Piezoelectric device, movable device, and method for manufacturing piezoelectric device

Abstract

An object of the present invention is to provide a piezoelectric device that can prevent the periphery of the upper electrode from being lost due to the propagation of arc discharge, even if there is a defect in the piezoelectric layer at the periphery of the upper electrode. [Solution] A piezoelectric device has a structure in which a piezoelectric layer and an upper electrode are stacked in this order on a lower electrode. A structure that locally increases the length of the shortest path from the peripheral edge of the upper electrode, through the surface of the peripheral edge of the piezoelectric layer, or to the upper surface or peripheral edge of the lower electrode is provided in one or more locations on the peripheral edge of the upper electrode, the peripheral edge of the piezoelectric layer, or either the upper surface or peripheral edge of the lower electrode.

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric device in which a piezoelectric layer is sandwiched between upper and lower electrodes. [Background technology]

[0002] Piezoelectric devices, which have a piezoelectric layer sandwiched between upper and lower electrodes, are used in systems with microstructures such as MEMS (Micro Electro Mechanical Systems). Piezoelectric devices are used as actuators for optical elements and other devices by applying a voltage from the electrodes to the piezoelectric layer, causing the piezoelectric layer to expand and contract. Piezoelectric devices are also used as sensors that detect pressure and displacement by detecting the electrical signals generated by the piezoelectric layer when external pressure is applied to the piezoelectric layer, and as power generation devices that convert pressure into electricity.

[0003] Such piezoelectric devices are generally formed by sequentially stacking a lower electrode layer, a piezoelectric layer, and an upper electrode layer on a substrate and patterning them into the desired shape. However, during the deposition of the piezoelectric layer, minute foreign particles may be mixed into the piezoelectric layer, or recesses may be formed. Such foreign particles or recesses may cause defects in the piezoelectric layer, and the withstand voltage of the piezoelectric layer may be locally reduced at the defect. Therefore, when a voltage is applied to the piezoelectric layer from the upper and lower electrode layers, a short circuit may occur at the defect in the piezoelectric layer.

[0004] For this reason, the invention disclosed in Patent Document 1 involves stacking a lower electrode layer, a piezoelectric layer, and an upper electrode layer in this order, and then applying a voltage between the lower electrode layer and the upper electrode layer that is greater than the withstand voltage of the defect in the piezoelectric layer. This causes dielectric breakdown in the defect, removing the piezoelectric layer and upper electrode in the defect and forming a through-hole. Therefore, when the piezoelectric device is actually used, the defect with a low withstand voltage has been removed, so no short circuit occurs between the upper and lower electrode layers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-207938 Summary of the Invention [Problem to be solved by the invention]

[0006] In a piezoelectric device, the region of the piezoelectric layer where the upper electrode is mounted is the driving region. Therefore, it is desirable to mount the upper electrode so that it covers the entire top surface of the piezoelectric layer. Therefore, the periphery of the upper electrode is designed to be positioned as close as possible to or coincident with the periphery of the piezoelectric layer.

[0007] As described in Patent Document 1, in the manufacturing process, a step of applying a voltage between upper and lower electrodes that is equal to or greater than the withstand voltage of the defects in the piezoelectric layer is carried out, thereby removing the defects in the piezoelectric layer through dielectric breakdown.

[0008] However, according to experiments conducted by the inventors, it was found that when a defect in the piezoelectric layer exists at the edge of the upper electrode, applying a voltage between the upper and lower electrodes to remove the defect causes an arc discharge to occur between the edge of the upper electrode and the lower electrode. Moreover, this arc discharge propagates in a chain reaction from the defect along the edge of the upper electrode. As a result, the upper electrode is lost over a long distance along the edge of the upper electrode, with a width of several tens to several hundreds of micrometers.

[0009] Even if the periphery of the upper electrode and the exposed portion of the lower electrode are close to each other, under normal conditions (when a normal operating voltage is applied at room temperature), Paschen's law prevents arc discharge from occurring. However, if a defect exists in the piezoelectric layer located near the periphery of the upper electrode and a process of causing dielectric breakdown is carried out to remove the defect, the temperature of the upper electrode and lower electrode near the point of dielectric breakdown will rise, causing arc discharge.

[0010] In our experiments, melting of Pt (melting point 2059 K), the material used for the upper and lower electrodes, was observed near the breakdown point, confirming that a temperature rise above the melting point of Pt had occurred. It is generally believed that the breakdown voltage of air drops sharply when the electrode temperature reaches approximately 2000 K. It is believed that an arc discharge occurs between the upper and lower electrodes, triggered by a breakdown at a defect near the edge. Once an arc discharge occurs, it raises the temperature of the adjacent upper and lower electrodes, triggering further arc discharges in a chain reaction, which then propagates over a long distance along the edge of the upper electrode.

