrate 3 where the electrode fingers 21, the busbar electrodes 22a and 22b are not disposed.

[0038] As shown in FIG. 1(b), the thickness of dielectric film 41 is smaller than the thickness h of the plurality of electrode fingers 11a and the plurality of electrode fingers 11b.

[0039] In the elastic wave device according to the present invention, "dielectric film 41 is arranged only in an area where electrode A (including electrode fingers, bus bar electrodes, etc.) is not arranged" means that dielectric film 41 does not substantially overlap electrode A in a planar view of substrate 3. "Dielectric film 41 does not substantially overlap electrode A" means that dielectric film 41 may be in contact with electrode A, and the overlapping area between dielectric film 41 and electrode A in a planar view of substrate 3 is less than 10% of the total area of ​​electrode A.

[0040] The dielectric film 41 can be made of silicon oxide, silicon nitride, aluminum oxide, yttrium oxide, tantalum oxide, titanium oxide, hafnium oxide, zirconium oxide, aluminum nitride, or sialon, or a material containing any of the above materials as a main component.

[0041] In elastic wave device 1 having the above configuration, the wavelength of elastic wave device 1 is defined as wavelength λ, which is the repetition period of multiple electrode fingers 11a or 11b constituting IDT electrode 10 shown in Fig. 1(b). The electrode finger pitch is ½ of wavelength λ. As shown in Fig. 1(a), overlap width L is the length in the y-axis direction of a region where multiple electrode fingers 11a and multiple electrode fingers 11b overlap when viewed in a direction (x-axis direction) parallel to piezoelectric layer 31 and perpendicular to the extension direction (y-axis direction) of multiple electrode fingers 11a and multiple electrode fingers 11b.

[0042] The above configuration makes it possible to provide a small-sized acoustic wave device 1 that allows adjustment of the relative bandwidth without degrading the Q value. The following describes how acoustic wave device 1 can achieve the above effects.

[0043] [2. Configuration of Acoustic Wave Device 500 According to Comparative Example] First, the configuration of a (conventional) elastic wave device 500 according to a comparative example will be described. FIG. 2 is a plan view and a cross-sectional view of elastic wave device 500 according to a comparative example. As shown in the figure, elastic wave device 500 includes a substrate 3, an IDT electrode 10, a reflective electrode 20, and a dielectric film 45. Elastic wave device 500 according to a comparative example differs from elastic wave device 1 according to an embodiment only in that dielectric film 45 is provided instead of dielectric film 41. In the following, a description of the same configuration as that of elastic wave device 1 according to an embodiment will be omitted, and the different configuration will be mainly described.

[0044] The dielectric film 45 is disposed on the substrate 3. As shown in (a) of FIG. 2, the dielectric film 45 is disposed in a region between the busbar electrodes 12a and 12b in a plan view of the substrate 3, and is also disposed in a region between the busbar electrodes 22a and 22b in a plan view of the substrate 3. Note that the dielectric film 45 is also disposed in a region overlapping with the electrode fingers 11a, 11b, and 21 and the busbar electrodes 12a, 12b, 22a, and 22b in a plan view of the substrate 3. That is, the dielectric film 45 is formed so as to cover the IDT electrode 10 and the reflective electrode 20. The dielectric film 45 may be made of, for example, silicon oxide.

[0045] According to the above configuration, it is possible to ensure the Q value by the above-mentioned layered structure of substrate 3, but the relative bandwidth is limited to a specific range. Furthermore, in order to ensure the capacitance of acoustic wave device 500 having a thin piezoelectric layer 31, acoustic wave device 500 must be made larger.

[0046] [3. Resonance Characteristics of Elastic Wave Device 1 in accordance with Example 1] Here, the resonance characteristics of elastic wave device 1 in accordance with the first embodiment will be described in comparison with the resonance characteristics of elastic wave device 500 in accordance with a comparative example.

[0047] FIG. 3A is a graph showing the relationship between the film thickness of the dielectric film and the rate of change in the relative bandwidth of the elastic wave devices according to Example 1 and Comparative Example. FIG. 3B is a graph showing the relationship between the film thickness of the dielectric film and the rate of change in Qmax of the elastic wave devices according to Example 1 and Comparative Example. FIG. 3C is a graph showing the relationship between the rate of change in Qmax and the rate of change in the relative bandwidth of the elastic wave devices according to Example 1 and Comparative Example. In each figure, the rate of change in the relative bandwidth represents the ratio of the relative bandwidth of the elastic wave device according to Example 1 or Comparative Example to the ratio of the relative bandwidth when the dielectric film is not formed. In each figure, the rate of change in Qmax represents the ratio of the Qmax of the elastic wave device according to Example 1 or Comparative Example to the Qmax when the dielectric film is not formed.

[0048] Furthermore, in evaluation of the resonance characteristics of the elastic wave device 1 in accordance with Example 1 and the elastic wave device 500 in accordance with the comparative example, (1) Wavelength λ=2μm (2) Main electrode layer of IDT electrode 10: Material: Aluminum, Film thickness: 100 nm (3) Adhesion layer of IDT electrode 10: Material: titanium, thickness: 10 nm (4) Piezoelectric layer 31: Material: lithium tantalate, thickness: 400 nm (5) Low sound velocity layer 32: Material: silicon oxide, thickness: 300 nm (6) High sound velocity layer 33: Material: Silicon nitride, thickness: 300 nm (7) Support substrate 34: Material: Silicon (111) It was decided.

[0049] With the parameters set as above, the resonance characteristics were evaluated by the finite element method assuming that the acoustic wave device has an infinite periodic structure. In addition, the fractional bandwidth and Qmax were set as indices for evaluating the resonance characteristics.

[0050] The fractional bandwidth is expressed as (antiresonant frequency - resonant frequency) / resonant frequency. The antiresonant frequency is the frequency at which the impedance of the elastic wave device is maximized, and the resonant frequency is the frequency at which the impedance of the elastic wave device is minimized.

[0051] Qmax is the Q value (=(2πfτ|S 11 |) / (1-|S 11 | 2 ) (Non-Patent Document 1, "2008 IEEE International Ultrasonics Symposium Proceedings, p. 431"), where f is the frequency and τ is the group delay velocity.

[0052] In general, loss due to viscosity of a dielectric film formed in a minute region of a laminated structure or the like is greater than loss due to a dielectric film formed on a single crystal piezoelectric substrate. Therefore, the thinner the film thickness of dielectric film 41 in elastic wave device 1 in accordance with Example 1 and the thinner the film thickness of dielectric film 45 in elastic wave device 500 in accordance with the comparative example, the lower the loss of the elastic wave device.

[0053] As shown in FIG. 3A, in both elastic wave device 1 according to the first embodiment and elastic wave device 500 according to the comparative example, the fractional bandwidth decreases as the thickness of dielectric film 41 (or 45) increases.

[0054] As shown in FIG. 3B, in both elastic wave device 1 according to the first embodiment and elastic wave device 500 according to the comparative example, as dielectric film 41 (or 45) becomes thicker, Qmax decreases.

[0055] However, as shown in FIG. 3C, elastic wave device 1 in accordance with Example 1 is able to change the fractional bandwidth while suppressing a decrease in Qmax (a decrease in the rate of change of Qmax) more than elastic wave device 500 in accordance with the comparative example.

