WO2023195513A1 - Elastic wave device and method for manufacturing same - Google Patents

Abstract

An elastic wave device 10 comprises an elastic wave element 11, a solder bump 12 electrically connected to the elastic wave element 11, and a terminal electrode 13 provided between the elastic wave element 11 and the solder bump 12. The elastic wave element 11 comprises a support member 20, a piezoelectric layer 21 provided on one main surface of the support member 20, and functional electrodes 22 provided on at least one main surface of the piezoelectric layer 21. The terminal electrode 13 is provided on one main surface of the support member 20.

Description

Acoustic wave device and its manufacturing method

The present invention relates to an elastic wave device and a method for manufacturing the same.

Conventionally, acoustic wave devices including a piezoelectric layer made of lithium niobate or lithium tantalate are known.

Patent Document 1 discloses a support in which a cavity is formed, a piezoelectric substrate provided on the support so as to overlap with the cavity, and a piezoelectric substrate provided on the piezoelectric substrate so as to overlap with the cavity. An acoustic wave device is provided with an IDT (Interdigital Transducer) electrode provided, and a plate wave is excited by the IDT electrode, wherein an edge of the cavity portion is provided with a plate wave excited by the IDT electrode. An elastic wave device is disclosed that does not include a straight portion extending parallel to the propagation direction of the wave.

Patent Document 2 discloses a configuration in which a plurality of acoustic wave elements are mounted on a mounting board by a flip chip bonding (FCB) method.

Japanese Patent Application Publication No. 2012-257019 International Publication No. 2013/146374

In an acoustic wave device such as that described in Patent Document 2, an acoustic wave element is mounted on a substrate via bumps. However, when an acoustic wave element is mounted on a substrate by flip-chip bonding, an impact is applied under the bump by ultrasonic waves, a load, etc., and as a result, cracks are likely to occur in the piezoelectric layer under the bump. In that case, there was a risk that the cracks would reach the piezoelectric layer of the resonator section where functional electrodes such as IDT electrodes were provided.

An object of the present invention is to provide an acoustic wave device that can suppress cracks that occur in the piezoelectric layer of a resonator section when an acoustic wave element is mounted on a substrate. Furthermore, an object of the present invention is to provide a method for manufacturing the above-mentioned elastic wave device.

An acoustic wave device of the present invention includes an acoustic wave element, a solder bump electrically connected to the acoustic wave element, and a terminal electrode provided between the acoustic wave element and the solder bump. . The acoustic wave element includes a support member, a piezoelectric layer provided on one main surface of the support member, and a functional electrode provided on at least one main surface of the piezoelectric layer. The terminal electrode is provided on the one main surface of the support member.

In the method for manufacturing an acoustic wave device of the present invention, a sacrificial layer is formed on a first main surface of a piezoelectric layer, and a support member having a recessed portion on a surface in contact with the sacrificial layer is formed so as to cover the sacrificial layer. a step of forming a cavity in a portion where the sacrificial layer is provided by removing the sacrificial layer; and a step of removing a region above the cavity in the piezoelectric layer. A step of forming a terminal electrode by plating on a portion where the sacrificial layer and the piezoelectric layer have been removed, and a step of forming a solder bump on the terminal electrode.

According to the present invention, it is possible to provide an acoustic wave device that can suppress cracks that occur in the piezoelectric layer of the resonator section when an acoustic wave element is mounted on a substrate. Furthermore, according to the present invention, it is possible to provide a method for manufacturing the above elastic wave device.

FIG. 1 is a cross-sectional view schematically showing an example of the elastic wave device of the present invention. FIG. 2 is a plan view schematically showing an example of the layout of the elastic wave elements constituting the elastic wave device of the present invention. 3A is a cross-sectional view taken along line AA in FIG. 2. FIG. FIG. 3B is a cross-sectional view taken along line BB in FIG. 2. FIG. 4 is a cross-sectional view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate. FIG. 5 is a cross-sectional view schematically showing an example of the process of forming a dielectric layer. FIG. 6 is a cross-sectional view schematically showing an example of the process of bonding the support substrate to the dielectric layer. FIG. 7 is a cross-sectional view schematically showing an example of the process of thinning the piezoelectric substrate. FIG. 8 is a cross-sectional view schematically showing an example of the process of forming functional electrodes and wiring electrodes. FIG. 9 is a cross-sectional view schematically showing an example of the process of forming a through hole. FIG. 10 is a cross-sectional view schematically showing an example of the process of removing the sacrificial layer. FIG. 11 is a cross-sectional view schematically showing an example of a step of forming a sacrificial layer on a piezoelectric substrate at a position different from that in FIG. 4. FIG. 12 is a cross-sectional view schematically showing an example of the process of forming the support member. FIG. 13 is a cross-sectional view schematically showing an example of the process of removing the sacrificial layer. FIG. 14 is a cross-sectional view schematically showing an example of a process of removing a part of the piezoelectric layer. FIGS. 15A, 15B, and 15C are cross-sectional views schematically showing an example of the process of forming a terminal electrode. FIG. 16 is a cross-sectional view schematically showing an example of the process of forming electrodes such as wiring electrodes. FIG. 17 is a cross-sectional view schematically showing an example of the process of forming solder bumps. FIG. 18 is a schematic perspective view showing the appearance of an example of an elastic wave device that utilizes bulk waves in thickness shear mode. FIG. 19 is a plan view showing the electrode structure on the piezoelectric layer of the acoustic wave device shown in FIG. 18. FIG. 20 is a cross-sectional view of a portion taken along line AA in FIG. 18. FIG. 21 is a schematic front sectional view for explaining Lamb waves propagating through a piezoelectric film of an acoustic wave device. FIG. 22 is a schematic front sectional view for explaining a thickness shear mode bulk wave propagating through a piezoelectric layer of an elastic wave device. FIG. 23 is a diagram showing the amplitude direction of the bulk wave in the thickness shear mode. FIG. 24 is a diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 18. FIG. 25 is a diagram showing the relationship between d/2p and the fractional band as a resonator of an acoustic wave device, where p is the distance between the centers of adjacent electrodes and d is the thickness of the piezoelectric layer. FIG. 26 is a plan view of another example of an elastic wave device that utilizes bulk waves in thickness shear mode. FIG. 27 is a reference diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 18. FIG. 28 is a diagram showing the relationship between the fractional band and the amount of phase rotation of spurious impedance normalized by 180 degrees as the magnitude of spurious when a large number of elastic wave resonators are configured according to the present embodiment. It is. FIG. 29 is a diagram showing the relationship between d/2p, metallization ratio MR, and fractional band. FIG. 30 is a diagram showing a map of fractional bands with respect to Euler angles (0°, θ, ψ) of LiNbO ₃ when d/p is brought as close to 0 as possible. FIG. 31 is a partially cutaway perspective view for explaining an example of an elastic wave device that uses Lamb waves. FIG. 32 is a cross-sectional view schematically showing an example of an elastic wave device that uses bulk waves.

