JPH0660458A - Single plate optical disk and recording and reproducing method for the same - Google Patents

Abstract

PURPOSE:To provide an optical disk having satisfactory recording sensitivity and satisfactory signal quality, capable of rewriting by overwriting and excellent in weather resistance. CONSTITUTION:A transparent interference layer 2, a 1st magneto-optical layer 31 of GdFeCo, a 2ndi magneto-optical layer 32 of TbFeCr, a dielectric protective layer 4 and a heat radiating metal layer 5 are successively laminated on a discoid substrate 1 to produce the objective single PLATE optical disk. Information is recorded in this disk by applying a modulating magnetic field to the disk while irradiating the disk with high power laser light and the recorded information is reproduced by irradiating the disk with low power laser light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single plate optical disk and a recording / reproducing method thereof, and more particularly to a single plate for writing information by modulating a magnetic field and reading information by laser light utilizing a magneto-optical effect. The present invention relates to an optical disc and a recording / reproducing method thereof.

[0002]

2. Description of the Related Art An optical disc for reading information by laser light has a high recording density and thus has an excellent feature as a mass storage device. In particular, a single plate optical disk is expected because of its compactness.

Generally, as a rewritable optical disk, a magneto-optical disk utilizing the Kerr effect is used.

Next, a conventional single-plate optical disk will be described with reference to the drawings.

FIG. 7 is a sectional view showing the basic structure of a conventional single-plate optical disk.

FIG. 7 shows an example of a typical conventional single-plate optical disk.

The single-plate optical disk shown in FIG. 7 has a transparent interference layer 102 on a disk substrate 101, and a vertically magnetizable amorphous ferrimagnetic alloy of an iron group transition metal and a rare earth transition metal. A magneto-optical layer 103, a dielectric protective layer 104 thereon, a metal reflective layer 105 such as an Al alloy thereon,
An organic protective layer 106 is provided in that order.

The laser light for writing and reading enters through the disk substrate 101 and is focused so as to have a diameter of about φ1.4 μm in the vicinity of the magneto-optical layer 103.
Focused by the servo. Wavelength 8 for laser light source
A semiconductor laser of about 300 Å is used.

For writing information, the magneto-optical layer 103 is irradiated by irradiating laser light of high power corresponding to the information.
Absorbs the energy of the laser beam, converts it into heat energy, raises the temperature to near the Curie temperature, and then applies a recording bias magnetic field to the area including this part to change the magnetization of this part to another. Orient it in the opposite direction to the part.

Information is read by irradiating the magneto-optical layer 103 with linearly polarized laser light of low power and optically detecting the reflected light from the magneto-optical layer 103 through an analyzer. Since the magneto-optical film has the effect of rotating the polarization plane of the reflected light by the Kerr effect, the fact that the rotation angle θ _k of the polarization plane of the reflected light differs depending on the direction of the perpendicular magnetization of the magneto-optical layer 103 is used. The information corresponding to the direction of magnetization can be read out as a light quantity change by passing the light through an analyzer before entering the photodetector.

The material of the magneto-optical layer 103 is, for example,
A ternary alloy of TbFeCo and a ternary alloy of DyFeCo have been proposed (Japanese Patent Publication No. 1-293727). Since such a magneto-optical material is very easily oxidized, the transparent interference layer 10
By sandwiching it with the dielectric protection layer 104, the magneto-optical layer 103 is prevented from being oxidized.

Since θ _k of the magneto-optical material is usually small, the transparent interference layer 102, the dielectric protection layer 104, and the metal reflection layer 105 are included.
The read signal is amplified due to the multiple interference effect due to.

On the other hand, as another information writing method, a high power laser beam is applied to the magneto-optical layer 103 through the disk substrate 101, and magnetic fields having different polarities are applied from the side opposite to the laser beam corresponding to binary information to be recorded. A method has been proposed in which the magnetization is oriented according to the information by applying the voltage (Japanese Patent Publication No. 60-4880).
6).

This method is called a magnetic field modulation method, and has received attention because it allows overwrite rewriting.

[0015]

In the above-mentioned conventional single-plate optical disk and its recording / reproducing method, a truly practical optical disk having good recording sensitivity, good signal quality and excellent weather resistance, and recording / reproducing thereof are provided. There was no way.

