JP2003157565A - Correction mirror for wave front aberration and optical disk device using the mirror - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a correction mirror for wavefront aberration having the mirror substrate with a structure which realizes low power consumption and causes no overflow of an adhesive when the substrate is adhered to a piezoelectric element, and to provide an optical disk device equipped with the above correction mirror for wavefront aberration. SOLUTION: In the correction mirror for wavefront aberration to be mounted on an optical pickup of an optical disk device and having the mirror substrate 6 the surface of which is displaced by the effect of a piezoelectric element 2, the back face of the mirror substrate 6 is provided with a plurality of grooves 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc device, and more particularly to a wavefront aberration correction mirror mounted on a pickup of the optical disc device.

[0002]

2. Description of the Related Art In general, information recording media using optical disks include CDs and DVDs. Since the recording density of the DVD is higher than that of the CD, the conditions for reading and writing information are strict. For example, it is ideal that the optical axis of the optical pickup and the disc surface are vertical, but in reality, the disc is made of resin, so it has a considerable swell, and when this is rotated, the optical axis of the optical pickup and the disc surface are rotated. The plane is not always vertical (hereinafter referred to as tilt).

8A and 8B are explanatory views for explaining the tilt. FIG. 8A is a CD and FIG. 8B is a DVD. As shown in FIG. 8, the recording layer 104 of the disc has the resin layer 102 interposed therebetween. Therefore, if the disc surface is not vertical, the optical path is bent and the spot cannot be correctly focused on the disc, so that coma aberration 103 occurs. This coma aberration 10
If 3 is larger than the permissible amount, there is a problem that correct reading and writing cannot be performed.

As a means for reducing the influence of tilt,
The resin layer 102 between the objective lens 101 and the recording layer 104 may be thinned. Compared with the CD shown in FIG. 8A, the DVD shown in FIG. 8B has half the thickness of the resin layer 102 between the objective lens 101 and the recording layer 104 in order to achieve this effect. .

However, in order to perform higher density recording than DVD by this method, the resin layer is made thinner to further reduce the influence of tilt, but dust and scratches are formed on the disc. In such a case, a new problem occurs that the signal cannot be read and written correctly. Therefore, tilt the optical axis with the actuator (tilt)
The current situation is that it is supported.

As a technique for optically correcting the tilt, Japanese Patent Laid-Open No. 10-79135 using a liquid crystal, Japanese Patent Laid-Open No. 5-144056 using a transparent piezoelectric element, and Japanese Patent Laid-Open No. 5-333274 using a variable mirror are known. Publications and the like have been proposed.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
There is also a method of compensating for coma by controlling the phase using a liquid crystal plate as in Japanese Patent Publication No. 5, but in this method, the amount of light is attenuated because the laser passes through the liquid crystal plate, and the energy required for writing is obtained. However, due to the characteristics of the liquid crystal, it is difficult to use it for the high frequency operation required for tangential tilt control.

Further, Japanese Patent Application Laid-Open No. 5-144056 discloses
In fact, a high voltage is required to obtain the required displacement with the transparent piezoelectric element alone, which is not practical for use in an optical pickup or the like.

Further, Japanese Patent Laid-Open No. 5-333274 discloses
Although this is a method of controlling the phase by deforming the mirror itself with a laminated piezoelectric element, wiring is not taken into consideration when it is used for small parts such as an optical pickup, and it becomes complicated and the assembly cost becomes high. Even if problems such as wiring can be solved, the laminated piezoelectric element has to be made quite small, which is technically difficult and costly.

A method of correcting the wavefront aberration by a unimorph or bimorph-shaped wavefront aberration correction mirror using a piezoelectric element reduces the influence of tilt which causes a problem when reading and writing information as described above at a low voltage and a small size. Also considered to be advantageous.

FIG. 9 is a sectional view of a wavefront aberration correction mirror using a piezoelectric element. A reflective film 1 is formed on the surface of the mirror substrate 6.
Is formed, and the insulating film 7 and the wiring electrode 4 are respectively formed on the back side, and the piezoelectric element 2 is bonded to the back surface of the mirror substrate 6. Further, the mirror substrate 6 is fixed by the fixing portion 3 of the fixing base substrate 8.

