JPH0440638A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain an always specified recording sensitivity by using a material having the temp. characteristics of a thermal conductivity as an underlying layer or protective layer or intermediate layer. CONSTITUTION:If the thin film of such a material which has the small thermal conductivity at room temp. and has the thermal conductivity increasing with an increase in temp. is provided in contact with a recording film, the thermal conductivity of the underlying layer is larger on the inner periphery where the temp. rise is larger and, therefore, the heat generated in the recording film is rapidly transferred to the underlying layer and the temp. rise of the recording film itself decreases. On the other hand, the thermal conductivity of the underlying layer is smaller on the outer periphery where the temp. rise is smaller an, therefore, the heat generated in the recording film is hardly transferred to the underlying layer. The recording sensitivity nearly constant over the entire surface of the disk is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which information is recorded or erased by irradiation with a light beam.

[Conventional technology]

When recording on a conventional optical recording medium, especially an optical disk, it is common to rotate the disk at a constant rotational speed. Therefore, the linear velocity changes depending on the position in the radial direction of the disk to be recorded, and the recording sensitivity differs. That is, the linear velocity increases toward the outer periphery of the disk, resulting in poor recording sensitivity.

Therefore, as described in Japanese Patent Application Laid-Open No. 63-102052, measures have been taken to obtain a constant recording sensitivity over the entire surface of the disk by changing the thickness or composition of the recording film in the radial direction of the disk. It had been taken.

However, such optical discs are difficult to manufacture and are extremely expensive.

[Problem to be solved by the invention]

An object of the present invention is to provide an optical disc that can provide constant recording sensitivity over the entire surface of the disc without changing the composition or thickness of the recording film in the radial direction.

[Means to solve the problem]

The above object can be achieved by using a material that has low thermal conductivity at room temperature and increases in thermal conductivity as the temperature increases, as the underlayer, protective layer, or intermediate layer of the recording film.

In the following explanation, when several types of films are laminated on a substrate in addition to the recording film, the film on the substrate will be referred to as a base layer, the film laminated on top of the recording film will be referred to as a protective layer, and the base layer and recording layer will be referred to as a protective layer. The film in between is an intermediate layer.

When a disk rotating at a constant angular velocity is irradiated with light of a constant intensity, the temperature rise in the recording film decreases as it goes toward the outer periphery of the disk. As a result, differences in recording sensitivity occur in the radial direction of the disk. Here, the amount of laser power required to record recording points of the same size will be referred to as recording sensitivity. Therefore, if a material with the above-mentioned thermal conductivity temperature characteristics is used as the underlayer, protective layer, or intermediate layer, the temperature rise of the recording film will be constant in the radial direction of the disk, so that the recording sensitivity will always be constant. is obtained. This effect is particularly remarkable when a SUS film or an Al alloy film is used.

Since the temperature rise of the recording film varies depending on the type of recording film and the rotation speed, it is necessary to select materials so that the thermal conductivity value and temperature change of the underlayer, protective layer, or intermediate layer are appropriate. This can be adjusted by changing the composition ratio of the SUS film or Al alloy film. Furthermore, by appropriately selecting the thickness of each film, it is possible to adjust the temperature rise of the recording film to be constant.

[Effect]

When a disk rotating at a constant angular velocity is irradiated with light of a constant intensity, the energy of the light irradiated per unit area per unit time decreases as it goes toward the outer periphery of the disk. For this reason, the temperature rise of the recording film becomes smaller toward the outer periphery, and the recording sensitivity becomes worse.

Here, in contact with the recording film, the thermal conductivity is low at room temperature,
If a thin film of a material (here used as the base film as an example) whose thermal conductivity increases as the temperature rises is provided, the heat conductivity of the base film is high at the inner periphery where the temperature rises, so the recording film The generated heat is quickly transmitted to the underlayer, and the temperature rise of the recording film itself is reduced. On the other hand, at the outer periphery where the temperature rise is smaller, the thermal conductivity of the base film is lower, so that the heat generated in the recording film is less likely to be transmitted to the base film.

As a result, by appropriately adjusting the thermal conductivity value, temperature change, and film thickness of the base film, the temperature rise of the recording film at the outer periphery can be made almost the same as the temperature rise at the inner periphery.

