piezoelectric device

Abstract

A piezoelectric device (100) includes an outer base (110), a protruding base (120), and only one cantilever beam portion (130). The protruding base (120) has a protruding portion (121) and a top end portion (122). The protruding portion (121) protrudes from an inner peripheral surface (111) of the outer base (110) toward a center (C) of a ring shape. The top end portion (122) is connected to the protruding portion (121) and is located at the center (C). The cantilever beam portion (130) is connected to the top end portion (122), separated from the protruding portion (121), and extends. The cantilever beam portion (130) has a fixed end portion (131) and a free peripheral end portion (132). The fixed end portion (131) is connected to the top end portion (122). The free peripheral end portion (132) is located at a position along the inner peripheral surface (111). The protruding portion (121) is located between one end (132a) and the other end (132b) of the free peripheral end portion (132).

Description

Technical Field

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

[0002] The following documents disclose the structure of a piezoelectric device: Japanese Patent Publication No. 2014-515214 (Patent Document 1), U.S. Patent No. 5633552 (Patent Document 2), and Japanese Patent Application Publication No. 2017-041824 (Patent Document 3).

[0003] Patent Document 1 describes a piezoelectric device, which is a MEMS transducer comprising a substrate and multiple cantilever beams. Each cantilever beam has a tapered tip and is adjacent to each other. Each cantilever beam has a base end, a top end, and a main body. The main body is positioned between the base end and the top end. Each cantilever beam is arranged such that its top end extends toward a common imaginary point. Each cantilever beam is attached to the substrate along its base end, but not along its main body.

[0004] The piezoelectric device described in Patent Document 2 is a micromechanical device comprising a frame and at least one cantilever structure. The frame has an opening. The cantilever structure is mounted on the frame in a localized area around the opening. The cantilever structure covers most of the opening. The cantilever structure comprises three sublayers. The three sublayers are a first sublayer, a second sublayer, and a third sublayer. The second sublayer is adjacent to the first and third sublayers. The first and third sublayers are substantially formed of the same first material and have approximately the same average stress. The second sublayer is formed of a second material and has a minimum stress and a maximum stress. The difference between the maximum and minimum stresses is smaller than the magnitude of the average stress of the first sublayer. The opening may also be square.

[0005] The piezoelectric device described in Patent Document 3 is a detection device for elastic waves transmitted through air, and has a cantilever structure. The cantilever structure has a fixed end and a free end. The cantilever structure includes a first electrode and a second electrode. The first electrode is plate-shaped and bends under the action of the elastic wave, thereby vibrating. The second electrode is plate-shaped and is positioned opposite the first electrode at a predetermined distance. The cantilever structure detects the elastic wave based on the change in capacitance between the first and second electrodes. The end of the second electrode in the direction from the fixed end toward the free end is located closer to the fixed end than to the free end.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Publication No. 2014-515214

[0009] Patent Document 2: Specification of U.S. Patent No. 5633552

[0010] Patent Document 3: Japanese Patent Application Publication No. 2017-041824 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] The piezoelectric device described in Patent Document 1 includes multiple cantilever beams. When the piezoelectric device is driven, these multiple cantilever beams sometimes vibrate with different phases. In this case, the device characteristics of the piezoelectric device are actually reduced. The piezoelectric devices described in Patent Documents 2 and 3 each include a single cantilever structure, i.e., a cantilever beam portion. However, for a piezoelectric device with only one beam portion, compared to a piezoelectric device with multiple beam portions, the force pushing the medium around the beam portion is smaller, thus resulting in lower device characteristics.

[0013] Therefore, in a piezoelectric device with only one beam, it is considered to increase the volume of the medium surrounding the beam that is pushed out by the beam when a predetermined voltage is applied by increasing the area of ​​the beam when viewed from the direction of the beam's vibration, thereby improving the device's characteristics. However, sometimes increasing the area of ​​the beam can lead to a decrease in the inherent resonant frequency of the beam.

[0014] The present invention was made in view of the above-mentioned problems, and its object is to provide a piezoelectric device that can suppress the change of the resonant frequency of the beam and improve the characteristics of the device.

[0015] Solution for solving the problem

[0016] The piezoelectric device according to the present invention includes an outer base, a protruding base, and only one cantilever beam portion. The outer base is annular and has an inner circumferential surface. The protruding base has a protrusion and a top portion. The protrusion protrudes from the inner circumferential surface of the outer base toward the center of the annulus. The top portion is connected to the protrusion and located at the aforementioned center. The cantilever beam portion is connected to the top portion, separate from the protrusion, and extends outward. The cantilever beam portion includes a piezoelectric body layer, a first electrode layer, and a second electrode layer. The first electrode layer is disposed on one side of the piezoelectric body layer. The second electrode layer is disposed such that it is at least partially opposite to the first electrode layer through the piezoelectric body layer. The cantilever beam portion has a fixed end and a free circumferential end. The fixed end is connected to the top portion. The free circumferential end is located along the inner circumferential surface. The protrusion is located between one end and the other end of the free circumferential end.

[0017] The effects of the invention

[0018] According to the present invention, the variation of the resonant frequency of the beam can be suppressed and the characteristics of the device can be improved. Attached Figure Description

[0019] Figure 1This is a perspective view of the piezoelectric device according to Embodiment 1 of the present invention, viewed from one side.

[0020] Figure 2 This is a perspective view obtained by observing the piezoelectric device of Embodiment 1 of the present invention from another side.

[0021] Figure 3 This is a top view of the piezoelectric device according to Embodiment 1 of the present invention.

[0022] Figure 4 Observe from the direction of the arrow on line IV-IV Figure 3 The cross-sectional view obtained from the piezoelectric device.

[0023] Figure 5 Observe from the direction of the arrow on line V-V Figure 3 The cross-sectional view obtained from the piezoelectric device.