[0011] Such arc discharges may occur not only during the process of removing defects in the piezoelectric layer during the manufacture of a piezoelectric device, but may also occur during use of the completed piezoelectric device 100 when defects remaining in the piezoelectric layer cause dielectric breakdown due to changes over time.

[0012] An object of the present invention is to provide a piezoelectric device that can prevent the periphery of the upper electrode from being lost due to arc discharge even if there is a defect in the piezoelectric layer at the periphery of the upper electrode. [Means for solving the problem]

[0013] To achieve the above object, the present invention provides a piezoelectric device having a piezoelectric layer and an upper electrode stacked in this order on a lower electrode, wherein the peripheral edge of the upper electrode, the peripheral edge of the piezoelectric layer, and either the top surface or the peripheral edge of the upper electrode are provided with one or more structures that locally increase the distance of the shortest path from the peripheral edge of the upper electrode, passing through the surface of the peripheral edge of the piezoelectric layer, to the top surface or the peripheral edge of the lower electrode. [Effects of the Invention]

[0014] According to the present invention, even if an arc discharge occurs between the peripheral edge of the upper electrode and the lower electrode when a defect in the piezoelectric layer causes dielectric breakdown and the arc discharge propagates along the edge of the upper electrode, the arc discharge can be extinguished when it reaches a position where a structure is provided that locally increases the distance of the shortest path from the peripheral edge of the upper electrode through the surface of the peripheral edge of the piezoelectric layer to the top surface or end of the lower electrode, thereby preventing further loss of the peripheral edge of the upper electrode. [Brief explanation of the drawings]

[0015] [Figure 1] 1A is a top view of a piezoelectric device 100 according to one embodiment of the present invention, FIG. 1B is a cross-sectional view taken along line AA, FIG. 1C is a cross-sectional view taken along line BB, and FIG. 1D is a cross-sectional view taken along line CC. [Figure 2] 1A is a top view of a piezoelectric device 100 according to a first modification of the present embodiment, FIG. 1B is a DD cross-sectional view, and FIG. 1C is an EE cross-sectional view. [Figure 3] 1A is a top view of a piezoelectric device 100 according to a second modification of the present embodiment, FIG. 1B is a cross-sectional view taken along line FF, and FIG. 1C is a cross-sectional view taken along line GG. [Figure 4] 1 is a photograph of a piezoelectric device in which an arc discharge occurs. [Figure 5] FIG. 1 is a top view of an optical deflector 1 according to an embodiment. [Figure 6] 2 is an enlarged view of a portion of a notch 141 of the optical deflector 1 according to the embodiment. FIG. [Figure 7] 5(a) to 5(d) are cross-sectional views showing the manufacturing process of the outer piezoelectric actuator 5 (piezoelectric device 100) of the optical deflector 1 of the embodiment. [Figure 8] 5(a) to 5(c) are cross-sectional views showing the manufacturing process of the outer piezoelectric actuator 5 (piezoelectric device 100) of the optical deflector 1 of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will now be described.

[0017] <Summary> First, an overview of a piezoelectric device 100 according to this embodiment will be described. FIG. 1 shows a top view and a cross-sectional view of the piezoelectric device 100 according to this embodiment. The piezoelectric device 100 according to this embodiment is configured to include an upper electrode 27 and a lower electrode 26 that sandwich a piezoelectric layer 28. The operation of the piezoelectric device 100 may be like an actuator, in which a voltage is applied to the piezoelectric layer 28 from the upper electrode 27 and the lower electrode 26 to displace the piezoelectric layer 28, or like a piezoelectric sensor or power generation device, in which a voltage generated in the piezoelectric layer 28 when a force is applied thereto is output to the outside via the upper electrode 27 and the lower electrode 26.

[0018] Specifically, the piezoelectric device 100 includes a support layer 35, a lower electrode 26 disposed on the support layer 35, a piezoelectric layer 28 disposed on the lower electrode 26, and an upper electrode 27 disposed on the piezoelectric layer 28. In other words, the piezoelectric layer 28 is sandwiched between the lower electrode 26 and the upper electrode 27.

[0019] The lower electrode 26, the piezoelectric layer 28, and the upper electrode 27 are patterned into the shape of a predetermined cantilever 23 (here, a rectangle), and one short side of the rectangle is connected by a connecting portion 120. This forms a piezoelectric device 100 in which multiple cantilevers 23 are connected by the connecting portion 120.

[0020] The piezoelectric layer 28 is slightly smaller than the lower electrode 26, and the upper electrode 27 is slightly smaller than the piezoelectric layer 28. The periphery of the piezoelectric layer 28 is separated by a distance D1 from the periphery of the lower electrode 26. The periphery of the upper electrode 27 is separated by a distance D2 from the periphery of the piezoelectric layer 28.

