JP2006145962A - Two-dimensional optical deflector and optical apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-dimensional optical deflector that reduces deflection of a movable mirror, in a biaxial driving optical deflector having a gimbals structure. <P>SOLUTION: The optical deflector is equipped with gimbals torsionally rotatably supported on one side with a first torsion bar, a holder torsionally rotatably supporting the gimbals in the axial direction orthogonal to the rotary shaft of a second movable mirror, and a driving means for torsionally rotating the movable mirror and the gimbals. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical deflector manufactured by a micromechanics technique.

  The optical deflector is used for, for example, an application for deflecting laser light. There is a galvanometer mirror as a scanning mirror that deflects and scans laser light. The driving principle of the galvanometer mirror is that when a current is passed through a moving coil arranged in a magnetic field, an electromagnetic force is generated in relation to the current and the magnetic flux, and a torque proportional to the current is generated. Using the galvanometer principle that the movable coil rotates to an angle at which this torque and spring force are balanced, and the presence or absence of current is detected by swinging the pointer through this movable coil. A reflecting mirror is provided on the rotating shaft instead of the pointer.

  However, a galvanomirror requires a mechanically wound drive coil and a large yoke for generating a magnetic field, and there is a limit to downsizing these mechanical elements mainly because of output torque. At the same time, the size of the entire device for deflecting the light has been increased due to the space for assembling the constituent members.

  As a small-sized optical deflector, there is an optical deflector manufactured using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique. For example, Non-Patent Document 1 proposes a Torsional Scanning Mirror formed of silicon by K.E.Petersen et al. In this optical deflector, as shown in FIG. 11, the mechanically movable portion 3 includes a mirror 3a as an optical deflector and a beam 3b that supports the mirror 3a, and between the mirror 3a and the fixed electrode 2 formed on the substrate. The torsional moment is applied to the beam by the electrostatic attractive force generated by applying a driving voltage to the beam, and the mirror 3a is deflected to change the deflection angle. The maximum deflection angle of the mirror part is uniquely determined by the gap interval t0 between the mirror part and the substrate. In an optical deflector, the larger the deflection angle, the better, and this requires a large gap interval. If the gap is increased, the distance between the fixed electrode and the mirror is increased, and the driving voltage is remarkably increased. Conversely, in order to achieve a low voltage, it is necessary to shorten the gap interval and suppress the deflection angle, and the reduction of the drive voltage and the increase of the deflection angle are contradictory issues.

As shown in FIG. 12, an actuator having a structure in which the above deflectors are arranged so as to be biaxially deflectable has been developed (Patent Document 2). That is, the movable mirror is supported on the gimbal by two torsion bars, the gimbal is supported on the substrate by two torsion bars, and the drive axis of the movable mirror and the gimbal has a structure orthogonal to each other, facing the movable part. It is driven by electrostatic attraction between the electrodes. In this configuration, a biaxial optical deflector capable of forming an image by raster scanning can be provided by setting the resonance frequency of the movable mirror and the gimbal to a desired value. In addition, an actuator that drives the movable mirror and the gimbal by forming a coil on the movable mirror and the gimbal having this configuration and arranging a permanent magnet close to the coil is also disclosed.
IBM J.RES.DEVELOP., VOL.24, NO5,9,1980.P631-637 JP 60-1007017 A

  In the actuator having the gimbal structure as described above, the movable mirror and the gimbal are both supported on the cymbal and the support by the torsion bar, respectively. For this reason, the movable mirror is bent due to the following causes.

1. 1. Stress generated at the time of bonding or bonding the cymbal structure and the substrate on which the counter electrode is formed 2. Stress due to heat generation of the coil formed on the cymbal Stress caused by the difference in coefficient of thermal expansion between the material forming the cymbal structure and the member to be joined to it due to temperature changes in the external environment. For example, when the cymbal structure is used in an image forming apparatus, Causes a drop.

  The present invention has been made in view of the above viewpoint, and an object of the present invention is to provide a two-dimensional optical deflector that reduces bending of a movable mirror in a biaxial drive optical deflector having a gimbal structure.

  In order to achieve the above object, the present invention provides an optical deflector described in the following (1) to (8).