An object of the present invention is to laminate at least a transparent interference layer, a first magneto-optical layer of GdFeCo, a second magneto-optical layer of TbFeCr, a dielectric protective layer and a metal heat dissipation layer on a disk substrate. By producing a single-plate optical disk with the above-mentioned drawbacks, a practical single-disk optical disk with excellent weather resistance, good recording sensitivity, good signal quality, and overwrite rewriting, and its recording / reproducing To provide a method.

[0017]

In the single plate optical disc of the first invention, a transparent interference layer, a first magneto-optical layer, a second magneto-optical layer, a dielectric protective layer and a metal heat dissipation layer are provided on a disc substrate. By providing at least this order in this order, a high power laser beam is focused on the first magneto-optical layer through the disk substrate and irradiated, and magnetic fields of different polarities are applied to the irradiated area in correspondence with the binary information. And writing a low power laser beam through the disc substrate to the first
Is a single-disc optical disk in which information is read out by irradiating while converging on and moving the magneto-optical layer of the first magneto-optical layer, wherein the first magneto-optical layer is GdFeCo and the second magneto-optical layer is TbFeCr. Configured to be.

In the single plate optical disk of the second invention, a protective layer of an organic material is provided on the metal heat dissipation layer of the single plate optical disk of the first invention.

In the single plate optical disk of the third invention, a NiCr alloy protective layer is provided between the metal heat dissipation layer and the organic protective layer of the single plate optical disk of the second invention.

In the single plate optical disk of the fourth invention, the transparent interference layer of any one of the first to third inventions is silicon nitride and the dielectric protective layer is silicon nitride. I am configuring.

In the single plate optical disk of the fifth invention, the transparent interference layer of the single disk optical disk of any one of the first to third inventions is hydrogenated silicon carbide, and the dielectric protective layer is hydrogenated carbonized. It is configured to be silicon.

In the single plate optical disk of the sixth invention, a SiO ₂ back coat layer is provided on the disk substrate opposite to the transparent interference layer of the single plate optical disk of any one of the first to fifth inventions. ing.

In the recording / reproducing method for a single-plate optical disk according to the seventh aspect of the present invention, at least a transparent interference layer, a first magneto-optical layer of GdFeCo, a second magneto-optical layer of TbFeCr, on a disk substrate, The dielectric protective layer and the metal heat dissipation layer,
2 for single-layer optical discs that are stacked in this order
A method of recording / reproducing value information, in which a high-power laser beam is focused onto a first magneto-optical layer through a disk substrate and applied, and magnetic fields having different polarities are applied corresponding to binary information to be recorded. The information is written by the method described above, and the information is read by irradiating the first magneto-optical layer while focusing and moving the low power laser beam through the disk substrate.

In the recording / reproducing method for a single-plate optical disk according to the eighth aspect of the present invention, the power of the laser beam for writing information is modulated by the recording / reproducing method for the single-plate optical disk according to the seventh aspect.

[0025]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a sectional view showing the basic structure of a single-plate optical disk according to an embodiment of the first invention, and FIG. 2 shows the basic structure of a single-disk optical disk according to the embodiment of the second invention. FIG. 3 is a sectional view showing the basic structure of a single-plate optical disk according to an embodiment of the third invention. FIG. 4 is a basic structure of a single-disk optical disk according to the embodiment of the fourth invention. FIG. 5 is a sectional view showing the basic structure of a single-plate optical disk according to an embodiment of the fifth invention, and FIG. 6 is a basic structure of a single-disk optical disk according to the embodiment of the sixth invention. FIG.

The single-plate optical disk shown in FIG. 1 is provided with a transparent interference layer 2 on a disk substrate 1 and GdFeCo on the transparent interference layer 2.
The first magneto-optical layer 31 of an amorphous alloy ferrimagnetic material having a high Curie temperature, and the second magneto-optical layer 31 of an amorphous alloy ferrimagnetic material of TbFeCr capable of being perpendicularly magnetized at a low Curie temperature. 32, a dielectric protective layer 4 is sequentially provided thereon, and a heat dissipation layer 5 of a metal film is provided thereon.

