piezoelectric elements

Abstract

The piezoelectric element (100) includes a piezoelectric layer (110), a first electrode layer (120), a second electrode layer (130), and a connecting electrode (140). The piezoelectric layer (110) has a first surface (111), a second surface (112), and a through hole (113). The second electrode layer (130) is located on the second surface (112) side of the piezoelectric layer (110). The second electrode layer (130) faces the through hole (113). The second electrode layer (130) contains silicon as its main component. The connecting electrode (140) is disposed on the connecting surface (131) of the second electrode layer (130) facing the through hole (113). The connecting electrode (140) is formed of metal. The surface roughness (Ra) of the connecting surface (131) is greater than that of the main surface (132) of the second electrode layer (130) other than the connecting surface (131).

Description

Technical Field

[0001] This invention relates to a piezoelectric element. Background Technology

[0002] Japanese Patent Application Publication No. 2018-041788 (Patent Document 1) and Japanese Patent Application Publication No. 2009-302661 (Patent Document 2) disclose the structure of a piezoelectric element. Patent Document 1 describes a piezoelectric element comprising a piezoelectric thin film and a pair of electrodes. The piezoelectric thin film is laminated on a support substrate. The pair of electrodes are disposed with respect to the piezoelectric thin film. An electrode formed on the back side of the piezoelectric thin film is connected to a wiring electrode. The electrodes and wiring metal can be formed from a metal thin film.

[0003] Patent Document 2 describes a piezoelectric element comprising a silicon substrate, a piezoelectric film, and a conductive film. The piezoelectric film, formed of a piezoelectric material such as aluminum nitride (AlN), is disposed on the silicon substrate. The conductive film, formed of a conductive material, is disposed on the piezoelectric film. The conductive film, for example, is formed of a metal or alloy. The conductive film is disposed on and between the piezoelectric films, and is in contact with the n-type region of the silicon layer and the piezoelectric film.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-041788

[0007] Patent Document 2: Japanese Patent Application Publication No. 2009-302661 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] In the piezoelectric element described in Patent Document 1, the wiring electrode and the electrode formed on the back side of the piezoelectric film are both made of metal, thus ensuring the tightness of the wiring electrode with the electrode. However, in the case of a piezoelectric element such as that described in Patent Document 2, where one electrode layer contains silicon as the main component, the tightness of the electrode layer with the metal electrode is insufficient, and the resistance becomes high at the interface between the electrode layer and the metal electrode.

[0010] The present invention was made in view of the above-mentioned problems, and its object is to provide a piezoelectric element that can suppress the high resistance at the junction of an electrode layer containing silicon as the main component and a connecting electrode formed of metal.

[0011] Solution for solving the problem

[0012] The piezoelectric element according to the present invention includes a piezoelectric body layer, a first electrode layer, a second electrode layer, and a connecting electrode. The piezoelectric body layer has a first surface, a second surface, and a through-hole. The second surface faces the first surface. The through-hole extends from the first surface to the second surface. The first electrode layer is disposed on the first surface side of the piezoelectric body layer. The second electrode layer is located on the second surface side of the piezoelectric body layer. The second electrode layer is at least partially separated from the first electrode layer by the piezoelectric body layer. The second electrode layer faces the through-hole. The second electrode layer contains silicon as its main component. The connecting electrode is disposed on the connecting surface of the second electrode layer facing the through-hole. The connecting electrode is formed of metal. The surface roughness Ra of the connecting surface is greater than the surface roughness Ra of the main surface (excluding the connecting surface) of the piezoelectric body layer side of the second electrode layer.

[0013] The effects of the invention

[0014] According to the present invention, it is possible to suppress the high resistance at the junction of the second electrode layer containing silicon as the main component and the connecting electrode formed of metal. Attached Figure Description

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

[0016] Figure 2 Observe from the direction of the arrow on line II-II Figure 1 The cross-sectional view obtained from the piezoelectric element.

