WO2023199837A1 - Elastic wave device - Google Patents

Abstract

An elastic wave device 10 comprises: a support member 20 having a cavity 23 in one main surface thereof; a piezoelectric layer 21 provided on the one main surface of the support member 20 so as to cover the cavity 23; and a functional electrode 22 provided on at least one of the main surfaces of the piezoelectric layer 21 so as to at least partially overlap with the cavity 23 when viewed from the thickness direction of the piezoelectric layer 21. The support member 20 includes a first substrate 31 and an intermediate layer 41 provided between the first substrate 31 and the piezoelectric layer 21. The support member 20 contains the same type of material as the piezoelectric layer 21.

Description

elastic wave device

The present invention relates to an elastic wave device.

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.

Japanese Patent Application Publication No. 2012-257019

In an acoustic wave device as described in Patent Document 1, when the support body (hereinafter referred to as a support substrate) is made of silicon (Si), the material of the support substrate and the material of the piezoelectric substrate (hereinafter referred to as a piezoelectric layer) are Since the coefficients of linear expansion are different, stress is applied to the piezoelectric layer above the cavity, and there is a risk that cracks may occur in the piezoelectric layer.

An object of the present invention is to provide an elastic wave device that can prevent cracks from occurring in a piezoelectric layer.

The elastic wave device of the present invention includes a support member having a cavity on one main surface, a piezoelectric layer provided on the one main surface of the support member so as to cover the cavity, and at least one of the piezoelectric layers. A functional electrode is provided on the main surface so that at least a portion thereof overlaps with the cavity when viewed from the thickness direction of the piezoelectric layer. The support member includes a first substrate and an intermediate layer provided between the first substrate and the piezoelectric layer. The support member contains the same kind of material as the piezoelectric layer.

According to the present invention, it is possible to provide an acoustic wave device that can prevent cracks from occurring in the piezoelectric layer.

FIG. 1 is a cross-sectional view schematically showing an example of an elastic wave device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a calculation model of the elastic wave device. FIG. 3 is an enlarged cross-sectional view of a portion surrounded by a broken line in FIG. 2. FIG. FIG. 4 is a plan view showing the relationship between the Y direction shown in FIG. 2 and functional electrodes. FIG. 5 is a graph showing the dependence of the coefficient of linear expansion in the X direction on the maximum principal stress of the portion indicated by the arrow in FIG. FIG. 6 is a graph showing the dependence of the linear expansion coefficient in the X direction on the reduction rate of the relative maximum principal stress. FIG. 7 is a graph showing the relationship between the coefficient of linear expansion in the X direction and the cut angle of the piezoelectric layer. FIG. 8 is a cross-sectional view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate. FIG. 9 is a cross-sectional view schematically showing an example of the process of forming the intermediate layer. FIG. 10 is a cross-sectional view schematically showing an example of the process of bonding the first substrate to the intermediate layer. FIG. 11 is a cross-sectional view schematically showing an example of a process of thinning a piezoelectric substrate. FIG. 12 is a cross-sectional view schematically showing an example of the process of forming functional electrodes, busbar electrodes, and wiring electrodes. FIG. 13 is a cross-sectional view schematically showing an example of the process of forming a through hole. FIG. 14 is a cross-sectional view schematically showing an example of the process of removing the sacrificial layer. FIG. 15 is a cross-sectional view schematically showing another example of the elastic wave device according to the first embodiment of the present invention. FIG. 16 is a cross-sectional view schematically showing an example of an elastic wave device according to a second embodiment of the present invention. FIG. 17 is a cross-sectional view schematically showing another example of the elastic wave device according to the second embodiment of the present invention. FIG. 18 is a cross-sectional view schematically showing still another example of the elastic wave device according to the second embodiment of the present invention. FIG. 19 is a sectional view schematically showing a first modification of the elastic wave device according to the first embodiment of the present invention. FIG. 20 is a sectional view schematically showing a second modification of the elastic wave device according to the first embodiment of the present invention. 21A to 21E are cross-sectional views schematically showing an example of a method of forming a cavity on the first substrate side of the support member. FIG. 22 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. 23 is a plan view showing the electrode structure on the piezoelectric layer of the acoustic wave device shown in FIG. 22. FIG. 24 is a cross-sectional view of a portion taken along line AA in FIG. 22. FIG. 25 is a schematic front sectional view for explaining Lamb waves propagating through the piezoelectric film of the acoustic wave device. FIG. 26 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. 27 is a diagram showing the amplitude direction of the bulk wave in the thickness shear mode. FIG. 28 is a diagram showing an example of resonance characteristics of the elastic wave device shown in FIG. 22. FIG. 29 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. 30 is a plan view of another example of an elastic wave device that uses thickness-shear mode bulk waves. FIG. 31 is a reference diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 22. FIG. 32 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. 33 is a diagram showing the relationship between d/2p, metallization ratio MR, and fractional band. FIG. 34 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. 35 is a partially cutaway perspective view for explaining an example of an elastic wave device that uses Lamb waves. FIG. 36 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."

