JPH04103034A - Information recording method for phase variation type optical disk - Google Patents

Abstract

PURPOSE:To execute the high density recording by taking two kinds of phase states of an amorphous phase of a recording mark center part and a coarse crystal phase of a recording mark peripheral part. CONSTITUTION:Light power of a recording pulse P of a light beam is set so that an amorphous (b) formed part of the center part, and coarse crystal (a), (c) parts of its peripheral part become a high level H2 and a low level H1, respectively. Also, the rear step side of the amorphous (b) formed part is set to a level H3 being lower by (h) so that a recording mark of a tear type is not formed. A state that a regular pattern of this binary information is written in a recording track T becomes an initial state of the recording track T. Recording of information to this recording track T is executed by crystallizing the recording mark M of the amorphous phase (b) by the light beam B, and varying a recording pattern of its part. In such a way, recording is executed at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to a method for recording information on a phase change optical disc used for recording and reproducing information.

(Prior Art) In recent years, optical disks have been attracting attention as a large capacity memory.

Optical discs are broadly divided into playback-only types represented by CDs (compact discs), write-only types that can be recorded once and represented by electronic document files, and rewritable types that allow recording and erasure. .

Among the rewritable types, so-called phase-change optical disks, in which recording and erasing are performed by reversibly changing the recording film between a crystalline phase and an amorphous phase by laser beam irradiation, are attracting attention.

- Optical discs using chalcogenide-based materials for the recording film are being considered as phase-change optical discs used for recording and reproducing information. The conventional technology for phase-change optical disks is detailed in "Rewritable Optical Disk Materials" (written by Masahiro Okuda, published by Kogyo Chosenkai Co., Ltd., first published on May 20, 1989).

A phase change type optical disk records and reproduces information by utilizing phase changes between a crystalline phase and an amorphous phase of a chalcogenide recording film. A conventional phase change optical disk operates as follows.

1) Since the recording film formed by sputtering, vapor deposition, etc. is amorphous, the recording film is turned into a crystalline phase by heat annealing treatment or light beam irradiation. This is called initialization or crystallization.

2) A short, high-power recording pulse melts the crystalline recording film, rapidly cools it, and turns it into an amorphous state, forming recording marks.

3) Crystallize the recording mark in the amorphous phase with a long pulse and low power erasing pulse to erase the recording mark.

Further, it is also being considered to perform override by superimposing recording power on erasing power.

(Conventional Example 1) FIG. 5 schematically shows the recording pulse P used when recording by the conventional recording method and the metal structure of the recording mark M at that time. When recording on a rotating optical disk using the conventional recording pulse P, the recording mark M on the track T becomes wavy, and the amorphous portion and coarse crystal portions a and c do not have a predetermined width. In particular, the widths of the coarse crystal parts a (!:c) before and after the amorphous part are not the same.This is because the recording beam moves before the coarse crystal part a on the front end side of the recording mark M is sufficiently heated. This is because heating is insufficient, and conversely, the coarse crystal portion C on the rear end side of the recording mark M is heated more than necessary due to the residual heat effect from the already heated portion.

Therefore, with the conventional recording method, it is impossible to record the widths of the amorphous portion and the coarse crystal portions a and c of the recording mark M to predetermined values.

(Conventional example 2) FIG. 6 schematically shows an outline of a conventional recording method.

In this conventional example, a continuous groove (group) G of an optical disc D,
An example is shown in which recording is performed on a recording track T consisting of a land portion R sandwiched between G.

The signal level is 0, 1 . The recording laser pulse P is modulated into two values, and recording is performed with a recording laser pulse P corresponding to the two values. The recording track T is initially crystallized in advance, and the initially crystallized recording track T has fine crystals. An amorphous recording mark M is formed on the initialization track T by a recording laser pulse P.
form and record.

In response to the recording laser pulse P, the center is amorphous,
A wave-shaped recording mark M whose peripheral portion is made of coarse crystals a and C is formed. In reproducing the recorded information, binary information is reproduced with the amorphous portion at the center of the recording mark set to level 1 and the fine crystal molecules at the initial crystallized portion set to level 0.