Hereinafter, the elastic wave device of the present invention will be explained.

In the first, second and third aspects, the acoustic wave device of the present invention includes a piezoelectric layer made of lithium niobate or lithium tantalate, a first electrode and a first electrode facing each other in a direction crossing the thickness direction of the piezoelectric layer. 2 electrodes.

In the first aspect, a bulk wave in a thickness shear mode such as a primary thickness shear mode is used. Further, in the second aspect, the first electrode and the second electrode are adjacent electrodes, and when the thickness of the piezoelectric layer is d and the distance between the centers of the first electrode and the second electrode is p, d/ p is set to be 0.5 or less. Thereby, in the first and second aspects, the Q value can be increased even when miniaturization is promoted.

Furthermore, in the third aspect, Lamb waves are used as plate waves. Then, resonance characteristics due to the Lamb wave described above can be obtained.

In a fourth aspect, the acoustic wave device of the present invention includes a piezoelectric layer made of lithium niobate or lithium tantalate, and an upper electrode and a lower electrode that face each other in the thickness direction of the piezoelectric layer with the piezoelectric layer in between. In a fourth aspect, bulk waves are utilized.

Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

The drawings shown below are schematic, and their dimensions, aspect ratios, etc. may differ from the actual product.

Note that each embodiment described in this specification is an illustrative example, and parts of the configurations can be partially replaced or combined between different embodiments. In addition, unless there is a particular distinction between the embodiments, they will simply be referred to as "the elastic wave device of the present invention."

FIG. 1 is a cross-sectional view schematically showing an example of the elastic wave device of the present invention. FIG. 2 is a plan view schematically showing an example of the layout of the elastic wave elements constituting the elastic wave device of the present invention. 3A is a cross-sectional view taken along line AA in FIG. 2. FIG. FIG. 3B is a cross-sectional view taken along line BB in FIG. 2.

The elastic wave device 10 shown in FIG. 13.

As shown in FIGS. 1 and 3A, the acoustic wave element 11 includes a support member 20, a piezoelectric layer 21, and a functional electrode 22.

The support member 20 includes, for example, a support substrate 23 and a dielectric layer (also referred to as an intermediate layer, an insulating layer, or a bonding layer) 24 provided between the support substrate 23 and the piezoelectric layer 21. In this way, the support member 20 may have the dielectric layer 24 on one main surface on which the piezoelectric layer 21 is provided.

The support substrate 23 is made of silicon (Si), for example.

Dielectric layer 24 is made of silicon oxide (SiO _x ), such as silicon dioxide (SiO ₂ ), for example.

It is preferable that the support member 20 has a cavity 25 on one main surface (lower main surface in FIG. 1, upper main surface in FIG. 3A).

The cavity 25 may or may not penetrate the support member 20 in the thickness direction (vertical direction in FIGS. 1 and 3A). When the support member 20 includes the support substrate 23 and the dielectric layer 24, for example, the cavity 25 may be provided so as to penetrate the dielectric layer 24 in the thickness direction; A cavity 25 may be provided.

The piezoelectric layer 21 is provided on one main surface of the support member 20 (the lower main surface in FIG. 1, the upper main surface in FIG. 3A). When the support member 20 has the cavity 25, the piezoelectric layer 21 is provided on one main surface of the support member 20 so as to cover the cavity 25.

The piezoelectric layer 21 is made of, for example, lithium niobate (LiNbO _x ) or lithium tantalate (LiTaO _x ). In that case, the piezoelectric layer 21 may be composed of LiNbO ₃ or LiTaO ₃ .

The functional electrode 22 is provided on at least one main surface of the piezoelectric layer 21. In the example shown in FIGS. 1 and 3A, the functional electrode 22 is provided on one main surface of the piezoelectric layer 21 (the lower main surface in FIG. 1, the upper main surface in FIG. 3A).

As shown in FIGS. 1 and 3A, the functional electrode 22 is provided so that at least a portion thereof overlaps with the cavity 25 when viewed from the thickness direction of the piezoelectric layer 21 (vertical direction in FIGS. 1 and 3A). It is preferable. When viewed from the thickness direction of the piezoelectric layer 21, the functional electrode 22 may be provided so that the entirety thereof overlaps with the cavity 25, or a part of the functional electrode 22 may be provided so as to overlap with the cavity 25. .

The functional electrode 22 is, for example, an IDT electrode provided on one main surface of the piezoelectric layer 21.

The functional electrode 22 is electrically connected to the terminal electrode 13. As shown in FIGS. 2 and 3A, a wiring electrode 14 for connecting the functional electrode 22 and the terminal electrode 13 is provided on one main surface of the support member 20. The wiring electrode 14 may be a single layer, or may be a laminate in which two or more metal layers are stacked.

As shown in FIG. 2, a plurality of joints having a cross-sectional structure shown in FIG. 3B are provided on the outer periphery of the elastic wave device 10.

As shown in FIGS. 1 and 3B, the terminal electrode 13 is provided on one main surface (the lower main surface in FIG. 1, the upper main surface in FIG. 3B) of the support member 20. Terminal electrode 13 is joined to solder bump 12 . It is preferable that the terminal electrode 13 is a plated electrode formed by a plating process.

In a conventional acoustic wave device, a terminal electrode is provided on one main surface of a piezoelectric layer, and a bump electrode is joined to the terminal electrode.

