Elastic wave device and method for manufacturing elastic wave device

Abstract

An elastic wave device (1) is provided with: a piezoelectric layer (31) having main surfaces (31a, 31b) opposite each other; a functional electrode disposed on at least one of the main surface (31a) side and the main surface (31b) side of the piezoelectric layer (31); a support substrate (35) disposed on the main surface (31b) side of the piezoelectric layer (31); a dielectric layer disposed between the piezoelectric layer (31) and the support substrate (35); and a bonding layer (33) disposed between the piezoelectric layer (31) and the support substrate (35). The bonding layer (33) contains a first metal element and oxygen. The thickness of the bonding layer (33) is greater than 0 nm and smaller than 100 nm. The electronegativity of the first metal element is 0.8-1.5 inclusive.

Description

Acoustic wave device and method of manufacturing the same

[0001] The present invention relates to an acoustic wave device and a method for manufacturing an acoustic wave device.

[0002] Patent Document 1 discloses an acoustic wave device having a structure in which a support substrate, an oxide layer, a metal oxide layer containing titanium (Ti), an oxide layer, a dielectric layer, a piezoelectric layer, and an IDT (InterDigital Transducer) electrode are stacked in this order. With this structure, a first stack of a support substrate, an oxide layer, and a titanium metal layer is stacked with a second stack of a piezoelectric layer, an oxide layer, and a titanium metal layer in a manufacturing process, thereby forming an acoustic wave device that is stably and firmly bonded in a non-heated environment.

[0003] JP 2015-222970 A

[0004] However, in the acoustic wave device disclosed in Patent Document 1, the oxidation state of the metal oxide layer becomes unstable, and the thinner the dielectric layer becomes, the worse the resonance characteristics of the acoustic wave device become.

[0005] Therefore, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an acoustic wave device in which deterioration of resonance characteristics is suppressed, and a method for manufacturing the acoustic wave device.

[0006] In order to achieve the above-mentioned object, an acoustic wave device according to one embodiment of the present invention comprises a piezoelectric layer having a first main surface and a second main surface facing each other, a functional electrode arranged on at least one of the first main surface side and the second main surface side of the piezoelectric layer, a support substrate arranged on the second main surface side of the piezoelectric layer, a dielectric layer arranged between the piezoelectric layer and the support substrate, and a first bonding layer arranged between the piezoelectric layer and the support substrate, wherein the first bonding layer contains a first metal element and oxygen, the thickness of the first bonding layer is greater than 0 nm and less than 100 nm, and the electronegativity of the first metal element is 0.8 or more and 1.5 or less.

[0007] Furthermore, an acoustic wave device according to one aspect of the present invention comprises a piezoelectric layer having a first main surface and a second main surface facing each other, a functional electrode arranged on at least one of the first main surface side and the second main surface side of the piezoelectric layer, a support substrate arranged on the second main surface side of the piezoelectric layer, a dielectric layer arranged between the piezoelectric layer and the support substrate, and a first bonding layer arranged between the piezoelectric layer and the support substrate, wherein the first bonding layer contains a first metal element and oxygen, and the first metal element is any one of yttrium, scandium, and zirconium.

[0008] Furthermore, a method for manufacturing an acoustic wave device according to one aspect of the present invention includes the steps of: forming an oxide layer on at least one of a first main surface side of a piezoelectric substrate having first and second main surfaces opposing each other and a third main surface side of a support substrate having third and fourth main surfaces opposing each other; forming a first bonding film made of a metal element having an electronegativity of 0.8 or more and 1.5 or less on the first main surface side of the piezoelectric substrate after the oxide layer forming step; forming a second bonding film made of a metal element having an electronegativity of 0.8 or more and 1.5 or less on the third main surface side of the support substrate after the oxide layer forming step; bonding the first bonding film and the second bonding film together after the first bonding film forming step and the second bonding film forming step; and forming a functional electrode on the second main surface side of the piezoelectric substrate after the first bonding film forming step.

[0009] Furthermore, a method for manufacturing an acoustic wave device according to one aspect of the present invention includes the steps of: forming a first bonding film containing a metal element and oxygen on a first main surface side of a piezoelectric substrate having first and second main surfaces opposing each other; forming a second bonding film containing a metal element and oxygen on a third main surface side of a support substrate having third and fourth main surfaces opposing each other; bonding the first bonding film and the second bonding film together after the steps of forming the first bonding film and the second bonding film; and forming a functional electrode on the second main surface side of the piezoelectric substrate after the step of bonding the first bonding film and the second bonding film.

[0010] According to the present invention, it is possible to provide an acoustic wave device in which deterioration of resonance characteristics is suppressed, and a method for manufacturing the acoustic wave device.

[0011] FIG. 1 illustrates a plan view and a cross-sectional view of an acoustic wave device according to an embodiment. FIG. 2A illustrates a cross-sectional view of an acoustic wave device according to a first modification of an embodiment. FIG. 2B illustrates a cross-sectional view of an acoustic wave device according to a second modification of an embodiment. FIG. 2C illustrates a cross-sectional view of an acoustic wave device according to a third modification of an embodiment. FIG. 2D illustrates a cross-sectional view of an acoustic wave device according to a fourth modification of an embodiment. FIG. 3A illustrates a cross-sectional view of an acoustic wave device according to a fifth modification of an embodiment. FIG. 3B illustrates a cross-sectional view of an acoustic wave device according to a sixth modification of an embodiment. FIG. 3C illustrates a cross-sectional view of an acoustic wave device according to a seventh modification of an embodiment. FIG. 4A illustrates a cross-sectional view of an acoustic wave device according to an eighth modification of an embodiment. FIG. 4B illustrates a cross-sectional view of an acoustic wave device according to a ninth modification of an embodiment. FIG. 4C illustrates a cross-sectional view of an acoustic wave device according to a tenth modification of an embodiment. FIG. 5A illustrates a graph showing the phase-frequency characteristics of acoustic wave devices according to examples 1 and 3. FIG. 5B illustrates the frequency characteristics of the Q-values ​​of the main modes of the acoustic wave devices according to examples 1 and 3. FIG. 6A illustrates a graph showing the phase-frequency characteristics of acoustic wave devices according to comparative examples 1 and 3. FIG. 6B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave devices according to Comparative Examples 1 and 3. FIG. 7A is a graph showing the relationship between the total film thickness of the silicon oxide layers and the Q value of the main mode of the acoustic wave devices according to the examples and comparative examples. FIG. 7B is a graph showing the relationship between the total film thickness of the silicon oxide layers and the phase of the higher-order mode of the acoustic wave devices according to the examples and comparative examples. FIG. 8A is a graph showing the relationship between the film thickness of the bonding layer of the acoustic wave device according to Example 4 and the deterioration amount of the frequency temperature coefficient. FIG. 8B is a graph showing the relationship between the film thickness of the bonding layer of the acoustic wave device according to Example 4 and the phase of the higher-order mode. FIG. 9 is a graph showing the relationship between the film thickness of the bonding layer of the acoustic wave device according to Example 5 and the amount of wafer warpage. FIG. 10 is a graph showing the relationship between the film thickness of the bonding layer and the Q value of the main mode of the acoustic wave devices according to the examples and comparative examples. FIG. 11 is a graph showing the relationship between the distance from the piezoelectric layer to the bonding layer and the Q value of the main mode of the acoustic wave devices according to the examples and comparative examples. FIG. 12A is a graph showing the frequency characteristics of the phase of the acoustic wave device according to Example 13.FIG. 12B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave device in accordance with Example 13. FIG. 13A is a graph showing the frequency characteristics of the phase of the acoustic wave device in accordance with Example 14. FIG. 13B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave device in accordance with Example 14. FIG. 14A is a cross-sectional view of an acoustic wave device in accordance with an embodiment. FIG. 14B is a graph showing the concentration profile of yttrium in the stacking direction of an acoustic wave device in accordance with an embodiment. FIG. 15 is a cross-sectional view of an acoustic wave device in accordance with Modification 11 of the embodiment. FIG. 16 is a cross-sectional view of an acoustic wave device in accordance with Modification 12 of the embodiment. FIG. 17 is a cross-sectional view of an acoustic wave device in accordance with Modification 13 of the embodiment. FIG. 18 is a flowchart showing a method for manufacturing an acoustic wave device in accordance with an embodiment. FIG. 19 is a flowchart showing a method for manufacturing an acoustic wave device in accordance with Modification 14 of the embodiment. FIG. 20A is a graph showing the frequency characteristics of the phase of the acoustic wave devices in accordance with Examples 15 and 16. FIG. 20B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave devices in accordance with Examples 15 and 16. 21A is a graph showing frequency characteristics of the phase of the acoustic wave devices according to Examples 17 and 18. FIG. 21B is a graph showing frequency characteristics of the Q value of the main mode of the acoustic wave devices according to Examples 17 and 18.

[0012] Hereinafter, 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, component arrangements, and connection configurations 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 recited in independent claims will be described as optional components. Furthermore, the sizes or size ratios of the components shown in the drawings are not necessarily strict.

[0013] It should be noted that the drawings are schematic diagrams in which emphasis, omission, or adjustment of proportions has been appropriately made to illustrate the present invention, and are not necessarily strictly illustrated, and may differ from the actual shapes, positional relationships, and proportions. In the drawings, the same reference numerals are used to denote substantially the same components, and redundant explanations may be omitted or simplified.

[0014] In the circuit configurations of the present disclosure, "connected" includes not only direct connection by connection terminals and / or wiring conductors, 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] Furthermore, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of elements, such as "rectangle," and numerical ranges do not only represent strict meanings, but also include substantially equivalent ranges, for example, including an error of 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 insertion loss within the passband.

[0017] Furthermore, in the resonance characteristics of the acoustic wave device disclosed herein, the resonance frequency and anti-resonance frequency are derived, for example, by contacting an RF probe with two input / output electrodes of the acoustic wave device when the acoustic wave device is not connected to other circuit elements, and measuring the reflection characteristics (impedance characteristics) using a network analyzer or the like.

[0018] In addition, in this disclosure, 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 present in any one of single crystal, polycrystalline, and amorphous states, or in a mixture of these states.

[0019] In the layer structure of the present invention, "Layer A is arranged on the main surface C of Layer B" includes not only Layer A being arranged in contact with the main surface C of Layer B, but also Layer A being arranged above main surface C without contacting main surface C (for example, Layer A being stacked on another layer arranged in contact with main surface C).

[0020] In addition, in the present disclosure, two signals being in phase means that the phases are substantially the same, including a range in which the phases of the two signals differ by about 30%, for example.

[0021] 1A and 1B are a plan view and a cross-sectional view, respectively, of an acoustic wave device 1 according to an embodiment of the present invention. 1A is a plan view (see-through) of a main surface 31a of a piezoelectric layer 31 from the positive side of the z-axis. 1B is a cross-sectional view taken along line Ib-Ib in 1A of the present invention, viewed from the negative side of the y-axis.

