JPH01236444A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To prevent the corrosion of a thin magnetic material film and to improve durability by forming 1st and 2nd silicon nitride films in such a manner that the degrees of nitridation vary from each other. CONSTITUTION:The 1st silicon nitride film film 2a, the thin magnetic material film 3 and the 2nd silicon nitride film 2b are successively laminated on a transparent substrate 1 in such a manner that the light is irradiated thereon from the transparent substrate side. Further, a supporting substrate 5 is stuck via a adhesive agent film 4 on the 2nd silicon nitride film 2b to obtain the magneto- optical disk. The degrees of nitridation of the 1st and 2nd silicon nitride films 2a, 2b vary from each other. The corrosion of the thin magnetic material film 3 is prevented and the durability is improved by providing a pair of the protective films 2a, 2b consisting of the silicon nitride varied in the degrees of nitridation between the protective film 2a on the incident side in the light incident direction and the protective film 2b on the other side with respect to the two thin protective films 2a, 2b sandwiching the thin magnetic material film 3 in such a manner.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a magneto-optical recording carrier in which a magnetic recording film is an amorphous alloy thin film mainly composed of rare earth metal elements and transition metal elements, and in particular, it is capable of recording, reproducing and erasing information. Na E
-D RAW (Erasable-Dlrect R
The present invention relates to a magneto-optical disk of the eadAfter Vrlte) type.

Background Art Rare earth metal-transition metal alloy thin films formed under certain conditions exhibit uniaxial magnetic anisotropy (easy axis of magnetization) perpendicular to the film surface.
It is known to have Taking advantage of this property, magneto-optical disks made of multilayer alloy thin films have been developed.

The principle of recording and reproducing information on a magneto-optical disk is to first locally heat the alloy thin film to a temperature near its Curie temperature or compensation temperature by focusing a laser beam on the alloy thin film.

At this time, a magnetic field is applied uniformly in the direction perpendicular to the film surface in accordance with the information to be recorded in the heated portion of the alloy thin film, and by utilizing the thermal effect of thermal demagnetization or reversal of magnetic poles, the magnetic field is uniformly applied in one direction. A small reversal magnetic domain is arbitrarily formed within the plane of a film that is magnetized in a similar manner. After that, from the rotation of the eccentric axis and the change in ellipticity of this inverted magnetic domain,
The presence or absence of reversed magnetic domains can be detected as a signal. In this way, the presence or absence of reversed magnetic domains in the magneto-optical disk can be determined by '1', '
By making it compatible with Om, it becomes possible to record and reproduce recorded information. ' Conventional rare earth metal-transition metal alloys, e.g. TbFe
, GdTbFe, TbFeCo, GdC0, etc. are attracting attention as recording film materials for magneto-optical disks because they have a relatively low Keneally point, a low compensation temperature, a high coercive force, and their magneto-optical effect and magnetic properties are suitable as magneto-optical recording materials. and its practical application is progressing.

However, since these alloys are easily oxidized, their properties change over time and deteriorate in a high-temperature, humid atmosphere during laser beam irradiation, resulting in a lack of long-term reliability and stability problems. Therefore, in order to prevent oxidation of the alloy, a protective film is provided between the substrate and the recording film to prevent corrosive substances contained in the substrate and oxygen that has passed through the substrate from the atmosphere.
A structure is adopted that blocks corrosive substances such as moisture.

For example, the structure of the conventional magneto-optical disk is
As disclosed in Japanese Patent No. 2-27458, a magneto-optical disk as shown in the enlarged partial sectional view of FIG. 3 is known. Such a magneto-optical disk has a protective film 12 made of transparent silicon nitride and a thin magnetic film 13 made of TbDyFe, GdTbFe, etc. stacked in this order on the main surface of a transparent substrate 11 made of glass, synthetic resin, etc. , magnetic thin film 13
It has a structure in which a support substrate 15 is attached thereon via an adhesive film 14. As described above, rare earth-transition metal-based magnetic thin films are susceptible to rust and have durability problems, and therefore require a protective film. As shown in FIG. 3, laser light 8 generally enters through a substrate 11 and a protective film 12 and is reflected by a magnetic thin film 13. Therefore, the protective film 12 is made of a transparent material and made of Si3N4.
In addition to 5iQ2. S10. ZnS etc. are used.

However, silicon nitride Si3 NJ is used as a protective film.
When using , the adhesion between the substrate and the protective film and between the protective film and the magnetic thin film is weak and the mechanical bond is unbalanced. Therefore, pinholes are likely to occur during film formation, resulting in peeling of the substrate and protective film or cracking of the magnetic thin film. Further, when used as a magneto-optical disk, there is a drawback that the error rate is extremely deteriorated by irradiation with laser light or the like during long-term recording and reproduction, and durability is reduced.

SUMMARY OF THE INVENTION In order to eliminate such drawbacks, the purpose of the present invention is to provide a rare earth-transition metal magneto-optical material that maintains the Kerr rotation angle during playback and has durability and reliability for long-term storage with little change in characteristics over time. The goal is to provide discs.

