Piezoelectric device

Abstract

Unnecessary waves are suppressed while suppressing deterioration in the resonance characteristics of a main wave. A piezoelectric device disclosed herein comprises: a piezoelectric laminate having a thickness in a first direction and having an upper surface that is a surface on one side in the first direction and a lower surface that is a surface on the other side in the first direction; a support member provided on the lower surface side of the piezoelectric laminate; an upper electrode provided on the upper surface side of the piezoelectric laminate; and a lower electrode provided on the lower surface side of the piezoelectric laminate. The piezoelectric laminate has a plurality of piezoelectric layers including a single crystal. Each of the plurality of piezoelectric layers is different from the other piezoelectric layers adjacent in the first direction in terms of at least one of material, crystal structure, or polarization direction. The plurality of piezoelectric layers include at least one set of piezoelectric layers having the same material and crystal structure. In at least one of the sets of piezoelectric layers, the crystal orientation of one of the piezoelectric layers is different from the crystal orientation of the other piezoelectric layers.

Description

Piezoelectric devices

[0001] This invention relates to a piezoelectric device.

[0002] Patent Document 1 discloses a BAW (Bulk Acoustic Wave) element having two piezoelectric layers between a first electrode and a second electrode, wherein the polarization directions of the two piezoelectric layers are opposite to each other.

[0003] U.S. Patent Application Publication No. 2022 / 0321100

[0004] If the crystal orientation of all piezoelectric layers in the BAW element according to Patent Document 1 is high, unwanted waves in the BAW resonator are not suppressed, and therefore the piezoelectric device characteristics are susceptible to the influence of unwanted waves. On the other hand, if the crystal orientation of all piezoelectric layers in the BAW element according to Patent Document 1 is low, the resonance characteristics of the main wave deteriorate, which is a factor in the degradation of the piezoelectric device characteristics.

[0005] The present invention aims to solve the above-mentioned problems and to provide a piezoelectric device that suppresses unwanted waves while suppressing the degradation of the main wave's resonance characteristics.

[0006] A piezoelectric device according to one aspect of the present invention comprises a piezoelectric laminate having thickness in a first direction and having an upper surface which is one side in the first direction and a lower surface which is the other side in the first direction; a support member provided on the lower side of the piezoelectric laminate; an upper electrode provided on the upper side of the piezoelectric laminate; and a lower electrode provided on the lower side of the piezoelectric laminate, wherein the piezoelectric laminate has a plurality of piezoelectric layers including a single crystal, each of the plurality of piezoelectric layers differs from other adjacent piezoelectric layers in the first direction in at least one of the material, crystal structure and polarization direction, the plurality of piezoelectric layers include at least one set of piezoelectric layers having the same material and crystal structure, and in at least one set of piezoelectric layers, the crystal orientation of one piezoelectric layer differs from the crystal orientation of the other piezoelectric layer.

[0007] According to the present invention, it is possible to provide a piezoelectric device that suppresses unwanted waves while suppressing the degradation of the main wave's resonance characteristics.

[0008] Figure 1 is a schematic plan view showing an example of a piezoelectric device according to the first embodiment. Figure 2 is a schematic cross-sectional view along the line II-II in Figure 1. Figure 3 is a schematic cross-sectional view showing an example of a piezoelectric device according to a modified example of the first embodiment. Figure 4A is a pole view of a laminate of piezoelectric layers. Figure 4B is a pole view of a laminate of piezoelectric layers. Figure 5 is a schematic cross-sectional view showing the manufacturing process of a piezoelectric device according to the first embodiment.

[0009] Embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure. Each embodiment described in this disclosure is illustrative, and modifications where partial substitution or combination of configurations is possible between different embodiments, as well as aspects common to the first embodiment in the second and subsequent embodiments, will be omitted, with only the differences being described. In particular, similar effects due to similar configurations will not be mentioned sequentially for each embodiment. Furthermore, numerical values ​​in this disclosure include rounding.

[0010] In the following explanation, unless otherwise specified, one direction and the opposite direction (reverse direction) of that direction will be distinguished. That is, when one direction and the other direction are the same, it means that the direction is parallel to the other direction and that the two directions are in the same direction. Also, when one direction and the other direction are opposite directions (reverse direction), they are in different directions. In this disclosure, when two directions are the same, it includes the case where the angle between the two directions is between -3° and +3°. That is, when two directions are opposite, it includes the case where the angle between the opposite direction of one of the two directions and the other direction is between -3° and +3°.

[0011] (First Embodiment) Figure 1 is a schematic plan view showing an example of a piezoelectric device according to the first embodiment. Figure 2 is a schematic cross-sectional view along the line II-II in Figure 1. The piezoelectric device 1 according to the first embodiment comprises a support member 10, a piezoelectric laminate 20, an upper electrode 31, and a lower electrode 32. The piezoelectric device 1 is a resonator that utilizes bulk waves, i.e., a BAW (Bulk Acoustic Wave) element. In the first embodiment, the piezoelectric device 1 is a piezoelectric element configured to utilize, for example, thickness sliding vibration or thickness longitudinal vibration of the piezoelectric laminate 20. In the following description, the bulk wave with the largest coupling coefficient will be described as the main wave, and unwanted waves will be described as bulk waves other than the main wave. In the following description, the thickness direction of the piezoelectric laminate 20 will be described as the Z direction, the direction perpendicular to the Z direction will be described as the X direction, and the direction perpendicular to both the Z direction and the X direction will be described as the Y direction. In this disclosure, the Z direction is an example of the "first direction". Furthermore, in the following explanation, the Z direction may be described as upward, and the direction opposite to the Z direction as downward.

[0012] (Piezoelectric Laminate) The piezoelectric laminate 20 is a flat plate-shaped laminate having thickness in the Z direction. The piezoelectric laminate 20 has an upper surface 20a and a lower surface 20b. The thickness of the piezoelectric laminate 20 is not particularly limited, but is preferably 1 μm or less. This makes it possible to obtain good resonance characteristics. The piezoelectric laminate 20 is a laminate containing a plurality of piezoelectric layers. The plurality of piezoelectric layers will be described later.

[0013] Furthermore, the piezoelectric laminate may be provided with through holes that communicate with the space 13, which will be described later. In this case, the through holes are provided at positions that overlap with the space 13 when viewed in plan in the Z direction. The through holes may or may not penetrate the upper electrode and the lower electrode.

[0014] (Functional Electrode) The upper electrode 31 is provided on the upper surface 20a of the piezoelectric laminate 20. The lower electrode 32 is provided on the lower surface 20b of the piezoelectric laminate 20. The upper electrode 31 and the lower electrode 32 are examples of the "functional electrode" of this disclosure. The upper electrode 31 and the lower electrode 32 are made of metals or alloys such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), and molybdenum (Mo). The upper electrode 31 and the lower electrode 32 may be laminates of two or more layers made of different materials, and may have an adhesion layer made of titanium (Ti), nickel-chromium alloy (NiCr), etc.

