JPH0622069B2 - Magneto-optical disk - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magneto-optical disk, and more particularly to a magneto-optical disk having a novel dielectric film.

[Conventional technology]

A magneto-optical disk that irradiates a magneto-optical recording medium layer with a light beam to record, reproduce, and erase information can record rewritable information at a high density, and is therefore expected to have a wide range of uses. ing.

As a structure of this type of magneto-optical disk, conventionally, on a transparent substrate formed of a transparent polymer material such as glass, polycarbonate, acrylic, epoxy, polymethylpentene,
The first layer protects the magneto-optical recording medium described below and
Of the information reading light, the light reflected by the magneto-optical recording medium film is internally reflected multiple times (interference) to increase the apparent Kerr rotation angle of the reading reflected light and improve the reproduction C / N ratio (enhancement effect). , SiO ₂ , SiO, CeO ₂ etc. dielectric film, Tb-Fe system, Tb-Fe-Co system, Gd-Tb-Fe as the second layer
A magneto-optical recording medium film having a film thickness of more than 300 Å and a third layer for protecting the magneto-optical recording medium.
Those formed by forming a dielectric film such as O ₂ , SiO, CeO ₂ or a metal film such as Al, Bi, Pb (Japanese Patent Laid-Open No. 59-110056,
No. 59-121368) or on a transparent substrate, as a first layer, a dielectric film for protecting the later-described magneto-optical recording medium, as a second layer a magneto-optical recording medium film having a film thickness of 300 Å or less, and as a third layer. The magneto-optical recording medium film is protected, and the read light of the information transmitted through this film is subjected to multiple reflection (interference) between this film and the metal film described later to increase the apparent Faraday rotation angle of the read light for reading and to reproduce. A dielectric film for improving the C / N ratio (enhancement effect), and a metal film formed as a fourth layer (Japanese Patent Laid-Open Nos. 60-129951 and 60-20).
No. 9947) and the like are known as the most promising ones from the viewpoint of providing a magneto-optical disk which is sufficiently practical.

[Problems to be solved by the invention]

However, in the magneto-optical disk having the above structure,
The prevention of the dropout of the magneto-optical recording information and the improvement of the reproduction C / N ratio have not been completely achieved.

An object of the present invention is to solve these problems and provide a magneto-optical disk which is excellent in both long-term durability and magneto-optical recording / reproducing characteristics and which is sufficiently practical.

[Means for solving problems]

The present invention, in order to achieve the above object, in the structure of the known magneto-optical disk, the composition of the dielectric film as the interference film is LiNbO _x , LiTaO _x , or LiNb _1-y Ta _y O _x (however, A magneto-optical disk characterized by being expressed by 1.5 ≦ x <3 and 0 <y <1. Further, in the present invention, the composition of the dielectric film as the interference film is LiNbO _x , LiTaO _x , or LiNb _1-y Ta _y O
_x (however, 1.5 ≦ x <3, 0 <y <1),
Moreover, the composition of the dielectric film other than the interference film is LiNbO _z , LiTaO _z ,
Or LiNb _1-w Ta _w O _z (however, 1.5 ≦ z <3, 0 <w <
A magneto-optical disk characterized by being represented by 1).

[Work]

In the present invention, the composition of the dielectric film as the interference film is LiNb.
O _x , LiTaO _x , LiNb _1-y Ta _y O _x (provided that 1.5 ≦ x <3, 0
It must be represented by <y <1). (1) This component has a stoichiometric composition ratio (LiNbO ₃ , LiTaO ₃ , LiNb _1-y Ta
_{Since y} O ₃ is stable in a wide range in which the oxygen content is smaller than 0 <y <1), the interference film has a known effect of absorbing oxygen from the outside to prevent oxidation of the magneto-optical recording medium. (2) This dielectric film has a refractive index of 2.2 to 2.4 for light having a wavelength of 600 to 830 nm, and is transparent, so the enhancement effect is utilized. This is because the Kerr rotation angle can be increased and the reproduced signal can be read without fail without reducing the reflectance too much. And
X and y showing the composition of this dielectric are 1.5 ≦, respectively.
Conditions such that x <3 and 0 <y <1 are set. x is 1.5
If less than, the film loses transparency due to lack of oxygen,
The enhancement effect cannot be utilized effectively, and when the ratio is 3 or more, excess oxygen is generated and weakly bonded oxygen contributes to the oxidation of the magneto-optical recording medium, thereby significantly deteriorating the magneto-optical characteristics of this medium.