[0022] 1, the acoustic wave device 1 includes a substrate 30, an IDT electrode 10, and a reflective electrode 20. Note that the acoustic wave device 1 shown in FIG. 1 is intended to illustrate a typical structure of an acoustic wave resonator that constitutes the acoustic wave device 1, and the number and length of electrode fingers that constitute the IDT electrode 10 and the reflective electrode 20 are not limited to this.

[0023] The substrate 30 has piezoelectric properties and includes a piezoelectric layer 31, a silicon oxide layer 32, a bonding layer 33, a silicon nitride layer 34, and a support substrate 35, as shown in FIG.

[0024] The piezoelectric layer 31 has opposing main surfaces 31a (first main surface) and 31b (second main surface), and is disposed above the silicon oxide layer 32, the bonding layer 33, the silicon nitride layer 34, and the support substrate 35 (positive direction of the z-axis).

[0025] For example, lithium tantalate, lithium niobate, or a material containing any of these materials as a main component can be used for the piezoelectric layer 31. Note that the piezoelectric layer 31 can also be made of a material such as quartz or potassium nitride.

[0026] The silicon oxide layer 32 is an example of a first dielectric film and includes silicon oxide layers 321 and 322. The silicon oxide layer 321 is disposed between the piezoelectric layer 31 and the bonding layer 33 and includes at least one of silicon oxide and silicon oxynitride. The silicon oxide layer 322 is disposed between the bonding layer 33 and the silicon nitride layer 34 and includes at least one of silicon oxide and silicon oxynitride. Each of the silicon oxide layers 321 and 322 functions as a low acoustic velocity layer whose bulk wave acoustic velocity is lower than that of the piezoelectric layer 31 and the support substrate 35.

[0027] Each of the silicon oxide layers 321 and 322 may be made of a dielectric material such as silicon oxide, silicon oxynitride, glass, lithium oxide, tantalum pentoxide, or a compound of silicon oxide to which fluorine, carbon, or boron has been added, or a material containing any of the above materials as its main component.

[0028] The silicon nitride layer 34 is an example of a second dielectric film, and contains silicon nitride. The silicon nitride layer 34 is disposed between the silicon oxide layer 322 and the support substrate 35. The silicon nitride layer 34 functions as a high acoustic velocity layer in which the bulk wave acoustic velocity is higher than the bulk wave acoustic velocity of the silicon oxide layers 321 and 322.

[0029] The silicon nitride layer 34 may be made of silicon nitride, silicon oxynitride, amorphous silicon, polysilicon, aluminum oxide, aluminum nitride, or a material containing any of the above as a main component. Furthermore, the silicon nitride layer 34 may be made of silicon, aluminum oxide, silicon carbide, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, quartz crystal, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a DLC (diamond-like carbon) film, diamond, or a material containing any of the above as a main component.

[0030] The stack of silicon oxide layers 321 and 322 and silicon nitride layer 34 is an example of a dielectric layer, and is disposed between piezoelectric layer 31 and support substrate 35 .

[0031] The bonding layer 33 is an example of a first bonding layer, and is disposed between the piezoelectric layer 31 and the support substrate 35. In the present embodiment, the bonding layer 33 is disposed between the silicon oxide layer 321 and the silicon oxide layer 322. The bonding layer 33 contains a first metal element and oxygen.

[0032] The bonding layer 33 is formed of at least one of a first bonding film and a second bonding film used in a manufacturing process of the acoustic wave device 1, which will be described later. In the manufacturing process, a first stack including the piezoelectric layer 31 (piezoelectric substrate) and the first bonding film and a second stack including the support substrate 35 and the second bonding film are bonded together with the first bonding film and the second bonding film facing each other.

[0033] The first metal element is any one of yttrium (Y), scandium (Sc), and zirconium (Zr), and is preferably yttrium (Y).

[0034] The first metal element may be a metal element having a Pauling electronegativity of 0.8 or more and 1.5 or less. Examples of metal elements that satisfy the above-mentioned electronegativity (0.8 or more and 1.5 or less) include yttrium (Y), scandium (Sc), zirconium (Zr), tantalum (Ta), hafnium (Hf), magnesium (Mg), calcium (Ca), strontium (Sr), lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), and actinides (Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No).

[0035] When the first metal element is a metal element that satisfies the above-mentioned electronegativity (0.8 or more and 1.5 or less), the thickness of the bonding layer 33 is greater than 0 nm and less than 100 nm.

[0036] The Pauling's electronegativity of the first metal element is preferably 0.8 or more and 1.3 or less. Examples of metal elements that satisfy the above-mentioned electronegativity (0.8 or more and 1.3 or less) include yttrium (Y), hafnium (Hf), calcium (Ca), strontium (Sr), lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), and actinides (Ac, Th, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No).

[0037] Furthermore, it is more preferable that the Pauling's electronegativity of the first metal element is 0.8 or more and 1.25 or less. Examples of metal elements that satisfy the above-mentioned electronegativity (0.8 or more and 1.25 or less) include yttrium (Y), calcium (Ca), strontium (Sr), lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), and actinides (Ac, Am).

[0038] As described above, bonding layer 33 has either (1) a Pauling electronegativity of the first metal element of 0.8 or more and 1.5 or less, and a thickness of bonding layer 33 of greater than 0 nm and less than 100 nm, or (2) the first metal element is any one of yttrium (Y), scandium (Sc), and zirconium (Zr). However, bonding layer 33 may contain elements other than the first metal element, as long as the first metal element is the main component of the metal elements contained in bonding layer 33. Component analysis of the metal elements contained in bonding layer 33 can be performed using at least one of EDX (energy dispersive X-ray spectroscopy), XPS (X-ray photoelectron spectroscopy), and RBS (electron backscattering spectroscopy).

[0039] Preferably, only one bonding layer 33 containing the first metal element and oxygen is disposed between the piezoelectric layer 31 and the support substrate 35. This can suppress the generation of unwanted waves in the acoustic wave device 1.

[0040] The support substrate 35 is disposed on the main surface 31b side of the piezoelectric layer 31 and supports the IDT electrode 10, the reflective electrode 20, the piezoelectric layer 31, the silicon oxide layer 32, the bonding layer 33, and the silicon nitride layer 34.

[0041] The support substrate 35 can be made of, for example, a piezoelectric material such as silicon, aluminum nitride, aluminum oxide, lithium niobate, or quartz; a ceramic material such as 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 containing any of the above materials as a main component.

[0042] The IDT electrode 10 is an example of a functional electrode and is arranged on the main surface 31a. As shown in FIG. 1A, the IDT electrode 10 has a plurality of electrode fingers 11a and a plurality of electrode fingers 11b, and busbar electrodes 12a and 12b. The plurality of electrode fingers 11a are an example of a plurality of first electrode fingers and are arranged parallel to each other. The plurality of electrode fingers 11b are an example of a plurality of second electrode fingers and are arranged parallel to each other. The plurality of electrode fingers 11a and the plurality of electrode fingers 11b are arranged parallel to each other so as to be interdigitated with each other.

[0043] 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 intersecting the extension direction of the electrode fingers 11a (the y-axis direction in FIG. 1 ). The 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. The busbar electrode 12b extends in a direction intersecting the extension direction of the electrode fingers 11b (the y-axis direction in FIG. 1 ). The busbar electrode 12a and the busbar electrode 12b are arranged opposite each other with the electrode fingers 11a and the electrode fingers 11b sandwiched therebetween. The other ends of the electrode fingers 11a face the busbar electrode 12b, and the other ends of the electrode fingers 11b face the busbar electrode 12a.

[0044] 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 11 a and the electrode fingers 11 b. The reflective electrodes 20 are configured to confine a predetermined high-frequency signal that resonates in the IDT electrode 10 within the IDT electrode 10. Note that the reflective electrodes 20 may not be provided in the acoustic wave device 1.

[0045] The IDT electrode 10 has a layered structure of, for example, titanium (Ti), aluminum (Al), and titanium (Ti). However, the IDT electrode 10 is not limited to the above layered structure, and may be made of a material containing at least one of copper (Cu), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), and chromium (Cr), or an alloy or layered film containing some of these metals.

[0046] A dielectric film or an insulating film may be disposed between the IDT electrode 10 and the main surface 31a. A protective film may be disposed to cover the IDT electrode 10. The protective film may contain at least one of silicon oxide, silicon nitride, and silicon oxynitride, for example. The protective film may be made of a material such as tantalum pentoxide, amorphous silicon, polycrystalline silicon, aluminum oxide, aluminum nitride, or silicon carbide, or may be a laminate film of these materials.

[0047] According to the above-described configuration of the acoustic wave device 1, the IDT electrode 10, the reflective electrode 20, and the piezoelectric layer 31 form a single acoustic wave resonator having a resonant frequency at which the impedance is minimized and an anti-resonant frequency at which the impedance is maximized.

[0048] In the acoustic wave device 1 according to this embodiment, the IDT electrode 10 may have a piston structure. Specifically, the tip of the electrode finger may be thickened (2D piston) or a load film may be disposed at the tip of the electrode finger (3D piston) to create a difference in acoustic velocity between the center and tip of the electrode finger. This makes it possible to suppress transverse mode ripples occurring in the acoustic wave device 1.

[0049] When forming a low acoustic velocity region by thickening the tips of the electrode fingers, it is preferable to set the electrode finger duty to 0.4 or more and 0.6 or less in order to provide a sufficient difference in acoustic velocity between the main portion and the low acoustic velocity region. When providing a difference in acoustic velocity by arranging a load film at the tips of the electrode fingers, it is not necessary to set the electrode finger duty to 0.4 or more and 0.6 or less, but if the electrode finger duty is made too small, the electrode finger resistance increases, and if it is made too large, the risk of electrostatic breakdown increases, so it is preferable to set the electrode finger duty to 0.1 or more and 0.9 or less.

[0050] The wavelength λ and electrode finger duty D of the acoustic wave device 1 are defined as follows. The wavelength λ of the IDT electrode 10 is a unit of length defined by the repetition period of the electrode fingers 11 a (or 11 b). The electrode finger pitch p of the IDT electrode 10 is ½ of the wavelength λ. The electrode finger duty D of the IDT electrode 10 is the line width (electrode finger width) occupancy rate of the electrode fingers 11 a and 11 b, and is the ratio of the line width L to the sum of the line width L and the space width S, and is defined as L / (L+S).

[0051] In addition, when the electrode finger duty D of the IDT electrode 10 is not constant, the electrode finger duty D of the IDT electrode 10 is equal to the average electrode finger duty D of the IDT electrode 10. ＡＶＥ The average electrode finger duty D of the IDT electrode 10 is defined as ＡＶＥ The total number of electrode fingers 11a and 11b included in the IDT electrode 10 is Ni, and the total line width obtained by adding the line width L of (Ni-1) electrode fingers is L. ＡＬＬ The total space width obtained by adding up the (Ni-1) space widths S included in the IDT electrode 10 is S ＡＬＬ In this case, L ＡＬＬ / (L ＡＬＬ +S ＡＬＬ ) is defined as

[0052] Furthermore, when the IDT electrode 10 has a 2D piston structure and the electrode finger width at the tip end is wider than that at the center, the electrode finger duty D of the IDT electrode 10 is defined as the electrode finger duty at the center. Furthermore, when the IDT electrode 10 has a 2D piston structure but the electrode finger width at the tip end is not wider than that at the center, the electrode finger duty D of the IDT electrode 10 is defined as the average electrode finger duty in the range excluding both ends of the overlap width region of the electrode fingers. Furthermore, when the electrode finger width varies periodically in the overlap width direction of the electrode fingers, the electrode finger duty D of the IDT electrode 10 is defined as the average electrode finger duty in the overlap width region of the electrode fingers.

