JP2020014088A - Acoustic wave resonator, filter, and multiplexer - Google Patents

Abstract

To improve the characteristics of an acoustic wave resonator.SOLUTION: An acoustic wave resonator includes a substrate, a lower electrode provided on the substrate, a first piezoelectric layer provided on the lower electrode and made of a single crystal material, and a second piezoelectric layer provided on the first piezoelectric layer and made of a single crystal material, an upper electrode provided on the piezoelectric layer so as to form a resonance region facing the lower electrode with at least a portion of the piezoelectric layer interposed therebetween, and an insertion film provided on at least a part of the resonance region between the first piezoelectric layer and the second piezoelectric layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an elastic wave resonator, a filter, and a multiplexer, for example, an elastic wave resonator having a piezoelectric layer made of a single crystal material, and a manufacturing method thereof, a filter, and a multiplexer.

  It is known that a temperature compensating film having a temperature coefficient of an elastic constant opposite to that of an elastic constant of a piezoelectric layer is provided at a central portion in a thickness direction of a piezoelectric layer of an elastic wave resonator such as a piezoelectric thin film resonator ( For example, Patent Document 1).

JP-A-58-137317

  By providing the temperature compensation film, the temperature coefficient of the resonance frequency of the elastic wave vibrator can be reduced. In order to insert an insertion film such as a temperature compensation film between the two piezoelectric layers, an insertion film is formed on the lower piezoelectric layer, and an upper piezoelectric layer is formed on the insertion film. However, when an attempt is made to form a piezoelectric layer on the insertion film, the piezoelectricity of the upper piezoelectric layer deteriorates. For this reason, the electromechanical coupling coefficient decreases.

  The present invention has been made in view of the above problems, and has as its object to improve the characteristics of an elastic wave resonator.

  The present invention comprises a substrate, a lower electrode provided on the substrate, a first piezoelectric layer provided on the lower electrode and made of a single crystal material, and a single piezoelectric material provided on the first piezoelectric layer. A piezoelectric layer having a second piezoelectric layer, an upper electrode provided on the piezoelectric layer so as to form a resonance region opposed to the lower electrode with at least a portion of the piezoelectric layer interposed therebetween, and An acoustic wave resonator comprising: an insertion film provided in at least a part of the resonance region between a piezoelectric layer and the second piezoelectric layer.

  In the above configuration, a configuration is provided in which an insulating film made of a material different from the insertion film is provided between the first piezoelectric layer and the second piezoelectric layer in a region other than the region where the insertion film is provided. Can be.

  In the above configuration, the first piezoelectric layer and the second piezoelectric layer may be joined via the insertion film and the insulating film, and may not be in contact with the first piezoelectric layer and the second piezoelectric layer. it can.

  In the above configuration, an interface between the first piezoelectric layer and the insertion film and the insulating film is substantially flat, and an interface between the second piezoelectric layer and the insertion film and the insulating film is substantially flat. It can be.

  In the above configuration, the first piezoelectric layer and the second piezoelectric layer may be directly joined in a region other than the region where the insertion film is provided.

  In the above configuration, an interface between the first piezoelectric layer and the insertion film and the second piezoelectric layer may be substantially flat.

  In the above configuration, the elastic constant of the insertion film may have a temperature coefficient having an opposite sign to the temperature coefficient of the elastic constant of the piezoelectric layer.

  In the above structure, the first piezoelectric layer and the second piezoelectric layer may be made of aluminum nitride, lithium tantalate, or lithium niobate.

  The present invention is a filter including the elastic wave resonator.

  The present invention is a multiplexer including the above filter.

  According to the present invention, the characteristics of the elastic wave resonator can be improved.

FIG. 1A is a plan view of the elastic wave resonator according to the first embodiment, and FIG. 1B is a cross-sectional view taken along a line AA in FIG. FIGS. 2A to 2C are cross-sectional views (part 1) illustrating the method of manufacturing the elastic wave resonator according to the first embodiment. FIGS. 3A and 3B are cross-sectional views (part 2) illustrating the method of manufacturing the elastic wave resonator according to the first embodiment. FIGS. 4A to 4C are cross-sectional views (part 3) illustrating the method of manufacturing the elastic wave resonator according to the first embodiment. 5A to 5C are cross-sectional views (No. 4) illustrating the method of manufacturing the acoustic wave resonator according to the first embodiment. FIGS. 6A and 6B are cross-sectional views illustrating a method of manufacturing the elastic wave resonator according to the first modification of the first embodiment. FIGS. 7A to 7C are cross-sectional views illustrating a method of manufacturing the elastic wave resonator according to the second modification of the first embodiment. 8A to 8C are cross-sectional views (part 1) illustrating a method for manufacturing an elastic wave resonator according to Modification 3 of Example 1. FIG. FIGS. 9A and 9B are cross-sectional views (part 2) illustrating the method of manufacturing the elastic wave resonator according to Modification 3 of Example 1. FIG. 10A is a circuit diagram of a filter according to the second embodiment, and FIG. 10B is a circuit diagram of a duplexer according to a first modification of the second embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1A is a plan view of the elastic wave resonator according to the first embodiment, and FIG. 1B is a cross-sectional view taken along a line AA in FIG. The left side of the figure shows the series resonator S of the ladder type filter, and the right side shows the parallel resonator P.

