piezoelectric device

Abstract

The recess (113) has a polygonal or circular shape as viewed in a direction orthogonal to the main surface. If the number of sides constituting the polygon is n, the radius of a circumscribed circle (C) of an imaginary regular polygon constituted by n sides having the same length (L1) as the shortest side among the sides is r, and the maximum thickness of the diaphragm portion on the recess (113) in the stacked portion is d, then in the case of 3 ≤ n ≤ 7, r ≤ 197.7dn is satisfied. ‑0.6698 In the case of 8 ≤ n or the case where the shape of the recess (113) is circular, r ≤ 52.69d is satisfied.

Description

Technical Field

[0001] This invention relates to piezoelectric devices. Background Technology

[0002] As a prior art document disclosing the structure of a piezoelectric device, there is "Single crystal FBAR with LiNbO3 and LiTaO3", Proceedings of Symposium on Ultrasonic Electronics, Vol. 28, (2007), pp. 151-152 (Non-Patent Document 1). In the piezoelectric device described in Non-Patent Document 1, a space is formed below the piezoelectric layer sandwiched between the electrodes.

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent literature 1: "Single crystal FBAR with LiNbO3 and LiTaO3", Proceedings of Symposium on Ultrasonic Electronics, Vol. 28, (2007), pp. 151-152 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In structures where a space is formed beneath a piezoelectric layer, the piezoelectric layer may sometimes bend downwards or become uneven in thickness, which can degrade the characteristics of the piezoelectric device.

[0008] The present invention was made in view of the above-mentioned problems, and its object is to provide a piezoelectric device that can suppress the degradation of properties caused by bending of the piezoelectric layer or unevenness of the thickness of the piezoelectric layer.

[0009] Technical solutions for solving the problem

[0010] The piezoelectric device according to the present invention comprises a base and a stacked portion. The base includes a main surface and another main surface located opposite to the main surface, and has a recess formed on one of the main surfaces. The stacked portion is stacked on one of the main surfaces of the base, such that it covers the recess from above. The stacked portion includes a single-crystal piezoelectric layer and a pair of electrode layers at least above the recess. The pair of electrode layers apply a voltage to the single-crystal piezoelectric layer. Viewed from a direction orthogonal to the main surface, the recess has a polygonal or circular shape. If the number of sides constituting the polygon is set to n, the radius of the circumcircle of the imaginary regular polygon formed by the n sides having the same length as the shortest side among the multiple sides is set to r, and the maximum thickness of the membrane portion located on the recess in the stacked portion is set to d, then in the case of 3≤n≤7, r≤197.7dn -0.6698 When 8 ≤ n or the above-mentioned concave part has a circular shape, r ≤ 52.69d is satisfied.

[0011] Invention Effects

[0012] According to the present invention, it is possible to suppress the degradation of the characteristics of piezoelectric devices caused by bending of the piezoelectric layer or unevenness in the thickness of the piezoelectric layer. Attached Figure Description

[0013] Figure 1 This is a top view showing the structure of the piezoelectric device according to Embodiment 1 of the present invention.

[0014] Figure 2 From the direction of the arrow on line II-II Figure 1 The piezoelectric device shown is an observed cross-sectional view.

[0015] Figure 3 yes Figure 2 A partially enlarged view of section III in the cross-sectional view of the piezoelectric device shown.

[0016] Figure 4 This is a figure showing the results of a simulation analysis of the distribution of deformation in a regular polygonal membrane section.

[0017] Figure 5 This is a graph showing the results of a simulation analysis of the relationship between the depth of the concave portion and the deformation of the circular diaphragm portion.

[0018] Figure 6 This is a graph showing the results of a simulation analysis of the relationship between the internal pressure of the concave portion and the deformation of the circular diaphragm portion.

[0019] Figure 7 This is a graph showing the results of a simulation analysis of the relationship between the lengths of the longitudinal and transverse sides of a rectangular diaphragm and the deformation of the diaphragm.

[0020] Figure 8 The graph shows the results of a simulation analysis of the relationship between the radius r of the circumcircle C of the polygonal diaphragm portion, which is 20% of the maximum thickness of the diaphragm portion, the maximum thickness d of the diaphragm portion, and the number of sides constituting the polygon.

[0021] Figure 9 Based on Figure 8 The graph shown illustrates the relationship between the number of sides n that make up the polygon and the slope a of the approximate straight line.

