JP2005341788A - Microactuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microactuator wherein a multishaft moves in a tilted manner, a movable portion of light weight and high rigidity is fit, and a high-speed operation at a lower voltage is attained. <P>SOLUTION: The microactuator 100 includes a base 1, a first comb-type electrode 2 supported by the base 1, a movable portion 6 having a second comb-type electrode 8 opposing the first comb type electrode 2, and at least one reinforcement rib 9 protruding toward the base 1, and an elastic support portion 3 for supporting the movable portion 6 so as to allow the movable portion 6 to be displaced, with respect to the base 1. The height of the second comb-type electrode 8 and the height of at least one reinforcing rib 9 are made to be different from each other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a microactuator that includes a comb-shaped electrode and displaces a movable part using an electrostatic force. The microactuator of the present invention is used, for example, as a micromirror device having a light reflecting surface on a movable part.

  A microactuator to which micromachining technology is applied is used, for example, as an optical scanning device in a laser printer, a scanner, a display, or the like, or as an optical switching device that switches light input and output to an optical fiber.

  Patent Document 1 discloses a microactuator that includes a comb electrode and functions as an optical deflector. The movable part of the optical deflector includes a mirror surface that functions as a light reflecting surface. The movable part is supported by two beams provided on the same straight line, and the electrostatic force generated between the comb electrode provided on the movable part and the comb electrode provided on the base causes 2 Tilt the beam as a torsional rotation axis. This optical deflector has a simpler structure than an optical deflector that uses a motor to rotate a polygon mirror, and can be formed in a batch in a semiconductor process, making it easy to reduce the size and manufacturing costs. Can be expected.

  The comb-shaped electrode provided in the movable part of the optical deflector has protrusions that function as comb teeth extending in a direction orthogonal to the tilt axis, and a groove is formed between the protrusions. The comb-shaped electrode included in the base also has protrusions that are comb teeth extending in a direction orthogonal to the tilt axis, and a groove is formed between the protrusions. The comb tooth part of the movable part and the comb tooth part of the base are opposed to each other with a gap therebetween. The movable part is reinforced by the comb tooth part of the movable part projecting toward the base.

This optical deflector is a uniaxial tilt mirror, and these comb teeth portions are arranged so that the gap between the comb teeth portion of the movable portion and the comb teeth portion of the base does not change when the movable portion is tilted. It extends only in the direction perpendicular to the rotation axis.
JP 2000-147419 A

  However, the above-described optical deflector has the following problems.

  In the optical deflector described above, the comb-tooth portion of the movable portion extends along only one direction orthogonal to the tilt axis, and the movable portion is not reinforced in the other directions, so the rigidity of the movable portion is low. There's a problem. If the rigidity of the movable part is low, when an Au film or a dielectric multilayer film is formed on the surface of the movable part in order to increase the light reflectivity, the thermal expansion coefficient between the material of these films and the material of the movable part There is a problem that warpage occurs in the movable part due to the difference between them and the flatness of the light reflecting surface is deteriorated.

  In order to increase the rigidity of the movable part, it is conceivable to increase the height of the comb tooth part. However, if the comb-tooth portion is raised to a height required to obtain the rigidity required for the movable portion, the weight of the movable portion increases, so that a larger driving force is required to drive the movable portion. Further, when the weight of the movable part is increased, the resonance frequency of the movable part is lowered, so that there is a problem that the movable part cannot be driven at a high speed.

  In addition, the movable part of the microactuator described above only tilts in one axis. However, as another type of microactuator, the comb tooth part is stretched along a plurality of directions, and the movable part is tilted in multiple axes. There are microactuators to be performed. In such a microactuator, when the height of the comb tooth portion is increased in order to increase the rigidity of the movable portion, when the movable portion is tilted, the comb tooth portion provided on the movable portion and the base are provided. There is a problem of contact with the comb teeth. In order to avoid such contact, if the gap between the comb teeth is widened, there is a problem that the generated electrostatic force is reduced. Further, since the weight of the movable portion increases when the height of the comb tooth portion is increased, there are problems that a large driving force as described above is required and that the movable portion cannot be driven at a high speed. Thus, there was a trade-off between both the rigidity and weight of the movable part and between the rigidity of the movable part and the electrostatic force.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a microactuator that is capable of multi-axis tilting, has a lightweight and highly rigid movable part, and can operate at low voltage and high speed. There is.

  The microactuator of the present invention includes a base, a first comb electrode supported by the base, a second comb electrode facing the first comb electrode, and at least one protruding in the direction of the base. A movable portion having two reinforcing ribs, and an elastic support portion that supports the movable portion so that the movable portion can be displaced with respect to the base. The height of the second comb electrode and the at least one The height of the reinforcing rib is different from each other.

  In one embodiment, the height of the at least one reinforcing rib is higher than the height of the second comb electrode.

  In one embodiment, the second comb-shaped electrode includes a plurality of comb-tooth portions, and the thickness of the at least one reinforcing rib is greater than the thickness of each of the plurality of comb-tooth portions.

  In one embodiment, the second comb electrode includes a plurality of comb teeth, and the plurality of comb teeth extend in a direction from the inside toward the outside of the movable portion.

