JP2002329315A - Information recording method, information reproducing method, information recording and reproducing method, and phase-change recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information recording and reproducing method which can realize multi-leveled recording by a simple recording pulse strategy. SOLUTION: The information recording and reproducing method records and reproduces multi-leveled information in a phase-change recording medium, and multi-leveled information is recorded by changing the mark length in the disk tangential direction in accordance with recording information with a period P which is 0.5 to 1.0 of a recording and reproducing beam diameter defined by 1/e<2> of a peak value. Since the ratio of an amorphous mark to the base in the crystalline state is changed when the mark length is changed, the multi- leveled information can be recorded by changing the mark length in many stages, and therefore, the recording many stages in accordance with the ratio of the amorpnous mark to the base in the crystalline state, change of the reflected light quantity accompanied with change of the mark length is detected to reproduce multi-valued information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording method, an information reproducing method, an information recording / reproducing method, and a phase change type recording medium intended for high recording density by multi-value recording.

[0002]

2. Description of the Related Art As an optical recording medium for recording / reproducing information with a laser beam, there is a rewritable phase change recording medium using a phase change material for a recording layer. This phase-change type recording medium uses a material in which a reversible phase change between amorphous and crystal is generated by light irradiation as a recording layer, and can be recorded / erased by a simple optical system and erases already recorded information. However, new information can be easily recorded.

In such a recording method using a phase change, binary recording of the presence or absence of a recording mark is generally performed.
By multi-value recording that writes multiple pieces of information in one recording unit,
Attempts have been made to increase the density of information and transfer data at high speed.

For example, according to JP-A-8-287468 and JP-A-11-25456, a method of changing the area, shape and structure of recording pits so that the average reflectivity is multi-step, A method of defining a plurality of combinations of recording mark positions and arrangements has been proposed.

[0005]

In order to increase the recording density by multi-value recording, it is necessary to reduce the size of one recording unit. It is also important to increase the dynamic range of the change in reflectance within the small unit. Also, a complicated recording pulse strategy should be avoided in terms of recording speed and drive cost.

In view of the above points, the conventional multi-level recording method disclosed in the above-mentioned Japanese Patent Application Laid-Open Nos. 8-287468 and 11-25456 has disadvantages such as a complicated recording pulse strategy. There is probably room for improvement.

Therefore, according to the present invention, an information recording method capable of realizing multi-value recording by a simple recording pulse strategy,
An object of the present invention is to provide an information reproducing method, an information recording / reproducing method, and a phase change recording medium.

[0008]

According to the first aspect of the present invention,
An information recording method for recording multi-valued information on a phase change recording medium, wherein a disc tangent is recorded at a period of 0.5 to 1.0 of a recording / reproducing beam diameter represented by 1 / e ² of a peak value. By changing the mark length in the media direction according to the information to be recorded, the mark length is recorded as multi-value information.

Therefore, in the phase change recording medium, the ratio between the amorphous mark and the base in the crystalline state changes due to the change in the mark length. By changing the mark length in multiple steps, multivalued information can be recorded, and the recording pulse strategy for that can be simplified.

According to a second aspect of the present invention, in the information recording method of the first aspect, a recording pulse strategy for modulating a power level at two or more levels is used, and at least one power level is changed according to the information to be recorded. Thereby, the mark length is changed.

Therefore, the mark length can be changed in multiple stages with a dimension smaller than the beam diameter by a simple recording pulse strategy for changing at least one power level.

According to a third aspect of the present invention, in the information recording method of the first aspect, a recording pulse strategy for modulating a power level at two or more levels is used, and at least one power level is held in accordance with the information to be recorded. The length of the mark is changed by changing the length of the mark.

Therefore, the mark length can be changed in multiple steps with a dimension equal to or smaller than the beam diameter by a simple recording pulse strategy that changes the time for holding at least one power level.

According to a fourth aspect of the present invention, in the information recording method according to the first aspect, a recording pulse strategy for modulating a power level at two or more levels is used, and at least one power level and one level are set according to the information to be recorded. The mark length is changed by independently changing the time for holding the two power levels.

Therefore, the mark length can be changed more finely in multiple steps by independently changing the at least one power level and the time for holding the at least one power level.

According to a fifth aspect of the present invention, in the information recording method of the second or fourth aspect, the power levels to be modulated are three levels of a recording level, an erasing level, and a bias level (where recording level> erasing level> Bias level)
The power level that changes the level according to the information to be recorded is the erasing level.