[0021] 1(a), in the piezoelectric device 100 having such a structure, the defective portion 29a present in the piezoelectric layer 28 is removed by a defect removal step. Specifically, in the defect removal step, a voltage that is greater than the withstand voltage of the defective portion 29a in the piezoelectric layer 28 and less than the withstand voltage of the piezoelectric layer 28 without any defects is applied between the upper electrode 27 and the lower electrode 26. This causes dielectric breakdown in the piezoelectric layer 28 at the defective portion 29a, and the piezoelectric layer 28 at the defective portion 29a can be removed.

[0022] However, according to experiments by the inventors, when a defect 29a is present in the piezoelectric layer 28 at the peripheral edge of the upper electrode 27 as shown in Fig. 1(a), performing the defect removal step will cause an arc discharge to occur between the peripheral edge of the upper electrode 27 and the lower electrode 26. This arc discharge propagates in a chain reaction from the defect 29a along the peripheral edge of the upper electrode 27, resulting in the formation of a region 130 in which the peripheral edge b of the upper electrode 27 has disappeared over a width W (approximately several tens to several hundreds of µm) (see Fig. 1(d)).

[0023] In order to suppress the phenomenon of arc discharge propagating along the edge of the upper electrode 27, it is effective to increase the length of the shortest path from the peripheral edge of the upper electrode 27 through the surface of the peripheral edge of the piezoelectric layer 28 to the upper surface or peripheral edge of the lower electrode 26. Increasing the length of this shortest path reduces the electric field strength applied from the upper electrode 27 and the lower electrode 26 to the air near the peripheral edge of the upper electrode 27, making it possible to avoid arc discharge.

[0024] However, if the sum of distances D1 and D2 is increased over the entire periphery of the upper electrode 27 in order to increase the length of the shortest path from the periphery of the upper electrode 27 through the surface of the periphery of the piezoelectric layer 28 to the upper surface or periphery of the lower electrode 26, the area of ​​the upper electrode 27 will be reduced. As a result, if the piezoelectric device 100 is an actuator, the area over which a voltage can be applied from the upper electrode 27 to the piezoelectric layer 28 will be reduced. Furthermore, if the piezoelectric device 100 is a piezoelectric sensor or a piezoelectric power generation device, the area over which the upper electrode 27 can extract (output) the voltage generated by the piezoelectric layer 28 will be reduced. As a result, in either case of the device, the operating efficiency will be reduced.

[0025] Therefore, in this embodiment, a structure 140 is provided at one or more locations between the periphery of the upper electrode 27 and the lower electrode 26, for locally increasing the length of the shortest distance between them.

[0026] 1(a) to 1(d), this structure 140 is, for example, a notch 141 provided on the periphery of the upper electrode 27 in top view. The notch 141 is formed by cutting out the periphery of the upper electrode 27 with a length (length in the periphery direction of the cantilever 23) L and a width M, thereby exposing the member (piezoelectric layer 28 in this embodiment) located below the upper electrode 27. As a result, the width of the upper electrode 27 is partially reduced by the width M of the notch 141.

[0027] 2(a) to 2(c) show top views and cross-sectional views of modified examples, and the structure 140 may be a protrusion 142 provided on the periphery of the piezoelectric layer 28 in a top view. The protrusion 142 protrudes outward from the periphery of the piezoelectric layer 28 within the main plane of the piezoelectric layer 28.

[0028] Furthermore, the structure 140 may be a notch (recess) 143 provided in the upper surface of the lower electrode 26, as shown in the top view and cross-sectional view of another modified example in FIGS. 3(a) to 3(c). The notch 143 is provided on the shortest path from the peripheral edge of the upper electrode 27 through the surface of the peripheral edge of the piezoelectric layer 28 to the upper surface or peripheral edge of the lower electrode 26. In the example of FIGS. 3(a) to 3(c), the notch 143 is provided in a region of the upper surface of the lower electrode 26 outside the peripheral edge of the piezoelectric layer 28 when viewed from above. The lower electrode 26 is removed in the area where the notch 143 is provided. Alternatively, as shown in FIG. 3(c), the depth of the notch 143 (in the thickness direction of the lower electrode 26) may be made to match the thickness of the lower electrode 26, so that the member below the lower electrode 26 (the support layer 35 in this embodiment) is exposed in the area where the notch 143 is provided.

[0029] In the structure 140 such as the notch 141, the longer the length of the shortest path from the periphery of the upper electrode 27 through the surface of the periphery of the piezoelectric layer 28 to the upper surface or periphery of the lower electrode 26, the weaker the electric field strength of the air in contact with this shortest path, making it less likely that an arc discharge will occur even if a temperature rise occurs. Furthermore, with distance from the location where breakdown occurs, the temperature of the upper electrode 27 decreases, so the air's breakdown electric field does not decrease and an arc discharge does not occur. Therefore, it is desirable to design the width M (see FIG. 1(a)) of the structure 140 such as the notch 141 so that the electric field applied to the gas (air) in contact with the path between the upper electrode 27 and the lower electrode 26 is strong enough to prevent an arc discharge even at the temperature at which breakdown occurs, and to design the length L (the length in the periphery direction of the cantilever 23) (see FIG. 1(a)) of the structure 140 such as the notch 141 so that the temperature rise due to the heat generated by breakdown is sufficiently suppressed.