  In one embodiment, the second comb electrode includes a plurality of comb teeth, and the plurality of comb teeth have a concentric shape.

  In one embodiment, the at least one reinforcing rib is provided on an outer peripheral portion of the movable portion.

  In one embodiment, the second comb-shaped electrode includes a plurality of comb teeth, and the plurality of comb teeth and the at least one reinforcing rib extend in the same direction.

  In one embodiment, the second comb electrode includes a plurality of comb teeth, and the plurality of comb teeth and the at least one reinforcing rib extend in directions perpendicular to each other.

  In one embodiment, the height of the second comb electrode is lowered along the direction from the inner side to the outer side of the movable part.

  In one embodiment, the second comb-shaped electrode includes a plurality of comb-tooth portions, and the thickness of each of the plurality of comb-tooth portions is reduced along the direction from the inside to the outside of the movable portion. .

  In one embodiment, the elastic support portion supports the movable portion so that the movable portion can be tilted in two axes with respect to the base.

  In one embodiment, the elastic support portion supports the movable portion such that the movable portion can be displaced in a vertical direction with respect to the base and tilted biaxially with respect to the base.

  In one embodiment, the movable part includes a light reflecting surface.

  According to the microactuator of the present invention, since the movable portion includes the reinforcing rib, the rigidity of the movable portion can be increased. Moreover, the rigidity of a movable part can be raised more by making the height of a reinforcement rib higher than a comb-shaped electrode. Since it is not necessary to increase the height of the comb teeth portion in order to increase the rigidity, the horizontal gap between the comb teeth portions that mesh with each other can be narrowed, and the movable portion can be reduced in weight. Thereby, the movable part can be driven at a high speed with a low voltage. Further, since the rigidity of the movable part is high, the flatness of the light reflecting surface can be made extremely high when the movable part has a light reflecting surface.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
A first embodiment of a microactuator according to the present invention will be described with reference to FIGS.

  First, FIG. 1 and FIG. 2 will be referred to. 1 and 2 are exploded perspective views schematically showing the microactuator 100 of the present embodiment. FIG. 1 is an exploded perspective view when the microactuator 100 is viewed obliquely from above, and FIG. 2 is an exploded perspective view when the microactuator 100 is viewed obliquely from below. In FIG. 1, a part of the movable part is cut away, and a cross section of the rear surface of the movable part is also shown. The microactuator 100 is manufactured by micromachining technology using a semiconductor process or MEMS (Micro Electro Mechanical System) technology.

  The microactuator 100 includes a base 1, a plurality of first comb electrodes 2 supported by the base 1, a movable part 6, and the movable part 6 so that the movable part 6 can be displaced relative to the base 1. The elastic support part 3 to support is provided. The base 1 includes a drive circuit (not shown) for applying a voltage to the first comb electrode 2 and an insulating layer (not shown) provided on the drive circuit. A plurality (three in this embodiment) of first comb electrodes 2 and elastic support portions 3 are provided in a regular hexagonal region on the insulating layer of the base 1. The first comb electrode 2 functions as a fixed electrode. Each of the first comb electrodes 2 includes a plurality of first comb teeth portions 2a. The plurality of first comb teeth 2a extends along the direction from the inside to the outside of the regular hexagonal region.

  The elastic support portion 3 includes three support posts 4 positioned on the outer peripheral side of the regular hexagonal region of the base 1 and a fixing portion 5 positioned at the center of the regular hexagonal region. The fixed part 5 fixes the elastic support part 3 and the movable part 6. A beam portion extends from each of the support posts 4 toward the fixing portion 5, and the beam portion and the fixing portion 5 are floated from the base 1 by a predetermined amount. The elastic support part 3 and the movable part 6 are fixed by coupling the fixed part 5 and the central post 7 of the movable part 6. The elastic support portion 3 supports the movable portion 6 so that the movable portion 6 can be displaced in the vertical direction with respect to the base 1 and can be tilted biaxially with respect to the base 1.

  The planar shape of the movable part 6 is a hexagon. The planar shape and size of the movable part 6 are variously designed according to the use of the microactuator 100 and the required performance. In the present embodiment, the width of the movable portion 6 is about 100 (μm). The movable portion 6 includes a light reflecting surface 6a and a plurality (three in the present embodiment) of second comb electrodes 8. The light reflecting surface 6 a is located on the surface of the movable portion 6 opposite to the surface facing the base 1. The second comb electrode 8 is provided on the surface of the movable portion 6 facing the base 1 and functions as a movable electrode. Each of the second comb-shaped electrodes 8 faces a corresponding one of the first comb-shaped electrodes 2. Each of the second comb electrodes 8 includes a plurality of second comb teeth 8a. The plurality of second comb teeth 8 a extend along the direction from the inner side to the outer side of the movable part 6. The 1st comb-tooth part 2a and the 2nd comb-tooth part 8a are facing in the state which mutually meshed | interposed with the gap.

