Optical reflection element

Abstract

This optical reflection element comprises a movable part (11) that rotates about a rotation axis. The movable part (11) is provided with: a substrate (110); a reflective film (130) formed on the upper surface of the substrate (110); and a protective film (120) that completely covers the periphery of the reflective film (130). The protective film (120) includes: a first protective film (121) that covers at least the entirety of the lower surface of the reflective film (130); and a second protective film (122) that is not the first protective film (121), the first and second protective films being made of materials having substantially the same thermal expansion coefficients.

Description

Optical Reflective Elements

[0001] The present invention relates to an optical reflecting element in which a movable part on which a reflecting surface is formed is rotated about a rotation axis.

[0002] There is known an optical reflecting element in which a movable part having a reflective surface is rotated about a rotation axis. For example, Patent Document 1 below describes an optical scanning device (optical reflecting element) in which a movable part is rotated about two axes. A mirror is disposed in the area of ​​the movable part on a substrate. The mirror is formed by laminating a metal film, a low refractive index film, a high refractive index film, and a protective film in this order on the upper surface of the substrate.

[0003] JP 2015-41075 A

[0004] In the optical reflecting element as described above, peeling may occur at the joint between the substrate and the metal film (reflective film), or at the joint between the metal film and the low refractive index film, etc. Such peeling may allow substances (e.g., sulfur-based gases) to enter the film, which may cause deterioration of the reflective film.

[0005] In view of the above problem, an object of the present invention is to provide an optical reflecting element capable of suppressing deterioration of the reflecting film.

[0006] The optical reflecting element according to a main aspect of the present invention includes a movable part that rotates about a rotation axis. The movable part includes a substrate, a reflective film formed on the upper surface of the substrate, and a protective film that completely covers the periphery of the reflective film. The protective film has a first portion that covers at least the entire lower surface of the reflective film, and a second portion other than the first portion, which are made of materials with substantially the same thermal expansion coefficient.

[0007] According to the optical reflecting element of this aspect, the protective film completely covers the periphery of the reflective film, thereby preventing the intrusion of substances that impair the reflective film. Furthermore, since the first and second portions of the protective film have substantially equal thermal expansion coefficients, there is substantially no difference in thermal expansion or thermal contraction between the first and second portions. This prevents delamination at the joint between the first and second portions due to thermal expansion or thermal contraction. Therefore, substances that degrade the reflective film (e.g., sulfur-based gases) from penetrating the reflective film through such delamination. This reliably prevents degradation of the reflective film.

[0008] As described above, according to the present invention, an optical reflecting element capable of suppressing deterioration of the reflective film can be provided.

[0009] 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.

[0010] FIG. 1 is a plan view schematically showing the configuration of an optical reflecting element according to the first embodiment, as viewed from above (positive side along the Z axis). FIGS. 2(a) and 2(b) are cross-sectional views schematically showing a substrate and a layered structure near the center according to the first embodiment. FIGS. 3(a) and 3(b) are cross-sectional views schematically showing a substrate and a layered structure near the center according to the first embodiment. FIG. 4 is a cross-sectional view schematically showing a configuration of a movable portion according to the first embodiment. FIG. 5(a) is a cross-sectional view schematically showing a substrate and a layered structure near the center according to a first modified example of the first embodiment. FIG. 5(b) is a cross-sectional view schematically showing a configuration of a movable portion according to the first modified example of the first embodiment. FIG. 6(a) is a cross-sectional view schematically showing a substrate and a layered structure near the center according to a second modified example of the first embodiment. FIG. 6(b) is a cross-sectional view schematically showing a configuration of a movable portion according to the second modified example of the first embodiment. FIGS. 7(a) and 7(b) are cross-sectional views schematically showing a substrate and a layered structure near the center according to the second embodiment. Fig. 8 is a cross-sectional view schematically showing the configuration of a movable section according to embodiment 2. Fig. 9 is a cross-sectional view schematically showing the configuration of a movable section according to modified example 1 of embodiment 2. Fig. 10 is a cross-sectional view schematically showing the configuration of a movable section according to modified example 2 of embodiment 2. Fig. 11 is a plan view schematically showing the configuration of an optical reflecting element according to embodiment 3 when viewed from above (positive side of the Z axis).

[0011] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, each drawing is labeled with mutually orthogonal X, Y, and Z axes. The Y-axis direction is parallel to the rotation axis R0 of the optical reflecting element 1. The positive Z-axis direction is the vertically upward direction, which is the thickness direction (height direction) of the optical reflecting element 1.

