JP2008086067A - Movable structural body and optical element equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make comb teeth hardly contact with each other even if lengths of the comb teeth are elongated, and to make a swing angle of a movable plate large. <P>SOLUTION: This optical element comprises the movable plate 2 having a mirror film for reflecting light, and a frame which is formed so as to surround the movable plate 2. The movable plate 2 is supported to the frame by twist springs arranged at both sides of the plate, and constituted so as to be turnable while twisting the twist springs. Comb-tooth electrodes 5 are arranged at the side end of the movable plate 2 and fixed electrode parts 3b of the frame 3. The comb teeth 2c, 3c which constitute the comb-tooth electrodes 5 are formed into tapered shapes so as to be thinned from their roots toward tips at their widths. Since the comb teeth 2c, 3c are hardly warped due to large resonance frequencies generated therein, the comb teeth 2c, 3c hardly contact with each other. Electrostatic capacities of the comb-tooth electrodes 5 can be increased by elongating the comb-tooth lengths of the comb teeth 2c, 3c, and thereby large torque can be applied to the movable plate 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a movable structure that is mounted on an optical device and used for an optical element that scans light incident from the outside.

  Conventionally, for example, an optical device such as a barcode reader has been mounted with an optical element that swings a movable plate provided with a mirror and scans light incident on the mirror. As such an optical element, there is known an optical element mounted with a small movable structure formed by using a micromachining technique as shown in Patent Document 1, Patent Document 2, and Patent Document 3, for example. ing. The movable structure of the optical element shown in these Patent Documents 1 to 3 has comb-tooth electrodes composed of a plurality of comb teeth.

  FIGS. 9A and 9B show an example of a comb electrode of such a movable structure. The comb-tooth electrode 85 has a plurality of comb teeth 82c and 83c formed so as to mesh with the movable plate 82 of the movable structure and the frame portion 83 of the movable structure opposite thereto. Each comb tooth 82c, 83c is formed so as to have a constant width dimension w from its root portion to its tip portion. The comb teeth 82c and 83c are configured to mesh with each other with a predetermined gap g. The movable plate 82 of the movable structure is driven by an electrostatic force generated between the comb teeth 82c and 83c when a voltage is applied to the comb electrode 85.

Here, Patent Document 1 shows a scanning device having a support frame on one surface of a movable plate and configured so that the mirror surface does not deform dynamically. In this scanning device, the support frame is formed such that the mass decreases as it goes to both sides of the movable plate, and the moment of inertia when the movable plate is rotated is small, so that it can be operated at high speed. Patent Document 2 discloses a deflection mirror in which each comb tooth of a comb electrode of a movable plate has a trapezoidal shape in which a cross section of the comb tooth gradually increases from the top surface to the back surface of the movable plate. Has been. In this deflection mirror, the comb teeth of the comb-teeth electrodes are formed so as to have a trapezoidal cross section, so that an electrostatic force can be effectively applied between the comb-teeth electrodes so that the drive voltage can be lowered. It is configured. Patent Document 3 discloses a two-axis electrostatic micromirror element that rotates a movable plate around two rotation axes to deflect or scan a light beam two-dimensionally. This micromirror element is composed of an SOI (Silicon on Insulator) substrate, and the electrodes constituting the comb electrodes are formed in different silicon layers, whereby a voltage can be applied to the comb electrodes. It is configured as follows.
JP 2006-79078 A JP 2005-266666 A Japanese Patent Laid-Open No. 2004-13099

