Piezoelectric device

Abstract

A piezoelectric device is provided, in which a first recess (132) is formed in a first opposed surface (131) of a single-crystal piezoelectric layer (130) that faces a main surface (111) of a base (110). The single-crystal piezoelectric layer (130) is joined to the main surface (111) of the base (110) at a portion other than the first recess (132) in the first opposed surface (131). At least a part of a lower electrode layer (150) that constitutes at least a part of a pair of electrode layers and extends along the base (110) side of the single-crystal piezoelectric layer (130) is located within the first recess (132). The surface roughness Ra of a second opposed surface (151) of the lower electrode layer (150) that faces the main surface (111) of the base (110) is larger than the surface roughness Ra of the first opposed surface (131) of the single-crystal piezoelectric layer (130).

Description

Technical Field

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

[0002] As an existing document that discloses the structure of a piezoelectric device, there is "Single crystal FBAR with LiNbO3 and LiTaO3", Proceedings of Symposium on Ultrasonic Electronics, Vol.28, (2007), PP.151-152 (Non-Patent Document 1). In the piezoelectric device described in Non-Patent Document 1, a space is formed between the lower electrode layer formed on the piezoelectric layer and the substrate.

[0003] Prior Art Documents

[0004] Non-Patent Documents

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

[0006] Problems to be Solved by the Invention

[0007] In the piezoelectric device described in Non-Patent Document 1, when the lower electrode layer and the substrate are joined to each other during the excitation of the piezoelectric device, the excitation characteristics of the piezoelectric device become unstable.

[0008] The present invention has been completed in view of the above problems, and an object thereof is to provide a piezoelectric device with stable excitation characteristics.

[0009] Means for Solving the Problems

[0010] The piezoelectric device of the present invention includes a base portion and a stacked portion. The base portion includes one main surface and another main surface located on the side opposite to the one main surface. The stacked portion is stacked on one main surface side of the base portion. The stacked portion includes a single crystal piezoelectric layer and a pair of electrode layers for applying a voltage to the single crystal piezoelectric layer. A first recess is formed in a first opposed surface of the single crystal piezoelectric layer that faces the one main surface of the base portion. The single crystal piezoelectric layer is joined to the one main surface of the base portion at portions other than the first recess in the first opposed surface. At least a part of a lower electrode layer that constitutes at least a part of the pair of electrode layers and extends along the base portion side of the single crystal piezoelectric layer is located within the first recess. The surface roughness (Ra) of a second opposed surface of the lower electrode layer that faces the one main surface of the base portion is larger than the surface roughness (Ra) of the first opposed surface of the single crystal piezoelectric layer.

[0011] Advantages of the Invention

[0012] According to the present invention, the excitation characteristics of the piezoelectric device can be stabilized. Description of the Drawings

[0013] Figure 1 It is a cross-sectional view taken laterally showing the structure of the piezoelectric device according to Embodiment 1 of the present invention.

[0014] Figure 2 It is a cross-sectional view of the single crystal piezoelectric layer showing the state before forming the first recess in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0015] Figure 3 It is a cross-sectional view of the single crystal piezoelectric layer showing the state in which the first recess is formed in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0016] Figure 4 It is a cross-sectional view showing the state in which the lower electrode layer is provided within the first recess in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0017] Figure 5 It is a cross-sectional view of the base portion before being joined to the single crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0018] Figure 6 It is a cross-sectional view showing the state after joining the first opposed surface of the single crystal piezoelectric layer to the one main surface of the base portion in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0019] Figure 7 It is a cross-sectional view showing the state in which the upper surface of the single crystal piezoelectric layer is shaved off in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0020] Figure 8It is a cross-sectional view showing the structure of the piezoelectric device according to Embodiment 2 of the present invention.

[0021] Figure 9 It is a cross-sectional view showing a state in which a reinforcing lower electrode layer is provided on a part of the second opposing surface of the lower electrode layer in the manufacturing method of the piezoelectric device according to Embodiment 2 of the present invention.

[0022] Figure 10 It is a cross-sectional view showing a state in which a second recess and a protrusion are formed in the base in the manufacturing method of the piezoelectric device according to Embodiment 2 of the present invention.