By applying a potential to the piezoelectric element 2, the piezoelectric element 2 is displaced and the surface of the mirror substrate 6 can be displaced. At this time, since the piezoelectric element electrode 5 is divided into the left and right from the center, different displacements can be generated by changing the polarity and the voltage, and the coma aberration can be corrected.

At this time, the mirror substrate 6 is required to be thin so that it can be easily displaced. However, if the mirror substrate 6 is made thin, the surface of the mirror substrate 6 is likely to bend due to the stress of the wiring electrode 4 formed on the back surface. Become. Although some deflection can be canceled with an offset voltage, a large deflection will increase the offset voltage, making it impossible to achieve low power consumption.

Further, when the piezoelectric element 2 is attached to the rear surface of the mirror, if the adhesive is not applied in an appropriate amount, the adhesive may run out.

The present invention provides a wavefront aberration correction mirror having a mirror substrate having a structure capable of realizing low power consumption and having no adhesive sticking out at the time of bonding with a piezoelectric element, and an optical disk device provided with the wavefront aberration correction mirror. The purpose is to provide.

[0016]

In order to achieve the above object, the invention according to claim 1 is mounted on an optical pickup of an optical disk device and has a wavefront aberration correction mirror having a mirror substrate whose surface is displaced by the action of a piezoelectric element. In (1), a wavefront aberration correction mirror having a plurality of grooves on the back surface of the mirror substrate is the most main feature.

According to a second aspect of the present invention, in a wavefront aberration correction mirror which is mounted on an optical pickup of an optical disc device and has a mirror substrate whose surface is displaced by the action of a piezoelectric element, a plurality of recesses are formed on the back surface of the mirror substrate. The main feature is the provided wavefront aberration correction mirror.

The invention according to claim 3 is mainly characterized in that the groove pitch is 500 μm or less, and the groove width is 20% or less of the pitch.

In the invention according to claim 4, the pitch of the recesses is 400 μm or less, and the opening area ratio of the recesses is 60.
The main feature is the wavefront aberration correction mirror according to claim 2, which is at least 80%.

The fifth aspect of the present invention is characterized mainly in the wavefront aberration correction mirror according to the first or second aspect, in which the cross-sectional shape of the groove or recess is formed into a V shape by anisotropic etching.

A sixth aspect of the invention is characterized mainly in the wavefront aberration correction mirror according to the second aspect, in which a wiring electrode is formed on the back surface except the recess.

The seventh aspect of the invention is characterized mainly in an optical disk device equipped with the wavefront aberration correction mirror according to any one of the first to sixth aspects.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. The invention according to claim 1 will be described. Figure 1
1A is a diagram showing a first example of a mirror substrate in a wavefront aberration correction mirror according to an embodiment of the present invention, and FIG.
Is a rear view of the mirror substrate, (b) is a sectional view, and (c) is an enlarged sectional view of a main part.

As shown in FIG. 1, the back side of the mirror substrate 6 is provided with a plurality of grooves 9. Further, as shown in FIG. 1C, the wiring electrode 4 is provided on the back side of the mirror substrate 6.
Are formed, and the piezoelectric element 2 is bonded by the adhesive 10.

In this embodiment, the mirror substrate 6 is a silicon wafer having a thickness of 300 μm. Groove 9 on the back side
Are processed by etching or the like so as to have a width of 100 μm, a depth of 200 μm, and a pitch of 500 μm so as to be orthogonal to each other, and a wiring electrode 4 made of Al is formed thereon by a sputtering method to a thickness of about 0.3 μm. The piezoelectric element 2 is attached onto the surface 4 by the adhesive 10 and wiring such as wire bonding is performed to complete the wavefront aberration correction mirror.

The electrodes of the piezoelectric element 2 are divided into two parts on the right and left sides, and by applying potentials having different polarities to each other, the left and right operations (for example, the right side is a convex surface and the left side is a concave surface) can be performed.

