JPS6134747A - Photoelectromagnetic multilayered film medium - Google Patents

Abstract

PURPOSE:To obtain the titled compact recording medium with improved recording, reproducing, and erasing performances of information and especially with improved S/N by constituting the protective film or the interference film of a photoelectromagnetic recording medium, wherein a protective film, a photoelectromagnetic recording film, and an interference film, if necessary, are provided on a substrate, of a transparent semiconductor film. CONSTITUTION:An amorphous photoelectromagnetic recording layer of Tb25Fe85 etc. is provided directly on a transparent substrate of glass, polymethyl methacrylate or on an interference film which is formed on the substrate as required. A protective layer is provided on the recording layer to form a photoelectromagnetic multilayered film medium. The interference layer or the protective layer is formed of an element semiconductor film of Ge, amorphous Ge-Si, and amorphous carbon, and oxide film among Y2O3, Ta2O5, SiO2-TiO2, LiNb2O3, etc., a sulfide film of CdS, etc., a boride film of ZrB2, etc., a carbide film of SiC, a nitride film of BN, etc., and a semiconductor film of an intermetallic compd. such as GaAs or a transparent organic material film such as polyvinyl carbazole having >=200 deg.C vitrification temp. Consequently, a recording medium with improved photoelectromagnetic characteristic and S/N and having excellent durability is obtained.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to magneto-optical recording for recording, reproducing, and erasing information using laser light, and particularly improves the figure of merit and improves reproduction speed.
The present invention relates to a magneto-optical multilayer film medium with improved /N ratio.

[Background of the invention]

Increasing amount of information 2 As devices become more compact, recording density will continue to increase, and magneto-optical recording, which has high density, large capacity, and allows arbitrary reading and rewriting of information, has recently been attracting attention. In magneto-optical recording, a magnetic thin film (perpendicular magnetization film) with an axis of easy magnetization perpendicular to the film surface is used, and by creating reversed magnetic domains at arbitrary positions with a light beam, the direction of magnetization can be adjusted. then it 1
ip.

110 #l binary information is recorded. On the other hand, reading out a binary signal that has undergone such inversion recording is usually done using a polar
・Use Kerr effect or Faraday effect.

Conventionally, perpendicularly magnetized films such as MnB1-based crystalline films and rare earth-transition metal-based amorphous thin films have been proposed as these magnetic thin films for magneto-optical recording. For example, there is one described in the 7th Japanese Society of Applied Magnetics Academic Lecture Abstracts (1983, 11), p. 224. Among them, rare earth-transition metal-based amorphous thin films have no grain boundaries, have low media noise, and are easy to manufacture over large areas, so their current availability is considered promising. However, in the method of reading information from these amorphous perpendicularly magnetized films using reflected light and transmitted light through the polar Kerr effect and Faraday effect, the Kerr rotation angle or Faraday rotation angle of the film itself is small. , playback signal (S/N
Another disadvantage is that the C/N ratio is low. Therefore, in order to increase the level of this reproduced signal, S10 was used as an interference film.
- S iO2t T 102 .

Bi, O,, ZrO,, Si, a-8t, AQN+Si
Attempts have been made to improve the S/N ratio by combining thin films such as , N4, and amorphous perpendicularly magnetized films to form a multilayer structure. In addition, rare earth-transition metal-based amorphous films are easily oxidized, resulting in deterioration of characteristics, so SiO
,,AnN.

Si, N, etc. are also used as a protective film.

However, in the multilayer film structure reported above, although the Kerr rotation angle increases by about 1.5 times, the reflectance of the medium itself decreases to about 20% or less compared to the case of a perpendicularly magnetized film alone. As a result, there is a problem that either a large increase in reproduction S/N ratio cannot be obtained, or the life of the protective film is short, and the characteristics of the perpendicularly magnetized film itself deteriorate due to oxidation or the like.

The purpose of the present invention is to use a semiconductor thin film that is dense, hard, and has a high refractive index, or a transparent organic substance with a vitrification temperature of 200°C or higher as an interference film and/or a protective film, thereby creating a film that is sufficiently suitable for practical use with little change over time. The object of the present invention is to provide a magneto-optical multilayer film medium with a high S/N ratio.

[Summary of the invention]

The structure of the present invention for achieving the above object uses Qe, amorphous Ge-
Elemental semiconductor film selected from Si, amorphous carbon, diamond thin film, Y2O,l, AQ20. ,'Ta
2O,,,Nb2O5tZnO, Bad, MgO, Cr
2O,,Fe,O,.

