JP7654482B2 - Acoustic Wave Devices, Filters, Multiplexers, and Wafers - Google Patents

Description

The present invention relates to acoustic wave devices, filters, multiplexers, and wafers.

Surface acoustic wave resonators are known as acoustic wave resonators used in communication devices such as smartphones. It is known that the piezoelectric layer that forms the surface acoustic wave resonator is attached to a support substrate. It is known to provide a temperature compensation layer between the support substrate and the piezoelectric layer (for example, Patent Document 1). It is known to provide a low acoustic velocity film with a lower acoustic velocity than the piezoelectric layer between the support substrate and the piezoelectric layer, and a high acoustic velocity film with a higher acoustic velocity than the piezoelectric layer between the low acoustic velocity film and the support substrate (for example, Patent Document 2).

JP 2019-201345 A JP 2015-115870 A

The invention described in Patent Document 2 suppresses spurious signals by roughening the top surface of the support substrate between the support substrate and the high acoustic velocity film. However, processing is required to roughen the top surface of the support substrate to make it suitable for suppressing spurious signals, which increases manufacturing costs. For this reason, there is a demand for other methods to suppress spurious signals.

The present invention was developed in consideration of the above problems, and aims to suppress spurious signals.

The present invention is an elastic wave device comprising: a support substrate; a piezoelectric layer provided on the support substrate; a pair of comb-shaped electrodes having a plurality of electrode fingers provided on the piezoelectric layer; and an insulating layer provided between the support substrate and the piezoelectric layer, in which a plurality of regions having different sound velocities of propagating bulk waves are repeatedly arranged in the arrangement direction of the plurality of electrode fingers, the plurality of regions being provided from one surface to the other surface of each of the plurality of layers facing each other in the thickness direction, and in which the plurality of regions of one layer and the plurality of regions of the other layer are at least partially offset from each other in the arrangement direction in which the regions have approximately the same sound velocities of bulk waves.

In the above configuration, the multiple regions of the layer that is located closest to the piezoelectric layer among the multiple layers can be configured to be repeatedly arranged in the arrangement direction so that each of the multiple regions overlaps the entirety of one of the multiple electrode fingers in the arrangement direction.

In the above configuration, a temperature compensation layer is provided between the insulating layer and the piezoelectric layer, and has a temperature coefficient of elastic constant whose sign is opposite to that of the temperature coefficient of elastic constant of the piezoelectric layer, the distance from the surface of the temperature compensation layer facing the insulating layer to the surface of the piezoelectric layer on which the pair of comb electrodes are provided is 2λ or less, the insulating layer has a bulk wave whose sound speed is faster than that of the temperature compensation layer, and the layer closest to the piezoelectric layer is in contact with the temperature compensation layer.

In the above configuration, the length of each of the multiple regions in the arrangement direction can be configured to be 0.5 to 1 times the average pitch of the multiple electrode fingers.

In the above configuration, the length of each of the multiple regions in the thickness direction can be configured to be 0.5 to 4 times the average pitch of the multiple electrode fingers.

In the above configuration, the multiple regions of one of the adjacent layers can be repeatedly arranged in the arrangement direction with respect to the multiple regions of the other layer with a phase difference of 0.5 to 1 times the average pitch of the multiple electrode fingers.

In the above configuration, the boundaries between the multiple regions can be inclined when viewed in a cross section parallel to the arrangement direction.

In the above configuration, the multiple regions are composed of a first region and a second region in which the sound velocity of the bulk waves propagating through the first region is slower than that of the first region, and the sound velocity of the bulk waves propagating through the second region is 1.01 times to 1.1 times that of the piezoelectric layer, and the sound velocity of the bulk waves propagating through the first region is 1.2 times or more that of the second region.

The present invention is a filter including the acoustic wave device described above.

The present invention is a multiplexer including the filter described above.

The present invention is a wafer comprising: a support substrate; a piezoelectric layer provided on the support substrate, the piezoelectric layer being a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X -propagation lithium niobate layer; and an insulating layer provided between the support substrate and the piezoelectric layer, in which a plurality of layers are stacked, in which a plurality of regions having different sound velocities of propagating bulk waves are repeatedly arranged in an X-axis direction of a crystal orientation of the piezoelectric layer, the plurality of regions being provided from one surface to the other surface of each of the plurality of layers opposing each other in a thickness direction, and the plurality of regions of one layer and the plurality of regions of the other layer among the plurality of layers have at least a portion of a region having substantially the same sound velocities of bulk waves that is shifted in the X-axis direction.

The present invention makes it possible to suppress spurious signals.

FIG. 1A is a plan view of an acoustic wave device in accordance with a first embodiment, and FIG. 1B is a cross-sectional view thereof. 2A to 2D are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. 3A to 3C are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. 4A to 4C are cross-sectional views of models A, B, and C used in the first simulation. FIG. 5(a) shows the simulation results of the admittance |Y| of model C, and FIG. 5(b) shows the simulation results of the admittance |Y| of models A to C in the frequency range of 3000 MHz to 4500 MHz. 6A to 6C are cross-sectional views of models C, D, and E used in the second simulation. FIG. 7(a) shows the simulation results of the admittance |Y| of models C and D, and FIG. 7(b) shows the simulation results of the admittance |Y| of models C to E in the frequency range of 3000 MHz to 4500 MHz. 8A and 8B are cross-sectional views of models F and G used in the third simulation. FIG. 9A shows the simulation results of the admittance |Y| of models F and G, and FIG. 9B shows the simulation results of the admittance |Y| of models F and G in the frequency range of 3000 MHz to 4500 MHz. 10A to 10G are cross-sectional views of models E and HM used in the fourth simulation. 11(a) to 11(d) show the simulation results of the admittance |Y| of Model A, and Models E, and HJ. 12(a) to 12(c) show the simulation results of the admittance |Y| of model A and models KM. FIG. 13 is a graph showing the relationship between the length in the Z direction of the region in each layer constituting the boundary layer and high frequency spurious. 14A to 14D show simulation results (part 1) of admittance |Y| when the density of the region of model F is changed. 15(a) to 15(c) show simulation results (part 2) of admittance |Y| when the density of the region of model F is changed. 16(a) and 16(b) are graphs showing the relationship between the density or sound speed of each region in the boundary layer and high frequency spurious signals. FIG. 17 is a cross-sectional view of an acoustic wave device in accordance with a first modification of the first embodiment. FIG. 18 is a circuit diagram of a filter in accordance with the second embodiment. FIG. 19 is a block diagram of a duplexer in accordance with the third embodiment. FIG. 20A is a plan view of a wafer according to the fourth embodiment, and FIG. 20B is a cross-sectional view thereof.

