Optical reflection element

Abstract

An optical reflection element comprises a fixed part and a movable part (40) that is rotatably supported by the fixed part with respect to a rotational axis (R10). The movable part (40) has: a central part (41) that has a structure obtained by removing a base layer and an oxide film from an SOI wafer in which a base layer, an oxide film, and an active layer are laminated, and that has a reflective surface (40a) disposed on the upper surface of the active layer; a rib part (42) that is disposed outside the central part (41) with a gap (GP) therebetween; and a flexible spring part (60), both ends of which are connected to the rib part (42), and which is connected to the central part (41) between both ends.

Description

Optical Reflective Elements

[0001] The present invention relates to an optical reflecting element having a movable portion on which a reflecting surface is formed.

[0002] An optical reflecting element having a movable part on which a reflective surface is formed is known. In this type of optical reflecting element, for example, the reflective surface is disposed on a movable part that rotates about a rotation axis, and a beam incident on the reflective surface is scanned as the movable part rotates.

[0003] Japanese Patent Application Laid-Open No. 2006-101494 (Patent Document 1) describes an optical scanner including a movable body that can swing around an axis and a drive unit that swings the movable body around the axis. The movable body includes a light reflecting plate and a support frame that surrounds the light reflecting plate and is thicker than the light reflecting plate. Each part of the optical scanner is formed by removing unnecessary portions of an SOI (Silicon On Insulator) wafer using various etching methods such as dry etching and wet etching.

[0004] JP 2013-222155 A

[0005] In the production of an SOI wafer, a base layer is thermally oxidized at a temperature of approximately 1100°C to form an oxide film on the surface of the base layer, and then an active layer is bonded to the oxide film. The base layer has a larger thermal expansion coefficient than the oxide film, and tends to shrink more than the oxide film when returned to room temperature, causing compressive stress from the base layer to act on the oxide film. When such an SOI wafer is processed to remove the base layer and oxide film from the central region of the movable part and form a rib portion in the peripheral region, the removal of the base layer in the central region partially releases the compressive stress acting on the oxide film in the rib portion, causing the oxide film to expand. This causes a force from the oxide film to act on the active layer in the central region toward the center of the movable part, resulting in deflection of the active layer in the central region.

[0006] In view of the above problem, an object of the present invention is to provide an optical reflecting element that can suppress deflection of a movable portion when a rib portion is formed on the movable portion by processing an SOI wafer.

[0007] The optical reflecting element according to a main aspect of the present invention comprises a fixed portion and a movable portion supported by the fixed portion so as to be rotatable about a rotation axis, the movable portion having a structure in which a base layer, an oxide film, and an active layer are stacked on an SOI wafer, with the base layer and the oxide film removed, the movable portion having a central portion with a reflective surface disposed on an upper surface of the active layer, a rib portion disposed outside the central portion with a gap therebetween, and a flexible spring portion having both ends connected to the rib portion and connected between the both ends to the central portion.

[0008] In the production of an SOI wafer, a base layer is thermally oxidized at a temperature of approximately 1100°C to form an oxide film on the surface of the base layer, and then an active layer is bonded to the oxide film. The base layer has a larger thermal expansion coefficient than the oxide film and tends to shrink relative to the oxide film when returned to room temperature, causing compressive stress from the base layer to act on the oxide film. When such an SOI wafer is processed to remove the base layer and oxide film from the central region of the movable part and form a rib portion in the peripheral region, the removal of the base layer in the central region partially releases the compressive stress acting on the oxide film in the rib portion, causing the oxide film to expand. This causes a force from the oxide film to act on the central active layer in the direction toward the center of the central part, resulting in bending of the central active layer.

[0009] In contrast, in the optical reflecting element according to this embodiment, the central portion and the rib portion are disposed with a gap therebetween, and a spring portion is provided whose both ends are connected to the rib portion and whose space between the both ends is connected to the central portion. As a result, the expansion of the oxide film in the rib portion is absorbed by the spring portion and is less likely to propagate to the central portion, making it less likely for the central portion to bend. Therefore, when the rib portion is formed on the movable portion using an SOI wafer, it is possible to suppress the bending of the movable portion.

[0010] As described above, according to the present invention, it is possible to provide an optical reflecting element that can suppress deflection of the movable portion when a rib portion is formed on the movable portion by processing an SOI wafer.

[0011] 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.

[0012] FIG. 1 is a plan view schematically showing the configuration of an optical reflecting element according to the first embodiment. FIGS. 2(a) to 2(d) are cross-sectional views showing a procedure for producing an SOI wafer according to the first embodiment. FIGS. 3(a) and 3(b) are a plan view and a cross-sectional view, respectively, schematically showing the configuration of a movable portion according to a first comparative example. FIGS. 4(a) and 4(b) are a plan view and a cross-sectional view, respectively, schematically showing the configuration of a movable portion according to a second comparative example. FIG. 5(a) is a plan view schematically showing the configuration of a movable portion according to the first embodiment. FIG. 5(b) is a plan view showing in detail the vicinity of the end of the movable portion on the negative side of the Y-axis according to the first embodiment. FIG. 6(a) is a cross-sectional view taken along C3-C4 in the plan view of FIG. 5(a) according to the first embodiment. FIG. 6(b) is a cross-sectional view taken along C1-C2 in the plan view of FIG. 5(a) according to the first embodiment. FIGS. 7(a) and 7(b) are diagrams showing the size setting of the movable portion according to the simulations of the first and second comparative examples, respectively. FIG. 8 is a diagram showing the size setting of the movable portion according to the simulation of the first embodiment. FIG. 9A is a plan view schematically illustrating the configuration of a movable section according to the second embodiment. FIG. 9B is a plan view showing in detail the vicinity of the end of the movable section on the negative side of the Y-axis according to the second embodiment. FIG. 10A is a plan view schematically illustrating the configuration of a movable section according to the second embodiment. FIG. 10B is a plan view showing in detail the vicinity of the end of the movable section on the negative side of the Y-axis according to the second embodiment. FIG. 11 is a plan view schematically illustrating the configuration of a movable section according to a modified example of the second embodiment. FIG. 12 is a diagram illustrating the size setting of the movable section according to a simulation of the second embodiment. FIG. 13 is a simulation result showing the deformation rate with respect to the connection angle according to the second embodiment. FIGS. 14A and 14B are simulation results showing the distribution of the deformation degree of the central section according to the second embodiment. FIGS. 15A and 15B are simulation results showing the distribution of the deformation degree of the central section according to the second embodiment. FIG. 16 is a simulation result showing the deformation rate with respect to the length of the connecting section according to the second embodiment. 17(a) and 17(b) are a plan view and a cross-sectional view, respectively, that schematically show the configuration of a movable part according to embodiment 3. Figures 18(a) and 18(b) are a plan view and a cross-sectional view, respectively, that schematically show the configuration of a movable part according to embodiment 4.FIG. 19 shows simulation results illustrating the distribution of the degree of deformation of the central portion according to the fourth embodiment. FIGS. 20(a) and 20(b) are a plan view and a cross-sectional view, respectively, that schematically illustrate the configuration of the movable portion according to the fifth embodiment. FIG. 21 shows simulation results illustrating the distribution of the degree of deformation of the central portion according to the fifth embodiment. FIGS. 22(a) and 22(b) are a plan view and a cross-sectional view, respectively, that schematically illustrate the configuration of the movable portion according to the sixth embodiment. FIG. 23 is a cross-sectional view that schematically illustrates the configuration of the movable portion according to a modified example of the sixth embodiment. FIGS. 24(a) to 24(c) are plan views that schematically illustrate the configuration of the movable portion according to a modified example of the arrangement of the spring portion. FIGS. 25(a) to 25(c) are plan views that schematically illustrate the configuration of the movable portion according to a modified example of the shape of the spring portion. FIGS. 26(a) to 26(c) are plan views that schematically illustrate the configuration of the movable portion according to a modified example of the shape of the central portion and the rib portion. 27(a) and 27(b) are plan views each showing a schematic configuration of a movable portion according to a modified example of the shape of the central portion and the rib portion, and Fig. 28 is a plan view showing a schematic configuration of an optical reflecting element according to a modified example of the vibration portion.

[0013] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0014] 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 positive direction of the Z axis is the vertically upward direction.

[0015] First Embodiment FIG. 1 is a plan view schematically showing the configuration of an optical reflecting element 1. As shown in FIG.

[0016] The optical reflecting element 1 includes a fixed portion 10, a pair of vibrating portions 21 to 24, a pair of connecting portions 31 to 34, a pair of connecting beams 35, a movable portion 40, and eight driving portions 50. The optical reflecting element 1 is configured to be point symmetric with respect to a center C10. The optical reflecting element 1 is formed by processing an SOI wafer 100 (see FIG. 2(d)). The generation of the SOI wafer 100 will be described later with reference to FIGS. 2(a) to 2(d).

[0017] The fixed part 10 is configured in a frame shape. In a plan view, the pair of vibrating parts 21 to 24, the pair of connecting parts 31 to 34, and the pair of connecting beams 35 are located within an opening 11 that penetrates the fixed part 10 in the Z-axis direction at the center of the fixed part 10, and are disposed between the fixed part 10 and the movable part 40. On the positive side and the negative side of the X-axis of the movable part 40, pairs of vibrating parts 21 to 24, connecting parts 31 to 34, and connecting beam 35 are disposed, respectively. The pairs of vibrating parts 21 to 24 located on the positive side and the negative side of the X-axis of the movable part 40 each have a meander shape in a plan view.