[0022] Figure 10 This is a cross-sectional view showing the state in which a lower electrode layer is provided on the lower surface of a single-crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0023] Figure 11 This is a cross-sectional view showing a state in which an intermediate layer is provided on the lower surface of both the lower electrode layer and the single-crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0024] Figure 12 This is a cross-sectional view showing the state in which the lower surface of the intermediate layer is flattened in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0025] Figure 13 This is a cross-sectional view showing the state before the recess is formed in the base during the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0026] Figure 14 This is a cross-sectional view showing the state in which a recess is formed in the base during the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0027] Figure 15 This illustrates that in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention, the base is made with... Figure 12 A cross-sectional view showing the joint state of multiple layers.

[0028] Figure 16 This is a cross-sectional view showing the state after the base is joined to the lower surface of the intermediate layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0029] Figure 17 This is a cross-sectional view showing the state after the upper surface of the single-crystal piezoelectric layer has been cut off in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0030] Figure 18This is a cross-sectional view showing the state in which an upper electrode layer is provided on the upper surface of a single-crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0031] Figure 19 This is a cross-sectional view showing the structure of a piezoelectric device according to a first variation of Embodiment 1 of the present invention.

[0032] Figure 20 This is a cross-sectional view showing the structure of a piezoelectric device according to a second variation of Embodiment 1 of the present invention.

[0033] Figure 21 This is a cross-sectional view showing the structure of a piezoelectric device according to the third variation of Embodiment 1 of the present invention.

[0034] Figure 22 This is a cross-sectional view showing the structure of a piezoelectric device according to the fourth variation of Embodiment 1 of the present invention.

[0035] Figure 23 This is a cross-sectional view showing the structure of the piezoelectric device according to Embodiment 2 of the present invention. Detailed Implementation

[0036] Hereinafter, piezoelectric devices according to various embodiments of the present invention will be described with reference to the figures. In the following description of the embodiments, the same or corresponding parts in the figures will be labeled with the same reference numerals, and their descriptions will not be repeated.

[0037] (Implementation Method 1)

[0038] Figure 1 This is a top view showing the structure of the piezoelectric device according to Embodiment 1 of the present invention. Figure 2 From the direction of the arrow on line II-II Figure 1 The piezoelectric device shown is an observed cross-sectional view. Figure 3 yes Figure 2 A partially enlarged view of section III in the cross-sectional view of the piezoelectric device shown. Figure 1 The internal structure of the piezoelectric device is shown in the diagram using dotted lines.

[0039] like Figure 1 as well as Figure 2 As shown, the piezoelectric device 100 according to Embodiment 1 of the present invention includes a base 110 and a laminated portion 120.

[0040] The base 110 includes a main surface 111 and another main surface 112 located on the opposite side of the main surface 111. The base 110 has a recess 113 formed on one of the main surfaces 111.

[0041] In this embodiment, the width of the opening on one of the main surfaces 111 in the recess 113 is narrower than the width of the bottom of the recess 113. Alternatively, the width of the opening in the recess 113 may be equal to the width of the bottom, or it may be wider than the width of the bottom. Hereinafter, the area above the opening of the recess 113 will sometimes be referred to as the upper part of the recess 113.

[0042] like Figure 2 As shown, the recess 113 is covered from above by a stacked portion 120 stacked on one main surface 111 side of the base 110. In this embodiment, the interior of the recess 113 becomes a sealed space.

[0043] In the piezoelectric device 100 of this embodiment, the pressure inside the recess 113 is negative. Alternatively, the pressure inside the recess 113 may be atmospheric pressure or positive pressure.

[0044] In this embodiment, the base 110 is made of Si. However, the material constituting the base 110 is not limited to Si.

[0045] The stack 120 includes a single-crystal piezoelectric layer 130 and a pair of electrode layers. A voltage is applied to the single-crystal piezoelectric layer 130 by the pair of electrode layers. In this embodiment, the pair of electrode layers consists of an upper electrode layer 140 and a lower electrode layer 150. The stack 120 also includes an intermediate layer 160.

[0046] The single-crystal piezoelectric layer 130 is located above the base 110. The single-crystal piezoelectric layer 130 is configured such that at least a portion of it lies above the recess 113. The single-crystal piezoelectric layer 130 is curved into a convex shape towards the base 110 in the region above the recess 113. The single-crystal piezoelectric layer 130 is flat in the region not above the recess 113.

[0047] The single-crystal piezoelectric layer 130 has a hole 131. The hole 131 is formed to penetrate the single-crystal piezoelectric layer 130 vertically. In this embodiment, the hole 131 is located above a main surface 111 of the base 110, but not above the recess 113.