In this conventional recording method, the coarse crystal parts a and c at the peripheral part of the recording mark M are included in the size of the recording mark M, and the initial crystallized part r or the crystal part of the erased part forms the recording mark M.
were separated. Therefore, if an attempt is made to increase the density by closely packing the recording marks M, the reproduced signals of the closest patterns will overlap, making it difficult to increase the density beyond the size of the recording marks M.

(Problem to be Solved by the Invention) Conventionally, the size of the recording mark M was determined by the size of the focused spot of the light beam, and furthermore, in order to perform high-density recording, it was necessary to use a light beam with a shorter wavelength. is necessary.

Therefore, it is possible to reduce the size of the recording mark M and increase the density in recording and reproduction using a conventional semiconductor laser.
It was difficult. If recording marks M are packed closely together, it becomes difficult to separate the reproduced signals, and conventional recording and reproducing methods have a limit to increasing the density.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an information recording method for a phase-change optical disk that can improve the recording density limit due to the size of recording marks caused by the diffraction limit of a light beam.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides a phase change method for recording information by irradiating a light beam and causing a change in state in the irradiated area. This is a method for recording information on type optical discs, in which a recording track is formed with a regular pattern of an amorphous phase in the center irradiated with a light beam and a crystalline phase in the periphery, and an amorphous mark is created by irradiating the light beam. It records information by crystallizing it.

(Function) The structure of recording marks on a phase-change optical disk is determined by the cooling rate of melting and cooling during recording. That is, the portion where the cooling rate during melting and solidification is higher than the critical cooling rate for amorphization becomes amorphous, and the portion that does not reach the critical cooling rate crystallizes. Since crystal growth occurs in the direction along the heat flow, the recording mark has an amorphous phase at its center, and a metal structure consisting of coarse radial columnar crystals at the center.

The cooling rate of the recording film of a phase-change optical disk during recording varies somewhat depending on the recording film itself, but is more significantly influenced by the layer configurations of the protective film, reflective film, substrate material, etc. It also depends on the pulse shape of the recording light beam.

Therefore, it is possible to adjust the width of the amorphous phase at the center of the recording mark and the width of the coarse crystalline phase at the periphery to a predetermined width by controlling the cooling rate of the recording mark based on its layer structure, light beam pulse profile, etc. It is possible.

From the above, it is possible to perform high-density recording by creating two types of phase states: an amorphous phase at the center of the recording mark and a coarse crystalline phase at the periphery of the recording mark, and making each phase state correspond to information. I can do it.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment in which a recording track T is formed by the recording method of the present invention. This embodiment shows an example in which recording was performed on a recording track T of a land portion R sandwiched between continuous grooves (groups) G and G.

First, in the present invention, the recording track T is formed as follows.

The recording track T is initially crystallized in advance, and the initial crystallization track T has fine crystals. A recording mark M is formed on the initialization track T by a recording laser pulse P, and recording is performed. In response to the recording laser pulse P, a recording mark M is formed whose central portion is amorphous and whose peripheral portion is composed of coarse crystals a and c. The amorphous portion at the center of the recording mark M is set to level 1, and the coarse crystalline portions a and c at the periphery of the recording mark M are set to level O, and are made to correspond to binary information.

Then, the optical power of the recording pulse P of the light beam B is set so that the central amorphous crystal forming part is at a high level H2, and the peripheral part of the coarse crystals a and c is at a low level H7. has been done.

Further, the level H3, which is lower by h, is set on the rear side of the portion where the amorphous layer is formed so that a record mark of the amount of tears is not formed.

In the recording method of the present invention, the state in which this regular pattern of binary information is written on the recording track T is
The initial state is For example, 1°0.1,0,1,0.
A pattern of . . . is recorded in advance on the recording track T.

Next, as shown in FIG. 2, information is recorded on this recording track T by crystallizing the recording mark M of the amorphous phase with a light beam B and changing the recording pattern of that part. . Since the crystallization optical power requires less optical power than the optical power of the amorphous beam B, it is suitable for increasing the recording speed. Furthermore, since the recording power can be lower than in the past, the life of the light source such as a semiconductor laser is also improved.