[0017] Figure 3 This is a cross-sectional view showing the structure of the piezoelectric element in the first modified example of Embodiment 1 of the present invention.

[0018] Figure 4 This is a cross-sectional view showing the structure of the piezoelectric element in the second variation of Embodiment 1 of the present invention.

[0019] Figure 5 This is a cross-sectional view of a piezoelectric substrate prepared in the manufacturing method of a piezoelectric element according to Embodiment 1 of the present invention.

[0020] Figure 6 This is a cross-sectional view of a laminated substrate containing a second electrode layer prepared in the manufacturing method of a piezoelectric element according to Embodiment 1 of the present invention.

[0021] Figure 7 This is a cross-sectional view showing the state in which the piezoelectric substrate is bonded to a laminated substrate including a second electrode layer in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention.

[0022] Figure 8 This is a cross-sectional view showing the state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention.

[0023] Figure 9 This is a cross-sectional view showing the state in which the first electrode layer is provided in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention.

[0024] Figure 10 This is a cross-sectional view showing the state in which a through hole is provided in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention.

[0025] Figure 11 This is a cross-sectional view showing the state in which the connecting electrodes are set in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention.

[0026] Figure 12 This is a cross-sectional view showing the structure of the piezoelectric element according to Embodiment 2 of the present invention. Detailed Implementation

[0027] Hereinafter, piezoelectric elements according to various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the embodiments, the same or equivalent parts in the drawings will be labeled with the same reference numerals, and their descriptions will not be repeated.

[0028] (Implementation Method 1)

[0029] Figure 1 This is a schematic top view showing the piezoelectric element according to Embodiment 1 of the present invention. Figure 2 Observe from the direction of the arrow on line II-II Figure 1 The cross-sectional view obtained from the piezoelectric element.

[0030] like Figure 1 and Figure 2 As shown, the piezoelectric element 100 of Embodiment 1 of the present invention includes a piezoelectric body layer 110, a first electrode layer 120, a second electrode layer 130, a connecting electrode 140, an outer connecting electrode 145, and a base 150.

[0031] like Figure 2 As shown, the piezoelectric layer 110 has a first surface 111, a second surface 112, and a through hole 113. The second surface 112 is opposite to the first surface 111. The through hole 113 extends from the first surface 111 to the second surface 112.

[0032] In this embodiment, the piezoelectric layer 110 is composed of an alkali metal niobate compound or an alkali metal tantalate compound. In this embodiment, the alkali metal contained in the aforementioned alkali metal niobate compound or alkali metal tantalate compound is formed from at least one of lithium, rubidium, and cesium. Specifically, in this embodiment, the piezoelectric layer 110 is formed from a single-crystal material containing lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), but the piezoelectric layer 110 may not be composed of a single-crystal material.

[0033] The first electrode layer 120 is disposed on the first surface 111 side of the piezoelectric layer 110. An adhesive layer is located between the first electrode layer 120 and the piezoelectric layer 110. The first electrode layer 120 is, for example, made of a metal such as Al or Pt. The adhesive layer is, for example, made of Ti or NiCr.

[0034] The second electrode layer 130 is located on the second surface 112 side of the piezoelectric layer 110. The second electrode layer 130 is at least partially separated from the first electrode layer 120 by the piezoelectric layer 110. In this embodiment, the second electrode layer 130 is separated from the first electrode layer 120 only by the piezoelectric layer 110 and the natural oxide film layer of the second electrode layer 130 described later.

