Elastic wave device

Abstract

Provided is an elastic wave device that improves resonance characteristics in a high-order mode. The elastic wave device comprises: a piezoelectric laminate having a first main surface and a second main surface on the opposite side from the first main surface in a first direction; an electrode provided on at least one among the first main surface and the second main surface of the piezoelectric laminate; and a support member provided on the second main surface side of the piezoelectric laminate and having an acoustic reflection part on the second main surface side of the piezoelectric laminate. At least a portion of the electrode is disposed so as to overlap the acoustic reflection part in a plan view in the first direction. The piezoelectric laminate comprises: a first piezoelectric layer having the second main surface; an intermediate layer laminated on the first piezoelectric layer; and a second piezoelectric layer laminated on the intermediate layer. At least one among the material and the polarization direction of the intermediate layer is different from that of the first piezoelectric layer. At least one among the material and the polarization direction of the intermediate layer is different from that of the second piezoelectric layer.

Description

Elastic wave device

[0001] This invention relates to an elastic wave apparatus.

[0002] Patent documents 1 and 2 describe elastic wave apparatus having IDT electrodes.

[0003] U.S. Patent No. 11349450, International Publication No. 2021 / 060523

[0004] The elastic wave apparatus described in Patent Documents 1 and 2 sometimes utilizes higher-order modes in order to use high frequencies without thinning the piezoelectric layer. In this case, the primary mode may become an unwanted wave for the higher-order mode, potentially degrading the resonance characteristics.

[0005] The present invention aims to provide an elastic wave apparatus that improves resonance characteristics in higher-order modes.

[0006] An elastic wave apparatus according to one embodiment comprises a piezoelectric laminate having a first main surface and a second main surface opposite to the first main surface in the first direction, an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric laminate, and a support member provided on the second main surface side of the piezoelectric laminate and having an acoustic reflecting portion on the second main surface side of the piezoelectric laminate, wherein at least a part of the electrode is arranged to overlap with the acoustic reflecting portion when viewed in plan in the first direction, and the piezoelectric laminate comprises a first piezoelectric layer having the second main surface, an intermediate layer laminated on the first piezoelectric layer, and a second piezoelectric layer laminated on the intermediate layer, wherein at least one of the material and polarization direction of the intermediate layer is different from that of the first piezoelectric layer, and at least one of the material and polarization direction of the intermediate layer is different from that of the second piezoelectric layer.

[0007] The elastic wave apparatus of the present invention can improve the resonance characteristics in higher-order modes.

[0008] Figure 1 is a plan view showing the elastic wave apparatus of the first embodiment. Figure 2 is a cross-sectional view taken along line II-II' of Figure 1. Figure 3 is an enlarged cross-sectional view showing region A shown in Figure 2. Figure 4 is a schematic cross-sectional view illustrating the bulk wave of the thickness slip mode propagating through the piezoelectric layer of the first embodiment. Figure 5 is a plan view showing an example in which a pair of electrodes are provided in the elastic wave apparatus of the first embodiment. Figure 6 is a diagram illustrating the resonance characteristics of the elastic wave apparatus according to the first embodiment. Figure 7 shows the d of the resonance characteristics of the elastic wave apparatus according to the first embodiment. ｍ / d ｐ This is a diagram illustrating the dependency. Figure 8 is a diagram illustrating the resonance characteristics of the elastic wave apparatus according to the second embodiment. Figure 9 shows the d of the resonance characteristics of the elastic wave apparatus according to the second embodiment. ｍ / d ｐ This is a diagram illustrating the dependency. Figure 10A is a diagram illustrating the resonance characteristics of the elastic wave apparatus according to the third embodiment. Figure 10B is a diagram illustrating the resonance characteristics of the elastic wave apparatus according to the third embodiment. Figure 10C is a diagram illustrating the resonance characteristics of the elastic wave apparatus according to the third embodiment. Figure 10D is a diagram illustrating the resonance characteristics of the elastic wave apparatus according to the third embodiment. Figure 10E is a diagram illustrating the resonance characteristics of the elastic wave apparatus according to the third embodiment. Figure 11 is a diagram illustrating the resonance characteristics of the elastic wave apparatus according to the fourth embodiment. Figure 12 is a flowchart illustrating the ion slicing method used in the manufacture of the elastic wave apparatus according to the fifth embodiment. Figure 13 is a schematic cross-sectional view illustrating the ion slicing method used in the manufacture of the elastic wave apparatus according to the fifth embodiment. Figure 14 is a schematic cross-sectional view showing the elastic wave apparatus according to the sixth embodiment.

[0009] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited by these embodiments. Each embodiment described in this disclosure is illustrative, and partial substitution or combination of configurations is possible between different embodiments. In modifications and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects due to similar configurations will not be mentioned sequentially for each embodiment. Furthermore, in this disclosure, the symbol "±" indicates that a range of numerical values ​​following it is permitted. That is, for example, a±b refers to a range of a-b or greater and a+b or less.

[0010] (First Embodiment) Figure 1 is a plan view showing an elastic wave apparatus of the first embodiment. Figure 2 is a cross-sectional view taken along line II-II' in Figure 1. Figure 3 is an enlarged cross-sectional view showing region A shown in Figure 2.

[0011] As shown in Figures 1 and 2, the elastic wave apparatus 10 according to the first embodiment includes a piezoelectric laminate 20, an IDT electrode 30 (electrode), and a support substrate 11 (support member). As shown in Figure 2, the elastic wave apparatus 10 is constructed by stacking the piezoelectric laminate 20 and the IDT electrode 30 in that order so as to overlap with the support substrate 11.

[0012] The elastic wave apparatus 10 according to the first embodiment is an elastic wave apparatus that excites thickness-slip modes using a piezoelectric laminate 20, and is an elastic wave apparatus that excites thickness-slip higher-order modes (higher-order modes) which are modes whose frequencies are integer multiples of the thickness-slip primary mode (primary mode). By utilizing higher-order modes, it is possible to use high frequencies without using thin layers of piezoelectric material. On the other hand, when utilizing higher-order modes, the primary mode becomes an unwanted wave, so it is necessary to suppress the primary mode.

