Piezoelectric elements

Abstract

In the piezoelectric element (100), the second electrode layer (130) is located on the second surface (112) side of the single crystal piezoelectric layer (110). A hole portion (131) facing the through hole (113) is formed in the second electrode layer (130). The second electrode layer (130) is composed of Pt, Ti, Al, Cu, Au, Ag, Mg or an alloy containing at least one of these metals as a main component. The third electrode layer (140) is arranged on the side of the second electrode layer (130) opposite to the single crystal piezoelectric layer (110). The third electrode layer (140) is provided to have at least a portion which is spaced apart from the edge portion (132) of the hole portion (131) and is located outside the edge portion (132) of the hole portion (131) when viewed from a direction perpendicular to the second surface (112). The third electrode layer (140) is composed of Ni or an alloy containing Ni as a main component.

Description

Technical Field

[0001] The present invention relates to piezoelectric elements. Background Art

[0002] As a document that discloses the structure of a piezoelectric element, there is Japanese Patent Publication No. 2008-244725 (Patent Document 1). The piezoelectric element described in Patent Document 1 is a piezoelectric thin film device including a single or multiple piezoelectric thin film resonators. The piezoelectric thin film device includes a piezoelectric thin film, an electrode, and a support. The electrodes are respectively formed on the two main surfaces of the piezoelectric thin film, and are opposed to each other in the opposing area with the piezoelectric thin film separated therefrom. The lower surface electrode is formed on the lower surface of the piezoelectric thin film, and the upper surface electrode is formed on the upper surface of the piezoelectric thin film. The support supports the piezoelectric thin film. A via hole is formed in the piezoelectric thin film that passes through the lower surface and the upper surface of the piezoelectric thin film. In the manufacturing method of the piezoelectric element, the piezoelectric thin film is etched to form a via hole that passes through the upper surface and the lower surface of the piezoelectric thin film to expose the lower surface electrode.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-244725 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In the conventional piezoelectric element, when a through hole is formed by etching from the first surface side to the second surface side of the single crystal piezoelectric layer, the etching may not be stopped, and a through hole may be formed in the electrode layer located on the second surface side in a continuous manner with the through hole. In addition, if the etching is not stopped after the through hole is formed in the electrode layer, an undesirable hole may be formed in a member located on the side of the electrode layer opposite to the single crystal piezoelectric layer side in a continuous manner with the through hole in the electrode layer by etching.

[0008] The present invention has been made in view of the above-mentioned problems, and its object is to provide a piezoelectric element which can suppress the formation of holes in a member located on the side of an electrode layer opposite to the side of a single crystal piezoelectric layer when a through hole is formed in a single crystal piezoelectric layer.

[0009] Means for solving problems

[0010] The piezoelectric element of the first aspect of the present invention comprises a single crystal piezoelectric layer, a first electrode layer, a second electrode layer and a third electrode layer. The single crystal piezoelectric layer has a first surface, a second surface and a through hole. The second surface is located on the opposite side of the first surface. The through hole extends from the first surface to the second surface. The first electrode layer is arranged on the first surface side of the single crystal piezoelectric layer. The second electrode layer is located on the second surface side of the single crystal piezoelectric layer. At least a part of the second electrode layer is opposite to the first electrode layer across the single crystal piezoelectric layer. A hole portion facing the through hole is formed in the second electrode layer. The second electrode layer is composed of Pt, Ti, Al, Cu, Au, Ag, Mg or an alloy containing at least one of these metals as a main component. The third electrode layer is arranged on the side of the second electrode layer opposite to the single crystal piezoelectric layer side. The third electrode layer is arranged to have at least a portion that is located at a position outside the edge of the hole portion at a distance from the edge of the hole portion when viewed from a direction perpendicular to the second surface. The third electrode layer is composed of Ni or an alloy containing Ni as a main component.

[0011] The piezoelectric element of the second aspect of the present invention comprises a single crystal piezoelectric layer, a first electrode layer, a second electrode layer and a third electrode layer. The single crystal piezoelectric layer has a first surface, a second surface and a through hole. The second surface is located on the opposite side of the first surface. The through hole extends from the first surface to the second surface. The first electrode layer is arranged on the first surface side of the single crystal piezoelectric layer. The second electrode layer is located on the second surface side of the single crystal piezoelectric layer. At least a portion of the second electrode layer is opposite to the first electrode layer across the single crystal piezoelectric layer. A hole portion facing the through hole is formed in the second electrode layer. The third electrode layer is arranged on the side of the second electrode layer opposite to the single crystal piezoelectric layer side. The third electrode layer is arranged to have at least a portion which is spaced apart from the edge of the hole portion and is located outside the edge of the hole portion when viewed from a direction perpendicular to the second surface. The material constituting the third electrode layer is made of CF compared to the material constituting the second electrode layer. 4 The etching rate of the gas is low.

[0012] Effects of the Invention

[0013] According to the present invention, when forming a through hole in the single crystal piezoelectric layer, it is possible to suppress the formation of a hole in a member located on the side of the electrode layer opposite to the single crystal piezoelectric layer side. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a top view of the piezoelectric element according to the first embodiment of the present invention.