The single plate optical disc may be used for writing / reading information by making laser light incident through the disc substrate 1 with the structure as shown in FIG. 1, but as shown in FIG. UV protection resin protective layer 6
May be provided. Furthermore, as shown in FIG. 3, a NiCr alloy protective layer 7 may be provided between the metal heat dissipation layer 5 and the organic protective layer 6.

As a single-plate optical disk with further improved reliability, a SiO ₂ back coat layer 9 may be provided on the disk substrate opposite to the transparent interference layer 2 as shown in FIGS. 4, 5 and 6. is there.

Further, as another single plate optical disc having improved reliability, the surface shape of the organic protective layer 6 may be finely roughened instead of being a mirror surface.

As the disc substrate 1, a polycarbonate resin plate, a glass plate with a photopolymer, or an acrylic resin plate with a photopolymer is used. It is desirable to form guide grooves or guide pits for tracking servo on the disk substrate 1. The track pitch is approximately 0.8 to 1.6 μm. Silicon nitride or hydrogenated silicon carbide is particularly desirable as the material of the transparent interference layer 2.

As the material of the dielectric protective layer 4, silicon nitride or hydrogenated silicon carbide is particularly desirable.

The material of the metal heat dissipation layer 5 is an Al alloy,
Au alloy is preferable, but AlTi, AlCr, AlNi
Cr, AlTa and AuCu are particularly desirable.

As the alloy of the NiCr protective layer 7, one having a Ni content of 80% by weight is particularly desirable.

The laser light for writing and reading enters through the disk substrate 1 and is focused by the focusing servo so as to have a diameter of about φ1.0 to φ1.4 μm in the vicinity of the first magneto-optical layer 31.

The laser light source has a wavelength of 6700 to 8
A semiconductor laser of about 300 Å is used.

The coercive force of the film of the first magneto-optical layer 31 is relatively small at the reading temperature, and the coercive force of the film of the second magneto-optical layer 32 is relatively large at the reading temperature. The first magneto-optical layer 31 and the second magneto-optical layer 32 are exchange-coupled at the reading temperature, and the first magneto-optical layer 31 and the second magneto-optical layer 3 at the initial writing temperature.
Almost no exchange coupling with 2.

In writing information, at least the first magneto-optical layer 31 is irradiated by focusing and irradiating the first magneto-optical layer 31 with a high-power laser beam through the disk substrate 1.
To absorb the energy of the laser light, convert it into heat energy, and heat it up to raise the temperature of the second magneto-optical layer 32 to near the Curie temperature, and in this state, record in the area including this portion. By applying a magnetic field having a polarity corresponding to the desired binary information, the direction of perpendicular magnetization of the second magneto-optical layer 32 is associated with the binary information.

In the state where the temperature after the irradiation of the high power laser beam is lowered, the written second magneto-optical layer 3 is formed.
The direction of the perpendicular magnetization of 2 is transferred to the first magneto-optical layer 31 having a high Curie temperature.

The method of irradiating a high-power laser beam is as follows.
Information can be written at a high density by irradiating the power intermittently instead of a constant power, or by irradiating the power so that the power decreases from the beginning to the end of recording.

The information is read out by irradiating the first magneto-optical layer 31 with a linearly polarized focused laser beam of low power and optically detecting the reflected light from the first magneto-optical layer 31 through an analyzer. Since the magneto-optical film has the effect of rotating the plane of polarization of reflected light by the Kerr effect, the rotation angle θ of the plane of polarization of reflected light is
By utilizing the fact that _k varies depending on the direction of perpendicular magnetization of the magneto-optical film, it is possible to read the information corresponding to the direction of magnetization as a change in the amount of light through the analyzer before the reflected light enters the photodetector.

The combination of the material of the first magneto-optical layer 31 and the material of the second magneto-optical layer 32, which has good write / read characteristics and good high temperature and high humidity storage resistance, is Although the detailed reason is not clear, the first magneto-optical layer 3
GdFeCo as 1 and Tb as the second magneto-optical layer 32
It was found that it was FeCr, and the present invention was reached.

