Optical reflective element

Abstract

To provide an optical reflective element that can achieve miniaturization while maintaining the rotational characteristics of the movable part. [Solution] The optical reflective element comprises a movable part having a reflective surface and a meander-shaped drive unit 30 that rotates the movable part about a pivot axis. The drive unit 30 has an active layer 201 that extends over the entire drive unit 30, an intermediate layer 202 positioned on the lower surface of the active layer 201 in the meander-shaped folded portion, and a base layer 203 positioned below the intermediate layer 202. In the meandering direction of the meander shape, the inside of the intermediate layer 202 is recessed outward from the inside of the base layer 203.

Description

Technical Field

[0001] The present invention relates to an optical reflection element including a movable part having a reflection surface formed thereon.

Background Art

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

[0003] Patent Document 1 below describes an optical reflection element including a movable part having a mirror formed thereon, a driving part that repeatedly rotates the movable part, and a fixed part that supports the driving part. The driving part includes four vibrating parts connected so as to form a meander shape, and a reinforcing part is disposed on the lower surface of an end where two vibrating parts are connected to each other. Thereby, the rigidity of the driving part is increased.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In an optical reflection element such as that of Patent Document 1 above, it is desired to miniaturize the optical reflection element by shortening the length in the meandering direction of the meander shape while maintaining a desired resonance frequency and deflection angle with respect to the rotation of the movable part. However, shortening the length in the meandering direction of the meander shape makes it difficult to achieve a desired resonance frequency and deflection angle.

[0006] In view of such problems, an object of the present invention is to provide an optical reflection element capable of achieving miniaturization while maintaining the rotational characteristics of the movable part. [Means for solving the problem]

[0007] An optical reflective element according to the main aspect of the present invention comprises a movable part having a reflective surface and a meander-shaped drive unit that rotates the movable part about a pivot axis. The drive unit has an active layer that extends throughout the entire drive unit, an intermediate layer disposed on the lower surface of the active layer in the folded portion of the meander shape, and a base layer disposed below the intermediate layer. In the meandering direction of the meander shape, the inside of the intermediate layer is recessed outward from the inside of the base layer.

[0008] According to the optical reflective element of this embodiment, in the meandering direction of the meander shape, the inside of the intermediate layer located on the lower surface of the folded portion of the active layer recedes outward from the inside of the base layer located below the intermediate layer. This makes it possible to suppress an increase in the resonant frequency of the movable part and a decrease in the deflection angle of the movable part, even if the length in the meandering direction of the meander shape is shortened. Therefore, it is possible to miniaturize the optical reflective element while maintaining the rotational characteristics of the movable part. [Effects of the Invention]

[0009] As described above, the present invention provides an optical reflective element that can be miniaturized while maintaining the rotational characteristics of the movable part.

[0010] The effects and significance of the present invention will become even clearer from the description of the embodiments shown below. However, the embodiments shown below are merely examples of how to implement the present invention, and the present invention is not limited in any way to those described in the embodiments below. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic plan view of the configuration of an optical reflective element as seen from the surface side, according to an embodiment. [Figure 2] Figure 2 is a schematic bottom view showing the configuration of the optical reflective element as seen from the back side according to the embodiment. [Figure 3]Figure 3 is a schematic side view showing the C1-C2 end face of Figure 2 according to an embodiment. [Figure 4] Figure 4 is a schematic bottom view showing the configuration of the drive unit on the negative X-axis side as seen from the back side, according to an embodiment. [Figure 5] Figures 5(a) and 5(b) schematically show the etching process of the intermediate layer in a comparative example. [Figure 6] Figures 6(a) and 6(b) schematically show the etching process of the intermediate layer according to the embodiment. [Figure 7] Figure 7 is a schematic side view showing the C1-C2 end face of Figure 2, illustrating an example of a change in the shape of the intermediate layer. [Figure 8] Figure 8 is a schematic bottom view showing the drive unit configuration on the negative X-axis side as seen from the back side, relating to an example of a change in the shape of the intermediate layer. [Figure 9] Figures 9(a) and 9(b) schematically show the etching process of the intermediate layer in relation to an example of changing the shape of the intermediate layer. [Figure 10] Figure 10 is a table showing the simulation results of the comparative example, embodiment, and modified model. [Figure 11] Figures 11(a) to (c) are schematic side views showing the end face of the drive unit for a comparative example, an embodiment, and a modified example, respectively. [Figure 12] Figure 12 is a schematic bottom view showing the configuration of the optical reflective element as seen from the back side, relating to an example of a modified rib shape. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the figures. For convenience, mutually orthogonal X, Y, and Z axes are indicated in each figure. The positive direction of the Z axis is the vertically upward direction.

[0013] Figure 1 is a schematic plan view of the configuration of the optical reflective element 1 as seen from the surface side (in the negative Z-axis direction).

[0014] The optical reflection element 1 includes a movable part 10, a pair of connecting parts 20, a pair of driving parts 30, a pair of connecting parts 40, and a fixed part 50. The optical reflection element 1 has a point-symmetric shape about the center C10 in a plan view. The optical reflection element 1 is formed by processing a SOI wafer, and each part of the optical reflection element 1 is integrally connected by an active layer 201 described later.