[0013] The piezoelectric laminate 20 is a flat plate-shaped laminate containing a piezoelectric material, having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric laminate 20 comprises a first piezoelectric layer 21, a second piezoelectric layer 22, and an intermediate layer 23. In the examples of Figures 2 and 3, the piezoelectric laminate 20 is laminated in the order of the first piezoelectric layer 21, the intermediate layer 23, and the second piezoelectric layer 22. That is, the intermediate layer 23 is laminated between the main surface 21a of the first piezoelectric layer 21 and the main surface 22b of the second piezoelectric layer 22, the first main surface 20a corresponds to the main surface 22a of the second piezoelectric layer 22, and the second main surface 20b corresponds to the main surface 21b of the first piezoelectric layer.

[0014] In the first embodiment, it is preferable that either the second piezoelectric layer 22 or the intermediate layer 23 is epitaxially grown at the interface between them. That is, it is preferable that at least one of the second piezoelectric layer 22 and the intermediate layer 23 is formed from an epitaxially grown piezoelectric material. In this disclosure, epitaxial growth refers to the growth of a crystalline thin film. That is, in the first embodiment, it is preferable that the second piezoelectric layer 22 forms a continuous crystalline structure with the intermediate layer 23 on its main surface 22b. More specifically, it is preferable that the second piezoelectric layer 22 forms a continuous crystalline structure with the intermediate layer 23 on a part of its main surface 22b. It is preferable that the main surface 22b of the second piezoelectric layer 22 forms a completely continuous crystalline structure with the intermediate layer 23. This improves the manufacturability of the elastic wave apparatus 10. Here, whether or not the second piezoelectric layer 22 or the intermediate layer 23 is epitaxially grown can be determined by measurement using X-ray diffraction (XRD).

[0015] In the first embodiment, it is preferable that at the interface between the first piezoelectric layer 21 and the intermediate layer 23, either layer is formed of a piezoelectric material grown epitaxially. That is, at least one of the first piezoelectric layer 21 and the intermediate layer 23 is preferably formed of a piezoelectric material grown epitaxially. In other words, it is preferable that the first piezoelectric layer 21 forms a crystal structure continuous with the intermediate layer 23 on the main surface 21a. More specifically, it is preferable that a part of the first piezoelectric layer 21 forms a crystal structure continuous with the intermediate layer 23 on the main surface 21a. It is preferable that the main surface 21a of the first piezoelectric layer 21 forms a crystal structure completely continuous with the intermediate layer 23. Thereby, the manufacturability of the elastic wave device 10 can be improved. Here, whether the first piezoelectric layer 21 or the intermediate layer 23 is grown epitaxially can be determined by measurement with XRD.

[0016] Here, the epitaxially grown layer can be formed, for example, by a chemical vapor deposition (CVD) method, a molecular beam epitaxy (MBE) method, sputtering, an atomic layer deposition (ALD) method, or the like. Note that the intermediate layer 23 may be formed by polishing a piezoelectric material or by ion implantation, in addition to being formed by epitaxial growth.

[0017] The first piezoelectric layer 21 and the second piezoelectric layer 22 are formed of lithium niobate (LiNbO ３ ). Alternatively, the first piezoelectric layer 21 and the second piezoelectric layer 22 may be made of lithium tantalate (LiTaO ３ ). The cut angle of LiNbO ３ or LiTaO ３ is a Z cut in the first embodiment. In the present disclosure, being a Z cut means that the Euler angles (φ, θ, ψ) of the piezoelectric material are (0° ± 5°, 0° ± 5°, any angle). The cut angle of LiNbO ３ or LiTaO ３The cut angle may be a rotational Y-cut or an X-cut. Preferably, the propagation direction is ±30° for Y propagation and X propagation. Preferably, the first piezoelectric layer 21 and the second piezoelectric layer 22 are lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO) ３ ) includes a 120°±10° rotation Y-cut or a 90°±10° rotation Y-cut.

[0018] In the first embodiment, the intermediate layer 23 is made of a piezoelectric material. The intermediate layer 23 is made of lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO) ３ ) may be formed of this. This reduces the lattice misfit between the first piezoelectric layer 21 and the second piezoelectric layer 22, thereby promoting epitaxial growth in the formation of the intermediate layer 23 and the second piezoelectric layer 22, and improving the manufacturability of the elastic wave apparatus 10. In the first embodiment, it is a Z cut. LiNbO of the intermediate layer 23 ３ ya LiTaO ３ The cutting angle may be a rotational Y-cut or an X-cut.

[0019] In the first embodiment, the polarization directions of the first piezoelectric layer 21 and the second piezoelectric layer 22 are the same. However, the polarization direction of the intermediate layer 23 is different from the polarization directions of the first piezoelectric layer and the second piezoelectric layer 22. This allows for the suppression of first-order modes over higher-order modes. Preferably, the polarization direction of the intermediate layer 23 is opposite to the polarization direction of the first piezoelectric layer and the second piezoelectric layer 22. This allows for the suppression of first-order modes while suppressing the attenuation of higher-order modes. In this disclosure, the polarization direction refers to the direction of spontaneous polarization. The spontaneous polarization directions of the first piezoelectric layer 21, the second piezoelectric layer 22, and the intermediate layer 23 can be observed with SPM (Scanning Probe Microscopy). Specifically, in a PRM (Piezo Response Microscope) observation image of a cross-section of the piezoelectric laminate 20 along the stacking direction (Z direction described later), regions with different spontaneous polarization directions appear as regions showing different colors. This makes it possible to measure the direction of spontaneous polarization of the first piezoelectric layer 21, the second piezoelectric layer 22, and the intermediate layer 23.

[0020] Here, the polarization direction of the piezoelectric material can be determined, for example, by performing a polarization treatment that involves applying a pulsed voltage at a high temperature. By performing this polarization treatment, partial polarization reversal within the piezoelectric single crystal is corrected to obtain a piezoelectric material with the desired polarization direction.

[0021] The thickness of the piezoelectric laminate 20 is not particularly limited, but to effectively excite the thickness sliding mode, it is preferably 50 nm to 1000 nm. The thickness of the piezoelectric laminate 20 according to the first embodiment is, for example, about 400 nm (0.4 μm).

[0022] As shown in Figure 3, in the following description, the thicknesses of the first piezoelectric layer 21, the second piezoelectric layer 22, and the intermediate layer 23 are d, respectively. ｐ１ d ｐ２ d ｍ This will be explained as follows. Also, the sum of the thickness of the first piezoelectric layer 21 and the second piezoelectric layer, i.e., d ｐ１ +d ｐ２ to d ｐ It is sometimes explained as follows. In the first embodiment, d ｐ１ and d ｐ２ Since this is equal to d ｐ１ = d ｐ２ = d ｐ It is / 2.