[0023] Figure 11 It is a cross-sectional view showing a state after the first opposing surface of the single crystal piezoelectric layer is joined to one main surface of the base in the manufacturing method of the piezoelectric device according to Embodiment 2 of the present invention.

[0024] Figure 12 It is a cross-sectional view showing a state in which the upper surface of the single crystal piezoelectric layer is shaved in the manufacturing method of the piezoelectric device according to Embodiment 2 of the present invention.

[0025] Figure 13 It is a cross-sectional view showing a state in which a hole portion is provided in the single crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 2 of the present invention.

[0026] Figure 14 It is a cross-sectional view showing the structure of the piezoelectric device according to Embodiment 3 of the present invention.

[0027] Figure 15 It is a cross-sectional view showing the structure of the piezoelectric device according to Embodiment 4 of the present invention. Detailed Embodiments

[0028] Hereinafter, the piezoelectric devices according to the embodiments of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same or corresponding parts in the drawings are denoted by the same reference numerals, and their description will not be repeated.

[0029] (Embodiment 1)

[0030] Figure 1 It is a cross-sectional view showing the structure of the piezoelectric device according to Embodiment 1 of the present invention. As Figure 1 shown, the piezoelectric device 100 according to Embodiment 1 of the present invention includes a base 110 and a stacked portion 120.

[0031] The base 110 includes one main surface 111 and another main surface 112 located on the side opposite to the one main surface 111. In the present embodiment, the base 110 is made of Si. However, the material constituting the base 110 is not limited to Si.

[0032] The stacked portion 120 is stacked on one main surface 111 side of the base portion 110. The stacked portion 120 includes a single crystal piezoelectric layer 130 and a pair of electrode layers. The pair of electrode layers applies a voltage to the single crystal piezoelectric layer 130. In the present embodiment, the pair of electrode layers is composed of an upper electrode layer 140 and a lower electrode layer 150.

[0033] The single crystal piezoelectric layer 130 is located at a position above the base portion 110. In the present embodiment, the single crystal piezoelectric layer 130 is located on one main surface 111 of the base portion 110. A first recess 132 is formed in a first opposed surface 131 of the single crystal piezoelectric layer 130 that faces the one main surface 111 of the base portion 110. In the present embodiment, when viewed from a direction orthogonal to the first opposed surface 131, the outer shape of the first recess 132 is circular, but it may also be elliptical or polygonal, or any other arbitrary shape. The single crystal piezoelectric layer 130 is joined to the one main surface 111 of the base portion 110 at portions other than the first recess 132 in the first opposed surface 131.

[0034] In the present embodiment, the inside of the first recess 132 becomes a sealed space. In the piezoelectric device 100 of the present embodiment, the pressure inside the first recess 132 is a negative pressure. It should be noted that the pressure inside the first recess 132 may also be atmospheric pressure or a positive pressure.

[0035] The single crystal piezoelectric layer 130 is made of lithium tantalate or lithium niobate. The polarization states of the single crystal piezoelectric layer 130 made of lithium tantalate or lithium niobate are the same. The single crystal piezoelectric layer 130 may also be made of quartz.

[0036] The upper electrode layer 140 is disposed on the upper side of the single crystal piezoelectric layer 130. In the present embodiment, the upper electrode layer 140 is disposed on the upper side of a part of the single crystal piezoelectric layer 130. It should be noted that a close contact layer made of, for example, Ti, Cr, Ni, or NiCr may be disposed between the upper electrode layer 140 and the single crystal piezoelectric layer 130. The upper electrode layer 140 is made of a metal such as Al, Pt, Mo, or W, for example.

[0037] The upper electrode layer 140 is disposed such that at least a part of the upper electrode layer 140 is located above the first recess 132. In the present embodiment, a pair of upper electrode layers 140 are formed above the first recess 132 with an interval therebetween.

[0038] The pair of upper electrode layers 140 are respectively connected to the first lead wiring 160. The first lead wiring 160 is made of a metal such as Au, Pt, or Al, for example. A close contact layer may also be formed between the first lead wiring 160 and the upper electrode layer 140. The close contact layer is made of, for example, Ti, Cr, Ni, or NiCr. In addition, the first lead wiring 160 is in ohmic contact with the upper electrode layer 140.