The following describes an embodiment of the present invention with reference to the drawings.

1(a) is a plan view of an acoustic wave device 100 according to a first embodiment, and FIG. 1(b) is a cross-sectional view of the acoustic wave device 100 according to the first embodiment. The arrangement direction of the electrode fingers 23 is the X direction, the extension direction of the electrode fingers 23 is the Y direction, and the stacking direction (thickness direction) of the support substrate 10 and the piezoelectric layer 14 is the Z direction. The X direction, Y direction, and Z direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric layer 14. When the piezoelectric layer 14 is a rotated Y-cut X-propagation layer, the X direction is the X-axis direction of the crystal orientation.

1(a) and 1(b), the acoustic wave device 100 has a piezoelectric layer 14 provided on a support substrate 10. A temperature compensation layer 12 is provided between the support substrate 10 and the piezoelectric layer 14. A boundary layer 11 is provided between the temperature compensation layer 12 and the support substrate 10. A bonding layer 13 is provided between the temperature compensation layer 12 and the piezoelectric layer 14. The bonding layer 13 may not be provided. The interface between the support substrate 10 and the boundary layer 11 is a flat surface, and the interface between the boundary layer 11 and the temperature compensation layer 12 is a flat surface. The interface between the temperature compensation layer 12 and the piezoelectric layer 14 or the bonding layer 13 is also a flat surface. The thicknesses of the boundary layer 11, the temperature compensation layer 12, the bonding layer 13, and the piezoelectric layer 14 are T1, T2, T3, and T4, respectively.

The boundary layer 11 is formed by stacking multiple layers 11a, 11b, 11c, and 11d. The interfaces between the multiple layers 11a to 11d are flat surfaces. The multiple layers 11a to 11d have multiple regions 15, 16 in which the sound speed of the propagating bulk waves is different. The regions 15, 16 are provided from one surface to the other surface of each of the multiple layers 11a to 11d that face each other in the Z direction, and are arranged alternately in the X direction. In at least some of the multiple layers 11a to 11d, adjacent layers are arranged such that the regions 15 and/or regions 16 in which the sound speed of the bulk waves is approximately the same are shifted in the X direction.

An elastic wave resonator 20 is provided on the piezoelectric layer 14. The elastic wave resonator 20 has an IDT (Interdigital Transducer) 21 and a reflector 25. The reflectors 25 are provided on both sides of the IDT 21 in the X direction. The IDT 21 and the reflector 25 are formed by a metal film 27 on the piezoelectric layer 14.

The IDT 21 includes a pair of comb electrodes 22 facing each other. The comb electrodes 22 include a plurality of electrode fingers 23 and a bus bar 24 to which the plurality of electrode fingers 23 are connected. The region where the electrode fingers 23 of the pair of comb electrodes 22 intersect is the intersection region 26. The length of the intersection region 26 is the aperture length. The pair of comb electrodes 22 are provided facing each other so that the electrode fingers 23 are almost alternated in at least a part of the intersection region 26. The elastic wave excited by the plurality of electrode fingers 23 in the intersection region 26 propagates mainly in the X direction. The pitch of one of the pair of comb electrodes 22 is almost the wavelength λ of the elastic wave. If the pitch of the plurality of electrode fingers 23 is D, the wavelength λ of the elastic wave is almost twice the pitch D. The reflector 25 reflects the elastic wave (surface acoustic wave) excited by the electrode fingers 23 of the IDT 21. As a result, the elastic wave is confined within the intersection region 26 of the IDT 21.

The piezoelectric layer 14 is, for example, a single crystal lithium tantalate layer or a single crystal lithium niobate layer, for example, a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer.

The support substrate 10 is, for example, a sapphire substrate, a silicon substrate, a spinel substrate, a quartz substrate, a crystal substrate, an alumina substrate, or a silicon carbide substrate. The sapphire substrate is a single crystal _Al2O3 substrate, the silicon substrate is a single crystal or polycrystalline silicon substrate, and the spinel substrate is a polycrystalline _{MgAl2O4 substrate} . The quartz _substrate is an amorphous _SiO2 substrate, the crystal substrate is a single crystal _SiO2 substrate, and the silicon carbide substrate is a polycrystalline or single crystal SiC substrate. The linear expansion coefficient of the support substrate 10 in the X direction is smaller than the linear expansion coefficient of the piezoelectric layer 14 in the X direction. This allows the frequency temperature dependency of the elastic wave resonator 20 to be reduced.

The temperature compensating layer 12 has a temperature coefficient of elastic constant with a sign opposite to that of the temperature coefficient of elastic constant of the piezoelectric layer 14. For example, the temperature coefficient of elastic constant of the piezoelectric layer 14 is negative, and the temperature coefficient of elastic constant of the temperature compensating layer 12 is positive. The temperature compensating layer 12 is, for example, a silicon oxide (SiO ₂ ) layer with no additive or with an additive element such as fluorine, for example, an amorphous layer. By providing the temperature compensating layer 12, the frequency temperature coefficient of the elastic wave resonator 20 can be reduced. When the temperature compensating layer 12 is mainly composed of silicon oxide, the sound velocity of the bulk wave propagating through the temperature compensating layer 12 becomes slower than the sound velocity of the bulk wave propagating through the piezoelectric layer 14. The main component being silicon oxide means that the total of oxygen and silicon is 50 at% (atomic %) or more, and may be 80 at% or more. Each of oxygen and silicon is 10 at% or more, and may be 20 at% or more.

The speed of sound of the bulk waves propagating through the boundary layer 11 is faster than the speed of sound of the bulk waves propagating through the temperature compensating layer 12. That is, the speed of sound of the bulk waves in both regions 15 and 16 of the multiple layers 11a to 11d that make up the boundary layer 11 is faster than that of the temperature compensating layer 12. This causes the energy of the main response to be trapped within the piezoelectric layer 14 and the temperature compensating layer 12. The boundary layer 11 is, for example, polycrystalline or amorphous, and is, for example, an aluminum oxide layer, a silicon layer, an aluminum nitride layer, a silicon nitride layer, or a silicon carbide layer. Multiple layers of different materials may be provided as the boundary layer 11.

