JPH06223413A - Optical disk - Google Patents

Abstract

PURPOSE:To enable reproduction at high SN to increase the quantity of reproducing light by forming the reflection layer of the disk of reflection layers made of multilayered dielectric films to lower the thermal conductivity thereof, thereby increasing the recording and erasing sensitivity to laser pits. CONSTITUTION:The optical disk consisting of a substrate 1 consisting of a polycarbonate transparent resin, a protective layer 2 consisting of ZnS, an optical information recording layer 3 consisting of a GeTe2Sb4 alloy, the reflection layers 4 made of the multilayered dielectric films consisting of SiO2 and TiO2 and an acrylate resin layer 5 is provided. The reflection layers 4 made of the multilayered dielectric films are formed by alternately laminating two kinds of the dielectric substance layers 4a, 4b in, for example, 10 layers, all at optical film thicknesses of lambda/4 to a wavelength lambda of the laser beam to be used for recording, erasing and reproducing. As a result, the thermal conductivity is lowered and, therefore, the recording and erasing sensitivity to the laser pits is increased and the reproduction at the high SN to increase a reproducing quantity is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc for recording information with a laser beam or the like.

[0002]

2. Description of the Related Art In recent years, information related fields such as computers and communications have been developed, and among them, an optical disk has been partially put into practical use as a recording medium capable of storing a huge amount of image data.

For optical disks, researches and developments have been actively pursued for technical problems such as enabling recording and erasing operations and for improving reliability for practical use.

An optical disk usually has a structure in which a thin film layer of a protective layer and an optical information recording layer is laminated on a transparent substrate such as glass or plastic.

Recording and erasing are carried out by heating the optical information recording layer in accordance with the laser beam intensity by laser light to change the characteristics of the optical information recording layer, that is, a so-called heat mode recording system. ing.

As the laser light source, a semiconductor laser that is small and light and capable of directly modulating the light intensity is used.

As a rewritable optical disc, as an optical information recording layer, a phase change optical disc having an optical recording medium made of a chalcogen material or the like as an information recording carrier, which is a change in optical characteristics of a crystalline phase and an amorphous phase, and a magnetic material. There is a magneto-optical disk having an information recording carrier which is a change in optical characteristics due to a difference in magnetization direction of an optical information recording layer made of.

As the optical information recording layer of the former phase change optical disk, a chalcogen material such as Te or Se, or a material obtained by adding Sb, Ge, In or the like is used.

In recording on a phase change optical disk, an optical information recording layer aligned in a crystalline phase is heated to its melting point by irradiation with laser light and amorphized in the course of cooling to form a recording bit.

Further, erasing is performed by heating the optical information recording layer on which the amorphous recording bits are formed to a temperature reaching a crystallization temperature lower than the melting point and recrystallizing, and reproducing is performed.
This is performed by irradiating the optical information recording layer with a low-power laser beam that does not cause a change in the optical information recording layer and detecting the difference in the amount of reflected light between the amorphous recording bit and the crystalline phase.

For the optical information recording layer of the latter magneto-optical disk, a magnetic material such as an alloy of a rare earth metal element such as Tb and a ferromagnetic transition metal of Fe or Co is used.

Recording on a magneto-optical disk is performed by heating the optical information recording layer to near the Curie point by irradiating a laser beam while applying an external magnetic field and then cooling the optical information recording layer by magnetizing in a certain direction and recording bits. To form.

Further, erasing is performed by heating the optical information recording layer on which recording bits are formed again near the Curie point and magnetizing it by an external magnetic field applied in a direction opposite to that at the time of recording, and reproducing is performed by a reproducing laser beam. The rotation of the polarization plane due to the Kerr effect when the light is recorded on the optical information recording layer is detected as a difference in the amount of light transmitted through the analyzer.

In the reproduction of the optical disk by the phase change and the magneto-optical, it is possible to increase the signal-to-noise ratio because of the sensitivity characteristic of the photo detector such as the photodiode.
It is necessary to obtain a sufficient amount of reflected light from the optical disc.

For this reason, conventionally, the optical information recording layer is thickened, or A having a large reflectance on the back surface side of the optical information recording layer.
A metal layer such as u or Al is provided to increase the reflectance.

However, when the optical information recording layer is thickened, the heat capacity of the optical information recording layer is increased, the recording sensitivity is lowered, and the characteristics are deteriorated due to repeated overwriting, so that the latter structure having a metal reflective layer is used. Often.

The metal reflection layer serves as a heat conduction layer and affects the temperature change of the optical information recording layer during recording / erasing.

On the other hand, in order to record / reproduce data at a high speed as a data file memory, it is necessary to increase the number of revolutions of the optical disk to increase the peripheral speed with respect to the optical head and to increase the transfer rate.

However, when the peripheral speed is increased, the laser irradiation time is relatively shortened. Therefore, in recording / erasing, the laser requires high power to heat the optical information recording layer to the recording or erasing temperature. .

