JPH0675305B2 - Magneto-optical recording medium - Google Patents

Description

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 configuration of a conventionally known magneto-optical recording medium is as shown in FIG. 6, in which 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 provided on the supporting substrate 1. The magneto-optical recording layer 3 made of a film is formed. As a magneto-optical recording layer
Known crystalline magnetic thin films such as MnBi, MnCuBi, MnTiBi, MnAlGe, and PtCo, or amorphous magnetic thin films obtained as alloys of rare earths such as Gd, Tb, Dy, and Ho with transition metals such as Fe, Co, and Ni. There is.

In addition, as shown in FIG.
There is also known a medium structure in which a groove 11 having a 000Å period of 1.6 to 2.5 μm is formed in a concentric circle shape or a spiral shape, and the magneto-optical recording layer 3 is formed on the support substrate 1. The groove 11 formed here is used for tracking access of the laser condensed beam used for recording or reproducing / erasing information on the recording medium.

In addition, as a conventionally known magneto-optical recording medium,
As shown in the figure, the reflection layer 4 is formed on the magneto-optical recording layer 3 on the protective layer 2, and the laser light 20 incident from the substrate side is reflected from the surface 21 of the magneto-optical recording layer 3 and the magneto-optical recording. There is one in which the magneto-optical effect of the magneto-optical recording layer 3 is enhanced by utilizing the reflected light 22 that has passed through the layer 3 and is reflected by the reflective layer 4. Also in the medium having this structure, as shown in FIG. 9, there is known a medium using the support substrate 1 having the concentric or spiral groove 11 as in FIG. However, in the previously known magneto-optical recording medium, the magneto-optical recording layer 3 and the reflective layer 4 are used.
Since the film thickness is constant in the radial direction, when recording / reproducing / erasing information by rotating the medium at a constant angular velocity, the recording power and the reproducing power are changed according to the radial position. However, there was a drawback that the erase power had to be changed. (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 certain thickness greatly depend on the linear velocity of the medium. .

(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 provide a constant optimum recording power and an optimum recording power in the radial direction without depending on the linear velocity by a simple medium structure. An object of the present invention is to provide a novel magneto-optical recording medium having a reproducing power and an optimum erasing power, and having a 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. Protective layer, a magneto-optical recording layer formed on the protective layer, and a reflective layer formed on the magneto-optical recording layer, and the thickness of the reflective layer becomes thinner toward the outer periphery of the magneto-optical recording medium. It was done like this.

(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. FIG. 1 is a sectional view showing an example of a magneto-optical recording medium according to the present invention. The protective layer 2 is formed on the supporting substrate 1, the magneto-optical recording layer 3 is further formed on the protective layer 2, and the reflective layer 4 is further formed on the magneto-optical recording layer 3. As the supporting substrate 1, an organic resin material such as polymethylmethacrylate, polycarbonate, epoxy or glass is used, and a type in which a groove 11 for laser beam tracking is formed in advance as shown in FIG. 2 is also used. As the protective layer 2, a layer that prevents water from penetrating from the substrate side and does not absorb at the laser wavelength used is used. For example, SiO, SiO ₂ , CeO ₂ , ZrO ₂ , T
iO ₂ , Bi ₂ O ₃ , WO ₂ , SnO ₂ , Sb ₂ O ₃ , 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, Si ₃ N ₄ , ZnS, Sb
Sulfides such as ₂ S ₃ and CdS, fluorides such as ThF ₄ , MgF ₂ , LaF ₃ , NdF ₃ , CeF ₃ and PbF _2, and semiconductors such as Si and Ge are used. As the magneto-optical recording layer 3, rare earth metals such as Gd, Tb, Dy and Ho, and F
Amorphous magnetic thin films made of alloys with transition metals such as e, Co and Ni are used. For example, GdCo, GdTbCo, GdTbFe
Co, TbFe, TbFeCo, TbDyFeCo, GdTbFe, GdTbDyFe, TbCo, TbDyC
o, TbFeNi, etc. Al, Cu, Ti, Ag, A as the reflective layer 4
Metals such as u and Pt are used. The reflective layer 4 is formed by changing the film thickness from the inner circumference to the outer circumference of the medium, and the film thickness decreases toward the outer circumference. This is a feature of the magneto-optical recording medium according to the present invention.