[0048] The single-crystal piezoelectric layer 130 is composed of lithium tantalate or lithium niobate. The single-crystal piezoelectric layer 130 composed of lithium tantalate or lithium niobate has the same polarization state.

[0049] The upper electrode layer 140 is disposed above the single crystal piezoelectric layer 130. The upper electrode layer 140 is configured such that at least a portion of the upper electrode layer 140 is located above the recess 113.

[0050] In this embodiment, the upper electrode layer 140 is disposed on the upper side of a portion of the single-crystal piezoelectric layer 130. Alternatively, a close-fitting layer made of Ti or the like may be disposed between the upper electrode layer 140 and the single-crystal piezoelectric layer 130.

[0051] The lower electrode layer 150 is configured to sandwich the single-crystal piezoelectric layer 130 and oppose at least a portion of the upper electrode layer 140. At least a portion of the lower electrode layer 150 is located above the recess 113. The lower electrode layer 150 is configured to sandwich the single-crystal piezoelectric layer 130 above the recess 113 and oppose at least a portion of the upper electrode layer 140.

[0052] A portion of the lower electrode layer 150 is configured to be located below the aperture 131 formed in the single-crystal piezoelectric layer 130. In this embodiment, the lower electrode layer 150 is formed to cover the aperture 131 of the single-crystal piezoelectric layer 130 from below. Lead-out wiring connected to the lower electrode layer 150 may also be formed within the aperture 131.

[0053] Alternatively, the lower electrode layer 150 may be formed to cover the area below the hole 131 of the single-crystal piezoelectric layer 130, separated by a tight-fitting layer. Regarding the material of the tight-fitting layer, there are no particular limitations as long as it is a material with both conductivity and tight-fitting properties. For example, the tight-fitting layer may be composed of Ti, Cr, Ni, or NiCr.

[0054] The intermediate layer 160 is stacked to cover the lower electrode layer 150 from below. In this embodiment, the intermediate layer 160 is configured to be in contact with the lower surface of the lower electrode layer 150 and the portion of the lower surface of the single-crystal piezoelectric layer 130 that is not covered by the lower electrode layer 150. Furthermore, as... Figure 2 as well as Figure 3 As shown, the lower surface 161 of the intermediate layer 160 is connected to a main surface 111 of the base 110.

[0055] In this embodiment, above the recess 113, the laminated portion 120 bends into a convex shape toward the other main surface 112. For example... Figure 3 As shown, the lower surface 161 of the intermediate layer 160 located above the recess 113 is curved into a convex shape towards the other main surface 112. In the region not located above the recess 113, the lower surface 161 of the intermediate layer 160 is flat. The height difference between the region above the recess 113 and the region not located above the recess 113 in the lower surface 161 of the intermediate layer 160 is Lc.

[0056] like Figure 2 as well as Figure 3As shown, in the region not located above the recess 113, the intermediate layer 160 and the base 110 are directly connected to each other. Alternatively, the intermediate layer 160 and the base 110 may not be directly connected to each other. The intermediate layer 160 and the base 110 may also be connected to each other via a metal layer.

[0057] In this embodiment, the intermediate layer 160 is made of SiO2. The material of the intermediate layer 160 is not limited to SiO2, as long as it is an insulating material. For example, the intermediate layer 160 may also be made of an organic material that has electrical insulation and thermal insulation properties.

[0058] In this embodiment, the stacked portion 120 includes at least a single-crystal piezoelectric layer 130, an upper electrode layer 140, a lower electrode layer 150, and an intermediate layer 160 above the recess 113.

[0059] In this embodiment, when viewed from a direction orthogonal to a main surface 111, the recess 113 has a rectangular shape. Among the sides forming the rectangle, the length of the shorter side is L1 and the length of the longer side is L2. However, when viewed from a direction orthogonal to a main surface 111, the shape of the recess 113 is not limited to a rectangle; it can also be a polygon or a circle.

[0060] like Figure 1 As shown, viewed from a direction orthogonal to a main surface 111, if the number of sides of the polygon constituting the shape of the recess 113 is set to n, the radius of the circumcircle C of the imaginary regular polygon formed by the n sides whose length L1 is the same as the shortest side among the aforementioned sides is set to r, and the maximum thickness of the film portion Mb located on the recess 113 in the stacked portion 120 is set to d, then in the case of 3≤n≤7, r≤197.7dn is satisfied. -0.6698 When 8≤n or the concave part 113 is circular, r≤52.69d is satisfied.