[0023] In the first embodiment, that is, when the intermediate layer 23 is made of a piezoelectric material, the thickness d of the intermediate layer 23 ｍ The sum of the thickness of the first piezoelectric layer 21 and the thickness of the second piezoelectric layer d ｐ The ratio (d ｍ / d ｐ ) is preferably 1.6 or less, and more preferably 0.3 or more. This makes the higher-order modes larger than the first-order modes, thereby improving the resonance characteristics in the higher-order modes. d ｍ / d ｐ It is even more preferable that this value be between 0.5 and 0.75. This allows for suppression from the first-order mode, thereby further improving the resonance characteristics in higher-order modes.

[0024] The support substrate 11 (support member) is positioned opposite the second main surface 20b of the piezoelectric laminate 20. The support substrate 11 has a recess 14 (energy confinement portion) that opens to the second main surface 20b side of the piezoelectric laminate 20. More specifically, the support substrate 11 has a bottom portion 12 and a wall portion 13 provided in a frame shape on the upper surface of the bottom portion 12. The recess 14 is formed in the space enclosed by the bottom portion 12 and the wall portion 13. The recess 14 is also called a cavity portion or hollow portion. The piezoelectric laminate 20 is laminated on the upper surface of the wall portion 13 of the support substrate 11. At least a part of the IDT electrode 30, which will be described later, is positioned so as to overlap with the recess 14 (energy confinement portion) when viewed in plan in the Z direction, which will be described later. In this way, the elastic wave device 10 has a so-called membrane structure in which the recess 14 is provided on the second main surface 20b side of the piezoelectric laminate 20. In this embodiment, the recess 14 (energy confinement portion) is an acoustic reflection portion.

[0025] The support member may include a support substrate 11 and a bonding (insulating) layer. The piezoelectric laminate 20 is bonded to the support substrate 11 directly or via the bonding (insulating) layer. The recess 14 may be formed in the bonding (insulating) layer. In that case, the support substrate 11 and the bonding layer may have a frame-like shape, thereby forming the recess 14. Alternatively, the recess 14 may be formed in the bonding layer.

[0026] The support substrate 11 is made of silicon (Si). The surface orientation of the Si on the side facing the piezoelectric laminate 20 may be (100) or (110), or it may be (111). Preferably, high-resistivity Si with a resistivity of 4 kΩ or more is desirable. However, the support substrate 11 can also be made of an appropriate insulating material or semiconductor material. As materials for the support substrate 11, for example, piezoelectric materials such as aluminum oxide, lithium tantalate, lithium niobate, and quartz; various ceramics such as alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectrics such as diamond and glass; and semiconductors such as gallium nitride can be used.

[0027] The IDT (Interdigital Transuducer) electrode 30 is provided on the first main surface 20a of the piezoelectric laminate 20. As shown in Figure 1, the IDT electrode 30 has a first electrode finger 31, a second electrode finger 32, a first busbar electrode 33, and a second busbar electrode 34. The plurality of first electrode fingers 31 extend in the Y direction, and one end in the extending direction is connected to the first busbar electrode 33. The plurality of second electrode fingers 32 extend in the Y direction, and the other end in the extending direction is connected to the second busbar electrode 34. The plurality of first electrode fingers 31 and the plurality of second electrode fingers 32 are arranged alternately in the X direction with spacing between them. The first busbar electrode 33 and the second busbar electrode 34 each extend in the X direction and are arranged opposite each other in the Y direction. Multiple first electrode fingers 31 and multiple second electrode fingers 32 are arranged between the first busbar electrode 33 and the second busbar electrode 34.

[0028] Furthermore, the IDT electrode 30 is not limited to a configuration having a plurality of first electrode fingers 31 and a plurality of second electrode fingers 32, but may also include a configuration with at least one first electrode finger 31 whose base end is connected to the first busbar electrode 33 and at least one second electrode finger 32 whose base end is connected to the second busbar electrode 34.

[0029] In the following description, the thickness direction (lamination direction) of the piezoelectric laminate 20 may be referred to as the Z direction or the first direction, the extension direction of the first electrode finger 31 and the second electrode finger 32 may be referred to as the Y direction, and the arrangement direction of the first electrode finger 31 and the second electrode finger 32 may be referred to as the X direction. Also, in the following description, in the Z direction, the direction from the support substrate 11 toward the outermost IDT electrode 30 may be referred to as up or upward, and the direction from the IDT electrode 30 toward the support substrate 11 may be referred to as down or downward.

[0030] The distance between the centers of the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the electrode pitch) is preferably in the range of 1 μm or more and 10 μm or less. The electrode pitch is the distance between the center of the width dimension of the first electrode finger 31 in a direction perpendicular to the extending direction of the first electrode finger 31 and the center of the width dimension of the second electrode finger 32 in a direction perpendicular to the extending direction of the second electrode finger 32. The width of the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the electrode width), that is, the dimension in the direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 32, is preferably in the range of 150 nm or more and 1000 nm or less.

[0031] Furthermore, if there are multiple instances of at least one of the first electrode fingers 31 and the second electrode fingers 32 (i.e., if the first electrode fingers 31 and the second electrode fingers 32 are considered as a pair of electrode sets, there are 1.5 or more pairs of electrode sets), the electrode pitch between the first electrode fingers 31 and the second electrode fingers 32 refers to the average value of the distance between the centers of adjacent first electrode fingers 31 and second electrode fingers 32 among the 1.5 or more pairs of first electrode fingers 31 and second electrode fingers 32.

[0032] Furthermore, in the first embodiment, since a Z-cut piezoelectric layer is used, the direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 32 is perpendicular to the polarization direction of the first piezoelectric layer 21 and the second piezoelectric layer 22. This does not apply if at least one of the first piezoelectric layer 21 and the second piezoelectric layer 22 uses a piezoelectric material with a different cut angle. Here, "perpendicular" is not limited to strictly perpendicular, but may also be approximately perpendicular (for example, the angle between the direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 32 and the polarization direction is 90° ± 10°).

[0033] The IDT electrode 30 (first electrode finger 31, second electrode finger 32, first busbar electrode 33, and second busbar electrode 34) is made of a suitable metal or alloy such as Al or AlCu alloy. In the first embodiment, the IDT electrode 30 has a structure in which an Al film is laminated on a titanium (Ti) film. However, an adhesion layer other than a Ti film may be used. Alternatively, an AlCu alloy film may be used instead of an Al film.

