JP2007121464A - Tilt mirror element and method of driving the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive tilt mirror element which drives a mirror part at a high speed and a large amplitude. <P>SOLUTION: The tilt mirror element 1 is provided with: a mirror part 2 which switches the optical paths of a light beam by reflecting the light beam on a mirror face 2a; a supporting frame part 3 which is formed around the outer circumferential part of the mirror part 2; torsion hinge parts 4 which move and positionally support the mirror part 2 with respect to the supporting frame part 3; movable comb electrodes 5a and fixed comb electrodes 5b which are so provided to engage with the side wall parts of the mirror part 2 and the side wall parts of the supporting frame part 3 which face to the side wall parts of the mirror part 2, and swing the mirror part 2 by using the electrostatic force generated by applying an electric voltage; and a pair of flat plate fixed electrodes 8a and 8b which are provided at the positions which face the mirror face 2a and swing the mirror part 2 by using the electrostatic force generated on the mirror part 2 by applying an electric voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tilt mirror element that switches an optical path of a light beam and a method for driving the tilt mirror element, which is suitable for application in the optical communication field and optical equipment fields such as a barcode reader, laser reader, area sensor, projection display, and optical switch. .

Conventionally, as a tilt mirror element equipped with an electrostatic gap closing type actuator, a pair of fixed plate electrodes are provided facing the mirror part configured as a movable electrode, and it is generated between the electrodes as voltage is applied A device that deflects a light beam by oscillating a mirror portion using an electrostatic force is known (see Patent Document 1). Moreover, as a tilt mirror element equipped with an electrostatic vertical comb type actuator, a movable comb (comb-tooth) electrode and a fixed comb electrode are respectively provided on a part of the outer peripheral part of the mirror part and a substrate surface facing the part, and a voltage is applied to the electrode. There is known a technique in which a light beam is deflected by swinging a mirror portion by utilizing an electrostatic force generated between electrodes in response to the application of (see Patent Document 2).
JP-A-60-57051 (see FIG. 2) Japanese Patent No. 3011144 (see FIG. 3)

  By the way, in a tilt mirror element equipped with an electrostatic gap closing actuator, the electrostatic force generated between the electrodes is almost inversely proportional to the square of the distance between the electrodes. Becomes smaller. For this reason, in order to make the mirror portion swingable with a large amplitude, it is desirable that the distance between the electrodes be short. However, when the distance between the electrodes is short, the electrodes may come into contact with each other when the mirror portion is swung. From such a background, according to the configuration of the conventional tilt mirror element, the distance between the electrodes must be designed in a range where the electrodes do not contact each other. It was difficult.

  On the other hand, in a tilt mirror element including an electrostatic vertical comb type actuator, if the movable comb electrode and the fixed comb electrode are completely overlapped on the same plane in the initial state, the electrostatic force is orthogonal to the mirror part. Since no force is generated, the mirror portion cannot be started to swing. Therefore, in order to start the oscillation of the mirror portion, a step structure is formed in which the movable comb electrode and the fixed comb electrode are positioned on different planes, and the suction force generated by applying a voltage between the electrodes is used. It is necessary to start the oscillation of the mirror part.

  However, the process of accurately manufacturing the step structure as described above by aligning the position of the movable comb electrode and the fixed comb electrode is very complicated, so that the yield is greatly reduced particularly when the electrodes are fine. The device price can be high. In addition, if the displacement of the mirror part increases and the movable comb electrode and the fixed comb electrode do not overlap at all, the electrostatic force hardly acts between the electrodes. Is limited, and it is difficult to move the mirror section at high speed and with a large amplitude.

  The present invention has been proposed in view of the above-described circumstances, and an object thereof is to provide an inexpensive tilt mirror element capable of moving a mirror unit at high speed and with a large amplitude, and a driving method thereof. is there.

  In order to solve the above-described problems, a tilt mirror element according to the present invention includes a mirror unit that switches an optical path of a light beam by reflecting the light beam on a mirror surface, and a support frame unit that is formed on the outer periphery of the mirror unit. And a connecting portion that moves and holds the mirror portion with respect to the support frame portion, and a side wall portion of the mirror portion and a side wall portion of the support frame portion that faces the side wall portion, and is applied with a voltage. Using the electrostatic force generated between the comb electrode that swings the mirror part using the electrostatic force generated by the mirror part and the mirror part provided at a position facing the mirror surface. A pair of flat plate fixed electrodes that swing the mirror portion.