  The movable portion 6 includes at least one reinforcing rib 9 that protrudes in the direction of the base 1 from the surface of the movable portion 6 that faces the base 1. The reinforcing rib 9 reinforces the movable part 6 and increases the rigidity of the movable part 6. In the present embodiment, the movable part 6 includes a plurality of reinforcing ribs 9. The reinforcing ribs 9 are provided on the outer peripheral portion of the movable portion 6 and extend radially from the central portion of the movable portion 6 toward each vertex of the hexagon. Three of the radially extending reinforcing ribs 9 respectively pass through a corresponding one of the second comb electrodes 8, and a plurality of second comb electrodes 8 included in the corresponding second comb electrode 8 are provided. It extends along the same direction as the two comb teeth 8a.

  Among the reinforcing ribs 9, the three reinforcing ribs 9 positioned above the elastic support portion 3 have the same height as the second comb-shaped electrode 8, and a predetermined amount of space is formed from the elastic support portion 3. The other reinforcing ribs 9 and the height of the second comb electrode 8 are different from each other. Specifically, the height of the reinforcing rib 9 that passes through the second comb electrode 8 and extends in the same direction as the corresponding second comb tooth portion 8a is equal to the height of the second comb electrode 8 (that is, Higher than the height of the second comb tooth portion 8a). Further, the height of the reinforcing rib 9 provided on the outer peripheral portion of the movable portion 6 is higher than the height of the second comb electrode 8. The height of these reinforcing ribs 9 is, for example, about 1.5 to 2 times higher than the height of the second comb electrode 8. The height of the 1st and 2nd comb-tooth parts 2a and 8a is about 10-20 (micrometer), for example, and the height of the reinforcement rib 9 is about 15-40 (micrometer), for example. Since the height of these reinforcing ribs 9 is higher than the height of the second comb-shaped electrode 8, the rigidity of the movable portion 6 can be further increased.

  A driving voltage is independently applied to each of the three first comb electrodes 2 from a driving circuit. The elastic support portion 3 is connected to the ground via a drive circuit, and the movable portion 6 is connected to the ground via the elastic support portion 3. When a driving voltage is applied to the first comb electrode 2, the movable portion 6 is attracted toward the base 1 by an electrostatic force acting between the first comb electrode 2 and the second comb electrode 8. A restoring force and a restoring torque are generated in the elastic support portion 5 in accordance with the displacement of the movable portion 6 with respect to the base 1. The movable portion 6 performs a vertical displacement with respect to the base 1 and a biaxial tilt with respect to the base 1 so that the restoring force and the restoring torque and the electrostatic force are balanced.

  FIG. 3 is a cross-sectional view of the microactuator 100 along the line 3A-3A shown in FIG. 1, and shows a cross section along the elastic support portion 3 passing through the center of the microactuator 100.

  A gap is provided between the base 1 and the elastic support portion 3 so as to ensure a desired displacement range of the movable portion 6. Similarly, a gap is provided between the elastic support portion 3 and the reinforcing rib 9 positioned above the elastic support portion 3 so as to ensure a desired displacement range of the movable portion 6. The movable portion 6 tilts around the rotation center 10 located at the joint portion between the elastic support portion 3 and the central post 7.

  FIGS. 4A and 4B are partial cross-sectional views of the microactuator 100 taken along the line 3A-3A shown in FIG. 1, and show a state in which the movable portion 6 is displaced.

  The state shown in FIG. 4A is a state in which the same voltage is applied to all the first comb-shaped electrodes 2 and the movable part 6 is translated downward by the maximum distance s and is movable by the electrostatic force acting between the electrodes. The part 6 is sucked downward and the elastic support part 3 is bent.

  The state shown in FIG. 4B shows a state in which the movable portion 6 is inclined by the maximum angle θ by making the voltages applied to the first comb-shaped electrode 2 different from each other. The gaps between the components are set so that the gaps remain in the portion that is displaced downward most due to the inclination.

  Naturally, when the application of the driving voltage is stopped, the movable portion 6 returns to the original position and posture by the elastic restoring force and restoring torque of the elastic support portion 3.

  In order to form the first and second comb electrodes 2 and 8 and the reinforcing rib 9, for example, plasma etching called DRIE (Deep Reactive Ion Etching) is used. Grooves are formed in the base 1 by DRIE, and a sacrificial layer and a structure are further deposited in the grooves to form those constituent elements. The groove formed by DRIE has a width dependency, and the groove depth increases as the groove width increases. Therefore, the height of the reinforcing rib 9 can be made higher than the height of the second comb-shaped electrode 8 by performing patterning so that the width of the reinforcing rib 9 is wider than that of the second comb-shaped electrode 8. Further, the rigidity of the movable portion 6 can be further increased by making the thickness of the reinforcing rib 9 larger than the thickness of each of the second comb tooth portions 8a. The thickness of the first and second comb teeth 2a and 8a is, for example, about 1.0 to 3.0 (μm), and the thickness of the reinforcing rib 9 is, for example, about 2.0 to 5.0 (μm). ).

  FIG. 5 is a cross-sectional view of the microactuator 100 taken along line 5A-5A shown in FIG. 1, and shows how the first comb electrode 2 and the second comb electrode 8 are engaged with each other.