[0013] The following embodiments describe an optical reflecting element that scans a beam incident on a reflecting surface by rotating the reflecting surface. This optical reflecting element is mounted, for example, on an image display device that displays a predetermined image by scanning the beam. However, the device in which the optical reflecting element is mounted is not limited to this. For example, an optical reflecting element having the following configuration may be mounted on an object detection device that detects the presence or absence of an object in the projection direction of the beam and the distance to the object.

[0014] First Embodiment FIG. 1 is a plan view schematically showing the configuration of an optical reflecting element 1 when viewed from above (positive side along the Z axis).

[0015] The optical reflecting element 1 includes a movable portion 11, two drive portions 12, two torsion portions 13, two connecting portions 14, and a fixed portion 15. The optical reflecting element 1 has a rectangular outline in a plan view. The optical reflecting element 1 has a shape that is symmetrical in the Y-axis direction and in the X-axis direction with respect to the center C0 of the movable portion 11.

[0016] Movable portion 11 is supported by fixed portion 15 via two torsion portions 13 and two connecting portions 14 so as to be rotatable about rotation axis R0. Rotation axis R0 extends parallel to the length direction (Y axis direction) of optical reflecting element 1 at the midpoint in the width direction (X axis direction) of optical reflecting element 1. A reflective surface 11a is formed on the upper surface (surface on the positive side of the Z axis) of movable portion 11. The configuration of reflective surface 11a will be described later with reference to FIG. 4.

[0017] The two torsion sections 13 have a beam-like shape extending along the rotation axis R0 and are arranged to sandwich the movable section 11 in the Y-axis direction. One end of the torsion section 13 on the Y-axis positive side is connected to the side surface of the movable section 11 on the Y-axis positive side, and the other end is connected to the connecting section 14 on the Y-axis positive side. One end of the torsion section 13 on the Y-axis negative side is connected to the side surface of the movable section 11 on the Y-axis negative side, and the other end is connected to the connecting section 14 on the Y-axis negative side.

[0018] The two connecting portions 14 have a plate-like shape extending along the rotation axis R0. The connecting portions 14 connect the drive portion 12 and the torsion portion 13 to the fixed portion 15.

[0019] The two driving units 12 each include a piezoelectric actuator 12b as a driving source and rotate the movable unit 11 about a rotation axis R0. Each of the two driving units 12 is formed by a tuning fork vibrator. That is, the two driving units 12 are formed by arranging the two tuning fork vibrators in opposite directions along the rotation axis R0.

[0020] Each drive unit 12 has a pair of arm units 12a extending in an L shape from the connecting unit 14. A piezoelectric actuator 12b for driving the movable unit 11 is disposed on the upper surface of the portion of each arm unit 12a extending in the Y-axis direction.

[0021] The piezoelectric actuator 12b has a layered structure in which an upper electrode layer and a lower electrode layer are respectively arranged above and below a piezoelectric layer. The piezoelectric layer is made of a piezoelectric material with a high piezoelectric constant, such as lead zirconate titanate (PZT). The material of the piezoelectric layer is not limited to PZT, and piezoelectric materials with other compositions may also be used. The upper electrode layer and the lower electrode layer are made of a material with low electrical resistance and high heat resistance, such as platinum (Pt) or gold (Au). The piezoelectric actuator 12b is formed on the upper surface of the arm portion 12a by a method such as sputtering.

[0022] Fixed portion 15 has a frame shape with a rectangular outline in a plan view. The outer contour of fixed portion 15 forms the outer contour of optical reflecting element 1. Fixed portion 15 supports movable portion 11, drive portion 12, and torsion portion 13 via two connecting portions 14.

[0023] Two terminals 16 are arranged on the upper surface of the fixed portion 15. The terminal 16 on the Y-axis positive side is connected to the two piezoelectric actuators 12b on the Y-axis positive side via wiring (not shown). The terminal 16 on the Y-axis negative side is connected to the two piezoelectric actuators 12b on the Y-axis negative side via wiring (not shown).

[0024] Two electrode pads 16a connected to the upper electrode layers of the corresponding piezoelectric actuators 12b and two electrode pads 16b connected to the lower electrode layers of the corresponding piezoelectric actuators 12b for connecting these lower electrode layers to ground are arranged on the upper surface of the terminal portion 16. The electrode pads 16a and 16b are exposed upward.

[0025] The base portion of the optical reflecting element 1 is made up of an active layer (Si), a box layer (SiO ２ The SOI wafer is formed by processing a silicon-on-insulator (SOI) wafer in which a silicon layer (Si) and a base layer (Si) are stacked in this order from above.