[0053] The wavelength λ, electrode finger pitch p, and electrode finger duty D of the IDT electrode 10 can be measured by using a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), or a transmission electron microscope (TEM) to view the main surfaces 31 a and 31 b of the piezoelectric layer 31 on which the IDT electrode 10 is formed in a plan view and / or to view a cut surface perpendicular to the extension direction of the electrode fingers 11 a and 11 b in a cross section, thereby measuring the line width L and space width S.

[0054] In the acoustic wave device according to this embodiment, the IDT electrode 10 is used as the functional electrode. However, the functional electrode may be a laminate in which a first planar electrode, a piezoelectric film, and a second planar electrode are laminated.

[0055] Generally, metal elements with low electronegativity tend to donate electrons and be easily oxidized, while metal elements with high electronegativity tend to accept electrons and be less likely to be oxidized. As a result, bonding layers containing metal elements with high electronegativity are incompletely oxidized, leaving a thin conductive layer. Due to the influence of this conductive layer, if the thickness of the dielectric layer (silicon oxide layer) placed between the piezoelectric layer and the bonding layer becomes thin, the resonance characteristics of the acoustic wave device will deteriorate.

[0056] In contrast, in the acoustic wave device 1 according to this embodiment, the bonding layer 33 containing a metal element with low electronegativity becomes an oxide layer with low conductivity without leaving any conductive layer. As a result, even if the thickness of the silicon oxide layer 32 is reduced, the main mode resonance characteristics of the acoustic wave device 1 do not deteriorate. Therefore, it is possible to provide an acoustic wave device 1 in which deterioration of the main mode resonance characteristics is suppressed.

[0057] [2. Stacked Structure of Acoustic Wave Devices According to Modifications 1 to 10] Acoustic wave devices according to the present invention include acoustic wave devices according to the following modifications 1 to 10.

[0058] FIG. 2A is a cross-sectional view of an acoustic wave device according to a first modification of the embodiment. FIG. 2B is a cross-sectional view of an acoustic wave device according to a second modification of the embodiment. FIG. 2C is a cross-sectional view of an acoustic wave device according to a third modification of the embodiment. FIG. 2D is a cross-sectional view of an acoustic wave device according to a fourth modification of the embodiment. As shown in FIGS. 2A to 2D , the acoustic wave devices according to the first to fourth modifications include a piezoelectric layer 31, a silicon oxide layer 32, a bonding layer 33, a silicon nitride layer 34, and a support substrate 35. The silicon oxide layer 32 and the silicon nitride layer 34 form a dielectric layer. The acoustic wave devices according to the first to fourth modifications differ from the acoustic wave device 1 according to the embodiment only in the position of the bonding layer 33. Hereinafter, for the acoustic wave devices according to the first to fourth modifications, a description of the same configuration as the acoustic wave device 1 according to the embodiment will be omitted, and the different configurations will be mainly described.

[0059] As shown in FIG. 2A , in the acoustic wave device according to Modification 1, the bonding layer 33 is disposed between the piezoelectric layer 31 and the silicon oxide layer 32. As shown in FIG. 2B , in the acoustic wave device according to Modification 2, the bonding layer 33 is disposed between the silicon oxide layer 32 and the silicon nitride layer 34. As shown in FIG. 2C , in the acoustic wave device according to Modification 3, the bonding layer 33 is disposed between the silicon nitride layer 341 and the silicon nitride layer 342. Note that the silicon nitride layer 341 and the silicon nitride layer 342 each have the same material composition as the silicon nitride layer 34. As shown in FIG. 2D , in the acoustic wave device according to Modification 4, the bonding layer 33 is disposed between the silicon nitride layer 34 and the support substrate 35.

[0060] In the acoustic wave devices according to Modifications 1 to 4, the bonding layer 33 containing a metal element with low electronegativity becomes an oxide layer with low conductivity without leaving any conductive layer. As a result, even if the thickness of the silicon oxide layer 32 is reduced, the main mode resonance characteristics of the acoustic wave device are not deteriorated. Therefore, an acoustic wave device in which deterioration of the main mode resonance characteristics is suppressed can be provided.

[0061] FIG. 3A is a cross-sectional view of an acoustic wave device according to a fifth modification of the embodiment. FIG. 3B is a cross-sectional view of an acoustic wave device according to a sixth modification of the embodiment. FIG. 3C is a cross-sectional view of an acoustic wave device according to a seventh modification of the embodiment. As shown in FIGS. 3A to 3C, the acoustic wave devices according to the fifth to seventh modifications include a piezoelectric layer 31, a silicon oxide layer 32, a bonding layer 33, and a support substrate 35. The silicon oxide layer 32 constitutes a dielectric layer. Compared to the acoustic wave device 1 according to the embodiment, the acoustic wave devices according to the fifth to seventh modifications do not include a silicon nitride layer 34 and the bonding layer 33 is disposed in a different position. Hereinafter, the acoustic wave devices according to the fifth to seventh modifications will be described, focusing on the different configurations and omitting the description of the same configurations as the acoustic wave device 1 according to the embodiment.

[0062] 3A, in the acoustic wave device according to Modification 5, the bonding layer 33 is disposed between the piezoelectric layer 31 and the silicon oxide layer 32. As shown in FIG. 3B, in the acoustic wave device according to Modification 6, the bonding layer 33 is disposed between the silicon oxide layer 321 and the silicon oxide layer 322. As shown in FIG. 3C, in the acoustic wave device according to Modification 7, the bonding layer 33 is disposed between the silicon oxide layer 32 and the support substrate 35.

[0063] In the acoustic wave devices according to Modifications 5 to 7, the bonding layer 33 containing a metal element with low electronegativity becomes an oxide layer with low conductivity without leaving any conductive layer. As a result, even if the thickness of the silicon oxide layer 32 is reduced, the resonance characteristics of the main mode of the acoustic wave device are not deteriorated. Therefore, an acoustic wave device with reduced deterioration in the resonance characteristics can be provided.

[0064] FIG. 4A is a cross-sectional view of an acoustic wave device according to an eighth modification of the embodiment. FIG. 4B is a cross-sectional view of an acoustic wave device according to a ninth modification of the embodiment. FIG. 4C is a cross-sectional view of an acoustic wave device according to a tenth modification of the embodiment. As shown in FIGS. 4A to 4C, the acoustic wave devices according to the eighth to tenth modifications include a piezoelectric layer 31, a silicon nitride layer 34, a bonding layer 33, and a support substrate 35. The silicon nitride layer 34 forms a dielectric layer. Compared to the acoustic wave device 1 according to the embodiment, the acoustic wave devices according to the eighth to tenth modifications do not include the silicon oxide layer 32 and the bonding layer 33 is disposed in a different position. Hereinafter, the acoustic wave devices according to the eighth to tenth modifications will be described, focusing on the different configurations and omitting the description of the same configurations as the acoustic wave device 1 according to the embodiment.

[0065] As shown in Fig. 4A, in the acoustic wave device according to Modification 8, the bonding layer 33 is disposed between the piezoelectric layer 31 and the silicon nitride layer 34. As shown in Fig. 4B, in the acoustic wave device according to Modification 9, the bonding layer 33 is disposed between the silicon nitride layer 341 and the silicon nitride layer 342. As shown in Fig. 4C, in the acoustic wave device according to Modification 10, the bonding layer 33 is disposed between the silicon nitride layer 34 and the support substrate 35.

[0066] In the acoustic wave devices according to Modifications 8 to 10, the bonding layer 33 containing a metal element with low electronegativity becomes an oxide layer with low conductivity without leaving any conductive layer. As a result, even if the thickness of the silicon nitride layer 34 is reduced, the resonance characteristics of the main mode of the acoustic wave device do not deteriorate. Therefore, an acoustic wave device with reduced deterioration in the resonance characteristics can be provided.

[0067] [3. Resonance Characteristics of Acoustic Wave Devices According to Examples 1 to 3] Resonance characteristics of acoustic wave devices that are examples of the acoustic wave device 1 according to this embodiment will be described in detail below.

[0068] Table 1 shows the structural parameters of the acoustic wave devices according to Examples 1 to 3 and Comparative Examples 1 to 3.

[0069]

[0070] The acoustic wave devices according to Examples 1 to 3 and the acoustic wave devices according to Comparative Examples 1 to 3 have the same layered structure, in which a support substrate, a silicon nitride layer, a silicon oxide layer, a bonding layer, a silicon oxide layer, and a piezoelectric layer are stacked in this order. Furthermore, the acoustic wave devices according to Examples 1 to 3 have different thicknesses of the silicon oxide layer 321 disposed between the piezoelectric layer 31 and the bonding layer 33, while the acoustic wave devices according to Comparative Examples 1 to 3 have different thicknesses of the silicon oxide layer disposed between the piezoelectric layer and the bonding layer. Furthermore, the bonding layer 33 of the acoustic wave devices according to Examples 1 to 3 is made of yttrium (Y) oxide, while the bonding layer of the acoustic wave devices according to Comparative Examples 1 to 3 is made of titanium (Ti) oxide.

[0071] FIG. 5A is a graph showing the phase-frequency characteristics of the acoustic wave devices according to Examples 1 and 3. FIG. 5B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave devices according to Examples 1 and 3. FIG. 6A is a graph showing the phase-frequency characteristics of the acoustic wave devices according to Comparative Examples 1 and 3. FIG. 6B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave devices according to Comparative Examples 1 and 3. FIG. 7A is a graph showing the relationship between the total film thickness of the silicon oxide layers and the Q value of the main mode of the acoustic wave devices according to Examples 1 to 3 and Comparative Examples 1 to 3. FIG. 7B is a graph showing the relationship between the total film thickness of the silicon oxide layers and the phase of the higher-order mode of the acoustic wave devices according to Examples 1 to 3 and Comparative Examples 1 to 3.

[0072] 5A and 7B, the phase (maximum value) of the higher-order mode decreases as the silicon oxide layer becomes thinner in the acoustic wave devices according to Examples 1 to 3. Also, as shown in FIGS. 6A and 7B, the phase (maximum value) of the higher-order mode decreases as the silicon oxide layer becomes thinner in the acoustic wave devices according to Comparative Examples 1 to 3.

[0073] 6B and 7A, the Q value of the main mode deteriorates when the silicon oxide layer is thinned in the acoustic wave devices according to Comparative Examples 1 to 3. In contrast, the Q value of the main mode does not deteriorate when the silicon oxide layer is thinned in the acoustic wave devices according to Examples 1 to 3, as shown in FIGS.