  A distance Gs between the height of the tip portion of the first comb tooth portion 2a and the height of the root portion of the second comb tooth portion 8a is longer than the stroke length of the movable portion 6. Similarly, the distance Gs between the height of the tip portion of the second comb tooth portion 8a and the height of the root portion of the first comb tooth portion 2a is longer than the length of the stroke of the movable portion 6. The distance Gs corresponds to the height of the gap around the tip of each of the first and second comb teeth 2a and 8a. The distance Gs is, for example, about 3.0 to 10 (μm). The first comb tooth portion 2a and the second comb tooth portion 8a are engaged with each other by overlapping by a length L. The length L is, for example, about 10 to 20 (μm). The height (Gs + L) of the first and second comb tooth portions 2a and 8a is set to the minimum necessary height according to the stroke length of the movable portion 6 and the required electrostatic force. On the other hand, the reinforcing rib 9 is set higher than the first and second comb teeth 2a and 8a, and the rigidity of the movable portion 6 is increased. The reinforcing rib 9 increases the rigidity of the movable portion 6, whereby the heights of the first and second comb tooth portions 2 a and 8 a can be reduced to the minimum necessary level, and the light reflecting surface 6 a of the movable portion 6 can be obtained. The thickness of the region can be reduced. Thereby, the weight of the movable part 6 can be significantly reduced while ensuring the necessary rigidity of the movable part 6. The weight of the movable portion 6 including the reinforcing rib 9 is such that the movable portion having the same rigidity without the reinforcing rib 9 (that is, the thickness of the light reflecting surface 6a region is large and / or the height of the second comb tooth portion 8a is high). For example, the weight of the movable portion can be reduced by about 2 to 5 times. Further, when an Au film or a dielectric multilayer film is formed on the light reflection surface 6a in order to increase the reflectance of the light reflection surface 6a, even if the rigidity of the movable portion 6 is insufficient with only the second comb electrode 8, Since the rigidity of the movable part 6 can be increased by the reinforcing rib 9, the light reflecting surface 6a with good flatness can be obtained. By forming the depth of the groove facing the reinforcing rib 9 in the first comb-shaped electrode 2 deeply corresponding to the height of the reinforcing rib 9, the height of the gap around the tip of the reinforcing rib 9 is increased. The height is made equal to the height of the gap around the tip of the second comb tooth portion 8a.

  FIGS. 6A and 6B are cross-sectional views of the microactuator 100 taken along the line 5A-5A shown in FIG. 1, and show a state in which the movable portion 6 is displaced.

  The state shown in FIG. 6A is a state in which the same voltage is applied to all the first comb electrodes 2 and the movable portion 6 is translated downward by the maximum distance s. Since the movable portion 6 does not move in the lateral direction, the first comb tooth portion 2a and the second comb tooth portion 8a do not interfere with each other. The horizontal gap between the first comb tooth portion 2a and the second comb tooth portion 8a is g1, and the gap between the reinforcing rib 9 and the first comb tooth portion 2a is g2.

  The state shown in FIG. 6B shows a state where the movable part 6 is inclined by the maximum angle θ by making the applied voltages to the first comb-shaped electrodes 2 different from each other. In this case, the movable part 6 tilts around the rotation center 10. At a position at a distance H from the rotation center 10 (that is, a position at the height of the tip portion of the first comb tooth portion 2a), the second comb-shaped electrode 8 moves maximum Hθ in the horizontal direction. The distance H is substantially equal to the height (Gs + L) of the first and second comb teeth 2a and 8a. In the microactuator 100, since the height (Gs + L) is set to the minimum necessary height, Hθ is also minimized. Increasing the horizontal gap g1 between the comb teeth in order to avoid interference between the comb teeth reduces the generated electrostatic force, but the height (Gs + L) is minimized, so g1 is reduced. I can do it. The gap g2 between the reinforcing rib 9 and the first comb tooth portion 2a may be equal to g1, and the reinforcing rib 9 does not interfere with the first comb electrode 2.

  In this way, by making the height of the second comb-shaped electrode 8 that generates an electrostatic force different from the height of the reinforcing rib 9 that increases the rigidity of the movable portion 6, the movable portion 6 is not reduced without reducing the driving force. The rigidity of the can be sufficiently increased. Thereby, the movable part 6 which is light and has high rigidity and good flatness of the light reflecting surface is obtained.

(Embodiment 2)
With reference to FIG. 7, a second embodiment of the microactuator according to the present invention will be described.

  FIG. 7 is a plan view schematically showing the movable portion 16 of the present embodiment. In the present embodiment, the microactuator 100 includes a movable portion 16 instead of the movable portion 6.

  The movable part 16 further includes at least one (a plurality in this embodiment) reinforcing ribs 11 in addition to the components of the movable part 6. Each of the reinforcing ribs 11 passes through a corresponding one of the second comb electrodes 8 and extends in a direction perpendicular to the direction in which the second comb teeth 8a included in the corresponding second comb electrode 8 extend. Extending along. The reinforcing rib 11 has the same height as the reinforcing rib 9 higher than the height of the second comb tooth portion 8a. In the present embodiment, the first comb electrode 2 has a groove (not shown) corresponding to the reinforcing rib 11. The relationship of the distance between the reinforcing rib 11 and the first comb electrode 2 is set similarly to the relationship of the distance between the reinforcing rib 9 and the first comb electrode 2. Since the movable portion 16 includes the reinforcing rib 11, the rigidity of the movable portion 16 can be further increased as compared with the movable portion 6.