[0039] The lower electrode layer 150 is arranged to face at least a part of each of the pair of upper electrode layers 140 with the single crystal piezoelectric layer 130 therebetween. In the present embodiment, the lower electrode layer 150 forms a part of the pair of electrode layers. The upper electrode layers 140 are electrically connected to each other via the lower electrode layer 150.

[0040] The lower electrode layer 150 extends along the base 110 side of the single crystal piezoelectric layer 130. Specifically, the lower electrode layer 150 extends along the bottom surface of the first recess 132 of the single crystal piezoelectric layer 130. In the present embodiment, the lower electrode layer 150 is only located within the first recess 132. However, the position where the lower electrode layer 150 is arranged is not limited to within the first recess 132, and at least a part of the lower electrode layer 150 may be located within the first recess 132. The lower electrode layer 150 is made of a metal such as Al, Pt, Mo, or W, for example.

[0041] As Figure 1 shown, the dimension t1 of the thickness of the lower electrode layer 150 is equal to or less than the dimension H1 of the depth of the first recess 132. Preferably, in order to make the excitation characteristics of the piezoelectric device 100 more stable, it is preferred that the dimension t1 of the thickness of the lower electrode layer 150 is less than the dimension H1 of the depth of the first recess 132.

[0042] The surface roughness (Ra) of the second facing surface 151 of the lower electrode layer 150 facing one main surface 111 of the base 110 is larger than the surface roughness (Ra) of the first facing surface 131 of the single crystal piezoelectric layer 130. It should be noted that the surface roughness (Ra) is the arithmetic mean roughness (JIS B 0601). In the present embodiment, the surface roughness (Ra) of the second facing surface 151 of the lower electrode layer 150 is 0.5 nm or more and 5.0 nm or less.

[0043] Hereinafter, a method for manufacturing the piezoelectric device 100 according to Embodiment 1 of the present invention will be described.

[0044] Figure 2 is a cross-sectional view of the single crystal piezoelectric layer showing the state before the formation of the first recess in the method for manufacturing the piezoelectric device according to Embodiment 1 of the present invention. Figure 3 is a cross-sectional view of the single crystal piezoelectric layer showing the state in which the first recess has been formed in the method for manufacturing the piezoelectric device according to Embodiment 1 of the present invention.

[0045] Figure 2 The thickness of the single crystal piezoelectric layer 130 at the time of formation shown is thicker than the thickness of the single crystal piezoelectric layer 130 finally included in the piezoelectric device 100 of the present embodiment.

[0046] As Figure 3As shown, the first recess 132 is formed in the single crystal piezoelectric layer 130 by performing reactive ion etching (RIE) or the like on the single crystal piezoelectric layer 130 from the side of the first opposing surface 131 of the single crystal piezoelectric layer 130.

[0047] Figure 4 FIG. is a cross-sectional view showing a state in which a lower electrode layer is provided in the first recess of the single crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. As Figure 4 shown, the lower electrode layer 150 is provided in the first recess 132 of the single crystal piezoelectric layer 130 by a lift-off method, a plating method, an etching method, or the like.

[0048] Figure 5 FIG. is a cross-sectional view of the base before being joined to the single crystal piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 6 FIG. is a cross-sectional view showing a state after joining the first opposing surface of the single crystal piezoelectric layer to one main surface of the base in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0049] As Figure 5 and Figure 6 shown, the first opposing surface 131 of the single crystal piezoelectric layer 130 is joined to one main surface 111 of the base 110 by surface activation bonding, atomic diffusion bonding, or the like. A bonding layer including Ti or the like may be interposed between the bonding surfaces. Thus, the inside of the first recess 132 becomes a closed space.

[0050] In the present embodiment, in order to suppress foreign matter from entering the inside of the first recess 132, the single crystal piezoelectric layer 130 is joined to the base 110 under a vacuum pressure. In this case, the above-mentioned vacuum pressure may be any one of low vacuum, medium vacuum, high vacuum, and ultra-high vacuum. Since the single crystal piezoelectric layer 130 is joined to the base 110 in this way, the pressure inside the first recess 132 becomes negative pressure.

[0051] It should be noted that the atmosphere when joining the single crystal piezoelectric layer 130 to the base 110 is not limited to under vacuum pressure. The single crystal piezoelectric layer 130 may be joined to the base 110 at atmospheric pressure, or may be joined to the base 110 at a pressure higher than atmospheric pressure.

