Piezoelectric drive element

Abstract

A piezoelectric driving element (1) is provided with: a support (10); a plate-like movable part (21) on which a rib (22) is disposed; a pair of meandering piezoelectric actuators (40) each having one end (end part (40a)) supported by the support (10); and a coupling part (50) which couples the other end (end part (40b)) of each of the pair of piezoelectric actuators (40) and the movable part (21) and has higher rigidity than the movable part (21).

Description

Technical Field

[0001] The present invention relates to a piezoelectric drive element that drives a movable part by a piezoelectric actuator, and is suitable for use, for example, when light is scanned by a mirror disposed on the movable part.

Background Art

[0002] In recent years, piezoelectric drive elements that rotate a movable part have been developed using MEMS (Micro Electro Mechanical System) technology. In this type of piezoelectric drive element, by disposing a mirror on the movable part, the light incident on the mirror can be scanned at a predetermined deflection angle.

[0003] For example, Patent Document 1 below describes an optical deflector including a piezoelectric actuator having a meander structure. The piezoelectric actuator includes a plurality of piezoelectric cantilevers having a support and a piezoelectric body formed on the support. The ends of the plurality of piezoelectric cantilevers are mechanically connected so as to accumulate respective bending deformations, and each piezoelectric cantilever is independently bent and deformed by application of a drive voltage.

[0004] Further, Non-Patent Document 1 below describes a structure in which the outer periphery of a movable part on which a mirror is formed is reinforced with ribs in order to suppress the deflection of the mirror in this type of optical deflector.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] As described above, when the outer periphery of the movable part is reinforced by ribs, although the warping of the movable part is suppressed, the mass of the ribs becomes a load, and the resonance frequency of the element part including the movable part decreases. Such a decrease in the resonance frequency leads to a decrease in driving characteristics such as a decrease in vibration resistance and a decrease in controllability of the movable part.

[0008] In view of such problems, an object of the present invention is to provide a piezoelectric drive element capable of suppressing warping of a movable part while suppressing a decrease in driving characteristics of the movable part.

Means for Solving the Problems

[0009] The first aspect of the present invention relates to a piezoelectric drive element. The piezoelectric drive element according to this aspect includes a support, a plate - shaped movable part on which ribs are arranged, one end of which is supported by the support , rotating the movable part about the rotation axis a pair of meander - type piezoelectric actuators, and a connecting part that connects the other ends of the pair of piezoelectric actuators and the movable part and has higher rigidity than the movable part. In a direction parallel to the plate surface of the movable part and perpendicular to the rotation axis, the width of the movable part is smaller than the width of the pair of piezoelectric actuators, the other ends of the pair of piezoelectric actuators are at the ends of the width of the piezoelectric actuator, and the connecting part is connected to the movable part at a position away from the rotation axis.

[0010] According to the piezoelectric drive element according to this aspect, warping of the plate - shaped movable part is suppressed by the ribs. Further, by increasing the rigidity of the connecting part, the rigidity of the element part (piezoelectric actuator, connecting part, and movable part) is increased. Thereby, the resonance frequency of the element part can be increased. Therefore, it is possible to suppress warping of the movable part while suppressing a decrease in driving characteristics of the movable part.

[0011] The second aspect of the present invention relates to a piezoelectric drive element. The piezoelectric drive element according to this aspect includes a support, a plate-shaped movable part on which ribs are arranged, and one end of which is supported by the support , rotating the movable part about the rotation axis a pair of meander-shaped piezoelectric actuators, and a connecting part that connects the other ends of the pair of piezoelectric actuators and the movable part. In a direction parallel to the plate surface of the movable part and perpendicular to the rotation axis, the width of the movable part is smaller than the width of the pair of piezoelectric actuators, and the other ends of the pair of piezoelectric actuators are at the ends of the width of the piezoelectric actuator, The connecting part is a straight line connecting the connection position between the connecting part and the piezoelectric actuator and the center of the movable part extends along, or the straight line and the rotation axis and is connected to the movable part so as to be substantially included in the range between at a position away from the rotation axis the connecting part and the piezoelectric actuator.

[0012] According to the piezoelectric drive element according to this aspect, the warping of the plate-shaped movable part is suppressed by the ribs. Further, the connecting part is connected to the movable part so as to be substantially included in the range between the straight line connecting the connection position between the connecting part and the piezoelectric actuator and the center of the movable part, and the rotation axis of the movable part by the piezoelectric actuator. Therefore, the moment of inertia of the connecting part with respect to the rotation axis can be suppressed. As a result, the resonance frequency of the element part (piezoelectric actuator, connecting part, and movable part) can be increased. Therefore, it is possible to suppress the warping of the movable part while suppressing the deterioration of the driving characteristics of the movable part.

Advantages of the Invention

[0013] As described above, according to the present invention, it is possible to provide a piezoelectric drive element capable of suppressing the warping of the movable part while suppressing the deterioration of the driving characteristics of the movable part.

[0014] The effects or significance of the present invention will become clearer from the description of the embodiments shown below. However, the embodiments shown below are merely examples when implementing the present invention, and the present invention is not limited to those described in the following embodiments at all.

Brief Description of the Drawings

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[0016] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

Embodiments for Carrying Out the Invention

[0017] In the following embodiments, the piezoelectric driving element is an element for rotating a mirror about a rotation axis R10 and scanning a target area using the light incident on the mirror. This type of piezoelectric driving element is sometimes called an optical deflector or a mirror actuator. Note that the piezoelectric driving element is not limited to rotating a mirror, and may rotate a member or a film other than the mirror. The following embodiments are one embodiment of the present invention, and the present invention is not limited to the following embodiments in any way.