[0056] The thickness of dielectric film 41 is smaller than the thicknesses of electrode fingers 11a and electrode fingers 11b.

[0057] In other words, according to the elastic wave device 1 of the first embodiment, by disposing a dielectric film 41 that is thinner than the IDT electrode 10, it is possible to provide a small-sized elastic wave device 1 that is capable of adjusting the relative bandwidth without degrading the Q value.

[0058] It is preferable that the thickness of dielectric film 41 is 50% or less of the thickness of electrode fingers 11a and 11b, which makes it possible to make the rate of change of Qmax 75% or more.

[0059] Furthermore, it is desirable that the thickness of dielectric film 41 be 20% or less of the thickness of electrode fingers 11a and 11b, which makes it possible to make the rate of change in Qmax 90% or more.

[0060] In the elastic wave device 1 of the first embodiment, the formation area of ​​the dielectric film 41 is preferably a combination of (1) only the area between the busbar electrodes 12a and 12b in a planar view of the substrate 3 where the electrode fingers 11a, the electrode fingers 11b, and the busbar electrodes 12a and 12b are not arranged, (2) only the area between the busbar electrodes 22a and 22b in a planar view of the substrate 3 where the electrode fingers 21, the busbar electrodes 22a and 22b are not arranged, and (3) the area between the IDT electrode 10 and the reflective electrode 20.

[0061] According to this, the dielectric film 41 has no discontinuous portions structurally over the region from the IDT electrode 10 to the reflective electrode 20, so that the generation of unwanted waves and losses due to discontinuous portions can be suppressed.

[0062] Fig. 4A is a graph showing the relationship between the film thickness of dielectric film 41 and the rate of change in relative bandwidth when the relative dielectric constant of dielectric film 41 is changed in elastic wave device 1 in accordance with Example 1. Fig. 4B is a graph showing the relationship between the film thickness of dielectric film 41 and the rate of change in Qmax when the relative dielectric constant of dielectric film 41 is 3.75 in elastic wave device 1 in accordance with Example 1. Fig. 4C is a graph showing the relationship between the relative dielectric constant and the rate of decrease in relative bandwidth when the rate of change in Qmax is 80% in elastic wave device 1 in accordance with Example 1.

[0063] As shown in FIG. 4A, in the elastic wave device 1 according to the first embodiment, the thicker the dielectric film 41, the smaller the relative bandwidth. Furthermore, the larger the relative dielectric constant, the larger the change in the relative bandwidth with respect to the thickness of the dielectric film 41, and the thinner the film thickness, the larger the relative bandwidth can be adjusted. Furthermore, the loss due to the viscosity of the dielectric film formed in a fine region such as a laminated structure is larger than the loss due to the dielectric film formed on the single crystal piezoelectric substrate. Therefore, a thinner dielectric film 41 is advantageous in terms of low loss. Furthermore, as shown in FIG. 4B, the thicker the dielectric film 41, the lower the Qmax. Therefore, a thinner dielectric film 41 is advantageous in terms of suppressing degradation of the Q value.

[0064] As shown in FIG. 4C, if the rate of change of Qmax is 80%, then in order to reduce the relative bandwidth by 5% (reduction rate of relative bandwidth = 5%), the relative dielectric constant must be 5 or more. Also, if the rate of change of Qmax is 80%, then in order to reduce the relative bandwidth by 7% (reduction rate of relative bandwidth = 7%), the relative dielectric constant must be 10 or more. Furthermore, if the rate of change of Qmax is 80%, then in order to reduce the relative bandwidth by 10% (reduction rate of relative bandwidth = 10%), the relative dielectric constant must be 20 or more.

[0065] In other words, by setting the relative dielectric constant to 5 or more, 10 or more, or 20 or more, the effect of adjusting the relative bandwidth can be increased with only a small decrease in the Q value.

[0066] In addition, the capacitance of acoustic wave device 1 can be increased by increasing the relative dielectric constant of dielectric film 41. From this perspective as well, acoustic wave device 1 can be made more compact.

[0067] In bands 2, 3, 5, 7, 8, and 9 for LTE (Long Term Evolution) used in 3GPP (registered trademark) (3rd Generation Partnership Project), and bands n2, n3, n5, n7, n8, and n9 for 5G (5th Generation)-NR (New Radio), the difference in frequency band between the uplink operating band and the downlink operating band is about 5%. When the elastic wave device 1 according to the present embodiment is applied as an elastic wave resonator constituting a high-frequency filter having the uplink operating band or the downlink operating band of these bands as the passband, the relative dielectric constant of the dielectric film 41 is set to 5 or more, so that the difference in passband width can be adjusted to about 5% while suppressing deterioration of the Q value of the elastic wave resonator. This makes it possible to optimize a transmission filter including the uplink operating band in the passband and a reception filter including the downlink operating band in the passband by using the elastic wave device 1 according to the present embodiment.

[0068] In addition, in band 28 for LTE and band n28 for 5G-NR, the difference in frequency band between the uplink operating band and the downlink operating band is approximately 7%, so by setting the relative dielectric constant of dielectric film 41 to 10 or more, the difference in passband width can be adjusted to approximately 7% while suppressing deterioration of the Q value of the acoustic wave resonator.

[0069] In addition, in band 1 for LTE and band n1 for 5G-NR, the difference in frequency band between the uplink operating band and the downlink operating band is approximately 10%, so by setting the relative dielectric constant of dielectric film 41 to 20 or more, the difference in passband width can be adjusted to approximately 10% while suppressing deterioration of the Q value of the acoustic wave resonator.

[0070] Next, the relationship between the acoustic impedance of the IDT electrode 10 and the dielectric film 41 will be described.

[0071] The acoustic impedance of the IDT electrode 10 is R IDT The thickness of the electrode fingers 11a and 11b is t IDTand the acoustic impedance of the dielectric film 41 disposed between the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is R DIE The thickness of the dielectric film 41 is t DIE In this case, the relational expression 1 is satisfied.

[0072] R IDT ×t IDT >R DIE ×t DIE (Formula 1)

[0073] Here, the acoustic impedance is (ρ×E) where ρ is density and E is Young's modulus. 1 / 2 It is expressed as:

[0074] Acoustic impedance R of the IDT electrode 10 IDT is the acoustic impedance R of the dielectric film 41. DIE When the thickness t of the dielectric film 41 is smaller than that of the surface acoustic wave resonator, the surface acoustic wave leaks out of the acoustic wave resonator, and the resonance characteristics of the acoustic wave device are degraded. DIE is the thickness t IDT By making the thickness thinner than that of the substrate 1, leakage of surface acoustic waves can be suppressed, and an acoustic wave device 1 with high performance can be obtained.

[0075] For example, if the IDT electrode 10 is made of aluminum (E=70 GPa, ρ=2.7 g / cm 3 ), the dielectric film 41 is made of silicon oxide (E=72 GPa, ρ=2.2 g / cm 3 ), acoustic impedance R IDT and acoustic impedance R DIE Since the values ​​are very close to each other, it is desirable to make the dielectric film 41 thinner than the IDT electrode 10. Furthermore, when the dielectric constant of the dielectric film 41 is large, the impedance becomes higher than that of silicon oxide (SiO2), so it is desirable to make the dielectric film 41 thinner than the IDT electrode 10.