  As shown in FIGS. 1A and 1B, a lower electrode 12 is provided on a substrate 10. The cavity 30 is formed by the depression on the upper surface of the substrate 10. A lower electrode 12 is provided on a substrate 10. An insulating film 24 is provided in a region where the lower electrode 12 is not provided. The piezoelectric layer 14a is provided on the lower electrode 12 and the insulating film 24. An insertion film 28 is provided on the piezoelectric layer 14a. The insulating film 26 is provided in a region where the insertion film 28 is not provided. The piezoelectric layer 14b is provided on the insertion film 28 and the insulating film 26. The piezoelectric layers 14a and 14b form the piezoelectric layer 14. An upper electrode 16 is provided on the piezoelectric layer 14b. The mass load film 20 is provided on the upper electrode 16 of the parallel resonator P. The series resonator S is not provided with the mass load film 20. The mass load film 22 is provided on the mass load film 20 of the parallel resonator P and on the upper electrode 16 of the series resonator S.

  A region where the lower electrode 12 and the upper electrode 16 face each other with at least a part of the piezoelectric layer 14 interposed therebetween is a resonance region 50. The resonance region 50 is a region where elastic waves in the thickness longitudinal vibration mode resonate. The air gap 30 is provided so as to include the resonance region 50 in a plan view.

  The insertion film 28 is a temperature compensation film, and the elastic constant of the insertion film 28 has a temperature coefficient of a sign opposite to that of the elastic constant of the piezoelectric layer 14. Thereby, a temperature coefficient of frequency (TCF) such as a resonance frequency is reduced. Therefore, the temperature characteristics of the elastic wave resonator are improved. From the viewpoint of reducing the TCF, it is preferable that the insertion film 28 completely include the resonance region 50 in plan view.

  The polarization directions 15a and 15b (for example, the C-axis direction of aluminum nitride) of the piezoelectric layers 14a and 14b are preferably substantially the same. The materials of the piezoelectric layers 14a and 14b are preferably the same. It is preferable that the thicknesses of the piezoelectric layers 14a and 14b are substantially the same. Thereby, the temperature compensation effect of the insertion film 28 is maximized. Each of the piezoelectric layers 14a and 14b is a single crystal substrate and has a flat plate shape, and the upper and lower surfaces of each of the piezoelectric layers 14a and 14b are substantially flat. The thickness of the lower electrode 12 and the thickness of the insulating film 24 are substantially the same, and the thickness of the insertion film 28 and the thickness of the insulating film 26 are substantially the same.

  The mass load film 20 is a film for making the resonance frequencies of the parallel resonator P and the series resonator S different, and is provided so as to include the resonance region 50. The mass load film 22 is a film for finely adjusting the resonance frequency. The resonance frequency of the resonator can be adjusted by the area of the mass load film 22 in the resonance region 50 with respect to the area of the resonance region 50.

  As the substrate 10, for example, a silicon substrate, a sapphire substrate, a spinel substrate, a glass substrate, or a quartz substrate can be used. As the piezoelectric layers 14a and 14b, for example, a single crystal aluminum nitride substrate, a single crystal lithium tantalate substrate, or a single crystal lithium niobate substrate can be used.

  As the lower electrode 12 and the upper electrode 16, Ru (ruthenium), Cr (chromium), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), A single-layer film of platinum (Pt), rhodium (Rh), iridium (Ir), or the like, or a stacked film thereof can be used.

  As the insertion film 28, for example, a silicon oxide film or a silicon oxide film to which an impurity such as fluorine is added can be used. As the insulating films 26 and 24, for example, a resin film such as polyimide can be used.

