JPH0766577B2 - Magneto-optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magneto-optical recording medium for recording / reproducing / erasing information by using a laser beam.

(Prior Art and Its Problems) Optical disk memories are considered as a new memory to replace the current magnetic disk memories because they can be accessed with high density, large capacity and high speed. Among them, a magneto-optical disk using a magneto-optical recording medium has received the most attention because it has rewritability, and has been actively researched and developed in recent years.

The structure of a magneto-optical recording medium which has been conventionally known is such that, as shown in FIG. 7, glass or an organic resin is used as the supporting substrate 1, and the perpendicular magnetization having the magnetization in the direction perpendicular to the substrate is used on the supporting substrate 1. The magneto-optical recording layer 3 made of a film is formed. MuBi, MuCuBi, MnTi as the magneto-optical recording layer
Bi, MnAlGe, PtCo and other crystalline magnetic thin film, or Gd, Tb,
Amorphous magnetic thin films obtained as alloys of rare earths such as Dy and Ho and transition metals such as Fe, Co and Ni are known.
In addition, as shown in FIG.
Grooves 11 having a 000Å ° cycle of 1.6 to 2.5 μm are formed in a concentric or spiral shape, and the magneto-optical recording layer 3 is formed on the supporting substrate 1.
Also known is a medium configuration that forms the. The groove 11 formed here records or reproduces information on a recording medium,
It is used for tracking access of the laser focused beam used for erasing.

In addition, as a conventionally known magneto-optical recording medium,
As shown in the figure, there is a type in which the magneto-optical recording layer 3 is sandwiched between the spacer 2 and the protective layer 2 '. By sandwiching the magneto-optical recording layer 3 with the spacer 2 and the protective layer 2 ′, it is possible to prevent moisture and oxygen from penetrating into the magneto-optical recording layer 3 from the substrate side and the film surface side, and to prevent the magneto-optical recording layer from penetrating. It is possible to prevent the change with time and deterioration of No. 3. Also in the medium having this structure, as shown in FIG. 10, there is known a medium using the support substrate 1 having concentric or spiral grooves 11 as in FIG. However, since the magneto-optical recording layer 3, the spacer 2 and the protective layer 2 ′ are formed so that the film thicknesses thereof are constant in the radial direction in the previously known magneto-optical recording medium, etc. When information is recorded, reproduced, or erased by rotating the medium at an angular velocity, there is a drawback that the recording power, the reproduction power, and the erasing power must be changed according to the radial position. (For example, Kawakubo et al .; IEICE Technical Report MR84-39) This is because the optimum recording power, optimum reproducing power, and optimum erasing power of a medium with a constant film thickness greatly depend on the linear velocity of the medium. is there.

(Object of the Invention) An object of the present invention is to solve the above-mentioned drawbacks of the conventional magneto-optical recording medium, and to achieve a constant optimum recording power and optimum reproducing power in the radial direction without depending on the linear velocity by a simple medium structure. The present invention provides a novel magneto-optical recording medium having optimum erasing power and good recording / reproducing / erasing performance.

(Structure of the Invention) In order to achieve the above object, the present invention is a magneto-optical recording medium for recording / reproducing / erasing information by using a laser beam, which is formed on a disk-shaped support substrate and the disk-shaped support substrate. Provided spacers, a magneto-optical recording layer formed on the spacers, and a protective layer formed on the magneto-optical recording layer, and one of the spacer thickness and the protective layer thickness is magneto-optical. The outer circumference of the recording medium is made thinner.

Before explaining the principle of the present invention, the principle of magneto-optical recording will be described.

In magneto-optical recording, by irradiating the recording layer with a laser beam, the temperature of the recording layer is raised to the Curie temperature or higher to temporarily eliminate the magnetization, and the magnetization of the recording layer is reversed in the externally applied magnetic field direction during the cooling process. , Make a record. In this process, the amount of temperature rise of the recording layer is determined by the specific heat, density, and volume of the recording layer, and the heat capacity of the recording medium, which is determined by the specific heat, density, and volume of the protective film and spacers adjacent to the recording layer. . Naturally, the amount of light absorbed in the recording layer is a major factor that determines the amount of temperature rise, but even if the amount of absorbed light is the same, the amount of temperature rise is small when the heat capacity of the recording medium is large.

The present invention is based on such a recording principle and relates to a magneto-optical recording medium rotating at a constant angular velocity.

The principle of the present invention is to provide a difference in the heat capacities of the inner and outer circumferences of the disc so as to equalize the difference in recording sensitivity between the inner and outer circumferences of the disc when used at a constant angular velocity rotation. That is, the film thickness of the protective film or the spacer is reduced so that the thermal capacity of the recording medium is small in the outer peripheral portion where the linear velocity is high, the laser irradiation time to the same location is short, and the temperature rise amount is likely to decrease relatively. Set thin. On the contrary, the heat capacity is not reduced in the inner peripheral portion without reducing the film thickness of the protective film or the spacer as compared with the outer peripheral portion.
By doing this, low recording power,
Recording / erasing / reproduction can be performed with low erasing power and low reproducing power.