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, X, Y, and Z axes orthogonal to each other are appended to each figure, and the positive Z-axis direction is the vertically upward direction.

[0019] Figs. 1 and 2 are plan views schematically showing the configuration of the piezoelectric driving element 1. Figs. 1 and 2 are plan views when the piezoelectric driving element 1 is viewed in the negative Z-axis direction and the positive Z-axis direction, respectively.

[0020] Referring to Figs. 1 and 2, the piezoelectric driving element 1 includes a support 10, a movable part 21, ribs 22, a mirror 30, a pair of piezoelectric actuators 40, and a pair of connecting parts 50.

[0021] The support 10 is a frame-shaped member having an opening in the center. The movable part 21 has a plate shape and a circular shape. The rib 22 has a ring shape and is disposed near the outer periphery of the surface on the negative Z-axis side of the movable part 21. When viewed in the Z-axis direction, the outer shape of the rib 22 coincides with the outer shape of the movable part 21. The mirror 30 has a circular shape and is disposed on the surface on the positive Z-axis side of the movable part 21. When viewed in the Z-axis direction, the shape of the mirror 30 coincides with the shape of the movable part 21. The positive Z-axis side of the mirror 30 is a mirror surface, and light incident on the mirror surface from the positive Z-axis side is reflected by the mirror surface.

[0022] The two piezoelectric actuators 40 are respectively disposed on the positive X-axis side and the negative X-axis side of the movable part 21, and are arranged and configured symmetrically with respect to the center 21a of the movable part 21 in a plan view. The outer ends 40a of the two piezoelectric actuators 40 in the X-axis direction are respectively supported by the support 10.

[0023] The two connecting parts 50 are connected to the movable part 21 at positions symmetric with respect to the center 21a of the movable part 21. The two connecting parts 50 are respectively disposed on the positive Y-axis side and the negative Y-axis side of the movable part 21, and are arranged and configured symmetrically with respect to the center 21a of the movable part 21 in a plan view. The connecting part 50 has a beam shape. The connecting part 50 connects the inner end 40b of the piezoelectric actuator 40 in the X-axis direction and the movable part 21. The two connecting parts 50 are L-shaped in a plan view.

[0024] The piezoelectric actuator 40 is a so-called meander-type actuator. That is, the piezoelectric actuator 40 includes two vibrating portions 41 and two vibrating portions 42 that are alternately connected so as to form a meander shape. The vibrating portions 41 and 42 have a rectangular shape in plan view and are connected to adjacent vibrating portions at one end in the Y-axis direction. In the piezoelectric actuator 40, the odd-numbered vibrating portions from the outside are the vibrating portions 41, and the even-numbered vibrating portions from the outside are the vibrating portions 42.

[0025] In the piezoelectric actuator 40 on the positive X-axis side, the end portion on the positive Y-axis side of the outermost vibrating portion 41 is the end portion 40a connected to the support 10, and the end portion on the positive Y-axis side of the innermost vibrating portion 42 is the end portion 40b connected to the connecting portion 50. In the piezoelectric actuator 40 on the negative X-axis side, the end portion on the negative Y-axis side of the outermost vibrating portion 41 is the end portion 40a connected to the support 10, and the end portion on the negative Y-axis side of the innermost vibrating portion 42 is the end portion 40b connected to the connecting portion 50. A reinforcing portion 40c (see FIG. 2) is disposed on the negative Z-axis side in the vicinity where the vibrating portion 41 and the vibrating portion 42 are connected, and on the negative Z-axis side of the end portions 40a and 40b.

[0026] The vibrating portions 41 and 42 have upper electrodes 101 and 102 on the upper surface (the surface on the positive Z-axis side). Both of the upper electrodes 101 and 102 are disposed on the upper surface sides of the vibrating portions 41 and 42 along the meander shape of the piezoelectric actuator 40 from the end portion 40a to the end portion 40b. The upper electrode 101 is disposed on the upper surface side of the vibrating portion 41 with an area substantially equal to that of the vibrating portion 41, and is linearly disposed along the edge of the vibrating portion 42 on the upper surface side of the vibrating portion 42. On the other hand, the upper electrode 102 is disposed on the upper surface side of the vibrating portion 42 with an area substantially equal to that of the vibrating portion 42, and is linearly disposed along the edge of the vibrating portion 41 on the upper surface side of the vibrating portion 41. The upper electrodes 101 and 102 extend to the outside of the end portion 40a and are connected to a driving portion (not shown) for applying a voltage.

[0027] Fig. 3(a) is a diagram schematically showing the configuration when the C11-C12 cross-section of the piezoelectric actuator 40 on the negative X-axis side of Fig. 1, where the vibrating portion 41 is cut by a plane parallel to the X-Z plane, is viewed in the positive Y-axis direction.

[0028] Note that the configuration shown in Fig. 3(a) is the same for the other vibrating portions 41 of the piezoelectric actuator 40 on the negative X-axis side. Also, the cross-sectional configuration of the vibrating portion 42 of the piezoelectric actuator 40 on the negative X-axis side is a configuration in which the upper electrode 101 is the upper electrode 102 and the upper electrode 102 is the upper electrode 101 in Fig. 3(a). Further, the cross-sectional configuration of the piezoelectric actuator 40 on the positive X-axis side is a configuration obtained by inverting the configuration of Fig. 3(a) in the X-axis direction.

