Piezoelectric element and method for manufacturing the same

Abstract

The piezoelectric element (100) includes a piezoelectric layer (110), a first electrode layer (120), a second electrode layer (130), and a connection electrode (140). The second electrode layer (130) is at least partially opposed to the first electrode layer (120) with the piezoelectric layer (110) interposed therebetween. The second electrode layer (130) has a connection surface (131). The connection surface (131) faces a through hole (113) in a region of the second electrode layer (130) that is not opposed to the first electrode layer (120). The connection electrode (140) is provided on the connection surface (131). The difference in position between the connection surface (131) and a portion other than the connection surface (131) in the surface of the second electrode layer (130) on the piezoelectric layer (110) side is 5 nm or less.

Description

Technical Field

[0001] The present invention relates to a piezoelectric element and a method for manufacturing the same. Background Art

[0002] As a document that discloses the structure of a piezoelectric element, there is Japanese Patent Application Laid-Open No. 2009-302661 (Patent Document 1). The piezoelectric element described in Patent Document 1 includes a silicon substrate, a piezoelectric film, and a conductor film. The piezoelectric film is formed of a piezoelectric material such as aluminum nitride (AlN) and is provided on the silicon substrate. The conductor film is formed of a conductive material and is provided on the piezoelectric film. The conductor film is disposed between the piezoelectric film and on the piezoelectric film, and is in contact with the n-type region of the silicon layer and the piezoelectric film. The AlN film is formed by reactive magnetron sputtering, and is patterned by RIE (Reactive Ion Etching) using a chlorine-based gas.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-302661 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In a conventional piezoelectric device, after laminating a piezoelectric layer and an electrode layer (lower electrode) on top of each other, a through hole that penetrates the piezoelectric layer is formed by etching from the side opposite to the electrode layer side. The portion of the electrode layer facing the through hole is etched simultaneously with the formation of the through hole. Therefore, in a conventional piezoelectric device, in the portion of the electrode layer facing the through hole, it is actually inevitable to generate a recess, and there is a problem such as disorder in the crystallinity of the electrode layer. Also, the connection electrode located in the through hole is joined to the above-mentioned portion of the electrode layer with disordered crystallinity, so the electrical connection at the joint between the electrode layer and the connection electrode becomes insufficient, and sometimes an open circuit defect occurs.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a piezoelectric element capable of suppressing the occurrence of an open circuit defect at the joint between an electrode layer and a connection electrode.

[0009] Solutions for Solving the Problems

[0010] The piezoelectric element according to the first aspect of the present invention includes a piezoelectric layer, a first electrode layer, a second electrode layer, and a connection electrode. The piezoelectric layer has a first surface, a second surface, and a through hole. The second surface faces the first surface. The through hole penetrates from the first surface to the second surface. The first electrode layer is provided on the first surface. The second electrode layer is located on the second surface side of the piezoelectric layer. The second electrode layer is at least partially opposed to the first electrode layer with the piezoelectric layer therebetween. The second electrode layer has a connection surface. The connection surface faces the through hole in a region of the second electrode layer that is not opposed to the first electrode layer. The connection electrode is provided on the connection surface. The difference in position between the connection surface and the portion other than the connection surface of the surface on the piezoelectric layer side of the second electrode layer is 5 nm or less.

[0011] The piezoelectric element according to the second aspect of the present invention includes a piezoelectric layer, a first electrode layer, a second electrode layer, and a connection electrode. The piezoelectric layer has a first surface, a second surface, and a through hole. The second surface faces the first surface. The through hole penetrates from the first surface to the second surface. The first electrode layer is provided on the first surface. The second electrode layer is located on the second surface side of the piezoelectric layer. The second electrode layer is at least partially opposed to the first electrode layer with the piezoelectric layer therebetween. The second electrode layer has a connection surface. The connection surface faces the through hole in a region of the second electrode layer that is not opposed to the first electrode layer. The connection electrode is provided on the connection surface. The through hole expands as it goes from the first surface toward the second surface.

[0012] The method for manufacturing a piezoelectric element according to the aspect of the present invention includes a step of forming a recess in a piezoelectric substrate, a step of forming a piezoelectric layer, a step of disposing a second electrode layer, and a step of laminating a first electrode layer. The piezoelectric substrate has a first main surface and a second main surface opposed to the first main surface. In the step of forming a recess in the piezoelectric substrate, the recess is formed on the second main surface side by an etching method. In the step of forming a piezoelectric layer, after grinding the piezoelectric substrate from the first main surface side and then polishing, the first surface is exposed, and the bottom of the recess is removed to form a through hole formed by the inner surface of the recess. The piezoelectric layer has a first surface, a second surface, and a through hole. The second surface faces the first surface. The through hole penetrates from the first surface to the second surface. In the step of disposing a second electrode layer, the second electrode layer is disposed on the second surface side of the piezoelectric layer so as to at least partially face the through hole. In the step of laminating a first electrode layer, the first electrode layer is laminated on the first surface side of the piezoelectric layer so as to be at least partially opposed to the second electrode layer with the piezoelectric layer therebetween.

[0013] Effects of the Invention

[0014] According to the present invention, it is possible to suppress the occurrence of disconnection defects at the joint between the electrode layer and the connection electrode. Description of the Drawings

[0015] Figure 1It is a schematic plan view showing a piezoelectric element according to Embodiment 1 of the present invention.

[0016] Figure 2 It is a cross-sectional view obtained by observing the piezoelectric element in the direction of the arrow of line II-II. Figure 1 of the piezoelectric element.

[0017] Figure 3 It is a cross-sectional view showing a state in which a concave portion is formed in a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0018] Figure 4 It is a cross-sectional view showing a laminated substrate including a second electrode layer prepared in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0019] Figure 5 It is a cross-sectional view showing a state in which a piezoelectric substrate is bonded to a laminated substrate including a second electrode layer in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0020] Figure 6 It is a cross-sectional view showing a state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0021] Figure 7 It is a cross-sectional view showing a state in which a first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0022] Figure 8 It is a cross-sectional view showing a state in which a connection electrode is provided in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0023] Figure 9 It is a cross-sectional view showing a state in which a connection electrode is provided on a second electrode layer in the method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention.

[0024] Figure 10 It is a cross-sectional view showing a state in which a piezoelectric substrate is bonded to a laminated substrate including a second electrode layer in the method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention.

[0025] Figure 11 It is a cross-sectional view showing a state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention.

[0026] Figure 12 It is a cross-sectional view showing a state in which a first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention.

[0027] Figure 13 It is a cross-sectional view showing a piezoelectric element according to Embodiment 3 of the present invention.

[0028] Figure 14 It is a cross-sectional view showing a state in which a connection electrode is filled in a through hole in the method for manufacturing a piezoelectric element according to Embodiment 3 of the present invention.

[0029] Figure 15 It is a cross-sectional view showing a piezoelectric element according to Embodiment 4 of the present invention.

[0030] Figure 16 It is a cross-sectional view showing a state in which a bonding layer is laminated on a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention.

[0031] Figure 17 It is a cross-sectional view showing a state immediately before a second bonding layer is bonded to a first bonding layer in a case where the bonding layer is formed of a plurality of layers in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention.

[0032] Figure 18 It is a cross-sectional view showing a state in which a bonding layer on a piezoelectric substrate is bonded to a laminated substrate including a second electrode layer in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention.

[0033] Figure 19 It is a cross-sectional view showing a state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention.

