KR980011179A - Phase-change optical disc - Google Patents

Abstract

The present invention relates to a phase change type optical disc. A phase-change type optical disk in which a first dielectric film, a recording film, a second dielectric film, and a reflective film are sequentially stacked on a substrate, wherein the recording film comprises first, second, and third recording films, And the material of the third recording film is (GeTe) x (Sb2Te3) 1-x, but 1/3 x 1/2, and the material of the second recording film is (GeTe) x (Sb2Te3) 1-xSby, x 1/2, 0 < y 1/2, the information can be erased at a high speed without degrading the repeatability of information recording / erasing.

Description

Phase-change optical disc

FIG. 1 is a schematic cross-sectional view showing a conventional phase change type optical disc.

FIG. 2 is a schematic cross-sectional view showing a phase change type optical disc according to the present invention.

FIG. 3 is a graph showing the erasure ratio change according to the disk rotation speed.

FIG. 4 is a graph showing CNR changes according to the number of recordings.

DESCRIPTION OF THE REFERENCE NUMERALS

11: substrate 12: first dielectric film

13: recording film 14: second dielectric film

15: reflection film 21: substrate

22: first dielectric film 23: first recording film

24: second recording film 25: third recording film

26: second dielectric film 27: reflective film

[TECHNICAL FIELD OF THE INVENTION AND RELATED ART OF THE SAME]

The present invention relates to a phase-change type optical disk, and more particularly to a phase-change type optical disk in which a main recording film having excellent recording / erasure repeatability is used together with a crystallization promoting recording film which is easy to crystallize, To an erasable phase change type optical disc.

FIG. 1 is a cross-sectional view showing the structure of a conventional phase change type optical disc. Specifically, a first dielectric film 12, a recording film 13, a second dielectric film 14, and a reflective film 15 are sequentially stacked on a substrate 11.

As the material of the recording film, Ge-Sb-Te, which is a calcogenide compound capable of reversible change of an amorphous state and a crystalline state, is usually used.

The basic principle of the phase change type optical disc is based on the change in the atomic arrangement of the recording material. That is, when the recording material is heated and cooled by the high-output laser beam, the recording material becomes an amorphous recording portion and the recording material is heated and cooled with a low-output laser beam to form an erased portion in the crystalline state to record and erase information . The reproduction of the information is made by the reflectance difference between the amorphous phase and the crystalline phase.

The phase-change type optical disc has various advantages as compared with the magneto-optical disc.

First, a magneto-optical disk is subjected to a two-step process of erasing and recording information in order to rewrite the recorded information, whereas the phase-change optical disk is directly overwritten by rewriting information by adjusting the intensity of the laser light. ) Method.

Second, since the phase change type optical disk does not require an external magnetic field, the configuration of the apparatus is simple.

Third, the reproduction of information of the phase-change type optical disc is performed by the difference of the reflectance between the crystalline phase and the amorphous phase. Generally, the reflectance difference is about 15 to 30%, which is about 2 to 3% 10 times larger than that of magneto-optical disk.

Recently, there have been many studies on the speed-up of phase-change optical discs, but there has been no significant progress. This is because the recording of information, that is, the amorphization of the recording film, becomes easier as the rotation speed of the disk increases as the rotation speed of the disk increases. However, erasing of information, that is, crystallization of the recording film, It is difficult to lose. Therefore, in order to increase the speed of the phase-change optical disc, it is important that the erasing process (crystallization of the recording film) is performed quickly.

Much research has been made on promoting the crystallization of the recording film to cope with the increase in the speed of the phase change type optical disc. For example, a study on a dielectric film capable of promoting crystallization of a recording film (N. Ohshima, 4th Japan phase change recording study abstract, p12, 1992) and a thin film between a recording film and a dielectric film (T. Kobayashi, Proceedings of the 6th Japan Phase Change Recording Research Conference, p. 93, 1994) was conducted by inserting a tungsten layer to promote the crystallization speed of the recording film.