[0015] As shown in Figure 1, the upper electrode 31 has a circular main electrode portion 31a and an extended portion 31b that extends from the main electrode portion 31a in a direction perpendicular to the Z direction. The lower electrode 32 has a circular main electrode portion 32a and an extended portion 32b that extends from the main electrode portion 32a in a direction perpendicular to the Z direction. When viewed from above in the Z direction, the circular main electrode portion 31a of the upper electrode 31 and the circular main electrode portion 32a of the lower electrode 32 are superimposed. In other words, the piezoelectric laminate 20 is sandwiched between the circular main electrode portion 31a of the upper electrode 31 and the circular main electrode portion 32a of the lower electrode 32. As a result, bulk waves are excited in the region between the circular main electrode portion 31a of the upper electrode 31 and the circular main electrode portion 32a of the lower electrode 32. Note that the shapes of the upper electrode 31 and the lower electrode 32 are merely examples and are not limited thereto. In the following explanation, the region where the upper electrode 31 and the lower electrode 32 overlap when viewed in a plan view in the Z direction may be described as the excitation region C.

[0016] (Support Member) The support member 10 is provided facing the lower surface 20b of the piezoelectric laminate 20. In the first embodiment, the support member 10 comprises a support substrate 11 and an intermediate layer 12. The support substrate 11 is made of, for example, silicon (Si), quartz, etc. The intermediate layer is provided on the piezoelectric laminate 20 side relative to the support substrate 11. The intermediate layer 12 is made of a dielectric material such as silicon oxide, or a layer with a high defect level density such as polycrystalline silicon (a so-called trap-rich layer). When the intermediate layer is a trap-rich layer, the intermediate layer 12 can trap electrons and holes generated in the support substrate 11 by heat and light in a short time, and can suppress fluctuations in the electrical conductivity of the support substrate 11 due to said electrons and holes. Note that the support member 10 is not limited to the above, and may be made of, for example, a support substrate 11.

[0017] The support member 10 has a space 13. In the example in Figure 2, the space 13 is the space inside a recess provided on the piezoelectric laminate 20 side of the intermediate layer 12. The space 13 is provided so as to overlap with the excitation region C when viewed in plan in the Z direction. As a result, the bulk wave associated with the driving of the piezoelectric device 1 is reflected by the space 13. In the example in Figure 1, the region overlapping with the space 13 when viewed in plan in the Z direction is circular, but this is merely an example, and it may be another shape, such as a rectangle.

[0018] (Piezoelectric Layers) In the example shown in Figure 2, the piezoelectric laminate 20 comprises a plurality of piezoelectric layers: a first piezoelectric layer 21, a second piezoelectric layer 22, a third piezoelectric layer 23, and a fourth piezoelectric layer 24. In the piezoelectric laminate 20, the first piezoelectric layer 21, the second piezoelectric layer 22, the third piezoelectric layer 23, and the fourth piezoelectric layer 24 are stacked in the Z direction from the upper surface 20a to form the laminate. Therefore, the upper surface of the first piezoelectric layer 21 corresponds to the upper surface 20a of the piezoelectric laminate 20, and the lower surface of the fourth piezoelectric layer 24 corresponds to the lower surface 20b of the piezoelectric laminate 20. In the following description, when the first piezoelectric layer 21, the second piezoelectric layer 22, the third piezoelectric layer 23, and the fourth piezoelectric layer 24 are not specifically distinguished, they may simply be referred to as "piezoelectric layers." Furthermore, the first piezoelectric layer 21, the second piezoelectric layer 22, the third piezoelectric layer 23, and the fourth piezoelectric layer 24 are sometimes collectively referred to as "multiple piezoelectric layers."

[0019] In this disclosure, a piezoelectric layer refers to a piezoelectric layer in the piezoelectric laminate 20 that has the same material, crystal structure, and polarization direction continuously, excluding areas affected by local defects, segregation, or foreign matter. In other words, each of the multiple piezoelectric layers differs from other piezoelectric layers adjacent to it in the Z direction in at least one of the following: material, crystal structure, and polarization direction. In this disclosure, having the same crystal structure means belonging to the same crystal point group in crystal structure analysis. In this disclosure, polarization direction refers to the direction of spontaneous polarization.

[0020] The plurality of piezoelectric layers include at least one set of piezoelectric layers having the same material and crystal structure. In the first embodiment, the first piezoelectric layer 21, the second piezoelectric layer 22, the third piezoelectric layer 23, and the fourth piezoelectric layer 24 all have the same material and crystal structure. Furthermore, the polarization direction of the piezoelectric layer is different from the polarization direction of other adjacent piezoelectric layers in the Z direction.

[0021] In a pair of piezoelectric layers having the same material and crystal structure, where the piezoelectric layers are adjacent in the Z direction, it is preferable that the polarization direction of one piezoelectric layer is opposite to that of the other piezoelectric layer. In the example in Figure 2, the polarization direction P1 of the first piezoelectric layer 21 is opposite to the polarization direction P2 of the second piezoelectric layer 22, the polarization direction P2 of the second piezoelectric layer 22 is opposite to the polarization direction P3 of the third piezoelectric layer 23, and the polarization direction P3 of the third piezoelectric layer 23 is opposite to the polarization direction P4 of the fourth piezoelectric layer 24. This improves the resonance characteristics of the piezoelectric device 1 and suppresses unwanted waves. Note that the polarization directions P1 to P4 of each piezoelectric layer shown in Figure 2 are merely examples and are not limited thereto.

[0022] The polarization direction of the piezoelectric layer can be determined by SPM (Scanning Probe Microscopy) and XRD (X-ray Diffraction). Specifically, by observing two mutually orthogonal cross-sections along the Z direction of the piezoelectric laminate 20 (for example, a cross-section parallel to the XZ plane and a cross-section parallel to the YZ plane) and a surface oriented in the Z direction using a PRM (Piezo Response Microscope), it is possible to determine whether the measurement surface is positive or negative polarization or a surface without piezoelectric response. Furthermore, by determining the crystal orientation of the piezoelectric layer using XRD and combining the information obtained from SPM and XRD, the polarization direction of the piezoelectric layer can be determined.

[0023] The multiple piezoelectric layers contain single crystals. Preferably, the multiple piezoelectric layers contain single crystals of the same piezoelectric material. The multiple piezoelectric layers may contain lithium niobate (LiNbO) as the single crystal of the piezoelectric material. ３ ) or lithium tantalate (LiTaO) ３ It is preferable that the piezoelectric layer contains a single crystal of ) which improves the resonance characteristics. In this disclosure, it is said that the piezoelectric layer contains a single crystal that all crystal orientations can be identified. That is, for example, if the piezoelectric layer contains lithium niobate or lithium tantalate, it can be said that the piezoelectric layer contains a single crystal of lithium niobate or lithium tantalate if the a-axis and c-axis of the crystal can be identified. Whether or not the crystal orientation of the piezoelectric layer can be identified can be determined by measuring the cross-section of the piezoelectric laminate 20 along the Z direction for each piezoelectric layer by X-ray diffraction measurement (XRD). Note that the multiple piezoelectric layers are not limited to being made of single crystals, and amorphous regions may be included due to manufacturing variations, etc.