[0074] That is, in the acoustic wave device according to the embodiment, by thinning the silicon oxide layer 321, it is possible to suppress the deterioration of the Q value in the main mode and reduce the spurious response in the higher-order mode at the same time.

[0075] 7B, the thickness of the silicon oxide layer 32 is preferably 250 nm or less. In other words, since the wavelength λ of the IDT electrode 10 of the acoustic wave devices according to Examples 1 to 3 is 2 μm, the normalized film thickness of the silicon oxide layer 32 (thickness of the silicon oxide layer 32 / wavelength λ) is preferably 0.125. This allows the phase of the excitation signal in the higher mode to be 0° or less.

[0076] 7B, the thickness of the silicon oxide layer 32 is preferably 160 nm or less. In other words, the normalized film thickness of the silicon oxide layer 32 is preferably 0.08. This allows the phase of the higher-order mode excitation signal to be −30° or less.

[0077] [4. Resonance Characteristics of the Acoustic Wave Device According to Example 4] Table 2 shows structural parameters of the acoustic wave device according to Example 4.

[0078]

[0079] 8A is a graph showing the relationship between the thickness of the bonding layer 33 and the deterioration amount of the temperature coefficient of frequency (TCF) in the acoustic wave device according to Example 4. FIG. 8B is a graph showing the relationship between the thickness of the bonding layer 33 and the phase of the higher-order mode in the acoustic wave device according to Example 4.

[0080] As shown in Figure 8A, when the thickness of the bonding layer 33 is 100 nm or more, the deterioration amount of the temperature coefficient of frequency (TCF) is 1 ppm / °C or more. When the acoustic wave device according to Example 4 is applied to an acoustic wave filter, communication quality is degraded at high temperatures (50°C or higher) and low temperatures (0°C or lower). Furthermore, as shown in Figure 8B, when the thickness of the bonding layer 33 is greater than 100 nm, the phase of the higher-order mode is -30°C or higher, significantly degrading communication performance in the communication band including the frequency of the higher-order mode. Furthermore, when the thickness of the bonding layer 33 is 0 nm, i.e., when the bonding layer 33 is not provided, a manufacturing method in which the piezoelectric layer 31 and the support substrate 35 are bonded together via the bonding layer 33 cannot be used.

[0081] As described above, in the acoustic wave device according to Example 4, it is preferable that the film thickness of the bonding layer 33 is greater than 0 nm and less than 100 nm. This can suppress the deterioration of the resonance characteristics at high and low temperatures, and can keep the phase of the excitation signal in the higher mode at −30° or less.

[0082] 5. Resonance Characteristics of the Acoustic Wave Device According to the Fifth Example Table 3 shows structural parameters of the acoustic wave device according to the fifth example.

[0083]

[0084] The acoustic wave device according to Example 5 differs from the acoustic wave device according to Example 1 in that the film thickness of the bonding layer 33 is varied in the range of 2 to 10 nm. Furthermore, the acoustic wave device according to Example 5 uses a 4-inch silicon wafer (aggregate substrate) as the support substrate 35. That is, a plurality of acoustic wave devices are collectively formed on the 4-inch silicon wafer (aggregate substrate).

[0085] FIG. 9 is a graph showing the relationship between the thickness of the bonding layer 33 and the amount of wafer warpage in the acoustic wave device according to Example 5. The wafer warpage shown on the vertical axis in FIG. 9 indicates the amount of warpage of the silicon wafer (aggregate substrate) before the acoustic wave devices are singulated. As shown in FIG. 9 , the greater the thickness of the bonding layer 33, the greater the amount of warpage of the silicon wafer. If the amount of warpage of the silicon wafer is 500 μm or more, the silicon wafer is more likely to be damaged or cracked during the wafer suction process and wafer polishing process when processing the silicon wafer. As shown in FIG. 9 , if the thickness of the bonding layer 33 is 20 nm or more, the amount of warpage of the silicon wafer is 500 μm or more. Therefore, it is preferable that the thickness of the bonding layer 33 is less than 20 nm. This can suppress damage and cracking of the support substrate 35.

[0086] It is more preferable that the thickness of the bonding layer 33 is less than 17 nm. This makes it possible to keep the amount of warping of the silicon wafer to 400 μm or less, and further suppress breakage and cracking of the support substrate 35.

[0087] 6. Resonance Characteristics of Acoustic Wave Devices According to Examples 6 and 7 Table 4 shows the structural parameters of the acoustic wave devices according to Examples 6 and 7 and Comparative Example 4.

[0088]

[0089] The acoustic wave devices according to Examples 6, 7, and Comparative Example 4 all have the same layered structure, with a support substrate, a silicon nitride layer, a silicon oxide layer, a bonding layer, a silicon oxide layer, and a piezoelectric layer stacked in that order. The bonding layer 33 of the acoustic wave device according to Example 6 is made of yttrium (Y) oxide, and the thickness of the bonding layer 33 is varied in the range of 0.3 to 1.0 nm. The bonding layer 33 of the acoustic wave device according to Example 7 is made of zirconium (Zr) oxide, and the thickness of the bonding layer 33 is varied in the range of 0.3 to 0.8 nm. The bonding layer of the acoustic wave device according to Comparative Example 4 is made of titanium (Ti) oxide, and the thickness of the bonding layer is varied in the range of 0.3 to 0.4 nm.

[0090] 10 is a graph showing the relationship between the film thickness of the bonding layer and the Q value of the main mode in the acoustic wave devices according to Examples 6 and 7 and Comparative Example 4. As shown in the figure, in the acoustic wave devices according to Examples 6 and 7, the change in the Q value of the main mode with respect to the change in film thickness of the bonding layer 33 is smaller than in the acoustic wave device according to Comparative Example 4.

[0091] As a result, in the acoustic wave devices according to Examples 6 and 7, it is possible to suppress variations in resonance characteristics due to variations in the film thickness of the bonding layer 33 during manufacturing. Furthermore, from the viewpoint of ensuring the bonding strength of the bonding layer 33, it is possible to increase the film thickness of the bonding layer 33.

[0092] 7. Resonance Characteristics of Acoustic Wave Devices According to Examples 8 to 12 Table 5 shows the structural parameters of the acoustic wave devices according to Examples 8 to 12.

[0093]

[0094] The acoustic wave devices according to Examples 8 to 12 each include a support substrate 35, a silicon nitride layer 34, a silicon oxide layer 32, a bonding layer 33, and a piezoelectric layer 31, and the position of the bonding layer 33 differs from one another. The bonding layer 33 of each of Examples 8 to 12 is made of yttrium (Y) oxide.

[0095] The acoustic wave device according to the eighth embodiment has the same stacked structure as the acoustic wave device according to the second modification shown in FIG. 2B, and the bonding layer 33 is disposed between the silicon oxide layer 32 and the silicon nitride layer 34.

[0096] The acoustic wave devices according to Examples 9, 10, and 11 have the same stacked structure as the acoustic wave device according to Example 1, and the bonding layer 33 is disposed between the silicon oxide layer 321 and the silicon oxide layer 322. Examples 9 to 11 differ in the film thickness ratio between the silicon oxide layers 321 and 322.

[0097] The acoustic wave device in accordance with Example 12 has the same layered structure as the acoustic wave device in accordance with Modification 1 shown in FIG. 2A, and the bonding layer 33 is disposed between the piezoelectric layer 31 and the silicon oxide layer 32.

[0098] 11 is a graph showing the relationship between the distance from the piezoelectric layer to the bonding layer and the main-mode Q value of the acoustic wave devices according to the examples and the comparative example. As shown in the figure, in Examples 9 to 12, compared to Comparative Example 1, the Q value of the main mode is improved by having bonding layer 33 made of yttrium (Y) oxide and by having bonding layer 33 disposed between silicon oxide layers 321 and 322 or between piezoelectric layer 31 and silicon oxide layer 32. Furthermore, in Examples 8 to 12, the Q value of the main mode is improved as the distance from piezoelectric layer 31 to bonding layer 33 decreases. This not only improves the deterioration of the characteristics of the acoustic wave device according to Comparative Example 1, which includes a bonding layer made of titanium (Ti) oxide, but also improves the Q value of the main mode by positioning bonding layer 33 made of yttrium (Y) oxide closer to piezoelectric layer 31.

[0099] 8. Resonance Characteristics of Acoustic Wave Devices According to Examples 13 and 14 Table 6 shows structural parameters of the acoustic wave devices according to Examples 13 and 14.

[0100]

[0101] The acoustic wave devices according to Examples 13 and 14 do not include a silicon oxide layer 32, but include a support substrate 35, a silicon nitride layer 34, a bonding layer 33, and a piezoelectric layer 31, and differ from each other in the location of the bonding layer 33. The bonding layer 33 of the acoustic wave devices according to Examples 13 and 14 is made of yttrium (Y) oxide.

[0102] The acoustic wave device in accordance with Example 13 has the same layered structure as the acoustic wave device in accordance with Modification 8 shown in FIG. 4A, and the bonding layer 33 is disposed between the piezoelectric layer 31 and the silicon nitride layer 34.

[0103] The acoustic wave device in accordance with Example 14 has the same stacked structure as the acoustic wave device in accordance with Modification 9 shown in FIG. 4B, and the bonding layer 33 is disposed between the silicon nitride layer 341 and the silicon nitride layer 342.

[0104] 12A is a graph showing the frequency characteristics of the phase of the acoustic wave device in accordance with Example 13. FIG. 12B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave device in accordance with Example 13. FIG. 13A is a graph showing the frequency characteristics of the phase of the acoustic wave device in accordance with Example 14. FIG. 13B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave device in accordance with Example 14.

[0105] 12A to 13B, in the acoustic wave devices according to Examples 13 and 14, the Q value of the main mode does not deteriorate, and the spurious response of higher modes is reduced. In other words, even if the layer adjacent to the bonding layer 33 is a non-oxide layer rather than the silicon oxide layer 32, the bonding layer 33 is composed of yttrium (Y) and oxygen, forming a favorable oxide layer, and therefore an acoustic wave device with a high Q value of approximately 3000 can be provided. Furthermore, a high Q value can be ensured even without a low acoustic velocity layer such as the silicon oxide layer 32, and the acoustic velocity of the acoustic wave can be increased, so an acoustic wave filter compatible with higher frequencies can be provided.

[0106] [9. Distribution of First Metal Element in Bonding Layer] Next, the concentration profile of the first metal element in the bonding layer 33 will be described.

[0107] 14A is a cross-sectional view of an acoustic wave device 1 according to an embodiment, and FIG. 14B is a graph showing a concentration profile of yttrium element in the stacking direction of an acoustic wave device 1 according to an embodiment.