[0020]

Such a conventional optical disc uses a laser other than the semiconductor laser in order to limit the power when the current semiconductor laser is used and to reduce the size and weight of the optical disc device. Therefore, it is necessary to improve the sensitivity in recording and erasing the optical disc. Further, in the case where a structure having a metal reflection layer having a high reflectance is used to improve the reproduction characteristics, there is a limit to the improvement of sensitivity due to heat conduction to the metal reflection film, and it is possible to satisfy these two characteristics. was difficult.

The present invention solves the above problems, and an object of the present invention is to provide an optical disk having a high reflectance and a high recording / erasing sensitivity.

[0022]

In order to achieve the above object, the present invention provides a protective layer on a substrate, an optical information recording layer for recording an information signal by a temperature change caused by laser light irradiation,
It is characterized in that the reflective layer of an optical disc formed by laminating reflective layers is formed of a dielectric multilayer reflective layer.

[0023]

According to the present invention, since the reflective layer is a multi-layered film made of a dielectric material, the thermal conductivity is lower than that of the metal reflective layer, so that the optical information recording film is heated by the laser during recording / erasing. Since it cannot be prevented, it is highly sensitive to the amount of laser light and has a high reflection wavelength band in the laser light wavelength band, so that high reflectance can be obtained.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing the structure of an optical disk according to an embodiment of the present invention. In FIG. 1, 1 is thickness 1.
2mm polycarbonate transparent resin substrate, 2 is 150nm thick
ZnS protective layer, 3 is a 250 nm thick GeTe ₂ Sb ₄ alloy optical information recording layer, 4 is a dielectric multilayer reflective layer made of SiO ₂ and TiO ₂ , and 5 is an acrylate resin layer of 5 μm.

The dielectric multilayer reflective layer 4 has an optical film thickness of λ / 4 for the wavelength λ of the laser beam used for recording, erasing and reproducing the two types of dielectric layers 4a and 4b, and alternates. It is made by stacking 10 layers.

The optical film thickness is a numerical value represented by the product of the physical film thickness and the refractive index of the film. In this embodiment, a laser beam having a wavelength of 820 nm is used for recording, erasing and reproducing, and a film having a thickness of 140 nm is used. Si
O ₂ layer (bending rate 1.46) and 82 nm thick TiO ₂ layer (bending rate 2.5)
From the optical information recording layer 3 side, in this order, 5 layers each,
10 layers were laminated.

The ZnS protective layer 2, the GeTe ₂ Sb ₄ alloy optical information recording layer 3, and the dielectric multilayer reflective layer 4 were formed by magnetron sputtering, and the acrylate resin layer 5 was formed by spin coating.

FIG. 3 is a sectional view showing the structure of a conventional optical disk for comparison, and the same symbols as those in FIG. 1 indicate the same elements. Here, in the conventional example, instead of the dielectric multilayer reflection layer 4 in the configuration of the optical disc of the present example, the thickness is changed.
A 130 nm Al reflective layer 6 is provided.

The reflectance is 15% in both this embodiment and the conventional example.
Was the same.

As an evaluation of recording sensitivity, a peripheral speed of 25 m /
FIG. 2 shows the recording and erasing characteristics of the optical information recording layer 3 when the laser beam of 15 mW was irradiated for 40 ns under the same temperature condition as the irradiation time of the laser spot of 1 μm diameter in s in this embodiment and the conventional example. Shown in.

In this embodiment (solid line), the heat conduction from the optical information recording layer 3 is smaller than that in the conventional example (broken line), and therefore the melting point of the optical information recording layer 3 is exceeded even with an extremely short laser pulse. It turns out that the temperature has been reached and recording is possible.

According to the present invention, it is possible to realize an optical disc having a low minimum laser power capable of recording and erasing and having a sufficient reflectance.

[0033]

As described above, the optical disc of the present invention has a low minimum laser power capable of recording and erasing and has a sufficient reflectance, so that an optical disc having a high transfer rate and a large reproduction signal can be obtained. Becomes

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an optical disc according to an embodiment of the present invention.

FIG. 2 is a diagram showing recording and erasing characteristics according to a temperature change of this embodiment and a conventional example.

FIG. 3 is a cross-sectional view showing a configuration of a conventional optical disc.

[Explanation of symbols]

1 ... Substrate, 2 ... ZnS protective layer, 3 ... GeTe ₂ Sb ₄ alloy optical information recording layer, 4 ... Dielectric multilayer reflective layer, 5 ... Acrylate resin layer, 6 ... Al reflective layer.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 29, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

The optical film thickness is a numerical value represented by the product of the physical film thickness and the refractive index of the film. In this embodiment, laser light having a wavelength of 820 nm is used for recording, erasing and reproducing, and the thickness is 14
SiO ₂ layer 0nm and (refraction index 1.46), the thickness of 82n
TiO ₂ layer of m (the refraction index of 2.5), from the optical information recording layer 3 side, by respective five layers in this order, and laminating total 10 layers.

Claims (1)

[Claims] 1. A protective layer on a substrate, and an optical information recording layer for recording an information signal by a temperature change caused by irradiation of laser light,
An optical disc in which a dielectric multilayer reflective layer is formed as the reflective layer of an optical disc in which reflective layers are laminated.