[0026] When optical reflecting element 1 is produced, reflecting surface 11a, piezoelectric actuator 12b, terminal portion 16, electrode pads 16a, 16b, etc. are formed on the upper surface side of the SOI wafer. Next, unnecessary portions of the SOI wafer are removed by etching or the like so as to form the outline of optical reflecting element 1 in a plan view. As a result, movable portion 11, drive portion 12, torsion portion 13, connecting portion 14, and fixed portion 15 are connected by common substrate 110 (see FIG. 2(a)) made of an active layer, and opening 15a penetrating vertically is formed around movable portion 11.

[0027] Furthermore, the box layer and base layer of the SOI wafer are etched to remove unnecessary portions of the box layer and base layer. As a result, a rib is formed on the outer periphery of the lower surface of the movable part 11, and a base part is formed on the entire lower surface of the fixed part 15. This ensures the mechanical strength of the movable part 11 and the fixed part 15.

[0028] Optical reflecting element 1 is used by being electrically connected to an external circuit board or the like via electrode pads 16 a, 16 b. Electrode pads 16 a, 16 b are connected to the external circuit board or the like by wiring means such as wire bonding. Electrode pads 16 a, 16 b may also be connected to the external circuit board or the like via a support substrate. In this case, the support substrate has a plurality of electrode pads arranged in positions facing the plurality of electrode pads on optical reflecting element 1, and optical reflecting element 1 is adhered to the support substrate, whereby electrode pads 16 a, 16 b are connected to the external circuit board or the like.

[0029] When the optical reflecting element 1 is driven, an AC voltage is applied to the four piezoelectric actuators 12b to resonantly drive the movable portion 11 at the natural frequency (resonance frequency) of the optical reflecting element 1. As a result, each of the four piezoelectric actuators 12b is deformed due to the inverse piezoelectric effect. At this time, the AC voltages applied to two piezoelectric actuators 12b aligned in the Y-axis direction are set to the same phase, and the AC voltages applied to two piezoelectric actuators 12b aligned in the X-axis direction are set to opposite phases. As a result, the deformation direction (amplitude direction) of the two piezoelectric actuators 12b on the positive side of the X-axis is opposite to the deformation direction (amplitude direction) of the piezoelectric actuator 12b on the negative side of the X-axis.

[0030] In this way, the deformation of the four piezoelectric actuators 12b causes the deformation of the arm portion 12a, and the movable portion 11 is resonantly driven at a predetermined resonance frequency around the rotation axis R0 via the two torsion portions 13. As a result, light of a predetermined wavelength band that is incident on the movable portion 11 from above is reflected by the reflecting surface 11a of the movable portion 11 and irradiated onto the target area.

[0031] Next, the procedure for forming the movable portion 11 will be described with reference to FIGS.

[0032] Figures 2(a) to 3(b) are cross-sectional views schematically showing substrate 110 and the laminated structure near center C0, and Figure 4 is a cross-sectional view schematically showing the configuration of movable section 11. The cross-sectional views of Figures 2(a) to 4 are views of the C1-C2 cross section when optical reflecting element 1 is cut along a plane parallel to the X-Z plane passing through center C0, as viewed in the positive direction of the Y axis.

[0033] 2(a) to 3(b) show only the upper end vicinity of the substrate 110 (active layer) of the SOI wafer for convenience, and FIG. 4 shows only the upper end vicinity of the substrate 110 that has been subjected to the etching process for convenience. Each layer of the stacked structure is formed by a PVD (physical vapor deposition) method typified by sputtering or evaporation, a CVD (chemical vapor deposition) method, a liquid phase deposition method typified by a sol-gel method, or the like. Each layer of the stacked structure is removed by applying a resist, dry etching, wet etching, or the like.

[0034] As shown in FIG. 2A , a first protective film 121 and a reflective film 130 are stacked in this order on the upper surface of the SOI wafer substrate 110. In this embodiment, the reflective film 130 is made of silver (Ag) or a silver (Ag) alloy. The silver alloy is, for example, an alloy made of silver (Ag), palladium (Pd), and copper (Cu), and an APC (registered trademark) alloy can be used as the silver alloy. The reflective film 130 may be made of two layers with a metal film such as titanium (Ti) as a base.

[0035] Next, from the state shown in Fig. 2(a), the reflective film 130 located outside the vicinity of the center C0 is removed by etching, thereby leaving the reflective film 130 in the region corresponding to the reflective surface 11a (see Fig. 1) as shown in Fig. 2(b).

[0036] 2(b), as shown in FIG. 3(a), a second protective film 122 is formed on the upper surfaces of the first protective film 121 and the reflective film 130. For example, a material that can provide moisture resistance to the reflective film 130 is selected as the material for the second protective film 122. Furthermore, a material with high transmittance is selected as the material for the second protective film 122 so that light incident on the reflective film 130 from above can be transmitted therethrough.