[0015] The movable part 10 has a circular contour in a plan view. The center of the movable part 10 coincides with the position of the center C10 of the optical reflection element 1. On the upper surface of the movable part 10 (the upper surface of the active layer 201 described later), a reflecting surface 11 for reflecting light is formed. Usually, since the upper surface of the active layer 201 has a sufficient reflectivity by the production of the SOI wafer, the upper surface of the active layer 201 can be used as the reflecting surface 11. In addition, the reflectivity of the reflecting surface 11 may be enhanced by polishing the upper surface of the active layer 201 of the movable part 10. Alternatively, an optical reflection film may be separately formed on the upper surface of the active layer 201 of the movable part 10, and the upper surface of the optical reflection film may be used as the reflecting surface 11.

[0016] The connecting part 20 has an L shape in a plan view. The pair of connecting parts 20 are connected to the ends of the movable part 10 on the positive side and the negative side of the X axis.

[0017] The driving part 30 has a meander shape (serpentine shape) in a plan view. The driving part 30 is connected to the connecting part 20 at the end 30a on the movable part 10 side, and is connected to the connecting part 40 at the end 30c on the side opposite to the movable part 10. The ends 30a and 30c have a rectangular shape in a plan view. The folded-back part 30b of the meander shape of the driving part 30 has a rectangular shape in a plan view and extends in the X-axis direction. The pair of driving parts 30 are arranged so as to sandwich the movable part 10 in the X-axis direction, and rotate the movable part 10 about the rotation axis R10 via the pair of connecting parts 20.

[0018] Each drive unit 30 comprises one diaphragm 31 and four piezoelectric elements 32. The diaphragm 31 comprises four vibrating parts 31a. Each of the four vibrating parts 31a has a rectangular shape in plan view and extends in the Y-axis direction. The four vibrating parts 31a are arranged in a line with a predetermined gap between them in the X-axis direction.

[0019] The piezoelectric body 32 is formed on the upper surface of the vibrating part 31a and is a so-called piezoelectric transducer. A piezoelectric transducer is sometimes called a piezoelectric actuator. The piezoelectric body 32 has a layered structure consisting of an upper electrode layer 211, a piezoelectric body layer 212, and a lower electrode layer 213, which will be described later. When a driving voltage is applied to the piezoelectric body 32, the piezoelectric body layer 212 within the piezoelectric body 32 deforms due to the inverse piezoelectric effect, and the vibrating part 31a on which the piezoelectric body 32 is formed vibrates in a way that causes it to bend. The piezoelectric body 32 is connected to electrodes on the fixed part 50 via wiring on the diaphragm 31. Cables (external wiring) connected to external devices are connected to the electrodes on the fixed part 50 by wire bonding, for example.

[0020] Of the four vibrating parts 31a of a single diaphragm 31, a first drive voltage with the same phase is applied to the piezoelectric elements 32 on the first and third vibrating parts 31a from the inside, and a second drive voltage with the same phase is applied to the piezoelectric elements 32 on the second and fourth vibrating parts 31a from the inside. At this time, the first drive voltage and the second drive voltage are in opposite phase to each other. As a result, the diaphragm 31 having a meander shape rotates about the pivot axis R10, and the movable part 10 supported by the pair of diaphragms 31 rotates about the pivot axis R10.

[0021] The fixed part 50 is frame-shaped, and an opening 51 is formed in the center of the fixed part 50, penetrating it in the Z-axis direction. The movable part 10, a pair of connecting parts 20, a pair of drive parts 30, and a pair of connecting parts 40 are located within the opening 51. The fixed part 50 supports the pair of drive parts 30 via the pair of connecting parts 40.

[0022] Figure 2 is a schematic bottom view showing the configuration of the optical reflective element 1 as seen from the back side (in the positive Z-axis direction).

[0023] In Figure 2, the ribs 101-104 and 111-113, which are formed on the back side (negative Z-axis side) of the optical reflective element 1 and protrude in the negative Z-axis direction, are shown as halftone dots for convenience. As will be described later, each rib is composed of an intermediate layer 202 and a base layer 203. That is, in Figure 2, the optical reflective element 1 is composed of an active layer 201, an intermediate layer 202 and a base layer 203 in the halftone dot area, and is composed of only the active layer 201 in the area other than the halftone dot area. However, as will be described later, in some parts of the ribs 111-113, the intermediate layer 202 is recessed inward relative to the base layer 203.

[0024] A rib 101 having an annular shape in plan view is formed on the back surface of the active layer 201 that constitutes the movable part 10. A rib 102 is formed on the back surface of the active layer 201 that constitutes the connecting part 20. One rib 111, three ribs 112, and one rib 113 are formed on the back surface of the active layer 201 that constitutes one diaphragm 31. Rib 111 is formed on the back surface of the active layer 201 at end 30a, rib 112 is formed on the back surface of the active layer 201 at folded part 30b, and rib 113 is formed on the back surface of the active layer 201 at end 30c. A rib 103 is formed on the back surface of the active layer 201 that constitutes the connecting part 40. A rib 104 is formed on the back surface of the active layer 201 that constitutes the fixed part 50.

[0025] Figure 3 is a schematic side view showing the C1-C2 end face of Figure 2.

