Optical reflective device

Abstract

An optical reflective device according to the present invention is provided with: a movable part (30); a reflective surface disposed in the movable part (30); frame parts (16, 26) that are disposed, in a plan view, outside the movable part (30) with a prescribed gap therebetween and that are connected to the movable part (30); beamlike torsion parts (14, 24) that extend along the rotation axis (R0); connection parts (15, 25) for connecting ends of the torsion parts (14, 24) to the frame parts (16, 26); a pair of drive units connected to the other ends of the torsion parts (14, 24); and fixing parts for supporting the pair of drive units. The rigidity of the connection parts (15, 25) is higher than that of the torsion parts (14, 24). At each of boundaries between the connection parts (15, 25) and the torsion parts (14, 24), joint surfaces including at least a pair of joint surfaces (S12) are formed. The pair of joint surfaces (S12) are symmetrical relative to the rotation axis (R0), and angles formed between the surfaces and the rotation axis (R0) at the corresponding torsion part (14, 24) side are acute angles.

Description

Optical Reflective Elements

[0001] The present invention relates to an optical reflecting element that rotates a reflecting surface about a rotation axis.

[0002] In recent years, optical reflecting elements that rotate a reflecting surface using MEMS (Micro Electro Mechanical System) technology have been developed. This type of optical reflecting element can cause a beam incident on the reflecting surface to scan at a predetermined deflection angle. Such optical reflecting elements are mounted, for example, in image display devices such as head-up displays and head-mounted displays. In addition, this type of optical reflecting element can also be used in laser radars that detect objects using laser light.

[0003] As described above, in a configuration in which light is scanned by rotating the reflective surface, the reflective surface may bend due to the inertial force generated when the reflective surface repeatedly rotates. If this bending causes the reflective surface to deform into a concave or convex shape, the beam will spread along the scan line. For this reason, it is preferable to minimize bending of the reflective surface when it rotates.

[0004] Patent Document 1 listed below describes an optical reflecting element that rotates a mirror using a so-called tuning fork vibrator. In this optical reflecting element, a frame is connected to the end of a drive beam that extends along a rotation axis, and a mirror is further connected to this frame. The rigidity of the frame is greater than the rigidity of the mirror. A piezoelectric actuator is disposed on each of a pair of arms that are arranged on either side of the drive beam. When the piezoelectric actuator is driven, the pair of arms vibrates, and the drive beam rotates about the rotation axis. This causes the frame and mirror to rotate repeatedly.

[0005] In this configuration, the frame is interposed between the mirror and the drive beam, which suppresses deflection of the mirror during rotation, thereby suppressing beam expansion due to mirror deflection and improving beam scanning accuracy.

[0006] International Publication No. 2031 / 046612

[0007] As described above, the configuration of Patent Document 1 allows the action of the frame to suppress deflection of the mirror when the mirror rotates. However, when an optical reflecting element having the above configuration is used in, for example, a laser scanning image display device, it is required that the mirror be driven at a high frequency and a large deflection angle. In this case, a larger inertial force is generated in the mirror, so a configuration is required that can further suppress deflection of the mirror.

[0008] In view of such problems, the present invention aims to provide an optical reflecting element that can effectively suppress deflection of the movable part and the reflecting surface even when the movable part on which the reflecting surface is formed is driven at a high frequency and a large deflection angle.

[0009] The optical reflecting element according to a main aspect of the present invention comprises a movable part that rotates about a rotation axis, a reflecting surface disposed on the movable part, a frame part that is disposed outside the movable part with a predetermined gap in a plan view and is connected to the movable part at two positions symmetrical about the rotation axis, a beam-shaped torsion part that extends along the rotation axis, a connection part that connects one end of the torsion part to the frame part, a pair of drive parts that are connected to the other end of the torsion part and rotate the torsion part about the rotation axis, and a fixing part that supports the pair of drive parts. The connection part has higher rigidity than the torsion part. At least a pair of joint surfaces are formed at the boundary between the torsion part and the connection part. The pair of joint surfaces are symmetrical about the rotation axis, and each of the angles that the torsion part side forms with the rotation axis is an acute angle.

[0010] In the optical reflecting element according to this aspect, at least one pair of bonding surfaces is symmetrical about the rotation axis and forms an acute angle with the rotation axis of the torsion section, so that stress generated when the movable section rotates is easily dispersed across the pair of bonding surfaces. This makes it possible to gently deflect the frame section when the movable section rotates, thereby suppressing deflection of the movable section connected to the frame section. Therefore, even when the movable section is driven at a high frequency and a large deflection angle, deflection of the movable section and the reflecting surface can be effectively suppressed.

[0011] As described above, according to the present invention, it is possible to provide an optical reflecting element that can effectively suppress deflection of the movable portion and the reflecting surface even when the movable portion is driven at a high frequency and a large deflection angle.

[0012] The effects and significance of the present invention will become more apparent from the following description of the embodiments, however, the embodiments shown below are merely examples of how the present invention can be implemented, and the present invention is not limited to the embodiments described below.