[0076] In addition, when the IDT electrode 10 is a laminate of layers A and B, and the dielectric film 41 is a laminate of layers C and D, the acoustic impedance is defined as follows. AThe thickness of the A layer is t A and the acoustic impedance of layer B is R B The thickness of the B layer is t B and the acoustic impedance of the C layer disposed between the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is R C The thickness of the C layer is t C and the acoustic impedance of the D layer disposed between the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is R D The thickness of the D layer is t D In this case, the relational expression of Equation 2 is satisfied.

[0077] R A ×t A +R B ×t B >R C ×t C +R D ×t D (Formula 2)

[0078] That is, when the IDT electrode 10 is a laminate of n layers (n is a natural number) and the dielectric film 41 is a laminate of m layers (m is a natural number), the acoustic impedance of the kth layer of the IDT electrode 10 is defined as R IDTk The film thickness of the k-th layer of the IDT electrode 10 is t IDTk and the acoustic impedance of the k-th layer of the dielectric film 41 disposed between the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is R DIEk The thickness of the k-th layer of the dielectric film 41 disposed between the electrode fingers 11a and the electrode fingers 11b is t DIEk In this case, the relational expression 3 is satisfied.

[0079]

number

[0080] The material of the dielectric film 41 is not limited to silicon oxide. The material of the dielectric film 41 will be described below.

[0081] FIG. 5A is a graph showing the relationship between the film thickness of the dielectric film 41 and the rate of change of the relative bandwidth when the dielectric film 41 is silicon nitride or silicon oxide. FIG. 5B is a graph showing the relationship between the film thickness of the dielectric film 41 and the rate of change of the relative bandwidth when the dielectric film 41 is yttrium oxide or silicon oxide. FIG. 5C is a graph showing the relationship between the film thickness of the dielectric film 41 and the rate of change of the relative bandwidth when the dielectric film 41 is aluminum oxide or silicon oxide. FIG. 5D is a graph showing the relationship between the film thickness of the dielectric film 41 and the rate of change of the relative bandwidth when the dielectric film 41 is tantalum oxide or silicon oxide. FIG. 5E is a graph showing the relationship between the film thickness of the dielectric film 41 and the rate of change of the relative bandwidth when the dielectric film 41 is titanium oxide or silicon oxide. FIG. 5F is a graph showing the relationship between the film thickness of the dielectric film 41 and the rate of change of the relative bandwidth when the dielectric film 41 is hafnium oxide or silicon oxide. FIG. 5G is a graph showing the relationship between the film thickness of the dielectric film 41 and the rate of change of the relative bandwidth when the dielectric film 41 is zirconium oxide or silicon oxide. FIG. 5H is a graph showing the relationship between the film thickness of dielectric film 41 and the rate of change in relative bandwidth when dielectric film 41 is made of sialon or silicon oxide.

[0082] As shown in Figures 5A to 5H, when the dielectric film 41 is made of silicon nitride, yttrium oxide, aluminum oxide, tantalum oxide, titanium oxide, hafnium oxide, zirconium oxide, or sialon, it can be seen that in any of these cases, the adjustment range of the relative bandwidth can be made wider than when the dielectric film 41 is made of silicon oxide.

[0083] In addition, by using a high dielectric constant material such as silicon nitride (SiN), yttrium oxide (Y2O3), aluminum oxide (Al2O3), tantalum oxide (Ta2O5), hafnium oxide (HfO2), zirconium oxide (ZrO2), sialon, or aluminum nitride (AlN) as the material for dielectric film 41, it is possible to adjust the relative bandwidth of acoustic wave device 1 with a thin dielectric film 41.

[0084] Furthermore, by using a material such as aluminum oxide (Al2O3) or yttrium oxide (Y2O3) that has a higher thermal conductivity than the material constituting the piezoelectric layer 31 as the dielectric film 41, the heat dissipation properties are improved when the acoustic wave device 1 is used as a high-frequency filter, making it possible to improve the power resistance of the high-frequency filter.

[0085] Next, a description will be given of the material of piezoelectric layer 31. Fig. 6 is a graph showing the relationship between the thickness of dielectric film 41 and the rate of change in relative bandwidth when piezoelectric layer 31 of elastic wave device 1 in accordance with Example 1 is made of lithium niobate.

[0086] The resonance characteristics shown in FIG. 6 were obtained by setting the parameters of acoustic wave device 1 as follows.

[0087] (1) Wavelength λ=2μm (2) Main electrode layer of IDT electrode 10: Material: Aluminum, Film thickness: 160 nm (3) Adhesion layer of IDT electrode 10: Material: titanium, thickness: 12 nm (4) Piezoelectric layer 31: Material: lithium niobate, thickness: 1100 nm (5) Low sound velocity layer 32: Material: silicon oxide, thickness: 210 nm (6) High sound velocity layer 33: Material: Silicon nitride, thickness: 380 nm (7) Support substrate 34: Material: Silicon (111) It was decided.

[0088] 6, even when the material of the piezoelectric layer 31 is lithium niobate, it is possible to adjust the relative bandwidth in the same way as when the material of the piezoelectric layer 31 is lithium tantalate. Note that the material of the piezoelectric layer 31 may be, for example, quartz crystal, aluminum nitride, or PZT, and the same effect can be obtained as when the material of the piezoelectric layer 31 is lithium tantalate or lithium niobate.

[0089] [4. Configuration of Elastic Wave Device 1A According to Modification Example 1] In the acoustic wave device according to the present invention, the formation region of dielectric film 41 is not limited to the formation region shown in FIG.

[0090] 7A is a plan view of an elastic wave device 1A in accordance with Modification 1. As shown in the figure, elastic wave device 1A includes a substrate 3, an IDT electrode 10, a reflective electrode 20, and a dielectric film 41. Elastic wave device 1A in accordance with this modification differs from elastic wave device 1 in accordance with Example 1 in the region in which dielectric film 41 is formed. Therefore, in the following description of elastic wave device 1A in accordance with this modification, a description of the same components as those of elastic wave device 1 in accordance with Example 1 will be omitted, and the description will focus on the different components.

[0091] Dielectric film 41 is an example of a first dielectric film, and is disposed on substrate 3. As shown in Fig. 7A, dielectric film 41 is formed on piezoelectric layer 31, and is disposed only in a region (region of intersection width L in Fig. 7A) where electrode fingers 11a and electrode fingers 11b overlap when viewed in a direction (x-axis direction) parallel to piezoelectric layer 31 and perpendicular to the extension direction (y-axis direction) of electrode fingers 11a and electrode fingers 11b, where electrode fingers 11a and 11b are not disposed.

[0092] Furthermore, the thickness of dielectric film 41 is smaller than the thickness of the electrode fingers 11a and 11b.

