JPH0196843A - High density information recording carrier - Google Patents

Abstract

PURPOSE:To simultaneously satisfy practical durability and a C/N by providing a Kerr effect enhancement thin film layer between the surface of a magneto- optical recording material layer and a protecting layer composed of an inorganic glass thin film. CONSTITUTION:On a transparent plastic substrate, an intermediate protecting layer composed of an inorganic glass thin film is formed. The magneto-optical recording layer is formed on the intermediate protecting layer. Further, a surface protecting layer composed of the inorganic glass thin film is formed on the magneto-optical recording material layer as necessary. Between at least one side surface of the magneto-optical recording material layer and the protecting layer composed of the inorganic glass thin film, a Kerr effect enhancement thin film layer is provided, in a high density recording support to use the magneto-optical property of such a constitution. It is desirable that the Kerr effect enhancement thin film layer is composed of chromium oxide. Thus, while a high C/N is maintained, the durability can be further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-density information recording carrier used in an optical recording/reproducing device that records and reproduces information using laser light. The present invention relates to a high-density information recording carrier made of plastic that has excellent properties, and further relates to a high-density information recording carrier for magneto-optical recording and reproduction that has excellent magneto-optical properties.

Conventional technology.

In high-density information recording carriers, the most important technical point at present is the improvement in durability, that is, reliability, when a plastic substrate is used.

In other words, a recording layer formed on a plastic substrate, which has various advantages over a glass substrate, is subject to deterioration or deterioration due to moisture or monomer remaining in the plastic substrate, or moisture entering through the plastic substrate. There was a drawback.

The present inventor is the applicant of the present patent application
No. 61-289560 proposed providing a thin film of alkali-free glass between the plastic substrate and the recording layer as a method for solving the above-mentioned drawbacks.

Although this method surprisingly extends the durability of the optical disk and is completely satisfactory, the magneto-optical effect remains the same as before, so a practical C/N value cannot be obtained.

In order to solve the above-mentioned problem, the present applicant proposed
No. 2-24458, "Magneto-Optical Disk", it was shown that it is possible to provide a magneto-optical disk having a high C/N value while maintaining durability.

In other words, the feature of JP-A-62-24458 is that a Kerr effect enhancement thin film layer is provided between at least the magneto-optical recording material layer and the intermediate protective layer to increase the C/N value. The Kerr effect enhancement thin film mentioned above is Si○
, 5i02, A I 203, AIN, ZnS.

5iNSTi, W.

However, the above-mentioned high-density information recording carriers are no longer able to satisfy the recent strict demands regarding durability.

Problems to be Solved by the Invention The purpose of the present invention is to further develop the above-mentioned invention in order to solve the above-mentioned problems, and to provide high-density information recording that further improves durability while maintaining a high C/N value. The purpose is to provide a carrier.

Means for Solving the Invention The present invention is characterized by a high-density information recording carrier that satisfies practical durability and C/N value at the same time by using the above-mentioned alkali-free glass protective film and Kerr effect enhancement thin film layer in combination. It is in. That is, the high-density information recording carrier according to the present invention includes a transparent plastic substrate, an intermediate protective layer made of an inorganic glass thin film formed on this substrate, and a magneto-optical recording material layer formed on this intermediate protective layer. In the high-density information recording carrier using magneto-optical, the surface protective layer is formed of an inorganic glass thin film on the magneto-optical recording material layer provided according to the method, wherein at least one surface of the magneto-optical recording material layer is provided. A Kerr effect enhancement thin film layer is provided between the protective layer and the protective layer.

The above-mentioned transparent plastic substrate and high-density information recording layer used in the present invention are disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 60-177 filed by the present applicant.
Since it is explained in detail in the specification of No. 449, it will be cited here and the details will be omitted.

Further, the inorganic glass thin film layer constituting the above-mentioned intermediate and surface protective layer used in the present invention is
No. 289560, this inorganic glass thin film layer contains alkali metals, namely Ll, Na, K,
1% by weight of Rb5Cs in terms of alkali metal oxide
Hereinafter, it is preferable that the glass be made of alkali-free glass containing only 0.8% by weight or less.

The above-mentioned alkali-free glass thin film can be formed by any method such as using a plurality of vapor deposition sources so that the alkali metal component is 1% by weight or less, preferably 0.8% by weight or less in terms of alkali metal oxide, on a plastic substrate. Alkali-free glass may be formed by vapor-depositing each component at the same time, but industrially, alkali-free glass with the above characteristics is prepared and then applied to a plastic substrate using physical vapor deposition methods such as vapor deposition, sputtering, and ion blasting. Preferably, it is formed upward.

The amount of alkali metal is 1% by weight in terms of alkali metal oxide.
If it exceeds this, cracks will occur in the recording layer and the BER will increase. Although the reason for this is not clear, it is thought that the recording layer deteriorates due to reaction with moisture or monomer passing through the alkali metal plastic substrate or moisture in the outside air. It is more preferable that the alkali metal pot contains 0.8% by weight or less in terms of alkali metal oxide, and preferably as little as possible without impairing the properties of the glass.

However, industrially it is difficult to reduce the alkali metal content to zero, and there is no practical problem if it is 1% by weight or less.

Note that the above-mentioned alkali-free glass does not include so-called silicate glass consisting only of SiO□.

That is, although it has been well known to deposit 8102 alone as a moisture-resistant protective layer, this silicate glass thin film has almost no moisture resistance.