On the other hand, in the elastic wave device 10, as shown in FIG. 3B, the terminal electrode 13 is provided on one main surface of the support member 20, and the solder bump 12 is bonded to the terminal electrode 13 as a bump electrode. . As described above, when an acoustic wave element is mounted on a substrate by flip-chip bonding, an impact is likely to be applied to the bottom of the bump due to ultrasonic waves, a load, or the like. However, in the acoustic wave device 10, since the terminal electrode 13 is placed under the solder bump 12, an impact is applied to the terminal electrode 13 compared to a conventional structure in which a piezoelectric layer is placed under the bump electrode. It won't break even if you use it. This eliminates the impact of ultrasonic waves or loads, thereby suppressing cracks that occur in the piezoelectric layer 21 of the resonator section (for example, the section where the functional electrode 22 is provided on the cavity section 25) shown in FIG. 3A. can do.

As shown in FIGS. 1 and 3B, it is preferable that the piezoelectric layer 21 is not provided on the portion of the support member 20 where the solder bumps 12 are located. That is, it is preferable that the terminal electrode 13 be provided directly on one main surface of the support member 20.

It is preferable that the support member 20 has a recess 26 on one main surface, and the terminal electrode 13 is provided in the recess 26.

When the terminal electrode 13 is a plating electrode, it is preferable that the plating seed layer 15 is provided in the recess 26 and that the terminal electrode 13 is provided on the plating seed layer 15.

The metal constituting the terminal electrode 13 is not particularly limited, and examples thereof include Ni, Pd, and the like. Similarly, even when the terminal electrode 13 is a plating electrode, examples of the metal constituting the terminal electrode 13 include metals commonly used in plating, such as Ni and Pd.

The plating seed layer 15 is composed of two layers, for example, a Ti film and a Cu film thereon.

As shown in FIG. 1, the acoustic wave device 10 preferably further includes a wiring board 30.

The wiring board 30 is configured by a printed wiring board, for example. The printed wiring board is formed from a glass cloth/epoxy resin copper-clad laminate.

The wiring board 30 is electrically connected to the acoustic wave element 11 via the terminal electrodes 13 and solder bumps 12. Specifically, external terminals 31 provided on the upper surface of wiring board 30 are bonded to solder bumps 12 . As described above, the acoustic wave element 11 is mounted on the wiring board 30.

As shown in FIG. 1, in this embodiment, a hollow space is formed by the terminal electrode 13 of the acoustic wave element 11, the solder bump 12, and the wiring board 30 facing the functional electrode 22 on the piezoelectric layer 21. . As a result, a so-called chip size package (CSP) structure is realized.

Preferably, a plurality of via conductors 32 are provided inside the wiring board 30.

It is preferable that the acoustic wave element 11 on the wiring board 30 is sealed with a sealing body 33. The material constituting the sealing body 33 is preferably a resin, and more preferably a material in which an inorganic filler such as a metal is mixed into a resin material such as an epoxy resin, a silicone resin, a fluororesin, or an acrylic resin.

The elastic wave device of the present invention is manufactured, for example, by the following method. In addition, the elastic wave device of the present invention may be manufactured in the state of individual pieces, or may be manufactured by producing an aggregate and then separating it into individual pieces.

First, an example of a method for manufacturing the portion shown in FIG. 3A will be described.

FIG. 4 is a cross-sectional view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate.

As shown in FIG. 4, a sacrificial layer 50 is formed on the piezoelectric substrate 41.

As the piezoelectric substrate 41, for example, a substrate made of LiNbO ₃ or LiTaO ₃ is used.

As the material for the sacrificial layer 50, an appropriate material that can be removed by etching, which will be described later, is used. For example, ZnO or the like is used.

The sacrificial layer 50 can be formed, for example, by the following method. First, a ZnO film is formed by sputtering. Thereafter, resist coating, exposure and development are performed in this order. Next, a pattern of the sacrificial layer 50 is formed by performing wet etching. Note that the sacrificial layer 50 may be formed by other methods.

FIG. 5 is a cross-sectional view schematically showing an example of the process of forming a dielectric layer.

As shown in FIG. 5, after forming the dielectric layer 24 to cover the sacrificial layer 50, the surface of the dielectric layer 24 is planarized.

As the dielectric layer 24, for example, a SiO ₂ film or the like is formed. The dielectric layer 24 can be formed by, for example, a sputtering method. Planarization of the dielectric layer 24 can be performed, for example, by chemical mechanical polishing (CMP).

FIG. 6 is a cross-sectional view schematically showing an example of the process of bonding the support substrate to the dielectric layer.

As shown in FIG. 6, the support substrate 23 is bonded to the dielectric layer 24. Thereby, the support member 20 is formed.

FIG. 7 is a cross-sectional view schematically showing an example of the process of thinning the piezoelectric substrate.

As shown in FIG. 7, the piezoelectric substrate 41 is thinned. As a result, the piezoelectric layer 21 is formed. The piezoelectric substrate 41 can be thinned by, for example, a smart cut method, polishing, or the like.

FIG. 8 is a cross-sectional view schematically showing an example of the process of forming functional electrodes and wiring electrodes.

As shown in FIG. 8, the functional electrode 22 and the wiring electrode 14 are formed on one main surface of the piezoelectric layer 21. The functional electrode 22 and the wiring electrode 14 can be formed by, for example, a lift-off method.

FIG. 9 is a cross-sectional view schematically showing an example of the process of forming a through hole.

As shown in FIG. 9, through holes 51 are formed in the piezoelectric layer 21. The through hole 51 is formed to reach the sacrificial layer 50. The through hole 51 can be formed by, for example, a dry etching method. The through hole 51 is used as an etching hole.

FIG. 10 is a cross-sectional view schematically showing an example of the process of removing the sacrificial layer.

As shown in FIG. 10, the sacrificial layer 50 is removed using the through hole 51. When the material of the sacrificial layer 50 is ZnO, the sacrificial layer 50 can be removed, for example, by wet etching using a mixed solution of acetic acid, phosphoric acid, and water (acetic acid: phosphoric acid: water = 1:1:10). can.

By removing the sacrificial layer 50, a cavity 25 is formed in the support member 20.

Through the above steps, the part (acoustic wave element 11) shown in FIG. 3A is manufactured.

Next, an example of a method for manufacturing the portion shown in FIG. 3B will be described.

FIG. 11 is a cross-sectional view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate at a position different from that in FIG. 4.