  As the mass load films 20 and 22, for example, an insulating film such as a silicon oxide film or a silicon nitride film, and the metal films exemplified as the lower electrode 12 and the upper electrode 16 can be used.

  When the resonance frequency is about 2.3 GHz, the piezoelectric layers 14a and 14b are each a single-crystal aluminum nitride layer having a thickness of, for example, 400 nm, and the lower electrode 12 and the upper electrode 16 are, for example, Ru films having a thickness of 145 nm.

[Production Method of Example 1]
FIGS. 2A to 5C are cross-sectional views illustrating a method of manufacturing the elastic wave resonator according to the first embodiment. As shown in FIG. 2A, a piezoelectric substrate made of a single crystal material is prepared as a piezoelectric layer 14a. The piezoelectric layer 14a is, for example, a piezoelectric substrate grown and sliced by a pulling method. Therefore, the upper surface and the lower surface of the piezoelectric layer 14a are substantially flat. The polarization direction 15a is upward, but may be any direction such as downward or lateral.

  As shown in FIG. 2B, an insertion film 28 is formed on the piezoelectric layer 14a. The insertion film 28 is formed by, for example, a sputtering method or a vacuum evaporation method, and is patterned by an etching method or a lift-off method. The size of the insertion film 28 is the same as or larger than the resonance region 50.

  As shown in FIG. 2C, an insulating film 26 is formed on the piezoelectric layer 14a in a region where the insertion film 28 is not formed so as to surround the insertion film 28. The insulating film 26 is, for example, a resin film such as a polyimide film. The upper surfaces of the insertion film 28 and the insulating film 26 are substantially flat, and the thicknesses of the insertion film 28 and the insulating film 26 are substantially the same. The insulating film 26 is formed by, for example, a spin coating method, and the upper surfaces of the insertion film 28 and the insulating film 26 are planarized by a CMP (Chemical Mechanical Polishing) method or the like.

  As shown in FIG. 3A, a piezoelectric substrate made of a single crystal material is prepared as a piezoelectric layer 14b. The upper and lower surfaces of the piezoelectric layer 14b are substantially flat. The material of the piezoelectric layer 14b is preferably the same as that of the piezoelectric layer 14a, but may be different. The thickness of the piezoelectric layer 14b is preferably substantially the same as the thickness of the piezoelectric layer 14a, but may be different. The polarization direction 15b is preferably substantially the same as the polarization direction 15a, but may be different.

  As shown in FIG. 3B, the upper electrode 16 is formed on the piezoelectric layer 14b. The upper electrode 16 is formed using, for example, a sputtering method or a vacuum evaporation method, and is patterned using an etching method or a lift-off method. The upper electrode 16 is formed in the resonance region 50 and a lead-out region where the upper electrode 16 is drawn from the resonance region 50.

  As shown in FIG. 4A, a depression 36 is formed on the upper surface of the substrate 10 which has a flat plate shape and whose upper and lower surfaces are substantially flat. The size of the recess 36 is the same as or larger than the resonance region 50.

  As shown in FIG. 4B, a sacrificial layer 38 is formed in the depression 36. The upper surface of the sacrificial layer 38 and the upper surface of the substrate 10 are substantially flat. The sacrificial layer 38 is selected from a material that can be easily dissolved in an etching solution or an etching gas such as magnesium oxide (MgO), zinc oxide (ZnO), germanium (Ge), or silicon oxide.

  As shown in FIG. 4C, the lower electrode 12 is formed on the substrate 10. The lower electrode 12 is formed by, for example, a sputtering method or a vacuum evaporation method, and is patterned by an etching method or a lift-off method. The lower electrode 12 is formed in the resonance region 50 and an extraction region from which the lower electrode 12 is extracted from the resonance region 50. An insulating film 24 is formed on the substrate 10 in a region where the lower electrode 12 is not formed so as to surround the lower electrode 12. The insulating film 24 is, for example, a resin film such as a polyimide film. The upper surfaces of the lower electrode 12 and the insulating film 24 are substantially flat, and the thickness of the lower electrode 12 and the insulating film 24 are substantially the same. The insulating film 24 is formed by, for example, a spin coating method, and the upper surfaces of the insertion film 28 and the insulating film 26 are flattened by a CMP method or the like.

  As shown in FIG. 5A, the lower surface of the piezoelectric layer 14a of FIG. 2C is joined to the lower electrode 12 and the insulating film 24 of FIG. 4C. The bonding method is, for example, by activating the upper surfaces of the lower electrode 12 and the insulating film 24 and the lower surface of the piezoelectric layer 14a, and directly bonding the upper surfaces of the lower electrode 12 and the insulating film 24 and the lower surface of the piezoelectric layer 14a at room temperature. Do. For activation, an ion beam, a neutral beam, or plasma is used.