The regions 15 and 16 provided in the multiple layers 11a to 11d that form the boundary layer 11 may be made of different materials, or may be made of the same material but with different densities, so that the sound speed of the propagating bulk waves is different. The regions 15 and 16 may also have different sound speeds of the propagating bulk waves by other methods. Note that at least one of the regions 15 and 16 may have a faster sound speed of the bulk waves than the temperature compensation layer 12.

The sound velocity of the bulk waves propagating through the support substrate 10 is faster than the sound velocity of the bulk waves propagating through the boundary layer 11, and is preferably, for example, 1.1 times or more the sound velocity of the bulk waves propagating through the boundary layer 11. The sound velocity of the bulk waves propagating through the support substrate 10 is preferably 2.0 times or less the sound velocity of the bulk waves propagating through the boundary layer 11.

The sound velocity of the bulk wave propagating through the temperature compensating layer 12 may be faster than the sound velocity of the bulk wave propagating through the piezoelectric layer 14, but since elastic waves are more likely to exist within the temperature compensating layer 12, it is preferable that the sound velocity is slower than the sound velocity of the bulk wave propagating through the piezoelectric layer 14, and is preferably 0.99 times or less. If the sound velocity of the bulk wave propagating through the temperature compensating layer 12 becomes too slow, it becomes difficult for elastic waves to exist within the piezoelectric layer 14, so the sound velocity of the bulk wave propagating through the temperature compensating layer 12 is preferably 0.9 times or more faster than the sound velocity of the bulk wave propagating through the piezoelectric layer 14.

The sound velocity of the bulk wave propagating through the bonding layer 13 is faster than the sound velocity of the bulk wave propagating through the temperature compensation layer 12. The bonding layer 13 is, for example, polycrystalline or amorphous, and is, for example, an aluminum oxide layer, a silicon layer, an aluminum nitride layer, a silicon nitride layer, or a silicon carbide layer. It is preferable that the sound velocity of the bulk wave propagating through the boundary layer 11 and the bonding layer 13 is faster than the sound velocity of the bulk wave propagating through the piezoelectric layer 14.

The metal film 27 is a film whose main component is, for example, aluminum, copper, or molybdenum. An adhesive film such as a titanium film or a chromium film may be provided between the electrode fingers 23 and the piezoelectric layer 14. The adhesive film is thinner than the electrode fingers 23. An insulating film may be provided to cover the electrode fingers 23. The insulating film may function as a protective film and a temperature compensation film.

When the IDT 21 excites surface acoustic waves, which are the main mode, in the piezoelectric layer 14, it also excites unwanted waves such as bulk waves. The range in which the energy of the surface acoustic waves exists is up to a depth of about 2λ from the top surface of the piezoelectric layer 14, and is particularly present in the range from the top surface of the piezoelectric layer 14 to λ. On the other hand, unwanted waves such as bulk waves exist up to 10λ or more from the top surface of the piezoelectric layer 14. When the bulk waves are reflected by the top surface of the support substrate 10 and return to the IDT 21, they cause spurious noise.

In order to suppress spurious emissions, it has been proposed to form irregularities on the upper surface of the support substrate 10 to scatter bulk waves. However, attempting to form irregularities suitable for scattering bulk waves on the upper surface of the support substrate 10 would increase manufacturing costs. Therefore, in Example 1, instead of forming irregularities on the upper surface of the support substrate 10, the boundary layer 11 is formed from multiple layers 11a to 11d. Details of this point will be given later.

[Production method]
2(a) to 3(c) are cross-sectional views showing a manufacturing method of the acoustic wave device 100 according to the first embodiment. The manufacturing method shown in Fig. 2(a) to 3(c) is performed in a wafer state, and the wafer is finally diced into individual pieces to form the acoustic wave devices 100. Although a plurality of acoustic wave devices 100 are formed on the wafer, Fig. 2(a) to 3(c) show only one acoustic wave device.

As shown in FIG. 2(a), a wafer-like support substrate 10 with a flat surface is prepared. The arithmetic mean roughness Ra of the surface of the support substrate 10 is, for example, 1 nm or less. An insulating film 15a is formed on the support substrate 10 by, for example, a sputtering method or a CVD (Chemical Vapor Deposition) method, and then the insulating film 15a is removed by, for example, an etching method to form a patterned insulating film 15a. The insulating film 15a may also be formed by, for example, a lift-off method.

2(b), an insulating film 16a having a different sound velocity of the propagating bulk wave from that of the insulating film 15a is formed on the support substrate 10 by, for example, a sputtering method or a CVD method. The insulating films 15a and 16a may be made of different materials to have different sound velocities of the propagating bulk wave, or the same material may be used to have different densities by changing the film formation method to have different sound velocities of the propagating bulk wave, or other methods may be used to make the sound velocities of the propagating bulk wave different. After that, the insulating film 16a is polished by, for example, a CMP (Chemical Mechanical Polishing) method until the insulating film 15a is exposed. This forms a layer 11a having a region 15 made of the insulating film 15a and a region 16 made of the insulating film 16a.

As shown in FIG. 2(c), after forming a resist pattern 90 on the layer 11a, an insulating film 16a is formed by, for example, a sputtering method or a CVD method.

As shown in FIG. 2(d), after removing the resist pattern 90, an insulating film 15a is formed on the layer 11a by, for example, a sputtering method or a CVD method. Then, the insulating film 15a is polished by, for example, a CMP method until the insulating film 16a is exposed. This forms a layer 11b having a region 15 made of the insulating film 15a and a region 16 made of the insulating film 16a.

As shown in FIG. 3(a), the same steps as those in FIG. 2(c) and FIG. 2(d) are repeated to form layers 11c and 11d. This forms boundary layer 11 consisting of layers 11a to 11d. Then, temperature compensation layer 12 is formed on boundary layer 11 by, for example, sputtering or CVD.

As shown in FIG. 3(b), the piezoelectric substrate 17 is bonded to the upper surface of the temperature compensation layer 12 via the bonding layer 13. The temperature compensation layer 12 and the piezoelectric substrate 17 may be bonded together without the bonding layer 13. For example, a surface activation method is used for bonding.