[0018] The movable portion 40 has a circular outline in a plan view. The movable portion 40 is supported by the fixed portion 10 so as to be rotatable about a rotation axis R10 via a pair of vibrating portions 21 to 24, a pair of connecting portions 31 to 34, and a pair of connecting beams 35. The center of the movable portion 40 coincides with the position of the center C10 of the optical reflecting element 1. The movable portion 40 has a central portion 41 disposed in the central region, and a rib portion 42 disposed outside the central portion 41 with a gap therebetween. The rib portion 42 has a structure that protrudes in the negative direction of the Z axis relative to the central portion 41.

[0019] The upper surface of the central portion 41 (the upper surface of the active layer 103 corresponding to the central portion 41, which will be described later) is a reflective surface 40a that reflects light. Normally, the upper surface of the active layer 103 has sufficient reflectivity due to the generation of the SOI wafer 100, so the upper surface of the active layer 103 can be used as the reflective surface 40a. If the reflectivity of the upper surface of the active layer 103 is insufficient, the reflectivity of the upper surface of the active layer 103 may be increased by polishing the upper surface of the active layer 103. The configuration of the movable portion 40 will be described later with reference to FIGS. 5( a) to 6(b).

[0020] A driving unit 50 is disposed on the upper surface of each pair of vibrating units 21-24. The driving unit 50 has a layer structure consisting of a lower electrode layer, a piezoelectric layer, and an upper electrode layer. The driving unit 50 is connected to electrodes on the fixed unit 10 via the vibrating units 21-24, the connecting units 31-34, and wiring on the fixed unit 10. A cable (external wiring) leading to an external device is connected to the electrode on the fixed unit 10 by wire bonding.

[0021] When a drive voltage of the same phase is applied to the drive units 50 on the vibrating units 21 and 23, the piezoelectric layers in the drive units 50 on the vibrating units 21 and 23 deform due to the inverse piezoelectric effect, causing the vibrating units 21 and 23 to vibrate and flex. On the other hand, when a drive voltage of the opposite phase to the drive voltage applied to the drive units 50 on the vibrating units 21 and 23 is applied to the drive units 50 on the vibrating units 22 and 24, the piezoelectric layers in the drive units 50 on the vibrating units 22 and 24 deform due to the inverse piezoelectric effect, causing the vibrating units 22 and 24 to flex. In this way, the deformation of the vibrating units 21 to 24 causes the movable unit 40 to rotate about the rotation axis R10.

[0022] 2A to 2D are cross-sectional views showing the procedure for producing the SOI wafer 100. FIG.

[0023] As shown in FIG. 2A, a base layer 101 made of silicon (Si) is subjected to a thermal oxidation treatment at approximately 1100° C. As a result, silicon dioxide (SiO ２ 2B, for the sake of convenience, only the oxide film 102 formed on the top surface of the base layer 101 is shown.

[0024] 2(c), an active layer 103 made of silicon (Si) is bonded to the upper surface of the oxide film 102 at about 300° C. to the structure of the base layer 101 and oxide film 102 shown in FIG. 2(b). In this way, the SOI wafer 100 is completed.

[0025] When the SOI wafer 100 is then returned to room temperature, the SOI wafer 100 shrinks in a direction parallel to the surface, as shown in FIG. 2(d). At this time, the linear thermal expansion coefficient of the base layer 101 (Si) is 3.9×10 －６ and the oxide film 102 (SiO ２ ) has a linear thermal expansion coefficient of 0.5 × 10 －６ Therefore, the base layer 101 is more likely to shrink than the oxide film 102. As a result, a compressive stress is applied to the oxide film 102 by the base layer 101.

[0026] However, when the movable part 40 is formed by processing the SOI wafer 100 produced in this manner, a warp occurs in the central part 41 of the movable part 40, and a warp also occurs in the reflective surface 40a on the upper surface of the movable part 40. In this case, light incident on the reflective surface 40a cannot be properly reflected. Below, with reference to Comparative Examples 1 and 2, the occurrence of warp on the upper surface of the movable part 40 will be described.

[0027] 3A and 3B are a plan view and a cross-sectional view, respectively, that schematically show the configuration of the movable portion 40 according to Comparative Example 1. Fig. 3B is a cross-sectional view taken along C1-C2 in the plan view of Fig. 3A.

[0028] In the plan view shown in Fig. 3(a), the same materials as those in the cross-sectional view shown in Fig. 3(b) are indicated by the same diagonal lines as in Fig. 3(b) for the sake of convenience. Note that in the following figures, when plan views and cross-sectional views are shown together, the same materials will be indicated by the same diagonal lines.

[0029] As shown in FIG. 3A, the movable portion 40 of Comparative Example 1 includes a central portion 41 and a rib portion 42. In a plan view, the central portion 41 has a circular shape, and the rib portion 42 has a ring shape. The outer and inner contours of the rib portion 42 are circular. The central portion 41 is disposed inside the rib portion 42. As shown in FIGS. 3A and 3B, the central portion 41 is composed of an active layer 103. The rib portion 42 is composed of a base layer 101, an oxide film 102, and the active layer 103.

[0030] The movable portion 40 of Comparative Example 1 is formed by removing, by etching, the base layer 101 and the oxide film 102 in the central region (the inner region of the rib portion 42) of the underside of the SOI wafer 100 shown in FIG. 2(d). However, as described with reference to FIG. 2(d), when the environmental temperature is returned to room temperature, the oxide film 102 is subjected to a force in a contracting direction due to the compressive stress of the base layer 101. In other words, at room temperature, the oxide film 102 is in a more contracted state than when the base layer 101 is not present.

[0031] In this state, when the base layer 101 and oxide film 102 in the central region of the underside of the SOI wafer 100 are removed, the oxide film 102 in the rib portion 42 is released from the compressive stress and expands horizontally, as shown in Figure 3(b) . This generates a force (torque) that rotates the active layer 103 at the boundary B between the central portion 41 and the rib portion 42, lifting the active layer 103 in the central portion 41 upward and causing a deflection in the reflecting surface 40a on the upper surface of the movable portion 40 (the upper surface of the active layer 103).

[0032] In contrast, in Comparative Example 2, a gap GP is provided between the central portion 41 and the rib portion 42 , and the central portion 41 and the rib portion 42 are connected by the spring portion 43 .

[0033] 4A and 4B are a plan view and a cross-sectional view, respectively, that schematically show the configuration of the movable portion 40 according to Comparative Example 2. Fig. 3B is a cross-sectional view taken along C1-C2 in the plan view of Fig. 3A.

[0034] 4A, the movable portion 40 of Comparative Example 2 includes a central portion 41 and a rib portion 42 similar to those of Comparative Example 1. In a plan view, the central portion 41 has a circular shape, and the rib portion 42 has a ring shape. The contours of the outer periphery and the inner periphery of the rib portion 42 are both circular.

[0035] However, in Comparative Example 2, a gap GP is provided between the central portion 41 and the rib portion 42, and four spring portions 43 are disposed in this gap GP. The four spring portions 43 are made of flexible members. The four spring portions 43 extend in radial directions around the center C10 on the X-axis negative side, the X-axis positive side, the Y-axis negative side, and the Y-axis positive side of the central portion 41, respectively.

[0036] Specifically, the spring portion 43 on the X-axis negative side connects the end of the central portion 41 on the X-axis negative side to the inner periphery of the rib portion 42 that faces this end in the X-axis direction. The spring portion 43 on the X-axis positive side connects the end of the central portion 41 on the X-axis positive side to the inner periphery of the rib portion 42 that faces this end in the X-axis direction. The spring portion 43 on the Y-axis negative side connects the end of the central portion 41 on the Y-axis negative side to the inner periphery of the rib portion 42 that faces this end in the Y-axis direction. The spring portion 43 on the Y-axis positive side connects the end of the central portion 41 on the Y-axis positive side to the inner periphery of the rib portion 42 that faces this end in the Y-axis direction.

[0037] As shown in Fig. 4(b), the layered structure of the central portion 41 and the rib portion 42 is the same as that of Comparative Example 1 shown in Fig. 3(b). The spring portion 43 is formed of the active layer 103, and is integrally formed with the active layer 103 of the central portion 41 and the active layer 103 of the rib portion 42.

[0038] Also in Comparative Example 2, when the base layer 101 and oxide film 102 in the central region (the region inside the rib portion 42) of the underside of the SOI wafer 100 are removed during the formation of the movable portion 40, the oxide film 102 of the rib portion 42 is released from the compressive stress and expands horizontally, as shown in Figure 4(b) . This generates a force (torque) that rotates the active layer 103 at the connection position P0 between the spring portion 43 and the rib portion 42, lifting the active layer 103 in the central portion 41 upward and causing a deflection in the reflecting surface 40a on the upper surface of the movable portion 40 (the upper surface of the active layer 103).

[0039] However, in Comparative Example 2, the entire outer periphery of the central portion 41 is not connected to the rib portion 42, and the central portion 41 and the rib portion 42 are connected only by the spring portion 43, so that the expansion of the oxide film 102 on the rib portion 42 is not easily transmitted to the central portion 41. Furthermore, the expansion of the oxide film 102 on the rib portion 42 is absorbed by the spring portion 43 and is not easily transmitted to the central portion 41. Therefore, the deflection of the reflecting surface 40a in Comparative Example 2 is smaller than that in Comparative Example 1.

[0040] However, even in Comparative Example 2, the expansion of the oxide film 102 of the rib portion 42 is still transmitted to the central portion 41, which may cause the reflective surface 40a to bend and prevent the incident light from being properly reflected. Therefore, it is necessary to further suppress the expansion of the oxide film 102 of the rib portion 42 from being transmitted to the central portion 41.

[0041] Therefore, in the first embodiment, in order to further suppress the deflection of the reflecting surface 40a, the spring portion 60 connecting the central portion 41 and the rib portion 42 is configured as follows.