A specific example will be described below. [Specific Example 1] A disk substrate 1 made of a polycarbonate resin having a guide groove formed therein and having a diameter of 86 mm and a thickness of 1.20 mm is placed in a sputtering apparatus, vacuum-exhausted to 3 × 10 ⁻⁷ Torr or less, and then polycarbonate. The resin surface was reverse-sputtered by about 7 Å, and then a silicon target was sputtered with a mixed gas of argon and nitrogen to form a transparent interference layer 2 of 800 Å thick silicon nitride. Next, a GdFeCo target (Gd: Fe: Co = 20.5: 65.0: 14.
5 atomic%) by sputtering with argon gas 1
70 angstrom thick GdFeCo amorphous first
Of the TbFeCr target (Tb: Fe: Cr = 18.6: 79.4: 2.0).
(Atomic%) by sputtering with argon gas to 70
An amorphous second magneto-optical film 32 of TbFeCr having a thickness of 0 angstrom was provided. Then, a silicon target was sputtered with a mixed gas of argon and nitrogen to form a silicon nitride dielectric protective layer 4 having a thickness of 800 angstroms. AlCr alloy target (Cr
Content of 1.0% by weight) is sputtered with argon gas to form a metal heat dissipation layer 5 having a thickness of 200 angstroms.
Was set up. Then, the metal heat dissipation layer 5 is taken out from the sputtering apparatus into the atmosphere, a UV curable resin is spin-coated on the metal heat dissipation layer 5, and UV irradiation is performed to provide a protective layer 6 of the UV curable resin having a thickness of 10 μm. A single-plate optical disk was manufactured.

This single-disc optical disk is rotated at 3600 rpm, and a semiconductor laser beam having a wavelength of 7800 angstroms is applied to the first magneto-optical layer 31 through the disk substrate 1 while squeezing it to about φ1.3 μm to modulate and apply a magnetic field. did. Modulation frequency of 1 at 50% duty while irradiating laser power of 4 mW at a radius of 30 mm
Overwriting was performed by applying a magnetic field of ± 250 oersted at MHz, and when reading was performed by irradiating with a laser power of 0.5 mW, C / N of 45 dB was obtained, recording sensitivity was good and signal quality was also high. It was confirmed that it is a good single plate optical disc and its recording / reproducing method.

It was confirmed that there is no problem in recording / reproducing information even after storing this single plate optical disc in a high temperature and high humidity environment of 80 ° C. and 80% for 200 hours, and it is a practical single plate optical disc and its recording / reproducing method. Was done. [Specific Example 2] A polycarbonate resin disk substrate 1 having a guide groove formed therein and having a diameter of 86 mm and a thickness of 1.20 mm is placed in a sputtering apparatus, vacuum-exhausted to 3 × 10 ⁻⁷ Torr or less, and then polycarbonate. The resin surface was reverse-sputtered by about 7 Å, and then a silicon target was sputtered with a mixed gas of argon and nitrogen to form a transparent interference layer 2 of 800 Å thick silicon nitride. Next, a GdFeCo target (Gd: Fe: Co = 20.5: 65.0: 14.
5 atomic%) by sputtering with argon gas 1
70 angstrom thick GdFeCo amorphous first
Of the TbFeCr target (Tb: Fe: Cr = 18.6: 79.4: 2.0).
(Atomic%) by sputtering with argon gas to 70
An amorphous second magneto-optical film 32 of TbFeCr having a thickness of 0 angstrom was provided. Then, a silicon target was sputtered with a mixed gas of argon and nitrogen to form a silicon nitride dielectric protective layer 4 having a thickness of 800 angstroms. AlCr alloy target (Cr
Content of 1.0% by weight) is sputtered with argon gas to form a metal heat dissipation layer 5 having a thickness of 200 angstroms.
Was set up. A NiCr alloy target (content of Ni: 80% by weight) was sputtered thereon with an argon gas to form a protective layer 7 having a thickness of 300 Å.
After this, the NiCr was taken out from the sputtering device into the atmosphere,
UV protection resin is spin coated on the protective layer 7 of
By irradiating, a protective layer 6 of UV curable resin having a thickness of 10 μm was provided, and a single plate optical disk having a structure as shown in FIG.