FIG. 4 is a diagram for explaining the principle of the above-described magneto-optical recording medium of the present invention, and shows the relationship between the optimum recording power, the optimum reproducing power, and the optimum erasing power with respect to the linear velocity.
When the thickness of the protective film or the spacer is increased to increase the heat capacity, each required optimum power shifts to the high power side. On the other hand, if a medium structure having a small heat capacity on the high linear velocity side is adopted, recording / reproduction / erasing can be performed with the same power as on the low linear velocity side.

(Detailed Description of Configuration) The present invention has solved the problems of the prior art by adopting the above configuration. Hereinafter, details of the present invention will be described with reference to the drawings.

1 (a) and 1 (b) are sectional views showing an example of a magneto-optical recording medium according to the present invention. Spacer 2 on support substrate 1
And a magneto-optical recording layer 3 is formed on the spacer 2.
And a protective layer 2 ′ is further formed on the magneto-optical recording layer 3. An organic resin material such as polymethylmethacrylate, polycarbonate, epoxy or glass is used as the supporting substrate 1, and a groove 11 for laser beam tracking is previously formed as shown in FIGS. 2 (a) and 2 (b). Also used. As the spacer 2, a spacer that prevents moisture from penetrating and oxygen from entering from the substrate side and does not absorb at the laser wavelength used is used. For example, SiO, SiO ₂ , CeO ₂ , ZrO ₂ , TiO ₂ , Bi
₂ O ₃ , WO ₂ , SnO ₂ , Sb ₂ O, Al ₂ O ₃ MgO, ThO ₂ , La ₂ O ₃ , In
₂ O ₃ , oxides such as Nd ₂ O ₃ , nitrides such as AlN and Si ₃ N ₄ , Zn
S, Sb ₂ O ₃ , sulfides such as CdS, ThF ₄ , MgF ₂ , LaF ₃ , Nd
Fluorides such as F ₃ , CeF ₃ and PbF ₂ and semiconductors such as Si and Ge are used. As the magneto-optical recording layer 3, Gd, Tb, Dy, Ho
An amorphous magnetic thin film made of an alloy of a rare earth metal such as Al and a transition metal such as Fe, Co, or Ni is used. For example, GdCo, GdTbCo, GdTbFeCo, TbFe, TbFeCo, TbDyFeC
o, GdTbFe, GdTbDyFe, TbCo, TbDyCo, TbFeNi, etc. As the protective layer 2 ', the same material as that used for the spacer 2 can be used.

Either the spacer 2 or the protective layer 2'is formed by changing the film thickness in the radial direction of the medium, that is, from the inner circumference to the outer circumference of the medium, and the film thickness becomes thinner toward the outer circumference. This is,
This is a feature of the magneto-optical recording medium according to the present invention. The spacer 2 protective layer 2'and the magneto-optical recording layer 3 are formed by a film forming method such as a vacuum evaporation method and a sputtering method. In order to form the spacer 2 or the protective layer 2 ′ so that the film thickness becomes thinner from the inner circumference to the outer circumference, as shown in FIG. 3, a vapor deposition source or a vapor deposition source is placed at an eccentric position with respect to the rotation center of the disk 4. A film forming apparatus having a sputtering source 5 is used. By forming the film while rotating the disk 4 by the motor 6, a magneto-optical recording medium having a desired film thickness distribution in the radial direction can be easily obtained. Here, 7 is an exhaust system, 8 is an introduced gas cylinder, and 9 is a vacuum chamber. FIGS. 4 (a), (b) and (c) are diagrams showing the relationships between the optimum recording power, the optimum reproducing power, the optimum erasing power and the linear velocity of the magneto-optical recording medium, respectively. As a parameter, the film thickness of the spacer 2 or the protective layer 2'of the medium having the configuration shown in FIGS. 1 and 2 is taken. The optimum recording power mentioned here is a recording power that can form a recording bit most faithfully to a recording signal. The optimum reproduction power is the reproduction power that maximizes the C / N of the reproduction signal, that is, the ratio of the reproduction signal level and the noise signal level. Furthermore, the optimum erasing power is the erasing power that can completely erase the optimum recorded bit. Optimum recording power,
Both the optimum reproducing power and the optimum erasing power shift to the higher power side as the linear velocity increases. Further, as the film thickness of the spacer 2 or the protective layer 2'becomes thicker, each optimum power becomes larger even at the same linear velocity. On the contrary, in order to keep the optimum power constant with respect to the linear velocity, it is necessary to change the film thickness of the spacer 2 or the protective layer 2 '. When the spacer 2 or the protective layer 2'has a uniform thickness in the radial direction, as can be seen from FIG. 4, the optimum recording power, reproducing power, and erasing power must be changed according to the radial position. The spacer 2 as in the magneto-optical recording medium according to the present invention
Alternatively, the optimum power can be made constant with respect to the radial position by changing the film thickness of either one of the protective layers 2'in the radial direction as shown in FIG. 5 so that the film thickness decreases toward the outer peripheral portion.