(Embodiment 3)
A third embodiment of the microactuator according to the present invention will be described with reference to FIG.

  FIG. 8 is a plan view schematically showing the movable portion 26 of the present embodiment. In the present embodiment, the microactuator 100 includes a movable portion 26 instead of the movable portion 6.

  The movable portion 26 includes a plurality of second comb electrodes 28 instead of the plurality of second comb electrodes 8 of the movable portion 6. Each of the second comb electrodes 28 includes a plurality of second comb teeth 8b having a concentric shape. In the present embodiment, the first comb tooth portion 2a also has a concentric shape (not shown) corresponding to the second comb tooth portion 8b. Since the second comb teeth 8b intersect with the reinforcing ribs 9 extending radially at right angles, the rigidity of the movable portion can be increased. Further, since the positional relationship between the first comb electrode 2 and the second comb electrode 28 is the same regardless of the tilting direction of the movable portion 26, the driving force can be obtained in a balanced manner.

  Further, the horizontal suction force generated by the variation in the horizontal gap between the first comb tooth portion 2a and the second comb tooth portion 8b is always in the radial direction. Since the elastic support portion 3 that supports the movable portion 26 extends radially and has high radial rigidity, the second comb electrode 28 is not attracted in the horizontal direction and does not come into contact with the first comb electrode 2. An effect can also be obtained.

(Embodiment 4)
A fourth embodiment of the microactuator according to the present invention will be described with reference to FIGS.

  First, FIG. 9 will be referred to. FIG. 9 is a plan view schematically showing the movable portion 36 of the present embodiment. In the present embodiment, the microactuator 100 includes a movable portion 36 instead of the movable portion 6.

  The movable portion 36 includes a plurality of second comb electrodes 38 instead of the plurality of second comb electrodes 8 of the movable portion 6. Each of the second comb electrodes 38 includes a plurality of second comb teeth 8c. The thickness of each of the plurality of second comb teeth 8 c is reduced along the direction from the inner side to the outer side of the movable part 36. That is, the width w2 on the outer peripheral side of the second comb tooth portion 8c is made smaller than the width w1 on the center side of the movable portion 36. In the present embodiment, the thickness of the first comb tooth portion 2a is increased along the direction from the inside to the outside of the movable portion 36 corresponding to the shape of the second comb tooth portion 8c (not shown). ), The horizontal gap between the first comb tooth portion 2a and the second comb tooth portion 8c is kept constant. Thereby, the movable part 36 can be further reduced in weight compared with the movable part 6 without reducing the rigidity of the movable part 36.

  In FIG. 10, the cross-sectional shape of the 2nd comb-tooth part 8c is shown. The height of the second comb tooth portion 8 c is lowered along the direction from the inner side to the outer side of the movable portion 36. When the first comb-shaped electrode 2 and the second comb-shaped electrode 38 are formed by DRIE, the height of the second comb-tooth portion 8c is decreased as the width of the second comb-tooth portion 8c is reduced due to the width dependency of DRIE. In the second comb tooth portion 8c having such a shape, the height L2 on the outer peripheral side is lower than the height L1 on the inner peripheral side. With such a shape, there is a margin in the space around the outer peripheral side of the second comb tooth portion 8c. Therefore, even when the second comb tooth portion 8c is lowered by the tilting of the movable portion 36, the second comb tooth portion 8c Contact with the elastic support portion 3 can be prevented, and a more reliable microactuator can be obtained.

(Embodiment 5)
With reference to FIGS. 11-17, embodiment of the manufacturing method of the microactuator 100 of this invention is described. 11 to 17 are cross-sectional views schematically showing an embodiment of a method for manufacturing a microactuator of the present invention. FIG. 11A to FIG. 17A correspond to the cross section of the microactuator 100 along the line 5A-5A shown in FIG. 1, and FIG. 11B to FIG. This corresponds to the cross section of the microactuator 100 along line 3A. In order to simplify the explanation, in the present embodiment, the number of first and second comb teeth 2a and 8a shown in the drawing is smaller than the number shown in FIG. The number of the 1st and 2nd comb-tooth parts 2a and 8a is arbitrary. All the manufacturing processes are performed at a temperature lower than 450 ° C. which is a general heat resistance temperature of a drive circuit (CMOS circuit or the like) provided in the base 1.

  First, reference is made to FIG. 11A and FIG. A first conductive layer 301 is formed on the base 1. The first conductive layer 301 is formed in a desired shape using a sputtering method, photolithography, an etching technique, or the like. The material of the first conductive layer 301 is, for example, aluminum. The thickness of the first conductive layer 301 is, for example, about 0.5 to 1.0 (μm). Note that the material of the first conductive layer 301 may be polysilicon, and in this case, the first conductive layer 301 is formed using an LPCVD (Low Pressure Chemical Vapor Deposition) method. The first conductive layer 301 is a portion that becomes the base portion of the first comb-shaped electrode 2 and the support post 4 of the elastic support portion 3.