In a normal mirror, the mirror substrate 6 is designed to be thin so that a large amount of displacement can be taken. However, in the present invention, the groove 9 is provided without changing the thickness of the mirror substrate 6, and the mirror is formed by this groove 9. The displacement amount of the substrate 6 is set to be large. That is, the groove 9 acts as a spring and the mirror substrate 6
Is being displaced.

In the case of an ordinary mirror, the wiring electrode 4 on the back surface
Although the mirror surface is bent in a convex shape due to the stress (tensile stress) in the present invention, most of the wiring electrodes 4 are formed in the thick portion of the mirror substrate 6 in the present invention, so that the influence of the stress is reduced. Further, in the present invention, the internal stress of the wiring electrode 4 is dispersed as shown by the arrow in FIG.

In addition, when the piezoelectric element 2 is attached with the adhesive 10, it is difficult to apply a small amount of the adhesive 10, and a problem occurs due to the adhesive 10 protruding to the periphery of the piezoelectric element 2. In the invention, the excess adhesive 10 enters the groove 9 and does not protrude to the periphery of the piezoelectric element 2, so that the manufacturing yield is improved.

By providing and controlling such a wavefront aberration correction mirror on the optical axis of the optical pickup as shown in FIG. 2, it is possible to reduce coma aberration due to tilt.

FIG. 2 is a block diagram of an optical pickup equipped with the wavefront aberration correction mirror of the present invention. The laser light emitted from the laser element is collimated by the laser optical system 25, passes through the deflection beam splitter 24, is reflected by the wavefront aberration correction mirror 20, is further reflected by the rising mirror 23, and is an objective lens and an objective optical system. The light is focused at 22 and focused on the optical disk 21.

The laser light reflected from the optical disk 21 passes through the objective lens and the objective optical system 22, is reflected by the rising mirror 23, is further reflected by the wavefront aberration correction mirror 20, passes through the deflection beam splitter 24, and is reflected by the light beam. It is condensed by the detection optical system 26 and detected by the photodetector. A detection element for tilt detection is also installed in this detection element.

FIG. 3 is a table for explaining the wavefront aberration shape and the wavefront aberration correction mirror shape. 3A shows a wavefront aberration shape before tilt correction, FIG. 3B shows a mirror shape for wavefront correction, FIG. 3C shows a wavefront aberration shape after correction, and FIG. The mirror surface shape is shown.

In the optical pickup shown in FIG. 2, when the optical disk 21 is tilted from a position perpendicular to the optical axis of the laser light, the wavefront of the laser light reflected and returned from the optical disk is disturbed, for example, FIG. Wavefront aberration (coma aberration) as shown in (1) occurs. Here, the horizontal axis is the cross section of the surface of the wavefront aberration correction mirror shown in FIG. 9, and the vertical axis is the wavefront aberration.

That is, in the optical pickup shown in FIG. 2, the mirror surface of the wavefront aberration correction mirror is a flat surface when the disc is tilted, and the wavefront aberration of the reflected light reflected by the flat surface is shown. If the optical disk 21 is perpendicular to the optical axis of the laser light, the wavefront will be the same straight line as the horizontal axis without causing the aberration as shown in FIG.

FIG. 3B shows an example in which the wavefront aberration correction mirror shown in FIG. 9 is operated so as to intentionally generate the aberration, and the wavefront aberration of the reflected light is represented. Here, the horizontal axis is the cross section of the mirror surface of the wavefront aberration correction mirror, and the vertical axis is the wavefront aberration.

It is assumed that the optical disc is tilted and the wavefront of the reflected light from the disc is as shown in FIG. 3 (a). Figure 3 shows the ideal wavefront of the reflected light when the disc is not tilted.
If the wavefront aberration correction mirror is controlled so as to be as in (b), the wavefront of the reflected light reflected from the wavefront aberration correction mirror becomes flat, and the wavefront aberration can be corrected. However, in an actual mirror, both ends are fixed, so the shape is as shown in FIG. 3D, but the wavefront of the reflected light is as shown in FIG.
As shown in FIG. 3C, it can be seen that the wavefront aberration is reduced as compared with FIG.