[0052] Figure 7 FIG. is a cross-sectional view showing a state in which the upper surface of the single crystal piezoelectric layer has been shaved in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. As Figure 7As shown, the upper surface of the single-crystal piezoelectric layer 130 is removed by CMP (Chemical Mechanical Polishing) or the like so that the single-crystal piezoelectric layer 130 has a desired thickness. In this case, the thickness of the single-crystal piezoelectric layer 130 is adjusted to obtain a desired amount of expansion and contraction of the single-crystal piezoelectric layer 130 by applying a voltage.

[0053] It should be noted that a peeling layer may be formed by previously performing ion implantation on the upper surface side of the single-crystal piezoelectric layer 130. In this case, before removing the upper surface of the single-crystal piezoelectric layer 130 by CMP or the like, the peeling layer is peeled off, whereby the thickness adjustment of the single-crystal piezoelectric layer 130 becomes easy.

[0054] As Figure 1 shown, an upper electrode layer 140 is provided on a part of the upper surface of the single-crystal piezoelectric layer 130 by a peeling method, a plating method, an etching method, or the like. In this way, the stacked portion 120 is stacked on one main surface 111 side of the base 110. Further, a first lead wiring 160 is formed so as to be connected to the upper surface of the upper electrode layer 140 by a photolithography method, a peeling method, or the like.

[0055] Through the above-described steps, the piezoelectric device 100 of Embodiment 1 of the present invention shown in Figure 1 is manufactured.

[0056] As described above, in the piezoelectric device 100 of the present embodiment, the surface roughness (Ra) of the second opposed surface 151 of the lower electrode layer 150 that faces one main surface 111 of the base 110 is larger than the surface roughness (Ra) of the first opposed surface 131 of the single-crystal piezoelectric layer 130. Thus, assuming that the second opposed surface 151 of the lower electrode layer 150 and one main surface 111 of the base 110 are joined to each other during excitation of the piezoelectric device 100, the joining strength can be reduced. As a result, it is possible to suppress the excitation characteristics of the piezoelectric device 100 from becoming unstable due to the joining of the second opposed surface 151 of the lower electrode layer 150 and one main surface 111 of the base 110. That is, the excitation characteristics of the piezoelectric device 100 can be stabilized.

[0057] In the piezoelectric device 100 of the present embodiment, the surface roughness (Ra) of the second opposed surface 151 of the lower electrode layer 150 is 0.5 nm or more and 5.0 nm or less. Thus, it is difficult for the second opposed surface 151 of the lower electrode layer 150 and one main surface 111 of the base 110 to be joined to each other, and therefore, the excitation characteristics of the piezoelectric device 100 can be made more stable.

[0058] In the piezoelectric device 100 of the present embodiment, the lower electrode layer 150 is only located within the first recess 132. Thus, when bonding the single crystal piezoelectric layer 130 and the base 110 to each other, high-precision alignment between the single crystal piezoelectric layer 130 and the base 110 is not required, and thus, the single crystal piezoelectric layer 130 and the base 110 can be easily bonded. In addition, when the single crystal piezoelectric layer 130 vibrates by applying a voltage through the upper electrode layer 140 and the lower electrode layer 150, it is possible to suppress the vibration from spreading to the periphery of the piezoelectric device 100 through the lower electrode layer 150 and attenuating. As a result, the excitation efficiency of the piezoelectric device 100 can be improved.

[0059] In the piezoelectric device 100 of the present embodiment, the dimension t1 of the thickness of the lower electrode layer 150 is equal to or less than the dimension H1 of the depth of the first recess 132. Thus, even if one main surface 111 of the base 110 is a flat surface without a recess, the lower electrode layer 150 can be accommodated within the first recess 132. As a result, the structure of the piezoelectric device 100 can be made simple.

[0060] (Embodiment 2)

[0061] Hereinafter, the piezoelectric device according to Embodiment 2 of the present invention will be described with reference to the drawings. The main difference between the piezoelectric device according to Embodiment 2 of the present invention and the piezoelectric device 100 according to Embodiment 1 of the present invention is that a second recess is formed in one main surface of the base, and the lower electrode layer is in contact with the base. Therefore, the same structure as that of the piezoelectric device 100 according to Embodiment 1 of the present invention will not be described again.