  (1) A movable mirror, a gimbal that supports the movable mirror on one side so as to be torsionally rotated by a first torsion bar, and a gimbal that is torsionally rotated by a second torsion bar in an axial direction perpendicular to the rotation axis of the movable mirror A support body capable of supporting, a first drive means for twisting and rotating the movable mirror with respect to the gimbal, and a second drive means for twisting and rotating the gimbal with respect to the support body. To do.

  And (2) a fixed electrode disposed at a position facing the movable mirror, and a movable electrode formed on the movable mirror, wherein the fixed electrode and the movable electrode cause the movable mirror to move by electrostatic attraction. The optical deflector according to (1), wherein the optical deflector is a first driving unit that twists and rotates with respect to the gimbal.

  (3) A movable comb electrode formed on the movable mirror and a fixed comb electrode formed on the gimbal so as to be spaced apart from the movable comb electrode may The optical deflector according to (1), wherein the optical deflector is a first driving unit that twists and rotates with respect to the gimbal.

  (4) The permanent magnet and the coil formed on the cymbal are second driving means for torsionally rotating the gimbal with respect to the support by electromagnetic force. The optical deflector according to (3).

  (5) The optical deflector according to (1) to (4), wherein the first torsion bar is one.

  (6) The optical deflector according to any one of (1) to (5), wherein the first driving means is means for resonantly driving the movable mirror.

  (7) The optical deflector according to any one of (1) to (6), wherein the second driving means is means for driving the gimbal to resonate.

  An optical apparatus comprising the light deflector according to (8) and (1) to (7) and a light source.

  According to the present invention, it is possible to provide a two-dimensional optical deflector in which the deflection of the movable mirror is reduced in the biaxial drive optical deflector having a gimbal structure. Further, by using the comb-shaped electrode, the displacement angle was large, and the device could be driven at a low voltage. Further, according to the present invention, it is possible to provide an image forming apparatus that has a compact configuration, can be driven at a low voltage, has a large deflection angle, and can reduce the deflection of the movable mirror, thereby obtaining a high-definition image. It was.

  The present invention is characterized in that, in a two-dimensional optical deflector having a gimbal structure, the movable mirror is cantilevered with respect to the cymbal by a torsion bar. The details and operation will be described below with typical examples. FIG. 1 is a top view showing a configuration of an embodiment of an optical deflector of the present invention. FIG. 2 is a cross-sectional view showing the configuration of an embodiment of the optical deflector of the present invention. FIG. 3 is a diagram for explaining the cymbal deflection of the optical deflector according to the present invention. FIG. 4 is a diagram for explaining the two-dimensional deflection of the optical deflector according to the present invention.

  In this embodiment, the cymbal 101 cantilever-supports the movable mirror 102 by the first torsion bar 103 so as to be torsionally rotated. The support body 104 supports the gimbal 101 by the second torsion bar 105 so that the gimbal 101 can be torsionally rotated. The second torsion bar may be one or two. The gimbal 101, the movable mirror 102, the first torsion bar 103, the support 104, and the second torsion bar 105 may be integrally formed by removing single crystal silicon. The coil 106 is formed on a gimbal on which an insulating layer (not shown) is formed. The wiring of the coil 106 is connected to the contact pad 107 on the support through the second torsion bar 105 on which an insulating layer (not shown) is formed. An intermediate insulating layer 108 is formed at the wiring extraction portion from the innermost periphery of the coil 106 in order to avoid electrical connection with the outer peripheral coil. For example, polyimide can be used for the intermediate insulating layer 108. In addition, fixed electrodes 109 and 110 are formed on the substrate 111. The fixed electrodes 109 and 110 are disposed at positions facing the back surface of the movable mirror 102. A spacer 112 is disposed between the support 104 and the substrate 111, and even when the movable mirror 102 is twisted, the substrate 111 on which the fixed electrodes 109 and 110 are formed and the movable mirror 102 do not interfere with each other. The support and the spacer, and the spacer and the substrate are each fixed with an adhesive (not shown). In addition, the permanent magnets 113 and 114 are disposed at positions that are substantially symmetrical with respect to the second torsion bar 105 and that different magnetic poles face each other. A magnetic path may be formed by arranging a soft magnetic material in the vicinity of the permanent magnet.