[0024] In at least one pair of piezoelectric layers having the same material and crystal structure, the crystal orientation of one piezoelectric layer differs from that of the other piezoelectric layer. This allows for the excitation of good resonant waves by the piezoelectric layer with relatively high crystal orientation, while selectively attenuating unwanted waves with low coupling coefficients by the piezoelectric layer with relatively low crystal orientation, while suppressing the attenuation of the main wave with a large coupling coefficient.

[0025] The similarity and degree of crystal orientation of piezoelectric layers are determined based on the pole diagram of the piezoelectric layer. Figures 4A and 4B are pole diagrams of a piezoelectric layer laminate. Here, the method for evaluating the crystal orientation of a piezoelectric layer will be explained in detail using Figures 4A and 4B. First, the piezoelectric laminate 20 is cut out and fixed on a stage made of an amorphous material such as glass to prepare the measurement sample. Then, focusing on a specific crystal plane, the crystal plane is fixed at the X-ray diffraction angle, and the measurement sample is rotated on the stage while being measured with an XRD, thereby obtaining pole diagrams as shown in Figures 4A and 4B as X-ray diffraction intensity distribution diagrams. Then, by comparing the size of the Bragg diffraction spots appearing in the pole diagram, the degree of crystal orientation can be determined. As a specific example, the spread and concentration of Bragg diffraction spots S1A and S2A in Figure 4A are smaller and the concentration is higher than that of Bragg diffraction spots S1B and S2B in Figure 4B. From this, it can be concluded that the piezoelectric layer in Figure 4A has a different crystal orientation than the piezoelectric layer in Figure 4B, and that its crystal orientation is higher than that of the piezoelectric layer in Figure 4B.

[0026] The measurement samples shown in Figures 4A and 4B have a lower piezoelectric layer on the stage and an upper piezoelectric layer laminated on the lower piezoelectric layer. Since the piezoelectric layers transmit X-rays related to XRD, the pole diagrams shown in Figures 4A and 4B show Bragg diffraction spots S1A and S1B of the upper piezoelectric layer and Bragg diffraction spots S2A and S2B of the lower piezoelectric layer. In addition, in the example of Figures 4A and 4B, the polarization directions of the upper piezoelectric layer and the lower piezoelectric layer are opposite to each other, so spots S2A and S2B appear at positions where spots S1A and S1B are rotated 180° around the center of the pole diagram. As shown in Figures 4A and 4B, if the polarization directions of the piezoelectric layers are different, Bragg diffraction spots appear at different positions in the pole diagram, so the degree of crystal orientation can be determined from the pole diagram of a piezoelectric laminate containing multiple piezoelectric layers. Therefore, the degree of crystal orientation of the piezoelectric layers can be determined based on the pole diagram of a piezoelectric laminate containing multiple piezoelectric layers. Furthermore, the degree of crystal orientation of the piezoelectric layer may be determined based on pole figures obtained by grinding a single layer of piezoelectric material from both the upper and lower sides of the piezoelectric layer and using that as the measurement sample.

[0027] The crystal orientation becomes higher as the atomic arrangement is more aligned along the array of the ideal crystal structure on any crystal plane of the piezoelectric body included in the piezoelectric layer to be compared. More specifically, it can be said that when the crystal orientation is high, the inclination due to crystal distortion is small, or the ratio of the lattice regions deviated from the ideal crystal structure is small. Conversely, when the crystal orientation is low, it can be said that the inclination due to crystal distortion is large, or the ratio of the lattice regions deviated from the ideal crystal structure is large. Therefore, as the amorphous structure in the piezoelectric layer decreases, the crystal orientation becomes higher, and as the amorphous structure in the piezoelectric layer increases, the crystal orientation becomes lower.

[0028] When the piezoelectric laminate 20 includes a group of three or more piezoelectric layers having the same material and crystal structure, it is preferable that the relationship between the high and low crystal orientations of the piezoelectric layers included in the group of the piezoelectric layers is vertically symmetric with respect to the layer at the center of the piezoelectric laminate 20. More specifically, when the number of piezoelectric layers included in the group of the piezoelectric layers is 2n + 1 or 2n + 2 (n is a natural number of 1 or more) and k is a natural number of 1 or more and n or less, the high and low of the crystal orientation of the k-th piezoelectric layer counted from the upper surface 20a side with respect to the crystal orientation of the (k + 1)-th piezoelectric layer counted from the upper surface 20a side is the same as the high and low of the crystal orientation of the k-th piezoelectric layer counted from the lower surface 20b side with respect to the crystal orientation of the (k + 1)-th piezoelectric layer counted from the lower surface 20b side. Thereby, unnecessary waves generated due to the vertical asymmetry of the crystal orientation of the piezoelectric layer can be suppressed.

[0029] In the example shown in Figure 2, the piezoelectric laminate 20 includes a group consisting of four piezoelectric layers with the same material and crystal structure, so the number of piezoelectric layers included in the group is expressed as 2n + 2 (n = 1). In the example shown in Figure 2, the crystal orientation of the first piezoelectric layer 21, which is the first piezoelectric layer counted from the upper surface 20a, is higher than that of the second piezoelectric layer 22, which is the second piezoelectric layer counted from the upper surface 20a, while the crystal orientation of the fourth piezoelectric layer 24, which is the first piezoelectric layer counted from the lower surface 20b, is higher than that of the third piezoelectric layer 23, which is the second piezoelectric layer counted from the lower surface 20b. In other words, the relationship between the crystal orientation of the first piezoelectric layer 21 and the second piezoelectric layer 22 is the same as the relationship between the crystal orientation of the fourth piezoelectric layer 24 and the third piezoelectric layer 23. In other words, the relationship between the crystal orientation of the four piezoelectric layers included in the group of piezoelectric layers is symmetrical vertically with respect to the second piezoelectric layer 22 and the third piezoelectric layer 23 located in the center of the piezoelectric laminate 20.

[0030] As a piezoelectric layer with relatively high crystal orientation, a single crystal of a piezoelectric material grown by liquid-phase epitaxial growth can be used. Alternatively, as a piezoelectric layer with relatively low crystal orientation, a piezoelectric material grown in the vapor phase can be used, and a layer containing elements other than the constituent elements of the piezoelectric material may also be used. Here, a layer made of a piezoelectric material grown in the vapor phase may be used as the piezoelectric layer with relatively high crystal orientation, and a layer containing elements other than the constituent elements of the piezoelectric material may be used as the piezoelectric layer with relatively low crystal orientation.

[0031] In the above explanation, the crystal orientation of the first piezoelectric layer 21 is higher than that of the second piezoelectric layer 22, and the crystal orientation of the fourth piezoelectric layer 24 is higher than that of the third piezoelectric layer 23. However, the explanation is not limited to this example, and the crystal orientation of the first piezoelectric layer 21 may be lower than that of the second piezoelectric layer 22, and the crystal orientation of the fourth piezoelectric layer 24 may be lower than that of the third piezoelectric layer 23.

