Acoustic wave device, filter, multiplexer, and method of manufacturing acoustic wave device

Abstract

The invention discloses an acoustic wave device, a filter, a multiplexer, and a method of manufacturing the acoustic wave device. An acoustic wave device includes: a piezoelectric layer disposed such that a portion of the piezoelectric layer is between a lower electrode and an upper electrode and having a through hole along a resonance region; an insertion film provided between the lower electrode and the piezoelectric layer and having a resistivity higher than those of the lower electrode and the upper electrode; a first film disposed on a side portion of the lower electrode; a second film disposed between a side surface of the upper electrode and the first film; and a third film disposed between a side surface of the upper electrode and the second film or between the first film and the second film, a concentration of the first element in the third film being higher than a concentration of the first element in the second film, and a concentration of the second element in the third film being lower than a concentration of the second element in the second film.

Description

Technical Field

[0001] Certain aspects of the present disclosure relate to an acoustic wave device, a filter, a multiplexer, and a method of manufacturing the acoustic wave device. Background Art

[0002] Filters and duplexers using piezoelectric thin film resonators are known as filters and duplexers for high-frequency circuits of radio terminals such as portable terminals. The piezoelectric thin film resonator is provided with a piezoelectric layer disposed on a substrate, and a lower electrode and an upper electrode disposed on the substrate, and the piezoelectric layer is disposed between the lower electrode and the upper electrode. The region where the lower electrode and the upper electrode face each other and the piezoelectric layer is disposed between them is a resonance region that excites acoustic waves. It is known to use a lithium niobate layer or a lithium tantalate layer as the piezoelectric layer (for example, Patent Document 1). It is known to suppress the leakage of acoustic waves by providing through holes along the resonance region in the piezoelectric layer (for example, Non-Patent Document 1).

[0003] [Prior art literature]

[0004] [Patent Document]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2008-42871

[0006] [Non-Patent Literature 1] Ting Wu et al., “Application of Free Side Edges to Thickness Shear Bulk Acoustic Resonator on Lithium Niobate for Suppression of Transverse Resonance,” Second Meeting Paper of the Acoustic Wave Device Technology Alliance, March 8, 2021. Summary of the invention

[0007] Technical issues

[0008] When the piezoelectric layer is etched to form a through hole along the resonance region, a portion of the lower electrode may be etched. In this case, the material removed by etching the piezoelectric layer and the lower electrode may adhere to the side surface of the upper electrode. When the etched material of the lower electrode adheres to the side surface of the upper electrode, the lower electrode and the upper electrode may be short-circuited through the adhesive film, and the device characteristics may deteriorate.

[0009] In view of the above circumstances, an object of the present disclosure is to suppress a short circuit between a lower electrode and an upper electrode.

[0010] Technical Solution

[0011] According to a first aspect of the embodiment, there is provided an acoustic wave device, comprising: a substrate; a lower electrode disposed above the substrate; an upper electrode disposed above the lower electrode; a piezoelectric layer disposed above the substrate, and at least a portion of the piezoelectric layer is interposed between the lower electrode and the upper electrode, the piezoelectric layer having a through hole along a resonance region in which the lower electrode and the upper electrode overlap each other in a plan view and the at least a portion of the piezoelectric layer is interposed between the lower electrode and the upper electrode, the through hole exposing at least a portion of the lower electrode; an insertion film disposed between one or both of the lower electrode and the piezoelectric layer and between the upper electrode and the piezoelectric layer, the insertion film having a resistivity higher than that of the lower electrode and the upper electrode; a first film in contact with a side surface of the lower electrode and extending upward from the side surface of the lower electrode to one side of the side surface of the upper electrode, the first film containing the a constituent element of a lower electrode; a second film which contacts the side surface of the piezoelectric layer and extends upward from the side surface of the piezoelectric layer to a region between the side surface of the upper electrode and the first film, the second film having a higher concentration of the constituent element of the piezoelectric layer than the first film; and a third film which contacts the side surface of the insertion film and extends upward from the side surface of the insertion film to extend to at least one of a region between the side surface of the upper electrode and the second film and a region between the first film and the second film, wherein a concentration of a first element in the third film is higher than a concentration of the first element in the second film, the first element being a constituent element of the insertion film and different from a constituent element of the piezoelectric layer, and a concentration of a second element in the third film is lower than a concentration of the second element in the second film, the second element being the constituent element of the piezoelectric layer and different from a constituent element of the insertion film.

[0012] In the above configuration, the second film and the third film may have a lower concentration of the constituent element of the lower electrode than the first film.

[0013] In the above configuration, the second film and the third film may not contain the constituent elements of the lower electrode.

[0014] In the above configuration, the first film can have a lower concentration of the constituent element of the insertion film than the third film.

[0015] In the above configuration, the insertion film may be an inorganic insulating film.

[0016] In the above configuration, the insertion film may be formed to contain at least one of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum oxide, zirconium oxide, silicon carbide, yttrium oxide, hafnium oxide, titanium oxide, and magnesium oxide.

[0017] In the above configuration, the piezoelectric layer may be a single-crystal lithium tantalate layer or a single-crystal lithium niobate layer.

[0018] In the above construction, the lower electrode and the upper electrode can excite thickness shear vibration in the piezoelectric layer in the resonance region, the two through holes can be arranged in a manner with the resonance region inserted between them, and the vibration direction of the thickness shear vibration can be a direction that intersects with the direction in which the two through holes face each other in a manner with the resonance region inserted between them.

[0019] In the above configuration, the maximum distance between the through hole and the piezoelectric layer in the resonance region may be 3.2 times or less of the thickness of the piezoelectric layer in the resonance region.

[0020] According to a second aspect of the embodiment, there is provided a filter including the above-mentioned acoustic wave device.

[0021] According to a third aspect of the embodiment, there is provided a multiplexer including the above-mentioned filter.

[0022] According to a fourth aspect of the embodiment, a method for manufacturing an acoustic wave device is provided, comprising: forming a lower electrode, a piezoelectric layer and an upper electrode in sequence on a substrate; forming an insertion film arranged on at least one region between the lower electrode and the piezoelectric layer and between the piezoelectric layer and the upper electrode, the insertion film having a resistivity higher than that of the lower electrode and the upper electrode; etching the piezoelectric layer, the insertion film and the lower electrode on a side portion of a resonance region where the lower electrode and the upper electrode overlap and the piezoelectric layer is interposed therebetween so as to form a through hole in the piezoelectric layer along the resonance region, so that a second film adhered by etching the piezoelectric layer is formed between a first film adhered by etching the lower electrode and a side surface of the upper electrode, and so that a third film adhered by etching the insertion film is formed on at least one of a region between the side surface of the upper electrode and the second film and a region between the first film and the second film.