As shown in FIG. 11, a sacrificial layer 50 is formed on the piezoelectric substrate 41 at a position different from that in FIG. The sacrificial layer 50 is formed in a portion located below the solder bump 12, which will be described later.

FIG. 12 is a cross-sectional view schematically showing an example of the process of forming the support member.

As shown in FIG. 12, the support member 20 provided with the piezoelectric layer 21 and the sacrificial layer 50 is formed by the same method as in FIGS. 5 to 7.

Through the above steps, the laminate 52 is produced. In the laminate 52, a sacrificial layer 50 is formed on the first main surface 21a of the piezoelectric layer 21, and a support member 20 having a recess 26 on a surface in contact with the sacrificial layer 50 is formed so as to cover the sacrificial layer 50. There is.

FIG. 13 is a cross-sectional view schematically showing an example of the process of removing the sacrificial layer.

As shown in FIG. 13, by removing the sacrificial layer 50, a cavity 53 is formed in the portion where the sacrificial layer 50 is provided.

Although not shown in FIG. 13, the step of forming the cavity 53 is a step of penetrating the piezoelectric layer 21 from the second main surface 21b (see FIG. 12) side to the sacrificial layer 50, as in FIGS. 9 and 10. It is preferable to include the steps of forming a hole and removing the sacrificial layer 50 by etching using the through hole.

FIG. 14 is a cross-sectional view schematically showing an example of the process of removing a part of the piezoelectric layer.

As shown in FIG. 14, the region above the cavity 53 in the piezoelectric layer 21 is removed. For example, it is preferable to remove the piezoelectric layer 21 on the sacrificial layer 50 using a fluid or the like.

FIGS. 15A, 15B, and 15C are cross-sectional views schematically showing an example of the process of forming a terminal electrode.

As shown in FIGS. 15A, 15B, and 15C, the terminal electrode 13 is formed by plating on the portion where the sacrificial layer 50 and the piezoelectric layer 21 have been removed.

The step of forming the terminal electrode 13 preferably includes a step of forming a plating seed layer 15 and a step of forming the terminal electrode 13 on the plating seed layer 15 by plating. The plating seed layer 15 is formed by, for example, a sputtering method. The terminal electrode 13 is formed, for example, by electrolytic plating or the like.

More preferably, the step of forming the terminal electrode 13 further includes a step of forming a resist 54, and a step of peeling off the resist 54 after forming the terminal electrode 13.

FIG. 16 is a cross-sectional view schematically showing an example of the process of forming electrodes such as wiring electrodes.

It is preferable that the step of forming electrodes such as the wiring electrode 14 described in FIG. 8 is performed after forming the terminal electrode 13. Specifically, the step of forming electrodes such as wiring electrode 14 is preferably performed after forming terminal electrode 13 and before forming solder bumps 12, which will be described later.

FIG. 17 is a cross-sectional view schematically showing an example of the process of forming solder bumps.

As shown in FIG. 17, solder bumps 12 are formed on terminal electrodes 13.

Through the above steps, the part shown in FIG. 3B is manufactured.

If necessary, the acoustic wave element 11 to which the solder bumps 12 are bonded may be mounted on the wiring board 30 by flip-chip bonding, and then the acoustic wave element 11 may be sealed with the sealing body 33. Through the above steps, the elastic wave device 10 shown in FIG. 1 is manufactured.

Below, details of an elastic wave device that utilizes a thickness-shear mode and plate waves will be explained. Note that the following description uses an example in which the functional electrode is an IDT electrode. The elastic wave device in the following example corresponds to an acoustic wave element in the present invention, and the intermediate layer corresponds to a dielectric layer in the present invention.

FIG. 18 is a schematic perspective view showing the appearance of an example of an elastic wave device that utilizes bulk waves in thickness shear mode. FIG. 19 is a plan view showing the electrode structure on the piezoelectric layer of the acoustic wave device shown in FIG. 18. FIG. 20 is a cross-sectional view of a portion taken along line AA in FIG. 18.

The acoustic wave device 1 has a piezoelectric layer 2 made of, for example, LiNbO ₃ . The piezoelectric layer 2 may be made of LiTaO ₃ . The cut angle of LiNbO ₃ or LiTaO ₃ is, for example, a Z cut, but may also be a rotational Y cut or an X cut. Preferably, the propagation directions of Y propagation and X propagation are ±30°. The thickness of the piezoelectric layer 2 is not particularly limited, but in order to effectively excite the thickness shear mode, it is preferably 50 nm or more and 1000 nm or less. The piezoelectric layer 2 has a first main surface 2a and a second main surface 2b that face each other. On the first main surface 2a of the piezoelectric layer 2, an electrode 3 and an electrode 4 are provided. Here, electrode 3 is an example of a "first electrode", and electrode 4 is an example of a "second electrode". In FIGS. 18 and 19, the plurality of electrodes 3 are the plurality of first electrode fingers connected to the first busbar electrode 5. In FIGS. The plurality of electrodes 4 are a plurality of second electrode fingers connected to the second busbar electrode 6. The plurality of electrodes 3 and the plurality of electrodes 4 are interposed with each other. Electrode 3 and electrode 4 have a rectangular shape and have a length direction. The electrode 3 and the adjacent electrode 4 face each other in a direction perpendicular to this length direction. These plurality of electrodes 3, electrodes 4, first busbar electrodes 5, and second busbar electrodes 6 constitute an IDT (Interdigital Transducer) electrode. The length direction of the electrodes 3 and 4 and the direction perpendicular to the length direction of the electrodes 3 and 4 are both directions that intersect the thickness direction of the piezoelectric layer 2. Therefore, it can be said that the electrode 3 and the adjacent electrode 4 face each other in the direction intersecting the thickness direction of the piezoelectric layer 2. Further, the length direction of the electrodes 3 and 4 may be replaced with the direction perpendicular to the length direction of the electrodes 3 and 4 shown in FIGS. 18 and 19. That is, in FIGS. 18 and 19, the electrodes 3 and 4 may be extended in the direction in which the first busbar electrode 5 and the second busbar electrode 6 are extended. In that case, the first busbar electrode 5 and the second busbar electrode 6 will extend in the direction in which the electrodes 3 and 4 extend in FIGS. 18 and 19. A plurality of pairs of structures in which an electrode 3 connected to one potential and an electrode 4 connected to the other potential are adjacent to each other are provided in a direction perpendicular to the length direction of the electrodes 3 and 4. There is. Here, the expression "electrode 3 and electrode 4 are adjacent" does not mean that electrode 3 and electrode 4 are arranged so as to be in direct contact with each other, but when electrode 3 and electrode 4 are arranged with a gap between them. refers to Further, when the electrode 3 and the electrode 4 are adjacent to each other, no electrode connected to the hot electrode or the ground electrode, including the other electrodes 3 and 4, is arranged between the electrode 3 and the electrode 4. This logarithm does not need to be an integer pair, but may be 1.5 pairs, 2.5 pairs, or the like. The center-to-center distance between the electrodes 3 and 4, that is, the pitch, is preferably in the range of 1 μm or more and 10 μm or less. Note that the center-to-center distance between the electrodes 3 and 4 refers to the center of the width dimension of the electrode 3 in the direction orthogonal to the length direction of the electrode 3, and the width dimension of the electrode 4 in the direction orthogonal to the length direction of the electrode 4. It is the distance between the center of Furthermore, if there is a plurality of at least one of the electrodes 3 and 4 (when the electrodes 3 and 4 are a pair of electrode sets, and there are 1.5 or more pairs of electrode sets), the distance between the centers of the electrodes 3 and 4 refers to the average value of the distance between the centers of adjacent electrodes 3 and 4 among 1.5 or more pairs of electrodes 3 and 4. Further, the width of the electrodes 3 and 4, that is, the dimension in the opposing direction of the electrodes 3 and 4, is preferably in the range of 150 nm or more and 1000 nm or less.