[0024] Figure 6 This is a partial cross-sectional view schematically showing the cantilever beam portion of the piezoelectric device according to Embodiment 1 of the present invention during its operation.

[0025] Figure 7 This is a partial cross-sectional view schematically showing the cantilever beam portion of the piezoelectric device according to Embodiment 1 of the present invention during operation.

[0026] Figure 8 This is a perspective view showing the state of vibration in the desired vibration mode of the piezoelectric device according to Embodiment 1 of the present invention through simulation.

[0027] Figure 9 This is a cross-sectional view showing the state in which a second electrode layer is provided on a piezoelectric single crystal substrate in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0028] Figure 10 This is a cross-sectional view showing the state in which the first support layer is provided in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0029] Figure 11 This is a cross-sectional view showing the state in which the laminate is bonded to the first support layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0030] Figure 12 This is a cross-sectional view showing the state in which a piezoelectric single crystal substrate is cut to form a piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0031] Figure 13 This is a cross-sectional view showing the state in which the first electrode layer is provided in the piezoelectric body layer during the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0032] Figure 14This is a cross-sectional view showing the state in which a slit is formed from the side of the piezoelectric layer opposite to the support layer side to the upper surface of the support layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0033] Figure 15 This is a cross-sectional view showing the state in which a through hole is formed from the side of the piezoelectric body layer opposite to the support layer side to the upper surface of the second electrode layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0034] Figure 16 This is a top view showing the piezoelectric device according to Embodiment 2 of the present invention.

[0035] Figure 17 This is a perspective view of the piezoelectric device according to Embodiment 3 of the present invention, viewed from one side.

[0036] Figure 18 This is a perspective view obtained by observing the piezoelectric device of Embodiment 3 of the present invention from another side.

[0037] Figure 19 This is a top view of the piezoelectric device according to Embodiment 4 of the present invention.

[0038] Figure 20 This is a cross-sectional view of the piezoelectric device according to Embodiment 5 of the present invention. Detailed Implementation

[0039] Hereinafter, piezoelectric devices according to various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the embodiments, the same or equivalent parts in the drawings will be labeled with the same reference numerals, and their descriptions will not be repeated.

[0040] (Implementation Method 1)

[0041] Figure 1 This is a perspective view of the piezoelectric device according to Embodiment 1 of the present invention, viewed from one side. Figure 2 This is a perspective view obtained by observing the piezoelectric device of Embodiment 1 of the present invention from another side. Figure 3 This is a top view of the piezoelectric device according to Embodiment 1 of the present invention.

[0042] like Figures 1-3 As shown, the piezoelectric device 100 includes an outer base 110, a protruding base 120, and a single cantilever beam portion 130.

[0043] The outer base 110 is annular and has an inner circumferential surface 111. In this embodiment, when viewed axially from the central axis of the annular shape of the outer base 110, the inner circumferential surface 111 is located on an imaginary circle.

[0044] The protruding base 120 has a protrusion 121 and a top portion 122. The protrusion 121 protrudes from the inner circumferential surface 111 of the outer base 110 toward the annular center C. When viewed axially from the central axis, the protrusion 121 protrudes in a straight line. When viewed axially from the central axis, the width of the protrusion 121 in the orthogonal direction to the protrusion direction is approximately constant. Furthermore, the approximately constant width of the protrusion 121 includes cases where the dimension of the width of the protrusion 121 is within ±5% of the average dimension of the width of the protrusion 121.

[0045] The top portion 122 is connected to the protrusion 121 and is located at the center C. In this embodiment, when viewed axially from the central axis, the top portion 122 has a semi-circular shape. When viewed axially from the central axis, the diameter of the top portion 122 is the same as the width of the protrusion 121.

[0046] The cantilever beam portion 130 is connected to the top portion 122, separate from and extends out of the protrusion 121. The cantilever beam portion 130 has a fixed end portion 131, a free circumferential end portion 132, and two side ends 133.

[0047] The fixed end 131 is connected to the top end 122. Specifically, when viewed axially from the central axis, the fixed end 131 is connected to the circumferential surface of the top end 122 other than the portion connected to the protrusion 121. That is, when viewed axially from the central axis, the fixed end 131 is arc-shaped.

[0048] The free peripheral end portion 132 is located along the inner peripheral surface 111. In this embodiment, when viewed axially from the annular central axis of the outer base 110, the free peripheral end portion 132 is located on an imaginary circle. That is, when viewed axially from the aforementioned central axis, this imaginary circle is located concentric with the arc-shaped fixed end portion 131.

[0049] A first slit 134 is formed between the free peripheral end portion 132 and the inner peripheral surface 111. The width of the first slit 134 is approximately constant in the direction along the inner peripheral surface 111. Furthermore, the approximately constant width of the first slit 134 includes cases where the width of the first slit 134 is within ±5% of the average width of the first slit 134. A protrusion 121 is located between one end 132a and the other end 132b of the free peripheral end portion 132. One end 132a and the other end 132b of the free peripheral end portion 132 are positioned such that the first slit 134 reaches the protrusion 121. More preferably, one end 132a and the other end 132b of the free peripheral end portion 132 are positioned on the side opposite to the tip portion 122 side such that the first slit 134 reaches the protrusion 121.

[0050] A second slit 135, connecting to the first slit 134, is formed between each of the two side ends 133 and the protrusion 121. The width of the second slit 135 is approximately constant in the protruding direction of the protrusion 121. Furthermore, the approximately constant width of the second slit 135 includes cases where the width of the second slit 135 is within ±5% of the average width of the second slit 135. The two side ends 133 each form the second slit 135, and the two ends 131a, 131b of the fixed end 131 are connected to the two ends 132a, 132b of the free peripheral end 132 with the shortest possible distance. The width of the first slit 134 and the width of the second slit 135 are approximately the same. Therefore, the force exerted by the cantilever beam portion 130 on the surrounding medium or the force borne by the cantilever beam portion 130 from the medium can be suppressed and released from the larger slit in the first slit 134 and the second slit 135. Furthermore, when the width of the first slit 134 and the width of the second slit are approximately the same, the following case applies: the absolute value of the difference between the width of the first slit 134 and the width of the second slit 135 is less than 5% of the width of the first slit 134 or the width of the second slit 135.