[0035] The second electrode layer 130 faces the through hole 113. The connecting surface 131 in the second electrode layer 130 faces the through hole 113. Additionally, the second electrode layer 130 faces the second surface 112 of the piezoelectric layer 110. The main surface 132 in the second electrode layer 130 faces the piezoelectric layer 110. The connecting surface 131 is located inside the second electrode layer 130 relative to the main surface 132 in a direction perpendicular to the second surface 112. The shortest distance between the connecting surface 131 and the main surface 132 in the direction perpendicular to the second surface 112 is 5 nm or more. For example, the shortest distance between the connecting surface 131 and the main surface 132 in the direction perpendicular to the second surface 112 can be 100 nm or less. Furthermore, the shortest distance between the connecting surface 131 and the main surface 132 refers to the distance in the direction perpendicular to the second surface 112 between the point on the connecting surface 131 located closest to the main surface 132 in the direction perpendicular to the second surface 112 and the point on the main surface 132 located closest to the connecting surface 131 in the direction perpendicular to the second surface 112. The second electrode layer 130 also has an inner surface 133 that connects the connecting surface 131 and the main surface 132 to each other in the direction perpendicular to the second surface 112.

[0036] In this embodiment, the second electrode layer 130 contains silicon as a main component. Specifically, the second electrode layer 130 is a doped single-crystal silicon layer. In the second electrode layer 130, the main surface 132 is covered by a silicon oxide film 135. The thickness of the silicon oxide film 135 is approximately 2 nm or less. Furthermore, in this embodiment, the connection surface 131 is not covered by the silicon oxide film 135. In addition, in this specification, "containing silicon as a main component" means "containing 50 atm% or more of silicon".

[0037] In addition, the connection surface 131 can also be covered by a silicon oxide film formed by the natural oxidation of silicon contained in the second electrode layer 130 on the surface of the second electrode layer 130. Figure 3 This is a cross-sectional view showing the structure of the piezoelectric element in the first modified example of Embodiment 1 of the present invention. Figure 3As shown, in the piezoelectric element 100a of the first modification of Embodiment 1 of the present invention, the connecting surface 131 is covered by a silicon oxide film 135a. However, in this modification, the silicon oxide film 135a covering the connecting surface 131 is thinner than the silicon oxide film 135 covering the main surface 132. In this modification, the shortest distance between the connecting surface 131 and the main surface 132 in the direction perpendicular to the second surface 112 is less than 5 nm.

[0038] like Figure 2 As shown, in the piezoelectric element 100 of Embodiment 1 of the present invention, the surface roughness Ra of the connecting surface 131 is greater than the surface roughness Ra of the main surface 132, which is the portion of the surface other than the connecting surface 131 on the piezoelectric layer 110 side of the second electrode layer 130. Specifically, the surface roughness Ra of the connecting surface 131 is 30 nm or more and less than 1 μm. The surface roughness Ra of the main surface 132 is more than 0.05 nm and less than 1 nm.

[0039] In this embodiment, the surface roughness Ra of the connecting surface 131 and the surface roughness Ra of the main surface 132 are calculated by directly observing the cross-section of the piezoelectric element 100 perpendicular to the main surface 132 using a transmission electron microscope (TEM). In this specification, surface roughness Ra refers to the value obtained by formula (1) when the roughness curve is represented by y = f(x) and expressed in micrometers, extracted from the roughness curve along the direction of its mean line, with the X-axis taken in the direction of the mean line of the extracted portion and the Y-axis taken in the direction of longitudinal magnification. That is, the definition of surface roughness Ra in this specification is based on JIS B 0601:2013. In this embodiment, the reference length l in the calculation of the surface roughness Ra is 1 μm.

[0040] [Number 1]

[0041]

[0042] like Figure 2As shown, the connecting electrode 140 is provided on the connecting surface 131 facing the through hole 113 in the second electrode layer 130. The connecting electrode 140 is also provided on the inner surface 133. Furthermore, the connecting electrode 140 is continuously provided from the connecting surface 131 to the inner surface 114 of the through hole 113 and the first surface 111. Therefore, when viewed from a direction perpendicular to the first surface 111, the outer edge of the connecting electrode 140 is located outside the through hole 113. In addition, the width of the connecting electrode 140 on the connecting surface 131 in the direction parallel to the second surface 112 is larger than the shortest distance between the connecting surface 131 and the main surface 132 in the direction perpendicular to the second surface 112. Furthermore, the width of the connecting electrode 140 on the connecting surface 131 in the direction parallel to the second surface 112 is determined by directly observing the cross-section of the piezoelectric element 100 perpendicular to the second surface 112 using a transmission electron microscope (TEM) in such a way that the spacing between the inner surfaces 114 opposite each other in the piezoelectric layer 110 is minimized, and measuring the length of the portion of the connecting electrode 140 that contacts the connecting surface 131.