[0029] The vibrating portion 41 includes a device layer 110, a thermal oxide film 120, a lower electrode 130, a piezoelectric body 140, and upper electrodes 101 and 102. The device layer 110 is composed of an Si substrate, the thermal oxide film 120 is composed of SiO2, the lower electrode 130 is composed of a metal electrode film, the piezoelectric body 140 is composed of, for example, lead zirconate titanate (PZT), and the upper electrodes 101 and 102 are disposed on the upper surface of the piezoelectric body 140. In the X-axis direction, the width of the device layer 110 is slightly longer than those of the thermal oxide film 120, the lower electrode 130, and the piezoelectric body 140. Since Fig. 3(a) shows the vibrating portion 41, in the X-axis direction, the upper electrode 101 is longer than the upper electrode 102, but in the case of the vibrating portion 42, in the X-axis direction, the upper electrode 102 is longer than the upper electrode 101.

[0030] Fig. 3(b) is a diagram schematically showing the configuration when the C21-C22 cross-section of the piezoelectric actuator 40 on the negative X-axis side of Fig. 1, where the vicinity of the end on the negative Y-axis side of the vibrating portion 42 is cut by a plane parallel to the Y-Z plane, is viewed in the negative X-axis direction.

[0031] Note that the structure shown in Fig. 3(b) is the same for the vicinity of the Y-axis negative-side end of the other vibrating part 42 of the piezoelectric actuator 40 on the negative side of the X-axis. Also, the structure in the vicinity of the Y-axis positive-side end of the vibrating part 41 of the piezoelectric actuator 40 on the negative side of the X-axis is the structure obtained by inverting the structure of Fig. 3(b) in the Y-axis direction. Further, the structures in the vicinity of the Y-axis negative-side end of the vibrating part 41 and the Y-axis positive-side end of the vibrating part 42 of the piezoelectric actuator 40 on the negative side of the X-axis are the same as the structure of Fig. 3(b), except that the upper electrodes 101 and 102 are arranged in the Y-axis direction in the vicinity of the ends as shown in Fig. 1. Also, the structure of the cross-section of the piezoelectric actuator 40 on the positive side of the X-axis is the structure obtained by inverting the structure of Fig. 3(b) in the X-axis direction.

[0032] As shown in Fig. 3(b), at the end of the vibrating part 41 connected to the adjacent vibrating part 42, in addition to the structure of Fig. 3(a), a reinforcing part 40c is arranged on the negative side of the Z-axis of the device layer 110. The reinforcing part 40c includes a base layer 150 and thermal oxide films 151 and 152. The base layer 150 is constituted by a Si substrate, and the thermal oxide films 151 and 152 are constituted by SiO2. Note that the device layer 110 protrudes in the Y-axis direction more than the thermal oxide film 120, the lower electrode 130, and the piezoelectric body 140, and the reinforcing part 40c is arranged at the Y-axis direction end of the device layer 110. The reinforcing part 40c linearly extends in the X-axis direction to the ends of the adjacent vibrating parts 42.

[0033] In the piezoelectric actuator 40, the device layer 110 has the same shape as the outer shape of the piezoelectric actuator 40 shown in Figs. 1 and 2. Based on the device layer 110, as shown in Figs. 3(a) and (b), each part of the piezoelectric actuator 40 is arranged by semiconductor film formation processing. Thereby, as shown in Fig. 1, the vibrating parts 41 and 42 are formed in the piezoelectric actuator 40.

[0034] Fig. 3(c) is a diagram schematically showing the structure when, in Fig. 1, the movable part 21, the rib 22, the mirror 30, and the connecting part 50 are cut by a plane parallel to the Y-Z plane passing through the center 21a of the movable part 21 and viewed in the negative X-axis direction.

[0035] The movable part 21 includes a device layer 210. The device layer 210 is composed of an Si substrate. The mirror 30 is an optical reflection film formed on the upper surface of the device layer 210. The mirror 30 is composed of, for example, a dielectric multilayer film, a metal film, or the like. The rib 22 includes a base layer 220 and thermal oxide films 221 and 222. The base layer 220 is composed of an Si substrate, and the thermal oxide films 221 and 222 are composed of SiO2. The connecting part 50 includes the device layer 210, the base layer 220, and the thermal oxide films 221 and 222. In Embodiment 1, in a direction parallel to the X-Y plane, the device layer 210 extends across the regions of the movable part 21 and the connecting part 50, and the base layer 220 and the thermal oxide films 221 and 222 extend across the regions of the rib 22 and the connecting part 50.

[0036] The movable part 21, the rib 22, and the connecting part 50 are formed by processing a SOI substrate composed of an Si substrate and SiO2 formed on the surface of the Si substrate. First, a SOI substrate including the device layer 210 and the thermal oxide film 221 and a SOI substrate including the base layer 220 and the thermal oxide film 222 are bonded together. A masking process is performed on the regions corresponding to the rib 22 and the connecting part 50, and the region corresponding to the hole in the center of the rib 22 is removed by etching. Then, the masking member is removed, and the mirror 30 is formed on the upper surface of the movable part 21.

[0037] Note that the device layer 110 constituting the piezoelectric actuator 40 and the device layer 210 of the components other than the piezoelectric actuator 40 (the movable part 21, the rib 22, and the connecting part 50) are integrally formed by a common Si substrate.

[0038] Also, not only the movable part 21, the rib 22, and the connecting part 50, but also the entire piezoelectric driving element 1 is formed by processing a SOI substrate. That is, by performing masking, etching, etc. on the SOI substrate, each part of the piezoelectric driving element 1 is formed collectively.