[0037] 3A, a joint J1 where the first protective film 121 and the second protective film 122 are closely overlapped is formed on the outside of the reflective film 130, and the side surface (outer end) of the reflective film 130 is covered with the protective film 120 made up of the first protective film 121 and the second protective film 122. In FIG. 3A, the joint J1 is shown by a dashed line for convenience.

[0038] 3A, the protective film 120 outside the region corresponding to the movable portion 11 (see FIG. 1) is removed by etching, whereby the outer ends of the first protective film 121 and the second protective film 122 are aligned at the same position in a plan view, as shown in FIG.

[0039] Next, from the state shown in FIG. 3(b), the SOI wafer is formed into a circular shape in plan view to match the contour of the movable part 11 (see FIG. 1). Furthermore, on the underside of the substrate 110 in the range of the movable part 11, the box layer and base layer near the center C0 are removed so that ribs made of the box layer and base layer are formed around the periphery. In this way, the movable part 11 is completed as shown in FIG. 4. The reflective surface 11a of the movable part 11 (see FIG. 1) is composed of a reflective film 130 and a second protective film 122.

[0040] 1, since the movable portion 11 has a circular shape in a plan view, the cross-sectional structures of the protective film 120 and the reflective film 130 are the same as those in FIG. 4 over the entire periphery. That is, any cross section along any plane passing through the center C0 and perpendicular to the X-Y plane is the same as that in FIG.

[0041] 4, in the movable portion 11, the second protective film 122 has a thickness W1, and a width in the XY plane of a joint J1 between the first protective film 121 and the second protective film 122 is W2. In this embodiment, the first protective film 121 and the second protective film 122 are formed and etched so that W1<W2. In this embodiment, the thickness W1 is set to 60 nm, and the width W2 is set to 10 μm, for example.

[0042] Furthermore, as shown in FIG. 4, the protective film 120 covers the entire periphery of the reflective film 130, thereby preventing substances that may damage the reflective film 130 (for example, sulfur-based gases) from entering from the outside.

[0043] According to the inventors' investigations, it has been found that if a difference in thermal expansion or thermal contraction occurs between the first protective film 121 and the second protective film 122, peeling may occur at the joint J1 between the first protective film 121 and the second protective film 122. If such peeling occurs, substances that inhibit the reflective film 130 (e.g., sulfur-based gases) may enter, potentially deteriorating the reflective film 130. In contrast, in this embodiment, the first protective film 121 and the second protective film 122 are made of the same material, and therefore the thermal expansion coefficients of the first protective film 121 and the second protective film 122 are equal to each other. This prevents peeling at the joint J1 between the first protective film 121 and the second protective film 122 due to thermal expansion or thermal contraction.

[0044] From the above, in this embodiment, the first protective film 121 and the second protective film 122 are both made of aluminum oxide (Al ２ O ３ The first protective film 121 and the second protective film 122 are made of silicon nitride (Si ３ N ４ ) may be configured.

[0045] When the first protective film 121 and the second protective film 122 are made of the same material as in this embodiment, the boundary between the first protective film 121 and the second protective film 122, i.e., the joint J1, may substantially disappear and become unrecognizable in the state of the completed movable part 11 shown in Fig. 4. However, even in this case, the protective film 120 is made up of a first portion that covers at least the entire area of ​​the lower surface of the reflective film 130 and a second portion other than the first portion, and these portions are made of materials with substantially the same thermal expansion coefficient.

[0046] <Effects of First Embodiment> According to the first embodiment, the following effects are achieved.

[0047] As shown in Fig. 1, optical reflecting element 1 includes movable part 11 that rotates about rotation axis R0. As shown in Fig. 4, movable part 11 includes substrate 110, reflective film 130 formed on the upper surface of substrate 110, and protective film 120 that covers the entire periphery of reflective film 130. Protective film 120 includes first protective film 121 (first portion) that covers at least the entire lower surface of reflective film 130, and second protective film 122 (second portion) other than first protective film 121 (first portion), which are made of materials with substantially the same thermal expansion coefficient.

[0048] According to this configuration, the protective film 120 completely covers the periphery of the reflective film 130, thereby preventing the intrusion of substances that may impair the reflective film 130. Furthermore, because the first and second portions of the protective film 120 have substantially equal thermal expansion coefficients, there is substantially no difference in thermal expansion or thermal contraction between the first and second portions. This prevents peeling at the joint J1 between the first and second portions due to thermal expansion or thermal contraction. This prevents substances that may degrade the reflective film 130 (e.g., sulfur-based gases) from penetrating the reflective film through such peeling. This reliably prevents degradation of the reflective film 130.