[0034] Here, the crossing region C (excitation region) shown in Figure 1 is the region where the first electrode finger 31 and the second electrode finger 32 overlap when viewed in the X direction. The length of the crossing region C is the dimension in the extending direction of the first electrode finger 31 and the second electrode finger 32 in the crossing region C. In this embodiment, the length of the crossing region C is, for example, 40 μm.

[0035] During operation, an AC voltage is applied between a plurality of first electrode fingers 31 and a plurality of second electrode fingers 32. More specifically, an AC voltage is applied between a first busbar electrode 33 and a second busbar electrode 34. This makes it possible to obtain resonance characteristics using the bulk wave of the thickness-slip mode excited in the piezoelectric laminate 20.

[0036] Furthermore, in the elastic wave apparatus 10, when the thickness of the piezoelectric laminate 20 is d and the pitch between the multiple pairs of first electrode fingers 31 and second electrode fingers 32 is p, d / p is set to 0.5 or less. As a result, the bulk wave of the thickness-slip first mode is effectively excited, and good resonance characteristics can be obtained. More preferably, d / p is 0.24 or less, in which case even better resonance characteristics can be obtained.

[0037] In the elastic wave apparatus 10 of the first embodiment, because it has the above configuration, even if the logarithm of the first electrode finger 31 and the second electrode finger 32 is reduced in an attempt to miniaturize it, a decrease in the Q value is unlikely to occur. This is because it is a resonator that does not require reflectors on both sides, resulting in low propagation loss. Furthermore, the reason why the above-mentioned reflectors are not required is because it utilizes a bulk wave in the thickness-slip mode.

[0038] Figure 4 is a schematic cross-sectional view illustrating the bulk wave of the thickness slip mode propagating through the piezoelectric layer of the first embodiment.

[0039] As shown in Figure 4, in the elastic wave device 10 of the first embodiment, since the vibration displacement is in the thickness sliding direction, the wave propagates almost entirely in the direction connecting the first main surface 20a and the second main surface 20b of the piezoelectric laminate 20, i.e., in the Z direction, and resonates. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. And since the resonance characteristics are obtained by the propagation of this Z-direction wave, a reflector is not required. Therefore, no propagation loss occurs when the wave propagates to the reflector. Accordingly, even if the number of electrode pairs consisting of the first electrode finger 31 and the second electrode finger 32 is reduced in an attempt to miniaturize the device, a decrease in the Q value is unlikely to occur.

[0040] In the elastic wave device 10, at least one pair of electrodes consisting of a first electrode finger 31 and a second electrode finger 32 are arranged. However, since waves are not propagated in the X direction, it is not necessarily required that there be multiple pairs of electrodes consisting of the first electrode finger 31 and the second electrode finger 32. In other words, it is sufficient that at least one pair of electrodes is provided.

[0041] For example, the first electrode finger 31 is an electrode connected to a hot potential, and the second electrode finger 32 is an electrode connected to a ground potential. However, the first electrode finger 31 may be connected to a ground potential and the second electrode finger 32 may be connected to a hot potential. In the first embodiment, at least one pair of electrodes are either electrodes connected to a hot potential or electrodes connected to a ground potential, as described above, and no floating electrodes are provided.

[0042] Figure 5 is a plan view showing an example in which a pair of electrodes is provided in the elastic wave apparatus of the first embodiment. In the elastic wave apparatus 10, a pair of electrodes having a first electrode finger 31 and a second electrode finger 32 is provided on the first main surface 20a of the piezoelectric laminate 20. In Figure 5, K is the crossover width. As described above, in the elastic wave apparatus 10 of this disclosure, the number of electrode pairs may be one. Even in this case, if the above d / p is 0.5 or less, the bulk wave of the thickness slip mode can be effectively excited.

[0043] Figure 6 illustrates the resonance characteristics of the elastic wave apparatus according to the first embodiment. The design parameters of the elastic wave apparatus according to Figure 6 are as follows. Note that the elastic wave apparatus 10 according to the first embodiment is not limited to the following design. First piezoelectric layer 21: 120° rotated Y-cut lithium niobate (thickness d ｐ１ : 0.1 μm) Intermediate layer 23: -60° rotated Y-cut lithium niobate (thickness d ｍ : 0.1 μm) Second piezoelectric layer 22: 120° rotated Y-cut lithium niobate (thickness d ｐ２ IDT electrode: Ti / AlCu laminate (thickness of each layer: 12 nm / 70 nm) Electrode line width: 0.69 μm

[0044] As shown in Figure 6, in the elastic wave apparatus 10 according to the first embodiment, the polarization direction of the intermediate layer 23 is different from the polarization direction of the first piezoelectric layer and the second piezoelectric layer 22, thereby suppressing the first-order mode M more than the higher-order mode H. This improves the resonance characteristics in the higher-order modes.

[0045] Figure 7 shows the resonance characteristics of the elastic wave apparatus according to the first embodiment. ｍ / d ｐ This is a diagram illustrating the dependency. Figure 7 shows the thickness d of the intermediate layer 23 for the elastic wave apparatus related to Figure 6. ｍ By changing d ｍ / d ｐ The results of measuring the impedance ratio between higher-order modes and first-order modes by changing the parameters are shown. In this disclosure, the impedance ratio refers to the ratio of the impedance at the resonant frequency to the impedance at the anti-resonant frequency.

[0046] As shown in Figure 7, d ｍ / d ｐ When d is 1.6 or less, the impedance ratio of the higher-order modes exceeds that of the primary mode, thus suppressing the primary mode and improving the resonance characteristics in the higher-order modes. ｍ / d ｐ When the value is between 0.5 and 0.75, the impedance ratio of the primary mode is particularly small, indicating that the primary mode can be further suppressed and the resonance characteristics in higher-order modes can be further improved.

[0047] (Second Embodiment) The second embodiment differs from the first embodiment in that the intermediate layer 23 is made of a dielectric material instead of a piezoelectric material. As a result, the first-order mode is suppressed more than the higher-order mode, and thus the resonance characteristics in the higher-order mode can be improved.

[0048] In the second embodiment, the dielectric material used for the intermediate layer 23 is, for example, titanium oxide (TiO ２ ), thallium oxide (TaO ２ ), β-type manganese oxide (MnO ２ ), germanium oxide (GeO ２ ) and others can be used. Among these, titanium dioxide (TiO ２ It is preferable to use a titanium oxide that contains at least one of the following types: rutile, anatase, and brookite. This improves the dielectric constant of the intermediate layer 23.