[0042] Fig. 5A is a plan view schematically showing the configuration of the movable portion 40 according to the embodiment 1. Fig. 5B is a plan view showing in detail the vicinity of the end portion of the movable portion 40 on the negative side of the Y axis.

[0043] The central portion 41 and the rib portion 42 have the same configuration as those of Comparative Example 2 shown in Figures 4(a) and (b). That is, in a plan view, the central portion 41 has a circular shape, and the rib portion 42 has a ring shape. The outer and inner contours of the rib portion 42 are circular. The central portion 41 is disposed inside the rib portion 42 with a gap GP therebetween.

[0044] In the first embodiment, four spring portions 60 are arranged in the gap GP. The four spring portions 60 are arranged on the negative X-axis side, the positive X-axis side, the negative Y-axis side, and the positive Y-axis side of the central portion 41, respectively. The spring portions 60 are flexible and are made of the active layer 103.

[0045] The spring portion 60 includes a beam portion 61 and a connecting portion 62. The beam portion 61 extends in a direction perpendicular to the radial direction centered on the center C10, and linearly connects two connection positions P1 where the spring portion 60 and the rib portion 42 are connected. The connecting portion 62 extends in the radial direction centered on the center C10, and linearly connects the beam portion 61 and the central portion 41. One end of the connecting portion 62 is connected to the central position of the beam portion 61 in the extension direction of the beam portion 61, and the other end of the connecting portion 62 is connected to an end of the central portion 41.

[0046] When forming the movable portion 40, a cylindrical SOI wafer 100 (see FIG. 2(d)) is used. As shown in FIG. 5(a), the base layer 101 and oxide film 102 in the central region (the region inside the rib portion 42) are removed by etching. The base layer 101 and oxide film 102 removed by etching are cylindrical. As a result, a layer consisting only of the active layer 103 is formed in the central region of the movable portion 40, and the rib portion 42 is formed in the peripheral region. Thereafter, etching is performed so as to form the spring portion 60 shown in FIG. 5(a) between the central portion 41 and the rib portion 42. In this way, a gap GP is formed between the central portion 41 and the rib portion 42, and the movable portion 40 of embodiment 1 is completed.

[0047] FIG. 6A is a cross-sectional view taken along the line C3-C4 in the plan view of FIG.

[0048] The beam portion 61 and the rib portion 42 are connected at a connection position P1. Specifically, the active layer 103 constituting the beam portion 61 and the active layer 103 constituting the rib portion 42 are integrally formed.

[0049] FIG. 6B is a cross-sectional view taken along the line C1-C2 in the plan view of FIG.

[0050] The beam portion 61 and the central portion 41 are connected by a connecting portion 62. Specifically, the active layer 103 that constitutes the spring portion 60 and the active layer 103 that constitutes the central portion 41 are integrally formed.

[0051] Returning to FIG. 5B , in the first embodiment, when the base layer 101 and the oxide film 102 in the central region (the inner region of the rib portion 42) of the underside of the SOI wafer 100 are removed during the formation of the movable portion 40, the oxide film 102 of the rib portion 42 expands horizontally. This generates a force (torque) that rotates the active layer 103 at the connection position P1. At this time, in the first embodiment, an expansion force F due to the expansion of the oxide film 102 is applied from the rib portion 42 to the spring portion 60 at the connection position P1 in the normal direction of the inner periphery of the rib portion 42 (the radial direction centered on the center C10). In the first embodiment, the expansion forces F generated at both ends of the beam portion 61 in the direction in which the beam portion 61 extends cancel each other out. Therefore, only the expansion force F generated at both ends of the beam portion 61 in the direction perpendicular to the direction in which the beam portion 61 extends is transmitted to the central portion 41 via the spring portion 60.

[0052] Specifically, the angle (hereinafter referred to as the "connection angle") between the normal direction of the inner periphery of the rib portion 42 at the connection position P1 and the direction in which the beam portion 61 extends at the connection position P1 is defined as θ. In this case, the expansion force F is decomposed into a component F cos θ in the direction in which the beam portion 61 extends at the connection position P1 (hereinafter referred to as the "first direction"), and a component F sin θ in a direction perpendicular to the first direction (hereinafter referred to as the "second direction"). Since equal expansion forces F are generated at the connection positions P1 on both ends of one spring portion 60, the components of the first direction at the connection positions P1 on both ends of the spring portion 60 are equal but in opposite directions, and therefore cancel each other out.

[0053] As a result, only the component in the second direction at connection positions P1 on both ends of the spring portion 60 is transmitted to the central portion 41 via the spring portion 60. Furthermore, the distance from connection positions P1 to the central portion 41 is the sum of half the length of the beam portion 61 in the first direction and the length of the connecting portion 62 in the second direction, and this sum is longer than the radial length of the spring portion 43 in Comparative Example 1. Therefore, the component F sin θ applied to the spring portion 60 at connection positions P1 is transmitted to the central portion 41 while being sufficiently absorbed by the beam portions 61 and the connecting portions 62, so that the force applied from the rib portion 42 to the central portion 41 can be suppressed compared to Comparative Example 1.

[0054] 5(b), for convenience, only the action of the spring portion 60 on the Y-axis negative side out of the four spring portions 60 has been described, but the spring portion 60 on the Y-axis negative side and the other three spring portions 60 have the same configuration and are similarly arranged in the movable portion 40. Therefore, the force applied from the rib portion 42 to the central portion 41 via the spring portion 60 can also be similarly suppressed in the other three spring portions 60.

[0055] <Simulation of deflection occurring in the central portion of embodiment 1> Next, the inventors conducted a simulation to investigate the degree of deflection occurring in the central portion 41 of comparative examples 1 and 2 and embodiment 1 due to the expansion of the oxide film 102 of the rib portion 42.

[0056] 7A, 7B, and 8 are diagrams showing the size settings of the movable part 40 in the simulations of Comparative Examples 1 and 2 and Embodiment 1, respectively.

[0057] As shown in FIG. 7( a), in Comparative Example 1, the diameter R0 of the central portion 41 was 1500 μm. As shown in FIG. 7( b), in Comparative Example 2, the diameter R1 of the central portion 41 was 1500 μm, and the diameter R2 of the inner periphery of the rib portion 42 was 1800 μm. The length L11 of the spring portion 43 was 150 μm, and the width W11 of the spring portion 43 was 30 μm. As shown in FIG. 8, in Embodiment 1, the diameter R1 of the central portion 41 was 1500 μm, and the diameter R2 of the inner periphery of the rib portion 42 was 1800 μm. The length L21 of the connecting portion 62 was 10 μm, and the width W21 of the connecting portion 62 was 30 μm. The width W22 of the beam portion 61 was 30 μm.

[0058] The inventors performed a simulation in which movable portions 40 of Comparative Examples 1 and 2 and Embodiment 1 were formed under the conditions shown in Figures 7(a) to 8, and the maximum deformation amount of central portion 41 in the positive direction of the Z axis due to expansion of oxide film 102 of rib portion 42 was measured. Then, the ratios of the maximum deformation amounts of Comparative Example 2 and Embodiment 1 to the maximum deformation amount of Comparative Example 1 (hereinafter referred to as "deformation ratios") were calculated. As a result, the deformation ratio of Comparative Example 2 was 15.4%, and the deformation ratio of Embodiment 1 was 11.6%.

[0059] From the above, it was found that, according to Comparative Example 2, the deflection of the central portion 41 can be suppressed more than in Comparative Example 1, but according to Embodiment 1, the deflection of the central portion 41 can be suppressed even more than in Comparative Example 2.

[0060] <Effects of First Embodiment> According to the first embodiment, the following effects are achieved.

[0061] The movable portion 40 has a central portion 41, a rib portion 42, and a spring portion 60. The central portion 41 has a structure in which the base layer 101, the oxide film 102, and the active layer 103 are stacked on an SOI wafer 100 (see FIG. 2(d)), but the base layer 101 and the oxide film 102 are removed, and the central portion 41 has a reflective surface 40a disposed on the upper surface of the active layer 103. The rib portion 42 is disposed outside the central portion 41 via a gap GP. The spring portion 60 is flexible. Both ends of the spring portion 60 are connected to the rib portion 42, and the space between both ends of the spring portion 60 is connected to the central portion 41.

[0062] In the production of the SOI wafer 100, the base layer 101 is thermally oxidized at a temperature of approximately 1100°C to form an oxide film 102 on the surface of the base layer 101, and then the active layer 103 is bonded to the oxide film 102. The base layer 101 has a larger thermal expansion coefficient than the oxide film 102 and tends to shrink compared to the oxide film 102 when returned to room temperature. At this time, the base layer 101 applies compressive stress to the oxide film 102. When such an SOI wafer 100 is processed to remove the base layer 101 and the oxide film 102 from the central region of the movable part 40 and form a rib portion 42 in the peripheral region, the removal of the base layer 101 from the central region partially releases the compressive stress applied to the oxide film 102 of the rib portion 42, causing the oxide film 102 to expand. As a result, the oxide film 102 applies a force to the active layer 103 in the central portion 41 toward the center of the central portion 41, resulting in bending of the active layer 103 in the central portion 41.

[0063] In contrast, according to the above-described configuration, the central portion 41 and the rib portion 42 are disposed with the gap GP therebetween, and the spring portion 60 is provided with both ends connected to the rib portion 42 and the space between the ends connected to the central portion 41. As a result, the expansion of the oxide film 102 of the rib portion 42 is absorbed by the spring portion 60 and is less likely to propagate to the central portion 41, making it less likely that the central portion 41 will bend. Therefore, when the rib portion 42 is formed on the movable portion 40 using the SOI wafer 100, it is possible to suppress bending of the movable portion 40.