[0015] Figure 2 Observe from the direction of the arrow on line II-II Figure 1 Cross-sectional view of a piezoelectric element.

[0016] Figure 3This is a cross-sectional view showing a through hole and the periphery of the through hole in the piezoelectric element according to the first embodiment of the present invention.

[0017] Figure 4 This is a cross-sectional view showing a through hole and the periphery of the through hole in a piezoelectric element according to a first modified example of the first embodiment of the present invention.

[0018] Figure 5 This is a cross-sectional view showing a through hole and the periphery of the through hole in a piezoelectric element according to a second modified example of the first embodiment of the present invention.

[0019] Figure 6 This is a cross-sectional view showing the periphery of a through hole of a piezoelectric element according to a third modified example of the first embodiment of the present invention.

[0020] Figure 7 This is a cross-sectional view showing a state where a second electrode layer and a third electrode layer are provided on a piezoelectric single crystal substrate in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention.

[0021] Figure 8 This is a cross-sectional view showing a state in which an intermediate layer is provided on the second principal surface side of a piezoelectric single crystal substrate in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention.

[0022] Fig. 9 This is a cross-sectional view showing a state where the intermediate layer is polished in the method for manufacturing the piezoelectric element according to the first embodiment of the present invention.

[0023] Fig.10 This is a cross-sectional view showing a state in which a laminated substrate including a base portion is prepared in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention.

[0024] Fig.11 This is a cross-sectional view showing a state where a laminated substrate is bonded to an intermediate layer in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention.

[0025] Fig.12 This is a cross-sectional view showing a state in which a piezoelectric single crystal substrate is cut to form a piezoelectric layer in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention.

[0026] Fig.13 This is a cross-sectional view showing a state where a first electrode layer is provided in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention.

[0027] Fig.14 This is a cross-sectional view showing a state in which a through hole is provided in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention.

[0028] Fig.15 It is a diagram showing a through hole and the periphery of the through hole in a piezoelectric element of a comparative example.

[0029] Fig.16 It is a cross-sectional view of a piezoelectric element according to Embodiment 2 of the present invention.

[0030] Fig.17 This is a cross-sectional view showing a state in which a single-layer substrate including a base portion is prepared in a method for manufacturing a piezoelectric element according to a second embodiment of the present invention.

[0031] Fig.18 This is a cross-sectional view showing a state where a single-layer substrate is bonded to an intermediate layer in a method for manufacturing a piezoelectric element according to a second embodiment of the present invention.

[0032] Fig.19 This is a cross-sectional view showing a state in which a piezoelectric single crystal substrate is cut to form a piezoelectric layer in a method for manufacturing a piezoelectric element according to a second embodiment of the present invention.

[0033] Fig. 20 This is a cross-sectional view showing a state where a first electrode layer is provided in a method for manufacturing a piezoelectric element according to a second embodiment of the present invention.

[0034] Fig.21 This is a cross-sectional view showing a state in which a through hole is provided in a method for manufacturing a piezoelectric element according to a second embodiment of the present invention.

[0035] Fig. 22 It is a cross-sectional view of a piezoelectric element according to Embodiment 3 of the present invention.

[0036] Fig.23 It is a cross-sectional view of a piezoelectric element according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0037] Hereinafter, a piezoelectric element according to each embodiment of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same or corresponding parts in the drawings are denoted by the same reference numerals, and their description will not be repeated.

[0038] (Implementation Method 1)

[0039] Figure 1 It is a top view of the piezoelectric element according to the first embodiment of the present invention. Figure 2 Observe from the direction of the arrow on line II-II Figure 1 Cross-sectional view of a piezoelectric element.

[0040] like Figure 1 and Figure 2As shown, the piezoelectric element 100 according to the first embodiment of the present invention includes a single crystal piezoelectric layer 110, a first electrode layer 120, a second electrode layer 130, a third electrode layer 140, and a base 150. In this embodiment, the first electrode layer 120, the second electrode layer 130, and the third electrode layer 140 may be epitaxial growth films.

[0041] like Figure 2 As shown, the single crystal piezoelectric layer 110 has a first surface 111 , a second surface 112 , and a through hole 113 . The second surface 112 is located on the opposite side of the first surface 111 .

[0042] Figure 3 1 is a cross-sectional view showing a through hole and the periphery of the through hole of the piezoelectric element according to Embodiment 1 of the present invention. Figure 3 As shown, the through hole 113 penetrates from the first surface 111 to the second surface 112. In addition, an inner cross section 114 is formed in the single crystal piezoelectric layer 110, and the inner cross section 114 faces the through hole 113.

[0043] In this embodiment, the single crystal piezoelectric layer 110 contains a lithium compound. Specifically, the lithium compound is lithium niobate (LiNbO 3 ) or lithium tantalate (LiTaO 3 ).

[0044] like Figure 1 and Figure 2 As shown, the first electrode layer 120 is provided on the first surface 111 side of the single crystal piezoelectric layer 110. The first electrode layer 120 is made of Al or Pt, etc. In addition, an adhesion layer of Ti or the like may be provided between the first electrode layer 120 and the single crystal piezoelectric layer 110.

