Piezoelectric device

Abstract

The connecting portion (130) is arranged to fold back between a pair of beam portions (120). The connecting portion (130) includes a first connecting portion, a second connecting portion, and a bridging portion. The first connecting portion extends along the slit and is connected to one of the pair of beam portions (120). The second connecting portion extends along the slit and is connected to the other of the pair of beam portions (120). The bridging portion is located between the slit and the opening portion and is connected to the first connecting portion and the second connecting portion respectively. The plurality of beam portions (120) are respectively located at positions sandwiched by slits extending in mutually intersecting directions, and are connected to each other in the circumferential direction of the annular base portion (110) via the connecting portion (130).

Description

Technical Field

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

[0002] As a document disclosing the structure of a piezoelectric device, there is the specification of U.S. Patent Application Publication No. 2019 / 0110132 (Patent Document 1). The piezoelectric device described in Patent Document 1 includes a plurality of plates and a plurality of springs. The plurality of springs respectively connect two adjacent plates to each other. The plurality of springs respectively include a first spring arm and a second spring arm that sandwich a gap between two adjacent plates therebetween. The first spring arm and the second spring arm respectively include portions that surround the etched portions of the plates.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Specification of U.S. Patent Application Publication No. 2019 / 0110132 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the piezoelectric device disclosed in Patent Document 1, the root of the spring is disposed at the top end of the plate as the beam portion on the side opposite to the fixed end side. Stress concentration occurs at the root of the spring. Therefore, when springs are respectively disposed at two end edges that intersect at the top end of the plate and the roots of the two springs are close to each other, there is a possibility that cracks are generated between the roots and the excitation characteristics are reduced.

[0008] The present invention has been completed in view of the above problems, and an object thereof is to provide a piezoelectric device that can suppress a reduction in excitation characteristics by separating stress concentration portions from each other in a plurality of beam portions.

[0009] Solutions to Solve the Problems

[0010] The piezoelectric device based on the present invention includes an annular base portion, a plurality of beam portions, and a connecting portion. The plurality of beam portions have fixed end portions connected to the base portion and tip end portions located on the side opposite to the fixed end portions, and extend from the fixed end portions toward the tip end portions. The connecting portion connects a pair of beam portions adjacent to each other in the circumferential direction of the base portion among the plurality of beam portions. The plurality of beam portions are each a piezoelectric vibration portion including a plurality of layers. A slit and an opening are provided between the pair of beam portions. The slit is formed by a part of a pair of adjacent end edges of the pair of beam portions. The opening is spaced apart from the slit and is located at a position adjacent to the tip end portions of the pair of beam portions, and is formed by another part of the pair of end edges. The connecting portion is provided so as to fold back between the pair of beam portions. The connecting portion includes a first connecting portion, a second connecting portion, and a bridging portion. The first connecting portion extends along the slit and is connected to one of the pair of beam portions. The second connecting portion extends along the slit and is connected to the other of the pair of beam portions. The bridging portion is located between the slit and the opening and is connected to the first connecting portion and the second connecting portion respectively. The plurality of beam portions are respectively located at positions sandwiched by slits extending in mutually crossing directions, and are mutually connected in the circumferential direction via the connecting portion.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to suppress a decrease in the excitation characteristics of the piezoelectric device by separating stress concentration portions from each other in the respective plurality of beam portions. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a plan view of the piezoelectric device according to Embodiment 1 of the present invention.

[0014] Figure 2 is a cross-sectional view obtained by observing the piezoelectric device in the direction of the arrow of line II-II Figure 1 of the piezoelectric device.

[0015] Figure 3 is an enlarged partial plan view showing Figure 1 Part III.

[0016] Figure 4 is a partial plan view of the piezoelectric device according to the first modification of Embodiment 1 of the present invention.

[0017] Figure 5 is a plan view of the piezoelectric device according to the second modification of Embodiment 1 of the present invention.

[0018] Figure 6 is a partial cross-sectional view obtained by observing the piezoelectric device shown in the direction of the arrow of line VI-VI Figure 5 of the piezoelectric device.

[0019] Figure 7 is a plan view of the piezoelectric device according to the third modification of Embodiment 1 of the present invention.

[0020] Figure 8 is a partial cross-sectional view obtained by observing the piezoelectric device shown in the direction of the arrow along line VIII-VIII. Figure 7 The piezoelectric device shown is a partial cross-sectional view obtained by observing the piezoelectric device shown in the direction of the arrow along line VIII-VIII.

[0021] Figure 9 is a partial cross-sectional view obtained by observing the piezoelectric device shown in the direction of the arrow along line IX-IX. Figure 7 The piezoelectric device shown is a partial cross-sectional view obtained by observing the piezoelectric device shown in the direction of the arrow along line IX-IX.

[0022] Figure 10 is a partial cross-sectional view schematically showing a part of the beam portion of the piezoelectric device according to Embodiment 1 of the present invention.

[0023] Figure 11 is a partial cross-sectional view schematically showing a part of the beam portion of the piezoelectric device according to Embodiment 1 of the present invention during driving.

[0024] Figure 12 is a perspective view that represents, by simulation, the state of vibration of the piezoelectric device according to Embodiment 1 of the present invention in the fundamental vibration mode.

[0025] Figure 13 is a cross-sectional view showing the state in which the second electrode layer is provided on the piezoelectric single crystal substrate in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0026] Figure 14 is a cross-sectional view showing the state in which the first support portion is provided in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0027] Figure 15 is a cross-sectional view showing the state in which the laminate is joined to the first support portion in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0028] Figure 16 is a cross-sectional view showing the state in which the piezoelectric single crystal substrate is cut to form a piezoelectric body layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0029] Figure 17 is a cross-sectional view showing the state in which the first electrode layer is provided on the piezoelectric body layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0030] Figure 18 is a cross-sectional view showing the state in which the groove portion and the recess portion are provided in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0031] Figure 19 is a cross-sectional view showing the state in which the first connection electrode layer and the second connection electrode layer are provided in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0032] Figure 20 It is a top view of the piezoelectric device according to Embodiment 2 of the present invention.

[0033] Figure 21 It is a cross-sectional view obtained by observing the piezoelectric device Figure 20 in the direction of the arrow along line XXII-XXII.

[0034] Figure 22 It is a partial top view showing the structure of the connection portion of the piezoelectric device according to Embodiment 2 of the present invention.

[0035] Figure 23 It is a graph showing the results of simulation analysis.

[0036] Figure 24 It is a partial top view showing the shape of the connection portion of the piezoelectric device according to the first modification of Embodiment 2 of the present invention.

[0037] Figure 25 It is a partial top view showing the shape of the connection portion of the piezoelectric device according to the second modification of Embodiment 2 of the present invention.

[0038] Figure 26 It is a partial top view showing the shape of the connection portion of the piezoelectric device according to the third modification of Embodiment 2 of the present invention.

[0039] Figure 27 It is a partial top view showing the shape of the connection portion of the piezoelectric device according to the fourth modification of Embodiment 2 of the present invention.

[0040] Figure 28 It is a partial top view showing the shape of the connection portion of the piezoelectric device according to the fifth modification of Embodiment 2 of the present invention.

[0041] Figure 29 It is a partial top view showing the shape of the connection portion of the piezoelectric device according to the sixth modification of Embodiment 2 of the present invention.

[0042] Figure 30 It is a partial top view showing the shape of the connection portion of the piezoelectric device according to the seventh modification of Embodiment 2 of the present invention. Detailed Embodiments

[0043] Hereinafter, with reference to the drawings, the piezoelectric devices according to the 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.

[0044] (Embodiment 1)

[0045] Figure 1 It is a top view of the piezoelectric device according to Embodiment 1 of the present invention. Figure 2 It is a view obtained by observing in the direction of the arrow along line II-IIFigure 1 A cross-sectional view obtained from a piezoelectric device. Figure 3 is an enlarged view showing Figure 1 a partial top view of part III.

[0046] As Figures 1 to 3 shown, the piezoelectric device 100 of Embodiment 1 of the present invention includes an annular base portion 110, a plurality of beam portions 120, and a connecting portion 130. For the piezoelectric device 100 of this embodiment, the plurality of beam portions 120 can each be bent and vibrated and can be used as an ultrasonic transducer.

[0047] As Figure 1 shown, the piezoelectric device 100 of Embodiment 1 of the present invention includes four beam portions 120 as the plurality of beam portions 120 and four connecting portions 130 as the connecting portion 130. The four beam portions 120 are respectively located at positions along the same plane. The four beam portions 120 respectively extend toward the center of the annular base portion 110 and are adjacent to each other in the circumferential direction of the base portion 110. One of the four connecting portions 130 is disposed between each pair of adjacent beam portions 120 among the four beam portions 120 to connect the adjacent pair of beam portions 120.