[0064] The central portion 41 is connected to approximately the center of the spring portion 60 .

[0065] With this configuration, the forces transmitted from the rib portions 42 through both ends of the spring portion 60 tend to cancel each other out, thereby suppressing the force transmitted from the rib portions 42 to the central portion 41 and suppressing deflection of the central portion 41 of the movable portion 40.

[0066] The spring portion 60 has a beam portion 61 that connects both ends of the spring portion 60 in a straight line.

[0067] With this configuration, among the force components applied from the rib portion 42 to both ends of the spring portion 60, the force components in the direction in which the spring portion 60 extends from the connection position P1 tend to cancel each other out.

[0068] The spring portion 60 is made of the same material as the central portion 41 .

[0069] According to this configuration, spring portion 60 and central portion 41 can be formed at the same time, which simplifies the manufacturing process of optical reflecting element 1.

[0070] In the first embodiment, the connection angle θ at both ends of the spring portion 60 is set by the normal direction of the rib portion 42 according to the connection position P1. In contrast, in the second embodiment, an angle adjustment portion 42a is formed in the rib portion 42 so that the connection angle θ can be set regardless of the connection position P1.

[0071] Fig. 9A is a plan view schematically showing the configuration of the movable section 40 according to the second embodiment, and Fig. 9B is a plan view showing in detail the vicinity of the end of the movable section 40 on the negative side of the Y axis.

[0072] In the second embodiment, unlike the first embodiment, an angle adjustment portion 42a is formed at a connection position P1 of the rib portion 42 where both ends of each spring portion 60 are connected. Specifically, the angle adjustment portion 42a is a protrusion that protrudes from the inner surface of the rib portion 42 relative to the rib portion 42. In this case, the connection position P1 is the position where the angle adjustment portion 42a of the rib portion 42 and both ends of the spring portion 60 are connected. The angle adjustment portion 42a has a side that extends linearly at the connection position P1.

[0073] In the second embodiment, the normal direction of the side of the angle adjustment portion 42a at the connection position P1 is closer to the extension direction of the beam portion 61 than the normal direction of the inner peripheral portion of the rib portion 42 at the connection position P1 in the first embodiment shown in FIG. 5B . That is, the connection angle θ in the second embodiment is smaller than the connection angle θ in the first embodiment. As a result, when the expansion force F applied to the spring portion 60 in the normal direction from the side of the angle adjustment portion 42a is decomposed into a first-direction component and a second-direction component, the first-direction components at both ends of the spring portion 60 cancel each other, as in the first embodiment. Furthermore, because the connection angle θ in the second embodiment is smaller than that in the first embodiment, the second-direction component of the expansion force F in the second embodiment is smaller than that in the first embodiment. Therefore, the force applied from the rib portion 42 to the central portion 41 can be suppressed more effectively than in the first embodiment.

[0074] Here, as shown in FIGS. 10(a) and 10(b), the side of the angle adjustment portion 42a at the connection position P1 may be inclined in the opposite direction to that shown in FIG. 9(b) with respect to the first direction.

[0075] 10(a) and 10(b), the angle adjustment portion 42a is formed so that the side of the angle adjustment portion 42a at the connection position P1 is inclined in the opposite direction to that in Fig. 9(b). If the sign of the connection angle θ is positive when the normal to the side of the angle adjustment portion 42a at the connection position P1 is inclined toward the central portion 41 with respect to the direction in which the spring portion 60 extends from the connection position P1 as shown in Fig. 9(b), then the sign of the connection angle θ in the configuration of Fig. 10(b) is negative.

[0076] In this case, when the expansion force F acting on the spring portion 60 in the normal direction from the edge of the angle adjustment portion 42a is decomposed into a component in the first direction and a component in the second direction, the first direction components at both ends of the spring portion 60 cancel each other out, as in the case of Figure 9(b). On the other hand, since the expansion force F is directed toward the opposite side of the central portion 41 with respect to the direction in which the beam portion 61 extends from the connection position P1, the second direction component of the expansion force F in Figure 10(b) is opposite to the second direction component of the expansion force F in Figure 9(a). Therefore, with the configurations of Figures 10(a) and 10(b), a force pulling the ends of the central portion 41 in the outward direction is generated, compared to the configurations of Figures 9(a) and 9(b), and therefore it is possible to further suppress deflection of the central portion 41.

[0077] 9(a) to 10(b), the angle adjustment portion 42a is a protrusion that protrudes from the inner surface of the rib portion 42 relative to the rib portion 42, but is not limited to this. As shown in Fig. 11, the angle adjustment portion 42a may be a recess that is recessed inward of the rib portion 42 on the inner surface of the rib portion 42. As shown in Fig. 11, in this case as well, the connection position P1 is the position where the angle adjustment portion 42a of the rib portion 42 and both ends of the spring portion 60 are connected. The angle adjustment portion 42a has a side that extends linearly at the connection position P1.

[0078] <Simulation of Deflection Occurring in the Central Portion of the Second Embodiment> The inventors conducted a simulation to investigate the degree of deflection that occurs in the central portion 41 of the second embodiment due to the expansion of the oxide film 102 of the rib portion 42 .

[0079] FIG. 12 is a diagram showing the size setting of the movable part 40 in the simulation of the second embodiment.

[0080] In the second embodiment, the diameter R1 of the central portion 41, the diameter R2 of the inner peripheral portion of the rib portion 42, the length L21 of the connecting portion 62, the width W21 of the connecting portion 62, and the width W22 of the beam portion 61 were set to the same conditions as those in the first embodiment described with reference to Fig. 8. Also, in the second embodiment, the connection angles θ at the eight connection positions P1 in one movable portion 40 were set to the same angle. In this simulation, the angle adjustment portion 42a shown in Figs. 9(a) to 10(b) was assumed, and the connection angle θ was changed in 15° increments within the range of -30° to 75°.

[0081] The inventors performed a simulation in which movable portion 40 of embodiment 2 was formed with a plurality of different connection angles θ under the conditions shown in Fig. 12 and the maximum deformation amount of central portion 41 in the Z-axis direction due to expansion of oxide film 102 of rib portion 42 was measured. Then, for each connection angle θ, the ratio (deformation rate) of the maximum deformation amount of embodiment 2 to the maximum deformation amount of comparative example 1 measured under the conditions shown in Fig. 7(a) was calculated.

[0082] FIG. 13 shows the simulation results showing the deformation rate versus the connection angle θ.

[0083] 13 , it was found that when the connection angle θ was reduced from 75° to 0°, the deformation rate of the central portion 41 also decreased accordingly. The reason for this is that as the connection angle θ decreased, the component of the expansion force F in the second direction gradually decreased from the direction toward the central portion 41, and became almost zero when the connection angle θ became 0°.

[0084] It was also found that when the connection angle θ was reduced from 0° to −15°, the deformation rate of the central portion 41 further decreased accordingly. This is because, when the connection angle θ became a negative value, a force pulling the central portion 41 outward was generated, and the rotational force (torque) at the connection position P1 moved the center of the central portion 41 in the negative direction of the Z axis. It was also found that when the connection angle θ was reduced from −15° to −30°, the deformation rate of the central portion 41 suddenly increased accordingly. This is because the rotational force (torque) at the connection position P1 moved the end of the central portion 41 in the positive direction of the Z axis.

[0085] The reason why the deformation rate does not reach a minimum when the connection angle θ is 0° is that, at the connection position P1, the expansion force F is not actually generated only in the normal direction of the rib portion 42, but a certain amount of expansion force is also generated in directions other than the normal direction. Due to such expansion forces in directions other than the normal direction, the deformation rate does not reach a minimum even when the connection angle θ is 0°, and the deformation rate reaches a minimum when the connection angle θ is in the range of -15° to 0°.

[0086] 14(a) to 15(b) are simulation results showing the distribution of the degree of deformation of the central portion 41. FIG.

[0087] 14(a) to 15(b) show the distribution of the deformation ratio when the connection angle θ is 30°, 0°, −15°, and −30°, respectively. In FIG. 14(a), the deformation ratio is greatest at the center of the central portion 41, and the deformation ratio in each of FIGS. 14(a) to 15(b) is normalized by setting the deformation ratio at this position (7.1%) to 100%. Hereinafter, the normalized deformation ratio will be referred to as the "degree of deformation." Note that while the distribution of the degree of deformation is normally shown in color, the distribution of the degree of deformation in FIGS. 14(a) to 15(b) is shown in grayscale for convenience.

[0088] 14(a), when the connection angle θ is 30°, the degree of deformation is maximum (100%) at the center of the central portion 41 and minimum (approximately 0%) at the ends on the negative X-axis side, positive X-axis side, negative Y-axis side, and positive Y-axis side of the central portion 41. The reason for this distribution of the degree of deformation is that the component of the expansion force F in the second direction is directed toward the central portion 41, and a torque that pushes up the spring portion 60 is generated at the connection position P1.

[0089] 14(b), when the connection angle θ is 0°, the degree of deformation is maximum (39.4%) at the center of the central portion 41 and minimum (approximately 0%) at the ends on the negative X-axis side, positive X-axis side, negative Y-axis side, and positive Y-axis side of the central portion 41. In this case, although the component of the expansion force F in the second direction becomes zero, the central portion 41 still bends due to the expansion force in the direction other than the normal direction that is generated at the connection position P1.

[0090] 15( a), when the connection angle θ is −15°, the degree of deformation is greatest (6.7%) at the center of the central portion 41 and is uniform throughout the central portion 41. In this case, the maximum degree of deformation is smallest, and it can be seen that the deflection of the central portion 41 is most effectively suppressed.