[0049] The first protective film 121 (first portion) and the second protective film 122 (second portion) are made of the same material.

[0050] With this configuration, the first part and the second part have the same thermal expansion coefficient, so that peeling due to thermal expansion or thermal contraction at the joint J1 between the first part and the second part can be reliably prevented.

[0051] The same material constituting the first protective film 121 (first portion) and the second protective film 122 (second portion) is Al. ２ O ３ or Si ３ N ４ is.

[0052] According to this configuration, the material is Al ２ O ３In this case, moisture resistance of the reflective film 130 can be realized, and the adhesion between the reflective film 130 and the substrate 110 can be improved. ３ N ４ In this case, moisture resistance can be achieved for the reflective film 130, and Si ３ N ４ The toughness (mechanical strength) of the reflective film 130 can effectively protect the upper surface of the reflective film 130 .

[0053] As shown in FIG. 4, the junction J1 between the first protective film 121 (first portion) and the second protective film 122 (second portion) is larger than the film thickness W1 of the second protective film 122 (second portion) and extends in a direction parallel to the XY plane (planar direction).

[0054] According to this configuration, the width of the joint J1 between the first and second parts is increased, so that peeling at the joint J1 between the first and second parts can be reliably prevented.

[0055] The reflective film 130 is made of silver or a silver alloy.

[0056] This configuration can increase the reflectivity of the reflective film 130. Furthermore, although the reflectivity of silver and silver alloys decreases when they are sulfurized by sulfur-based gases, when the entire surface of the reflective film 130 is covered with the protective film 120 as described above, it is possible to prevent sulfur-based gases from entering the reflective film 130 from the outside. This makes it possible to suppress deterioration of the reflective film 130.

[0057] <First Modification of First Embodiment> In the first embodiment, the first protective film 121 is formed to be wider in the planar direction than the reflective film 130, but the first protective film 121 and the reflective film 130 may be the same size in a planar view.

[0058] The procedure for forming the movable portion 11 according to this modified example will be described with reference to FIGS.

[0059] 2B, the first protective film 121 other than the region of the reflective film 130 in plan view is removed by etching, so that the first protective film 121 has the same size as the reflective film 130 in plan view, as shown in FIG.

[0060] 5(a), a second protective film 122 is formed, and the outer portion of the second protective film 122 is removed by etching so that the outer edge of the first protective film 121 is covered by the second protective film 122. In this case, the joint J1 between the first protective film 121 and the second protective film 122 extends in the Z-axis direction. In this way, the movable portion 11 is completed as shown in FIG. 5(b).

[0061] In this modified example, similarly to the first embodiment, the protective film 120 made up of the first protective film 121 and the second protective film 122 covers the entire periphery of the reflective film 130, and therefore the protective film 120 can prevent the intrusion of substances that would inhibit the reflective film 130. Furthermore, the first protective film 121 and the second protective film 122 have the same thermal expansion coefficient, and therefore peeling at the joint J1 due to thermal expansion or thermal contraction can be prevented.

[0062] <Modification 2 of Embodiment 1> In Embodiment 1, the first protective film 121 is formed parallel to the substrate 110, and a stepped portion is formed in the second protective film 122 so that the second protective film 122 covers the outer edge of the reflective film 130. However, the present invention is not limited to this, and a stepped portion may be formed in the first protective film 121 so that the first protective film 121 covers the outer edge of the reflective film 130, and the second protective film 122 may be formed parallel to the substrate 110.

[0063] The procedure for forming the movable portion 11 according to this modified example will be described with reference to FIGS.

[0064] As shown in FIG. 6A, a recess R1 is formed near the center of a first protective film 121 formed on the upper surface of a substrate 110, and a reflective film 130 is formed in the recess R1.

[0065] 6(a), a second protective film 122 is formed, and the second protective film 122 outside the first protective film 121 is removed by etching. In this case, the junction J1 between the first protective film 121 and the second protective film 122 extends parallel to the XY plane. In this way, the movable section 11 is completed as shown in FIG. 6(b).

[0066] In this modified example, similarly to the first embodiment, the protective film 120 made up of the first protective film 121 and the second protective film 122 covers the entire periphery of the reflective film 130, and therefore the protective film 120 can prevent the intrusion of substances that would inhibit the reflective film 130. Furthermore, the first protective film 121 and the second protective film 122 have the same thermal expansion coefficient, and therefore peeling at the joint J1 due to thermal expansion or thermal contraction can be prevented.

[0067] Second Embodiment In a second embodiment, a third protective film 140 is further formed on the movable portion 11 shown in Fig. 4. Other configurations of the second embodiment are the same as those of the first embodiment.