[0013] FIG. 1 is a perspective view showing the configuration of an optical reflecting element according to an embodiment when viewed from above. FIG. 2 is a perspective view showing the configuration of an optical reflecting element according to an embodiment when viewed from below. FIG. 3 is a plan view showing the configuration of an optical reflecting element according to an embodiment when viewed from below. FIGS. 4(a) and 4(b) are perspective views of the vicinity of a movable portion according to an embodiment when viewed from above and below, respectively, and FIGS. 4(c) and 4(d) are plan views of the vicinity of a movable portion according to an embodiment when viewed from above and below, respectively. FIG. 5 is a cross-sectional view taken along A1-A1 of FIG. 4(a) according to an embodiment. FIG. 6 is a perspective view showing the structure of a connecting portion according to an embodiment. FIGS. 7(a) and 7(b) are perspective views of the vicinity of a movable portion according to a comparative example when viewed from above and below, respectively. FIGS. 7(c) and 7(d) are plan views of the vicinity of a movable portion according to a comparative example when viewed from above and below, respectively. FIG. 8(a) is a graph showing verification results according to a comparative example. FIG. 8(b) is a graph showing verification results according to an embodiment. FIG. 9( a) shows a simulation result of the stress distribution of an oxide film in the configuration of a comparative example, and FIG. 9( b) shows a simulation result of the stress distribution of an oxide film in the configuration of the embodiment. FIG. 10( a) is a plan view schematically showing stress propagation according to a comparative example. FIG. 10( b) is a plan view schematically showing stress propagation according to the embodiment. FIG. 11( a) is a plan view of the vicinity of a movable portion according to Modification Example 1, viewed from below. FIG. 11( b) is a plan view of the vicinity of a movable portion according to Modification Example 2, viewed from below. FIG. 12( a) is a plan view of the vicinity of a movable portion according to Modification Example 3, viewed from below. FIG. 12( b) is a plan view of the vicinity of a movable portion according to Modification Example 4, viewed from below. FIG. 13 is a plan view of an optical reflecting element according to Modification Example 5, viewed from below.

[0014] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, each drawing is labeled with mutually orthogonal X, Y, and Z axes. The Y axis direction is parallel to the rotation axis of the optical reflecting element, and the Z axis direction is the thickness direction of the optical reflecting element.

[0016] 1 and 2 are perspective views showing the configuration of optical reflecting element 1 when viewed from above and below, respectively, and Fig. 3 is a plan view showing the configuration of optical reflecting element 1. Fig. 3 shows a plan view of optical reflecting element 1 when viewed from below (the negative side of the Z axis).

[0017] 1 to 3, the optical reflecting element 1 includes a first drive unit 10, a second drive unit 20, and a movable part 30. A reflective surface 40 is disposed on the upper surface of the movable part 30. In a plan view, the optical reflecting element 1 has a shape that is symmetrical in the X-axis direction and the Y-axis direction. In a plan view, the movable part 30 and the reflective surface 40 are circular.

[0018] The reflecting surface 40 is formed, for example, by laminating a dielectric multilayer film on the upper surface of the movable portion 30. The movable portion 30 and the reflecting surface 40 may be formed from the same material. In this case, for example, the reflecting surface 40 may be formed by mirror-finishing the upper surface of the movable portion 30.

[0019] The first drive unit 10 and the second drive unit 20 repeatedly rotate the movable part 30 about the rotation axis R0 in response to a drive signal supplied from a drive circuit (not shown). The reflective surface 40 reflects light incident from above the movable part 30 in a direction according to the swing angle of the movable part 30. As a result, the light (e.g., laser light) incident on the reflective surface 40 is deflected and scanned as the movable part 30 rotates.

[0020] The first drive unit 10 includes a drive section 11, a fixed section 12, a support section 13, a torsion section 14, a connection section 15, and a frame section 16. The movable section 30, the drive section 11, the fixed section 12, the support section 13, the torsion section 14, the connection section 15, and the frame section 16 are aligned along the rotation axis R0.

[0021] The second drive unit 20 includes a drive section 21, a fixed section 22, a support section 23, a torsion section 24, a connection section 25, and a frame section 26. The movable section 30, the drive section 21, the fixed section 22, the support section 23, the torsion section 24, the connection section 25, and the frame section 26 are aligned along the rotation axis R0.

[0022] The first drive unit 10 and the second drive unit 20 are arranged facing opposite directions with the movable part 30 in between. The frame part 16 of the first drive unit 10 and the frame part 26 of the second drive unit 20 are each connected to the movable part 30.

[0023] The driving unit 11 is a tuning fork vibrator. The driving unit 11 includes a pair of arms 111 extending in an L-shape from a rotation axis R0, and piezoelectric drivers 112 formed on the upper surfaces of the pair of arms 111. The piezoelectric drivers 112 are formed on the upper surfaces of the linear portions of the arms 111 extending in the Y-axis direction.

[0024] The driving unit 21 is a tuning fork vibrator. The driving unit 21 includes a pair of arm portions 211 extending in an L-shape from the rotation axis R0, and piezoelectric driving bodies 212 formed on the upper surfaces of the pair of arm portions 211. The piezoelectric driving bodies 212 are formed on the upper surfaces of the linear portions of the arm portions 211 extending in the Y-axis direction.