[0051] The narrower the widths of the first slit 134 and the second slit 135, the better the device characteristics of the piezoelectric device 100. For example, when the piezoelectric device 100 is used as an ultrasonic transducer, the narrower the widths of the first slit 134 and the second slit 135, the better the force exerted by the cantilever beam portion 130 on the medium surrounding the cantilever beam portion 130, or the force borne by the cantilever beam portion 130 from the medium, can be released from the first slit 134 and the second slit 135. The widths of the first slit 134 and the second slit 135 are preferably 10 μm or less, and more preferably 1 μm or less.

[0052] Furthermore, in the piezoelectric device 100 of Embodiment 1 of the present invention, from the viewpoint of facilitating the bending vibration of the cantilever beam portion 130, the shortest distance from the fixed end 131 to the free peripheral end 132 is preferably at least 5 times the thickness of the cantilever beam portion 130 in the axial direction of the aforementioned central axis.

[0053] Next, the components that make up the cantilever beam 130 will be described. Figure 4 Observe from the direction of the arrow on line IV-IV Figure 3 A cross-sectional view obtained from a piezoelectric device. Figure 4 And the following explanation Figure 5 The diagram illustrates the thickness of each component.

[0054] like Figure 3 and Figure 4As shown, the cantilever beam portion 130 includes a piezoelectric layer 10, a first electrode layer 20, a second electrode layer 30, and a support layer 40.

[0055] like Figure 4 As shown, the piezoelectric layer 10 is made of a single-crystal material. The cutting orientation of the piezoelectric layer 10 is appropriately selected to achieve the desired device characteristics. In this embodiment, the piezoelectric layer 10 is formed by thinning a single-crystal substrate, specifically a rotary Y-cut substrate. Furthermore, the cutting orientation of this rotary Y-cut substrate is specifically 30°. Additionally, the thickness of the piezoelectric layer 10 is, for example, 0.3 μm or more and 5.0 μm or less.

[0056] The material constituting the piezoelectric layer 10 is appropriately selected to enable the piezoelectric device 100 to exhibit the desired device characteristics. In this embodiment, the piezoelectric layer 10 is composed of an inorganic material. Specifically, the piezoelectric layer 10 is composed of a basic niobate-based compound or a basic tantalate-based compound. In this embodiment, the alkali metal contained in the aforementioned basic niobate-based compound or the aforementioned basic tantalate-based compound is at least one selected from lithium, sodium, and potassium. In this embodiment, the piezoelectric layer 10 is composed of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

[0057] The first electrode layer 20 is disposed on one side of the piezoelectric layer 10 along the axial direction of the aforementioned central axis. The second electrode layer 30 is disposed such that it is at least partially opposite to the first electrode layer 20 in the cantilever beam portion 130, separated by the piezoelectric layer 10. Furthermore, in this embodiment, sealing layers (not shown) are respectively disposed between the first electrode layer 20 and the piezoelectric layer 10, and between the second electrode layer 30 and the piezoelectric layer 10.

[0058] When viewed from the axial direction of the central axis of the inner circumferential surface 111, i.e., the axial direction of the aforementioned annular central axis, the area of ​​the opposing region between the first electrode layer 20 and the second electrode layer 30 in the cantilever beam portion 130 is more than 90% of the area of ​​the cantilever beam portion 130. For example... Figure 3 and Figure 4 As shown, in this embodiment, when viewed from the aforementioned axial direction, the first electrode layer 20 and the second electrode layer 30 completely overlap with the cantilever beam portion 130. That is, in this embodiment, the area of ​​the opposing region between the first electrode layer 20 and the second electrode layer 30 in the cantilever beam portion 130 is approximately the same as the area of ​​the cantilever beam portion 130. Furthermore, the area of ​​the opposing region being approximately the same as the area of ​​the cantilever beam portion 130 includes cases where the area of ​​the opposing region is 95% or more of the area of ​​the cantilever beam portion 130.

[0059] In this embodiment, the first electrode layer 20 and the second electrode layer 30 are each made of Pt. Alternatively, the first electrode layer 20 and the second electrode layer 30 may be made of other materials such as Al. The sealing layer is made of Ti. Alternatively, the sealing layer may be made of other materials such as NiCr. Alternatively, the first electrode layer 20, the second electrode layer 30, and the sealing layer may be epitaxially grown films. When the piezoelectric layer 10 is made of lithium niobate (LiNbO3), from the viewpoint of suppressing the diffusion of the material constituting the sealing layer into the first electrode layer 20 or the second electrode layer 30, it is preferable that the sealing layer is made of NiCr. This improves the reliability of the piezoelectric device 100.

[0060] In this embodiment, the thickness of each of the first electrode layer 20 and the second electrode layer 30 is, for example, 0.05 μm or more and 0.2 μm or less. The thickness of the sealing layer is, for example, 0.005 μm or more and 0.05 μm or less.

[0061] like Figure 4 As shown, the support layer 40 is disposed axially along the central axis on the side of the second electrode layer 30 of the piezoelectric layer 10 and on the side of the second electrode layer 30 opposite to the side of the piezoelectric layer 10. The support layer 40 has a first support layer 41 and a second support layer 42 stacked on the side of the first support layer 41 opposite to the side of the piezoelectric layer 10. In this embodiment, the first support layer 41 is made of SiO2, and the second support layer 42 is made of single-crystal Si. In this embodiment, from the viewpoint of bending vibration of the cantilever beam portion 130, it is preferable that the thickness of the support layer 40 is thicker than the thickness of the piezoelectric layer 10. The mechanism of bending vibration of the cantilever beam portion 130 will be described later.