As shown in FIG. 3(c), the upper surface of the piezoelectric substrate 17 is polished, for example, by CMP to form a thin piezoelectric layer 14. Then, an acoustic wave resonator 20 made of a metal film 27 is formed on the upper surface of the piezoelectric layer 14. Finally, the wafer is divided into individual pieces to form the acoustic wave device 100.

[First Simulation]
The first simulation for evaluating spurious emissions will be described. The first simulation was performed on models A, B, and C with different structures of the boundary layer 11, and the admittance of each model was simulated. The simulation conditions common to models A, B, and C are as follows. The density of the material in regions 15 and 16 of the boundary layer 11 was made different to make the sound speed of the propagating bulk wave different. Regions 15 and 16 are provided in the entire intersection region 26 in the state shown in the figure described later. The following simulation conditions are also common to the second to fifth simulations described later.
Elastic wave wavelength λ: 1.5 μm
Support substrate 10: sapphire substrate Boundary layer 11: aluminum oxide layer with a thickness of 4λ Region 15 of boundary layer 11: aluminum oxide with a density of 3150 kg/ ^m3 Region 16 of boundary layer 11: aluminum oxide with a density of 4500 kg/ ^m3 Temperature compensation layer 12: silicon oxide layer with a thickness of 0.2λ Piezoelectric layer 14: 42° Y-cut X-propagation lithium tantalate layer with a thickness of 0.3λ Electrode fingers 23: laminated film of an aluminum film with a thickness of 90 nm provided on a titanium film with a thickness of 60 nm Number of pairs of electrode fingers 23: 1 pair Duty ratio: 50%
Aperture length: λ/32

Figures 4(a) to 4(c) are cross-sectional views of models A, B, and C used in the first simulation. In order to clarify the figures, hatching of the support substrate 10, temperature compensation layer 12, piezoelectric layer 14, and electrode fingers 23 is omitted in Figures 4(a) to 4(c), and for the boundary layer 11, hatching is applied only to region 16, with hatching of region 15 being omitted (the same applies to the following similar figures).

4A, in model A, the entire boundary layer 11 is defined as region 15. That is, the entire boundary layer 11 is made of aluminum oxide having a density of 3150 kg/m ^3. In this way, model A is a model equivalent to a comparative example, since the boundary layer 11 is not made of a plurality of laminated layers having regions 15 and 16.

As shown in Fig. 4(b), in model B, the boundary layer 11 is divided into two in the X direction under a pair of electrode fingers 23, one of which is region 15 made of aluminum oxide having a density of 3150 kg/ ^m3 , and the other is region 16 made of aluminum oxide having a density of 4500 kg/ ^m3 . That is, the boundary layer 11 is composed of one layer 11a having regions 15 and 16 arranged in the X direction. In model B, the length of regions 15 and 16 in the Z direction is 4λ, and the length in the X direction is 0.5λ. In this way, model B is a model corresponding to a comparative example, since the boundary layer 11 is not composed of a plurality of layers having regions 15 and 16 stacked.

As shown in FIG. 4C, in model C, the boundary layer 11 is divided into two in the Z direction and the X direction under a pair of electrode fingers 23, and the region located at +Z and +X and the region located at -Z and -X among the four regions are defined as region 15 made of aluminum oxide having a density of 3150 kg/ ^m3 , and the region located at +Z and -X and the region located at -Z and +X are defined as region 16 made of aluminum oxide having a density of 4500 kg/ ^m3 . That is, the boundary layer 11 is defined as a laminate of two layers 11a and 11b each having a region 15 and a region 16 arranged in the X direction. The region 15 of the layer 11a and the region 15 of the layer 11b are shifted in the X direction, and the region 16 of the layer 11a and the region 16 of the layer 11b are shifted in the X direction. In model C, the length of the regions 15 and 16 of the layers 11a and 11b in the Z direction is 2λ, and the length of the regions 15 and 16 in the X direction is 0.5λ. Thus, model C is a model that corresponds to the embodiment.

Figure 5(a) shows the simulation results of admittance |Y| of model C, and Figure 5(b) shows the simulation results of admittance |Y| of models A to C in the frequency range of 3000 MHz to 4500 MHz. As shown in Figures 5(a) and 5(b), high-frequency spurious was suppressed in model C compared to models A and B. The reason why high-frequency spurious was suppressed in model C is thought to be as follows. The boundary layer 11 of model C is formed by stacking two layers 11a and 11b, in which regions 15 and 16 where the sound speed of the propagating bulk waves is different are arranged in the X direction. Region 15 of layer 11a and region 15 of layer 11b are arranged with a shift in the X direction, and region 16 of layer 11a and region 16 of layer 11b are arranged with a shift in the X direction. As a result, the bulk waves that pass from the piezoelectric layer 14 through the temperature compensation layer 12 and reach the boundary layer 11 are scattered by regions 15 and 16 of layers 11a and 11b, and as a result, high-frequency spurious emissions are suppressed.

According to the first embodiment, as shown in FIG. 1B, a boundary layer 11 (insulating layer) is provided between the support substrate 10 and the piezoelectric layer 14. The boundary layer 11 is formed by stacking a plurality of layers 11a to 11d in which a plurality of regions 15, 16 in which the sound speed of the propagating bulk waves is different are repeatedly arranged in the X direction. In each of the plurality of layers 11a to 11d, the regions 15, 16 are provided from one surface to the other surface facing each other in the Z direction. In at least a part of the regions 15, 16 of one layer among the plurality of layers 11a to 11d, the regions 15 and/or regions 16 in which the sound speed of the bulk waves is approximately the same are arranged with a shift in the X direction. As a result, the bulk waves are scattered by the regions 15, 16 of the layers 11a to 11d, so that spurious caused by the bulk waves can be suppressed. The sound speed of the bulk waves being approximately the same allows for a difference within the manufacturing error range.

In the first embodiment, in order to scatter the bulk waves and suppress spurious signals, it is preferable that the regions 15 and 16 of one layer and the regions 15 and 16 of the other layer among the multiple layers 11a to 11d are arranged with a shift in the X direction, so that the sound velocities of the bulk waves are approximately the same in all the adjacent regions 15 and 16 of the other layer.

In order to allow the bulk waves to reach the boundary layer 11, the thickness T2 of the temperature compensation layer 12 is preferably 1.5 times (0.75λ) or less, and more preferably 1 time (0.5λ) or less, the average pitch D of the electrode fingers 23. In order to allow the temperature compensation function of the temperature compensation layer 12 to be exerted, the thickness T2 of the temperature compensation layer 12 is preferably 0.2 times (0.1λ) or more, and more preferably 0.4 times (0.2λ) or more, the average pitch D of the electrode fingers 23. The average pitch D of the electrode fingers 23 can be calculated by dividing the width of the IDT 21 in the X direction by the number of electrode fingers 23.