[0025] The piezoelectric drivers 112, 212 have a layered structure in which electrode layers are disposed above and below piezoelectric thin films 112a, 212a of a predetermined thickness. The piezoelectric thin films 112a, 212a are made of a piezoelectric material with a high piezoelectric constant, such as lead zirconate titanate (PZT). The electrodes are made of a material with low electrical resistance and high heat resistance, such as platinum (Pt). The piezoelectric drivers 112, 212 are disposed on the upper surfaces of the arm portions 111, 211 by forming a layered structure including the piezoelectric thin films 112a, 212a and the upper and lower electrodes on the upper surfaces of these portions using a method such as sputtering.

[0026] The pair of drive units 11 are connected to the fixed unit 12 via the support unit 13. The pair of drive units 21 are connected to the fixed unit 22 via the support unit 23.

[0027] The torsion portions 14, 24 have a beam-like shape extending along the rotation axis R0. The cross sections of the torsion portions 14, 24 are rectangular. Here, the cross sections of the torsion portions 14, 24 are square. The cross sections of the torsion portions 14, 24 may also have other shapes, such as a rectangle or a circle.

[0028] A pair of drive units 11 are connected to the end of torsion unit 14 on the positive side of the Y axis, and the end of torsion unit 14 on the negative side of the Y axis is connected to frame unit 16 via connection unit 15. Furthermore, a pair of drive units 21 are connected to the end of torsion unit 24 on the negative side of the Y axis, and the end of torsion unit 24 on the positive side of the Y axis is connected to frame unit 26 via connection unit 25.

[0029] The substrate of the optical reflecting element 1 has the same contour as the optical reflecting element 1 in a plan view and a constant thickness. The reflecting surface 40 and the piezoelectric drivers 112, 212 are arranged in corresponding areas on the upper surface of the substrate. A predetermined material is further laminated on the lower surface of the portions of the substrate corresponding to the fixed portions 12, 22, the connecting portion 15, and the frame portion 16, thereby increasing the thickness of each of these portions. A predetermined material is also laminated in an area along the outer periphery of the lower surface of the movable portion 30, thereby forming a rib along the outer periphery of the lower surface of the movable portion 30. The material laminated on the substrate may be a different material from the substrate, or may be the same material as the substrate.

[0030] The substrate is integrally formed, for example, from silicon or the like. However, the material constituting the substrate is not limited to silicon and may be other materials. The material constituting the substrate is preferably a material with high mechanical strength and Young's modulus, such as metal, crystalline, glass, or resin. In addition to silicon, titanium, stainless steel, Elinvar, brass alloy, or the like can be used as such materials. The same applies to the material laminated on the substrate. An oxide film is formed in the region of the substrate where the laminated structure is to be formed, and a material for increasing the thickness is laminated on top of this oxide film.

[0031] 1, when the piezoelectric drivers 112 and 212 are driven by a drive signal, the pair of arms 111 and the pair of arms 211 vibrate in the Z-axis direction, and the torsion units 14 and 24 rotate repeatedly around the rotation axis R0. As a result, the movable unit 30 rotates repeatedly together with the frame unit 16, and the reflecting surface 40 rotates repeatedly.

[0032] Next, the structures of the connection portions 15, 25 and the frame portions 16, 26 will be described in more detail.

[0033] 4(a) and (b) are perspective views of the vicinity of the movable portion 30 as seen from above and below, respectively, and Figures 4(c) and (d) are plan views of the vicinity of the movable portion 30 as seen from above and below, respectively. Figure 5 is a cross-sectional view taken along A1-A1 in Figure 4(a).

[0034] As shown in Figures 4(b) and (d), ribs 31 are formed along the outer periphery of the movable part 30. As described above, the ribs 31 are formed by further laminating a material on the lower surface of the substrate. That is, as shown in Figure 5, an oxide film L3 is formed on the lower surface of the substrate layer L1 in the region of the ribs 31, and a material layer L2 is formed on the lower surface of this oxide film L3. The ribs 31 increase the rigidity of the movable part 30 and suppress deflection of the movable part 30 during rotation.

[0035] 4(a) to 4(d), a pair of frame portions 16, 26 are disposed outside the movable portion 30 in a plan view. The frame portions 16, 26 are disposed outside the movable portion 30 with predetermined gaps 17, 27 therebetween, and are connected to the movable portion 30 at two positions P11 symmetrical with respect to the rotation axis R0. The gaps 17, 27 extend in an arc shape along a circle concentric with the center of the movable portion 30. The width of the gaps 17, 27 is constant except for both ends. The frame portions 16, 27 are formed in an arc shape along the gaps 17, 27.

[0036] The frame portions 16, 26 have a greater thickness and thus a higher rigidity than the region of the movable portion 30 other than the ribs 31. That is, as shown in Fig. 5, an oxide film L3 is formed in the region of the frame portions 16, 26 on the lower surface of the base layer L1, and a material layer L2 is formed on the lower surface of this oxide film L3. This makes the frame portions 16, 26 more rigid than the rigidity of the movable portion 30 other than the ribs 31. As shown in Fig. 5, the gaps 17, 27 penetrate vertically.

[0037] 4B, the thickness of the connecting portions 15, 25 is greater than the thickness of the torsion portions 14, 24. This makes the rigidity of the connecting portions 15, 25 greater than the rigidity of the torsion portions 14, 24.

