JP2002056554A - Galvano micro mirror and optical disk device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk device capable of seeking at high speed by using an electrostatically driven galvano micro mirror the mirror substrate of which is reduced in weight to decrease the moment of inertia with respect to the galvano micro mirror and the optical disk device using it. SOLUTION: In the galvano micro mirror provided with the mirror substrate 1 having a mirror forming part 5 in which a mirror surface 5a reflecting a light beam is formed, a shaft part 4a which supports the mirror forming part 5, and an electrode forming part 6 which forms an electrode for turning the mirror forming part 5 around the shaft part by electrostatic force, the thickness of the electrode forming part 6 is formed less than the thickness of the mirror forming part 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvano micromirror and an optical disk apparatus using the same, and more particularly to a galvano micromirror of an electrostatic drive system.

[0002]

2. Description of the Related Art In an optical disk device, for example, a magneto-optical disk device, an optical head which seeks to a track position where information is recorded and reproduced by a light beam is provided with an objective lens for focusing the light beam on the optical disk surface and reflection of the light beam. A galvano micromirror that controls the position of irradiation is mounted, and the semiconductor laser light source and photodetector are not mounted on the optical head but fixed to a base or the like.

For example, as shown in the configuration diagram of an optical disk device according to the prior art in FIG. 7, a fixed optical system 113 such as a semiconductor laser 111 and a photodetector 112 is fixed to a base (not shown). The light beam L is emitted to an objective lens 116 mounted in an optical head 115 via a reflection mirror 117 which is also fixedly arranged.

[0004] The objective lens 116 focuses the light beam L on a track on the optical disk 110 and guides the reflected light to the photodetector 112 again in the reverse path. The optical head 115 is driven in a tracking direction X and a focusing direction Y by driving means (not shown).

[0005] A minute change in the incident angle of the laser light on the objective lens 116 is corrected by controlling the swing angle of the galvanomirror 114. There is an electrostatic drive control method as this angle control method.

For example, a galvano micromirror disclosed in Japanese Patent Application No. 11-183253 has an electrode substrate 20 and a mirror substrate 21 as shown in an exploded perspective view of FIG.
The mirror substrate 21 includes a frame-shaped base portion 22 and a mirror portion 23. The base portion 22 and the mirror portion 23 are formed by a pair of torsion bar portions 24 that support the mirror portion 23 to be twisted within a predetermined angle range. Are linked.

On one main surface (front surface) of the mirror portion 23,
A mirror surface 25 is formed, and a first electrode 26 including a pair of electrodes 26a and 26b is formed on the other back surface of the mirror portion 23. The mirror substrate 21 is configured to be line-symmetric about the axis of the torsion bar portion 24.

On the surface of the electrode substrate 20 facing the mirror portion 23, a through-hole 27 having a line-symmetrical shape with respect to the axis of the torsion bar portion 24, and a pair of electrodes 26a and 26b opposed to each other. A second electrode 28 composed of electrodes 28a and 28b is formed.

The electrode 26a and the electrode 26b of the first electrode 26 have a common potential, and the electrode 28a and the electrode 28b of the second electrode 28
Are electrically insulated from each other and connected to the control device.

When the potential of the first electrode 26 is set to, for example, 0 V and a positive or negative voltage is applied to the electrodes 28a and 28b of the second electrode 28, an electrostatic attractive force acts between the electrodes, and the torsion bar portion 24 is twisted. Then, the mirror part 23 rotates (swings).

The swing angle at this time can be controlled by changing the applied voltage, and the irradiation position of the light beam is controlled by changing the reflection direction of the light beam.

[0012]

The galvano micromirror used in the optical disk device has a high flatness on the mirror surface, and at the same time, precisely positions the light beam at the track position for recording and reproducing information on the optical disk at high speed. It is necessary to control the angle of the mirror surface at high speed so that the light can be radiated.