This single-disc optical disk is rotated at 3600 rpm, and a semiconductor laser beam having a wavelength of 7800 angstroms is applied to the first magneto-optical layer 31 through the disk substrate 1 while squeezing the laser beam to about φ1.3 μm to modulate and apply a magnetic field. did. Overwriting is performed by applying a magnetic field of ± 250 Oersted at a modulation frequency of 1 MHz with a duty of 50% while irradiating a laser power of 4.5 mW at a radius of 30 mm, and reading is performed by irradiating a laser power of 0.5 mW. As a result, a C / N of 45 dB was obtained, and it was confirmed that the single-disk optical disc had good recording sensitivity and good signal quality, and a recording / reproducing method thereof.

It was confirmed that there is no problem in recording / reproducing information even after storing this single plate optical disc in a high temperature and high humidity environment of 80 ° C. and 80% for 200 hours, and it is a practical single plate optical disc and its recording / reproducing method. Was done. [Specific Example 3] A polycarbonate resin disk substrate 1 having a guide groove formed therein and having a diameter of 86 mm and a thickness of 1.20 mm is placed in a sputtering apparatus. First, the surface of the polycarbonate resin opposite to the guide groove is set to about 7 angstroms. Reverse sputtering was performed to some extent, and then a silicon target was sputtered with a mixed gas of argon and oxygen to form a back coat layer 9 of SiO _{2 having} a thickness of about 500 Å. Next, the surface of the polycarbonate resin on the same side as the guide groove is reverse-sputtered by about 7 angstroms, and then a silicon target is sputtered with a mixed gas of argon and nitrogen to form a transparent interference layer 2 of 800 angstroms of silicon nitride. Provided. next,
GdFeCo target (Gd: Fe: Co = 20.
(5: 65.0: 14.5 atomic%) by sputtering with argon gas to obtain 170 angstrom thick GdF.
The amorphous first magneto-optical film 31 of eCo is provided, and the TbFeCr target (Tb: Fe: Cr = 18.
(6: 79.4: 2.0 at.%) By sputtering with argon gas to obtain 700 angstrom thick TbFe.
An amorphous second magneto-optical film 32 of Cr was provided. Then, a silicon target was sputtered with a mixed gas of argon and nitrogen to form a silicon nitride dielectric protective layer 4 having a thickness of 800 angstroms. AlCr on it
A metal heat dissipation layer 5 having a thickness of 200 angstrom was provided by sputtering an alloy target (the content of Cr is 1.0% by weight) with argon gas. A NiCr alloy target (content of Ni: 80% by weight) was sputtered thereon with an argon gas to form a protective layer 7 having a thickness of 300 Å. After that, the protective layer 7 of NiCr is taken out into the air from the sputtering apparatus, spin coated with a UV curable resin on the protective layer 7 of NiCr, and the protective layer 6 having a thickness of 10 μm of the UV curable resin is provided by UV irradiation. A single-plate optical disk having the constitution was produced.

This single-disc optical disk is rotated at 3600 rpm, and a semiconductor laser beam having a wavelength of 7800 angstroms is applied to the first magneto-optical layer 31 by squeezing it onto the first magneto-optical layer 31 to approximately 1.3 μm while modulating and applying a magnetic field. did. Overwriting is performed by applying a magnetic field of ± 250 Oersted at a modulation frequency of 1 MHz with a duty of 50% while irradiating a laser power of 4.5 mW at a radius of 30 mm, and reading is performed by irradiating a laser power of 0.5 mW. As a result, a C / N of 45 dB was obtained, and it was confirmed that the single-disk optical disc had good recording sensitivity and good signal quality, and a recording / reproducing method thereof.

It was confirmed that there is no problem in recording / reproducing information even after storing this single plate optical disc in a high temperature and high humidity environment of 80 ° C. and 80% for 200 hours, and it is a practical single disc optical disc and its recording / reproducing method. Was done. [Specific Example 4] In the same manner as in Specific Example 1, a single plate optical disk was prepared in which only the transparent interference layer 2 and the dielectric protective layer 4 were changed to hydrogenated silicon carbide having a thickness of 750 angstrom and a thickness of 750 angstrom, respectively.

When recording / reproducing was performed in the same manner as in Example 1, it was confirmed that the single-disk optical disc had good recording sensitivity and good signal quality, and a recording / reproducing method thereof.