[0093] This allows the relative bandwidth to be adjusted without decreasing the capacitance per unit area of ​​elastic wave device 1A using a laminated substrate structure. Moreover, by forming dielectric film 41 only between the electrode fingers, the capacitance per unit area can be increased compared to a conventional elastic wave device in which dielectric film 41 is not formed, and elastic wave device 1A can be made smaller. Furthermore, compared to a conventional elastic wave device in which a dielectric film is formed over the entire surface including the electrode fingers, it is possible to adjust the relative bandwidth without degrading the Q value of the elastic wave device.

[0094] [5. Configuration of Elastic Wave Device 1B According to Modification Example 2] 7B is a plan view of an elastic wave device 1B according to Modification 2. As shown in the figure, elastic wave device 1B includes a substrate 3, an IDT electrode 10, a reflective electrode 20, and a dielectric film 41. Elastic wave device 1B according to this modification has a different region in which dielectric film 41 is formed compared to elastic wave device 1 according to Example 1. Therefore, in the following, a description of the same components as those of elastic wave device 1 according to Example 1 will be omitted and the different components will be mainly described.

[0095] Dielectric film 41 is an example of a first dielectric film, and is disposed on substrate 3. As shown in Fig. 7B, dielectric film 41 is formed on piezoelectric layer 31, and is disposed only in a region between busbar electrode 12a and busbar electrode 12b in a plan view of substrate 3, in which multiple electrode fingers 11a and 11b and busbar electrodes 12a and 12b are not disposed.

[0096] This allows the relative bandwidth to be adjusted without decreasing the capacitance per unit area of ​​acoustic wave device 1B using a laminated substrate structure. Moreover, by sandwiching dielectric film 41 only between the electrode fingers, the capacitance per unit area can be increased compared to a conventional acoustic wave device in which dielectric film 41 is not formed, and acoustic wave device 1B can be made smaller. Furthermore, compared to a conventional acoustic wave device in which a dielectric film is formed over the entire surface including the electrode fingers, it is possible to adjust the relative bandwidth without degrading the Q value of the acoustic wave device.

[0097] [6. Configuration of Elastic Wave Device 1C in accordance with Example 2] 8 is (a) a plan view and (b) a cross-sectional view of an elastic wave device 1C in accordance with a second embodiment. As shown in the figure, elastic wave device 1C includes a substrate 3, an IDT electrode 10, a reflective electrode 20, and dielectric films 41 and 42. Elastic wave device 1C in accordance with the second embodiment differs from elastic wave device 1 in accordance with the first embodiment in that a dielectric film 42 is added. Therefore, in the following description, the same components as those of elastic wave device 1 in accordance with the first embodiment will not be described, and the different components will be mainly described.

[0098] Dielectric film 41 is an example of a first dielectric film, and is disposed on substrate 3. Dielectric film 41 is disposed only in a region between busbar electrode 12a and busbar electrode 12b in a planar view of substrate 3, in which multiple electrode fingers 11a and 11b and busbar electrodes 12a and 12b are not disposed, and is disposed only in a region between busbar electrode 22a and busbar electrode 22b in a planar view of substrate 3, in which multiple electrode fingers 21 and busbar electrodes 22a and 22b are not disposed.

[0099] As shown in FIG. 8(b), the thickness of the dielectric film 41 is smaller than the thickness h of the electrode fingers 11a and 11b.

[0100] The dielectric film 42 is an example of a second dielectric film, and is disposed on the dielectric film 41, the plurality of electrode fingers 11a, 11b, and 22, and the bus bar electrodes 12a, 12b, 22a, and 22b. The dielectric film 42 is different from the dielectric film 41 in material or composition.

[0101] According to this, the formation of the dielectric film 42 can suppress short-circuit defects between the electrode fingers caused by dust from the outside and characteristic deterioration due to humidity.

[0102] The dielectric film 42 is, for example, any one of silicon oxide, silicon nitride, and silicon oxynitride.

[0103] It is preferable that the relative dielectric constant of dielectric film 42 is lower than the relative dielectric constant of dielectric film 41. This can prevent dielectric film 42 from deteriorating the Q value of acoustic wave device 1C.

[0104] It is also desirable that the thickness of dielectric film 42 be smaller than the thickness of dielectric film 41. This can prevent the Q value of elastic wave device 1C from being deteriorated by dielectric film 42. Note that by adjusting the thickness of dielectric film 42, it is possible to adjust the antiresonant frequency and resonant frequency of elastic wave device 1C.

[0105] [7 Configurations of acoustic wave resonators, high-frequency filters, and filter circuits using acoustic wave device 1] 9A is a diagram illustrating an electrode configuration of an elastic wave resonator according to an embodiment and a diagram illustrating an elastic wave resonator. An elastic wave device 1 in accordance with a first embodiment can be used as elastic wave resonator 50 illustrated in FIG.

[0106] 9B is a diagram illustrating an electrode configuration of a longitudinally coupled resonator in accordance with an embodiment and a diagram illustrating the longitudinally coupled resonator. An acoustic wave device 1 in accordance with a first embodiment can be used as a longitudinally coupled resonator (DMS) 60 illustrated in FIG.

[0107] 10A is a circuit diagram of a ladder-type high-frequency filter 4 according to an embodiment. As shown in the figure, the high-frequency filter 4 includes series arm resonators 51, 52, and 53 connected in series to a path connecting two input / output terminals, and parallel arm resonators 54 and 55 connected between the path connecting the series arm resonators 51, 52, and 53 and ground. Each of the series arm resonators 51 to 53 and the parallel arm resonators 54 and 55 is an elastic wave resonator using the elastic wave device 1 in accordance with the first embodiment. With the above configuration, the high-frequency filter 4 constitutes a ladder-type high-frequency filter.

[0108] This makes it possible to adjust the fractional bandwidth of acoustic wave device 1 constituting high frequency filter 4 without degrading the Q value, thereby providing high frequency filter 4 with optimized pass characteristics.

[0109] In high frequency filter 4, dielectric films 41 (first dielectric films) of at least two of series arm resonators 51 to 53 and parallel arm resonators 54 and 55 may have different film thicknesses, materials, or compositions. This makes it possible to combine acoustic wave resonators with different relative bandwidths, thereby providing, for example, a high frequency filter 4 with excellent steepness and a wide band.

[0110] 10B is a circuit diagram of a high-frequency filter 4A including a vertically coupled resonator according to an embodiment. As shown in the figure, the high-frequency filter 4A includes a series arm resonator 51 and a vertically coupled resonator 60 connected in series to a path connecting two input / output terminals, and a parallel arm resonator 54 connected between the path connecting the series arm resonator 51 and the vertically coupled resonator 60 and ground. Each of the series arm resonator 51, the parallel arm resonator 54, and the vertically coupled resonator 60 is an elastic wave resonator using the elastic wave device 1 according to the first embodiment. With the above configuration, the high-frequency filter 4A constitutes a vertically coupled high-frequency filter.

[0111] This makes it possible to adjust the fractional bandwidth of acoustic wave device 1 constituting high frequency filter 4A without degrading the Q value, thereby providing high frequency filter 4A with optimized pass characteristics.

[0112] In the high frequency filter 4A, the dielectric films 41 (first dielectric films) of at least two of the series arm resonators 51, the parallel arm resonators 54, and the longitudinally coupled resonators 60 may have different thicknesses, materials, or compositions. This makes it possible to combine acoustic wave resonators with different relative bandwidths, thereby providing, for example, a high frequency filter 4A that has excellent steepness and a wide band.