  In addition, the tilt mirror element driving method according to the present invention includes a mirror part that switches an optical path of a light beam by reflecting the light beam on a mirror surface, a support frame part formed on an outer peripheral part of the mirror part, and a support frame The connecting portion for moving and maintaining the position of the mirror portion relative to the portion and the side wall portion of the mirror portion and the side wall portion of the support frame portion facing the side wall portion are provided to engage with each other, and static electricity generated by applying a voltage is provided. A comb electrode that swings the mirror portion using electric power and a mirror electrode that is provided at a position opposite to the mirror surface and that uses electrostatic force generated between the mirror portion when voltage is applied. A tilt mirror element driving method comprising a pair of moving plate-fixed electrodes, wherein the mirror portion is prevented from swinging by utilizing an electrostatic force generated between the mirror portion and the plate-fixed electrode. Oscillates the mirror part by using the electrostatic force generated between the mirror part and the fixed plate electrode together with the electrostatic force generated between the comb electrode on the mirror part side and the comb electrode on the support frame part side. There is a step to do.

  According to the tilt mirror element and the driving method thereof according to the present invention, the mirror part can be swung by using the electrostatic force generated between the mirror part and the pair of flat plate fixed electrodes. There is no need to form such a step structure of the comb electrode, and the tilt mirror element can be manufactured at low cost.

  Further, according to the tilt mirror element and the driving method thereof according to the present invention, the electrostatic force generated between the comb electrode on the mirror portion side and the comb electrode on the support frame portion side, and generated between the mirror portion and the pair of flat plate fixed electrodes. By using the electrostatic force together, the swinging of the mirror portion can be accelerated, so that the mirror surface can be moved at a high speed and with a large amplitude.

  Hereinafter, a configuration of a tilt mirror element according to an embodiment of the present invention and a driving method thereof will be described with reference to the drawings.

[Configuration of tilt mirror element]
First, the configuration of the tilt mirror element 1 according to the embodiment of the present invention will be described with reference to FIGS. 1 to 3. 1, 2, and 3 show a bird's-eye view, a top view, and a side view of the tilt mirror element 1 as viewed from the direction of the arrow A shown in FIG. 2.

  As shown in FIG. 1, a tilt mirror element 1 according to an embodiment of the present invention includes a mirror unit 2 that switches an optical path of a light beam by reflecting the light beam on a mirror surface 2 a made of gold or aluminum, and a mirror unit 2. The support frame part 3 formed on the outer peripheral part of the mirror and the torsion hinge part 4 for moving and holding the mirror part 2 with respect to the support frame part 3 are provided. Further, the movable comb electrode 5a and the fixed comb electrode 5b are engaged with the side wall portion of the mirror portion 2 not connected to the torsion hinge portion 4 and the side wall portion of the support frame portion 3 facing the side wall portion, respectively. Is formed.

  As shown in FIGS. 1 and 2, the upper surfaces of the support frame 3 and the torsional hinge 4 have electrode pads 6a, 6c and so that voltage can be applied to the movable comb electrode 5a and the fixed comb electrode 5b, respectively. An electrode pad 6b is provided. An insulating separation gap 7 is formed between the support frame portion 3 and the torsion hinge portion 4 to ensure insulation between the support frame portion 3 and the torsion hinge portion 4.

  As shown in FIGS. 1 and 3, a glass substrate 9 having a pair of flat plate fixed electrodes 8 a and 8 b formed on the upper surface is bonded to the lower surface of the support frame portion 3. Further, a window portion is formed on the lower surface of the support frame portion 3 so that the mirror portion 2 can be swung by an electrostatic force generated between the movable comb electrode 5a and the pair of flat plate fixed electrodes 8a and 8b. The back surface of the part 2 is exposed (see FIG. 8).

  In the present embodiment, the mirror part 2, the support frame part 3, the torsion hinge part 4, the movable comb electrode 5a, and the fixed comb electrode 5b are formed by a lower Si substrate 10a and an upper Si substrate 10b as shown in FIG. It is integrally formed using an SOI (Silicon On Insulator) wafer sandwiching the Si oxide film 11.

[Manufacturing method of tilt mirror element]
Next, a manufacturing method of the tilt mirror element 1 will be described with reference to FIGS.