In this embodiment, when using a Z-cut piezoelectric layer, the direction perpendicular to the length direction of the electrodes 3 and 4 is the direction perpendicular to the polarization direction of the piezoelectric layer 2. This is not the case when a piezoelectric material having a different cut angle is used as the piezoelectric layer 2. Here, "orthogonal" is not limited to strictly orthogonal, but approximately orthogonal (for example, the angle between the direction orthogonal to the length direction of the electrodes 3 and 4 and the polarization direction is 90°±10°) But that's fine.

A support substrate 8 is laminated on the second main surface 2b side of the piezoelectric layer 2 with an intermediate layer (also called a bonding layer) 7 interposed therebetween. The intermediate layer 7 and the support substrate 8 have a frame-like shape, and have openings 7a and 8a, as shown in FIG. Thereby, a cavity 9 is formed. The cavity 9 is provided so as not to hinder the vibration of the excitation region C (see FIG. 19) of the piezoelectric layer 2. Therefore, the support substrate 8 is laminated on the second main surface 2b with the intermediate layer 7 interposed therebetween at a position that does not overlap with the portion where at least one pair of electrodes 3 and 4 are provided. Note that the intermediate layer 7 may not be provided. Therefore, the support substrate 8 can be laminated directly or indirectly on the second main surface 2b of the piezoelectric layer 2.

The intermediate layer 7 is made of silicon oxide, for example. However, other than silicon oxide, an appropriate insulating material such as silicon oxynitride or alumina can be used. The support substrate 8 is made of Si. The plane orientation of the Si surface on the piezoelectric layer 2 side may be (100), (110), or (111). Preferably, Si has a high resistivity of 4 kΩ or more. However, the support substrate 8 can also be constructed using an appropriate insulating material or semiconductor material. Examples of materials for the support substrate 8 include aluminum oxide, lithium tantalate, lithium niobate, piezoelectric materials such as crystal, alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, and starch. Various ceramics such as tite and forsterite, dielectrics such as diamond and glass, semiconductors such as gallium nitride, etc. can be used.

The plurality of electrodes 3, electrodes 4, first busbar electrode 5, and second busbar electrode 6 are made of an appropriate metal or alloy such as Al or AlCu alloy. In this embodiment, the electrode 3, the electrode 4, the first busbar electrode 5, and the second busbar electrode 6 have a structure in which an Al film is laminated on a Ti film. Note that an adhesive layer other than the Ti film may be used.

During driving, an AC voltage is applied between the plurality of electrodes 3 and the plurality of electrodes 4. More specifically, an AC voltage is applied between the first busbar electrode 5 and the second busbar electrode 6. Thereby, it is possible to obtain resonance characteristics using the thickness shear mode bulk wave excited in the piezoelectric layer 2. Further, in the acoustic wave device 1, when the thickness of the piezoelectric layer 2 is d, and the distance between the centers of any adjacent electrodes 3, 4 among the plurality of pairs of electrodes 3, 4 is p, d/p is 0. It is considered to be 5 or less. Therefore, the bulk wave in the thickness shear mode is effectively excited, and good resonance characteristics can be obtained. More preferably, d/p is 0.24 or less, in which case even better resonance characteristics can be obtained. Note that when there is a plurality of at least one of the electrodes 3 and 4 as in this embodiment, that is, when there are 1.5 or more pairs of electrodes 3 and 4 when the electrodes 3 and 4 are one pair of electrodes, The distance p between the centers of the adjacent electrodes 3 and 4 is the average distance between the centers of the adjacent electrodes 3 and 4.

Since the elastic wave device 1 of this embodiment has the above configuration, even if the logarithm of the electrodes 3 and 4 is reduced in an attempt to achieve miniaturization, the Q value is unlikely to decrease. This is because the resonator does not require reflectors on both sides and has little propagation loss. Further, the reason why the reflector is not required is because the bulk wave in the thickness shear mode is used. The difference between the Lamb wave used in a conventional elastic wave device and the thickness-shear mode bulk wave will be explained with reference to FIGS. 21 and 22.

FIG. 21 is a schematic front sectional view for explaining Lamb waves propagating through a piezoelectric film of an acoustic wave device. As shown in FIG. 21, in the elastic wave device described in Patent Document 1 (Japanese Patent Publication No. 2012-257019), waves propagate in the piezoelectric film 201 as indicated by arrows. Here, in the piezoelectric film 201, the first main surface 201a and the second main surface 201b are opposite to each other, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the Z direction. It is. The X direction is the direction in which the electrode fingers of the IDT electrodes are lined up. As shown in FIG. 21, in the Lamb wave, the wave propagates in the X direction as shown. Since it is a plate wave, the piezoelectric film 201 vibrates as a whole, but since the wave propagates in the X direction, reflectors are placed on both sides to obtain resonance characteristics. Therefore, wave propagation loss occurs, and when miniaturization is attempted, that is, when the number of logarithms of electrode fingers is reduced, the Q value decreases.