[0061] In this embodiment, since n = 4, r ≤ 197.7 × d × 4 is satisfied. -0.6698 =78.1d.

[0062] In this embodiment, the maximum thickness d of the diaphragm portion Mb is the maximum thickness between the upper surface of the upper electrode layer 140 and the lower surface 161 of the intermediate layer 160 in a direction orthogonal to a main surface 111 in the portion above the recess 113.

[0063] The following describes the simulation results that calculated the relationship between the radius r of the circumcircle C and the maximum thickness d of the diaphragm portion Mb. As simulation analysis conditions, the base 110 is made of Si, and the single-crystal piezoelectric layer 130 is made of lithium niobate. The deformation caused by the bending of the diaphragm portion Mb was calculated using the FEM (Finite Element Method).

[0064] Figure 4 This is a graph showing the results of a simulation analysis of the deformation distribution in a regular polygonal diaphragm section. (Example) Figure 4 As shown, the deformation is greatest in the central part of the diaphragm portion Mb and smallest at the edge of the diaphragm portion Mb.

[0065] Figure 5 This is a graph showing the results of a simulation analysis of the relationship between the depth of the concave portion and the deformation of the circular diaphragm portion. Figure 5 In the figure, the deformation amount (μm) of the diaphragm portion is shown on the vertical axis, and the depth (μm) of the recess is shown on the horizontal axis. In addition, as simulation analysis conditions, the thickness of the diaphragm portion Mb is set to 500nm, the radius of the diaphragm portion Mb is set to 100μm, and the pressure inside the recess 113 is set to 0.5Pa.

[0066] like Figure 5 As shown, even if the depth of the recess 113 is changed from 5 μm to 70 μm, the deformation of the diaphragm portion Mb remains approximately constant.

[0067] Figure 6 This is a graph showing the results of a simulation analysis of the relationship between the internal pressure of the concave portion and the deformation of the circular diaphragm portion. Figure 6 In the figure, the deformation amount (μm) of the diaphragm portion is shown on the vertical axis, and the internal pressure (Pa) of the recess is shown on the horizontal axis. In addition, as simulation analysis conditions, the thickness of the diaphragm portion Mb is set to 500nm, the radius of the diaphragm portion Mb is set to 100μm, and the depth of the recess 113 is set to 70μm.

[0068] like Figure 6 As shown, even if the pressure inside the recess 113 changes from 0.01 Pa to 1000 Pa, the deformation of the diaphragm portion Mb remains approximately constant.

[0069] Figure 7 This is a graph showing the results of a simulation analysis of the relationship between the lengths of the longitudinal and transverse sides of a rectangular diaphragm and the deformation of the diaphragm. Figure 7In the diagram, the vertical axis shows the length (μm) of the longitudinal side of the rectangular diaphragm portion Mb, and the horizontal axis shows the length (μm) of the transverse side of the rectangular diaphragm portion Mb. Contour lines illustrating the deformation of the diaphragm portion Mb are also shown. Furthermore, as simulation analysis conditions, the thickness of the diaphragm portion Mb is set to 400 nm, the depth of the recess 113 is set to 50 μm, and the internal pressure of the recess 113 is set to 0.5 Pa.

[0070] like Figure 7 As shown, in the region where the deformation of the membrane portion Mb is small (below 80 nm), the deformation of the membrane portion Mb is determined by the length of the shorter side among the longitudinal and transverse sides of the rectangular membrane portion Mb. That is, the deformation of the membrane portion Mb is determined by the length of the shorter side among the sides constituting the rectangular membrane portion Mb.

[0071] Figure 8 This is a graph showing the results of a simulation analysis of the relationship between the radius r of the circumcircle C of a polygonal diaphragm portion where the deformation is 20% of the maximum thickness of the diaphragm portion, the maximum thickness d of the diaphragm portion, and the number of sides constituting the polygon. Figure 8 In the diagram, the radius r (μm) of the circumcircle C, where the deformation of the diaphragm portion is 20% of its maximum thickness, is shown on the vertical axis, and the maximum thickness d (μm) of the diaphragm portion is shown on the horizontal axis. Furthermore, as simulation analysis conditions, the depth of the recess 113 is set to 50 μm, and the internal pressure of the recess 113 is set to 0.5 Pa. Additionally, if the deformation of the diaphragm portion Mb is less than 20% of the maximum thickness d of the diaphragm portion Mb, the degradation of the piezoelectric device 100's characteristics can be suppressed.