  Next, the first sacrificial layer 201 is formed on the base 1 by using a photolithography method. The material of the first sacrificial layer 201 is, for example, a photosensitive organic material such as a photoresist and photosensitive polyimide. More preferably, the material of the first sacrificial layer 201 is a high-viscosity material (for example, SU-8 and SU-10 (both trade names) manufactured by MicroChem) that can obtain a high aspect shape. The first sacrificial layer 201 is provided in order to form a space below the elastic support portion 3 in a manufacturing process described later.

  Reference is now made to FIGS. 12 (a) and 12 (b). A second conductive layer 302 is formed on the first conductive layer 301 and the first sacrificial layer 201 by using a low temperature sputtering method. The material of the second conductive layer 302 is the same material (aluminum) as that of the first conductive layer 301. The thickness of the second conductive layer 302 is, for example, about 0.5 to 2.0 (μm). The second conductive layer 302 is a portion that becomes the base portion of the first comb electrode 2 and the support posts 4 and beam portions of the elastic support portion 3.

  Next, the second sacrificial layer 202 is formed on the base 1 and the first conductive layer 301 by using a photolithography method. The material of the second sacrificial layer 202 is the same as the material of the first sacrificial layer 201. The second sacrificial layer 202 is provided in order to form a space below the reinforcing rib 9 in a manufacturing process described later.

  Reference is now made to FIGS. 13 (a) and 13 (b). A third sacrificial layer 203 is formed on the structure shown in FIGS. 12 (a) and 12 (b). The material of the third sacrificial layer 203 is, for example, a photosensitive organic material such as a photoresist and photosensitive polyimide. More preferably, the material of the third sacrificial layer 203 is a high-viscosity type material (for example, SU-8 and SU-10 (both trade names) manufactured by MicroChem) that can obtain a high aspect shape. However, a material different from that of the second sacrificial layer 202 is used as the material of the third sacrificial layer 203, and the second sacrificial layer 202 is removed when a part of the third sacrificial layer 203 is removed in a manufacturing process described later. To prevent it.

  Next, the third sacrificial layer 203 is exposed and developed to form the through holes 501 to 503. The through hole 501 is used to form the first comb tooth portion 2a. The through hole 502 is used to form the reinforcing rib 9. The through hole 503 is used to form the central post 7.

  Reference is now made to FIGS. 14 (a) and 14 (b). A third conductive layer 303 is formed on the third sacrificial layer 203. The third conductive layer 303 is embedded in the through holes 501 to 503 to form a protrusion shape. The third conductive layer 303 embedded in the through hole 501 is integrated with the second conductive layer 302 to form the comb tooth portion 2a. The third conductive layer 303 embedded in the through hole 502 forms the reinforcing rib 9. The third conductive layer 303 embedded in the through hole 503 is integrated with the second conductive layer 302 to form the central post 7.

  The material of the third conductive layer 303 is the same material (aluminum) as the second conductive layer 302, and the third conductive layer 303 is formed by low-temperature sputtering. As the sputtering conditions, in order to embed the material in the entire through holes 501 to 503, a condition capable of forming a film with a uniform thickness on the side surfaces of the through holes 501 to 503 is selected. Such conditions are disclosed in the following documents, for example.

  K. A. Shaw et al. "SCREAM I: a single mask, single-crystal silicon, reactive ion processing process for microelectromechanical structures," Sensors & Actors, 40. 63-70 (1994)

  Further, in order to embed the above material in the entire through holes 501 to 503, the direction of sputtered particles incident on the base 1 from the Al target is determined using a collimated sputtering method or a long throw sputtering method. 1 may be aligned in a direction perpendicular to 1.

  Next, a first mask layer 401 is formed on the third conductive layer 303. The material of the first mask layer 401 is, for example, silicon oxide. The first mask layer 401 is used as a mask when the third conductive layer 303 is etched. Although the third conductive layer 303 may be etched using a wet etching method, here, the third conductive layer 303 is etched using a plasma etching method using a chlorine-based gas. The etching conditions are set so that the selection ratio between the third conductive layer 303 and the third sacrificial layer 203 is increased, and the etching of the third sacrificial layer 203 is suppressed.

  FIG. 14A and FIG. 14B show the third conductive layer 303 left after the etching. Since Al etching is performed in a state where the first mask layer 401 is removed from the upper part of the through hole 501, the upper part of the third conductive layer 303 embedded in the through hole 501 is removed. That is, the upper end of the first comb tooth portion 2 a is etched back to a position lower than the upper surface of the third sacrificial layer 203. The height of the remaining first comb teeth 2a is, for example, about 10 to 20 (μm). In order to perform Al etching with the first mask layer 401 left above the through holes 502 and 503, the third conductive layer 303 above the through holes 502 and 503 (FIGS. 13A and 13B). Remains unremoved.

  After the Al etching, the first mask layer 401 is removed.