[First embodiment]
FIG. 1 is a cross-sectional view schematically showing an example of an elastic wave device according to a first embodiment of the present invention.

The elastic wave device 10 shown in FIG. 1 includes a support member 20, a piezoelectric layer 21, and a functional electrode 22.

The support member 20 has a cavity 23 on one main surface (the upper main surface in FIG. 1).

The piezoelectric layer 21 is provided on one main surface of the support member 20 so as to cover the cavity 23.

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 FIG. 1, the functional electrode 22 is provided on one main surface (the upper main surface in FIG. 1) of the piezoelectric layer 21.

The functional electrode 22 is provided so that at least a portion thereof overlaps with the cavity 23 when viewed from the thickness direction of the piezoelectric layer 21 (vertical direction in FIG. 1). 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 23, or a part of the functional electrode 22 may be provided so as to overlap with the cavity 23. .

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

In the example shown in FIG. 1, the functional electrode 22 is connected to a busbar electrode and wiring electrode 24, and a two-layer wiring 25.

The support member 20 includes a first substrate 31 and an intermediate layer (also referred to as a bonding layer or an insulating layer) 41 provided between the first substrate 31 and the piezoelectric layer 21.

The intermediate layer 41 is made of silicon oxide (SiO _x ) such as silicon dioxide (SiO ₂ ), for example.

The cavity 23 may or may not penetrate the support member 20 in the thickness direction (vertical direction in FIG. 1). For example, the cavity 23 may be provided so as to penetrate the intermediate layer 41 in the thickness direction, or the cavity 23 may be provided so as not to penetrate the intermediate layer 41 in the thickness direction.

The support member 20 contains the same kind of material as the piezoelectric layer 21.

In this specification, the term "materials of the same kind" includes not only cases where the materials are completely the same, but also cases where the crystallinity or orientation is different, and cases where the presence or absence or concentration of additives is different. The same applies to the following.

In the acoustic wave device 10, by holding the piezoelectric layer 21 on which the functional electrode 22 is provided with the support member 20 containing the same material as the piezoelectric layer 21, it is possible to reduce the difference in linear expansion coefficient between the two. can. Thereby, stress on the membrane portion 21M, which is a part of the piezoelectric layer 21, can be reduced and cracks generated in the piezoelectric layer 21 can be prevented.

In this specification, the portion of the piezoelectric layer located in the region overlapping with the cavity when viewed from the thickness direction is also referred to as a "membrane portion."

The thickness of the first substrate 31 may be the same as the thickness of the piezoelectric layer 21, may be greater than the thickness of the piezoelectric layer 21, or may be smaller than the thickness of the piezoelectric layer 21. The thickness of the first substrate 31 may be the same as the thickness of the intermediate layer 41, may be greater than the thickness of the intermediate layer 41, or may be smaller than the thickness of the intermediate layer 41.