[0048] In this embodiment, the four beam portions 120 are configured to be rotationally symmetric with respect to the center of the base portion 110. The four connecting portions 130 are also configured to be rotationally symmetric with respect to the center of the base portion 110.

[0049] The base portion 110 is connected to the fixed end portions 121 of the plurality of beam portions 120. The base portion 110 has an annular shape when viewed from the stacking direction of the plurality of layers described later. Specifically, it has a rectangular annular shape. In addition, the shape of the base portion 110 when viewed from the above stacking direction is not particularly limited as long as it is annular. The outer peripheral side surface of the base portion 110 may be a polygonal shape or a circular shape when viewed from the above stacking direction, and the inner peripheral side surface may also be a polygonal shape or a circular shape.

[0050] As Figure 2 shown, the plurality of beam portions 120 are respectively piezoelectric vibration portions including a plurality of layers 10. In addition, in Figure 1 , each layer of the plurality of layers 10 is not shown. Details of the structure of the plurality of layers 10 will be described later.

[0051] As Figure 1As shown, the plurality of beam portions 120 each have a fixed end portion 121 and a top end portion 122. The fixed end portion 121 is connected to the base portion 110. The fixed end portions 121 of the plurality of beam portions 120 are located in the same imaginary plane. The fixed end portions 121 of the plurality of beam portions 120 are connected to the inner peripheral surface of the annular base portion 110 when viewed from the lamination direction. The fixed end portions 121 of the plurality of beam portions 120 are located adjacent to each other on the inner peripheral surface when viewed from the lamination direction. In the present embodiment, the fixed end portions 121 of the plurality of beam portions 120 are located at positions corresponding one-to-one to the plurality of sides of the rectangular annular inner peripheral surface of the base portion 110 when viewed from the lamination direction.

[0052] In the present embodiment, the top end portions 122 of the plurality of beam portions 120 are located near the center of the annular base portion 110 when viewed from the lamination direction. The plurality of beam portions 120 extend from the fixed end portion 121 toward the top end portion 122. That is, in the extending direction of each of the plurality of beam portions 120, the top end portion 122 is located at the end on the opposite side to the fixed end portion 121. In the present embodiment, the plurality of beam portions 120 extend in a manner along the same imaginary plane in the state where the piezoelectric device 100 is not driven.

[0053] As Figure 1 shown, the plurality of beam portions 120 each have a tapered outer shape when viewed from the lamination direction. Specifically, the plurality of beam portions 120 each have a substantially triangular outer shape when viewed from the lamination direction. The extending direction of each of the plurality of beam portions 120 is the direction connecting the center of the fixed end portion 121 and the top end portion 122.

[0054] In the present embodiment, from the viewpoint of facilitating bending vibration, it is preferable that the length of the extending direction of each of the plurality of beam portions 120 is at least 5 times or more the dimension of the thickness of each of the plurality of beam portions 120 in the lamination direction. In addition, in Figure 2 it, the thickness of each of the plurality of beam portions 120 is schematically shown.

[0055] As Figure 1 and Figure 3 shown, a slit 141 and an opening 142 are provided between a pair of beam portions 120 adjacent to each other in the circumferential direction of the base portion 110 among the plurality of beam portions 120. In the present embodiment, an outer peripheral slit 143 is also provided.

[0056] The slit 141 is formed by a part of a pair of adjacent end edges of a pair of beam portions 120. When viewed from the lamination direction, the slit 141 is located at positions along both sides extending from the fixed end portion 121 toward the top end portion 122 in the substantially triangular outer shape of each of the plurality of beam portions 120.

[0057] The opening 142 is spaced apart from the slit 141 and is located at a position adjacent to the top end portions 122 of the pair of beam portions 120 respectively, and is formed by another part of a pair of adjacent end edges of the pair of beam portions 120. When viewed from the stacking direction, the opening 142 is located on the extension line of the slit 141. When viewed from the stacking direction, the opening 142 is located at the center of the annular base portion 110.

[0058] The outer peripheral slit 143 is spaced apart from the slit 141 and extends along the following first connecting portion 132A and second connecting portion 132B respectively and communicates with the opening 142. Specifically, the outer peripheral slit 143 is composed of two slits that sandwich the connecting portion 130 therebetween and extend in parallel.

[0059] When viewed from the stacking direction, the widths of the slit 141 and the outer peripheral slit 143 are preferably 10 μm or less, more preferably 1 μm or less.

[0060] As Figure 1 and Figure 3 shown, the connecting portion 130 connects a pair of beam portions 120 that are adjacent to each other in the circumferential direction of the base portion 110 among the plurality of beam portions 120. The connecting portion 130 is provided in a manner that folds back between the pair of beam portions 120.

[0061] The connecting portion 130 has a first end portion 133A and a second end portion 133B. The connecting portion 130 is connected to one of the pair of beam portions 120 at the first end portion 133A. The connecting portion 130 is connected to the other of the pair of beam portions 120 at the second end portion 133B. The second end portion 133B is arranged at a gap from the first end portion 133A in the direction in which the pair of beam portions 120 are arranged. In the present embodiment, the connecting portion 130 has only one first end portion 133A and only one second end portion 133B.

[0062] Specifically, the connecting portion 130 includes a first connecting portion 132A, a second connecting portion 132B, and a bridging portion 131. The first connecting portion 132A extends along the slit 141 and is connected to one of the pair of beam portions 120. The second connecting portion 132B extends along the slit 141 and is connected to the other of the pair of beam portions 120.

[0063] The bridging portion 131 is located between the slit 141 and the opening 142 and is connected to the first connecting portion 132A and the second connecting portion 132B respectively. The bridging portion 131 extends in a manner along the direction in which the adjacent first connecting portion 132A and second connecting portion 132B are arranged.

[0064] The first connecting portion 132A is connected to a portion of the bridging portion 131 on one beam portion side of the pair of beam portions 120. The second connecting portion 132B is connected to a portion of the bridging portion 131 on the other beam portion side of the pair of beam portions 120.

[0065] In the present embodiment, when viewed from the above stacking direction, the bridging portion 131, the first connecting portion 132A, and the second connecting portion 132B each have a rectangular outer shape, but the outer shape of each of the bridging portion 131, the first connecting portion 132A, and the second connecting portion 132B is not particularly limited. When viewed from the above stacking direction, the outer shape of each of the first connecting portion 132A and the second connecting portion 132B may also be a substantially elliptical shape or a polygonal shape. It may also be that, in each of the bridging portion 131, the first connecting portion 132A, and the second connecting portion 132B, the side surface extending in the above stacking direction is curved when viewed from the above stacking direction.

[0066] As Figure 3 shown, in the present embodiment, the dimensions of the length L of each of the first connecting portion 132A and the second connecting portion 132B are substantially the same as each other. The dimensions of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B are substantially the same as each other. The dimension of the length L of each of the first connecting portion 132A and the second connecting portion 132B is larger than the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B. The dimension of the length L of each of the first connecting portion 132A and the second connecting portion 132B is larger than the dimension of the shortest length b from the bridging portion 131 to the center of the base portion 110. The dimension of the length L of each of the first connecting portion 132A and the second connecting portion 132B is larger than the dimension of the maximum width a of the bridging portion 131. The dimension of the maximum width a of the bridging portion 131 is larger than the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B.

[0067] The smaller the dimension of the length L of each of the first connecting portion 132A and the second connecting portion 132B, the more firmly the pair of beam portions 120 are connected to each other, and the smaller the vibration deviation of the pair of beam portions 120. The larger the dimension of the length L of each of the first connecting portion 132A and the second connecting portion 132B, the more the resonance frequency of the vibration of each of the pair of beam portions 120 can be suppressed from becoming higher. The larger the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B, the more firmly the pair of beam portions 120 are connected to each other. The smaller the dimension of the shortest length b from the bridging portion 131 to the center of the base portion 110, the more firmly the pair of beam portions 120 are connected to each other, and the more the amount of air passing through the opening portion 142 during the excitation of the piezoelectric device 100 can be reduced, so that the loss of the piezoelectric device 100 can be reduced. The dimension of the maximum width a of the bridging portion 131 affects the resonance frequency of the connecting portion 130 when the connecting portion 130 vibrates.

[0068] In the present embodiment, the dimension of the length L of each of the first connecting portion 132A and the second connecting portion 132B is, for example, 10 μm or more and 200 μm or less. The dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is, for example, 10 μm. The dimension of the shortest length b from the bridging portion 131 to the center of the base portion 110 is, for example, 25 μm. The dimension of the maximum width a of the bridging portion 131 is, for example, 15 μm.

[0069] Here, a piezoelectric device according to a first modification of Embodiment 1 of the present invention in which the shape of the connecting portion is different will be described.