[0062] Next, the components constituting the protruding base 120 will be described. For example... Figure 4 As shown, the protruding base 120 and the cantilever beam portion 130 similarly include a piezoelectric layer 10, a first electrode layer 20, a second electrode layer 30, and a support layer 40. In an in-plane direction orthogonal to the aforementioned central axis, the piezoelectric layer 10, the first electrode layer 20, the second electrode layer 30, and the support layer 40 of the protruding base 120 are continuous with the piezoelectric layer 10, the first electrode layer 20, the second electrode layer 30, and the support layer 40 of the cantilever beam portion 130.

[0063] like Figure 3 and Figure 4 As shown, in the top portion 122, the second electrode layer 30 is arranged such that it is at least partially opposite to the first electrode layer 20, separated by the piezoelectric layer 10. Figure 3 As shown, in the protrusion 121, the second electrode layer 30 is arranged in a manner that separates it from the first electrode layer 20 by passing over the piezoelectric layer 10.

[0064] like Figure 4 As shown, the protruding base 120 further includes a substrate layer 50. The substrate layer 50 is connected to the side of the support layer 40 opposite to the side of the second electrode layer 30. The substrate layer 50 includes a first substrate layer 51 and a second substrate layer 52 stacked on the side of the first substrate layer 51 opposite to the side of the support layer 40. In this embodiment, the first substrate layer 51 is made of SiO2, and the second substrate layer 52 is made of single-crystal Si.

[0065] Next, the components constituting the outer base 110 will be described. Figure 5 Observe from the direction of the arrow on line V-V Figure 3 A cross-sectional view obtained from a piezoelectric device. For example... Figure 4 and Figure 5 As shown, the outer base 110 and the protruding base 120 similarly include a piezoelectric layer 10, a first electrode layer 20, a second electrode layer 30, a support layer 40, and a substrate layer 50. In an in-plane direction orthogonal to the central axis, the piezoelectric layer 10, the first electrode layer 20, the second electrode layer 30, the support layer 40, and the substrate layer 50 of the outer base 110 are continuous with the piezoelectric layer 10, the first electrode layer 20, the second electrode layer 30, the support layer 40, and the substrate layer 50 of the protruding base 120.

[0066] like Figure 3 and Figure 5 As shown, in the outer base 110, the second electrode layer 30 is arranged in a manner that separates it from the first electrode layer 20 by the piezoelectric layer 10.

[0067] like Figure 3 and Figure 5 As shown, the outer base 110 also includes a first connecting electrode layer 60 and a second connecting electrode layer 70.

[0068] The first connecting electrode layer 60 is electrically connected to the first electrode layer 20 through a sealing layer (not shown) and exposed to the outside. Specifically, the first connecting electrode layer 60 is disposed on the side of the first electrode layer 20 of the outer base 110 opposite to the piezoelectric layer 10 side.

[0069] The second connecting electrode layer 70 is electrically connected to the second electrode layer 30 through a sealing layer (not shown) and exposed to the outside. Specifically, the second connecting electrode layer 70 is disposed on the side of the second electrode layer 30 of the outer base 110 opposite to the side of the support layer 40.

[0070] The thickness of each of the first connecting electrode layer 60 and the second connecting electrode layer 70 is, for example, 0.1 μm or more and 1.0 μm or less. The thickness of each of the sealing layer connected to the first connecting electrode layer 60 and the sealing layer connected to the second connecting electrode layer 70 is, for example, 0.005 μm or more and 0.1 μm or less.

[0071] In this embodiment, the first connecting electrode layer 60 and the second connecting electrode layer 70 are made of Au. The first connecting electrode layer 60 and the second connecting electrode layer 70 may also be made of other conductive materials such as Al. The sealing layer connected to the first connecting electrode layer 60 and the sealing layer connected to the second connecting electrode layer 70 are respectively made of, for example, Ti. These sealing layers may also be made of NiCr.

[0072] like Figure 2 and Figure 4 As shown, the piezoelectric device 100 of this embodiment also includes an opening 140. The opening 140 is formed by being surrounded by an outer base 110, a protruding base 120, and a cantilever beam portion 130. The opening 140 opens to the side opposite to the cantilever beam portion 130. Figure 2 As shown, when the piezoelectric device 100 is viewed from the substrate layer 50 side, the opening 140 has a concave shape formed by being surrounded by the outer base 110 and the protruding base 120.

[0073] Here, the mechanism of vibration of the cantilever beam portion 130 in the piezoelectric device 100 of Embodiment 1 of the present invention will be explained. Figure 6 This is a schematic partial cross-sectional view of the cantilever beam portion of the piezoelectric device according to Embodiment 1 of the present invention. Figure 7 This is a partial cross-sectional view schematically showing the cantilever beam portion during the operation of the piezoelectric device according to Embodiment 1 of the present invention. Furthermore, in Figure 6 and Figure 7 The first electrode layer 20 and the second electrode layer 30 are not shown in the figure.

[0074] like Figure 6 and Figure 7 As shown, in this embodiment, in the cantilever beam portion 130, the piezoelectric layer 10 functions as a stretching layer capable of extending and contracting in the in-plane direction of a plane orthogonal to the axial direction of the central axis, while the layers other than the piezoelectric layer 10 function as constraint layers. In this embodiment, the support layer 40 primarily functions as a constraint layer. Thus, the constraint layer and the stretching layer are stacked in an orthogonal direction to the stretching direction of the stretching layer. Furthermore, in the cantilever beam portion 130, a reverse stretching layer may be included instead of a constraint layer. This reverse stretching layer is capable of contracting in the in-plane direction when the stretching layer extends in the in-plane direction, and extending in the in-plane direction when the stretching layer contracts in the in-plane direction.