The first substrate 31 is made of the same kind of material as the piezoelectric layer 21, for example. Thus, the first substrate 31 is preferably a piezoelectric substrate. Specifically, the first substrate 31 is made of, for example, lithium niobate (LiNbO _x ) or lithium tantalate (LiTaO _x ). In that case, the first substrate 31 may be made of LiNbO ₃ or LiTaO ₃ .

In order to verify the quantitative effect when the first substrate 31 is a piezoelectric substrate, the following two-dimensional model is used to evaluate the relationship between the linear expansion coefficient of the first substrate 31 and the stress that causes cracks in the membrane portion 21M. A simulation was conducted.

FIG. 2 is a cross-sectional view showing a calculation model of the elastic wave device. FIG. 3 is an enlarged cross-sectional view of a portion surrounded by a broken line in FIG. 2. FIG. FIG. 4 is a plan view showing the relationship between the Y direction shown in FIG. 2 and functional electrodes.

The elastic wave device 10A shown in FIG. 2 includes a support member 20, a piezoelectric layer 21, a functional electrode 22 (see FIG. 4), a single-layer electrode 24A, and a double-layer electrode 25A. The support member 20 has a cavity 23 on one main surface (the upper main surface in FIG. 2).

The support member 20 includes a first substrate 31 and an intermediate layer 41 provided between the first substrate 31 and the piezoelectric layer 21.

The constituent material of the piezoelectric layer 21 is lithium niobate (LiNbO ₃ ), the functional electrode 22 is an IDT electrode, and the constituent material of the intermediate layer 41 is silicon dioxide (SiO ₂ ).

It is thought that cracks in the membrane portion 21M occur in the vicinity of the piezoelectric layer 21 and the intermediate layer 41 and in the region of the piezoelectric layer 21 where the functional electrode 22 is not provided. Additionally, twisted hackles, which are characteristic of ceramic cracks, have been observed. It is generally believed that cracks in ceramics are caused by principal stress generated within the ceramic.

Based on the above, the maximum value of the principal stress (also referred to as maximum principal stress) in the portion indicated by the arrow in FIG. 3, where it is thought that cracks are likely to occur in the membrane portion 21M, was calculated by simulation.

The calculation conditions used for the simulation are shown below.
Stress generation conditions: Heat to the maximum reflow temperature (270°C).
Material conditions:
(1) When the first substrate 31 is made of Si, the orientation of lithium niobate in the piezoelectric layer 21 is changed.
(2) When the first substrate 31 is made of the same lithium niobate as the piezoelectric layer 21, the orientation of the lithium niobate in the piezoelectric layer 21 is changed.

FIG. 5 is a graph showing the dependence of the linear expansion coefficient in the X direction on the maximum principal stress in the portion indicated by the arrow in FIG.

From FIG. 5, when the first substrate 31 is made of lithium niobate (LN substrate), the linear expansion coefficient of the piezoelectric layer 21 in the X direction is smaller than when the first substrate 31 is made of Si (Si substrate). It can be seen that the larger the value, the smaller the maximum principal stress.

FIG. 6 is a graph showing the dependence of the coefficient of linear expansion in the X direction on the reduction rate of the relative maximum principal stress.

When the relative reduction rate of the maximum principal stress was calculated from the results of FIG. 5, as shown in FIG. 6, if the coefficient of linear expansion of the piezoelectric layer 21 in the It is expected that the effect will be reduced by 5% or more.

FIG. 7 is a graph showing the relationship between the coefficient of linear expansion in the X direction and the cut angle of the piezoelectric layer.

From FIG. 7, if the cut angle of the piezoelectric layer 21 is in the range of 90 degrees or more and 163 degrees or less, a linear expansion coefficient of 0.8 ppm/℃ or more can be obtained, so the maximum principal stress can be reduced by 5% or more. expected.

