JPH06180872A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To decrease probability of writing error signals and to increase the laser power margin for recording for CNR by forming a recording layer in a manner that the film thickness on grooves is larger than the film thickness on lands where recording is done. CONSTITUTION:A disk substrate consisting of polycarbonate resin and having spiral grooves on the one surface is disposed in a sputtering device having a substrate holder which can revolve and rotate, and reactive sputtering is done to form a dielectric layer 4. Then a recording layer 3 is formed to about 50nm thickness and etched to form a recording layer 3 of about 25nm thickness having a smooth surface on a land part. Then a dielectric layer 2 is formed by the same method, and a reflecting layer 1 is formed thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium capable of recording, reproducing and erasing information by irradiating a recording film formed of a multi-layered thin film on a substrate with laser light. is there.

[0002]

2. Description of the Related Art In recent years, with the increase in the amount of information, there has been an urgent need to develop a recording medium capable of recording a large amount of information. Among them, optical discs that can record and reproduce high-density information using laser light have already been put into practical use.

Optical discs include a write-once type that can be recorded only once and a rewritable type that can erase recorded information and can be rewritten many times. When used as an external memory of a computer in the future, rewriting of information is possible. A rewritable type that can perform is promising.

In a rewritable optical disk, information is recorded and erased by heating the laser beam and applying an external magnetic field to change the magnetization direction of the magnetic layer, and the polarization direction of the laser beam is rotated by the Kerr Kerr effect. A method has been put into practical use in which high-density information recording / reproduction can be performed by reading information by using the. As the recording medium,
For example, in JP-A-59-217248, a protective layer made of a dielectric is first provided on a substrate, then a recording layer mainly made of a ferromagnetic material is provided, and a protective layer made of a dielectric is further provided. With or without a direct reflection layer,
In addition to the Kerr effect, a structure has been proposed in which the magneto-optical effect is increased by using the Faraday effect of light transmitted through the magnetic layer in combination.

An optical modulation recording method is a recording method generally used for rewritable optical disks. In this method, the magnetization of the recording film is aligned in the direction opposite to the direction of the external magnetic field, and the recording location is locally heated by laser light corresponding to the signal to be recorded. When the temperature of the heated portion reaches near the Curie temperature, the coercive force becomes very small, the magnetization is reversed in the same direction as the external magnetic field, and a bit is formed. Since it is necessary to form a large bit in order to detect the bit by the reproduction signal, it is necessary to increase the laser power to increase the spread of heat.

[0006]

However, if the laser power is increased too much, the distance between adjacent bits in the circumferential direction of the disk becomes small, and
Waveform interference occurs as a read signal when reading a bit. This waveform interference increases jitter.

This means that the reproduction signal amplitude is deteriorated,
It causes a decrease in CNR (Carrier / Noise Ratio).

The problem to be solved by the present invention is to reduce the probability of writing an erroneous signal with respect to fluctuations in the recording laser power due to disturbances such as laser noise, crosstalk, circuit noise, and vibration, and facilitate drive design. Therefore, the jitter does not increase even if the recording laser power increases,
It is to provide a magneto-optical recording medium having a large margin of recording laser power with respect to CNR.

[0009]

In order to solve the above problems, the present invention provides a protective layer made of a transparent dielectric material, a recording layer made of a magnetic material, and a reflective layer on a substrate having a groove portion and a land portion. In a disk-shaped magneto-optical recording medium having a multi-layered recording film formed by a sputtering method, the film thickness on the groove portion of the recording layer is larger than the film thickness on the land portion for recording. A magneto-optical recording medium is provided.

The magneto-optical recording medium of the present invention has a recording film in which a protective layer, a recording layer and a reflective layer are sequentially laminated on the substrate, or a protective layer, a recording layer and a dielectric material on the substrate. It may have a recording film in which a protective layer composed of layers and a reflective layer are sequentially laminated.

The substrate used in the present invention is, for example,
Examples thereof include a substrate in which a guide groove is directly formed in resin or glass such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin, and a substrate in which a guide groove is formed on a flat plate of glass or resin by a photopolymer method.

