JP2550698B2 - Magneto-optical recording medium - Google Patents

Description

The present invention relates to a magneto-optical recording medium for recording information magneto-optically using laser light and reading the recorded magnetic information by utilizing the magneto-optical effect. Regarding

[Conventional technology]

In recent years, the practical application of rewritable magneto-optical memory has been considered promising. A magneto-optical recording medium used in this magneto-optical memory is made of a transition metal amorphous material containing a rare earth element such as TbFeCo, and a perpendicularly magnetized thin film having an easy axis of magnetization in a direction perpendicular to the disk surface is made of glass, It is formed on a substrate such as resin. Information is recorded by thermomagnetic writing on the magnetic thin film with laser light, and recorded information is reproduced by the reflected light from the magnetic thin film due to the magnetization optical polar Kerr effect. This is done by detecting the rotation of the polarization plane (Kerr rotation).

[Problems to be Solved by the Invention]

However, the Kerr rotation angle θk of the magnetic thin film currently used as the perpendicular magnetization thin film is 0.3 ° to 0.4 °, and the modulation degree is small at about 1% depending on the recording bit of the reproducing light, and the read CN ratio at the time of reproducing is sufficient. Not being a problem. Play CN
It is reported that the ratio of the medium is constant if the ratio is 40 dB or more, and it is said that the ratio is preferably 45 dB or more to improve reliability. Therefore, when the dielectric film such as Si ₃ N ₄ or AlN is placed between the magnetic thin film and the substrate to reduce the reflectivity of the recording medium, the apparent Kerr rotation angle is increased to improve the CN ratio. Ways to improve have been proposed.

However, when Si ₃ N ₄ , AlN, etc. are used as the material of the dielectric film, the thin film layer cracks due to the internal stress entering during sputtering, and moisture in the atmosphere penetrates into the magnetic film through this crack and corrodes the film. Therefore, if left in the atmosphere, the recording and reproducing characteristics deteriorate. Further, if the film thickness of the dielectric thin film layer is inappropriate, the reflectance of the recording medium does not decrease sufficiently, the apparent Kerr rotation angle θk does not increase, and the recording and reproducing characteristics cannot be improved.

On the other hand, recording and erasing of information on the magneto-optical recording medium are performed by using a semiconductor laser. However, when the disc rotation speed is increased to increase the information transfer rate, a laser is irradiated onto one point on the recording medium. The irradiation time of the beam is shortened, and in the semiconductor laser, the temperature of the recording medium may not reach the operating point for recording and erasing, that is, the Curie temperature.

An object of the present invention is to solve the above-mentioned problems and to record at a high disk rotation speed by using a semiconductor laser without lowering a reproducing CN ratio improved by disposing a dielectric layer between a magnetic thin film and a substrate. An object is to provide a magneto-optical recording medium capable of recording and erasing on the medium. Another object of the present invention is to provide a magneto-optical recording medium which is excellent in corrosion resistance and does not crack in the dielectric film even in the atmosphere.

[Means for solving the problem]

The present invention, in order to solve the above problems, in a magneto-optical recording medium comprising a magnetic thin film having a concave easy magnetization axis in the direction perpendicular to the substrate surface via a dielectric layer, in the magneto-optical recording medium, the dielectric layer, SiAlO with a thickness of 40-120 nm containing 0.5-4.5 atomic% Cu
It is characterized by consisting of N film.

[Action]

Compared to Si ₃ N ₄ and AlN, the SiAlON film has smaller internal stress during sputtering and less cracks, so it does not corrode the magnetic thin film, and if the film thickness is 40 to 120 nm, it reduces the reflectance of the recording medium. As a result, the reproduction CN ratio exceeds 45 dB and high recording sensitivity can be obtained. Then, by adding 0.5 to 4.5 atom% of Cu, the reproducing CN ratio can be secured at 45 dB or more, while the laser power required for signal recording and erasing can be reduced.

〔Example〕

FIG. 1 is a sectional view showing the structure of a magneto-optical recording medium according to an embodiment of the present invention. That is, various dielectric layers 2 according to the present invention are laminated on a transparent substrate 1 made of glass, resin, etc., an amorphous magnetic thin film 3 of TbFe, TbFeCo, etc. is formed thereon, and further a dielectric film is formed. The protective layer 4 is laminated.

In the following Reference Examples and Examples, a fully degassed 5.25-inch polycarbonate plate is used as the substrate 1, and the magnetic thin film 3 is made of Tb formed by a sputtering method.
_{A 23} Fe ₆₉ Co ₈ or Tb ₂₄ Fe ₇₀ Co ₆ film was used, and as the protective layer 4, the same material as the dielectric layer 2 was formed to a thickness of 100 nm by the same method.

Reference Example 1: This is a reference example using SiAlON as the dielectric layer 2. SiAl
The ON thin film uses a SiAlON sintered target and the argon gas pressure is 0.
Various thicknesses were formed by the RF magnetron sputtering method under the conditions of 6 Pa and sputtering power of 300 W. After forming the dielectric layer 2, the magnetic thin film 3 is sputtered with TbFeCo without breaking the vacuum.
Argon gas pressure 0.2Pa, sputter power for alloy target
Performed by DC magnetron sputtering method under condition 6 of 300 W, 70 nm
A Tb ₂₃ Fe ₆₉ Co ₈ film having a thickness of 100 μm was obtained.