[0072] like Figure 8 As shown, the relationship between the radius r (μm) of the circumcircle C of the diaphragm portion Mb, which is 20% of the maximum thickness of the diaphragm portion Mb, and the maximum thickness d (μm) of the diaphragm portion allows for linear approximations for the number of sides n constituting the polygon. In the approximate line La with n=3, the relationship r=102.7d is satisfied; in the approximate line Lb with n=12, the relationship r=54.1d is satisfied. Furthermore, in the case of n=100, the shape of the diaphragm portion Mb is approximately circular.

[0073] Figure 9 Based on Figure 8 The graph shown illustrates the relationship between the number of sides *n* constituting the polygon and the slope *a* of the approximate straight line. Figure 9 In the diagram, the slope 'a' of the approximate straight line is shown on the vertical axis, and the number of sides 'n' that make up the polygon is shown on the horizontal axis.

[0074] like Figure 9As shown, when 3 ≤ n ≤ 7, the relationship between the number of sides n constituting the polygon and the slope a of the approximate straight line allows for curve approximation. Specifically, when 3 ≤ n ≤ 7, in the approximate curve Lc, a = 197.7n is satisfied. -0.6698 The relationship is as follows. When 8 ≤ n, a converges to 52.69.

[0075] That is, by satisfying r ≤ 197.7dn when 3 ≤ n ≤ 7. -0.6698 This allows the deformation of the diaphragm portion Mb to be less than 20% of the maximum thickness d of the diaphragm portion Mb, thereby suppressing the degradation of the characteristics of the piezoelectric device 100.

[0076] By satisfying r ≤ 52.69d when 8 ≤ n, the deformation of the diaphragm portion Mb can be kept below 20% of the maximum thickness d of the diaphragm portion Mb, thereby suppressing the degradation of the characteristics of the piezoelectric device 100. Even when the diaphragm portion Mb is circular, by satisfying r ≤ 52.69d, the deformation of the diaphragm portion Mb can still be kept below 20% of the maximum thickness d of the diaphragm portion Mb, thereby suppressing the degradation of the characteristics of the piezoelectric device 100.

[0077] The manufacturing method of the piezoelectric device 100 according to Embodiment 1 of the present invention will be described below.

[0078] Figure 10 This is a cross-sectional view showing a state in which a lower electrode layer is provided on the lower surface of a single-crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. The thickness of the single-crystal piezoelectric layer 130 during formation is thicker than the thickness of the single-crystal piezoelectric layer 130 ultimately included in the piezoelectric device 100 according to this embodiment.

[0079] like Figure 10 As shown, a lower electrode layer 150 is formed on the lower surface of the single crystal piezoelectric layer 130 by means of peeling, plating or etching.

[0080] Figure 11 This is a cross-sectional view showing a state in which an intermediate layer is provided on the lower surface of both the lower electrode layer and the single-crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 11 As shown, an intermediate layer 160 is formed on the lower surface of the lower electrode layer 150 and the single crystal piezoelectric layer 130 by means of CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition).

[0081] Figure 12This is a cross-sectional view showing the state in which the lower surface of the intermediate layer is flattened during the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 12 As shown, the lower surface of the intermediate layer 160 is flattened by chemical mechanical polishing (CMP).

[0082] Figure 13 This is a cross-sectional view showing the state before the recess is formed in the base during the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 14 This is a cross-sectional view showing the state in which a recess is formed in the base during the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0083] like Figure 13 as well as Figure 14 As shown, a recess 113 is formed on the base 110 from one of the main surfaces 111 sides of the base 110 by deep reactive ion etching (DRIE) or the like.

[0084] Figure 15 This illustrates that in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention, the base is made with... Figure 12 A cross-sectional view showing the joint state of multiple layers. Figure 16 This is a cross-sectional view showing the state after the base is joined to the lower surface of the intermediate layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0085] like Figure 15 as well as Figure 16 As shown, a main surface 111 of the base 110 is bonded to the lower surface 161 of the intermediate layer 160 through surface activation bonding or atomic diffusion bonding. As a result, the interior of the recess 113 becomes a sealed space.

[0086] In this embodiment, to prevent foreign matter from intruding into the interior of the recess 113, the intermediate layer 160 and the base 110 are joined under vacuum pressure. In this case, the vacuum pressure can be any of low vacuum, medium vacuum, high vacuum, and ultra-high vacuum. Because the intermediate layer 160 and the base 110 are joined in this way, the pressure inside the recess 113 becomes negative. Furthermore, because the pressure inside the recess 113 becomes negative, the lower surface 161 of the intermediate layer 160 bends into a convex shape towards the other main surface 112 above the recess 113.