[0043] In addition, the connecting electrode can also be located separately from the inner surface 114 of the through hole 113. Figure 4 This is a cross-sectional view showing the structure of the piezoelectric element in the second modification of Embodiment 1 of the present invention. Figure 4 As shown, in this modified example, the connecting electrode 140b is located at a position separate from the inner surface 114 of the through hole 113. The width of the connecting electrode 140b on the connecting surface 131 in the direction parallel to the second surface 112 is larger than the maximum distance between the connecting electrode 140b and the inner surface 114 of the through hole 113 in the direction parallel to the second surface 112.

[0044] like Figure 2 As shown, the connecting electrode 140 is formed of metal. For example, the connecting electrode 140 is made of Au. Alternatively, an adhesive layer may be formed between the connecting electrode 140 and the second electrode layer 130. This adhesive layer may be made of, for example, Ti or NiCr. Furthermore, the connection surface 131 between the connecting electrode 140 and the second electrode layer 130 is in ohmic contact.

[0045] like Figure 2 As shown, in this embodiment, the laminate 101 includes at least a first electrode layer 120, a piezoelectric layer 110, and a second electrode layer 130. The laminate 101 also includes a connecting electrode 140 and an outer connecting electrode 145. The base 150 supports the laminate 101.

[0046] like Figure 2 As shown, the base 150 is located on the side of the second electrode layer 130 of the laminate 101. Figure 1As shown, the base 150 is formed in a ring shape along the periphery of the surface of the base 150 side of the laminate 101 when viewed from the lamination direction of the laminate 101.

[0047] like Figure 2 As shown, in this 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 of the silicon oxide layer 151 opposite to the side of the second electrode layer 130. In this embodiment, the material constituting the base body 152 is not particularly limited, and the base body 152 is formed of monocrystalline silicon.

[0048] like Figure 2 As shown, the opening 103 is located inside the base 150 when viewed from the stacking direction of the laminate 101. Figure 1 As shown, the end edge of the opening 103 has a rectangular shape when viewed from the aforementioned stacking direction, and extends along the aforementioned stacking direction. Furthermore, the shape of the opening 103 is not particularly limited.

[0049] like Figure 1 and Figure 2 As shown, in this embodiment, a membrane portion 104 is formed in the laminate 101. The membrane portion 104 overlaps with the opening 103 when viewed from the lamination direction, but does not overlap with the base 150. A through slit 105 is provided in the laminate 101, communicating with the opening 103 located inside the base 150 when viewed from the lamination direction. More specifically, the through slit 105 is provided in the membrane portion 104.

[0050] The piezoelectric element 100 in this embodiment transmits electricity to the piezoelectric element 100 via a pie Figure 2 A voltage is applied between the outer connecting electrode 145 and the connecting electrode 140 to... Figure 2 A voltage is applied between the first electrode layer 120 and the second electrode layer 130. This drives the piezoelectric layer 110 located between the first electrode layer 120 and the second electrode layer 130 to deform. As a result, the diaphragm portion 104 can bend and vibrate significantly in the lamination direction of the laminate 101.

[0051] The following describes a method for manufacturing a piezoelectric element according to Embodiment 1 of the present invention. Furthermore, the following... Figures 5 to 11 The states shown are in relation to Figure 2 The same sectional view is illustrated.

[0052] Figure 5 This is a cross-sectional view of the piezoelectric substrate prepared in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention. Figure 5As 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.

[0053] Figure 6 This is a cross-sectional view of a laminated substrate including a second electrode layer prepared in the manufacturing method of a piezoelectric element according to Embodiment 1 of the present invention. Figure 6 As shown, a multilayer substrate 102S comprising a second electrode layer 130 and a base 150 is prepared. In this embodiment, the multilayer substrate 102S is an SOI (Silicon on Insulator) substrate.