The dielectric layer 2 of the magneto-optical recording medium thus obtained
When the film thickness d of the SiAlON thin film was changed from 0 to 170 nm, the CN ratio during signal reproduction and the optimum recording laser power P _wopt during signal recording were measured. Measurement is with a pickup position radius of 30 mm
And 60mm, disk speed 1800rpm, recording frequency 1.88MH
z, applied magnetic field of 400 Oe, and reproduction laser power of 1 mW. Second
In the measurement results shown in the figure, the reproducing CN ratio is shown by a line 21 when measured at a radius of 30 mm, and the optimum recording power P _wopt is shown by a line 22 when measured at a radius of 60 mm.

As is clear from FIG. 2, the film thickness d of the SiOlON thin film is 40
The CN ratio exceeds 45 dB required for digital recording in the range of _up to 120 nm, and P _wopt of 8 to _8.5 mW achieves high recording sensitivity.

In addition, in the recording medium of the example, there was no crack generation at the time when Si ₃ N ₄ or AlN was used as the dielectric.

Furthermore, 1000 in a constant temperature and humidity chamber with a temperature of 60 ° C and a relative humidity of 90%.
As a result of examining the characteristic change after leaving for a while, as shown in FIG. 3, the recycled CN ratio did not change, and neither crack nor corrosion product was confirmed.

Therefore, in the embodiments described below, the dielectric layer 2
The film thickness was decided to be within the range of 40 to 120 nm.

Example 1: An example using SiAlON with Cu added as the dielectric layer 2. The dielectric layer 2 is formed under the same conditions as in Example 1 by using a SiAlON sintered target in which Cu pieces having dimensions of 1 mm × 1 mm × 40 mm are embedded, and the SiAlON dielectric layer 2 containing Cu 2.0 atomic% is formed. It is formed to a thickness of 90 nm, and subsequently, Example 1
DC magnetron sputtering under the same conditions as Tb ₂₄ Fe ₇₀ Co ₆
The magnetic thin film 3 was formed to a thickness of 70 nm. Similarly, SiAlON
A magneto-optical recording medium having a dielectric layer 2 having a different Cu content was prepared only by changing the Cu piece embedded in the sintering target. In the magneto-optical recording medium having the SiAlON dielectric layer containing 2.0 atomic% _Cu , the optimum recording laser power P _wopt for signal recording and the erasing laser power P _{E for} signal erasing are both 4.5 m.
It is a sufficiently low value as W, and the reproduction CN ratio exceeds 45 dB at 53d.
B was obtained. However, with the SiAlON dielectric layer containing 10.0 atomic% _Cu , both P _wopt and P _E are 4.0 mW, which is 2.0 atomic%, which is not so different, but the reproduction CN ratio is 41 dB, which is less than 45 dB. Fig. 4 shows the relationship between the Cu content and the regenerated CN ratio, P _wopt , and P _E by lines 41, 42, and 43, respectively, when the amount of Cu contained in the SiAlON dielectric layer 2 exceeds 0.1 atomic%. _Therefore , P _wopt and P _{E begin} to decrease, and when it exceeds 6.0 atomic%, the reproduction CN ratio deteriorates to 45 dB or less. In particular, when the Cu content is in the range of 0.5 to 4.5 atom%, the reproduction CN ratio is 52 to 53 dB, and P _wopt and P _E are 4.5 to 5.0 mW, which are almost uniform characteristics.

〔The invention's effect〕

According to the present invention, the dielectric layer is disposed between the magnetic thin film and the substrate to lower the reflectance of the recording medium and to increase the apparent Kerr rotation angle. C
By using the SiAlON film with u added, we were able to obtain a magneto-optical recording medium with excellent recording sensitivity and erasing characteristics, while ensuring the reproduction CN ratio of 45 dB or more.

[Brief description of drawings]

FIG. 1 is a sectional structural view of a magneto-optical recording medium of an embodiment of the present invention, and FIG. 2 is a SiAlON film thickness and reproduction of a medium of a reference example of the present invention.
Relationship diagram of CN ratio, FIG. 3 is a relationship diagram of the standing time in high humidity of the medium of the reference example of the present invention and the regeneration CN ratio, and FIG. 4 is the Cu content in the SiAlON film and the regeneration CN ratio. FIG. 3 is a relational diagram with optimum recording laser power and erasing laser power. 1 ... Substrate, 2 ... Dielectric layer, 3 ... Magnetic thin film, 4 ...
Protective layer.

Claims (1)

(57) [Claims] 1. A magneto-optical recording medium comprising a magnetic thin film on a substrate having an easy axis of magnetization perpendicular to the substrate surface via a dielectric layer, wherein the dielectric layer contains Cu of 0.5 to 4.5 atomic%. A magneto-optical recording medium comprising a SiAlON film having a thickness of 40 to 120 nm.