  As shown in FIG. 5B, the lower surface of the piezoelectric layer 14b of FIG. 3B is bonded onto the insertion film 28 and the insulating film 26 of FIG. The joining method is the same as in FIG. Thus, the piezoelectric layer 14 is formed from the piezoelectric layers 14a and 14b. Further, a resonance region 50 in which the lower electrode 12 and the upper electrode 16 face each other is formed.

  As shown in FIG. 5C, a mass load film 20 is formed on the upper electrode 16 of the parallel resonator P. The mass load film 22 is formed on the mass load film 20 of the parallel resonator P and on the upper electrode 16 of the series resonator S.

  After that, the sacrificial layer 38 is removed to form the gap 30, whereby the elastic wave resonator shown in FIGS. 1A and 1B is obtained.

[Modification 1 of Embodiment 1]
FIGS. 6A and 6B are cross-sectional views illustrating a method of manufacturing the elastic wave resonator according to the first modification of the first embodiment. As shown in FIG. 6A, in FIG. 2B of the first embodiment, the insertion film 28 is formed on the entire upper surface of the piezoelectric layer 14a.

  As shown in FIG. 6B, by subsequently performing the same manufacturing process as in the first embodiment, the elastic wave resonator according to the first modification of the first embodiment is obtained. By forming the insertion film 28 over the entire piezoelectric layer 14a as in the first modification of the first embodiment, the step of forming the insulating film 26 in FIG. 2C can be omitted.

[Modification 2 of Embodiment 1]
FIGS. 7A to 7C are cross-sectional views illustrating a method of manufacturing the elastic wave resonator according to the second modification of the first embodiment. As shown in FIG. 7A, after FIG. 2C of the first embodiment, a bonding layer 27 is formed on the entire surface of the insertion film 28 and the insulating film 26. The bonding layer 27 is formed by a sputtering method or a vacuum evaporation method. The bonding layer 27 is, for example, a metal film such as titanium, chromium, or nickel, or a piezoelectric layer such as polycrystalline aluminum nitride.

  Then, as shown in FIG. 7B, the manufacturing steps of FIG. 3A to FIG. 5A of the first embodiment are performed. As in FIG. 5B, the lower surface of the piezoelectric layer 14b is joined to the upper surface of the joining layer 27. The bonding layer 27 allows the insertion film 28 and the insulating film 26 to be easily bonded to the piezoelectric layer 14b.

  As shown in FIG. 7C, by subsequently performing the manufacturing process of FIG. 5C of the first embodiment, the elastic wave resonator according to the second modification of the first embodiment is obtained. The bonding layer 27 may be formed on the insertion film 28 as in the second modification of the first embodiment.

[Modification 3 of Embodiment 1]
FIGS. 8A to 9B are cross-sectional views illustrating a method of manufacturing the elastic wave resonator according to the third modification of the first embodiment. As shown in FIG. 8A, a piezoelectric layer 14a is prepared. The thickness of the piezoelectric layer 14a is larger than that of the first embodiment by the thickness of the insertion film 28.

  As shown in FIG. 8B, a depression 29 having a depth corresponding to the thickness of the insertion film 28 is formed in a region where the insertion film 28 is provided on the upper surface of the piezoelectric layer 14a. The depression 29 is formed using, for example, a dry etching method.

  As shown in FIG. 8C, the insertion film 28 is formed in the depression 29. The upper surface of the insertion film 28 and the upper surface of the piezoelectric layer 14a are made substantially flat.

  As shown in FIG. 9A, thereafter, the manufacturing steps of FIGS. 3A to 5A of the first embodiment are performed. As in FIG. 5B, the lower surface of the piezoelectric layer 14b is joined to the upper surfaces of the insertion film 28 and the piezoelectric layer 14a. As shown in FIG. 9B, the elastic wave resonator according to the third modification of the first embodiment is obtained by subsequently performing the manufacturing process of the first embodiment shown in FIG. 5C. In a region other than the region where the insertion film 28 is formed as in the third modification of the first embodiment, the piezoelectric layers 14a and 14b may be directly bonded.