[0023] In the above configuration, the piezoelectric layer, the insertion film, and the lower electrode may be etched by ion milling.

[0024] Technical Effects

[0025] According to the present disclosure, a short circuit between the lower electrode and the upper electrode can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a plan view of an acoustic wave device according to a first embodiment;

[0027] Figure 2A is along Figure 1 A cross-sectional view taken along line AA in FIG.

[0028] Figure 2B is along Figure 1A cross-sectional view taken along line BB in FIG.

[0029] Figure 3A and Figure 3B is a diagram illustrating the relationship between the crystal orientation of the piezoelectric layer and the vibration direction of thickness shear vibration when the piezoelectric layer is a lithium niobate layer or a lithium tantalate layer;

[0030] Figure 4 is a cross-sectional view of model A used in the simulation;

[0031] Figure 5 is the simulation result of ΔY relative to the distance between the through hole and the resonance area in model A;

[0032] FIG. 6A to FIG. 6C is a cross-sectional view (part 1) illustrating a method of manufacturing an acoustic wave device according to a first embodiment;

[0033] Fig. 7A and Figure 7B is a cross-sectional view (part 2) illustrating the method of manufacturing the acoustic wave device according to the first embodiment;

[0034] Figure 8 is a cross-sectional view near the through hole in the first embodiment;

[0035] Fig. 9A and Fig. 9B is a cross-sectional view (part 1) illustrating a step of forming a through hole in the first embodiment;

[0036] FIG. 10A to FIG. 10C is a cross-sectional view (part 2) illustrating a step of forming a through hole in the first embodiment;

[0037] Fig.11 is a diagram illustrating experimental results of component analysis in the first embodiment;

[0038] Fig.12 is a cross-sectional view near the through hole in the first modification of the first embodiment;

[0039] Fig.13 is a cross-sectional view near the through hole in the second modification of the first embodiment;

[0040] Fig.14 is a cross-sectional view near the through hole in the comparative example;

[0041] Fig.15 is a diagram illustrating experimental results of component analysis in a comparative example;

[0042] Fig.16A and Fig. 16B is a cross-sectional view of an acoustic wave device according to a second embodiment;

[0043] Fig.17 is a circuit diagram of a filter according to a third embodiment; and

[0044] Fig.18 is a circuit diagram of a duplexer according to a fourth embodiment. DETAILED DESCRIPTION

[0045] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0046] [First embodiment]

[0047] Figure 1 is a plan view of the acoustic wave device 100 according to the first embodiment. Figure 2A is along Figure 1 A cross-sectional view taken along line AA in FIG. Figure 2B is along Figure 1 A cross-sectional view taken along line BB in FIG. Figure 1 In FIG. 1 , the lower electrode 12, the piezoelectric layer 14 and the upper electrode 16 are mainly illustrated. For the sake of clarity, Figure 1 In FIG. 5 , the resonance region 50 is shaded, and the through hole 22 is represented by a line thicker than the lines of other parts, and Figure 2B , films formed on the side surfaces of the upper electrode 16 and the like are not illustrated. The normal direction of the piezoelectric layer 14 is defined as the Z direction, and directions orthogonal to each other in the plane direction of the piezoelectric layer 14 are defined as the X direction and the Y direction.

[0048] like Figure 1 , Figure 2A and Figure 2B As shown, the acoustic wave device 100 is a piezoelectric thin film resonator including a lower electrode 12, a piezoelectric layer 14 and an upper electrode 16. A sound reflecting film 30 is provided on the substrate 10, and a piezoelectric layer 14 is provided on the sound reflecting film 30. The upper surface and the lower surface of the piezoelectric layer 14 are flat surfaces. The upper electrode 16 and the lower electrode 12 are respectively provided above and below the piezoelectric layer 14. In a plan view, the region where the lower electrode 12 and the upper electrode 16 overlap in a manner in which at least a portion of the piezoelectric layer 14 is interposed between them is a resonance region 50. The planar shape of the resonance region 50 is, for example, roughly rectangular. The rectangle has four sides that are approximately straight lines. One pair of the four sides extends roughly in the Y direction, and the other pair of the four sides extends roughly in the X direction.

[0049] For example, the substrate 10 is a silicon substrate, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a crystal substrate, a glass substrate, a ceramic substrate, a GaAs substrate, etc. The piezoelectric layer 14 is, for example, a single crystal lithium niobate layer or a single crystal lithium tantalate layer. The thickness of the piezoelectric layer 14 is, for example, about 200nm to 1000nm. The lower electrode 12 and the upper electrode 16 are, for example, a single layer film of ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh) or iridium (Ir) or a laminated film thereof. The thickness of each of the lower electrode 12 and the upper electrode 16 is, for example, about 20nm to 150nm. The lower electrode 12 and the upper electrode 16 are formed by, for example, a metal element different from the constituent elements of the piezoelectric layer 14.

[0050] When high-frequency power is applied between the lower electrode 12 and the upper electrode 16, an acoustic wave is excited in the piezoelectric layer 14 in the resonance region 50. The wavelength λ of the acoustic wave is approximately twice the thickness of the piezoelectric layer 14. When the piezoelectric layer 14 is a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer, an acoustic wave is excited in the piezoelectric layer 14, wherein the displacement of the acoustic wave oscillates in a direction substantially perpendicular to the Z direction (i.e., the strain direction relative to the thickness). This vibration is called thickness shear vibration. The direction in which the displacement of the thickness shear vibration is the largest (i.e., the displacement direction of the thickness shear vibration) is defined as the vibration direction 60 of the thickness shear vibration. In this case, the vibration direction 60 of the thickness shear vibration is the Y direction. The lower electrode 12 and the upper electrode 16 are drawn out from the resonance region 50 in the Y direction which is the same as the vibration direction 60 of the thickness shear vibration.

[0051] The sound reflecting film 30 includes a film 32 with low acoustic impedance and a film 34 with high acoustic impedance. The film 32 with low acoustic impedance and the film 34 with high acoustic impedance are alternately arranged in the resonance region 50. For example, the thickness of the films 32 and 34 in the resonance region 50 is substantially λ / 4 (λ is the wavelength of the sound wave). Therefore, the sound reflecting film 30 reflects the sound wave. The number of layers of the films 32 and 34 can be freely set. The sound reflecting film 30 can be formed by laminating at least two layers with different acoustic properties and having a space between them. The substrate 10 can be formed by at least one of the two layers with different acoustic properties of the sound reflecting film 30. For example, the sound reflecting film 30 can be formed by arranging a single layer of films with different acoustic impedances in the substrate 10. In a plan view, the laminated portion of the film 32 and the film 34 overlaps the resonance region 50 and has the same size as the resonance region 50 or is larger than the resonance region 50. By making the laminated portion of the film 32 and the film 34 larger than the resonance region 50 in a plan view, the sound waves leaking from the resonance region 50 in an inclined direction can be reflected by the sound reflecting film 30, and the degradation of the characteristics can be suppressed. The film 32 having a low acoustic impedance is, for example, a silicon oxide (SiO2) film, and the film 34 having a high acoustic impedance is, for example, a tungsten (W) film.