From the results of FIGS. 5, 6, and 7, when the piezoelectric layer 21 is made of lithium niobate such as LiNbO ₃ , if the rotational Y cut angle of the piezoelectric layer 21 is in the range of 90 degrees or more and 163 degrees or less, Since the effect of reducing the maximum principal stress by 5% or more is expected, it is considered to be effective against cracks. Therefore, it is preferable that the piezoelectric layer 21 is made of lithium niobate such as LiNbO ₃ and that the rotational Y-cut angle of the piezoelectric layer 21 is in the range of 90 degrees or more and 163 degrees or less. In particular, it is preferable that the piezoelectric layer 21 and the first substrate 31 are made of lithium niobate such as LiNbO ₃ and that the rotational Y-cut angle of the piezoelectric layer 21 is in the range of 90 degrees or more and 163 degrees or less.

The elastic wave device of the present invention is manufactured, for example, by the following method.

FIG. 8 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. 8, a sacrificial layer 50 is formed on the piezoelectric substrate 30.

As the piezoelectric substrate 30, 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. 9 is a cross-sectional view schematically showing an example of the process of forming the intermediate layer.

As shown in FIG. 9, after forming the intermediate layer 41 to cover the sacrificial layer 50, the surface of the intermediate layer 41 is planarized.

As the intermediate layer 41, for example, a SiO ₂ film or the like is formed. The intermediate layer 41 can be formed by, for example, a sputtering method. The intermediate layer 41 can be planarized by, for example, chemical mechanical polishing (CMP).

FIG. 10 is a cross-sectional view schematically showing an example of the process of bonding the first substrate to the intermediate layer.

As shown in FIG. 10, the first substrate 31 is bonded to the intermediate layer 41. Thereby, the support member 20 is formed.

As the first substrate 31, a piezoelectric substrate made of, for example, LiNbO ₃ or LiTaO ₃ is used.

FIG. 11 is a cross-sectional view schematically showing an example of the process of thinning the piezoelectric substrate.

As shown in FIG. 11, the piezoelectric substrate 30 is thinned. As a result, the piezoelectric layer 21 is formed. The piezoelectric substrate 30 can be thinned by, for example, a smart cut method, polishing, or the like.

FIG. 12 is a cross-sectional view schematically showing an example of the process of forming functional electrodes, busbar electrodes, and wiring electrodes.

As shown in FIG. 12, a functional electrode 22, a busbar electrode, and a wiring electrode 24 are formed on one main surface of the piezoelectric layer 21. The functional electrode 22, the bus bar electrode, and the wiring electrode 24 can be formed by, for example, a lift-off method. Although not shown, a two-layer wiring 25 (see FIG. 1) is also formed on one main surface of the piezoelectric layer 21.

FIG. 13 is a cross-sectional view schematically showing an example of the step of forming a through hole.

As shown in FIG. 13, 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. 14 is a cross-sectional view schematically showing an example of the process of removing the sacrificial layer.

As shown in FIG. 14, 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 23 is formed in the support member 20.

Through the above steps, the elastic wave device 10 is obtained.

FIG. 15 is a cross-sectional view schematically showing another example of the elastic wave device according to the first embodiment of the present invention.

As in the elastic wave device 10B shown in FIG. 15, the support member 20 may further include a second substrate 32 made of Si on the opposite side of the intermediate layer 41 with the first substrate 31 in between.

The thickness of the second substrate 32 may be the same as the thickness of the first substrate 31, may be greater than the thickness of the first substrate 31, or may be smaller than the thickness of the first substrate 31. The thickness of the second substrate 32 may be the same as the thickness of the piezoelectric layer 21, may be greater than the thickness of the piezoelectric layer 21, or may be smaller than the thickness of the piezoelectric layer 21. The thickness of the second substrate 32 may be the same as the thickness of the intermediate layer 41, may be greater than the thickness of the intermediate layer 41, or may be smaller than the thickness of the intermediate layer 41.

It is preferable that the outer circumferential edge of the second substrate 32 be located outside the outer circumferential edge of the first substrate 31 when viewed from the thickness direction. That is, it is preferable that the outer periphery of the first substrate 31 is located inside the outer periphery of the second substrate 32 when viewed from the thickness direction.

An intermediate layer 42 may be provided between the first substrate 31 and the second substrate 32.