Ferrite, pbo, Sin, -Tie.

S' i 0 , - T a 20 , , PbTi0
．． , LiNb0. , LiTaO3゜BaTiO3
oxide film selected from CdS, sulfide film selected from PbS, tetrapolide g Z r B 2pTiB2
A boride film selected from S i C* Ba Ct A carbide selected from aluminum carbide, BN.

A semiconductor thin film such as a nitride film selected from TiN, ZrN, NbN, VN, and TaN, and an intermetallic compound such as GaAs is used.

Generally, magneto-optical recording media are glass or PMMA.

It has a multilayer film structure in which a perpendicularly magnetized recording film is sandwiched between an interference film and a protective film using a substrate made of UV or AQ, etc., on which a perpendicularly magnetized film is sandwiched between an interference film and a protective film by sputtering or vapor deposition. Information is recorded and reproduced by applying semiconductor laser light from either the substrate side or the recording film side opposite to the substrate. Therefore, the interference film must be transparent to the semiconductor laser light.
The protective film also needs to be transparent when used as an interference film.

In general, the main cause of deterioration of the characteristics of rare earth-iron group amorphous recording films is oxidation, so as a protective film, it is recommended to use a dense, hard, highly transparent, and stable protective film with excellent oxidation resistance and corrosion resistance. A suitable membrane is required. On the other hand, since the refractive index n of commonly used transparent disk substrates (glass, UV, PMMA, etc.) is about 1.5, in order to amplify the Kerr rotation angle with an interference film, n is about 1.5. It is desirable to use a film with good transparency, which is different from 5. In order to further amplify the Kerr rotation angle, a transparent film with a large n is desirable.

Therefore, in order to obtain a film that satisfies these conditions, the present inventors used glass as a substrate and a typical Tb-Fe amorphous film as a recording film, and sputtered various single element or compound films. The above-mentioned multilayer film structure was formed using a method or a vapor deposition method, and the interference effect of the Kerr rotation angle as a magneto-optical recording medium, changes over time, etc. were evaluated. As a result, it was found that the semiconductor thin film shown below has better corrosion resistance and oxidation resistance than conventional materials, and the amplification factor of the Kerr rotation angle is more than twice as large. It turned out to be extremely good.

The semiconductor thin film is described below.

(1) Ge, a-Go, S 1 as an elemental semiconductor film
x (0<x<1), a-c (amorphous carbon), diamond thin film.

(2) Y, Oa, AQ, O, as oxides.

Ta205l Nb2O5tZnot Bad.

Mg0gCr20. p F Iil x On p
Ferrite.

PbO,Sin,-Tie,,Sin,-T a ,
O,, PbTi0jt LiNb0i * LiTa0
a saTiOa (3) Sulfide: CdS, Pb5 (4) Boride: ZrB2. TiB2. As tetrapolide (5) carbide, S i C, B4Ct 7/L/
As micarbide (6) nitride, B N, T i N, Z r
N, N b NV N y Ta N (7) As an intermetallic compound, Ga As and transparent organic substances such as polyvinyl carbazole and its derivatives are formed by vapor deposition and as an interference film and/or a protective film. It was found that the same effect as the above semiconductor thin film can be obtained.

[Embodiments of the invention]

The present invention will be explained in detail below with reference to Examples.

[Example 1] The thin film described in claim 2 of the patent was formed as an interference film to a thickness of 20 to 150 nm on a glass substrate with a thickness of 0.3 am and a diameter of 10 mm by sputtering or vapor deposition. A magneto-optical recording medium was produced by disposing a T b 15F ets amorphous film thereon by the same sputtering method or vapor deposition method. Using these magneto-optical recording media, the interference effect of the interference layer film was measured by irradiating He--Ne laser light (wavelength λ = 633 nm) from the glass substrate side. At this time, the interference film was produced by aiming at a film thickness d (=λ/4n, where refractive index) is expected to have the largest interference effect for each thin film.