The boundary layer 11 is not limited to four layers 11a to 11d stacked together, but may be two or more layers stacked together. From the viewpoint of scattering bulk waves by the boundary layer 11, it is preferable for the boundary layer 11 to have a larger number of stacked layers, preferably three or more layers, more preferably five or more layers, and even more preferably eight or more layers. In addition, since the spurious becomes larger when the thickness T1 of the boundary layer 11 is thin, the thickness T1 of the boundary layer 11 is preferably 1.4 times (0.7λ) or more of the average pitch D of the electrode fingers 23, more preferably two times (λ) or more, and even more preferably four times (2λ) or more.

From the viewpoint of confining the energy of the surface acoustic wave within the piezoelectric layer 14 and the temperature compensating layer 12, the distance (T2+T3+T4) between the surface of the temperature compensating layer 12 on the boundary layer 11 side and the surface of the piezoelectric layer 14 on the comb-shaped electrode 22 side is preferably 4 times (2λ) or less, more preferably 3 times (1.5λ) or less, the average pitch D of the electrode fingers 23. From the viewpoint of having the energy of the surface acoustic wave exist within the temperature compensating layer 12, the thickness T4 of the piezoelectric layer 14 is preferably 2 times (λ) or less, more preferably 1 time (0.5λ) or less, the average pitch D of the electrode fingers 23. If the piezoelectric layer 14 becomes too thin, it becomes difficult to excite the acoustic wave, so the thickness T4 of the piezoelectric layer 14 is preferably 0.2 times (0.1λ) or more, more preferably 0.4 times (0.2λ) or more, the average pitch D of the electrode fingers 23.

[Second Simulation]
6A to 6C are cross-sectional views of models C, D, and E used in the second simulation. Model C in FIG. 6A has been described in the first simulation, and therefore will not be described here.

As shown in FIG. 6(b), in model D, the boundary layer 11 is divided into two in the Z direction and into four in the X direction under a pair of electrode fingers 23, and of the four regions on the +Z side, the two regions located at the ends on the +X side and -X side are designated as region 15, and the two regions located in the center are designated as region 16. Of the four regions on the -Z side, the two regions located in the center are designated as region 15, and the two regions located at the ends on the +X side and -X side are designated as region 16.

As shown in FIG. 6(c), in model E, the boundary layer 11 is divided into two in the Z direction and into four in the X direction under a pair of electrode fingers 23, and of the four regions on the +Z side, the two regions located on the +X side are designated as regions 15, and the two regions located on the -X side are designated as regions 16. Of the four regions on the -Z side, the two regions located at the ends on the +X and -X sides are designated as regions 15, and the two regions located in the center are designated as regions 16.

In this way, in all of models C, D, and E, the boundary layer 11 is formed by stacking two layers 11a and 11b, each having a region 15 and a region 16 aligned in the X direction, with region 15 of layer 11a and region 15 of layer 11b being shifted in the X direction, and region 16 of layer 11a and region 16 of layer 11b being shifted in the X direction. In models C, D, and E, the length in the Z direction of regions 15 and 16 of layers 11a and 11b is 2λ, and the length in the X direction is 0.5λ.

In model C, regions 15 and 16 of layer 11a are each provided to overlap the entire X-direction of one electrode finger 23, and regions 15 and 16 of layer 11b are also each provided to overlap the entire X-direction of one electrode finger 23. In model D, region 15 of layer 11a is provided to overlap half of each of two electrode fingers 23 in the X-direction, and region 16 is also provided to overlap half of electrode finger 23. Similarly, region 16 of layer 11b is provided to overlap half of each of two electrode fingers 23 in the X-direction, and region 15 is also provided to overlap half of electrode finger 23. In model E, region 16 of layer 11a is provided to overlap half of each of two electrode fingers 23 in the X-direction, and region 15 is also provided to overlap half of electrode finger 23. Regions 15 and 16 of layer 11b are each provided to overlap the entire X-direction of one electrode finger 23.

Figure 7(a) shows the simulation results of the admittance |Y| of models C and D, and Figure 7(b) shows the simulation results of the admittance |Y| of models C to E in the frequency range of 3000 MHz to 4500 MHz. As shown in Figures 7(a) and 7(b), high-frequency spurious emissions were suppressed in model C compared to models D and E, and high-frequency spurious emissions were suppressed in model E compared to model D.

From the results of the second simulation, in Example 1, it is preferable that the regions 15 and 16 of the layer 11d, which is located closest to the piezoelectric layer 14 among the multiple layers 11a to 11d constituting the boundary layer 11, are aligned in the X direction so that each of the regions 15 and 16 overlaps the entire X direction of one electrode finger 23. This makes it possible to suppress high-frequency spurious as in models C and E. In addition, in Example 1, it is preferable that the layer 11d is a layer that is in contact with the temperature compensation layer 12. This makes it possible to suppress high-frequency spurious as in models C and E. In addition, in Example 1, it is preferable that the regions 15 and 16 are aligned in the X direction in all layers of the multiple layers 11a to 11d constituting the boundary layer 11 so that each of the regions 15 and 16 overlaps the entire X direction of one electrode finger 23. This makes it possible to suppress high-frequency spurious as in model C.

As shown in FIG. 6(a), in model C, the regions 15 and 16 of layer 11a are aligned with the regions 15 and 16 of layer 11b at a 0.5 λ offset in the X direction. As shown in FIG. 6(c), in model E, the regions 15 and 16 of layer 11a are aligned with the regions 15 and 16 of layer 11b at a 0.25 λ offset in the X direction. As shown in FIG. 7(b), high-frequency spurious is suppressed in both models C and E. Therefore, in the first embodiment, in terms of suppressing high-frequency spurious, it is preferable that the regions 15 and 16 of one adjacent layer among the multiple layers 11a to 11d are aligned with the regions 15 and 16 of the other layer at a phase difference of 0.25 λ or more and 0.5 λ or less in the X direction. In other words, it is preferable that the regions 15, 16 of one adjacent layer among the multiple layers 11a to 11d are arranged in the X direction with a phase difference of 0.5 to 1 times the average pitch D of the multiple electrode fingers 23 relative to the regions 15, 16 of the other layer.