In contrast, FIG. 22 is a schematic front cross-sectional view for explaining a thickness-shear mode bulk wave propagating through a piezoelectric layer of an elastic wave device. As shown in FIG. 22, in the elastic wave device 1 of this embodiment, since the vibration displacement is in the thickness-slip direction, the waves connect the first main surface 2a and the second main surface 2b of the piezoelectric layer 2. It propagates almost in the Z direction, and resonates. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Since resonance characteristics are obtained by the propagation of waves in the Z direction, a reflector is not required. Therefore, no propagation loss occurs when propagating to the reflector. Therefore, even if the number of electrode pairs consisting of electrodes 3 and 4 is reduced in an attempt to promote miniaturization, the Q value is unlikely to decrease.

FIG. 23 is a diagram showing the amplitude direction of the bulk wave in the thickness shear mode. As shown in FIG. 23, the amplitude direction of the bulk wave in the thickness shear mode is opposite between the first region 451 included in the excitation region C of the piezoelectric layer 2 and the second region 452 included in the excitation region C. FIG. 23 schematically shows a bulk wave when a voltage is applied between electrode 3 and electrode 4 such that electrode 4 has a higher potential than electrode 3. In FIG. The first region 451 is a region of the excitation region C between a virtual plane VP1 that is perpendicular to the thickness direction of the piezoelectric layer 2 and bisects the piezoelectric layer 2, and the first main surface 2a. The second region 452 is a region of the excitation region C between the virtual plane VP1 and the second principal surface 2b.

As mentioned above, in the elastic wave device 1, at least one pair of electrodes consisting of the electrode 3 and the electrode 4 are arranged, but since the wave is not propagated in the X direction, the elastic wave device 1 is made up of the electrodes 3 and 4. There does not necessarily have to be a plurality of pairs of electrodes. That is, it is only necessary that at least one pair of electrodes be provided.

For example, the electrode 3 is an electrode connected to a hot potential, and the electrode 4 is an electrode connected to a ground potential. However, the electrode 3 may be connected to the ground potential, and the electrode 4 may be connected to the hot potential. In this embodiment, at least one pair of electrodes is an electrode connected to a hot potential or an electrode connected to a ground potential, as described above, and no floating electrode is provided.

FIG. 24 is a diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 18. Note that the design parameters of the elastic wave device 1 that obtained this resonance characteristic are as follows.

Piezoelectric layer 2: LiNbO ₃ with Euler angles (0°, 0°, 90°), thickness = 400 nm.
When viewed in a direction perpendicular to the length direction of electrodes 3 and 4, the area where electrodes 3 and 4 overlap, that is, the length of excitation area C = 40 μm, the logarithm of electrodes consisting of electrodes 3 and 4 = 21 pairs, center distance between electrodes = 3 μm, width of electrodes 3 and 4 = 500 nm, d/p = 0.133.
Intermediate layer 7: silicon oxide film with a thickness of 1 μm.
Support substrate 8: Si substrate.

Note that the length of the excitation region C is a dimension along the length direction of the electrodes 3 and 4 of the excitation region C.

In the elastic wave device 1, the distances between the electrode pairs made up of the electrodes 3 and 4 were all equal in multiple pairs. That is, the electrodes 3 and 4 were arranged at equal pitches.

As is clear from FIG. 24, good resonance characteristics with a fractional band of 12.5% are obtained despite not having a reflector.

By the way, if the thickness of the piezoelectric layer 2 is d, and the center-to-center distance between the electrodes 3 and 4 is p, then in this embodiment, as described above, d/p is preferably 0.5 or less, More preferably it is 0.24 or less. This will be explained with reference to FIG. 25.

A plurality of elastic wave devices were obtained in the same way as the elastic wave devices that obtained the resonance characteristics shown in FIG. 24, except that d/2p was changed. FIG. 25 is a diagram showing the relationship between d/2p and the fractional band as a resonator of an acoustic wave device, where p is the distance between the centers of adjacent electrodes and d is the thickness of the piezoelectric layer.

As is clear from FIG. 25, when d/2p exceeds 0.25, that is, when d/p>0.5, the fractional band is less than 5% even if d/p is adjusted. On the other hand, if d/2p≦0.25, that is, d/p≦0.5, the fractional bandwidth can be increased to 5% or more by changing d/p within that range. In other words, a resonator having a high coupling coefficient can be constructed. Further, when d/2p is 0.12 or less, that is, when d/p is 0.24 or less, the fractional band can be increased to 7% or more. In addition, by adjusting d/p within this range, it is possible to obtain a resonator with an even wider specific band, and it is possible to realize a resonator with an even higher coupling coefficient. Therefore, it can be seen that by setting d/p to 0.5 or less, it is possible to construct a resonator that utilizes the bulk wave of the thickness shear mode and has a high coupling coefficient.

Note that, as described above, the at least one pair of electrodes may be one pair, and in the case of one pair of electrodes, the above p is the distance between the centers of adjacent electrodes 3 and 4. Furthermore, in the case of 1.5 or more pairs of electrodes, the average distance between the centers of adjacent electrodes 3 and 4 may be set to p.

Further, regarding the thickness d of the piezoelectric layer, if the piezoelectric layer 2 has thickness variations, a value obtained by averaging the thicknesses may be adopted.

FIG. 26 is a plan view of another example of an elastic wave device that utilizes bulk waves in thickness-shear mode.

In the elastic wave device 61, a pair of electrodes including an electrode 3 and an electrode 4 are provided on the first main surface 2a of the piezoelectric layer 2. Note that K in FIG. 26 is the intersection width. As described above, in the elastic wave device of this embodiment, the number of pairs of electrodes may be one. Even in this case, if the above-mentioned d/p is 0.5 or less, bulk waves in the thickness shear mode can be excited effectively.

In the elastic wave device of this embodiment, preferably, in the plurality of electrodes 3 and 4, for an excitation region that is an overlapping region when viewed in the direction in which any of the adjacent electrodes 3 and 4 are facing each other, It is desirable that the metallization ratio MR of the adjacent electrodes 3 and 4 satisfies MR≦1.75(d/p)+0.075. In that case, spurious can be effectively reduced. This will be explained with reference to FIGS. 27 and 28.

