JPH0863781A - Phase change type optical disk - Google Patents

Abstract

PURPOSE: To improve the overwriting characteristics of a phase change type optical disk and to obtain a novel phase change type optical disk capable of high density recording by making the reflectance of an amorphous recording mark higher than that of a crystalline part and therefore making the absorption factor of the crystalline part higher than that of the amorphous recording mark. CONSTITUTION: A 1st protective film 2, a recording film 3, a 2nd protective film 4 and a reflecting film 5 are laminated on a transparent substrate 1 to obtain a phase change type optical disk and the top of the reflecting film 5 is coated with a UV-curing resin 6 for protection. In order to make the reflectance of an amorphous recording mark higher than that, of a crystalline part and to therefore make the absorption factor of the crystalline part higher than that of the amorphous recording mark, the thickness of the 1st protective film is regulated to 80-120nm, e.g. when the thickness of the recording film of GeSbTe is 15nm, that of the 2nd protective film of ZnS-SiO2 is 20nm and that of the reflecting film of Al is 60nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase-change type optical disc in which information is recorded / reproduced / erased at a high density by using a laser beam, and particularly, a difference in reflectance and absorptivity between an amorphous portion and a crystalline portion. The present invention relates to a phase change type optical disc for recording.

[0002]

2. Description of the Related Art An optical disk recording system using laser light is capable of high-capacity recording and can be accessed at high speed in a non-contact manner. Optical discs are classified into a read-only type known as a compact disc and a laser disc, a write-once type that can be recorded by the user himself, and a rewritable type that can be repeatedly recorded and erased by the user. The write-once type / rewritable type optical disc is used as an external memory of a computer or as a document / image file.

Rewritable optical disks include phase-change optical disks that utilize the phase change of the recording film and magneto-optical disks that utilize the change of the magnetization direction of the perpendicular magnetization film. this house,
A phase change optical disc does not require an external magnetic field and
It is expected that rewriting type optical discs will become the mainstream in the future because they can be easily burnt.

Conventionally known is a rewritable so-called phase change type optical disk using a recording film which causes a phase change between a crystal and an amorphous by irradiation with laser light. In a phase-change type optical disk, a high power laser light spot corresponding to the information to be recorded is irradiated on the recording film to locally raise the temperature of the recording film, thereby causing a phase change between crystalline and amorphous. Recording is performed, and the change in the optical constants associated therewith is read as a reflected light intensity difference or a phase change by the low-power laser light for reproduction. For example, in a phase-change type optical disc using a recording film having a relatively slow crystallization time, the disc is rotated and the recording film formed on the disc is irradiated with laser light so that the temperature of the recording film is higher than the melting point. Then, after the laser light has passed therethrough, it is rapidly cooled to make the portion amorphous and recorded. At the time of erasing, the recording film is crystallized by holding the temperature of the recording film in a temperature range above the crystallization temperature and below the melting point for a time sufficient for crystallization to proceed. As a method for this purpose, there is known a method of irradiating a long oval laser light in the laser light traveling direction. In the case of performing pseudo-overwrite by two beams for recording new information while erasing the already recorded data, the elliptic laser light for erasing is changed to the circular laser light for recording. Arrange to irradiate first.

On the other hand, in a disc using an information recording film capable of high-speed crystallization, a single laser beam focused in a circular shape is used. The conventionally known method is to increase the power of laser light to 2
Crystallization or amorphization is performed by changing between two levels. That is, by irradiating the recording film with laser light having a power capable of raising the temperature of the recording film to a temperature equal to or higher than the melting point, most of the recording film becomes in an amorphous state upon cooling, while the recording film temperature decreases. The portion of the laser beam irradiated with the power so as to reach a temperature higher than the crystallization temperature and lower than the melting point becomes a crystalline state. The recording film of the phase-change optical disk is formed of a chalcogenide-based material such as GeSbTe-based or In-based.
SbTe system, InSe system, InTe system, AsTeGe
System, TeOx-GeSn system, TeSeSn system, SbSe
Bi-based, BiSeGe-based, etc. are used, and both are formed by a film-forming method such as a resistance heating vacuum evaporation method, an electron beam vacuum evaporation method, or a sputtering method. The state of the recording film immediately after film formation is a kind of amorphous state, and an initialization process in which the entire recording film is made crystalline in order to perform recording on this recording film to form an amorphous recording portion. Is done. Recording is accomplished by forming an amorphous portion within this crystallized state.

In the above-mentioned conventional disc, when reproducing by utilizing the difference in reflected light amount, a phase change type optical disc having an amorphous reflectance smaller than that of a crystalline state is used. The absorptance of the crystal part was smaller than that of the amorphous. When mark edge recording is performed by overwriting on a disc having such characteristics, distortion of the mark edge occurs due to the difference in absorption rate described above,
This has been an obstacle to high density recording.

For example, Japanese Laid-Open Patent Publication No. 2-128330 discloses the regulation of the absorptance of the recording film, but there is no description about the absorptance of the medium corresponding to the mark edge recording, and the unerased portion is reduced. Therefore, it merely stipulates that the difference in the absorptance between the crystal and the amorphous be kept small.

