Acoustic Wave Devices, Filters, Multiplexers, and Wafers

Abstract

To provide an elastic wave device that can suppress spurious elements, and a filter including the elastic wave device.SOLUTION: An elastic wave device 100 includes: a supporting substrate 10; a piezoelectric layer 14 located on the supporting substrate 10; a pair of comb-like electrodes 22 located on the piezoelectric layer 14, the electrodes having a plurality of electrode fingers 23; and a plurality of layers 11a to 11d. The layers 11a to 11d include regions 15 and 16 alternately arranged in an X-direction between the supporting substrate 10 and the piezoelectric layer 14, the sound speed of a propagating bulk wave being different from one another. In each of the layers 11a to 11d, the regions 15 and 16 are provided from one surface to another surface facing each other in the thick direction. The regions 15, 16 in one of the layers 11a to 11d and the regions 15 and 16 in another of the layers next to the one layer have a boundary layer 11 in which the regions 15 in which the sound speeds of bulk waves are practically the same are displaced in the X-direction at least partially.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to acoustic wave devices, filters, multiplexers, and wafers. [Background technology]

[0002] Surface acoustic wave resonators are known as acoustic wave resonators used in communication devices such as smartphones. It is known that a piezoelectric layer forming a surface acoustic wave resonator is attached to a support substrate. It is known that a temperature compensation layer is provided between the support substrate and the piezoelectric layer (for example, Patent Document 1). It is known that a low acoustic velocity film having a lower acoustic velocity than the piezoelectric layer is provided between the support substrate and the piezoelectric layer, and a high acoustic velocity film having a higher acoustic velocity than the piezoelectric layer is provided between the low acoustic velocity film and the support substrate (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-201345 A [Patent Document 2] JP 2015-115870 A Summary of the Invention [Problem to be solved by the invention]

[0004] 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 need for other methods to suppress spurious signals.

[0005] The present invention has been made in consideration of the above problems, and has an object to suppress spurious signals. [Means for solving the problem]

[0006] 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 provided on the piezoelectric layer and having a plurality of electrode fingers; and an insulating layer provided between the support substrate and the piezoelectric layer, in which a plurality of regions having different sound speeds of propagating bulk waves are repeatedly arranged in an arrangement direction of the plurality of electrode fingers, the plurality of regions in each of the plurality of layers being provided from one surface to the other surface opposing each other in the thickness direction, and in which the plurality of regions of one adjacent layer and the plurality of regions of the other adjacent layer have regions in which the sound speeds of bulk waves are approximately the same, the regions being shifted in the arrangement direction.

[0007] In the above configuration, the multiple regions of the layer among the multiple layers that is located closest to the piezoelectric layer can be configured to be repeatedly arranged in the arrangement direction so that each of the multiple regions overlaps an entire electrode finger among the multiple electrode fingers in the arrangement direction.

[0008] In the above configuration, a temperature compensation layer is provided between the insulating layer and the piezoelectric layer, and the sign of the temperature coefficient of the elastic constant is opposite to that 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.

[0009] In the above configuration, the length of each of the plurality of regions in the arrangement direction can be 0.5 to 1 times the average pitch of the plurality of electrode fingers.

[0010] In the above configuration, the length of each of the plurality of regions in the thickness direction can be 0.5 to 4 times the average pitch of the plurality of electrode fingers.

[0011] 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.

[0012] In the above configuration, boundaries between the plurality of regions may be inclined in a cross-sectional view parallel to the arrangement direction.

[0013] 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 in the first region is slower than that of the first region, and the sound velocity of the bulk waves propagating in the second region is 1.01 times or more and 1.1 times or less than that of the piezoelectric layer, and the sound velocity of the bulk waves propagating in the first region is 1.2 times or more than that of the second region.

[0014] The present invention is a filter including the acoustic wave device described above.

[0015] The present invention is a multiplexer including the filter described above.