〔Example〕

[Example 1] FIG. 1 shows an example of an optical recording medium according to the present invention. On a 5.25-inch polycarbonate substrate 1 having a guide groove, 100 SUs films were deposited as an underlayer 2 and as an intermediate layer 3. A fluororesin (polytetrafluoroethylene) film was formed on 100 sheets and a Te film was formed on 300 sheets as the recording layer 4 by sputtering, respectively, to produce a write-once (perforated) optical disk.

Here, the SUSU2O5 conductivity is as shown in Figure 2.
The higher the temperature, the smaller it becomes.

On the other hand, in a write-once optical disc having a conventional structure, as shown in FIG.
There are two layers of e-membrane.

The two types of optical disks described above were rotated at 180 rpm, and bits were recorded using an optical head equipped with a semiconductor laser with a wavelength of 830 nm. At this time, in conventional optical discs, as shown in Figure 4, the innermost circumference of the disc (radius 30 m +
) and the outermost periphery (radius 60 .mu.m), the laser power required to record a circular bit with a diameter of 0.8 μm was 7 mW at the innermost periphery and 10 mW at the outermost periphery. Here, the pulse width was set to 6Qnsec. In other words, in conventional optical discs, a larger laser power is required toward the outer periphery of the disc. On the other hand, when using the optical disc according to the present invention, the laser power for recording bits with a diameter of 0.8 μm is approximately equal for both the innermost and outermost peripheries.
It was Vv'. Therefore, by using the optical disc according to the present invention, bits of the same size can always be recorded with a substantially constant laser power. Further, even when the type of recording film and the rotation speed are different, by appropriately adjusting the composition and film thickness of the SUS film, it is possible to obtain almost constant recording sensitivity over the entire surface of the disk.

[Embodiment 2] FIG. 5 shows a magneto-optical disk which is an embodiment of the present invention. On a 5.25 inch polycarbonate substrate 1,
800 SiN films as base layer 6.

A T b Fe Co film was formed as the recording film 7 by 300 people, and an Al-Ti film was formed by 200 people as the protective film 8 by magnetron sputtering. This disc is 18
When the disk was rotated at 0 rpm and recording was performed, almost constant recording sensitivity was obtained from the inner circumference to the outer circumference of the disk, as shown in FIG. Furthermore, in the disk structure shown in Fig. 5,
Si between the T b Fe Co film and the Al2-Ti film
Similar results were obtained even when a dielectric material such as an N film was inserted. Furthermore, even in a phase change type optical disc, by using a SUS film or an Al alloy film as the underlayer, protective layer, and intermediate layer, almost constant recording sensitivity can be obtained over the entire surface of the disc.

〔Effect of the invention〕

By using the optical recording medium according to the present invention, at all recording points in the radial direction of a disk rotating at a constant angular velocity,
A certain recording sensitivity can be obtained.

[Brief explanation of drawings]

Figures 1 and 5 are cross-sectional views of optical recording media according to embodiments of the present invention, Figure 2 is a characteristic diagram showing temperature changes in thermal conductivity in SUS films and Al alloy films, and Figure 3 is a diagram of conventional optical recording media. FIG. 4 is a cross-sectional view of the optical recording medium, showing the embodiment of the present invention and the conventional example.
FIG. 2 is a characteristic diagram showing the linear velocity dependence of the laser power required to record a pit (recording point) with a diameter of 8 μm. 1... Polycarbonate substrate, 2... SUS film, 3
゜5...Fluororesin film, 4...Te film, 6...S
iN membrane,'vJ l □□□ 3rd ward'fJ2's Han X! a (voice/, 5et) Envy 5 Figure stain L fake (K)

Claims (1)

[Claims] 1. In an optical recording medium in which a recording film is provided on a predetermined substrate and information is recorded or erased by irradiating the recording film with light, as an underlayer, a protective layer, or an intermediate layer of the recording film. , an optical recording medium characterized by using a material that has a low thermal conductivity at room temperature and a high thermal conductivity at high temperatures. 2. As the base layer, protective layer or intermediate layer,
An optical recording medium characterized by using a SUS film or an Al alloy film.