[0070] Figure 4 is a partial top view of the piezoelectric device according to the first modification of Embodiment 1 of the present invention. In Figure 4 shows the same parts as those of the piezoelectric device 100 according to Embodiment 1 of the present invention shown in Figure 3 shown.

[0071] As Figure 4 shown, in the piezoelectric device 100a according to the first modification of Embodiment 1 of the present invention, the side surface of the bridging portion 131 in contact with the opening portion 142 is curved. By curving the side surface of the bridging portion 131 in this way, the internal stress at the connecting portion 130 can be reduced.

[0072] In addition, in the piezoelectric device 100a, the end portions on the side opposite to the opening portion 142 side of the outer peripheral slit 143 are curved so as to be separated from each other in such a manner that the width of the first connecting portion 132A increases as it approaches the first end portion 133A and the width of the second connecting portion 132B increases as it approaches the second end portion 133B.

[0073] Next, a plurality of layers 10 will be described. As Figure 2 shown, in the present embodiment, the plurality of layers 10 include a piezoelectric layer 11, a first electrode layer 12, and a second electrode layer 13.

[0074] The piezoelectric layer 11 is made of a single crystal piezoelectric body. The cutting orientation of the piezoelectric layer 11 is appropriately selected to exhibit desired device characteristics. In the present embodiment, the piezoelectric layer 11 is formed by thinning a single crystal substrate. Specifically, the single crystal substrate is a rotated Y-cut substrate. Specifically, the cutting orientation of the rotated Y-cut substrate is 30°. The thickness of the piezoelectric layer 11 is, for example, 0.3 μm or more and 5.0 μm or less. The single crystal piezoelectric body has a polarization axis. Details of the axial direction of the polarization axis will be described later.

[0075] The material constituting the piezoelectric layer 11 is appropriately selected so that the piezoelectric device 100 exhibits desired device characteristics. In the present embodiment, the piezoelectric layer 11 is made of an inorganic material. Specifically, the piezoelectric layer 11 is made of a compound of an alkaline niobate system or a compound of an alkaline tantalate system. In the present embodiment, the alkali metal contained in the compound of the alkaline niobate system or the compound of the alkaline tantalate system is composed of at least one of lithium, sodium, and potassium. In the present embodiment, the piezoelectric layer 11 is made of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

[0076] As Figure 2 shown, the first electrode layer 12 is disposed on one side of the piezoelectric layer 11 in the stacking direction of the plurality of layers 10. The second electrode layer 13 is disposed on the other side of the piezoelectric layer 11 so as to face at least a part of the first electrode layer 12 with the piezoelectric layer 11 interposed therebetween.

[0077] In the present embodiment, adhesion layers (not shown) are respectively disposed between the first electrode layer 12 and the piezoelectric layer 11, between the second electrode layer 13 and the piezoelectric layer 11, and between the second electrode layer 13 and the piezoelectric layer 11. Further, in each of the plurality of beam portions 120, the first electrode layer 12 and the second electrode layer 13 are respectively arranged so as not to face the slit 141, the opening 142, and the outer peripheral slit 143.

[0078] In the present embodiment, the first electrode layer 12 and the second electrode layer 13 are each made of Pt. The first electrode layer 12 and the second electrode layer 13 may also be made of other materials such as Al. The adhesion layer is made of Ti. The adhesion layer may also be made of other materials such as NiCr. The first electrode layer 12, the second electrode layer 13, and the above-mentioned adhesion layer may also be epitaxial growth films. In the case where the piezoelectric layer 11 is made of lithium niobate (LiNbO3), from the viewpoint of suppressing the diffusion of the material constituting the adhesion layer into the first electrode layer 12 or the second electrode layer 13, it is preferable that the adhesion layer is made of NiCr. Thereby, the reliability of the piezoelectric device 100 is improved.

[0079] In the present embodiment, the thickness of each of the first electrode layer 12 and the second electrode layer 13 is, for example, 0.05 μm or more and 0.2 μm or less. The thickness of the adhesion layer is, for example, 0.005 μm or more and 0.05 μm or less.

[0080] The plurality of layers 10 further includes a support layer 14. The support layer 14 is disposed on the side of the piezoelectric layer 11 opposite to the first electrode layer 12 side and on the side of the second electrode layer 13 opposite to the piezoelectric layer 11 side. The support layer 14 has a first support portion 14a and a second support portion 14b laminated on the side of the first support portion 14a opposite to the piezoelectric layer 11 side. In the present embodiment, the first support portion 14a is made of SiO2, and the second support portion 14b is made of single crystal Si. In the present embodiment, from the viewpoint of the bending vibration of the plurality of beam portions 120, it is preferable that the thickness of the support layer 14 is thicker than the thickness of the piezoelectric layer 11. In addition, the mechanism of the bending vibration of the plurality of beam portions 120 will be described later.

[0081] In addition, as Figure 2 shown, in the present embodiment, the connecting portion 130 is formed by the plurality of layers 10 of each of the plurality of beam portions 120 being continuous in the orthogonal direction orthogonal to the stacking direction. However, in the present embodiment, the plurality of layers 10 of the connecting portion 130 do not include the first electrode layer 12 and the second electrode layer 13.

[0082] Moreover, the members constituting the base portion 110 will be described. As Figure 2 shown, in the present embodiment, the base portion 110 includes a plurality of layers 10 similar to the plurality of beam portions 120. The plurality of layers 10 of the base portion 110 are formed by the plurality of layers 10 of the plurality of beam portions 120 being continuous. Specifically, the piezoelectric layer 11, the first electrode layer 12, the second electrode layer 13, and the support layer 14 constituting the base portion 110 are formed in a manner continuous with the piezoelectric layer 11, the first electrode layer 12, the second electrode layer 13, and the support layer 14 constituting the plurality of beam portions 120, respectively. And the base portion 110 further includes a substrate layer 15, a first connection electrode layer 20, and a second connection electrode layer 30.

[0083] The substrate layer 15 is connected to the side of the support layer 14 opposite to the piezoelectric layer 11 side in the axial direction of the central axis of the annular base portion 110. The substrate layer 15 includes a first substrate layer 15a and a second substrate layer 15b laminated on the side of the first substrate layer 15a opposite to the support layer 14 side in the axial direction of the central axis. In the present embodiment, the first substrate layer 15a is made of SiO2, and the second substrate layer 15b is made of single crystal Si.

[0084] As Figure 2 shown, the first connection electrode layer 20 is electrically connected to the first electrode layer 12 via a bonding layer (not shown) and exposed to the outside. Specifically, the first connection electrode layer 20 is disposed on the side of the second electrode layer 13 of the base portion 110 opposite to the support layer 14 side.

[0085] The thicknesses of the first connection electrode layer 20 and the second connection electrode layer 30 are each, for example, 0.1 μm or more and 1.0 μm or less. The thicknesses of the adhesion layers connected to the first connection electrode layer 20 and the adhesion layers respectively connected to the second connection electrode layer 30 are each, for example, 0.005 μm or more and 0.1 μm or less.

[0086] In the present embodiment, the first connection electrode layer 20 and the second connection electrode layer 30 are each made of Au. The first connection electrode layer 20 and the second connection electrode layer 30 may also be made of other conductive materials such as Al. The adhesion layers connected to the first connection electrode layer 20 and the adhesion layers connected to the second connection electrode layer 30 are each, for example, made of Ti. These adhesion layers may also be made of NiCr.

[0087] As Figure 2 shown, in the piezoelectric device 100 of the present embodiment, a hole portion 101 that opens on the side opposite to the piezoelectric body layer 11 side in the above-described stacking direction is formed. In the present embodiment, the hole portion 101 is a space surrounded by a base portion 110, a plurality of beam portions 120, a plurality of connection portions 130, and slits 141, an opening portion 142, and an outer peripheral slit 143.

[0088] Here, the axial direction of the polarization axis of the single crystal piezoelectric body constituting the piezoelectric body layer 11 will be described. Preferably, when the polarization axis of the single crystal piezoelectric body is projected onto a hypothetical plane orthogonal to the above-described stacking direction, the axial direction of the hypothetical axis extends along the same direction in any one of the plurality of beam portions 120, and when viewed from the above-described stacking direction, the angle formed with the extending direction of each of the plurality of slits 141 is not 45 degrees or 135 degrees.

[0089] More specifically, in the present embodiment, more preferably, the angle formed by the axial direction of the above-described hypothetical axis and the extending direction of each of the plurality of slits 141 when viewed from the above-described stacking direction is 0 degrees or more and 5 degrees or less, 85 degrees or more and 95 degrees or less, or 175 degrees or more and less than 180 degrees.