Therefore, when the power level to be modulated is three levels, the mark length can be changed in multiple steps with a dimension smaller than the beam diameter by a simple recording pulse strategy by changing the level of the erasing level.

According to a sixth aspect of the present invention, in the information recording method of the third or fourth aspect, the power levels to be modulated are three levels of a recording level, an erasing level and a bias level (where recording level> erasing level> Bias level)
Wherein the power level for changing the level holding time according to the information to be recorded is at least one of the recording level and the bias level.

Therefore, when the power level to be modulated is three levels, by changing the time for maintaining at least one of the recording level and the bias level, the mark length can be reduced to a dimension smaller than the beam diameter by a simple recording pulse strategy. Can be changed in multiple stages. Preferably, the time for maintaining both the recording level and the bias level is changed.

According to a seventh aspect of the present invention, there is provided a phase change recording medium, wherein the recording information is recorded on the recording layer as multi-valued information by the information recording method according to any one of the first to sixth aspects.

Therefore, it is possible to provide a phase-change type recording medium in which information density is increased by recording with a simple recording pulse strategy.

According to an eighth aspect of the present invention, in the phase change type recording medium according to the seventh aspect, the recording layer comprises SbTe having an Sb / Te ratio in a range of 2 to 5, Ag, In, and Gb.
at least one selected from e, Ga, B, Si and Al
Contains elemental species.

Therefore, by adopting such a recording layer structure, the laser power dependence of the crystallization speed appears strongly,
Further, since the crystallization speed is high, the phase change following property of the recording pulse is good, so that the information recording method according to claim 1, the information reproducing method according to claim 9, the information reproducing method according to claim 9, and the method according to claim 10.
It is suitable for the described information recording / reproducing method.

According to a ninth aspect of the present invention, there is provided an information reproducing method for reproducing multi-valued information from the phase-change recording medium according to the seventh or eighth aspect, wherein a change in a reflected light amount accompanying a change in a mark length is detected. Thus, the multi-value information is reproduced.

Therefore, in the case of the phase change type recording medium, when the mark pitch becomes equal to or less than the diffraction limit of the reproduction beam, the amplitude decreases, and the reflected light intensity is increased in multiple steps according to the ratio between the amorphous mark and the base in the crystalline state. Since multi-value information recorded by changing the mark length within a predetermined period according to the information to be recorded according to the invention to be recorded can detect the change in the reflected light intensity. Thereby, reproduction of multi-value information becomes possible.

According to a tenth aspect of the present invention, there is provided an information recording / reproducing method for recording / reproducing multi-valued information on / from a phase change recording medium, wherein a recording / reproducing beam diameter represented by 1 / e ² of a peak value. Is recorded as multivalued information by changing the mark length in the disc tangential direction in accordance with the information to be recorded in a period of 0.5 to 1.0, and a change in the amount of reflected light accompanying the change in the mark length is detected. Thus, the multi-value information is reproduced.

Therefore, in a phase change type recording medium, since the ratio between the amorphous mark and the base in the crystalline state changes due to the change in the mark length, the ratio between the amorphous mark and the base in the crystalline state changes at a predetermined cycle in relation to the recording / reproducing beam diameter. By changing the mark length in multiple steps, multivalued information can be recorded, and the recording pulse strategy for that can be simplified. Also, in the case of a phase change recording medium, when the mark pitch is equal to or less than the diffraction limit of the reproduction beam, the amplitude decreases, and the reflected light intensity can be changed in multiple stages according to the ratio between the amorphous mark and the base in the crystalline state. Therefore, for multi-valued information recorded by changing the mark length within a predetermined period according to the information to be recorded as described above, it is possible to reproduce the multi-valued information by detecting a change in the reflected light intensity. Become.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows an outline of an information recording / reproducing method according to the present embodiment. FIG. 1A shows a beam shape of a recording / reproducing beam B and a phase change mark shape in a phase change recording medium.

One mark M is formed in one unit (recording unit) U. At this time, the information recording method of the present embodiment is based on changing the length of the mark M in the tangential direction (mark length) in multiple stages according to the information to be recorded. As the mark length changes, the ratio between the amorphous mark and the crystalline base in one unit U changes. Therefore, in the present embodiment,
The length L of one unit U is set to 0.5 to 1.0, more preferably 0.75 to 1.0, of the beam diameter φ expressed by 1 / e ^2.
The mark M is formed at a constant period P corresponding to the unit length L.