[0030] By providing such structure 140, even if the arc discharge propagates in a chain reaction along the periphery of the upper electrode 27, it can be stopped when the arc discharge reaches structure 140. In contrast, if structure 140 is not provided, the arc discharge propagates in a chain reaction over a long distance, as shown in the photograph of a piezoelectric device in which an actual arc discharge occurs in FIG.

[0031] The width M and length L (see FIGS. 1(a) and 6) of the structure 140 such as the notch 141 that can stop the propagation of the arc discharge vary depending on the voltage applied between the upper electrode 27 and the lower electrode 26 during the defect removal process in the manufacture of the piezoelectric device 100 or when the finished product is in use, and the material that makes up the piezoelectric layer 28. For example, when the applied voltage is approximately 30 V and the piezoelectric layer 28 is made of PZT (lead zirconate titanate), it has been confirmed through experiments that the arc discharge stops when the distance between the upper electrode 27 and the lower electrode 26 is approximately 20 μm or more. Therefore, it is desirable that the width M and length L of the structure 140 such as the notch 141 be 20 μm or more.

[0032] In this embodiment, the structures 140 such as the notches 141 are arranged to stop a chain reaction of arc discharges occurring between the upper electrode 27 and the lower electrode 26, and therefore, even if there is only one structure 140 such as the notch 141, an effect can be obtained. However, it is preferable that the structures 140 such as the notches 141 are provided in multiple locations at predetermined intervals, because this allows the chain reaction of arc discharges to be stopped early at a distance within the intervals between the multiple structures 140 such as the notches 141.

[0033] When structures 140 such as notches 141 are provided at a predetermined interval T, it is assumed that a region 130 of width W of the upper electrode 27 is lost due to arc discharge over the distance T between two structures 140, and it is desirable to design the distance T so that the area of ​​the lost region 130 (width W × distance T) is 5% or less of the area of ​​the upper electrode 27 of the cantilever 23. If it is 5% or less, the decrease in the operational efficiency of the piezoelectric device 100 falls within an acceptable range. The width W of the lost region 130 is a value determined in advance by experiment or the like.

[0034] 1 to 3 only show examples in which the shape of the notch 141, protrusion 142, or notch 143 is rectangular, any structure 140 may be used as long as it can locally increase the length of the shortest path from the peripheral edge of the upper electrode 27 through the surface of the peripheral edge of the piezoelectric layer 28 to the upper surface or peripheral edge of the lower electrode 26. For example, the notch 141, protrusion 142, or notch 143 may have other shapes, such as a triangle or semicircle.

[0035] As described above, by providing structure 140 that locally increases the length of the shortest path from the peripheral portion of upper electrode 27 through the surface of the peripheral portion of piezoelectric layer 28 to the upper surface or peripheral portion of lower electrode 26, it is possible to suppress the occurrence of arc discharge during the defect removal step in the manufacturing process. Furthermore, by providing structure 140, it is possible to suppress the occurrence of arc discharge near exposed upper electrode 27 and lower electrode 26 even when the piezoelectric device 100 is used after completion. This has the effect of extending the product life and suppressing the decrease in efficiency over time.

[0036] An optical deflector 1 that uses the piezoelectric device 100 of this embodiment as an actuator will be described below.

[0037] (Configuration of optical deflector 1) 5 is a top view of an optical deflector 1 configured using an actuator that uses the piezoelectric device 100 of this embodiment. When viewed from above, the side of the optical deflector 1, which has a rectangular, flat-plate shape, from which the reflective surface of the mirror section 2 can be seen is referred to as the "top surface," and the opposite side is referred to as the "back surface." The origin O of the orthogonal X, Y, and Z axes is the center of the mirror section 2, the Z axis is the thickness direction of the optical deflector 1, and the X and Y axes are the longitudinal and lateral directions of the rectangular, flat-plate-shaped optical deflector 1.

[0038] The optical deflector 1 includes a mirror section 2, inner piezoelectric actuators 3a and 3b, a movable frame 4 as a movable support section, outer piezoelectric actuators 5a and 5b, and a fixed frame 6. The outer shape of the fixed frame 6 is rectangular. The long and short sides of the fixed frame 6 are parallel to the X-axis and Y-axis, respectively.

[0039] The outer piezoelectric actuators 5a and 5b are configured by the piezoelectric device 100 of this embodiment described above.

[0040] In Figure 5, axes Lx and Ly are two axes about which the mirror section 2 rotates back and forth (forward and reverse). The axes Lx and Ly intersect at right angles at the center (origin O) of the mirror section 2. The inner piezoelectric actuators 3a and 3b are supplied with a first drive voltage from a drive unit (not shown), causing the mirror section 2 to rotate back and forth around the axis Ly at a first frequency (e.g., 30 kHz). The outer piezoelectric actuators 5a and 5b are supplied with a second drive voltage from the drive unit, causing the mirror section 2 to rotate back and forth around the axis Lx at a second frequency (e.g., 60 Hz).