[0062] Figure 8 is a cross-sectional view showing the structure of the piezoelectric device according to Embodiment 2 of the present invention. As Figure 8 shown, the piezoelectric device 200 according to Embodiment 2 of the present invention includes a base 110 and a stacked portion 220.

[0063] In the present embodiment, a second recess 113 is formed at a position on one main surface 111 of the base 110 that is opposite to the first recess 132. When viewed in a direction orthogonal to one main surface 111, the outer shape of the second recess 113 is circular, but it may also be elliptical or polygonal, or any other arbitrary shape.

[0064] As Figure 8 shown, the second recess 113 is covered from above by the stacked portion 220 laminated on one main surface 111 side of the base 110. In the present embodiment, the interiors of the first recess 132 and the second recess 113 form a sealed space.

[0065] In the piezoelectric device 200 of the present embodiment, the pressure inside the first concave portion 132 and the second concave portion 113 is negative pressure. It should be noted that the pressure inside the first concave portion 132 and the second concave portion 113 may also be atmospheric pressure or positive pressure.

[0066] In the present embodiment, in a portion of the single crystal piezoelectric layer 130 above the lower electrode layer 150, a hole portion 133 is provided that penetrates from the upper surface on the side opposite to the first opposing surface 131 to the bottom surface of the first concave portion 132.

[0067] A part of the lower electrode layer 150 is arranged to be located below the hole portion 133 formed in the single crystal piezoelectric layer 130. In the present embodiment, the lower electrode layer 150 is formed to cover the hole portion 133 of the single crystal piezoelectric layer 130 from below.

[0068] As Figure 8 shown, a second lead-out wiring 270 is provided that is electrically connected to the lower electrode layer 150 through the hole portion 133. Specifically, the second lead-out wiring 270 is connected to the upper surface of the lower electrode layer 150 within the hole portion 133, penetrates through the hole portion 133, and is led out along the upper surface of the single crystal piezoelectric layer 130 on the side opposite to the base portion 110 side.

[0069] The second lead-out wiring 270 is made of a metal such as Au, Pt, or Al, for example. A bonding layer may also be formed between the second lead-out wiring 270 and the lower electrode layer 150. The bonding layer is made of Ti, Cr, Ni, or NiCr, for example. In addition, the second lead-out wiring 270 is in ohmic contact with the lower electrode layer 150.

[0070] It should be noted that the lower electrode layer 150 may also be formed to cover the lower part of the hole portion 133 of the single crystal piezoelectric layer 130 via a bonding layer. The material of the bonding layer may be any material having conductivity and adhesiveness, and is not particularly limited. The bonding layer is made of Ti, Cr, Ni, or NiCr, for example.

[0071] In the present embodiment, the base portion 110 includes a protruding portion 114 that protrudes into the second concave portion 113 from the bottom of the second concave portion 113. It should be noted that the protruding portion 114 may not necessarily be provided. As Figure 8 shown, the depth of the second concave portion 113 is H2, and the height of the protruding portion 114 from the bottom of the second concave portion 113 is H3, satisfying the relationship of H3 < H2.

[0072] The protruding portion 114 has a cylindrical shape. The shape of the protruding portion 114 is not limited to a cylindrical shape, and may also be a prismatic shape or any other arbitrary shape.

[0073] When viewed from a direction orthogonal to one main surface 111, the entire interior of the hole portion 133 overlaps with the upper surface 114t of the protruding portion 114. When viewed from a direction orthogonal to one main surface 111, the area inside the hole portion 133 is equal to or less than the area of the upper surface 114t of the protruding portion 114.

[0074] In the present embodiment, a reinforcing lower electrode layer 250 is provided between the lower electrode layer 150 and the upper surface 114t of the protruding portion 114. The reinforcing lower electrode layer 250 does not necessarily have to be conductive and does not necessarily have to be made of metal.

[0075] As Figure 8 shown, the thickness of the lower electrode layer 150 in the portion where the voltage is applied to the single crystal piezoelectric layer 130 is t1, and the combined thickness of the lower electrode layer 150 and the reinforcing lower electrode layer 250 in the portion between the upper surface 114t of the protruding portion 114 and the hole portion 133 is t2, satisfying the relationship t2 > t1.