As shown in FIG. 7B, high-frequency spurious is suppressed in model C compared to model E. Therefore, in terms of suppressing high-frequency spurious, it is preferable that the regions 15 and 16 of one adjacent layer are arranged with a phase difference of 0.3λ to 0.5λ with respect to the regions 15 and 16 of the other layer, more preferably with a phase difference of 0.4λ to 0.5λ, and even more preferably with a phase difference of 0.45λ to 0.5λ. In other words, it is preferable that the regions 15 and 16 of one adjacent layer are arranged with a phase difference of 0.6 to 1 times the average pitch D of the multiple electrode fingers 23 with respect to the regions 15 and 16 of the other layer, more preferably with a phase difference of 0.8 to 1 times, and even more preferably with a phase difference of 0.9 to 1 times.

[Third Simulation]

Figures 8(a) and 8(b) are cross-sectional views of models F and G used in the third simulation. As shown in Figure 8(a), in model F, the boundary layer 11 is divided into four in the Z direction and into two in the X direction under a pair of electrode fingers 23, so that regions 15 and 16 of the four layers 11a to 11d are arranged in a lattice pattern. Regions 15 and 16 of layers 11a to 11d are each provided to overlap one entire electrode finger 23. In model F, the length in the Z direction of regions 15 and 16 of layers 11a to 11d is λ, and the length in the X direction is 0.5λ.

As shown in FIG. 8(b), in model G, the boundary layer 11 is divided into four in the Z direction and the X direction under a pair of electrode fingers 23, and the regions 15 and 16 of the four layers 11a to 11d are arranged in a lattice pattern. Each of the regions 15 and 16 of the layers 11a to 11d is provided so as to overlap half of one electrode finger 23. In model G, the length in the Z direction of the regions 15 and 16 of the layers 11a to 11d is λ, and the length in the X direction is 0.25λ.

Figure 9 (a) shows the simulation results of the admittance |Y| of models F and G, and Figure 9 (b) shows the simulation results of the admittance |Y| of models F and G in the frequency range of 3000 MHz to 4500 MHz. As shown in Figure 9, high-frequency spurious was suppressed more in model F than in model G.

From the third simulation result, in Example 1, in terms of suppressing high-frequency spurious, the length in the X direction of the regions 15 and 16 of the layers 11a to 11d constituting the boundary layer 11 is preferably 0.25λ to 0.5λ, more preferably 0.3λ to 0.5λ, and even more preferably 0.4λ to 0.5λ. In other words, the length in the X direction of the regions 15 and 16 of the layers 11a to 11d constituting the boundary layer 11 is preferably 0.5 to 1 times the average pitch D of the multiple electrode fingers 23, more preferably 0.6 to 1 times, and even more preferably 0.8 to 1 times.

[Fourth Simulation]

Figures 10(a) to 10(g) are cross-sectional views of models E and H to M used in the fourth simulation. Model E in Figure 10(a) is explained in the second simulation, so its explanation is omitted here.

In model E in FIG. 10(a), the boundary layer 11 has a two-layer laminate structure, whereas in model H, the boundary layer 11 has a three-layer laminate structure as shown in FIG. 10(b), in model I, the boundary layer 11 has a four-layer laminate structure as shown in FIG. 10(c), and in model J, the boundary layer 11 has a six-layer laminate structure as shown in FIG. 10(d). In model K, the boundary layer 11 has a 10-layer laminate structure as shown in FIG. 10(e), in model L, the boundary layer 11 has a 25-layer laminate structure as shown in FIG. 10(f), and in model M, the boundary layer 11 has a 50-layer laminate structure as shown in FIG. 10(g). In model H, the length of each layer region 15, 16 in the Z direction is 1.33 λ, and the length in the X direction is 0.5 λ. In model I, the length of each layer region 15, 16 in the Z direction is 1 λ, and the length in the X direction is 0.5 λ. In model J, the length in the Z direction of the regions 15 and 16 of each layer is 0.67λ, and the length in the X direction is 0.5λ. In model K, the length in the Z direction of the regions 15 and 16 of each layer is 0.4λ, and the length in the X direction is 0.5λ. In model L, the length in the Z direction of the regions 15 and 16 of each layer is 0.16λ, and the length in the X direction is 0.5λ. In model M, the length in the Z direction of the regions 15 and 16 of each layer is 0.08λ, and the length in the X direction is 0.5λ.

Figures 11(a) to 11(d) show the simulation results of admittance |Y| for models E, and H to J. Figures 12(a) to 12(c) show the simulation results of admittance |Y| for models K to M. For comparison, Figures 11(a) to 11(d) and 12(a) to 12(c) also show the simulation results of admittance |Y| for model A (see Figure 4(a)). As shown in Figures 11(a) to 11(c) and 12(a) to 12(c), high-frequency spurious emissions were suppressed more in models E, H to M than in model A.

Figure 13 is a graph showing the relationship between the Z-direction length of regions 15 and 16 in each layer that makes up the boundary layer 11 and high-frequency spurious emissions. The horizontal axis of Figure 13 is the Z-direction length of regions 15 and 16. The vertical axis is the difference |ΔY| between the maximum and minimum admittance values in the high-frequency spurious emissions. In Figure 13, the results for models E and H to M are shown with white circles, and the results for model A are shown with black circles. As shown in Figure 13, high-frequency spurious emissions were most suppressed when the Z-direction length of regions 15 and 16 was 1λ.

From the fourth simulation result, in Example 1, in terms of suppressing high-frequency spurious, the Z-direction length of regions 15, 16 of layers 11a to 11d constituting boundary layer 11 is preferably 0.25λ to 2λ, more preferably 0.5λ to 1.5λ, and even more preferably 0.8λ to 1.2λ. In other words, the Z-direction length of regions 15, 16 of layers 11a to 11d constituting boundary layer 11 is preferably 0.5 to 4 times the average pitch D of the multiple electrode fingers 23, more preferably 1 to 3 times, and even more preferably 1.6 to 2.4 times. This makes it possible to suppress high-frequency spurious.

[Fifth Simulation]
In the fifth simulation, model F shown in FIG. 8A was used, and the admittance was simulated when the density of region 15 was fixed at 3150 kg/ ^m3 and the density of region 16 was varied.