  When manufacturing the tilt mirror element 1, first, the upper Si substrate 10b of the SOI wafer is patterned by a photolithography process and an ICP (Inductively Coupled Plasma) etching process using the Si oxide film 11 as a stopper. As shown to (a), (b), the mirror part 2, the support frame part 3, the torsion hinge part 4, the movable comb electrode 5a, the fixed comb electrode 5b, and the insulation separation gap 7 are integrally formed.

  The film thickness of the upper Si substrate 10b is determined in consideration of the required spring constant of the torsion hinge 4 and the flatness of the mirror surface 2a. The film thickness of the lower Si substrate 10a depends on the deflection angle of the mirror part 2, the torque of the electrostatic gap closing actuator formed by the movable comb electrode 5a and the pair of flat plate fixed electrodes 8a and 8b, and the mechanical properties of the substrate in process. Determine in consideration of strength. Specifically, in this embodiment, the thicknesses of the lower Si substrate 10a, the Si oxide film 11, and the upper Si substrate 10b of the SOI wafer are 300, 2, and 30 [μm], respectively.

  Next, after depositing a reflection film such as gold or aluminum on the surface of the upper Si substrate 10b by sputtering, the reflection film is patterned by a photolithography process, as shown in FIGS. 5A and 5B. Mirror surface 2a and electrode pads 6a, 6b, 6c are formed. Next, as shown in FIGS. 6A and 6B, the mirror portion 2, the twisted hinge portion 4, the movable comb electrode 5a, and the fixed comb electrode 5b are formed by a photolithography process and a KOH etching process of the lower Si substrate 10a. The lower Si substrate 10a corresponding to the position is removed.

  Next, when the support frame portion 3 and the glass substrate 9 are joined in a process to be described later, the pair of flat plate fixed electrodes 8a and 8b on the glass substrate 9 overlap with the lower Si substrate 10a, thereby supporting the support frame portion 3 and the glass substrate. 7A and 7B, a lower Si substrate at a position corresponding to the pair of flat plate fixed electrodes 8a and 8b by a photolithography process and an etching process, as shown in FIGS. The notch 21 is formed by removing 10a. Note that the depth of the notch 21 may be larger than the thickness of the pair of flat plate fixed electrodes 8a and 8b, but in the present embodiment, the depth is set to 10 [μm].

  Next, as shown in FIG. 8, the mirror portion 2 is obtained by removing the oxide film 11 corresponding to the positions of the mirror portion 2, the twisted hinge portion 4, the movable comb electrode 5a, and the fixed comb electrode 5b with dilute hydrofluoric acid. And the torsion hinge 4 can be moved. In this process, as shown in FIG. 8, a reflective film 22 is formed on the back surface of the mirror portion 2 similarly to the front surface using a mask having an opening at a position corresponding to the mirror portion 2, and the mirror portion. 2 may be improved.

  Next, after depositing a metal such as gold on the upper surface of the glass substrate 9, the metal deposited by the photolithography process is patterned, thereby forming the glass substrate 9 as shown in FIGS. 9A and 9B. A pair of flat plate fixed electrodes 8a and 8b are formed on the upper surface. The glass substrate 9 may be a silicon substrate that has an insulating property by covering the upper surface with an oxide film. Finally, the support frame portion 3 and the glass substrate 9 are joined by an anodic bonding method or the like while adjusting the pair of flat plate fixed electrodes 8a and 8b so as to face the mirror portion 2 and the twisted hinge portion 4. Thereby, the manufacturing process of the tilt mirror element 1 is completed.

  In the present embodiment, the chip including one tilt mirror element 1 is illustrated as one unit. However, in practice, a wafer including a plurality of chips is provided before or immediately after the bonding process of the support frame 3 and the glass substrate 9. The manufacturing process shall be carried out in the state of. Then, at the timing when the manufacturing process is completed, the chips are individually separated by dicing, and if it has already been joined, the desired tilt mirror element 1 can be obtained. Otherwise, the tilt mirror element 1 can be obtained by bonding the chip to the glass substrate 9.

[Tilt mirror element driving method]
Finally, a driving method of the tilt mirror element 1 will be described with reference to FIGS.