[0034] Figure 20 It is a cross-sectional view showing a state in which a first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention.

[0035] Figure 21 It is a cross-sectional view showing a state in which a connection electrode is provided in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention.

[0036] Figure 22 It is a cross-sectional view showing a piezoelectric element according to Embodiment 5 of the present invention.

[0037] Figure 23 It is a cross-sectional view showing a piezoelectric element according to Embodiment 6 of the present invention.

[0038] Figure 24 It is a cross-sectional view showing a state in which a second electrode layer is provided on a laminated substrate in the method for manufacturing a piezoelectric element according to Embodiment 6 of the present invention.

[0039] Figure 25 It is a cross-sectional view showing a state in which a piezoelectric substrate is bonded to a second electrode layer provided on a laminated substrate in the method for manufacturing a piezoelectric element according to Embodiment 6 of the present invention.

[0040] Figure 26It is a cross-sectional view showing a state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 6 of the present invention.

[0041] Figure 27 It is a cross-sectional view showing a state in which a first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 6 of the present invention.

[0042] Figure 28 It is a cross-sectional view showing a state in which a connection electrode is provided in the method for manufacturing a piezoelectric element according to Embodiment 6 of the present invention.

[0043] Figure 29 It is a cross-sectional view showing the piezoelectric element according to Embodiment 7 of the present invention.

[0044] Figure 30 It is a cross-sectional view showing the piezoelectric element according to Embodiment 8 of the present invention.

[0045] Figure 31 It is a cross-sectional view showing a state immediately before a second bonding layer is bonded to a first bonding layer in a case where the bonding layer is formed of multiple layers in the method for manufacturing a piezoelectric element according to Embodiment 8 of the present invention.

[0046] Figure 32 It is a cross-sectional view showing a state in which a bonding layer on a piezoelectric substrate is bonded to a second electrode layer provided on a stacked substrate in the method for manufacturing a piezoelectric element according to Embodiment 8 of the present invention.

[0047] Figure 33 It is a cross-sectional view showing a state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 8 of the present invention.

[0048] Figure 34 It is a cross-sectional view showing a state in which a first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 8 of the present invention.

[0049] Figure 35 It is a cross-sectional view showing a state in which a connection electrode is provided in the method for manufacturing a piezoelectric element according to Embodiment 8 of the present invention.

[0050] Figure 36 It is a cross-sectional view showing the piezoelectric element according to Embodiment 9 of the present invention. Detailed Embodiments

[0051] Hereinafter, with reference to the drawings, piezoelectric elements according to respective embodiments of the present invention will be described. 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.

[0052] (Embodiment 1)

[0053] Figure 1 is a schematic top view of the piezoelectric element according to Embodiment 1 of the present invention. Figure 2 is a cross-sectional view obtained by observing the piezoelectric element Figure 1 in the direction of the arrow of line II-II.

[0054] As Figure 1 and Figure 2 shown, the piezoelectric element 100 according to Embodiment 1 of the present invention includes a piezoelectric body layer 110, a first electrode layer 120, a second electrode layer 130, a connection electrode 140, an outer connection electrode 145, and a base 150.

[0055] As Figure 2 shown, the piezoelectric body layer 110 has a first surface 111, a second surface 112, and a through hole 113. The second surface 112 is located on the side opposite to the first surface 111 and faces the first surface 111. The through hole 113 penetrates from the first surface 111 to the second surface 112. The through hole 113 expands as it goes from the first surface 111 toward the second surface 112. Specifically, the through hole 113 continuously expands from the first surface 111 toward the second surface 112.

[0056] In the present embodiment, the piezoelectric body layer 110 is made of a compound of alkali metal niobate or a compound of alkali metal tantalate. In the present embodiment, the alkali metal contained in the above-mentioned compound of alkali metal niobate or the above-mentioned compound of alkali metal tantalate is formed by at least one of lithium, rubidium, and cesium. The piezoelectric body layer 110 is made of, for example, lithium niobate (LiNbO3) or lithium tantalate (LiTaO3). In the present embodiment, the piezoelectric body layer 110 is formed of a single crystal.

[0057] The first electrode layer 120 is provided on the first surface 111 of the piezoelectric body layer 110. A bonding layer is located between the first electrode layer 120 and the piezoelectric body layer 110. The first electrode layer 120 is made of a metal such as Al or Pt, for example. The above-mentioned bonding layer is made of Ti or NiCr, for example.

[0058] The second electrode layer 130 is located on the side of the second surface 112 of the piezoelectric body layer 110. The second electrode layer 130 is at least partially opposed to the first electrode layer 120 with the piezoelectric body layer 110 interposed therebetween. In the present embodiment, the second electrode layer 130 is opposed to the first electrode layer 120 only with the piezoelectric body layer 110 and the natural oxide film layer of the second electrode layer 130 described later interposed therebetween. That is, the second electrode layer 130 is connected to the second surface 112 of the piezoelectric body layer 110.

[0059] The second electrode layer 130 faces the through hole 113. The second electrode layer 130 has a connection surface 131. The connection surface 131 in the second electrode layer 130 faces the through hole 113 in a region not opposite to the first electrode layer 120. The difference in the direction perpendicular to the first surface 111 between the position of the connection surface 131 and the position of the portion other than the connection surface 131 in the surface of the second electrode layer 130 on the piezoelectric layer 110 side is 5 nm or less. In other words, when the portion other than the connection surface 131 in the surface of the second electrode layer 130 on the piezoelectric layer 110 side is used as a reference surface, the connection surface 131 is located within a range of 5 nm or less relative to this reference surface in the direction from the first surface 111 toward the second surface 112. In addition, in the present embodiment, a step is formed in the surface of the second electrode layer 130 on the piezoelectric layer 110 side such that the above reference surface and the connection surface 131 are separated from each other. In the present embodiment, the size of the height of the step formed by the reference surface and the connection surface 131 in the direction perpendicular to the first surface 111 is 5 nm or less. The above difference, the position of the connection surface 131 relative to the reference surface, and the size of the height can be confirmed by directly observing the cross section when the piezoelectric element 100 is vertically cut with respect to the first surface 111 using a transmission electron microscope (TEM: Transmission Electron Microscope).

[0060] The portion other than the connection surface 131 on the piezoelectric layer 110 side of the second electrode layer 130 is covered with a native oxide film layer. The connection surface 131 of the second electrode layer 130 may also be covered with a native oxide film layer, but it is preferably removed at the joint with the connection electrode 140 described later. In the present embodiment, the native oxide film layer located on the connection surface 131 is removed.

[0061] The second electrode layer 130 contains silicon as a main component. In the present embodiment, the second electrode layer 130 contains single-crystalline silicon as a main component. More specifically, the second electrode layer 130 is composed of single-crystalline silicon doped with an element that reduces the resistivity of the second electrode layer 130. The second electrode layer 130 is doped with an element such as boron (B), aluminum (Al), gallium (Ga), phosphorus (P), arsenic (As), or antimony (Sb), for example. In the present embodiment, it is preferable that the resistivity of the material constituting the second electrode layer 130 is low, specifically, preferably 20 mΩ·cm or less. In addition, in the present embodiment, the etching rate of the material constituting the second electrode layer 130 in reactive ion etching (RIE) using CF4 gas is greater than the etching rate of the material constituting the piezoelectric layer 110. Specifically, the above etching rate of the material constituting the second electrode layer 130 is 1.5 times or more the etching rate of the material constituting the piezoelectric layer 110.