[0032] Also, the thickness of the piezoelectric layer is not particularly limited and can be, for example, about 500 nm. In this case, the resonance characteristics in the band near 4 GHz can be made good. Also, in the example of FIG. 2, the thicknesses of the respective piezoelectric layers are equal, but not limited to this, and the thickness of at least one of the plurality of piezoelectric layers may be different from the thickness of at least one other piezoelectric layer.

[0033] As described above, an example of the piezoelectric device according to the first embodiment has been described, but the piezoelectric device according to the first embodiment is not limited to that described above.

[0034] For example, the piezoelectric laminate 2 may include piezoelectric layers having different materials or crystal structures. Also, between the piezoelectric layers, a layer made of a material other than a piezoelectric material, such as a dielectric layer such as silicon oxide (SiO ２ ), or a conductor layer such as an electrode may be provided.

[0035] FIG. 3 is a schematic cross-sectional view showing an example of a piezoelectric device according to a modified example of the first embodiment. For example, an acoustic multilayer film 15 may be provided on the support member 10 instead of the space portion 13. In the piezoelectric device 1A according to the modified example shown in FIG. 3, the acoustic multilayer film 15 has a laminated structure of low acoustic impedance layers 15a, 15c, 15e having a relatively low acoustic impedance and high acoustic impedance layers 15b, 15d having a relatively high acoustic impedance. The low acoustic impedance layers 15a, 15c, 15e are, for example, dielectric films such as SiO ２ , SiOC, polymers, or metal layers such as Al. The high acoustic impedance layers 15b, 15d are, for example, metal layers such as W, Pt, Mo, or dielectric layers such as tantalum oxide, tungsten oxide, aluminum nitride. When the acoustic multilayer film 15 is used, bulk waves can be confined in the piezoelectric laminate 20 without using the space portion 13. Note that the number of laminations of the acoustic multilayer film 15 shown in FIG. 3 is merely an example and is not limited thereto.

[0036] Furthermore, although the above description described an embodiment in which the piezoelectric laminate consists of four piezoelectric layers, the number of piezoelectric layers included in the piezoelectric laminate may be three or five or more. In these cases as well, unwanted waves of thickness longitudinal vibration and thickness sliding vibration can be suppressed by making the displacement direction of the thickness longitudinal vibration and thickness sliding vibration of the piezoelectric layer or piezoelectric film the same as described above.

[0037] As described above, the piezoelectric device 1 according to the first embodiment comprises a piezoelectric laminate 20 having thickness in a first direction (Z direction) and having an upper surface 20a which is one side of the first direction and a lower surface 20b which is the other side of the first direction, a support member 10 provided on the lower surface 20b side of the piezoelectric laminate 20, an upper electrode 31 provided on the upper surface 20a side of the piezoelectric laminate 20, and a lower electrode provided on the lower surface 20b side of the piezoelectric laminate 20. The piezoelectric laminate 20 has a plurality of piezoelectric layers (first piezoelectric layer 21 to fourth piezoelectric layer 24) including single crystals, and each of the plurality of piezoelectric layers differs from other adjacent piezoelectric layers in the first direction in at least one of the material, crystal structure, and polarization direction. The plurality of piezoelectric layers include at least one set of piezoelectric layers having the same material and crystal structure. In at least one set of piezoelectric layers, the crystal orientation of one piezoelectric layer differs from the crystal orientation of the other piezoelectric layer.

[0038] As a result, the piezoelectric layer with relatively low crystal orientation can attenuate unwanted waves with small coupling coefficients, while the piezoelectric layer with relatively high electrical conductivity can suppress the attenuation of the main wave with large coupling coefficients. More specifically, in the piezoelectric layer with relatively low crystal orientation, the attenuation of unwanted waves with small coupling coefficients is greater than that of the main wave with large coupling coefficients, allowing for selective attenuation of unwanted waves. On the other hand, the presence of the piezoelectric layer with relatively high crystal orientation can suppress the attenuation of the main wave by the piezoelectric layer with relatively low crystal orientation. Therefore, the resonance characteristics of the main wave can be maintained in a good state while suppressing unwanted waves, and the deterioration of the resonance characteristics of the main wave can be suppressed.

[0039] In a preferred embodiment, the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure. When the number of piezoelectric layers included in the group consisting of piezoelectric layers is 2n+1 or 2n+2 (where n is a natural number of 1 or more), and k is a natural number between 1 and n, for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the upper surface 20a side in the group consisting of piezoelectric layers is higher than the crystal orientation of the (k+1)th piezoelectric layer counted from the upper surface 20a side in the group consisting of piezoelectric layers, and for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the lower surface 20b side in the group consisting of piezoelectric layers is higher than the crystal orientation of the (k+1)th piezoelectric layer counted from the lower surface 20b side in the group consisting of piezoelectric layers. As a result, the relationship between the crystal orientations of the plurality of piezoelectric layers is symmetrical vertically with respect to the layer in the center of the piezoelectric laminate 20, thereby suppressing unwanted waves generated due to the vertical asymmetry of the crystal orientation of the piezoelectric layers.

[0040] In a preferred embodiment, the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure. When the number of piezoelectric layers included in the group consisting of piezoelectric layers is 2n+1 or 2n+2 (where n is a natural number of 1 or more), and k is a natural number between 1 and n, for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the upper surface 20a side in the group consisting of piezoelectric layers is lower than the crystal orientation of the (k+1)th piezoelectric layer counted from the upper surface 20a side in the group consisting of piezoelectric layers, and for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the lower surface 20b side in the group consisting of piezoelectric layers is lower than the crystal orientation of the (k+1)th piezoelectric layer counted from the lower surface 20b side in the group consisting of piezoelectric layers. As a result, the relationship between the crystal orientations of the plurality of piezoelectric layers is symmetrical vertically with respect to the layer in the center of the piezoelectric laminate 20, thereby suppressing unwanted waves generated due to the vertical asymmetry of the crystal orientation of the piezoelectric layers.

[0041] In a preferred embodiment, in at least one pair of piezoelectric layers, the piezoelectric layers are adjacent to each other in a first direction. In a pair of piezoelectric layers where the piezoelectric layers are adjacent to each other in a first direction, the polarization direction of each piezoelectric layer is opposite to the polarization direction of the other piezoelectric layer. This allows for further improvement of the resonance characteristics of the piezoelectric device 1 and further suppression of unwanted waves.

[0042] In a preferred embodiment, at least one of the plurality of piezoelectric layers includes a single crystal of lithium niobate or lithium tantalate. This improves the resonance characteristics.

[0043] Furthermore, the piezoelectric device according to the first embodiment may further include at least one of a conductor and a dielectric between the piezoelectric layers. In this case as well, it is possible to suppress unwanted waves while maintaining the resonance characteristics of the main wave, thereby suppressing deterioration of the resonance characteristics of the main wave.