[0039] Here, due to the thermal stress generated during the formation of the mirror 30, the movable part 21 is usually prone to warping and bending. In contrast, in the first embodiment, since the rib 22 is pre-formed on the back surface side of the movable part 21, the warping and bending of the movable part 21 during the formation of the mirror 30 can be suppressed. Further, since the connecting part 50 is thicker than the movable part 21, it has higher rigidity than the movable part 21. That is, the connecting part 50 is configured to be less likely to bend. As a result, the vibration by the piezoelectric actuator 40 is likely to be transmitted to the movable part 21.

[0040] Next, the driving of the piezoelectric driving element 1 configured as shown in FIGS. 1 to 3(c) will be described.

[0041] During the driving of the piezoelectric driving element 1, a voltage is applied to the upper electrodes 101 and 102 so that the movable part 21 and the mirror 30 repeatedly rotate and vibrate about the rotation axis R10 (see FIGS. 1 and 2). When a voltage is applied to the upper electrodes 101 and 102, a voltage is applied to the piezoelectric body 140 (see FIGS. 3(a) and (b)) located immediately below the upper electrodes 101 and 102, and due to the inverse piezoelectric effect of the piezoelectric body 140, the vibrating parts 41 and 42 are deformed so as to bend in the positive Z-axis direction or the negative Z-axis direction.

[0042] Specifically, the upper part electrode 101 of the piezoelectric actuator 40 on the positive X-axis side and the upper part electrode 102 of the piezoelectric actuator 40 on the negative X-axis side are applied with voltages of the same phase, and the upper part electrode 102 of the piezoelectric actuator 40 on the positive X-axis side and the upper part electrode 101 of the piezoelectric actuator 40 on the negative X-axis side are applied with voltages of opposite phases. By making the phases of the voltages applied to the upper electrodes 101 and 102 opposite, the two adjacent vibrating parts 41 and 42 are displaced in opposite directions. As a result, these displacements are accumulated about the rotation axis R10, and the movable part 21 and the mirror 30 repeatedly rotate and vibrate.

[0043] <Effect of Embodiment 1> According to the first embodiment, the following effects are achieved.

[0044] The rib 22 is disposed on the plate-shaped movable part 21. Further, a connecting part 50 having higher rigidity than the movable part 21 connects the end part 40b of the piezoelectric actuator 40 and the movable part 21. According to this configuration, the warping of the plate-shaped movable part 21 is suppressed by the rib 22. Further, since the rigidity of the connecting part 50 is increased, the rigidity of the element part (the piezoelectric actuator 40, the connecting part 50, and the movable part 21) is increased. Thereby, the resonance frequency of the element part can be increased, and a decrease in the driving characteristics of the mirror 30 can be suppressed.

[0045] In the first embodiment, a reinforcing part 40c is disposed at the Y-axis direction ends of the vibrating parts 41 and 42. When the reinforcing part 40c is provided in this way, the rigidity of the element part (the piezoelectric actuator 40, the connecting part 50, and the movable part 21) is increased. Thereby, in addition to the effect by the connecting part 50, the resonance frequency of the element part can be further increased.

[0046] The connecting part 50 has a larger thickness than the movable part 21. In this way, by adjusting the thickness of the connecting part 50, the rigidity of the connecting part 50 can be easily increased.

[0047] The end part of the connecting part 50 extends to the rib 22 and is connected to the rib 22. That is, the connecting part 50 is directly connected to the rib 22. Thereby, since the pair of piezoelectric actuators 40 are connected by a high-rigidity structure body (the connecting part 50 and the rib 22), the rigidity of the element part (the piezoelectric actuator 40, the connecting part 50, and the movable part 21) is increased, and the resonance frequency of the element part can be increased. Therefore, a decrease in the driving characteristics of the movable part 21 can be further suppressed.

[0048] As shown in FIG. 3(c), the rib 22 and the connecting part 50 are made of the same material (Si substrate), and the connecting part 50 has the same thickness as the sum of the thicknesses of the movable part 21 and the rib 22. Thereby, since the rib 22 and the connecting part 50 can be formed simultaneously, the manufacture of the piezoelectric driving element 1 becomes easy.

[0049] The connecting portion 50 is connected to the movable portion 21 at a position symmetric with respect to the center 21a of the movable portion 21. According to this configuration, the connecting portion 50 can support the movable portion 21 in a well-balanced manner, so that the movable portion 21 can be driven stably.

[0050] The mirror 30 is disposed on the movable portion 21. Thereby, while suppressing the warpage of the mirror 30, the mirror 30 can be driven at a high resonance frequency. Therefore, the quality of the light (for example, laser light) reflected by the mirror 30 can be improved, and the light can be scanned at high speed.

[0051] <Embodiment 2> In Embodiment 2, the connection method of the connecting portion 50 to the movable portion 21 is changed from that in Embodiment 1. The configuration other than the connection method of the connecting portion 50 is the same as that in Embodiment 1.

[0052] FIG. 4 is a plan view schematically showing the configuration of the piezoelectric driving element 1.

[0053] The straight line L1 is a straight line connecting the connection position (end portion 40b) of the connecting portion 50 and the piezoelectric actuator 40 and the center 21a of the movable portion 21. The connecting portion 50 is connected to the movable portion 21 so as to be substantially included in the range (range of the angle θ) between the straight line L1 and the rotation axis R10 of the movable portion 21 by the piezoelectric actuator 40. In this way, when the connecting portion 50 is arranged so as to be substantially included in the range of the angle θ, the moment of inertia of the connecting portion 50 with respect to the rotation axis R10 can be suppressed.