Alternatively, the intermediate layer 42 may not be provided between the first substrate 31 and the second substrate 32. That is, the first substrate 31 and the second substrate 32 may be directly bonded.

The material constituting the intermediate layer 42 is preferably the same type of material as the material constituting the intermediate layer 41.

The thickness of the intermediate layer 42 may be the same as the thickness of the intermediate layer 41, may be greater than the thickness of the intermediate layer 41, or may be smaller than the thickness of the intermediate layer 41. The thickness of the intermediate layer 42 may be the same as the thickness of the piezoelectric layer 21, may be greater than the thickness of the piezoelectric layer 21, or may be smaller than the thickness of the piezoelectric layer 21. The thickness of the intermediate layer 42 may be the same as the thickness of the first substrate 31, may be greater than the thickness of the first substrate 31, or may be smaller than the thickness of the first substrate 31. The thickness of the intermediate layer 42 may be the same as the thickness of the second substrate 32, may be greater than the thickness of the second substrate 32, or may be smaller than the thickness of the second substrate 32.

[Second embodiment]
In the elastic wave device according to the second embodiment of the present invention, the support member further includes a second substrate made of Si on the opposite side of the intermediate layer with the first substrate in between. Furthermore, a third substrate made of Si or metal is provided with a gap between the piezoelectric layer and the main surface of the piezoelectric layer opposite to the cavity, and the second substrate and the third substrate are metal-bonded. Hermetically sealed.

In the acoustic wave device according to the second embodiment of the present invention, as in the first embodiment, the piezoelectric layer provided with the functional electrode is held by a support member containing the same kind of material as the piezoelectric layer, so that both The difference in linear expansion coefficient can be reduced. This can reduce stress on the membrane portion, which is a part of the piezoelectric layer, and prevent cracks from occurring in the piezoelectric layer.

On the other hand, in the hermetically sealed package structure in which wafers are bonded together using metal bonding such as Au-Au bonding or solder bonding, which is generally used to realize a compact and low-profile structure, the supporting member is of the same type as the piezoelectric layer. In the case of containing a material, there is a problem in that it is difficult to reduce the thickness by grinding because the flexural strength is weaker than that of a Si substrate which is commonly used as a support substrate.

Therefore, the support member further includes a second substrate made of Si, and the second substrate made of Si and the third substrate made of Si or metal are hermetically sealed by metal bonding, thereby improving the grindability of the substrate. As a result, a low-profile, hermetically sealed package structure can be realized.

FIG. 16 is a cross-sectional view schematically showing an example of an elastic wave device according to the second embodiment of the present invention.

The elastic wave device 10C shown in FIG. 16 includes a support member 20, a piezoelectric layer 21, and a functional electrode 22.

The support member 20 has a cavity 23 on one main surface (the upper main surface in FIG. 16).

The piezoelectric layer 21 is provided on one main surface of the support member 20 so as to cover the cavity 23.

The functional electrode 22 is provided on at least one main surface of the piezoelectric layer 21. In the example shown in FIG. 16, the functional electrode 22 is provided on one main surface (the upper main surface in FIG. 16) of the piezoelectric layer 21.

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

In the example shown in FIG. 16, the functional electrode 22 is connected to a busbar electrode and wiring electrode 24, and a two-layer wiring 25.

The support member 20 includes a first substrate 31 and an intermediate layer 41 provided between the first substrate 31 and the piezoelectric layer 21.

Similar to the first embodiment, the support member 20 contains the same type of material as the piezoelectric layer 21. The first substrate 31 is made of the same kind of material as the piezoelectric layer 21, for example. The intermediate layer 41 is made of silicon oxide (SiO _x ) such as silicon dioxide (SiO ₂ ), for example.

The support member 20 further includes a second substrate 32 made of Si on the opposite side of the intermediate layer 41 with the first substrate 31 in between.

The intermediate layer 42 may be provided between the first substrate 31 and the second substrate 32, or the intermediate layer 42 may not be provided.