[0113] 10C is a circuit diagram of a high-frequency filter 4B including a plurality of longitudinally coupled resonators according to an embodiment. As shown in the figure, the high-frequency filter 4B includes longitudinally coupled resonators 61 and 62 connected in series to a path connecting two input / output terminals. Each of the longitudinally coupled resonators 61 and 62 is an elastic wave resonator using the elastic wave device 1 according to the first embodiment. With the above configuration, the high-frequency filter 4B constitutes a longitudinally coupled high-frequency filter.

[0114] This makes it possible to adjust the fractional bandwidth of acoustic wave device 1 constituting high frequency filter 4B without degrading the Q value, thereby providing high frequency filter 4B with optimized pass characteristics.

[0115] In high frequency filter 4B, dielectric films 41 (first dielectric films) of longitudinally coupled resonators 61 and 62 may have different thicknesses, materials, or compositions. This makes it possible to combine acoustic wave resonators with different relative bandwidths, thereby providing high frequency filter 4B that has excellent steepness and a wide band, for example.

[0116] Moreover, the filter circuit according to the present embodiment includes a plurality of high frequency filters, which are any one of high frequency filters 4, 4A, and 4B. Here, the plurality of high frequency filters included in the filter circuit share one substrate 3. Also, a dielectric film 41 (first dielectric film) included in a first high frequency filter of the plurality of high frequency filters and a dielectric film (first dielectric film) included in a second high frequency filter of the plurality of high frequency filters are different in film thickness, material, or composition.

[0117] According to this, a plurality of high frequency filters with different passband widths can be formed on the same substrate, so that a filter circuit constituted by a plurality of high frequency filters can be made compact.

[0118] [8 Effects, etc.] As described above, elastic wave device 1 of Example 1, elastic wave device 1B of Variation 2, and elastic wave device 1C of Example 2 each include substrate 3, IDT electrode 10 arranged on substrate 3, and dielectric film 41 arranged on substrate 3. Substrate 3 has piezoelectric layer 31, low acoustic velocity layer 32, and high acoustic velocity layer 33, in this order. IDT electrode 10 has multiple electrode fingers 11a and 11b, busbar electrode 12a connecting multiple electrode fingers 11a, and busbar electrode 12b connecting multiple electrode fingers 11b. Dielectric film 41 is arranged on piezoelectric layer 31 only in the region between busbar electrode 12a and busbar electrode 12b in a planar view of substrate 3 where multiple electrode fingers 11a and 11b and busbar electrodes 12a and 12b are not arranged. The thickness of dielectric film 41 is smaller than the thickness of multiple electrode fingers 11a and 11b.

[0119] This allows the relative bandwidth to be adjusted without decreasing the capacitance per unit area of ​​an acoustic wave device using a laminated substrate structure. Moreover, by sandwiching dielectric film 41 only between the electrode fingers, the capacitance per unit area can be increased compared to a conventional acoustic wave device in which dielectric film 41 is not formed, and the acoustic wave device can be made smaller. Furthermore, compared to a conventional acoustic wave device in which a dielectric film is formed over the entire surface including the electrode fingers, it is possible to adjust the relative bandwidth without degrading the Q value of the acoustic wave device.

[0120] For example, the elastic wave device 1 of Example 1 and the elastic wave device 1C of Example 2 further include a reflective electrode 20 arranged adjacent to the IDT electrode 10 in a direction perpendicular to the extension direction of the multiple electrode fingers 11a and 11b, the reflective electrode 20 having multiple electrode fingers 21 parallel to the multiple electrode fingers 11a and 11b, a bus bar electrode 22a connecting one ends of the multiple electrode fingers 21, and a bus bar electrode 22b connecting the other ends of the multiple electrode fingers 21, and the dielectric film 41 is arranged on the piezoelectric layer 31 only in a region between the bus bar electrodes 12a and 12b in a planar view of the substrate 3 where the multiple electrode fingers 21, the bus bar electrodes 12a and 12b are not arranged, and is arranged on the piezoelectric layer 31 only in a region between the bus bar electrodes 22a and 22b in a planar view of the substrate 3 where the multiple electrode fingers 21, the bus bar electrodes 22a and 22b are not arranged.

[0121] This allows the relative bandwidth to be adjusted without decreasing the capacitance per unit area of ​​an acoustic wave device using a laminated substrate structure. Moreover, by sandwiching dielectric film 41 only between the electrode fingers, the capacitance per unit area can be increased compared to a conventional acoustic wave device in which dielectric film 41 is not formed, and the acoustic wave device can be made smaller. Furthermore, compared to a conventional acoustic wave device in which a dielectric film is formed over the entire surface including the electrode fingers, it is possible to adjust the relative bandwidth without degrading the Q value of the acoustic wave device.

[0122] For example, in the acoustic wave devices 1, 1A, 1B, and 1C, the acoustic impedance of the IDT electrode 10 is R IDT The thickness of the electrode fingers 11a and 11b is t IDT and the acoustic impedance of the dielectric film 41 disposed between the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is R DIE The thickness of the dielectric film 41 is t DIE In this case, R IDT ×t IDT >R DIE ×t DIE , satisfying the relationship.

[0123] This makes it possible to suppress leakage of surface acoustic waves, and to obtain an acoustic wave device with high performance.

[0124] In addition, for example, in the acoustic wave devices 1, 1A, 1B, and 1C, the IDT electrode 10 is a laminate of n layers (n is a natural number), the dielectric film 41 is a laminate of m layers (m is a natural number), and the acoustic impedance of the kth layer of the IDT electrode 10 is R IDTk The film thickness of the k-th layer of the IDT electrode 10 is t IDTk and the acoustic impedance of the k-th layer of the dielectric film 41 disposed between the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is R DIEk The thickness of the k-th layer of the dielectric film 41 is t DIEk In this case,

number

[0125] According to this, when IDT electrode 10 and dielectric film 41 are each formed of a laminate, leakage of surface acoustic waves can be suppressed, and an acoustic wave device with high performance can be obtained.

[0126] For example, in acoustic wave devices 1, 1A, 1B, and 1C, dielectric film 41 has a relative dielectric constant of 5 or more.

[0127] According to this, it is possible to adjust the relative bandwidth by 5% when the rate of change of Qmax is 80%.

[0128] For example, in acoustic wave devices 1, 1A, 1B, and 1C, dielectric film 41 has a relative dielectric constant of 10 or more.

[0129] According to this, when the rate of change of Qmax is 80%, it is possible to adjust the relative bandwidth by 7%.

[0130] For example, in acoustic wave devices 1, 1A, 1B, and 1C, the thickness of dielectric film 41 is 50% or less of the thickness of electrode fingers 11a and 11b.

[0131] This makes it possible to adjust the relative bandwidth while keeping the rate of change of Qmax at 75% or more.

[0132] For example, in acoustic wave devices 1, 1A, 1B, and 1C, the thickness of dielectric film 41 is 20% or less of the thickness of electrode fingers 11a and 11b.

[0133] This makes it possible to adjust the relative bandwidth while keeping the rate of change of Qmax at 90% or more.