  By the way, in the movable structure as described above, in order to increase the deflection angle from the horizontal direction of the movable plate, it is necessary to increase the capacitance of the comb electrode and increase the torque applied to the movable plate. In order to increase the capacitance of the comb electrode, the length of the comb tooth constituting the comb electrode (hereinafter referred to as comb tooth length) is increased within a range that can be set in consideration of the size of the movable structure. do it. However, if the length of the comb teeth is increased, the tips of the comb teeth are easily displaced, the rigidity is lowered, and adjacent comb teeth are easily brought into contact with each other. That is, as the comb tooth length increases, the resonance frequency of the comb teeth decreases and becomes close to the resonance frequency of the movable plate. Therefore, the comb teeth resonate in the horizontal direction when the movable plate is driven (FIG. 9B). ) In the direction of arrow D), and the comb teeth are easily brought into contact with each other. Further, when the comb electrode is formed, when the movable structure is lifted from the etching solution tank, the comb teeth adjacent to each other are easily brought into contact with each other due to the surface tension of the liquid. Once the comb teeth contact each other, the intermolecular force acting between the comb teeth does not leave the comb teeth in contact with each other, and the movable structure becomes inoperable. Moreover, when the comb tooth length is long, the comb tooth is easily broken at the root portion or the like. In order to increase the resonance frequency of the comb teeth so that the comb teeth are difficult to bend, the width of each comb tooth may be increased, but the number of comb teeth that can be arranged in the limited width of the comb electrode is limited. As a result, the capacitance of the comb electrode is reduced, and the deflection angle of the movable plate cannot be increased. As described above, the comb tooth length of the comb electrode needs to be set in view of the yield rate and practicality at the time of manufacture, and there is a limit to increase the capacitance of the comb electrode.

  The present invention has been made in view of the above problems, and even if the length of the comb teeth is increased, the comb teeth are difficult to contact each other, the capacitance of the comb electrodes is large, and the deflection angle of the movable plate is increased. It is an object to provide a movable structure that can be enlarged and an optical element including the movable structure.

  In order to achieve the above object, the invention of claim 1 is directed to a movable plate, a torsion spring that pivotally supports the movable plate on both side portions, a frame portion that supports the torsion spring, and the movable plate. A comb-tooth electrode having a plurality of comb teeth provided so as to mesh with a part of the frame portion and the frame portion opposed thereto, and a comb-tooth electrode on the movable plate side and a comb-tooth electrode on the frame portion side The movable plate is configured such that the movable plate swings when a voltage is applied therebetween, and a comb tooth width of the comb electrode is greater than a tip portion of the comb tooth root portion. It is characterized by being configured to be thinner.

  According to a second aspect of the present invention, in the movable structure of the first aspect, the comb teeth of the comb-teeth electrode are formed in a tapered shape whose width gradually decreases from the root portion to the tip end portion of the comb teeth. .

  According to a third aspect of the present invention, in the movable structure according to the first aspect, the comb teeth of the comb-teeth electrode are formed such that the width gradually decreases from the root part to the tip part of the comb tooth. is there.

  A fourth aspect of the invention includes the movable structure according to any one of the first to third aspects, wherein the movable plate is provided with a mirror structure, and the movable plate swings. Thus, the light incident on the mirror structure is scanned.

  According to the first aspect of the present invention, since the width of the comb teeth of the comb electrode is configured so that the tip portion is narrower than the root portion of the comb electrode, the resonance frequency of the comb teeth is increased. The comb teeth are difficult to bend, and even if the length of the comb teeth is increased, the comb teeth are less likely to contact each other, and the comb teeth are less likely to be damaged. Accordingly, it is possible to increase the capacitance of the comb-teeth electrode by increasing the length of the comb teeth, to apply a large torque to the movable plate, and to increase the deflection angle of the movable plate.

  According to the invention of claim 2, since the comb teeth of the comb-teeth electrode are formed in a tapered shape whose width is narrowed from the root portion to the tip portion of the comb teeth, the comb teeth are configured so as to be difficult to bend, A plurality of comb teeth can be efficiently arranged in a predetermined space. Since the number of comb teeth that can be arranged increases, it is possible to increase the capacitance of the comb electrodes while ensuring the rigidity and strength of the comb teeth, and to increase the deflection angle of the movable plate. it can.