Therefore, if a galvano micromirror having a thickness of several 100 μm is manufactured by processing a bulk substrate, there is no problem with the flatness of the mirror surface, but the mass of the mirror part increases and the mass of the mirror part increases. Therefore, the moment of inertia becomes large and high-speed seek cannot be performed. Therefore, it is necessary to reduce the mass of the mirror unit.

For this reason, for example, Japanese Patent Application Laid-Open No. 6-214181.
Japanese Patent Application Laid-Open Publication No. H10-157, “mirror for optical scanner” discloses that the weight of the mirror is reduced and the high-speed response is improved. The disclosed driving method of the mirror for the optical scanner is not an electrostatic driving method, but by forming a plurality of recesses on the back surface opposite to the light reflecting surface of the mirror, the mass can be reduced without reducing the thickness of the mirror. The aim is to reduce the weight. However, there is a limit to the weight reduction due to the formation of the concave portion because the flatness of the mirror surface is maintained with high accuracy.

On the other hand, when a blue light beam having a short wavelength, for example, 400 nm is used as a light source in order to increase the recording density of the optical disk, aluminum or gold having a high reflectance even if thin on the surface of the mirror forming portion. Even if the mirror surface is formed using a metal film as described above, there is a problem that the phase is rotated when the mirror surface is reflected, and erroneous information is recorded and reproduced.

In order to avoid this, it is necessary to form a mirror surface by laminating a dielectric layer of, for example, SiO ₂ and Ta ₂ O _{5 on} the surface of the mirror forming portion. Therefore, the mirror surface warps. If a dielectric layer for canceling this warp is also laminated on the back surface of the mirror forming portion, there is a problem that the weight cannot be reduced by forming a plurality of concave portions disclosed in the above-mentioned JP-A-6-214181.

In view of the above problems, the present invention provides an optical disk apparatus capable of performing high-speed seek using the galvano micromirror by reducing the weight of the mirror substrate of the galvano micromirror of the electrostatic drive type to reduce the moment of inertia. The purpose is to provide.

[0018]

According to a first aspect of the present invention, there is provided a galvano micromirror according to the present invention, comprising: a mirror forming portion having a mirror (mirror surface) for reflecting a light beam; A mirror substrate having a shaft portion supporting a mirror forming portion and an electrode forming portion formed with electrodes for rotating the mirror forming portion around the shaft portion by electrostatic force; The electrode forming portion is formed to be thinner than the thickness.

According to a second aspect of the present invention, the galvano micromirror according to the first aspect is incorporated in an optical path of the light beam in an optical head which seeks along with an objective lens for focusing the light beam on the optical disk surface. It consists of.

With this configuration, since the mirror forming portion is not processed such as a concave portion, the weight of the mirror forming portion can be reduced without impairing the flatness of the mirror surface (reflection surface) of the mirror forming portion. it can.

Further, since the present invention is applied to a short wavelength light source, even when a dielectric layer is laminated on the front and back surfaces of the mirror forming portion, the weight of the mirror forming portion can be reduced while maintaining the flatness of the mirror surface with high accuracy. By incorporating the lightened galvanometer micromirror into the optical head, high-speed seek of the optical disk device becomes possible.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The gist of the present invention will be described below in detail with reference to the embodiments shown in the drawings. A structure in which a mirror (mirror surface) having a high flatness and a high flatness is provided on one surface, and the center of both ends of a mirror portion having electrodes for electrostatic drive formed on the other surface or both surfaces is supported by two shaft portions. A description will be given of an example of a galvano micromirror for an optical disk device having a primary resonance frequency of about 100 Hz to several KHz and controlling the mirror surface in an angle range of about ± 0.1 °.

FIG. 1 is a side sectional view of a galvano micromirror of a first embodiment according to the present invention, FIG. 2 is an exploded perspective view of FIG.
FIG. 3 is a side view of the assembly of FIG. 2, and FIG. 4 is a perspective view showing a back surface shape of the mirror substrate of FIG.