[0026] The optical reflective element 1 is formed by processing a single SOI wafer in which an active layer 201, an intermediate layer 202, and a base layer 203 are stacked in the negative Z-axis direction. The active layer 201 and the base layer 203 are made of, for example, silicon (Si), and the intermediate layer 202, sometimes called an intermediate oxide film, is made of, for example, silicon dioxide (SiO2).

[0027] In the manufacturing process of the optical reflective element 1, a surface layer 221 is formed on the upper surface of the SOI wafer. The surface layer 221 is made of, for example, silicon dioxide (SiO2). On the upper surface of the surface layer 221, a lower electrode layer 213, a piezoelectric layer 212, and an upper electrode layer 211 are stacked sequentially upwards. The upper electrode layer 211 is made of, for example, gold (Au). The piezoelectric layer 212 is made of, for example, PZT (lead zirconate titanate: Pb(Zr,Ti)O3). The lower electrode layer 213 is made of, for example, platinum (Pt). The upper electrode layer 211, piezoelectric layer 212, lower electrode layer 213, and surface layer 221 are processed by dry etching to form a piezoelectric body 32. Note that the materials constituting the upper electrode layer 211, piezoelectric layer 212, and lower electrode layer 213 are not limited to these.

[0028] Next, the active layer 201, base layer 203, and intermediate layer 202 are processed in order. The active layer 201 is processed by dry etching from the positive Z-axis side, while the base layer 203 and intermediate layer 202 are processed by dry etching and wet etching from the negative Z-axis side. The processing of the base layer 203 and intermediate layer 202 will be explained later with reference to Figures 6(a) and (b).

[0029] In this way, an active layer 201 is formed that extends over the entire optical reflective element 1, and ribs 101-104 and 111-113 are formed on the back side of the optical reflective element 1. The ribs 101-104 and 111-113 are composed of an intermediate layer 202 and a base layer 203, and the base layer 203 of each rib is formed to be thicker than the active layer 201. The formation of each of these parts is carried out collectively in a series of steps.

[0030] Figure 4 is a schematic bottom view showing the configuration of the drive unit 30 on the negative X-axis side as seen from the back side (positive Z-axis direction).

[0031] The ends 30a, 30c and the folded portion 30b are composed of the active layer 201, the intermediate layer 202, and the base layer 203, as described above. In Figure 4, for convenience, the area of ​​the base layer 203 is shown as halftone dots.

[0032] At the ends 30a, 30c and the folded portion 30b, the region of each part, when viewed in the Z-axis direction, coincides with the region of the base layer 203 of each part. Furthermore, in the meandering direction (Y-axis direction) of the meander shape of the drive unit 30, the inside of the intermediate layer 202 is set back outward from the inside of the base layer 203 at each of the ends 30a, 30c and the folded portion 30b. In Figure 4, for convenience, the setback position of the intermediate layer 202 is shown by a long dashed line. In other words, at each of the ends 30a, 30c and the folded portion 30b, the position of the end of the intermediate layer 202 on the rotation axis R10 side (the position shown by the long dashed line) is set back in the direction away from the rotation axis R10 than the position of the end of the base layer 203 on the rotation axis R10 side.

[0033] Generally, the intermediate layer 202 is formed by dry etching. This results in the intermediate layer 202 and the base layer 203 having the same area when viewed in the Z-axis direction. On the other hand, in this embodiment, as described above, the inside of the intermediate layer 202 is recessed relative to the inside of the base layer 203 in the direction away from the pivot axis R10. Below, the difference in the formation procedure of the intermediate layer 202 will be explained between a comparative example in which the intermediate layer 202 is formed to have the same area as the base layer 203 and an embodiment in which the inside of the intermediate layer 202 is recessed relative to the inside of the base layer 203.

[0034] Figures 5(a) and 5(b) schematically show the etching process of the intermediate layer 202 in a comparative example. Figures 5(a) and 5(b) are side views similar to those in Figure 3.

[0035] Figure 5(a) shows the state before etching of the intermediate layer 202, i.e., the piezoelectric element 32, surface layer 221, active layer 201, and base layer 203 have been etched, and the resist 231 has been placed on the negative Z-axis side of the base layer 203. In Figure 5(a), the intermediate layer 202 extends across the entire area of ​​the optical reflective element 1.

[0036] In the comparative example, dry etching is performed from the negative Z-axis side on the configuration shown in Figure 5(a), and as shown in Figure 5(b), the area of ​​the intermediate layer 202 is aligned with the area of ​​the base layer 203 when viewed in the Z-axis direction. Subsequently, the resist 231 is removed.

[0037] Figures 6(a) and 6(b) schematically show the etching process of the intermediate layer 202 according to the embodiment.

[0038] Figure 6(a), like Figure 5(a), shows the state before etching of the intermediate layer 202. However, in Figure 6(a), the resist 231 is also placed in the region corresponding to the area between the drive unit 30 and the fixed unit 50, compared to Figure 5(a).

[0039] In this embodiment, compared to the configuration shown in Figure 6(a), wet etching is performed on the center of the drive unit 30, and dry etching is performed on the other areas. As a result, as shown in Figure 6(b), when viewed in the Z-axis direction, the inside of the intermediate layer 202 of the drive unit 30 recedes outward relative to the inside of the base layer 203 of the drive unit 30. Subsequently, the resist 231 is removed.