  According to the invention of claim 3, since the comb teeth of the comb electrode are formed so that the width is gradually reduced from the root portion to the tip portion of the comb teeth, the stiffness of the comb teeth is the same as described above. In addition, the plurality of comb teeth can be efficiently arranged while securing the strength, and the deflection angle of the movable plate can be further increased.

  According to the invention of claim 4, it is possible to apply a large torque to the movable plate provided with the mirror structure by making the comb teeth longer while making the comb teeth difficult to contact each other. Accordingly, the deflection angle of the movable plate is increased, and light can be scanned at a wide angle.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 1 and 2 show an example of an optical element according to this embodiment. The optical element 1 is, for example, a small movable structure configured by molding a silicon substrate (not shown) composed of conductive silicon and an insulating oxide film using a micromachining technique or the like. It is composed of the body. The optical element 1 is mounted on, for example, a barcode reader, a projector device that projects an image on an external screen, or an optical device such as an optical switch, and is incident from an external light source (not shown). It has a function of scanning light and the like.

  The optical element 1 is a substantially rectangular element, and has a circular movable plate 2 at the center thereof. Around the movable plate 2, a frame portion 3 is formed so as to surround the movable plate 2. The movable plate 2 is pivotally supported on the frame portion 3 by beam-shaped torsion springs 4 arranged so as to be coaxially arranged on both sides thereof. A comb electrode 5 for driving the movable plate 2 is formed between the frame portion 3 and the movable plate 2. These members are both formed on the same silicon substrate, and when the movable plate 2 is in a stationary state where it is not driven, the movable plate 2, the frame portion 3, and the torsion spring 4 are arranged substantially horizontally. It is configured.

  The movable plate 2 has its center of gravity located in the vicinity of the axis where the two torsion springs 4 are arranged on both sides of the movable plate 2, and when the comb electrode 5 is driven to swing, the torsion spring 4 serves as a rotation axis and the arrow in FIG. As shown by F, it swings while maintaining balance. On the upper surface of the movable plate 2, for example, a circular mirror film (mirror structure) 2a for reflecting light incident from the outside is formed. The mirror film 2a is a metal film such as aluminum or gold selected according to the type of light source used together with the optical element 1. The movable plate 2 is circular in the present embodiment, and the longitudinal direction of the torsion spring 4, that is, the dimension in the direction substantially perpendicular to the swing axis is smaller on the torsion spring 4 side than the center side of the movable plate 2. It is configured. Therefore, compared with the case where the dimension of the movable plate 2 is equal on the center side and the torsion spring 4 side, the moment of inertia around the torsion spring 4 of the movable plate 2 is small, and the movable plate 2 and the torsion spring 4 are configured. The resonance frequency of the vibration system is large, and the movable plate 2 can be operated at high speed.

  The frame portion 3 includes a support portion 3a that supports the torsion spring 4, and two fixed electrode portions 3b that are arranged so as to surround two side end portions that are free ends when the movable plate 2 is swung. have. The support portion 3a and the fixed electrode portion 3b are electrically insulated from each other by removing silicon at the boundary between the support portion 3a and the fixed electrode portion 3b. An electrode pad (not shown) connected to an external electric circuit is formed on each of the support portion 3a and the two fixed electrode portions 3b, and the potentials of the support portion 3a and each fixed electrode portion 3b are mutually connected. It is configured so that it can be changed independently. This electrode pad is formed of, for example, the same metal film as the mirror film 2a.