  In the gimbal structure having this configuration, the movable mirror 102 is angularly displaced with respect to the cymbal 101 by an electrostatic attractive force acting between the fixed electrodes 109 and 110. When the movable mirror 102 is set to GND and a positive voltage is applied to the fixed electrode 109, the movable mirror is attracted to the fixed electrode 109. Further, the movable mirror is attracted to the fixed electrode 110 by applying a positive voltage to the fixed electrode 110. By repeating this alternately, the movable mirror 102 is angularly displaced with respect to the gimbal 101. If the frequency of the drive voltage is set to the torsional resonance frequency of the movable mirror 102 and the first torsion bar 103, the movable mirror 102 can be driven to resonate. In this case, the driving voltage for generating the same displacement angle can be greatly reduced as compared with the case of non-resonant driving.

  Further, as shown in FIG. 3, the gimbal 101 is angularly displaced with respect to the support 104 by an electromagnetic force generated by the action of the magnetic field generated by energizing the coil 106 and the magnetic field of the permanent magnet. If the direction in which the coil 106 is energized is reversed, angular displacement occurs in the opposite direction.

  As described above, by combining the electrostatic drive that causes the angular displacement of the movable mirror 102 and the electromagnetic drive that causes the angular displacement of the cymbal 101, the angular displacement of the gimbal 101 is superimposed on the angular displacement of the movable mirror 102. Thus, two-dimensional deflection as shown in FIG. 4 is possible.

  In the optical deflector having this configuration, since the support 104 is fixed to the spacer 112 and the substrate 111 with an adhesive, a stress is generated in the support 104 due to a difference in thermal expansion coefficient due to an external temperature change. The mirror 102 is cantilevered by the gimbal 101 by the first torsion bar 103, and the movable mirror 102 does not bend. In addition, since the stress generated in the first torsion bar 103 due to the temperature change is smaller than in the case of supporting both ends, the shift amount of the resonance frequency due to the temperature change can be reduced. The amount can be easily controlled.

  Hereinafter, the present invention will be described in detail with reference to examples.

  In this example, an optical deflector having the gimbal structure shown in FIGS. 5 to 9 was designed and manufactured. FIG. 5 is a top view showing the configuration of the optical deflector of the present invention. 6 is a cross-sectional view taken along the line A-A ′ of the optical deflector of FIG. 5 (a state where the movable mirror is angularly displaced with respect to the gimbal). FIG. 7 is a top view showing a main manufacturing method of the optical deflector of the present invention. FIG. 8 is a cross-sectional view taken along the line B-B ′ in FIG. 7 showing a main method for manufacturing the optical deflector of the present invention. FIG. 9 is a view for explaining electrode separation of the optical deflector of the present invention.

  In this embodiment, an SOI substrate in which an insulating layer 501 is sandwiched between first and second silicon layers 502 and 503 is used. The thickness of the first silicon layer 502 is 100 μm, and the thickness of the second silicon layer 503 is 250 μm. The movable mirror 504, the gimbal 505, the first torsion bar 506, the second torsion bar 507, and the support 508 are formed by removing the first silicon layer 502. A through hole 509 is provided in the second silicon layer 503 and does not hinder the rotational movement of the movable mirror 504 and the gimbal 505. The support body 508 is fixed to a support frame formed of a second silicon layer with the insulating layer 501 interposed therebetween.

  The cymbal 505 cantilever-supports the movable mirror 504 by the first torsion bar 506 so as to be torsionally rotated. The support body 508 supports the gimbal 505 by the second torsion bar 507 so as to be able to twist and rotate. An electrode support 510 and a movable comb electrode 511 are formed on the movable mirror 504. A fixed comb-shaped electrode 512 is formed on the gimbal 505 so as to be spaced apart from the movable comb-shaped electrode 511. An electrode separation layer 513 made of an insulator is formed on the gimbal 505 and the support body 508.

  The coil 514 is formed on a gimbal on which an insulating layer (not shown) is formed. The wiring of the coil 514 is connected to the contact pad 515 on the support through the second torsion bar 507 on which an insulating layer (not shown) is formed. An intermediate insulating layer 516 made of polyimide is formed at the wiring extraction portion from the innermost periphery of the coil 514 in order to avoid electrical connection with the outer peripheral coil.