[0090] In addition, more preferably, when viewed from the above-described stacking direction, the angle formed by the extending direction of each of the plurality of beam portions 120 and the axial direction of the above-described hypothetical axis when viewed from the above-described stacking direction is 40 degrees or more and 50 degrees or less, or 130 degrees or more and 140 degrees or less. Preferably, the above-described relationship holds for the axial direction of the hypothetical axis of the piezoelectric device 100 of the present embodiment with respect to any one of the slits 141 and the bridging portion 131. The reason for the preferred range for each angle related to the above-described hypothetical axis will be described later.

[0091] In the present embodiment, the axial direction of the above-described hypothetical axis faces a specific direction, but the axial direction of the above-described hypothetical axis is not particularly limited.

[0092] In addition, in the present embodiment, since the single crystal piezoelectric body has a polarization axis, thermal stress is generated in the plurality of beam portions 120, and sometimes the plurality of beam portions 120 are warped when viewed from the orthogonal direction orthogonal to the stacking direction. A deformation example in which the plurality of beam portions 120 are warped will be described below.

[0093] Figure 5 It is a top view of the piezoelectric device according to the second modification of Embodiment 1 of the present invention. Figure 6 It is viewed from the arrow direction of line VI-VI Figure 5 The partial cross-sectional view obtained by observing the piezoelectric device shown.

[0094] As Figure 5 shown, in the piezoelectric device 100b according to the second modification of Embodiment 1 of the present invention, when viewed from the stacking direction, the angle formed by the axial direction of the imaginary axis and the plurality of slits 141 is 45 degrees.

[0095] Therefore, in this modification, when viewed from the stacking direction, the length L1 from the center of the connecting portion 130 to the end portion on the opposite side of one of the pair of beam portions 120 in the axial direction of the imaginary axis is different from the length L2 from the center of the connecting portion 130 to the end portion on the opposite side of the other beam portion 120 in the pair of beam portions 120. In addition, the end portion of one of the pair of beam portions 120 on the side opposite to the center side of the connecting portion 130 in the axial direction of the imaginary axis when viewed from the stacking direction is not the fixed end portion 121. On the other hand, the end portion of the other beam portion 120 on the side opposite to the center side of the connecting portion 130 in the axial direction of the imaginary axis when viewed from the stacking direction is the fixed end portion 121. Therefore, when thermal stress is applied to the plurality of beam portions 120, the pair of beam portions 120 are warped in different ways near the connecting portion 130.

[0096] In the piezoelectric device 100b of this modification, the above-described thermal stress is applied to the plurality of beam portions 120. As a result, as Figure 6 shown, in the state where the piezoelectric device 100b is not driven, the end portions of the pair of beam portions 120 near the center of the connecting portion 130 are located at positions different from each other in the stacking direction.

[0097] Figure 7 It is a top view of the piezoelectric device according to the third modification of Embodiment 1 of the present invention. Figure 8 It is viewed from the arrow direction of line VIII-VIII Figure 7 The partial cross-sectional view obtained by observing the piezoelectric device shown. Figure 9 It is viewed from the arrow direction of line IX-IX Figure 7 The partial cross-sectional view obtained by observing the piezoelectric device shown.

[0098] As Figure 7 shown, in the piezoelectric device 100c according to the third modification of Embodiment 1 of the present invention, when viewed from the stacking direction, the angles formed by the axial direction of the imaginary axis of the single crystal piezoelectric body and the respective slits 141 are 0 degrees or 90 degrees.

[0099] Therefore, in this modification, when viewed from the stacking direction, the length L1 from the center of the connecting portion 130 to the end portion on the opposite side of one of the pair of beam portions 120 in the axial direction of the imaginary axis is the same as the length L2 from the center of the connecting portion 130 to the end portion on the opposite side of the other beam portion 120 in the pair of beam portions 120. In addition, in the axial direction of the imaginary axis when viewed from the stacking direction, the distance from the end portion near the center of the connecting portion 130 to the fixed end portion 121 of one of the pair of beam portions 120 is the same as the distance from the end portion near the center of the connecting portion 130 to the fixed end portion 121 of the other beam portion 120.

[0100] Moreover, in the piezoelectric device 100c of this modification, by applying a thermal stress to the plurality of beam portions 120, the plurality of beam portions 120 are warped respectively. As a result, as Figure 8 shown, in the state where the piezoelectric device 100c is not driven, the end portions on the center side of the connecting portion 130 of the pair of beam portions 120 near the center of the connecting portion 130 are located at substantially the same position in the stacking direction. Thus, in this modification, even when the plurality of beam portions 120 are warped due to thermal stress respectively, it is possible to suppress breakage of the connecting portion 130, and particularly suppress breakage of the bridging portion 131.

[0101] As described above, by comparing the piezoelectric device 100b according to the second modification and the piezoelectric device 100c according to the third modification of Embodiment 1 of the present invention, as compared with the state where the angle formed by the axial direction of the imaginary axis and the respective extending directions of the plurality of slits 141 is 45 degrees or 135 degrees when viewed from the stacking direction, the closer to 0 degrees or 90 degrees, the more it is possible to suppress the case where the difference in displacement caused by the thermal stress of the pair of beam portions 120 becomes large.

[0102] In addition, as Figure 9 shown, in the piezoelectric device 100c according to the third modification of Embodiment 1 of the present invention, when each of the pair of beam portions 120 is viewed from the slit 141 side, the pair of beam portions 120 are inclined in any one direction of the stacking direction respectively.

[0103] The piezoelectric device 100 according to Embodiment 1 of the present invention is configured such that the plurality of beam portions 120 can be bent and vibrated respectively. Here, the mechanism of the bending vibration of the plurality of beam portions 120 will be described.

[0104] Figure 10It is a partial cross-sectional view schematically showing a beam portion of the piezoelectric device according to Embodiment 1 of the present invention. Figure 11 It is a partial cross-sectional view schematically showing the beam portion during driving of the piezoelectric device according to Embodiment 1 of the present invention. In addition, Figure 10 and Figure 11 the first electrode layer and the second electrode layer are not shown in

[0105] As Figure 10 and Figure 11 shown, in the present embodiment, among the plurality of beam portions 120, the piezoelectric layer 11 functions as a telescopic layer capable of telescoping in the in-plane direction orthogonal to the above-described stacking direction, and the layers other than the piezoelectric layer 11 function as constraint layers. In the present embodiment, the main support layer 14 functions as a constraint layer. In this way, the constraint layer is stacked on the telescopic layer in the direction orthogonal to the telescopic direction of the telescopic layer. In addition, the plurality of beam portions 120 may include a reverse telescopic layer instead of the constraint layer, and the reverse telescopic layer can contract in the in-plane direction when the telescopic layer elongates in the in-plane direction and elongate in the in-plane direction when the telescopic layer contracts in the in-plane direction.

[0106] And when the piezoelectric layer 11 as the telescopic layer is about to telescope in the above-described in-plane direction, the support layer 14, which is the main part of the constraint layer, constrains the telescoping of the piezoelectric layer 11 on the bonding surface with the piezoelectric layer 11. In addition, in the present embodiment, in each of the plurality of beam portions 120, the piezoelectric layer 11 as the telescopic layer is only located on one side of the stress neutral plane N of each of the plurality of beam portions 120. The position of the center of gravity of the support layer 14 mainly constituting the constraint layer is located on the other side of the stress neutral plane N. Thus, as Figure 10 and Figure 11 shown, when the piezoelectric layer 11 as the telescopic layer telescopes in the above-described in-plane direction, the plurality of beam portions 120 bend in the orthogonal direction orthogonal to the above-described in-plane direction respectively. In addition, the longer the separation distance between the stress neutral plane N and the piezoelectric layer 11, the larger the displacement amount of each of the plurality of beam portions 120 when the plurality of beam portions 120 bend respectively. In addition, the greater the stress for the piezoelectric layer 11 to telescope, the larger the above-described displacement amount. In this way, the plurality of beam portions 120 bend and vibrate starting from the fixed end portion 121 in the orthogonal direction of the above-described in-plane direction respectively.

[0107] Moreover, in the piezoelectric device 100 of the present embodiment, by providing the connection portion 130, vibration in the fundamental vibration mode is easily generated, and generation of vibration in the composite vibration mode is suppressed. The fundamental vibration mode means that the phases are the same when the plurality of beam portions 120 bend and vibrate respectively, and the entire plurality of beam portions 120 are displaced in either the upward or downward direction. On the other hand, the composite vibration mode means a mode in which the phase of at least one of the plurality of beam portions 120 is inconsistent with the phases of the other beam portions 120 when the plurality of beam portions 120 bend and vibrate respectively.