The pattern previously recorded on the recording track T may be any regular pattern, but it is desirable to use a pattern suitable for high-density recording.

The recorded information is reproduced by detecting changes in the recording pattern.

Further, erasure of the recorded information is performed by irradiating the crystallized recording mark M with a light pulse of a level capable of making it amorphous, thereby making it amorphous.

In this recording method, there is a regularity in that both sides of the amorphous phase of the recording mark M are coarse crystal phases. By overriding the track T that has been recorded once, it is also possible to make the coarse crystal phase continuous.

FIG. 3 schematically shows an example of the layer structure of a phase change optical disc D to which the present invention can be applied. Also in the present invention, the layer structure of a conventional phase change optical disk can be used.

In FIG. 3, a phase-change optical disk D capable of high-density recording to which the present invention can be applied includes a first disk substrate 10, a protective layer 11, a recording layer 12, and Protective layer 13, reflective layer 14, and protective layer 15
It consists of

This layer structure is an example of a single disk, and it is also possible to make a double-sided optical disk by bonding two single disk optical disks with the surface with the recording layer 12 on the inside.

In addition, depending on the application, protective layer 11, protective layer 13, reflective layer 1
4. The protective layer 15 can also be omitted.

The optical disk substrate 10 is made of a material that is transparent and has little change over time.
For example, acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate resins, epoxy resins,
It is made of styrene resin, glass, etc. Continuous grooves, sample servo marks, preformat marks, etc. are formed depending on the recording format.

The recording layer 12 is made of a material whose state changes when irradiated with the light beam B. Such phase change materials include GeTe, TeSe, and Ge5bSe.
chalcogenide-based amorphous semiconductors such as TeOx-based, InSe-based, Ge5bTe-based, InSb-based, Ga
Compound semiconductor materials such as Sb-based and In5bTe-based materials can be used. This recording layer 12 can be formed by a vacuum deposition method, a sputtering method, or the like.

In practice, the thickness of this recording layer 12 is several 01 to several μ■
Preferably, the range is within the range.

The protective layers 11 and 13 are disposed to sandwich the recording layer 12, and have the role of preventing the recording layer 12 from scattering or being punctured by the recording beam irradiation.

It also has the role of controlling thermal diffusion for heating and cooling the recording layer 12 during recording. This protective layer 11゜13 is S i
02. S io, All N, AN 203Zr02.
TiO2, Ta2O3, ZnS, Si.

Alternatively, Ge or the like can be formed by a vacuum evaporation method, a sputtering method, or the like.

Practically speaking, it is preferable that the protective layers 11 and 13 have a thickness of several nanoliters to several micrometers.

The reflective layer 14 has the effect of optically enhancing the optical changes in the recording layer to increase the reproduced signal and the effect of cooling the recording layer. This reflective layer 14 is made of Au.

AI* A metal film such as Cu or Ni-Cr alloy can be formed by a vacuum evaporation method, a sputtering method, or the like. Practically speaking, the thickness of the reflective layer 14 is preferably from several nanoliters to several micrometers.

The protective layer 15 is provided to prevent scratches, dents, etc. when handling the phase change type optical disc D, and is usually formed of an ultraviolet curing resin or the like. The protective layer 15 is formed, for example, by applying an ultraviolet curable resin onto the surface of the reflective layer 14 by a spin-coding method and curing it by irradiating ultraviolet rays. The thickness of the protective layer 15 is preferably in the range of several micrometers to several hundred micrometers in practical terms.

In order to perform high-density recording according to the present invention, it is necessary to control the cooling rate of the recording layer 12 during recording. This cooling rate is controlled by the above-mentioned protective layer 11.13 and reflective layer 1.
4. This is possible by setting the material and film thickness of the recording layer 12 to a predetermined material and film thickness.