The protective layer 2, the magneto-optical recording layer 3, and the reflective layer 4 are formed by a film forming method such as a vacuum evaporation method and a sputtering method. In order to form the reflective layer 4 so that the film thickness becomes thinner toward the outer periphery, as shown in FIG. 3, a film forming apparatus having an evaporation source or a sputtering source 6 at a position eccentric to the rotation center of the disk 5 is formed. To use. Reference numeral 9 is an exhaust system, and 10 is an introduced gas. By forming the film while rotating the desk 5 by the motor 8, a magneto-optical recording medium having a desired film thickness distribution in the radial direction can be easily obtained. 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. As a parameter, the film thickness of the reflective layer 4 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. The optimum recording power, the optimum reproducing power, and the optimum erasing power all shift to the higher power side as the linear velocity increases. Further, as the film thickness of the reflective layer 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 reflective layer.

If the thickness of the reflective layer is uniform in the radial direction, the optimum recording power, reproducing power, and erasing power must be changed according to the radial position, as can be seen from FIG. The optimum power can be made constant with respect to the radial position by changing the film thickness of the reflective layer in the radial direction as in the magneto-optical recording medium as shown in FIG. 5 so that the film thickness decreases toward the outer peripheral portion.

(Example) A protective film made of Si ₃ N ₄ , a GdTbFe film, 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,
Cu reflective films were sequentially formed by rotating the disk by the sputtering method without breaking the vacuum. For the deposition of Si ₃ N _4, the target was Si and the reactive sputtering method using Ar + N ₂ mixed gas was adopted. The film thickness was 700Å and was adjusted with a shield plate placed between the disk and the target so that it would be uniform in the radial direction. The GdTbFe film was prepared by the sputtering method using a composite target composed of Gd, Tb, and Fe. The film thickness is 500Å, and Si ₃ is made uniform in the radial direction.
It was adjusted with a shield plate like N ₄ . Cu reflective film has a radius of 29 mm
The film thickness was 1500 Å and the film was sputtered to a radius of 58 mm to 500 Å. Here, the disk was eccentrically rotated with respect to the Cu sputter source.

Next, information was recorded / reproduced / erased using the prepared magneto-optical recording medium. The medium was rotated at 30 revolutions per second to record, reproduce, and erase. The optimum recording power, reproducing power, and erasing power were constant at a radius of 29 mm to 58 mm, and good recording / reproducing / erasing could be performed.

(Effects 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, optimum reproducing power, and optimum erasing power are constant in the radial direction of the magneto-optical recording medium when used at a constant angular velocity, the radial position is set to the same as in the conventional example. Accordingly, it is not necessary to change each power, 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 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 and 2 are cross-sectional views showing an example of the structure of a magneto-optical recording medium to which the present invention is applied, and FIG. 3 is a schematic view of a film forming apparatus used for producing the magneto-optical recording medium according to the present invention. 4 (a), (b) and (c) show the relationship between the optimum recording power, the optimum reproducing power, the optimum erasing power and the linear velocity of the magneto-optical recording medium, and FIG. 5 is the magneto-optical recording according to the present invention. FIG. 6, FIG. 6 and FIG. 7 showing the radial thickness distribution of the reflective layer of the medium.
FIGS. 8, 8 and 9 are sectional views showing the structure of a conventional magneto-optical recording medium. In the figure, 1 ... Support substrate, 2 ... Protective layer, 3 ... Magneto-optical recording layer, 4 ... Reflective layer, 5 ... Disk, 6 ... Deposition source or sputter source, 7 ... Vacuum chamber, 8 ... motor,
9 ... Exhaust system, 10 ... Introduced gas, 11 ... Groove, 20, 21, 22
...... It is laser light.

Claims (1)

[Claims] 1. A magneto-optical recording medium in which information is recorded / reproduced / erased by using a laser beam, a disc-shaped supporting substrate, a protective layer formed on the disc-shaped supporting substrate, and a protective layer formed on the protective layer. A magneto-optical recording medium comprising a magneto-optical recording layer and a reflective layer formed on the magneto-optical recording layer, wherein the thickness of the reflective layer is thinner toward the outer periphery of the magneto-optical recording medium.