As shown in FIGS. 1 and 2, the galvano micromirror comprises a mirror substrate 1 and a pair of electrode substrates 2, ie, a first electrode substrate 2a and a second electrode substrate 2b. The mirror substrate 1 is configured to be sandwiched between the first electrode substrate 2a and the second electrode substrate 2b from both sides. In addition, the second in FIG.
The electrode substrate 2b is shown as viewed from the mating surface, and is inverted and stacked in the direction of the arc arrow. (Mirror substrate 1 and first
The electrode substrate 2a is a perspective view seen from above, and the second electrode substrate 2b is a perspective view seen from below. In FIG. 2, reference numerals 1a, 2a-1, and 2b-1 denote external connection electrode pads of the mirror substrate 1, the first electrode substrate 2a, and the second electrode substrate 2b, respectively. The size of the substrate is gradually increased so as to be connected to an external control device.

The mirror substrate 1 comprises a frame-shaped base 3 and a mirror section 4, and the mirror section 4 comprises a mirror forming section 5 and an electrode forming section 6, that is, a left side 6a and a right side 6b. The mirror forming portion 5 and the electrode forming portions 6a and 6b have different thicknesses, and are separated by step positions of the thicknesses. The mirror forming unit 5 includes a mirror 5a, that is, a mirror surface (reflection surface), and the electrode forming unit 6 includes electrodes described below.

The base portion 3 and the mirror portion 4 are integrally connected by a pair of shaft portions 4a which support the mirror surface 5a of the mirror portion 4 to be able to be twisted within an angle range of about ± 0.1 °, that is, a torsion bar portion. Therefore, the portion between the frame-shaped base 3 and the mirror portion 4 is cut by the through groove 4b except for the two torsion bar portions 4a.

The mirror section 4 has a mirror surface 5a on which a metal film of high reflectivity such as aluminum is deposited on one main surface (front surface) of the mirror forming section 5, and is centered on the axis of the torsion bar section 4a. It is configured to have a line-symmetrical shape. The electrode forming portions 6 on both the left and right sides of the mirror portion 4 have a pair of electrodes 7 on the back surface.
a first electrode 7 composed of a pair of electrodes 8a and 8b on the surface.

The first electrode substrate 2a and the second electrode substrate 2b sandwiching the mirror substrate 1 from both sides are connected to the mirror surface 5 of the mirror section 4.
a through-holes 9 and 10 formed through the respective opposing portions of the torsion bar 4a and having a line-symmetrical shape about the axis of the torsion bar portion 4a. Through hole 1 on second electrode substrate 2b side
0 is for passing the light beam and the reflected light, and the first
Although the through hole 9 on the electrode substrate 2a side is not always necessary,
This is effective in reducing the damping of the mirror unit by the air layer in the space between the first electrode substrate and the mirror unit and reducing the weight of the entire galvano micromirror.

The first electrode substrate 2a overlaid on the lower side of the mirror substrate 1 is opposed to the pair of electrodes 7a and 7b.
A third electrode composed of 1a and 11b is provided. The second electrode substrate 2b overlaid on the mirror substrate 1 includes a fourth electrode composed of a pair of electrodes 12a and 12b opposed to the pair of electrodes 8a and 8b.

The electrode 7a and the electrode 8a, and the electrode 7b and the electrode 8b are connected to connection holes 13 formed through the respective electrode regions.
Are electrically connected to each other through a conductor 13a (filled with conductive paste or pattern wiring) provided therein, and set to a common potential via the wiring pattern 14 and the terminal pad 1a (see FIGS. 1 and 2).

The electrodes 11a and 11b of the third electrode and the electrodes 12a and 12b of the fourth electrode are electrically insulated. The electrode 11a and the electrode 11b of the third electrode are connected to a control device (not shown) via the terminal pad 2a-1 (see FIG. 2) by the wiring pattern 15.

