JPH0383238A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To improve writing sensitivity while maintaining reading stability by providing a layer having higher thermal conductivity than that of a protective film in a manner that the thickness of the layer gradually decreases from the most inner circumference edge of a recording area in the disk to a specified radius range. CONSTITUTION:On a glass substrate 1, there are formed a base protective film 2 and recording film 3, and then a high thermal conductive layer 5 comprising Al is formed to cover from the most inner part R1 of the recording area 10 to the position of radius r. The layer 5 is formed by sputtering Al in a manner that the thickness of the layer decreases from the most inner circumference R1 to zero at the position where the distance from R1 is 2/3 of the distance from R1 to the most outer circumference R0. By this method, the high thermal conductive layer is formed in the inner area where the line velocity is slow, by which heat generated by laser beam irradiation is effectively diffused from the inner recording film to reduce the recording sensitivity of the inner area. Thereby, reading stability in the inner area can be maintained while writing sensitivity of the outer area can be improved.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a magneto-optical disk, particularly a magneto-optical disk using a constant angular velocity method, and provides a magneto-optical disk that has improved writing sensitivity while sufficiently ensuring successive stability. With the purpose of Continuously extending to a predetermined position on the top, the disc is provided concentrically with respect to the center of the disk, and has a thickness that gradually decreases from the innermost circumferential portion to the predetermined position.

[Industrial application field]

The present invention relates to a magneto-optical disk, particularly a magneto-optical disk of a constant angular velocity type.

[Conventional technology]

In general, recording media are required to have high writing sensitivity and at the same time, to ensure that the recorded information is not destroyed or erased by the successive operation itself, that is, to have successive successive stability. Regarding the successive stability in magneto-optical disks, for example, M, Ma
eda et al, “5tudy on Read
-out 5tability of TbFeCo
Magneto-Optical Disks”, 198
9. Intera + ag t! A-8, to be
It is explained in detail in published in IBBB trans, etc.

Recording (writing) is performed on a magneto-optical disk by heating a recording film with a laser beam, and the recorded information is also output using a laser beam. Successive printing is performed with a lower laser power than writing. This is to prevent the recorded information written on the disk from being destroyed or erased by the continuous laser beam heating.

The minimum laser power for writing (minimum write power) and the maximum laser power for not destroying or erasing the recorded information due to repeated flashing (maximum allowable continuous power) are basically the It is determined by the Curie temperature of the material used. High writing sensitivity requires a low minimum writing power, that is, a low Curie temperature of the recording film material, while high successive stability requires a low maximum allowable It is necessary that the output power is large, that is, the Curie temperature of the recording film material is high.

In this way, improving the writing sensitivity of a magneto-optical disk and improving successive printing stability are basically in a contradictory relationship. Therefore, depending on the application, it is necessary to design a device that emphasizes either writing sensitivity or successive stability, or to suppress both of them to a certain level.

Such design constraints are particularly severe in the case of magneto-optical disks of a constant angular velocity type.

In other words, in a magneto-optical disk using a constant angular velocity method, the linear velocity is larger on the outer circumference than on the inner circumference of the recording area of the disk, so the laser beam irradiation time per unit length of the recording film is shorter on the outer circumference. Become. Therefore, the actual writing sensitivity of the disk is relatively low on the outer circumferential side of the disk and high on the inner circumferential side. Of course, on the contrary, the actual successive stability is relatively higher on the outer circumference side and lower on the inner circumference side. For example, in the case of a general magneto-optical disk in which the recording film is made of the same material for the entire recording area of the disk (that is, the Curie temperature of the recording film is constant in the entire recording area), the innermost periphery of the recording area of the disk The writing sensitivity and successive stability from the outermost periphery of the disc change in response to changes in linear velocity and in response to the radial distance from the center of the disk.

In this way, under the situation where write sensitivity and successive stability (i.e., minimum write power and maximum read power) gradually decrease and increase, respectively, along the disk radial direction, for a given write power and read power, the maximum The range of design choices that can be made to ensure write sensitivity in the outermost periphery, where the minimum write power is large, while ensuring successive stability in the innermost periphery, where the allowable continuous writing power is small, is extremely narrow. . Therefore,
Under such design constraints, it has been extremely difficult to simultaneously improve writing sensitivity and successive stability.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical disk that has improved writing sensitivity while sufficiently ensuring read stability.