[0054] <Simulation Regarding Driving Characteristics> The inventors performed simulations using the finite element method for Model 1 corresponding to the configuration of Embodiment 1, Model 2 corresponding to the configuration of Embodiment 2, and the driving characteristics of a comparative example different from Embodiments 1 and 2, respectively. In this simulation, the configuration of the piezoelectric drive element 1 is substantially the same as the configuration shown in FIGS. 1 and 4. Hereinafter, in this simulation, configurations different from FIGS. 1 and 4 and the sizes of each part will be described. For the configurations similar to the comparative example among the configurations of Models 1 and 2, reference will be made to the configurations of the comparative examples shown in FIGS. 5(a) to (c) for explanation.

[0055] FIG. 5(a) is a plan view schematically showing the configuration of the comparative example.

[0056] In this simulation, in all cases of the comparative example and Models 1 and 2, the diameter d11 of the movable part 21 was set to 1.5 mm. The width d12 of the piezoelectric actuator 40 in the X-axis direction was set to 2.3 mm, and the width d13 of the piezoelectric actuator 40 in the Y-axis direction was set to 1.8 mm.

[0057] In the comparative example, as shown in FIG. 5(a), compared with the configuration of Embodiment 1 shown in FIG. 1, a connecting part 51 was arranged instead of the connecting part 50. The shape of the connecting part 51 in plan view is the same as that of the connecting part 50 of Embodiment 1, but the thickness of the connecting part 51 is smaller than that of the connecting part 50 of Embodiment 1.

[0058] FIG. 5(b) is a diagram schematically showing the configuration when the C41 - C42 cross-section when the piezoelectric actuator 40 is cut by a plane parallel to the Y-Z plane in the configuration of the comparative example of FIG. 5(a) is viewed in the negative X-axis direction.

[0059] In this simulation, in all cases of the comparative example and Models 1 and 2, the thickness d14 of the device layer 110 was set to 10 μm, the thickness d15 of the piezoelectric body 140 was set to 3 μm, and the thickness d16 of the base layer 150 and the thermal oxide films 151 and 152 was set to 270 μm.

[0060] FIG. 5(c) shows the movable part 21 and the rib 2 in FIG. 5(a). 2、FIG. 0 is a diagram schematically showing a configuration when the mirror 30 and the connecting portion 51 are cut by a plane parallel to the Y-Z plane passing through the center 21a of the movable portion 21, as viewed in the negative X-axis direction.

[0061] In this simulation, in all cases of the comparative example and Models 1 and 2, the thickness of the device layer 210 was set to 10 μm, the same as the thickness d14 in FIG. 5(b), and the thicknesses of the base layer 220 and the thermal oxide films 221 and 222 were set to 270 μm, the same as the thickness d16 in FIG. 5(b).

[0062] In the comparative example, as shown in FIG. 5(c), the connecting portion 51 was composed of only the device layer 210, similar to the movable portion 21. Since the connecting portion 51 in the comparative example has the same thickness as the movable portion 21, the rigidity of the connecting portion 51 is lower than that of the connecting portions 50 in Models 1 and 2. In the comparative example, the rigidity of the connecting portion 51 in the Z-axis direction is the same as the rigidity of the movable portion 21 itself in a state where the rib 22 is not arranged.

[0063] FIG. 6(a) is a plan view schematically showing the configuration of Model 1 corresponding to Embodiment 1.

[0064] As described above, the configuration of Model 1 is the same as that of the comparative example in plan view. However, in Model 1, similar to Embodiment 1, the movable portion 21, the rib 22, and the piezoelectric actuator 40 are connected by a connecting portion 50 different from that of the comparative example. Also, in both cases of Models 1 and 2, in addition to the rib 22 shown in FIG. 1, a rib 23 linearly extending in the Y-axis direction was arranged on the surface of the movable portion 21 on the negative Z-axis side.

[0065] FIG. 6(b) is a diagram schematically showing a configuration when the movable portion 21, the ribs 22 and 23, the mirror 30, and the connecting portion 50 in the configuration of Model 1 in FIG. 6(a) are cut by a plane parallel to the Y-Z plane passing through the center 21a of the movable portion 21, as viewed in the negative X-axis direction.

[0066] As described above, in the configuration of Model 1, the thickness of the device layer 210 is the same as the thickness d14 (10 μm) of the comparative example shown in FIG. 5(c), and the thicknesses of the base layer 220 and the thermal oxide films 221 and 222 are the same as the thickness d16 (270 μm) of the comparative example shown in FIG. 5(c). However, in Model 1, the connecting portion 50 is composed of the device layer 210, the base layer 220, and the thermal oxide films 221 and 222.

[0067] FIG. 6(c) is a plan view schematically showing the configuration of Model 2 corresponding to Embodiment 2.

[0068] In Model 2, the position where the connecting portion 50 is connected to the movable portion 21 and the rib 22 is set as the position at an angle θ1 with respect to the rotation axis R10 around the center 21a of the movable portion 21. Here, the angle θ1 is set to 30°. Also in this case, the connecting portion 50 is substantially included in the range between the straight line L1 (see FIG. 4) and the rotation axis R10. Also in Model 2, similar to Model 1, the connecting portion 50 is composed of the device layer 210, the base layer 220, and the thermal oxide films 221 and 222. Each dimension of Model 2 was set in the same manner as Model 1, except for the arrangement method of the connecting portion 50.