[0054] Figure 7 This is a cross-sectional view showing the state in which the piezoelectric substrate is bonded to a laminated substrate including a second electrode layer in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention. Figure 7 As shown, the piezoelectric substrate 110S is bonded to the laminated substrate 102S by surface activation bonding or atomic diffusion bonding. Specifically, the piezoelectric substrate 110S is bonded to the second electrode layer 130. More specifically, the piezoelectric substrate 110S is bonded to the silicon oxide film 135 on the second electrode layer 130.

[0055] Figure 8 This is a cross-sectional view showing the state in which a piezoelectric layer is formed by cutting a piezoelectric substrate in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention. Figure 8 As shown, the piezoelectric layer 110 is formed by polishing the piezoelectric substrate 110S using grinding and CMP (Chemical Mechanical Polishing).

[0056] Furthermore, when cutting the piezoelectric substrate 110S, a release layer can be formed by pre-implanting ions into the first main surface 111S side of the piezoelectric substrate 110S. By pre-forming this release layer before bonding the piezoelectric substrate 110S to the second electrode layer 130, the piezoelectric layer 110 can be formed by peeling off the release layer after bonding. The piezoelectric layer 110 can also be formed by cutting the release layer using grinding or CMP.

[0057] Figure 9 This is a cross-sectional view showing the state in which the first electrode layer is provided in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention. Figure 9 As shown, the first electrode layer 120 is formed on the first surface 111 of the piezoelectric layer 110 in a desired pattern using photolithography or vapor deposition / lifting methods.

[0058] Figure 10 This is a cross-sectional view showing the state in which a through hole is provided in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention. For example... Figure 10 As shown, through-holes 113 are formed in the piezoelectric layer 110, for example, by etching such as RIE (Reactive Ion Etching). At this time, a portion of the second electrode layer 130 facing the through-holes 113 is removed simultaneously with the formation of the through-holes 113. This exposes the connection surface 131, which is formed by removing all of the silicon oxide film 135 from the second electrode layer 130. The etching described above is performed to give the connection surface 131 a desired surface roughness Ra. Furthermore, in a first variation of Embodiment 1 of the present invention, only a portion of the silicon oxide film 135 of the second electrode layer 130 needs to be removed.

[0059] Figure 11 This is a cross-sectional view showing the state in which the connecting electrodes are provided in the manufacturing method of the piezoelectric element according to Embodiment 1 of the present invention. Figure 11 As shown, the connecting electrode 140 and the outer connecting electrode 145 are formed using photolithography or vapor deposition / lifting methods.

[0060] Next, a through slit 105 is formed in the laminate 101 by RIE. Furthermore, the base body 152 is cut from the side of the base 150 opposite to the side of the second electrode layer 130 by deep reactive ion etching (DeepRIE). Finally, the silicon oxide layer 151 is cut by RIE to form the opening 103.

[0061] Through the above-described processes, such as Figure 1 and Figure 2 The piezoelectric element 100 of Embodiment 1 of the present invention is shown as described.

[0062] As described above, in the piezoelectric element 100 of Embodiment 1 of the present invention, the piezoelectric layer 110 has a first surface 111, a second surface 112, and a through hole 113. The through hole 113 extends from the first surface 111 to the second surface 112. The second electrode layer 130 is located on the second surface 112 side of the piezoelectric layer 110. The second electrode layer 130 faces the through hole 113. The second electrode layer 130 contains silicon as its main component. A connecting electrode 140 is provided on the connecting surface 131 of the second electrode layer 130 facing the through hole 113. The connecting electrode 140 is formed of metal. The surface roughness Ra of the connecting surface 131 is greater than the surface roughness Ra of the main surface 132 of the piezoelectric layer 130 other than the connecting surface 131 on the piezoelectric layer 110 side.