[0108] 14A , in the acoustic wave device 1, the bonding layer 33 has opposing interfaces 33 a (first interface) and 33 b (second interface). As shown in FIG. 14B , the bonding layer 33 includes, along the stacking (z-axis) direction, a first region including the interface 33 a, a second region including the interface 33 b, and a third region sandwiched between the first and second regions. To measure the yttrium concentration in the bonding layer 33, a cross section of the acoustic wave device 1 was observed with a TEM, and EDX analysis was performed in the stacking (z-axis) direction to measure the signal intensity of the yttrium element.

[0109] 14B , the signal intensity of the yttrium element in the third region is higher than the signal intensity of the yttrium element in the first region and the signal intensity of the yttrium element in the second region, i.e., the content of the yttrium element in the third region is higher than the content of the yttrium element in the first region and the content of the yttrium element in the second region.

[0110] [10. Layer Structure of Acoustic Wave Devices According to Modifications 11 to 13] Next, acoustic wave filters according to Modifications 11 to 13, which have different IDT electrode arrangements or piezoelectric layer layer layers, will be described.

[0111] 15 is a cross-sectional view of an acoustic wave device 2 according to an eleventh modification of the embodiment. As shown in the figure, the acoustic wave device 2 includes a substrate 30 and IDT electrodes 10 and 40. The acoustic wave device 2 according to this modification differs from the acoustic wave device 1 according to the embodiment in that the IDT electrode 40 is provided. Therefore, the following description of the acoustic wave device 2 according to this modification will omit a description of the same configuration as the acoustic wave device 1 according to the embodiment, and will focus on the different configuration.

[0112] The IDT electrode 40 is an example of a functional electrode, is disposed on the main surface 31b, and is covered with a silicon oxide layer 321. As shown in FIG. 15 , the IDT electrode 40 has a plurality of electrode fingers 41a and a plurality of electrode fingers 41b, and busbar electrodes 42a (not shown) and 42b (not shown). The plurality of electrode fingers 41a are an example of a plurality of first electrode fingers and are arranged parallel to each other. The plurality of electrode fingers 41b are an example of a plurality of second electrode fingers and are arranged parallel to each other. The plurality of electrode fingers 41a and the plurality of electrode fingers 41b are arranged parallel to each other so as to be interdigitated with each other.

[0113] The busbar electrode 42a is an example of a first busbar electrode and is configured to connect one ends of the plurality of electrode fingers 41a to each other. The busbar electrode 42b is an example of a second busbar electrode and is configured to connect one ends of the plurality of electrode fingers 41b to each other. The busbar electrodes 42a and 42b are arranged opposite each other with the plurality of electrode fingers 41a and the plurality of electrode fingers 41b interposed therebetween.

[0114] When the main surfaces 31a and 31b are viewed in plan, it is preferable that the electrode fingers 41a overlap with the electrode fingers 11a in a one-to-one relationship, and the electrode fingers 41b overlap with the electrode fingers 11b in a one-to-one relationship. The electrode fingers 41a and the electrode fingers 11a are excited in phase, and the electrode fingers 41b and the electrode fingers 11b are excited in phase. This makes it possible to suppress spurious responses such as higher-order modes.

[0115] The IDT electrode 40 has a laminated structure of, for example, titanium (Ti), aluminum (Al), and platinum (Pt). However, the IDT electrode 40 is not limited to the above laminated structure, and may be made of a material containing at least one of copper (Cu), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), and chromium (Cr), or an alloy or laminated film containing some of these metals.

[0116] According to the above configuration, higher-order modes are suppressed over a wide range by forming the IDT electrodes 10 and 40 on both main surfaces of the piezoelectric layer 31. Note that since the bonding layer 33 and the IDT electrode 40 are disposed close to each other, the resonance characteristics of the acoustic wave device 2 are affected by the conductance component of the bonding layer 33. However, the bonding layer 33 has one of the following characteristics: (1) the Pauling's electronegativity of the first metal element is 0.8 or more and 1.5 or less, and (2) the first metal element is any one of yttrium, scandium, and zirconium, thereby reducing the effect of the conductance component of the bonding layer 33.

[0117] 16 is a cross-sectional view of an acoustic wave device 3 according to a twelfth embodiment of the present invention. As shown in the figure, the acoustic wave device 3 includes a substrate 30 and an IDT electrode 40. The acoustic wave device 3 according to this modification is different from the acoustic wave device 2 according to the eleventh embodiment of the present invention in that the IDT electrode 10 is not disposed on the main surface 31 a.

[0118] According to the above configuration, the IDT electrode 10 is not disposed on the main surface 31 a of the piezoelectric layer 31, thereby suppressing changes in characteristics that may occur when a foreign object is placed on the main surface 31 a. Note that, since the bonding layer 33 and the IDT electrode 40 are disposed close to each other, the resonance characteristics of the acoustic wave device 3 are affected by the conductance component of the bonding layer 33. However, the bonding layer 33 has any one of the following characteristics: (1) Pauling's electronegativity is 0.8 or more and 1.5 or less, and (2) the first metal element is any one of yttrium, scandium, and zirconium, thereby reducing the effect of the conductance component of the bonding layer 33.

[0119] 17 is a cross-sectional view of an acoustic wave device 4 according to a thirteenth modification of the embodiment. As shown in the figure, the acoustic wave device 4 includes a substrate 30A and an IDT electrode 10. The acoustic wave device 4 according to this modification has a different piezoelectric layer configuration than the acoustic wave device 1 according to the embodiment. Therefore, the following description of the acoustic wave device 4 according to this modification will omit a description of the same configuration as the acoustic wave device 1 according to the embodiment, and will focus on the different configuration.

[0120] The substrate 30A has piezoelectric properties, and includes a piezoelectric layer 31A, a silicon oxide layer 32, a bonding layer 33, a silicon nitride layer 34, and a support substrate 35, as shown in FIG.

[0121] The piezoelectric layer 31A includes piezoelectric films 311 and 312 and a bonding layer 36. The piezoelectric layer 31A has a configuration in which the piezoelectric film 312, the bonding layer 36, and the piezoelectric film 311 are stacked in this order from the support substrate 35 side (the negative z-axis direction).

[0122] The piezoelectric film 311 (first piezoelectric film) and the piezoelectric film 312 (second piezoelectric film) may each be made of, for example, lithium tantalate or lithium niobate, or a material primarily composed of either of these materials. The piezoelectric films 311 and 312 are made of, for example, lithium tantalate and have Euler angles of (0°, −50°, 0°). The thickness of the piezoelectric film 311 is, for example, 400 nm, and the thickness of the piezoelectric film 312 is, for example, 50 to 200 nm. Note that the piezoelectric films 311 and 312 may be made of different materials. Alternatively, the piezoelectric films 311 and 312 may have the same composition but different Euler angles.

[0123] The bonding layer 36 is an example of a second bonding layer, and is disposed between the piezoelectric film 311 and the piezoelectric film 312. The bonding layer 36 contains a second metal element and oxygen.

[0124] The second metal element is any one of yttrium (Y), scandium (Sc), and zirconium (Zr), and is preferably yttrium (Y).

[0125] The second metal element may be a metal element having a Pauling electronegativity of 0.8 or more and 1.5 or less. Examples of metal elements that satisfy the above-mentioned electronegativity (0.8 or more and 1.5 or less) include yttrium (Y), scandium (Sc), zirconium (Zr), tantalum (Ta), hafnium (Hf), magnesium (Mg), calcium (Ca), strontium (Sr), lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), and actinides (Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No).

[0126] Note that bonding layer 36 may contain elements other than the second metal element, as long as the second metal element is the main component of the metal elements contained in bonding layer 36. Note that the component analysis of the metal elements contained in bonding layer 36 can be performed using at least one of EDX, XPS, and RBS.

[0127] The piezoelectric layer 31A is formed by bonding together a first laminate in which a part of the bonding layer 36 is formed on the piezoelectric film 311 and a second laminate in which the other part of the bonding layer 36 is formed on the piezoelectric film 312.

[0128] With the above configuration, for example, as the film thickness of the piezoelectric film 312 increases from 50 nm to 200 nm, the relative bandwidth of the acoustic wave device 4 can be reduced, for example, from 4% to 2%.

[0129] By bonding the two piezoelectric films 311 and 312 via the bonding layer 36, it is possible to adjust the relative bandwidth, which cannot be achieved with a single piezoelectric substrate, without causing significant deterioration in characteristics or reduction in capacity.

[0130] In the acoustic wave device 4 according to the thirteenth modification, the stacked structure of the silicon oxide layer 32, the bonding layer 33, the silicon nitride layer 34, and the support substrate 35 may be the same as that of the acoustic wave devices according to the first to tenth modifications.

[0131] 11. Method for Manufacturing Acoustic Wave Device 1 According to Embodiment Next, a method for manufacturing the acoustic wave device 1 according to the embodiment will be described. Fig. 18 is a flowchart showing a method for manufacturing the acoustic wave device 1 according to the embodiment.

[0132] First, a silicon oxide layer 321 (oxide layer) is formed on the first main surface side of a piezoelectric substrate having first and second main surfaces facing each other (S11), and a silicon oxide layer 322 (oxide layer) is formed on the third main surface side of a support substrate 35 having third and fourth main surfaces facing each other (S12).

[0133] The piezoelectric substrate preferably contains either lithium tantalate or lithium niobate.

[0134] The total thickness of the silicon oxide layer 321 formed in step S11 and the silicon oxide layer 322 formed in step S12 is preferably 250 nm or less, which makes it possible to manufacture an acoustic wave device 1 in which excitation signals in higher modes are suppressed.

[0135] In the method for manufacturing the acoustic wave device 1, at least one of step S11 and step S12 may be performed. Furthermore, a silicon nitride layer 34 may be formed on the third main surface of the support substrate 35 before step S12. Furthermore, an IDT electrode 40 may be formed on the first main surface of the piezoelectric substrate before step S11. If the IDT electrode 40 is formed on the first main surface of the piezoelectric substrate, a step of planarizing the surface of the silicon oxide layer 321 may be performed after step S11.

[0136] Next, a first bonding film made of a metal element having a Pauling electronegativity of 0.8 or more and 1.5 or less is formed on the first main surface of the piezoelectric substrate (S21). A second bonding film made of a metal element having a Pauling electronegativity of 0.8 or more and 1.5 or less is formed on the third main surface of the support substrate 35 (S22). Examples of metal elements satisfying the above-mentioned electronegativity (0.8 or more and 1.5 or less) include Y, Sc, Zr, Ta, Hf, Mg, Ca, Sr, lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), and actinides (Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, and No).

[0137] The metal elements of the first and second bonding films preferably have Pauling's electronegativity of 0.8 or more and 1.3 or less. Examples of metal elements that satisfy the above electronegativity (0.8 or more and 1.3 or less) include Y, Hf, Ca, Sr, lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), and actinides (Ac, Th, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, and No).

[0138] It is more preferable that the metal elements of the first bonding film and the second bonding film have Pauling's electronegativity of 0.8 or more and 1.25 or less. Examples of metal elements that satisfy the above electronegativity (0.8 or more and 1.25 or less) include Y, Ca, Sr, lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), and actinides (Ac, Am).

[0139] The metal element constituting the first bonding film and the second bonding film is preferably any one of Y, Sc, and Zr, and more preferably Y.