The elastic wave device 10C further includes a third substrate 33 made of Si or metal. The third substrate 33 is provided at a distance from the piezoelectric layer 21 so as to face the main surface of the piezoelectric layer 21 on the side opposite to the cavity 23 .

The third substrate 33 is made of, for example, Si. In that case, the second substrate 32 and the third substrate 33 are both Si substrates.

Alternatively, the third substrate 33 is made of metal. In that case, the third substrate 33 is, for example, a metal substrate made of Cu or the like.

The thickness of the third substrate 33 may be the same as the thickness of the first substrate 31, may be greater than the thickness of the first substrate 31, or may be smaller than the thickness of the first substrate 31. Further, the thickness of the third substrate 33 may be the same as the thickness of the second substrate 32, may be greater than the thickness of the second substrate 32, or may be smaller than the thickness of the second substrate 32.

As shown in FIG. 16, the second substrate 32 and the third substrate 33 are hermetically sealed by metal bonding.

The metal bond is, for example, Au-Au bond or solder bond.

In the example shown in FIG. 16, the second substrate 32 and the third substrate 33 are hermetically sealed by a metal seal 35 and a solder seal 37.

The elastic wave device 10C further includes a terminal electrode 45 that is electrically connected to the functional electrode 22.

In the example shown in FIG. 16, the terminal electrode 45 is exposed on the surface of the second substrate 32 on the opposite side to the first substrate 31. That is, the terminal electrode 45 is arranged on the second substrate 32 side.

Specifically, the terminal electrode 45 is provided so as to penetrate the support member 20 in the thickness direction.

Solder balls 47 are provided on the surface of the second substrate 32 on the opposite side from the first substrate 31. The solder ball 47 is electrically connected to the functional electrode 22 via the terminal electrode 45, the two-layer wiring 25, and the like.

FIG. 17 is a cross-sectional view schematically showing another example of the elastic wave device according to the second embodiment of the present invention.

As in the acoustic wave device 10D shown in FIG. 17, the cross sections of the piezoelectric layer 21, intermediate layer 41, and first substrate 31 may have a tapered shape toward the piezoelectric layer 21 side. When the intermediate layer 42 is provided between the first substrate 31 and the second substrate 32, the cross section of the intermediate layer 42 may also have a tapered shape toward the piezoelectric layer 21 side. In this way, the cross sections of the support member 20 and the piezoelectric layer 21 excluding the second substrate 32 may have a tapered shape toward the piezoelectric layer 21 side.

FIG. 18 is a cross-sectional view schematically showing still another example of the elastic wave device according to the second embodiment of the present invention.

In the acoustic wave device 10E shown in FIG. 18, the terminal electrode 45 is exposed on the surface of the third substrate 33 on the opposite side from the piezoelectric layer 21. That is, the terminal electrode 45 is arranged on the third substrate 33 side.

In the example shown in FIG. 18, the terminal electrode 45 penetrates the third substrate 33 in the thickness direction and reaches the surface of the second substrate 32 on the first substrate 31 side. A two-layer wiring 25 extending to the surface of the second substrate 32 on the first substrate 31 side is connected to the terminal electrode 45.

Solder balls 47 are provided on the surface of the third substrate 33 on the opposite side from the piezoelectric layer 21. The solder ball 47 is electrically connected to the functional electrode 22 via the terminal electrode 45, the two-layer wiring 25, and the like.

As shown in FIG. 18, the cross sections of the piezoelectric layer 21, intermediate layer 41, and first substrate 31 may have a tapered shape toward the piezoelectric layer 21 side. When the intermediate layer 42 is provided between the first substrate 31 and the second substrate 32, the cross section of the intermediate layer 42 may also have a tapered shape toward the piezoelectric layer 21 side. In this way, the cross sections of the support member 20 and the piezoelectric layer 21 excluding the second substrate 32 may have a tapered shape toward the piezoelectric layer 21 side.