Next, the invention according to claim 2 will be described. Figure 4
4A is a diagram showing a second example of the mirror substrate in the wavefront aberration correction mirror according to the embodiment of the present invention, and FIG.
Is a rear view of the mirror substrate, (b) is a sectional view, and (c) is an enlarged sectional view of a main part.

As shown in FIG. 4, the back side of the mirror substrate 6 has a plurality of recesses 11. Further, as shown in FIG. 4C, the wiring electrode 4 is provided on the back side of the mirror substrate 6.
Are formed, and the piezoelectric element 2 is bonded by the adhesive 10.

The mirror substrate 6 is a silicon wafer and has a thickness of 3
The width of one side of the recess 11 on the back side is 3 μm.
It is processed by etching or the like to have a depth of 00 μm, a depth of 200 μm, and a pitch of 400 μm. The wiring electrode 4, the piezoelectric element 2 and the like are attached by the method described above.

In the present invention, the concave portion 11 is provided without changing the thickness of the mirror substrate 6, and since the large number of the concave portions 11 exist, the displacement of the entire mirror substrate 6 can be made large. That is, the convex portion functions like a beam to reduce the deflection of the mirror substrate 6.

The invention according to claim 3 will be described. In the present invention according to claim 1, the groove 9 has a pitch of 500 μm.
The width is set to m or less and the width is set to 20% or less of the pitch.

The groove 9 plays a role like a spring for displacing the mirror surface, and the amount of displacement changes depending on the pitch of the groove 9. From the results obtained from the experiment, pitch 500
It was found that the required amount of displacement can be obtained when the thickness is less than μm.

If the pitch is small, a large amount of displacement can be obtained with a small force, but since it becomes sensitive to stress etc. accordingly, it is necessary to design an appropriate value.
It is desirable that the thickness be 0 μm or less. Since the number of the grooves 9 increases as the pitch decreases, the opening area of the grooves 9 increases and is easily affected by stress. Therefore, the width of the grooves 9 is preferably 20% or less of the pitch.

In this embodiment, the Si substrate (300 μm
(Thickness) as the mirror substrate 6, and the pitch of the grooves 9 is 500 μ.
m, the width was 100 μm, and the depth was 200 μm, and an Al film was formed as the wiring electrode 4 by a sputtering method to a thickness of 0.3 μm. Further, the piezoelectric element 2 is attached and wiring is performed, whereby the wavefront aberration correction mirror is completed. In this design, the width of the groove 9 is 20% of the pitch.

The mirror substrate 6 is 0.1 μm due to Al stress.
It was in a warped state. By applying a 1V offset voltage to the piezoelectric element 2, the mirror substrate 6 could be made substantially flat, and when 5V was applied to the piezoelectric element 2, a displacement of 0.4 μm could be obtained. Since the offset voltage is 1V, the displacement is 0.1V per 1V.
μm. The mirror substrate 6 is used to correct coma.
The amount of displacement was estimated to be about 0.2 μm, so a sufficient amount of displacement could be obtained.

The invention according to claim 4 will be described. In the present invention according to claim 2, the pitch of the concave portions 11 is set to 40.
It is set to 0 μm or less, and the opening area ratio of the recess 11 is set to 60% or more and 80% or less. Here, the opening area ratio has an effect on the displacement of the mirror substrate 6, and the required displacement amount is obtained from 60% to 80% from the experimental result.

In this embodiment, the Si substrate (300 μm
(Thickness) as the mirror substrate 6 and the pitch of the recesses 11 is
μm, one side is 300 μm, and the depth is 200 μm.
An Al film for the wiring electrode 4 is 0.3 μm by the sputtering method.
A film was formed. Further, the piezoelectric element 2 is attached and wiring is performed, whereby the wavefront aberration correction mirror is completed. In this design, the opening area ratio of the recess is approximately 60%.