  The support frame formed of the second silicon layer 503 is fixed to the substrate with an adhesive (not shown). In addition, the permanent magnets 517 and 518 are disposed at positions that are substantially symmetrical with respect to the second torsion bar 507 and that different magnetic poles face each other.

  Here, main manufacturing methods of the optical deflector of this embodiment will be described with reference to FIGS. FIG. 8 is a cross-sectional view taken along the line B-B ′ of FIG. 7.

First, an electrode separation pattern is formed on the SOI substrate with a thermal oxide film (8-a)
Next, a trench is formed in the first silicon layer using ICP-RIE (8-b). An electrode isolation layer is formed in this trench.

Next, the surface on which the trench is formed is thermally oxidized (8-c)
Next, Poly-Si is deposited on the thermal oxide film to fill the trench (8-d)
Next, the surface on which Poly-Si is deposited is polished to remove other than Poly-Si buried in the trench (8-e)
Next, after etching the thermal oxide film exposed on the surface with hydrofluoric acid, thermal oxidation is performed again to cover Poly-Si with the thermal oxide film, and a thermal oxide film is also formed on the back surface of the SOI (8-f).
Next, the pattern of the movable part (gimbals, first and second torsion bars, movable mirror, support) and contact pad is formed by etching the thermal oxide film (8-g).
Next, a coil, coil wiring, and contact pad are formed (8-h)
Next, an intermediate insulating layer is formed to take out the coil wiring from the innermost circumference of the coil, and the coil wiring from the innermost circumference is formed (8-i)
Next, the first silicon layer is etched from the surface of the SOI substrate using ICP-RIE (8-j)
Next, the second silicon layer is etched from the back surface of the SOI substrate using ICP-RIE (8-k).
Finally, the insulating layer of the SOI substrate exposed in the steps (8-j) and (8-k) is removed and the movable part is released (8-l).
The movable comb electrode formed on the edge of the movable mirror formed integrally by removing the same silicon layer and the fixed comb electrode formed on the gimbal are electrically connected via the first torsion bar. Thus, it is considered that separate potentials cannot be applied to the movable comb electrode and the fixed comb electrode. However, in this configuration, an electrode separation layer made of an insulator is formed on the gimbal and the support, thereby forming FIG. Different potentials can be applied to the filled portion and the white portion.

  GND was applied to the movable comb electrode, and a sinusoidal drive voltage was applied to the fixed comb electrode. The frequency of the sine wave was set to the torsional resonance frequency for the movable mirror and the gimbal of the first torsion bar. The movable mirror made an angular displacement movement in which the angular displacement amount was a sine wave with respect to the gimbal. By using the comb-shaped electrode, the driving voltage for generating the same displacement angle can be greatly reduced as compared with the case of the parallel plate-type electrode. In addition, the gimbal is angularly displaced with respect to the support by an electromagnetic force generated by the action of the magnetic field generated by energizing the coil and the magnetic field of the permanent magnet. If the direction of energizing the coil is reversed, the angular displacement is reversed. By combining the electrostatic drive for angularly moving the movable mirror and the electromagnetic drive for angularly displacing the cymbal as described above, the angular displacement of the movable mirror is superimposed on the angular displacement of the gimbal, enabling two-dimensional angular displacement. It was.

  In the biaxial optical deflector having this configuration, since the support frame is fixed to the substrate with an adhesive, a stress is generated in the support due to a change in the external temperature, but the movable mirror has a torsion bar. Therefore, the movable mirror does not bend. In addition, since the stress generated in the torsion bar due to temperature change is small compared to the case where both ends are supported, the shift amount of the resonance frequency due to temperature change can be reduced. Especially in the case of resonance driving, the angular displacement amount can be controlled. It became easy.