[0038] The connection portions 15, 25 have thickness ranges 15a, 25a (hereinafter referred to as "bonding ranges 15a, 25a") that are connected to the torsion portions 14, 24, and thickness ranges 15b, 25b (hereinafter referred to as "non-bonding ranges 15b, 25b") that are not connected to the torsion portion 14. The bonding ranges 15a, 25a correspond to the base layer L1 in Fig. 5, and the non-bonding ranges 15b, 25b correspond to the material layer L2 and oxide film L3 in Fig. 5. The connection portions 15, 25 have a greater rigidity than the torsion portions 14, 24 by being wider in thickness than the torsion portions 14, 24 by the non-bonding ranges 15b, 25b.

[0039] Fig. 6 is a perspective view showing the structure of the connection portions 15, 25. For convenience, Fig. 6 shows the torsion portions 14, 24 in a see-through state, and the torsion portions 14, 24 are indicated by dashed lines.

[0040] In the joining range 15a, a joining surface between the torsion portion 14 and the connection portion 15 is formed at the boundary between the torsion portion 14 and the connection portion 15. Here, a pair of joining surfaces S11, a pair of joining surfaces S12, and one joining surface S13 are formed at the boundary between the torsion portion 14 and the connection portion 15. In Fig. 6, of the pair of joining surfaces S12, the joining surface S12 on the negative side of the X-axis is hidden by the part of the connection portion 15 on the negative side of the X-axis and is therefore not visible.

[0041] The pair of joint surfaces S12 are surfaces parallel to the Y-Z plane and parallel to the rotation axis R0 in a plan view. Furthermore, the pair of joint surfaces S12 are inclined in opposite directions by the same angle with respect to the rotation axis R0 in a plan view. Of the angles formed by each of the pair of joint surfaces S12 and the rotation axis R0, the angle θ (see FIG. 4(d)) on the torsion portion 14 side is an acute angle. Here, the angle θ is set to approximately 45°. The joint surface S12 is a plane parallel to the Z axis. The joint surface S13 is approximately perpendicular to the rotation axis R0. The shape of the joint surface S13 in a plan view is an arc with the same diameter as the outer periphery of the frame portion 16.

[0042] The non-bonding area 15b is formed with a pair of wall surfaces S21 that connect to the pair of bonding surfaces S11 in the negative direction of the Z axis, and a pair of wall surfaces S22 that connect to the pair of bonding surfaces S12 in the negative direction of the Z axis. Furthermore, the non-bonding area 15b is formed with a wall surface S23 that connects to the bonding surface S13 in the negative direction of the Z axis. The bonding surface S11 and the wall surface S21 connected thereto are parallel to each other and are flush with each other. The bonding surface S12 and the wall surface S22 connected thereto are parallel to each other and are flush with each other. The bonding surface S13 and the wall surface S23 connected thereto are parallel to each other and are flush with each other.

[0043] A pair of wall surfaces S21, a pair of wall surfaces S22, and a wall surface S23 are formed in the non-bonding area 15b, and thereby bonding surfaces S11, S12, and S13 extending from these wall surfaces in the positive direction of the Z axis are formed in the bonding area 15a. That is, the shapes of the pair of bonding surfaces S11, S12, and S13 in a plan view are determined by the shapes of the pair of wall surfaces S21, S22, and S23 in a plan view. Since adjacent wall surfaces S21, S22 and adjacent wall surfaces S22, S23 abut each other on their boundaries, adjacent bonding surfaces S11, S12 and adjacent bonding surfaces S12, S13 also abut each other on their boundaries.

[0044] Similar to the joining area 15a of the connection portion 15, the joining area 25a of the connection portion 25 on the negative side of the Y axis also has a pair of joining surfaces S11, a pair of joining surfaces S12, and a pair of joining surfaces S13. Similarly to the non-joining area 15b of the connection portion 15, the non-joining area 25b of the connection portion 25 on the negative side of the Y axis also has a pair of wall surfaces S21, a pair of wall surfaces S22, and a pair of wall surfaces S23. The pair of joining surfaces S11 on the connection portion 25 side are also parallel to the rotation axis R0. The angle θ between the pair of joining surfaces S12 on the connection portion 25 side and the rotation axis R0 on the torsion portion 24 side is also an acute angle (here, approximately 45°).

[0045] In this embodiment, by forming a pair of bonding surfaces S11 and a pair of bonding surfaces S12 on the connecting portions 15 and 25 in this manner, stress applied from the torsion portions 14 and 24 to the connecting portions 15 and 25 during rotation of the movable portion 30 is suppressed. This suppresses deflection of the frame portions 16 and 26, and as a result, suppresses deflection of the movable portion 30 and the reflecting surface 40. This effect will be described below in comparison with a comparative example.

[0046] Figures 7(a) and (b) are oblique views of the area around the movable part 30 of the optical reflecting element 1 according to the comparative example, as viewed from above and below, respectively, and Figures 7(c) and (d) are plan views of the area around the movable part 30 of the optical reflecting element 1 according to the comparative example, as viewed from above and below, respectively.

[0047] In the comparative example, as shown in Figures 7(a) to 7(d), only the configuration of the connecting portions 18, 28 differs from the connecting portions 15, 25 of the above embodiment. The configuration of the optical reflecting element 1 other than the connecting portions 18, 28 is the same as the configuration of the embodiment shown in Figures 1 to 6. That is, in the comparative example, the thickness of the connecting portions 18, 28 is the same as the thickness of the torsion portions 14, 24. The connecting portions 18, 28 are composed only of the base material layer L1 of Figure 5.