  FIG. 3 shows the comb electrode 5. The comb electrode 5 includes a plurality of comb teeth 2c formed at the side end of the movable plate 2 and a plurality of comb teeth 3c formed at a portion of the fixed electrode portion 3b facing the side end of the movable plate 2. It is what is called a vertical electrostatic comb. FIG. 4 shows the comb teeth 2c and 3c. In this embodiment, the comb teeth 2c and 3c have a width dimension of the root portion on the movable plate 2 side or the fixed electrode portion 3b side as w1, as shown by the dimension line in FIG. It is formed so that the width dimension of the distant tip portion is w2 smaller than w1. The comb teeth 2c and 3c are formed in a tapered shape with a taper angle (side angle) set to θ so that the width gradually decreases from the root portion to the tip portion from w1 to w2. The comb-teeth electrode 5 is configured such that the above-described tapered comb teeth 2c and 3c are arranged so as to mesh with each other while maintaining a gap g of, for example, several micrometers. A voltage is applied to the comb-tooth electrode 5 between the comb teeth 2c on the movable plate 2 side and the comb teeth 3c on the fixed electrode portion 3b side through an electrode pad on the frame portion 3 from an external electric circuit or the like. It is driven by. When a voltage is applied between the comb teeth 2c and 3c of the comb-teeth electrode 5, a force attracting each other due to electrostatic force is generated between the comb teeth 2c and 3c. The force generated when the comb electrode 5 is driven acts on the side edge of the movable plate 2 substantially perpendicularly to the movable plate 2, thereby applying electrostatic torque to the movable plate 2. It is driven to swing.

  Here, an example of the manufacturing process of the optical element 1 will be described. First, the movable plate 2, the frame portion 3, the torsion spring 4, the comb electrode 5 and the like are formed on the silicon substrate to form a plurality of movable structures. This movable structure is formed, for example, by processing a silicon substrate using a so-called bulk micromachining technique. Thereafter, a metal film is formed on the upper surface of the silicon substrate by using a method such as sputtering. Then, by patterning this metal film, a mirror film 2 a is formed on the upper surface of the movable plate 2, and an electrode pad is formed on the upper surface of the frame portion 3. After the mirror film 2a and the electrode pads are formed, the silicon substrate and a supporting substrate such as glass that supports the silicon substrate are bonded by anodic bonding or the like. Then, after that, a plurality of elements formed on the silicon substrate are individually cut to manufacture the optical element 1. By manufacturing a plurality of optical elements 1 simultaneously through such a series of steps, the manufacturing cost can be reduced. In addition, the manufacturing process of the optical element 1 is not restricted to this, For example, you may form one by one by laser processing, ultrasonic processing, etc.

  Next, the operation of the optical element 1 configured as described above will be described with reference to FIG. The movable plate 2 of the optical element 1 is driven when the comb electrode 5 generates a driving force at a predetermined driving frequency. The comb-teeth electrode 5 is, for example, an electrode pad disposed on the fixed electrode portion 3b in a state where the electrode pad disposed on the support portion 3a is connected to the ground potential and the comb teeth 2c of the movable plate 2 is at the reference potential. The electric potential is periodically changed, and a voltage having a predetermined driving frequency is applied between the comb teeth 2c and 3c to drive. In the comb-teeth electrode 5, two comb teeth 2 c provided at both ends of the movable plate 2 are changed by simultaneously changing the potential of the two comb teeth 3 c to a predetermined drive potential (for example, several tens of volts). At the same time, they are attracted to the comb teeth 3c facing each other by electrostatic force. In this embodiment, as shown in the figure, for example, a rectangular wave voltage is applied to the comb-teeth electrode 5, and a driving force is generated periodically. In many cases, the movable plate 2 formed as described above generally has a dimensional error or the like at the time of molding, so that the movable plate 2 is not in a horizontal posture but is tilted slightly in a stationary state. . For this reason, even when the comb-shaped electrode 5 is driven even in a stationary state, a driving force in a direction substantially perpendicular to the movable plate 2 is applied to the movable plate 2, and the movable plate 2 rotates about the torsion spring 4. .