[0069] Under the above conditions, the inventor first measured the warp of the mirror 30 based on the thermal stress obtained by the preliminary experiment and the conditions of this simulation in the non-driven state. Next, the inventor drove the piezoelectric drive element 1 to rotate the movable portion 21 and the mirror 30, and measured the resonance frequency of the element portion (piezoelectric actuator 40, connecting portion, and movable portion 21) and the swing angle around the rotation axis R10 at this time.

[0070] FIG. 7 is a table showing the results of this simulation.

[0071] The value of the warp became 30 nm or less in all cases of the comparative example and Models 1 and 2. When the inventor measured the warp of the mirror 30 when the ribs 22 and 23 were not arranged, the value of the warp became as large as several hundred nm. In this simulation, it was confirmed that the warp was suppressed in all cases as described above by arranging the rib 22 in the movable part 21 in the case of the comparative example and arranging the ribs 22 and 23 in the movable part 21 in the cases of Models 1 and 2.

[0072] The value of the resonance frequency was 367 Hz in the comparative example, 465 Hz in Model 1, and 495 Hz in Model 2. In this simulation, a higher resonance frequency was obtained for Model 1 than for the comparative example, and furthermore, a higher resonance frequency was obtained for Model 2 than for Model 1. From this, it was confirmed that a higher resonance frequency can be obtained by increasing the thickness of the connecting part 50 to increase the rigidity. Also, it was confirmed that an even higher resonance frequency can be obtained by arranging the connecting part 50 as in Model 2 to reduce the moment of inertia of the connecting part 50.

[0073] The value of the deflection angle was 38.8° in the comparative example and 40.4° in Models 1 and 2. In this simulation, larger deflection angles were obtained for Models 1 and 2 than for the comparative example. It is presumed that the reason for the small deflection angle in the comparative example is that the thickness of the connecting part 51 was set small and the rigidity of the element part (piezoelectric actuator 40, connecting part 51, and movable part 21) was low. On the other hand, the reason for the large deflection angles in Models 1 and 2 is presumed to be that the thickness of the connecting part 50 was set large and the rigidity of the element part (piezoelectric actuator 40, connecting part 50, and movable part 21) became high, so that the rotational moment generated by the piezoelectric actuator 40 was propagated to the movable part 21 without being impaired at the connecting part 50. Therefore, from the viewpoint of expanding the deflection angle, it can be said that it is preferable that the rigidity of the connecting part 50 is high.

[0074] <Effects of Embodiment 2> According to Embodiment 2, the following effects are achieved.

[0075] The connecting portion 50 is connected to the movable portion 21 so as to be substantially included in the range between the straight line L1 and the rotation axis R10 (rotation axis). That is, most of the connecting portion 50 is arranged so as to be included in the above range, and the connecting portion 50 is substantially included in the above range. According to this configuration, since the connecting portion 50 is positioned in a range approaching the rotation axis R10, the moment of inertia of the connecting portion 50 with respect to the rotation axis R10 can be suppressed. Therefore, the resonance frequency of the element portion (piezoelectric actuator 40, connecting portion 50, and movable portion 21) can be increased, and further reduction in the driving characteristics of the mirror 30 can be suppressed.

[0076] <Modified Example> The configuration of the piezoelectric driving element 1 can be variously changed in addition to the configuration shown in the above embodiment.

[0077] For example, in the above-described Embodiments 1 and 2, as shown in FIGS. 1 and 4, the connecting portion 50 had an L shape, but it may have other shapes.

[0078] For example, as shown in FIG. 8(a), the connecting portion 50 may linearly extend at an angle with respect to the X-axis and the Y-axis in the X-Y plane. Also in this case, since the connecting portion 50 is substantially included in the range between the straight line L1 and the rotation axis R10, the moment of inertia of the connecting portion 50 is suppressed. Further, as shown in FIG. 8(b), the connecting portion 50 may have a curved shape.

[0079] Also, in the above-described Embodiments 1 and 2, the rib 22 had a ring shape in plan view, but the rib for suppressing the warping of the movable portion 21 is not limited to the ring shape. For example, as shown in FIGS. 6(a) and 6(c), a linear rib 23 may be added in the radial direction of the rib 22. Further, as shown in FIG. 9(a), in addition to the ribs 22 and 23, a linear rib 24 may be further added in the radial direction of the rib 22. In this case, the rib 22 and the rib 23 are arranged so as to be orthogonal to each other, for example. Also, the rib 22 may have a rectangular shape in plan view. Further, in the configuration of FIG. 9(a), the rib 22 may be omitted.

[0080] In the above-described Embodiments 1 and 2, the ring-shaped rib 22 is disposed on the outer peripheral portion of the movable portion 21. However, the present invention is not limited to this, and as shown in FIG. 9(b), the rib 22 may be disposed slightly inside from the outer peripheral portion of the movable portion 21. Also in this case, the rib 22 and the connecting portion 50 are integrally formed of the same material. Further, in the case of the configuration shown in FIG. 9(b), as shown in FIG. 10(a), the rib 22 and the connecting portion 50 do not necessarily have to be integrally configured. However, from the viewpoint of improving the resonance frequency, it is preferable that the rib 22 and the connecting portion 50 are integrally configured, and the pair of piezoelectric actuators 40 are connected by a highly rigid structure including the rib 22 and the connecting portion 50.

