KR950001876B1 - Producing method for optical recording medium - Google Patents

Abstract

The method performs a heat treatment for amorphous thin film of transition metal at Curie temperature after evaporation in order to obtain stable magnetic charateristics. The method prevents the optical record disk from heat-damaging. The method comprises the steps of: forming the amorphous film of the transition metal; heating the amorphous film a near Curie temperture for 30 to 60 minutes; applying the heat-treated film under a magnetic field where time-dependent variations of magnetic force is within ± 5%, and the field has a single-directional force if heated.

Description

Method of manufacturing optical record carrier

1 is a block diagram of a manufacturing apparatus for manufacturing an optical recording medium according to the present invention.

2 is a state diagram of the initial value of the coercive force Hc of the thin film according to the present invention after the heat treatment.

3 is a state diagram showing a change in the coercive force Hc with respect to the heat treatment time according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical recording medium, and more particularly, to a method for manufacturing an optical recording medium having stable magneto-optical properties by heat treatment near a Curie temperature after deposition in the manufacture of an amorphous thin film of rare earth or transition metal. .

The optical disc, which is a recording medium capable of recording and reproducing information by irradiating a laser beam, has the advantage of recording a higher density of information than conventional magnetic recording media, and also has random access and low-cost manufacturing cost per bit. As an information recording medium that can replace a substantial portion of the optical disc for reproduction, compact discs and video discs have already been commercialized and are in the mass distribution stage.

The WORM (Write Once Read Many) type, which can be written once by the user, has been commercialized by each company since the early 80s as a large-capacity filling system, and is expected to expand in the future due to standardization.

Erasable type optical discs that can be erased like a conventional magnetic recording medium have been proposed recently, but among them, an amorphous alloy thin film of a rare earth-transition metal using a magneto-optical effect is used. It is expected as a generation of erasable optical disk material.

In addition, a phase change type has been proposed as an erasable disk material, which is a type that allows information to be recorded, reproduced, and erased by simply using a difference in optical characteristics due to a change in phase depending on the temperature of the material. The advantage is that a driver of the same mechanism as a conventional WORM type driver can be used.

The magneto-optical recording material using a rare earth-transition metal (RE-TM) thin film during recording is the most expected material for erasable optical disks. The recording principle is to heat the recording layer to near the Curie temperature using a laser beam. Recording is performed by an external magnetic field modulated by the signal to be recorded.

At the time of reproduction, the laser beam lower than that at the time of recording can be irradiated to reproduce the recorded information by the difference in the rotational direction of the Kerr rotational angle according to the magnetization direction.

As the recording material, the rare earths include terbium (Tb), gadolinium (Gd), dysprosium (Dy), and iron (Fe), carbon (Co), and the like. have.

As a manufacturing method, a thin film is mainly formed using an alloy target by sputtering, and at this time, the composition, coercivity, saturation magnetization, rotation angle, etc. of the film is influenced by gas pressure, bias voltage, and substrate temperature. The limiting magneto-optical properties change.

In addition, the rare-earth-transition metal (RE-TM) film is in an amorphous state, and various properties change due to a change in the thin film logic caused by heating during recording, erasing, or external environmental changes. The regeneration characteristics change.

The method for manufacturing an optical recording medium according to the present invention is a method for preparing an amorphous thin film of rare earth-transition metal and heat-treating it below the crystallization temperature of the thin film to stabilize the overall magnetochemical effect. N can be obtained, and at the time of recording, it is possible to continuously use a laser power of an appropriate size due to the temperature dependency of a constant Hc.

The crystallization temperature refers to a transition temperature between amorphous and crystalline, and the change in the basic properties of the film can be prevented by performing a heat treatment at or below the crystallization temperature.

The crystallization temperature varies depending on the composition of the material and is generally much higher than the Curie temperature. Therefore, when the Curie temperature is recorded, heat treatment is performed near the Curie temperature of the material.

In addition, the recording material for performing the compensation type recording is heat-treated at a temperature near the highest coercive force at the recording time of the material.

In the case of the glass which withstands the high temperature during the heat treatment according to the present invention, there is no problem even if the transition metal heat treatment is performed in a general heating apparatus, but in the case of the plastic substrate such as polycarbonate (PC), the deformation of the substrate is caused by the general heat treatment method. It is not heat treated.

Therefore, in the present invention, a heat treatment apparatus having the configuration as shown in FIG. 1 is used, and an inert atmosphere gas such as N ₂ or Ar is injected into the heat treatment chamber to prevent oxidation during temperature heating.

Hereinafter, a method of manufacturing an optical recording medium according to the present invention will be described in detail with reference to the accompanying drawings.

1 shows a heat treatment apparatus used to implement a method for manufacturing an optical recording medium according to the present invention, in which a mirror 2 is inclined in front of a laser body 1, and a thin film is provided in an airtight chamber 6. The spindle 8 for rotating is provided, and the connection lens 3 for connecting the reflected laser beam is provided on one side, and the magnetic field generating head 5 is installed below it.

The disk 4 to be heat treated is positioned between the focusing lens 3 and the magnetic field generating head 5. On the other side, the gas inlet 7 is formed.

Referring to the disk manufacturing method according to the device configuration having such a configuration, the beam emitted from the laser body 1 raises only the surface temperature of the disk 4, and the temperature of the substrate hardly rises.

At this time, the magnetic flux from the magnetic field generating head 5 causes the magnetization to be constantly upward over the entire surface of the disk.

At this time, by increasing the temperature, it is possible to have a much smaller magnetic field than at room temperature by applying monotonization. When the Curie temperature is over, the coercive force Hc of the material becomes ＂0＂, which makes it easy to magnetize in the external magnetic direction. Therefore, when the magnetic field is applied while heating directly above Curie temperature, all domains on the disk surface are magnetized in a certain direction.

To illustrate in more detail, FIG. 2 shows the coercive force Hc of the film (Gd), turbium (Tb), and iron (Fe) film for the repeated heating and cooling operations by modulating the laser power as in recording. Changes after initial value versus heat treatment are shown.

Here, it can be seen that the thin film that has not been heat-treated begins to gradually decrease the coercive force Hc after about 300 times, and the coercive force Hc hardly changes in the thin film heat-treated by heating and cooling at about 150 ° C. for 1 hour. have.

Coercivity Hc is a measure of magnetization reversal for the external magnetic field and is an important factor in determining record retention and minimum vertical magnetization magnitude.

The change in coercive force Hc after heat treatment is within ± 5%.

3 is a state diagram showing the change in the coercive force Hc with respect to the heat treatment time, it can be seen that it starts to change from 30 minutes and stabilizes almost constant after 90 minutes. Here, the heat treatment time refers to the time required for heat treatment over the entire surface of the disk.

As described above, the present invention has a stable coercive force Hc in the manufacture of a rare earth-transition metal film, which is a magneto-optical recording material, by performing heat treatment at an appropriate temperature after thin film deposition in order to prevent deterioration of characteristics due to repetitive recording and reproducing operations. In this case, it is possible to prevent deterioration of the disc quality over time when used as an information recording optical disc.

Claims (1)

After forming an amorphous thin film of rare-earth-transition metal, heat-treat it for 30 to 90 minutes immediately above the Curie temperature of the material, and change the coercive force with time within ± 5%, and apply a magnetic field having a certain direction when heating. A method of manufacturing an optical recording medium.

Images