[0134] Furthermore, for example, in acoustic wave devices 1, 1A, 1B, and 1C, piezoelectric layer 31 includes any one of lithium tantalate and lithium niobate.

[0135] Furthermore, for example, in the acoustic wave devices 1, 1A, 1B, and 1C, the dielectric film 41 includes any one of silicon nitride, aluminum oxide, yttrium oxide, tantalum oxide, titanium oxide, hafnium oxide, zirconium oxide, aluminum nitride, and sialon.

[0136] This allows the adjustment range of the relative bandwidth to be wider than when the dielectric film 41 is made of silicon oxide.

[0137] For example, in the acoustic wave devices 1, 1A, 1B, and 1C, the IDT electrode 10 includes a main electrode layer made of aluminum and an adhesion layer disposed between the main electrode layer and the piezoelectric layer 31.

[0138] According to this, by using aluminum, which has low density and low resistance, as the main electrode layer, the film thickness of the IDT electrode 10 can be set large, so that the IDT electrode 10 having low resistance can be formed.

[0139] For example, the thermal conductivity of dielectric film 41 is higher than the thermal conductivity of piezoelectric layer 31 in acoustic wave devices 1, 1A, 1B, and 1C.

[0140] This improves heat dissipation when the acoustic wave device is used as a high-frequency filter, thereby enabling the high-frequency filter using the acoustic wave device to have improved power durability.

[0141] For example, acoustic wave device 1C further includes dielectric film 42 that is disposed on IDT electrode 10 and dielectric film 41 and has a different material or composition from dielectric film 41.

[0142] According to this, since the dielectric film 42 is formed, it is possible to suppress short circuit defects between the electrode fingers caused by dust from the outside and deterioration of characteristics due to humidity.

[0143] For example, the relative dielectric constant of dielectric film 42 is lower than the relative dielectric constant of dielectric film 41 in elastic wave device 1C.

[0144] This can prevent dielectric film 42 from deteriorating the Q value of acoustic wave device 1C.

[0145] For example, in elastic wave device 1C, dielectric film 42 has a smaller thickness than dielectric film 41.

[0146] This can prevent dielectric film 42 from deteriorating the Q value of acoustic wave device 1C.

[0147] Furthermore, for example, in the acoustic wave device 1C, the dielectric film 42 includes any one of silicon oxide, silicon nitride, and silicon oxynitride.

[0148] Moreover, elastic wave device 1 in accordance with Example 1, elastic wave device 1A in accordance with Modification 1, elastic wave device 1B in accordance with Modification 2, and elastic wave device 1C in accordance with Example 2 each include a substrate 3, an IDT electrode 10 disposed on substrate 3, and a dielectric film 41 disposed on substrate 3. Substrate 3 has piezoelectric layer 31, low acoustic velocity layer 32, and high acoustic velocity layer 33, in this order. IDT electrode 10 includes a plurality of electrode fingers 11a and 11b, a bus bar electrode 12a connecting the plurality of electrode fingers 11a, and a bus bar electrode 12b connecting the multiple electrode fingers 11b. The dielectric film 41 is disposed on the piezoelectric layer 31 only in areas where the multiple electrode fingers 11a and the multiple electrode fingers 11b overlap when viewed in a direction parallel to the piezoelectric layer 31 and perpendicular to the extension direction of the multiple electrode fingers 11a and 11b, and where the multiple electrode fingers 11a and 11b are not disposed in a planar view of the substrate 3. The thickness of the dielectric film 41 is smaller than the thickness of the multiple electrode fingers 11a and 11b.

[0149] According to this, by disposing dielectric film 41 that is thinner than IDT electrode 10 in the above-mentioned specified region, it is possible to provide a small-sized acoustic wave device 1 (and 1A to 1C) that allows adjustment of the relative bandwidth without degrading the Q value.

[0150] Moreover, high frequency filters 4, 4A, and 4B in accordance with the present preferred embodiment include any one of acoustic wave devices 1, 1A, 1B, and 1C.

[0151] According to this, the fractional bandwidth of the acoustic wave device constituting the high frequency filter can be adjusted without degrading the Q value, making it possible to provide a high frequency filter with optimized pass characteristics.

[0152] For example, each of the high-frequency filters 4, 4A and 4B includes a plurality of elastic wave devices 1, 1A, 1B or 1C, and a dielectric film 41 included in a first elastic wave device among the plurality of elastic wave devices has a different film thickness, material or composition from a dielectric film 41 included in a second elastic wave device among the plurality of elastic wave devices.

[0153] This makes it possible to combine elastic wave resonators with different fractional bandwidths, thereby providing, for example, a high-frequency filter with excellent steepness and a wide band.

[0154] Moreover, the filter circuit according to this embodiment includes a plurality of high frequency filters 4, 4A or 4B, the plurality of high frequency filters sharing one substrate 3, and a dielectric film 41 of a first high frequency filter among the plurality of high frequency filters and a dielectric film 41 of a second high frequency filter among the plurality of high frequency filters have different film thicknesses, materials or compositions.

[0155] According to this, a plurality of high frequency filters with different passband widths can be formed on the same substrate, so that a filter circuit constituted by a plurality of high frequency filters can be made compact.

[0156] (Other embodiments) Although the acoustic wave device, high frequency filter, and filter circuit according to the present invention have been described above with reference to embodiments, examples, and modifications, the present invention is not limited to the above-described embodiments, examples, and modifications. The present invention also includes other embodiments realized by combining any of the components in the above-described embodiments, examples, and modifications, and modifications obtained by applying various modifications conceived by a person skilled in the art to the above-described embodiments, examples, and modifications without departing from the spirit of the present invention.

[0157] The following describes features of the acoustic wave devices, high-frequency filters, and filter circuits described based on the above-described embodiments, examples, and modifications.

[0158] <1> A substrate; an IDT (InterDigital Transducer) electrode disposed on the substrate; a first dielectric film disposed on the substrate; The substrate is a piezoelectric layer on which the IDT electrodes are formed; a high acoustic velocity layer in which a bulk wave acoustic velocity is faster than an elastic wave acoustic velocity in the piezoelectric layer; a low acoustic velocity layer disposed between the piezoelectric layer and the high acoustic velocity layer, the low acoustic velocity layer having a bulk wave with a sound velocity slower than that of a bulk wave propagating through the piezoelectric layer; The IDT electrode is a plurality of first electrode fingers and a plurality of second electrode fingers arranged parallel to each other; a first bus bar electrode configured to connect one ends of the first electrode fingers to each other; a second bus bar electrode configured to connect one ends of the second electrode fingers to each other and disposed opposite the first bus bar electrode with the first electrode fingers and the second electrode fingers interposed therebetween, the first dielectric film is disposed on the piezoelectric layer only in a region between the first bus bar electrode and the second bus bar electrode in a plan view of the substrate, in a region in which the first electrode fingers, the second electrode fingers, the first bus bar electrode, and the second bus bar electrode are not disposed, the first dielectric film has a thickness smaller than that of the first electrode fingers and that of the second electrode fingers;

[0159] <2> moreover, a reflective electrode disposed adjacent to the IDT electrode in a direction perpendicular to an extension direction of the first electrode fingers and the second electrode fingers, The reflective electrode is a plurality of third electrode fingers parallel to the plurality of first electrode fingers and the plurality of second electrode fingers; a third bus bar electrode connecting one ends of the third electrode fingers to each other; a fourth bus bar electrode connecting the other ends of the third electrode fingers to each other, The first dielectric film is are arranged on the piezoelectric layer only in a region between the first bus bar electrode and the second bus bar electrode in a plan view of the substrate, where the first electrode fingers, the second electrode fingers, the first bus bar electrode, and the second bus bar electrode are not arranged, and the third electrode fingers are disposed on the piezoelectric layer only in a region between the third bus bar electrode and the fourth bus bar electrode in a plan view of the substrate, where the third electrode fingers, the third bus bar electrode, and the fourth bus bar electrode are not disposed. <1> The acoustic wave device according to claim 1 .