[0045] The second electrode layer 130 is located on the second surface 112 side of the single crystal piezoelectric layer 110. At least a portion of the second electrode layer 130 is opposed to the first electrode layer 120 via the single crystal piezoelectric layer 110. Therefore, from the viewpoint of piezoelectric efficiency in the single crystal piezoelectric layer 110, the second electrode layer 130 is preferably composed of a material with a lower resistivity than the material constituting the third electrode layer 140.

[0046] like Figure 3 As shown, a hole 131 facing the through hole 113 is formed in the second electrode layer 130. In this embodiment, the hole 131 penetrates the second electrode layer 130 in a direction perpendicular to the second surface 112. The hole 131 may not penetrate the second electrode layer 130.

[0047] The second electrode layer 130 is composed of Pt, Ti, Al, Cu, Au, Ag, Mg, or an alloy containing at least one of these metals as a main component. It should be noted that the main component of a component refers to a component whose atomic concentration in the component is greater than 50% relative to all components. In this embodiment, the second electrode layer 130 contains Pt as a main component. In addition, a close-fitting layer such as Ti or NiCr may also be located between the second electrode layer 130 and the single crystal piezoelectric layer 110.

[0048] like Figure 1 and Figure 2 As shown, the third electrode layer 140 is arranged on the side of the second electrode layer 130 opposite to the single crystal piezoelectric layer 110 side.

[0049] like Figure 3 As shown, the third electrode layer 140 is provided so as to have at least a portion which is spaced apart from the edge 132 of the hole 131 and is located at a position outside the edge 132 of the hole 131 when viewed from a direction perpendicular to the second surface 112. Specifically, the third electrode layer 140 is provided so as to have an outer peripheral edge 142 which surrounds the edge 132 of the hole 131 and is spaced apart from the edge 132 of the hole 131 when viewed from a direction perpendicular to the second surface 112. In the present embodiment, the minimum dimension L of the above-mentioned interval between the edge 132 and the outer peripheral edge 142 is larger than the dimension of the average thickness of the second electrode layer 130. For example, the minimum dimension L of the above-mentioned interval is 10 times or more the dimension of the average thickness of the second electrode layer 130.

[0050] like Figure 2 and Figure 3 As shown in FIG. 1 , when viewed from a direction perpendicular to the second surface 112, the outer periphery 142 of the third electrode layer 140 is located at an inner side than the outer periphery of the second electrode layer 130. In this embodiment, the average thickness of the second electrode layer 130 is thinner than the average thickness of the third electrode layer 140. It should be noted that the average thickness of the second electrode layer 130 and the third electrode layer 140 refers to the following values: Figure 3 When observing the piezoelectric element 100 of this embodiment in the cross-section as shown, the thickness of each of the second electrode layer 130 and the third electrode layer 140 is measured at five locations randomly selected from the portion where the second electrode layer 130 and the third electrode layer 140 contact each other, and the thickness of these five locations is averaged to obtain a value.

[0051] The third electrode layer 140 is made of Ni, W, Mo, Ta, or an alloy containing Ni as a main component, such as NiCr. In this embodiment, the third electrode layer 140 is made of Ni or an alloy containing Ni as a main component. In addition, a close contact layer such as Ti or NiCr may also be located between the second electrode layer 130 and the third electrode layer 140.

[0052] The material constituting the third electrode layer 140 is made of CF. 4 The etching rate of the gas is low. The material constituting the third electrode layer 140 is made of CF compared to the material constituting the single crystal piezoelectric layer 110. 4 The etching rate of the gas is low.

[0053] Here, in the piezoelectric element 100 according to the first embodiment of the present invention, a recessed portion may be further formed in the third electrode layer 140 .

[0054] Figure 4 1 is a cross-sectional view showing a through hole and the periphery of the through hole of a piezoelectric element according to a first modified example of the first embodiment of the present invention. Figure 4 As shown, in the first variation of the first embodiment of the present invention, the third electrode layer 140 is provided with a recess 141a facing the hole 131 of the second electrode layer 130. In this variation, the recess 141a is formed along the inner side surface 133 of the second electrode layer 130, and is located at a position closer to the inside than the edge 132 of the hole 131 when viewed from a direction perpendicular to the second surface 112.

[0055] Figure 5 1 is a cross-sectional view showing a through hole and the periphery of the through hole of a piezoelectric element according to a second modified example of the first embodiment of the present invention. Figure 5 As shown, in the second variation of the first embodiment of the present invention, the third electrode layer 140 is provided with a recess 141b facing the hole 131 of the second electrode layer 130 so as to correspond to the entirety of the hole 131. In this variation, the recess 141b is formed so that the inner side surface 133 of the hole 131 and the inner surface of the recess 141b are continuous with each other.

[0056] In addition, the piezoelectric element 100 according to the first embodiment of the present invention may be further provided with a connection electrode. Figure 6 1 is a cross-sectional view showing a through hole and the periphery of the through hole of a piezoelectric element according to a third modified example of the first embodiment of the present invention. Figure 6 As shown, in the third variation of the first embodiment of the present invention, Figure 5 The through hole 113 in the second modified example of the first embodiment of the present invention shown in FIG. 1 is provided with a connection electrode 180 c .