The focus of these studies is to form a crystallization promoting film on at least one side of the recording film which can lower the activation energy required for crystallization of the recording film. This utilizes the interfacial property between the crystallization promoting film and the recording film, so that crystallization occurs preferentially at the interface where the activation energy is lowered, and this acts as a seed of the crystallization of the entire recording film.

However, these attempts have not yet been extensively verified because it is necessary to confirm the interfacial stability between the recording film and the crystallization promoting film or between the crystallization promoting film and the dielectric film, and the thermal stability of the entire disk. When the stability is deteriorated, there arises a problem that the repeatability of recording / erasure of the optical disk is deteriorated.

Therefore, it is required to use a more stable crystallization promoting film in order to secure the recording / erasing repeatability of the entire disk while improving the erasing characteristics of the recording film due to high-speed rotation.

On the other hand, T. Matsushita et al. Have investigated the effect of adding Sb to Ge2Sb2Te5, which is currently used as a recording film (Phys. Stat. Sol. (A), 133, 395, 1992). As a result, the crystallization temperature becomes higher, the activation energy necessary for crystallization becomes larger, which is disadvantageous from the viewpoint of the crystallization speed, but it is advantageous in terms of the write / erase repeatability.

[Technical Problem]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a phase change type optical disc capable of eliminating the above problem and capable of erasing information at high speed, and having excellent write / erase repeatability of the disc.

[Structure and operation of the invention]

According to an aspect of the present invention, there is provided a phase-change type optical disk comprising a substrate, a first dielectric film, a recording film, a second dielectric film, and a reflection film sequentially laminated on the substrate, Wherein the material of the first recording film and the third recording film is (GeTe) x (Sb2Te3) 1-x, but 1/3 ?? x? 1/2, and the material of the second recording film (GeTe) x (Sb2Te3) 1-xSby, wherein 1/3? X? 1/2 and 0 <y ?? 1/2.

In the present invention, it is preferable that the thickness of the first and third recording films is 1 to 5 nm and the thickness of the second recording film is 10 to 25 nm.

In the present invention, the recording film has a three-layer structure of a two-layer crystallization promoting film and a main recording film formed therebetween to improve the fast erasing and recording / erasing repeatability of information.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 2 is a schematic cross-sectional view showing the structure of a phase change type optical disc according to the present invention. Specifically, a first dielectric film 22 made of ZnS-SiO2, a Ge2Sb2Te5 crystallization promoting recording film 23, a (Ge2Sb2Te5) Sb0.5 main recording film 24, a Ge2Sb2Te5 crystallization promoting recording film A second dielectric film 26 made of ZnS-SiO2, and a reflective film 27 made of an Al alloy are stacked in this order.

Hereinafter, the working principle of the present invention will be described.

The recording film of the present invention has a three-layer structure. When these materials are used as the main recording film (Ge2Sb2Te5) Sb0.5 having excellent recording / erasure repeatability and Ge2Sb2Te5 which is easy to crystallize is formed on both surfaces of the main recording film, Ge2Sb2Te5 is first crystallized upon crystallization, Crystallization of the entire recording film can be more easily caused by acting as a seed of the recording film crystallization.

In addition, since the main recording film occupies almost all of the entire recording film, it is also possible to prevent the recording / erasure repeatability of the entire recording film from deteriorating.

Particularly, when Ge2Sb2Te5 is used as the crystallization accelerating film, the stability of the interface is not a problem because the crystallization promoting film and the main recording film have no difference in the constituent elements, and the interfacial stability of the crystallization accelerating film and the dielectric film has already been studied It is more advantageous than using a new material as a crystallization promoting film.

Hereinafter, the present invention will be described based on Examples and Comparative Examples, but the present invention is not limited thereto.