  The material used for the insertion film 28 such as a temperature compensation film is, for example, a silicon oxide film to which silicon oxide or fluorine is added, and has a higher acoustic impedance than aluminum nitride, lithium tantalate or lithium niobate used for the piezoelectric layers 14a and 14b. Low. Therefore, if the insertion film 28 is provided in at least a part of the resonance region 50 between the piezoelectric layers 14a and 14b, the electromechanical coupling coefficient deteriorates. Further, when the polycrystalline piezoelectric layer 14b is provided on the insertion film 28 by a sputtering method or the like, the orientation of the piezoelectric layer 14b is deteriorated, and the electromechanical coupling coefficient is deteriorated.

  When the insertion film 28 is provided between the piezoelectric layer 14 and the upper electrode 16, the orientation of the piezoelectric layer 14 does not deteriorate. However, compared to the case where the insertion film 28 is provided in the piezoelectric layer 14, the same temperature compensation effect cannot be obtained unless the insertion film 28 is made thicker. As a result, the electromechanical coupling coefficient deteriorates.

  According to the first embodiment and its modification, the piezoelectric layer 14a (first piezoelectric layer) and the piezoelectric layer 14b (second piezoelectric layer) are made of a single crystal material. A piezoelectric layer made of a single crystal material has high piezoelectricity. Thereby, the electromechanical coupling coefficient of the elastic wave resonator can be increased. Also, the orientation of the piezoelectric layer 14b on the insertion film 28 does not deteriorate compared to the polycrystalline piezoelectric layer 14b. Thereby, the electromechanical coupling coefficient of the elastic wave resonator can be further increased. Thus, the characteristics of the elastic wave resonator can be improved.

  As shown in FIG. 2B, an insertion film 28 is formed on the upper surface of the piezoelectric layer 14a made of a single crystal material. As shown in FIG. 5B, with the insertion film 28 formed on the piezoelectric layer 14a, the lower surface of the piezoelectric layer 14b (second piezoelectric layer) made of a single crystal material is joined to the insertion film 28. As shown in FIG. 5A, the lower electrode 12 is formed on the lower surface of the piezoelectric layer 14a. As shown in FIG. 3B, the upper electrode 16 is formed on the upper surface of the piezoelectric layer 14b so that the insertion film 28 is provided on at least a part of the resonance region 50. By manufacturing the elastic wave resonator in this manner, the insertion film 28 can be provided between the piezoelectric layers 14a and 14b made of single crystal. Further, since the piezoelectric layer 14b is not formed on the insertion film 28 by using a sputtering method or the like, it is possible to suppress the piezoelectricity of the piezoelectric layer 14b from deteriorating. Therefore, the electromechanical coupling coefficient of the elastic wave resonator can be improved.

  As shown in FIG. 2C, an insulating film 26 made of a material different from that of the insertion film 28 is formed in a region other than the region where the insertion film 28 is provided on the upper surface of the piezoelectric layer 14a. As shown in FIG. 5B, the piezoelectric layers 14a and 14b are joined via the insertion film 28 and the insulating film 26, and do not contact the piezoelectric layers 14a and 14b. Thereby, the insertion film 28 can be formed between the flat piezoelectric layers 14a and 14b.

  It is difficult to join the piezoelectric layer 14b with the insertion film 28 and the insulating film 26 (particularly at room temperature) unless the joining surface is flat. Therefore, the interface between the piezoelectric layer 14a and the insertion film 28 and the insulating film 26 is made substantially flat, and the interface between the piezoelectric layer 14b and the insertion film 28 and the insulating film 26 is made substantially flat. Thereby, the piezoelectric layer 14b, the insertion film 28, and the insulating film 26 can be easily joined. The term “substantially flat” means, for example, flat to the extent that bonding is easy.

  As shown in FIG. 9A, the lower surface of the piezoelectric layer 14b is joined to the insertion film 28 so that the piezoelectric layers 14a and 14b are directly joined in a region other than the region where the insertion film 28 is provided. Thus, the step of forming the insulating film 26 can be omitted. When the piezoelectric layers 14a and 14b are directly joined, an amorphous layer having a thickness of 10 nm or less may be formed between the piezoelectric layers 14a and 14b. In effect, they are directly joined.

  The interface between the piezoelectric layer 14a and the insertion film 28 and the piezoelectric layer 14b is made substantially flat. Thereby, the piezoelectric layer 14a and the insertion film 28 can be easily joined to the piezoelectric layer 14b.

  When the piezoelectric layers 14a and 14b are formed by a sputtering method or the like, the piezoelectric layers 14a and 14b have a continuous columnar structure. In this case, when the piezoelectric layers 14a and 14b are in contact with each other, a crack is formed across the piezoelectric layers 14a and 14b. When the piezoelectric layers 14a and 14b are directly joined as shown in FIG. 9A, it is possible to suppress the formation of cracks over the piezoelectric layers 14a and 14b.

