JPS62192040A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To improve recording and erasing sensitivity without deteriorating in corrosion resistance of a recording medium by forming a protective layer to be provided between a substrate and optical recording layer into a continuous film having specific thickness. CONSTITUTION:The protective layer 3 consisting of a ZnS film or the like, the optical recording layer 4 consisting of a GdTbFe film or the like and if necessary, an auxiliary protective layer 5 are laminated by a method such as vapor deposition or sputtering on the light transmittable substrate 1 consisting of a plastic or coated with the plastic. The protective layer 3 is formed to the continuous layer having <=1,000Angstrom thickness. The recording and erasing sensitivity is improved by reducing the film thickness of the protective layer 3 in the above-mentioned manner; in addition, the satisfactory corrosion resistance is provided to the medium by forming the protective layer into the continuous film having no pinholes.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording medium in which recording and erasing are performed by R temperature generated by irradiation with various energy rays such as laser light.

(Problems to be Solved by the Invention) [Prior Art] In recent years, research and development of optical memory devices using laser light as high-density, large-capacity memories has been carried out at a rapid pace.In particular, magneto-optical recording has attracted attention as an old rewritable recording method, and the optical magnetic recording medium used for this recording is highly anticipated as a rewritable optical memory element.

Conventionally, the material constituting the magneto-optical recording layer of an optical-magnetic recording medium used for such magneto-optical recording is 1 nB.
Typical examples include i, f-, garnet type, and rare earth-transition metal amorphous type. Mn1l
The i-type has a high Curie temperature, so it requires a high-power laser for recording, and it has a lot of grain boundary noise, which makes it impossible to reproduce with a high S/N ratio. Because of its high transmittance, it had the disadvantage of requiring a high-power laser for recording. Among these, the rare earth-transition metal amorphous system has a low Curie temperature and relatively low light transmittance, and is therefore expected to compensate for the drawbacks of both.

This type of technology will be described in more detail below with reference to the drawings.

FIG. 4 is a schematic cross-sectional view of a typical conventionally used optical magnetic recording medium.

In FIG. 4, 1 is polymethylmethacrylate-1=(
62 is a light-transmitting substrate made of plastic such as PMMA), polycarbonate, or glass, and is generally a plate-shaped substrate of various shapes such as a donut shape. Currently, rare earth-transition metal amorphous systems such as TbFe, GdTbFe, and TbFeGo are widely used.

Recording/writing/erasing information on such an optical magnetic recording medium is generally performed as follows.

First, the recording medium is magnetized in a certain direction perpendicular to the substrate 1, and then a spot of laser light is irradiated from the substrate 1 side.

The magnetization direction may be any desired direction as long as it is constant. The laser beam irradiated onto the substrate 1 passes through the substrate 1 and reaches the magneto-optical recording layer 2 . As a result, absorption of light occurs in the part of the magneto-optical recording layer 2 where the laser beam 1 (q) is irradiated, and this part reaches the Curie point or more of the layer constituting material due to a local increase in humidity, and the magnetization disappears. When a magnetic field is applied in the opposite direction to the recorded magnetization direction to the part where the magnetization has disappeared, the magnetization is reversed in the part, and a reversed magnetic domain is formed whose magnetization direction is different from that of the part not irradiated with the laser beam. Information is recorded. To erase the record, the recorded portion of the magneto-optical recording layer 2 is re-irradiated with laser light to increase the temperature by 1" above the Curie point, and magnetize the recorded portion in the opposite direction to that at the time of recording. This is done by returning the magnetization direction to the recording start state by applying .

To reproduce recording, a laser beam whose power is lowered to such an extent that the temperature of the magneto-optical recording layer 2 does not rise above one Curie point is applied to the substrate 1.
This is done by irradiating from the side and reading the magnetization direction of the recorded portion using the magnetic Kerr effect or the like.

Magneto-optical recording media such as those mentioned above, especially those that use a rare earth-transition metal amorphous thread alloy for the magneto-optical recording layer and plastic for the substrate, are susceptible to corrosion due to oxygen, moisture, etc. that enter through the substrate. In order to prevent this and improve corrosion resistance, there is a layer of 540 mm between the substrate and the recording layer.
It has been common practice to provide a protective layer of an inorganic material such as , 5i02, N2, ZnS, or the like. In this case, the thickness of the protective layer was on the order of several thousand to obtain sufficient corrosion resistance.