  In the tilt mirror element 1, in the initial state (time T <time T1 shown in FIG. 11), the mirror portion 2 (movable comb electrode 5a) and the fixed comb electrode 5b are on the same plane. Even if a voltage is applied to 5a and the fixed comb electrode 5b, only an electrostatic force in the same plane as the mirror part 2 is generated, and the mirror part 2 does not move due to a balance of forces. In this state, when a voltage is applied between the mirror portion 2 and the flat plate fixed electrode 8b (time T1 <time T <0), the electrostatic force generated between the mirror portion 2 and the flat plate fixed electrode 8b causes the electrostatic force generated in FIG. As shown, the mirror unit 2 starts to swing.

  When the mirror unit 2 starts to oscillate, when a voltage is applied between the mirror unit 2 and the fixed comb electrode 5b (time T2 <time T <time T3), it is generated between the movable comb electrode 5a and the fixed comb electrode 5b. When the movable comb electrode 5a and the fixed comb electrode 5b are attracted by the electrostatic force, a force for moving the mirror unit 2 in the plane vertical direction is generated, and the mirror unit 2 is in the opposite direction to that at the time of activation as shown in FIG. Start rotating. The electrostatic force accelerates the rotation of the mirror unit 2 until the mirror unit 2 and the support frame unit 3 become parallel. However, the mirror unit 2 rotates even if the equilibrium state shown in FIG. Continue.

  Next, when a voltage is applied between the mirror part 2 and the flat plate fixed electrode 8a (time T3 <time T <time T4), the rotational force is increased by the electrostatic force, and the spring force of the torsion hinge part 4 is increased. At the balanced timing, the swing angle becomes a maximum as shown in FIG. Next, the mirror unit 2 rotates in the opposite direction by the spring force of the torsional hinge unit 4 and returns to the equilibrium state again. At this time, as shown in FIG. 10E, (time T5 <time T <time T6) By applying a voltage again between the mirror part 2 and the fixed comb electrode 5b, the rotation of the mirror part 2 is accelerated. Then, after passing the equilibrium state, until the deflection angle of the mirror unit 2 takes the maximum value, as shown in FIG. 10F (time T6 <time T <time T7), the mirror unit 2 and the plate fixed electrode 8b again. A voltage is applied between

  Thereafter, as shown in FIG. 10 (g), the mirror portion 2 rotates in the reverse direction by the spring force and returns to the state shown in FIG. 10 (b) again, so that the mirror portion 2 and the fixed comb electrode 5b are rotated in the same direction. Rapid rotation by applying a voltage in between. As described above, the mirror unit 2 can be continuously swung by repeatedly performing the voltage supply pattern to each electrode. In particular, by making the repetition frequency coincide with the mechanical resonance frequency of the mirror, the amplitude of the shake of the mirror unit 2 can be increased.

  As is clear from the above description, the tilt mirror element 1 according to the embodiment of the present invention includes a mirror unit 2 that switches the optical path of the light beam by reflecting the light beam on the mirror surface 2a, and an outer peripheral part of the mirror unit 2. A support frame portion 3 formed on the support frame portion 3, a torsion hinge portion 4 that moves and holds the mirror portion 2 relative to the support frame portion 3, a side wall portion of the mirror portion 2, and a side wall of the support frame portion 3 that faces the side wall portion. The movable comb electrode 5a and the fixed comb electrode 5b, which are provided so as to mesh with the portion and swing the mirror portion 2 by using an electrostatic force generated by applying a voltage, and a position facing the mirror surface 2a. And a pair of flat plate fixed electrodes 8a and 8b that swing the mirror unit 2 using an electrostatic force generated between the mirror unit 2 and a voltage applied thereto.

  That is, the tilt mirror element 1 according to the embodiment of the present invention includes an electrostatic vertical comb type actuator composed of a movable comb electrode 5a and a fixed comb electrode 5b, a mirror portion 2, and a pair of flat plate fixed electrodes 8a and 8b. An electrostatic gap closing type actuator is provided. According to such tilt mirror element 1, at the time of initial startup, the movable comb electrode 5a and the fixed comb electrode 5b are completely overlapped on the same plane by using an electrostatic gap closing type actuator. Even with a structure without the swaying movement, the mirror unit 2 can start to swing. Further, during the steady operation, the electrostatic vertical comb type actuator and the electrostatic gap closing type actuator are driven in a complementary manner according to the angle of the mirror unit 2, so that an average high torque can be generated. Can be moved at high speed and with a large amplitude.