[0049] The intermediate layer 23 is preferably formed from an epitaxially grown dielectric, similar to the first embodiment. This improves the manufacturability of the elastic wave apparatus 10.

[0050] Table 1 shows LiNbO ３ This table shows the lattice misfit rate when an intermediate layer made of various dielectrics is epitaxially formed on the Z-cut plane of a single crystal. Here, in Table 1, (001) refers to the (001) plane being LiNbO ３ This refers to contact with the Z-cut surface. Table 2 shows LiNbO ３ and LiTaO ３ This is a table explaining the crystal structure of [the material].

[0051] As shown in Table 1, titanium oxide (TiO2) is used as the dielectric for the intermediate layer 23. ２ ), thallium oxide (TaO ２ ), β-type manganese oxide (MnO ２ ), germanium oxide (GeO ２ By using ), Z-cut LiNbO ３ Because the lattice misfit rate for the first piezoelectric layer 21, which is made of [material], is small, the intermediate layer 23 can be formed well. Also, as shown in Table 1, titanium oxide (TiO) is used as the dielectric for the intermediate layer 23. ２By using ), Z-cut LiNbO ３ As shown in Table 2, the lattice misfit rate for the first piezoelectric layer 21, which is made of LiTaO, is particularly small, so the intermediate layer 23 can be formed more effectively. ３ LiNbO ３ Since it has a similar crystal structure, Z-cut LiTaO ３ The lattice misfit rate when an intermediate layer made of various dielectric materials is epitaxially formed on the first piezoelectric layer made of the same material is approximately the same as that shown in Table 1.

[0052]

[0053]

[0054] In the second embodiment, that is, when the intermediate layer 23 is made of a dielectric, the thickness d of the intermediate layer 23 ｍ The sum of the thickness of the first piezoelectric layer 21 and the thickness of the second piezoelectric layer d ｐ The ratio (d ｍ / d ｐ ) is preferably 1 or greater. This makes the higher-order modes larger than the first-order modes, thereby improving the resonance characteristics in the higher-order modes.

[0055] Figure 8 illustrates the resonance characteristics of the elastic wave apparatus according to the second embodiment. The design parameters of the elastic wave apparatus according to Figure 8 are as follows. Note that the elastic wave apparatus according to the second embodiment is not limited to the following design. First piezoelectric layer 21: 120° rotated Y-cut lithium niobate (thickness d ｐ１ : 0.1 μm) Intermediate layer 23: Titanium oxide (thickness d ｍ : 0.25 μm) Second piezoelectric layer 22: 120° rotated Y-cut lithium niobate (thickness d ｐ２ : 0.1 μm) IDT electrode: Ti / AlCu laminate (thickness of each layer: 12 nm / 390 nm) Electrode line width: 0.6 μm

[0056] As shown in Figure 8, in the elastic wave apparatus according to the second embodiment, the first-order mode M is suppressed more than the higher-order mode H because the intermediate layer 23 is made of a dielectric material. This improves the resonance characteristics in the higher-order modes.

[0057] Figure 9 shows the resonance characteristics of the elastic wave apparatus according to the second embodiment. ｍ / d ｐ This is a diagram illustrating the dependency. Figure 9 shows the thickness d of the intermediate layer 23 for the elastic wave apparatus related to Figure 8. ｍ By changing d ｍ / d ｐ The results of measuring the impedance ratio between higher-order modes and first-order modes by changing the parameters are shown.

[0058] As shown in Figure 9, d ｍ / d ｐ When the value is 1 or greater, the impedance ratio of the higher-order modes exceeds that of the primary mode, thus suppressing the primary mode and improving the resonance characteristics in the higher-order modes.

[0059] (Third Embodiment) In the third embodiment, the thickness d of the first piezoelectric layer 21 ｐ１ The thickness d between the second piezoelectric layer 22 and the second piezoelectric layer 22 ｐ２ It differs from the second embodiment in that it is smaller in scale. This allows for the reduction of spurious emissions at frequencies between the primary mode and higher-order modes.

[0060] In the third embodiment, the sum of the thicknesses of the first piezoelectric layer 21 and the second piezoelectric layer 22 is d ｐ The thickness d of the first piezoelectric layer 21 relative to ｐ１ ratio d ｐ１ / d ｐ It is preferable that the value is greater than 0.3 and less than 0.5. This allows for a further reduction of spurious emissions at frequencies between the primary mode and higher-order modes.

[0061] Figures 10A to 10E illustrate the resonance characteristics of the elastic wave apparatus according to the third embodiment. Figures 10A to 10E show the thickness d of the first piezoelectric layer 21. ｐ１ The resonance characteristics of elastic wave devices with thicknesses of 0.14 μm, 0.12 μm, 0.10 μm, 0.08 μm, and 0.06 μm are shown. The design parameters for each elastic wave device are as follows. Note that the elastic wave device according to the third embodiment is not limited to the following design. First piezoelectric layer 21: 120° rotated Y-cut lithium niobate Intermediate layer 23: Titanium oxide (thickness d ｍ: 0.25 μm), the second piezoelectric layer 22: 120° rotated Y-cut lithium niobate, IDT electrode: Ti / AlCu laminate (each layer thickness: 12 nm / 390 nm), electrode line width: 0.6 μm

[0062] As shown in FIGS. 10A to 10E, the thickness d of the first piezoelectric layer 21 ｐ１ is smaller than the thickness d with the second piezoelectric layer 22 ｐ２ In the elastic wave device according to FIGS. 10D and 10E, the thickness d of the first piezoelectric layer 21 ｐ１ is larger than the thickness d with the second piezoelectric layer 22 ｐ２ It can be seen that the spurious S at the frequency between the primary mode M and the higher-order mode H is suppressed compared to the elastic wave device according to FIGS. 10A to 10C. Therefore, by making the thickness d of the first piezoelectric layer 21 ｐ１ smaller than the thickness d with the second piezoelectric layer 22 ｐ２ the spurious S can be suppressed and the resonance characteristics in the higher-order mode can be improved.

[0063] As shown in FIGS. 10A to 10E, the ratio d ｐ of the thickness d of the first piezoelectric layer 21 to the sum d ｐ１ of the thicknesses of the first piezoelectric layer 21 and the second piezoelectric layer 22 ｐ１ d ｐ In the elastic wave device according to FIG. 10D, where d ｐ１ d ｐ is greater than 0.3 and less than 0.5, it can be seen that the spurious S is further suppressed compared to the elastic wave devices according to FIGS. 10A to 10C and FIG. 10E. Therefore, by making d ｐ１ d ｐ greater than 0.3 and less than 0.5, the spurious S can be further suppressed and the resonance characteristics in the higher-order mode can be further improved.