[0076] That is, in the lower electrode layer including the lower electrode layer 150 and the reinforcing lower electrode layer 250, the portion between the upper surface 114t of the protruding portion 114 and the hole portion 133 is thicker than the portion where the voltage is applied to the single crystal piezoelectric layer 130.

[0077] The upper surface 114t of the protruding portion 114 is in contact with the lower electrode layer. In the present embodiment, the upper surface 114t of the protruding portion 114 is in contact with the reinforcing lower electrode layer 250.

[0078] As described above, in the present embodiment, the lower electrode layer including the lower electrode layer 150 and the reinforcing lower electrode layer 250 includes a region where the dimension t2 of the thickness of the lower electrode layer is larger than the dimension H1 of the depth of the first concave portion 132, and in this region, it is in contact with the protruding portion 114 of the base portion 110 located in the second concave portion 113.

[0079] The surface roughness (Ra) of the second opposed surface 251 of the reinforcing lower electrode layer 250 that faces the upper surface 114t of the protruding portion 114 is larger than the surface roughness (Ra) of the first opposed surface 131 of the single crystal piezoelectric layer 130. In the present embodiment, the surface roughness (Ra) of the second opposed surface 251 of the reinforcing lower electrode layer 250 is 0.5 nm or more and 5.0 nm or less.

[0080] Hereinafter, a method for manufacturing the piezoelectric device 200 according to Embodiment 2 of the present invention will be described.

[0081] Up to Figures 2 to 4 the steps shown, the method for manufacturing the piezoelectric device 200 according to Embodiment 2 of the present invention is the same as the method for manufacturing the piezoelectric device 100 according to Embodiment 1 of the present invention.

[0082] Figure 9 This is a cross-sectional view showing a state in which a reinforcing lower electrode layer is provided on a part of the second opposing surface of the lower electrode layer in the method for manufacturing a piezoelectric device according to Embodiment 2 of the present invention. As Figure 9 shown, the reinforcing lower electrode layer 250 is provided on a part of the second opposing surface 151 of the lower electrode layer 150 by a peeling method, a plating method, an etching method, or the like.

[0083] Figure 10 This is a cross-sectional view showing a state in which a second recess and a protrusion are formed in the base in the method for manufacturing a piezoelectric device according to Embodiment 2 of the present invention. As Figure 10 shown, deep reactive ion etching (DRIE) or the like is performed on the base 110 from one main surface 111 side of the base 110 to form a second recess 113 and a protrusion 114 in the base 110.

[0084] Figure 11 This is a cross-sectional view showing a state after the first opposing surface of the single crystal piezoelectric layer is joined to one main surface of the base in the method for manufacturing a piezoelectric device according to Embodiment 2 of the present invention.

[0085] As Figure 11 shown, the first opposing surface 131 of the single crystal piezoelectric layer 130 is joined to one main surface 111 of the base 110 by surface activation bonding, atomic diffusion bonding, or the like. A bonding layer including Ti or the like may be interposed between the bonding surfaces. Thus, the interiors of the first recess 132 and the second recess 113 become sealed spaces. At this time, a state is achieved in which the reinforcing lower electrode layer 250 is in contact with the upper surface 114t of the protrusion 114.

[0086] Figure 12 This is a cross-sectional view showing a state in which the upper surface of the single crystal piezoelectric layer has been shaved in the method for manufacturing a piezoelectric device according to Embodiment 2 of the present invention. As Figure 12 shown, the upper surface of the single crystal piezoelectric layer 130 is shaved by CMP or the like so that the single crystal piezoelectric layer 130 has a desired thickness.

[0087] Figure 13 This is a cross-sectional view showing a state in which holes are provided in the single crystal piezoelectric layer in the method for manufacturing a piezoelectric device according to Embodiment 2 of the present invention. As Figure 13 shown, holes 133 are provided in the single crystal piezoelectric layer 130 by an etching method such as RIE.

[0088] As Figure 8As shown, an upper electrode layer 140 is provided on a part of the upper surface of the single crystal piezoelectric layer 130 by a peeling method, a plating method, an etching method, or the like. In this way, the stacked portion 220 is stacked on one main surface 111 side of the base 110. It should be noted that a through slit communicating with the first recess 132 may also be provided in the stacked portion 220 by RIE or the like.