The electrode 12a and the electrode 12b of the fourth electrode are closer to the outer surface than the conductor 16a (by filling with conductive paste or pattern wiring) provided in the connection hole 16 so as to enable electrical connection with the outside. And connected to the control device (not shown) from the terminal pad 2b-1 via the wiring pattern 17 shown by the dotted line.

Now, the mirror surface 5a is connected to the torsion bar 4
To rotate counterclockwise around the axis a, a positive (or negative) angle control voltage is applied to the electrodes 11b and 12a with respect to the electrodes 7b and 8a having a potential of 0 V, for example. To rotate the surface 5a clockwise, the electrode 11a and the electrode 1 are moved with respect to the electrode 7a and the electrode 8b having a potential of 0 V, for example.
A positive (or negative) angle control voltage is alternately applied to 2b. By applying the voltage in this manner, an electrostatic attraction acts between the electrodes, and the torsion bar portion 4a is twisted and the mirror portion 4 can be rotated.

The mirror section 4 can be swung by alternately applying the two types of voltages. The swing angle control at this time is performed by changing the applied voltage according to the detection output of the reflected light, and the irradiation position of the light beam can be controlled by changing the reflection direction of the light beam.

In the first embodiment, the mirror substrate 1
With a thickness of 300 μm and an area of 7 mm × 6.5 mm, (1,
Using a silicon wafer having anisotropy of (0,0) plane,
It is formed through an anisotropic etching process using a known photolithography technique. The mirror forming part 5 has an area of 2 mm
× 3 mm, thickness 300 μm, cross-sectional area of torsion bar 4 a is 50 μm in thickness × 50 μm in width and 500 μm in length
μm.

The thickness of the electrode forming portions 6 on both left and right sides of the mirror portion 4 (the size of one side region is 1.5 mm × 4.0 mm) is
By removing the thickness of the mirror section 4 by 200 μm from the 300 μm thickness by wet or dry etching to make it 100 μm thin, the mass of the electrode forming section 6 of the mirror section 4 can be reduced to about 60% as compared with a non-thin mirror. ,
The acceleration of the galvano micromirror can be increased.

Even if the thickness of the electrode forming part 6 is reduced to 100 μm, no warpage occurs on the mirror surface 5a after assembling into a galvano-mirror or during swinging, and the electrode forming part 6 has a thickness of several hundred nm or less. Even if warping or bending occurs, it does not affect the operation performance of the galvano micromirror for the optical disk device.

FIG. 5 is a side sectional view of a mirror substrate according to a second embodiment of the present invention. The galvano micromirror has a short wavelength effective for high-density recording of information, for example, 400 n.
m, a blue light beam such as a blue light beam, and SiO ₂ and Ta ₂ O ₅ or SiO ₂
The dielectric layer 21a, such as ₂ and TiO _2, by laminating 21b to form a mirror surface. Dielectric layer 21 laminated on back surface
“b” cancels the residual stress of the dielectric layer 21a stacked as the mirror surface. The other components of the mirror substrate 1 and the pair of electrode substrates 2 sandwiching the mirror substrate 1, that is, the first electrode substrate 2a and the second electrode substrate 2b are the same as those in the first embodiment, and the description thereof is omitted. .

The dielectric layer 21 is provided on the front and back surfaces of the mirror forming portion 5.
Also, when the electrodes 21a and 21b are stacked, the thickness of the electrode forming portion 6 is set to 1
By reducing the thickness to 00 μm, the mass of the mirror forming portion can be reduced to about 60% as in the first embodiment while maintaining the flatness of the mirror surface with high accuracy, and the acceleration of the galvano micromirror is increased. it can.

The bonding operation of the mirror substrate and the electrode substrate may be performed after each of them is cut into chips, or a silicon wafer on which the chip patterns of the mirror substrate and the electrode substrate are formed may be bonded in a wafer state. Alternatively, it may be cut into chips after the attachment.