[0041] The inner piezoelectric actuators 3a and 3b are arranged symmetrically about the Y axis when viewed from above. Both inner piezoelectric actuators 3a and 3b are composed of cantilevers with piezoelectric structures. The inner piezoelectric actuators 3a and 3b are connected to each other at both ends in the Y axis direction, and together they form an elliptical ring that is elongated vertically in the Y axis direction and surrounds the mirror section 2. The movable frame 4 is formed as an annular frame with an elliptical outline that is elongated vertically in the Y axis direction on both the inner and outer peripheries, and its inner periphery surrounds the elliptical ring formed by the inner piezoelectric actuators 3a and 3b.

[0042] The torsion bars 21a and 21b protrude linearly outward from the mirror part 2 along the Y axis, connect to the elliptical ring formed by the inner piezoelectric actuators 3a and 3b, and then protrude further outward, with their ends connected to the inner periphery of the movable frame 4. The axis Ly coincides with the center line of the torsion bars 21a and 21b.

[0043] The outer piezoelectric actuators 5a and 5b are arranged inside a rectangular fixed frame 6. The outer piezoelectric actuators 5a and 5b are arranged symmetrically about the Y axis when viewed from above. The mirror section 2, the inner piezoelectric actuators 3a and 3b, and the movable frame 4 are located between the outer piezoelectric actuators 5a and 5b.

[0044] The outer piezoelectric actuators 5a and 5b are configured by the piezoelectric device 100 shown in Fig. 1. However, the arrangement of the cantilevers 23 differs from that shown in Fig. 1; in the outer piezoelectric actuators 5a and 5b shown in Fig. 5, multiple cantilevers 23 are connected in series in a meandering arrangement.

[0045] 6, the cantilever 23 has a structure similar to that of the piezoelectric device 100 in Fig. 1, in which a lower electrode 26, a piezoelectric layer 28, and an upper electrode 27 are stacked in this order on a support layer 35. The stacking direction is the Z direction, with the lower electrode 26 located on the back side of the piezoelectric device 100 and the upper electrode 27 located on the top side of the piezoelectric device 100.

[0046] At the periphery of the upper electrode 27, notches 141 are provided at regular intervals T (for example, 500 μm) as a structure 140 that locally increases the distance between the periphery of the upper electrode 27 and the lower electrode 26. In the example of FIG. 5, the notches 141 are rectangular, and the width M and length L of the notches 141 are designed to be 20 μm or more.

[0047] The longitudinal direction of each cantilever 23 is parallel to the Y-axis direction, and the cantilevers 23 are arranged side by side in the X-axis direction. The ends of the multiple cantilevers 23 in the Y-axis direction are connected to adjacent cantilevers 23 in the X-axis direction, forming a meander array.

[0048] In each of the outer piezoelectric actuators 5a, 5b, the cantilevers 23 located at both ends in the X-axis direction have a length half that of the other cantilevers 23, and are connected to the fixed frame 6 and the movable frame 4 on the X-axis, respectively. The end of the cantilever 23 connected to the fixed frame 6 forms the base end of the outer piezoelectric actuators 5a, 5b, and the end of the cantilever 23 connected to the movable frame 4 forms the tip end of the outer piezoelectric actuators 5a, 5b.

[0049] A plurality of electrode pads 16a, 16b are arranged on the surface of each short side of the fixed frame 6. The electrode pad 16a is connected to the inner piezoelectric actuator 3a and the outer piezoelectric actuator 5a. The upper electrode pad 16b is connected to the inner piezoelectric actuator 3b and the outer piezoelectric actuator 5b.

[0050] (Action of optical deflector 1) The operation of the optical deflector 1 will now be described. Hereinafter, the inner piezoelectric actuators 3a and 3b will not be distinguished from each other and will be collectively referred to as the "inner piezoelectric actuator 3." The outer piezoelectric actuators 5a and 5b will not be distinguished from each other and will be collectively referred to as the "outer piezoelectric actuator 5."

[0051] The optical deflector 1 is installed as a two-dimensional scanner in a video device (such as a projector) or a vehicle headlight. The optical deflector 1 is housed in a package, and electrode pads 16 of the optical deflector 1 are connected to terminals of the package by bonding wires (not shown). A driving voltage is supplied to the piezoelectric bodies of the inner piezoelectric actuator 3 and the outer piezoelectric actuator 5 from the electrode pads 16.

[0052] Light (for example, laser light) from a light source (for example, a semiconductor laser light source) not shown is incident on the center of the mirror portion 2 of the optical deflector 1 (origin O of the three-axis coordinate system).

[0053] The outer piezoelectric actuator 5 is actuated by a drive voltage from the electrode pad 16 to rotate the movable frame 4 back and forth around the X axis at the second frequency, causing the mirror section 2 to rotate back and forth around the axis Lx at the second frequency.