The thickness of the above alkali-free glass thin film is 100 to 2.00
Preferably, the number is 0. If the number is less than 100, the protective role is insufficient, and if it exceeds 2.00 OA, problems such as laser absorption will occur, and it is also not economical. The present invention is particularly preferably applied to an optical disk using a magneto-optical recording material made of an amorphous rare earth-transition metal alloy such as TbFeCo as a high-density information recording layer. It is clear that the present invention is applicable to all other high-density recording carriers using recording materials that are subject to deterioration due to external moisture or the like.

A feature of the present invention is that a Kerr effect enhancement thin film layer is provided between at least the magneto-optical recording material layer and the intermediate protective layer to increase the C/N value.

Note that the above-mentioned surface protective layer is provided as necessary, and can be omitted when two high-density information recording carriers are bonded together and/or when a moisture-resistant reflective layer is used.

The Kerr effect enhancement thin film itself is known,
Its action is generally to provide a dielectric layer and increase the apparent Kerr rotation angle through repeated reflections.Generally, 5iO1A1203, AIN.

Zn5SSiN or the like is used. These Kerr effect enhancement thin film layers can be formed by well-known physical vapor deposition methods, such as sputtering, and the film thickness varies depending on the material, but is generally 50 to 150 nm.

A further feature of the present invention is that the Kerr effect enhancement thin film layer is comprised of chromium oxide.

In the method for forming the above-mentioned chromium oxide thin film, industrially it is preferable to prepare chromium oxide and form it on a plastic substrate using a physical vapor deposition method such as vapor deposition, sputtering, or ion blasting. Further, as another forming method, forming metallic chromium by a well-known physical vapor deposition method in an oxygen atmosphere also gives good results.

A film thickness of about 50 to 150 nm is suitable as a Kerr effect enhancement thin film, and the optimum film thickness is actually:
Determined by experiment.

Although it is not clear why the durability of a high-density information recording carrier medium is improved when a chromium oxide thin film layer is used as the Kerr effect enhancement thin film layer than when a conventional 5iO1ZriSSSiN etc. is used, it is possible to form a film using the above method. This is thought to be because the chromium oxide thin film produced is dense, and therefore chromium oxide is chemically more stable against corrosion-causing substances than other thin films (SiOlZnS, SiN, etc.). In other words, this seems to be because the provision of the chromium oxide layer can effectively suppress the progress of corrosion of the recording layer due to oxygen, moisture, and the like.

Effects of the Invention As mentioned above, by using an alkali-free glass film as the protective film and a chromium oxide film as the Kerr effect enhancement thin film, it is possible to produce high-density information that further improves durability while maintaining a high C/N value. A record carrier can be provided.

Hereinafter, the present invention will be explained in more detail using Examples.
This does not limit the invention.

The plastic substrate used as an example has a diameter of 130 mm and a thickness of 1.2 mm.
An acrylic substrate (PMMA) and a polycarbonate substrate (PC) were prepared. On these substrates, inorganic glasses having the respective compositions shown in Table 1 were formed by sputtering using a sputtering device (RF magnetron battering device manufactured by Japan Vacuum Technology Co., Ltd.) to a thickness of 500 mm, and then a Kerr effect enhancement layer was formed. Chromium oxide was made into a 900A thin film by sputtering, and Gd was applied on top of it.
A recording layer of 0, +2Tbo, 12Feo, 76 was formed to a thickness of 1000 mm using the above sputtering apparatus, and then each of the same inorganic glasses was sputtered using the same method as above to form a thin film layer of 1000 mm thick. Samples A, B, C).

The obtained high-density information recording carrier was evaluated based on the C/N value (writing frequency = IMl (z, resolution bandwidth = 30 to 7), and 4
The results are shown in Table 1, which was judged based on the amount of change in C/N after being maintained at 5° C. and 90% RH for 30 days and 60 days.

Comparative Example 1 A high-density information recording carrier was fabricated and evaluated in the same manner as in Example D, except that ZnS was formed by sputtering instead of the chromium oxide film as the Kerr effect enhancement thin film in Example.

E, F). The results are shown in Table 2.

Comparative Example 2 A disk (sample G) was produced in exactly the same manner as sample A, except that the chromium oxide layer of the above example was not formed. The results are shown in Table 2.

As can be seen from Tables 1 and 2, when the alkali metal (Na) is 1% by weight or less in terms of alkali metal oxide (Na20), the C/N change amount becomes small and the Kerr effect enhancement layer of the present invention It can be seen that the C/N value can be increased by using a chromium oxide layer.

Table 1

Claims (4)

[Claims] (1) A transparent plastic substrate, an intermediate protective layer made of an inorganic glass thin film formed on this substrate, a magneto-optical recording material layer formed on this intermediate protective layer, and the magneto-optical layer provided as necessary. In a high-density information recording carrier using magneto-optical technology, which has a surface protective layer made of an inorganic glass thin film formed on a recording material layer, there is provided a layer between at least one surface of the magneto-optical recording material layer and the protective layer. A high-density information recording carrier, characterized in that it is provided with a Kerr effect enhancement thin film layer. (2) The high density according to claim 1, wherein the inorganic glass thin film layer is made of alkali-free glass containing only 1% by weight or less of alkali metal in terms of alkali metal oxide. Information record carrier. (3) The high-density information recording carrier according to claim 2, wherein the amount of the alkali metal is 0.8% by weight or less in terms of alkali metal oxide. (4) The high-density information recording carrier according to any one of claims 1 to 3, wherein the Kerr effect enhancement thin film layer is made of chromium oxide.