[0057] like Figure 6As shown, in this modification, the connection electrode 180c is continuously provided from the inner side surface 133 of the hole portion 131 constituting the second electrode layer 130 to the portion of the third electrode layer 140 facing the hole portion 131. In this modification, the connection electrode 180c is provided over the entire inner surface of the recess 141b. In addition, the connection electrode 180c is continuously provided from the inner side surface 133 of the hole portion 131 constituting the second electrode layer 130 to the inner cross section 114 of the single crystal piezoelectric layer 110.

[0058] like Figure 2 As shown in FIG. 1 , the piezoelectric element 100 according to the first embodiment of the present invention further includes an intermediate layer 160 and a support layer 170. In this embodiment, the intermediate layer 160 is provided on the surface of the third electrode layer 140 opposite to the second electrode layer 130, the portion of the second electrode layer 130 opposite to the single crystal piezoelectric layer 110 that is not covered by the third electrode layer 140, and the portion of the second surface 112 of the single crystal piezoelectric layer 110 that is not covered by the second electrode layer 130. The intermediate layer 160 is made of, for example, SiO 2 The layers composed of etc.

[0059] In this embodiment, the support layer 170 is provided on the surface of the intermediate layer 160 opposite to the single crystal piezoelectric layer 110. The support layer is made of Si, for example. A bonding layer made of metal may be further provided between the intermediate layer 160 and the support layer 170.

[0060] like Figure 2 As shown, in the piezoelectric element 100 according to the first embodiment of the present invention, the stack 101 includes at least a first electrode layer 120, a single crystal piezoelectric layer 110, a second electrode layer 130, and a third electrode layer 140. In this embodiment, the stack 101 further includes an intermediate layer 160 and a support layer 170. The base 150 supports the stack 101.

[0061] The base portion 150 is located on the side opposite to the first electrode layer 120 side of the stacked body 101. The base portion 150 is formed in a ring shape so as to be along the periphery of the stacked body 101 when viewed from the stacking direction of the stacked body 101.

[0062] like Figure 2 As shown, in this embodiment, the base 150 includes a silicon oxide layer 151 located on the stacked body 101 side and a single crystal silicon layer 152 located on the side opposite to the stacked body 101 side. In this embodiment, the silicon oxide layer 151 is in contact with the support layer 170.

[0063] like Figure 1 and Figure 2As shown, in the piezoelectric element 100 of this embodiment, the opening 102 is located inside the base 150 when viewed from the stacking direction. In addition, in this embodiment, a membrane portion 103 is formed on the stacked body 101. The membrane portion 103 overlaps with the opening 102 when viewed from the stacking direction, but does not overlap with the base 150.

[0064] The piezoelectric element 100 of this embodiment is driven by applying a voltage between the first electrode layer 120 and the second electrode layer 130, so that the single crystal piezoelectric layer 110 located between the first electrode layer 120 and the second electrode layer 130 is deformed. As a result, the membrane portion 103 can bend and vibrate greatly in the stacking direction of the stacked body 101. The piezoelectric element 100 of this embodiment can be used as an ultrasonic transducer, for example.

[0065] Hereinafter, a method for manufacturing a piezoelectric element according to the first embodiment of the present invention will be described. Figures 7 to 14 The cross-sectional view shown is through the Figure 2 The same cross-section but not the same figure.

[0066] Figure 7 1 is a cross-sectional view showing a state where a second electrode layer and a third electrode layer are provided on a piezoelectric single crystal substrate in a method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. Figure 7 As shown, the piezoelectric single crystal substrate 110S has a first main surface 111S and a second main surface 112S located on the opposite side of the first main surface 111S. The second electrode layer 130 is provided on the second main surface 112S. The third electrode layer 140 is provided on the surface of the second electrode layer 130 on the opposite side of the piezoelectric single crystal substrate 110S. The second electrode layer 130 and the third electrode layer 140 are respectively provided by patterning using a photolithography method or an evaporation lift-off method or the like.

[0067] Figure 8 1 is a cross-sectional view showing a state where an intermediate layer is provided on the second main surface side of a piezoelectric single crystal substrate in a method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. Figure 8 As shown, the intermediate layer 160 is provided on each surface of the piezoelectric single crystal substrate 110S, the second electrode layer 130 and the third electrode layer 140 by a CVD (Chemical Vapor Deposition) method or a PVD (Physical Vapor Deposition) method.

[0068] Fig. 9 1 is a cross-sectional view showing a state where the intermediate layer is ground in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention. Fig. 9As shown, the surface of the intermediate layer 160 on the side opposite to the piezoelectric single crystal substrate 110S side is flattened by chemical mechanical polishing (CMP) or the like.

[0069] Fig.10 1 is a cross-sectional view showing a state in which a laminated substrate including a base is prepared in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. Fig.10 As shown in FIG. 1 , a laminated substrate 104S including a support layer 170 and a base 150 is prepared. In this embodiment, the laminated substrate 104S is a SOI (Silicon o n Insulator, Silicon on Insulator) substrate.

[0070] Fig.11 1 is a cross-sectional view showing a state where a laminated substrate is bonded to an intermediate layer in a method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. Fig.11 As shown, the intermediate layer 160 is bonded to the support layer 170 side of the laminated substrate 104S.