[0044] (Manufacturing Method) Figure 5 is a schematic cross-sectional view showing the manufacturing process of a piezoelectric device according to the first embodiment. Hereinafter, an example of a method for manufacturing a piezoelectric device according to the first embodiment will be described using Figure 5. The method for manufacturing a piezoelectric device according to Figure 5 includes the steps of forming a piezoelectric laminate 20 on a temporary substrate B (steps S11 to S14), forming a lower electrode 32 (step S15), forming a sacrificial layer 13S (step S16), forming an intermediate layer 12 (step S17), joining a support substrate 11 (step S18), removing the temporary substrate B (step S19), forming an upper electrode 31 (step S20), and forming a space 13 (step S21).

[0045] In the step of forming the piezoelectric laminate 20 on the temporary substrate B (steps S11 to S14), the piezoelectric laminate 20 is formed by sequentially forming multiple piezoelectric layers on the temporary substrate B from the bottom surface 20b side. In the example in Figure 5, the first piezoelectric layer 21 and the fourth piezoelectric layer 24 are piezoelectric layers with relatively high crystal orientation, while the second piezoelectric layer 22 and the third piezoelectric layer 23 are piezoelectric layers with relatively low crystal orientation, and are formed by different methods.

[0046] In the step of forming the first piezoelectric layer 21 (step S11), the first piezoelectric layer 21 with relatively high crystal orientation is formed on the temporary substrate B by, for example, the following method. First, the piezoelectric ingot grown with LPE is sliced ​​and cut out, and the surface is finished by planarization, smoothing, etc. Since the growth of single crystals proceeds very slowly in LPE, a piezoelectric ingot with high crystal orientation can be obtained. Then, the cut piezoelectric ingot is bonded to the temporary substrate B, and the piezoelectric ingot is thinned and the surface is smoothed. Specifically, by grinding, lapping, polishing, etc. on the piezoelectric ingot, the first piezoelectric layer 21 with a smooth main surface is formed. Note that the method of forming the first piezoelectric layer 21 with relatively high crystal orientation is not limited to the above, and for example, the first piezoelectric layer may be formed by smoothing the surface of a piezoelectric film obtained by the ion slicing method. Here, the ion slicing method is a process in which ions are implanted onto the entire surface of a wafer made from an LPE-grown piezoelectric ingot with a constant acceleration voltage and dose to form an ion concentration peak layer, a temporary substrate B is bonded to the wafer surface, and then the piezoelectric film is separated from the ion concentration peak layer by heating to obtain a piezoelectric film.

[0047] In the step of forming the second piezoelectric layer 22 (step S12), for example, the second piezoelectric layer 22 with relatively low crystal orientation is formed by the following method. The surface of the first piezoelectric layer 21 on which the second piezoelectric layer 22 is provided is treated with hydrofluoric acid to remove the altered layer caused by grinding or polishing of the first piezoelectric layer 21. Then, the second piezoelectric layer 22 is deposited by a vapor phase growth method such as CVD (Chemical Vapor Deposition) while heating the surface of the first piezoelectric layer 21. As a result, the second piezoelectric layer 22 is a layer with lower crystal orientation than the first piezoelectric layer 21 obtained by LPE. In addition, the polarization direction P2 of the second piezoelectric layer 22 is in the opposite direction to the polarization direction P1 of the first piezoelectric layer 21. After that, the second piezoelectric layer 22 is thinned and smoothed by CMP or the like. At this time, it is preferable that the surface roughness Ra is 1 nm or less. Furthermore, the method for forming the second piezoelectric layer 22, which has relatively low crystal orientation, is not limited to the above. For example, the second piezoelectric layer 22 may be formed by sputtering instead of CVD as a vapor phase growth method.

[0048] In the step of forming the third piezoelectric layer 23 (step S13), the third piezoelectric layer 23, which has a relatively low crystal orientation, is formed in the same manner as in the step of forming the second piezoelectric layer 22 (step S12). As a result, the polarization direction P3 of the third piezoelectric layer 23 is in the opposite direction to the polarization direction P2 of the second piezoelectric layer 22.

[0049] In the step of forming the fourth piezoelectric layer 24 (step S14), the fourth piezoelectric layer 24, which has a relatively high crystal orientation, is formed in the same manner as in the step of forming the first piezoelectric layer 21 (step S11). Here, the piezoelectric ingot that will become the fourth piezoelectric layer 24 is provided such that its polarization direction P4 is opposite to the polarization direction P3 of the third piezoelectric layer 23.

[0050] By steps S11 to S14 described above, a piezoelectric laminate 20 is formed, which includes piezoelectric layers with relatively low crystal orientation (second piezoelectric layer 22 and third piezoelectric layer 23) and piezoelectric layers with relatively high crystal orientation (first piezoelectric layer 21 and fourth piezoelectric layer 24). As a result, unwanted waves with small coupling coefficients can be attenuated by the piezoelectric layers with relatively low crystal orientation, and the attenuation of main waves with large coupling coefficients can be suppressed by the piezoelectric layers with relatively high electrical conductivity. Therefore, it is possible to maintain good resonance characteristics of the main wave while suppressing unwanted waves, and to suppress deterioration of the resonance characteristics of the main wave. Furthermore, by combining LPE, which is used to obtain piezoelectric layers with high crystal orientation at a high cost, and vapor phase growth, which is used to obtain piezoelectric layers with low crystal orientation at a low cost, in the formation of the piezoelectric laminate 20, it is possible to provide a piezoelectric device 1 with excellent resonance characteristics while suppressing the manufacturing cost of the piezoelectric device 1.

[0051] In the step of forming the lower electrode 32 (step S15), the lower electrode 32 is patterned on the lower surface 20b side of the piezoelectric laminate 20 by a method such as the vapor deposition lift-off method.

[0052] In the step of forming the sacrificial layer 13S (step S16), the sacrificial layer 13S is formed on the lower surface 20b side of the piezoelectric laminate 20. The sacrificial layer 13S is made of, for example, zinc oxide.

[0053] In the step of forming the intermediate layer 12 (step S17), the intermediate layer 12 is formed so as to cover the lower electrode 32 and the sacrificial layer 13S. The surface of the intermediate layer 12 is planarized and smoothed.

[0054] In the step of joining the support substrate 11 (step S18), the support member 10 is joined to the intermediate layer 12. The intermediate layer 12 and the support member 10 are joined directly, for example, by hydrophilic bonding of a thin film of the same material as the intermediate layer 12 that has been previously formed on the surface of the support substrate 11 to the intermediate layer 12. Here, hydrophilic bonding is performed by the following method. First, the surfaces to be joined are exposed to oxygen plasma and then particle removal is performed by brush cleaning. Then, the surfaces of the support substrate 11 and the intermediate layer 12 are bonded together in the atmosphere and heat treated to join the intermediate layer 12 and the support substrate 11.

[0055] In the step of removing the temporary substrate B (step S19), the temporary substrate B is removed by slicing and grinding it. This exposes the upper surface 20a.

[0056] In the step of forming the upper electrode 31 (step S20), the upper electrode 31 is patterned on the upper surface 20a of the piezoelectric laminate 20 by a method such as the vapor deposition lift-off method.