[0052] In the resonance region 50, an insertion film 18 is provided between the lower electrode 12 and the piezoelectric layer 14. The insertion film 18 has the same size as the resonance region 50 or is larger than the resonance region 50 in a plan view. The insertion film 18 is a film having a volume resistivity higher than that of the lower electrode 12 and the upper electrode 16, and is, for example, a silicon oxide (SiO2) film. The thickness of the insertion film 18 is, for example, about 5 nm to 20 nm, and is, for example, 10% or less of the thickness of the piezoelectric layer 14. A protective film 20 is provided to cover the piezoelectric layer 14 and the upper electrode 16. The protective film 20 is an insulating film, and is, for example, a silicon oxide (SiO2) film, a silicon nitride (SiN) film, an aluminum oxide (Al2O3) film, or the like.

[0053] The piezoelectric layer 14 is formed with a pair of through holes 22 that sandwich the resonance region 50 in the X direction and extend along the resonance region 50 in the Y direction. The through holes 22 are dug to a portion of the lower electrode 12. The distance between one of the pair of through holes 22 and the piezoelectric layer 14 in the resonance region 50 is substantially the same as the distance between the other of the pair of through holes 22 and the piezoelectric layer 14 in the resonance region 50. For example, the through holes 22 have a substantially rectangular shape in a plan view. The through holes 22 prevent the acoustic waves excited in the resonance region 50 from leaking to the outside.

[0054] Here, the relationship between the crystal orientation of the piezoelectric layer 14 and the vibration direction 60 of the thickness shear vibration in the case where the piezoelectric layer 14 is a lithium niobate layer or a lithium tantalate layer will be described. First, the Euler angle In the right-handed XYZ coordinate system, the normal direction of the upper surface of the piezoelectric layer 14 is defined as the Z direction, and the directions orthogonal to the Z direction and to each other in the surface direction of the upper surface of the piezoelectric layer 14 are defined as the X direction and the Y direction. The X direction, the Y direction, and the Z direction are defined as the X-axis direction, the Y-axis direction, and the Z-axis direction of the crystal orientation, respectively. Next, the XYZ coordinate system is rotated around the Z direction from the +X direction to the +Y direction by an angle In Angle After the rotation, the XYZ coordinate system rotates from the +Y direction to the +Z direction by an angle θ around the X direction. After the rotation by angle θ, the XYZ coordinate system rotates from the +X direction to the +Y direction around the Z direction by an angle ψ. The Euler angle obtained by this rotation is defined as use The Euler angles expressed include the equivalent Euler angles.

[0055] Figure 3A and Figure 3B 3 is a diagram illustrating the relationship between the crystal orientation of the piezoelectric layer 14 and the vibration direction 60 of the thickness shear vibration when the piezoelectric layer 14 is a lithium niobate layer or a lithium tantalate layer. Figure 3A and Figure 3BThe dashed arrow on the left indicates the crystal axis orientation of the piezoelectric layer 14. The solid arrow on the right corresponds to Figure 1 , Figure 2A and Figure 2B The X, Y and Z directions in the Figure 3A As shown, the +X direction, the +Y direction, and the +Z direction are defined as the +X axis direction, the +Y axis direction, and the +Z axis direction of the crystal orientation of the piezoelectric layer 14, respectively. Figure 3B As shown, from Figure 3A Starting from the state, the +Y direction and the +Z direction rotate 105° from the +Y direction to the -Z direction around the X direction on the YZ plane. When the +Y direction and the +Z direction rotate in this way, the direction in which the +Z axis direction of the crystal orientation rotates 105° toward the +Y axis direction is the +Z direction. At this time, the Y direction is the vibration direction 60 of the thickness shear vibration. The Euler angles are (0°, -105°, 0°). When the Euler angles derived by the same method as above are (0°, -105°, 90°), the X direction is the vibration direction 60 of the thickness shear vibration. Each angle of the Euler angle is allowed to be within the range of ±5°, and more preferably within the range of ±1°.

[0056] [simulation]

[0057] Figure 4 is a cross-sectional view of model A used in the simulation. Figure 4 As shown, model A includes a sound reflecting film 30 on a substrate 10, and the sound reflecting film 30 includes a film 32 having a low acoustic impedance and a film 34 having a high acoustic impedance. The piezoelectric layer 14 is provided on the sound reflecting film 30. The lower electrode 12 and the upper electrode 16 are provided so as to sandwich the piezoelectric layer 14 between the lower electrode 12 and the upper electrode 16. Thus, a resonance region 50 is formed. A through hole 22 located on a side of the resonance region 50 is provided in the piezoelectric layer 14.

[0058] Model A was simulated for ΔY when the distance L between the through hole 22 and the resonance region 50 was changed. ΔY was calculated by obtaining the difference between the absolute value of admittance Y at the resonance frequency and the absolute value of admittance Y at the antiresonance frequency from the simulation results of the frequency characteristics of admittance Y. The simulation conditions were as follows.

[0059] Substrate 10: Silicon substrate

[0060] Film 32 with low acoustic impedance: Silicon oxide (SiO2) film with a thickness of 150 nm in the resonance region 50 Film 34 with high acoustic impedance: Tungsten (W) film with a thickness of 115 nm in the resonance region 50

[0061] Lower electrode 12: Aluminum (Al) film with a thickness of 44nm

[0062] Piezoelectric layer 14: single crystal lithium niobate (LiNbO3) layer with a thickness of 310nm

[0063] Upper electrode 16: Aluminum (Al) film with a thickness of 44 nm

[0064] Width W of through hole 22: 1.0 μm

[0065] Sound wave length: 620nm

[0066] Figure 5 The simulation results of ΔY with respect to the distance L between the through hole 22 and the resonance region 50 in the model A are shown as an example. Figure 5 As shown, as the distance L increases to a distance L of about 1000 nm, ΔY decreases. When the distance L exceeds 1000 nm, the decrease in ΔY is saturated, and ΔY is almost the same value and constant. From this result, from the perspective of suppressing the increase in device size while suppressing the deterioration of device characteristics, the through hole 22 is preferably formed at a position where the distance L from the resonance region 50 is 1.0 μm or less. In other words, the through hole 22 is preferably formed at a position where the distance L from the resonance region 50 is 1.6λ or less.