[0040] <Example of changing the shape of the intermediate layer> In Figures 3 and 4, in the drive unit 30, only the inside of the intermediate layer 202 is recessed outward from the inside of the base layer 203. However, the outside of the intermediate layer 202 and the X-axis end of the intermediate layer 202 may also be recessed inward. For example, as shown in Figures 7 and 8, the intermediate layer 202 of the drive unit 30 may be recessed around its entire circumference relative to the base layer 203.

[0041] Figures 7 and 8 are a side view similar to Figure 3 and a bottom view similar to Figure 4, respectively, relating to this modified example.

[0042] As shown in Figures 7 and 8, in this modified example, the only difference compared to the embodiments in Figures 3 and 4 is the position of the end of the intermediate layer 202 in the drive unit 30. That is, as shown in Figure 8, in each of the folded portions 30b in this modified example, the ends of the intermediate layer 202 around the entire circumference (positive Y-axis side, negative Y-axis side, positive X-axis side, and negative X-axis side) are recessed relative to the outer shape of the base layer 203 of each folded portion 30b. The positive X-axis end of the intermediate layer 202 at end 30a is connected to the intermediate layer 202 of the connecting portion 20, and the negative X-axis end of the intermediate layer 202 at end 30c is connected to the intermediate layer 202 of the connecting portion 40.

[0043] Figures 9(a) and 9(b) schematically show the etching process of the intermediate layer 202 in this modified example.

[0044] Figure 9(a), like Figure 5(a), shows the state before etching of the intermediate layer 202. In the modified example, compared to the configuration in Figure 9(a), wet etching is performed on the center of the drive unit 30, and also on other areas. As a result, as shown in Figure 9(b), when viewed in the Z-axis direction, the area around the intermediate layer 202 of the drive unit 30 recedes inward relative to the area around the base layer 203 of the drive unit 30. Subsequently, the resist 231 is removed.

[0045] Although the area around the intermediate layer 202 of the fixing part 50 also recedes inward relative to the area around the base layer 203 of the fixing part 50, since the fixing part 50 is constructed in a frame shape as shown in Figure 1, even if the intermediate layer 202 of the fixing part 50 recedes as shown in Figure 9(b), the strength of the fixing part 50 is hardly affected.

[0046] <Verification through simulation> Next, we simulated how the rotational characteristics of the optical reflective element change when the length of each part is changed in the models corresponding to the comparative examples, embodiments, and modifications described above.

[0047] In this verification, the length L11 (see Figure 1) of the diaphragm 31 (vibrating part 31a) in the Y-axis direction was changed. At this time, the length L13 (see Figure 1) between the end of the diaphragm 31 and the end of the opening 51 of the fixing part 50 in the Y-axis direction was kept constant, and the length L12 (see Figure 1) of the optical reflecting element in the Y-axis direction was changed in accordance with the change in length L11.

[0048] In the embodiment model, the length L2 (see Figure 4) by which the inner side of the intermediate layer 202 of the drive unit 30 (the end on the pivot axis R10 side) recedes outward was set to 80 μm. In the modified example model, the length L3 (see Figure 8) by which the ends of the drive unit 30 on the positive X-axis side, negative X-axis side, positive Y-axis side, and negative Y-axis side recedes relative to the ends of the outer shape of the base layer 203 was set to 40 μm. However, in the modified example model, as shown in Figure 8, only one end of the ends 30a and 30c in the X-axis direction was receded.

[0049] Furthermore, in each model, the Y-axis length of the base layer 203 of the drive unit 30 was set to 100 μm, the diameter of the movable part 10 to 1500 μm, the thickness of the active layer 201 to 9 μm, the thickness of the intermediate layer 202 to 1 μm, the thickness of the base layer 203 to 300 μm, and the thickness of the surface layer 221 to 1 μm.

[0050] Under the conditions described above, the resonant frequency of the movable part 10 and the maximum deflection angle of the movable part 10 with respect to the XY plane were calculated by simulation when the lengths L11 and L12 were varied.

[0051] Figure 10 is a table showing the simulation results of the comparative example, embodiment, and modified model.

[0052] In the table in Figure 10, the dashed line indicates the standard configuration when the length L11 of the diaphragm 31 is 1350 μm and the length L12 of the optical reflector is 1550 μm. According to the standard configuration, the simulation results showed that the resonant frequency of the movable part 10 was 600.7 Hz and the deflection angle of the movable part 10 was 26.6°. In addition, each row in Figure 10 also shows the ratio (%) of the length L11, L12, resonant frequency, and deflection angle to the standard configuration. In the standard configuration, the ratios of the length L11, L12, resonant frequency, and deflection angle are all 100%.