[0075] Furthermore, when the piezoelectric layer 10, which serves as a stretching layer, is to stretch or contract in the aforementioned in-plane direction, the support layer 40, which is the main part of the constraint layer, constrains the stretching or contraction of the piezoelectric layer 10 at the interface with the piezoelectric layer 10. Additionally, in this embodiment, in the cantilever beam portion 130, the piezoelectric layer 10, which serves as a stretching layer, is located only on one side of the stress neutral plane N of the cantilever beam portion 130. The center of gravity of the support layer 40, which mainly constitutes the constraint layer, is located on the other side of the stress neutral plane N. Thus, as... Figure 6 and Figure 7 As shown, when the piezoelectric layer 10, which serves as a stretching layer, stretches and contracts in the in-plane direction of the aforementioned plane, the cantilever beam portion 130 bends in an orthogonal direction orthogonal to the aforementioned plane. Furthermore, the greater the separation distance between the stress-neutral plane N and the piezoelectric layer 10, the greater the displacement of the cantilever beam portion 130 when it bends. Additionally, the greater the stress on the piezoelectric layer 10 that is about to stretch and contract, the greater the displacement. Thus, the cantilever beam portion 130 bends in an orthogonal direction orthogonal to the aforementioned plane... Figures 1-5 The fixed end 131 shown is the starting point for bending vibration.

[0076] Moreover, such as Figure 1 As shown, the piezoelectric device 100 of this embodiment has only one cantilever beam portion 130. Therefore, the reduction in device characteristics caused by the vibration of multiple cantilever beam portions with different phases in a piezoelectric device arranged in a manner where multiple cantilever beam portions are arranged adjacently does not occur. Figure 8 This is a perspective view illustrating the state of the piezoelectric device according to Embodiment 1 of the present invention, expressed through simulation, in a desired vibration mode. Figure 8 In the text, a portion of the components are omitted when referring to the piezoelectric device 100. Figure 8 In the diagram, the cantilever beam section 130 is represented by a lighter color indicating a greater axial displacement along the aforementioned central axis. Additionally, in... Figure 8 In the middle, it indicates the 130-degree direction of the cantilever beam. Figure 4 The piezoelectric device 100 is shown in a state of displacement on the side of the first electrode layer 20. For example... Figure 8 As shown, the cantilever beam 130 is driven to vibrate from the free circumferential end 132 side to the fixed end 131.

[0077] The piezoelectric device 100 of this embodiment has improved device characteristics, especially when used as an ultrasonic transducer. Hereinafter, the function of the piezoelectric device 100 when used as an ultrasonic transducer will be described.

[0078] First, such as Figure 3 As shown, when ultrasonic waves are generated using the piezoelectric device 100, a voltage is applied between the first connecting electrode layer 60 and the second connecting electrode layer 70. Furthermore, as... Figures 3-5As shown, a voltage is applied between the first electrode layer 20, which is connected to the first connecting electrode layer 60, and the second electrode layer 30, which is connected to the second connecting electrode layer 70. Therefore, in the cantilever beam portion 130, a voltage is also applied between the first electrode layer 20 and the second electrode layer 30, which are opposite to each other and separated by the piezoelectric layer 10. In this way, the piezoelectric layer 10 expands and contracts in the in-plane direction of the aforementioned plane, and therefore, according to the above mechanism, the cantilever beam portion 130 bends and vibrates in an orthogonal direction orthogonal to the aforementioned plane. This applies a force to the medium surrounding the piezoelectric device 100, causing the medium to vibrate and thereby generating ultrasonic waves.

[0079] Furthermore, in the piezoelectric device 100 of this embodiment, the cantilever beam portion 130 has an inherent mechanical resonant frequency. Therefore, when the applied voltage is a sinusoidal voltage and the frequency of the sinusoidal voltage is close to the aforementioned resonant frequency, the displacement of the cantilever beam portion 130 when bending increases.

[0080] When detecting ultrasonic waves using the piezoelectric device 100, the medium surrounding the cantilever beam portion 130 vibrates due to the ultrasonic waves, applying force to the cantilever beam portion 130 from the surrounding medium, causing the cantilever beam portion 130 to bend and vibrate. When the cantilever beam portion 130 bends and vibrates, stress is applied to the piezoelectric layer 10. By applying stress to the piezoelectric layer 10, charges are induced in the piezoelectric layer 10. Using the charges induced in the piezoelectric layer 10, a potential difference is generated between the first electrode layer 20 and the second electrode layer 30, which are separated by the piezoelectric layer 10. This potential difference is detected in the first connecting electrode layer 60 connected to the first electrode layer 20 and the second connecting electrode layer 70 connected to the second electrode layer 30. Therefore, ultrasonic waves can be detected in the piezoelectric device 100.

[0081] Furthermore, when the ultrasonic wave being tested contains many specific frequency components and these frequency components are close to the aforementioned resonant frequency, the displacement of the cantilever beam 130 during bending vibration increases. This increase in displacement leads to an increase in the aforementioned potential difference.

[0082] Thus, when the piezoelectric device 100 of this embodiment is used as an ultrasonic transducer, the resonant frequency of the cantilever beam portion 130 becomes important.

[0083] Furthermore, in the piezoelectric device 100, if the shortest distance from the fixed end 131 to the free peripheral end 132 is different, the resonant frequency of the cantilever beam portion 130 will change. In this embodiment, the free peripheral end 132 is located along the inner peripheral surface 111, and the protrusion 121 is located between one end 132a and the other end 132b of the free peripheral end 132. Therefore, it is designed such that the shortest distance from the fixed end 131 to the free peripheral end 132 is a predetermined length and the resonant frequency of the cantilever beam portion 130 is near the frequency of a sinusoidal voltage. As described above, the length of the free peripheral end 132 is extended along the inner peripheral surface 111 and the protrusion 121 is located between one end 132a and the other end 132b of the free peripheral end 132, thereby increasing the area of ​​the cantilever beam portion 130. Therefore, for example, when a predetermined voltage is applied to the piezoelectric layer 10, the volume of the medium surrounding the cantilever beam 130 pushed out by the cantilever beam 130 increases, thereby improving the device characteristics of the piezoelectric device 100. That is, for the piezoelectric device 100, changes in the resonant frequency of the cantilever beam 130 can be suppressed and the device characteristics can be improved.