For example, in order to increase the cooling rate of the recording layer 12, the thickness of the recording layer 12 is made thinner, the material of the protective layers 11 and 13 is made of a material with high thermal conductivity, and the thickness of the reflective layer 14 is made thicker. It is also effective to use a material with high thermal conductivity for the reflective layer 14.

Furthermore, in order to perform high-density recording according to the present invention, it is also effective to modify the profile of the recording laser pulse.

FIG. 4 schematically shows an example of a recording laser pulse profile effective for realizing the present invention and the metal structure of the recording mark M at that time.

In this example, a recording pulse P with increased optical power at the rising edge of the recording pulse P is used. This is an example of an override recording pulse in which a recording pulse is superimposed on the optical power of the erase level. By using such recording pulses, amorphous parts and coarse crystal parts a can be recorded.

A recording mark M can be formed with the width of C being a predetermined width. Therefore, high-density recording is possible with the amorphous portion b1 and the coarse crystal portions a and b.

Therefore, the structure of the recording marks M on the phase change optical disk D is determined by the cooling rate of melting and cooling during recording. That is, the portion where the cooling rate during melting and solidification is higher than the critical cooling rate for amorphization becomes amorphous, and the portion that does not reach the critical cooling rate crystallizes. Since crystal growth occurs in the direction along the heat flow, the recording mark M has an amorphous phase at its center, and a metal structure consisting of coarse radial columnar crystals at its center.

The cooling rate of the recording film of the phase-change optical disc D during recording varies somewhat depending on the recording film itself, but is more significantly influenced by the layer configurations of the protective film, reflective film, substrate material, etc. It also depends on the pulse shape of the recording light beam B.

Therefore, by controlling the cooling rate of the recording mark M based on its layer structure, light beam pulse profile, etc., the width of the amorphous phase at the center of the recording mark and the coarse crystalline phase a at the periphery are adjusted.
It is possible to set the width of c to a predetermined width.

From the above, high-density recording is possible by creating two types of phase states: amorphous phase b at the center of the recording mark and coarse crystalline phases a and c at the periphery of the recording mark, and making each phase state correspond to information. can be done.

In addition, in the above-mentioned embodiment, the recording mark M is placed on the land portion R.
is formed in the above example, but it may be formed in the group portion G or both.

In addition, it goes without saying that the present invention is not limited to the one embodiment described above, and can be implemented in various modifications without changing the gist.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a recording system with higher density than the conventional phase change optical disc recording system. Further, the density can be increased using a light beam of a conventional wavelength without using a particularly short wavelength light beam for the purpose of high density. Furthermore, the recording method of the present invention can be applied using a light beam with a shorter wavelength than the conventional one, and in that case, higher density is possible.

Further, according to the present invention, the power of the light beam during recording can be significantly reduced, which is effective in increasing the recording speed and extending the life of the light source.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing an outline of a high-density recording method for a phase-change optical disc according to an embodiment, and FIG. 2 is a diagram schematically showing an outline of a high-density recording method for a phase-change optical disc according to an embodiment of the present invention. 3 is a sectional view of a phase change optical disk recording medium to which the present invention is applied, and FIG. 4 is a diagram schematically showing recording pulses used in the present invention and recording marks at that time. FIG. 5 is a diagram schematically showing a conventional recording pulse and recording marks at that time, and FIG. 6 is a diagram schematically showing an outline of binary recording on a conventional phase change optical disk. DESCRIPTION OF SYMBOLS 10... Optical disk substrate, 11... Protective layer, 12...
...Recording layer, 13...Protective layer, 14...Protective layer, 15
...Protective layer, a... Coarse crystal part, b... Amorphous part, C... Coarse crystal part, B... Light beam, D... Optical disk, M... Recording mark . Figure 1 Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 1 Figure 1

Claims (1)

[Claims] (1) An information recording method for a phase-change optical disc in which information is recorded by irradiating a light beam to cause a state change in the irradiated area, the method comprising: an amorphous phase at the center of the light beam irradiation and the surrounding area; 1. A method for recording information on a phase-change optical disc, characterized in that a recording track is formed from a regular pattern of crystalline phases, and information is recorded by crystallizing an amorphous mark by irradiation with a light beam.