When the mark pitch becomes equal to or less than the diffraction limit of the reproduction beam B, the amplitude decreases, and the reflected light intensity can be changed in multiple stages according to the ratio between the amorphous mark in the unit U and the base in the crystalline state. . Therefore, in the present embodiment, by changing the mark length in the unit U in multiple steps according to the information to be recorded and recording the multivalued information, the multilevel information is recorded, and the change in the reflected light intensity is detected. This is to reproduce multi-value information.

Here, a method of controlling the mark length to a size smaller than the beam diameter φ will be described. First, the laser power is modulated at two levels, more preferably at three levels or more. FIG. 1B shows a recording pulse strategy according to the present embodiment, in which a rectangular wave whose power level is modulated at three levels is used. Set the laser power to the recording level Pw, bias level Pb, erasing level P
The modulation is performed in the order of e (where Pw>Pe> Pb), and a mark M is formed in each unit U.

In FIG. 1, part (A) shows an example of controlling the mark length, in which at least one power level, preferably an erase level Pe, is changed in accordance with information to be recorded. By changing the erasing level Pe, the timing at which the rear end Me portion of the mark M is erased can be changed. When the erasing level Pe is lowered as in Pe1, the crystallization speed is reduced and the erasing timing is delayed, so that the mark length of the mark M to be recorded becomes longer. When the erase level Pe is increased as in Pe3,
Since the crystallization speed becomes faster and the erasing timing approaches the emission waveform, the mark length of the mark M to be recorded becomes shorter.
Therefore, the erase level Pe is set to Pe1, Pe2, P
The mark length in the unit U (the area occupied by the mark M in the unit U) can be changed by changing in a plurality of stages as shown by e3. More specifically, the erasing level Pe is determined by the relationship with the recording level Pw.
It is desirable to change e / Pw in the range of 0.0 to 0.7.

In FIG. 1, part (a) shows an example of controlling the mark length, in which the time for holding at least one power level is changed according to the information to be recorded.
Here, according to the information to be recorded, the time for retaining the recording level Pw or the bias level Pb at that level (=
Tw and Tb (corresponding to the pulse width) are changed in several steps. As a more preferable example, an example is shown in which the ratio Tw / Tb of these holding times Tw and Tb is set in the range of 0.3 to 1.5, and both (Tw, Tb) are changed.

When forming the short mark M, the holding times Tw and Tb are shortened. When forming a long mark M, the holding times Tw and Tb are lengthened. The mark M is lengthened by increasing the holding time Tw. By extending the holding time Tb, the cooling time is extended, and the mark M is further extended by the skirting of the mark rear end Me portion.

As will be described later, if the level of the erasing level Pe and the holding times Tw and Tb of the recording level Pw and the bias level Pb are simultaneously and independently changed, the mark length can be reduced. More fine control is possible.

Such control of the recording method is preferable by setting the recording layer material of the phase change recording medium to the following composition. The layer configuration is a general four-layer phase change type recording medium 1 as shown in FIG. 2, and the material of the recording layer 4 is characterized. SbTe is used for the parent phase of the recording layer 4. The ratio Sb / Te of SbTe is 2 to 5, more preferably 3 to 4. SbTe as a base layer and A as an additive element
The composition contains at least one element selected from g, In, Ge, Ga, B, Si, and Al. Preferably, AgInSbTe, GeAgInSbTe, GeI
The composition is nSbTe, GeGaSbTe, GaSbTe, or the like. According to the composition of the recording layer 2, the laser power dependence of the crystallization speed appears strongly, and since the crystallization speed is high, the phase change following property with respect to the recording pulse is good. Become.

[0038]

EXAMPLE An example based on the above embodiment will be described.

As shown in FIG. 2, the structure of the phase change recording medium 1 is as follows: a polycarbonate substrate 2 / ZnS-SiO ₂ layer 3 / recording layer 4 / ZnS-SiO ₂ layer 5 / Ag layer 6 / overcoat layer 7. This is a laminated structure. The composition of the recording layer 4 is
Ge-3at%, Ga-7at%, Sb-65at%, Te-25
at%. The track pitch is 0.4 μm, the numerical aperture NA of the optical system is 0.65, and the wavelength of the laser beam used is 4
05 nm.