FIG. 27 is a reference diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 18. A spurious signal indicated by arrow B appears between the resonant frequency and the anti-resonant frequency. Note that d/p=0.08 and the Euler angles of LiNbO ₃ (0°, 0°, 90°). Further, the metallization ratio MR was set to 0.35.

The metallization ratio MR will be explained with reference to FIG. 19. In the electrode structure of FIG. 19, when focusing on a pair of electrodes 3 and 4, it is assumed that only this pair of electrodes 3 and 4 are provided. In this case, the area surrounded by the dashed line C becomes the excitation region. This excitation region is the region where the electrode 3 overlaps the electrode 4 when the electrode 3 and the electrode 4 are viewed in a direction perpendicular to the length direction of the electrodes 3 and 4, that is, in a direction in which they face each other. and a region between electrodes 3 and 4 where electrodes 3 and 4 overlap. Then, the area of the electrodes 3 and 4 in the excitation region C with respect to the area of this excitation region becomes the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of the metallized portion to the area of the excitation region.

Note that when multiple pairs of electrodes are provided, MR may be the ratio of the metallized portion included in all the excitation regions to the total area of the excitation regions.

FIG. 28 is a diagram showing the relationship between the fractional band and the amount of phase rotation of spurious impedance normalized by 180 degrees as the magnitude of spurious when a large number of elastic wave resonators are configured according to the present embodiment. It is. Note that the specific band was adjusted by variously changing the thickness of the piezoelectric layer and the dimensions of the electrode. Further, although FIG. 28 shows the results when a Z-cut piezoelectric layer made of LiNbO ₃ is used, the same tendency is obtained when piezoelectric layers with other cut angles are used.

In the area surrounded by the ellipse J in FIG. 28, the spurious is as large as 1.0. As is clear from FIG. 28, when the fractional band exceeds 0.17, that is, exceeds 17%, a large spurious with a spurious level of 1 or more will affect the pass band even if the parameters that make up the fractional band are changed. Appear within. That is, as in the resonance characteristic shown in FIG. 27, a large spurious signal indicated by arrow B appears within the band. Therefore, it is preferable that the fractional band is 17% or less. In this case, by adjusting the thickness of the piezoelectric layer 2, the dimensions of the electrodes 3 and 4, etc., the spurious can be reduced.

FIG. 29 is a diagram showing the relationship between d/2p, metallization ratio MR, and fractional band. Among the above elastic wave devices, various elastic wave devices having different d/2p and MR were constructed and the fractional bands were measured.

The hatched area on the right side of the broken line D in FIG. 29 is the area where the fractional band is 17% or less. The boundary between the hatched area and the unhatched area is expressed as MR=3.5(d/2p)+0.075. That is, MR=1.75(d/p)+0.075. Therefore, preferably MR≦1.75 (d/p)+0.075. In that case, it is easy to set the fractional band to 17% or less. More preferably, it is the region to the right of MR=3.5(d/2p)+0.05 indicated by the dashed line D1 in FIG. That is, if MR≦1.75(d/p)+0.05, the fractional band can be reliably set to 17% or less.

FIG. 30 is a diagram showing a map of fractional bands with respect to Euler angles (0°, θ, ψ) of LiNbO ₃ when d/p is brought as close to 0 as possible.

The hatched areas in FIG. 30 are areas where a fractional band of at least 5% can be obtained, and the range of the area can be approximated by the following equations (1), (2), and (3). ).
(0°±10°, 0° to 20°, arbitrary ψ) ...Formula (1)
(0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ² /900) ^1/2 ) or (0°±10°, 20° to 80°, [180 °-60° (1-(θ-50) ² /900) ^1/2 ] ~ 180°) ...Formula (2)
(0°±10°, [180°-30° (1-(ψ-90) ² /8100) ^1/2 ] ~ 180°, arbitrary ψ) ...Formula (3)
Therefore, the Euler angle range of formula (1), formula (2), or formula (3) above is preferable because the fractional band can be made sufficiently wide.

FIG. 31 is a partially cutaway perspective view for explaining an example of an elastic wave device that utilizes Lamb waves.

The elastic wave device 81 has a support substrate 82. The support substrate 82 is provided with an open recess on the upper surface. A piezoelectric layer 83 is laminated on the support substrate 82 . Thereby, a cavity 9 is formed. An IDT electrode 84 is provided on the piezoelectric layer 83 above the cavity 9 . Reflectors 85 and 86 are provided on both sides of the IDT electrode 84 in the elastic wave propagation direction. In FIG. 31, the outer peripheral edge of the cavity 9 is shown by a broken line. Here, the IDT electrode 84 includes a first busbar electrode 84a, a second busbar electrode 84b, an electrode 84c as a plurality of first electrode fingers, and an electrode 84d as a plurality of second electrode fingers. and has. The plurality of electrodes 84c are connected to the first busbar electrode 84a. The plurality of electrodes 84d are connected to the second busbar electrode 84b. The plurality of electrodes 84c and the plurality of electrodes 84d are interposed with each other.

In the elastic wave device 81, by applying an alternating current electric field to the IDT electrode 84 on the cavity 9, a Lamb wave as a plate wave is excited. Since the reflectors 85 and 86 are provided on both sides, the resonance characteristic due to the Lamb wave described above can be obtained.

In this way, the elastic wave device of the present invention may utilize plate waves such as Lamb waves.

Furthermore, the elastic wave device of the present invention may utilize bulk waves. That is, the elastic wave device of the present invention can also be applied to a bulk acoustic wave (BAW) element. In this case, the functional electrodes are an upper electrode and a lower electrode.

FIG. 32 is a cross-sectional view schematically showing an example of an elastic wave device that uses bulk waves.

The elastic wave device 90 includes a support substrate 91. A cavity 93 is provided so as to penetrate the support substrate 91. A piezoelectric layer 92 is laminated on a support substrate 91 . An upper electrode 94 is provided on the first main surface 92a of the piezoelectric layer 92, and a lower electrode 95 is provided on the second main surface 92b of the piezoelectric layer 92. Although not shown, an intermediate layer may be provided between the support substrate 91 and the piezoelectric layer 92.