[0091] 15(b), when the connection angle θ is −30°, the degree of deformation is greatest (approximately 37.3%) at the ends of the central portion 41 on the negative X-axis side, positive X-axis side, negative Y-axis side, and positive Y-axis side, and is least (approximately 0%) at the center of the central portion 41. The reason for this distribution of the degree of deformation is that the component of the expansion force F in the second direction is directed toward the outside of the central portion 41, and a torque that presses down on the spring portion 60 is generated at the connection position P1.

[0092] Next, under the conditions of Fig. 12, the inventors fixed the connection angle θ at 30° and changed the length L21 of the connecting portion 62 in increments of 25 µm within a range of 10 µm to 85 µm. The inventors formed the movable portion 40 of embodiment 2 with a plurality of lengths L21 and performed a simulation to measure the maximum deformation amount in the Z-axis direction of the central portion 41 due to the expansion of the oxide film 102 of the rib portion 42. Then, for each length L21 of the connecting portion 62, the ratio (deformation rate) of the maximum deformation amount of embodiment 2 to the maximum deformation amount of comparative example 1 measured under the conditions of Fig. 7(a) was calculated.

[0093] FIG. 16 shows the results of a simulation showing the deformation rate versus the length L21 of the connecting portion 62.

[0094] As shown in FIG. 16 , it was found that shortening the length L21 from 85 μm to 10 μm also reduced the deformation rate of the central portion 41. This is thought to be because, when the length of the connecting portion 62 is long, the length of the beam portion 61 is shortened, making it more difficult for the beam portion 61 to absorb the force applied from the rib portion 42 to the spring portion 60 at the connection position P1, making it more likely for the central portion 41 to bend. The results in FIG. 16 suggest that it is best to keep the length L21 of the connecting portion 62 as short as possible. It is also possible to set the length L21 to 0 μm, so that the beam portion 61 and the central portion 41 are directly connected. In this case, it is thought that the force applied to the spring portion 60 is more easily absorbed by the beam portion 61, thereby further suppressing the bending of the central portion 41.

[0095] 9A to 11, the rib portion 42 includes an angle adjustment portion 42a for setting the connection angle θ (the angle between the normal direction of the rib portion 42 at the connection position P1 between the rib portion 42 and the spring portion 60 and the direction in which the spring portion 60 extends from the connection position P1).

[0096] The force transmitted from the rib portion 42 to the central portion 41 changes depending on the connection angle θ. According to the above configuration, the connection angle θ can be easily set by the angle adjustment portion 42a.

[0097] The angle adjusting portion 42a is a protruding portion that protrudes from the rib portion 42 (see FIGS. 9(a) to 10(b)), or a recessed portion that is recessed inward of the rib portion 42 (see FIG. 11).

[0098] According to this configuration, the connection angle θ can be smoothly set. Furthermore, when the angle adjustment portion 42a is a protrusion, the angle can be easily set regardless of the shape of the rib portion 42.

[0099] If the sign of the connection angle θ (the angle formed) when the normal to the rib portion 42 at the connection position P1 is inclined toward the central portion 41 with respect to the direction in which the spring portion 60 extends from the connection position P1 is taken to be positive, then it is preferable that the connection angle θ (the angle formed) be set to 0° or less, as shown in the simulation results of Figure 13.

[0100] According to this configuration, of the force components applied from the rib portion 42 to the spring portion 60, the component in the direction perpendicular to the extension direction of the spring portion 60 (second direction) can be directed outward from the movable portion 40. This makes it possible to suppress the force component directed from the rib portion 42 to the central portion 41.

[0101] Furthermore, as shown in the simulation results of FIG. 13, it is preferable that the connection angle θ (formed angle) is set to be equal to or greater than −30° and equal to or less than 0°.

[0102] According to this configuration, the deformation rate can be suppressed to the greatest extent possible, and therefore, the deflection of the central portion 41 can be reliably suppressed.

[0103] In the first embodiment, both ends of the spring portion 60 are connected to the circular inner periphery of the rib portion 42. In contrast, in the third embodiment, both ends of the spring portion 60 are positioned more outward than in the second embodiment, and are connected to notches 42b formed in the inner periphery of the rib portion 42.

[0104] 17A and 17B are a plan view and a cross-sectional view, respectively, that schematically show the configuration of the movable portion 40 according to the third embodiment.

[0105] As shown in FIG. 17( a), in the third embodiment, unlike the first embodiment shown in FIGS. 5( a) and 5(b), a notch 42b is formed on the inner surface of the rib portion 42 at a position where the spring portion 60 is disposed. The notch 42b is cut away in a direction away from the center C10 of the central portion 41. Outside the notch 42b, the outer surface of the rib portion 42 protrudes outward. The spring portion 60 is accommodated in the notch 42b. As shown in FIG. 17( b), both ends of the spring portion 60 are connected to the active layer 103 of the rib portion 42 located outside the notch 42b. As a result, both ends of the spring portion 43 are connected to the rib portion 42 at connection positions P1 outside the inner periphery of the rib portion 42 other than the notch 42b.

[0106] <Effects of embodiment 3> A notch 42b cut out in a direction away from the center C10 of the central portion 41 is provided on the inner surface of the rib portion 42, and both ends of the spring portion 60 are connected to the rib portion 42 at the notch 42b.

[0107] 17A, this configuration makes it possible to make the distance L31 from the center C10 of the central portion 41 to the inner periphery of the rib portion 42 excluding the notch 42b shorter than the distance L32 from the center C10 of the central portion 41 to the connection position P1 between the spring portion 60 and the rib portion 42. Therefore, the rib portion 42 can be disposed closer to the central portion 41 while maintaining a constant radial width of the rib portion 42, thereby making it possible to reduce the weight of the rib portion 42 compared to the first embodiment. This makes it possible to suppress a decrease in the drive efficiency of the movable portion 40.

[0108] In the first embodiment, the active layer 103 is disposed in the entire region of the rib portion 42. In contrast, in the third embodiment, the active layer 103 is removed from the entire region of the rib portion 42 except for the connection portion 42c corresponding to the connection position P1 with the spring portion 60.

[0109] 18A and 18B are a plan view and a cross-sectional view, respectively, that schematically show the configuration of the movable portion 40 according to the fourth embodiment.

[0110] 5(a) and 5(b), in the fourth embodiment, connecting portions 42c for supporting both ends of the spring portion 60 are provided corresponding to eight connecting positions P1. The connecting portions 42c are formed of the active layer 103, and the connecting portions 42c and the beam portion 61 are integrally formed. Furthermore, the active layer 103 is removed from the entire region of the rib portion 42 other than the connecting portions 42c. This makes it difficult for the expansion of the oxide film 102 that occurs during the formation of the movable portion 40 to propagate to the active layer 103.

[0111] 18A and 18B, the active layer 103 is removed from the entire region of the rib portion 42 except for the connecting portion 42c, but this is not limiting, and at least a portion of the active layer 103 may be removed from the entire region of the rib portion 42 except for the connecting portion 42c. In this case, as compared to the first embodiment, the removal of the active layer 103 from the rib portion 42 can suppress the expansion of the oxide film 102 that occurs during the formation of the movable portion 40 from propagating to the active layer 103.

[0112] <Simulation of Deflection Occurring in the Central Portion of the Fourth Embodiment> The inventors conducted a simulation to investigate the degree of deflection that occurs in the central portion 41 of the fourth embodiment due to the expansion of the oxide film 102 of the rib portion 42 .

[0113] In this simulation, the same simulation conditions as those shown in FIG. 12 were used, and the connection angle θ was set to 30°. Furthermore, in this simulation, as shown in FIGS. 18( a) and 18(b), the active layer 103 was removed from the entire region of the rib portion 42 except for the connection portion 42c. Under the above conditions, the inventors formed the movable portion 40 of the second embodiment and performed a simulation to measure the maximum deformation amount in the Z-axis direction of the central portion 41 due to the expansion of the oxide film 102 of the rib portion 42. The maximum value of the deformation rate of the second embodiment (with the active layer 103 in the rib portion 42) measured under the above conditions was set to 100%, and the deformation rate of the fourth embodiment (without the active layer 103 in the rib portion 42) was normalized to calculate the degree of deformation of the fourth embodiment.

[0114] FIG. 19 shows the results of a simulation showing the distribution of the degree of deformation of the central portion 41. As shown in FIG.

[0115] In this simulation, the degree of deformation was greatest (87%) at the center of the central portion 41 and was least (approximately 0%) at the ends on the negative X-axis side, positive X-axis side, negative Y-axis side, and positive Y-axis side of the central portion 41. This result shows that removing the active layer 103 of the rib portion 42 can suppress the deflection of the central portion 41 compared to the first and second embodiments.

[0116] <Effects of Fourth Embodiment> The rib portion 42 has a structure in which at least a part of the active layer 103 is removed from the SOI wafer 100 (see FIG. 2B).

[0117] According to this configuration, since at least a portion of the active layer 103 is removed in the rib portion 42, the expansion of the oxide film 102 is less likely to propagate to the active layer 103, and bending of the active layer 103 in the central portion 41 is even less likely to occur.

[0118] Fifth Embodiment In the fourth embodiment, the active layer 103 is removed from the entire region of the rib portion 42 except for the connection portion 42 c. In contrast, in the fifth embodiment, the oxide film 102 is further removed from the entire region of the rib portion 42 except for the connection portion 42 c.

[0119] 20A and 20B are a plan view and a cross-sectional view, respectively, that schematically show the configuration of the movable portion 40 according to the fifth embodiment.

[0120] In the fifth embodiment, compared to the fourth embodiment, the oxide film 102 and the active layer 103 are removed from the entire region of the rib portion 42 except for the connecting portion 42 c. This makes it even more difficult for the expansion of the oxide film 102 that occurs during the formation of the movable portion 40 to propagate to the active layer 103.