It was confirmed that there is no problem in recording / reproducing information even after storing this single plate optical disc in a high temperature and high humidity environment of 80 ° C. and 80% for 200 hours, and it is a practical single plate optical disc and its recording / reproducing method. Was done.

[0052]

As described above, the single plate optical disc and the recording / reproducing method thereof according to the present invention are
Irradiation of high power laser light onto at least a single-plate optical disk produced by laminating a transparent interference layer, a first magneto-optical layer of GdFeCo, a second magneto-optical layer of TbFeCr, a dielectric protective layer and a metal heat dissipation layer. At the same time, by applying a modulation magnetic field to record information and reproducing the information by irradiating low power laser light, the recording sensitivity is good, the signal quality is good, overwrite rewriting is possible, and the weather resistance is also excellent. It has the effect of becoming a thing.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the basic structure of a single-plate optical disk according to an embodiment of the first invention.

FIG. 2 is a sectional view showing a basic structure of a single-plate optical disk according to an embodiment of the second invention.

FIG. 3 is a sectional view showing the basic structure of a single-plate optical disk according to an embodiment of the third invention.

FIG. 4 is a sectional view showing the basic structure of a single-plate optical disc according to an embodiment of the present invention.

FIG. 5 is a sectional view showing the basic structure of a single-plate optical disk according to an embodiment of the fifth invention.

FIG. 6 is a sectional view showing the basic structure of a single-plate optical disk according to an embodiment of the sixth invention.

FIG. 7 is a sectional view showing a basic structure of a conventional single-plate optical disk.

[Explanation of symbols]

1, 101 Disk substrate 2, 102 Transparent interference layer 31 First magneto-optical layer of GdFeCo 32 Second magneto-optical layer of TbFeCr 4, 104 Dielectric protective layer 5 Metal heat dissipation layer 6, 106 Organic protective layer 7 NiCr Protective layer 9 SiO ₂ back coat layer 103 Magneto-optical layer 105 Metal reflective layer

Claims (8)

[Claims] 1. A transparent interference layer, a first magneto-optical layer, a second magneto-optical layer, a dielectric protection layer and a metal heat dissipation layer are provided at least in this order on a disk substrate, and high power laser light is applied to the disk. Information is written by focusing and irradiating the first magneto-optical layer through a substrate and applying magnetic fields having different polarities corresponding to the binary information to the illuminated area, thereby writing laser light of low power to the disk. A single-disk optical disc, wherein information is read out by irradiating while focusing on the first magneto-optical layer through a substrate and moving the first magneto-optical layer, wherein the first magneto-optical layer is GdFeCo and the second magneto-optical layer is The single-disk optical disc, wherein the magneto-optical layer is TbFeCr. 2. The single-plate optical disk according to claim 1, wherein a protective layer of an organic material is provided on the metal heat dissipation layer. 3. The single plate optical disk according to claim 2, further comprising a NiCr alloy protective layer provided between the metal heat dissipation layer and the organic protective layer. 4. The single-disk optical disc according to claim 1, wherein the transparent interference layer is silicon nitride and the dielectric protective layer is silicon nitride. 5. The single plate according to claim 1, wherein the transparent interference layer is hydrogenated silicon carbide and the dielectric protective layer is hydrogenated silicon carbide. optical disk. 6. The single-disk optical disc according to claim 1, further comprising a back coat layer of SiO ₂ provided on the disc substrate opposite to the transparent interference layer. 7. A disk substrate, at least a transparent interference layer, a first magneto-optical layer of GdFeCo, and TbFeCr.
A second magneto-optical layer, a dielectric protection layer, and a metal heat dissipation layer are stacked in this order to record and reproduce binary information on a single-plate optical disc, Information is written by irradiating the first magneto-optical layer with laser light focused through the disk substrate and applying magnetic fields having different polarities corresponding to the binary information to be recorded, and laser light with low power is written. Is read and written by irradiating the first magneto-optical layer through the disk substrate while focusing and moving the first magneto-optical layer. 8. The recording / reproducing method for a single-plate optical disk according to claim 7, wherein the power of the laser light when writing information is modulated.