JPH07272272A - Initializing method of phase transition type optical disk - Google Patents

Abstract

PURPOSE:To obtain an initializing method of a phase transition optical disk by which stable overwriting characteristics are obtainable from initial recording to after repetition. CONSTITUTION:Initialization is executed under a condition under which the temp. rising quantity at the time of irradiation with a laser is equaled in the initialized parts and amorphous parts. More specifically, light energy is supplied to the phase transition optical disk in such a manner that the absorbance Ai of the initialized parts subjected to photoirradiation and the absorbance Aa of the amorphous parts satisfy Ai>Aa. The light energy at which a relation between the length Mi of the recording marks recorded on the initialized parts subjected to photoirradiation and the length Ma of the recording marks overwritten and recorded on the amorphous parts attains ¦Mi-Ma¦<0.05mum is supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium for recording and erasing information by utilizing a change in optical constants accompanying a phase change induced by a difference in thermal history, that is, a phase change optical disk.

[0002]

2. Description of the Related Art Magneto-optical disks and phase change optical disks are known as optical information recording media for recording / erasing / reproducing information by irradiating laser light. Among them, for example, in a phase change optical disc, as shown in FIG.
A four-layer structure in which a lower protective layer 2, a recording layer 3, an upper protective layer 4, and a reflective layer 5 are provided in this order on a substrate 1 is usually used. Information recording / erasing is induced by the difference in thermal history of temperature rise / cooling by laser light irradiation.
It is performed by utilizing the phase change between crystals. That is, the recording layer is melted and rapidly cooled to be amorphized for recording,
In addition, erasing is performed by keeping the temperature above the crystallization temperature for a certain time to crystallize. Signal reproduction is performed by utilizing the difference in reflectance between amorphous and crystalline. The film thickness of each of the lower protective layer 2, the recording layer 3, the upper protective layer 4, and the reflective layer 5 is optimized from the viewpoints of sensitivity, C / N, erasing rate, rewritable repetition number, and the like.

Mark edge recording in which information is provided at both ends of a recording mark is effective for increasing the recording density. However, in a phase-change optical disk that uses the reflectance difference between crystalline and amorphous for signal reproduction, the absorptance of the crystal part and the absorptance of the amorphous part are often different. The absorption rate of the crystal part is higher than that of the crystal part. In such a case, the width and length of the formed mark are affected by whether the state before the new recording was crystalline or amorphous, and the jitter greatly increases due to overwriting. Therefore, in order to reduce the jitter and realize the mark edge recording in the phase change optical disk, it is necessary to make the temperature rise amount at the time of laser light irradiation equal in the amorphous portion and the crystal portion. By the way, considering that the crystalline state has a higher thermal conductivity and the latent heat is larger, it is desirable that the absorptance of the crystal part is larger than that of the amorphous part.

In a phase change optical disk, since the recording film immediately after film formation is in an amorphous state, the recording film must be crystallized, that is, initialized before starting recording. As a method of initialization, a method using a laser beam and a method using a flash lamp are known. The state change of the phase change optical disk due to repeated overwrite from the initialized state can be expressed as shown in FIG. Jitter in the initial overwriting is the difference in absorptivity A _a rate of absorption initializing unit A _i and the recording amorphous portion, also, the jitter after repetitive overwriting, erasing of the absorption rate A _e and non It depends on the difference in the absorption rate A _a of the crystalline portion. In order to have low jitter after repeated overwriting, it is necessary to make the absorptance of the crystal part larger than that of the amorphous part as described above. That is, it is necessary to optimize the film thickness of each layer of the medium structure shown in FIG. 2 so that A _e > A _a . As a method for realizing this, there is known a method using Si or Au having a film thickness of 20 nm or less for the reflective layer (Japanese Patent Laid-Open No. 1-149).
No. 238).

[0005]

However, no specific study has been made on the initialization method in these medium configurations. The initialization methods proposed so far are disclosed in Japanese Patent Laid-Open No. 3-278338, in which the laser beam diameter is lengthened to secure a time for keeping the temperature above the crystallization temperature.
As in Japanese Patent Laid-Open No. 4-209317, in which the compositional distribution of the recording layer is made non-uniform by initialization, the erasing rate and C / N
In many cases, the purpose is to improve the power consumption or shorten the initialization time. However, the phase change optical disc has a problem that the initial overwrite and the repeated overwrite have different jitters and erase rates. Further, in the mark edge recording, the jitter may increase even if the erasing rate is high, and it cannot be said that the initialization condition for increasing the erasing rate is suitable for the mark edge recording.