[0089] Furthermore, the first lead wiring 160 is formed to be connected to the upper surface of the base 110 by a photolithography method, a peeling method, or the like on the upper electrode layer 140.

[0090] Finally, the second lead wiring 270 is formed by a photolithography method, a peeling method, or the like. Through the above procedures, the Figure 8 piezoelectric device 200 of Embodiment 2 of the present invention shown is manufactured.

[0091] As described above, in the piezoelectric device 200 of the present embodiment, a second recess 113 is formed at a position on one main surface 111 of the base 110 opposite to the first recess 132. The lower electrode layer includes a region where the dimension t2 of the thickness of the lower electrode layer is larger than the dimension H1 of the depth of the first recess 132, and in this region, it is in contact with the protruding portion 114 of the base 110 located in the second recess 113. Thus, the stacked portion 220 is supported by the protruding portion 114, and it is possible to suppress the portion on the first recess 132 in the stacked portion 220 from bending toward the second recess 113 side, and it is possible to suppress cracks from occurring in the stacked portion 220 when the second lead wiring 270 is formed.

[0092] (Embodiment 3)

[0093] Hereinafter, the piezoelectric device of Embodiment 3 of the present invention will be described with reference to the drawings. The main difference between the piezoelectric device of Embodiment 3 of the present invention and the piezoelectric device 200 of Embodiment 2 of the present invention is that the second recess and the reinforcing lower electrode layer are not provided. Therefore, the same structure as that of the piezoelectric device 200 of Embodiment 2 of the present invention will not be described again.

[0094] Figure 14 is a transverse cross-sectional view showing the structure of the piezoelectric device of Embodiment 3 of the present invention. As Figure 14 shown, the piezoelectric device 300 of Embodiment 3 of the present invention includes a base 110 and a stacked portion 320.

[0095] In the present embodiment, a pair of electrode layers is composed of an upper electrode layer 140 and a lower electrode layer 150. However, a pair of electrode layers may also be composed of only the lower electrode layer 150. Specifically, it may be configured such that in the lower electrode layer 150, a pair of comb-shaped electrode layers is formed, and the piezoelectric device 300 applies a voltage to the single crystal piezoelectric layer 130 located between the comb-shaped electrode layers.

[0096] In the piezoelectric device 300 of the present embodiment, the surface roughness (Ra) of the second opposed surface 151 of the lower electrode layer 150 that faces one main surface 111 of the base 110 is larger than the surface roughness (Ra) of the first opposed surface 131 of the single crystal piezoelectric layer 130. Thus, assuming that the portion on the first recess 132 in the stacked portion 320 bends toward the base 110 side and the second opposed surface 151 of the lower electrode layer 150 and one main surface 111 of the base 110 are joined to each other, the joining strength can be reduced. As a result, it is possible to suppress the excitation characteristics of the piezoelectric device 300 from becoming unstable due to the joining of the second opposed surface 151 of the lower electrode layer 150 and one main surface 111 of the base 110. That is, the excitation characteristics of the piezoelectric device 300 can be stabilized.

[0097] (Embodiment 4)

[0098] Hereinafter, the piezoelectric device according to Embodiment 4 of the present invention will be described with reference to the drawings. The main difference between the piezoelectric device according to Embodiment 4 of the present invention and the piezoelectric device 100 according to Embodiment 1 of the invention is that a lower electrode for extraction is provided. Therefore, the same structure as that of the piezoelectric device 100 according to Embodiment 1 of the present invention will not be described again.

[0099] Figure 15 is a cross-sectional view showing the structure of the piezoelectric device according to Embodiment 4 of the present invention. As Figure 15 shown, the piezoelectric device 400 according to Embodiment 4 of the present invention includes a base 110 and a stacked portion 420. The piezoelectric device 400 further includes an intermediate layer 410 provided between the base 110 and the stacked portion 420.

[0100] The stacked portion 420 is stacked on one main surface 111 side of the base 110 via the intermediate layer 410. The first opposed surface 131 of the single crystal piezoelectric layer 130 is joined to one main surface 411 of the intermediate layer 410. The intermediate layer 410 is made of SiO2. The material of the intermediate layer 410 is not limited to SiO2 and may be an insulator. For example, the intermediate layer 410 may also be made of an organic material having electrical insulation and heat insulation properties.