[0140] Next, the first bonding film and the second bonding film are bonded (S30). In step S30, the acoustic wave device may be placed in a vacuum atmosphere. After step S30, the second main surface of the piezoelectric substrate may be thinned. In at least one of step S30 and the step of thinning the piezoelectric substrate, the acoustic wave device may be heated at a temperature equal to or lower than the Curie point of the piezoelectric substrate. This can increase the bonding strength between the first bonding film and the second bonding film. Furthermore, oxidation of the first bonding film and the second bonding film can be stabilized, resulting in stable productivity.

[0141] The process of thinning the piezoelectric substrate can be performed by polishing such as CMP (Chemical Mechanical Polishing), milling using argon ions, or chemical polishing such as RIE (Reactive Ion Etching). Alternatively, ions may be implanted into the piezoelectric substrate to a predetermined depth in advance, and the surface layer of the piezoelectric substrate may be peeled off using the ion implantation layer after step S30.

[0142] Finally, the IDT electrode 10 is formed on the second main surface of the piezoelectric substrate (S40). After step S40, a protective film may be formed on the surface of the IDT electrode 10, and wiring may be formed to connect the IDT electrode 10 to an external circuit.

[0143] According to the above manufacturing method, the bonding layer formed by bonding the first bonding film and the second bonding film contains a metal element with low electronegativity, and therefore becomes an oxide layer with low conductivity. As a result, even if the thickness of the silicon oxide layer 32 is reduced, the main mode resonance characteristics of the acoustic wave device 1 are not deteriorated. Therefore, it is possible to manufacture an acoustic wave device 1 in which deterioration of the main mode resonance characteristics is suppressed.

[0144] The thickness of the bonding layer formed by bonding the first and second bonding films is preferably greater than 0 nm and less than 100 nm, which makes it possible to manufacture an acoustic wave device 1 in which the deterioration of resonance characteristics at high and low temperatures is suppressed and excitation signals in higher modes are suppressed.

[0145] Furthermore, it is more desirable that the thickness of the bonding layer formed by bonding the first bonding film and the second bonding film be less than 20 nm, which makes it possible to manufacture the acoustic wave device 1 in which damage and cracking of the support substrate 35 are suppressed.

[0146] 12. Method for Manufacturing Acoustic Wave Device According to Modification 14 Next, a method for manufacturing an acoustic wave device according to Modification 14 will be described. Fig. 19 is a flowchart showing a method for manufacturing an acoustic wave device according to Modification 14 of the embodiment.

[0147] First, a first bonding film containing a metal element and oxygen is formed on the first principal surface of a piezoelectric substrate having first and second principal surfaces facing each other (S11), and a second bonding film containing a metal element and oxygen is formed on the third principal surface of a support substrate 35 having third and fourth principal surfaces facing each other (S12).

[0148] The piezoelectric substrate preferably contains either lithium tantalate or lithium niobate.

[0149] The metal elements contained in the first and second bonding films preferably have Pauling's electronegativity of 0.8 or more and 1.5 or less. Examples of metal elements that satisfy the above electronegativity (0.8 or more and 1.5 or less) include Y, Sc, Zr, Ta, Hf, Mg, Ca, Sr, lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), and actinides (Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, and No).

[0150] It is more preferable that the metal elements contained in the first bonding film and the second bonding film have Pauling's electronegativity of 0.8 or more and 1.3 or less. Examples of metal elements that satisfy the above electronegativity (0.8 or more and 1.3 or less) include Y, Hf, Ca, Sr, lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), and actinides (Ac, Th, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, and No).

[0151] It is more preferable that the metal elements contained in the first bonding film and the second bonding film have Pauling's electronegativity of 0.8 or more and 1.25 or less. Examples of metal elements that satisfy the above electronegativity (0.8 or more and 1.25 or less) include Y, Ca, Sr, lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), and actinides (Ac, Am).

[0152] The metal element contained in the first bonding film and the second bonding film is preferably any one of Y, Sc, and Zr, and more preferably Y.

[0153] Note that, before step S11, a silicon oxide layer 32 or a silicon nitride layer 34 may be formed on the first main surface of the piezoelectric substrate. Also, before step S12, a silicon oxide layer 32 or a silicon nitride layer 34 may be formed on the third main surface of the support substrate 35. Also, before step S11, an IDT electrode 40 may be formed on the first main surface of the piezoelectric substrate. Note that if the IDT electrode 40 is formed on the first main surface of the piezoelectric substrate, a step of forming an oxide layer on the first main surface of the piezoelectric substrate and the IDT electrode 40 and planarizing the surface of the oxide layer may be performed after step S11.

[0154] Next, the first bonding film and the second bonding film are bonded (S20). In step S20, the acoustic wave device may be placed in a vacuum atmosphere. After step S20, the second main surface of the piezoelectric substrate may be thinned. In at least one of step S20 and the step of thinning the piezoelectric substrate, the acoustic wave device may be heated at a temperature equal to or lower than the Curie point of the piezoelectric substrate. This can increase the bonding strength between the first bonding film and the second bonding film while suppressing characteristic degradation. Furthermore, oxidation of the first bonding film and the second bonding film can be stabilized, resulting in stable productivity.

[0155] The process of thinning the piezoelectric substrate can be performed by polishing such as CMP, milling using argon ions, or chemical polishing such as RIE. Alternatively, ions may be implanted into the piezoelectric substrate to a predetermined depth in advance, and the surface layer of the piezoelectric substrate may be peeled off using the ion implantation layer after step S20.

[0156] Finally, the IDT electrode 10 is formed on the second main surface of the piezoelectric substrate (S30). After step S30, a protective film may be formed on the surface of the IDT electrode 10, and wiring may be formed to connect the IDT electrode 10 to an external circuit.

[0157] According to the above manufacturing method, the bonding layer formed by bonding the first bonding film and the second bonding film contains a metal element with low electronegativity, and therefore becomes an oxide layer with low conductivity. As a result, even if the thickness of the silicon oxide layer 32 is reduced, the main mode resonance characteristics of the acoustic wave device 1 are not deteriorated. Therefore, it is possible to manufacture an acoustic wave device 1 in which deterioration of the main mode resonance characteristics is suppressed.

[0158] The thickness of the bonding layer formed by bonding the first and second bonding films is preferably greater than 0 nm and less than 100 nm, which makes it possible to manufacture an acoustic wave device in which the deterioration of resonance characteristics at high and low temperatures is suppressed and excitation signals of higher modes are suppressed.

[0159] Furthermore, it is more desirable that the thickness of the bonding layer formed by bonding the first bonding film and the second bonding film is less than 20 nm, which makes it possible to manufacture an acoustic wave device in which damage and cracking of the support substrate 35 are suppressed.

[0160] 13 Resonance Characteristics of Acoustic Wave Devices According to Examples 15 to 18 Table 7 shows the structural parameters of the acoustic wave devices according to Examples 15 to 18.

[0161]

[0162] The acoustic wave devices according to Examples 15 to 18 are stacked in this order: a support substrate 35, a silicon nitride layer 34, a silicon oxide layer 322, a bonding layer 33, a silicon oxide layer 321, and a piezoelectric layer 31. The acoustic wave devices according to Examples 15 and 16 are fabricated using the method for manufacturing the acoustic wave device 1 according to the embodiment, with the first and second bonding films made of only yttrium (Y). The thicknesses of the silicon oxide layers 321 differ between Examples 15 and 16. The acoustic wave devices according to Examples 17 and 18 are fabricated using the method for manufacturing the acoustic wave device 1 according to the embodiment, with the first and second bonding films made of only scandium (Sc). The thicknesses of the silicon oxide layers 321 differ between Examples 17 and 18.

[0163] 20A is a graph showing the frequency characteristics of the phase of the acoustic wave devices according to Examples 15 and 16. FIG. 20B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave devices according to Examples 15 and 16. FIG. 21A is a graph showing the frequency characteristics of the phase of the acoustic wave devices according to Examples 17 and 18. FIG. 21B is a graph showing the frequency characteristics of the Q value of the main mode of the acoustic wave devices according to Examples 17 and 18.

[0164] As shown in FIGS. 20B and 21B, in the acoustic wave devices according to Examples 15 to 18, by using yttrium (Y) or scandium (Sc), which have low electronegativity, as the bonding film, it is possible to suppress deterioration of the Q value of the main mode regardless of the film thickness of the silicon oxide layer.

[0165] Furthermore, the metals yttrium (Y) and scandium (Sc) can be deposited by vapor deposition and DC sputtering, which is advantageous in terms of particle suppression during the manufacturing process. Furthermore, since they are elemental metals and not compounds, the composition can be easily adjusted during film deposition, simplifying the manufacturing process.

[0166] 20A and 21A , in the acoustic wave devices according to Examples 16 and 18, the phase (maximum value) of the higher-order mode is reduced by thinning the silicon oxide layer 321. That is, in the acoustic wave devices according to Examples 16 and 18, the reduction in the thickness of the silicon oxide layer 321 can both suppress deterioration of the Q value in the main mode and reduce spurious responses in the higher-order mode.

[0167] [14 Effects, etc.] As described above, the acoustic wave device 1 according to the embodiment includes a piezoelectric layer 31 having principal surfaces 31 a and 31 b facing each other, a functional electrode disposed on at least one of the principal surfaces 31 a and 31 b of the piezoelectric layer 31, a support substrate 35 disposed on the principal surface 31 b of the piezoelectric layer 31, a dielectric layer disposed between the piezoelectric layer 31 and the support substrate 35, and a bonding layer 33 disposed between the piezoelectric layer 31 and the support substrate 35, wherein the bonding layer 33 contains a first metal element and oxygen, the thickness of the bonding layer 33 is greater than 0 nm and less than 100 nm, and the Pauling's electronegativity of the first metal element is 0.8 or more and 1.5 or less.

[0168] According to this, the bonding layer 33 containing the first metal element with low electronegativity becomes an oxide layer with low conductivity without leaving any conductive layer. As a result, even if the thickness of the dielectric layer is reduced, the main mode resonance characteristics of the acoustic wave device 1 do not deteriorate. Therefore, it is possible to provide an acoustic wave device 1 in which deterioration of the main mode resonance characteristics is suppressed. Furthermore, because the thickness of the bonding layer 33 is less than 100 nm, it is possible to suppress deterioration of the resonance characteristics at high and low temperatures and suppress spurious responses in higher modes.

[0169] Furthermore, for example, in the acoustic wave device 1, the thickness of the bonding layer 33 is less than 20 nm.

[0170] This can prevent warping of the wafer on which the acoustic wave devices 1 are collectively formed, and can prevent damage and cracking of the support substrate 35 (wafer).

[0171] Furthermore, for example, in the acoustic wave device 1, the Pauling electronegativity of the first metal element is not less than 0.8 and not more than 1.3.

[0172] This can further reduce the conductivity of the bonding layer 33. Therefore, it is possible to provide an acoustic wave device 1 in which the deterioration of the main mode resonance characteristics is further suppressed.