However, inorganic materials have higher thermal conductivity than plastics9, and the thermal energy absorbed by the magneto-optical recording layer due to laser beam irradiation is mainly released to the protective layer, causing a decrease in the temperature of the magneto-optical recording layer, resulting in recording. The drawback was that it caused a decrease in sensitivity. In order to improve the recording sensitivity, a laser beam with higher power is required, but there is a limit to the power due to economic considerations and the durability of the recording medium.

The present invention was made in view of the problem described in F, and its purpose is to improve recording sensitivity while maintaining sufficient corrosion resistance.
- An object of the present invention is to provide an optical recording medium that can perform

[Means for solving problems]

In order to achieve the above object, the present inventor has repeatedly researched the corrosion resistance of optical recording media having protective layers and recording layers made of various materials, and found that setting the thickness of the protective layer to 1000 Å or less is possible. It has been found that this method is extremely effective for improving recording/erasing sensitivity. We also discovered that if the protective layer is a continuous film rather than a discontinuous film in the form of islands, there will be no 1TQ difference in corrosion resistance depending on the difference in the thickness of the protective layer, which led us to complete the present invention. Ta.

That is, the present invention provides a plastic substrate or a substrate covered with plastic, an optical recording layer formed on the substrate and in which recording is performed using temperature increase due to absorption of optical energy, and 11 "recording". J, an optical recording medium comprising a protective layer of jHH% mechanical material provided between the plate and the optical recording layer, wherein the protective layer has a thickness of 1000 mm.
This is an optical recording medium characterized by being made of a continuous film with a thickness of Å or less.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing a basic aspect of the optical recording medium of the present invention.

In FIG. 1, 1 is a transparent substrate made of various plastic materials such as PMMA and polycarbonate, or a transparent substrate formed by coating an inorganic material such as glass quartz with a plastic material. Usually, the shape of the substrate 1 is disk-shaped, but it is not particularly limited.
It can be whatever you want. 3 is a protective layer that satisfies the above requirements. The constituent material of the protective layer 3 is SiO, 5i02.
ON, SiN.

Si(:, ZnS, UN, SrF2.CeF2.Z
One type of inorganic material such as n5e, GeSe, etc., or a mixture of two or more of these can be used. The protective layer 3 may be composed of a multilayer film of two or more layers.

In more detail, the protective layer 3 is a continuous pattern, except for local pinholes caused by dust or scratches on the substrate, or dust adhering during film formation.
This refers to a film that does not have pinholes.

4 is an optical recording layer, the material of which is TbFc.
, GdTbFc, TbFc(:a, GdTbF
Rare-class I transition metal amorphous systems such as eCo are preferably used. It is also possible to use MnB11 of time luck, garnet type, etc., and +A- due to absorption of light energy.
It is sufficient if recording can be done by using m. Reference numeral 5 denotes an auxiliary protective layer for protecting the optical recording layer 4 from oxygen, moisture, etc. entering from the opposite direction of the substrate 1. It is desirable that the auxiliary protective layer 5 also satisfy the same requirements as the protective layer 3, but in the present invention, it is particularly important to avoid the disadvantages that occur when the inorganic protective layer 3 is provided between the substrate 1 and the optical recording layer 4. Since we are focusing on overcoming the
There is no particular limit as to whether or not the installation is done and the material.

The method for laminating the protective layer 3, optical recording layer 4, and auxiliary protective layer 5 on the substrate 1 is not particularly limited, but specific examples include vapor deposition, CVD, sputtering, ion Typical examples include film forming methods such as the brating method.

The protective layer 3 can be formed as a continuous film by appropriately selecting one or more of the film forming method and its film forming conditions, but the film thickness of the protective layer 3 should be 500 Å or more. Generally, a continuous film can be formed using the above method.

(Example) Hereinafter, the present invention will be explained in more detail based on Examples.