Example 1 A spacer made of Si ₂ N ₄ , GdTbFe on a polymethylmethacrylate substrate (120 mm diameter, 1.2 mm thickness) having a spiral wound groove with a depth of 700 Å, a width of 0.8 μm and a pitch of 2.5 μm.
The film and a protective film made of Si ₂ N ₄ were successively formed by rotating the disk by a sputtering method without breaking the vacuum. The film forming apparatus shown in FIG. 6 was used for film forming. The disk 4 has two spatula sauces 21 and 22 which are eccentric from the rotation center of the disk 4. One spatula sauce 21
Is a Si target, and the other spatula sauce 22 is Gd, T
A composite type target composed of b and Fe was used. Si ₃ N ₄ film is 2
After evacuating to less than × 10 ^-7 Torr, add Ar × N ₂ mixed gas to 1 × 10 ^-2 Torr
It was formed by introduction and reactive sputtering. GdTb
The Fe film was formed by sputtering using Ar gas. The first-layer spacer formed on the substrate is a shield plate 23 having a fan-shaped opening placed between the disk and the target.
Was adjusted so that the film thickness was uniform in the radial direction.
The film thickness was 700Å °. Second magneto-optical recording layer-GdTbF
The e film was also formed to have a uniform film thickness in the radial direction by using the same shield plate as the first layer.

The film thickness was 1000Å °. No shield plate was used to form the third protective film. The film thickness was 29 mm in radius, 1000 Å °, and radius was 58.
It was 700Å ° in mm.

Next, recording information using the created magneto-optical recording medium. Playback. It was erased. The medium is rotated at 30 rpm, and laser light is incident from the substrate side for recording and reproduction. It was erased. Optimal recording power in a radius of 29 mm to 58 mm. Good read and erase power, and good recording. Playback. I was able to erase it.

(Example-2) A magneto-optical recording medium was prepared in the same manner as in Example-1. The film thickness of the first layer spacer Si ₂ N ₄ is 100 with a radius of 29 mm.
0Å °, radius of 58mm and 700Å °, the second layer of GdTbFe film and the third protective layer of Si ₂ N ₄ are uniformly distributed in the radial direction to 100.
It was set at 0Å ° and 950Å °. The created medium was rotated at 30 revolutions per second and laser light was incident from the protective film side for recording. Playback. It was erased. Optimal recording power in a radius of 29 mm to 58 mm. Playback power. Erasure power was constant and good recording. Playback. I was able to erase it.

(Effect of the Invention) As described above, the present invention has the following effects as compared with the conventional example.

Since the medium is designed so that the optimum recording power and the optimum erasing power are constant in the radial direction of the magneto-optical recording medium when used at a constant angular velocity, each power is adjusted according to the radial position as in the conventional example. It is not necessary to change the device configuration, and the device configuration can be simplified.

By eccentricizing the disk rotation center with respect to the position of the vapor deposition source or the sputtering source, it is possible to easily create a medium having a desired film thickness distribution in the radial direction.

The present invention can be applied to both the method of injecting laser light from the substrate side and the method of injecting laser light from the protective film side.

The present invention can be applied to all magneto-optical recording media used at a constant angular velocity rotation. That is, not limited to the embodiment of the present invention,
It can be applied to magneto-optical recording media having various film structures using various protective layer materials, magneto-optical recording materials, and reflective layer materials.

[Brief description of drawings]

1 (a) and 1 (b) and FIGS. 2 (a) and 2 (b) are cross-sectional views showing a configuration example of a magneto-optical recording medium to which the present invention is applied,
FIG. 3 is a schematic view of a film forming apparatus used for producing a magneto-optical recording medium according to the present invention, and FIGS. 4 (a), (b) and (c) are optimum recording power and optimum reproducing power of the magneto-optical recording medium. FIG. 5 is a diagram showing the relationship between the optimum erasing power and linear velocity, FIG. 5 is a diagram showing the radial thickness distribution of the protective layer of the magneto-optical recording medium according to the present invention, and FIG. 6 is an embodiment of the present invention. FIG. 7, FIG. 8, FIG. 9, FIG. 9 and FIG. 10 are schematic sectional views of the film forming apparatus used in FIG. In the figure, 1 ... Support substrate, 2 ... Spacer, 2 '... Protective layer, 3 ... Magneto-optical recording layer, 4 ... Disk, 5 ... Deposition source or sputter source, 6 ... Motor, 7 ... Exhaust system, 8 ... Introduced gas cylinder, 9 ... Vacuum chamber, 11 ...
Grooves, 21, 22 ... Spatuta sauce, 23 ... Shield plates.

Claims (1)

[Claims] 1. A magneto-optical recording medium for rotating at a constant angular velocity for recording / reproducing / erasing information by using a laser beam, a disc-shaped supporting substrate, a spacer formed on the disc-shaped supporting substrate and the spacer. A magneto-optical recording layer formed on the magneto-optical recording layer and a protective layer formed on the magneto-optical recording layer, and either the thickness of the spacer or the thickness of the protective layer becomes thinner toward the outer periphery of the magneto-optical recording medium. And a magneto-optical recording medium.