[0067] [Manufacturing method]

[0068] FIG. 6A to FIG. 7B is a cross-sectional view illustrating a method of manufacturing the acoustic wave device 100 according to the first embodiment. FIG. 6A to FIG. 7B is with Figure 1 The cross-sectional view of the portion corresponding to the line BB in FIG. Fig. 6A As shown, a piezoelectric substrate is prepared as the piezoelectric layer 14. An insertion film 18 and a lower electrode 12 are formed on the piezoelectric layer 14. The insertion film 18 and the lower electrode 12 are formed by, for example, a sputtering method, a vacuum evaporation method, or a CVD (chemical vapor deposition) method, and then they are patterned into a desired shape by, for example, a photolithography method and an etching method. The insertion film 18 and the lower electrode 12 may be formed by a lift-off method.

[0069] like Figure 6B As shown, a sound reflecting film 30 is formed on the piezoelectric layer 14 to cover the insertion film 18 and the lower electrode 12. The sound reflecting film 30 is formed by alternately forming a film 32 having a low acoustic impedance and a film 34 having a high acoustic impedance, and patterning the film 34 having a high acoustic impedance into a desired shape. The film 32 having a low acoustic impedance and the film 34 having a high acoustic impedance are formed by, for example, a sputtering method or a CVD method, and the film 32 having a low acoustic impedance and the film 34 having a high acoustic impedance are patterned by, for example, a photolithography method and an etching method. Then, the upper surface of the sound reflecting film 30 is flattened by, for example, a CMP (chemical mechanical polishing) method.

[0070] like Figure 6CAs shown, the sound reflecting membrane 30 is bonded to the substrate 10. For example, the bonding is performed using a surface activation method. A bonding layer such as a silicon film may be provided between the substrate 10 and the sound reflecting membrane 30. Next, the piezoelectric layer 14 is thinned to a desired thickness. For example, the membrane is thinned using a grinding method and / or a CMP method. For example, the piezoelectric layer 14 is made to have a substantially desired thickness by using a grinding method, and the upper surface is flattened by using a CMP method. This makes the upper surface of the piezoelectric layer 14 flat to the extent of manufacturing errors.

[0071] like Fig. 7A As shown, an upper electrode 16 and a protective film 20 are formed on the piezoelectric layer 14. The upper electrode 16 and the protective film 20 are formed by depositing a film using, for example, a sputtering method, a vacuum evaporation method, or a CVD method, and then patterning the film into a desired shape using, for example, a photolithography method and an etching method. The upper electrode 16 may be formed by a lift-off method. A resonance region 50 is formed in which the lower electrode 12 and the upper electrode 16 overlap in a plan view in such a manner that at least a portion of the piezoelectric layer 14 is interposed therebetween.

[0072] like Figure 7B As shown, the piezoelectric layer 14 on the side of the resonance region 50 is removed, and the through hole 22 along the resonance region 50 is formed in the piezoelectric layer 14. For example, the piezoelectric layer 14 is removed by photolithography and etching. For example, the piezoelectric layer 14 is removed by dry etching (for example, by ion milling using argon (Ar) gas). At this time, over-etching is performed so that the through hole 22 penetrating the piezoelectric layer 14 is ensured to be formed. Therefore, the insertion film 18 and the lower electrode 12 are also etched. The above process completes the formation of the acoustic wave device 100 according to the first embodiment.

[0073] [Near the through hole]

[0074] Figure 8 2 is a cross-sectional view of the vicinity of the through hole 22 in the first embodiment. Figure 8 As shown, a film 40 containing the material of the protective film 20 is formed on the side surface of the protective film 20. A film 41 containing the material of the upper electrode 16 is formed from the side surface of the upper electrode 16 to the side surface of the film 40. A film 42 containing the material of the piezoelectric layer 14 is formed from the side surface of the piezoelectric layer 14 to the side surface of the film 41. A film 43 containing the material of the insertion film 18 is formed from the side surface of the insertion film 18 to the side surface of the film 42. A film 44 containing the material of the lower electrode 12 is formed from the side surface of the lower electrode 12 to the side surface of the film 43. Since the films 40, 41, 42, 43 and 44 are adhesive films adhered when the through-hole 22 is formed, they do not take a regular crystal structure state, that is, they contain a large proportion of amorphous.

[0075] The maximum distance L between the through hole 22 and the piezoelectric layer 14 in the resonance region 50 is 1.0 μm or less. Figure 5 As shown, it is possible to suppress the increase in device size while suppressing the degradation of device characteristics. From the viewpoint of suppressing the degradation of device characteristics, the distance L is preferably 0.8 μm or less, more preferably 0.5 μm or less, and further preferably 0.2 μm or less.

[0076] The process of forming the thin films 40 , 41 , 42 , 43 , and 44 will be described with reference to the drawings. 9A to 10C 2 is a cross-sectional view illustrating a step of forming the through hole 22 in the first embodiment. Fig. 9A As shown, a mask layer 70 made of photoresist is formed on the upper electrode 16. The mask layer 70 is formed at a position inside the edge of the upper electrode 16.

[0077] like Fig. 9B As shown, the protective film 20 and the upper electrode 16 are etched using the mask layer 70 as a mask. Etching is performed by a dry etching method (e.g., an ion milling method using Ar gas). The material removed during etching of the protective film 20 adheres to the side surface of the protective film 20 and the side surface of the mask layer 70, and a film 40 containing the material of the protective film 20 is formed from the side surface of the protective film 20 to the side surface of the mask layer 70. The material removed during etching of the upper electrode 16 adheres to the side surface of the upper electrode 16 and the film 40, and a film 41 containing the material of the upper electrode 16 is formed from the side surface of the upper electrode 16 to the side surface of the film 40.

[0078] like Fig. 10A As shown, after etching the protective film 20 and the upper electrode 16, the piezoelectric layer 14 is etched using the mask layer 70 as a mask. As described above, etching is performed by a dry etching method (e.g., an ion milling method using Ar gas). The material removed during the etching of the piezoelectric layer 14 adheres to the side surface of the piezoelectric layer 14 and the side surface of the film 41, and a film 42 containing the material of the piezoelectric layer 14 is formed from the side surface of the piezoelectric layer 14 to the side surface of the film 41.

[0079] like Fig. 10B As shown, after etching the piezoelectric layer 14, the insertion film 18 is etched using the mask layer 70 as a mask. As described above, etching is performed by a dry etching method (e.g., an ion milling method using Ar gas). The material removed during etching of the insertion film 18 adheres to the side surface of the insertion film 18 and the side surface of the film 42, and a film 43 containing the material of the insertion film 18 is formed from the side surface of the insertion film 18 to the side surface of the film 42.

[0080] like Fig. 10CAs shown, after etching the insertion film 18, the lower electrode 12 is etched using the mask layer 70 as a mask. The reason for performing etching until the lower electrode 12 is that when the through hole 22 does not penetrate the piezoelectric layer 14, the device characteristics will deteriorate, so over-etching is performed so that the through hole 22 is ensured to penetrate the piezoelectric layer 14. As described above, etching is performed by a dry etching method (for example, an ion milling method using Ar gas). The material removed during etching the lower electrode 12 adheres to the side surface of the lower electrode 12 and the side surface of the film 43, and a film 44 containing the material of the lower electrode 12 is formed from the side surface of the lower electrode 12 to the side surface of the film 43.

