JPS63200345A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To improve the sensitivity of a magnetic disk by laminating an Si layer, protective layer, magnetic layer and protective layer successively on a transparent substrate and forming the Si layer to a prescribed thickness. CONSTITUTION:The Si layer, protective layer, magnetic layer, protective layer and metallic layer are respectively laminated on the transparent substrate. The Si layer has a large refractive index and has an effect of confining light at 50-200Angstrom thickness. The sensitivity thereof decreases when the thickness exceeds the threshold. The magnetic disk having the high sensitivity is thus easily obtd.

Description

[Detailed description of the invention] The present invention relates to a highly sensitive magneto-optical disk.

<Prior Art> In recent years, various bit writing methods using laser light have been studied as high-density recording methods. Among them, a magneto-optical disk has a structure in which a magnetic recording layer, a protective layer, etc. are provided on a substrate, and the recording medium is locally heated with laser light to write 0.1 information as a difference in the direction of magnetization. It is read using the magneto-optical effect. Unlike the perforated type, this method allows for repeated writing and erasing, so it is called a rewritable optical disk, and active development is underway with the aim of putting it into practical use.

The magnetic recording layer is a perpendicularly magnetized film (hereinafter referred to as a magnetic layer) made of a combination of rare earth elements (Gd, Tb, Dy, etc.) and transition metals (Fe, Co) formed on a substrate by vapor deposition or sputtering. obtained by letting

<Problem that the invention seeks to solve> However, the magnetic layer alone (1) Oxidative deterioration is extremely rapid and impractical.

(2) A sufficient magneto-optical effect is not obtained, and the S/N of the reproduced signal is insufficient.

In order to solve these two problems, it is common practice to form the magnetic layer into a sandwich structure with a transparent dielectric film (hereinafter referred to as a protective layer) having an appropriate refractive index and thickness. It is being said. Various compounds have been proposed for this protective layer, such as oxides such as silicon oxide, zirconium oxide, titanium oxide, and bismuth oxide, nitrides such as aluminum nitride and silicon nitride, and sulfides such as zinc sulfide.

However, in recent years, studies have been made to increase the number of rotations of the disk for the purpose of faster access, but in this case, there is a problem that the conventional structure lacks sensitivity. This problem is especially serious when a material with high thermal conductivity, such as silicon nitride or aluminum nitride, is used as the protective layer, and a higher-power, more expensive laser light source is required. In order to improve the medium sensitivity, measures have been taken to change the composition of the magnetic layer, but this method has the disadvantage that the characteristics of the magnetic layer composition change.

Taking the above problems into consideration, the present inventors conducted various studies in order to improve the sensitivity of magneto-optical media, and found that by adding a Si layer of an appropriate thickness between the substrate and the protective layer,
It was discovered that the sensitivity was greatly improved, and the present invention was developed.

That is, an object of the present invention is to provide a highly sensitive magneto-optical disk.

<Means for Solving the Problems> The present invention provides (1) a protective layer (8), a magnetic recording layer, and an insulating layer (It) provided on a transparent substrate to record, reproduce, and erase information using a laser beam; In magneto-optical disks,
The thickness between the transparent substrate and the protective layer (8) exceeds 50,
An object of the present invention is to provide a magneto-optical disk characterized by having a Si layer having a thickness of 200 Å or less.

The present invention will be explained in detail below.

The magneto-optical disk according to the present invention basically has the following laminated structure. That is, transparent substrate/Si layer/protective layer (A)/magnetic recording layer (hereinafter referred to as magnetic [)/protection 11 (1
1)/Metal layer. Two of these are protection 1(A).

(B) may be made of the same material, or may have a composite structure in which two or more different materials are combined. Further, the last metal layer is for providing a car enhancement effect, and is not necessarily required depending on the purpose and characteristics.

Examples of the transparent substrate used in the present invention include ordinary substrates for magneto-optical disks having low birefringence, such as glass, methacrylic resin, and polycarbonate resin.

SiN is formed on this substrate by electron beam evaporation, sputtering, or the like. This SiN has a high refractive index, and its provision creates a light confinement effect, improving the sensitivity of the disk medium.
It has high thermal conductivity and also has the property of reducing sensitivity. Therefore, the effect on sensitivity when a Si layer is provided is expressed as the sum of the above-mentioned reciprocal effects, so the thickness of this film is important. *If the sti is too thin, the light confinement effect will be small; If it is not substantially useful for improving sensitivity, and if it is too thick, the sensitivity and amount of reflected light will be significantly lowered due to the high thermal conductivity and light absorption by Si itself. Therefore, the thickness of SiN is specifically more than 50 and less than 200 Å, preferably 60 to 200 Å.
It is necessary to have 180 people. If within this range, C/N
It is possible to change the sensitivity according to the thickness without reducing the film thickness, etc., but the specific value to be set should be determined by taking into account the required characteristics of the medium such as reflectance and sensitivity. It should be determined within the above range.