[0008]

The absorptance control of the phase change type optical disk will be described in detail with reference to the drawings.

FIG. 3 is a cross-sectional view of a phase change type optical disk for explaining absorption rate control of the phase change type optical disk.

The structure of the phase change type optical disk is the transparent substrate 3
On the first protective film 32, recording film 33, second protective film 34,
This is a so-called four-layer reflection film structure in which the reflection films 35 are sequentially laminated and further an ultraviolet curable resin 36 or the like is applied for protection. Here, conventionally, a configuration has been adopted in which the amorphous reflectance of the recording film 33 is smaller than the reflectance in the crystalline state. That is, when the reflectance of the amorphous portion is Ra and the reflectance of the crystalline portion is Rc, Ra <Rc. In this case, the change of the optical constant due to the phase change of the recording film 33 can be efficiently converted into the change of the reflectance, and a good reproduction signal can be secured, but most of the light is reflected by the reflective film 35. Therefore, if it is attempted to secure a large reflectance difference due to the change of the optical constant of the recording film 33, the absorptance of the recording film 33 is inevitably smaller than that of the amorphous portion. There was a flaw. When the absorption rate of the amorphous portion is Aa and the absorption rate of the crystalline portion is Ac, Ac <Aa. As described above, when the absorptance of the crystalline portion is small, the thermal conductivity of crystalline material is generally higher than that of amorphous material, and the latent heat required for melting is also large. There is a difference in the temperature rising state of the recording film depending on whether it is crystalline or amorphous.

FIG. 4 is a diagram showing a phase change recording mechanism for explaining the absorption rate control of the phase change type optical disk.

In order to have information on the mark edge,
It is essential to accurately form the edge shape. When the absorption rate control is insufficient as shown in FIG. 4, the overwrite signal is modulated by the signal component before overwrite,
In particular, edge shape distortion occurs near the mark edge. We have found, as a result of our research, that this is one of the factors that limit the overwrite jitter reduction.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to make the reflectance of an amorphous recording mark higher than that of a crystalline portion and the absorption rate of the crystalline portion to be higher than that of an amorphous portion. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks, improve the overwrite characteristics of a phase-change optical disk, and provide a novel phase-change optical disk that enables high-density recording.

Therefore, the phase change type optical disk of the present invention uses reversible phase change between the crystal and amorphous of the information recording film, and records information by the phase change of the information recording film by laser light irradiation. A phase-change type optical disc for reproducing and erasing, comprising a transparent substrate, a first protective film formed on the transparent substrate, and a phase-change information recording film formed on the first protective film.
It has a second protective film formed on the recording film and a reflective film formed on the second protective film, and the reflectance of the amorphous recording mark of the information recording film is Ra and the reflection of the crystal part is The absorption rate of the amorphous recording mark is Aa, and the absorption rate of the crystalline portion is Ac.
In this case, Ra> Rc and Ac> Aa.

In the phase change type optical disk of the present invention, ZnS-SiO ₂ is used as the first protective film, GeSbTe is used as the phase change type information recording film, and ZnS-SiO _{2 is used} as the second protective film.
By using Al as the reflection film, and GeSbTe
The film thickness of the recording film is 10 nm to 20 nm, ZnS-SiO
₂ The thickness of the second protective film is 15 nm to 30 nm, and the thickness of the Al reflective film is 50 nm to 150 nm.
The film thickness of nS-SiO ₂ is set in the range of 80 nm to 120 nm.

[0016]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a diagram showing the reflectance and absorptance characteristics of an embodiment of the phase change type optical disk according to the present invention.

In the phase change type optical disk of the present embodiment, the reflectance and the absorptivity characteristics of the amorphous recording mark are set to be higher than that of the crystalline portion.
The feature is that the absorptance of the crystal part is made larger than that of the amorphous part.

FIG. 2 is a sectional view of the phase change type optical disk of this embodiment.

The phase change type optical disk of this embodiment has a structure in which a first protective film 2, a recording film 3, a second protective film 4, and a reflective film 5 are laminated on a transparent substrate 1. An ultraviolet curable resin 6 is applied on the reflective film 5 for protection. Disc-shaped glass or plastic is used for the transparent substrate 1. The first protective film 2 and the second protective film 4 are made of SiO ₂ ,
_{Si3 N4, AlN, TiO 2,} ZnS, ZnS-Si
A dielectric material such as O ₂ is used. As the recording film 3, a chalcogenide-based material such as GeSbTe-based or In
SbTe system, InSe system, InTe system, AsTeGe
System, TeOx-GeSn system, TeSeSn system, SbSe
Bi type, BiSeGe type, etc. are used. The reflective film 6 is made of a material having a high reflectance and a high thermal conductivity, especially A
Metals such as 1, Au, Cu, and Ag are used. In addition,
An ultraviolet curable resin 6 is applied to the uppermost layer for protection.

The feature of this embodiment lies in the structure of the optical disc in which the difference in absorption rate is controlled. The reflectance of the amorphous recording mark is made higher than that of the crystalline portion, whereby the state where the absorptance of the crystalline portion is higher than that of the amorphous portion is realized.