[0081] [experiment]

[0082] In the first embodiment, the film 32 having low acoustic impedance, the lower electrode 12, the insertion film 18, the piezoelectric layer 14, the upper electrode 16, and the protective film 20 are formed of the following materials and have the following film thicknesses, and the through hole 22 is formed by an ion milling method using Ar gas. When the through hole 22 is formed, the lower electrode 12 is etched by about 22 nm by over-etching.

[0083] Film with low acoustic impedance 32: Silicon oxide film

[0084] Lower electrode 12: Aluminum film with a thickness of 44nm

[0085] Insertion film 18: 20 nm thick silicon oxide film

[0086] Piezoelectric layer 14: Lithium niobate layer with a thickness of 310 nm

[0087] Upper electrode 16: Aluminum film with a thickness of 44nm

[0088] Protective film 20: 20nm thick silicon oxide film

[0089] At this time, Figure 8 The composition analysis of the films 41, 42, 43, and 44 was performed at the position indicated by arrow A in FIG. The composition analysis was performed by energy dispersive X-ray spectroscopy (EDX).

[0090] Fig.11 FIG. 2 is a diagram illustrating the experimental results of component analysis in the first embodiment. Fig.11 In , the horizontal axis represents the distance from the side surface of the upper electrode 16 in the direction of arrow A when the position of the side surface of the upper electrode 16 is set to the origin 0, and the vertical axis represents the concentration. Table 1 illustrates the experimental results of the component analysis in the first embodiment.

[0091] [Table 1]

[0092]

[0093] Unit: atomic % Fig.11 As shown in Table 1, the film 41 contains aluminum (Al). It can be understood from this that the film 41 is formed by adhesion of the material removed during the etching of the upper electrode 16. Carbon (C) is considered to be carbon taken in by etching the mask layer 70 made of photoresist. Oxygen (O) is considered to be introduced from oxygen contained in the films 40 and 42 containing the material removed during the etching of the protective film 20 and the piezoelectric layer 14. Silicon (Si) is considered to be introduced from silicon contained in the film 40. Argon (Ar) is considered to be a gas used in the ion milling method. Niobium (Nb) is considered to be introduced from niobium contained in the film 42.

[0094] Film 42 does not contain aluminum, and has a niobium concentration higher than that of the other films 41, 43 and 44, and a silicon concentration lower than that of film 43. For example, the niobium concentration in film 42 is 1.3 times or more or 1.5 times the niobium concentration in film 44. It can be understood from this that film 42 is formed by adhesion of materials removed during etching of the piezoelectric layer 14. It is believed that the carbon is carbon absorbed by etching the mask layer 70. It is believed that the high oxygen concentration is because oxygen, which is a constituent element of the piezoelectric layer 14, is absorbed when the piezoelectric layer 14 is etched. It is believed that silicon is introduced from the silicon contained in film 43. Argon is believed to be a gas used in the ion milling method. The reason why film 42 is believed to contain lithium (Li), which is a constituent element of the piezoelectric layer 14, is that lithium is light and difficult to absorb.

[0095] The film 43 does not contain aluminum, and has a silicon concentration higher than that of the other films 41, 42, and 44, and a niobium concentration lower than that of the film 42. For example, the silicon concentration of the film 43 is 1.8 times or more and 2.0 times or more of the silicon concentration of the film 42. The niobium concentration in the film 43 is 0.8 times or less and 0.7 times or less of the niobium concentration in the film 42. It can be understood from this that the film 43 is formed by the adhesion of the material removed during the etching of the insertion film 18. The carbon is considered to be carbon absorbed by etching the mask layer 70. The high oxygen concentration is considered to be because oxygen, which is a constituent element of the insertion film 18, is absorbed when the insertion film 18 is etched. Argon is considered to be a gas used in the ion milling method. The niobium is considered to be introduced from the niobium contained in the film 42.

[0096] The film 44 contains aluminum. It can be understood from this that the film 44 is formed by adhesion of the material removed during etching of the lower electrode 12. Carbon is considered to be carbon taken in by etching the mask layer 70. Oxygen and silicon are considered to be taken in by etching the film 32 having low acoustic impedance, and oxygen contained in the film 43 is introduced. Argon is considered to be a gas used in the ion milling method. Niobium is considered to be introduced from niobium contained in the films 42 and 43.

[0097] For example, the thicknesses of the films 41, 42, 43, and 44 correspond to the etching amounts of the upper electrode 16, the piezoelectric layer 14, the insertion film 18, and the lower electrode 12. For example, when the piezoelectric layer 14 is thicker than the upper electrode 16, the insertion film 18, and the lower electrode 12, the film 42 is thicker than the films 41, 43, and 44. When the thickness of the upper electrode 16 is greater than the thickness of the insertion film 18 and the etching amount of the lower electrode 12, the film 41 is thicker than the films 43 and 44. When the thickness of the insertion film 18 and the etching amount of the lower electrode 12 are substantially the same as each other, the thicknesses of the films 43 and 44 are substantially the same as each other.

[0098] [Modifications]

[0099] Fig.12 2 is a cross-sectional view of the vicinity of the through hole 22 in the first modification of the first embodiment. Fig.12 As shown, in the acoustic wave device 110 according to the first modification of the first embodiment, in the resonance region 50, the insertion film 18 is not provided between the lower electrode 12 and the piezoelectric layer 14, but alternatively, an insertion film 18a is provided between the piezoelectric layer 14 and the upper electrode 16. In a plan view, the insertion film 18a has the same size as or larger than the resonance region 50. Therefore, a film 43a containing the material of the insertion film 18a is formed from the side surface of the insertion film 18a to the side surface of the film 41. A film 42 containing the material of the piezoelectric layer 14 is formed from the side surface of the piezoelectric layer 14 to the side surface of the film 43a. The other components of the first modification of the first embodiment are the same as those of the first embodiment, and thus descriptions thereof are omitted.

[0100] Fig.13 2 is a cross-sectional view of the vicinity of the through hole 22 in the second modification of the first embodiment. Fig.13 As shown, in the acoustic wave device 120 according to the second modification of the first embodiment, in addition to the insertion film 18 provided between the lower electrode 12 and the piezoelectric layer 14, an insertion film 18a is provided between the piezoelectric layer 14 and the upper electrode 16 in the resonance region 50. Therefore, a film 43a containing the material of the insertion film 18a is formed from the side surface of the insertion film 18a to the side surface of the film 41. A film 42 containing the material of the piezoelectric layer 14 is formed from the side surface of the piezoelectric layer 14 to the side surface of the film 43a. The other components of the second modification of the first embodiment are the same as those of the first embodiment, and thus descriptions thereof are omitted.