  Next, FIG. 15A and FIG. 15B will be referred to. A second mask layer 402 is formed on the structure shown in FIGS. 14 (a) and 14 (b). The second mask layer 402 is provided for use as a mask when the third sacrificial layer 203 is etched and for forming a gap above the first comb tooth portion 2a in the manufacturing process described later. The material of the second mask layer 402 is, for example, silicon oxide, but may be an organic material such as BCB (Benzo Cyclo Butene), PAE (Poly Array Ether), Aromatic hydrocarbon, Parylene, or PTFE (Poly Tetra Fluoro Ethylene).

  The second mask layer 402 is embedded in the gap on the third conductive layer 303 in the through hole 501. By removing the embedded second mask layer 402 in the manufacturing process described later, a gap above the first comb-tooth portion 2a is formed.

  Next, a photoresist (not shown) is applied, exposed and developed, and this photoresist is applied from a region other than the upper part of the third conductive layer 303 (that is, the upper part of the through holes 502 and 503) to be the reinforcing rib and the support post 4. Remove. The remaining photoresist is used as a mask layer (not shown). In this state, the second mask layer 402 is etched for a predetermined time. Since the thickness of the second mask layer 402 located on the first comb-tooth portion 2a is thick, the second mask layer 402 in these portions remains at a predetermined thickness (for example, about 2.0 to 10 (μm)). It is. The other portions of the second mask layer 402 are removed except for these portions and portions covered with a photoresist (not shown).

  Next, the third sacrificial layer 203 is etched. When the second mask layer 402 is silicon oxide, dry etching using oxygen plasma is preferable. When the second mask layer 402 is an organic material different from the material of the third sacrificial layer 203, wet etching using an organic solvent or the like may be used. The upper portion of the third sacrificial layer 203 not protected by the second mask layer 402 is removed, leaving the lower portion. The thickness below the remaining third sacrificial layer 203 is, for example, about 2.0 to 10 (μm).

  Next, FIG. 16A and FIG. 16B will be referred to. A fourth sacrificial layer 204 is formed with a substantially uniform thickness on the structure shown in FIGS. 15 (a) and 15 (b). The material of the fourth sacrificial layer 204 is a photoresist or a photosensitive polyimide. In order to form the fourth sacrificial layer 204 with a uniform thickness, it is preferable to use a pulse spray method (registered trademark, Nordson) or a vapor deposition polymerization method. The thickness of the fourth sacrificial layer 204 is, for example, about 0.5 to 1.0 (μm).

  The fourth sacrificial layer 204 is exposed and developed, and the fourth sacrificial layer 204 is removed from the upper portion of the third conductive layer 303 (that is, the upper portion of the through holes 502 and 503) to be the reinforcing rib 9 and the support post 4. Subsequently, the second mask layer 402 is removed from these same regions by etching to expose the third conductive layer 303.

  Next, a fourth conductive layer 304 is formed on the fourth sacrificial layer 204 and the exposed third conductive layer 303 by low-temperature sputtering. The material of the fourth conductive layer 304 is the same material (aluminum) as that of the third conductive layer 303. The fourth conductive layer 304 is a portion that becomes the movable portion 6.

  The fourth conductive layer 304 is smoothed by a CMP (Chemical Mechanical Polishing) process. The upper surface of the fourth conductive layer 304 functions as the light reflecting surface 6 a of the movable part 6. Next, the layer deposited around the reinforcing rib 9 on the outer periphery of the movable portion 6 (that is, the region between the microactuators 100 adjacent to each other) is removed by photolithography. The horizontal length of each movable part 6 is, for example, about 100 to 200 (μm).

Next, the movable part 6 (fourth conductive layer 304) is released. Release is a two-step process. First, the first to fourth sacrificial layers 201 to 204 are removed by oxygen plasma etching. Since the third sacrificial layer 203 is thick, it is easy to secure an etchant flow path. Therefore, even when the outer area of the microactuator 100 is as large as 1600 μm ² or more, these sacrificial layers can be removed without forming an etching hole in the upper part. Next, the second mask layer 402 is removed using hydrogen fluoride gas. Thereby, as shown in FIGS. 17A and 17B, the release of the movable portion 6 is completed, and the microactuator 100 is completed.

  Since the reinforcing rib 9 has a thin film sandwich structure formed in the vertical direction in the through hole, the residual stress is small, and the flatness of the light reflecting surface 6a can be made extremely high. Since the height of the comb tooth portion 8a of the movable portion 6 and the height of the reinforcing rib 9 can be different from each other, each can be formed at an optimum height according to electrostatic or rigid requirements. it can.

  The first comb-tooth portion 2a is connected to the base portion of the first comb-shaped electrode 2 in the shortest distance in the vertical direction, and the comb-tooth portion 8a of the movable portion 6 is connected to the lower surface of the movable portion in the shortest distance in the vertical direction. . For this reason, the comb teeth themselves are not easily deformed, and pull-in due to unnecessary deformation of the comb teeth can be prevented even if the interval between the comb teeth is narrowed.

  Further, by setting the thicknesses of the third and fourth sacrificial layers 203 and 204 and the second mask layer 402 to desired thicknesses, the horizontal gap and the vertical gap between the comb teeth portions can be reduced. Can be set to a desired length, so that it is possible to achieve both an increase in electrostatic force by reducing the horizontal gap and an increase in the movable stroke of the movable portion 6 by increasing the vertical gap.