The magneto-optical disk of the present invention has a first disk on a transparent substrate.
a silicon nitride film, a magnetic thin film having an axis of easy magnetization perpendicular to the film surface made of an amorphous rare earth metal-transition metal alloy;
The magneto-optical disk is formed by sequentially stacking a second silicon nitride film, and is characterized in that the degrees of nitridation of the first and second silicon nitride films are different from each other.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an enlarged partial sectional view of the magneto-optical disk of this embodiment. Such a magneto-optical disk includes a first silicon nitride film 2a, a magnetic thin film 3, and a second silicon nitride film 2b on a transparent substrate 1 so that light is irradiated from the transparent substrate side.
It has a structure in which these are laminated in order. Further, a support substrate 5 is attached onto the second silicon nitride film 2b via an adhesive film 4 to obtain a magneto-optical disk. The degrees of nitridation of the first and second silicon nitride films 2m and 2b are different from each other.

Silicon nitride alone is S LN, S i3 NJ,
5i2N2, but in the form of a thin film formed by sputtering or the like, it can be expressed as 5iNx (degree of nitridation: x) by the presence of silicon and nitrogen.

In the magneto-optical disk of this embodiment, the substrate 1. A polycarbonate injection substrate is used as the support substrate 5, and an organic adhesive is used as the adhesive 4. The material of the substrate 1 may be glass or synthetic resin as long as it is a transparent and flat disk. A guide groove for guiding the laser beam 8 may be formed in advance on the main surface of the substrate.

In this example, since the difference in thermal expansion between the substrate, silicon nitride, and rare earth-transition metal alloy is large, the interface direction of the substrate-protective film and protective film-magnetic thin film that occurs during reproduction and recording using laser light. In view of the fact that repeated partial strain accelerates the deterioration of each thin film, it was decided to sandwich a magnetic thin film between the first and second silicon nitride films and to make these silicon nitride films have different degrees of nitridation. Therefore, we focused on the difference in the degree of nitridation between the first protective film 2a and the second protective film 2b that sandwich the magnetic thin film 3. Four types of magneto-optical disks were prepared as Examples and Comparative Examples as shown in Table 1 by varying the degree of nitridation of the J2 silicon nitride film and using a known thin film deposition method.

In addition, the values in the table are XPS (Xray Photo
electron spectroscopy: AI
When the binding energy intensity of the core electrons of silicon nitride was measured by Ka-X-ray photoelectron spectroscopy),
Photoelectron spectrum of nitrogen N15 (binding energy 397
eV±2eV) and photoelectron spectrum of silicon 5i2p
(bonding energy 101eV±2eV) and the peak integrated intensity ratio Nls/5L2p, which is the nitridation degree X of SiNx
is expressed relatively.

Figure 2 shows the 70'C-9 of each of the obtained magneto-optical disks.
The graph shows the change in bit error rate over time in a constant temperature and humidity test at 0%. The vertical axis shows the bit error rate, and the horizontal axis shows the elapsed time since the magneto-optical disk was manufactured. In the graph, ◇ is for Comparative Example 1, ◎ is for Comparative Example 2
, O indicates a plot of each bit error rate of the first embodiment, and Δ indicates a plot of each bit error rate of the second embodiment.

As shown in FIG. 2, Examples 1 and 2 have little deterioration in error rate, and in particular, Example 1 shows almost no deterioration. Further, the number of visually visible pinholes after film formation is also very small compared to other comparative examples. In the conventional silicon nitride protective film, the X (nitridation degree) of SiNx is not limited, but according to Example 1, the peak intensity ratio of the first protective film is 1.9±0.
．． 2, and the peak intensity ratio of the second protective film is 1.3.
It has been found that the most preferable durability of the magneto-optical disk can be obtained when the value is within the range of ±0.2.

Effects of the Invention As described above, according to the present invention, two protective thin films sandwiching a magnetic thin film are nitrided so that the degree of nitridation is different between the protective film on the incident side and the protective film on the other side in the direction of light incidence. Since the pair of protective films made of silicon is provided, it is possible to obtain a magneto-optical disk in which corrosion of the magnetic thin film is prevented and durability is improved.

[Brief explanation of the drawing]

FIG. 1 is an enlarged partial cross-sectional view of a rare earth-transition metal-based magneto-optical disk according to the present invention, FIG. 2 is a graph showing changes over time in the bit error rate of the optical disk according to the present invention in a constant temperature and humidity test, and FIG. 3 is a conventional FIG. 2 is an enlarged partial cross-sectional view of the optical disc of FIG. Explanation of symbols of main parts 1...Substrate 2a...First protective film 3...Magnetic thin film 2b...Second protective film 4... ... Adhesive layer 5 ... Support substrate applicant Pioneer Corporation

Claims (3)

[Claims] (1) On a transparent substrate, a first silicon nitride film, a magnetic thin film made of an amorphous rare earth metal-transition metal alloy and having an axis of easy magnetization perpendicular to the film surface, and a second silicon nitride film are laminated in order. 1. A magneto-optical disk comprising: a magneto-optical disk, wherein the first and second silicon nitride films have different degrees of nitridation. (2) The magneto-optical disk according to claim 1, wherein the degree of nitridation of the first silicon nitride film is greater than the degree of nitridation of the second silicon nitride film. (3) Peak integrated intensity ratio Nls/Si of the first silicon nitride film at the binding energy of core electrons measured by AlKα-X-ray photoelectron spectroscopy, which indicates the degree of nitridation of the silicon nitride film
2p is in the range of 1.9±0.2, and the peak intensity ratio Nls/Si2p of the second silicon nitride film is 1.3±0.
3. The magneto-optical disk according to claim 2, wherein the magneto-optical disk is 2.