JPH02108258A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To prevent the degradation in C/N at the time of reproduction by providing a thick heat radiating layer to a small-diameter substrate and a thin heat radiating layer or no layer at all to a large-diameter substrate, on which the same recording layer and heat radiating layer are respectively laminated. CONSTITUTION:A groove forming resin layer 2 having grooves consisting of a UV curing type resin, a protective film 3 consisting of Si3N4, the recording layer 4consisting of a GdFeCo alloy layer and TbFe alloy layer, the heat radiating layer 5 of 200Angstrom thickness consisting of Al, and a protective film 3 consisting of Si3N4 are successively laminated on the disk substrate 1 having 200mm diameter and thereafter an adhesive agent layer 6 for sealing is provided thereto. The sealing substrate 7 having 200mm diameter is stuck to this substrate. The magneto-optical disk 7 is produced in the same manner as mentioned above except by setting the diameters of both the disk substrate 1 and the sealing substrate 7 at 130mm and the thickness of the radiating layer 5 at 600Angstrom . The degradation in the C/N at the time of reproducing is prevented even if recording is made by using the disks of the different diameters without changing the recording conditions.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a novel magneto-optical recording medium.

[Conventional technology]

Recently, efforts have been made to develop optical recording and reproducing methods, recording devices, reproducing devices, and recording media used therein that satisfy various requirements including high density, large capacity, high access speed, and high recording and reproducing speed. Efforts are being made.

Among a wide range of optical recording and reproducing methods, magneto-optical recording and reproducing methods are the most popular because of their unique advantage of being able to record information, erase it, and record new information over and over again. It's full of great charm.

The magneto-optical disk used in this magneto-optical recording and reproducing method (
The recording medium has a single layer or multiple layers of perpendicular magnetization film as a recording layer. This magnetized film is made of, for example, amorphous GdF.
e and GdCo.

GdFeCo, ,TbFe5TbCo.

Made of TbFeCo, etc. The recording layer generally forms concentric or spiral trunks on which information is recorded. Here, in this specification, either "upward" or "downward" with respect to the membrane surface is referred to as "A direction".
, the other is defined as "inverted A direction". The information that should be recorded is
The bit (B1), which is previously binarized and has magnetization in the "A direction", and the bit B+, BO, which has magnetization in the "reverse A direction", is either 1.0 of the digital signal. and the other, respectively. However, the magnetization of the track to be recorded is generally aligned in the "reverse A direction" by applying a strong external magnetic field before recording. This process is called initialization.

On top of that, the bit with magnetization in the “A direction” (
It is recorded by the presence or absence of B1) and/or bit length.

In the formation of the xL principle, the characteristics of the laser, i.e. the spatial and temporal C = excellent cohesiveness, are used to advantage, almost the same as the diffraction limit determined by the wavelength of the laser light. The beam is narrowed down to an extremely small spot. The focused light is irradiated onto the track surface, and information is recorded by forming bits with a diameter of 1 μm or less on the recording layer. In optical recording, theoretically about 10” bits/cfl
Recording densities up to I can be achieved. This is because the laser beam can be condensed into a spot with a diameter almost as small as its wavelength.

As shown in FIG. 2, in magneto-optical recording, a laser beam (L) is focused on F of the recording layer (4) and heated. During this time, a recording magnetic field (Hb) in a direction opposite to the initialized direction is externally applied to the heated portion. Then, the coercive force Hc of the locally heated portion decreases and becomes smaller than the recording magnetic field (Hb). As a result, the magnetization of that portion is aligned in the direction of the recording magnetic field (Hb). A reversely magnetized bit is thus formed.

Ferromagnetic materials and ferrimagnetic materials have different magnetization and temperature dependence of Hc. Ferromagnetic materials have Hc that decreases near the Curie point, and recording is performed based on this phenomenon. Therefore, it is referred to as Tc writing (Curie point writing).

On the other hand, ferrimagnetic materials have a compensation temperature below the Curie point, where the magnetization (M) becomes zero. Conversely, Hc becomes extremely large near this temperature, and as the temperature deviates from this temperature, Hc drops rapidly. This reduced He is overcome by the relatively weak recording magnetic field (l(b)).