[0057] In the step of forming the space 13 (step S21), the sacrificial layer 13S is removed to form the space 13. The removal of the sacrificial layer 13S is performed, for example, by wet etching, in which etching holes are made in the piezoelectric laminate 20 and an etching solution is injected.

[0058] By following the steps described above, the piezoelectric device 1 according to the first embodiment can be manufactured. However, the method for manufacturing the piezoelectric device according to this disclosure is not limited to the method described above and can be modified as appropriate.

[0059] For example, a piezoelectric layer with low crystal orientation may be fabricated by vapor phase growth with trace amounts of elements other than the constituent elements of the piezoelectric material. A piezoelectric layer with high crystal orientation may be fabricated by cutting an ingot made of LPE, or by vapor phase growth.

[0060] (Second Embodiment) In the second embodiment, the piezoelectric device differs from the first embodiment in that, in a set of piezoelectric layers having the same material and crystal structure but different crystal orientations, the electrical conductivity of one piezoelectric layer is different from that of the other piezoelectric layer. As a result, the dielectric strength can be improved by the piezoelectric layer with relatively low electrical conductivity, and deterioration of the piezoelectric body due to charge can be suppressed, while the piezoelectric layer with relatively high electrical conductivity can suppress the accumulation of charge on the functional electrode 30, thereby suppressing deterioration and destruction of the piezoelectric layer.

[0061] In the second embodiment, when the piezoelectric laminate includes a group of three or more piezoelectric layers having the same material and crystal structure, it is preferable that the electrical conductivity of the piezoelectric layers at both ends in the Z direction is different from the electrical conductivity of the piezoelectric layers other than those at both ends in the Z direction. In the example in Figure 2, the electrical conductivity of the first piezoelectric layer 21 and the fourth piezoelectric layer 24 at both ends in the Z direction is greater than the electrical conductivity of the second piezoelectric layer 22 and the third piezoelectric layer 23, which are piezoelectric layers other than those at both ends in the Z direction. This improves the symmetry of the charge distribution of the piezoelectric laminate 20 in the Z direction, thereby further suppressing degradation and destruction of the piezoelectric layers. In the example shown in Figure 2, the electrical conductivity of the piezoelectric layers at both ends in the Z direction is greater than that of the piezoelectric layers other than those at both ends in the Z direction. However, the explanation is not limited to this example, and the electrical conductivity of the piezoelectric layers at both ends in the Z direction may be less than that of the piezoelectric layers other than those at both ends in the Z direction.

[0062] Here, the relative magnitudes of the electrical conductivity of piezoelectric layers with identical materials and crystal structures can be measured by the following method. A piezoelectric laminate is removed, and two piezoelectric layers to be compared in terms of electrical conductivity are obtained by grinding. These are then fixed to a semiconducting substrate such as a Si substrate, either directly or via conductive tape, to serve as measurement samples. A certain amount of charge is then charged to each piezoelectric layer of the measurement sample by exposing it to corona plasma under the same conditions. The time it takes for the charge on the surface of the piezoelectric layer to be halved (charge half-life time) is measured using a surface potential meter after the charge charging by corona plasma is stopped. The ratio of the thickness of the piezoelectric layer to the charge half-life time is then calculated, and the relative magnitudes of the electrical conductivity can be determined by comparing the magnitudes of these ratios.

[0063] In the second embodiment, it is preferable that at least one of the plurality of piezoelectric layers contains at least one of Ni, Fe, Mn, and Cr. In particular, it is more preferable that the piezoelectric layer with relatively high electrical conductivity among the plurality of piezoelectric layers contains at least one of Ni, Fe, Mn, and Cr. As a result, the piezoelectric layer containing at least one of Ni, Fe, Mn, and Cr has improved electrical conductivity compared to a piezoelectric layer consisting only of piezoelectric materials with the same composition and crystal structure, thereby suppressing degradation and breakdown of the piezoelectric layer.

[0064] As described above, in the piezoelectric device according to the second embodiment, in at least one set of piezoelectric layers, the electrical conductivity of one piezoelectric layer is different from that of the other piezoelectric layer. This allows for improved voltage resistance by using a piezoelectric layer with relatively low electrical conductivity, suppressing degradation of the piezoelectric body due to charge, while the piezoelectric layer with relatively high electrical conductivity suppresses the accumulation of charge on the functional electrode 30, thereby suppressing degradation and destruction of the piezoelectric layer.

[0065] As a desirable aspect, the plurality of piezoelectric layers include a group of three or more piezoelectric layers having the same material and crystal structure. The electrical conductivity of the piezoelectric layers (the first piezoelectric layer 21 and the fourth piezoelectric layer 24) at both ends in the first direction among the group of piezoelectric layers is different from the electrical conductivity of the piezoelectric layers (the second piezoelectric layer 22 and the third piezoelectric layer 23) other than the piezoelectric layers at both ends in the first direction. Thereby, the symmetry of the charge distribution of the piezoelectric laminate 20 in the Z direction can be improved, so that deterioration and destruction of the piezoelectric layer can be more suppressed.

[0066] As a desirable aspect, in at least one pair of the piezoelectric layer sets, one of the piezoelectric layers contains at least one of Ni, Fe, Mn, and Cr. Thereby, in the piezoelectric layer containing at least one of Ni, Fe, Mn, and Cr, the electrical conductivity is improved compared to the piezoelectric layer made of a piezoelectric material, so that deterioration and destruction of the piezoelectric layer can be suppressed.

[0067] Here, the piezoelectric device according to the second embodiment can be manufactured in the same manner as the piezoelectric device according to the first embodiment, except that a piezoelectric layer having a relatively high electrical conductivity is formed by vapor growth by containing a metal containing at least one of Ni, Fe, Mn, and Cr.

[0068] (Third Embodiment) In the third embodiment, in a set of piezoelectric layers having the same material and crystal structure but different crystal orientations, the piezoelectric constant d of one of the piezoelectric layers ３３ is different from the piezoelectric device according to the first embodiment in that it is different from the piezoelectric constant d of the other piezoelectric layer ３３ Thereby, by changing the resonance frequency, anti-resonance frequency, coupling coefficient, etc. of unnecessary waves, the influence of unnecessary waves on the resonance characteristics of the main wave can be reduced.