[0048] The width of the connection portions 18, 28 gradually increases toward the frame portions 16, 26. The connection portions 18, 28 are connected to the frame portion 16 at a joint surface S30. The shape of the joint surface S30 in a plan view is an arc. 7B and 7D show the edge of the joint surface S30 on the negative side of the Z axis. The joint surface S30 extends from this arc-shaped edge in the positive direction of the Z axis of the frame portions 16, 26 to the lower surface of the connection portion 18 on the negative side of the Z axis.

[0049] The inventors conducted simulations to determine the deflections of the frame portions 16, 26 and the movable portion 30 for the optical reflecting element 1 according to the comparative example and the optical reflecting element 1 according to the above embodiment.

[0050] In this simulation, the diameter of the movable portion 30 (including the rib 31) was set to 1.0 mm, and the radial widths of the frame portions 16, 26 and the radial widths of the gaps 17, 27 were all set to 25 μm. The thickness of the base layer L1 shown in FIG. 5 was set to 150 μm, and the thickness of the material layer L2 was set to 140 μm. The thickness of the oxide film L3 was set to 1 μm. For the optical reflecting element 1 of the comparative example and the embodiment configured in this manner, the reflecting surface 40 (movable portion 30) was repeatedly rotated at 60 kHz. The optical scanning angle (optical total angle) of the reflecting surface 40 due to the repeated rotation was set to 65° in both the comparative example and the embodiment.

[0051] In the verification, the amount of deflection of each part (divided element) when the movable part 30 and the frame parts 16, 26 are in the most deflected state when the movable part 30 is rotated according to the above conditions was found by the finite element method. The amount of deflection was found as the difference in height between the position of each part of the movable part 30 and the frame parts 16, 26 when the movable part 30 and the frame parts 16, 26 are rotated without deflection (reference position) and the actual position of each part of the movable part 30 and the frame parts 16, 26 (varied position).

[0052] A positive sign is assigned to the difference when each part is displaced upward from its undeflected state, and a negative sign is assigned to the difference when each part is displaced downward from its undeflected state. The position of each part is assigned a positive sign when it moves away from the rotation axis R0 in one direction parallel to the reflecting surface 40 and perpendicular to the rotation axis R0, and a negative sign is assigned to the position on the reference plane when it moves away from the rotation axis R0 in the other direction parallel to the reflecting surface 40 and perpendicular to the rotation axis R0.

[0053] FIG. 8A is a graph showing the verification results according to the comparative example, and FIG. 8B is a graph showing the verification results according to the embodiment.

[0054] 8(a) and 8(b), the horizontal axis indicates the position of each of the above-mentioned parts, and the vertical axis indicates the amount of deflection at each position. Here, the amount of deflection (amount of positional deviation in the height direction) of each part when viewed parallel to the rotation axis R0 is plotted on the graph. The units of the vertical and horizontal axes are μm.

[0055] In Figures 8(a) and (b), the data group that changes in a sinusoidal manner indicates the amount of deflection at each position of the frame portions 16 and 26, and the data group in the form of a straight band with the vertical axis value near zero indicates the amount of deflection at each position of the movable portion 30.

[0056] 8A and 8B, in the configuration of the embodiment, the fluctuation width W11 of the amount of deflection of the frame portions 16, 26 is reduced compared to the fluctuation width W12 of the amount of deflection of the frame portions 16, 26 in the configuration of the comparative example. Furthermore, in the configuration of the embodiment, the fluctuation width W21 of the amount of deflection of the movable portion 30 is reduced compared to the fluctuation width W22 of the amount of deflection of the movable portion 30 in the configuration of the comparative example. Specifically, in the configuration of the comparative example, the fluctuation width W22 of the amount of deflection of the movable portion 30 was 64 nm. In contrast, in the configuration of the embodiment, the fluctuation width W21 of the amount of deflection of the movable portion 30 was 53 nm, which was reduced by approximately 20% compared to the comparative example.

[0057] As described above, in the configuration of the embodiment, the deflection of the movable part 30 when it rotates is more effectively suppressed than in the comparative example, and the deformation of the reflecting surface 40 into a concave or convex surface during the rotation operation is effectively suppressed, thereby more reliably suppressing the beam from spreading on the scanning line.

[0058] 8B, in the configuration of the embodiment, the deflection of the frame portions 16, 26 is larger than the sinusoidal waveform in the regions G1, G2. However, since the regions G1, G2 are located close to the rotation axis R0, they are less likely to affect the deflection of the movable portion 30.

[0059] That is, as shown in FIG. 4B , the movable portion 30 is connected to the frame portions 16 and 26 at positions P11 near the ends furthest from the positive and negative X-axis sides. Therefore, when the frame portions 16 and 26 are rotated, the deflection in the ranges near these positions P11 significantly affects the deflection of the movable portion 30. These ranges near P11 correspond to ranges R11 and R12 in FIGS. 8A and 8B . On the other hand, regions G1 and G2 are located inside the ranges R11 and R12 and are not included in the ranges R11 and R12. Therefore, the deflection of the frame portions 16 and 26 in the regions G1 and G2 is less likely to affect the deflection of the movable portion 30. As a result, in the configuration of the embodiment, despite the large deflection occurring in the regions G1 and G2, the deflection of the movable portion 30 is suppressed compared to the comparative example.