[0160] <3> The acoustic impedance of the IDT electrode is R IDT The thickness of the first electrode fingers and the second electrode fingers is t IDT year, The acoustic impedance of the first dielectric film disposed between the first electrode fingers and the second electrode fingers is defined as R DIE The thickness of the first dielectric film is t DIE In this case, R IDT ×t IDT >R DIE ×t DIE Fulfilling the relationship, <1> or <2> The acoustic wave device according to claim 1 .

[0161] <4> The IDT electrode is a laminate of n layers (n is a natural number), the first dielectric film is a laminate of m layers (m is a natural number), and the acoustic impedance of the kth layer of the IDT electrode is R IDTk The film thickness of the k-th layer of the IDT electrode is t IDTk and the acoustic impedance of the k-th layer of the first dielectric film disposed between the plurality of first electrode fingers and the plurality of second electrode fingers is R DIEk The film thickness of the k-th layer of the first dielectric film is t DIEk In this case,

number

[0162] <5> The first dielectric film has a relative dielectric constant of 5 or more. <1> ~ <4> 2. The acoustic wave device according to claim 1 ,

[0163] <6> The first dielectric film has a relative dielectric constant of 10 or more. <1> ~ <4> 2. The acoustic wave device according to claim 1 ,

[0164] <7> a thickness of the first dielectric film is 50% or less of a thickness of the first electrode fingers and the second electrode fingers; <1> ~ <6> 2. The acoustic wave device according to claim 1 ,

[0165] <8> a thickness of the first dielectric film is 20% or less of a thickness of the first electrode fingers and the second electrode fingers; <1> ~ <6> 2. The acoustic wave device according to claim 1 ,

[0166] <9> The piezoelectric layer includes any one of lithium tantalate and lithium niobate. <1> ~ <8> 2. The acoustic wave device according to claim 1 ,

[0167] <10> The first dielectric film includes any one of silicon nitride, aluminum oxide, yttrium oxide, tantalum oxide, titanium oxide, hafnium oxide, zirconium oxide, aluminum nitride, and sialon. <1> ~ <9> 2. The acoustic wave device according to claim 1 ,

[0168] <11> The IDT electrode is A main electrode layer made of aluminum; an adhesion layer disposed between the main electrode layer and the piezoelectric layer; <1> ~ <10> 2. The acoustic wave device according to claim 1 ,

[0169] <12> The thermal conductivity of the first dielectric film is higher than the thermal conductivity of the piezoelectric layer. <1> ~ <11> 2. The acoustic wave device according to claim 1 ,

[0170] <13> moreover, a second dielectric film disposed on the IDT electrode and the first dielectric film, the second dielectric film being different in material or composition from the first dielectric film; <1> ~ <12> 2. The acoustic wave device according to claim 1 ,

[0171] <14> The second dielectric film has a lower dielectric constant than the first dielectric film. <13> The acoustic wave device according to claim 1 .

[0172] <15> The thickness of the second dielectric film is smaller than the thickness of the first dielectric film. <13> The acoustic wave device according to claim 1 .

[0173] <16> The second dielectric film includes any one of silicon oxide, silicon nitride, and silicon oxynitride. <13> ~ <15> 2. The acoustic wave device according to claim 1 ,

[0174] <17> A substrate; an IDT (InterDigital Transducer) electrode disposed on the substrate; a first dielectric film disposed on the substrate; The substrate is a piezoelectric layer on which the IDT electrodes are formed; a high acoustic velocity layer in which a bulk wave acoustic velocity is faster than an elastic wave acoustic velocity in the piezoelectric layer; a low acoustic velocity layer disposed between the piezoelectric layer and the high acoustic velocity layer, the low acoustic velocity layer having a bulk wave with a sound velocity slower than that of a bulk wave propagating through the piezoelectric layer; The IDT electrode is a plurality of first electrode fingers and a plurality of second electrode fingers arranged parallel to each other; a first bus bar electrode configured to connect one ends of the first electrode fingers to each other; a second bus bar electrode configured to connect one ends of the second electrode fingers to each other and disposed opposite the first bus bar electrode with the first electrode fingers and the second electrode fingers interposed therebetween, the first dielectric film is disposed on the piezoelectric layer only in a region where the first electrode fingers and the second electrode fingers overlap when viewed in a direction parallel to the piezoelectric layer and perpendicular to an extension direction of the first electrode fingers and the second electrode fingers, the first dielectric film only being disposed in a region where the first electrode fingers and the second electrode fingers are not disposed in a plan view of the substrate, the first dielectric film has a thickness smaller than that of the first electrode fingers and that of the second electrode fingers;

[0175] <18> <1> ~ <17> A high-frequency filter comprising the acoustic wave device according to any one of claims 1 to 5.

[0176] <19> <1> ~ <17> a plurality of the elastic wave devices according to any one of claims 1 to 4, the first dielectric film of a first elastic wave device of the plurality of elastic wave devices and the first dielectric film of a second elastic wave device of the plurality of elastic wave devices have different thicknesses, materials, or compositions; <18> The high frequency filter according to claim 1.

[0177] <20> <18> or <19> A plurality of high frequency filters according to the above-mentioned the plurality of high frequency filters share one of the substrates; a first dielectric film of a first high frequency filter of the plurality of high frequency filters and a first dielectric film of a second high frequency filter of the plurality of high frequency filters have a different thickness, material, or composition. [Industrial Applicability]

[0178] INDUSTRIAL APPLICABILITY The present invention can be widely used as an acoustic wave device, a high frequency filter, and a filter circuit disposed in a front end portion of communication devices such as mobile phones. [Explanation of symbols]

[0179] 1, 1A, 1B, 1C, 500 Elastic Wave Device 3. Substrate 4, 4A, 4B High Frequency Filter 10 IDT electrodes 11a, 11b, 21 electrode fingers 12a, 12b, 22a, 22b Busbar electrodes 20 reflective electrode 31 Piezoelectric layer 32 Low sound speed layer 33 High-sonic layer 34 Support substrate 41, 42, 45 Dielectric film 50 Elastic wave resonator 51, 52, 53 Series arm resonators 54, 55 Parallel arm resonators 60, 61, 62 Vertically coupled resonators