[0053] According to the results of the comparative example, when the length L11 of the diaphragm 31 is set to 92.6% of that of the standard configuration, the length L12 of the optical reflector element becomes 93.5% of that of the standard configuration, resulting in a smaller optical reflector element. At this time, the resonant frequency becomes 652.9 Hz (ratio 108.7%), which is higher than that of the standard configuration. The deflection angle becomes 24.7° (ratio 92.9%), which is smaller than that of the standard configuration. From this, it can be seen that in the comparative example, shortening the length L11 of the diaphragm 31 causes a large change in the resonant frequency and deflection angle compared to the standard configuration. Therefore, in the comparative example, it is difficult to achieve miniaturization of the optical reflector element while maintaining rotational characteristics.

[0054] On the other hand, according to the results of the embodiment, when the length L11 of the diaphragm 31 is set to 91.1% of the standard configuration, the length L12 of the optical reflector 1 becomes 92.3% of the standard configuration, and the optical reflector 1 becomes smaller. At this time, the resonant frequency becomes 601.2 Hz (ratio is 100.1%), and the deflection angle becomes 26.9° (ratio is 101.1%). Therefore, in the embodiment, even if the length L11 of the diaphragm 31 is made sufficiently shorter than the standard configuration, the resonant frequency and deflection angle do not fluctuate significantly compared to the standard configuration. Thus, in the embodiment, it is possible to achieve miniaturization of the optical reflector 1 while maintaining rotational characteristics.

[0055] Furthermore, according to the results of the modified example, if the length L11 of the diaphragm 31 is reduced to 94.7% of that of the standard configuration, the length L12 of the optical reflector 1 becomes 95.4% of that of the standard configuration, resulting in a smaller optical reflector 1. At this time, the resonant frequency becomes 600.7 Hz (ratio 100%), and the deflection angle becomes 26.7° (ratio 100.4%). Therefore, even in the modified example, it can be seen that even if the length L11 of the diaphragm 31 is made significantly shorter than that of the standard configuration, the resonant frequency and deflection angle do not fluctuate significantly compared to the standard configuration. Thus, even in the modified example, it is possible to achieve miniaturization of the optical reflector 1 while maintaining the rotational characteristics.

[0056] Furthermore, according to the results of the embodiment and modified example in Figure 10, the ratio of the resonant frequency and deflection angle to the standard configuration is almost the same, but the length L12 of the optical reflective element 1 in the embodiment is 92.3% of that of the standard configuration, while the length L12 of the optical reflective element 1 in the modified example is 95.4% of that of the standard configuration. From this, it can be seen that, according to the embodiment, the length L12 of the optical reflective element 1 can be shortened by about 3.1% compared to the modified example while maintaining the rotational characteristics. Thus, according to the embodiment, the optical reflective element 1 can be further miniaturized compared to the modified example while maintaining the rotational characteristics.

[0057] Next, the effects of the embodiments and their modifications will be described.

[0058] Figures 11(a) to (c) are schematic side views showing the end faces of the drive unit 30 for a comparative example, an embodiment, and a modified example, respectively.

[0059] As shown in Figure 11(a), in the comparative example, the length of the Y-axis direction range in which the active layer 201 flexes is L4, which corresponds to the gap between a pair of opposing base layers 203 in the Y-axis direction. In this case, if the Y-axis direction length L11 of the drive unit 30 is shortened, the length L4 of the Y-axis direction range in which the active layer 201 of the drive unit 30 flexes becomes shorter, and the active layer 201 in this range becomes less flexible. As a result, the resonance frequency of the movable part 10 rotated by the drive unit 30 increases, and the deflection angle of the movable part 10 decreases.

[0060] On the other hand, as shown in Figure 11(b), in this embodiment, the length by which the inside of the intermediate layer 202 recedes in the Y-axis direction is L2, and the length L51 of the Y-axis direction range in which the active layer 201 flexes is L4 + L2 × 2. Therefore, even if the Y-axis direction length L11 of the drive unit 30 is shortened, the Y-axis direction range in which the active layer 201 of the drive unit 30 flexes can be made longer than in the comparative example. Thus, according to this embodiment, the increase in the resonance frequency of the movable part 10 can be suppressed and the decrease in the deflection angle of the movable part 10 can be suppressed compared to the comparative example.

[0061] Similarly, as shown in Figure 11(c), in the modified example, the length by which the inside of the intermediate layer 202 recedes in the Y-axis direction is L3, and the length L52 of the Y-axis direction range in which the active layer 201 flexes is L4 + L3 × 2. Therefore, even if the Y-axis direction length L11 of the drive unit 30 is shortened, the Y-axis direction range in which the active layer 201 of the drive unit 30 flexes, length L52, can be increased compared to the comparative example. Thus, according to the modified example, the increase in the resonance frequency of the movable part 10 can be suppressed and the decrease in the deflection angle of the movable part 10 can be suppressed compared to the comparative example.

[0062] In the above simulation, the length L2 of the embodiment is 80 μm, and the length L3 of the modified example is 40 μm. Therefore, the length L51 of the embodiment is L4 + 80 μm × 2, and the length L52 of the modified example is L4 + 40 μm × 2. Thus, if the total amount of retraction in the Y-axis direction of one intermediate layer 202 is the same, it is easier to maintain rotational characteristics by retracting the inside of the intermediate layer 202 and not retracting the outside of the intermediate layer 202, as in the embodiment.

[0063] <Effects of the embodiment and the example of changing the shape of the intermediate layer> The following effects are achieved by the embodiments and examples of changes in the shape of the intermediate layer.