Further, it is desirable that this dielectric film is formed to have a film thickness of 200 to 1200Å. When the film thickness is less than 200Å, the film non-uniformity due to pinholes and the like increases, and the dropout of information occurs due to the oxidation of the magneto-optical recording medium layer, and the effect of protecting this medium layer is insufficient and the enhancement effect is Not fully exerted. On the other hand, when the film thickness exceeds 1200Å, the variation in the film thickness increases, and the enhancement effect cannot be effectively used.

As the dielectric film or the metal film other than the interference film, any of known films and compositions of the interference film can be used. When the composition of the interference film is used, the composition of the interference film and the composition other than the interference film may be the same or different. And, it is desirable that the film thickness of this layer is formed to 200 Å or more. If the film thickness is less than 200Å,
The non-uniformity of the film due to pinholes and the like increases and the effect of protecting the film of the magneto-optical recording medium cannot be sufficiently obtained.

The film of each layer of the present invention can be formed by high frequency sputtering, direct current sputtering, vacuum deposition or the like.

〔Example〕

Hereinafter, examples of the present invention will be described together with comparative examples and conventional examples.

The first layer and then the second layer were formed on a 1.2 mm thick polycarbonate grooved transparent substrate by high frequency sputtering.
A magneto-optical recording medium film having a composition of Tb _0.27 Fe _0.60 Co _0.13 was further formed as a third layer. Table 1 shows the components, compositions and film thicknesses of the first and third layers in this case.

The magneto-optical disk thus obtained was recorded at a recording frequency of 2 MHz and a laser power of 4 mw and reproduced at a reproducing laser power of 1 mw. The reproduced initial C / N ratio
Relative value A to the case of using SiO as the first layer (Test No. 1, conventional example), and the magneto-optical disk at a temperature of 60.
Table 1 shows the time-dependent C / N ratio regenerated after 1000 hours of exposure in an atmosphere of 90 ° C. and 90% relative humidity, as a relative value B to the regenerated initial C / N ratio in each test.

In each of the examples, the initial C / N ratio relative value was 1.
25 or more, and a relative C / N ratio with time is larger than 0.95, that is, it has very high magneto-optical recording / reproducing characteristics,
A magneto-optical disk excellent in long-term durability has been obtained.
However, in any of the conventional example and the comparative example, a magneto-optical disk having excellent magneto-optical recording / reproducing characteristics and long-term durability has not been obtained.

The present invention is not limited to the configurations of the respective embodiments described above. For example, a configuration in which an ultraviolet curable resin is further applied on the dielectric or metal film as the third layer or the fourth layer, It is possible to realize a structure in which a magneto-optical disk having the structure of the example is opposed to each other to form a facing space with a spacer, and the space is filled with an inert gas.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to provide a magneto-optical disk having extremely high magneto-optical recording / reproducing characteristics and excellent long-term durability.

Further, the magneto-optical disk of the present invention also has the following advantages in manufacturing. That is, the film formation rate of the novel dielectric material of the present invention is about 3 times or more as compared with the case of manufacturing a conventional magneto-optical disk by forming a known dielectric material. Therefore, the influence of the radiant heat from the target or the vapor deposition source on the transparent substrate during the manufacture of the magneto-optical disk can be greatly reduced, and the productivity can be greatly improved.

Claims (2)

[Claims] 1. A magneto-optical disk having a dielectric film as an interference film, wherein the composition of the dielectric is LiNbO _x , LiTaO _x , or LiNb _1-y Ta _y O _x (where 1.5 ≦ x <3 , 0 <y <
A magneto-optical disk characterized by being represented by 1). 2. A magneto-optical disk having a dielectric film as an interference film, wherein the composition of the dielectric is LiNbO _x , LiTaO _x , or LiNb _1-y Ta _y O _x (where 1.5 ≦ x <3 , 0 <y <
1) and the composition of the dielectric film other than the interference film is
LiNbO _z , LiTaO _z , or LiNb _1-w Ta _w O _z (however, 1.5 ≦
A magneto-optical disk characterized in that x <3, 0 <y <1).