  During steady oscillation of the movable plate 2, the transition of the deflection angle with respect to the horizontal plane of the movable plate 2 is indicated by a solid line having a substantially sinusoidal shape in the figure. Further, in the upper part of the drawing, changes in the postures of the comb teeth 2c and 3c of the comb electrode 5 at each time when the movable plate 2 is swung are shown. The movable plate 2 is rotated by the inertial force from the horizontal state (time t0) where the deflection angle is 0 degree, and the inertial force in the rotating direction of the movable plate 2 and the restoring force of the torsion spring 4 are equal at time t1. Then, the rotation of the movable plate 2 in that direction stops. When the deflection angle of the movable plate 2 is maximized, the movable plate 2 is rotated in a direction opposite to the previous rotation direction by the restoring force of the torsion spring 4 (indicated by a one-dot chain line in the figure). Here, during a period from time t1 to time t2 when the movable plate 2 becomes horizontal again, a driving voltage is applied to the comb-teeth electrode 5, and the movable plate 2 receives the torque generated by the restoring force of the torsion spring 4 and the comb-teeth electrode. 5 is added with electrostatic torque (indicated by a broken line in the figure) due to electrostatic force generated by 5. When the movable plate 2 is in a horizontal state at the time t2, and is rotated by the inertia force as it is and the swing angle is maximized at the time t3, the driving voltage is applied to the comb electrode 5 again. Then, the movable plate 2 starts to rotate again in the opposite direction from the time t3 by the torque generated by the restoring force of the torsion spring 4 and the electrostatic torque generated by the comb electrode 5. The movable plate 2 oscillates by repeating the rotation by the driving force of the comb electrode 5 and the restoring force of the torsion spring 4 with the time from time t0 to t4 as one cycle. The comb electrode 5 is driven by applying a voltage having a frequency approximately twice the resonance frequency of the vibration system constituted by the movable plate 2 and the torsion spring 4 as described above, and the movable plate 2 is driven with a resonance phenomenon. The swing angle is increased. Note that the voltage application mode and drive frequency of the comb electrode 5 are not limited to those described above. For example, even if the drive voltage is configured to be applied in a sine waveform, the comb teeth 2c and 3c The comb-teeth electrode 5 may be configured to be driven by changing both of the potentials. The torque applied to the movable plate 2 preferably changes in a substantially sinusoidal shape as shown by a two-dot chain line in the figure, but the electrostatic torque by the comb-tooth electrode 5 is as shown by a dotted line in the figure, This occurs only when the comb teeth 2c and 3c of the comb-tooth electrode 5 approach each other and overlap each other, and thus occurs as indicated by the broken line in the figure.

Here, the comb-teeth electrode 5 of the optical element 1 is formed in a tapered shape whose width is narrowed from the root part to the tip part of the comb teeth 2c and 3c as described above, and the rigidity of the comb teeth 2c and 3c is increased. It is configured to be high and difficult to bend. The resonance frequency f of each comb tooth 2c, 3c regarded as a cantilever beam in the horizontal direction (the direction of arrow D in FIG. 4) uses the Young's modulus E of the comb teeth 2c, 3c and the density ρ of the comb teeth 2c, 3c, When the width of the comb teeth is approximated to (w1 + w2) / 2, it can be expressed as the following formula as a function of the comb tooth length l.

  In the present embodiment, the widths and lengths of the comb teeth 2c and 3c of the comb-tooth electrode 5 are set based on the results of various calculations performed in view of the resonance frequencies of the comb teeth 2c and 3c. Hereinafter, the setting of the width of the comb teeth 2c and 3c and the length of the comb teeth will be described with reference to FIGS. FIG. 6 shows, for example, three types of comb teeth 2c and 3c having a tip end width w2 of 2 μm and a taper angle θ set to 0.5 deg, 0.3 deg, and 0 deg. The value of the resonance frequency of the comb teeth 2c and 3c with respect to the comb tooth length is shown. From the figure, it can be seen that the comb teeth 2c and 3c having a larger taper angle θ and a larger width w1 at the root portion have a higher resonance frequency at the same comb tooth length. Since the comb teeth 2c and 3c must be configured so that the comb teeth 2c and 3c do not come into contact with each other and do not resonate with the oscillation of the movable plate 2 when the movable plate 2 is driven, the resonance frequency of the comb teeth 2c and 3c is The resonance frequency of the movable plate 2 must be higher. That is, the comb teeth lengths of the comb teeth 2c and 3c are set based on the resonance frequency of the movable plate 2. For example, when the resonance frequency when the movable plate 2 is driven is 16 kHz, the taper angle θ is 0.5 deg. , 0.3 deg, and 0 deg, the maximum comb tooth length is set to a length of 750 μm or less, 600 μm or less, or 400 μm or less.