[0054] The operation of the outer piezoelectric actuator 5 will now be described in detail. Each outer piezoelectric actuator 5 is made up of multiple cantilevers 23 arranged in a meandering pattern. If the cantilevers 23 are numbered in order from the base end (fixed frame 6 side) to the tip end (movable frame 4 side) of the outer piezoelectric actuator 5, the odd-numbered cantilevers 23 and the even-numbered cantilevers 23 are supplied with driving voltages of the same frequency but opposite phases, and they deform so that the convex sides of the bending deformation are in opposite directions.

[0055] As a result, the cantilevers 23 constituting the meander array bend in opposite directions to those adjacent to each other in the X-axis direction when the outer piezoelectric actuator 5 is actuated. At this time, the accumulated amount of relative rotation of the tip end with respect to the base end of each cantilever 23 becomes the amount of rotation (torsion) of the inner piezoelectric actuator 3 with respect to the outer piezoelectric actuator 5 around the axis Lx.

[0056] On the other hand, the inner piezoelectric actuator 3 causes the torsion bar 21 to reciprocate around the axis Ly, which is its central axis, at a first frequency by a first drive voltage from the electrode pad 16. The first frequency is set to the resonance frequency of the mirror part 2 around the axis Ly to ensure a high frequency. Note that the second frequency, which is the frequency of the reciprocating rotation of the mirror part 2 around the axis Lx, is set to a non-resonance frequency.

[0057] In this way, the mirror unit 2 rotates back and forth around the axis Ly at a resonant frequency, and rotates back and forth around the axis Lx at a non-resonant frequency. Light from a light source (not shown) is reflected at the center of the mirror unit 2 and emitted as scanning light in a direction corresponding to the rotation angle around the axes Lx and Ly at that time.

[0058] (Method of manufacturing the outer piezoelectric actuator 5 (piezoelectric device 100)) The manufacturing process of the outer piezoelectric actuator 5 (piezoelectric device 100) will be described with reference to Figures 7(a) to 7(d) and 8(a) to 8(d). Figures 7(a) to 7(d) and 8(a) to 8(d) are cross-sectional views of the outer piezoelectric actuator 5 (piezoelectric device 100) during the manufacturing process.

[0059] 7(a), an SOI wafer is prepared as a support layer 35, in which a thermally oxidized SiO2 film 35b is formed on a Si substrate 35a, and a silicon single crystal layer 35c is formed thereon. A lower electrode film 36 is formed on the silicon single crystal layer 35c by a sputtering method or the like. The lower electrode film 36 is a film that will be processed into the lower electrode 26 in a later step.

[0060] For example, as the lower electrode film 36, a Ti film and a Pt film are formed in this order, and then a conductive thin film made of any one of SrRuO3 (SRO: strontium ruthenate), LaNiO3 (LNO: lanthanum nickelate), and BaRuO3 (BRO: barium ruthenate), each having a perovskite crystal structure, is formed thereon.

[0061] 7(b), a piezoelectric film 29 having a thickness of 3 to 5 μm is formed on the lower electrode film 36. The piezoelectric film 29 is a film that will be processed into a piezoelectric layer 28 in a later step.

[0062] Examples of piezoelectric materials that can be used to form the piezoelectric film 29 include PZT (lead zirconate titanate), PNZT (lead zirconate titanate niobate), PLZT (lead lanthanum zirconate titanate), PLT (lead lanthanum titanate), PMN (lead magnesium niobate), and PMNN (lead manganese niobate). PZT, in particular, has strong piezoelectric properties and is therefore preferable for achieving low power consumption and miniaturization.

[0063] The piezoelectric film 29 can be formed by sputtering, ion plating, MOCVD (Metal Organic Chemical Vapor Deposition), PLD (Pulse Laser Deposition), MBE (Molecular Beam Epitaxy), CSD (Chemical Solution Deposition), sol-gel method, or the like.

[0064] During the deposition process of the piezoelectric film 29, defects 29a such as voids, depressions or protrusions on the surface, and minute cracks are formed in the piezoelectric film 29 due to abnormal deposition areas or foreign matter on the surface of the lower electrode film 36, foreign matter mixed into the piezoelectric material during deposition of the piezoelectric film 29, or abnormal growth. While the number of defects 29a formed can be reduced by ingeniously modifying the deposition process, it is difficult to completely eliminate them. The size and shape of the defects 29a vary depending on the cause and location of their occurrence, but they have a lower dielectric strength than normal areas. The defects 29a are removed in the defect removal process shown in Figure 8(a) below.

[0065] 7(c), an upper electrode film 37 is formed on the piezoelectric film 29. The upper electrode film 37 is a film that will be processed into the upper electrode 27 in a later step.