FIG. 3 shows recording conditions and mark length measurement results of this embodiment. The unit length was 0.5 μm, and the length of the mark M recorded in this cycle in the tangential direction was measured. The horizontal axis indicates the time of Tw + Tb obtained by adding the above-mentioned holding times Tw and Tb, and the respective holding times Tw and Tb
Is changing. Here, Tw / Tb = 0.7. The vertical axis is the mark length, which is a value obtained by measuring the distance between the front and rear ends of the mark M at the track center.

The mark length is reduced by increasing the power level ratio Pe / Pw. Further, the holding time Tw,
The mark length is shortened by shortening Tb. FIG.
In the states F, E, and D shown in the figure, Tw + Tb time is fixed,
A change when the power level ratio Pe / Pw is changed from 0.4 to 0.6 is shown. In the states C and B, the power level ratio is fixed at Pe / Pw = 0.6 and the time Tw + Tb is changed. Shows the change.

As described above, the mark length of the mark M is 0.4
It can be changed in five steps in the range from μm to 0.1 μm. When combined with the state A in which the mark M is not recorded, six levels of reflected light can be formed in the unit U having a length of 0.5 μm.

FIG. 4 is a diagram for explaining a recording signal and a reproduction waveform, and FIG. 4A shows a change in a mark shape (mark length). The unit length is 0.5 μm. State A
F correspond to the conditions of FIG. 3 and are recorded by a recording pulse strategy as shown in FIG. 4B. FIG.
(C) shows a reproduction waveform from the phase change recording medium 1 on which the mark M is recorded in this manner, and the vertical axis shows a change in reflected light intensity. The reflected light intensity changes stepwise due to the inter-mark interference. Since the occupied area of the amorphous mark changes, the intensity level changes.

By using the recording pulse strategy as shown in FIG. 4B to record on the recording layer 4 having the above-described composition, the reflected light level can be changed in six steps with a simple single recording pulse strategy. be changed. That is, recording / reproduction of six-value information becomes possible.

[0045]

According to the information recording method of the first aspect of the present invention, in a phase change recording medium, the ratio between the amorphous mark and the base in the crystalline state changes due to the change in the mark length. By changing the mark length equal to or smaller than the beam diameter in multiple steps at predetermined intervals in relation to the beam diameter, multilevel information can be recorded, and the recording pulse strategy for that can be simplified.

According to the second aspect of the present invention, in the information recording method according to the first aspect, with respect to a recording pulse strategy for modulating a power level at two or more levels, a simple recording pulse strategy for changing at least one power level is used. The mark length can be changed in multiple stages with a dimension smaller than the beam diameter.

According to the third aspect of the present invention, in the information recording method according to the first aspect, with respect to a recording pulse strategy for modulating a power level at two or more levels, a simple method of changing a time for holding at least one power level. With a recording pulse strategy, the mark length can be changed in multiple steps with a dimension smaller than the beam diameter.

According to a fourth aspect of the present invention, in the information recording method according to the first aspect, at least one power level and at least one power level are related to a recording pulse strategy for modulating a power level at two or more levels. By changing the holding time independently, the mark length can be changed more finely in multiple steps.

According to the fifth aspect of the present invention, in the information recording method of the second or fourth aspect, when the power level to be modulated is three levels, a simple recording pulse strategy is achieved by changing the level of the erase level. , The mark length can be changed in multiple steps with a dimension smaller than the beam diameter.

According to the sixth aspect of the present invention, in the information recording method according to the third or fourth aspect, when the power level to be modulated is three levels, at least one of the recording level and the bias level is maintained. By changing the time, the mark length can be changed in multiple steps with a dimension equal to or smaller than the beam diameter with a simple recording pulse strategy.

According to the seventh aspect of the present invention, it is possible to provide a phase change type recording medium in which information density is increased by recording using a simple recording pulse strategy.

According to the eighth aspect of the present invention, in the phase-change recording medium according to the seventh aspect, by specifying the composition of the recording layer, the laser power dependence of the crystallization speed appears strongly, and Since the multiplexing speed is high, the phase change following property with respect to the recording pulse is good, so that it is suitable for the information recording method according to claims 1 to 6, the information reproducing method according to claim 9, and the information recording / reproducing method according to claim 10. Becomes

According to the information reproducing method of the ninth aspect of the present invention, in the case of a phase change type recording medium, when the mark pitch becomes equal to or less than the diffraction limit of the reproducing beam, the amplitude decreases and the difference between the amorphous mark and the base in the crystalline state is reduced. The multi-valued information recorded by changing the mark length within a predetermined period according to the information to be recorded according to the invention as claimed in claim 1, since the reflected light intensity can be changed in multiple stages according to the ratio. With regard to (1), multivalued information can be reproduced by detecting a change in the intensity of the reflected light.