  FIG. 7 shows the relationship between the electrostatic torque generated by the comb electrode 5 and the deflection angle of the movable plate 2. In the figure, as described above, each comb tooth 2c having a tip width w2 of 2 μm and comb tooth length-taper angle θ combinations of 750 μm-0.5 deg, 600 μm-0.3 deg, and 400 μm-0 deg, respectively. 3c is a static electrode when the comb-tooth electrode 5 is configured by arranging 5, 10, and 14 within the comb-teeth electrode 5 having a width of 200 μm while ensuring a gap g between the comb-teeth of 5 μm. Electric torque is shown. The electrostatic torque is based on the assumption that the root of the comb tooth 2c of the movable plate 2 is located 90 μm away from the rotation axis of the movable plate 2, and the electrostatic force of the comb electrode 5 is the center of gravity position of the comb tooth 2c. It is calculated assuming that When the taper angle θ is applied to the comb teeth 2c and 3c to increase the width of the root portion, the interval at which the comb teeth 2c and 3c can be arranged increases, and the number of comb teeth 2c and 3c that can be arranged in a certain space is increased. On the other hand, the comb tooth length can be set longer than 400 μm to 600 μm in the case of θ = 0.3 deg than in the case of the taper angle θ = 0 deg. At this time, the change in the capacitance of the comb-teeth electrode 5 is more greatly affected by the difference in the comb-teeth length than the difference in the number of the comb-teeth 2c and 3c. The electrostatic torque applied to the movable plate 2 becomes larger when θ = 0.3 deg. On the other hand, when the taper angle θ = 0.3 deg of the comb teeth 2c and 3c is compared with the case of θ = 0.5 deg, the comb tooth length is longer when θ = 0.5 deg. It can be seen that the number of comb teeth 2c and 3c is reduced, and the electrostatic torque is lower over the entire deflection angle of the movable plate 2 than when θ = 0.3 deg. As described above, in the present embodiment, the taper angle θ of the comb teeth 2c and 3c is set to 0.3 deg, and the electrostatic torque is set to be the largest. That is, in the present embodiment, the width of the comb teeth 2c and 3c and the comb tooth length of the comb electrode 5 are set to a long comb tooth length while maintaining the rigidity of the comb teeth 2c and 3c. In consideration of the demerit that the number of the comb teeth 2c and 3c is reduced so that the electric torque is increased, it is set after actually performing the calculation under various constraint conditions. At this time, the widths and lengths of the comb teeth 2c and 3c are preferably set to optimum values calculated by calculation so that the electrostatic torque of the comb electrode 5 is maximized. It is not limited.

  Thus, in the optical element 1 of the present embodiment, since the comb teeth 2c and 3c are tapered, the resonance frequency of the comb teeth 2c and 3c can be increased as compared with the case where the taper angle θ = 0 deg. The comb teeth 2c and 3c are difficult to bend, and even if the length of the comb teeth is increased, the comb teeth 2c and 3c are difficult to contact each other, and the comb teeth 2c and 3c are not easily damaged. Therefore, it is possible to increase the electrostatic capacity of the comb-teeth electrode 5 by increasing the comb-teeth length of the comb teeth 2c and 3c, and to apply a large electrostatic torque to the movable plate 5. Can be larger. In addition, since the comb teeth 2c and 3c are tapered, the plurality of comb teeth 2c and 3c can be arranged in a space-efficient manner in the space in which the comb electrode 5 is arranged. Therefore, the number of comb teeth 2c and 3c that can be arranged is increased, and the deflection angle of the movable plate 2 can be further increased while ensuring the rigidity and strength of the comb teeth 2c and 3c. As a result, the mirror film 2a can be swung with a large swing angle, and light can be scanned at a wider angle.