[0071] Fig.12 1 is a cross-sectional view showing a state in which a piezoelectric single crystal substrate is cut to form a piezoelectric layer in the method for manufacturing a piezoelectric element according to the first embodiment of the present invention. Fig.11 and Fig.12 As shown, for example, the first principal surface 111S side portion of the piezoelectric single crystal substrate 110S is ground and thinned by a grinder, and then the opposite side portion is polished and flattened by CMP or the like, thereby forming the single crystal piezoelectric layer 110.

[0072] It should be noted that a peeling layer may be formed by pre-implanting ions on the first principal surface 111S side of the piezoelectric single crystal substrate 110S. By pre-forming the peeling layer before bonding the piezoelectric single crystal substrate 110S to the stacked substrate 104S, the peeling layer can be peeled off after bonding to form the single crystal piezoelectric layer 110. After peeling off the peeling layer, the piezoelectric single crystal substrate 110S may be further polished by CMP or the like to form the single crystal piezoelectric layer 110.

[0073] Fig.13 1 is a cross-sectional view showing a state where a first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. Fig.13 As shown, the first electrode layer 120 is stacked on the first surface 111 side of the single crystal piezoelectric layer 110 so that at least a portion of the first electrode layer 120 faces the second electrode layer 130 via the single crystal piezoelectric layer 110. The first electrode layer 120 is provided by patterning using photolithography or vapor deposition lift-off.

[0074] Fig.14 1 is a cross-sectional view showing a state in which a through hole is provided in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. Fig.14 As shown, in this embodiment, by using CF 4 Reactive ion etching (RIE) is performed by gas to form through holes 113 in the single crystal piezoelectric layer 110 and holes 131 in the second electrode layer 130. In the second to fourth variants of the piezoelectric element of the first embodiment of the present invention, RIE is continued to be performed on the third electrode layer 140 after the holes 131 are formed, thereby further forming Figures 4 to 6 Recesses 141a, 141b are shown.

[0075] Finally, if Figure 2 As shown, the single crystal silicon layer 152 and the silicon oxide layer 151 are cut from the side of the base 150 opposite to the single crystal piezoelectric layer 110 by deep reactive ion etching (Deep RIE), thereby forming the opening 102. Figure 6 The connecting electrode 180c is arranged as shown.

[0076] Through the above process, the Figures 1 to 6 The piezoelectric element 100 according to the first embodiment of the present invention is as shown.

[0077] Here, a piezoelectric element of a comparative example will be described. Fig.15 FIG. 2 is a diagram showing a through hole and the periphery of the through hole of a piezoelectric element of a comparative example. Fig.15 As shown, in the piezoelectric element of the comparative example, unlike the piezoelectric element 100 of embodiment 1 of the present invention, the third electrode layer 940 faces the through hole 113, and the second electrode layer 930 is located on the second surface 112 of the single crystal piezoelectric layer 110, and is located on the side of the third electrode layer 940 opposite to the side of the single crystal piezoelectric layer 110.

[0078] In this comparative example, when etching is performed to form the through hole 113, the third electrode layer 940 can also suppress the etching of the member on the side opposite to the single crystal piezoelectric layer 110 of the second electrode layer 930. However, in this comparative example, the second electrode layer 930 has a neck 935 that connects the portion of the second electrode layer 930 located on the surface of the third electrode layer 940 on the side opposite to the single crystal piezoelectric layer 110 and the portion located on the second surface 112 of the single crystal piezoelectric layer 110. Therefore, stress is concentrated on the neck 935, and cracks may occur. In addition, when such cracks occur, the third electrode layer 940 and the second electrode layer 930 are substantially electrically connected only on the peripheral side surface of the third electrode layer 940, and therefore, a sufficient contact area may not be ensured between the third electrode layer 940 and the second electrode layer 930.

[0079] On the other hand, in the piezoelectric element 100 according to the first embodiment of the present invention, the third electrode layer 140 is arranged on the side of the second electrode layer 130 opposite to the single crystal piezoelectric layer 110 side. The third electrode layer 140 is provided so as to have at least a portion which is located outside the edge 132 of the hole 131 at a distance therefrom when viewed from a direction perpendicular to the second surface 112. The second electrode layer 130 is composed of Pt, Ti, Al, Cu, Au, Ag, Mg, or an alloy containing at least one of these metals as a main component. The third electrode layer 140 is composed of Ni or an alloy containing Ni as a main component.

[0080] Thus, by disposing the third electrode layer 140 that functions as an etching stopper when forming the through hole 113 as described above, stress concentration on the second electrode layer 130 can be alleviated. Furthermore, the generation of cracks in the second electrode layer 130 can be suppressed.

[0081] As described above, the piezoelectric element 100 according to the first embodiment of the present invention includes the third electrode layer 140 below the second electrode layer 130 .

[0082] Thus, when the through hole 113 is formed by etching from the first surface side to the second surface side of the single crystal piezoelectric layer 110, the etching can be stopped in the second electrode layer 130. Furthermore, the formation of a hole in a member located on the side of the second electrode layer 130 opposite to the single crystal piezoelectric layer 110, that is, a member located on the side of the third electrode layer 140 opposite to the single crystal piezoelectric layer 110, can be suppressed.