[0101] [Comparison example]

[0102] Fig.14 2 is a cross-sectional view near the through hole 22 in the comparative example. Fig.14As shown, in the acoustic wave device 500 according to the comparative example, the insertion film 18 is not provided between the lower electrode 12 and the piezoelectric layer 14. For this reason, a film 44 containing the material of the lower electrode 12 is formed from the side surface of the lower electrode 12 to the side surface of the film 42 in contact with the film 42 containing the material of the piezoelectric layer 14 formed from the side surface of the piezoelectric layer 14 to the side surface of the film 41. That is, the film 43 containing the material of the insertion film 18 is not formed between the film 42 and the film 44. The other components of the comparative example are the same as those of the first embodiment, and thus descriptions thereof are omitted.

[0103] [experiment]

[0104] In the comparative example, the film 32 having low acoustic impedance, the lower electrode 12, the piezoelectric layer 14, the upper electrode 16, and the protective film 20 were formed of the following materials and had the following film thicknesses, and the through hole 22 was formed by an ion milling method using Ar gas. When the through hole 22 was formed, the lower electrode 12 was etched by about 22 nm by over-etching.

[0105] Film with low acoustic impedance 32: Silicon oxide film

[0106] Lower electrode 12: Aluminum film with a thickness of 44nm

[0107] Piezoelectric layer 14: Lithium niobate layer with a thickness of 310 nm

[0108] Upper electrode 16: Aluminum film with a thickness of 44nm

[0109] Protective film 20: 20nm thick silicon oxide film

[0110] At this time, Fig.14 Component analysis was performed on the films 41, 42, and 44 at the positions indicated by arrow A in FIG. Component analysis was performed by energy dispersive X-ray spectroscopy (EDX).

[0111] Fig.15 is a diagram illustrating the experimental results of component analysis in the control example. Fig.15 In FIG. 2 , the horizontal axis represents the distance from the side surface of the upper electrode 16 in the direction of arrow A when the position of the side surface of the upper electrode 16 is set as the origin 0, and the vertical axis represents the concentration. Table 2 illustrates the experimental results of the component analysis in the comparative example.

[0112] [Table 2]

[0113]

[0114] Unit: atomic % Fig.15As shown in Table 2, film 41 contains aluminum. It can be understood that film 41 is formed by adhesion of material removed during etching of upper electrode 16. Film 42 does not contain aluminum and has a niobium concentration higher than that of films 41 and 44. It can be understood that film 42 is formed by adhesion of material removed during etching of piezoelectric layer 14. Film 44 includes aluminum. It can be understood that film 44 is formed by adhesion of material removed during etching of lower electrode 12.

[0115] In the control example, Fig.14 As shown, the film 44 is arranged to be in contact with the film 42. Since the film 41 is formed by the adhesion of the material removed during the etching of the upper electrode 16, the film 41 has conductivity. Since the film 44 is formed by the adhesion of the material removed during the etching of the lower electrode 12, the film 44 has conductivity. Although the film 42 is formed by the adhesion of the material removed during the etching of the piezoelectric layer 14, the film 42 has low insulation performance because the film 42 is amorphous and the film quality is poor. Therefore, the film 41 and the film 44 are electrically connected at the thin part of the film 42, and the lower electrode 12 and the upper electrode 16 can be short-circuited through the films 41, 42 and 44. The short circuit deteriorates the device characteristics. Although the insulation performance increases as the thickness of the film 42 increases, it is difficult to increase the thickness of the film 42 because the film 42 corresponds to the thickness of the piezoelectric layer 14, and the thickness of the piezoelectric layer 14 is determined by the wavelength of the desired sound wave.

[0116] On the other hand, in the first embodiment and its variations, as Figure 8 , Fig.12 and Fig.13 As shown, at least one of the insertion films 18 and 18a having a resistivity higher than that of the lower electrode 12 and the upper electrode 16 is provided between at least one of the lower electrode 12 and the upper electrode 16 and the piezoelectric layer 14. For this purpose, at least one of the films 43 and 43a as a film to which the material removed during etching of the insertion films 18 and 18a adheres is formed on at least one region between the films 44 and 42 and between the side surface of the upper electrode 16 and the film 42. Since the film 44 (first film) is a film to which the material removed during etching of the lower electrode 12 adheres, the film 44 is connected to the lower electrode 12 and contains Al as a constituent element of the lower electrode 12, as shown in FIG. Fig.11and as shown in Table 1. Since film 42 (second film) is a film to which the material removed during the etching of the piezoelectric layer 14 adheres, the concentration of Nb as a constituent element of the piezoelectric layer 14 is higher than the concentration of Nb of film 44. Since films 43 and 43a (third film) are films to which the material removed during the etching of the insertion films 18 and 18a adheres, the concentration of Si as a constituent element of the insertion films 18 and 18a and not a constituent element of the piezoelectric layer 14 is higher than the concentration of Si of film 42, and the concentration of Nb as a constituent element of the piezoelectric layer 14 and not a constituent element of the insertion films 18 and 18a is lower than the concentration of Nb of film 42. Since the films 43 and 43a are films to which the material having a resistivity higher than that of the lower electrode 12 and the upper electrode 16, which is removed during the etching of the insertion films 18 and 18a, adheres, the films 43 and 43a have higher insulation properties than the film 41, which is a film to which the material removed during the etching of the upper electrode 16 adheres, and the film 44, which is a film to which the material removed during the etching of the lower electrode 12 adheres. Therefore, by providing at least one of the film 43 and the film 43a between the film 41 and the film 44, electrical connection between the film 41 and the film 44 is suppressed. Therefore, short circuit between the lower electrode 12 and the upper electrode 16 can be suppressed.

[0117] In the manufacturing method of the first embodiment and its variants, as Fig. 7A As shown, the lower electrode 12, the piezoelectric layer 14 and the upper electrode 16 are formed in this order on the substrate 10, and at least one of the insertion films 18 and 18a is formed on at least one region between the lower electrode 12 and the piezoelectric layer 14 and between the piezoelectric layer 14 and the upper electrode 16 (see also Fig.12 and Fig.13 ).like Figure 7B and 9A to 10C As shown, the piezoelectric layer 14, the insertion films 18 and 18a, and the lower electrode 12 on the side of the resonance region 50 are etched to form the through hole 22 in the piezoelectric layer 14. At this time, the film 42 (second film) adhered by etching the piezoelectric layer 14 is formed between the film 44 (first film) adhered by etching the lower electrode 12 and the side surface of the upper electrode 16, and at least one of the films 43 and 43a (third film) adhered by etching the insertion films 18 and 18a is formed on at least one region between the side surface of the upper electrode 16 and the film 42 and between the film 44 and the film 42 (see also Fig.12 and Fig.13 ). Therefore, at least one of the films 43 and 43a is provided between the film 41 and the film 44, so that the electrical connection between the film 41 and the film 44 is suppressed, and the short circuit between the lower electrode 12 and the upper electrode 16 can be suppressed.