As described above, the galvano micromirror having a structure in which the weight of the mirror forming portion is reduced to reduce the moment of inertia is excellent in high-speed response performance in a high-frequency region during a seek operation. As shown in the figure, the same components as those of the conventional optical disk device are denoted by the same reference numerals).
By incorporating 0 into the optical path of the optical head 115 together with the objective lens 116, high-speed seek to the information track of the optical disk 110 becomes possible. In particular, it can be applied to a light source of a blue light beam having a short wavelength to contribute to high-density recording of information.

In the above description of the present invention, the mirror substrate is sandwiched between the first electrode substrate and the second electrode substrate from both sides. As described above, the swing control of the mirror surface can be performed by the electrostatic drive system.

In the above description, the mirror part is rotated (oscillated).
Although the torsion bar is supported by a torsion bar, it may be a rotating shaft that is pivotally connected by a bearing or the like and cannot be twisted.

In the above description, electrodes are formed on both sides of the mirror forming portion. However, as long as the mirror portion is supported by rotation (oscillation), the present invention can be applied to a case where electrodes are formed on one side. Further, the thickness of the electrode forming portion may be such that the boundary with the mirror forming portion is smoothly connected by a curved surface or an inclined surface instead of a right-angled step. These deformed structures exhibit the same functions and effects as those of the above-described second embodiment.

[0045]

As described in detail above, according to the present invention,
While maintaining the same high flatness of the mirror surface as in the prior art, the weight of the mirror forming portion can be reduced and the moment of inertia thereof can be reduced, so that the acceleration performance of the galvano micromirror for the optical disk device can be improved.

Also, by incorporating the galvano micromirror having a small moment of inertia into the optical head of the optical disk apparatus, high-speed seek to a track position for recording and reproducing information becomes possible, and high-density recording of information by a short wavelength light beam is achieved. It has an extremely useful effect in industry that can contribute to

[Brief description of the drawings]

FIG. 1 is a side sectional view of a galvano micromirror according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view of FIG. 1;

FIG. 3 is an assembled side view of FIG. 2;

FIG. 4 is a perspective view showing a back surface shape of the mirror substrate of FIG. 1;

FIG. 5 is a side sectional view of a mirror substrate according to a second embodiment of the present invention;

FIG. 6 is a configuration diagram of an optical disk device using a galvano micromirror according to the present invention.

FIG. 7 is a configuration diagram of an optical disk device according to a conventional technique.

FIG. 8 is an exploded perspective view of a galvano micromirror according to the related art.

[Explanation of symbols]

 1: mirror substrate 2: pair of electrode substrates 2a: first electrode substrate 2b: second electrode substrate 3: base 4: mirror 4a: shaft (torsion bar) 4b: through groove 5: mirror forming 5a: mirror (Mirror surface) 6: electrode forming portion 7: first electrode 7a, 7b: pair of electrodes 8: second electrode 8a, 8b: pair of electrodes 9, 10: through hole 11: third electrode 11a, 11b: pair of electrodes Electrode 12: Fourth electrode 12a, 12b: A pair of electrodes 21a, 21b: Dielectric layer 100: Galvano micro mirror

Continued on the front page F term (reference) 2H041 AA12 AB14 AC06 AZ02 AZ08 2H045 AB16 AB73 DA32 5D118 AA01 AA13 DC07 EA00 5D119 AA01 AA08 CA05 JA52

Claims (2)

[Claims] A mirror forming portion having a mirror for reflecting the light beam; a shaft supporting the mirror forming portion; and a mirror for rotating the mirror forming portion around the shaft by electrostatic force. A galvano micromirror, comprising: a mirror substrate having an electrode forming portion on which an electrode is formed, wherein the thickness of the electrode forming portion is smaller than the thickness of the mirror forming portion. 2. The optical disk according to claim 1, wherein the galvano micromirror according to claim 1 is incorporated in an optical path of the light beam in an optical head that seeks together with an objective lens that focuses the light beam on the optical disk surface. apparatus.