  In addition, this invention is not limited to the structure of the said embodiment, A various deformation | transformation is possible suitably in the range which does not change the meaning of invention. For example, the shape of the comb teeth constituting the comb electrode does not have to be a taper shape, and may be formed so that the width gradually decreases from the root portion to the tip portion of the comb teeth, for example. FIG. 8 shows an example of comb teeth formed so that the width becomes narrower step by step, for example. The comb teeth 12c are formed to be narrowed in three steps from the root portion to the tip portion, and a plurality of comb teeth 12c can be arranged efficiently as in the optical element 1 described above. It is configured. Thus, in the present invention, the comb teeth only need to be configured such that the width of the tip portion is narrower than the root portion of the comb teeth. Compared to the case where the width is uniform from the root part to the tip part, the horizontal resonance frequency of the comb teeth is increased, and even if the length of the comb teeth is increased, the comb teeth are difficult to come into contact with each other. It is possible to increase the deflection angle of the plate.

  Moreover, the movable plate does not need to be formed in a circle, and may have another shape such as a rectangle or a rhombus. The present invention can be applied not only to an optical element in which a mirror film is formed on a movable plate but also to a movable structure having a movable plate that is driven to swing by a comb electrode.

The top view which shows an example of the optical element which concerns on one Embodiment of this invention. The perspective view which shows the said optical element. The top view which shows the comb-tooth electrode of the said optical element. The perspective view which shows the comb tooth of the said comb-tooth electrode. The time chart which shows an example of operation | movement of the said optical element. The graph which shows the relationship between the comb-tooth length of the said comb-tooth, and the resonance frequency of the said comb-tooth horizontal direction. The graph which shows the relationship between the deflection angle of the movable plate at the time of operation | movement of the said optical element, and the electrostatic torque generated by the comb-tooth electrode at that time. The perspective view which shows one modification of the said comb tooth. (A) is a top view which shows the comb-tooth electrode of the conventional optical element, (b) is a perspective view which shows the comb-tooth of the comb-tooth electrode.

Explanation of symbols

1 Optical element (movable structure)
2 Movable plate 2a Mirror film (mirror structure)
2c, 3c, 12c Comb teeth 3 Frame part 4 Torsion spring 5 Comb electrodes

Claims (4)

A movable plate, a torsion spring that pivotally supports the movable plate on both sides, a frame portion that supports the torsion spring, a part of the movable plate, and the frame portion that faces the movable plate so as to mesh with each other Provided with a comb-teeth electrode having a plurality of comb teeth, and when the voltage is applied between the comb-teeth electrode on the movable plate side and the comb-teeth electrode on the frame side, the movable plate A movable structure configured to swing;
The movable structure characterized in that the width of the comb teeth of the comb-teeth electrode is configured such that the tip portion is narrower than the root portion of the comb teeth.   2. The movable structure according to claim 1, wherein the comb teeth of the comb-teeth electrode are formed in a tapered shape whose width gradually decreases from a root portion to a tip portion of the comb teeth.   2. The movable structure according to claim 1, wherein the comb teeth of the comb-teeth electrode are formed so that a width gradually decreases from a root portion to a tip portion of the comb teeth. A movable structure according to any one of claims 1 to 3,
An optical element, wherein the movable plate is provided with a mirror structure, and the light incident on the mirror structure is scanned when the movable plate swings.

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