[0064] As shown in Figure 1, the optical reflective element 1 comprises a movable part 10 having a reflective surface 11, and a meander-shaped drive unit 30 that rotates the movable part 10 about a pivot axis R10. As shown in Figures 3 and 7, the drive unit 30 has an active layer 201 that extends over the entire drive unit 30, an intermediate layer 202 positioned on the lower surface of the active layer 201 in the meander-shaped folded portion 30b, and a base layer 203 positioned below the intermediate layer 202. As shown in Figures 4 and 8, in the meandering direction (Y-axis direction) of the meander shape, the inside of the intermediate layer 202 is recessed outward from the inside of the base layer 203.

[0065] With this configuration, in the meandering direction of the meander shape, the inside of the intermediate layer 202, which is located on the lower surface of the active layer 201 of the folded portion 30b, recedes outward from the inside of the base layer 203, which is located below the intermediate layer 202. As shown in the simulation results of Figure 10, even if the length L11 in the meandering direction of the meander shape is shortened, it is possible to suppress the increase in the resonant frequency of the movable part 10 and the decrease in the deflection angle of the movable part 10. Therefore, it is possible to miniaturize the optical reflective element 1 while maintaining the rotational characteristics of the movable part 10.

[0066] As shown in Figures 3 and 4, in the meandering direction (Y-axis direction) of the meander shape, only the inside of the intermediate layer 202 of the drive unit 30 is recessed outward from the inside of the base layer 203 located below the intermediate layer 202.

[0067] With this configuration, as shown in the simulation results in Figure 10, compared to the case where the entire circumference of the intermediate layer 202 is recessed relative to the base layer 203, as in the modified examples in Figures 7 and 8, even if the meandering length L11 of the meander shape is shortened, the increase in the resonant frequency of the movable part 10 and the decrease in the deflection angle of the movable part 10 can be suppressed more effectively.

[0068] As shown in Figure 1, the optical reflective element 1 includes a connecting portion 20 that connects the end portion 30a of the drive portion 30 on the movable portion 10 side to the movable portion 10. At the end portion 30a of the drive portion 30 connected to the connecting portion 20, an intermediate layer 202 is arranged on the lower surface of the active layer 201, and a base layer 203 is arranged below this intermediate layer 202. As shown in Figures 4 and 8, in the meandering direction (Y-axis direction) of the meander shape, at the end portion 30a of the drive portion 30 on the movable portion 10 side, the inside of the intermediate layer 202 is recessed outward from the inside of the base layer 203.

[0069] In this configuration, at the end 30a of the drive unit 30 connected to the connecting unit 20, the intermediate layer 202 recedes outward from the inside of the base layer 203, making the active layer 201 of the drive unit 30 on the connecting unit 20 side more flexible. As a result, the resonant frequency of the movable part 10 tends to decrease, and the deflection angle of the movable part 10 tends to increase. Therefore, even if the meandering length L11 of the meandering shape is shortened, the increase in the resonant frequency of the movable part 10 and the decrease in the deflection angle of the movable part 10 can be suppressed.

[0070] As shown in Figure 1, the optical reflective element 1 comprises a fixed portion 50 and a connecting portion 40 that connects the fixed portion 50 to the end portion 30c of the drive portion 30 on the opposite side of the movable portion 10. At the end portion 30c of the drive portion 30 connected to the connecting portion 40, an intermediate layer 202 is arranged on the lower surface of the active layer 201, and a base layer 203 is arranged below this intermediate layer 202. As shown in Figures 4 and 8, in the meandering direction (Y-axis direction) of the meander shape, at the end portion 30c of the drive portion 30 on the opposite side of the movable portion 10, the inside of the intermediate layer 202 is recessed outward from the inside of the base layer 203.

[0071] In this configuration, at the end 30c of the drive unit 30 connected to the connecting unit 40, the intermediate layer 202 recedes outward from the inside of the base layer 203, making the active layer 201 of the drive unit 30 on the connecting unit 40 side more flexible. As a result, the resonant frequency of the movable part 10 tends to decrease, and the deflection angle of the movable part 10 tends to increase. Therefore, even if the meandering length L11 of the meandering shape is shortened, the increase in the resonant frequency of the movable part 10 and the decrease in the deflection angle of the movable part 10 can be suppressed.

[0072] The base layer 203 of the drive unit 30 is thicker than the active layer 201 of the drive unit 30.

[0073] In this configuration, ribs 111-113 are formed by the intermediate layer 202 and the base layer 203 at the meander-shaped end 30a, folded portion 30b, and end 30c. This increases the strength of the ends 30a, 30c, and folded portion 30b.

[0074] The drive unit 30 includes a piezoelectric element 32.

[0075] This configuration allows the meander-shaped drive unit 30 to deform smoothly, and the movable part 10 to rotate smoothly around the pivot axis R10.

[0076] <Example of rib shape modification> In the above embodiments and modifications, the shapes of ribs 111, 112, and 113 in plan view matched the shapes of end portion 30a, folded portion 30b, and end portion 30c, respectively. However, the shapes of ribs 111 to 113 do not necessarily have to match the shapes of their corresponding portions.