According to the information recording / reproducing method according to the tenth aspect of the present invention, in the phase change recording medium, the ratio between the amorphous mark and the base in the crystalline state changes by changing the mark length. By changing the mark length less than the beam diameter in multiple steps at a predetermined cycle in relation to the diameter, it is possible to record multi-valued information, and the recording pulse strategy for that can be simplified, and the phase change In the case of a type recording medium, when the mark pitch is equal to or less than the diffraction limit of the reproduction beam, the amplitude decreases, and the reflected light intensity can be changed in multiple stages according to the ratio between the amorphous mark and the base in the crystalline state. For multi-valued information recorded by changing the mark length within a predetermined period according to the information to be recorded as described above, the change in the reflected light intensity is detected. It is possible to playback of the multi-level information I.

[Brief description of the drawings]

FIG. 1 shows an outline of an information recording / reproducing method according to an embodiment of the present invention, in which (a) is an explanatory diagram showing a beam shape and a phase change mark shape, and (b) is a pulse waveform diagram showing a recording pulse strategy. It is.

FIG. 2 is a schematic sectional view showing a layer configuration of a phase change recording medium.

FIG. 3 is an explanatory diagram showing recording conditions and mark length actual measurement results according to an embodiment of the present invention.

FIG. 4 shows an outline of an information recording / reproducing method according to an embodiment of the present invention, and FIG. 4 (a) is an explanatory diagram showing a phase change mark shape;
(B) is a pulse waveform diagram showing a recording pulse strategy,
(C) is a waveform diagram showing a reproduction waveform.

[Explanation of symbols]

 Reference Signs List 1 phase change type recording medium 4 recording layer Pw recording level Pe erase level Pb bias level Tw holding time Tb holding time

Continued on the front page F term (reference) 5D029 JA01 JB11 5D090 AA01 BB05 CC05 DD01 EE02 EE05 FF12 KK04 5D119 AA22 BA01 BB04 HA48

Claims (10)

[Claims] 1. An information recording method for recording multi-valued information on a phase change recording medium, comprising: a recording / reproducing beam diameter of 0.1 / e ² of a peak value;
An information recording method in which a mark length in a disc tangential direction is changed according to information to be recorded in a period of 5 to 1.0 to record as multi-value information. 2. The information according to claim 1, wherein a recording pulse strategy that modulates a power level at two or more levels is used, and the mark length is changed by changing at least one power level according to the information to be recorded. Recording method. 3. A recording pulse strategy for modulating a power level at two or more levels, wherein the mark length is changed by changing a time for holding at least one power level in accordance with the information to be recorded. 1. The information recording method according to 1. 4. A recording pulse strategy for modulating a power level at two or more levels, wherein at least one power level and a time for holding one power level are independently changed according to the information to be recorded. 2. The information recording method according to claim 1, wherein the mark length is changed. 5. The power level to be modulated is three levels of a recording level, an erasing level and a bias level (where recording level> erasing level> bias level), and the power level is changed according to information to be recorded. The information recording method according to claim 2, wherein is the erase level. 6. The power level to be modulated is three levels of a recording level, an erasing level, and a bias level (where recording level> erasing level> bias level), and the time for which the level is held in accordance with the information to be recorded is determined. 5. The information recording method according to claim 3, wherein the power level to be changed is at least one of the recording level and the bias level. 7. A phase-change recording medium in which recording information is recorded as multi-valued information on a recording layer by the information recording method according to any one of claims 1 to 6. 8. The recording layer has an Sb / Te ratio of 2 to 5.
, SbTe in the range of Ag, In, Ge, Ga,
8. The phase change recording medium according to claim 7, comprising at least one element selected from B, Si, and Al. 9. An information reproducing method for reproducing multi-valued information from a phase-change recording medium according to claim 7, wherein the multi-valued information is detected by detecting a change in a reflected light amount accompanying a change in a mark length. An information reproducing method that reproduces the information. 10. An information recording / reproducing method for recording / reproducing multi-valued information on / from a phase change type recording medium, wherein a recording / reproducing beam diameter represented by 1 / e ² of a peak value is 0.
In a period of 5 to 1.0, the mark length in the disc tangential direction is changed in accordance with the information to be recorded, thereby recording as multi-valued information. An information recording / reproducing method for reproducing multi-valued information.