[0062] In the present embodiment, since the second electrode layer 130 contains silicon as a main component, the natural oxide film layer is silicon oxide. In the present embodiment, the thickness of the natural oxide film is about 1 nm or more and 2 nm or less.

[0063] In the present embodiment, the interface 190 between the second electrode layer 130 and the piezoelectric layer 110 is constituted by an interface joint portion formed by surface activation bonding or atomic diffusion bonding.

[0064] In the present embodiment, the piezoelectric layer 110 is formed of a single crystal, and the second electrode layer 130 contains single crystal silicon as a main component. Therefore, the electromechanical conversion efficiency of the piezoelectric element 100 is good.

[0065] As Figure 2 shown, the connection electrode 140 is provided on the connection surface 131 of the second electrode layer 130 facing the through hole 113. In the present embodiment, the connection electrode 140 is located at a position separated from the inner surface 114 of the through hole 113. The connection electrode 140 is made of Au, for example. Alternatively, an adhesion layer may be formed between the connection electrode 140 and the second electrode layer 130. The adhesion layer is made of Ti or NiCr, for example.

[0066] As Figure 2 shown, in the present embodiment, the laminate 101 includes at least the piezoelectric layer 110, the first electrode layer 120, and the second electrode layer 130. In addition, the laminate 101 further includes the connection electrode 140 and the outer connection electrode 145. The base 150 supports the laminate 101.

[0067] As Figure 2 shown, the base 150 is located on the second electrode layer 130 side of the laminate 101. As Figure 1 shown, the base 150 is formed in a ring shape so as to follow the periphery of the surface on the base 150 side of the laminate 101 when viewed from the stacking direction of the laminate 101.

[0068] As Figure 2 shown, in the present embodiment, the base 150 includes a silicon oxide layer 151 and a base body 152. The silicon oxide layer 151 is in contact with the second electrode layer 130. The base body 152 is in contact with the silicon oxide layer 151 on the side opposite to the second electrode layer 130 side of the silicon oxide layer 151. In the present embodiment, the material constituting the base body 152 is not particularly limited, and the base body 152 is formed of single crystal silicon.

[0069] As Figure 2 shown, the opening 103 is located inside the base 150 when viewed from the stacking direction of the laminate 101. The edge of the opening 103 has a circular outer shape when viewed from the stacking direction and extends along the stacking direction, but the shape of the outer shape of the opening 103 is not particularly limited.

[0070] As Figure 1 and Figure 2 shown, in the present embodiment, a diaphragm portion 102 is formed in the laminate 101. The diaphragm portion 102 overlaps with the opening 103 when viewed from the lamination direction and does not overlap with the base portion 150.

[0071] The piezoelectric element 100 of the present embodiment is driven by applying a voltage between the outer connection electrode 145 and the connection electrode 140 as shown in Figure 2 to apply a voltage between the first electrode layer 120 and the second electrode layer 130 as shown in Figure 2 . Thereby, it is driven in such a manner that the piezoelectric layer 110 located between the first electrode layer 120 and the second electrode layer 130 is deformed. Thereby, the diaphragm portion 102 can vibrate with a large amplitude in the lamination direction of the laminate 101.

[0072] Hereinafter, a method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention will be described. The method for manufacturing the piezoelectric element 100 according to the embodiment of the present invention at least includes a step of forming a recess 113S in the piezoelectric substrate 110S, a step of forming the piezoelectric layer 110, a step of disposing the second electrode layer 130, and a step of laminating the first electrode layer 120. In addition, the following Figures 3 to 8 shown states are illustrated in the same cross-section as Figure 2 the same.

[0073] Figure 3 is a cross-sectional view showing a state in which a recess is formed in the piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0074] As Figure 3 shown, the piezoelectric substrate 110S has a first main surface 111S and a second main surface 112S located on the side opposite to the first main surface 111S. The second main surface 112S faces the first main surface 111S. In the step of forming the recess 113S in the piezoelectric substrate 110S, the recess 113S is formed on the second main surface 112S side by an etching method. The etching method for forming the recess 113S may be either dry etching or wet etching. As will be described later, the depth of the recess 113S is appropriately adjusted to be the depth at which the through hole 113 can be formed by the recess 113S.

[0075] Figure 4 is a cross-sectional view of preparing a laminated substrate including a second electrode layer in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. As Figure 4 shown, a laminated substrate 104S including the second electrode layer 130 and the base portion 150 is prepared. In the present embodiment, the laminated substrate 104S is an SOI (Silicon on Insulator) substrate.

[0076] Figure 5 This is a cross-sectional view showing the state in which a piezoelectric substrate is bonded to a stacked substrate including a second electrode layer in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. As Figure 5 shown, in the present embodiment, after forming the recess 113S in the piezoelectric substrate 110S, the second electrode layer 130 is bonded to the piezoelectric substrate 110S. Further, in the present embodiment, the piezoelectric substrate 110S is bonded to the stacked substrate 104S by surface-activated bonding or atomic diffusion bonding. Thus, in the present embodiment, since the layers included in the substrate can be used as electrode layers, there is no need for a process of further laminating an electrode layer on the substrate.

[0077] Figure 6 This is a cross-sectional view showing the state in which the piezoelectric substrate is cut to form a piezoelectric layer in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. As Figure 6 shown, in the process of forming the piezoelectric layer 110, after thinning the piezoelectric substrate 110S by grinding from the first main surface 111S side using, for example, a grinding machine, polishing is performed using CMP (Chemical Mechanical Polishing) or the like to make it flat, thereby exposing the first surface 111, and the bottom of the recess 113S is removed to form a through-hole 113 formed by the inner surface 114 of the recess 113S.

[0078] Thus, in the method for manufacturing the piezoelectric element 100 of the present embodiment, the second electrode layer 130 is disposed on the second surface 112 side of the piezoelectric layer 110 so as to at least partially face the through-hole 113.

[0079] Alternatively, a release layer may be formed by injecting ions in advance to the second main surface 112S side of the piezoelectric substrate 110S. By forming this release layer in advance before bonding the piezoelectric substrate 110S to the second electrode layer 130, the release layer can be peeled off after bonding to form the piezoelectric layer 110.

[0080] Figure 7 This is a cross-sectional view showing the state in which the first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0081] Thus, in the process of laminating the first electrode layer 120, the first electrode layer 120 is laminated on the first surface 111 side of the piezoelectric layer 110 so as to at least partially face the second electrode layer 130 with the piezoelectric layer 110 interposed therebetween. The first electrode layer 120 is formed into a desired pattern using a vapor deposition peeling method or the like.

[0082] Figure 8It is a cross-sectional view showing the state where the connection electrodes are provided in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. As Figure 8 shown, the connection electrode 140 and the outer connection electrode 145 are formed using a vapor deposition and stripping method or the like. In the present embodiment, before forming the connection electrode 140, the natural oxide film layer of the second electrode layer 130 at the connection surface 131 is removed by an etching method such as wet etching. By removing the natural oxide film layer, since the thickness of the natural oxide film layer is about 1 nm or more and 2 nm or less, the difference in the direction perpendicular to the first surface 111 between the position of the connection surface 131 and the portion other than the connection surface 131 in the surface of the second electrode layer 130 on the piezoelectric layer 110 side is 5 nm or less. When the thickness of the layer removed by the etching method is very thin, such as 5 nm or less, the contact resistance at the connection surface 131 does not increase significantly due to the modification of the connection surface 131 or the like. That is, in the present embodiment, by removing the above-mentioned natural oxide film layer, although not shown in Figure 8 , the surface of the second electrode layer 130 on the piezoelectric layer 110 side becomes a concave shape in which the connection surface 131 is recessed.