[Means to solve the problem]

According to the present invention, in a magneto-optical disk of a constant angular velocity type, a layer having a higher thermal conductivity than a protective film for the recording film is provided on the innermost periphery of the recording area of the disk. This is achieved by a magneto-optical disk characterized in that the magneto-optical disk is provided continuously from the innermost circumferential portion to a predetermined position on the radius of the disk, concentrically with respect to the center of the disk, and with a thickness that gradually decreases from the innermost circumferential portion to the predetermined position. Ru.

On the inner circumferential side where the linear velocity is slow, a layer with high thermal conductivity provided on the recording film (hereinafter referred to as "high thermal conductivity layer") records the heat introduced into the recording film by laser beam irradiation. Efficiently escapes from the membrane. As a result, the same effect as when the sensitivity of the recording film is substantially lowered on the inner circumferential side is obtained, and the successive stability on the inner circumferential side is increased. In other words, the gradual decrease and increase changes in the writing sensitivity and successive stability in the radial direction are alleviated, and the conventional limitations in improving characteristics caused by this are eliminated, and the degree of freedom in design is greatly increased.

The recording film of a magneto-optical disk is protected from the outside by a protective film. In order to obtain the above effect, the high thermal conductivity layer of the present invention provided on the recording film needs to have higher thermal conductivity than this protective film. The protective film is generally formed of oxide, nitride, etc., and in that case, a layer of a metal with high thermal conductivity such as Af is suitable as the high thermal conductive layer.

The position on the disk radius from the innermost circumference of the disk recording area to which the highly thermally conductive layer is provided can be determined as a design specification depending on the use of the disk.

Of course, it can be provided halfway from the innermost circumference to the outermost circumference, or it can be provided from the innermost circumference to the outermost circumference, that is, in the entire recording area of the disk.

The highly thermally conductive layer is provided as a continuous layer and concentrically from the innermost periphery to the above-mentioned predetermined position. As a result, the effect of conductive cooling can be obtained in the predetermined inner recording area.

The magnitude of the conductive cooling effect of a high thermal conductivity layer depends on its thickness, and the thicker the layer, the greater the conductive cooling effect. Therefore, in order to alleviate the gradual decrease in writing sensitivity and gradual increase in stability along the radial direction from the innermost periphery of the recording area, the thickness of the high thermal conductive layer is gradually decreased from the innermost periphery to the above-mentioned predetermined position. It is necessary.

[For production]

In the magneto-optical disk of the present invention, a highly thermally conductive layer is provided on the recording film on the inner peripheral side, where the linear velocity is slow, and the heat introduced by laser beam irradiation is efficiently released from the inner peripheral recording film. This substantially lowers the recording film sensitivity of the recording film and improves the successive stability on the inner circumferential side.

This results in a radial gradual decrease in writing sensitivity and successive stability.
Gradual changes are moderated.

In the following, the invention will be explained in more detail by means of examples with reference to the accompanying drawings.

〔Example〕

The magneto-optical disk of the present invention shown in FIGS. 1(al) and 1(a2) was prepared. Figure (al) is a plan view showing the recording area 10 of the magneto-optical disk and the highly thermally conductive layer 5 provided on the inner peripheral portion thereof, and (a2) is a cross section taken along line A-A in (al). It is a diagram.

A Tb 3102 base protective film 2 with a thickness of about 1100 nm is formed on a glass 2P substrate 1 by sputtering, and a TbFeC film 2 with a thickness of about 1100 nm is formed thereon.