[0083] In the piezoelectric element 100 according to the first embodiment of the present invention, the material constituting the third electrode layer 140 is CF 20 wt % higher than the material constituting the second electrode layer 130 . 4 The etching rate of the gas is low.

[0084] Thus, by configuring the CF 4 The third electrode layer 140 is etched by the gas at a lower etching rate than the second electrode layer 130, so that the third electrode layer 140 functions as an etching stopper and can alleviate stress concentration on the second electrode layer 130. Furthermore, the generation of cracks in the second electrode layer 130 can be suppressed.

[0085] In the present embodiment, the third electrode layer 140 is provided to have an outer peripheral edge 142 which surrounds the hole 131 at a distance from the edge 132 of the hole 131 when viewed from a direction perpendicular to the second surface 112 .

[0086] This can further suppress the formation of holes in members other than the third electrode layer 140 among the members located on the side of the second electrode layer 130 opposite to the single crystal piezoelectric layer 110 side.

[0087] In this embodiment, the material constituting the third electrode layer 140 is CF 20 , which is smaller than the material constituting the single crystal piezoelectric layer 110. 4 The etching rate of the gas is low.

[0088] Thus, by making the third electrode layer 140 of a material that is harder to etch than the single crystal piezoelectric layer 110 , penetration of the third electrode layer 140 can be further suppressed.

[0089] In this embodiment, the hole 131 penetrates the second electrode layer 130 in a direction perpendicular to the second surface 112. The connection electrode 180c may be provided continuously from the inner side surface 133 of the hole 131 constituting the second electrode layer 130 to the portion of the third electrode layer 140 facing the hole 131.

[0090] Thus, a conductive path directly from the connection electrode 180 c to the second electrode layer 130 and a conductive path through the third electrode layer 140 to the second electrode layer 130 are formed, so that the resistance of the entire electrode can be reduced.

[0091] In this embodiment, the minimum dimension L of the interval is greater than the average thickness of the second electrode layer 130 .

[0092] Thus, a sufficient area can be ensured in the contact area between the second electrode layer 130 and the third electrode layer 140. Figure 6 In the conductive path from the connection electrode 180 c through the third electrode layer 140 to the second electrode layer 130 as shown, resistance can be reduced.

[0093] In the present embodiment, the third electrode layer 140 may be provided with recessed portions 141 a and 141 b facing the hole portion 131 of the second electrode layer 130 .

[0094] Therefore, when the connection electrode 180 c is provided, the contact area between the connection electrode 180 c and the third electrode layer 140 can be increased, and the contact resistance between the connection electrode 180 c and the third electrode layer 140 can be reduced.

[0095] In the present embodiment, the connection electrode 180 c may be provided over the entire inner surface of the recessed portions 141 a and 141 b .

[0096] Thus, a voltage can be applied to the third electrode layer 140 via the connection electrode 180 c in a state where the contact resistance between the connection electrode 180 c and the third electrode layer 140 is further reduced.

[0097] In the present embodiment, the single crystal piezoelectric layer 110 includes a lithium compound. Even in the case where the single crystal piezoelectric layer 110 is relatively difficult to be etched due to the inclusion of a lithium compound as in the present embodiment, the stress concentration on the second electrode layer 130 can be alleviated by configuring the third electrode layer 140 as described above. Furthermore, the generation of cracks in the second electrode layer 130 can be suppressed.

[0098] In this embodiment, the lithium compound is lithium niobate (LiNbO 3 ) or lithium tantalate (LiTaO 3 ). As a result, the dielectric constant of the single crystal piezoelectric layer 110 can be reduced. Furthermore, the driving efficiency of the piezoelectric element 100 can be improved.

[0099] In the present embodiment, the second electrode layer 130 contains Pt as a main component. This can reduce the resistance of the second electrode layer 130 .

[0100] In the present embodiment, the first electrode layer 120 , the second electrode layer 130 , and the third electrode layer 140 are each an epitaxial growth film, thereby improving fatigue characteristics of each electrode layer and improving the reliability of the entire piezoelectric element 100 .

[0101] The piezoelectric element 100 of the present embodiment further includes a base 150 that supports the stacked body 101 including at least the first electrode layer 120, the single crystal piezoelectric layer 110, the second electrode layer 130, and the third electrode layer 140. The base 150 is located on the side of the stacked body 101 opposite to the first electrode layer 120 side. The base 150 is formed along the periphery of the stacked body 101 when viewed from the stacking direction of the stacked body 101.

[0102] Thus, the driving of the single crystal piezoelectric layer 110 can be converted into the bending vibration of the membrane portion 103 .

[0103] In this embodiment, the base 150 includes a silicon oxide layer 151 located on the stacked body 101 side and a single crystal silicon layer 152 located on the side opposite to the stacked body 101. Thus, the piezoelectric element 100 of this embodiment can be used as an ultrasonic transducer.