In other words, recording becomes possible. This recording process is T,.

,. This is called writing (compensation point writing).

However, it is not necessary to be particular about the Curie point or its vicinity, or the vicinity of the compensation temperature. In short, at a predetermined temperature higher than room temperature, a recording magnetic field (1-1
If b) is applied, recording is possible.

Incidentally, users are also seeking magneto-optical disks with a small recording capacity, that is, disks with a small diameter.

[Problem to be solved by the invention]

In this way, a single magneto-optical recording device can be used for small-diameter disks without changing the recording conditions such as rotation speed and laser beam intensity from those for large-diameter disks (although it is troublesome to change them). (This has the disadvantage that users dislike it and the device becomes complicated.) It has been found that when information is recorded, the C/N ratio decreases when it is reproduced.

Therefore, an object of the present invention is to prevent the C/N ratio from decreasing during reproduction even when recording is performed using disks of different diameters without changing the recording conditions.

[Means to solve problems]

When we investigated the reason why the C/N ratio decreases when a disk with a small diameter is used, we found that the recorded bit length becomes longer. After further research, we found that the cause of the longer bit length was
When the number of rotations is the same, the linear velocity becomes slower, and therefore, when the laser beam has the same intensity, the amount of beam irradiated to the recording layer per <unit area x unit time> increases, and as a result, It has been found that this is because the temperature increases and the area heated above the temperature required to form the bit expands. This phenomenon is the same as when the recording sensitivity of the magnetic layer (recording N) is high.

Therefore, the inventor initially decided to
The idea was to change the composition of the recording layer (Tli layer) to provide a recording layer with low recording sensitivity, that is, a high Curie point. However, when manufacturing disks with different diameters using one manufacturing device, it is extremely troublesome to change the composition for each different diameter.

By the way, in the case of a magneto-optical disk having a recording layer with high recording sensitivity, it has been proposed to provide a heat dissipation layer to reduce the sensitivity. (For example, see Japanese Patent Application Laid-Open No. 57-169996).

Therefore, for small-diameter disks, by providing a new heat dissipation layer or attaching it thickly, heat can be dissipated quickly even when the amount of beam is large, which reduces recording sensitivity. As a result, they came up with the idea that the recording sensitivity could be made the same as that of a disk with a large diameter, and came up with the present invention.

That is, in the present invention, by providing a relatively thick heat dissipation layer on a disk with a small diameter and providing a relatively thin heat dissipation layer on a disk with a large diameter, or by not providing a relatively thin heat dissipation layer on a disk with a large diameter, This disc is designed so that the recording sensitivity is the same even if the diameter of the disc is different.

[Effect]

In the present invention, even if the magneto-optical disks have different diameters, their recording sensitivities are the same, so recording can be performed using a single magneto-optical recording device without changing recording conditions such as rotation speed and laser beam intensity. be able to.

Basically, a disk only needs to have a magnetic recording layer and a heat dissipation layer, but generally these layers are laminated on a disk substrate to form a disk.

As the substrate, for example, glass, plastic, ceramic, aluminum, etc. are used.

On the substrate, a thin molding layer in which uneven tracks are formed, a dielectric layer, a reflective layer, an interference film, a Kerr effect enhancing film, a protective film, etc. may be formed in advance.

As the protective film, for example, S i O, A At 03,
Zr0= , ZnS, An! N, S 13 N4, etc. are used.

As the magnetic recording layer (perpendicular magnetization film), for example, TbFe
5GdFe, DyFe, GdCo, HoCo, GdTb
Fe, GdDyFe.

TbDyFe, GdFeCo, TbFeCo,
Rare earth-transition metal amorphous alloys such as GdDyFeCo and GdTbFeCo are mainly used.

The heat dissipation layer itself is known and can be made of materials such as:
Metals such as AJ, Cu, and Ag, semiconductors such as Si and Ge, and engineering ceramics such as silicon nitride, silicon carbide, aluminum nitride, and boron nitride are used. The thickness of the heat dissipation layer is thicker for a disk with a smaller diameter, and thinner or not provided for a disk with a larger diameter.