[0016] The present invention relates to a support substrate, and a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium tantalate layer provided on the support substrate. X Propagation the wafer comprising: a piezoelectric layer which is a lithium niobate layer; and an insulating layer provided between the support substrate and the piezoelectric layer, in which a plurality of layers are stacked, the plurality of layers having a plurality of regions in which the sound velocities of propagating bulk waves are different, 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 facing each other in a thickness direction in each of the plurality of layers, the plurality of regions being shifted in the X-axis direction in at least a portion of the plurality of regions of one layer and the plurality of regions of the other layer, the plurality of regions being shifted in the X-axis direction in at least a portion of the regions in the adjacent layer, in which the sound velocities of bulk waves are approximately the same. Effect of the Invention

[0017] According to the present invention, spurious signals can be suppressed. [Brief description of the drawings]

[0018] [Figure 1] 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. [Diagram 2] 2(a) to 2(d) are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Diagram 3] 3(a) to 3(c) are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 4] 4(a) to 4(c) are cross-sectional views of models A, B, and C used in the first simulation. [Diagram 5] 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. [Figure 6] 6(a) to 6(c) are cross-sectional views of models C, D, and E used in the second simulation. [Figure 7] 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. [Figure 8] 8(a) and 8(b) are cross-sectional views of models F and G used in the third simulation. [Figure 9] FIG. 9(a) shows the simulation results of the admittance |Y| of models F and G, and FIG. 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. [Figure 10] 10(a) to 10(g) are cross-sectional views of models E and HM used in the fourth simulation. [Figure 11]Figures 11(a) to 11(d) show the simulation results of the admittance |Y| for Model A, Model E, and Models H to J. [Figure 12] 12(a) to 12(c) show the simulation results of the admittance |Y| of Model A and Models K to M. [Figure 13] 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. [Figure 14] Figures 14(a) to 14(d) show the simulation results (part 1) of the admittance |Y| when the density of the region of model F is changed. [Figure 15] Figures 15(a) to 15(c) show the simulation results (part 2) of the admittance |Y| when the density of the region of model F is changed. [Figure 16] 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 emissions. [Figure 17] FIG. 17 is a cross-sectional view of an acoustic wave device in accordance with a first modification of the first embodiment. [Figure 18] FIG. 18 is a circuit diagram of a filter in accordance with the second embodiment. [Figure 19] FIG. 19 is a block diagram of a duplexer in accordance with the third embodiment. [Figure 20] FIG. 20(a) is a plan view of a wafer according to Example 4, and FIG. 20(b) is a cross-sectional view. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0020] 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, the Y direction, and the Z direction do not necessarily correspond to the X-axis direction and the 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.

[0021] As shown in FIG. 1(a) and FIG. 1(b), an acoustic wave device 100 has a piezoelectric layer 14 provided on a support substrate 10. A temperature compensating layer 12 is provided between the support substrate 10 and the piezoelectric layer 14. A boundary layer 11 is provided between the temperature compensating layer 12 and the support substrate 10. A bonding layer 13 is provided between the temperature compensating 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 compensating layer 12 is a flat surface. The interface between the temperature compensating 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 compensating layer 12, the bonding layer 13, and the piezoelectric layer 14 are T1, T2, T3, and T4, respectively.

[0022] The boundary layer 11 is formed by stacking a plurality of layers 11a, 11b, 11c, and 11d. The interfaces between the layers 11a to 11d are flat surfaces. The layers 11a to 11d have a plurality of regions 15, 16 in which the sound velocities of the propagating bulk waves are different. The regions 15, 16 are provided from one surface to the other surface of each of the layers 11a to 11d that face each other in the Z direction, and are arranged alternately in the X direction. In the adjacent layers among the layers 11a to 11d, the regions 15 and / or regions 16 in which the sound velocities of the bulk waves are substantially the same are at least partially shifted in the X direction.

[0023] An acoustic wave resonator 20 is provided on the piezoelectric layer 14. The acoustic 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.