[0083] Finally, through deep reactive ion etching (Deep RIE), an opening 103 of the piezoelectric element 100 of the present embodiment is formed from the side of the base 150 opposite to the second electrode layer 130 side. In addition, in the present embodiment, the silicon oxide layer 151 is etched to form the opening 103, but the silicon oxide layer 151 may not be etched, or a part of the silicon oxide layer 151 in the stacking direction of the stacked substrate 104S may be etched.

[0084] Through the above steps, the piezoelectric element 100 of Embodiment 1 of the present invention as shown in Figure 1 and Figure 2 is manufactured.

[0085] As described above, in the piezoelectric element 100 of Embodiment 1 of the present invention, the second electrode layer 130 has a connection surface 131. The connection surface 131 faces the through hole 113 in the region of the second electrode layer 130 that does not face the first electrode layer 120. The connection electrode 140 is provided on the connection surface 131 of the second electrode layer 130 that faces the through hole 113. The difference between the position of the connection surface 131 and the portion other than the connection surface 131 in the surface of the second electrode layer 130 on the piezoelectric layer 110 side is 5 nm or less.

[0086] Thus, in the present embodiment, the connection surface 131 is not affected by the etching for forming the through hole 113 and the difference in the above positions is 5 nm or less, thereby suppressing the crystallization disorder of the connection surface 131 of the second electrode layer 130. Furthermore, the generation of an open circuit defect at the joint between the connection surface 131 of the second electrode layer 130 and the connection electrode 140 can be suppressed.

[0087] The through hole 113 expands as it goes from the first surface 111 toward the second surface 112.

[0088] Thus, the resistivity of the joint between the second electrode layer 130 and the connection electrode 140 can be reduced. That is, for the through hole 113, the cross-sectional area of the end portion on the second surface 112 side is larger than the cross-sectional area of the end portion on the first surface 111 side, so that the connection area between the second electrode layer 130 and the connection electrode 140 can be enlarged and the contact resistance between the second electrode layer 130 and the connection electrode 140 can be reduced.

[0089] In particular, in the case of forming the connection electrode 140 by the lift-off method, the formation of the connection electrode 140 becomes easy, so that it is difficult to generate a connection defect between the connection electrode 140 and the second electrode layer 130, and the yield of the piezoelectric element 100 is improved.

[0090] The through hole 113 continuously expands from the first surface 111 toward the second surface 112.

[0091] Thus, compared with the case where the inner surface of the through hole 113 is formed in a stepped shape, the formation process of the through hole 113 can be reduced.

[0092] The connection electrode 140 is located at a position separated from the inner surface 114 of the through hole 113.

[0093] Thus, the connection electrode 140 does not contact the corner formed by the inner surface 114 of the through hole 113 and the first surface 111 where stress concentration easily occurs, so that the generation of cracks in the connection electrode 140 can be suppressed.

[0094] In the reactive ion etching using CF4 gas, the etching rate of the material constituting the second electrode layer 130 is higher than the etching rate of the material constituting the piezoelectric layer 110.

[0095] In the present embodiment, even when the second electrode layer 130 is more easily etched than the piezoelectric layer 110 due to the difference in the etching rate as described above, the difference in the above positions is 5 nm or less and the connection surface 131 is also in a state not affected by the etching for forming the through hole 113. Therefore, the crystallization disorder of the connection surface 131 of the second electrode layer 130 can be suppressed. Furthermore, the generation of an open circuit defect at the joint between the connection surface 131 of the second electrode layer 130 and the connection electrode 140 can be suppressed.

[0096] The piezoelectric layer 110 is composed of a compound of an alkali metal niobate or a compound of an alkali metal tantalate. The alkali metal contained in the compound of the alkali metal niobate or the compound of the alkali metal tantalate is formed of at least one of lithium, rubidium, and cesium. The second electrode layer 130 contains silicon as a main component.

[0097] Thereby, the dielectric constant of the piezoelectric layer 110 can be made relatively low. In addition, the resistance of the piezoelectric layer 110 becomes high, so that the voltage applied to the piezoelectric layer 110 with respect to the second electrode layer 130 containing silicon as a main component becomes large, and the driving efficiency of the piezoelectric element 100 can be improved.

[0098] The piezoelectric layer 110 is composed of lithium niobate. Thereby, the piezoelectric constant of the piezoelectric layer 110 can be increased compared with the case where the piezoelectric layer 110 is composed of other compounds of alkali metal niobates or compounds of alkali metal tantalates, and thus the device characteristics of the piezoelectric element 100 can be improved.

[0099] The piezoelectric layer 110 is composed of lithium tantalate. Thereby, the dielectric constant of the piezoelectric layer 110 becomes lower compared with the case where the piezoelectric layer 110 is composed of other compounds of alkali metal niobates or compounds of alkali metal tantalates, so that the resistance of the piezoelectric layer 110 becomes high, the driving efficiency of the piezoelectric element 100 is improved, and the device characteristics of the piezoelectric element 100 can be improved.

[0100] The second electrode layer 130 contains single crystal silicon as a main component. Thereby, the bonding strength between the piezoelectric layer 110 and the second electrode layer 130 is increased, and the electromechanical conversion efficiency of the piezoelectric layer 110 can be improved.

[0101] The piezoelectric element 100 further includes a base 150 that supports a laminate 101 including at least the first electrode layer 120, the piezoelectric layer 110, and the second electrode layer 130. The base 150 is located on the side of the second electrode layer 130 of the laminate 101, and is formed in a ring shape so as to follow the periphery of the surface on the base 150 side of the laminate 101 when viewed in the stacking direction of the laminate 101.

[0102] Thereby, the driving of the piezoelectric layer 110 can be converted into the bending vibration of the diaphragm portion 102, and the device characteristics of the piezoelectric element 100 can be improved.

[0103] The base 150 includes a silicon oxide layer that contacts the second electrode layer 130. The second electrode layer 130 is composed of single crystal silicon doped with an element that reduces the resistivity of the second electrode layer 130.

[0104] Thus, the second electrode layer 130 and the base 150 can be simultaneously connected to the piezoelectric layer 110 using a stacked substrate, and the current efficiency of the second electrode layer 130 can be improved.

[0105] The method for manufacturing the piezoelectric element 100 according to an embodiment of the present invention includes a step of forming a recess 113S in the piezoelectric substrate 110S, a step of forming the piezoelectric layer 110, a step of disposing the second electrode layer 130, and a step of stacking the first electrode layer 120. The piezoelectric substrate 110S has a first main surface 111S and a second main surface 112S opposite to the first main surface 111S. In the step of forming the recess 113S in the piezoelectric substrate 110S, the above-described recess 113S is formed on the second main surface 112S side using an etching method. In the step of forming the piezoelectric layer 110, after grinding the piezoelectric substrate 110S from the first main surface 111S side and then polishing, the first surface 111 is exposed, and the bottom of the recess 113S is removed to form a through hole 113 formed by the inner surface 114 of the recess 113S. In the step of disposing the second electrode layer 130, the second electrode layer 130 is disposed on the second surface 112 side of the piezoelectric layer 110 so as to at least partially face the through hole 113. In the step of stacking the first electrode layer 120, the first electrode layer 120 is stacked on the first surface 111 side of the piezoelectric layer 110 so as to at least partially face the second electrode layer 130 with the piezoelectric layer 110 interposed therebetween.