[0084] For example, if the resonant frequency of the cantilever beam portion 130 of the piezoelectric device 100 according to Embodiment 1 of the present invention is designed to be around 40kHz, and the piezoelectric layer 10 is made of lithium niobate, the thickness of the piezoelectric layer 10 is 1μm, the thickness of the first electrode layer 20 and the second electrode layer 30 is 0.1μm, the thickness of the first support layer 41 is 0.8μm, the thickness of the second support layer 42 is 3.8μm, and the shortest distance from the fixed end 131 to the free peripheral end 132 of the cantilever beam portion 130 is 400μm, then the free peripheral end 132 is designed such that it runs along the inner peripheral surface 111 and the protrusion 121 is located between one end 132a and the other end 132b of the free peripheral end 132.

[0085] The following describes a method for manufacturing the piezoelectric device 100 according to Embodiment 1 of the present invention. Figure 9 This is a cross-sectional view showing the state in which a second electrode layer is provided on a piezoelectric single-crystal substrate during the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 9 and what follows Figures 10-14 In, with Figure 4 The same sectional view is illustrated.

[0086] like Figure 9As shown, a bonding layer (not shown) is first formed on the lower surface of the piezoelectric single crystal substrate 10a, and then a second electrode layer 30 is formed on the side of the bonding layer opposite to the piezoelectric single crystal substrate 10a. The second electrode layer 30 is formed into a desired pattern by vapor deposition and lift-off. Alternatively, the second electrode layer 30 can be formed by sputtering over the entire lower surface of the piezoelectric single crystal substrate 10a and then etching to form the desired pattern. The second electrode layer 30 and the bonding layer can also be epitaxially grown.

[0087] Figure 10 This is a cross-sectional view showing the state in which the first support layer is provided in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0088] like Figure 10 As shown, a first support layer 41 is formed on the lower surfaces of both the piezoelectric single crystal substrate 10a and the second electrode layer 30 using methods such as CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition). Immediately after the first support layer 41 is formed, a portion of the lower surface of the first support layer 41 located on the side opposite to the second electrode layer 30 protrudes. Therefore, the lower surface of the first support layer 41 is planarized by cutting it using methods such as Chemical Mechanical Polishing (CMP).

[0089] Figure 11 This is a cross-sectional view showing the state in which the laminate is bonded to the first support layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0090] like Figure 11 As shown, a laminate 50a, consisting of a second support layer 42 and a substrate layer 50, is bonded to the lower surface of the first support layer 41 via surface activation bonding and atomic diffusion bonding. In this embodiment, the laminate 50a is an SOI (Silicon Insulator) substrate. Furthermore, by pre-planarizing the upper surface of the second support layer 42 using CMP, the yield of the piezoelectric device 100 is improved.

[0091] Figure 12 This is a cross-sectional view showing the state in which a piezoelectric single crystal substrate is cut to form a piezoelectric layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0092] like Figure 11 and Figure 12As shown, the upper surface of the piezoelectric single crystal substrate 10a is thinned by grinding with a grinding machine. The thinned upper surface of the piezoelectric single crystal substrate 10a is further polished by CMP or the like, so that the piezoelectric single crystal substrate 10a is formed into a piezoelectric layer 10.

[0093] Alternatively, a release layer can be formed by pre-implanting ions onto the upper surface of the piezoelectric single crystal substrate 10a, and the piezoelectric single crystal substrate 10a can be formed into a piezoelectric layer 10 by peeling off the release layer. Alternatively, the piezoelectric single crystal substrate 10a can be further polished using CMP or the like to form a piezoelectric layer 10.

[0094] Figure 13 This is a cross-sectional view showing the state in which the first electrode layer is provided in the piezoelectric body layer during the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention.

[0095] like Figure 13 As shown, an adhesive layer (not shown) is formed on the upper surface of the piezoelectric layer 10, and then a first electrode layer 20 is formed on the side of the adhesive layer opposite to the piezoelectric layer 10. The first electrode layer 20 is formed with a desired pattern by vapor deposition and lift-off. Alternatively, the first electrode layer 20 can be formed by sputtering over the entire surface of the upper surface of the piezoelectric layer 10 and then etching to form the desired pattern. The piezoelectric layer 10 and the adhesive layer can also be epitaxially grown.

[0096] Figure 14 This is a cross-sectional view showing the state in which the first slit is formed from the side of the piezoelectric layer opposite to the support layer side to the upper surface of the support layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 15 This is a cross-sectional view showing the state in which a through hole is formed from the side of the piezoelectric layer opposite to the support layer side to the upper surface of the second electrode layer in the manufacturing method of the piezoelectric device according to Embodiment 1 of the present invention. Figure 15 In, with Figure 5 The same sectional view is illustrated.

[0097] like Figure 14 As shown, a slit is formed in the piezoelectric layer 10 and the first support layer 41 by dry etching using RIE (Reactive Ion Etching). The slit can also be formed by wet etching using fluorinated nitric acid or the like. Furthermore, the second support layer 42 exposed to the slit is etched using DRIE (Deep Reactive Ion Etching) so that the slit reaches the upper surface of the substrate layer 50. Thus, the first slit 134 is formed. Figure 1 The second slit 135 shown is also formed in the same way as the first slit 134.

[0098] In addition, such as Figure 15 As shown, in the equivalent Figure 5 In the portion of the outer base 110 shown, the piezoelectric layer 10 is etched by the aforementioned dry etching or wet etching to partially expose the second electrode layer 30.