[0024] 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 cross is an intersection region 26. The length of the intersection region 26 is an aperture length. The pair of comb electrodes 22 are provided facing each other such that the electrode fingers 23 are substantially alternated in at least a part of the intersection region 26. The acoustic 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 substantially the wavelength λ of the acoustic wave. If the pitch of the plurality of electrode fingers 23 is D, the wavelength λ of the acoustic wave is substantially twice the pitch D. The reflector 25 reflects the acoustic wave (surface acoustic wave) excited by the electrode fingers 23 of the IDT 21. As a result, the acoustic wave is confined within the intersection region 26 of the IDT 21.

[0025] 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.

[0026] 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 makes it possible to reduce the frequency temperature dependence of the acoustic wave resonator 20.

[0027] The temperature compensating layer 12 has a temperature coefficient of elastic constant with a sign opposite to that 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 (SiO2) 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. The oxygen and silicon are each 10 at% or more, and may be 20 at% or more.

[0028] The acoustic velocity of the bulk wave propagating through the boundary layer 11 is faster than that of the temperature compensating layer 12. That is, the acoustic velocity of the bulk wave in both of the regions 15 and 16 of the layers 11a to 11d constituting the boundary layer 11 is faster than that of the temperature compensating layer 12. This allows 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. A plurality of layers made of different materials may be provided as the boundary layer 11.

[0029] The regions 15 and 16 provided in the layers 11a to 11d forming 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 velocities of the propagating bulk waves are different. The regions 15 and 16 may also have different sound velocities of the propagating bulk waves by other methods. At least one of the regions 15 and 16 may have a faster sound velocity of the bulk waves than the temperature compensation layer 12.

[0030] 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.

[0031] The sound velocity of the bulk waves propagating through the temperature compensating layer 12 may be faster than the sound velocity of the bulk waves propagating through the piezoelectric layer 14, but in order to facilitate the existence of elastic waves in the temperature compensating layer 12, it is preferably slower than the sound velocity of the bulk waves propagating through the piezoelectric layer 14, and is preferably 0.99 times or less. If the sound velocity of the bulk waves propagating through the temperature compensating layer 12 is too slow, it becomes difficult for elastic waves to exist in the piezoelectric layer 14, so the sound velocity of the bulk waves propagating through the temperature compensating layer 12 is preferably 0.9 times or more faster than the sound velocity of the bulk waves propagating through the piezoelectric layer 14.

[0032] 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.

[0033] The metal film 27 is a film containing, for example, aluminum, copper, or molybdenum as a main component. 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 so as to cover the electrode fingers 23. The insulating film may function as a protective film and a temperature compensation film.

[0034] 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 energy of the surface acoustic waves exists in a range up to a depth of about 2λ from the top surface of the piezoelectric layer 14, and particularly exists in a 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. If the bulk waves are reflected by the top surface of the support substrate 10 and return to the IDT 21, they will cause spurious responses.

[0035] In order to suppress spurious, it has been proposed to form irregularities on the upper surface of the support substrate 10 to scatter bulk waves. However, forming irregularities suitable for scattering bulk waves on the upper surface of the support substrate 10 increases manufacturing costs. Therefore, in the first embodiment, instead of forming irregularities on the upper surface of the support substrate 10, the boundary layer 11 is formed of a plurality of layers 11a to 11d. Details of this point will be described later.

[0036] [Manufacturing 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.

[0037] As shown in FIG. 2(a), a wafer-like support substrate 10 having 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, thereby forming a patterned insulating film 15a. The insulating film 15a may be formed by, for example, a lift-off method.

[0038] As shown in FIG. 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 may be made of the same material but with different densities by changing the film formation method to have different sound velocities of the propagating bulk wave, or may be made to have different sound velocities of the propagating bulk wave by other methods. After that, the insulating film 16a is polished by, for example, a CMP (Chemical Mechanical Polishing) method until the insulating film 15a is exposed. As a result, a layer 11a having a region 15 made of the insulating film 15a and a region 16 made of the insulating film 16a is formed.

[0039] As shown in FIG. 2(c), after a resist pattern 90 is formed on the layer 11a, an insulating film 16a is formed by, for example, sputtering or CVD.