14(a) to 14(d) and 15(a) to 15(c) are simulation results of admittance |Y| when the density of region 16 of model F is changed. In FIG. 14(a), the density of region 16 is 1500 kg/m ³ , in FIG. 14(b), 2000 kg/m ³ , in FIG. 14(c), 3000 kg/m ³ , in FIG. 14(d), 4000 kg/m ³ , in FIG. 15(a), 4500 kg/m ³ , in FIG. 15(b), 4873 kg/m ³ , and in FIG. 15(c), 6000 kg/m ³ . 14(a) to 14(d) and 15(a) to 15(c) also show the simulation results of the admittance |Y| of model A (see FIG. 4(a)) for comparison.

Figures 16(a) and 16(b) are graphs showing the relationship between the density or sound speed of region 16 in each layer constituting boundary layer 11 and the high frequency spurious. The horizontal axis in Figure 16(a) is the density of region 16, and the horizontal axis in Figure 16(b) is the sound speed of region 16. The vertical axis in Figures 16(a) and 16(b) is the difference |ΔY| between the maximum and minimum admittance values in the high frequency spurious. In Figures 16(a) and 16(b), the results of model F, in which the density (sound speed) of region 16 was changed, are shown with white circles, and the results of model A are shown with black circles.

As shown in Figures 14(a) to 14(d), 15(a) to 15(c), 16(a) and 16(b), the high frequency spurious was suppressed in all cases where the density of region 16 was varied in the range of 1500 kg/ ^m3 to 6000 kg/ ^m3 . This confirmed that by differentiating the acoustic velocity of the bulk waves in regions 15 and 16, spurious can be suppressed regardless of the difference in acoustic velocity.

The acoustic velocity of the bulk wave propagating through the piezoelectric layer 14, which is a rotated Y-cut X-propagation lithium tantalate layer, is 3750 m/s, and the acoustic velocity of the bulk wave propagating through the temperature compensating layer 12, which is a silicon oxide layer, is 3684 m/s. The acoustic velocity of the bulk wave propagating through the region 15, which is made of aluminum oxide with a density of 3150 kg/ ^m3 , is 4582 m/s. As shown in Fig. 16(b), when the region 16 has a bulk wave acoustic velocity close to that of the piezoelectric layer 14 and the temperature compensating layer 12, and the bulk wave acoustic velocity of the region 15 is faster than that of the region 16, the high frequency spurious suppression effect is large. Therefore, in Example 1, when the layers 11a to 11d constituting the boundary layer 11 are composed of the region 15 and the region 16 in which the sound velocity of the bulk waves propagating therethrough is slower than that of the region 15, the sound velocity of the bulk waves in the region 16 is preferably 1.01 to 1.1 times, more preferably 1.01 to 1.08 times, and even more preferably 1.01 to 1.05 times, compared to that of the piezoelectric layer 14. The sound velocity of the bulk waves in the region 15 is preferably 1.2 times or more, more preferably 1.25 times or more, and even more preferably 1.3 times or more, compared to that of the region 16. This makes it possible to effectively suppress spurious signals.

If the sound velocity of the bulk wave propagating through the boundary layer 11 is too fast, the bulk wave is likely to be reflected at the interface between the boundary layer 11 and the temperature compensation layer 12. Therefore, the sound velocity of the bulk wave propagating through the boundary layer 11 is preferably 2.0 times or less, and more preferably 1.5 times or less, of the sound velocity of the bulk wave propagating through the temperature compensation layer 12.

[Modification]
Fig. 17 is a cross-sectional view of an acoustic wave device 110 according to a first modification of the first embodiment. As shown in Fig. 17, in the acoustic wave device 110, the regions 15 and 16 of the multiple layers 11a to 11d constituting the boundary layer 11 have inclined side surfaces in cross-sectional view. The inclination angle θ is, for example, 40° to 89°. The other configurations are the same as those of the first embodiment, and therefore description thereof will be omitted.

As in the first modification of the first embodiment, the boundary between the regions 15 and 16 may be inclined in a cross-sectional view parallel to the X direction. This allows the bulk waves to be scattered effectively, and the spurious suppression effect is increased.

In the first embodiment and its modified example, the layers 11a to 11d have two regions 15, 16 in which the sound speed of the propagating bulk waves is different, but the layers may have three or more regions in which the sound speed of the propagating bulk waves is different. In this case, the three or more regions in each of the layers 11a to 11d are repeatedly arranged in the X direction, and the regions in one adjacent layer of the layers 11a to 11d and the regions in the other adjacent layer of the layers 11a to 11d have at least some regions in which the sound speed of the bulk waves is approximately the same, shifted in the X direction.

In the first embodiment and its modified examples, a case where the temperature compensating layer 12 is provided between the boundary layer 11 and the piezoelectric layer 14 has been shown as an example, but the temperature compensating layer 12 may not be provided. However, in order to reduce the frequency temperature coefficient of the elastic wave resonator 20, it is preferable that the temperature compensating layer 12 is provided.

Figure 18 is a circuit diagram of a filter 200 according to a second embodiment. As shown in Figure 18, the filter 200 has one or more series resonators S1 to S4 connected in series and one or more parallel resonators P1 to P3 connected in parallel between an input terminal Tin and an output terminal Tout. The acoustic wave device according to the first embodiment and its modified examples can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P3. The number of resonators in the ladder filter can be set as appropriate. The filter may be a multimode filter.

19 is a block diagram of a duplexer 300 according to the third embodiment. As shown in FIG. 19, in the duplexer 300, a transmission filter 30 is connected between a common terminal Ant and a transmission terminal Tx, and a reception filter 32 is connected between the common terminal Ant and a reception terminal Rx. The transmission filter 30 passes a signal in a transmission band among high-frequency signals input from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 32 passes a signal in a reception band among high-frequency signals input from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 30 and the reception filter 32 can be the filter of the second embodiment. Although a duplexer is shown as an example of a multiplexer, a triplexer, a quadplexer, or the like may also be used.

20(a) is a plan view of a wafer 400 according to Example 4, and FIG. 20(b) is a cross-sectional view of the wafer 400 according to Example 4. As shown in FIGS. 20(a) and 20(b), the wafer 400 has a piezoelectric layer 14 provided on a support substrate 10. A temperature compensation layer 12 is provided between the support substrate 10 and the piezoelectric layer 14. A boundary layer 11 is provided between the temperature compensation layer 12 and the support substrate 10. A bonding layer 13 is provided between the temperature compensation layer 12 and the piezoelectric layer 14, but the bonding layer 13 may not be provided.