[Other embodiments]
The elastic wave device of the present invention is not limited to the above embodiments, and various applications and modifications can be made within the scope of the present invention regarding the configuration, manufacturing conditions, etc. of the elastic wave device.

In the first and second embodiments of the present invention, the cavity is provided on the intermediate layer side of the support member, but the cavity may be provided on the first substrate side of the support member.

Hereinafter, a modification of the elastic wave device according to the first embodiment of the present invention will be described, but the same applies to the elastic wave device according to the second embodiment of the present invention.

FIG. 19 is a cross-sectional view schematically showing a first modification of the elastic wave device according to the first embodiment of the present invention.

In the elastic wave device 10F shown in FIG. 19, a cavity 23 is provided on the first substrate 31 side of the support member 20. An intermediate layer 41 is provided between the piezoelectric layer 21 and the cavity 23. The first substrate 31 is made of the same kind of material as the piezoelectric layer 21, for example.

As will be described later, the cavity 23 can be formed on the first substrate 31 side by diffusing various metals such as titanium (Ti) into the first substrate 31 using heat.

FIG. 20 is a sectional view schematically showing a second modification of the elastic wave device according to the first embodiment of the present invention.

Also in the elastic wave device 10G shown in FIG. 20, a cavity 23 is provided on the first substrate 31 side of the support member 20. As shown in FIG. 20, the intermediate layer 41 may not be provided between the piezoelectric layer 21 and the cavity 23.

FIGS. 21A to 21E are cross-sectional views schematically showing an example of a method for forming a cavity on the first substrate side of the support member.

First, as shown in FIG. 21A, a piezoelectric substrate 30 having an intermediate layer 41 provided on its surface is prepared.

Separately, as shown in FIG. 21B, a first substrate 31 in which a sacrificial layer 50 is embedded is prepared.

Next, as shown in FIG. 21C, the piezoelectric substrate 30 and the first substrate 31 are bonded by atomic diffusion bonding (ADB) so that the intermediate layer 41 and the sacrificial layer 50 face each other.

In the example shown in FIG. 21C, the piezoelectric substrate 30 and the first substrate 31 are bonded via a metal layer 52 such as Ti.

Subsequently, as shown in FIG. 21D, heat treatment is performed on the joined piezoelectric substrate 30 and first substrate 31. Due to the heat treatment, metal such as Ti contained in the metal layer 52 is diffused into the piezoelectric material (lithium niobate, etc.) of the first substrate 31.

Then, as shown in FIG. 21E, the piezoelectric substrate 30 is thinned to form the piezoelectric layer 21, and electrodes such as the functional electrode 22 are formed. Thereafter, the sacrificial layer 50 is removed using the through hole 51. The metal layer 52 on the sacrificial layer 50 is removed together with the sacrificial layer 50. As a result, a cavity 23 is formed on the first substrate 31 side of the support member 20.

In the following, details of an elastic wave device that utilizes a thickness shear mode and a plate wave will be described using as an example an elastic wave device in which the material of the support substrate corresponding to the first substrate is not limited to the same type of material as the piezoelectric layer. Note that the following description uses an example in which the functional electrode is an IDT electrode.

FIG. 22 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. 23 is a plan view showing the electrode structure on the piezoelectric layer of the acoustic wave device shown in FIG. 22. FIG. 24 is a cross-sectional view of a portion taken along line AA in FIG. 22.

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. 22 and 23, 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. 22 and 23. That is, in FIGS. 22 and 23, 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. 22 and 23. 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. 23) 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. 25 and 26.

FIG. 25 is a schematic front sectional view for explaining Lamb waves propagating through the piezoelectric film of the acoustic wave device. As shown in FIG. 25, 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. 25, 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.

On the other hand, FIG. 26 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. 26, 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. 27 is a diagram showing the amplitude direction of the bulk wave in the thickness shear mode. As shown in FIG. 27, 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. 27 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. 28 is a diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 22. 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. 28, 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. 29.

A plurality of elastic wave devices were obtained in the same manner as the elastic wave device that obtained the resonance characteristics shown in FIG. 28, except that d/2p was changed. FIG. 29 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. 29, 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. 30 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. 30 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. 31 and 32.