Example 1 An optical recording medium similar to that illustrated in FIG. 1 was prepared.

A protective layer 3 with a thickness of 5 is formed on a polycarbonate substrate 1.
A ZnS thin film of 0.00 was formed by vacuum evaporation. Then on top of that II! An optical recording layer 4 made of a GdTbFe thin film with a thickness of 2% and 1000% was formed by a sputtering method, and an auxiliary protective layer 5 made of a thin SiO film with a thickness of 3000% was further formed on it by a vacuum evaporation method. An optical recording medium was obtained. The above method was repeated to prepare a plurality of similar optical recording media.

These recording media have different output beam diameters: 1.
The anticonductor laser beam focused on 5 μ is lo(l ns (
The irradiated area was irradiated for a nanosecond) and the irradiated area was observed under a polarizing microscope to determine whether recording had taken place. As a result, the minimum laser power required for recording is 3.
It's 5mW.

Next, the A stern of protective layer 3 was made with 50 people, 100 people, 200 people, 300 people, 400 people, 600 people, 800 people, 1000 people, 1200 people, and 1500 people, respectively, and the rest was the same as the above method. Ten types of optical recording media were produced and the minimum laser output necessary for recording was investigated. The results are summarized in FIG. 2 as white dots (0). Furthermore, these optical recording media were left in an atmosphere of 60° C. and 90% humidity for 1000 hours, and the rate of decrease in coercive force was examined. The results are collectively shown in FIG. 3 as white dots (0).

Example 2 Eleven types of optical recording media were produced in the same manner as in Example 1, except that SiN was formed by sputtering as the protective layer 3, and the minimum laser output necessary for recording was investigated. The results are shown in FIG. 2 as black dots (.). Furthermore, these optical recording media were placed in an atmosphere of 60°C and 90% humidity for 100°C.
After leaving it for 0 hours, the rate of decrease in pedal holding force was examined. The results are shown in FIG. 3 as black dots (.).

From FIG. 2, it can be seen that when the protective layer 3 has a thickness of 1000 Å or less, the recording sensitivity is good regardless of the material (pattern L). From FIG. 3, when the protective layer 3 is made of ZnS, the coercive force decreases significantly at a thickness of 400 Å or less, and when the protective layer 3 is made of SiN, the coercive force decreases significantly at a thickness of 300 Å or less.
Below Å, the coercive force decreases significantly (Nekoguyu).

[Reference Example] On the same substrate as used in Example 1, only a ZnS film (same material as the protective layer in Example 1) was deposited with a thickness of 300, 400, or 500 layers using the same method as in Example 1. 3.
Seed samples were prepared. Similarly, SiN is applied to the substrate -F.
Three types of samples having IIQ (same material as the protective layer of Example 2) were prepared. When each sample was observed with an electron microscope, the thickness of the ZnS film was 400 Å or less, and the thickness of the SiN film was 300 Å.
It became a discontinuous film below.

From the results of the reference examples and the pattern patterns obtained in the examples, it can be said that the corrosion resistance of the optical recording layer medium is good if the protective layer 3 is a continuous film.

〔Effect of the invention〕

As explained above, according to the present invention, it has become possible to provide an optical magnetic recording medium with excellent storage stability and improved recording sensitivity.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the basic aspect of the optical recording medium of the present invention, and FIG. 2 is a schematic cross-sectional view showing the optical recording medium of the embodiment according to the present invention and the conventional optical recording medium of the comparative example. FIG. 3 is a diagram showing the change in coercive force of both of the optical recording media, and FIG. 4 is a schematic cross-sectional view of a conventional optical magnetic recording medium. l...Substrate, 2...Magneto-optical recording layer, 3...Protective layer, 4...
Optical recording layer, 5...auxiliary protective layer.

Claims (1)

[Claims] 1) a plastic substrate or a substrate covered with plastic; an optical recording layer formed on the substrate and recording using temperature increase due to absorption of optical energy;
An optical recording medium comprising a protective layer of an inorganic material provided between the substrate and an optical recording layer, wherein the protective layer is a continuous film having a thickness of 1000 Å or less. recording medium.