JPH0721877B2 - Optical information recording carrier - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device using a photosensitive recording material whose optical properties reversibly change upon irradiation with a laser beam.

2. Description of the Related Art As an optical disc in which information can be corrected and rewritten, a photosensitive material is formed in the form of a thin film on a disc substrate of a polymer resin such as acrylic resin, and the optical disc is heated by laser irradiation, It is generally used to perform recording and erasing by changing optical characteristics, that is, reflectance and transmittance, by rapid cooling and slow cooling.

As a recording material exhibiting the above characteristics, for example, a chalcogen compound or a metal compound containing tellurium with an addition of germanium, antimony, etc. is used, and by using these, the recording is made into a state generally called amorphous with low reflectance, and erasing is performed by heating. Optical information can be recorded and erased in real time by forming a crystalline state with high reflectance by slow cooling. As a light source, a semiconductor laser that satisfies high diaphragm performance, is small, and is capable of direct modulation is generally used.

Information recording, erasing, and reproducing operations are performed by irradiating the semiconductor laser 3 while rotating the disk 1 in the rotation direction 2 as shown in FIG. 100 μm, sway in radial direction 5. However, it is necessary to irradiate a desired track with laser light within a range of about ± 0.1 μm in order to perform high-density recording and accurately erase and reproduce information. Therefore, as shown in FIG. An uneven groove for guiding laser light is provided. Note that FIG. 4 is a sectional view of the structure in the vicinity of the recording film 6 in the radial direction 5 of FIG. That is, the recording film 6 is provided with a step difference of about 1000Å to form the recording track 4, and the recording film 6 of the protective layer 7 is covered with a constant thickness. By providing the step in this way, the recording track 4 can be identified (tracking) by the optical path length difference of the laser light, and the desired track can be accurately irradiated with the laser.

Problems to be Solved by the Invention However, in such a structure, there is a problem in that the heat propagation is hindered due to the step difference at the end 8 of the recording track 4, and the recording film 6 is locally damaged and thermally damaged. there were.

This is for the following reasons. To improve sensitivity,
Since the protective layer 7 uses a substance having low thermal conductivity, the recording film 6 generally has better thermal conductivity than the protective layer 7. Therefore, heat is sufficiently diffused toward the recording film in the central portion 9 of the recording track, but the end portion 8 is in contact with the protective layer 7 having poor thermal conductivity and the bent shape makes it easy for heat to accumulate, and thus the edge of the recording film is easily accumulated. In part 8, the temperature gradient becomes large as shown in FIG.
Therefore, the recording track end portion 8 tends to expand due to thermal expansion, but the protective layer 7 does not reach such a high temperature and thermal expansion is small. For this reason, stress is applied to the end portion 8 of the recording track, and as a result, a crack is generated, which causes a noise signal.

Means for Solving the Problems The technical means of the present invention for solving the above problems is to provide a thermal diffusion layer made of a material having a higher thermal conductivity than that of the protective layer only on the step portion between the adjacent recording tracks. Is.

Action The action of this technical means is as follows. That is, when the recording track is irradiated with the laser beam, the high thermal conductive material between the recording tracks smoothly receives the heat from the end portion of the recording track and acts to accelerate the diffusion of the heat, and the heat is applied to the end portion of the recording track. It will not accumulate.

Embodiment FIG. 1 shows an embodiment of the present invention and is a sectional view of the structure in the vicinity of the recording film 6 in the radial direction 5 of FIG. Elements common to those in FIG. 4 are designated by common numbers. In FIG. 1, 6 is a recording film, 4 is a recording track, 10 is a thermal diffusion layer, and 7 is a protective layer. The recording film has a change in optical constant before and after recording, that is, an amorphous state having a low reflectance by heating and quenching, and a crystalline state having a high reflectance by heating and slow cooling, such as a chalcogen compound, or tellurium, germanium, antimony. A metal oxide containing, for example, is used.
As the protective layer, a low thermal conductivity substance such as SiO ₂ is used in order to protect the recording film from chemical and mechanical aspects and to effectively utilize the heat applied to the recording film. As the thermal diffusion layer, a substance having higher thermal conductivity than the protective layer, for example, a carbon-based metal is suitable. What is important here is that heat is not accumulated in the end portions 8 of the recording tracks, so it is not necessary to provide heat diffusion layers above and below the recording tracks 4.
The thermal diffusion layer 10 is provided only in the portion in contact with the recording track end portion 4.

Next, the operation of the configuration of this embodiment will be described. The recording track 4 is irradiated with laser light during recording and erasing,
Since the central portion 9 of the laser light is usually stronger than the end portion 8 of the recording track, the temperature becomes higher in the central portion 9 of the recording track. Therefore, the heat flow is from the central portion 9 to the end portion 8 of the recording track.
However, since the end portion 8 of the recording track is in contact with the heat diffusion layer 10 having high thermal conductivity, heat does not accumulate at the end portion 8 and flows smoothly to the heat diffusion layer. FIG. 2 shows the recording track end portion 8 to the central portion 9 at this time.
As for the temperature distribution from the end portion 8 to the end portion 8, the temperature gradient becomes gentle at the recording track end portion 8 as described above, and the thermal stress applied to the recording track end portion 8 becomes small due to the difference in thermal expansion, so that the recording film 6 is affected. The problem of cracks does not occur. If the coefficient of thermal expansion of the thermal diffusion layer is close to the coefficient of thermal expansion of the recording film material, the above effect can be further enhanced.

EFFECTS OF THE INVENTION In the present invention, the thermal diffusion layer is provided between the recording tracks, so that the end portions of the recording tracks are not locally heated to a high temperature, and therefore excessive thermal stress does not occur at the end portions of the recording film. Therefore, it is possible to provide a highly reliable disk in which the recording film is not cracked and the noise signal generation factor is greatly reduced. Note that the effect of the present invention can be sufficiently achieved by the same action even if an optical disk having a recording film directly attached to a substrate is provided with a thermal diffusion layer having a higher thermal conductivity than the substrate without using a protective layer. .

[Brief description of drawings]

FIG. 1 is a radial sectional view of an optical disc according to an embodiment of the present invention, FIG. 2 is a temperature distribution diagram of the same radial direction, FIG. 3 is a schematic configuration diagram of the optical disc, and FIG. 4 is a conventional optical disc. A radial cross-sectional view and FIG. 5 are radial temperature distribution diagrams of the optical disk. 4 ... recording track, 7 ... protective layer, 10 ... thermal diffusion layer.

Claims (1)

[Claims] 1. An optical information recording carrier comprising a recording material made of a substance whose optical properties change depending on a light irradiation state, and a substance layer having a higher thermal conductivity than a protective layer for protecting the recording material provided between recording tracks.