  Further, according to the tilt mirror element 1 according to the embodiment of the present invention, the mirror part 2, the support frame part 3, the torsion hinge part 4, the movable comb electrode 5a, and the fixed comb electrode 5b are integrally formed using an SOI wafer. Therefore, the dimensional accuracy of the electrodes and the flatness of the mirror part 2 are improved, and the tilt mirror element 1 can be manufactured with high productivity and at low cost. In this embodiment, an SOI wafer is used. However, a polysilicon film that is made to have a volume on a silicon oxide film is used for the mirror part 2, the twisted hinge part 4, the movable comb electrode 5a, and the fixed comb electrode 5b. Also good.

  As mentioned above, although embodiment which applied the invention made by the present inventors was described, this invention is not limited by the description and drawing which make a part of indication of this invention by this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above-described embodiments are all included in the scope of the present invention.

It is a bird's-eye view which shows the structure of the tilt mirror element used as embodiment of this invention. It is a top view which shows the structure of the tilt mirror element used as embodiment of this invention. FIG. 3 is a side view of the tilt mirror element as viewed from the direction of arrow A shown in FIG. 2. It is the top view of the support frame part for demonstrating the manufacturing method of the tilt mirror element shown in FIG. 1, and the side view seen from the A arrow direction. It is the top view of the support frame part for demonstrating the manufacturing method of the tilt mirror element shown in FIG. 1, and the side view seen from the A arrow direction. It is the bottom view of the support frame part for demonstrating the manufacturing method of the tilt mirror element shown in FIG. 1, and the side view seen from A arrow direction. It is the bottom view of the support frame part for demonstrating the manufacturing method of the tilt mirror element shown in FIG. 1, and the side view seen from the B arrow direction. It is a bottom view of the support frame part for demonstrating the manufacturing method of the tilt mirror element shown in FIG. It is the top view of the glass substrate for demonstrating the manufacturing method of the tilt mirror element shown in FIG. 1, and the side view seen from A arrow direction. It is a figure which shows the voltage application pattern for demonstrating the drive method of the tilt mirror element shown in FIG. It is a figure which shows the voltage application timing for demonstrating the drive method of the tilt mirror element shown in FIG.

Explanation of symbols

1: tilt mirror element 2: mirror part 2a: mirror surface 3: support frame part 4: torsion hinge part 5a: movable comb electrode 5b: fixed comb electrodes 6a, 6b, 6c: electrode pad 7: insulation separation gaps 8a, 8b: Flat fixed electrode 9: Glass substrate 10a: Lower Si substrate 10b: Upper Si substrate 11: Si oxide film

Claims (3)

A mirror unit that switches the optical path of the light beam by reflecting the light beam on the mirror surface;
A support frame portion formed on the outer periphery of the mirror portion;
A connecting part that moves and holds the mirror part relative to the support frame part;
Comb electrode provided so as to mesh with the side wall portion of the mirror portion and the side wall portion of the support frame portion facing the side wall portion, and swings the mirror portion using electrostatic force generated by applying a voltage. When,
A pair of flat plate fixed electrodes provided at a position facing the mirror surface and swinging the mirror portion using an electrostatic force generated between the mirror portion when a voltage is applied. Tilt mirror element.   2. The tilt mirror element according to claim 1, wherein the mirror part, the support frame part, the connecting part, and the comb electrode are integrally formed using an SOI wafer. . A mirror part that switches an optical path of the light beam by reflecting the light beam on the mirror surface; a support frame part formed on the outer periphery of the mirror part; and a connecting part that moves and holds the mirror part with respect to the support frame part The comb electrode is provided so as to mesh with the side wall portion of the mirror portion and the side wall portion of the support frame portion facing the side wall portion, and swings the mirror portion using an electrostatic force generated when a voltage is applied. And a pair of flat plate fixed electrodes that are provided at a position facing the mirror portion and swing the mirror portion using an electrostatic force generated between the mirror portion when a voltage is applied. Driving method,
Starting swinging of the mirror part by utilizing an electrostatic force generated between the mirror part and the flat plate fixed electrode;
By using the electrostatic force generated between the mirror portion side comb electrode and the support frame portion side comb electrode and the electrostatic force generated between the mirror portion and the flat plate fixed electrode, the oscillation of the mirror portion is accelerated. And a step of driving a tilt mirror element.

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