[0069] In the third embodiment, when the piezoelectric laminate includes a group of three or more piezoelectric layers having the same material and crystal structure, among the piezoelectric layers included in the group of piezoelectric layers, the piezoelectric constant d of the piezoelectric layers at both ends in the Z direction ３３ is preferably different from the piezoelectric constant d of the piezoelectric layers other than the piezoelectric layers at both ends in the Z direction ３３ That is, in the example of FIG. 2, among the piezoelectric layers included in the group of piezoelectric layers, the piezoelectric constant d of the first piezoelectric layer 21 and the fourth piezoelectric layer 24 at both ends in the Z direction ３３The piezoelectric constant d is the piezoelectric constant of the second piezoelectric layer 22 and the third piezoelectric layer 23, which are piezoelectric layers other than the piezoelectric layers at both ends in the Z direction. ３３ It is preferable that it is different from the above. The piezoelectric constant d of the piezoelectric layers included in the group consisting of the piezoelectric layers when the resonator using the piezoelectric laminate 20 according to the first embodiment is operated. ３３ If the piezoelectric constant d is the same, unwanted waves may be generated in the same mode in each layer. In this case, unwanted waves with a large coupling coefficient are generated. On the other hand, the piezoelectric constant d of the first piezoelectric layer 21, the fourth piezoelectric layer 24, and the second piezoelectric layer 22, the third piezoelectric layer 23, which are included in the group consisting of the piezoelectric layers, ３３ If they are different, the piezoelectric constant d ３３ Because unwanted waves with different resonance states are generated between piezoelectric layers with different characteristics, the coupling coefficient of the unwanted waves becomes relatively smaller. As a result, the effect of suppressing unwanted waves in layers with low crystal orientation becomes relatively higher, and the influence of unwanted waves can be suppressed. In the example in Figure 2, the piezoelectric constant d of the piezoelectric layers at both ends in the Z direction (first piezoelectric layer 21, fourth piezoelectric layer 24) among the piezoelectric layers included in the group of piezoelectric layers is ３３ However, the piezoelectric constant d of the piezoelectric layers other than the piezoelectric layers at both ends in the Z direction (second piezoelectric layer 22, third piezoelectric layer 23) ３３ Smaller, but not limited to, the piezoelectric constant d of the piezoelectric layers at both ends in the Z direction among the piezoelectric layers included in the group consisting of the piezoelectric layers. ３３ However, the piezoelectric constant d of the piezoelectric layers other than the piezoelectric layers at both ends in the Z direction ３３ It can be larger.

[0070] Here, the piezoelectric constant d of piezoelectric layers with the same material and crystal structure is given. ３３ The relative magnitudes of the piezoelectric constants can be measured by the following method. The piezoelectric laminate is removed, and two piezoelectric layers to be used as a comparison of electrical conductivity are obtained by grinding. These are then placed on a conductive, hard base such as an aluminum jig to serve as the measurement sample. Then, using a Piezo-Response Microscope (PRM), the magnitude of the product of the displacement with respect to the electric field, the magnitude of the polarization component of the applied electric field vector, and the thickness of the piezoelectric layer is compared to determine the piezoelectric constant d ３３ It is possible to determine the size of something.

[0071] In the third embodiment, it is preferable that at least one of the plurality of piezoelectric layers contains at least one of Na, K, Mg, and Sc. In particular, the piezoelectric constant d of the plurality of piezoelectric layers ３３ It is more preferable that the piezoelectric layer with a relatively high piezoelectricity contains at least one of Na, K, Mg, and Sc. As a result, a piezoelectric layer containing at least one of Na, K, Mg, and Sc has a higher piezoelectric constant d than a piezoelectric layer consisting only of piezoelectric materials with the same composition and crystal structure. ３３ This improves the resonance characteristics of the main wave, thus reducing the influence of unwanted waves on its resonance characteristics.

[0072] As described above, in the piezoelectric device according to the third embodiment, in at least one set of piezoelectric layers, the piezoelectric constant d of one of the piezoelectric layers ３３ The piezoelectric constant d of the other piezoelectric layer is... ３３ This is different. By changing the state of unwanted waves, it is possible to maintain good resonance characteristics of the main wave, suppress the deterioration of the main wave's resonance characteristics, and reduce the influence of unwanted waves.

[0073] In a preferred embodiment, the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure. The piezoelectric constant d of the piezoelectric layers at both ends in the first direction (first piezoelectric layer 21 and fourth piezoelectric layer 24) of the group consisting of piezoelectric layers. ３３ This is the piezoelectric constant d of the piezoelectric layers other than the piezoelectric layers at both ends in the first direction (the second piezoelectric layer 22 and the third piezoelectric layer 23). ３３ This is different. As a result, the piezoelectric constant d ３３ Because unwanted waves with different resonance states are generated between piezoelectric layers with different characteristics, the coupling coefficient of these unwanted waves becomes relatively smaller. As a result, the effect of suppressing unwanted waves in layers with low crystal orientation becomes relatively higher, and the influence of unwanted waves can be suppressed.

[0074] In a preferred embodiment, in at least one set of piezoelectric layers, one of the piezoelectric layers contains at least one of Na, K, Mg, and Sc. Thus, in a piezoelectric layer containing at least one of Na, K, Mg, and Sc, the piezoelectric constant d is greater than that of a piezoelectric layer made of a piezoelectric material. ３３ This improves the resonance characteristics of the main wave, thus reducing the influence of unwanted waves on its resonance characteristics.

[0075] Here, the piezoelectric device according to the third embodiment has a piezoelectric constant d ３３ The piezoelectric device can be manufactured in the same manner as the piezoelectric device according to the first embodiment, except that a piezoelectric layer with a relatively high capacitance is formed by vapor phase growth containing a metal that includes at least one of Na, K, Mg, and Sc.

[0076] 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.

[0077] Furthermore, this disclosure may also take the following form.