[0060] Next, the inventors investigated the mechanism by which the deflection of the frame portions 16, 26 is suppressed in the configuration of the embodiment. First, the inventors conducted a simulation to determine the stress distribution that occurs in the oxide film L3 when the movable portion 30 is repeatedly rotated under the above simulation conditions.

[0061] 9A shows the simulation results of the stress distribution in the oxide film L3 in the configuration of the comparative example, and FIG. 9B shows the simulation results of the stress distribution in the oxide film L3 in the configuration of the embodiment. For convenience, the simulation results are shown in grayscale in FIGS. 9A and 9B, with the minimum value in blue and the maximum value in red.

[0062] 9(a) and 9(b) show the stress distribution when the movable part 30 is rotated at the maximum swing angle. While Figures 9(a) and 9(b) show the stress distribution at the end on the positive side of the Y axis, the stress distribution at the end on the negative side of the Y axis was also substantially similar to Figures 9(a) and 9(b).

[0063] As shown in FIG. 9A , in the configuration of the comparative example, stress is concentrated at a position P0 corresponding to the vicinity of the center of the bonding surface S30 (see FIGS. 7B and 7D ). In contrast, in the configuration of the embodiment, as shown in FIG. 9B , stress is dispersed to a position P1 corresponding to the pair of bonding surfaces S11, the pair of bonding surfaces S12, and the bonding surface S13 (see FIG. 6 ). It is believed that this stress distribution is caused by the deformation of the oxide film L3 accompanying the deformation of the base layer L1 adjacent to the oxide film L3 during the pivoting operation. Therefore, it is assumed that a stress distribution similar to that shown in FIG. 9A occurs at the bonding surface S30 in the configuration of the comparative example, and that a stress distribution similar to that shown in FIG. 9B occurs at the pair of bonding surfaces S11, the pair of bonding surfaces S12, and the bonding surface S13 in the configuration of the embodiment.

[0064] FIG. 10A is a plan view schematically showing the propagation of stress according to a comparative example, and FIG. 10B is a plan view schematically showing the propagation of stress according to the embodiment.

[0065] 10A, in the comparative example, when the torsion portion 14 rotates, stress concentrates in a region M0 at the center of the torsion portion 14, through which the rotation axis R0 passes. In the comparative example, because only the bonding surface S30, which is a circular arc shaped surface that bulges slightly in the Y-axis direction, exists, the stress in the region M0 propagates to a position P10 near the center of the bonding surface S30 in the X-axis direction. Therefore, in the oxide film L3, as shown in the above verification results, high stress is localized at a position P0 that is close in the Z-axis direction to the position P10 at the center of the bonding surface S30.

[0066] 10B , in addition to the bonding surface S13, a pair of bonding surfaces S11 that are symmetrical and parallel with respect to the rotation axis R0 and a pair of bonding surfaces S11 that are symmetrical with respect to the rotation axis R0 and inclined at a predetermined angle are arranged. That is, the pair of bonding surfaces S11, the pair of bonding surfaces S12, and the bonding surface S13 are arranged so as to surround the end of the region M0 on the negative side of the Y axis. Therefore, the stress localized in the region M0 is dispersed to the pair of bonding surfaces S11 and the pair of bonding surfaces S12 as well as the bonding surface S13.

[0067] As a result, the stress generated at position P11 near the center of each of the pair of bonding surfaces S11, the pair of bonding surfaces S12, and the bonding surface S13 is less than the stress generated at position P10 in the comparative example. Therefore, in the oxide film L3, as shown in the above verification results, the stress is dispersed to position P1, which is closer in the Z-axis direction to position P11 on the bonding surfaces S11, S12, and S13, and this stress is less than the stress generated at position P0 in the comparative example.

[0068] As described above, in the comparative example, the stress generated when the movable part 30 rotates is concentrated at one point on the bonding surface S30, resulting in a steep deflection distribution of the frame part 16 and a large amount of deflection of the movable part 30, as shown in Fig. 8(a). In contrast, in the embodiment, the stress generated when the movable part 30 rotates is distributed to the pair of bonding surfaces S11, the pair of bonding surfaces S12, and the bonding surface S13, resulting in a gentler deflection distribution of the frame part 16 than in the comparative example, as shown in Fig. 8(b), and the amount of deflection of the movable part 30 is reduced. As a result, the configuration of the embodiment can effectively reduce deformation of the reflecting surface 40 when the movable part 30 rotates, thereby reducing the spread of the scanning beam.

[0069] 10(b), the torsion portion 14 includes a shaft portion 14a extending along the rotation axis R0 and a wide portion 14b formed at the end of the shaft portion 14a on the frame portion 16 side. In a plan view, the wide portion 14b is wider than the shaft portion 14a and is connected to the connection portion 15 via a pair of joint surfaces S11, a pair of joint surfaces S12, and a pair of joint surfaces S13. The other end of the shaft portion 14a is connected to the pair of drive units 11.

[0070] Here, if the wide portion 14b has spring properties due to a surface spring, this spring property can contribute to gradual deflection distribution of the frame portion 16 when the shaft portion 14a rotates. In this case, in the configuration of the embodiment, in addition to dispersing stress on the joint surfaces S11 to S13, the spring property of the wide portion 14b can effectively suppress deflection of the frame portion 16.