[0106] In this way, since the recess 113S corresponding to the through hole 113 is formed using an etching method before the second electrode layer 130 is disposed on the piezoelectric substrate 110S, the second electrode layer 130 is not etched when the through hole 113 is formed. Accordingly, it is possible to suppress a case where the crystallinity of the connection surface 131 of the second electrode layer 130 is disordered, suppress an increase in the resistivity at the joint between the connection surface 131 of the second electrode layer 130 and the connection electrode 140, and further suppress the occurrence of an open-circuit defect in the second electrode layer 130.

[0107] Moreover, as described above, in the piezoelectric element 100 of the present embodiment, the etching rate of the material constituting the second electrode layer 130 in the reactive ion etching with CF4 gas is greater than the etching rate of the material constituting the piezoelectric layer 110. Therefore, if the through hole 113 is formed by an etching method after the second electrode layer 130 is disposed on the piezoelectric substrate 110S, the second electrode layer 130 is over-etched. Due to this over-etching, the surface modification or the thickness of the second electrode layer 130 becomes smaller, and thus the resistivity increases at the above-described joint portion. However, in the present embodiment, the through hole 113 is formed as described above, and thus the second electrode layer 130 is not over-etched when the through hole 113 is formed. Therefore, in the present embodiment, it is possible to suppress the increase in the resistivity at the above-described joint portion while using a material having an etching rate greater than the etching rate of the material constituting the piezoelectric layer 110 as the material constituting the second electrode layer 130.

[0108] In addition, since the through hole 113 is formed by the inner surface 114 of the recess 113S formed by an etching method from the second main surface 112S side of the piezoelectric substrate 110S, the through hole 113 can be formed in a shape that expands as it goes from the first surface 111 toward the second surface 112. Thereby, the connection area between the second electrode layer 130 and the connection electrode 140 can be expanded, and the contact resistance at the joint portion between the second electrode layer 130 and the connection electrode 140 can be reduced.

[0109] (Embodiment 2)

[0110] Hereinafter, the piezoelectric element of Embodiment 2 of the present invention will be described. The structure of the piezoelectric element of Embodiment 2 of the present invention is the same as the structure of the piezoelectric element 100 of Embodiment 1 of the present invention, but the manufacturing method of the piezoelectric element of Embodiment 2 of the present invention is different from the manufacturing method of the piezoelectric element 100 of Embodiment 1 of the present invention. Therefore, only the manufacturing method of the piezoelectric element of Embodiment 2 of the present invention will be described, and the structures that are the same as those of the manufacturing method of the piezoelectric element 100 of Embodiment 1 of the present invention will not be described repeatedly.

[0111] Figure 9 is a cross-sectional view showing a state in which a connection electrode is provided on the second electrode layer in the manufacturing method of the piezoelectric element of Embodiment 2 of the present invention. As Figure 9 shown, in the manufacturing method of the piezoelectric element of Embodiment 2 of the present invention, the connection electrode 140 is formed on the second electrode layer 130 before the second electrode layer 130 is disposed on the second surface 112 side of the piezoelectric layer 110. The connection electrode 140 can be formed by a method such as an evaporation method, a sputtering method, or a plating method.

[0112] Figure 10This is a cross-sectional view showing the state in which a piezoelectric substrate is bonded to a laminated substrate including a second electrode layer in the method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention. As Figure 10 shown, a piezoelectric substrate 110S having a recess 113S formed therein is bonded to the second electrode layer 130. At this time, the piezoelectric substrate 110S is bonded to the second electrode layer 130 in such a manner that the inner surface 114 of the recess 113S and the connection electrode 140 do not come into contact with each other. In the present embodiment, it is preferable that the natural oxide film of the entire second electrode layer 130 is removed by etching or the like before forming the connection electrode 140.

[0113] Figure 11 This is a cross-sectional view showing the state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention. As Figure 11 shown, a piezoelectric layer 110 is formed in the same manner as in the method for manufacturing the piezoelectric element 100 according to Embodiment 1 of the present invention.

[0114] Figure 12 This is a cross-sectional view showing the state in which the first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 2 of the present invention. As Figure 12 shown, the first electrode layer 120 is laminated by the same method as in the method for manufacturing the piezoelectric element 100 according to Embodiment 1 of the present invention. Finally, an opening 103 is formed by the same method as in the method for manufacturing the piezoelectric element 100 according to Embodiment 1 of the present invention.

[0115] Through the above-described steps, a piezoelectric element similar to the piezoelectric element 100 according to Figure 1 and Figure 2 shown in Embodiment 1 of the present invention can be manufactured.

[0116] (Embodiment 3)

[0117] Hereinafter, a piezoelectric element according to Embodiment 3 of the present invention will be described. The piezoelectric element according to Embodiment 3 of the present invention is mainly different from the piezoelectric element 100 according to Embodiment 1 of the present invention in the structure of the connection electrode. Therefore, the same structures as those of the piezoelectric element 100 according to Embodiment 1 of the present invention will not be described repeatedly.

[0118] Figure 13 This is a cross-sectional view showing the piezoelectric element according to Embodiment 3 of the present invention. As Figure 13As shown, in the piezoelectric element 300 of Embodiment 3 of the present invention, the through-hole 113 is filled with the connection electrode 340. Thereby, the peeling strength of the connection electrode 340 with respect to the second electrode layer 130 can be improved, and the reliability of the piezoelectric element 300 can be improved. In addition, when the piezoelectric element 300 is mounted by flip-chip bonding, the solder bumps 360 can be provided so as to overlap the through-hole 113 when viewed from a direction perpendicular to the first surface 111, and thus the piezoelectric element 300 can be miniaturized.

[0119] In addition, in the present embodiment, the through-hole 113 expands as it goes from the first surface 111 toward the second surface, so that it is possible to further suppress the peeling of the connection electrode 340 filled in the through-hole 113 toward a position outside the first surface 111.

[0120] Next, a method for manufacturing the piezoelectric element 300 of Embodiment 3 of the present invention will be described. In the method for manufacturing the piezoelectric element 300 of Embodiment 3 of the present invention, as Figure 7 shown, the through-hole 113 is formed in the same manner as in the method for manufacturing the piezoelectric element of Embodiment 1 of the present invention.

[0121] Figure 14 is a cross-sectional view showing a state in which the connection electrode is filled in the through-hole in the method for manufacturing the piezoelectric element of Embodiment 3 of the present invention. As Figure 14 shown, the connection electrode 340 and the outer connection electrode 145 are formed. In the present embodiment, the connection electrode 340 is formed using a plating method. Thereby, the through-hole 113 is filled with the connection electrode 340. The connection electrode 340 and the outer connection electrode 145 may be formed simultaneously, or one of the connection electrode 340 and the outer connection electrode 145 may be formed after the other is formed.

[0122] Finally, using the same method as in the method for manufacturing the piezoelectric element 100 of Embodiment 1 of the present invention, the opening 103 is formed. Through the above-described steps, the piezoelectric element 300 of Embodiment 3 of the present invention as Figure 13 shown can be manufactured.

[0123] (Embodiment 4)

[0124] Hereinafter, a piezoelectric element according to Embodiment 4 of the present invention will be described. The piezoelectric element according to Embodiment 4 of the present invention is mainly different from the piezoelectric element 100 of Embodiment 1 of the present invention in that it further includes a bonding layer. Therefore, the same structure as that of the piezoelectric element 100 of Embodiment 1 of the present invention will not be described repeatedly.