[0104] (Implementation Method 2)

[0105] The following describes a piezoelectric element according to Embodiment 2 of the present invention. The piezoelectric element according to Embodiment 2 of the present invention is different from the piezoelectric element 100 according to Embodiment 1 of the present invention mainly in that the structure of the base is different. Therefore, the same structure as the piezoelectric element 100 according to Embodiment 1 of the present invention will not be described again.

[0106] Fig.16 2 is a cross-sectional view of a piezoelectric element according to Embodiment 2 of the present invention. Fig.16 As shown, in piezoelectric element 200 according to Embodiment 2 of the present invention, base 250 is made of single crystal silicon. Base 250 and support layer 270 are made of the same member. Piezoelectric element 200 according to this embodiment can be used as a bulk wave resonator.

[0107] Hereinafter, a method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention will be described. Fig.17 2 is a cross-sectional view showing a state in which a single-layer substrate including a base is prepared in a method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention. Fig.17 As shown, a single-layer substrate 204S made of single-crystal silicon is prepared.

[0108] Fig.18 2 is a cross-sectional view showing a state where a single-layer substrate is bonded to an intermediate layer in a method for manufacturing a piezoelectric element according to a second embodiment of the present invention. Fig. 9 The intermediate layer 160 in the stack shown is Fig.17 The single layer substrates 204S are shown bonded.

[0109] Fig.19 This is a cross-sectional view showing a state in which a piezoelectric single crystal substrate is cut to form a piezoelectric layer in a method for manufacturing a piezoelectric element according to a second embodiment of the present invention. Fig. 20 This is a cross-sectional view showing a state where a first electrode layer is provided in a method for manufacturing a piezoelectric element according to a second embodiment of the present invention. Fig.21 2 is a cross-sectional view showing a state where a through hole is provided in a method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention. Figures 19 to 21As shown, in the manufacturing method of the piezoelectric element 200 according to the second embodiment of the present invention, a single crystal piezoelectric layer 110 is formed in the same manner as the manufacturing method of the piezoelectric element 100 according to the first embodiment of the present invention, a first electrode layer 120 is provided, and a through hole 113 and a hole portion 131 are formed. In addition, a recess is formed in the third electrode layer 140 as needed.

[0110] Finally, the single-layer substrate 204S is cut from the side opposite to the single-crystal piezoelectric layer 110 by deep reactive ion etching. Fig.16 The base 250 and the support layer 270 shown in FIG. Fig.16 The piezoelectric element 200 according to the second embodiment of the present invention is shown as shown.

[0111] In this embodiment, the second electrode layer 130 and the third electrode layer 140 are arranged similarly to the piezoelectric element 100 according to the first embodiment of the present invention, so that stress concentration on the second electrode layer 130 can be alleviated. Furthermore, the generation of cracks in the second electrode layer 130 can be suppressed.

[0112] (Implementation method 3)

[0113] The following describes a piezoelectric element according to Embodiment 3 of the present invention. The piezoelectric element according to Embodiment 3 of the present invention is different from the piezoelectric element 200 according to Embodiment 2 of the present invention mainly in that the structure of the first electrode layer is different. Therefore, the same structure as the piezoelectric element 200 according to Embodiment 2 of the present invention will not be described again.

[0114] Fig. 22 2 is a cross-sectional view of a piezoelectric element according to Embodiment 3 of the present invention. Fig. 22 As shown, in the piezoelectric element 300 of embodiment 3 of the present invention, when viewed from a direction perpendicular to the first surface 111, the first electrode layer 320 has a comb-shaped appearance. Thus, the piezoelectric element 300 can be used as a plate wave type elastic wave device. However, the "plate wave" mentioned here is a general term for various waves excited by the single crystal piezoelectric layer 110 with a film thickness of less than 1λ when the wavelength of the plate wave to be excited is set to 1λ. In addition, the piezoelectric element 300 of this embodiment does not have a supporting layer, so the intermediate layer 160 is in direct contact with the base 250.

[0115] In this embodiment, since the second electrode layer 130 and the third electrode layer 140 are arranged similarly to the piezoelectric element 100 according to the first embodiment of the present invention, stress concentration on the second electrode layer 130 can be alleviated. Furthermore, the generation of cracks in the second electrode layer 130 can be suppressed.

[0116] (Implementation 4)

[0117] The following describes a piezoelectric element according to a fourth embodiment of the present invention. The piezoelectric element according to the fourth embodiment of the present invention differs from the piezoelectric element 100 according to the first embodiment of the present invention mainly in that a through slit is formed. Therefore, the same structure as the piezoelectric element 100 according to the first embodiment of the present invention will not be described again.

[0118] Fig.23 4 is a cross-sectional view of a piezoelectric element according to a fourth embodiment of the present invention. Fig.23 As shown, in the piezoelectric element 400 according to the fourth embodiment of the present invention, a through slit 405 communicating with the opening 102 located inside the base 150 when viewed from the stacking direction is provided in the stacked body 101. This further increases the bending vibration of the membrane portion 103, and the device characteristics of the piezoelectric element 100 can be improved.

[0119] In the description of the above embodiments, the structures that can be combined may be combined with each other.