[0173] Furthermore, the acoustic wave device 1 according to the embodiment includes a piezoelectric layer 31 having opposing principal surfaces 31a and 31b, a functional electrode arranged on at least one of the principal surface 31a side and the principal surface 31b side of the piezoelectric layer 31, a support substrate 35 arranged on the principal surface 31b side of the piezoelectric layer 31, a dielectric layer arranged between the piezoelectric layer 31 and the support substrate 35, and a bonding layer 33 arranged between the piezoelectric layer 31 and the support substrate 35, wherein the bonding layer 33 contains a first metal element and oxygen, and the first metal element is any one of yttrium (Y), scandium (Sc), and zirconium (Zr).

[0174] According to this, the bonding layer 33 containing the first metal element, which is one of yttrium, scandium, and zirconium, each having low electronegativity, becomes an oxide layer with low conductivity without leaving any conductive layer. As a result, even if the thickness of the dielectric layer is reduced, the main mode resonance characteristics of the acoustic wave device 1 do not deteriorate. Therefore, it is possible to provide an acoustic wave device 1 in which deterioration of the main mode resonance characteristics is suppressed.

[0175] Furthermore, for example, in the acoustic wave device 1, the first metal element is yttrium (Y).

[0176] According to this, yttrium has the lowest electronegativity among yttrium, scandium, and zirconium, and therefore can further reduce the conductivity of bonding layer 33. Therefore, it is possible to provide acoustic wave device 1 in which deterioration of the main mode resonance characteristics is further suppressed.

[0177] Furthermore, for example, in the acoustic wave device 1, only one bonding layer 33 is disposed between the piezoelectric layer 31 and the support substrate 35.

[0178] This can suppress the generation of unwanted waves in the acoustic wave device 1.

[0179] For example, in the acoustic wave device 1, the bonding layer 33 has opposing interfaces 33a and 33b, and includes a first region including the interface 33a, a second region including the interface 33b, and a third region sandwiched between the first and second regions, and the content of the first metal element in the third region is higher than the content of the first metal element in the first region and the content of the first metal element in the second region.

[0180] Furthermore, for example, in the acoustic wave device 1, the dielectric layer includes a silicon oxide layer 32 containing at least one of silicon oxide and silicon oxynitride.

[0181] This allows the dielectric layer to function as a low acoustic velocity layer and also promotes oxidation of the bonding layer 33 during the manufacturing process.

[0182] Furthermore, for example, in the acoustic wave device 1, the functional electrode includes a plurality of electrode fingers 11 a and a plurality of electrode fingers 11 b arranged parallel to each other, a busbar electrode 12 a configured to connect one ends of the plurality of electrode fingers 11 a to each other, and a busbar electrode 12 b configured to connect one ends of the plurality of electrode fingers 11 b to each other and arranged opposite the busbar electrode 12 a across the plurality of electrode fingers 11 a and the plurality of electrode fingers 11 b, and when the repeating period of the plurality of electrode fingers 11 a is wavelength λ, the film thickness of the silicon oxide layer 32 is 0.125 × λ or less.

[0183] This makes it possible to suppress spurious responses in higher modes without deteriorating the resonance characteristics of the main mode.

[0184] Furthermore, for example, in the acoustic wave device 1, the silicon oxide layer 32 contains silicon oxide, and the film thickness of the silicon oxide layer 32 is 250 nm or less.

[0185] This makes it possible to suppress spurious responses in higher modes without deteriorating the resonance characteristics of the main mode.

[0186] Furthermore, for example, in the acoustic wave device 1 , the bonding layer 33 is disposed between the piezoelectric layer 31 and the silicon oxide layer 32 .

[0187] This minimizes the distance from the piezoelectric layer 31 to the bonding layer 33, making it possible to improve the Q value of the main mode.

[0188] For example, in the acoustic wave device 1, the dielectric layer further includes a silicon nitride layer 34 disposed between the silicon oxide layer 32 and the support substrate 35 and containing at least one of silicon nitride, silicon oxynitride, amorphous silicon, polysilicon, aluminum oxide, and aluminum nitride.

[0189] According to this, since the dielectric layer includes a low acoustic velocity layer and a high acoustic velocity layer, it is possible to suppress the acoustic waves from leaking to the support substrate 35 side.

[0190] Furthermore, for example, in the acoustic wave device 1, the dielectric layer does not include a silicon oxide layer containing at least one of silicon oxide and silicon oxynitride, but includes a silicon nitride layer 34 containing silicon nitride.

[0191] In this configuration, the silicon oxide layer 32 is not disposed between the piezoelectric layer 31 and the support substrate 35, but the bonding layer 33 and the silicon nitride layer 34 are disposed instead. Even in this configuration, the bonding layer 33 does not remain as a conductive layer and becomes an oxide layer with low conductivity, so that the main mode resonance characteristics of the acoustic wave device 1 do not deteriorate even if the thickness of the dielectric layer is reduced. Therefore, it is possible to provide an acoustic wave device 1 in which deterioration of the main mode resonance characteristics is suppressed.

[0192] In the acoustic wave device 1 , the bulk wave acoustic velocity of the silicon oxide layer 32 is lower than that of the piezoelectric layer 31 and the support substrate 35 , and the bulk wave acoustic velocity of the silicon nitride layer 34 is higher than that of the silicon oxide layer 32 .

[0193] In this case, the silicon oxide layer 32 can function as a low acoustic velocity layer, and the silicon nitride layer 34 can function as a high acoustic velocity layer.

[0194] Furthermore, for example, in the acoustic wave device 1, the piezoelectric layer 31 includes either lithium tantalate or lithium niobate.

[0195] For example, in the acoustic wave device 4 according to variant example 13, the piezoelectric layer 31A has a structure in which a piezoelectric film 311, a bonding layer 36, and a piezoelectric film 312 are stacked in this order, the bonding layer 36 contains a second metal element and oxygen, and the Pauling electronegativity of the second metal element is 0.8 or more and 1.5 or less.

[0196] By bonding the two piezoelectric films 311 and 312 via the bonding layer 36, it is possible to adjust the relative bandwidth, which cannot be achieved with a single piezoelectric substrate, without causing significant deterioration in characteristics or reduction in capacity.

[0197] Furthermore, for example, in the acoustic wave device 4, the second metal element is any one of yttrium, scandium, and zirconium.

[0198] According to this, bonding layer 36 containing the second metal element, which is any one of yttrium, scandium, and zirconium, which have low electronegativity, becomes an oxide layer with low conductivity without leaving a conductive layer, thereby achieving good bonding between piezoelectric film 311 and piezoelectric film 312. Therefore, it is possible to provide acoustic wave device 4 in which deterioration of the resonance characteristics of the main mode is suppressed.

[0199] Furthermore, a manufacturing method of acoustic wave device 1 according to the embodiment includes the steps of: forming an oxide layer on at least one of a first main surface side of a piezoelectric substrate having first and second main surfaces opposing each other and a third main surface side of support substrate 35 having third and fourth main surfaces opposing each other; forming a first bonding film made of a metal element having a Pauling electronegativity of 0.8 or more and 1.5 or less on the first main surface side of the piezoelectric substrate after the oxide layer forming step; forming a second bonding film made of a metal element having a Pauling electronegativity of 0.8 or more and 1.5 or less on the third main surface side of support substrate 35 after the oxide layer forming step; bonding the first bonding film and the second bonding film together after the first bonding film forming step and the second bonding film forming step; and forming a functional electrode on the second main surface side of the piezoelectric substrate after the first bonding film forming step.

[0200] According to this, the bonding layer 33 formed by bonding the first bonding film and the second bonding film contains a metal element with low electronegativity, and therefore becomes an oxide layer with low conductivity. As a result, even if the thickness of the silicon oxide layer 32 (oxide layer) is reduced, the main mode resonance characteristics of the acoustic wave device 1 are not deteriorated. Therefore, it is possible to manufacture an acoustic wave device 1 in which deterioration of the main mode resonance characteristics is suppressed.

[0201] Furthermore, a manufacturing method of an acoustic wave device according to Variation 14 includes the steps of: forming a first bonding film containing a metal element and oxygen on a first main surface side of a piezoelectric substrate having first and second main surfaces facing each other; forming a second bonding film containing a metal element and oxygen on a third main surface side of a support substrate having third and fourth main surfaces facing each other; bonding the first bonding film and the second bonding film together after the steps of forming the first bonding film and the second bonding film; and forming a functional electrode on the second main surface side of the piezoelectric substrate after the step of bonding the first bonding film and the second bonding film.

[0202] According to this, the bonding layer 33 formed by bonding the first bonding film and the second bonding film contains a metal element with low electronegativity, and therefore becomes an oxide layer with low conductivity. As a result, even if the distance between the piezoelectric layer 31 and the bonding layer 33 is reduced, the main mode resonance characteristics of the acoustic wave device are not deteriorated. Therefore, it is possible to manufacture an acoustic wave device in which deterioration of the main mode resonance characteristics is suppressed.

[0203] Furthermore, for example, the manufacturing method of the acoustic wave device 1 further includes, between the step of bonding the first bonding film and the second bonding film and the step of forming the functional electrode, a step of heating the piezoelectric substrate, the support substrate 35, the first bonding film, and the second bonding film at a temperature equal to or lower than the Curie point of the piezoelectric substrate.

[0204] This can increase the bonding strength of the first and second bonding films, and can stabilize the oxidation of the first and second bonding films, thereby stabilizing productivity.

[0205] While the acoustic wave device and the method for manufacturing the acoustic wave device 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 embodiments, examples, and modifications. The present invention also includes other embodiments realized by combining any of the components in the above embodiments, examples, and modifications, as well as modifications obtained by applying various modifications to the above embodiments, examples, and modifications that would occur to a person skilled in the art without departing from the spirit of the present invention.

[0206] The features of the acoustic wave device and the method for manufacturing the acoustic wave device described based on the above-described embodiment, example, and modified example will be described below.

[0207] <1> An acoustic wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposing each other; a functional electrode disposed on at least one of the first principal surface side and the second principal surface side of the piezoelectric layer; a support substrate disposed on the second principal surface side of the piezoelectric layer; a dielectric layer disposed between the piezoelectric layer and the support substrate; and a first bonding layer disposed between the piezoelectric layer and the support substrate, wherein the first bonding layer contains a first metal element and oxygen, a thickness of the first bonding layer is greater than 0 nm and less than 100 nm, and an electronegativity of the first metal element is 0.8 or more and 1.5 or less.

[0208] <2> The acoustic wave device according to <1>, wherein the first bonding layer has a thickness of less than 20 nm.

[0209] <3> The acoustic wave device according to <1> or <2>, wherein the first metal element has an electronegativity of 0.8 or more and 1.3 or less.

[0210] <4> An acoustic wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposing each other; a functional electrode disposed on at least one of the first principal surface side and the second principal surface side of the piezoelectric layer; a support substrate disposed on the second principal surface side of the piezoelectric layer; a dielectric layer disposed between the piezoelectric layer and the support substrate; and a first bonding layer disposed between the piezoelectric layer and the support substrate, wherein the first bonding layer contains a first metal element and oxygen, and the first metal element is any one of yttrium, scandium, and zirconium.