[0040] 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.

[0041] As shown in Fig. 3(a), layers 11c and 11d are formed by repeating the same steps as those shown in Fig. 2(c) and Fig. 2(d). As a result, a boundary layer 11 consisting of layers 11a to 11d is formed. Thereafter, a temperature compensation layer 12 is formed on the boundary layer 11 by, for example, a sputtering method or a CVD method.

[0042] 3(b), the piezoelectric substrate 17 is bonded to the upper surface of the temperature compensating layer 12 via the bonding layer 13. The temperature compensating layer 12 and the piezoelectric substrate 17 may be bonded to each other without the bonding layer 13. For example, a surface activation method is used for bonding.

[0043] 3(c), the upper surface of the piezoelectric substrate 17 is polished, for example, by a CMP method, 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 diced into individual pieces to form the acoustic wave devices 100.

[0044] [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 waves different. Regions 15 and 16 are provided in the entire intersection region 26 in a 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: Density is 3150 kg / m 3 Aluminum oxide Region 16 of boundary layer 11: Density is 4500 kg / m 3 Aluminum oxide Temperature compensation layer 12: a silicon oxide layer having a thickness of 0.2λ Piezoelectric layer 14: 42° Y-cut X-propagation lithium tantalate layer with a thickness of 0.3λ Electrode finger 23: a 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

[0045] 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, the temperature compensation layer 12, the piezoelectric layer 14, and the 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, and hatching of region 15 is omitted (the same applies to the following similar figures).

[0046] As shown in FIG. 4(a), in model A, the entire boundary layer 11 is defined as region 15. That is, the entire boundary layer 11 has a density of 3150 kg / m 3 In this manner, model A is a model equivalent to a comparative example, since boundary layer 11 is not formed of a plurality of layers having regions 15 and 16.

[0047] 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, and one of the two is a layer with a density of 3150 kg / m 3 the other is an area 15 made of aluminum oxide having a density of 4500 kg / m 3 In model B, the boundary layer 11 is composed of a single layer 11a having the regions 15 and 16 arranged in the X direction. In model B, the length of the 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 equivalent to a comparative example, since the boundary layer 11 is not composed of a plurality of layers having the regions 15 and 16 stacked together.

[0048] As shown in FIG. 4(c), 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 set to have a density of 3150 kg / m 3 The region 15 is made of aluminum oxide having a density of 4500 kg / m 3The region 16 is made of aluminum oxide. That is, the boundary layer 11 is formed by laminating two layers 11a and 11b, each having a region 15 and a region 16 aligned in the X direction. The region 15 of the layer 11a and the region 15 of the layer 11b are arranged with a shift in the X direction, and the region 16 of the layer 11a and the region 16 of the layer 11b are arranged with a shift in the X direction. In the 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, the model C is a model corresponding to the embodiment.

[0049] 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. As shown in FIG. 5(a) and FIG. 5(b), the high-frequency spurious was suppressed in model C compared to models A and B. The reason why the high-frequency spurious was suppressed in model C is considered to be as follows. The boundary layer 11 of model C is formed by laminating two layers 11a and 11b in which regions 15 and 16 in which the sound speed of the propagating bulk wave is different are arranged in the X direction. The region 15 of the layer 11a and the region 15 of the layer 11b are arranged with a shift in the X direction, and the region 16 of the layer 11a and the region 16 of the layer 11b are arranged with a shift in the X direction. It is believed that this causes the bulk waves that pass from piezoelectric layer 14 through temperature compensating layer 12 to reach boundary layer 11 to be scattered by regions 15 and 16 of layers 11a and 11b, thereby suppressing high frequency spurious emissions.