[0063] Therefore, at the connection surface 131, the adhesion between the second electrode layer 130, which contains silicon as the main component, and the connection electrode 140, which is formed of metal, is improved. Furthermore, it is possible to suppress the situation where the resistance increases at the junction of the second electrode layer 130 and the connection electrode 140.

[0064] In this embodiment, the connecting surface 131 is located inside the second electrode layer 130 relative to the main surface 132 in a direction perpendicular to the second surface 112.

[0065] To position the connection surface 131 as described above, the surface of the second electrode layer 130 located on the piezoelectric layer 110 side is processed to remove the natural oxide film layer of the second electrode layer 130 at the connection surface 131. This reduces the contact resistance between the second electrode layer 130 and the connection electrode 140 at the connection surface 131.

[0066] In the piezoelectric element 100 of Embodiment 1 of the present invention and the piezoelectric element 100a of the first modification of Embodiment 1 of the present invention, the main surface 132 is covered by a silicon oxide film 135. The connecting surface 131 is either not covered by a silicon oxide film or is covered by a silicon oxide film 135a. The silicon oxide film 135a covering the connecting surface 131 is thinner than the silicon oxide film 135 covering the main surface 132.

[0067] This reduces the contact resistance between the second electrode layer 130 and the connecting electrode 140.

[0068] In the piezoelectric element 100 of Embodiment 1 of the present invention, the shortest distance between the connecting surface 131 and the main surface 132 in the direction perpendicular to the second surface 112 is 5 nm or more.

[0069] As described above, by processing the main surface 132 of the second electrode layer 130 to fully separate the connecting surface 131 from the main surface 132, the natural oxide film layer of the second electrode layer 130 is sufficiently removed at the connecting surface 131. This sufficiently reduces the contact resistance between the second electrode layer 130 and the connecting electrode 140 at the connecting surface 131.

[0070] In this embodiment, the surface roughness Ra of the connecting surface 131 is 30 nm or more and less than 1 μm. The surface roughness Ra of the main surface 132 is less than 1 nm.

[0071] The surface roughness Ra of the connecting surface 131 is 20 nm or more and less than 1 μm, thereby further improving the adhesion between the second electrode layer 130 and the connecting electrode 140 and reducing the contact resistance between the second electrode layer 130 and the connecting electrode 140. In addition, the surface roughness Ra of the main surface 132 is less than 1 nm, thereby improving the bonding strength between the piezoelectric layer 110 and the second electrode layer 130.

[0072] In this embodiment, the surface roughness Ra of the main surface 132 exceeds 0.05 nm. Therefore, it is easy to set the surface roughness Ra of the main surface to a level that can improve the bonding strength between the piezoelectric layer 110 and the second electrode layer 130.

[0073] In this embodiment, the width of the connecting electrode 140 on the connecting surface 131 in the direction parallel to the second surface 112 is larger than the shortest distance between the connecting surface 131 and the main surface 132 in the direction perpendicular to the second surface 112.

[0074] Therefore, at the connection surface 131 having a surface roughness Ra as described above, the contact area between the connection electrode 140 and the second electrode layer 130 can be increased, thereby reducing the contact resistance between the connection electrode 140 and the second electrode layer 130.

[0075] In this embodiment, the second electrode layer 130 further has an inner surface 133 that connects the connecting surface 131 and the main surface 132 in a direction perpendicular to the second surface 112. The connecting electrode 140 is also provided on the inner surface 133.

[0076] Therefore, at the inner surface 133, the connecting electrode 140 and the second electrode layer 130 are also joined together, thus further improving the tightness between the second electrode layer 130 and the connecting electrode 140.

[0077] In this embodiment, the connection surface 131 of the connecting electrode 140 and the second electrode layer 130 are in ohmic contact.

[0078] Therefore, there is no Schottky barrier between the connecting electrode 140 and the second electrode layer 130, resulting in a smaller contact resistance between the connecting electrode 140 and the second electrode layer 130, and an improved motor conversion efficiency of the piezoelectric element 100.

