WO2023190697A1 - Elastic wave device - Google Patents

Abstract

This elastic wave device 10 comprises: a support member 20 that has a cavity 23 on one of the two main surfaces thereof; a piezoelectric layer 21 that is provided on the one main surface of the support member 20 so as to cover the cavity 23; and function electrodes 22 that are provided on at least one of the two main surfaces of the piezoelectric layer 21 such that at least some of the function electrodes 22 overlie the cavity 23 as viewed in the thickness direction of the piezoelectric layer 21. In the piezoelectric layer 21, cracks 24 are provided in a region which overlies the cavity 23 when viewed in the thickness direction of the piezoelectric layer 21 and in which the function electrodes 22 are not provided. The cracks 24 have a width smaller than the thickness of the piezoelectric layer 21 and continuously extend from the one main surface of the piezoelectric layer 21 to the other main surface thereof.

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.

Patent Document 2 discloses a supporting member having a recessed portion on its upper surface, and a supporting member having an upper surface and a lower surface, and is provided on the supporting member so as to cover the recessed portion of the supporting member, and the supporting member is provided with a recessed portion of the supporting member. A piezoelectric thin film having a portion located in a hollow space, and an IDT electrode provided on the upper surface of the piezoelectric thin film and having a plurality of electrode fingers, the plate is in S0 mode or SHO mode. It utilizes waves, and is provided on the upper surface or the lower surface of the piezoelectric thin film in a portion of the piezoelectric thin film located above the hollow space, and extends in the direction in which the electrode fingers of the IDT electrode extend. An elastic wave device is disclosed in which a plurality of grooves are provided.

Japanese Patent Application Publication No. 2012-257019 JP2017-224890A

Patent Document 1 describes an example of a method for forming a cavity, in which a piezoelectric substrate is formed with a frame made of a thin film made of SiO ₂ , SiN, etc. on a piezoelectric body, and a support substrate is arranged under the frame. The method is described.

Further, Patent Document 2 describes that after forming a sacrificial layer on a piezoelectric substrate, a supporting layer is provided to cover the sacrificial layer, and then a supporting substrate is bonded to the supporting layer. Further, Patent Document 2 describes that a piezoelectric substrate is made thinner to form a piezoelectric thin film, that an etching hole is formed in the piezoelectric thin film, and that a sacrificial layer is removed from the etching hole by wet etching. . This creates a hollow space within the support layer.

However, in acoustic wave devices in which through-holes such as etching holes are provided in the piezoelectric layer in the portion that overlaps with the cavity, an extra area is required for the through-holes, which tends to increase the element size. There is.

An object of the present invention is to provide an elastic wave device whose element size can be reduced.

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 piezoelectric layer has a width smaller than the thickness of the piezoelectric layer in a region that overlaps with the cavity and is not provided with the functional electrode when viewed from the thickness direction, and one main surface of the piezoelectric layer. A crack is provided that communicates from one main surface to the other main surface.

According to the present invention, it is possible to provide an elastic wave device whose element size can be reduced.

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 elastic wave device of the present invention. FIG. 3 is a cross-sectional view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate. FIG. 4 is a plan 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 the intermediate layer. FIG. 6 is a cross-sectional view schematically showing an example of the process of bonding the support substrate to the intermediate 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 a crack. FIG. 9 is a cross-sectional view schematically showing an example of the process of forming functional electrodes and wiring electrodes. FIG. 10 is a plan view schematically showing an example of the process of forming functional electrodes and wiring electrodes. FIG. 11 is a cross-sectional view schematically showing an example of the process of removing the protective electrode and the sacrificial layer. FIG. 12 is a cross-sectional view schematically showing an example of a state in which a protective resist for forming etching holes is provided. FIG. 13 is a cross-sectional view schematically showing an example of a state during etching. FIG. 14 is a side view schematically showing an example of the portion indicated by XIV in FIG. 13. FIG. 15 is a side view schematically showing an example of a piezoelectric layer in a portion where a crack is provided. FIG. 16 is a plan view schematically showing an example of a piezoelectric layer in a portion where a crack is provided. FIG. 17 is a cross-sectional view schematically showing another example of the elastic wave device of 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. 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.

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.

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 elastic wave device of the present invention. Note that FIG. 1 is an example of a cross-sectional view of the elastic wave device shown in FIG. 2 taken along line II.