[0101] In the present embodiment, a lower electrode 450 for extraction is provided between the intermediate layer 410 and the lower electrode layer 150. The lower electrode 450 for extraction is connected to the lower electrode layer 150 within the first recess 132 and is led out along the interface between the intermediate layer 410 and the single crystal piezoelectric layer 130. When viewed from a direction orthogonal to the first opposed surface 131, the lower electrode 450 for extraction is electrically connected to the second lead wiring 470 through the hole portion 133 outside the first recess 132.

[0102] In the piezoelectric device 400 of the present embodiment, the surface roughness (Ra) of the second opposed surface 151 of the lower electrode layer 150 that opposes one main surface 111 of the base portion 110 is larger than the surface roughness (Ra) of the first opposed surface 131 of the single crystal piezoelectric layer 130. Thus, assuming that the second opposed surface 151 of the lower electrode layer 150 and one main surface 411 of the intermediate layer 410 are joined to each other, the joining strength can be reduced. As a result, it is possible to suppress the excitation characteristics of the piezoelectric device 400 from becoming unstable due to the joining of the second opposed surface 151 of the lower electrode layer 150 and one main surface 411 of the intermediate layer 410. That is, the excitation characteristics of the piezoelectric device 400 can be stabilized.

[0103] In addition, when viewed in a direction intersecting the first opposed surface 131, the lower lead electrode 450 and the second lead wiring 470 are connected to each other outside the first recess 132, so that it is possible to suppress the portion on the first recess 132 in the stacked portion 420 from bending toward the intermediate layer 410 side. As a result, it is also difficult for the second opposed surface 151 of the lower electrode layer 150 and one main surface 411 of the intermediate layer 410 to be joined to each other. Therefore, the excitation characteristics of the piezoelectric device 400 can be stabilized.

[0104] In the description of the above embodiment, structures that can be combined may be combined with each other.

[0105] The embodiments disclosed this time are illustrative in all respects and should not be considered restrictive. The scope of the present invention is shown by the claims, not the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0106] Description of Reference Numerals

[0107] 100, 200, 300, 400 piezoelectric devices, 110 base portion, 111, 411 one main surface, 112 other main surface, 113 second recess, 114 protrusion, 114t upper surface, 120, 220, 320, 420 stacked portions, 130 single crystal piezoelectric layer, 131 first opposed surface, 132 first recess, 133 hole portion, 140 upper electrode layer, 150 lower electrode layer, 151, 251 second opposed surface, 160 first lead wiring, 250 reinforcing lower electrode layer, 270, 470 second lead wiring, 410 intermediate layer, 450 lower lead electrode.

Claims

1. A piezoelectric device comprising: a base portion including one main surface and another main surface located on the side opposite to the one main surface; and a stacked portion stacked on the one main surface side of the base portion, the stacked portion including a single crystal piezoelectric layer and a pair of electrode layers for applying a voltage to the single crystal piezoelectric layer, a first recess is formed in a first opposing surface of the single crystal piezoelectric layer that opposes the one main surface of the base portion, the single crystal piezoelectric layer is joined to the one main surface of the base portion at a portion other than the first recess in the first opposing surface, at least a part of a lower electrode layer that constitutes at least a part of the pair of electrode layers and extends along the base portion side of the single crystal piezoelectric layer is located within the first recess, the surface roughness Ra of a second opposing surface of the lower electrode layer that opposes the one main surface of the base portion is larger than the surface roughness Ra of the first opposing surface of the single crystal piezoelectric layer.

2. The piezoelectric device according to claim 1, wherein the surface roughness Ra of the second opposing surface of the lower electrode layer is 0.5 nm or more and 5.0 nm or less.

3. The piezoelectric device according to claim 1 or 2, wherein the lower electrode layer is only located within the first recess.

4. The piezoelectric device according to any one of claims 1 to 3, wherein the dimension of the thickness of the lower electrode layer is equal to or less than the dimension of the depth of the first recess.

5. The piezoelectric device according to any one of claims 1 to 3, wherein a second recess is formed at a position on the one main surface of the base portion that opposes the first recess, the lower electrode layer includes a region where the dimension of the thickness of the lower electrode layer is larger than the dimension of the depth of the first recess, and in this region, it is in contact with the base portion located within the second recess.

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