[0066] The material constituting the upper electrode film 37 is preferably a material having a higher melting point than the piezoelectric film 29. This is to prevent the upper electrode film 37 from melting and flowing into the through-hole 33 after the defect 29a has been removed when the defect 29a of the piezoelectric film 29 is evaporated and removed by causing dielectric breakdown to form the through-hole 31 in the subsequent defect removal step. Furthermore, the upper electrode film 37 is preferably a thin film so that it is removed together with the defect 29a in the defect removal step to form the through-hole 34.

[0067] Specifically, the upper electrode film 37 can be made of a thin film of, for example, Pt, Ti, Ir, IrO, or SRO, or a laminate thereof. The film can be formed by, for example, sputtering.

[0068] Next, as shown in FIG. 7(d), the upper electrode film 37 and the piezoelectric film 29 are patterned by photolithography and dry etching to be processed into the shapes of the upper electrode 27 and the piezoelectric layer .

[0069] Specifically, first, the piezoelectric film 29 is patterned into the shape of the outer piezoelectric actuator 5 (piezoelectric device 100) shown in Fig. 5. When protrusions 142 are provided on the piezoelectric layer 28 as shown in Fig. 2, the protrusions 142 are formed when the piezoelectric film 29 is patterned in this step.

[0070] Next, the upper electrode film 37 is patterned into the shape of the upper electrode 27 having notches 141 provided at regular intervals T on the periphery thereof, as shown in FIGS.

[0071] By patterning the upper electrode film 37 and the piezoelectric film 29, a part (exposed portion 39) of the lower electrode film 36 is exposed.

[0072] In addition, as shown in FIG. 3, when the lower electrode 26 is provided with a notch 143, the lower electrode film 36 is subsequently further patterned to form the notch 143.

[0073] Next, as shown in Figure 8(a), a defect removal process is performed. In the defect removal process, a voltage greater than the withstand voltage of the defect portion 29a but less than the withstand voltage of the piezoelectric layer 28 in a normal region without the defect portion 29a is applied between the upper electrode 27 and the lower electrode film 36. This causes dielectric breakdown in the defect portion 29a, evaporating the defect portion 29a due to Joule heat, and forming a through hole 33. At the same time, the upper portion of the defect portion 29a in the upper electrode film 37 is also destroyed and removed, forming a through hole 34. The combination of the through hole 33 and the through hole 34 forms a through hole 31.

[0074] Since the electric field resistance (dielectric strength) of the piezoelectric film 29 in the normal region varies depending on the film formation method and film formation conditions, the voltage applied in the defect removal process can be selected to be, for example, a voltage that is a predetermined value greater than the voltage corresponding to the maximum electric field resistance of the defective portion 29a.

[0075] When a voltage greater than the withstand voltage of the defect 29a is applied between the upper electrode 27 and the lower electrode film 36, if the defect 29a is present on the periphery of the upper electrode 27, an arc discharge may occur between the upper electrode 27 and the lower electrode film 36 as the temperature of the defect 29a rises.

[0076] The arc discharge propagates in a chain reaction along the periphery of the upper electrode 27, but in this embodiment, the notches 141 are provided at regular intervals T along the periphery of the upper electrode 27, so that the propagation of the arc discharge can be stopped at the position of the notches 141.

[0077] Therefore, the maximum length of the edge of the upper electrode 27 that is lost due to arc discharge can be limited to the interval T between the notches 141.

[0078] In this way, by providing the notches 141 at a constant interval T, the area of ​​the upper electrode 27 lost due to arc discharge can be reduced to an area that does not affect the operation of the outer piezoelectric actuator 5 (piezoelectric device 100), thereby improving yield and reliability.

[0079] Next, the lower electrode film 36 is patterned by photolithography and dry etching to form the lower electrode 26 of the outer piezoelectric actuator 5 (piezoelectric device 100).

[0080] Furthermore, as shown in FIG. 8(c), the upper electrode 27 and the piezoelectric layer 28 are processed by photolithography and dry etching techniques to expose the electrode contact portions of the upper electrode 27 and the lower electrode 26.

[0081] 8(d), a portion of the Si substrate 35a of the support layer 35 is removed from the back surface side to form the cantilever 23. The remaining portion of the Si substrate 35a becomes the connecting portion 120.

[0082] The Si substrate 35a can be removed by forming a resist pattern by photolithography and then removing it by deep-RIE (deep etching).

[0083] Then, wiring (not shown) for supplying voltage to the upper electrode 27 and the lower electrode 26 is formed.

[0084] In this way, the outer piezoelectric actuator 5 (piezoelectric device 100) can be formed.

[0085] The inner piezoelectric actuator 3a of the optical deflector 1 is also a piezoelectric device, and can be formed simultaneously with the outer piezoelectric actuator 5 in the same manufacturing process as the outer piezoelectric actuator 5. As described above, this embodiment provides a piezoelectric device 100 having a lower electrode 26, an upper electrode 27, and a piezoelectric layer 28 sandwiched between the lower electrode 26 and the upper electrode 27. One or more structures 140 are provided between the periphery of the upper electrode 27 and the lower electrode 26 to locally increase the distance therebetween. The structures 140 are formed as notches 141 in the upper electrode 27, protrusions 142 in the piezoelectric layer 28, or notches 143 in the lower electrode 26.