[0121] 20(a) and 20(b), the oxide film 102 and the active layer 103 are removed from the entire region of the rib portion 42 except for the connection portion 42c, but this is not limiting, and at least a portion of the oxide film 102 and the active layer 103 may be removed from the entire region of the rib portion 42 except for the connection portion 42c. In this case, too, compared to the fourth embodiment, the removal of the active layer 103 from the rib portion 42 can further suppress propagation of the expansion of the oxide film 102 that occurs during the formation of the movable portion 40 to the active layer 103.

[0122] <Simulation of Deflection Occurring in the Central Portion of the Fifth Embodiment> The inventors conducted a simulation to investigate the degree of deflection that occurs in the central portion 41 of the fifth embodiment due to the expansion of the oxide film 102 of the rib portion 42 .

[0123] In this simulation, the same simulation conditions as those shown in FIG. 12 were used, and the connection angle θ was set to 30°. Furthermore, in this simulation, as shown in FIGS. 20( a) and 20(b), the oxide film 102 and the active layer 103 were removed from the entire region of the rib portion 42 except for the connection portion 42c. Under the above conditions, the inventors formed the movable portion 40 of the fifth embodiment and performed a simulation to measure the maximum deformation amount in the Z-axis direction of the central portion 41 due to the expansion of the oxide film 102 of the rib portion 42. Then, the maximum value of the deformation rate of the second embodiment (with the oxide film 102 and the active layer 103 in the rib portion 42) measured under the above conditions was set to 100%, and the deformation rate of the fifth embodiment (without the oxide film 102 and the active layer 103 in the rib portion 42) was normalized to calculate the degree of deformation of the fourth embodiment.

[0124] FIG. 21 shows the results of a simulation showing the distribution of the degree of deformation of the central portion 41. As shown in FIG.

[0125] In this simulation, the degree of deformation was greatest (54%) at the center of central portion 41 and was least (approximately 0%) at the ends on the negative X-axis side, positive X-axis side, negative Y-axis side, and positive Y-axis side of central portion 41. This result shows that when oxide film 102 and active layer 103 of rib portion 42 are removed, the deflection of central portion 41 can be further suppressed compared to embodiment 4.

[0126] Effects of Fifth Embodiment Compared to the fourth embodiment, the rib portion 42 has a structure in which at least a part of the oxide film 102 is further removed from the SOI wafer 100 (see FIG. 2B).

[0127] According to this configuration, the volume of the oxide film 102, which is the source of the warp, is reduced, further reducing the displacement of the oxide film 102 due to expansion. As a result, warp of the central portion 41 can be further suppressed compared to the fourth embodiment.

[0128] <Embodiment 6> In embodiment 1, the upper surface of the active layer 103 in the central portion 41 is used as the reflective surface 40a that reflects light, but this is not limited thereto. An optical reflective film 71 may be separately disposed on the upper surface of the active layer 103 in the central portion 41, and the upper surface of the optical reflective film 71 may be used as the reflective surface 40a.

[0129] 22A and 22B are a plan view and a cross-sectional view, respectively, that schematically show the configuration of the movable portion 40 according to the sixth embodiment.

[0130] 5A and 5B, in the sixth embodiment, an optical reflection film 71 is formed on the upper surface of the active layer 103 that forms the central portion 41. The optical reflection film 71 is made of a highly reflective material (for example, a metal or metal compound such as gold, silver, copper, or aluminum, or silicon dioxide, titanium dioxide, or the like). The optical reflection film 71 may be made of a dielectric multilayer film.

[0131] In addition, in FIGS. 22( a ) and 22 ( b ), the optical reflection film 71 is formed inside the central portion 41 in plan view, but it may be formed in the same area as the central portion 41 .

[0132] 22(a) and 22(b), an optical reflection film may be formed not only on the upper surface but also on the lower surface of the active layer 103 in the central portion 41. In this case, as shown in Fig. 23, an optical reflection film 71 on the upper surface side of the central portion 41 and an optical reflection film 72 on the lower surface side of the central portion 41 are arranged so as to overlap in a plan view, i.e., to have the same size and be at the same position. Furthermore, the optical reflection films 71 and 72 have the same thickness and are made of the same material.

[0133] Advantages of Sixth Embodiment As shown in FIGS. 22A and 22B, the movable portion 40 further includes an optical reflection film 71 on the upper surface of the central portion 41, and the optical reflection film 71 forms a reflection surface 40a.

[0134] This configuration can improve the reflectivity compared to when the upper surface of the active layer 103 in the central portion 41 is used as the reflecting surface 40a.

[0135] As shown in FIG. 23, the movable portion 40 may further include an optical reflection film 72 (another optical reflection film) on the lower surface of the central portion 41 .

[0136] According to this configuration, by providing the optical reflective films 71, 72 on the upper and lower surfaces of the central portion 41, the stresses applied to the central portion 41 from the optical reflective film 71 on the upper surface and the optical reflective film 72 on the lower surface can be made approximately equal to each other. This makes it possible to improve the reflectivity of the reflective surface 40a while suppressing the occurrence of bending in the central portion 41.

[0137] Furthermore, because the upper surface optical reflection film 71 and the lower surface optical reflection film 72 are made of the same material, the two temperature characteristics can be matched. This causes the two optical reflection films 71, 72 to deform equally due to temperature changes, and therefore the stresses applied to the upper and lower surfaces of the central portion 41 by the two optical reflection films 71, 72 due to temperature changes can be made approximately equal to each other. This makes it possible to prevent the central portion 41 from being deflected by the two optical reflection films 71, 72.

[0138] Furthermore, for example, light incident on the optical reflection film 71 on the upper surface side can be reflected onto the object, while detection light can be irradiated onto the optical reflection film 72 on the lower surface side, and the rotational state of the movable part 40 can be detected by the reflection of light by the optical reflection film 72.

[0139] Note that even when the lower surface of the central portion 41 is used to reflect light for detection, the lower surface of the active layer 103 constituting the central portion 41 has sufficient reflectivity, and therefore the lower surface of the central portion 41 can be used as a reflecting surface instead of the optical reflection film 72. If the reflectivity of the lower surface of the central portion 41 is insufficient, the reflectivity of the lower surface of the central portion 41 may be increased by polishing the lower surface of the central portion 41. However, when the optical reflection film 71 is disposed on the upper surface of the central portion 41, disposing the optical reflection film 72 on the lower surface of the central portion 41 can suppress the occurrence of bending in the central portion 41, as described above.

[0140] <Modification of Spring Section Arrangement> In the first to fifth embodiments, the four spring sections 60 are arranged on the X-axis negative side, the X-axis positive side, the Y-axis negative side, and the Y-axis positive side of the central section 41, but the arrangement positions of the spring sections 60 are not limited to this. For example, the spring sections 60 may be arranged as shown in FIGS. 24( a) to 24(c).

[0141] In the modified example shown in FIG. 24( a), three spring portions 60 are arranged at 120° intervals in the circumferential direction of the center C10. In the modified example shown in FIG. 24( b), two spring portions 60 are arranged at 180° intervals in the circumferential direction of the center C10. As in the modified examples of embodiments 1 to 5 and FIGS. 24( a) and 24(b), by arranging multiple spring portions 60 at equal intervals in the circumferential direction of the center C10, the force transmitted from the rib portion 42 to the central portion 41 via each spring portion 60 is uniform around the center C10. This prevents variations in the deflection of the central portion 41, and enables the deflection of the central portion 41 to be suppressed.

[0142] In the first to fifth embodiments, four spring portions 60 may be arranged at positions rotated 45° around the center C10. In the modified example of Fig. 24(a), three spring portions 60 may be arranged at positions rotated 60° around the center C10. In the modified example of Fig. 24(b), two spring portions 60 may be arranged at positions rotated 90° around the center C10.

[0143] 24(c), one spring portion 60 is disposed at the end of the central portion 41 on the positive side of the X-axis. By reducing the number of spring portions 60 in this way, it is possible to further suppress the force transmitted from the rib portions 42 to the central portion 41. However, in order for the rib portions 42 to stably support the central portion 41, it is preferable that the number of spring portions 60 be at least two.

[0144] In the modification of FIG. 24( c ), one spring portion 60 may be disposed at any one of the ends of the central portion 41 on the negative side of the X axis, the negative side of the Y axis, and the positive side of the Y axis.

[0145] <Examples of Modifications to the Shape of the Spring Portion> In the first to fifth embodiments, the beam portion 61 of the spring portion 60 has a shape that follows a single straight line, but the shape of the beam portion 61 is not limited to this. For example, the beam portion 61 may have a shape as shown in Figures 25(a) to 25(c).

[0146] 25( a), the spring portion 60 includes a beam portion 61 extending in the circumferential direction of the center C10, a connecting portion 62 connecting an end of the central portion 41 to the center of the beam portion 61, and a connecting portion 63 connecting an end of the beam portion 61 to the rib portion 42. Four spring portions 60 are arranged at equal intervals in the circumferential direction of the center C10. The beam portions 61 of two adjacent spring portions 60 are connected to each other, and a common connecting portion 63 is provided between the two beam portions 61.

[0147] In the modified example shown in Fig. 25(b), similar to the modified example in Fig. 25(a), the spring portion 60 includes a beam portion 61 and connecting portions 62 and 63. However, in Fig. 25(b), the beam portion 61 has a bent shape along two straight lines, and two spring portions 60 are arranged at positions symmetrical with respect to the center C10.

[0148] In the modified example shown in Fig. 25(c), similar to the modified example shown in Fig. 25(a), the spring portion 60 includes a beam portion 61 and connecting portions 62 and 63. However, in Fig. 25(c), the beam portion 61 has a bent shape along six straight lines, and two spring portions 60 are arranged at positions symmetrical with respect to the center C10.