[0211] <5> The acoustic wave device according to <4>, wherein the first metal element is yttrium.

[0212] <6> The acoustic wave device according to any one of <1> to <5>, wherein the first bonding layer is a single layer disposed between the piezoelectric layer and the support substrate.

[0213] <7> The acoustic wave device according to any one of <1> to <6>, wherein the first bonding layer has a first interface and a second interface facing each other, and includes a first region including the first interface, a second region including the second interface, and a third region sandwiched between the first region and the second region, and a content of the first metal element in the third region is higher than a content of the first metal element in the first region and a content of the first metal element in the second region.

[0214] <8> The acoustic wave device according to any one of <1> to <7>, wherein the dielectric layer includes a first dielectric film containing at least one of silicon oxide and silicon oxynitride.

[0215] <9> The acoustic wave device according to <8>, wherein the functional electrode includes: 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 plurality of first electrode fingers together; and a second bus bar electrode configured to connect one ends of the plurality of second electrode fingers together and arranged to face the first bus bar electrode with the plurality of first electrode fingers and the plurality of second electrode fingers interposed therebetween; and wherein, when a repetition period of the plurality of first electrode fingers is a wavelength λ, a film thickness of the first dielectric film is 0.125×λ or less.

[0216] <10> The acoustic wave device according to <8>, wherein the first dielectric film contains silicon oxide, and the thickness of the first dielectric film is 250 nm or less.

[0217] <11> The acoustic wave device according to any one of <8> to <10>, wherein the first bonding layer is disposed between the piezoelectric layer and the first dielectric film.

[0218] <12> The acoustic wave device according to any one of <8> to <11>, wherein the dielectric layer further includes a second dielectric film disposed between the first dielectric film and the support substrate and including at least one of silicon nitride, silicon oxynitride, amorphous silicon, polysilicon, aluminum oxide, and aluminum nitride.

[0219] <13> The acoustic wave device according to any one of <1> to <7>, wherein the dielectric layer does not include a first dielectric film containing at least one of silicon oxide and silicon oxynitride, but includes a second dielectric film containing silicon nitride.

[0220] <14> The acoustic wave device according to <12>, wherein a bulk wave acoustic velocity of the first dielectric film is lower than a bulk wave acoustic velocity of the piezoelectric layer and the support substrate, and a bulk wave acoustic velocity of the second dielectric film is higher than a bulk wave acoustic velocity of the first dielectric film.

[0221] <15> The acoustic wave device according to any one of <1> to <14>, wherein the piezoelectric layer contains either lithium tantalate or lithium niobate.

[0222] <16> The acoustic wave device according to any one of <1> to <15>, wherein the piezoelectric layer has a configuration in which a first piezoelectric film, a second bonding layer, and a second piezoelectric film are laminated in this order, the second bonding layer contains a second metal element and oxygen, and the electronegativity of the second metal element is 0.8 or more and 1.5 or less.

[0223] <17> The acoustic wave device according to <16>, wherein the second metal element is any one of yttrium, scandium, and zirconium.

[0224] <18> A method for manufacturing an acoustic wave device, the method comprising: forming an oxide layer on at least one of a first main surface side of a piezoelectric substrate, the first main surface side having first and second main surfaces opposing each other, and a third main surface side of a support substrate, the third main surface side having third and fourth main surfaces opposing each other; forming a first bonding film made of a metal element having an electronegativity of 0.8 or more and 1.5 or less on the first main surface side of the piezoelectric substrate after the oxide layer forming step; forming a second bonding film made of a metal element having an electronegativity of 0.8 or more and 1.5 or less on the third main surface side of the support substrate after the oxide layer forming step; bonding the first bonding film and the second bonding film together after the first bonding film forming step and the second bonding film forming step; and forming a functional electrode on the second main surface side of the piezoelectric substrate after the first bonding film forming step.

[0225] <19> A method for manufacturing an acoustic wave device, comprising: forming a first bonding film containing a metal element and oxygen on a first main surface side of a piezoelectric substrate having first and second main surfaces opposing each other; forming a second bonding film containing a metal element and oxygen on a third main surface side of a support substrate having third and fourth main surfaces opposing each other; bonding the first bonding film and the second bonding film together after the steps of forming the first bonding film and the second bonding film; and forming a functional electrode on the second main surface side of the piezoelectric substrate after the steps of bonding the first bonding film and the second bonding film.

[0226] <20> The method for manufacturing an acoustic wave device according to <18> or <19>, further comprising the step of heating the piezoelectric substrate, the support substrate, the first bonding film, and the second bonding film at a temperature equal to or lower than the Curie point of the piezoelectric substrate, between the step of bonding the first bonding film and the second bonding film and the step of forming the functional electrode.

[0227] The present invention can be widely used as an acoustic wave device disposed in a front end portion of communication devices such as mobile phones.

[0228] 1, 2, 3, 4 Acoustic wave device 10, 40 IDT electrode 11a, 11b, 41a, 41b Electrode finger 12a, 12b, 42a, 42b Bus bar electrode 20 Reflecting electrode 30, 30A Substrate 31, 31A Piezoelectric layer 31a, 31b Main surface 32, 321, 322 Silicon oxide layer 33, 36 Bonding layer 33a, 33b Interface 34, 341, 342 Silicon nitride layer 35 Support substrate 311, 312 Piezoelectric film

Claims

1. An acoustic wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposing each other; a functional electrode disposed on at least one of the first principal surface side and the second principal surface side of the piezoelectric layer; a support substrate disposed on the second principal surface side of the piezoelectric layer; a dielectric layer disposed between the piezoelectric layer and the support substrate; and a first bonding layer disposed between the piezoelectric layer and the support substrate, wherein the first bonding layer contains a first metal element and oxygen, the thickness of the first bonding layer is greater than 0 nm and less than 100 nm, and the electronegativity of the first metal element is 0.8 or more and 1.5 or less.

2. The acoustic wave device according to claim 1, wherein the first bonding layer has a thickness of less than 20 nm.

3. The acoustic wave device according to claim 1 or 2, wherein the electronegativity of the first metal element is 0.8 or more and 1.3 or less.

4. An acoustic wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposing each other; a functional electrode disposed on at least one of the first principal surface side and the second principal surface side of the piezoelectric layer; a support substrate disposed on the second principal surface side of the piezoelectric layer; a dielectric layer disposed between the piezoelectric layer and the support substrate; and a first bonding layer disposed between the piezoelectric layer and the support substrate, wherein the first bonding layer contains a first metal element and oxygen, and the first metal element is one of yttrium, scandium, and zirconium.

5. The acoustic wave device according to claim 4, wherein the first metal element is yttrium.

6. The acoustic wave device according to any one of claims 1 to 5, wherein only one first bonding layer is disposed between the piezoelectric layer and the support substrate.

7. The acoustic wave device according to any one of claims 1 to 6, wherein the first bonding layer has a first interface and a second interface facing each other, and includes a first region including the first interface, a second region including the second interface, and a third region sandwiched between the first region and the second region, and the content of the first metal element in the third region is higher than the content of the first metal element in the first region and the content of the first metal element in the second region.

8. The acoustic wave device according to claim 1, wherein the dielectric layer includes a first dielectric film containing at least one of silicon oxide and silicon oxynitride.

9. The acoustic wave device according to claim 8, wherein the functional electrode includes: 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 plurality of first electrode fingers together; and a second bus bar electrode configured to connect one ends of the plurality of second electrode fingers together and arranged opposite the first bus bar electrode with the plurality of first electrode fingers and the plurality of second electrode fingers in between; and wherein, when the repeating period of the plurality of first electrode fingers is wavelength λ, the film thickness of the first dielectric film is 0.125 × λ or less.

10. The acoustic wave device according to claim 8, wherein the first dielectric film contains silicon oxide, and the film thickness of the first dielectric film is 250 nm or less.

11. The acoustic wave device according to any one of claims 8 to 10, wherein the first bonding layer is disposed between the piezoelectric layer and the first dielectric film.

12. The acoustic wave device according to any one of claims 8 to 11, wherein the dielectric layer further includes a second dielectric film disposed between the first dielectric film and the support substrate and including at least one of silicon nitride, silicon oxynitride, amorphous silicon, polysilicon, aluminum oxide, and aluminum nitride.

13. The acoustic wave device according to any one of claims 1 to 7, wherein the dielectric layer does not include a first dielectric film containing at least one of silicon oxide and silicon oxynitride, but includes a second dielectric film containing silicon nitride.

14. The acoustic wave device according to claim 12, wherein the bulk wave velocity of the first dielectric film is lower than the bulk wave velocity of the piezoelectric layer and the support substrate, and the bulk wave velocity of the second dielectric film is higher than the bulk wave velocity of the first dielectric film.

15. The acoustic wave device according to any one of claims 1 to 14, wherein the piezoelectric layer contains either lithium tantalate or lithium niobate.

16. The acoustic wave device according to any one of claims 1 to 15, wherein the piezoelectric layer has a configuration in which a first piezoelectric film, a second bonding layer, and a second piezoelectric film are laminated in this order, the second bonding layer contains a second metal element and oxygen, and the electronegativity of the second metal element is 0.8 or more and 1.5 or less.

17. The acoustic wave device according to claim 16, wherein the second metal element is any one of yttrium, scandium, and zirconium.

18. A method for manufacturing an acoustic wave device, comprising: forming an oxide layer on at least one of a first main surface side of a piezoelectric substrate having first and second main surfaces opposing each other and a third main surface side of a support substrate having third and fourth main surfaces opposing each other; after the oxide layer forming step, forming a first bonding film made of a metal element having an electronegativity of 0.8 or more and 1.5 or less on the first main surface side of the piezoelectric substrate; after the oxide layer forming step, forming a second bonding film made of a metal element having an electronegativity of 0.8 or more and 1.5 or less on the third main surface side of the support substrate; after the first bonding film forming step and the second bonding film forming step, bonding the first bonding film and the second bonding film together; and after the bonding the first bonding film and the second bonding film, forming a functional electrode on the second main surface side of the piezoelectric substrate.

19. A method for manufacturing an acoustic wave device, comprising: forming a first bonding film containing a metal element and oxygen on a first main surface side of a piezoelectric substrate having first and second main surfaces opposing each other; forming a second bonding film containing a metal element and oxygen on a third main surface side of a support substrate having third and fourth main surfaces opposing each other; bonding the first bonding film and the second bonding film together after the steps of forming the first bonding film and the second bonding film; and forming a functional electrode on the second main surface side of the piezoelectric substrate after the step of bonding the first bonding film and the second bonding film.

20. The method for manufacturing an acoustic wave device according to claim 18 or 19, further comprising a step of heating the piezoelectric substrate, the support substrate, the first bonding film, and the second bonding film at a temperature equal to or lower than the Curie point of the piezoelectric substrate between the step of bonding the first bonding film and the second bonding film and the step of forming the functional electrode.

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