[0068] A procedure for forming the movable portion 11 according to the second embodiment will be described with reference to FIGS.

[0069] 4, as shown in FIG. 7A, a third protective film 140 having a predetermined thickness is formed on the upper surfaces of the substrate 110 and the protective film 120. As a material for the third protective film 140, for example, a material that can realize warm water resistance for the reflective film 130 is selected. Furthermore, a material with high transmittance is selected as a material for the third protective film 140 so that light incident on the reflective film 130 from above can be transmitted. Furthermore, a material with a higher refractive index than the second protective film 122 is selected as a material for the third protective film 140 so that a dielectric multilayer film is formed by the second protective film 122 and the third protective film 140 and the reflectance of light incident on the reflective surface 11a (see FIG. 1) is increased.

[0070] From the above, in the second embodiment, the third protective film 140 is made of zirconium dioxide (ZrO ２ The third protective film 140 is made of ZrO ２ , TiO ２ , Nb ２ O ５ , CeO ２ , Ta ２ O ５ , HfO ２ , Si ３ N ４ , Y ２ O ３ , MgO, SiO ２ , MgF ２The film may be composed of a single layer of any one of the above or a laminated film of a combination of at least two of these.

[0071] Next, from the state shown in FIG. 7(a), the outer portion of the third protective film 140 is removed by etching so that the outer edge of the protective film 120 is covered by the third protective film 140, as shown in FIG. 7(b).

[0072] 7B, the SOI wafer is then formed into a circular shape in plan view to match the contour of the movable part 11, and ribs are formed on the underside of the substrate 110. In this way, the movable part 11 is completed as shown in Fig. 8. The reflective surface 11a of the movable part 11 (see Fig. 1) is composed of the reflective film 130, the second protective film 122, and the third protective film 140.

[0073] <Effects of Second Embodiment> According to the second embodiment, the following effects are achieved.

[0074] As shown in FIG. 8, optical reflecting element 1 further includes third protective film 140 (another protective film) that covers the upper and side surfaces of protective film 120 .

[0075] This configuration further protects the upper and side surfaces of the reflective film 130. Furthermore, by forming a dielectric multilayer film with the second protective film 122 (second portion) of the protective film 120 located on the upper surface of the reflective film 130 and the third protective film 140 (another protective film) located on the upper surface side of the second protective film 122 (second portion), the reflectance of the reflective film 130 can be increased.

[0076] The third protective film 140 (another protective film) is ZrO ２ , TiO ２ , Nb ２ O ５ , CeO ２ , Ta ２ O ５ , HfO ２ , Si ３ N ４ , Y ２ O ３ , MgO, SiO ２ , MgF ２ The film is composed of a single layer of any one of the above or a laminated film of a combination of at least two of these.

[0077] According to this configuration, another protective film having excellent resistance to warm water can be formed satisfactorily on the surface of the protective film 120 .

[0078] First Modification of Second Embodiment FIG. 9 is a cross-sectional view schematically showing the configuration of the movable portion 11 according to this modification.

[0079] In this modification, isotropic etching is used as the etching process for the protective film 120 (first protective film 121 and second protective film 122) from the state shown in Fig. 3(a) . As a result, the outer edge of the protective film 120 has a tapered shape with the lower portion widening outward, as shown by the dashed circle in Fig. 9 .

[0080] Next, similarly to the second embodiment, the third protective film 140 is formed and then etched. Isotropic etching is also used for the etching of the third protective film 140. As a result, the shape of the third protective film 140 near the outer edge of the protective film 120 is tapered, reflecting the shape of the edge of the protective film 120.

[0081] According to this modification, tapering the end of the protective film 120 improves adhesion of the third protective film 140 to the protective film 120. This improves the coverage of the third protective film 140 to the protective film 120.

[0082] <Modification 2 of Embodiment 2> In Embodiment 2, the first protective film 121 and the second protective film 122 are made of the same material, but this is not limited thereto, and the first protective film 121 and the second protective film 122 may be made of different materials as long as they have substantially the same thermal expansion coefficients.

[0083] FIG. 10 is a cross-sectional view schematically showing the configuration of the movable portion 11 according to this modified example.

[0084] In this modified example, the first protective film 121 and the second protective film 122 are made of different materials, as compared to the second embodiment shown in Fig. 8. However, as described in the first embodiment, materials having substantially the same thermal expansion coefficients are selected for the first protective film 121 and the second protective film 122, and a material with high transmittance is selected for the second protective film 122 so that light incident on the reflective film 130 from above can be transmitted. Furthermore, as described in the second embodiment, the material for the second protective film 122 is selected so that the refractive index of the second protective film 122 is smaller than the refractive index of the third protective film 140.

