JPS62226451A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To remarkably improve a noise characteristic and to improve reproduction C/N by forming a photosetting resin to be formed on a substrate thicker than the focal depth of a condensed beam so that the nonuniformity possessed by a substrate is eliminated. CONSTITUTION:There is the photosetting resin layer 5 on the flat substrate 1 and grooves 11 for tracking laser light are circularly or spirally formed on the resin layer. A spacer 2 is further formed on the layer 2 and a photomagnetic recording layer 3 is formed on the spacer 2. A protective layer 4 is formed on the layer 3. A polycarbonate molded on a disk is used for the substrate 1 and the grooves 11 are formed by the transfer from a stamper die to the layer 5. The resin layer is coated by a spin coating method on the substrate 1. A transparent material such as SiO2 or ZrO2 which is optically homogeneous and has no anisotropy is used for the spacer 2. The film thickness of the layer 5 is set larger than the focal depth length of the condensed beam of the laser light to be used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magneto-optical recording medium that records, reproduces and erases information using laser light.

(Prior Art) Optical disk memory is considered as a new memory to replace the current magnetic disk memory because it is capable of high density, large capacity, and high speed access. Among them, magneto-optical disks using magneto-optical recording media have attracted the most attention because they are rewritable, and research and development have been actively conducted in recent years.

As shown in FIG. 2, a conventionally known magneto-optical recording medium uses glass or transparent resin as a disk-shaped supporting substrate 1, and has magnetization on the substrate 1 in a direction perpendicular to the substrate. A magneto-optical recording layer 3 made of a perpendicularly magnetized film is formed. As the magneto-optical recording layer, MnB1. MnC
uB1. MnTiB1. Crystalline magnetic thin films such as MnAlGe, PtCo, or Gd, Tb, Dy, Ho,
Sm.

Amorphous magnetic thin films obtained as alloys of rare earth elements such as Nd and transition metals such as Fe, Co, and Ni are known. Further, as shown in FIG.
A medium configuration is also known in which grooves 11 with a pitch of 1.6 to 2.5 yen are formed in a thin spiral shape or the same circular shape, and a magneto-optical recording layer 3 is formed on the substrate 1. . The groove 11 formed here is used for tracking access of a focused laser beam used for recording information on a recording medium or for reproducing/erasing information.

In addition, the fourth type of conventionally known magneto-optical recording medium is
As shown in the figure, there is a type in which a magneto-optical recording layer 3 is sandwiched between a spacer 2 and a protective layer 4. This configuration can be found, for example, in Japanese Patent Application Laid-Open No. 110052/1983. Since the magneto-optical recording layer 3 is sandwiched between the spacer 2 and the protective layer 4, moisture and oxygen are prevented from penetrating into the magneto-optical recording layer 3 from the substrate side and the film side, and the aging of the magneto-optical recording layer 3 is prevented. Change and deterioration can be prevented. Also known is a medium having this structure, as shown in FIG. 5, which uses a substrate 1 having thinly wound or concentric grooves 11 similar to that in FIG. 3.

(Problems to be Solved by the Invention) Transparent resins used as the substrate 1 include polymethyl methacrylate, polycarbonate, and the like. Among them,
Polycarbonate, which has excellent deformability and hygroscopicity, is used as a substrate for optical disks. However, since polycarbonate has a large birefringence, when polycarbonate is used as a substrate in a magneto-optical disk that detects changes in the plane of polarization as a signal, it has the disadvantage that the plane of polarization is disturbed and noise increases.

An object of the present invention is to solve the drawbacks of the conventional magneto-optical recording medium, and to provide a new magneto-optical recording medium with a simple medium configuration, low noise, and good recording/reproducing/erasing characteristics.

(Means for Solving the Problems) According to the present invention, in a magneto-optical recording medium that records, reproduces and erases information using a laser beam, a polycarbonate resin flat substrate and a laser beam tracking formed on the substrate are provided. A photocurable resin layer having concentric or spiral grooves, a spacer formed on this resin layer, a magneto-optical recording layer formed on the spacer, and a magneto-optical recording layer formed on the magneto-optical recording layer. A magneto-optical recording medium is obtained, characterized in that the thickness of the sealing layer is greater than the depth of focus of the condensed beam of the laser beam.

FIG. 1 is a sectional view of a magneto-optical recording medium according to the present invention. A photocurable resin R5 is placed on a flat substrate 1, and a groove 11 for laser beam tracking is formed in the resin layer in a concentric or spiral shape.

Further, a spacer 2 is formed on the resin layer 5, a magneto-optical recording layer 3 is further formed on the spacer 2, and a protective layer 4 is further formed on the magneto-optical recording layer 3.

As the substrate 1, polycarbonate molded into a disc is used. A tracking groove 1 is provided in the photocurable resin layer 5.
1 is formed by transfer from a stamper mold.

The groove shape usually has a pitch of 1°6~2.5pm and a groove width of 0.6~
0.8 pm, groove depth 500-1000 people. As the photocurable resin, a resin is selected that has good transparency, is easy to peel off from the stamper, and has excellent adhesion to the substrate resin, that is, polycarbonate. The resin layer is applied onto the substrate by a spin code method. As the spacer 2, a transparent material that is optically homogeneous and has no anisotropy is used.

For example, SiO,5i02. CeO2, ZrO2, Ti
O2, Bi2O3, WO3, 5n02°5b203. A
lO3, MgO, Th02. La2O3, In2O3,
Oxides such as Nd2O3, AIN, Si3N4'!
TonoMide, ZnS, oxides such as Sb2S3°CdS, ThF4. MgF2. LaF3. NdF3. CeF3
Fluorides such as PbF2, and semiconductors such as Si and Ge are used. As the magneto-optical recording layer 3, Gd, Tb, Dy
An amorphous magnetic thin film made of an alloy of rare earth metals such as , Ho, and transition metals such as Fe, Co, and Ni is used.