[0099] And, as Figure 15 and Figure 5 As shown, in the portion corresponding to the outer base 110, adhesive layers (not shown) are respectively provided on the first electrode layer 20 and the second electrode layer 30, and then the first connecting electrode layer 60 and the second connecting electrode layer 70 are formed on the upper surface of each adhesive layer by vapor deposition and stripping. Alternatively, the first connecting electrode layer 60 and the second connecting electrode layer 70 can be formed by sputtering over the entire surface of the piezoelectric layer 10, the first electrode layer 20, and the exposed second electrode layer 30, and then by etching to form a desired pattern.

[0100] Finally, as Figure 14 and Figure 4 As shown, a portion of the substrate layer 50 is removed using DRIE. This forms the outer base 110, the protruding base 120, the cantilever beam portion 130, and the opening 140. Through the above-described process, as... Figures 1-5 The piezoelectric device 100 of Embodiment 1 of the present invention is manufactured as shown.

[0101] As described above, the piezoelectric device 100 of Embodiment 1 of the present invention includes an outer base 110, a protruding base 120, and a single cantilever beam portion 130. The outer base 110 is annular and has an inner peripheral surface 111. The protruding base 120 has a protrusion 121 and a top end 122. The protrusion 121 protrudes from the inner peripheral surface 111 of the outer base 110 toward the annular center C. The top end 122 is connected to the protrusion 121 and located at the aforementioned center C. The cantilever beam portion 130 is connected to the top end 122, separate from the protrusion 121, and extends outward. The cantilever beam portion 130 includes a piezoelectric layer 10, a first electrode layer 20, and a second electrode layer 30. The first electrode layer 20 is disposed on one side of the piezoelectric layer 10. The second electrode layer 30 is disposed such that it is at least partially opposite to the first electrode layer 20, separated from the piezoelectric layer 10. The cantilever beam portion 130 has a fixed end portion 131 and a free circumferential end portion 132. The fixed end portion 131 is connected to the top end portion 122. The free circumferential end portion 132 is located along the inner circumferential surface 111. A protrusion 121 is located between one end 132a and the other end 132b of the free circumferential end portion 132.

[0102] Therefore, in the piezoelectric device 100, when the change in the resonant frequency of the cantilever beam portion 130 is suppressed and a predetermined voltage is applied to the piezoelectric layer 10, the volume of the medium surrounding the cantilever beam portion 130 pushed out by the cantilever beam portion 130 increases, thereby improving the device characteristics. For example, when the piezoelectric device 100 is used as an ultrasonic transducer, when a predetermined voltage is applied to the piezoelectric layer 10, the sound pressure of the ultrasonic waves generated by the vibration of the cantilever beam portion 130 can be increased.

[0103] In this embodiment, when viewed from the axial direction of the central axis of the inner peripheral surface 111, i.e., the axial direction of the central axis of the aforementioned annular shape, the area of ​​the opposing region between the first electrode layer 20 and the second electrode layer 30 is more than 90% of the area of ​​the cantilever beam portion 130.

[0104] This improves the electromechanical coupling coefficient of the cantilever beam 130 as an oscillator. Furthermore, it improves the device characteristics of the piezoelectric device 100.

[0105] In this embodiment, the piezoelectric layer 10 is composed of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

[0106] This improves the piezoelectric properties of the piezoelectric layer 10, thereby improving the device characteristics of the piezoelectric device 100.

[0107] (Implementation Method 2)

[0108] The piezoelectric device according to Embodiment 2 of the present invention will be described below. The main difference between the piezoelectric device of Embodiment 2 and the piezoelectric device 100 of Embodiment 1 is the shape of the free peripheral end. Therefore, the same structure as the piezoelectric device 100 of Embodiment 1 will not be described again.

[0109] Figure 16 This is a top view showing the piezoelectric device according to Embodiment 2 of the present invention. Figure 16 As shown, in the piezoelectric device 200 of Embodiment 2 of the present invention, the shortest distance from the fixed end 131 to the free peripheral end 232 is constant throughout the entire range of the free peripheral end 232. This results in more uniform displacement of the cantilever beam as a whole, thus stabilizing the device characteristics of the piezoelectric device 200. Furthermore, the fact that the shortest distance from the fixed end 131 to the free peripheral end 232 is constant throughout the entire range includes cases where the aforementioned shortest distance is within ±5% of the average value of the aforementioned shortest distance.

[0110] Thus, in this embodiment, the cantilever beam portion 130 extends radially from the annular center of the outer base portion 110. In this embodiment, when viewed axially from the central axis of the annulus, the top portion 122 is rectangular, and it connects to the protrusion 121 at one of its four sides. The cantilever beam portion 130 connects to the other three sides of the top portion 122. When viewed axially from the central axis of the annulus, the inner circumferential surface 111 and the free circumferential end portion 232 are located on an imaginary, approximately rectangular shape with rounded corners.

[0111] Furthermore, in this embodiment, the shapes of the top end portion 122, the free peripheral end portion 232, and the inner peripheral surface 111 when viewed axially from the central axis of the annulus are not particularly limited. Alternatively, when viewed axially from the central axis of the annulus, the top end portion 122 may be approximately rectangular, elliptical, or circular with rounded corners. Alternatively, when viewed axially from the central axis of the annulus, the free peripheral end portion 232 and the inner peripheral surface 111 may be located on an imaginary circle or an imaginary ellipse, respectively.

[0112] (Implementation Method 3)

[0113] The piezoelectric device according to Embodiment 3 of the present invention will be described below. The main difference between the piezoelectric device of Embodiment 3 and the piezoelectric device 100 of Embodiment 1 is the shape of the top end. Therefore, the same structure as the piezoelectric device 100 of Embodiment 1 will not be described again.

[0114] Figure 17 This is a perspective view of the piezoelectric device according to Embodiment 3 of the present invention, viewed from one side. Figure 18 This is a perspective view obtained by observing the piezoelectric device of Embodiment 3 of the present invention from another side.