FIG. 31 is a reference diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 22. 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. 23. In the electrode structure of FIG. 23, 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. 32 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. Furthermore, although FIG. 32 shows the results when a Z-cut piezoelectric layer made of LiNbO ₃ is used, the same tendency occurs even when piezoelectric layers with other cut angles are used.

In the region surrounded by the ellipse J in FIG. 32, the spurious is as large as 1.0. As is clear from FIG. 32, 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 constituting the fractional band are changed. Appear within. That is, as in the resonance characteristic shown in FIG. 31, 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. 33 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. 33 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. 34 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. 34 are regions where a fractional band of at least 5% can be obtained, and the range of these regions 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. 35 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. 35, the outer periphery 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. 36 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, 10A, 10B, 10C, 10D, 10E, 10F, 10G Acoustic wave device 20 Support member 21 Piezoelectric layer 21M Membrane section 22 Functional electrode 23 Cavity 24 Bus bar electrode and wiring electrode 24A 1st layer electrode 25 2nd layer wiring 25A 2nd layer electrode 30 Piezoelectric substrate 31 1st substrate 32 2nd substrate 33 3rd substrate 35 Metal seal 37 Solder seal 41, 42 Intermediate layer 45 Terminal electrode 47 Solder ball 50 Sacrificial layer 51 Through hole 52 Metal layer 61 Acoustic 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 (20)

1. a support member having a hollow portion on one main surface;
   a piezoelectric layer provided on the one main surface of the support member so as to cover the cavity;
   a functional electrode provided on at least one main surface of the piezoelectric layer so that at least a portion thereof overlaps with the cavity when viewed from the thickness direction of the piezoelectric layer;
   Equipped with
   The support member includes a first substrate and an intermediate layer provided between the first substrate and the piezoelectric layer,
   The support member contains the same kind of material as the piezoelectric layer,
   Elastic wave device.
2. The first substrate is made of the same material as the piezoelectric layer,
   The elastic wave device according to claim 1.
3. the piezoelectric layer is made of lithium niobate,
   The rotational Y cut angle of the piezoelectric layer is in the range of 90 degrees or more and 163 degrees or less,
   The elastic wave device according to claim 1 or 2.
4. The support member further includes a second substrate made of Si on the opposite side of the intermediate layer with the first substrate in between.
   The elastic wave device according to any one of claims 1 to 3.
5. further comprising a third substrate made of Si or metal and provided at a distance from the piezoelectric layer so as to face the main surface of the piezoelectric layer on the opposite side to the cavity,
   the second substrate and the third substrate are hermetically sealed by metal bonding;
   The elastic wave device according to claim 4.
6. further comprising a terminal electrode electrically connected to the functional electrode,
   the terminal electrode is exposed on a surface of the second substrate opposite to the first substrate;
   The elastic wave device according to claim 5.
7. further comprising a terminal electrode electrically connected to the functional electrode,
   the terminal electrode is exposed on a surface of the third substrate opposite to the piezoelectric layer;
   The elastic wave device according to claim 5.
8. The metal bond is an Au-Au bond or a solder bond,
   The elastic wave device according to any one of claims 5 to 7.
9. The third substrate is made of Si,
   The elastic wave device according to any one of claims 5 to 8.
10. The piezoelectric layer is made of lithium niobate or lithium tantalate,
    The elastic wave device according to any one of claims 1 to 9.
11. 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 10.
12. 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 11.
13. It is configured to be able to utilize bulk waves in thickness-slip mode.
    The elastic wave device according to claim 11.
14. 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 11.
15. d/p≦0.24,
    The elastic wave device according to claim 14.
16. 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 11, 12, 14 or 15.
17. MR≦1.75(d/p)+0.05,
    The elastic wave device according to claim 16.
18. 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 11.
    (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)
19. Configured to utilize plate waves,
    The elastic wave device according to any one of claims 1 to 11.
20. 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.

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