[0087] Furthermore, the atmosphere at which the intermediate layer 160 and the base 110 are joined is not limited to vacuum pressure. The intermediate layer 160 can also be joined to the base 110 at atmospheric pressure, or at a pressure higher than atmospheric pressure. By joining the intermediate layer 160 and the base 110 under these atmospheres, the lower surface 161 of the intermediate layer 160 can be a flat surface, or it can be bent into a convex shape to the side opposite to the other main surface 112.

[0088] Figure 17 This is a cross-sectional view showing the state after the upper surface of the single-crystal piezoelectric layer has been removed in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 17 As shown, the upper surface of the single-crystal piezoelectric layer 130 is removed by CMP or the like to achieve a desired thickness. In this case, the thickness of the single-crystal piezoelectric layer 130 is adjusted to achieve a desired amount of stretching or shrinking due to the application of voltage. As the thickness of the single-crystal piezoelectric layer 130 decreases, the lower surface 161 of the intermediate layer 160 bends more significantly.

[0089] Alternatively, a release layer can be formed on the upper surface of the single-crystal piezoelectric layer 130 by ion implantation. In this case, the release layer is removed before the upper surface of the single-crystal piezoelectric layer 130 is removed by CMP or the like, thereby making it easier to adjust the thickness of the single-crystal piezoelectric layer 130.

[0090] Figure 18 This is a cross-sectional view showing a state in which an upper electrode layer is provided on the upper surface of a single-crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 18 As shown, an upper electrode layer 140 is formed on a portion of the upper surface of the single-crystal piezoelectric layer 130 by means of peeling, plating, or etching. In this manner, the stacked portion 120 is stacked on one main surface 111 side of the base 110. Furthermore, because the intermediate layer 160 and the base 110 are bonded under vacuum, the stacked portion 120 is bent into a convex shape above the recess 113 towards the other main surface 112 side.

[0091] Finally, holes 131 are formed on a portion of the upper surface of the single-crystal piezoelectric layer 130 by means of peeling, plating or etching.

[0092] Through the above-described processes, it is possible to manufacture products such as... Figure 2 The piezoelectric device 100 shown is related to Embodiment 1 of the present invention.

[0093] As described above, in the piezoelectric device 100 according to this embodiment, when viewed from a direction orthogonal to a main surface 111, the shape of the recess 113 is polygonal or circular. When viewed from a direction orthogonal to a main surface 111, if the number of multiple sides constituting the polygon that forms the shape of the recess 113 is set to n, the radius of the circumcircle C of the imaginary regular polygon formed by the n sides whose length L1 is the same as the shortest side among the multiple sides is set to r, and the maximum thickness of the diaphragm portion Mb located on the recess 113 in the stacked portion 120 is set to d, then when 3≤n≤7, r≤197.7dn is satisfied. -0.6698 When 8≤n or the concave part 113 is circular, r≤52.69d is satisfied.

[0094] Therefore, the deformation of the diaphragm portion Mb can be made to be less than 20% of the maximum thickness d of the diaphragm portion Mb, thereby suppressing the degradation of the characteristics of the piezoelectric device 100. That is, the degradation of the characteristics of the piezoelectric device 100 caused by the bending of the single crystal piezoelectric layer 130 or the unevenness of the thickness of the single crystal piezoelectric layer 130 can be suppressed.

[0095] In the piezoelectric device 100 of this embodiment, when viewed from a direction orthogonal to a main surface 111, the shape of the recess 113 is rectangular. Therefore, by simply adjusting the length L1 of the shorter side of the rectangle, the degradation of the characteristics of the piezoelectric device 100 can be suppressed.

[0096] In the piezoelectric device 100 of this embodiment, even if the pressure inside the recess 113 is negative, causing the single crystal piezoelectric layer 130 to bend into a convex shape towards the base 110, the diaphragm portion Mb satisfies the relationship between the radius r of the circumscribed circle C and the maximum thickness d of the diaphragm portion Mb. As a result, the deformation of the diaphragm portion Mb can be less than 20% of the maximum thickness d of the diaphragm portion Mb, thereby suppressing the decrease in the characteristics of the piezoelectric device 100.

[0097] Furthermore, when the pressure inside the recess 113 is positive, the bending direction of the diaphragm portion Mb becomes opposite. However, by satisfying the relationship between the radius r of the circumscribed circle C and the maximum thickness d of the diaphragm portion Mb, the deformation of the diaphragm portion Mb can be kept to less than 20% of the maximum thickness d of the diaphragm portion Mb, thereby suppressing the decrease in the characteristics of the piezoelectric device 100.