[0125] Figure 15 is a cross-sectional view showing the piezoelectric element according to Embodiment 4 of the present invention. As Figure 15As shown, in the piezoelectric element 400 according to Embodiment 4 of the present invention, the bonding layer 470 is disposed between the piezoelectric body layer 110 and a portion other than the connection surface 131 on the piezoelectric body layer 110 side of the second electrode layer 130. Thereby, the bonding strength between the piezoelectric body layer 110 and the second electrode layer 130 is improved.

[0126] In the present embodiment, the bonding layer 470 is also disposed on the inner surface 114 of the through-hole 113. Thereby, the environmental resistance of the inner surface 114 of the through-hole 113 is improved.

[0127] In the present embodiment, the bonding layer 470 is formed of silicon oxide (SiO2). Thereby, a bonding layer 470 having an appropriate thickness can be provided between the second electrode layer 130 and the piezoelectric body layer 110 while considering the dielectric constant of the bonding layer 470. The bonding layer 470 may also contain a metal.

[0128] In addition, the bonding layer 470 may be composed of a plurality of layers, and the plurality of layers may have a metal layer. In the case where the bonding layer 470 is composed of a plurality of layers, a portion of the bonding layer 470 that contacts the second electrode layer 130 may be composed of a natural oxide film layer of the second electrode layer 130. The natural oxide film layer is formed of SiO2, for example.

[0129] Hereinafter, a method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention will be described. In the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention, first, as Figure 3 shown, a recess 113S is formed in the piezoelectric body substrate 110S in the same manner as in the method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention.

[0130] Figure 16 is a cross-sectional view showing a state in which a bonding layer is laminated on a piezoelectric body substrate in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention. As Figure 16 shown, the bonding layer 470 is laminated on the second main surface 112S of the piezoelectric body substrate, the inner surface 114 of the recess 113S, and the bottom surface by using a CVD (Chemical Vapor Deposition) method, a PVD (Physical Vapor Deposition) method, or the like.

[0131] In addition, in the case where the bonding layer 470 is composed of a plurality of layers and a portion of the bonding layer 470 that contacts the second electrode layer 130 is composed of a natural oxide film layer of the second electrode layer 130, after laminating the first bonding layer by using the method of laminating the bonding layer 470, the second bonding layer as the natural oxide film layer may be bonded to the first bonding layer. Figure 17This is a cross-sectional view showing the state before the second bonding layer is bonded to the first bonding layer in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention, where the bonding layer is formed of multiple layers. As Figure 17 shown, the second bonding layer 472, which is the natural oxide film layer of the second electrode layer 130, is bonded to the stacked first bonding layer 471. Further, when bonding the first bonding layer 471 and the second bonding layer 472, by previously removing the natural oxide film layer of the portion of the second electrode layer 130 facing the recess 113S in the stacked substrate 104S, the second bonding layer 472 is prevented from facing the recess 113S.

[0132] Figure 18 This is a cross-sectional view showing the state where the bonding layer on the piezoelectric substrate is bonded to the stacked substrate including the second electrode layer in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention. As Figure 18 shown, the second electrode layer 130 and the piezoelectric substrate 110S are bonded to each other via the bonding layer 470 by surface-activated bonding or atomic diffusion bonding. Further, as Figure 16 shown, when the bonding layer 470 includes the first bonding layer 471 and the second bonding layer 472, the second electrode layer 130 and the piezoelectric substrate 110S are bonded to each other via the first bonding layer 471 and the second bonding layer 472.

[0133] Figure 19 This is a cross-sectional view showing the state where the piezoelectric substrate is cut to form a piezoelectric layer in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention. As Figure 19 shown, in the recess 113S, the bottom of the stacked bonding layer 470 and the bonding layer 470 are removed together.

[0134] Figure 20 This is a cross-sectional view showing the state where the first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention. As Figure 20 shown, the first electrode layer 120 is stacked on the first surface 111 side of the piezoelectric layer 110.

[0135] Figure 21 This is a cross-sectional view showing the state where the connection electrode is provided in the method for manufacturing a piezoelectric element according to Embodiment 4 of the present invention. As Figure 21 shown, the connection electrode 140 and the outer connection electrode 145 are formed in the same manner as the piezoelectric element 100 of Embodiment 1 of the present invention. And finally, by forming the opening 103, the piezoelectric element 400 of Embodiment 4 of the present invention shown in Figure 15 is manufactured.

[0136] (Embodiment 5)

[0137] Hereinafter, a piezoelectric element according to Embodiment 5 of the present invention will be described. The piezoelectric element according to Embodiment 5 of the present invention is mainly different from the piezoelectric element 400 according to Embodiment 4 of the present invention in the structure of the connection electrodes. Therefore, the same structures as those of the piezoelectric element 400 according to Embodiment 4 of the present invention will not be described repeatedly.

[0138] Figure 22 FIG. is a cross-sectional view showing the piezoelectric element according to Embodiment 5 of the present invention. In the piezoelectric element 500 according to Embodiment 5 of the present invention, similar to the piezoelectric element 300 according to Embodiment 3 of the present invention, the through hole 113 is filled with the connection electrode 340. Thereby, the peeling strength of the connection electrode 340 with respect to the second electrode layer 130 can be improved.

[0139] (Embodiment 6)

[0140] Hereinafter, a piezoelectric element according to Embodiment 6 of the present invention will be described. The piezoelectric element according to Embodiment 6 of the present invention is mainly different from the piezoelectric element 100 according to Embodiment 1 of the present invention in that the second electrode layer is provided separately from the stacked substrate. Therefore, the same structures as those of the piezoelectric element 100 according to Embodiment 1 of the present invention will not be described repeatedly.

[0141] Figure 23 FIG. is a cross-sectional view showing the piezoelectric element according to Embodiment 6 of the present invention. As Figure 23 shown, in the piezoelectric element 600 according to Embodiment 6 of the present invention, the piezoelectric body layer 110 is made of lithium niobate. The second electrode layer 630 is made of a metal material. The second electrode layer 630 is made of, for example, Al or Pt.

[0142] In the present embodiment, even when lithium niobate having an etching rate lower than that of the metal material used for the second electrode layer 630 is used for the piezoelectric body layer 110, the second electrode layer 630 is not etched when the through hole 113 is formed. Thereby, the disorder of the crystallinity of the second electrode layer 630 can be suppressed, and the occurrence of an open-circuit defect caused by insufficient electrical connection at the joint portion between the connection electrode 140 and the second electrode layer 630 in the connection surface 131 can be suppressed.

[0143] In the present embodiment, the silicon layer 680 is located on the surface of the second electrode layer 630 on the side opposite to the piezoelectric body layer 110 side. Thereby, the silicon layer 680 also functions as an electrode layer together with the second electrode layer 630, so that the current efficiency is improved.

[0144] Thus, in the present embodiment, the laminate 101 further includes the silicon layer 680. The base 150 is located on the silicon layer 680 side of the laminate 101.

[0145] Hereinafter, a method for manufacturing the piezoelectric element according to Embodiment 6 of the present invention will be described. Figure 24This is a cross-sectional view showing the state in which the second electrode layer is provided on the laminated substrate in the method for manufacturing a piezoelectric element according to Embodiment 6 of the present invention. As Figure 24 shown, in the present embodiment, the laminated substrate 104S includes a silicon layer 680 and a base portion 150. Then, the second electrode layer 630 is provided on the silicon layer 680 of the laminated substrate 104S by using a method such as CVD method or PVD method.