[0064] (Fourth Embodiment) The fourth embodiment is different from the second embodiment in that the cut angle of the first piezoelectric layer and the cut angle of the second piezoelectric layer are different. Thereby, the impedance ratio can be increased, and the resonance characteristics in the higher-order mode can be improved. Here, the similarity and difference between the cut angle of the first piezoelectric layer and the cut angle of the second piezoelectric layer can be determined by XRD.

[0065] Figure 11 illustrates the resonance characteristics of the elastic wave apparatus according to the fourth embodiment. Figure 11 shows the resonance characteristics related to higher-order modes of the elastic wave apparatus according to the second embodiment and the elastic wave apparatus according to the fourth embodiment. The design parameters for each elastic wave apparatus are as follows. Here, Figure 11 shows the resonance characteristics of an elastic wave apparatus in which the cut angle of the second piezoelectric layer 22 is rotated Y-cut by 120° as the second embodiment, while it shows the resonance characteristics of an elastic wave apparatus in which the cut angle of the second piezoelectric layer is rotated Y-cut by 160° as the fourth embodiment. Note that the elastic wave apparatus according to the fourth embodiment is not limited to the following design. First piezoelectric layer 21: 120° rotated Y-cut lithium niobate (thickness d ｐ１ : 0.1 μm) Intermediate layer 23: Titanium oxide (thickness d ｍ : 0.25 μm) Second piezoelectric layer 22: Lithium niobate (thickness d ｐ１ : 0.1 μm) IDT electrode: Ti / AlCu laminate (thickness of each layer: 12 nm / 390 nm) Electrode line width: 0.6 μm

[0066] As shown in Figure 11, the elastic wave apparatus according to the fourth embodiment, in which the first piezoelectric layer and the second piezoelectric layer have different cut angles, exhibits increased admittance at the resonant frequency and decreased admittance at the anti-resonant frequency compared to the elastic wave apparatus according to the second embodiment, in which the first and second piezoelectric layers have the same cut angle. Therefore, by making the cut angles of the first and second piezoelectric layers different, the impedance ratio is increased, and thus the resonance characteristics in higher-order modes can be improved.

[0067] (Fifth Embodiment) The fifth embodiment differs from the first embodiment in that at least one of the first piezoelectric layer 21, the second piezoelectric layer 22, and the intermediate layer 23 is formed of an ion slice. In this case as well, the resonance characteristics in higher-order modes can be improved.

[0068] Whether or not at least one of the first piezoelectric layer 21, the second piezoelectric layer 22, and the intermediate layer 23 is formed from ion slices can be determined by examining the hydrogen content in the thickness direction. More specifically, if the hydrogen content on the surface of the layer being measured is greater than the hydrogen content at the center in the thickness direction, then the layer being measured can be said to be formed from ion slices. This eliminates the need to prepare expensive materials such as pre-cut piezoelectric plates, thereby reducing the manufacturing cost of the elastic wave apparatus and improving manufacturability. Here, the hydrogen content on the surface and at the center in the thickness direction of the first piezoelectric layer 21, the second piezoelectric layer 22, and the intermediate layer 23 can be measured by secondary ion mass spectrometry (SIMS).

[0069] The ion slicing method used in the manufacture of the elastic wave apparatus according to the fifth embodiment will be described below, with the case of forming the first piezoelectric layer 21 as an example. Figure 12 is a flowchart illustrating the ion slicing method used in the manufacture of the elastic wave apparatus according to the fifth embodiment. Figure 13 is a schematic cross-sectional view illustrating the ion slicing method used in the manufacture of the elastic wave apparatus according to the fifth embodiment. Note that the steps described below are merely examples and are not limited thereto. In the example of Figure 13, the single crystal substrate 301 is a single crystal piezoelectric substrate made of the same material as the first piezoelectric layer, the base 302 is a support member in which a sacrificial layer 302a is provided in a recess of the support substrate 302b, and the composite substrate 305 is a laminate in which the first piezoelectric layer 21 is provided on the base 302.

[0070] First, He is applied to the mirror-polished main surface of the single-crystal substrate 301. ＋ An ion implantation process is performed to implant ions (step S1). Here, He ＋ The ion implantation energy is 150 keV, and the dose (ion implantation density) is 2 × 10⁻⁶. １６ atom / cm ２ This means that He ＋Ions accumulate at a depth of approximately 0.5 μm from the main surface of the single-crystal substrate 301, forming microcavities. As a result, the surface at a depth of approximately 0.5 μm from the main surface of the single-crystal substrate 301 becomes a delamination layer 303. Here, the thickness of the single-crystal thin film 304 can be adjusted by changing the energy during ion implantation. This suppresses the effect of substrate waviness and allows for the formation of a layer of constant thickness.

[0071] Next, a bonding process is performed in which the main surface of the base 302 is joined to the main surface of the single crystal substrate 301 (step S2). If the coefficients of linear expansion of the single crystal substrate 301 and the base 302 are different, a room-temperature direct bonding method is used to activate the main surfaces of the single crystal substrate 301 and the base 302 with plasma in a room-temperature environment and then bond them in a vacuum.

[0072] Next, the bonded single-crystal substrate 301 and base 302 are placed in a high-temperature environment of 500°C, and a peeling process is performed to break up the peeling layer 303 (step S3). As a result, microcavities grow in the peeling layer 303 due to thermal stress. Then, the portion of the single-crystal substrate 301 with a thickness of approximately 0.5 μm above the peeling layer 303 is peeled off as a single-crystal thin film 304, which is bonded to the base 302 to form a composite substrate 305.

[0073] Next, a polishing process is performed on the delamination surface of the composite substrate 305 by chemical mechanical polishing (CMP) (step S4). At this point, the roughness of the delamination surface from the composite substrate 305 is about 1 nm in root mean square (RMS) roughness, so the surface is mirror-polished by CMP to a surface roughness of 1 nm or less. In CMP, polishing is performed to a depth of approximately 100 nm.