Claims

1. A substrate; An IDT (InterDigital Transducer) electrode disposed on the substrate; a first dielectric film disposed on the substrate; The substrate is a piezoelectric layer on which the IDT electrodes are formed; a high acoustic velocity layer in which a bulk wave acoustic velocity is faster than an elastic wave acoustic velocity in the piezoelectric layer; a low acoustic velocity layer disposed between the piezoelectric layer and the high acoustic velocity layer, the low acoustic velocity layer having a bulk wave with a sound velocity slower than that of a bulk wave propagating through the piezoelectric layer; The IDT electrode is a plurality of first electrode fingers and a plurality of second electrode fingers arranged parallel to each other; a first bus bar electrode configured to connect one ends of the first electrode fingers to each other; a second bus bar electrode configured to connect one ends of the second electrode fingers to each other and disposed opposite the first bus bar electrode with the first electrode fingers and the second electrode fingers interposed therebetween, the first dielectric film is disposed on the piezoelectric layer only in a region between the first bus bar electrode and the second bus bar electrode in a plan view of the substrate, in which the first electrode fingers, the second electrode fingers, the first bus bar electrode, and the second bus bar electrode are not disposed, a thickness of the first dielectric film is smaller than a thickness of the first electrode fingers and a thickness of the second electrode fingers; Elastic wave device.

2. moreover, a reflection electrode disposed adjacent to the IDT electrode in a direction perpendicular to an extension direction of the first electrode fingers and the second electrode fingers, The reflective electrode is a plurality of third electrode fingers parallel to the plurality of first electrode fingers and the plurality of second electrode fingers; a third bus bar electrode connecting one ends of the third electrode fingers to each other; a fourth bus bar electrode connecting the other ends of the third electrode fingers to each other, The first dielectric film is the first electrode fingers, the second electrode fingers, the first bus bar electrode, and the second bus bar electrode are disposed on the piezoelectric layer only in a region between the first bus bar electrode and the second bus bar electrode in a plan view of the substrate, where the first electrode fingers, the second electrode fingers, the first bus bar electrode, and the second bus bar electrode are not disposed; and the third electrode fingers are disposed on the piezoelectric layer only in a region between the third bus bar electrode and the fourth bus bar electrode in a plan view of the substrate, where the third electrode fingers, the third bus bar electrode, and the fourth bus bar electrode are not disposed. The acoustic wave device according to claim 1 .

3. The acoustic impedance of the IDT electrode is R ＩＤＴ The thickness of the first electrode fingers and the second electrode fingers is t ＩＤＴ year, The acoustic impedance of the first dielectric film disposed between the first electrode fingers and the second electrode fingers is defined as R ＤＩＥ The thickness of the first dielectric film is t ＤＩＥ In this case, R ＩＤＴ ×t ＩＤＴ >R ＤＩＥ ×t ＤＩＥ Fulfilling the relationship, The acoustic wave device according to claim 1 .

4. The IDT electrode is a laminate of n layers (n is a natural number), the first dielectric film is a laminate of m layers (m is a natural number), and the acoustic impedance of the kth layer of the IDT electrode is R ＩＤＴｋ The film thickness of the k-th layer of the IDT electrode is t ＩＤＴｋ and the acoustic impedance of the k-th layer of the first dielectric film disposed between the plurality of first electrode fingers and the plurality of second electrode fingers is R ＤＩＥｋ The film thickness of the k-th layer of the first dielectric film is t ＤＩＥｋ In this case, [0010] Fulfilling the relationship, The acoustic wave device according to claim 1 .

5. The first dielectric film has a relative dielectric constant of 5 or more. The acoustic wave device according to claim 1 .

6. The first dielectric film has a relative dielectric constant of 10 or more. The acoustic wave device according to claim 1 .

7. a thickness of the first dielectric film is 50% or less of a thickness of the first electrode fingers and the second electrode fingers; The acoustic wave device according to claim 1 .

8. a thickness of the first dielectric film is 20% or less of a thickness of the first electrode fingers and the second electrode fingers; The acoustic wave device according to claim 1 .

9. The piezoelectric layer includes any one of lithium tantalate and lithium niobate. The acoustic wave device according to claim 1 .

10. The first dielectric film includes any one of silicon nitride, aluminum oxide, yttrium oxide, tantalum oxide, titanium oxide, hafnium oxide, zirconium oxide, aluminum nitride, and sialon. The acoustic wave device according to claim 1 .

11. The IDT electrode is A main electrode layer made of aluminum; an adhesion layer disposed between the main electrode layer and the piezoelectric layer; The acoustic wave device according to claim 1 .

12. The thermal conductivity of the first dielectric film is higher than the thermal conductivity of the piezoelectric layer. The acoustic wave device according to claim 1 .

13. moreover, a second dielectric film disposed on the IDT electrode and the first dielectric film, the second dielectric film being different in material or composition from the first dielectric film; The acoustic wave device according to claim 1 .

14. The second dielectric film has a lower dielectric constant than the first dielectric film. The acoustic wave device according to claim 13.

15. The thickness of the second dielectric film is smaller than the thickness of the first dielectric film. The acoustic wave device according to claim 13.

16. the second dielectric film includes any one of silicon oxide, silicon nitride, and silicon oxynitride; The acoustic wave device according to claim 13.

17. A substrate; An IDT (InterDigital Transducer) electrode disposed on the substrate; a first dielectric film disposed on the substrate; The substrate is a piezoelectric layer on which the IDT electrodes are formed; a high acoustic velocity layer in which a bulk wave acoustic velocity is faster than an elastic wave acoustic velocity in the piezoelectric layer; a low acoustic velocity layer disposed between the piezoelectric layer and the high acoustic velocity layer, the low acoustic velocity layer having a bulk wave with a sound velocity slower than that of a bulk wave propagating through the piezoelectric layer; The IDT electrode is a plurality of first electrode fingers and a plurality of second electrode fingers arranged parallel to each other; a first bus bar electrode configured to connect one ends of the first electrode fingers to each other; a second bus bar electrode configured to connect one ends of the second electrode fingers to each other and disposed opposite the first bus bar electrode with the first electrode fingers and the second electrode fingers interposed therebetween, the first dielectric film is disposed on the piezoelectric layer only in a region where the first electrode fingers and the second electrode fingers overlap when viewed in a direction parallel to the piezoelectric layer and perpendicular to an extension direction of the first electrode fingers and the second electrode fingers, the first dielectric film being disposed only in a region where the first electrode fingers and the second electrode fingers are not disposed in a plan view of the substrate, a thickness of the first dielectric film is smaller than a thickness of the first electrode fingers and a thickness of the second electrode fingers; Elastic wave device.

18. The elastic wave device according to claim 1, 2 or 17, High frequency filter.

19. A plurality of the elastic wave devices according to any one of claims 1 to 17 are provided, the first dielectric film of a first elastic wave device of the plurality of elastic wave devices and the first dielectric film of a second elastic wave device of the plurality of elastic wave devices have different thicknesses, materials, or compositions; 20. A high frequency filter according to claim 18.

20. A plurality of high frequency filters according to claim 18 are provided, the plurality of high frequency filters share one of the substrates; the first dielectric film of a first high frequency filter of the plurality of high frequency filters and the first dielectric film of a second high frequency filter of the plurality of high frequency filters have different thicknesses, materials, or compositions; Filter circuit.

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