[0115] like Figure 17 and Figure 18 As shown, in the piezoelectric device 300 of Embodiment 3 of the present invention, when viewed axially from the central axis of the annular shape, the width dimension of the top end portion 322 in the orthogonal direction orthogonal to the protrusion direction of the protrusion 121 is larger than the width dimension of the protrusion 121 in the orthogonal direction. This mitigates the stress during deformation of the cantilever beam portion 130, thus improving the reliability of the piezoelectric device 300.

[0116] In this embodiment, specifically, when viewed axially from the central axis of the annular shape, the top end 322 has a circular shape. When viewed axially from the central axis, the diameter of the top end 322 is larger than the width of the protrusion 121 in the orthogonal direction.

[0117] (Implementation Method 4)

[0118] The piezoelectric device according to Embodiment 4 of the present invention will be described below. The main difference between the piezoelectric device of Embodiment 4 and the piezoelectric device 100 of Embodiment 1 is the shape of the protrusion. Therefore, the same structure as that of the piezoelectric device 100 of Embodiment 1 will not be described again.

[0119] Figure 19 This is a top view of the piezoelectric device according to Embodiment 4 of the present invention. Figure 19 As shown, in the piezoelectric device 400 of Embodiment 4 of the present invention, the width dimension of the protrusion 421 in the orthogonal direction orthogonal to the protrusion direction of the protrusion 421 increases as it approaches the outer base 110. As a result, the strength of the protrusion 421 is improved, and thus the reduction in yield caused by the protruding base 120 bending at the protrusion 421 during the manufacture of the piezoelectric device 400 can be suppressed.

[0120] (Implementation Method 5)

[0121] The piezoelectric device according to Embodiment 5 of the present invention will be described below. The main difference between the piezoelectric device of Embodiment 5 and the piezoelectric device 100 of Embodiment 1 is the shape of the protruding base. Therefore, the same structure as the piezoelectric device 100 of Embodiment 1 will not be described again.

[0122] Figure 20 This is a cross-sectional view of the piezoelectric device according to Embodiment 5 of the present invention. Figure 20 In, with Figure 4 The same sectional view is illustrated.

[0123] like Figure 20 As shown, in the piezoelectric device 500 of Embodiment 5 of the present invention, the thickness of the protruding base 520 is thinner than the thickness of the outer base 110 along the axial direction of the central axis of the inner peripheral surface 111, i.e., along the axial direction of the annular central axis of the outer base 110. Therefore, when the piezoelectric device 500 is mounted on a mounting substrate, the outer base 110 is connected to the mounting substrate, while the protruding base 520, which has lower strength compared to the outer base 110, is not connected to the mounting substrate. Thus, it is possible to suppress the decrease in yield during the mounting process of the piezoelectric device 500.

[0124] In this embodiment, specifically, the thickness of the second substrate layer 52 protruding from the base 520 is thinner than the thickness of the second substrate layer 52 of the outer base 110 along the axial direction of the central axis of the inner peripheral surface 111.

[0125] In the above description of the embodiments, the combinable structures can also be combined with each other.

[0126] The embodiments disclosed herein should be considered illustrative in all respects and not limiting. The scope of the invention is defined by the claims rather than by the foregoing description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0127] Explanation of reference numerals in the attached figures

[0128] 10. Piezoelectric layer; 10a. Piezoelectric single crystal substrate; 20. First electrode layer; 30. Second electrode layer; 40. Support layer; 41. First support layer; 42. Second support layer; 50. Substrate layer; 50a. Laminate; 51. First substrate layer; 52. Second substrate layer; 60. First connecting electrode layer; 70. Second connecting electrode layer; 100, 200, 300, 400, 500. Piezoelectric device; 110. Outer base; 111, inner circumferential surface; 120, 520, protruding base; 121, 421, protrusion; 122, 322, top end; 130, cantilever beam portion; 131, fixed end; 131a, 131b, both ends; 132, 232, free circumferential end; 132a, one end; 132b, the other end; 133, side end; 134, first slit; 135, second slit; 140, opening.

Claims

1. A piezoelectric device, wherein, The piezoelectric device includes: The outer base is annular, and it has an inner circumferential surface; A protruding base having a protrusion projecting from the inner circumferential surface of the outer base toward the annular center and a apex connected to the protrusion and located at the center; and It has only one cantilever beam section, which is connected to the top end, separate from and extends out of the protruding portion. The cantilever beam portion includes: a piezoelectric layer; a first electrode layer disposed on one side of the piezoelectric layer; and a second electrode layer disposed such that it is at least partially opposite to the first electrode layer, separated by the piezoelectric layer. The cantilever beam portion has a fixed end connected to the top end and a free circumferential end located along the inner circumferential surface. The protrusion is located between one end and the other end of the free peripheral end.

2. The piezoelectric device according to claim 1, wherein, The entire range of the free circumferential end is constant from the shortest distance from the fixed end to the free circumferential end.

3. The piezoelectric device according to claim 1 or 2, wherein, The width dimension of the top portion in the orthogonal direction to the protrusion direction of the protrusion is larger than the width dimension of the protrusion in the orthogonal direction.

4. The piezoelectric device according to claim 1 or 2, wherein, The width dimension of the protrusion in the orthogonal direction to the protrusion direction increases as it approaches the outer base.

5. The piezoelectric device according to any one of claims 1 to 4, wherein, Along the axial direction of the central axis of the inner circumferential surface, the thickness of the protruding base is thinner than the thickness of the outer base.

6. The piezoelectric device according to any one of claims 1 to 5, wherein, When viewed axially from the central axis of the inner circumferential surface, the area of ​​the opposing region between the first electrode layer and the second electrode layer is more than 90% of the area of ​​the cantilever beam portion.

7. The piezoelectric device according to any one of claims 1 to 6, wherein, The piezoelectric layer is composed of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

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