The heat dissipation layer may be placed above or below the recording layer, but since it is desirable that the sensitivity during reproduction be as high as possible, it is desirable to provide it above the recording layer, considering that the beam will be irradiated from the substrate side. Further, it is preferable to provide a protective film on the recording layer or the heat dissipation layer provided thereon.

When providing a thick heat dissipation layer for a disk with a small diameter,
It is preferable that the total thickness of the layers responsible for the main heat capacity, including the heat dissipation layer and the recording layer, be approximately inversely proportional to the diameter of the disk.

The various layers are typically formed using thin film formation techniques such as (reactive or non-reactive) sputtering, ion blasting, and vacuum evaporation.

Finally, a protective glass or plastic substrate is attached using an adhesive to complete the magneto-optical disk.

[Reference example]

(11 First disk: φ = 200 mm As shown in Figure 1, grooves (groups) made of ultraviolet curing resin are placed on a disk substrate (1.2 m thick glass plate) with a diameter of 20 mm. Groove molded resin layer (thickness 70
μm), a protective film made of S i x Na (thickness 70
0), GdFeCo alloy layer (thickness 500) and Tb
After sequentially laminating a recording layer consisting of an Fe alloy layer (500 layers thick), a heat dissipation layer made of Al (200 layers thick), and a protective film made of 5isNa (700 layers thick), a sealing adhesive was applied. A sealing substrate with a diameter of 20,011 mm (thickness of 1.2 fi
A disk was manufactured by pasting together two glass plates (glass plates).

(2) Second disk: φ-130 mm - The second disk is the same as the first disk, except that the diameters of the disk substrate and sealing substrate are both 130 In, and the thickness of the heat dissipation layer is 600 mm. I made a disc.

(3) Third disk: φ-1301m disk substrate,
The third disk was manufactured in the same manner as the first disk, except that the diameter of the sealing substrate was 1301 cm, and the thickness of the heat dissipation layer was also unchanged.

〔Example〕

Commercially available magneto-optical recording/reproducing device (disk rotation speed is 180
(variable only in the range of 0 to 2400 rpm), and the intensity of the laser beam was set to 12 mW (on disk).
As such, information was recorded on the first disk and the second disk. Then, when it was reproduced and its C/N was measured,
The following results were obtained.

Table 1 [Comparative Example] Information was recorded on the first disk and the third disk in the same manner as in the example, and the C/N ratio was measured. Apply this result to the second
Shown in the table.

Table 2 (Effects of the invention) As described above, one recording/reproducing device can be used without greatly changing the number of rotations of the disk or the laser beam intensity (if the laser intensity is changed significantly, the wavelength will change depending on the power). , the laser noise may change, which makes it troublesome to have to control other elements.Also, although it is easy to change the rotation speed for the HI3 section, it is necessary to change the structure to make a large change. is complicated and troublesome)
When recording on disks with different diameters, according to the present invention, a disk with a small diameter should have a new or thicker heat dissipation layer, and a disk with a larger diameter should have a thinner or thicker heat dissipation layer. By using a layerless material, the recording sensitivity is uniform, so the C/N during playback is
There is no reduction in the ratio.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a disk used in an embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating the principle of magneto-optical recording. [Explanation of symbols of main parts] 1...Disc substrate 2...Groove molding resin layer 3...Protective film 4...Recording layer 5...・・・ 6 ・・・・・・ 7 ・・・・・・ L ・・・・・・ Hb・・・ Heat dissipation layer adhesive layer Sealing substrate Laser beam recording magnetic field

Claims (1)

[Scope of Claims] In two or more magneto-optical disks in which at least two identical recording layers and heat dissipation layers are laminated on two or more disc substrates having different diameters, the heat dissipation layer is provided on the smaller diameter substrate. 1. A magneto-optical disk characterized in that recording sensitivity is made uniform by providing a thin heat dissipation layer or not providing it at all on a thick and large diameter substrate.