A recording film 3 having a Curie temperature of 170 t was formed, and a highly thermally conductive layer 5 of An was formed thereon from the innermost peripheral portion R0 of the recording area IO to a position at a radius r. The thickness of the highly thermally conductive layer 5 is the innermost circumferential portion Rr of the disk recording area 10 (radius 55 mm
) is about 20 nm, and from the innermost circumference R1 to the outermost circumference Ro
The distance gradually decreases to position r, which is about 2/3 of the distance, and becomes substantially zero at position r, and from position r to the outermost circumference Ro (radius 9
5 mm) is essentially zero. Sputtering of AI was performed with a mask 7 placed between the substrate 1' on which the recording film was formed and the AI cover 8, as shown in FIG. There is a gap between these three as in normal sputtering. As for the shape of the mask 7, it is sufficient to have a simple circular transmission hole 6 as shown in the figure. When sputtering of AI is performed in this manner, the layer 5 of AI is formed with the sloped thickness as described above by spreading from the transmission hole to the surrounding area. The position r can be adjusted by adjusting the size of the transmission hole 6 of the mask 7, the distance between the substrate 1'' and the mask 7, the distance between the mask 7 and the target 8, etc. On the substrate on which the high thermal conductivity layer 5 is formed, a layer with a thickness of about 1
A top protective layer 4 of Tb-3i○2 of 00nrn was formed.

For comparison, a conventional magneto-optical disk shown in FIG. 2 without the high thermal conductivity layer 5 was also produced. The manufacturing method is the same as above except that the high thermal conductivity layer 5 of AA is not provided. However, in order to make a comparison based on Curie temperature, the Curie temperature of the recording film was set to two levels, 170° C. and 210° C., which are the same as above, by adjusting the composition of TbFeCo.

Curie temperature of the recording film of each manufactured magneto-optical disk,
Table 1 summarizes the presence or absence of the AI high thermal conductivity layer.

Table 1 The minimum write power and maximum allowable continuous output power of these magneto-optical disks were measured. The results are shown in Figure 4.

As can be seen from the figure, conventional example A has a high Curie temperature.
However, if the Curie temperature is lowered as in Conventional Example B in order to increase the writing sensitivity, the maximum allowable continuous power is a minimum of 1.6 mW. On the other hand, in the embodiment of the present invention, the writing sensitivity is reduced only on the innermost side, so the maximum value of the minimum writing power (the highest The minimum value of the maximum allowable continuous power is 1.8 m while keeping the outer circumference) to the same low level as conventional example B.
W (innermost periphery), and as a result, radial changes in the minimum write power and maximum allowable successive power are moderated.

In addition, in the above embodiment, the high heat conductive layer 5 is placed in the recording area 10.
Although we have explained an example in which the recording area 1 is provided up to a position r halfway on the radius of the recording area 1, as shown in FIGS.
The high thermal conductivity layer 5 of the present invention may be provided over the entire surface of the substrate.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to improve the writing sensitivity of an angular velocity-type magneto-optical disk while ensuring sufficient successive stability.

As a result, the degree of freedom in design increases significantly.

[Brief explanation of drawings]

FIGS. 1(al) and (a2) are a plan view and a cross-sectional view, respectively, showing an example of the magneto-optical disk of the present invention, and FIG.
bl) and (b2) are a plan view and a cross-sectional view, respectively, showing another example of the magneto-optical disk of the present invention, and Figures 2 (al) and (a2) are a plan view and a cross-section, respectively, showing a conventional magneto-optical disk. 3 is a perspective view schematically showing a sputtering method for forming a highly thermally conductive layer of the magneto-optical disk of the present invention, and FIG. 4 shows the radial position, minimum write power, and This is a graph showing the relationship between the maximum allowable continuous power. 2: Substrate, 2: Base protective film, 3: Recording film, 4: 5 = High thermal conductive layer, 7: Mask, 8: 10: Magneto-optical day top protective film. , 6: Recording area of transmission hole, target, and suf.

Claims (1)

[Claims] 1. In a magneto-optical disk using a constant angular velocity method, a layer with higher thermal conductivity than the protective film for the recording film is placed on the recording film from the innermost periphery of the recording area of the disc to a predetermined position on the radius of the disc. 1. A magneto-optical disk characterized in that the magneto-optical disks are provided continuously and concentrically with respect to the center of the disk, and have a thickness that gradually decreases from the innermost circumferential portion to the predetermined position.