[0074] The remaining single-crystal substrate 301 after the peeling process (step S3) can be mirror-polished using CMP on the peeled surface in the same way as the composite substrate 305, and then reused in the ion implantation process (step S1). Therefore, a large amount of single-crystal thin film 304 can be formed from the single-crystal substrate 301. As a result, in the elastic wave apparatus according to the fifth embodiment, the amount of material used to form the single-crystal thin film 304 can be reduced compared to the case where the single-crystal substrate 301 is directly bonded and then ground to form a layer, thereby reducing the environmental burden and manufacturing costs in the production of the elastic wave apparatus.

[0075] Through the above process, a composite substrate 305 on which a single crystal thin film 304 is formed is obtained.

[0076] Here, the ion slicing method described above is applied not only to the formation of the first piezoelectric layer but also to the formation of the second piezoelectric layer 22. In this case, the ion slicing method described above is applied assuming that the single-crystal substrate 301 is a single-crystal piezoelectric substrate made of the same material as the second piezoelectric layer 22, the base 302 is a support member on which the first piezoelectric layer and the intermediate layer 23 are provided, and the composite substrate 305 is a laminate on which the second piezoelectric layer 22 is provided on the base 302.

[0077] Furthermore, the ion slicing method described above can also be applied to the formation of the intermediate layer 23. In this case, the ion slicing method described above can be applied assuming that the single crystal substrate 301 is a single crystal substrate made of the same material as the intermediate layer 23, the base 302 is a support member on which the first piezoelectric layer 21 is provided, and the composite substrate 305 is a laminate on which the intermediate layer 23 is provided on the base 302.

[0078] Furthermore, the fifth embodiment can be combined with the first to fourth embodiments described above.

[0079] (Sixth Embodiment) Figure 14 is a schematic cross-sectional view showing an elastic wave apparatus according to the sixth embodiment. In the embodiments described above, a so-called membrane structure was described in which the support member has a recess 14 and the recess 14 is provided on the second main surface 20b side of the piezoelectric laminate 20, but the invention is not limited thereto.

[0080] As shown in Figure 14, in the elastic wave apparatus 10A according to the sixth embodiment, an acoustic multilayer film 43 is laminated on the second main surface 20b of the piezoelectric laminate 20. The acoustic multilayer film 43 has a laminated structure of low acoustic impedance layers 43a, 43c, and 43e with relatively low acoustic impedance and high acoustic impedance layers 43b and 43d with relatively high acoustic impedance. The low acoustic impedance layers 43a, 43c, and 43e are made of, for example, silicon oxide (SiO₂ ２ The layers are, for example, silicon nitride (SiN), aluminum oxide (Ai ２ O ３ ), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ These are dielectric layers such as ). When an acoustic multilayer film 43 is used, bulk waves in thickness slip mode can be confined within the piezoelectric laminate 20 without using the recess 14.

[0081] Furthermore, the materials of the low acoustic impedance layers 43a, 43c, and 43e and the high acoustic impedance layers 43b and 43d have a lower dielectric constant than the piezoelectric laminate 20.

[0082] In addition, the number of layers of low acoustic impedance layers 43a, 43c, 43e and high acoustic impedance layers 43b, 43d in the acoustic multilayer film 43 is not particularly limited. It is sufficient that at least one high acoustic impedance layer 43b, 43d is located further away from the piezoelectric laminate 20 than the low acoustic impedance layers 43a, 43c, 43e.

[0083] The low acoustic impedance layers 43a, 43c, and 43e and the high acoustic impedance layers 43b and 43d can be made of any suitable material as long as the above acoustic impedance relationship is satisfied. For example, the materials for the high acoustic impedance layers 43b and 43d include aluminum nitride (AlN), or metals such as tungsten (W) or platinum (Pt).

[0084] The configuration of the sixth embodiment can be combined with the first to fifth embodiments described above.

[0085] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included.

[0086] For example, the piezoelectric laminate 20 is not limited to consisting of three layers: a first piezoelectric layer 21, a second piezoelectric layer 22, and an intermediate layer 23, but may consist of four or more layers. In this case, for example, the piezoelectric laminate may be a laminate in which layers of the same material as the first piezoelectric layer 21 and layers of the same material as the intermediate layer 23 are alternately laminated. Here, it is preferable that the number of layers included in the laminate is odd, and that the first piezoelectric layer 21 is on the second main surface of the piezoelectric laminate, and that layers of the same material as the first piezoelectric layer are on the first main surface of the piezoelectric laminate. This makes it possible to suppress the primary mode while improving the resonance characteristics in modes that are odd multiples of the primary mode.

[0087] Furthermore, this disclosure may also take the following form.

[0088] (1) A piezoelectric laminate having a first main surface and a second main surface opposite to the first main surface in a first direction; an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric laminate; and a support member provided on the second main surface side of the piezoelectric laminate and having an acoustic reflecting portion on the second main surface side of the piezoelectric laminate, wherein at least a portion of the electrode is arranged to overlap with the acoustic reflecting portion when viewed in plan in the first direction, and the piezoelectric laminate comprises a first piezoelectric layer having the second main surface, an intermediate layer laminated on the first piezoelectric layer, and a second piezoelectric layer laminated on the intermediate layer, wherein at least one of the material and polarization direction of the intermediate layer is different from that of the first piezoelectric layer, and at least one of the material and polarization direction of the intermediate layer is different from that of the second piezoelectric layer. (2) The elastic wave apparatus according to (1), wherein the intermediate layer is made of a piezoelectric material, the polarization direction of the intermediate layer is different from that of the first piezoelectric layer, and the polarization direction of the intermediate layer is different from that of the second piezoelectric layer. (3) The sum of the thickness of the first piezoelectric layer and the thickness of the second piezoelectric layer is d ｐ , the thickness of the intermediate layer is dｍ In that case, d ｍ / d ｐ (2) The elastic wave apparatus described in (2), where d is 1.6 or less. (4) The sum of the thickness of the first piezoelectric layer and the thickness of the second piezoelectric layer is d ｐ , the thickness of the intermediate layer is d ｍ In that case, d ｍ / d ｐ (3) The elastic wave apparatus according to (3), wherein the intermediate layer comprises lithium niobate or lithium tantalate. (5) The elastic wave apparatus according to any one of (2) to (4). (6) The elastic wave apparatus according to (1), wherein the intermediate layer comprises a dielectric. (7) The sum of the thickness of the first piezoelectric layer and the thickness of the second piezoelectric layer is d ｐ , the thickness of the intermediate layer is d ｍ In that case, d ｍ / d ｐ(6) The elastic wave apparatus according to (6), wherein the ratio is 1 or greater. (8) The elastic wave apparatus according to (6) or (7), wherein the intermediate layer contains at least one titanium oxide from among rutile, anatase, and brookite types. (9) The elastic wave apparatus according to any one of (1) to (8), wherein the thickness of the first piezoelectric layer is less than the thickness of the second piezoelectric layer. (10) The elastic wave apparatus according to any one of (1) to (9), wherein the cut angle of the first piezoelectric layer is different from the cut angle of the second piezoelectric layer. (11) The elastic wave apparatus according to any one of (1) to (10), wherein the intermediate layer is an epitaxially grown layer. (12) The elastic wave apparatus according to any one of (1) to (11), wherein the second piezoelectric layer is an epitaxially grown layer. (13) The acoustic wave apparatus according to any one of (1) to (11), wherein in at least one of the first piezoelectric layer and the second piezoelectric layer, the hydrogen content on the main surface is greater than the hydrogen content at the center in the thickness direction. (14) The acoustic wave apparatus according to any one of (1) to (13), wherein the first piezoelectric layer and the second piezoelectric layer contain lithium niobate or lithium tantalate. (15) The acoustic wave apparatus according to any one of (1) to (14), wherein the electrode is an IDT electrode including a first busbar facing each other, a second busbar, at least one first electrode finger whose base end is connected to the first busbar, and at least one second electrode finger whose base end is connected to the second busbar. (16) The acoustic wave apparatus according to any one of (1) to (15), wherein the acoustic reflection portion is a recess opening to the piezoelectric laminate side, and the recess is provided in the support member. (17) The elastic wave apparatus according to (16), wherein the support member includes a support substrate and a bonding layer, and the recess is provided in the bonding layer.(18) The acoustic wave apparatus according to any one of (1) to (17), wherein the acoustic reflection portion is an acoustic reflection film comprising a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric laminate are arranged such that at least a part of the support member and at least a part of the piezoelectric laminate face each other with the acoustic reflection film in between.