[0012] As the material of the protective layer made of a dielectric, typically optical constants and transmittance is large, large SiN _X effect of protecting the recording layer, SiO _X, AlSiON, AlSi
_{N, AlN, AlTiN, Ta 2} O 5, ZnS , and the like.

As a material for forming the recording layer made of a magnetic material, for example, an alloy of a transition metal such as TbFeCo or NdDyFeCo and a rare earth metal, or Ti or T
Examples include alloys to which corrosion resistance imparting metals such as a and Cr are added. Particularly, Ti, which has excellent corrosion resistance, is preferable.

Examples of the material of the reflective layer include Al and alloys of Al and other metals. Among them, an alloy of Al and Ti, which is considered to have a large effect of protecting the recording film, is particularly preferable.

When the recording layer made of a magnetic material is formed such that the film thickness on the groove is larger than that on the land, the heat spread by increasing the laser power is generated in the circumferential direction (interval between adjacent bits). Can be conducted more in the radial direction (the direction in which heat escapes into the groove) instead of in the direction in which the heat is narrowed. For this reason, even when recording is performed with a relatively large laser power, the bit interval does not become narrow, the read signal does not cause waveform interference, and the increase in jitter is suppressed.

Further, in the magneto-optical recording medium of the present invention, a protective coat layer may be provided on the reflective layer and a hard coat layer may be provided on the surface of the substrate opposite to the magneto-optical recording layer.

Both organic and inorganic materials are used for the material of the protective coat layer. When forming an organic protective coat layer, methods such as a dipping method, a spin coat method, a roll coater method, and a vapor deposition method are used. on the other hand,
When forming the inorganic protective coat layer, a method such as a sputtering method, a vapor deposition method, an impregnation method or the like is used.

Of these protective coating methods, the spin coating method using an ultraviolet curable resin is preferable because it is a simple and quick method. In this method, an ultraviolet curable resin is discharged onto a substrate using a dispenser, the magneto-optical recording medium is rotated at a high speed, and the resin is spread by centrifugal force for application. The applied resin is then cured by UV irradiation. The spin coating method can also be suitably used for resins other than the ultraviolet curable resin. In any case, the resin used for the protective coat layer preferably has a pencil hardness of H or higher after curing.

The plastic substrate has insufficient scratch resistance, and in order to overcome such a drawback, a hard coat layer is provided on the surface opposite to the recording layer using a transparent material having high hardness. Is desirable. As a means for hard coating, a method of applying and curing an organic polymer such as a UV-curable resin containing a polyfunctional urethane acrylate and a photopolymerization initiator by a spin coating method, a 2P method or the like, a silicon dioxide by a precipitation method or a sputtering method, etc. And the like, a ceramic hard coat layer is not suitable for mass production due to poor productivity, and thus a hard coat layer using an ultraviolet curable resin is preferable.

The optical disk thus formed with a film may be used alone or may be used by laminating two optical disks.

[0021]

It has been found that the above method does not increase the jitter because the heat is diffused in the track direction even if the recording laser power is increased.

[0022]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples.

(Embodiment 1) A substrate made of a polycarbonate resin having a thickness of 1.2 mm and an outer diameter of 90 mm and having spiral grooves with a pitch of 1.6 μm on one side is provided with a substrate mounting portion capable of revolving. It is placed in a sputtering device that has it, and the inside of the sputtering device is 3 × 10 ⁻⁷ T
Evacuated below orr, the pressure of the mixed gas of Ar and N ₂ is 10 mTorr, and the content of nitrogen gas is 5 mol%
Subjected to reactive sputtering using a Si target in an atmosphere of, to form a dielectric layer thickness is from SiN _X of approximately 100 nm.

Next, when the Ar gas pressure is 3 mTorr and Tb
After forming a recording layer with a thickness of about 50 nm using a FeCo alloy target, etching is performed with a pressure of Ar gas of 3 mTorr to a depth of about 25 nm to form a recording layer with a smooth surface of about 25 nm. Filmed The etching rate at this time was 0.05 nm / sec.