  In the above-described embodiment, the shape of the movable portion is a regular hexagon, but the shape of the movable portion is not limited to this. For example, the shape of the movable part may be a rectangle (such as a square). The above-described effects can be obtained even with a vertically long movable portion whose aspect ratio is not 1: 1.

  The microactuator of the present invention is suitably used in the fields of optical devices and optical disc apparatuses that perform aberration correction, optical scanning, spectroscopy, and the like. Further, it is also suitably used in the fields of high-frequency circuits such as tunable capacitors, fluid control devices such as variable flow paths, and biotechnology. The microactuator of the present invention is useful as an actuator that changes the direction of light at high speed, and is particularly suitable as a micromirror device for an aberration-correcting micromirror array that requires high-precision flatness on the light reflecting surface. Used.

It is a disassembled perspective view which shows typically the microactuator by Embodiment 1 of this invention. It is a disassembled perspective view which shows typically the microactuator by Embodiment 1 of this invention. FIG. 3 is a cross-sectional view of the microactuator along line 3A-3A shown in FIG. (A) And (b) is a fragmentary sectional view of the microactuator along the 3A-3A line shown in Drawing 1, and shows the state where the movable part was displaced. FIG. 5 is a cross-sectional view of the microactuator along line 5A-5A shown in FIG. (A) And (b) is sectional drawing of the micro actuator along the 5A-5A line shown in FIG. 1, and has shown the state which the movable part displaced. It is a top view which shows typically the movable part of the microactuator by Embodiment 2 of this invention. It is a top view which shows typically the movable part of the microactuator by Embodiment 3 of this invention. It is a top view which shows typically the movable part of the microactuator by Embodiment 4 of this invention. It is a fragmentary sectional view which shows typically the comb-tooth part of the microactuator by Embodiment 4 of this invention. (A) And (b) is sectional drawing which shows typically the manufacturing method of the microactuator by Embodiment 5 of this invention. (A) And (b) is sectional drawing which shows typically the manufacturing method of the microactuator by Embodiment 5 of this invention. (A) And (b) is sectional drawing which shows typically the manufacturing method of the microactuator by Embodiment 5 of this invention. (A) And (b) is sectional drawing which shows typically the manufacturing method of the microactuator by Embodiment 5 of this invention. (A) And (b) is sectional drawing which shows typically the manufacturing method of the microactuator by Embodiment 5 of this invention. (A) And (b) is sectional drawing which shows typically the manufacturing method of the microactuator by Embodiment 5 of this invention. (A) And (b) is sectional drawing which shows typically the manufacturing method of the microactuator by Embodiment 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base 2 1st comb electrode 2a Comb tooth part 3 Elastic support part 4 Support post 5 Fixed part 6, 16, 26, 36 Movable part 7 Center post 8, 28, 38 2nd comb electrode 8a, 8b, 8c Comb teeth portion 9, 11 Reinforcement rib 10 Center of rotation 20 Movable portion 100 Microactuator

Claims (13)

The base,
A first comb electrode supported by the base;
A movable part comprising a second comb electrode facing the first comb electrode, and at least one reinforcing rib projecting in the direction of the base;
An elastic support part for supporting the movable part so that the movable part can be displaced with respect to the base;
The microactuator, wherein a height of the second comb electrode and a height of the at least one reinforcing rib are different from each other.   2. The microactuator according to claim 1, wherein a height of the at least one reinforcing rib is higher than a height of the second comb electrode. The second comb electrode includes a plurality of comb teeth.
2. The microactuator according to claim 1, wherein a thickness of the at least one reinforcing rib is greater than a thickness of each of the plurality of comb teeth portions. The second comb electrode includes a plurality of comb teeth.
2. The microactuator according to claim 1, wherein the plurality of comb teeth extend along a direction from the inside toward the outside of the movable portion. The second comb electrode includes a plurality of comb teeth.
The microactuator according to claim 1, wherein the plurality of comb teeth have a concentric shape.   The microactuator according to claim 1, wherein the at least one reinforcing rib is provided on an outer peripheral portion of the movable portion. The second comb electrode includes a plurality of comb teeth.
The microactuator according to claim 1, wherein the plurality of comb teeth and the at least one reinforcing rib extend in the same direction. The second comb electrode includes a plurality of comb teeth.
2. The microactuator according to claim 1, wherein the plurality of comb-tooth portions and the at least one reinforcing rib extend in directions perpendicular to each other.   2. The microactuator according to claim 1, wherein a height of the second comb electrode is lowered along a direction from the inner side to the outer side of the movable part. The second comb electrode includes a plurality of comb teeth.
2. The microactuator according to claim 1, wherein a thickness of each of the plurality of comb teeth portions is reduced along a direction from the inside to the outside of the movable portion.   2. The microactuator according to claim 1, wherein the elastic support portion supports the movable portion so that the movable portion can tilt in two axes with respect to the base.   2. The microactuator according to claim 1, wherein the elastic support part supports the movable part so that the movable part can be displaced in a vertical direction with respect to the base and tilted in two axes with respect to the base. 3. The microactuator according to claim 1, wherein the movable part includes a light reflecting surface.

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