[0050] According to the first embodiment, as shown in FIG. 1(b), 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-11d in which a plurality of regions 15, 16 in which the sound velocities of the propagating bulk waves are different are repeatedly arranged in the X direction. In each of the plurality of layers 11a-11d, the regions 15, 16 are provided from one surface to the other surface facing each other in the Z direction. Among the plurality of layers 11a-11d, the regions 15, 16 of one adjacent layer and the regions 15, 16 of the other adjacent layer are arranged such that the regions 15 and / or the regions 16 in which the sound velocities of the bulk waves are substantially the same are shifted in the X direction. As a result, the bulk waves are scattered by the regions 15, 16 of the layers 11a-11d, so that spurious caused by the bulk waves can be suppressed. The "sound velocities of the bulk waves being substantially the same" means that the difference in the sound velocities of the bulk waves is allowed to be within the range of manufacturing errors.

[0051] In the first embodiment, in order to scatter the bulk waves and suppress spurious signals, it is preferable that the regions 15, 16 of one layer and the regions 15, 16 of the other layer among the multiple layers 11a to 11d are arranged so that the sound velocities of the bulk waves therein are substantially the same, and that the regions 15 and the regions 16 are arranged so as to be shifted in the X direction.

[0052] In order to allow the bulk wave to reach boundary layer 11, thickness T2 of temperature compensating 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 electrode fingers 23. In order to allow temperature compensating layer 12 to exhibit its temperature compensation function, thickness T2 of temperature compensating 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 electrode fingers 23. The average pitch D of electrode fingers 23 can be calculated by dividing the width of IDT 21 in the X direction by the number of electrode fingers 23.

[0053] Boundary layer 11 is not limited to four layers 11a-11d laminated together, but may be two or more layers laminated together. From the viewpoint of scattering bulk waves by boundary layer 11, it is preferable that boundary layer 11 has a larger number of laminated layers, preferably three or more layers, more preferably five or more layers, and even more preferably eight or more layers. Furthermore, since a thin thickness T1 of boundary layer 11 increases spurious signals, thickness T1 of boundary layer 11 is preferably 1.4 times (0.7λ) or more of average pitch D of electrode fingers 23, more preferably two times (λ) or more, and even more preferably four times (2λ) or more.

[0054] 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 making 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.

[0055] [Second simulation] 6(a) to 6(c) are cross-sectional views of models C, D, and E used in the second simulation. Model C in FIG. 6(a) has been described in the first simulation, so description thereof will be omitted here.

[0056] 6(b), in model D, 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, 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, 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.

[0057] 6(c), in model E, 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, two regions located on the +X side are designated as regions 15, and two regions located on the -X side are designated as regions 16. Of the four regions on the -Z side, two regions located on the ends of the +X side and -X side are designated as regions 15, and two regions located in the center are designated as regions 16.

[0058] Thus, in all of models C, D, and E, boundary layer 11 is formed by stacking two layers 11a and 11b each having region 15 and 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 each of regions 15 and 16 of layers 11a and 11b is 2λ, and the length in the X direction is 0.5λ.

[0059] In model C, regions 15 and 16 of layer 11a are each provided to overlap one entire electrode finger 23 in the X direction, and regions 15 and 16 of layer 11b are also provided to overlap one entire electrode finger 23 in the X direction. 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 one entire electrode finger 23 in the X direction.

[0060] 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. As shown in Fig. 7(a) and Fig. 7(b), the high-frequency spurious was suppressed more in model C than in models D and E, and the high-frequency spurious was suppressed more in model E than in model D.

[0061] From the results of the second simulation, in the first embodiment, it is preferable that the regions 15 and 16 of the layer 11d located closest to the piezoelectric layer 14 among the layers 11a to 11d constituting the boundary layer 11 are aligned in the X direction so that the regions 15 and 16 overlap 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 the first embodiment, it is preferable that the layer 11d is a layer 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 the first embodiment, it is preferable that the regions 15 and 16 are aligned in the X direction in all layers among the layers 11a to 11d constituting the boundary layer 11 so that the regions 15 and 16 overlap the entire X direction of one electrode finger 23. This makes it possible to suppress high-frequency spurious as in model C.