[Example]

A phase change type optical disk having the same structure as the second embodiment was manufactured. That is, an optical disk was manufactured in the order of a PC substrate, a ZnS-SiO2 first dielectric film, a Ge2Sb2Te5 crystallization promoting film, a (Ge2Sb2Te5) Sb0.5 main recording film, a Ge2Sb2Te5 crystallization promoting film, a ZnS-SiO2 second dielectric film, Respectively. At this time, the thickness of the crystallization promoting film was 2 nm and the thickness of the film was 20 nm at regular intervals. Various physical properties of the manufactured phase change type optical disc were measured, and the results are shown in FIG. 3 and FIG. 4.

At this time, the evaluation of the disk was performed using the PPM (Pulse Position Modulation) / ZCAV (Zone Constant Angular Velocity) recording method and the RLL modulation method. The substrate had a track pitch of 0.9 탆 and a thickness of 0.6 탆. The wavelength of laser light used was 680 nm and NA (Numerical Aperture) was 0.6. The laser power used was 12mW for recording, 6mW for erasing, 1mW for reproducing and was directly rewritten by two signals of 2.12MHz and 8.47MHz.

[Comparative Example 1]

A phase change type optical disc as shown in FIG. That is, on the PC substrate, a ZnS-SiO2 first dielectric film, a (Ge2Sb2Te5) Sb0.5 recording film, a ZnS-SiO2 second dielectric film, and an Al alloy reflective film were formed in this order to manufacture an optical disk. Various physical properties of the manufactured optical disk were measured, and the results are shown in FIG. 3 and FIG. 4.

[Comparative Example 2]

A phase change type optical disc as shown in FIG. That is, an optical disk was fabricated by forming a ZnS-SiO2 first dielectric film, a Ge2Sb2Te5 recording film, a ZnS-SiO2 second dielectric film, and an Al alloy reflective film in this order on a PC substrate. Various physical properties of the manufactured optical disk were measured, and the results are shown in FIG. 3 and FIG. 4.

FIG. 3 shows the erase ratio change according to the disk rotation speed in the comparative example and the embodiment. The high erase ratio value at high speed means that it is easy to erase, which means that the crystallization speed is fast. In the case of Comparative Example 1 using a (Ge2Sb2Te5) Sb0.5 recording film having excellent recording / erasing repeatability but a composition which is difficult to perform in high-speed crystallization, it can be seen that as the disk rotation speed increases, the erasing ratio gradually decreases. It can be seen that it is not suitable for recording / erasing. On the other hand, in the case of Comparative Example 2 using a Ge2Sb2Te5 recording film whose recording / erasing repeatability is low but whose composition is known to be easy to achieve high-speed crystallization, and in the case of an embodiment employing it as a crystallization promoting film, It can be seen that the erasing ratio value is hardly changed.

FIG. 4 is a graph showing changes in CNR according to the number of times of repeated recording in Comparative Examples and Examples. FIG. In the case of Comparative Example 2, the write / erase repeatability was poor, whereas the case of Example and Comparative Example 1 was good.

As can be seen from FIG. 3 and FIG. 4, the optical disc of the embodiment utilizes only the advantages of the optical disc of the comparative example and does not deteriorate the write / erase repeatability while enabling fast erasing of information.

[Effects of the Invention]

As is apparent from the above description, the phase-change optical disc according to the present invention is capable of fast erasing of information without reducing the write / erase repeatability of the disc.

Claims (3)

A phase-change type optical disk in which a first dielectric film, a recording film, a second dielectric film, and a reflective film are sequentially stacked on a substrate, wherein the recording film comprises first, second, and third recording films, And the material of the third recording film is (GeTe) x (Sb2Te3) 1-x, but 1/3 x 1/2, and the material of the second recording film is (GeTe) x (Sb2Te3) 1-xSby, x 1/2, 0 &lt; y 1/2. &Lt; / RTI &gt; The phase-change type optical disk according to claim 1, wherein the first and third recording films have a thickness of 1 to 5 nm. The phase-change type optical disk according to claim 1, wherein the thickness of the second recording film is 10 to 25 nm. ※ Note: It is disclosed by the contents of the first application.