The mirror substrate 6 is about 0.1 due to Al stress.
It was in a warped state by μm. By applying a 1V offset voltage to the piezoelectric element 2, the mirror substrate 6 could be made substantially flat, and when 5V was applied to the piezoelectric element 2, a displacement of 0.3 μm could be obtained. The amount of displacement of the mirror substrate 6 is about 0.2 μ in order to correct coma.
Since it was estimated to be m, a sufficient amount of displacement could be obtained.

The invention according to claim 5 will be described. In the present invention according to claim 1 or 2, the groove 9 or the recess 11 has a V-shaped cross-sectional shape by anisotropic etching.

FIG. 5 is a diagram showing a third example and a fourth example of the mirror substrate in the wavefront aberration correction mirror according to the embodiment of the present invention. FIG. 5A shows the third example of the mirror substrate. The principal part top view and sectional drawing of an example are shown, (b) is the principal part top view and sectional view of a 4th example.

Anisotropic etching of silicon is a method of processing using a precise three-dimensional structure determined by the crystal plane of single crystal silicon, in particular, the property that the etching rate is different due to the difference in the plane orientation. By masking the crystal substrate and etching with KOH solution,
A shape as shown in FIG. 5A can be manufactured, and the angle θ at this time is 54.7 °, and this surface is the <111> surface.
By adjusting the mask size and etching time,
Since the shape as shown in (b) can also be produced, it can be used for the mirror substrate 6.

FIG. 6 is a diagram showing a method of manufacturing the mirror substrate in the wavefront aberration correction mirror according to the embodiment of the present invention.

As shown in FIG. 6A, the mask material 13 is formed on the mirror substrate 6 made of silicon, and the back surface mask material 13 is patterned by a photolithography process. The mask material 13 may be an insulating film that is insoluble in a KOH solution, and examples thereof include SiO ₂ , SiON, SiN, and Ta ₂ O ₅ , which can be formed by a sputtering method. The mask material 13 is patterned in a rectangular shape by dry etching or wet etching.

Next, the KOH solution is heated to about 90 ° C. and the silicon substrate in the mirror portion is etched to have a thickness of 100 μm, for example, to obtain a shape as shown in FIG. 6B. .

Next, as shown in FIG. 6C, the wiring electrode 4 is formed on the back surface of the mirror substrate 6 by sputtering or vapor deposition and patterned.

Next, as shown in FIG. 6 (d), the piezoelectric element 2 is attached and wired with a thin wire 12 to complete the wavefront aberration correction mirror.

The invention according to claim 6 will be described. In the invention according to claim 2, the wiring electrode is formed on the back surface except the recess.

FIG. 7 is a diagram showing a fifth example of the mirror substrate in the wavefront aberration correction mirror according to the embodiment of the present invention. A recess is formed in the mirror substrate 6 by etching, and A
1 is formed by the sputtering method, and Al in the recess is removed by the photolithography method to form the wiring electrode 4. That is, since the Al film is formed only on the thick portion of the mirror substrate 6, the mirror substrate 6 is less susceptible to the stress of the Al film.

As a result of patterning the Al film of the concave portion 11 of the mirror structure described in the fourth aspect of the invention by the photolithography method, the deflection amount of the mirror substrate 6 is 0.1 μm or less, which is smaller than that described above. The offset voltage also tended to decrease. Further, since the displacement amount is almost the same as that described above, lower voltage can be realized.

The invention according to claim 7 will be described. The present invention is an optical disk device such as a CD or a DVD equipped with the wavefront aberration correction mirror according to any one of claims 1 to 6. The wavefront aberration correction mirror according to the present invention is small and lightweight, and can be realized with a thickness of 1 mm or less.
It was possible to mount the optical pickup without changing the external dimensions of the optical pickup, and it was possible to correct coma aberration. Further, since it consumes little power, it can be used for mobile devices.

[0062]

According to the first aspect of the present invention, since the plurality of grooves are provided on the back surface of the mirror substrate, the influence of the stress of the wiring electrodes is less likely to occur, and a sufficient mirror displacement amount can be obtained even at a low voltage. You can

According to the second aspect of the present invention, since the plurality of concave portions are provided on the back surface of the mirror substrate, the influence of the stress of the wiring electrode is less likely to occur, and a sufficient mirror displacement amount can be obtained even at a low voltage. .