[0108] Figure 12 This is a perspective view that simulates the state of vibration in the fundamental vibration mode for the piezoelectric device of Embodiment 1 of the present invention. Specifically, in Figure 12 it shows a piezoelectric device 100 in a state where a plurality of beam portions 120 are displaced toward the first electrode layer 12 side respectively. Further, in Figure 12 the greater the displacement amount of the plurality of beam portions 120 displaced toward the first electrode layer 12 side respectively, the lighter the color. In addition, in Figure 12 the respective layers constituting the plurality of layers 10 are not shown.

[0109] As Figure 12 shown, for each of the plurality of beam portions 120, a pair of adjacent beam portions 120 are connected to each other by a connecting portion 130, thereby suppressing the generation of a composite vibration mode.

[0110] Moreover, in the connecting portion 130 of the piezoelectric device 100 of the present embodiment, the first end portion 133A and the second end portion 133B are respectively located at positions closer to the tip end portion 122 of the pair of beam portions 120 than to the fixed end portion 121. Thereby, the plurality of beam portions 120 are connected to each other relatively firmly, and thus the phases of the vibrations of the plurality of beam portions 120 are more likely to be synchronized. In addition, the connecting portion 130 of the piezoelectric device 100 of the present embodiment includes a bridging portion 131, and the connecting portion 130 folds back and connects between the pair of beam portions 120. Therefore, when the plurality of beam portions 120 vibrate, the first connecting portion 132A and the second connecting portion 132B function like leaf springs, the connecting portion 130 connects the pair of beam portions 120 to each other, and the first connecting portion 132A and the second connecting portion 132B are connected in series via the bridging portion 131, and the length of the connecting portion 130 as a leaf spring becomes longer, thereby being able to suppress the connection force from becoming too strong.

[0111] The piezoelectric device 100 of the present embodiment is likely to generate vibrations in the fundamental vibration mode and suppresses the generation of a composite vibration mode, so that the device characteristics are improved particularly when used as an ultrasonic transducer. Hereinafter, the functional effects of the piezoelectric device 100 when the piezoelectric device 100 of the present embodiment is used as an ultrasonic transducer will be described.

[0112] First, when the piezoelectric device 100 generates ultrasonic waves, to Figure 2A voltage is applied between the first connecting electrode layer 20 and the second connecting electrode layer 30 shown. Furthermore, a voltage is applied between the first electrode layer 12 connected to the first connecting electrode layer 20 and the second electrode layer 13 connected to the second connecting electrode layer 30. Moreover, in each of the plurality of beam portions 120, a voltage is applied between the first electrode layer 12 and the second electrode layer 13 opposite to each other via the piezoelectric layer 11. In this way, the piezoelectric layer 11 expands and contracts along the in-plane direction orthogonal to the above-mentioned stacking direction, so that according to the above-mentioned mechanism, the plurality of beam portions 120 are bent and vibrated respectively along the above-mentioned stacking direction. Thus, by applying a force to the medium around the plurality of beam portions 120 of the piezoelectric device 100, the medium vibrates, thereby generating ultrasonic waves.

[0113] In the piezoelectric device 100 of the present embodiment, each of the beams 120 has a unique mechanical resonance frequency. Therefore, when the applied voltage is a sinusoidal voltage with a frequency close to the resonance frequency, the beams 120 are displaced more when they are bent.

[0114] When the piezoelectric device 100 is used to detect ultrasonic waves, the medium around each of the plurality of beams 120 vibrates due to the ultrasonic waves, and a force is applied to each of the plurality of beams 120 from the medium around the beams 120, so that each of the plurality of beams 120 bends and vibrates. When each of the plurality of beams 120 bends and vibrates, stress is applied to the piezoelectric layer 11. By applying stress to the piezoelectric layer 11, electric charge is induced in the piezoelectric layer 11. Using the electric charge induced in the piezoelectric layer 11, a potential difference is generated between the first electrode layer 12 and the second electrode layer 13 that are opposite to each other across the piezoelectric layer 11. The potential difference is detected in the first connecting electrode layer 20 connected to the first electrode layer 12 and the second connecting electrode layer 30 connected to the second electrode layer 13. Thus, ultrasonic waves can be detected in the piezoelectric device 100.

[0115] In addition, when the ultrasonic wave to be detected contains many specific frequency components and the frequency components are close to the value of the above-mentioned resonance frequency, the displacement amount of each of the plurality of beam portions 120 during bending vibration increases. As the displacement amount increases, the above-mentioned potential difference increases.

[0116] Thus, when the piezoelectric device 100 of the present embodiment is used as an ultrasonic transducer, the design of the resonance frequencies of the plurality of beam portions 120 becomes important. The above resonance frequencies vary depending on the lengths of the plurality of beam portions 120 in their respective extending directions, the thicknesses in the axial direction of the central axis, the lengths of the fixed end portions 121 when viewed from this axial direction, and the density and elastic modulus of the material constituting the plurality of beam portions 120. Additionally, preferably, the plurality of beam portions each have the same resonance frequency as each other. For example, when the above thicknesses of the plurality of beam portions 120 are different from each other, by adjusting the lengths of the plurality of beam portions 120 in their respective extending directions, the plurality of beam portions 120 each have the same resonance frequency as each other.

[0117] For example, in Figures 1 to 3 the piezoelectric device 100 of Embodiment 1 of the present invention shown, when the resonance frequencies of the plurality of beam portions 120 are designed to be around 40 kHz, for the plurality of beam portions 120, the structural material of the piezoelectric layer 11 is set to lithium niobate, the thickness of the piezoelectric layer 11 is set to 1 μm, the thicknesses of the first electrode layer 12 and the second electrode layer 13 are each set to 0.1 μm, the thickness of the first support portion 14a is set to 0.8 μm, the thickness of the second support portion 14b is set to 1.4 μm, the shortest distance from the fixed end portion 121 to the tip end portion 122 of each of the plurality of beam portions 120 is set to 400 μm, and the length of the fixed end portion 121 when viewed from the above stacking direction is set to 800 μm.

[0118] Furthermore, the piezoelectric device 100 of the present embodiment is provided with the connection portion 130 having the above-described structure, and thus it is easy to generate vibrations in the fundamental vibration mode and suppress the generation of the composite vibration mode. Therefore, when the piezoelectric device 100 is used as an ultrasonic transducer, even when detecting ultrasonic waves having a frequency component identical to the resonance frequency, it is possible to suppress the phases of the vibrations of the plurality of beam portions 120 from being different from each other. Furthermore, it is possible to suppress the situation where the charges generated in the piezoelectric layer 11 of each of the plurality of beam portions 120 cancel each other out in the first electrode layer 12 or the second electrode layer 13 due to the different phases of the vibrations of the plurality of beam portions 120.

[0119] In this way, in the piezoelectric device 100, the device characteristics as an ultrasonic transducer are improved.

[0120] Hereinafter, a manufacturing method of the piezoelectric device 100 of Embodiment 1 of the present invention will be described. Figure 13 is a cross-sectional view showing a state in which a second electrode layer is provided on a piezoelectric single crystal substrate in the manufacturing method of the piezoelectric device of Embodiment 1 of the present invention. In Figure 13 and those shown below in Figures 14 to 19 are illustrated in the same cross-section as Figure 2 for the same cross-section.

[0121] AsFigure 13 As shown, first, an adhesion layer (not shown) is provided on the lower surface of the piezoelectric single crystal substrate 11a, and then a second electrode layer 13 is provided on the side of the adhesion layer opposite to the piezoelectric single crystal substrate 11a side. The second electrode layer 13 is formed into a desired pattern by the evaporation stripping method. Alternatively, the second electrode layer 13 may be formed by sputtering a coating on the entire surface of the lower surface of the piezoelectric single crystal substrate 11a and then forming a desired pattern by an etching method. The second electrode layer 13 and the adhesion layer may also be epitaxially grown.

[0122] Figure 14 is a cross-sectional view showing the state of providing the first support portion in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. As Figure 14 shown, the first support portions 14a are provided on the lower surfaces of the piezoelectric single crystal substrate 11a and the second electrode layer 13 respectively by a method such as CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition). Immediately after the first support portions 14a are provided, a portion of the lower surface of the first support portions 14a located on the side opposite to the second electrode layer 13 side bulges. Therefore, the lower surface of the first support portions 14a is cut and flattened by chemical mechanical polishing (CMP: Chemical Mechanical Polishing) or the like.

[0123] Figure 15 is a cross-sectional view showing the state of bonding the laminate to the first support portion in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. As Figure 15 shown, the laminate 16 composed of the second support portion 14b and the substrate layer 15 is bonded to the lower surface of the first support portion 14a by surface activation bonding or atomic diffusion bonding. In the present embodiment, the laminate 16 is an SOI (Silicon on Insulator) substrate. In addition, by previously flattening the upper surface of the second support portion 14b by CMP or the like, the yield of the piezoelectric device 100 is improved. Further, when the second support portion 14b is made of low-resistance Si, the second support portion 14b can function as a lower electrode layer, and in this case, it is possible to dispense with the formation of the second electrode layer 13 and the CMP of the lower surface of the first support portion 14a.

[0124] Figure 16 is a cross-sectional view showing the state of cutting the piezoelectric single crystal substrate to form a piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. As Figure 15 and Figure 16As shown, the upper surface of the piezoelectric single crystal substrate 11a is ground by a grinding machine to make it thinner. The thinned piezoelectric single crystal substrate 11a is further polished on its upper surface by CMP or the like to form the piezoelectric single crystal substrate 11a into a piezoelectric layer 11.

[0125] In addition, it may also be that an ion implantation layer is formed by implanting ions in advance on the upper surface side of the piezoelectric single crystal substrate 11a, and the piezoelectric single crystal substrate 11a is formed into the piezoelectric layer 11 by peeling off the above-mentioned ion implantation layer. Additionally, it may also be that the upper surface of the piezoelectric single crystal substrate 11a after peeling off the above-mentioned ion implantation layer is further polished by CMP or the like to form the piezoelectric single crystal substrate 11a into the piezoelectric layer 11.

[0126] Figure 17 It is a cross-sectional view showing a state in which a first electrode layer is provided on the piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. As Figure 17 shown, an adhesion layer (not shown) is provided on the upper surface of the piezoelectric layer 11, and then a first electrode layer 12 is provided on the side opposite to the piezoelectric layer 11 side of the adhesion layer. The first electrode layer 12 is formed into a desired pattern by the evaporation stripping method. It may also be that the first electrode layer 12 is formed by sputtering to deposit a film on the entire upper surface of the piezoelectric layer 11 and then forming a desired pattern by an etching method. The first electrode layer 12 and the adhesion layer may also be epitaxially grown.

[0127] Figure 18 It is a cross-sectional view showing a state in which a groove portion and a recess portion are provided in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. As Figure 18 shown, when viewed from the above lamination direction, in a region corresponding to a region closer to the inside than the base portion 110 of the piezoelectric device 100, a slit is formed in the piezoelectric layer 11 and the first support portion 14a by dry etching using RIE (Reactive Ion Etching) or the like. The above-mentioned slit may also be formed by wet etching using fluonitric acid or the like. Then, using DRIE (Deep Reactive Ion Etching), the second support portion 14b exposed to the above-mentioned slit is etched so that the above-mentioned slit reaches the upper surface of the substrate layer 15. Thereby, a groove portion 17 corresponding to the Figure 1 and Figure 2 shown slit 141, opening portion 142, and outer peripheral slit 143 of the piezoelectric device 100 is formed. Figure 18 shown in

[0128] Moreover, as Figure 18 shown, in a portion corresponding to the base portion 110 of the piezoelectric device 100, the piezoelectric layer 11 is etched by the above-mentioned dry etching or the above-mentioned wet etching so that a part of the second electrode layer 13 is exposed. Thereby, a recess portion 18 is formed.

[0129] Figure 19 This is a cross-sectional view showing the state in which the first connection electrode layer and the second connection electrode layer are provided in the method for manufacturing a piezoelectric device according to Embodiment 1 of the present invention. And, as Figure 19 shown, in a portion corresponding to the base portion 110, an adhesion layer (not shown) is provided on each of the first electrode layer 12 and the second electrode layer 13, and then the first connection electrode layer 20 and the second connection electrode layer 30 are provided on the upper surfaces of the respective adhesion layers by a vapor deposition peeling method. Alternatively, the first connection electrode layer 20 and the second connection electrode layer 30 may be formed by sputtering a laminate on the entire surfaces of the piezoelectric layer 11, the first electrode layer 12, and the exposed second electrode layer 13, and then forming a desired pattern by an etching method.

[0130] Finally, a part of the second substrate layer 15b in the substrate layer 15 is removed by DRIE, and then a part of the first substrate layer 15a is removed by RIE. Thus, as Figure 2 shown, a hole portion 101 is provided, and a plurality of beam portions 120 and connection portions 130 are formed.

[0131] Through the above-described steps, a piezoelectric device 100 according to Embodiment 1 of the present invention as Figures 1 to 3 shown is manufactured.

[0132] As described above, in the piezoelectric device 100 according to Embodiment 1 of the present invention, the connection portion 130 is provided so as to fold back between a pair of beam portions 120. The connection portion 130 includes a first connection portion 132A, a second connection portion 132B, and a bridging portion 131. The first connection portion 132A extends along the slit 141 and is connected to one of the pair of beam portions 120. The second connection portion 132B extends along the slit 141 and is connected to the other of the pair of beam portions 120. The bridging portion 131 is located between the slit 141 and the opening portion 142 and is connected to the first connection portion 132A and the second connection portion 132B, respectively. The plurality of beam portions 120 are respectively located at positions sandwiched by the slits 141 extending in a mutually intersecting direction, and are mutually connected in the circumferential direction of the annular base portion 110 via the connection portion 130.

[0133] According to this structure, in each of the plurality of beam portions 120, the first end portions 133A or the second end portions 133B, which are stress concentration portions, can be separated from each other, and a decrease in the excitation characteristics of the piezoelectric device 100 can be suppressed.

[0134] Further, in the case where the piezoelectric device 100a as in the first modification of the first embodiment of the present invention is bent in a separated manner at the end portion of the outer peripheral slit 143 on the side opposite to the opening portion 142 side, compared with the case where springs are respectively arranged at two end edges crossing each other at the top end of the plate in the piezoelectric device described in Patent Document 1 and the roots of the two springs are close to each other, it is also possible to separate the first end portions 133A or the second end portions 133B of the stress concentration portions of the plurality of beam portions 120, that is, the portions adjacent to the end portion of the outer peripheral slit 143 on the side opposite to the opening portion 142 side from each other, and the degradation of the excitation characteristics of the piezoelectric device 100a can be suppressed.

[0135] In the present embodiment, an outer peripheral slit 143 is further provided which extends along the first connecting portion 132A and the second connecting portion 132B at intervals from the slit 141 and communicates with the opening portion 142.

[0136] Thereby, the formation of the bridging portion 131 becomes easy, and it is possible to suppress the action of the connecting portion 130, particularly the bridging portion 131, from being hindered by the pair of beam portions 120 during the vibration of the plurality of beam portions 120.

[0137] In the present embodiment, the plurality of layers 10 include a piezoelectric layer 11, a first electrode layer 12, and a second electrode layer 13. The piezoelectric layer 11 is composed of a single crystal piezoelectric body. The first electrode layer 12 is disposed on one side of the piezoelectric layer 11 in the stacking direction of the plurality of layers 10. The second electrode layer 13 is disposed on the other side of the piezoelectric layer 11 so as to be at least partially opposed to the first electrode layer 12 with the piezoelectric layer 11 interposed therebetween. When the polarization axis of the single crystal piezoelectric body is projected onto a virtual plane orthogonal to the stacking direction, the axial direction of the virtual axis in any one of the plurality of beam portions 120 extends along the same direction, and when viewed from the stacking direction, it intersects the extending direction of each of the plurality of beam portions 120.

[0138] Thereby, in the piezoelectric device 100 in which the piezoelectric layer 11 is composed of a single crystal piezoelectric body having a polarization axis, even in the case where thermal stresses are respectively generated in a pair of beam portions 120, it is possible to reduce the deviation of the stress distribution generated in the connecting portion 130 and suppress the breakage of the connecting portion 130.

[0139] In the piezoelectric device 100 of the first embodiment of the present invention, when viewed from the stacking direction, the angle formed by the extending direction of each of the plurality of beam portions 120 and the axial direction of the virtual axis is 40 degrees or more and 50 degrees or less, or 130 degrees or more and 140 degrees or less.

[0140] Accordingly, even assuming that thermal stress is generated in the plurality of beam portions 120, the plurality of beam portions 120 each have substantially the same stress distribution in the extending direction, and thus the warping modes of the plurality of beam portions 120 are also substantially the same. Furthermore, a decrease in the device characteristics of the piezoelectric device 100 can be suppressed.

[0141] In the present embodiment, the piezoelectric layer 11 is made of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

[0142] Accordingly, the piezoelectric characteristics of the piezoelectric layer 11 can be improved, and thus the device characteristics of the piezoelectric device 100 can be improved.

[0143] (Embodiment 2)

[0144] Hereinafter, the piezoelectric device according to Embodiment 2 of the present invention will be described. The piezoelectric device according to Embodiment 2 of the present invention is different from the piezoelectric device 100 according to Embodiment 1 of the present invention in terms of the dimensional relationships of the respective extending lengths, minimum widths, and thicknesses of the specified first connection portion and the second connection portion. Therefore, the same structures as those of the piezoelectric device 100 according to Embodiment 1 of the present invention will not be described repeatedly.