[0079] In this embodiment, the connecting electrode 140 is continuously disposed from the connecting surface 131 to the inner surface 114 of the through hole 113 and the first surface 111.

[0080] Therefore, on the first surface 111, the electrode of the second electrode layer 130 can be removed together with the first electrode layer 120. Furthermore, an external electrode (not shown) connected to the connecting electrode 140 can be efficiently guided.

[0081] In this embodiment, the second electrode layer 130 is a doped single-crystal silicon layer. Because the second electrode layer 130 is single-crystal, the bonding strength with the piezoelectric layer 110 is improved, thereby increasing the motor conversion efficiency of the piezoelectric element 100. Furthermore, compared to the case where it is composed of an undoped single-crystal silicon layer, the resistance of the second electrode layer 130 can be reduced.

[0082] In this embodiment, the piezoelectric layer 110 is formed of a single-crystal material containing lithium niobate (LiNbO3) or lithium tantalate (LiTaO3). As a result, the bonding strength between the piezoelectric layer 110 and the second electrode layer 130 is improved, and the motor conversion efficiency of the piezoelectric element 100 is improved.

[0083] In this embodiment, the piezoelectric element 100 further includes a base 150 that supports a laminate 101 comprising at least a first electrode layer 120, a piezoelectric body layer 110, and a 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 along the periphery of the surface of the laminate 101 on the side of the base 150 when viewed from the lamination direction of the laminate 101.

[0084] Therefore, the driving force of the piezoelectric layer 110 can be converted into the bending vibration of the diaphragm portion 104, thereby improving the device characteristics of the piezoelectric element 100.

[0085] In this embodiment, a through slit 105 is provided in the laminate 101, which communicates with the opening 103 located inside the base 150 when viewed from the lamination direction.

[0086] As a result, the bending vibration of the diaphragm portion 104 is further increased, which can improve the device characteristics of the piezoelectric element 100.

[0087] Furthermore, in the piezoelectric element 100b of the second variation of Embodiment 1 of the present invention, the width of the connecting electrode 140b on the connecting surface 131 in the direction parallel to the second surface 112 is larger than the maximum distance between the connecting electrode 140 and the inner surface 114 of the through hole 113 in the direction parallel to the second surface 112.

[0088] As a result, the contact area between the connecting electrode 140 on the connecting surface 131 and the second electrode layer 130 becomes larger, thereby reducing the contact resistance between the connecting electrode 140 and the second electrode layer 130.

[0089] (Implementation Method 2)

[0090] The piezoelectric element of Embodiment 2 of the present invention will now be described. The piezoelectric element of Embodiment 2 of the present invention differs from the piezoelectric element of Embodiment 1 of the present invention primarily in the presence of an intermediate layer. Therefore, the same structure as the piezoelectric element 100 of Embodiment 1 of the present invention will not be described again.

[0091] Figure 12 This is a cross-sectional view showing the structure of the piezoelectric element according to Embodiment 2 of the present invention. Figure 12 In the middle, with Figure 2 The same sectional view is illustrated.

[0092] In the piezoelectric element 200 of Embodiment 2 of the present invention, an intermediate layer 260 is provided between the second electrode layer 130 and the piezoelectric body layer 110. This improves the bonding strength between the second electrode layer 130 and the piezoelectric body layer 110. The intermediate layer 260 can be a metal layer or a dielectric layer such as SiO2. In this embodiment, a through-hole is provided in the intermediate layer 260 in a manner continuous with the through-hole 113 provided in the piezoelectric body layer 110.

[0093] In each of the above embodiments, the contact state between the connecting electrode and the second electrode layer can be evaluated based on the movement of the diaphragm portion when a voltage is applied between the upper electrode layer and the lower electrode layer.

[0094] In the above description of the embodiments, the combinable structures can also be combined with each other.