[0062] As shown in FIG. 6(a), in model C, the regions 15 and 16 of the layer 11a are arranged with a phase difference of 0.5λ in the X direction with respect to the regions 15 and 16 of the layer 11b. As shown in FIG. 6(c), in model E, the regions 15 and 16 of the layer 11a are arranged with a phase difference of 0.25λ in the X direction with respect to the regions 15 and 16 of the layer 11b. 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 arranged with a phase difference of 0.25λ or more and 0.5λ or less with respect to the regions 15 and 16 of the other layer in the X direction. In other words, it is preferable that the regions 15, 16 of adjacent layers 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.

[0063] As shown in Fig. 7(b), 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 adjacent regions 15, 16 of one layer are arranged with a phase difference of 0.3λ to 0.5λ with respect to the regions 15, 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 adjacent regions 15, 16 of one layer are arranged with a phase difference of 0.6 to 1 times the average pitch D of the electrode fingers 23 with respect to the regions 15, 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.

[0064] [Third Simulation]

[0065] 8(a) and 8(b) are cross-sectional views of models F and G used in the third simulation. As shown in FIG. 8(a), in model F, 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 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.

[0066] 8(b), in model G, boundary layer 11 is divided into four in the Z direction and the X direction under a pair of electrode fingers 23, and regions 15, 16 of four layers 11a to 11d are arranged in a lattice pattern. Regions 15, 16 of layers 11a to 11d are each provided to overlap half of one electrode finger 23. In model G, the length in the Z direction of regions 15, 16 of layers 11a to 11d is λ, and the length in the X direction is 0.25λ.

[0067] 9(a) shows the simulation results of the admittance |Y| of models F and G, and FIG. 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 FIG. 9, high-frequency spurious was suppressed more in model F than in model G.

[0068] From the third simulation result, in Example 1, in order to suppress high frequency spurious, the length in the X direction of regions 15, 16 of layers 11a-11d constituting 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 regions 15, 16 of layers 11a-11d constituting boundary layer 11 is preferably 0.5 to 1 times the average pitch D of multiple electrode fingers 23, more preferably 0.6 to 1 times, and even more preferably 0.8 to 1 times.

[0069] [Fourth Simulation]

[0070] 10(a) to 10(g) are cross-sectional views of models E and H to M used in the fourth simulation. Model E in Fig. 10(a) has been described in the second simulation, and therefore will not be described here.

[0071] 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 ten-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 of the regions 15 and 16 in the Z direction of each layer is 0.67λ, and the length of the regions 15 and 16 in the X direction is 0.5λ. In model K, the length of the regions 15 and 16 in the Z direction of each layer is 0.4λ, and the length of the regions 15 and 16 in the X direction is 0.5λ. In model L, the length of the regions 15 and 16 in the Z direction of each layer is 0.16λ, and the length of the regions 15 and 16 in the X direction is 0. In model M, the length of the regions 15 and 16 in the Z direction of each layer is 0.08λ, and the length of the regions 15 and 16 in the X direction is 0.5λ.

[0072] Figs. 11(a) to 11(d) show the simulation results of the admittance |Y| of models E, and H to J. Figs. 12(a) to 12(c) show the simulation results of the admittance |Y| of models K to M. For comparison, Figs. 11(a) to 11(d) and 12(a) to 12(c) also show the simulation results of the admittance |Y| of model A (see Fig. 4(a)). As shown in Figs. 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.

[0073] Fig. 13 is a graph showing the relationship between the Z-direction length of regions 15, 16 in each layer constituting boundary layer 11 and high-frequency spurious. The horizontal axis in Fig. 13 is the Z-direction length of regions 15, 16. The vertical axis is the difference |ΔY| between the maximum and minimum admittance values ​​in the high-frequency spurious. In Fig. 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 Fig. 13, the high-frequency spurious was most suppressed when the Z-direction length of regions 15, 16 was 1λ.