[0145] Figure 20 is a top view of the piezoelectric device according to Embodiment 2 of the present invention. Figure 21 is a cross-sectional view obtained by observing the piezoelectric device in the direction of the arrow along line XXII-XXII Figure 20 of the piezoelectric device. Figure 22 is a partial top view showing the structure of the connection portion of the piezoelectric device according to Embodiment 2 of the present invention. In Figure 21 in order to facilitate observation, each layer is illustrated thickly.

[0146] As Figures 20 to 22 shown, the piezoelectric device 200 according to Embodiment 2 of the present invention includes a base portion 110, four beam portions 120, and four connection portions 230. The fixed end portions 121 of the four beam portions 120 are located at positions that are square when viewed in the stacking direction. Figure 20 The dimension of the shortest distance M between the opposing fixed end portions 121 among the fixed end portions 121 of the four beam portions 120 shown in

[0147] when viewed in the stacking direction is a dimension measured along a straight line that passes through the fixed end portion 121 and the top end portion 122 of the beam portion 120 having one of the opposing fixed end portions 121 in the shortest manner.

[0148] In the present embodiment, the first connecting portion 132A, the second connecting portion 132B, and the bridging portion 131 each have a constant width and extend linearly. The dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is the same as the dimension of the maximum width a of the bridging portion 131.

[0149] In the piezoelectric device 200, if the force for connecting the beam portions 120 to each other generated by the connecting portion 230 becomes too weak, a composite vibration mode is likely to occur. The ease of occurrence can be quantified by the resonance frequency of the composite vibration mode and the resonance frequency of the fundamental vibration mode. The more these resonance frequencies are separated, the more difficult it becomes to generate a composite vibration mode.

[0150] Here, the resonance frequency of the composite vibration mode varies according to the ratio of the out-of-plane bending stiffness of the four beam portions 120 and the connecting portion 230. In each of the beam portion 120 and the connecting portion 230, the bending stiffness mainly depends on parameters such as thickness, length, and the hardness and density of the structural material.

[0151] The four beam portions 120 and the connecting portion 230 are different from each other in that the beam portion 120 includes the first electrode layer 12 while the connecting portion 230 does not include the first electrode layer 12. However, since they have substantially the same laminated structure, the thickness, hardness, and density are substantially the same, and the ratio of the above-mentioned bending stiffness varies significantly according to the difference in their lengths. That is, by adjusting the ratio of the dimension of the extension length L of each of the first connecting portion 132A and the second connecting portion 132B to the dimension of the shortest distance M between the fixed end portions 121, the resonance frequency of the composite vibration mode can be changed.

[0152] Generally, in a sound device that utilizes the bending vibration of a relatively thin beam portion 120 as in the present embodiment, due to the load generated by air resistance, the Q value at resonance is suppressed to about 10. Thus, for example, even when the piezoelectric device 200 is used at a frequency shifted by ±5% from the resonance frequency, more than half of the energy at resonance can be input to the piezoelectric device 200, so that the usable frequency band can be widened. In particular, when the piezoelectric device 200 is mass-produced by MEMS (Micro Electro Mechanical Systems) processing, sometimes a deviation of about ±5% in the resonance frequency occurs according to the processing accuracy of MEMS. However, in the piezoelectric device 200 that can use a relatively large frequency band as described above, a significant deviation in the characteristics of the piezoelectric device 200 can be suppressed.

[0153] However, when there is a resonance frequency of the composite vibration mode within the available frequency band described above, the energy input to the piezoelectric device 200 is absorbed as the vibration energy of the composite vibration mode rather than the vibration energy of the fundamental vibration mode. In this case, the conversion efficiency of the piezoelectric device 200 decreases, and the Q value of the composite vibration mode is high, so the reverberation after the drive of the piezoelectric device 200 stops becomes longer.

[0154] In view of this problem, it is preferable that the resonance frequency of the composite vibration mode is 5% or more higher than the resonance frequency of the fundamental vibration mode. Then, regarding the ratio of the dimension of the extension length L of each of the first connecting portion 132A and the second connecting portion 132B to the dimension of the shortest distance M between the fixed ends 121 and the ratio of the difference between the secondary resonance frequency and the primary resonance frequency of each of the four beam portions 120 to the primary resonance frequency, simulation analysis is performed by changing the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B. The above-mentioned primary resonance frequency corresponds to the resonance frequency of the fundamental vibration mode, and the above-mentioned secondary resonance frequency corresponds to the resonance frequency of the composite vibration mode.

[0155] As the simulation analysis conditions, in the piezoelectric device 200 of the present embodiment, the dimension of the shortest distance M between the fixed ends 121 is set to 800 μm, the dimension of the thickness of the piezoelectric layer 11 is set to 1 μm, and the thickness of the support layer 14 is set to 2 μm. That is, the dimension of the thickness T shown is set to 3 μm. This thickness T corresponds to the thickness of each of the first connecting portion 132A and the second connecting portion 132B in the above-mentioned stacking direction. The dimensions of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B are set to three types: 6 μm, 10 μm, and 15 μm. Figure 21

[0156] Figure 23 Figure 23 is a graph showing the results of the simulation analysis. In Figure 23In the graph, the vertical axis represents the ratio (%) of the difference between the secondary resonance frequency fr2 and the primary resonance frequency fr1 of each of the four beam portions 120 to the primary resonance frequency fr1, and the horizontal axis represents the ratio (%) of the dimension of the extension length L of each of the first connecting portion 132A and the second connecting portion 132B to the dimension of the shortest distance M between the fixed ends 121. In addition, the data with the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B being 6 μm is represented by a solid line, the data with the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B being 10 μm is represented by a dashed-dotted line, and the data with the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B being 15 μm is represented by a dashed line. Moreover, a reference line with the ratio of the difference between the secondary resonance frequency fr2 and the primary resonance frequency fr1 of each of the four beam portions to the primary resonance frequency fr1 being 5% is represented by a dashed line.

[0157] As Figure 23 shown, it is confirmed that as the ratio [(L / M)×100(%)] of the dimension of the extension length L of each of the first connecting portion 132A and the second connecting portion 132B to the dimension of the shortest distance M between the fixed ends 121 increases, the ratio [(fr2−fr1) / fr1×100(%)] of the difference between the secondary resonance frequency fr2 and the primary resonance frequency fr1 of each of the four beam portions 120 to the primary resonance frequency fr1 decreases.

[0158] When the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is any one of 6 μm, 10 μm, and 15 μm, within the range where the ratio [(L / M)×100(%)] of the dimension of the extension length L of each of the first connecting portion 132A and the second connecting portion 132B to the dimension of the shortest distance M between the fixed ends 121 is 32% or less, the ratio [(fr2−fr1) / fr1×100(%)] of the difference between the secondary resonance frequency fr2 and the primary resonance frequency fr1 of each of the four beam portions 120 to the primary resonance frequency fr1 is 5% or more.

[0159] Therefore, in the present embodiment, when viewed from the above stacking direction, the ratio of the dimension of the extension length L of each of the first connecting portion 132A and the second connecting portion 132B to the dimension of the shortest distance M between the opposing fixed ends 121 among the fixed ends 121 of the four beam portions 120 is 32% or less. Thus, it is difficult to generate a composite vibration mode, and it is possible to suppress a decrease in the conversion efficiency of the piezoelectric device 200 and an increase in the reverberation time after the driving of the piezoelectric device 200 stops.

[0160] As described above, the resonance frequency of the composite vibration mode varies according to the ratio of the out-of-plane bending stiffnesses of the four beam portions 120 and the connecting portion 230. When it is assumed that the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is smaller than the dimension of the thickness T of each of the first connecting portion 132A and the second connecting portion 132B in the stacking direction, the in-plane bending stiffness of the four beam portions 120 and the connecting portion 230 will be lower than the out-of-plane bending stiffness. In this case, the resonance frequency of the composite vibration mode approaches the resonance frequency of the fundamental vibration mode, and it is sometimes difficult to ensure [(fr2 - fr1) / fr1 × 100(%)] to be 5% or more.

[0161] Therefore, in the present embodiment, the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is larger than the dimension of the thickness T of each of the first connecting portion 132A and the second connecting portion 132B in the stacking direction. Thereby, it is difficult to generate the composite vibration mode, and it is possible to suppress a decrease in the conversion efficiency of the piezoelectric device 200 and an increase in the reverberation time after the driving of the piezoelectric device 200 stops.