[0120] The embodiments disclosed this time should be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0121] Description of Reference Numerals

[0122] 100, 200, 300, 400 piezoelectric element, 101 laminated body, 102 opening, 103 membrane portion, 104S laminated substrate, 110 single crystal piezoelectric layer, 110S piezoelectric single crystal substrate, 111 first surface, 111S first principal surface, 112 second surface, 112S second principal surface, 113 through hole, 114 inner cross section, 120, 320 first electrode layer, 130, 930 second electrode layer, 131 hole portion, 132 edge portion, 133 inner side surface, 140, 940 third electrode layer, 141a, 141b recessed portion, 142 outer peripheral edge, 150, 250 base portion, 151 silicon oxide layer, 152 single crystal silicon layer, 160 intermediate layer, 170, 270 supporting layer, 180c connecting electrode, 204S single-layer substrate, 405 through slit, 935 neck portion.

Claims

1. A piezoelectric element comprising: a single crystal piezoelectric layer having a first surface, a second surface located on the opposite side of the first surface, and a through hole penetrating from the first surface to the second surface; A first electrode layer provided on the first surface side of the single crystal piezoelectric layer; a second electrode layer located on the second surface side of the single crystal piezoelectric layer, at least a portion of which is opposed to the first electrode layer via the single crystal piezoelectric layer, and has a hole portion facing the through hole; as well as a third electrode layer disposed on a side of the second electrode layer opposite to the single crystal piezoelectric layer side, and provided to have at least a portion spaced apart from an edge of the hole portion and located outside the edge of the hole portion when viewed from a direction perpendicular to the second surface, The second electrode layer is composed of Pt, Ti, Al, Cu, Au, Ag, Mg, or an alloy containing at least one of these metals as a main component. The third electrode layer is made of Ni or an alloy containing Ni as a main component.

2. The piezoelectric element according to claim 1, wherein The material constituting the third electrode layer has a lower etching rate when etched by CF4 gas than the material constituting the second electrode layer.

3. A piezoelectric element comprising: a single crystal piezoelectric layer having a first surface, a second surface located on the opposite side of the first surface, and a through hole penetrating from the first surface to the second surface; A first electrode layer provided on the first surface side of the single crystal piezoelectric layer; a second electrode layer located on the second surface side of the single crystal piezoelectric layer, at least a portion of which is opposed to the first electrode layer via the single crystal piezoelectric layer, and has a hole portion facing the through hole; as well as a third electrode layer disposed on a side of the second electrode layer opposite to the single crystal piezoelectric layer side, and provided to have at least a portion spaced apart from an edge of the hole portion and located outside the edge of the hole portion when viewed from a direction perpendicular to the second surface, The material constituting the third electrode layer has a lower etching rate when etched by CF4 gas than the material constituting the second electrode layer.

4. The piezoelectric element according to any one of claims 1 to 3, wherein The third electrode layer is provided to have an outer peripheral edge surrounding the edge of the hole portion at a distance therefrom when viewed in a direction perpendicular to the second surface.

5. The piezoelectric element according to any one of claims 1 to 4, wherein The material constituting the third electrode layer has a lower etching rate when etched using CF4 gas than the material constituting the single crystal piezoelectric layer.

6. The piezoelectric element according to any one of claims 1 to 5, wherein: The hole penetrates the second electrode layer in a direction perpendicular to the second surface. A connection electrode is provided continuously from the inner side surface of the hole portion constituting the second electrode layer to a portion of the third electrode layer facing the hole portion.

7. The piezoelectric element according to claim 6, wherein: The minimum dimension of the interval is larger than the dimension of the average thickness of the second electrode layer.

8. The piezoelectric element according to claim 6 or 7, wherein: An average thickness of the second electrode layer is thinner than an average thickness of the third electrode layer.

9. The piezoelectric element according to any one of claims 6 to 8, wherein: The third electrode layer is provided with a recessed portion facing the hole portion of the second electrode layer.

10. The piezoelectric element according to claim 9, wherein The connection electrode is provided over the entire inner surface of the recess.

11. The piezoelectric element according to any one of claims 1 to 10, wherein The single crystal piezoelectric layer contains a lithium compound.

12. The piezoelectric element according to claim 11, wherein The lithium compound is lithium niobate LiNbO3 or lithium tantalate LiTaO3.

13. The piezoelectric element according to any one of claims 1 to 12, wherein: The second electrode layer contains Pt as a main component.

14. The piezoelectric element according to any one of claims 1 to 13, wherein: The first electrode layer, the second electrode layer, and the third electrode layer are respectively epitaxial growth films.

15. The piezoelectric element according to any one of claims 1 to 14, wherein The piezoelectric element further includes a base portion supporting a stacked body including at least the first electrode layer, the single crystal piezoelectric layer, the second electrode layer, and the third electrode layer. The base portion is located on the side of the stacked body opposite to the first electrode layer side, and is formed along the periphery of the stacked body when viewed from the stacking direction of the stacked body.

16. The piezoelectric element according to claim 15, wherein The base portion includes a silicon oxide layer located on a stacked body side and a single crystal silicon layer located on a side opposite to the stacked body side.

17. The piezoelectric element according to claim 15 or 16, wherein: The stacked body is provided with a through slit communicating with the opening located on the inner side of the base portion when viewed from the stacking direction.

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