[0118] In the first embodiment and its modifications, the piezoelectric layer 14, the insertion films 18 and 18a, and the lower electrode 12 are etched using the ion milling method. This makes it possible to form the through hole 22 in the piezoelectric layer 14 regardless of the type of the piezoelectric layer 14. When the ion milling method is used, the material removed during etching may adhere to the side surface of the upper electrode 16 to form an adhesion film. In this case, as in the comparative example, when the insertion films 18 and 18a are not provided, a short circuit may occur between the lower electrode 12 and the upper electrode 16. Therefore, when the ion milling method is used, it is preferable to form at least one of the insertion films 18 and 18a on at least one region between the lower electrode 12 and the piezoelectric layer 14 and between the piezoelectric layer 14 and the upper electrode 16.

[0119] In the first embodiment and its modifications, since the film 42 is a film to which the material removed during etching of the piezoelectric layer 14 adheres, the concentration of Al as a constituent element of the lower electrode 12 is lower than that of the film 44, and the film 42 does not contain Al, for example, Fig.11 and as shown in Table 1. Since the films 43 and 43a are films to which the material removed during the etching of the insertion films 18 and 18a adheres, the concentration of Al as a constituent element of the lower electrode 12 is lower than the concentration of Al of the film 44, and the films 43 and 43a do not contain Al, for example. This suppresses the electrical connection between the films 41 and 44, and it is possible to suppress the short circuit between the lower electrode 12 and the upper electrode 16. The Al concentration in the films 42 and 43 is preferably 0.1 times or less, more preferably 0.02 times or less, and even more preferably 0.01 times or less of the Al concentration in the film 44. Since the film 44 is a film to which the material removed during the etching of the lower electrode 12 adheres, the concentration of Si as a constituent element of the insertion films 18 and 18a is lower than the concentration of Si in the films 43 and 43a, for example, 0.9 times or less of the Si concentration in the films 43 and 43a.

[0120] In the first embodiment and its modification, the insertion films 18 and 18a are silicon oxide films which are oxides of Si. In this case, the insulating properties of the films 43 and 43a, which are films to which the material removed during etching of the insertion films 18 and 18a adheres, can be improved. Therefore, the electrical connection between the film 41 and the film 44 is suppressed, and the short circuit between the lower electrode 12 and the upper electrode 16 can be suppressed. The insertion films 18 and 18a may be oxides of metal elements, or nitrides or carbides of metal elements, as long as the resistivity of the insertion films 18 and 18a is higher than the resistivity of the lower electrode 12 and the upper electrode 16. Specifically, the insulating film may be formed by including at least one of silicon oxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), aluminum oxide (Al2O3), tantalum oxide (Ta2O5), zirconium oxide (ZrO2), silicon carbide (SiC), yttrium oxide (Y2O3), hafnium oxide (HfO2), titanium oxide (TiO2), magnesium oxide (MgO), titanium nitride (TiN), vanadium nitride (VN), chromium nitride (CrN), niobium nitride (NbN), molybdenum nitride (MoN), hafnium nitride (HfN), tantalum nitride (TaN), tungsten nitride (WN), titanium carbide (TiC), vanadium carbide (VC), chromium carbide (CrC), niobium carbide (NbC), molybdenum carbide (MoC), hafnium carbide (HfC), tantalum carbide (TaC), and tungsten carbide (WC). In this specification, non-metals such as boron (B), silicon (Si), and germanium (Ge) are also considered as metal elements. The insertion films 18 and 18 a may be metal films as long as they have a higher resistivity than the lower electrode 12 and the upper electrode 16 .

[0121] In consideration of the insulating properties of the enhancement films 43 and 43a, the insertion films 18 and 18a are preferably inorganic insulating films. Specifically, the insertion films 18 and 18a are preferably formed to contain at least one of silicon oxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), aluminum oxide (Al2O3), tantalum oxide (Ta2O5), zirconium oxide (ZrO2), silicon carbide (SiC), yttrium oxide (Y2O3), hafnium oxide (HfO2), titanium oxide (TiO2), and magnesium oxide (MgO). The insulating film is a film having a resistivity of 10 8 Ω·cm or more films.

[0122] In the first embodiment and its variations, the piezoelectric layer 14 is a single crystal lithium tantalate layer or a single crystal lithium niobate layer. In this case, when the through hole 22 is formed in the piezoelectric layer 14, an ion milling method is used. Therefore, the material removed during etching is likely to adhere to the side surface of the upper electrode 16, etc. to form an adhesion film. Therefore, when the piezoelectric layer 14 is a single crystal lithium tantalate layer or a single crystal lithium niobate layer, at least one of the insertion films 18 and 18a is preferably formed on at least one region between the lower electrode 12 and the piezoelectric layer 14 or between the piezoelectric layer 14 and the upper electrode 16. The piezoelectric layer 14 may be a layer other than a single crystal lithium tantalate layer and a single crystal lithium niobate layer, and may be, for example, an aluminum nitride layer, a zinc oxide layer, a lead zirconate titanate layer, or a lead titanate layer.

[0123] In the first embodiment and its variations, the lower electrode 12 and the upper electrode 16 excite the piezoelectric layer 14 in the resonance region 50 to generate thickness shear vibration. Figure 1 As shown, two through holes 22 are provided in such a manner that the resonance region 50 is interposed therebetween, and the vibration direction 60 of the thickness shear vibration is a direction (e.g., Y direction) intersecting the direction (e.g., X direction) in which the two through holes 22 face each other with the resonance region 50 interposed therebetween. This makes it possible to suppress leakage of acoustic waves from the resonance region 50.

[0124] In the first embodiment and its modifications, the maximum distance L between the through hole 22 and the piezoelectric layer 14 in the resonance region 50 (see Figure 8 ) is 1.6λ or less, that is, 3.2 times or less of the thickness of the piezoelectric layer 14. This makes it possible to suppress the increase in device size while suppressing the degradation of device characteristics, such as Figure 5 From the viewpoint of suppressing degradation of device characteristics, the distance L is preferably 2.6 times or less, more preferably 1.6 times or less, and still more preferably 0.7 times or less, the thickness of the piezoelectric layer 14 .