The elastic wave device 10 shown in FIGS. 1 and 2 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 functional electrode 22 is provided on at least one main surface of the piezoelectric layer 21. In the example shown in FIGS. 1 and 2, 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 (Z direction in FIGS. 1 and 2). 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 piezoelectric layer 21 has a width smaller than the thickness of the piezoelectric layer 21 in a region that overlaps the cavity 23 and is not provided with the functional electrode 22 when viewed from the thickness direction, and has one main surface ( A crack 24 is provided that communicates from the upper main surface (in FIG. 1) to the other main surface (lower main surface in FIG. 1).

In the elastic wave device 10 shown in FIGS. 1 and 2, a crack 24 having a minute width is provided at the outer circumference of the membrane portion 21M, which is a part of the piezoelectric layer 21. Therefore, even if a cavity is formed by removing the sacrificial layer, for example, the etching solution for removing the sacrificial layer can enter the cracks 24, so there is no need to form etching holes. As a result, the element size can be reduced.

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."

As mentioned above, the width of the crack 24 (the length indicated by W ₂₄ in FIG. 1) is smaller than the thickness of the piezoelectric layer 21 (the length indicated by T ₂₁ in FIG. 1). Note that the width of the crack 24 means the width in a cross section along the thickness direction. Moreover, the thickness of the piezoelectric layer 21 means the dimension in the thickness direction.

The length of the crack 24 (the length indicated by _L24 in FIG. 2) is not particularly limited. Note that the length of the crack 24 means the dimension of the crack 24 in the extending direction.

The support member 20 may have an intermediate layer 41 (also referred to as an insulating layer or a bonding layer) on one main surface on which the piezoelectric layer 21 is provided. For example, the support member 20 includes a support substrate 42 and an intermediate layer 41 provided between the support substrate 42 and the piezoelectric layer 21.

The support substrate 42 is made of silicon (Si), for example.

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

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, for example, an IDT electrode provided on one main surface of the piezoelectric layer 21. Note that a wiring electrode 26 such as a two-layer wiring is connected to the functional electrode 22.

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

First, an example of the method for manufacturing an elastic wave device of the present invention will be described with reference to FIGS. 3 to 11.

FIG. 3 is a cross-sectional view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate. FIG. 4 is a plan view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate.

As shown in FIGS. 3 and 4, first, an inorganic sacrificial layer 40A is formed on the piezoelectric substrate 31.

Subsequently, an organic sacrificial layer 40B is formed on the piezoelectric substrate 31. In the example shown in FIGS. 3 and 4, an organic sacrificial layer 40B is formed on the short side of an inorganic sacrificial layer 40A.

Through the above steps, the sacrificial layer 40 is formed on the piezoelectric substrate 31.

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

As the material for the inorganic sacrificial layer 40A, an appropriate inorganic material that can be removed by etching, which will be described later, is used. For example, ZnO or the like is used.

The inorganic sacrificial layer 40A 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, wet etching is performed to form a pattern of the inorganic sacrificial layer 40A. Note that the inorganic sacrificial layer 40A may be formed by other methods.

As the material of the organic sacrificial layer 40B, an appropriate resin material that can be deformed by heat treatment, which will be described later, is used.

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

As shown in FIG. 5, after forming the intermediate layer 41 to cover the sacrificial layer 40, 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. 6 is a cross-sectional view schematically showing an example of the process of bonding the support substrate to the intermediate layer.

As shown in FIG. 6, a support substrate 42 is bonded to the intermediate layer 41. 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 31 is thinned. As a result, the piezoelectric layer 21 is formed. The piezoelectric substrate 31 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 a crack.

Heat treatment is performed on the support member 20 on which the piezoelectric layer 21 is formed. Since the organic sacrificial layer 40B expands or contracts due to heat, the membrane portion 21M is deformed. As a result, as shown in FIG. 8, a crack 24 is formed on the short side of the sacrificial layer 40.

FIG. 9 is a cross-sectional view schematically showing an example of the process of forming functional electrodes and wiring electrodes. FIG. 10 is a plan view schematically showing an example of the process of forming functional electrodes and wiring electrodes.

As shown in FIGS. 9 and 10, a functional electrode 22 and a wiring electrode 26 are formed on one main surface of the piezoelectric layer 21. The functional electrode 22 and the wiring electrode 26 can be formed by, for example, a lift-off method.

At this time, it is preferable to form a protective electrode 28 on the cracked portion in order to protect the crack during the process flow.

FIG. 11 is a cross-sectional view schematically showing an example of the process of removing the protective electrode and the sacrificial layer.