For example, GdCo, GdTbCo, GdTbFeCo
, TbFe, TbFeCo.

TbDyFeCo, GdTbFe, GdTbDyFe,
TbCo, TbDyCo.

For example, TbFeNi. As the protective layer 4, the same material as used for the spacer 2 can be used.

(Function) In FIG. 1, the thickness of the photocurable resin layer 5 is set to be thicker than the depth of focus of the condensed beam of the laser light used. The depth of focus of the focused beam can be found as follows: Depth of focus = (N, A,) 2 where λ is the wavelength of the laser beam, and N and A are the numerical apertures of the focusing lens. For example, λ=830nm, N,A,=
At 0.55 m, the depth of focus is 2.711 m. The focused laser beam has a constant spot diameter within the depth of focus near its focal point. The increase in noise caused by the birefringence of polycarbonate substrates, which has been a problem in the past, is largely due to the disturbance of the plane of polarization of the substrate near the focal point of the laser beam, that is, near the substrate, the spacer, and the magneto-optical recording layer.

In other words, the polycarbonate substrate, which causes the plane of polarization to be disturbed, is located near the focal point of the laser beam and within the depth of focus, which disturbs the plane of polarization of the laser beam and increases noise.

Therefore, as in the present invention, noise can be significantly reduced by forming a thick resin layer other than polycarbonate near the focal point of the laser beam and adopting a medium configuration in which no polycarbonate substrate exists within the focal depth distance.

(Example) As an example of the present invention, a polycarbonate flat substrate (13
0mm diameter, 1.2mm thickness) with 3μ of photocurable resin.
A thinly wound groove having a depth of 700 mm, a width of 0.8 pm, and a pitch of 1.6 pm was formed on the photocurable resin by spin-coding to a thickness of m, and by transferring from a stamper mold. Next, 5i3N41 was used as a spacer by magnetron sputtering.
1000 people in the desert, TbFeConN as magneto-optical recording layer
1000 people, and 1 protective layer made of Si3N4 film.
000 people successively formed films without breaking the vacuum.

Next, as a comparative example, we used a polycarbonate substrate (130 mm diameter, 1.6 mm thick) on which thinly wound grooves with a depth of 700 mm, a width of 0.8 pm, and a pitch of 1.6 pm were formed using an injection molding method.
．． 2"m) by magnetron sputtering, 1000 Si3N4 films were deposited as spacers, 1000 TbFeCo films were used as magneto-optical recording layers, and 1000 protective layers made of Si3N4 films were sequentially deposited without breaking the vacuum. Using a semiconductor laser with a wavelength of 8300 m as a light source and a magneto-optical head with a condenser lens having N and A of 0.55, the noise level of the two disks produced was measured through the polycarbonate substrate. The focus of the focused beam is on the surface aligned with the TbFeCo film.The disk was rotated at a linear speed of 10 m/see and the noise level at IMHz was measured using a spectrum analyzer. The noise is
7dB compared to the noise of the disc made as a comparative example
It was low.

Subsequently, when IMHz signals were recorded on both disks, there was no difference in carrier level between the two disks, and the disk having the photocurable resin layer according to the present invention showed a 7 dB better value in terms of reproduction CIN.

(Effects of the Invention) As described above, the magneto-optical recording medium according to the present invention has significantly improved noise characteristics compared to conventional media, and also has a reproduction C.
IN is improving.

This invention aims to eliminate the optical non-uniformity of the substrate by forming the photocurable resin on the substrate to be thicker than the depth of focus of the condensed beam. With the media structure of the present invention, even if there is not only disturbance in the polarization plane but also roughness such as scratches on the substrate surface, the smoothness of the magneto-optical recording layer surface can be improved by coating the resin. It is also effective in reducing noise associated with intensity fluctuations.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the structure of a magneto-optical recording medium to which the present invention is applied, and FIGS. 2, 3, 4 and 5 are sectional views showing the structure of a conventional magneto-optical recording medium. It is. In the figure, 1...Substrate, 2...Spacer, 3...Magneto-optical recording layer, 430. Protective layer, 5... Photocurable resin layer, 11.
...It's a groove. ,';゛Ui;,'1 ,I1Personal Patent Attorney 内U','Responsibility l Figure/2 Based ri i8;[2,
? To the varnish ζ-pu 3 ] Nine shoulders roasted 1 Zengko ``Ai 4: I dumb official f 1 Tsu de Kishio: Nomi F 1 e conversion 1 Geo〃shi n ≦ A Dano Z (branch) zu/: Haki Kawara 3: Ishiki ki konko f kan (屓 3rd figure 1: Motowo kyū 3: Mitsutoshiri, Kiboko Kuzu / 7 5th 4th figure y: $s net sword (1: j° 2:; shi(;Heap 3: Kounara Qiikisae 4: Say Iko 1st layer

Claims (1)

[Claims] A magneto-optical recording medium for recording, reproducing and erasing information using a laser beam, comprising: a polycarbonate resin substrate; a photocurable resin layer having concentric or spiral grooves for laser beam tracking formed on the substrate; It consists of a spacer formed on this resin layer, a magneto-optical recording layer formed on this spacer, and a protective layer formed on this magneto-optical recording layer. A magneto-optical recording medium characterized by being thicker than the depth of focus of a focused beam.