[0081] In the above-described Embodiments 1 and 2, the connecting portion 50 has a configuration in which the base layer 220 (Si substrate) is stacked on the same device layer 210 (Si substrate) as the movable portion 21, and is formed to have a greater thickness than the movable portion 21. However, as long as the connecting portion 50 has higher rigidity than the movable portion 21, the configuration of the connecting portion 50 is not limited to the above configuration. For example, the connecting portion 50 may be formed of a material having higher rigidity than the movable portion 21 and have the same thickness as the movable portion 21. Further, the connecting portion 50 may be formed of a material having lower rigidity than the movable portion 21 and be configured to have a greater thickness than the movable portion 21, so that as a result, higher rigidity than the movable portion 21 may be realized. Also, the connecting portion 50 has a two-layer structure of the device layer 210 and the base layer 220, but the number of layers of the connecting portion 50 is not limited to this.

[0082] Also, the connecting portion 50 may be reinforced by coating the periphery of the connecting portion 50 with a metal material, and the rigidity of the connecting portion 50 may be increased to be higher than that of the movable portion 21. FIG. 10(b) is a cross-sectional view schematically showing the configuration in this case. In FIG. 10(b), the connecting portion 50 is composed of the device layer 210 and the metal material 230, and the device layer 210 corresponding to the connecting portion 50 is coated with the metal material 230. When the metal material 230 is used in this way, the rigidity of the connecting portion 50 can be easily increased.

[0083] Also, in the above Embodiments 1 and 2, as shown in FIG. 11, a pair of piezoelectric actuators 40 may be arranged and configured to be line-symmetric with respect to the Y-Z plane passing through the center 21a of the movable part 21. In this case, the pair of piezoelectric actuators 40, the movable part 21, and the rib 22 are connected by one connecting part 50. The shape of the connecting part 50 in this case is a T-shape that is line-symmetric with respect to the Y-Z plane passing through the center 21a in plan view. The connecting part 50 includes a straight part 50a extending in the X-axis direction and a straight part 50b extending in the Y-axis direction. The straight part 50a connects the end 40b of the piezoelectric actuator 40 on the positive X-axis side and the end 40b of the piezoelectric actuator 40 on the negative X-axis side. The straight part 50b connects the center of the straight part 50a in the X-axis direction to the movable part 21 and the rib 22.

[0084] In the configuration shown in FIG. 11, a pair of piezoelectric actuators 40 are driven so as to generate rotational vibrations in the same direction as each other. Specifically, voltages of the same phase are applied to the electrodes 101 of the two piezoelectric actuators 40, and voltages of opposite phases are applied to the electrodes 102 of the two piezoelectric actuators 40. Thereby, the straight part 50a of the connecting part 50 rotates about the rotation axis R10, and the movable part 21 and the mirror 30 repeatedly rotate and vibrate. upper part voltages of the same phase are applied to the electrodes 101 of the two piezoelectric actuators 40, and voltages of opposite phases are applied to the electrodes 102 of the two piezoelectric actuators 40. upper part voltages of opposite phases are applied to the electrodes 102 of the two piezoelectric actuators 40. Thereby, the straight part 50a of the connecting part 50 rotates about the rotation axis R10, and the movable part 21 and the mirror 30 repeatedly rotate and vibrate.

[0085] In the above Embodiments 1 and 2, the connecting part 50 is configured to have higher rigidity than the movable part 21. On the other hand, the inventor examined whether the driving characteristics of the movable part 21 can be improved compared to the comparative example by adjusting the connecting part 50 as in the above Model 2 when the connecting part 50 does not have higher rigidity than the movable part 21.

[0086] Hereinafter, a modification example in this examination will be described.

[0087] The configuration of this modified example is the same as that of Embodiment 2 shown in FIGS. 4 and 6(c) in plan view. The connecting portion 50 of this modified example is connected to the movable portion 21 so as to be substantially included in the range between the straight line L1 connecting the connection position (end portion 40b) between the connecting portion 50 and the piezoelectric actuator 40 and the center 21a of the movable portion 21, and the rotation axis R10 of the movable portion 21 by the piezoelectric actuator 40. Further, the laminated structure of the connecting portion 50 of this modified example is configured in the same manner as the connecting portion 51 of the comparative example shown in FIG. 5(c). That is, the connecting portion 50 is configured to have the same thickness as the portion of the movable portion 21 in the range other than the rib 22 of the comparative example. Further, ribs 22 and 23 are arranged on the surface on the negative Z-axis side of the movable portion 21 of this modified example, in the same manner as in Embodiments 1 and 2 shown in FIGS. 6(a) to 6(c). The laminated structure of the movable portion 21 and the ribs 22 and 23 of this modified example is the same as that of Embodiments 1 and 2 shown in FIG. 6(b).

[0088] The inventor performed a simulation by the finite element method on the driving characteristics of Model 3 corresponding to the configuration of the modified example configured as described above, in the same manner as the simulation regarding the driving characteristics. Note that each dimension of Model 3 is the same as that of Model 2, except for the thickness of the connecting portion 50. Further, the thickness of the connecting portion 50 of Model 3 is the same as that of the comparative example.

[0089] FIG. 12 is a table showing the results of this simulation. For convenience, the simulation results of the comparative example in FIG. 7 are shown in FIG. 12.

[0090] The warpage value of Model 3 was 30 nm or less. Therefore, it was confirmed that, as in the comparative example in FIG. 7 and Models 1 and 2, the warpage was suppressed by arranging ribs on the movable portion 21.