The protective layers (^) and (B) used in the present invention include aluminum oxide, zirconium oxide, chromium oxide,
Oxides such as titanium oxide, bismuth oxide, silicon oxide,
Examples include nitrides such as silicon nitride and aluminum nitride, sulfides such as i-lead sulfide and cadmium sulfide, and carbides such as silicon carbide. In particular, as mentioned above, silicon nitride (
The present invention is effective for materials with high thermal conductivity such as SiNx) and aluminum nitride (AINx).

The method for producing these protective layers can be appropriately selected from various thin film forming techniques such as vapor deposition, sputtering, reactive sputtering, and plasma CVD.

The magnetic layer used in the present invention is not particularly limited, and may be made of rare earth elements (Gd, Tb, Dy, etc.) and transition metals (F e + G
o) Combinations can be adopted. These can be obtained by vapor deposition or sputtering using conventional methods for producing alloy thin films. Examples of the combination include TbFe and GdC.

Examples include three-element systems such as , three-element systems such as GdTbFe and TbFeCo, and four-element systems such as GdTbFeCo.

The thickness of these protective layers and magnetic layers is set to a desired value that maximizes the enhancement effect depending on the thickness of the Si layer, but is usually in the range of 100 to 2,000.

The metal layer is provided for the purpose of increasing the apparent Kerr rotation angle, and is not necessarily required, but if provided, metals with high reflectivity such as copper, aluminum, and chromium are suitable. In this case the thickness usually ranges from 200 to 800 people.

<Effects of the Invention> As described above, the sensitivity of the disk of the present invention can be improved by providing an appropriate thickness of 5 il between the substrate and the protective layer (A). By the way, when a magneto-optical disk is put to practical use in -a, for the purpose of making it easier to take it apart, it is necessary to bond the substrate on the above-mentioned laminated structure with an adhesive, or to use both sides. For this purpose, a method is used in which two sheets of the above-mentioned laminated structure are placed face to face and bonded together with an adhesive, but in these cases, a decrease in sensitivity due to heat dissipation through the adhesive layer is unavoidable. The present invention is also particularly effective.

<Example> Hereinafter, the present invention will be explained in detail using Examples.

Example 1 Polycarbonate was used as a substrate, Sk[ was formed by sputtering method, and SiNx was formed by reactive sputtering method.
The layers were deposited sequentially. The film thickness is 31 layers, 60 people, 80 people, 1
The three types of 5iNXji, 5iNXji, are 50% each for the 81 layer thickness to maximize the enhancement effect.
The numbers were 0, 400, and 250.

Approximately 900 TbFe layers are applied as a magnetic layer on these protective layers.
Co N was created by sputtering method. Furthermore, a SiNx protective layer was formed on this layer to a thickness of about 850 mm by reactive sputtering to obtain a recording medium with a four-layer structure.

Optimal recording power (recording power that minimizes the second harmonic) and C/N during playback when recording is performed on these recording media at a rotation speed of 1800 rpm, a recording position radius of 30, and a recording frequency of I MHz. are shown in Table 1.

Comparative Example 1 A recording medium was produced in the same manner as in Example 1, except that instead of having the 31 layer in Example 1, a SiNx layer was formed directly on the polycarbonate substrate by reactive sputtering to a thickness of approximately 850 mm. did.

Comparative Example 2 As an example of the 5ill film thickness in Example 1 being too thick, a Si layer 30 was formed on a polycarbonate substrate by sputtering.
0 people, 5iNIIIil 1 by reactive sputtering method
A recording medium was produced in the same manner as in Example 1 except that 00 persons were formed one after another.

Recording and reproducing tests were also conducted on the recording media of these comparative examples in the same manner as in Example 1. The results are shown in Table 1.

As is clear from the results shown in Table 1, the Si of Comparative Example 1
Compared to the case where N is not provided, in the case where SiN of Example 1 is provided, the optimum power required for recording decreases as the SiN film thickness increases, that is, the recording sensitivity is improved. Further, within this range, almost no change in C/N is observed.

On the other hand, Comparative Example 2 in which the thickness of the Si layer was increased to 300
With those, the reflectance was less than 5%, and sufficient focusing and tracking could not be performed, making recording and reproduction impossible.

Table 1

Claims (1)

[Claims] Protective layer (A), magnetic recording layer, protective layer (B) on transparent substrate
In a magneto-optical disk that records, reproduces and erases information using a laser beam provided with a transparent substrate and the protective layer (
S having a thickness of more than 50 Å and less than 200 Å during A)
Magneto-optical disk characterized by having an i-layer