As shown in FIG. 11, the protective electrode 28 is removed by a method such as etching.

Furthermore, as shown in FIG. 11, the sacrificial layer 40 is removed using the cracks 24. Specifically, the organic sacrificial layer 40B and the inorganic sacrificial layer 40A are removed by a method such as etching. When the material of the inorganic sacrificial layer 40A is ZnO, for example, the inorganic sacrificial layer 40A is wet etched using a mixed solution of acetic acid, phosphoric acid, and water (acetic acid: phosphoric acid: water = 1:1:10). Can be removed.

By removing the sacrificial layer 40, a cavity 23 is formed in the support member 20.

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

In the above method, the cracks 24 are formed in the piezoelectric layer 21 instead of forming etching holes for removing the sacrificial layer 40 in the piezoelectric layer 21, so the element size can be reduced.

Note that when attempting to form an etching hole in the piezoelectric layer 21, it is necessary to form the etching hole by dry etching since an appropriate wet etching solution does not exist.

FIG. 12 is a cross-sectional view schematically showing an example of a state in which a protective resist for forming etching holes is provided.

As shown in FIG. 12, the areas other than those where etching holes are to be formed are covered with a protective resist 50.

FIG. 13 is a cross-sectional view schematically showing an example of a state during etching.

As shown in FIG. 13, when forming etching holes 51 in the piezoelectric layer 21, even dry etching does not require chemical reaction conditions, so it must be performed under ion milling conditions. Therefore, during etching, the protective resist 50 is also etched.

FIG. 14 is a side view schematically showing an example of the portion indicated by XIV in FIG. 13.

As described above, the protective resist 50 is also etched during dry etching. Therefore, as shown in FIG. 14, uniform vertical streaks 52 are generated along the thickness direction (Z direction) of the piezoelectric layer 21 on the side surface of the piezoelectric layer 21 in the portion where the etching hole 51 is formed.

FIG. 15 is a side view schematically showing an example of a piezoelectric layer in a portion where a crack is provided. FIG. 16 is a plan view schematically showing an example of a piezoelectric layer in a portion where a crack is provided.

FIG. 15 shows the side surface of the piezoelectric layer 21, and FIG. 16 shows the surface layer of the piezoelectric layer 21.

In the cracks 24 provided in the piezoelectric layer 21, stress is concentrated on the surface layer, a starting point of the crack is generated due to the slippage of the crystal axis, and then it spreads due to the tensile stress existing in the plane of the piezoelectric layer. Therefore, as shown in FIG. 15, on the side surface of the piezoelectric layer 21 at the portion where the crack 24 is provided, there are vertical stripes 53 that meander in the thickness direction (Z direction) of the piezoelectric layer 21 and It is preferable that cleavage planes 54 without vertical stripes along the Z direction) coexist. The vertical stripes 53 occur near the starting point of the crack, and meander in the thickness direction of the piezoelectric layer 21 . On the other hand, the vertical stripes 53 are not present on the cleavage plane 54.

In the acoustic wave device 10, the piezoelectric layer 21 has cracks in the piezoelectric layer 21 in the thickness direction in addition to the cracks 24 in an area that overlaps the cavity 23 when viewed from the thickness direction of the piezoelectric layer 21 and is not provided with the functional electrode 22. It is preferable that no holes (for example, etching holes 51, etc.) passing through are provided. For example, it is preferable that uniform vertical stripes 52 along the thickness direction of the piezoelectric layer 21 do not exist on the side surfaces of the piezoelectric layer 21 .

When the piezoelectric layer 21 is viewed from the thickness direction, the cracks 24 are preferably provided in a region that overlaps with the outer peripheral edge of the cavity 23, as shown in FIG. In this case, the element area can be minimized. The crack 24 is preferably provided only in a region that overlaps with the outer periphery of the cavity 23, and more preferably only in a part of the region that overlaps with the outer periphery of the cavity 23.

When the piezoelectric layer 21 is viewed from the thickness direction, it is preferable that the cracks 24 are not provided in a region overlapping with the functional electrode 22 that straddles the outer peripheral edge of the cavity 23, as shown in FIG. In this case, the influence on the function of the element can be reduced.

The number, shape, size, etc. of the cracks 24 are not particularly limited. When a plurality of cracks 24 are provided, the shape, size, etc. of the cracks 24 viewed from the thickness direction of the piezoelectric layer 21 may be the same, or may be partially or completely different.