[0149] In the modified examples shown in Figures 25(a) to (c), the beam portion 61 has a bent or curved shape, but the entire beam portion 61 does not have to have a bent or curved shape, and only a part of the beam portion 61 may have a bent or curved shape.

[0150] As in the modified examples shown in Figures 25(a) to (c), when the beam portion 61 of the spring portion 60 includes a bent or curved shape, the length of the spring portion 60 can be sufficiently secured between the central portion 41 and the rib portion 42, making it easier for the spring portion 60 to absorb the force from the rib portion 42.

[0151] <Examples of Modifications to the Shape of the Central Portion and the Rib Portion> In the first to fifth embodiments, the central portion 41 is circular, the inner and outer contours of the rib portion 42 are circular, and the rib portion 42 is ring-shaped, but the shapes of the central portion 41 and the rib portion 42 are not limited to these. For example, the central portion 41 and the rib portion 42 may have shapes such as those shown in Figures 26(a) to 27(b).

[0152] 26(a), the shape of central portion 41 is square, and the contour shapes of the inner and outer peripheries of rib portion 42 are square, so that rib portion 42 has a square frame shape. In FIG. 26(a), spring portions 60 are disposed at the center of the sides of central portion 41 on the negative side and the positive side of the Y axis, respectively.

[0153] In the modification shown in FIG. 26( b ), spring portions 60 are arranged at the four corners of the central portion 41 , as compared with the modification shown in FIG. 26( a ).

[0154] In the modified example shown in FIG. 26(c), the beam portion 61 of the spring portion 60 has a bent shape along 12 straight lines, as compared with the modified example in FIG. 26(a).

[0155] 26(b), in the modified example shown in Fig. 27(a), spring portions 60 are arranged at the four corners of the central portion 41. However, in the modified example of Fig. 27(a), the spring portions 60 include beam portions 61 extending in an oblique direction, connecting portions 62 connected to the ends of the central portion 41, and connecting portions 63 connecting the connecting portions 62 to the centers of the beam portions 61. The connecting portions 63 of two spring portions 60 adjacent to each other in the X-axis direction are connected to each other, and a common connecting portion 62 is provided between the two connecting portions 63.

[0156] 27(a), in the modified example shown in Fig. 27(b), the connecting portion 63 in each spring portion 60 extends in the X-axis direction and the Y-axis direction from the center of the beam portion 61. The connecting portions 63 of two spring portions 60 adjacent to each other in the Y-axis direction are connected to each other, and a common connecting portion 62 is provided between these two connecting portions 63.

[0157] In the modified examples shown in FIGS. 26( a ) to 27 ( b ), the force transmitted from the rib portion 42 to the spring portion 60 is absorbed by the spring portion 60 , so that the deflection of the central portion 41 can be suppressed.

[0158] The shape of the central portion 41 is not limited to a circle or a square, but may be an ellipse or a rectangle. The contour shapes of the inner and outer peripheries of the rib portion 42 are not limited to a circle or a square, but may be an ellipse or a rectangle.

[0159] <Modification of Vibration Section> In the first embodiment, as shown in FIG. 1, the vibration sections 21 to 24 are arranged in a meandering shape, but in this modification, the vibration sections are arranged in a tuning fork shape.

[0160] FIG. 28 is a plan view schematically showing the configuration of an optical reflecting element 1 according to this modified example.

[0161] The optical reflecting element 1 includes a fixed portion 10, a pair of vibrating portions 221, a pair of vibrating portions 222, a pair of support portions 231, a pair of support portions 232, a movable portion 40, and four drive portions 50. The optical reflecting element 1 is configured to be symmetrical in the X-axis direction and the Y-axis direction with respect to a center C10. Note that in Fig. 28, the same components as those in embodiment 1 shown in Fig. 1 are denoted by the same reference numerals for convenience. Below, configurations different from embodiment 1 will be described.

[0162] The vibrating units 221 and 222 are L-shaped in plan view. The vibrating units 221 and 222 extend in the X-axis direction near their tips and in the Y-axis direction near their connections with the support units 231 and 232. The vibrating units 221 and 222 are connected to the fixed unit 10 via the support unit 231 near the rotation axis R10 and to the movable unit 40 via the support unit 232. The vibrating unit 221 is disposed on the Y-axis positive side of the rotation axis R10, and the vibrating unit 222 is disposed on the Y-axis negative side of the rotation axis R10. The support units 231 and 232 extend in the X-axis direction along the rotation axis R10. The vibrating units 221 and 222 located on the X-axis positive side or the X-axis negative side of the movable unit 40 are tuning-fork shaped in plan view.

[0163] The driving unit 50 is disposed on the upper surfaces of the vibrating units 221 and 222. The driving unit 50 is connected to electrodes on the fixed unit 10 via the vibrating units 221 and 222, the support unit 231, and wiring on the fixed unit 10. A cable (external wiring) connected to an external device is connected to the electrodes on the fixed unit 10 by wire bonding.

[0164] When a drive voltage is applied to the drive unit 50 on the vibrating unit 221, the piezoelectric layer in the drive unit 50 on the vibrating unit 221 deforms due to the inverse piezoelectric effect, causing the vibrating unit 221 to vibrate and flex. On the other hand, when a drive voltage that is in the opposite phase to the drive voltage applied to the drive unit 50 on the vibrating unit 221 is applied to the drive unit 50 on the vibrating unit 222, the piezoelectric layer in the drive unit 50 on the vibrating unit 222 deforms due to the inverse piezoelectric effect, causing the vibrating unit 222 to vibrate and flex. In this way, due to the deformation of the vibrating units 221 and 222, the movable unit 40 rotates about the rotation axis R10, as in the first embodiment.

[0165] In this modified example, the movable portion 40 is configured in the same manner as in embodiment 1. That is, as shown in Figures 5(a) and 5(b), the central portion 41 and the rib portion 42 are connected via the spring portion 60. As a result, similar to embodiment 1, the expansion of the oxide film 102 of the rib portion 42 is less likely to propagate to the active layer 103 of the central portion 41, and deflection of the central portion 41 is suppressed.

[0166] In the second to fifth embodiments and the modified examples, meandering vibration sections 21 to 24 of optical reflecting element 1 may be configured by tuning fork-shaped vibration sections 221 and 222, similar to the modified example.

[0167] <Other Modifications> In the above embodiment and modifications, the spring portion 60 is made of the same material as the active layer 103 of the central portion 41. However, the spring portion 60 may be made of a material (such as a metal or a resin) different from the material (silicon) of the active layer 103, as long as the material is flexible. In this case, in the manufacturing process of the movable portion 40, a gap is formed between the active layer 103 of the central portion 41 and the active layer 103 of the rib portion 42, and then the spring portion 60 is formed. Thereafter, the base layer 101 and the oxide film 102 are removed from the inner region of the rib portion 42. In this case, the thickness of the spring portion 60 may be greater than the thickness of the active layer 103 of the central portion 41.

[0168] In the above-described first to sixth embodiments, the beam portion 61 of the spring portion 60 is connected to the central portion 41 via the connecting portion 62 at the central position in the extension direction of the beam portion 61. However, this is not limited to this, and the beam portion 61 may be connected to the central portion 41 via the connecting portion 62 at a position other than the central position in the extension direction of the beam portion 61. However, when the central position of the beam portion 61 is connected to the connecting portion 62 as in the above-described first to sixth embodiments, the expansion forces F in the first direction transmitted from the rib portion 42 to both ends of the beam portion 61 are more likely to cancel each other out, and thus the deflection of the central portion 41 can be more effectively suppressed.

[0169] In the above-described embodiments 3 to 6, an angle adjusting portion 42a may be provided, as in the above-described embodiment 2. In the above-described embodiments 4 to 6, the spring portion 60 may be connected to the rib portion 42 via the notch 42b, as in the above-described embodiment 3. In the above-described embodiment 6, as in the above-described embodiment 4, the active layer 103 may be removed from the rib portion 42, and as in the above-described embodiment 5, the oxide film 102 and the active layer 103 may be removed from the rib portion 42.

[0170] In the above embodiment and modified example, the rib portion 42 is formed around the entire periphery in the outer region of the central portion 41, but it may be formed in a part of the outer region of the central portion 41. In this case, the part of the outer region of the central portion 41 where the rib portion 42 is not formed is composed of only the active layer 103.

[0171] In the above-described embodiment and modified examples, as shown in Figures 1 and 28, two drive units are arranged on either side of the movable part 40, but one of the two drive units may be omitted. For example, in the first embodiment shown in Figure 1, the configuration on the X-axis positive side of the movable part 40 may be omitted, and the movable part 40 may be supported by the connecting beam 35 on the X-axis negative side. In the modified example of the diaphragm shown in Figure 28, the configuration on the X-axis positive side of the movable part 40 may be omitted, and the movable part 40 may be supported by the first support part 232 on the X-axis negative side.

[0172] 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.

[0173] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0174] (Technology 1) An optical reflecting element comprising: a fixed portion; and a movable portion supported by the fixed portion so as to be rotatable about a rotation axis, wherein the movable portion has a structure in which a base layer, an oxide film, and an active layer are stacked on an SOI wafer, from which the base layer and the oxide film have been removed, and comprises: a central portion having a reflective surface arranged on an upper surface of the active layer; a rib portion arranged outside the central portion with a gap therebetween; and a flexible spring portion whose both ends are connected to the rib portion and whose space between the both ends is connected to the central portion.