[0086] Even if there is a defect in the piezoelectric layer 28 around the periphery of the upper electrode 27 and an arc discharge occurs between the upper electrode 27 and the lower electrode 26 during the defect removal process, the arc discharge can be extinguished when it reaches the structure 140 that increases the distance between them. This prevents further loss of the periphery of the upper electrode 27, and limits the lost area to an area that does not affect the operation of the piezoelectric device 100. This improves the manufacturing yield and product reliability.

[0087] (Application to products) The piezoelectric device of this embodiment can be used as an actuator, a piezoelectric sensor, a power generation device, etc. For example, as an actuator for an optical element, it can be used to configure a projector or a speaker. [Explanation of symbols]

[0088] 1 Optical deflector 2 Mirror section 3. Inner piezoelectric actuator 3a Inner piezoelectric actuator 3b Inner piezoelectric actuator 4 Movable frame 5. Outer piezoelectric actuator 5a Outer piezoelectric actuator 5b Outer piezoelectric actuator 6 Fixed Frame 16a Electrode pad 16b Electrode pad 17 Upper electrode 21 Torsion bar 23 Cantilever 26 Lower electrode 27 Upper electrode 28 Piezoelectric layer 29a Defective part 29 Piezoelectric film 31 Through hole 33 Through hole 34 Through hole 35 Support layer 35a Si substrate 35b Thermal oxide film 35c crystal layer 36 Lower electrode film 37 Upper electrode film 39 Exposed part 100 Piezoelectric Device 120 Connection section 130 areas 140 Structure 142 Protrusion

Claims

1. a piezoelectric layer and an upper electrode laminated in this order on a lower electrode; A piezoelectric device characterized in that the peripheral portion of the upper electrode, the peripheral portion of the piezoelectric layer, and either the top surface or the peripheral portion of the upper electrode are provided with one or more structures that locally increase the length of the shortest path from the peripheral portion of the upper electrode through the surface of the peripheral portion of the piezoelectric layer to the top surface or the peripheral portion of the lower electrode.

2. 2. The piezoelectric device according to claim 1, wherein the structure is one of a notch provided in the peripheral portion of the upper electrode, a protrusion provided in the peripheral portion of the piezoelectric layer, and a notch provided on the shortest path on the top surface of the lower electrode.

3. 2. The piezoelectric device according to claim 1, wherein the structures are provided at predetermined intervals in a plurality of locations on the periphery of the upper electrode, the periphery of the piezoelectric layer, and either the top surface or the periphery of the upper electrode.

4. 3. The piezoelectric device according to claim 2, wherein the protrusions of the piezoelectric layer protrude outward from the peripheral edge of the piezoelectric layer within a main plane of the piezoelectric layer.

5. the size of the lower electrode in a principal plane direction is larger than that of the piezoelectric layer; 2. The piezoelectric device according to claim 1, wherein the size of the upper electrode in the main plane direction is equal to or smaller than the size of the piezoelectric layer.

6. 2. The piezoelectric device according to claim 1, wherein the upper electrode and the lower electrode apply a voltage to the piezoelectric layer, causing the piezoelectric layer to expand and contract.

7. 2. The piezoelectric device according to claim 1, wherein the upper electrode and the lower electrode detect an electrical signal generated by the piezoelectric layer in response to pressure applied to the piezoelectric layer.

8. A movable apparatus having an object to be displaced and an actuator connected to the object, the actuator including a piezoelectric device according to any one of claims 1 to 7.

9. 9. The movable device according to claim 8, wherein the movable device is one of an optical deflector, a projector, and a speaker.

10. a laminate formation step of forming a laminate on a substrate, the laminate being formed by laminating a lower electrode layer, a piezoelectric layer, and an upper electrode layer in this order, each having a predetermined shape; a defect removal step of applying a voltage between the lower electrode layer and the upper electrode layer after forming the upper electrode layer that exceeds a withstand voltage of a defect included in the piezoelectric layer to remove the defect. The method for manufacturing a piezoelectric device is characterized in that the laminate formation process includes a process of forming a structure in one or more locations on the peripheral portion of the upper electrode, the peripheral portion of the piezoelectric layer, and either the top surface or the peripheral portion of the upper electrode, that locally increases the length of the shortest path that passes through the surface of the peripheral portion of the piezoelectric layer of the peripheral portion of the upper electrode to the top surface or the peripheral portion of the lower electrode.

11. 11. The method for manufacturing a piezoelectric device according to claim 10, wherein the step of forming the structure is a step of forming any one of a notch provided in the peripheral portion of the upper electrode, a protrusion provided in the peripheral portion of the piezoelectric layer, and a notch provided on the shortest path on the top surface of the lower electrode.

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