[0146] Figure 25 This is a cross-sectional view showing the state in which the piezoelectric substrate is bonded to the second electrode layer provided on the laminated substrate in the method for manufacturing a piezoelectric element according to Embodiment 6 of the present invention. As Figure 25 shown, the piezoelectric substrate 110S having the recess 113S formed therein as shown in Figure 3 is bonded to the second electrode layer 630 by surface activated bonding or atomic diffusion bonding.

[0147] Figure 26 This is a cross-sectional view showing the state in which the piezoelectric substrate is cut to form a piezoelectric layer in the method for manufacturing a piezoelectric element according to Embodiment 6 of the present invention. As Figure 26 shown, similar to the method for manufacturing the piezoelectric element 100 according to Embodiment 1 of the present invention, after the piezoelectric substrate 110S is thinned by grinding using a grinding machine, for example, and then polished by CMP or the like to make it flat, the piezoelectric layer 110 is formed. Thus, in the present embodiment, since the recess 113S corresponding to the through hole 113 is formed by an etching method before the second electrode layer 630 is disposed on the piezoelectric substrate 110S, the second electrode layer 630 is not etched when the through hole 113 is formed. Thereby, it is possible to suppress the disorder of the connection surface 131 of the second electrode layer 630 and suppress the increase in the resistivity at the joint portion between the connection surface 131 of the second electrode layer 630 and the connection electrode 140. Furthermore, it is possible to suppress the occurrence of an open circuit defect in the second electrode layer 630.

[0148] Moreover, as described above, in the piezoelectric element 600 of the present embodiment, when the piezoelectric layer 110 is made of lithium niobate and the etching rate of the metal material constituting the second electrode layer 630 is larger than the etching rate of lithium niobate, if the through hole 113 is formed by an etching method after the second electrode layer 630 is disposed on the piezoelectric substrate 110S, the second electrode layer 630 is over-etched. Due to this over-etching, the surface modification or the thickness of the second electrode layer 630 becomes smaller, so that the resistivity at the above joint portion increases. However, in the present embodiment, since the through hole 113 is formed as described above, the second electrode layer 630 is not over-etched when the through hole 113 is formed. Therefore, in the present embodiment, it is possible to use a metal material having an etching rate larger than the etching rate of lithium niobate as the second electrode layer 630 while suppressing the increase in the resistivity at the above joint portion.

[0149] Figure 27 is a cross-sectional view showing the state of setting the first electrode layer in the manufacturing method of the piezoelectric element according to Embodiment 6 of the present invention. As Figure 27 shown, the first electrode layer 120 is set in the same manner as in the manufacturing method of the piezoelectric element 100 according to Embodiment 1 of the present invention.

[0150] Figure 28 is a cross-sectional view showing the state of setting the connection electrode in the manufacturing method of the piezoelectric element according to Embodiment 6 of the present invention. As Figure 28 shown, the connection electrode 140 and the outer connection electrode 145 are formed. In the present embodiment, the connection surface 131 may be covered with a natural oxide film, but at the joint portion with the connection electrode 140, it is preferable to remove the above natural oxide film. In the present embodiment, it is preferable that, before forming the connection electrode 140, the natural oxide film layer on the entire connection surface 131 is removed by etching or the like. And by finally forming the opening 103, the piezoelectric element 600 according to Embodiment 6 of the present invention as Figure 23 shown is manufactured.

[0151] (Embodiment 7)

[0152] Hereinafter, the piezoelectric element according to Embodiment 7 of the present invention will be described. The piezoelectric element according to Embodiment 7 of the present invention is mainly different from the piezoelectric element 600 according to Embodiment 6 of the present invention in the structure of the connection electrode. Therefore, the same structures as those of the piezoelectric element 600 according to Embodiment 6 of the present invention will not be described repeatedly.

[0153] Figure 29 is a cross-sectional view showing the piezoelectric element according to Embodiment 7 of the present invention. In the piezoelectric element 700 according to Embodiment 7 of the present invention, like the piezoelectric element 300 according to Embodiment 3 of the present invention, the through hole 113 is filled with the connection electrode 340. Thereby, the peeling strength of the connection electrode 340 with respect to the second electrode layer 630 can be improved.

[0154] (Embodiment 8)

[0155] Hereinafter, the piezoelectric element according to Embodiment 8 of the present invention will be described. The piezoelectric element according to Embodiment 8 of the present invention is mainly different from the piezoelectric element 400 according to Embodiment 4 of the present invention in that the second electrode layer is provided separately from the laminated substrate and mainly in the structure of the connection electrode. Therefore, the same structures as those of the piezoelectric element 400 according to Embodiment 4 of the present invention will not be described repeatedly.

[0156] Figure 30 is a cross-sectional view showing the piezoelectric element according to Embodiment 8 of the present invention. As Figure 30As shown, in the piezoelectric element 800 of Embodiment 8 of the present invention, similar to the piezoelectric element 600 of Embodiment 6 of the present invention, the second electrode layer 630 is made of a metal material, and the silicon layer 680 is located on the surface of the second electrode layer 630 on the side opposite to the piezoelectric layer 110 side. Also in this embodiment, by the bonding layer 470 being located between the second electrode layer 630 made of a metal material and the piezoelectric layer 110, the bonding strength between the piezoelectric layer 110 and the second electrode layer 630 is increased.

[0157] Hereinafter, a method for manufacturing the piezoelectric element of Embodiment 8 of the present invention will be described. First, as Figure 16 shown, similar to the method for manufacturing the piezoelectric element 400 of Embodiment 4 of the present invention, a bonding layer 470 is formed on the piezoelectric substrate 110S having the recess 113S formed therein. And, as Figure 24 shown, similar to the method for manufacturing the piezoelectric element 600 of Embodiment 6 of the present invention, a second electrode layer 630 is provided on the silicon layer 680 of the laminated substrate 104S.

[0158] Here, similar to the method for manufacturing the piezoelectric element 400 of Embodiment 4 of the present invention, the bonding layer 470 is formed of silicon oxide (SiO2). The bonding layer 470 may also be composed of multiple layers. These multiple layers may also have a metal layer. In the case where the bonding layer 470 is composed of multiple layers, it may be that the portion of the bonding layer 470 in contact with the second electrode layer 630 is composed of the natural oxide film layer of the second electrode layer 630. Figure 31 is a cross-sectional view showing a state immediately before the second bonding layer is bonded to the first bonding layer in the case where the bonding layer is formed of multiple layers in the method for manufacturing the piezoelectric element of Embodiment 8 of the present invention. It is a view showing a state immediately before the second bonding layer is bonded to the first bonding layer in the case where the bonding layer is formed of multiple layers in the method for manufacturing the piezoelectric element of Embodiment 8 of the present invention. As Figure 31 shown, the second bonding layer 472 is bonded to the laminated first bonding layer 471. Further, in the case of bonding the first bonding layer 471 and the second bonding layer 472, by previously removing the portion of the second bonding layer 472 of the second electrode layer 630 facing the recess 113S of the piezoelectric substrate 110S, the second bonding layer 472 is prevented from facing the recess 113S.