[0071] The region M0 where the stress is greatest occurs near the central axis of the shaft portion 14a, and this stress is dispersed to the pair of bonding surfaces S11, S12, and S13 via the wide portion 14b. The pair of bonding surfaces S11, S12, and S13 are set to surround the end point of the central axis of the shaft portion 14a on the wide portion 14b side. This makes it easier to distribute the stress to these bonding surfaces S11 to S13, and makes it easier to make the deflection distribution of the frame portion 16 gentler.

[0072] <Effects of the embodiment> According to the above embodiment, the following effects can be achieved.

[0073] 9(b) and 10(b), stress generated when the movable part 30 rotates is easily dispersed over the pair of joint surfaces S11 and the pair of joint surfaces S12. As a result, as shown in FIG. 8(b), the bending of the frame parts 16, 26 when the movable part 30 rotates is gentle, and bending of the movable part 30 connected to the frame parts 16, 26 is suppressed. Therefore, even when the movable part 30 is driven at a high frequency and a large deflection angle, bending of the movable part 30 and the reflecting surface 40 can be effectively suppressed.

[0074] 6, the connection portions 15, 25 have a thickness range (non-bonding range 15b) that is greater than the thickness of the torsion portion 14 and is not connected to the torsion portion 14, and wall surfaces S21, S22 that connect to the bonding surfaces S11, S12 are formed in this thickness range (non-bonding range 15b). According to this configuration, by forming a pair of wall surfaces S21 and a pair of wall surfaces S22 in the non-bonding range 15b, a pair of bonding surfaces S11 and a pair of bonding surfaces S12 that connect to the pair of wall surfaces S21 and the pair of wall surfaces S22 in the positive direction of the Z axis can be formed in the bonding range 15a.

[0075] 6, the pair of joint surfaces S11 are parallel to the rotation axis R0, and the pair of joint surfaces S12 are non-parallel to the rotation axis R0. This allows the stress generated during repeated rotation of the movable part 30 to be distributed to the pair of joint surfaces S11 and also to the pair of joint surfaces S12. This effectively prevents the frame parts 16 and 26 from bending during rotation, and effectively prevents the movable part 30 and the reflecting surface 40 from bending.

[0076] 6 , the connecting portions 15, 25 have a pair of joint surfaces S11 (a first pair of joint surfaces) and a pair of joint surfaces S12 (a second pair of joint surfaces) that are positioned closer to the frame portions 16, 26 than the pair of joint surfaces S11 and form a larger angle with the rotation axis R0 than the pair of joint surfaces S11. As a result, the pair of joint surfaces S11 and the pair of joint surfaces S12 are positioned to surround the end of the torsion portion 14 on the negative side of the Y axis, and stress generated during repeated rotation is easily distributed to the pair of joint surfaces S11 and the pair of joint surfaces S12. Therefore, deflection of the frame portions 16, 26 during rotation can be effectively suppressed, and deflection of the movable portion 30 and the reflecting surface 40 can also be effectively suppressed.

[0077] 1 and 2, a first drive unit 10 including a frame portion 16, a torsion portion 14, a connection portion 15, a pair of drive portions 11, and a fixed portion 12, and a second drive unit 20 including a frame portion 26, a torsion portion 24, a connection portion 25, a pair of drive portions 21, and a fixed portion 22 are arranged in opposite directions with a movable portion 30 in between, and the frames 16, 26 of each drive unit are connected to the movable portion 30. In this way, by supporting and driving the movable portion 30 with each drive unit, the movable portion 30 can be driven stably with greater torque.

[0078] 1, the driving units 11 and 21 are tuning-fork type driving units and have piezoelectric thin films 112a and 212a as driving sources, thereby allowing the movable unit 30 to rotate smoothly and repeatedly about the rotation axis R0.

[0079] <Modifications> In the above embodiment, the pair of joining surfaces S11 and the pair of joining surfaces S12 are formed on the connecting portions 15, 25, but one of the joining surfaces may be omitted.

[0080] 11(a), a pair of joint surfaces S14 parallel to the rotation axis R0 and a joint surface S13 intersecting the rotation axis R0 may be formed on each of the connecting portions 15 and 25. Alternatively, as shown in FIG. 11(b), a pair of joint surfaces S14 inclined with respect to the rotation axis R0 and a joint surface S13 intersecting the rotation axis R0 may be formed on each of the connecting portions 15 and 25.

[0081] These configurations also allow the stress generated during repeated rotation of the movable part 30 to be distributed to the pair of joint surfaces S14 or the pair of joint surfaces S15. Therefore, deflection of the frames 16 and 26 during rotation can be effectively suppressed, and deflection of the movable part 30 and the reflecting surface 40 can be effectively suppressed.

[0082] In the above embodiment, the pair of joining surfaces S11 and the pair of joining surfaces S12 are flat surfaces, but these joining surfaces may be curved surfaces.

[0083] 12( a), a pair of joint surfaces S16 that face each other across the rotation axis R0 and a joint surface S13 that intersects with the rotation axis R0 may be formed on each of the connection portions 15 and 25. Here, the shape of the pair of joint surfaces S16 is set to a curved shape that is concave in a direction away from the rotation axis R0 and has a generatrix parallel to the Z axis. As in the above embodiment, the shape of such joint surfaces S16 can be set by adjusting the shape of the wall surface that connects to the joint surfaces S16 in the non-joining regions 15b of the connection portions 15 and 25 to the same shape as the joint surfaces S16 in a plan view.