[0091] The resonance frequency value of Model 3 was 405 Hz. In Model 3, although the resonance frequency was slightly lower than that of Models 1 and 2 in FIG. 7, a resonance frequency higher than that of the comparative example was obtained. From this, it was confirmed that even if the thickness of the connecting portion 50 was as small as that of the comparative example, a high resonance frequency could be obtained by reducing the moment of inertia of the connecting portion 50.

[0092] The value of the deflection angle of Model 3 was 39.9°. In Model 3, although the deflection angle was slightly smaller than that of Models 1 and 2 in FIG. 7, a larger deflection angle was obtained compared with the comparative example. From this, it was confirmed that even if the thickness of the connecting portion 50 was as small as that in the comparative example, a large deflection angle could be obtained by reducing the moment of inertia of the connecting portion 50 with respect to the rotation axis R10.

[0093] As described above, according to this modification example, since the connecting portion 50 is positioned in the range approaching the rotation axis R10, the moment of inertia of the connecting portion 50 with respect to the rotation axis R10 can be suppressed. Therefore, while suppressing the warping of the movable portion 21 by the rib 22, the resonance frequency of the element portion (the piezoelectric actuator 40, the connecting portion 50, and the movable portion 21) can be increased compared with the comparative example, and the deterioration of the driving characteristics of the mirror 30 can be suppressed.

[0094] In addition, in the above-described Embodiments 1 and 2, one piezoelectric actuator 40 includes two vibrating portions 41 and two vibrating portions 42, but the number of vibrating portions included in the piezoelectric actuator 40 is not limited to this.

[0095] In addition, in the above-described Embodiments 1 and 2, the mirror 30 is formed of a dielectric multilayer film, a metal film, or the like, but an optical reflection film other than the dielectric multilayer film and the metal film may be used.

[0096] In addition, the embodiments of the present invention can be appropriately modified in various ways within the scope of the technical idea shown in the claims.

Explanation of Reference Numerals

[0097] 1 Piezoelectric driving element 10 Support 21 Movable portion 21a Center 22, 23, 24 Ribs 30 Mirror 40 Piezoelectric actuator 40a End portion (one end) 40b End portion (the other end) 50 Connecting portion L1 Straight line R10 Rotating shaft

Claims

1. A support, a plate-shaped movable part with ribs arranged thereon, a pair of meander-shaped piezoelectric actuators having one end supported by the support and rotating the movable part about a rotation axis, a connecting part that connects the other ends of the pair of piezoelectric actuators and the movable part and has higher rigidity than the movable part, in a direction parallel to the plate surface of the movable part and perpendicular to the rotation axis, the width of the movable part is smaller than the width of the pair of piezoelectric actuators, the other ends of the pair of piezoelectric actuators are at the ends of the width of the piezoelectric actuator, the connecting part is connected to the movable part at a position away from the rotation axis, A piezoelectric driving element characterized by the above.

2. In the piezoelectric driving element according to Claim 1, the connecting part has a greater thickness than the movable part, A piezoelectric driving element characterized by the above.

3. In the piezoelectric driving element according to Claim 1 or 2, the end of the connecting part extends to the rib and is connected to the rib, A piezoelectric driving element characterized by the above.

4. In the piezoelectric driving element according to any one of Claims 1 to 3, the connecting part extends along a straight line connecting the connection position between the connecting part and the piezoelectric actuator and the center of the movable part, or is connected to the movable part so as to be substantially included in the range between the straight line and the rotation axis, A piezoelectric driving element characterized by the above.

5. In the piezoelectric driving element according to any one of Claims 1 to 4, the rib and the connecting part include a layer of the same material, the connecting part has the same thickness as the sum of the thicknesses of the movable part and the rib, A piezoelectric driving element characterized by the above.

6. In the piezoelectric driving element according to any one of Claims 1 to 5, the piezoelectric driving element is formed by processing an SOI substrate, A piezoelectric driving element characterized by the above.

7. In the piezoelectric driving element according to any one of Claims 1 to 6, the connecting part is connected to the movable part at a position symmetric with respect to the center of the movable part, A piezoelectric driving element characterized by the above.

8. In the piezoelectric driving element according to any one of Claims 1 to 7, a mirror is arranged on the movable part, A piezoelectric driving element characterized by the above.

9. A support, a plate-shaped movable part with ribs arranged thereon, a pair of meander-shaped piezoelectric actuators having one end supported by the support and rotating the movable part about a rotation axis, a connecting portion that connects the other ends of the pair of piezoelectric actuators to the movable portion; in a direction parallel to the plate surface of the movable portion and perpendicular to the rotation axis, the width of the movable portion is smaller than the width of the pair of piezoelectric actuators; the other ends of the pair of piezoelectric actuators are at the ends of the width of the piezoelectric actuator; the connecting portion extends along a straight line connecting the connection position between the connecting portion and the piezoelectric actuator and the center of the movable portion, or is connected to the movable portion at a position away from the rotation axis so as to be substantially included in the range between the straight line and the rotation axis; A piezoelectric drive element characterized by the above.

10. In the piezoelectric drive element according to claim 9, the connecting portion is connected to the movable portion at a position symmetric with respect to the center of the movable portion; A piezoelectric drive element characterized by the above.

11. In the piezoelectric drive element according to claim 9 or 10, the piezoelectric drive element is formed by processing an SOI substrate; A piezoelectric drive element characterized by the above.

12. In the piezoelectric drive element according to any one of claims 9 to 11, a mirror is disposed on the movable portion; A piezoelectric drive element characterized by the above.

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