FIG. 1 is a graph showing changes in optical disk reflectance and absorptance when the film thickness of the ZnS-SiO2 first protective film is changed. For example, the GeSbTe recording film has a film thickness of 15 nm, and the ZnS-SiO ₂ second protective film has a film thickness of 20 n.
When the film thickness of the Al reflective film is 60 nm, the desired condition can be realized within the range of the film thickness of the first protective film from 80 nm to 120 nm.

Further, the thickness of the GeSbTe recording film is set to 10
nm to 20 nm, the thickness of the ZnS-SiO ₂ second protective film is 15 nm to 30 nm, and the thickness of the Al reflection film is 50 nm.
To 150 nm and the thickness of the first protective film is set in the range of 80 nm to 120 nm, the reflectance of the amorphous recording mark is made larger than that of the crystalline portion in the laser wavelength region that can be used at present, and It is possible to realize a state in which the absorptance of the crystal part is larger than that of the amorphous part.

Next, the laser wavelength to be used is set to 830 nm and the reflectance of the amorphous recording mark is made larger than that of the crystalline portion, so that the absorptance of the crystalline portion is larger than that of the amorphous portion. The structure of the optical disc was determined so that the above could be realized, and the optical disc was created. The substrate 1 has a diameter of 130
A polycarbonate substrate with a pregroove having a thickness of 1.2 mm and a thickness of 1.2 mm was used. The first protective film 2 and the second protective film 4 are ZnS—SiO ₂ mixed films, and the recording film 3 is GeSbT.
e was continuously formed by a magnetron sputtering method using Al for the reflection film 5.

The film thickness of each layer was 100 nm for the first protective film, 15 nm for the recording film, 20 nm for the second protective film, and 60 nm for the reflective film. In this disc, the absorption rate at a wavelength of 830 nm is 80% for crystals and 55% for amorphous materials.
The reflectance was 11% for crystals and 21% for amorphous.

Next, the optical disk was overwritten and the characteristics were evaluated. An optical head equipped with a semiconductor laser having a wavelength of 830 nm was used for the measurement. The optical disk after initialization processing is rotated at a rotation speed of 3600 rpm, and a track with a radius of 30 mm is 8.4 MHz (Duty 50%).
The signal and the 2.2 MHz (Duty 50%) signal were alternately overwritten. The recording power and the erasing power are 10 mW and 5 m, respectively, so that the second harmonic distortion of the reproduced signal is minimized.
Set to W.

The reproduced signal jitter at the time of overwriting was 3.0 ns as a value after pulsing by twice differentiation. It was confirmed that there was not much difference from the jitter at the time of the first recording immediately after initialization, and that it showed good overwrite jitter characteristics.

[0028]

As described above, in the phase change type optical disk of the present invention, the reflectance of the amorphous recording mark is made larger than that of the crystalline portion with respect to the laser wavelength used, whereby the crystalline portion is By making the absorptivity of B to be larger than that of amorphous, it is possible to suppress the bit shape distortion at the time of overwriting and to suppress the increase in the jitter of the reproduced signal at the time of overwriting.

[Brief description of drawings]

FIG. 1 is a diagram showing reflectance and absorptance characteristics of an embodiment of a phase change optical disk according to the present invention.

FIG. 2 is a cross-sectional view of a phase change type optical disc of this embodiment.

FIG. 3 is a cross-sectional view of a phase-change optical disk for explaining absorption rate control of the phase-change optical disk.

FIG. 4 is a diagram showing a phase change recording mechanism for explaining absorption rate control of a phase change type optical disc.

[Explanation of symbols]

 1 Substrate 2 First protective film 3 Recording film 4 Second protective film 5 Reflective film 6 UV curable resin 31 Substrate 32 First protective film 33 Recording film 34 Second protective film 35 Reflective film 36 Ultraviolet curable resin

Claims (2)

[Claims] 1. A transparent substrate, a first protective film formed on the transparent substrate, a phase change type information recording film formed on the first protective film, and a phase change type information recording film. A second protective film formed on the second protective film and a reflective film formed on the second protective film, and a reversible phase change between the crystal and the amorphous phase change information recording film is prevented. Recording of information by changing the phase state of the phase-change type information recording film by laser light irradiation.
In a phase-change type optical disc for reproducing / erasing, a reflectance of an amorphous recording mark recorded on the phase-change information recording film is Ra, a reflectance of a crystal part of the phase-change information recording film is Rc, The absorption rate of the amorphous recording mark is Aa,
Ra: Rc and Ac> Aa, where Ac is the absorptance of the crystalline portion. 2. ZnS—SiO ₂ as the first protective film
GeSbTe is used as the phase change type information recording film, ZnS-SiO ₂ is used as the second protective film, and Al is used as the reflective film. The GeSbTe recording film has a thickness of 10 nm to 20 nm, and ZnS- The thickness of the SiO ₂ second protective film is set to 15 nm to 30 nm, the thickness of the Al reflective film is set to 50 nm to 150 nm, and the thickness of the first protective film ZnS-SiO ₂ is set to 80 nm to 120 nm. The phase change type optical disk according to claim 1, which is characterized in that.