According to the third aspect of the present invention, the pitch of the grooves is 500 μm or less, and the width of the grooves is specified to be 20% or less of the pitch, so that the degree of freedom in design can be increased.

According to the invention described in claim 4, the pitch of the recesses is 400 μm or less, and the opening area ratio of the recesses is 60.
The degree of freedom in design can be increased by defining the content to be not less than 80% and not more than 80%.

According to the fifth aspect of the present invention, since the cross-sectional shape of the groove or recess is formed in a V shape by anisotropic etching, the groove or recess can be manufactured with high dimensional accuracy, and the yield is improved. be able to.

According to the sixth aspect of the present invention, since the wiring electrode is formed on the back surface except the concave portion, the stress is applied only to the thick portion of the substrate, and the amount of bending of the mirror surface can be reduced.

According to the invention described in claim 7, since the wavefront aberration correction mirror according to any one of claims 1 to 6 is provided, it is possible to provide a compact and lightweight optical disk device.

[Brief description of drawings]

FIG. 1 is a diagram showing a first example of a mirror substrate in a wavefront aberration correction mirror according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical pickup equipped with the wavefront aberration correction mirror of the present invention.

FIG. 3 is a diagram for explaining a wavefront aberration shape and a wavefront aberration correction mirror shape.

FIG. 4 is a diagram showing a second example of the mirror substrate in the wavefront aberration correction mirror according to the embodiment of the present invention.

FIG. 5 is a diagram showing a third example and a fourth example of the mirror substrate in the wavefront aberration correction mirror according to the embodiment of the present invention.

FIG. 6 is a diagram showing the manufacturing method of the mirror substrate in the wavefront aberration correction mirror according to the embodiment of the invention.

FIG. 7 is a diagram showing a fifth example of a mirror substrate in the wavefront aberration correction mirror according to the embodiment of the present invention.

FIG. 8 is an explanatory diagram for explaining tilt.

FIG. 9 is a sectional view of a wavefront aberration correction mirror using a piezoelectric element.

[Explanation of symbols]

1 Reflective film 2 Piezoelectric element 3 Fixed part 4 wiring electrodes 5 Piezoelectric element electrode 6 mirror board 7 Insulating film 8 Base substrate for fixing 9 grooves 10 adhesive 11 recess 12 wires 13 Mask material 20 Wavefront aberration correction mirror 21 optical disc 22 Objective lens and objective optical system 23 Start-up mirror 24 Deflection Beam Splitter 25 Laser optical system 101 Objective lens 102 resin layer 103 Coma aberration 104 recording layer

Claims (7)

[Claims] 1. A wavefront aberration correction mirror, which is mounted on an optical pickup of an optical disk device and has a mirror substrate whose surface is displaced by the action of a piezoelectric element, wherein a plurality of grooves are provided on the back surface of the mirror substrate. Aberration correction mirror. 2. A wavefront aberration correction mirror which is mounted on an optical pickup of an optical disk device and has a mirror substrate whose surface is displaced by the action of a piezoelectric element, wherein a plurality of recesses are provided on the back surface of the mirror substrate. Aberration correction mirror. 3. The wavefront aberration correction mirror according to claim 1, wherein the pitch of the grooves is 500 μm or less, and the width of the grooves is 20% or less of the pitch. 4. The pitch of the recesses is 400 μm or less,
The wavefront aberration correction mirror according to claim 2, wherein the opening area ratio of the concave portions is 60% or more and 80% or less. 5. The cross-sectional shape of the groove or recess is formed in a V shape by anisotropic etching.
Alternatively, the wavefront aberration correction mirror described in 2. 6. The wavefront aberration correction mirror according to claim 2, wherein a wiring electrode is formed on the back surface except the recess. 7. An optical disk device comprising the wavefront aberration correction mirror according to claim 1. Description: