JP2515761B2 - Optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium structure, and particularly to an optical recording which has a high recording density and is suitable for improving a signal-to-noise ratio (C / N ratio). Regarding the medium.

[Prior Art] In a conventional optical recording medium, a recording bit is formed on a flat portion of a substrate as described in JP-A-52-10102. FIG. 2 shows a situation in which a recording bit is formed in the conventional example. Further, in the past, there were cases where the substrate was provided with irregularities, but this was for the purpose of tracking, and no consideration was given to controlling the heat conduction by changing the thickness of the magnetic film.

[Problems to be solved by the invention]

In the structure of the conventional optical recording medium described above, since the magnetic film or the phase change recording film has a large thermal conductivity, a large output laser beam is required at the time of writing, and the temperature rises in a wide range of the film surface. In addition, since the size of the recording bit becomes large, it has been a hindrance to high density recording. Further, in the conventional method, the position and shape of the write bit are changed due to the change of the write condition, which causes the read noise.

An object of the present invention is to solve the above problems and provide an optical recording medium having a high density and good signal-to-noise characteristics.

[Means for solving problems]

The purpose of the above is to attach a magnetic film to a substrate having irregularities in advance, and to provide a thin portion or a nonexistent portion of the magnetic film or the phase change recording film so that the magnetic domain wall or phase boundary of the recording bit is in that portion. Achieved by stopping.

[Action]

When the recording medium is irradiated with laser light at the time of writing, the magnetic film or the phase change recording film in the part corresponding to the bit is heated, and the heat is transferred to other parts of the recording medium by heat conduction. As shown in FIG. 3, when a thin portion or a broken portion of the recording film is formed by providing a convex portion on the substrate in a bit-concealed form, the substrate material has a thermal conductivity smaller than that of the recording layer, and thus the substrate convex portion is formed. Causes a large temperature difference, and the domain inversion region is defined by the portion surrounded by the convex portion of the substrate. In this structure, since the dissipation due to heat conduction is small, it is possible to record with a smaller laser output as compared with the conventional structure of FIG. Also,
Since the outer periphery of the recording bit is defined by a predetermined convex portion of the substrate, variations in the shape and position of the bit are reduced, noise during reproduction can be reduced, and high-density writing can be performed.

〔Example〕

 Hereinafter, the details of the present invention will be described with reference to Examples 1 to 3.

Example 1 As shown in FIG. 4, on a glass substrate 4 having a diameter of 13 cm,
The ultraviolet curable resin layer 5 is provided with a thickness of about 30 μm, and a metal master mold is used for the resin layer to form a peak-shaped convex portion having a height of 0.5 μm and a width of 0.5 μm. It was provided in parallel lines at 1 μm intervals. An amorphous recording film 2 made of Tb ₂₂ Fe ₆₈ Co ₁₀ (expressed in atomic fraction) was sputtered on the substrate by 1000 times.
It was formed with a membrane pressure of A. On top of that, 800 A of Si ₃ N ₄ is used as a protective film.
Formed to a thickness of. However, the protective film is omitted in the figure. When writing was performed on this recording medium under the conditions of a laser light output of 6 mW and an external magnetic field of 200 Oe, it was confirmed that an inverted magnetic domain having a shape defined by the convex portion of the substrate was formed as shown in FIG. The minimum laser power required for writing is 5 mW, which is 7 mW which is the minimum power when writing on the flat part of the substrate.
It is 20% smaller than the above, and it was confirmed that the application of the present invention allows the laser light output to be small. In this embodiment, the size of the recording bit is the same as that of the conventional one, but two bits can be written adjacent to each other across the peak of the convex portion of the substrate, so that the recording density is double that of the conventional method. In addition, the width of the writing bit within the range of the laser output for recording from 6 mW to 10 mW is the same as the interval between the peak-shaped substrate convex portions that are provided in advance, and the shape of the bit is very stable against variations in the laser output. Was confirmed.

Example 2 In the example shown in FIG. 1, the method for producing the substrate and the thin film is the same as in Example 1. However, in this embodiment, the peaks formed by the convex portions of the substrate are not parallel lines but 1 μm vertically and horizontally.
It was provided so as to make an m-square grid. When writing was performed on this recording medium under the conditions of a laser output of 7 mW and an external magnetic field of 200 Oe, it was confirmed that a square inverted magnetic domain 4 was formed as shown in FIG. The minimum laser output required for writing in this example was 4.5 mW, which was much smaller than the value of 7 mW in the conventional method. The recording areal density in this embodiment was about 100 Mb / cm ² , which was four times the value obtained by the conventional method.

[Third Embodiment] The film structures of the first and second embodiments can be directly applied to phase-change optical recording, the recording density can be doubled or quadrupled, and the laser light output required for recording can be reduced. be able to. This system is also useful for high density recording on optical cards.

〔The invention's effect〕

As described above, according to the present invention, the C / N ratio of the magneto-optical recording medium can be improved, the recording density can be increased four times, and the laser output required for writing can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing the structure of an optical recording medium of Example 2 of the present invention, and FIG. 2 is a diagram showing the structure of a conventional optical recording medium.
FIG. 3 is a diagram showing the structure of an optical recording medium according to the present invention, and FIG.
FIG. 1 is a diagram showing the structure of the optical recording medium of Example 1 of the present invention. 1 ... Substrate, 2 ... Magnetic recording layer, 3 ... Area where magnetic domain is reversed and bits are written, 4 ... Glass substrate, 5 ...
UV curable resin layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumiyoshi Kirino 1-280 Higashi Koigakubo, Kokubunji City Central Research Laboratory, Hitachi, Ltd. (56) References

Claims (1)

(57) [Claims] 1. An optical recording medium in which a convex portion is provided on a flat substrate in parallel lines, and a recording film made of a perpendicular magnetization film or a phase change recording film is formed on substantially the entire surface of the substrate. The recording film is formed on the side surface of the convex portion, and the thickness of the recording film on the side surface of the convex portion is the recording film in the recording film. The optical recording medium is configured to be thinner than the thickness of the optical recording medium.