[0159] Figure 32 is a cross-sectional view showing a state in which the bonding layer on the piezoelectric substrate is bonded to the second electrode layer provided on the laminated substrate in the method for manufacturing the piezoelectric element of Embodiment 8 of the present invention. As Figure 32 shown, the second electrode layer 630 and the piezoelectric substrate 110S are bonded to each other via the bonding layer 470 by surface activated bonding or atomic diffusion bonding. Further, as Figure 31As shown, in the case where the bonding layer 470 includes a first bonding layer 471 and a second bonding layer 472, the second electrode layer 630 and the piezoelectric substrate 110S are bonded to each other via the first bonding layer 471 and the second bonding layer 472.

[0160] Figure 33 is a cross-sectional view showing a state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the method for manufacturing a piezoelectric element according to Embodiment 8 of the present invention. As Figure 33 shown, in the recess 113S, the bottom of the bonding layer 470 bonded thereto and the bonding layer 470 are removed together.

[0161] Figure 34 is a cross-sectional view showing a state in which a first electrode layer is provided in the method for manufacturing a piezoelectric element according to Embodiment 8 of the present invention. As Figure 34 shown, the first electrode layer 120 is laminated on the first surface 111 side of the piezoelectric layer 110.

[0162] Figure 35 is a cross-sectional view showing a state in which a connection electrode is provided in the method for manufacturing a piezoelectric element according to Embodiment 8 of the present invention. As Figure 35 shown, the connection electrode 140 and the outer connection electrode 145 are formed in the same manner as the piezoelectric element 100 of Embodiment 1 of the present invention. And finally, by forming the opening 103, the piezoelectric element 800 of Embodiment 8 of the present invention shown in Figure 35 is manufactured.

[0163] (Embodiment 9)

[0164] Hereinafter, the piezoelectric element of Embodiment 9 of the present invention will be described. The piezoelectric element of Embodiment 9 of the present invention is mainly different from the piezoelectric element 800 of Embodiment 8 of the present invention in the structure of the connection electrode. Therefore, the same structures as those of the piezoelectric element 800 of Embodiment 8 of the present invention will not be described repeatedly.

[0165] Figure 36 is a cross-sectional view showing the piezoelectric element of Embodiment 9 of the present invention. In the piezoelectric element 900 of Embodiment 9 of the present invention, similar to the piezoelectric element 300 of Embodiment 3 of the present invention, the through hole 113 is filled with the connection electrode 340. Thereby, the peeling strength of the connection electrode 340 with respect to the second electrode layer 630 can be improved.

[0166] In the description of the above embodiments, structures that can be combined may be combined with each other.

[0167] It should be considered that the embodiments disclosed herein are illustrative in all aspects and not restrictive. The scope of the present invention is represented by the claims and not by the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0168] Explanation of Reference Numerals

[0169] 100, 300, 400, 500, 600, 700, 800, 900, piezoelectric elements; 101, laminate; 102, diaphragm portion; 103, opening; 104S, laminated substrate; 110, piezoelectric layer; 110S, piezoelectric substrate; 111, first surface; 111S, first main surface; 112, second surface; 112S, second main surface; 113, through-hole; 113S, recess; 114, inner surface; 120, first electrode layer; 130, 630, second electrode layer; 131, connection surface; 140, 340, connection electrode; 145, outer connection electrode; 150, base; 151, silicon oxide layer; 152, base body; 190, interface; 360, solder bump; 470, bonding layer; 471, first bonding layer; 472, second bonding layer; 680, silicon layer.

Claims

1. A piezoelectric element, wherein, the piezoelectric element includes: a piezoelectric layer having a first surface, a second surface opposite to 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; a second electrode layer located on the second surface side of the piezoelectric layer, at least partially facing the first electrode layer with the piezoelectric layer therebetween, and having a connection surface facing the through hole in a region not facing the first electrode layer; and a connection electrode provided on the connection surface, a difference in position between the connection surface and a portion other than the connection surface of the surface of the second electrode layer on the piezoelectric layer side is 5 nm or less, the through hole continuously expands from the first surface toward the second surface.

2. The piezoelectric element according to claim 1, wherein, the connection electrode is located at a position separated from the inner surface of the through hole.

3. The piezoelectric element according to claim 1, wherein, the through hole is filled with the connection electrode.

4. The piezoelectric element according to any one of claims 1 to 3, wherein, in reactive ion etching with CF4 gas, an etching rate of the material constituting the second electrode layer is greater than an etching rate of the material constituting the piezoelectric layer.

5. The piezoelectric element according to any one of claims 1 to 3, wherein, the piezoelectric layer is composed of a compound of alkali metal niobate or a compound of alkali metal tantalate, the alkali metal contained in the compound of alkali metal niobate or the compound of alkali metal tantalate is formed of at least one of lithium, rubidium, and cesium, the second electrode layer contains silicon as a main component.

6. The piezoelectric element according to claim 5, wherein, the piezoelectric layer is composed of lithium niobate.

7. The piezoelectric element according to claim 5, wherein, the piezoelectric layer is composed of lithium tantalate.

8. The piezoelectric element according to claim 5, wherein, the second electrode layer contains single crystal silicon as a main component.

9. The piezoelectric element according to any one of claims 1 to 3, wherein, the piezoelectric layer is composed of lithium niobate, the second electrode layer is composed of a metal material.

10. The piezoelectric element according to any one of claims 1 to 3, wherein, a bonding layer is located between a portion other than the connection surface of the second electrode layer on the piezoelectric layer side and the piezoelectric layer.

11. The piezoelectric element according to claim 10, wherein, the bonding layer is formed of silicon oxide.

12. The piezoelectric element according to claim 9, wherein, a silicon layer is located on a surface of the second electrode layer on the side opposite to the piezoelectric layer side.

13. The piezoelectric element according to any one of claims 1 to 3, wherein, the piezoelectric element further includes a base that supports a laminate including at least the first electrode layer, the piezoelectric layer, and the second electrode layer, the base is located on the second electrode layer side of the laminate, and is formed in a ring shape so as to follow the periphery of the surface of the laminate on the base side when viewed in the lamination direction of the laminate.

14. The piezoelectric element according to claim 13, wherein, The base includes a silicon oxide layer in contact with the second electrode layer. The second electrode layer is made of single-crystalline silicon doped with an element that reduces the resistivity of the second electrode layer.

15. A piezoelectric element, wherein the piezoelectric element includes: a piezoelectric layer having a first surface, a second surface opposite to 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; a second electrode layer located on the second surface side of the piezoelectric layer, at least partially facing the first electrode layer with the piezoelectric layer therebetween, and having a connection surface facing the through-hole in a region not facing the first electrode layer; and a connection electrode provided on the connection surface, wherein the through-hole continuously expands from the first surface toward the second surface.

16. A method for manufacturing a piezoelectric element, wherein the method for manufacturing the piezoelectric element includes the following steps: In a piezoelectric substrate having a first main surface and a second main surface opposite to the first main surface, a recess is formed on the second main surface side by an etching method; After grinding the piezoelectric substrate from the first main surface side and then polishing, the first surface is exposed, and the bottom of the recess is removed to form a through-hole formed by the inner surface of the recess, thereby forming a piezoelectric layer having the first surface, a second surface opposite to the first surface, and the through-hole penetrating from the first surface to the second surface; On the second surface side of the piezoelectric layer, a second electrode layer is disposed so as to at least partially face the through-hole; and On the first surface side of the piezoelectric layer, a first electrode layer is laminated so as to at least partially face the second electrode layer with the piezoelectric layer therebetween.

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