[0084] This configuration also allows the stress generated during repeated rotation of the movable part 30 to be distributed across the pair of joint surfaces S16. Therefore, deflection of the frames 16, 26 during rotation can be effectively suppressed, and deflection of the movable part 30 and the reflecting surface 40 can also be effectively suppressed.

[0085] In addition, in the above embodiment, the pair of joint surfaces S11 are parallel to the rotation axis R0, but the pair of joint surfaces S11 may be non-parallel to the rotation axis R0. For example, as shown in Fig. 12(b), the pair of joint surfaces S11 may be inclined so that the angle between the pair of joint surfaces S11 and the rotation axis R0 is an acute angle.

[0086] Also, as shown in Figure 12 (b), a gap 19 may be formed between the ends of the pair of joint surfaces S12 on the movable part 30 side, and the torsion parts 14, 24 and the connection parts 15, 25 may be separated in this gap 19.

[0087] This configuration also allows the stress generated during repeated rotation of the movable part 30 to be distributed between the pair of joint surfaces S11 and the pair of joint surfaces S12. Therefore, deflection of the frames 16 and 26 during rotation can be effectively suppressed, and deflection of the movable part 30 and the reflecting surface 40 can be effectively suppressed.

[0088] Similarly, in the modified examples shown in FIGS. 11(a) to 12(a), a gap penetrating in the Z-axis direction may be provided within the range of the joining surface S13.

[0089] In the above embodiment, the first drive unit 10 and the second drive unit 20 are arranged to sandwich the movable part 30 in the Y-axis direction. However, for example, as shown in Fig. 13, the second drive unit 20 may be omitted and the movable part 30 may be rotated by only the first drive unit 10. Even in this configuration, stress generated in the torsion part 14 during repeated rotation of the movable part 30 is distributed among the pair of joint surfaces S11, the pair of joint surfaces S12, and the joint surface S13, thereby suppressing deflection of the frame part 16. Therefore, deflection of the movable part 30 and the reflecting surface 40 during rotation can be effectively suppressed.

[0090] Furthermore, in the above embodiment and modified examples, the shape of the movable part 30 is circular, but the shape of the movable part 30 may be other shapes, such as a square. The shape of the optical reflecting element 1 in a planar view and the dimensions of each part of the optical reflecting element 1 can also be changed as appropriate. The simulation conditions shown in the verification, the optical scanning angle of the reflecting surface 40, and the frequency of repeated rotation are also examples, and the values ​​of the various parameters are not limited to these values.

[0091] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the technical ideas set forth in the claims.

[0092] REFERENCE SIGNS LIST 1 Optical reflecting element 10 First driving unit 20 Second driving unit 30 Movable part 40 Reflecting surface 11, 21 Driving part 12 Fixed part 15, 25 Connecting part 16, 26 Frame part 17, 27 Gap 112a, 212a Piezoelectric thin film S11, S12, S13, S14, S15, S16 Bonding surface S21, S22, S23 Wall surface

Claims

1. An optical reflecting element comprising: a movable part that rotates about a rotation axis; a reflective surface arranged on said movable part; a frame part that is arranged outside said movable part with a specified gap in a plan view and is connected to said movable part at two positions symmetrical about said rotation axis; a beam-shaped torsion part that extends along said rotation axis; a connection part that connects one end of said torsion part to said frame part; a pair of drive parts that are connected to the other end of said torsion part and rotate said torsion part about said rotation axis; and a fixing part that supports said pair of drive parts, wherein said connection part has higher rigidity than said torsion part, and at least a pair of joint surfaces are formed at the boundary between said torsion part and said connection part, and said pair of joint surfaces are symmetrical about said rotation axis and each of the angles that the torsion part side forms with said rotation axis is an acute angle.

2. An optical reflecting element according to claim 1, wherein the connecting portion has a thickness range that is greater than the thickness of the torsion portion and is not connected to the torsion portion, and a wall surface that connects to the bonding surface is formed within the thickness range.

3. An optical reflecting element according to claim 1 or 2, characterized in that the pair of bonding surfaces are parallel to the rotation axis.

4. An optical reflecting element according to claim 1 or 2, characterized in that the pair of bonding surfaces are not parallel to the rotation axis.

5. An optical reflecting element according to claim 1 or 2, characterized in that the at least one pair of bonding surfaces comprises a first pair of bonding surfaces and a second pair of bonding surfaces that are positioned closer to the frame portion than the first pair of bonding surfaces and that form a larger angle with the rotation axis than the first pair of bonding surfaces.

6. An optical reflecting element according to claim 5, wherein the first pair of bonding surfaces are parallel to the rotation axis.

7. An optical reflecting element according to any one of claims 1 to 6, characterized in that two drive units each having the frame portion, the torsion portion, the connection portion, the pair of drive portions and the fixed portion are arranged in opposite directions with the movable portion in between, and the frame portion of each drive unit is connected to the movable portion.

8. An optical reflecting element according to any one of claims 1 to 7, characterized in that the driving section has a piezoelectric thin film as a driving source.