[0074] From the fourth simulation result, in Example 1, in order to suppress high frequency spurious, the length in the Z direction of the regions 15 and 16 of the layers 11a to 11d constituting the boundary layer 11 is preferably 0.25λ or more and 2λ or less, more preferably 0.5λ or more and 1.5λ or less, and even more preferably 0.8λ or more and 1.2λ or less. In other words, the length in the Z direction of the regions 15 and 16 of the layers 11a to 11d constituting the 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.

[0075] [5th ​​Simulation] The fifth simulation uses model F shown in FIG. 8(a) and sets the density of region 15 to 3150 kg / m 3 The admittance was simulated when the density of region 16 was varied.

[0076] 14(a) to 14(d) and 15(a) to 15(c) show the simulation results of admittance |Y| when the density of region 16 of model F is changed. 3 Figure 14(b) shows the load of 2000 kg / m 3 Figure 14(c) shows the load of 3000 kg / m 3 Figure 14(d) shows the load of 4000 kg / m 3 Figure 15(a) shows the load of 4500 kg / m 3 Figure 15(b) shows 4873 kg / m 3 Figure 15(c) shows the load of 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.

[0077] 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 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 values ​​of admittance 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.

[0078] As shown in Figures 14(a) to 14(d), 15(a) to 15(c), and 16(a) and 16(b), the density of region 16 is set to 1500 kg / m 3 ~6000kg / m 3 From this, it was confirmed that by making the sound speed of the bulk waves in the regions 15 and 16 different, spurious emissions can be suppressed regardless of the difference in sound speed.

[0079] 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 compensation layer 12, which is a silicon oxide layer, is 3684 m / s. 3 The acoustic velocity of the bulk wave propagating through the region 15 made of aluminum oxide 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 compensation layer 12, and the bulk wave acoustic velocity in the region 15 is faster than that in the region 16, the suppression effect of high frequency spurious is large. Therefore, in the first embodiment, when the layers 11a to 11d constituting the boundary layer 11 are composed of the region 15 and the region 16 in which the bulk wave acoustic velocity is slower than that in the region 15, the bulk wave acoustic velocity in the region 16 is preferably 1.01 times or more and 1.1 times or less than that in the piezoelectric layer 14, more preferably 1.01 times or more and 1.08 times or less, and even more preferably 1.01 times or more and 1.05 times or less than that in the region 15. The bulk wave acoustic velocity in the region 15 is preferably 1.2 times or more than that in the region 16, more preferably 1.25 times or more, and even more preferably 1.3 times or more. This makes it possible to effectively suppress spurious signals.

[0080] 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 compensating 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 compensating layer 12.

[0081] [Variations] 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 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 in the first embodiment, and therefore description thereof will be omitted.

[0082] As in the first modification of the first embodiment, the boundary between the region 15 and the region 16 may be inclined in a cross-sectional view parallel to the X direction. This makes it possible to effectively scatter bulk waves, thereby increasing the effect of suppressing spurious emissions.

[0083] In the first embodiment and its modified example, the layers 11a-11d have two regions 15, 16 in which the sound velocities of the propagating bulk waves are different, but the layers 11a-11d may have three or more regions in which the sound velocities of the propagating bulk waves are different. In this case, the three or more regions in each of the layers 11a-11d are repeatedly arranged in the X direction, and the regions in one layer and the regions in the other layer adjacent to each other among the layers 11a-11d have at least some regions in which the sound velocities of the bulk waves are substantially the same, shifted in the X direction.

[0084] In the first embodiment and its modified examples, the temperature compensating layer 12 is provided between the boundary layer 11 and the piezoelectric layer 14, 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. EXAMPLES

[0085] Fig. 18 is a circuit diagram of a filter 200 according to a second embodiment. As shown in Fig. 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 modifications 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 of the ladder filter can be set as appropriate. The filter may be a multi-mode filter. EXAMPLES

[0086] FIG. 19 is a block diagram of a duplexer 300 according to a 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 inputted 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 inputted 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 has been shown as an example of a multiplexer, a triplexer, a quadplexer, or the like may also be used. EXAMPLES

[0087] Fig. 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 Fig. 20(a) and Fig. 20(b), the wafer 400 has a piezoelectric layer 14 provided on a support substrate 10. A temperature compensating layer 12 is provided between the support substrate 10 and the piezoelectric layer 14. A boundary layer 11 is provided between the temperature compensating layer 12 and the support substrate 10. A bonding layer 13 is provided between the temperature compensating layer 12 and the piezoelectric layer 14, but the bonding layer 13 may not be provided.