[0162] In addition, the shape of the connecting portion 230 defined by the above parameters that can be applied is not limited to the above shape. Here, the shape of the connecting portion of the modified example defined by the above parameters that can be applied will be described. In the following description of the modified example, the same structure as the connecting portion 230 of the piezoelectric device 200 of Embodiment 2 of the present invention will not be repeatedly described.

[0163] Figure 24 is a partial top view showing the shape of the connecting portion of the piezoelectric device according to the first modified example of Embodiment 2 of the present invention. As Figure 24 shown, in the first modified example of Embodiment 2 of the present invention, the bridging portion 131 of the connecting portion 230a has a semicircular shape centered on the tip of the slit 141 and with a radius of a. The dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is the same as the dimension of the maximum width a of the bridging portion 131.

[0164] Figure 25 is a partial top view showing the shape of the connecting portion of the piezoelectric device according to the second modified example of Embodiment 2 of the present invention. As Figure 25 shown, in the second modified example of Embodiment 2 of the present invention, the first connecting portion 132A, the second connecting portion 132B, and the bridging portion 131 of the connecting portion 230b each have a constant width and extend linearly. The dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is smaller than the dimension of the maximum width a of the bridging portion 131. In addition, the dimension of the maximum width a of the bridging portion 131 is equal to or less than twice the dimension of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B.

[0165] Figure 26 is a partial top view showing the shape of the connecting portion of the piezoelectric device according to the third modification of Embodiment 2 of the present invention. As Figure 26 shown, in the third modification of Embodiment 2 of the present invention, the bridging portion 131 of the connecting portion 230c has a semi-circular shape centered on the tip of the slit 141 and with a radius of a. The size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is smaller than the size of the maximum width a of the bridging portion 131. In addition, the size of the maximum width a of the bridging portion 131 is equal to or less than twice the size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B.

[0166] Figure 27 is a partial top view showing the shape of the connecting portion of the piezoelectric device according to the fourth modification of Embodiment 2 of the present invention. As Figure 27 shown, in the fourth modification of Embodiment 2 of the present invention, the portions on the bridging portion side of the first connecting portion 132A and the second connecting portion 132B of the connecting portion 230d and the bridging portion 131 each have a shape along a hypothetical square with a side length of 2a centered on the tip of the slit 141. The size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is smaller than the size of the maximum width a of the bridging portion 131. In addition, the size of the maximum width a of the bridging portion 131 is equal to or less than twice the size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B.

[0167] Figure 28 is a partial top view showing the shape of the connecting portion of the piezoelectric device according to the fifth modification of Embodiment 2 of the present invention. As Figure 28 shown, in the fifth modification of Embodiment 2 of the present invention, the portions on the bridging portion side of the first connecting portion 132A and the second connecting portion 132B of the connecting portion 230e and the bridging portion 131 each have a shape along a hypothetical circle with a radius of a centered on the tip of the slit 141. The size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is smaller than the size of the maximum width a of the bridging portion 131. In addition, the size of the maximum width a of the bridging portion 131 is equal to or less than twice the size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B.

[0168] Figure 29 is a partial top view showing the shape of the connecting portion of the piezoelectric device according to the sixth modification of Embodiment 2 of the present invention. As Figure 29As shown, in the sixth modification of Embodiment 2 of the present invention, a circular opening 141r with a diameter r is formed at the tip of the slit 141. The size of the diameter r is larger than the width of the slit 141 and is equal to or less than the size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B. The portions of the first connecting portion 132A and the second connecting portion 132B on the bridging portion side of the connecting portion 230f and the bridging portion 131 each have a shape along a hypothetical square with a side length of (2a + r) centered on the center of the opening 141r. The size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is equal to or less than the size of the maximum width a of the bridging portion 131. In addition, the size of the maximum width a of the bridging portion 131 is equal to or less than twice the size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B.

[0169] Figure 30 is a partial top view showing the shape of the connecting portion of the piezoelectric device according to the seventh modification of Embodiment 2 of the present invention. As Figure 30 shown, in the seventh modification of Embodiment 2 of the present invention, a circular opening 141r with a diameter r is formed at the tip of the slit 141. The size of the diameter r is larger than the width of the slit 141 and is equal to or less than the size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B. The portions of the first connecting portion 132A and the second connecting portion 132B on the bridging portion side of the connecting portion 230g and the bridging portion 131 each have a shape along a hypothetical circle with a radius of (a + r / 2) centered on the center of the opening 141r. The size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B is equal to or less than the size of the maximum width a of the bridging portion 131. In addition, the size of the maximum width a of the bridging portion 131 is equal to or less than twice the size of the minimum width W of each of the first connecting portion 132A and the second connecting portion 132B.

[0170] The embodiments disclosed herein should be considered illustrative in all respects 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.

[0171] Explanation of Reference Numerals

[0172] 10. Multiple layers; 11. Piezoelectric layer; 11a. Piezoelectric single crystal substrate; 12. First electrode layer; 13. Second electrode layer; 14. Support layer; 14a. First support portion; 14b. Second support portion; 15. Substrate layer; 15a. First substrate layer; 15b. Second substrate layer; 16. Stacked body; 17. Groove portion; 18. Recessed portion; 20. First connection electrode layer; 30. Second connection electrode layer; 100, 100a, 100b, 100c, 200. Piezoelectric device; 101. Hole portion; 110. Base portion; 120. Beam portion; 121. Fixed end portion; 122. Tip end portion; 130, 230, 230a, 230b, 230c, 230d, 230e, 230f, 230g. Connection portion; 131. Bridging portion; 132A. First connection portion; 132B. Second connection portion; 133A. First end portion; 133B. Second end portion; 141. Slit; 141r. Opening; 142. Opening portion; 143. Outer peripheral slit.

Claims

1. A piezoelectric device, wherein, the piezoelectric device includes: a ring-shaped base; a plurality of beam portions having fixed ends connected to the base and tip portions located on the side opposite to the fixed ends, extending from the fixed ends toward the tip portions; and a connecting portion that connects a pair of beam portions adjacent to each other in the circumferential direction of the base among the plurality of beam portions, the plurality of beam portions are respectively piezoelectric vibrating portions including a plurality of layers, between the pair of beam portions, there are provided: a slit formed by a part of a pair of adjacent end edges of the pair of beam portions; and an opening portion formed by another part of the pair of end edges, spaced apart from the slit and located at a position adjacent to the tip portions of the pair of beam portions respectively, the connecting portion is provided in a manner of folding back between the pair of beam portions, the connecting portion includes: a first connecting portion extending along the slit and connected to one of the pair of beam portions; a second connecting portion extending along the slit and connected to the other of the pair of beam portions; and a bridging portion located between the slit and the opening portion and connected to the first connecting portion and the second connecting portion respectively, the plurality of beam portions are respectively located at positions sandwiched by the slits extending in mutually intersecting directions, and are connected to each other in the circumferential direction via the connecting portion.

2. The piezoelectric device according to claim 1, wherein, the piezoelectric device further has an outer peripheral slit spaced apart from the slit and extending along the first connecting portion and the second connecting portion respectively and communicating with the opening portion.

3. The piezoelectric device according to claim 1 or 2, wherein, the plurality of layers have: a piezoelectric layer composed of a single crystal piezoelectric body; a first electrode layer disposed on one side of the piezoelectric layer in the stacking direction of the plurality of layers; and a second electrode layer disposed on the other side of the piezoelectric layer in such a manner as to be at least partially opposed to the first electrode layer with the piezoelectric layer interposed therebetween, when the polarization axis of the single crystal piezoelectric body is projected onto an imaginary plane orthogonal to the stacking direction, the axial direction of the imaginary axis extends along the same direction in any one of the plurality of beam portions, and when viewed from the stacking direction, it intersects the extending directions of the plurality of beam portions respectively.

4. The piezoelectric device according to claim 3, wherein, when viewed from the stacking direction, the angle formed by the axial direction of the imaginary axis and the extending directions of the plurality of beam portions is 40 degrees or more and 50 degrees or less or 130 degrees or more and 140 degrees or less.

5. The piezoelectric device according to claim 3 or 4, wherein, the piezoelectric layer is composed of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

6. The piezoelectric device according to any one of claims 1 to 5, wherein, the piezoelectric device includes 4 beam portions as the plurality of beam portions, the fixed ends of the 4 beam portions are located at positions that are square-shaped when viewed from the stacking direction, When viewed from the stacking direction, the ratio of the dimension of the extension length of each of the first connecting portion and the second connecting portion to the dimension of the shortest distance between the opposing fixed ends among the fixed ends of the four beam portions is 32% or less.

7. The piezoelectric device according to any one of claims 1 to 6, wherein the dimension of the minimum width of each of the first connecting portion and the second connecting portion is larger than the dimension of the thickness of each of the first connecting portion and the second connecting portion in the stacking direction.

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