  In the first embodiment and its modifications, the temperature compensation film for improving the temperature characteristics of the acoustic wave resonator has been described as an example of the insertion film 28, but the insertion film 28 is not provided in the central region of the resonance region 50. May be provided so as to surround the central region along the outer periphery of the resonance region 50. Thereby, it is possible to suppress the leakage of the elastic wave from the central region to the outside of the resonance region 50. Thus, the insertion film 28 may be provided in at least a part of the resonance region 50.

  Although the air gap 30 has been described as an example of the acoustic reflection layer that reflects the elastic waves in the piezoelectric layers 14a and 14b, an acoustic reflection film in which films having different acoustic impedances are stacked may be used instead of the air gap. Although the elliptical shape has been described as an example of the planar shape of the resonance region 50, a polygonal shape such as a square shape or a pentagon shape may be used.

  Second Embodiment A second embodiment is an example of a filter and a duplexer using the elastic wave resonator of the first embodiment and its modification. FIG. 10A is a circuit diagram of the filter according to the second embodiment. As shown in FIG. 10A, one or a plurality of series resonators S1 to S4 are connected in series between an input terminal T1 and an output terminal T2. One or a plurality of parallel resonators P1 to P3 are connected in parallel between the input terminal T1 and the output terminal T2. The piezoelectric thin-film resonators of the first embodiment and its modifications can be used for at least one of one or a plurality of series resonators S1 to S4 and one or a plurality of parallel resonators P1 to P3. The number of resonators of the ladder type filter and the like can be appropriately set.

  FIG. 10B is a circuit diagram of a duplexer according to a first modification of the second embodiment. As shown in FIG. 10B, a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. The reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 allows a signal in a transmission band among high-frequency signals input from the transmission terminal Tx to pass through the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 allows a signal in the reception band among the high-frequency signals input from the common terminal Ant to pass through the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment.

  Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may be used.

  As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the specific embodiments, and various modifications and changes may be made within the scope of the present invention described in the appended claims. Changes are possible.

DESCRIPTION OF SYMBOLS 10 Substrate 12 Lower electrode 14, 14a, 14b Piezoelectric layer 16 Upper electrode 20, 22 Mass load film 24, 26 Insulating film 28 Insertion film 30 Void 38 Sacrificial layer 40 Transmission filter 42 Reception filter 50 Resonance area

Claims (10)

Board and
A lower electrode provided on the substrate,
A first piezoelectric layer provided on the lower electrode and made of a single crystal material, and a second piezoelectric layer provided on the first piezoelectric layer and made of a single crystal material;
An upper electrode provided on the piezoelectric layer so as to form a resonance region facing the lower electrode with at least a part of the piezoelectric layer interposed therebetween,
An insertion film provided on at least a part of the resonance region between the first piezoelectric layer and the second piezoelectric layer;
An elastic wave resonator comprising:   2. The elastic wave according to claim 1, further comprising: an insulating film provided between the first piezoelectric layer and the second piezoelectric layer in a region other than the region where the insertion film is provided, and made of a material different from the insertion film. Resonator.   The acoustic wave resonance according to claim 2, wherein the first piezoelectric layer and the second piezoelectric layer are joined via the insertion film and the insulating film, and the first piezoelectric layer and the second piezoelectric layer are not contacted. vessel.   The interface between the first piezoelectric layer and the insertion film and the insulating film is substantially flat, and the interface between the second piezoelectric layer and the insertion film and the insulating film is substantially flat. Elastic wave resonator.   The elastic wave resonator according to claim 1, wherein the first piezoelectric layer and the second piezoelectric layer are directly joined to each other in a region other than a region where the insertion film is provided.   The elastic wave resonator according to claim 5, wherein interfaces between the first piezoelectric layer and the insertion film and the second piezoelectric layer are substantially flat.   The elastic wave resonator according to any one of claims 1 to 6, wherein an elastic constant of the insertion film has a temperature coefficient having an opposite sign to a temperature coefficient of an elastic constant of the piezoelectric layer.   The elastic wave resonator according to any one of claims 1 to 7, wherein the first piezoelectric layer and the second piezoelectric layer are made of aluminum nitride, lithium tantalate, or lithium niobate.   A filter comprising the elastic wave resonator according to claim 1. A multiplexer comprising the filter according to claim 9.

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