1 Acoustic wave device 2 Piezoelectric layer 2a First main surface of piezoelectric layer 2b Second main surface of piezoelectric layer 3 First electrode 4 Second electrode 5 First busbar electrode 6 Second busbar electrode 7 Intermediate layer 7a Opening Part 8 Support substrate 8a Opening 9 Cavity 10 Acoustic wave device 11 Acoustic wave element 12 Solder bump 13 Terminal electrode 14 Wiring electrode 15 Plating seed layer 20 Support member 21 Piezoelectric layer 21a First main surface of piezoelectric layer 21b Piezoelectric layer Second main surface 22 Functional electrode 23 Support substrate 24 Dielectric layer 25 Cavity 26 Recess 30 Wiring board 31 External terminal 32 Via conductor 33 Sealing body 41 Piezoelectric substrate 50 Sacrificial layer 51 Through hole 52 Laminated body 53 Cavity 54 Resist 61 Elasticity Wave device 81 Acoustic wave device 82 Support substrate 83 Piezoelectric layer 84 IDT electrode 84a First busbar electrode 84b Second busbar electrode 84c First electrode (first electrode finger)
84d Second electrode (second electrode finger)
85, 86 reflector 90 acoustic wave device 91 support substrate 92 piezoelectric layer 92a first main surface of piezoelectric layer 92b second main surface of piezoelectric layer 93 cavity 94 upper electrode 95 lower electrode 201 piezoelectric film 201a first main surface of piezoelectric film 1 principal surface 201b second principal surface of piezoelectric film 451 first region 452 second region C excitation region VP1 virtual plane

Claims (19)

1. an elastic wave element,
   a solder bump electrically connected to the acoustic wave element;
   a terminal electrode provided between the acoustic wave element and the solder bump;
   Equipped with
   The elastic wave element is
   a support member;
   a piezoelectric layer provided on one main surface of the support member;
   a functional electrode provided on at least one main surface of the piezoelectric layer;
   Equipped with
   The terminal electrode is provided on the one main surface of the support member,
   Elastic wave device.
2. A piezoelectric layer is not provided on a portion of the support member where the solder bump is located;
   The elastic wave device according to claim 1.
3. The support member has a recess on the one main surface,
   The terminal electrode is provided in the recess,
   The elastic wave device according to claim 1 or 2.
4. further comprising a wiring board electrically connected to the acoustic wave element via the terminal electrode and the solder bump,
   the acoustic wave element is mounted on the wiring board;
   The elastic wave device according to any one of claims 1 to 3.
5. The support member has a cavity on the one main surface,
   The piezoelectric layer is provided on the one main surface of the support member so as to cover the cavity,
   The functional electrode is provided so that at least a portion thereof overlaps with the cavity when viewed from the thickness direction of the piezoelectric layer.
   The elastic wave device according to any one of claims 1 to 4.
6. The elastic wave device according to any one of claims 1 to 5, wherein the support member includes a support substrate and an intermediate layer provided on the support substrate.
7. The piezoelectric layer is made of lithium niobate or lithium tantalate,
   The elastic wave device according to any one of claims 1 to 6.
8. The functional electrode includes one or more first electrodes, a first busbar electrode to which the one or more first electrodes are connected, one or more second electrodes, and the one or more second electrodes to which the functional electrode is connected. a second busbar electrode;
   The elastic wave device according to any one of claims 1 to 7.
9. The thickness of the piezoelectric layer is 2p or less, where p is the center-to-center distance between adjacent first electrodes and second electrodes among the one or more first electrodes and the one or more second electrodes. be,
   The elastic wave device according to claim 8.
10. It is configured to be able to utilize bulk waves in thickness-slip mode.
    The elastic wave device according to claim 8.
11. If the thickness of the piezoelectric layer is d, and the center-to-center distance between adjacent first and second electrodes among the one or more first electrodes and the one or more second electrodes is p, then d/ p≦0.5,
    The elastic wave device according to claim 8.
12. d/p≦0.24,
    The elastic wave device according to claim 11.
13. Of the one or more first electrodes and the one or more second electrodes, the area of the excitation region that overlaps when viewed in the direction in which adjacent first electrodes and second electrodes face each other, When the metallization ratio, which is the area ratio of the first electrode and the second electrode that match, is MR, the thickness of the piezoelectric layer is d, and the distance between the centers of the adjacent first and second electrodes is p, MR≦1.75(d/p)+0.075,
    The elastic wave device according to claim 8, 9, 11 or 12.
14. MR≦1.75(d/p)+0.05,
    The elastic wave device according to claim 13.
15. The Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate are in the range of the following formula (1), formula (2) or formula (3),
    The elastic wave device according to claim 8.
    (0°±10°, 0° to 20°, arbitrary ψ) ...Formula (1)
    (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ² /900) ^1/2 ) or (0°±10°, 20° to 80°, [180 °-60° (1-(θ-50) ² /900) ^1/2 ] ~ 180°) ...Formula (2)
    (0°±10°, [180°-30° (1-(ψ-90) ² /8100) ^1/2 ] ~ 180
    °, arbitrary ψ) ...Equation (3)
16. The elastic wave device according to any one of claims 1 to 8, which is configured to be able to utilize plate waves.
17. The piezoelectric layer has a second main surface facing the one main surface,
    The functional electrode has an upper electrode provided on the one main surface of the piezoelectric layer and a lower electrode provided on the other main surface,
    The acoustic wave device according to claim 1, wherein the upper electrode and the lower electrode face each other.
18. preparing a laminate in which a sacrificial layer is formed on a first main surface of a piezoelectric layer, and a support member having a recessed portion on a surface in contact with the sacrificial layer so as to cover the sacrificial layer;
    forming a cavity in a portion where the sacrificial layer is provided by removing the sacrificial layer;
    removing a region of the piezoelectric layer above the cavity;
    forming a terminal electrode by plating on a portion where the sacrificial layer and the piezoelectric layer have been removed;
    forming a solder bump on the terminal electrode;
    A method for manufacturing an elastic wave device, comprising:
19. The step of forming the cavity includes:
    forming a through hole in the piezoelectric layer from the second main surface side of the piezoelectric layer to the sacrificial layer;
    removing the sacrificial layer by etching using the through hole;
    The method for manufacturing an elastic wave device according to claim 18, comprising:

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