[0085] From the above, in this modification, the first protective film 121 is made of aluminum oxide (Al ２ O ３ , alumina), and the second protective film 122 is made of yttrium oxide (Y ２ O ３ , yttria), and the third protective film 140 is made of zirconium dioxide (ZrO ２ , zirconia).

[0086] The materials of the first protective film 121 and the second protective film 122 are not limited to those mentioned above. ２ , TiO ２ , Nb ２ O ５ , CeO ２ , Ta ２ O ５ , HfO ２ , Si ３ N ４ , Y ２ O ３ , MgO, SiO ２ , MgF ２ The film may be composed of a single layer of any one of the above or a laminated film of a combination of at least two of these.

[0087] According to this modification, the first protective film 121 (first portion) and the second protective film 122 (second portion) are made of different materials.

[0088] According to this configuration, although the first part and the second part are made of different materials, they have substantially the same thermal expansion coefficients, so that it is possible to reliably prevent peeling due to thermal expansion or thermal contraction at the joint J1 between the first part and the second part.

[0089] In addition, in embodiment 1, the first protective film 121 and the second protective film 122 may also be made of different materials as long as they have substantially the same thermal expansion coefficient.

[0090] Third Embodiment In the first and second embodiments, the driving unit 12 is a tuning fork type vibrator, but the driving unit 12 may be a vibrator of another type. In a third embodiment, the driving unit 12 is a meander type vibrator.

[0091] FIG. 11 is a plan view schematically showing the configuration of an optical reflecting element 1 according to the third embodiment.

[0092] In the third embodiment, compared to the first embodiment shown in Fig. 1, the pair of torsion units 13 is omitted, and the pair of driving units 12 are meandering vibrators. The driving units 12 include four rectangular arm units 12a connected to each other and four piezoelectric actuators 12b installed on the four arm units 12a. An inner end of the driving unit 12 is connected to the movable unit 11, and an outer end of the driving unit 12 is connected to the fixed unit 15 via a connecting unit 14.

[0093] In the third embodiment, the movable portion 11 is configured in the same manner as in Figures 4, 5(b), 6(b), 8, 9, and 10. This provides the same effects as in the first and second embodiments and the modified examples.

[0094] <Other Modifications> The configuration examples of the present invention are not limited to the above-described embodiment and modifications, and various modifications are possible.

[0095] 4, in the first embodiment, the outer edge of the protective film 120 is set back relative to the outer edge of the substrate 110 in a direction approaching the center C0, but the outer edge of the protective film 120 may overlap the outer edge of the substrate 110 in a plan view. This allows the width W2 of the bonding portion J1 to be increased, and peeling of the bonding portion J1 can be more reliably prevented.

[0096] 8 , in the second embodiment, the outer edge of the third protective film 140 is set back relative to the outer edge of the substrate 110 in a direction approaching the center C0, but the outer edge of the third protective film 140 may overlap the outer edge of the substrate 110 in a plan view. This allows the protective film 120 to be reliably covered by the third protective film 140.

[0097] In the second embodiment, the third protective film 140 is formed directly on the upper surface and side surfaces of the protective film 120, but this is not limiting and the third protective film 140 may be formed on the upper surface and side surfaces of the protective film 120 via another film. In this case as well, a material with high transmittance is selected as the material of the other film in order to transmit light incident on the reflective film 130 from above.

[0098] In the above embodiment and modified examples, the shape of the movable part 11 and the reflecting surface 11a is circular, but the shape of the movable part 11 and the reflecting surface 11a may be other shapes such as square, etc. Furthermore, the shape of the optical reflecting element 1 and the dimensions of each part can also be changed as appropriate.

[0099] 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.

[0100] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0101] (Technology 1) An optical reflecting element comprising a movable part that rotates about a rotation axis, the movable part comprising: a substrate; a reflective film formed on the upper surface side of the substrate; and a protective film that covers the entire periphery of the reflective film, wherein the protective film has a first portion that covers at least the entire lower surface of the reflective film, and a second portion other than the first portion, which are made of materials having substantially the same thermal expansion coefficient.

[0102] According to this technology, the protective film completely covers the periphery of the reflective film, thereby preventing the intrusion of substances that may impair the reflective film. Furthermore, since the first and second portions of the protective film have substantially equal thermal expansion coefficients, there is substantially no difference in thermal expansion or thermal contraction between the first and second portions. This prevents delamination at the interface between the first and second portions due to thermal expansion or thermal contraction. Therefore, substances that degrade the reflective film (e.g., sulfur-based gases) from penetrating the reflective film through such delamination. This reliably prevents degradation of the reflective film.