[0175] In the production of an SOI wafer, a base layer is thermally oxidized at a temperature of approximately 1100°C to form an oxide film on the surface of the base layer, and then an active layer is bonded to the oxide film. The base layer has a larger thermal expansion coefficient than the oxide film and tends to shrink relative to the oxide film when returned to room temperature, causing compressive stress from the base layer to act on the oxide film. When such an SOI wafer is processed to remove the base layer and oxide film from the central region of the movable part and form a rib portion in the peripheral region, the removal of the base layer in the central region partially releases the compressive stress acting on the oxide film in the rib portion, causing the oxide film to expand. This causes a force from the oxide film to act on the central active layer in the direction toward the center of the central part, resulting in bending of the central active layer.

[0176] In contrast, according to the above technology, the central portion and the rib portion are disposed with a gap therebetween, and a spring portion is provided whose both ends are connected to the rib portion and whose space between the both ends is connected to the central portion. As a result, the expansion of the oxide film of the rib portion is absorbed by the spring portion and is less likely to propagate to the central portion, making it less likely for the central portion to bend. Therefore, when the rib portion is formed on the movable portion using an SOI wafer, it is possible to suppress the bending of the movable portion.

[0177] (Technology 2) The optical reflecting element according to Technology 1, wherein the central portion is connected to a substantial center of the spring portion.

[0178] According to this technology, the forces transmitted from the rib portions via both ends of the spring portion tend to cancel each other out, thereby suppressing the force transmitted from the rib portion to the central portion and suppressing deflection of the central portion of the movable portion.

[0179] (Technology 3) In the optical reflecting element described in Technology 1 or 2, the rib portion is provided with an angle adjustment portion for setting the angle between the normal direction of the rib portion at the connection position between the rib portion and the spring portion and the direction in which the spring portion extends from the connection position.

[0180] The force transmitted from the rib portion to the central portion varies depending on the angle. According to the above technology, the angle can be easily set by the angle adjustment portion.

[0181] (Technology 4) In the optical reflecting element described in Technology 3, the angle adjusting portion is a protruding portion protruding from the rib portion or a recessed portion recessed inward of the rib portion.

[0182] This technology allows the angle between the normal direction of the rib at the connection position and the extension direction of the spring to be smoothly set. Furthermore, if the angle adjustment part is a protrusion, the angle can be easily set regardless of the shape of the rib.

[0183] (Technology 5) An optical reflecting element according to Technology 3 or 4, characterized in that, when the normal line is tilted toward the central portion with respect to the direction in which the spring portion extends, the angle is set to be 0° or less, assuming that the sign of the angle is positive.

[0184] This technology allows the component of the force applied from the rib to the spring, which is perpendicular to the direction of extension of the spring, to be directed outward from the movable part, thereby suppressing the component of the force directed from the rib to the center.

[0185] (Technology 6) The optical reflecting element according to Technology 5, wherein the angle is set to be equal to or greater than -30° and equal to or less than 0°.

[0186] This technique can reliably suppress the deflection of the central portion.

[0187] (Technology 7) The optical reflecting element according to any one of Technologies 1 to 6, wherein the spring portion has a beam portion having both ends linearly connected.

[0188] According to this technique, among the components of the force applied from the rib portion to both ends of the spring portion, the components of the force in the direction in which the spring portion extends tend to cancel each other out.

[0189] (Technology 8) The optical reflecting element according to any one of technologies 1 to 7, wherein the spring portion has a beam portion connecting the two ends, and the beam portion has a bent shape or a curved shape.

[0190] According to this technique, the spring portion can be made long enough to easily absorb the force from the rib portion.

[0191] (Technology 9) An optical reflecting element described in any one of technologies 1 to 8, characterized in that a notch cut out in a direction away from the center of the central part is provided on the inner surface of the rib portion, and both ends of the spring portion are connected to the rib portion at the notch.

[0192] According to this technology, the distance from the center of the central portion to the inner periphery of the rib portion other than the notch can be made shorter than the distance from the center of the central portion to the connection position between the spring portion and the rib portion. Therefore, the rib portion 42 can be positioned closer to the central portion 41 while maintaining a constant radial width of the rib portion 42, which makes it possible to reduce the weight of the rib portion 42 compared to the second embodiment. This makes it possible to suppress a decrease in the drive efficiency of the movable portion 40.

[0193] (Technology 10) The optical reflecting element according to any one of Techniques 1 to 9, wherein the spring portion is made of the same material as the central portion.

[0194] According to this technique, the spring portion and the central portion can be formed at the same time, which simplifies the manufacturing process of the optical reflecting element.

[0195] (Technology 11) The optical reflecting element according to Technology 10, wherein the spring portion is made of silicon (Si).

[0196] (Technology 12) The optical reflecting element according to any one of Techniques 1 to 11, wherein the rib portion has a structure in which at least a part of the active layer is removed from the SOI wafer.

[0197] According to this technique, at least a part of the active layer is removed in the rib portion, so that the expansion of the oxide film is less likely to propagate to the active layer, and bending of the active layer in the central portion is even less likely to occur.

[0198] (Technology 13) The optical reflecting element according to Technology 12, wherein the rib portion has a structure in which at least a part of the oxide film is further removed from the SOI wafer.

[0199] According to this technique, the volume of the oxide film 102, which is the source of the warp, is reduced, and thus the displacement of the oxide film 102 due to expansion is further reduced, thereby further suppressing the warp of the central portion 41.

[0200] (Technology 14) The optical reflecting element according to any one of Technologies 1 to 13, further comprising an optical reflecting film on the upper surface of the central portion, wherein the reflecting surface is formed by the optical reflecting film.

[0201] According to this technique, the reflectance can be improved compared to when the upper surface of the central active layer 103 is used as the reflecting surface 40a.

[0202] (Technology 15) The optical reflecting element according to Technology 14, further comprising another optical reflecting film on the lower surface of the central portion.

[0203] According to this technology, by providing optical reflective films on both the upper and lower surfaces of the central portion, the stresses applied to the central portion from the optical reflective films on the upper and lower surfaces can be made approximately equal to each other. This makes it possible to improve the reflectivity of the reflective surface while suppressing deflection of the central portion. Furthermore, by making the temperature characteristics of the optical reflective film on the upper surface and the temperature characteristics of the optical reflective film on the lower surface similar to each other, the deformations of the two optical reflective films due to temperature changes become approximately equal, thereby making it possible to make the stresses applied to the upper and lower surfaces of the central portion from the two optical reflective films due to temperature changes approximately equal to each other. This makes it possible to suppress deflection of the central portion due to the two optical reflective films. Furthermore, for example, light incident on the optical reflective film on the upper surface can be reflected toward an object, while light for detection can be irradiated onto another optical reflective film on the lower surface, and the rotation state of the movable part can be detected by the reflection of the light by the other optical reflective film.

[0204] REFERENCE SIGNS LIST 1 Optical reflecting element 10 Fixed portion 40 Movable portion 40a Reflecting surface 41 Center portion 42 Rib portion 42a Angle adjustment portion 42b Notch 60 Spring portion 61 Beam portion 71 Optical reflecting film 72 Optical reflecting film (another optical reflecting film) 100 SOI wafer 101 Base layer 102 Oxide film 103 Active layer C10 Center GP Gap R10 Rotation axis

Claims

1. An optical reflecting element comprising: a fixed portion; and a movable portion supported on the fixed portion so as to be rotatable about a rotation axis, wherein the movable portion has a structure in which a base layer, an oxide film, and an active layer are stacked on an SOI wafer, from which the base layer and the oxide film have been removed, the movable portion having a central portion having a reflective surface located on an upper surface of the active layer; a rib portion located outside the central portion with a gap therebetween; and a flexible spring portion whose both ends are connected to the rib portion and whose space between the both ends is connected to the central portion.

2. An optical reflecting element according to claim 1, characterized in that the central portion is connected to approximately the center of the spring portion.

3. An optical reflecting element as described in claim 1, characterized in that the rib portion is provided with an angle adjustment portion for setting the angle between the normal direction of the rib portion at the connection position between the rib portion and the spring portion and the direction in which the spring portion extends from the connection position.

4. An optical reflecting element according to claim 3, characterized in that the angle adjustment portion is a protrusion protruding from the rib portion, or a recessed portion recessed inwardly of the rib portion.

5. An optical reflecting element as described in claim 3, characterized in that, when the sign of the angle formed when the normal line is inclined toward the central portion with respect to the direction in which the spring portion extends is taken as positive, the angle is set to 0° or less.

6. The optical reflecting element according to claim 5, wherein the angle is set to be equal to or greater than -30° and equal to or less than 0°.

7. An optical reflecting element according to claim 1, wherein the spring portion has a beam portion having both ends connected in a straight line.

8. An optical reflecting element according to claim 1, wherein the spring portion includes a beam portion connecting both ends, and the beam portion includes a bent or curved shape.

9. An optical reflecting element as described in claim 1, characterized in that a notch cut in a direction away from the center of the central portion is provided on the inner surface of the rib portion, and both ends of the spring portion are connected to the rib portion at the notch.

10. An optical reflecting element according to claim 1, characterized in that the spring portion is made of the same material as the central portion.

11. The optical reflecting element according to claim 10, wherein the spring portion is made of silicon (Si).

12. An optical reflecting element according to claim 1, wherein the rib portion has a structure in which at least a part of the active layer is removed from the SOI wafer.

13. An optical reflecting element according to claim 12, wherein the rib portion has a structure in which at least a part of the oxide film is further removed from the SOI wafer.

14. An optical reflecting element according to any one of claims 1 to 13, further comprising an optical reflecting film on an upper surface of the central portion, the reflecting surface being formed by the optical reflecting film.

15. The optical reflecting element according to claim 14, further comprising another optical reflecting film on the lower surface of said central portion.

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