[0098] Of course, even if the pressure inside the recess 113 is the same as the pressure outside the piezoelectric device 100, by satisfying the relationship between the radius r of the circumscribed circle C and the maximum thickness d of the diaphragm portion Mb, the deformation of the diaphragm portion Mb can be kept to less than 20% of the maximum thickness d of the diaphragm portion Mb, thereby suppressing the decline in the characteristics of the piezoelectric device 100.

[0099] In the piezoelectric device 100 of this embodiment, the intermediate layer 160 is stacked to cover the lower electrode layer 150 from below. As a result, the lower surface of the lower electrode layer 150 is not exposed to the outside and the recess 113 is not exposed, thus suppressing the deterioration of the lower electrode layer 150.

[0100] In the piezoelectric device 100 of this embodiment, the lower surface 161 of the intermediate layer 160 is flat in the region not located above the recess 113. As a result, the intermediate layer 160 and the base 110 can be closely connected, suppressing the generation of interlayer delamination between the intermediate layer 160 and the base 110.

[0101] In the piezoelectric device 100 of this embodiment, the interior of the recess 113 is sealed, thereby preventing foreign matter from entering the interior of the recess 113.

[0102] Hereinafter, a modified example of the piezoelectric device 100 according to Embodiment 1 of the present invention will be described.

[0103] Figure 19 This is a cross-sectional view showing the structure of a piezoelectric device according to a first modification of Embodiment 1 of the present invention. Figure 19 In, with Figure 2 The same sectional view is illustrated. (See figure) Figure 19 As shown, in the piezoelectric device 100a according to the first modification of Embodiment 1 of the present invention, a recess 163 communicating with a recess 113 is formed in the intermediate layer 160. The bottom surface of the recess 163 constitutes a part of the lower surface 161 of the intermediate layer 160.

[0104] In the first modified example, the maximum thickness d of the diaphragm portion Mb is the maximum thickness between the upper surface of the upper electrode layer 140 and the bottom surface of the recess 163 in a direction orthogonal to a main surface 111 in the portion above the recess 113.

[0105] Figure 20 This is a cross-sectional view showing the structure of a piezoelectric device according to a second variation of Embodiment 1 of the present invention. Figure 20 In, with Figure 2 The same sectional view is illustrated. (See figure) Figure 20 As shown, in the piezoelectric device 100b according to the second modification of Embodiment 1 of the present invention, the intermediate layer 160 is not provided. The lower electrode layer 150 is disposed in the recess 113.

[0106] In the second variation, the maximum thickness d of the diaphragm portion Mb is the maximum thickness between the upper surface of the upper electrode layer 140 and the lower surface 151 of the lower electrode layer 150 in a direction orthogonal to a main surface 111 in the portion above the recess 113.

[0107] Figure 21 This is a cross-sectional view showing the structure of a piezoelectric device according to a third variation of Embodiment 1 of the present invention. Figure 21 In, with Figure 2 The same sectional view is illustrated. (See figure) Figure 21 As shown, in the piezoelectric device 100c according to the third variation of Embodiment 1 of the present invention, the intermediate layer 160 and the lower electrode layer 150 are not provided. The upper electrode layer 140c has a pair of electrode layers that are spaced apart from each other and a voltage is applied between them. A recess 133 communicating with the recess 113 is formed in the single crystal piezoelectric layer 130. The bottom surface of the recess 133 constitutes a part of the lower surface 132 of the single crystal piezoelectric layer 130.

[0108] In the third variation, the maximum thickness d of the diaphragm portion Mb is the maximum thickness between the upper surface of the upper electrode layer 140c and the bottom surface of the recess 133 in a direction orthogonal to a main surface 111 in the portion above the recess 113.

[0109] Figure 22 This is a cross-sectional view showing the structure of a piezoelectric device according to the fourth modification of Embodiment 1 of the present invention. Figure 22 In, with Figure 2 The same sectional view is illustrated. (See figure) Figure 22 As shown, in the piezoelectric device 100d according to the fourth variation of Embodiment 1 of the present invention, a SiO2 layer 114 and a Si layer 115 are provided between the base 110 and the intermediate layer 160. The base 110, the SiO2 layer 114, and the Si layer 115 are so-called SOI (Silicon on Insulator) substrates.

[0110] In the fourth variation, the maximum thickness d of the diaphragm portion Mb is the maximum thickness between the upper surface of the upper electrode layer 140 and the lower surface 114b of the SiO2 layer 114 in the portion above the recess 113, in a direction orthogonal to a main surface 111.