[0103] (Technology 2) The optical reflecting element according to Technology 1, wherein the first portion and the second portion are made of the same material.

[0104] According to this technology, the first part and the second part have the same thermal expansion coefficient, so that it is possible to reliably prevent peeling due to thermal expansion or thermal contraction at the joint between the first part and the second part.

[0105] (Technology 3) In the optical reflecting element according to Technology 2, the material is Al ２ O ３ or Si ３ N ４ An optical reflecting element characterized by:

[0106] According to this technique, the material is Al ２ O ３ In the case where the material is Si, moisture resistance can be realized for the reflective film, and adhesion between the reflective film and the substrate can be improved. ３ N ４ In this case, moisture resistance can be achieved for the reflective film, and Si ３ N ４ The toughness (mechanical strength) of the film effectively protects the upper surface of the reflective film.

[0107] (Technology 4) The optical reflecting element according to Technology 1, wherein the first portion and the second portion are made of different materials.

[0108] According to this technology, although the first part and the second part are made of different materials, they have substantially the same thermal expansion coefficients, so that it is possible to reliably prevent peeling due to thermal expansion or thermal contraction at the joint between the first part and the second part.

[0109] (Technology 5) The optical reflecting element described in any one of Technologies 1 to 4, characterized in that the joint portion between the first portion and the second portion extends in the planar direction to a greater extent than the film thickness of the second portion.

[0110] According to this technique, the width of the joint between the first and second parts is increased, so that it is possible to reliably prevent separation from occurring at the joint between the first and second parts.

[0111] (Technology 6) The optical reflecting element according to any one of Technologies 1 to 5, characterized in that the reflective film is made of silver or a silver alloy.

[0112] This technology can increase the reflectivity of the reflective film. Furthermore, although the reflectivity of silver and silver alloys decreases when they are sulfurized by sulfur-based gases, covering the entire surface of the reflective film with a protective film as described above can prevent sulfur-based gases from penetrating the reflective film from the outside. This can suppress deterioration of the reflective film.

[0113] (Technology 7) The optical reflecting element according to any one of Techniques 1 to 6, further comprising another protective film covering an upper surface side and a side surface side of the protective film.

[0114] This technique further protects the upper and side surfaces of the reflective film, and by forming a dielectric multilayer film with the second portion of the protective film located on the upper surface of the reflective film and another protective film located on the upper side of the second portion, the reflectivity of the reflective film can be increased.

[0115] (Technology 8) In the optical reflecting element according to Technology 7, the other protective film is ZrO ２ , TiO ２ , Nb ２ O ５ , CeO２ , Ta ２ O ５ , HfO ２ , Si ３ N ４ , Y ２ O ３ , MgO, SiO ２ , MgF ２ 1. An optical reflecting element comprising a single layer film of any one of the above or a laminated film of a combination of at least two of these.

[0116] According to this technique, another protective film having excellent resistance to warm water can be formed satisfactorily on the surface of the protective film.

[0117] REFERENCE SIGNS LIST 1 Optical reflecting element 11 Movable portion 101 Substrate 120 Protective film 121 First protective film (first portion) 122 Second protective film (second portion) 130 Reflective film 140 Third protective film (another protective film) J1 Joint portion R0 Rotation axis

Claims

1. An optical reflecting element comprising a movable part that rotates about a rotation axis, the movable part comprising: a substrate; a reflective film formed on the upper surface of the substrate; and a protective film that covers the entire periphery of the reflective film, wherein the protective film has a first portion that covers at least the entire lower surface of the reflective film, and a second portion other than the first portion, which are made of materials with substantially the same thermal expansion coefficient.

2. An optical reflecting element according to claim 1, wherein the first portion and the second portion are made of the same material.

3. The optical reflecting element according to claim 2, wherein the material is Al. ２ O ３ or Si ３ N ４ An optical reflecting element characterized by:

4. An optical reflecting element according to claim 1, wherein the first portion and the second portion are made of different materials.

5. An optical reflecting element according to claim 1, wherein the joint between the first portion and the second portion extends in the planar direction to a greater extent than the film thickness of the second portion.

6. An optical reflecting element according to claim 1, characterized in that the reflective film is made of silver or a silver alloy.

7. An optical reflecting element according to claim 1, further comprising another protective film covering the upper and side surfaces of said protective film.

8. The optical reflecting element according to claim 7, wherein the other protective film is ZrO ２ , TiO ２ , Nb ２ O ５ , CeO ２ , Ta ２ O ５ , HfO ２ , Si ３ N ４ , Y ２ O ３ , MgO, SiO ２ , MgF ２ 1. An optical reflecting element comprising a single layer film of any one of the above or a laminated film of a combination of at least two of these.

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