Further, in the same manner as above, the thickness is about 30 n.
A dielectric layer made of mSiN _x was formed. Finally, a reflective layer having a thickness of about 45 nm was formed using an Al target to manufacture a magneto-optical recording medium.

With respect to the magneto-optical recording medium manufactured by the above method, the recording / reproducing characteristics were measured with time using a magneto-optical disk evaluation device. For the measurement, a semiconductor laser with a wavelength of 830 nm was used, and the rotation speed of the disk was 1,800 rp.
m, recording frequency 2.9 MHz, recording laser output 4.5
Under the conditions of mW and reproduction laser output of 1.0 mW, CN with respect to recording laser power at a position of radius 24.1 mm
R was measured and the result is shown in FIG.

(Comparative Example 1) A dielectric layer made of SiN _{x was formed} to a thickness of about 100 nm on a substrate made of the same polycarbonate resin as that used in Example 1 by the same method as in Example 1. In the same manner as in Example 1, a 25 nm film was formed without etching the recording layer, and a dielectric layer and a reflective layer were sequentially formed to 30 nm and 45 nm to manufacture a magneto-optical recording medium.

FIG. 4 shows the measurement results of the recording / reproducing characteristics of the magneto-optical recording medium manufactured by the above method by the same method as in Example 1.

From the results shown in FIG. 4, it can be understood that the magneto-optical recording medium of Comparative Example 1 is inferior to that of Example 1 in the margin of the recording laser power with respect to the CNR.

(Comparative Example 2) A dielectric layer made of SiN _{x was formed} to a thickness of about 100 nm on a substrate made of the same polycarbonate resin as that used in Example 1 in the same manner as in Example 1, and subsequently, The thickness is about 40 nm in the same manner as in Example 1.
After the recording layer of No. 2 was provided, the recording layer was etched in the same manner as in the example with an Ar gas pressure of 3 mTorr and a depth of about 15 nm to form a recording layer having a thickness of about 25 nm.

Further, a dielectric layer made of SiN _x having a thickness of about 30 nm was formed in the same manner as in Example 1. Finally, a reflective layer having a thickness of about 45 nm was formed using an Al target to manufacture a magneto-optical recording medium.

With respect to the magneto-optical recording medium manufactured by the above method, recording / reproducing characteristics were measured with time in the same manner as in Example 1, and the results are shown in FIG.

From the results shown in FIG. 4, it can be understood that the magneto-optical recording medium of Comparative Example 2 is inferior to that of Example 1 in the margin of the recording laser power with respect to the CNR.

[0034]

In the magneto-optical recording medium of the present invention, the jitter does not increase even if the recording laser power is increased.
The margin of the recording laser power with respect to NR becomes large. This improvement in margin reduces the probability of writing an erroneous signal with respect to fluctuations in the recording laser power due to disturbances such as laser noise, crosstalk, circuit noise, and vibration.
It has the effect of facilitating the drive design.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the layer structure of a magneto-optical recording medium obtained in Example 1.

2 is a schematic cross-sectional view showing the layer structure of the magneto-optical recording medium obtained in Comparative Example 1. FIG.

3 is a schematic cross-sectional view showing the layer structure of a magneto-optical recording medium obtained in Comparative Example 2. FIG.

FIG. 4 is a chart showing the relationship between the recording laser power and CNR in Example 1 and Comparative Examples 1 and 2.

[Explanation of symbols]

 1 Reflective Layer 2 Protective Layer Made of Dielectric Material 3 Recording Layer Made of Magnetic Material 4 Protective Layer Made of Dielectric Material Magneto-optical recording medium of Example 1 Magneto-optical recording medium of Comparative Example 1 □ Magneto-optical recording of Comparative Example 2 Medium

Claims (1)

[Claims] 1. A disc having a multi-layered recording film in which a protective layer made of a transparent dielectric material, a recording layer made of a magnetic material and a reflective layer are formed on a substrate having a groove portion and a land portion by a sputtering method. A magneto-optical recording medium, wherein the film thickness on the groove portion of the recording layer is larger than the film thickness on the land portion for recording.