JPS6224458A - Photomagnetic disk - Google Patents

Abstract

PURPOSE:To obtain a photomagnetic disk which simultaneously satisfies practicable durability and C/N value by making combination use of a alkali-free glass protective film and thin Kerr-effect enhancement film layer. CONSTITUTION:This disk has an intermediate protective layer consisting of a thin inorg. glass film, photomagnetic recording material layer formed on the intermediate protective layer and surface protective layer consisting of the thin inorg. glass film formed on the photomagnetic recording material layer as necessary. The thin Kerr-effect enhancement film layer is provided between at least one surface of the photomagnetic recording material layer and the protective layer of such high-density information recording carrier. The thin inorg. glass film layer is preferably constituted of the alkali-free glass contg. an alkaline metal just at <=1wt% in terms of an alkaline metallic oxide. The thin Kerr-enhancement effect film is provided with a dielectric layer to increase the apparent Kerr rotating angle by the repetitive reflections thereof. SiO, Al2O3, AlN, ZnS, SiN, etc. are generally used for said film.

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, and particularly relates to The present invention relates to a high-density information storage carrier made of glass that has excellent durability, and further relates to a high-density information recording carrier for magneto-optical recording and reproduction that has excellent magneto-optical properties.

(Prior Art) Regarding magneto-optical disks, the most important technical point at present is how to improve durability, that is, reliability when using a plastic substrate.

In other words, a recording layer formed on a glass 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 penetrating through the plastic substrate. There was a drawback that it could be stored away.

In patent application No. 60-132148 titled "Optical Disk" filed on June 18, 1985, the inventor proposed a thin film of alkali-free glass between the plastic substrate and the recording layer as a method to solve the above-mentioned drawbacks. It was proposed to establish a

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 that a practical C/N value cannot be obtained.

(Object of the Invention) In order to solve the above-mentioned problems, the object of the present invention is to further develop the above-mentioned invention, and to achieve high C/R while maintaining durability.
It is an object of the present invention to provide a magneto-optical disk having a value of N.

(Structure of the Invention) The feature of the present invention is a magneto-optical disk that satisfies practical durability and C/N value at the same time by using the above-mentioned alkali-free glass retention film and Kerr effect enhancement thin film layer together. . 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, a magneto-optical recording material layer formed on this intermediate protective layer, In a high-density information recording carrier using magneto-optical, which has a surface protective layer made of an inorganic glass thin film formed on the magneto-optical recording material layer, which is provided as necessary, at least one of the magneto-optical recording material layers. A Kerr effect enhancement thin film layer is provided between the surface of the protective layer and the protective layer.

The transparent plastic substrate used in the present invention and the high eaves
The information recording layer is made of
Since it is explained in detail in the specification of No. 230, 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 was created by the applicant in 1985.
Patent application entitled ``Optical Disk'' filed on May 18, 1986-1
32148, this inorganic glass thin film layer contains alkali metals, namely Li, Na, K+
It is preferable to use an alkali-free glass containing Rb and Cs in an amount of 1% by weight or less, preferably 0.8% by weight or less in terms of alkali metal urinary oxide.

The above-mentioned alkali-free glass thin film can be formed using any method, for example, multiple Although each component of the above alkali-free glass may be simultaneously vapor-deposited from a vapor deposition source of It is preferable to form it on a plastic substrate using.

The amount of alkali metal is 1% by weight in terms of alkali metal oxide.
If it exceeds, cracks will occur in the recording layer and the BER will increase. The reason for this is not clear, but it is thought that the alkali metal reacts with moisture or monomer passing through the plastic substrate or with moisture in the outside air and deteriorates the recording layer. It is more preferable that the amount of the alkali metal is 0.8% by weight or less in terms of alkali metal oxide, and the smaller the amount is, the more preferable it is as long as it does not impair 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 the content is 1% by weight or less.

Note that the above-mentioned alkali-free glass does not include so-called silicate glass consisting only of sio2.

That is, although it has been well known to deposit 5io2 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 100~2.0O
OX is preferable; if it is less than 100X, the protective role is insufficient, and if it exceeds 2,00X, problems such as laser absorption will occur, and it is also not economical. In the present invention, for example, TbFeC is used as the high-density information recording layer.

It is particularly suitable for application to optical disks using magneto-optical recording materials made of rare earth-transition metal amorphous alloys such as, but the recording layer is susceptible to deterioration due to monomers in plastics, moisture, and/or moisture from the outside. Obviously, it is applicable to all other high-density record carriers using.

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 magneto-optical disks 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 to increase the apparent Kerr rotation angle due to its repeated reflections, and is generally made of Sin, Al2O3, AIN, Zns.

SiN 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.

The present invention will be explained below using Examples. 4.

(Example) As a plastic substrate, the diameter is 130 mm and the thickness is 1.2 mm.
A Japanese 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 form a thin film with a thickness of 500×, and then a Kerr effect enhancement layer was formed. ZnS was made into a 90OA thin film by sputtering, and GdO,1
A recording layer of 2Tb O, 12Fe O, 76 was formed to a thickness of 1000X using the above sputtering apparatus, and a thin film layer of 1000X was formed on top of it by sputtering each of the same inorganic glasses using the same method as above. (Samples A, B, C).

The obtained magneto-optical disk was evaluated by the C/N value (writing frequency - I MHz, resolution bandwidth = 30 KHz) and the C/N value after maintaining the disk at 45°C and 9012H% for 30 days.
Judgment was made based on the amount of change in N, and the results are shown in Table 1.

As a comparative example, a disk (sample D) was prepared in exactly the same manner as in sample A except that the ZnS layer was not formed. The results are also shown in Table 1.

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

(Hereafter, extra white) Table 1

Claims (1)

[Claims] 1) A transparent plastic substrate, an intermediate protective layer formed on this substrate made of an inorganic glass thin film, a magneto-optical recording material layer formed on this intermediate protective layer, and optionally A high-density information recording carrier using magneto-optics, which has a surface protection layer made of an inorganic glass thin film formed on the magneto-optical recording material layer, wherein at least one surface of the magneto-optical recording material layer and the protection layer are provided. A high-density information recording carrier, characterized in that a Kerr effect enhancement thin film layer is provided between the layers. 2) The high-density information recording according to claim 1, wherein the inorganic glass thin film layer is made of alkali-free glass containing less than 1% by weight of alkali metal in terms of alkali metal oxide. 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 Kerr effect enhancement thin film layer is made of SiO, S
The high-density information recording carrier according to claim 1, characterized in that it is made of at least one selected from iO_2, Al_2O_3, AlN, ZnS, and SiN.