[0077] Figure 12 is a schematic bottom view showing the configuration of the optical reflective element 1 as seen from the back side (in the positive Z-axis direction) in this modified example. For convenience, in Figure 12, the areas of ribs 101-104 and 111-113 (base layer 203) are shown as halftone dots.

[0078] In this modified example, the shape of the ends of the ribs 111 to 113 in the X-axis direction is different compared to the embodiment in Figure 2. Specifically, in two ribs adjacent to each other in the X-axis direction, the portion of one rib extending to the end and the portion of the other rib extending to the end that face the gap between these two ribs are offset in the Y-axis direction. In addition, of the opening 51 of the fixing portion 50, the portion facing the outer end of the rib 112, which is located furthest outward relative to the center C10, is set back in the outward direction.

[0079] Furthermore, in this modified example, as in the above embodiment, the inner side of the ribs 111-113 of the drive unit 30 is recessed outward in the Y-axis direction. That is, in the intermediate layer 202 provided on the ribs 111-113 of the drive unit 30, the end on the pivot axis R10 side is recessed in the direction away from the pivot axis R10 relative to the range of the base layer 203 shown by the halftone dots. In Figure 12, for convenience, the recessed position of the inner side of the intermediate layer 202 of the drive unit 30 is indicated by a long dashed line.

[0080] Here, since the thickness of the active layer 201 is sufficiently small, the machining limit width of the active layer 201 can also be sufficiently small. However, the thickness of the ribs (the sum of the thicknesses of the intermediate layer 202 and the base layer 203) is several times larger than the thickness of the active layer 201, so the machining limit width of the ribs is greater than the machining limit width of the active layer 201. For this reason, for example, when aligning the position of the ends of the active layer 201 with the position of the ends of the ribs, the spacing between adjacent active layers 201 cannot be made smaller than the machining limit width of adjacent ribs, resulting in problems such as an increased size of the optical reflective element.

[0081] In contrast, in this modified example, a larger gap is provided between adjacent ribs than between adjacent active layers 201, as shown in Figure 12. This allows the gap between adjacent active layers 201 to be made smaller than the processing limit width of the ribs during the etching process. Therefore, according to the configuration shown in Figure 12, the size of the optical reflective element 1 in the X-axis direction can be reduced.

[0082] <Other examples of changes> In the above embodiments and modifications, the ends of the intermediate layer 202 are recessed at two ribs located at both ends of one vibrating section 31a in the Y-axis direction. However, the invention is not limited to this, and the end of the intermediate layer 202 may be recessed at one rib located at one end of one vibrating section 31a in the Y-axis direction.

[0083] In the above example of changing the shape of the intermediate layer 202, the entire circumference of the intermediate layer 202 was recessed relative to the base layer 203 at the ends 30a, 30c and the folded portion 30b. However, it is not necessary for either one of the ends of the intermediate layer 202 in the X-axis direction to be recessed relative to the base layer 203, and it is not necessary for both ends of the intermediate layer 202 in the X-axis direction to be recessed relative to the base layer 203.

[0084] In the above embodiments and modifications, the meandering direction of the meander shape of the drive unit 30 was parallel to the Y-axis direction. However, it is not limited to this, and the meandering direction may be slightly deviated from the direction parallel to the Y-axis direction as long as it is substantially parallel to the Y-axis direction.

[0085] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the technical idea set forth in the claims.

[0086] (Note) The above description of embodiments discloses the following technologies.

[0087] (Technology 1) A movable part having a reflective surface, It comprises a meander-shaped drive unit that rotates the movable part with respect to the pivot axis, The aforementioned drive unit is The active layer extends throughout the entire drive unit, In the meander-shaped folded portion, an intermediate layer is disposed on the lower surface of the active layer, It comprises a base layer disposed below the intermediate layer, In the meandering direction of the meander shape, the inside of the intermediate layer is recessed outward from the inside of the base layer. An optical reflective element characterized by the following features.

[0088] According to this technology, in the meandering direction of the meander shape, the inner side of the intermediate layer located on the lower surface of the folded active layer recedes outward from the inner side of the base layer located below the intermediate layer. This suppresses the increase in the resonant frequency of the movable part and the decrease in the deflection angle of the movable part, even if the length of the meandering direction of the meander shape is shortened. Therefore, miniaturization of the optical reflective element can be achieved while maintaining the rotational characteristics of the movable part.

[0089] (Technology 2) In the optical reflective element described in Technology 1, In the meandering direction of the meander shape, only the inside of the intermediate layer is recessed outward from the inside of the base layer. An optical reflective element characterized by the following features.

[0090] This technology allows for more effective suppression of the increase in the resonant frequency of the movable part and the decrease in the deflection angle of the movable part, even when the meandering length of the meander shape is shortened.

[0091] (Technology 3) In the optical reflecting element described in Technology 1 or 2, The drive unit on the movable part side is provided with a connecting part that connects the end of the drive unit to the movable part, At the end portion connected to the connecting portion, the intermediate layer is positioned on the lower surface of the active layer, and the base layer is positioned below the intermediate layer. In the meandering direction of the meander shape, the inner side of the intermediate layer at the end is recessed outward from the inner side of the base layer at the end. An optical reflective element characterized by the following features.