[0095] The embodiments disclosed herein should be considered illustrative in all respects and not limiting. The scope of the invention is defined by the claims rather than by the foregoing description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0096] Explanation of reference numerals in the attached figures

[0097] 100, 100a, 100b, 200, piezoelectric element; 101, laminate; 102S, laminated substrate; 103, opening; 104, diaphragm portion; 105, through slit; 110, piezoelectric layer; 110S, piezoelectric substrate; 111, first surface; 111S, first main surface; 112, second surface; 112S, second main surface; 113, through hole; 114, inner surface; 120, first electrode layer; 130, second electrode layer; 131, connecting surface; 132, main surface; 133, inner surface; 135, 135a, silicon oxide film; 140, 140b, connecting electrode; 145, outer connecting electrode; 150, base; 151, silicon oxide layer; 152, base body; 260, intermediate 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 extending from the first surface to the second surface; The first electrode layer is disposed on the first surface side of the piezoelectric layer; A second electrode layer, located on the second surface side of the piezoelectric layer, at least partially separated from the first electrode layer by the piezoelectric layer, and facing the through-hole; and A connecting electrode is disposed on the connecting surface of the second electrode layer facing the through hole. The second electrode layer contains silicon as its main component. The connecting electrodes are formed of metal. The surface roughness Ra of the connecting surface is greater than the surface roughness Ra of the main surface (excluding the connecting surface) on the piezoelectric layer side of the second electrode layer. The connecting surface is located inside the second electrode layer relative to the main surface in a direction perpendicular to the second surface. The shortest distance between the connecting surface and the main surface in the direction perpendicular to the second surface is 5 nm or more.

2. The piezoelectric element according to claim 1, wherein, The main surface is covered with a silicon oxide film. The connection surface is either not covered by a silicon oxide film or is covered by a silicon oxide film. The silicon oxide film covering the connecting surface is thinner than the silicon oxide film covering the main surface.

3. The piezoelectric element according to claim 1 or 2, wherein, The surface roughness Ra of the connecting surface is greater than 30 nm and less than 1 μm. The surface roughness Ra of the main surface is less than 1 nm.

4. The piezoelectric element according to claim 3, wherein, The surface roughness Ra of the main surface exceeds 0.05 nm.

5. The piezoelectric element according to claim 1 or 2, wherein, The width of the connecting electrode on the connecting surface in the direction parallel to the second surface is larger than the shortest distance between the connecting surface and the main surface in the direction perpendicular to the second surface.

6. The piezoelectric element according to claim 1 or 2, wherein, The width of the connecting electrode on the connecting surface in the direction parallel to the second surface is greater than the maximum distance between the connecting electrode and the inner surface of the through hole in the direction parallel to the second surface.

7. The piezoelectric element according to claim 1 or 2, wherein, The second electrode layer also has an inner surface that connects the connecting surface to the main surface in a direction perpendicular to the second surface. The connecting electrode is also provided on the inner surface.

8. The piezoelectric element according to claim 1 or 2, wherein, The connecting electrode is in ohmic contact with the connecting surface of the second electrode layer.

9. The piezoelectric element according to claim 1 or 2, wherein, The connecting electrode is continuously disposed from the connecting surface to the inner surface of the through hole and the first surface.

10. The piezoelectric element according to claim 1 or 2, wherein, The second electrode layer is a doped single-crystal silicon layer.

11. The piezoelectric element according to claim 1 or 2, wherein, The piezoelectric layer is formed from a single-crystal material containing lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

12. The piezoelectric element according to claim 1 or 2, wherein, An intermediate layer is provided between the second electrode layer and the piezoelectric layer.

13. The piezoelectric element according to claim 1 or 2, wherein, The piezoelectric element also includes a base that supports a laminate comprising at least the first electrode layer, the piezoelectric body layer, and the second electrode layer. The base is located on the side of the second electrode layer of the laminate and is formed in a ring shape along the periphery of the surface of the base side of the laminate when viewed from the lamination direction of the laminate.

14. The piezoelectric element according to claim 13, wherein, The laminated body is provided with a through slit that communicates with an opening located inside the base when viewed from the lamination direction.

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