The method for forming the crack 24 is not limited to the method using the sacrificial layer 40.

The cavity 23 does not need to penetrate the support member 20 in the thickness direction, but may do so. When the support member 20 includes the intermediate layer 41 and the support substrate 42, for example, the cavity 23 may be provided so as to penetrate the intermediate layer 41 in the thickness direction, or may be provided so as not to penetrate the intermediate layer 41 in the thickness direction. A cavity 23 may be provided therein.

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

As in the elastic wave device 10A shown in FIG. 17, the cavity 23 may penetrate the support member 20 in the thickness direction. In the example shown in FIG. 17 , the support member 20 includes an intermediate layer 41 and a support substrate 42 .

In the elastic wave device 10A shown in FIG. 17, if a crack 24 communicating from one main surface of the piezoelectric layer 21 to the other main surface is provided, mechanical damage occurs when a pressure difference occurs between the front and back surfaces of the piezoelectric layer 21. Increases strength.

When manufacturing the acoustic wave device 10A shown in FIG. 17, a method for forming the membrane portion 21M of the piezoelectric layer 21 having the functional electrode 22 is, for example, using a bonded substrate in which a piezoelectric substrate is bonded to a support substrate via an intermediate layer. Examples include a method in which a layer including functional electrodes and wiring electrodes is formed in advance by a method such as lift-off, and then the support substrate on the back surface of the portion corresponding to the membrane portion 21M is removed, and then the intermediate layer is removed.

In addition, the method for manufacturing an acoustic wave device of the present invention can be applied and modified in various ways within the scope of the present invention.

In the following, details of an elastic wave device that utilizes a thickness-shear mode and a plate wave will be explained using an example of an elastic wave device in which no cracks are provided. Note that the following description uses an example in which the functional electrode is an IDT electrode.

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.

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 Section 8 Support substrate 8a Opening 9 Cavity 10, 10A Acoustic wave device 20 Support member 21 Piezoelectric layer 21M Membrane section 22 Functional electrode 23 Cavity 24 Crack 26 Wiring electrode 28 Protective electrode 31 Piezoelectric substrate 40 Sacrificial layer 40A Inorganic sacrificial layer 40B Organic sacrificial layer 41 Intermediate layer 42 Support substrate 50 Protective resist 51 Etching holes 52 Uniform vertical stripes 53 Vertical stripes 54 Cleavage plane 61 Acoustic wave device 81 Acoustic wave device 82 Support substrate 83 Piezoelectric layer 84 IDT electrode 84a 1st 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 T ₂₁ thickness of piezoelectric layer L ₂₄ length of crack W ₂₄ width of crack

Claims (14)

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 piezoelectric layer has a width smaller than the thickness of the piezoelectric layer in a region that overlaps with the cavity and is not provided with the functional electrode when viewed from the thickness direction, and one main surface of the piezoelectric layer. A crack is provided that communicates from one main surface to the other main surface,
   Elastic wave device.
2. On the side surface of the piezoelectric layer in the portion where the crack is provided, vertical streaks meandering in the thickness direction of the piezoelectric layer and cleavage planes without vertical streaks along the thickness direction of the piezoelectric layer are mixed.
   The elastic wave device according to claim 1.
3. The piezoelectric layer is provided with a hole that penetrates the piezoelectric layer in the thickness direction in addition to the crack in a region that overlaps with the cavity when viewed from the thickness direction of the piezoelectric layer and in which the functional electrode is not provided. has not been
   The elastic wave device according to claim 1 or 2.
4. When the piezoelectric layer is viewed from the thickness direction, the crack is provided in a region that overlaps with the outer peripheral edge of the cavity.
   The elastic wave device according to any one of claims 1 to 3.
5. When the piezoelectric layer is viewed from the thickness direction, the crack is not provided in a region overlapping with the functional electrode that straddles the outer peripheral edge of the cavity.
   The elastic wave device according to claim 4.
6. 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 5.
7. 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 6.
8. The piezoelectric layer is made of lithium niobate or lithium tantalate,
   The elastic wave device according to any one of claims 1 to 5.
9. It is configured to be able to utilize bulk waves in thickness-slip mode.
   The elastic wave device according to claim 8.
10. 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 6.
11. d/p≦0.24,
    The elastic wave device according to claim 10.
12. 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 6, 10 or 11.
13. MR≦1.75(d/p)+0.05,
    The elastic wave device according to claim 12.
14. 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) ...Formula (3)

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