(Image forming device)
This embodiment is an example of an image forming apparatus using an optical deflector according to the present invention. FIG. 10 shows the configuration of this embodiment. First, the modulation light source 1003 is directly modulated by the modulation signal 1002 output from the light source modulation driving unit 1001. In this embodiment, a red semiconductor laser is used as the direct modulation light source 1003. The direct modulation light source 1003 may be a red, blue, or green light source that can be directly modulated, and these may be mixed by a color mixing optical system. The output light 54 directly modulated from the direct modulation light source 1003 is applied to the reflection surface of the optical deflector 1005. Further, the reflected light deflected by the optical deflector 1005 passes through the correction optical system 1006 and is displayed as an image on the image display body 1007. The correction optical system 1006 is an optical system that corrects image distortion due to resonance scanning.

  The optical deflector 1005 is the optical deflector according to the first embodiment, and displays an image on the image display body 1007 by raster scanning the output light 1004 using the optical deflector 1005.

  According to this embodiment, it is possible to provide an image forming apparatus that has a compact configuration, can be driven at a low voltage, and can obtain a high-definition image with a large deflection angle.

It is a top view which shows one Embodiment of the optical deflector of this invention. It is sectional drawing which shows one Embodiment of the optical deflector of this invention. It is a figure explaining the angular displacement of the gimbal of one Embodiment of the optical deflector of this invention. It is a figure explaining the two-dimensional angular displacement of the optical deflector of this invention. It is a top view of the first embodiment of the optical deflector of the present invention. It is sectional drawing of the 1st Example of the optical deflector of this invention. It is a top view for demonstrating the manufacturing method of the 1st Example of the optical deflector of this invention. It is sectional drawing for demonstrating the manufacturing method of the 1st Example of the optical deflector of this invention. It is a figure explaining the electrode separation of the 1st example of the optical deflector of the present invention. It is a figure which shows the image forming apparatus using the optical deflector of this invention. It is a figure which shows a prior art example. It is a figure which shows another prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Gimbal 102 Movable mirror 103 1st torsion bar 104 Support body 105 2nd torsion bar 106 Coil 107 Contact pad 108 Intermediate insulation layer 109 Fixed electrode 110 Fixed electrode 111 Substrate 112 Spacer 113 Permanent magnet 114 Permanent magnet 501 Insulation layer 502 First One silicon layer 503 Second silicon layer 504 Movable mirror 505 Gimbal 506 First torsion bar 507 Second torsion bar 508 Support body 509 Through hole 510 Electrode support portion 511 Movable comb electrode 512 Fixed comb electrode 513 Electrode separation Layer 514 Coil 515 Contact pad 516 Intermediate insulating layer 517 Permanent magnet 518 Permanent magnet 1001 Light source modulation driver 1002 Modulated signal 1003 Directly modulated light source 1004 Directly modulated output 1005 optical deflector 1006 correction optical system 1007 image display

Claims (8)

A movable mirror,
A gimbal that supports the movable mirror on one side so that it can be rotated by a first torsion bar
A support that supports the gimbal by a second torsion bar so that the gimbal can be twisted and rotated in an axial direction perpendicular to the rotation axis of the movable mirror;
An optical deflector comprising: first driving means for twisting and rotating the movable mirror with respect to the gimbal; and second driving means for twisting and rotating the gimbal with respect to the support.   A fixed electrode disposed at a position facing the movable mirror; and a movable electrode formed on the movable mirror, wherein the fixed electrode and the movable electrode cause the movable mirror to move against the gimbal by electrostatic attraction. The optical deflector according to claim 1, wherein the optical deflector is the first driving unit that twists and twists.   A movable comb electrode formed on the movable mirror and a fixed comb electrode formed on the gimbal so as to be spaced from the movable comb electrode cause the movable mirror to move against the gimbal by electrostatic attraction. The optical deflector according to claim 1, wherein the optical deflector is the first driving unit that twists and twists.   The permanent magnet and a coil formed on the cymbal are the second driving means for torsionally rotating the gimbal with respect to the support by electromagnetic force. An optical deflector according to claim 1.   The optical deflector according to any one of claims 1 to 4, wherein the first torsion bar is one.   6. The optical deflector according to claim 1, wherein the first driving unit is a unit that drives the movable mirror to resonate.   The optical deflector according to claim 1, wherein the second driving unit is a unit that drives the gimbal to resonate.   An optical apparatus comprising the optical deflector according to claim 1 and a light source.

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