[0092] According to this technology, at the end of the drive unit connected to the coupling section, the intermediate layer recedes outward from the inside of the base layer, making the active layer of the drive unit on the coupling section side more flexible. This tends to lower the resonant frequency of the movable part and increase the deflection angle of the movable part. Therefore, even if the length in the meandering direction of the meander shape is shortened, the increase in the resonant frequency of the movable part and the decrease in the deflection angle of the movable part can be suppressed.

[0093] (Technology 4) In an optical reflective element described in any one of the three technical specifications, The fixing part, A connecting portion is provided that connects the end of the drive unit on the opposite side of the movable portion to the fixed portion, At the end portion connected to the connecting portion, the intermediate layer is positioned on the lower surface of the active layer, and the base layer is positioned below the intermediate layer. In the meandering direction of the meander shape, the inner side of the intermediate layer at the end is recessed outward from the inner side of the base layer at the end. An optical reflective element characterized by the following features.

[0094] According to this technology, at the end of the drive unit connected to the coupling section, the intermediate layer recedes outward from the inside of the base layer, making the active layer of the drive unit on the coupling section side more flexible. This tends to lower the resonant frequency of the movable part and increase the deflection angle of the movable part. Therefore, even if the length in the meandering direction of the meander shape is shortened, the increase in the resonant frequency of the movable part and the decrease in the deflection angle of the movable part can be suppressed.

[0095] (Technology 5) In an optical reflective element described in any one of the technical items 1 to 4, The base layer is thicker than the active layer. An optical reflective element characterized by the following features.

[0096] According to this technology, ribs are formed by the intermediate layer and base layer in the meander-shaped folded portion. This increases the strength of the folded portion.

[0097] (Technology 6) In an optical reflective element described in any one of the technical items 1 to 5, The aforementioned intermediate layer is composed of silicon dioxide (SiO2). An optical reflective element characterized by the following features.

[0098] (Technology 7) In an optical reflective element described in any one of the technical items 1 to 6, The base layer is made of silicon (Si). An optical reflective element characterized by the following features.

[0099] (Technology 8) In an optical reflective element described in any one of the technical items 1 through 7, The drive unit includes a piezoelectric element, An optical reflective element characterized by the following features.

[0100] This technology allows for the smooth deformation of the meander-shaped drive unit and the smooth rotation of the movable part around the pivot axis.

[0101] (Technology 9) In the optical reflecting element described in Technical 8, The piezoelectric material includes an upper electrode layer, a piezoelectric layer, and a lower electrode layer. An optical reflective element characterized by the following features. [Explanation of Symbols]

[0102] 1 Optical reflective element 10 Moving parts 11 Reflective surface 20 Connection part 30 Drive unit 30a end 30b Folded section 30c end 32 Piezoelectric material 40 Connection part 50 Fixed part 201 Active layer 202 Middle Class 203 Base Layer 211 Upper electrode layer 212 Piezoelectric layer 213 Lower electrode layer R10 pivot axis

Claims

1. A movable part having a reflective surface, It comprises a meander-shaped drive unit that rotates the movable part with respect to the pivot axis, The aforementioned drive unit is The active layer extends throughout the entire drive unit, In the meander-shaped folded portion, an intermediate layer is disposed on the lower surface of the active layer, It comprises a base layer disposed below the intermediate layer, In the meandering direction of the meander shape, the inside of the intermediate layer is recessed outward from the inside of the base layer. An optical reflective element characterized by the following features.

2. In the optical reflector described in claim 1, In the meandering direction of the meander shape, only the inside of the intermediate layer is recessed outward from the inside of the base layer. An optical reflective element characterized by the following features.

3. In the optical reflector described in claim 1, The drive unit on the movable part side is provided with a connecting part that connects the end of the drive unit to the movable part, At the end portion connected to the connecting portion, the intermediate layer is positioned on the lower surface of the active layer, and the base layer is positioned below the intermediate layer. In the meandering direction of the meander shape, the inner side of the intermediate layer at the end is recessed outward from the inner side of the base layer at the end. An optical reflective element characterized by the following features.

4. In the optical reflector described in claim 1, The fixing part, A connecting portion is provided that connects the end of the drive unit on the opposite side of the movable portion to the fixed portion, At the end portion connected to the connecting portion, the intermediate layer is positioned on the lower surface of the active layer, and the base layer is positioned below the intermediate layer. In the meandering direction of the meander shape, the inner side of the intermediate layer at the end is recessed outward from the inner side of the base layer at the end. An optical reflective element characterized by the following features.

5. In the optical reflector described in claim 1, The base layer is thicker than the active layer. An optical reflective element characterized by the following features.

6. In the optical reflector described in claim 1, The aforementioned intermediate layer is silicon dioxide (SiO ２ ) consists of, An optical reflective element characterized by the following features.

7. In the optical reflector described in claim 1, The base layer is made of silicon (Si). An optical reflective element characterized by the following features.

8. In the optical reflector described in claim 1, The drive unit includes a piezoelectric element, An optical reflective element characterized by the following features.

9. In the optical reflector described in claim 8, The piezoelectric material includes an upper electrode layer, a piezoelectric layer, and a lower electrode layer. An optical reflective element characterized by the following features.

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