[0088] 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 defined as the X-direction. The stacking direction (thickness direction) of the support substrate 10 and the piezoelectric layer 14 is defined as the Z-direction. The direction perpendicular to the X-direction and the Z-direction is defined as the Y-direction. The support substrate 10, the boundary layer 11, the temperature compensation layer 12, and the bonding layer 13 are made of the materials shown in the first embodiment.

[0089] The boundary layer 11 is formed by stacking a plurality of layers 11a-11d. The plurality of layers 11a-11d has a plurality of 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 plurality of layers 11a-11d that face each other in the Z direction, and are arranged alternately in the X direction. In at least a part of adjacent layers among the plurality of layers 11a-11d, the regions 15 and / or regions 16 in which the sound speed of the bulk waves is substantially the same are arranged so as to be shifted in the X direction.

[0090] 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 includes a plurality of layers 11a-11d in which a plurality of regions 15, 16 in which the acoustic velocity of the propagating bulk waves is different are repeatedly arranged in the X direction. In each of the plurality of layers 11a-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 among the plurality of layers 11a-11d and the regions 15, 16 of the other layer, the regions 15 and / or regions 16 in which the acoustic velocity of the bulk waves is substantially the same are shifted in the X direction. In this way, the layer structure of the wafer 400 is similar to 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 and forming an acoustic wave resonator on the piezoelectric layer 14, an acoustic wave device with suppressed spurious emissions can be obtained.

[0091] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to such specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0092] 10 Support substrate 11 Boundary layer 11a~11d layer 12 Temperature compensation layer 13 Bonding layer 14 Piezoelectric layer 15, 16 areas 15a, 16a Insulating film 17 Piezoelectric Substrate 20. Elastic Wave Resonator 21 IDT 22 Comb-shaped electrode 23 Electrode finger 24 Busbar 25 Reflector 26 Intersection Area 27 Metal Film 30 Transmission Filter 32 Receiving Filter 100, 110 Acoustic Wave Devices 200 Filters 300 Duplexer 400 wafers

Claims

1. 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 adjacent layer among the plurality of layers and the plurality of regions of the other adjacent layer have regions in which the sound speed of bulk waves is approximately the same, the regions being shifted in the arrangement direction.

2. 2. The acoustic wave device of claim 1, wherein the plurality of regions of the layer that is located closest to the piezoelectric layer are repeatedly arranged in the arrangement direction so that each of the plurality of regions overlaps an entire electrode finger of the plurality of electrode fingers in the arrangement direction.

3. 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.

4. The acoustic wave device according to claim 1 , wherein the length of each of the regions in the arrangement direction is between 0.5 and 1 times an average pitch of the electrode fingers.

5. The acoustic wave device according to claim 1 , wherein the length of each of the regions in the thickness direction is 0.5 to 4 times the average pitch of the electrode fingers.

6. 6. The acoustic wave device according to claim 1, wherein the plurality of regions of one of the adjacent layers are repeatedly arranged in the arrangement direction with respect to the plurality of regions of the other layer with a phase difference of 0.5 to 1 times the average pitch of the plurality of electrode fingers.

7. The acoustic wave device according to claim 1 , wherein boundaries between the plurality of regions are inclined in a cross-sectional view parallel to the arrangement direction.

8. The plurality of regions are composed of a first region and a second region in which the sound velocity of the bulk wave propagating in 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.

9. A filter comprising an acoustic wave device according to any one of claims 1 to 8.

10. A multiplexer including a filter according to claim 9.

11. 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 having regions in which the sound velocities of bulk waves are approximately the same being shifted in the X-axis direction at least in part.

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