As a result, the Kerr rotation angle of the Tb Fe amorphous film was 0.2 to 0.25° without the interference layer, but when the above interference layer was formed, the Kerr rotation angle increased by more than twice. It was found that it is suitable as an interference film. FIG. 1 is a schematic diagram as an embodiment of the present invention and a schematic characteristic diagram using the same. In the figure, the sample medium was formed by forming various transparent interference film layers with different film thicknesses d on a glass substrate, and disposing an amorphous film with a thickness of ~1000 T b 25 Fe ts on top of it. . Using the multilayer film medium, He-Ne laser light (λ = 63-3 nm) was emitted from the glass substrate side.
The graph shows the change in the Kerr rotation angle θ measured by irradiating the interference film with respect to the thickness of the interference film. In the figure, 1 represents the Ge film, 2 represents the Ta, O, film, 3 represents the SiC film, 4 represents the MgO film, 5 represents the Aρ203 film, and 6 represents the dependence of the Kerr rotation angle on the film thickness d of the BN film. As is clear from the figure, by optimizing the thickness d, the Kerr rotation angle can be increased by about twice or more.

[Example 2] An interference film, Tb Fe, was formed on a glass substrate with a thickness of 1.4 m+a and a diameter of 10 mm (7) by sputtering or vapor deposition.
An amorphous 25 7s film and a protective film were formed in this order, and the stability of the film properties of these media was examined. Both the interference film and the protective film have a thickness of about 1000 people, Qe, a-c, Ta, 05. MgO.

PbTi0g, CdS, ZrB2. Sac, B.N.

A film of TiN or the like was used, and the thickness of the TbFe amorphous film was also about 1000. The thus produced multilayer film medium was subjected to an accelerated test in an atmosphere at a temperature of 60° C. and a humidity of 95% to examine changes in Kerr rotation angle over time. As a result, the media using the conventional 840□ membrane deteriorated by more than 10% after two months, while the deterioration of the media using the above membrane was about 5%.
It turned out to be extremely small.

[Example 3] Using a glass substrate with a thickness of 0.3 aIll and a diameter of 10II + 1φ, a polyvinyl carbazole (thickness of 850 mm) -T bss F f3ts amorphous film (thickness ~ A magneto-optical multilayer recording medium was prepared by forming films in the order of 1,000 people) and polyvinyl carbazole.

The Kerr rotation angle measured from the glass substrate side of these multilayer film recording media is as high as 0.41 degrees (H e -N e laser wavelength), and T b2s F e,, in the case of a single amorphous film (θ
, = 0.22 degrees), a value approximately twice as high was obtained. In addition, when we conducted an accelerated test in an atmosphere with a temperature of 60°C and humidity of 95%, the deterioration of the Kerr rotation angle was approximately 5% even after 2 months.
or less, indicating high weather resistance.

〔Effect of the invention〕

As is clear from the above explanation, when the transparent semiconductor thin film of the present invention and the transparent organic thin film with a vitrification temperature of 200°C or higher are used as an interference film and/or a protective film of a magneto-optical recording medium, the Kerr rotation angle amplification effect can be achieved. It was found that the film had a large surface area, and also had excellent thermal stability, corrosion resistance, and oxidation resistance, and was found to be extremely excellent as a constituent film of a magneto-optical recording medium.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view as an embodiment of the present invention, and a diagram showing the relationship between the thickness d of the interference layer and the Kerr rotation angle θ when various transparent semiconductor films are used as the interference layer. It is.

Claims (1)

[Claims] 1. A magneto-optical multilayer film medium comprising a magneto-optical recording medium film, a protective film and/or an interference film, and a substrate, characterized in that the protective film and/or interference film is a transparent semiconductor thin film. Magneto-optical multilayer film media. 2. In claim 1, as the protective film and/or interference film, Ge, amorphous Ge-S
i, amorphous carbon, elemental semiconductor film selected from diamond thin film, Y_2O_3, Al_2O_3, T
a_2O_5, Nb_2O_5, ZnO, BaO, Mg
O, Cr_2O_3, Fe_2O_3, ferrite, P
bO, SiO_2-TiO_2, SiO_2-Ta_2
O_5, PbTiO_3, LiNbO_3, LiTaO
_3, oxide film selected from BaTiO_3, CdS,
Sulfide film selected from PbS, tetrabolide, ZrB
_2, boride film selected from TiB_2, SiC, B_
4C, carbide selected from aluminum carbide, BN, T
A magneto-optical multilayer film medium characterized by using a semiconductor thin film such as a nitride film selected from iN, ZrN, NbN, VN, and TaN, and an intermetallic compound such as GaAs. 3. A magneto-optical multilayer film medium according to claim 1, characterized in that the protective film and/or the interference film is made of a transparent organic substance with a vitrification temperature of 200° C. or higher.