[0089] 10, 10A Elastic wave device 11 Support substrate 14 Recess 20 Piezoelectric laminate 20a First main surface 20b Second main surface 21 First piezoelectric layer 22 Second piezoelectric layer 23 Intermediate layer 30 IDT electrode 31 First electrode finger 32 Second electrode finger 33 First busbar electrode 34 Second busbar electrode 43 Acoustic multilayer film

Claims

1. A piezoelectric laminate having a first main surface and a second main surface opposite to the first main surface in a first direction; an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric laminate; a support member provided on the second main surface side of the piezoelectric laminate and having an acoustic reflecting portion on the second main surface side of the piezoelectric laminate, wherein at least a portion of the electrode is arranged to overlap with the acoustic reflecting portion when viewed in plan in the first direction; the piezoelectric laminate comprises a first piezoelectric layer having the second main surface; an intermediate layer laminated on the first piezoelectric layer; and a second piezoelectric layer laminated on the intermediate layer, wherein at least one of the material and polarization direction of the intermediate layer is different from that of the first piezoelectric layer; and at least one of the material and polarization direction of the intermediate layer is different from that of the second piezoelectric layer.

2. The elastic wave apparatus according to claim 1, wherein the intermediate layer is made of a piezoelectric material, the polarization direction of the intermediate layer is different from that of the first piezoelectric layer, and the polarization direction of the intermediate layer is different from that of the second piezoelectric layer.

3. The sum of the thickness of the first piezoelectric layer and the thickness of the second piezoelectric layer is d. ｐ , the thickness of the intermediate layer is d ｍ In that case, d ｍ / d ｐ The elastic wave apparatus according to claim 2, wherein is 1.6 or less.

4. The sum of the thickness of the first piezoelectric layer and the thickness of the second piezoelectric layer is d. ｐ , the thickness of the intermediate layer is d ｍ In that case, d ｍ / d ｐ The elastic wave apparatus according to claim 3, wherein the coefficient is 0.5 or more and 0.75 or less.

5. The acoustic wave apparatus according to any one of claims 2 to 4, wherein the intermediate layer comprises lithium niobate or lithium tantalate.

6. The elastic wave apparatus according to claim 1, wherein the intermediate layer is made of a dielectric material.

7. Let the sum of the thickness of the first piezoelectric layer and the thickness of the second piezoelectric layer be d ｐ , and let the thickness of the intermediate layer be d ｍ . When this is the case, d ｍ / d ｐ is 1 or more. The elastic wave device according to claim 6.

8. The elastic wave apparatus according to claim 6 or 7, wherein the intermediate layer contains at least one titanium oxide selected from rutile, anatase, and brookite types.

9. The elastic wave apparatus according to any one of claims 1 to 8, wherein the thickness of the first piezoelectric layer is less than the thickness of the second piezoelectric layer.

10. The elastic wave apparatus according to any one of claims 1 to 9, wherein the cut angle of the first piezoelectric layer is different from the cut angle of the second piezoelectric layer.

11. The elastic wave apparatus according to any one of claims 1 to 10, wherein at least one of the first piezoelectric layer and the intermediate layer is an epitaxially grown layer.

12. The elastic wave apparatus according to any one of claims 1 to 11, wherein at least one of the second piezoelectric layer and the intermediate layer is an epitaxially grown layer.

13. The elastic wave apparatus according to any one of claims 1, 2, and 6, wherein in at least one of the first piezoelectric layer and the second piezoelectric layer, the hydrogen content on the main surface is greater than the hydrogen content at the center in the thickness direction.

14. The acoustic wave apparatus according to any one of claims 1 to 13, wherein the first piezoelectric layer and the second piezoelectric layer comprise lithium niobate or lithium tantalate.

15. The elastic wave apparatus according to any one of claims 1 to 14, wherein the electrode is an IDT electrode comprising a first busbar facing each other, a second busbar, at least one first electrode finger whose base end is connected to the first busbar, and at least one second electrode finger whose base end is connected to the second busbar.

16. The acoustic wave apparatus according to any one of claims 1 to 15, wherein the acoustic reflection portion is a recess opening to the piezoelectric laminate side, and the recess is provided in the support member.

17. The elastic wave apparatus according to claim 16, wherein the support member includes a support substrate and a bonding layer, and the recess is provided in the bonding layer.

18. The acoustic wave apparatus according to any one of claims 1 to 17, wherein the acoustic reflection portion is an acoustic reflection film comprising a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric laminate are arranged such that at least a portion of the support member and at least a portion of the piezoelectric laminate face each other with the acoustic reflection film in between.

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