[0111] (Implementation Method 2)

[0112] Hereinafter, the piezoelectric device according to Embodiment 2 of the present invention will be described with reference to the figures. The main difference between the piezoelectric device according to Embodiment 2 of the present invention and the piezoelectric device 100 according to Embodiment 1 of the present invention is that a hole is provided in the base, which extends from the bottom of the recess to another main surface of the base. Therefore, the same structure as the piezoelectric device 100 according to Embodiment 1 of the present invention will not be described again.

[0113] Figure 23 This is a cross-sectional view showing the structure of the piezoelectric device according to Embodiment 2 of the present invention. Figure 23In, with Figure 2 The same sectional view is illustrated. (See figure) Figure 23 As shown, in the piezoelectric device 200 according to Embodiment 2 of the present invention, a hole 170 is provided in the base 110, extending from the bottom of the recess 113 to another main surface 112. Viewed from a direction orthogonal to one main surface 111, the area of ​​the hole 170 is smaller than the area of ​​the diaphragm portion Mb. Viewed from a direction orthogonal to one main surface 111, the diameter D of the hole 170 is 140 μm or less. The hole 170 can be formed using a DRIE (Diagram of a piezoelectric device) or similar method.

[0114] In the piezoelectric device 200 according to Embodiment 2 of the present invention, a hole 170 is provided in the base 110, extending from the bottom of the recess 113 to another main surface 112. As a result, the pressure inside the recess 113 can be made equal to the pressure outside the piezoelectric device 200, and therefore, compared with the case where the pressure inside the recess 113 is negative, the amount of deformation caused by the bending of the diaphragm portion Mb can be reduced.

[0115] In the piezoelectric device 200 according to Embodiment 2 of the present invention, when viewed from a direction orthogonal to a main surface 111, the area of ​​the hole 170 is smaller than the area of ​​the diaphragm portion Mb. Therefore, it is possible to suppress the significant decrease in the rigidity of the base 110 due to the provision of the hole 170.

[0116] In the piezoelectric device 200 according to Embodiment 2 of the present invention, when viewed from a direction orthogonal to a main surface 111, the diameter D of the hole 170 is 140 μm or less. This prevents water or foreign matter from entering the recess 113 from the outside of the piezoelectric device 200 through the hole 170.

[0117] In the above description of the embodiments, the combinable structures can also be combined with each other.

[0118] The embodiments disclosed herein should be considered illustrative rather than restrictive in all respects. The scope of the invention is set forth not by the foregoing description but by the claims, and is intended to include all modifications equivalent to and within the scope of the claims.

[0119] Explanation of reference numerals in the attached figures

[0120] 100, 100a, 100b, 100c, 100d, 200: Piezoelectric device; 110: Base; 111, 112: Main surface; 113, 133, 163: Recess; 114: SiO2 layer; 115: Si layer; 114b, 132, 151, 161: Lower surface; 120: Stacked portion; 130: Single crystal piezoelectric layer; 131: Hole portion; 140, 140c: Upper electrode layer; 150: Lower electrode layer; 160: Intermediate layer; 170: Hole; C: Circumscribed circle; D: Diameter; Mb: Film portion.

Claims

1. A piezoelectric device comprising: The base includes a main surface and another main surface located on the opposite side of the main surface, and has a recess formed on the main surface; and The laminated portion is laminated on the main surface side of the base such that it covers the recess from above. The stacked portion includes, at least above the recess, a single-crystal piezoelectric layer and a pair of electrode layers to which a voltage is applied. The single-crystal piezoelectric layer is bent into a convex shape towards the base or into a convex shape opposite to the base. Viewed from a direction orthogonal to the main surface, the concave portion has a polygonal or circular shape. If we define the number of sides constituting the polygon as n, the radius of the circumcircle of the imaginary regular polygon formed by the n sides having the same length as the shortest side among the multiple sides as r, and the maximum thickness of the membrane portion located on the concave portion in the stacked portion as d, then When 3 ≤ n ≤ 7, r ≤ 197.7dn -0.6698 , When 8 ≤ n or the shape of the concave portion is circular, r ≤ 52.69d is satisfied.

2. The piezoelectric device according to claim 1, wherein, The recess has a rectangular shape.

3. The piezoelectric device according to claim 1 or claim 2, wherein, The pressure inside the recess is negative.

4. The piezoelectric device according to claim 1 or claim 2, wherein, The pressure inside the recess is positive pressure.

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