The piezoelectric layer 14 is a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer. The X-axis direction of the crystal orientation of the piezoelectric layer 14 is the X-direction. The stacking direction (thickness direction) of the support substrate 10 and the piezoelectric layer 14 is the Z-direction. The direction perpendicular to the X-direction and Z-direction is the Y-direction. The support substrate 10, boundary layer 11, temperature compensation layer 12, and bonding layer 13 are made of the materials shown in Example 1.

The boundary layer 11 is formed by stacking multiple layers 11a to 11d. The multiple layers 11a to 11d have multiple regions 15, 16 in which the sound speed of the propagating bulk waves is different. The regions 15, 16 are provided from one surface to the other surface of each of the multiple layers 11a to 11d that face each other in the Z direction, and are arranged alternately in the X direction. In at least some of the multiple layers 11a to 11d, adjacent layers are arranged such that the regions 15 and/or regions 16 in which the sound speed of the bulk waves is approximately the same are shifted in the X direction.

According to the fourth embodiment, the wafer 400 includes a support substrate 10, a piezoelectric layer 14 that is a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut lithium niobate layer provided on the support substrate 10, and a boundary layer 11 (insulating layer) provided between the support substrate 10 and the piezoelectric layer 14. The boundary layer 11 is formed by stacking a plurality of layers 11a to 11d in which a plurality of regions 15, 16 in which the sound speed of the propagating bulk waves is different are repeatedly arranged in the X direction. In each of the plurality of layers 11a to 11d, the regions 15, 16 are provided from one surface to the other surface that face each other in the Z direction. In at least a part of the regions 15, 16 of one layer of the plurality of layers 11a to 11d and the regions 15, 16 of the other layer, the regions 15 and/or regions 16 in which the sound speed of the bulk waves is approximately the same are shifted in the X direction. In this way, the layer structure of the wafer 400 is the same as the layer structure from the support substrate 10 to the piezoelectric layer 14 of the acoustic wave device 100 of Example 1. Therefore, by using the wafer 400 to form an acoustic wave resonator on the piezoelectric layer 14, an acoustic wave device with suppressed spurious emissions can be obtained.

Although the embodiment of the present invention has been described in detail above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

REFERENCE SIGNS LIST 10 Support substrate 11 Boundary layers 11a to 11d Layer 12 Temperature compensation layer 13 Bonding layer 14 Piezoelectric layer 15, 16 Regions 15a, 16a Insulating film 17 Piezoelectric substrate 20 Elastic wave resonator 21 IDT
22 comb-shaped electrode 23 electrode finger 24 bus bar 25 reflector 26 intersection region 27 metal film 30 transmit filter 32 receive filter 100, 110 acoustic wave device 200 filter 300 duplexer 400 wafer

Claims (11)

A support substrate;
a piezoelectric layer provided on the support substrate;
a pair of comb-shaped electrodes having a plurality of electrode fingers provided on the piezoelectric layer;
an insulating layer provided between the support substrate and the piezoelectric layer, in which a plurality of layers are stacked, in which a plurality of regions in which the sound speed of propagating bulk waves is different are repeatedly arranged in a row in the arrangement direction of the plurality of electrode fingers, and in each of the plurality of layers, the plurality of regions are provided from one surface to the other surface opposing each other in the thickness direction, and at least a portion of the plurality of regions of one layer and the plurality of regions of the other layer of the plurality of layers have regions in which the sound speed of bulk waves is approximately the same, the regions being shifted in the arrangement direction. The acoustic wave device according to claim 1, wherein the multiple regions of the layer that is located closest to the piezoelectric layer among the multiple layers are repeatedly arranged in the arrangement direction such that each of the multiple regions entirely overlaps one of the multiple electrode fingers in the arrangement direction. a temperature compensation layer provided between the insulating layer and the piezoelectric layer, the temperature compensation layer having a temperature coefficient of elastic constant of an opposite sign to that of the piezoelectric layer;
a distance from a surface of the temperature compensating layer facing the insulating layer to a surface of the piezoelectric layer on which the pair of comb electrodes are provided is 2λ or less;
The insulating layer has a bulk wave propagating therethrough at a higher acoustic velocity than the temperature compensating layer,
The acoustic wave device according to claim 2 , wherein the layer closest to the piezoelectric layer is in contact with the temperature compensating layer. The acoustic wave device according to any one of claims 1 to 3, wherein the length of each of the multiple regions in the arrangement direction is 0.5 to 1 times the average pitch of the multiple electrode fingers. The acoustic wave device according to any one of claims 1 to 4, wherein the length of each of the multiple regions in the thickness direction is 0.5 to 4 times the average pitch of the multiple electrode fingers. The acoustic wave device according to any one of claims 1 to 5, wherein the multiple regions of one adjacent layer are repeatedly arranged in the arrangement direction with respect to the multiple regions of the other adjacent layer with a phase difference of 0.5 to 1 times the average pitch of the multiple electrode fingers. The acoustic wave device according to any one of claims 1 to 6, wherein the boundaries between the regions are inclined in a cross-sectional view parallel to the arrangement direction. The plurality of regions are composed of a first region and a second region in which the sound velocity of the bulk wave propagating through the first region is slower,
The second region has a bulk wave propagating therethrough at a speed that is 1.01 times or more and 1.1 times or less than that of the piezoelectric layer;
The acoustic wave device according to claim 1 , wherein a sound velocity of a propagating bulk wave in the first region is 1.2 times or more faster than that in the second region. A filter including an acoustic wave device according to any one of claims 1 to 8. A multiplexer including the filter according to claim 9. A support substrate;
a piezoelectric layer provided on the support substrate, the piezoelectric layer being a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer;
a wafer comprising: an insulating layer provided between the support substrate and the piezoelectric layer, the insulating layer including a plurality of layers in which a plurality of regions having different sound velocities of propagating bulk waves are repeatedly arranged in an X-axis direction of a crystal orientation of the piezoelectric layer, the plurality of regions being provided from one surface to the other surface of each of the plurality of layers opposing each other in a thickness direction, the plurality of regions of one adjacent layer of the plurality of layers and the plurality of regions of the other adjacent layer having at least a portion of a region in which the sound velocities of bulk waves are approximately the same being shifted in the X-axis direction.

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