[0125] [Second Embodiment]

[0126] Fig.16A and Fig. 16B is a cross-sectional view of an acoustic wave device 200 according to the second embodiment. Fig.16A and Fig. 16B As shown, in the acoustic wave device 200 according to the second embodiment, an air gap 36 is provided instead of the sound reflecting film 30. The air gap 36 is formed in, for example, an insulating film 38 provided on the substrate 10, and communicates with the through hole 22. The other components of the second embodiment are the same as those of the first embodiment, and thus description thereof is omitted.

[0127] As in the first embodiment and its variations, the acoustic wave device may be a solid mounted resonator (SMR) in which a sound reflecting membrane 30 for reflecting sound waves is disposed below the lower electrode 12, or as in the second embodiment, the acoustic wave device may be a film bulk acoustic resonator (FBAR) in which an air gap 36 is disposed below the lower electrode 12.

[0128] [Third Embodiment]

[0129] Fig.17 is a circuit diagram of a filter 300 according to a third embodiment. Fig.17 As shown, in the filter 300 according to the third embodiment, one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave device according to the first embodiment, the variation of the first embodiment, or the second embodiment can be used for at least one of the series resonators S1 to S4 and the parallel resonators P1 to P3. The number of series resonators and parallel resonators can be appropriately set. Although the ladder filter is illustrated as an example of a filter, the filter may be a multi-mode filter.

[0130] In the third embodiment, the case where the acoustic wave device according to the first embodiment, the variation of the first embodiment, and the second embodiment is used for a filter is described as an example, but the present disclosure is not limited to this case. For example, the acoustic wave device can be used for an actuator used in an inkjet micro pump, an RF-MEMS switch, or an optical mirror, or for a sensor such as an acceleration sensor, a gyro sensor, or an energy harvesting sensor.

[0131] [Fourth Embodiment]

[0132] Fig.18 4 is a circuit diagram of a duplexer 400 according to a fourth embodiment. Fig.18 As shown, in the duplexer 400 according to the fourth embodiment, the transmission filter 80 is connected between the common terminal Ant and the transmission terminal Tx. The receiving filter 82 is connected between the common terminal Ant and the receiving terminal Rx. The transmission filter 80 transfers the signal in the transmission band of the high-frequency signal input from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses the signal of other frequencies. The receiving filter 82 transfers the signal in the receiving band of the high-frequency signal input from the common terminal Ant to the receiving terminal Rx as a reception signal, and suppresses the signal of other frequencies. At least one of the transmission filter 80 and the receiving filter 82 can be used as a filter of the second embodiment. Although the duplexer is shown as an example of a multiplexer, a triplexer or a quadplexer can also be used.

[0133] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to these specific embodiments, and various variations and modifications may be made within the scope of the gist of the present disclosure described in the claims.

Claims

1. An acoustic wave device, comprising: substrate; A lower electrode, which is disposed above the substrate; an upper electrode, the upper electrode being disposed above the lower electrode; a piezoelectric layer disposed above the substrate, with at least a portion of the piezoelectric layer interposed between the lower electrode and the upper electrode, the piezoelectric layer having a through hole along a resonance region in which the lower electrode and the upper electrode overlap each other in a plan view and the at least a portion of the piezoelectric layer is interposed between the lower electrode and the upper electrode, the through hole exposing at least a portion of the lower electrode; an insertion film provided at one or both of between the lower electrode and the piezoelectric layer and between the upper electrode and the piezoelectric layer, the insertion film having a resistivity higher than that of the lower electrode and the upper electrode; a first film that contacts the side surface of the lower electrode and extends upward from the side surface of the lower electrode to one side of the side surface of the upper electrode, the first film containing a constituent element of the lower electrode; a second film that contacts the side surface of the piezoelectric layer and extends upward from the side surface of the piezoelectric layer to a region between the side surface of the upper electrode and the first film, the second film having a higher concentration of constituent elements of the piezoelectric layer than the first film; as well as a third film which contacts the side surface of the insertion film and extends upward from the side surface of the insertion film to extend to at least one of a region between the side surface of the upper electrode and the second film and a region between the first film and the second film, wherein a concentration of a first element in the third film is higher than a concentration of the first element in the second film, the first element being a constituent element of the insertion film and different from a constituent element of the piezoelectric layer, and a concentration of a second element in the third film is lower than a concentration of the second element in the second film, the second element being the constituent element of the piezoelectric layer and different from the constituent element of the insertion film.

2. The acoustic wave device according to claim 1, wherein The second film and the third film have a lower concentration of a constituent element of the lower electrode than the first film.

3. The acoustic wave device according to claim 1 or 2, wherein: The second film and the third film do not include a constituent element of the lower electrode.

4. The acoustic wave device according to claim 1 or 2, wherein: The first film has a lower concentration of the constituent element of the insertion film than the third film.

5. The acoustic wave device according to claim 1 or 2, wherein: The insertion film is an inorganic insulating film.

6. The acoustic wave device according to claim 5, wherein: The insertion film is formed to contain at least one of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum oxide, zirconium oxide, silicon carbide, yttrium oxide, hafnium oxide, titanium oxide, and magnesium oxide.

7. The acoustic wave device according to claim 1 or 2, wherein: The piezoelectric layer is a single crystal lithium tantalate layer or a single crystal lithium niobate layer.

8. The acoustic wave device according to claim 7, wherein: The lower electrode and the upper electrode excite thickness shear vibration in the piezoelectric layer in the resonance region, Two through holes are provided in such a manner that the resonance region is interposed therebetween, and The vibration direction of the thickness shear vibration is a direction intersecting with the direction in which the two through holes face each other with the resonance region interposed therebetween.

9. The acoustic wave device according to claim 8, wherein: A maximum distance between the through hole and the piezoelectric layer in the resonance region is 3.2 times or less of a thickness of the piezoelectric layer in the resonance region.

10. A filter comprising the acoustic wave device according to claim 1 or 2.

11. A multiplexer comprising the filter according to claim 10.

12. A method for manufacturing an acoustic wave device, the method comprising the following steps: forming a lower electrode, a piezoelectric layer and an upper electrode in sequence on a substrate; forming an insertion film disposed on at least one region between the lower electrode and the piezoelectric layer and between the piezoelectric layer and the upper electrode, the insertion film having a resistivity higher than resistivities of the lower electrode and the upper electrode; On a side portion of a resonance region in which the lower electrode and the upper electrode overlap and the piezoelectric layer is interposed therebetween, the piezoelectric layer, the insertion film, and the lower electrode are etched so as to form a through hole in the piezoelectric layer along the resonance region, so that a second film adhered by etching the piezoelectric layer is formed between a first film adhered by etching the lower electrode and a side surface of the upper electrode, and so that a third film adhered by etching the insertion film is formed on at least one of a region between the side surface of the upper electrode and the second film and a region between the first film and the second film.

13. The method for manufacturing an acoustic wave device according to claim 12, wherein: The piezoelectric layer, the insertion film, and the lower electrode are etched by ion milling.

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