[0078] (1) A piezoelectric device comprising: a piezoelectric laminate having thickness in a first direction and having an upper surface which is one side in the first direction and a lower surface which is the other side in the first direction; a support member provided on the lower side of the piezoelectric laminate; an upper electrode provided on the upper side of the piezoelectric laminate; and a lower electrode provided on the lower side of the piezoelectric laminate, wherein the piezoelectric laminate has a plurality of piezoelectric layers including a single crystal, each of the plurality of piezoelectric layers differs from other adjacent piezoelectric layers in the first direction in at least one of the material, crystal structure and polarization direction, the plurality of piezoelectric layers include at least one set of piezoelectric layers having the same material and crystal structure, and in at least one of the sets of piezoelectric layers, the crystal orientation of one piezoelectric layer differs from the crystal orientation of the other piezoelectric layer. (2) The piezoelectric device according to (1), wherein the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure, and when the number of piezoelectric layers included in the group consisting of piezoelectric layers is 2n+1 or 2n+2 (where n is a natural number of 1 or more) and k is a natural number of 1 or more and n or less, for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the top side in the group consisting of piezoelectric layers is higher than the crystal orientation of the (k+1)-th piezoelectric layer counted from the top side in the group consisting of piezoelectric layers, and for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the bottom side in the group consisting of piezoelectric layers is higher than the crystal orientation of the (k+1)-th piezoelectric layer counted from the bottom side in the group consisting of piezoelectric layers. (3) The piezoelectric device according to (1), wherein the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure, and when the number of piezoelectric layers included in the group consisting of piezoelectric layers is 2n+1 or 2n+2 (where n is a natural number of 1 or more) and k is a natural number of 1 or more and n or less, for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the top side in the group consisting of piezoelectric layers is lower than the crystal orientation of the (k+1)-th piezoelectric layer counted from the top side in the group consisting of piezoelectric layers, and for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the bottom side in the group consisting of piezoelectric layers is lower than the crystal orientation of the (k+1)-th piezoelectric layer counted from the bottom side in the group consisting of piezoelectric layers.(4) A piezoelectric device according to any one of (1) to (3), wherein in at least one of the sets of piezoelectric layers, the electrical conductivity of one piezoelectric layer is different from that of the other piezoelectric layer. (5) A piezoelectric device according to (4), wherein the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure, and the electrical conductivity of the piezoelectric layers at both ends in the first direction of the group consisting of piezoelectric layers is different from that of the piezoelectric layers other than the piezoelectric layers at both ends in the first direction. (6) A piezoelectric device according to (4) or (5), wherein at least one piezoelectric layer in the group consisting of piezoelectric layers includes at least one of Ni, Fe, Mn, and Cr. (7) A piezoelectric constant d of one piezoelectric layer in at least one of the sets of piezoelectric layers. ３３ The piezoelectric constant d of the other piezoelectric layer is... ３３ A piezoelectric device according to any one of (1) to (6), which is different from the above. (8) The plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure, wherein the piezoelectric constant d of the piezoelectric layers at both ends in the first direction among the group consisting of piezoelectric layers ３３ The piezoelectric constant d of the piezoelectric layers other than the piezoelectric layers at both ends in the first direction is the piezoelectric constant d of the piezoelectric layers. ３３ A piezoelectric device according to (7), which is different from (8). (9) A piezoelectric device according to (7) or (8), wherein at least one piezoelectric layer from the group consisting of the piezoelectric layers comprises at least one of Na, K, Mg, and Sc. (10) A piezoelectric device according to any one of (1) to (9), wherein in at least one set of the piezoelectric layers, the piezoelectric layers are adjacent to each other in the first direction, and in the set of piezoelectric layers where the piezoelectric layers are adjacent to each other in the first direction, the polarization direction of one piezoelectric layer is opposite to the polarization direction of the other piezoelectric layer. (11) A piezoelectric device according to any one of (1) to (10), wherein at least one piezoelectric layer from the plurality of piezoelectric layers comprises a single crystal of lithium niobate or lithium tantalate. (12) A piezoelectric device according to any one of (1) to (11), further comprising at least one of a conductor and a dielectric between the piezoelectric layers.

[0079] 1, 1A Piezoelectric device 10 Support member 11 Support substrate 12 Intermediate layer 13 Space 15 Acoustic multilayer film 20 Piezoelectric laminate 20a Top surface 20b Bottom surface 21 First piezoelectric layer 22 Second piezoelectric layer 23 Third piezoelectric layer 24 Fourth piezoelectric layer 30 Functional electrode 31 Upper electrode 31a, 32a Main electrode portion 31b, 32b Extended portion 32 Lower electrode B Temporary substrate C Excitation region P1, P2, P3, P4 Polarization direction S1A, S2A, S1B, S2B Spot

Claims

1. A piezoelectric device comprising: a piezoelectric laminate having thickness in a first direction and having an upper surface which is one side of the first direction and a lower surface which is the other side of the first direction; a support member provided on the lower side of the piezoelectric laminate; an upper electrode provided on the upper side of the piezoelectric laminate; and a lower electrode provided on the lower side of the piezoelectric laminate, wherein the piezoelectric laminate has a plurality of piezoelectric layers including a single crystal, each of the plurality of piezoelectric layers differs from other adjacent piezoelectric layers in the first direction in at least one of the material, crystal structure and polarization direction, the plurality of piezoelectric layers include at least one set of piezoelectric layers having the same material and crystal structure, and in at least one of the sets of piezoelectric layers, the crystal orientation of one piezoelectric layer differs from the crystal orientation of the other piezoelectric layer.

2. The piezoelectric device according to claim 1, wherein the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure, and when the number of piezoelectric layers included in the group consisting of piezoelectric layers is 2n+1 or 2n+2 (where n is a natural number of 1 or more) and k is a natural number between 1 and n, for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the top side in the group consisting of piezoelectric layers is higher than the crystal orientation of the (k+1)-th piezoelectric layer counted from the top side in the group consisting of piezoelectric layers, and for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the bottom side in the group consisting of piezoelectric layers is higher than the crystal orientation of the (k+1)-th piezoelectric layer counted from the bottom side in the group consisting of piezoelectric layers.

3. The piezoelectric device according to claim 1, wherein the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure, and when the number of piezoelectric layers included in the group consisting of piezoelectric layers is 2n+1 or 2n+2 (where n is a natural number of 1 or more) and k is a natural number between 1 and n, for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the top side in the group consisting of piezoelectric layers is lower than the crystal orientation of the (k+1)th piezoelectric layer counted from the top side in the group consisting of piezoelectric layers, and for at least one k, the crystal orientation of the k-th piezoelectric layer counted from the bottom side in the group consisting of piezoelectric layers is lower than the crystal orientation of the (k+1)th piezoelectric layer counted from the bottom side in the group consisting of piezoelectric layers.

4. The piezoelectric device according to any one of claims 1 to 3, wherein in at least one of the sets of piezoelectric layers, the electrical conductivity of one piezoelectric layer is different from the electrical conductivity of the other piezoelectric layer.

5. The piezoelectric device according to claim 4, wherein the plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure, and the electrical conductivity of the piezoelectric layers at both ends in the first direction is different from the electrical conductivity of the piezoelectric layers other than the piezoelectric layers at both ends in the first direction.

6. The piezoelectric device according to claim 4 or 5, wherein at least one piezoelectric layer from the group consisting of the piezoelectric layers includes at least one of Ni, Fe, Mn, and Cr.

7. In at least one of the sets of piezoelectric layers, the piezoelectric constant d of one of the piezoelectric layers ３３ The piezoelectric constant d of the other piezoelectric layer is... ３３ A piezoelectric device according to any one of claims 1 to 6, which is different from the above.

8. The plurality of piezoelectric layers include a group consisting of three or more piezoelectric layers having the same material and crystal structure, and the piezoelectric constant d of the piezoelectric layers at both ends in the first direction among the group consisting of piezoelectric layers. ３３ The piezoelectric constant d of the piezoelectric layers other than the piezoelectric layers at both ends in the first direction is the piezoelectric constant d of the piezoelectric layers other than the piezoelectric layers at both ends. ３３ A piezoelectric device according to claim 7, which differs from the above.

9. The piezoelectric device according to claim 7 or 8, wherein at least one piezoelectric layer from the group consisting of the piezoelectric layers includes at least one of Na, K, Mg, and Sc.

10. A piezoelectric device according to any one of claims 1 to 9, wherein in at least one of the sets of piezoelectric layers, the piezoelectric layers are adjacent to each other in the first direction, and in the set of piezoelectric layers in which the piezoelectric layers are adjacent to each other in the first direction, the polarization direction of one piezoelectric layer is opposite to the polarization direction of the other piezoelectric layer.

11. The piezoelectric device according to any one of claims 1 to 10, wherein at least one of the plurality of piezoelectric layers comprises a single crystal of lithium niobate or lithium tantalate.

12. The piezoelectric device according to any one of claims 1 to 11, further comprising at least one of a conductor and a dielectric between the piezoelectric layers.

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