Therefore, an object of the present invention is to provide a method for initializing a phase change optical disk which can obtain stable overwrite characteristics from the beginning when mark edge recording is applied.

[0007]

In order to solve the above problems, the present invention relates to a method of initializing a phase change optical disc, wherein the relationship between the absorptance A _i of the initialized part and the absorptivity A _a of the amorphous part is set. Is initialized under the condition that A _i > A _a, and the length M of the recording mark recorded on the initialization part is
relationship between the length M _a recording mark recorded by overwriting on the _i and an amorphous _{portion, | M a -M i | <} 0.05μ
The feature is that initialization is performed under the condition that m is satisfied.

[0008]

There is both crystalline state [act] an initialization section and the erasing section, but the crystal state of the initialization unit is changed by the initialization process and the initialization condition, the initialization unit absorptance A _i and the erasing unit Absorption rates A _e are not always equal. Therefore, A _e ＞
Even if the medium configuration is optimized so as to be A _a , it is not possible to realize low jitter from the initial overwrite depending on the initialization conditions. For example, when initialization is performed using a focused laser beam with a diameter of about 1.5 μm, the optical characteristics of the initialization section change as shown in FIG. 1 due to the initialization power. Thus, if the absorption rate of the initialization unit A _i and absorptivity A _a of the recording unit has performed the initialization in A _i <initialization power P _i1 and P _i2 as a A _a, reflectivity between crystalline amorphous Although the C / N can be increased because the difference can be increased, the sensitivity is different between the initialized portion and the amorphous portion, so that the initial overwrite causes high jitter. In order to realize low jitter from the initial stage, it is necessary to perform initialization with the initialization power P _i0 that satisfies A _i > A _a .

Further, the optimal initializing conditions defined also using the relation between the mark length M _i of a mark to be formed on the initialization section, a mark length M _a mark formed on the amorphous part can do. Mark length distribution, the average value in the marks recorded on the initialization section M _i, Gaussian distribution with a standard deviation sigma _0, the average value M _a is a mark to be overwritten on the amorphous part, the standard deviation sigma ₀ It has a Gaussian distribution of. When performing overwriting at twice the recording frequency of the old recording data, jitter sigma is ^{_{σ 2 = σ 0 2 + (}} M a -M i) 2 / (4
* V ² ). Here, V represents the linear velocity.
To achieve an error rate of 10 ⁻⁴ or less, σ × V <0.
Since 03 μm is required, σ ₀ × V = 0.015 μm
Then, | M _a −M _I | <0.05 μm must be satisfied.

[0010]

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

FIG. 2 is a view showing a cross section of the optical information recording medium according to the present invention. It has a structure in which a lower protective layer 2, a recording layer 3, an upper protective layer 4, and a reflective layer 5 are sequentially laminated on a substrate 1.

[0012] Example 1 Polycarbonate (PC) is used as the substrate 1, 100 nm and ZnS-SiO ₂ as the lower protective layer 2, 17 nm _of Ge ₂ Sb ₂ Te ₅ as the recording layer 3, ZnS-SiO ₂ as the upper protective layer 4 Of 20 nm and Al as the reflection layer 5 of 60
nm was sequentially laminated by sputtering.

Using the above disk, the initialization power was changed to perform the initialization, and the change of the overwrite characteristic with the repetition was examined.

Initialization was performed by using a semiconductor laser having a wavelength of 830 nm and a focused beam diameter of 1.5 μm, and changing the initialization power to 6, 8 and 10 mW at a linear velocity of 7.5 m / s. The overwrite characteristics were measured using a semiconductor laser with a wavelength of 830 nm at 1.06 at a linear velocity of 11.3 m / s.
Signal of MHz, duty = 45% and 2.12 MHz, d
The signal of duty = 45% was alternately overwritten.

The reflectance and absorptance of the initialization portion changed as shown in FIG. 4 depending on the initialization power. The absorptance of the amorphous portion was 70%, and the absorptance of the erased portion after repeated overwriting was 80%. As shown in FIG. 5, the characteristic after repeated overwriting does not depend on the initialization condition. On the other hand, the initial overwrite characteristics vary greatly depending on the initialization conditions. Initialization power 8 mW with A _i = A _a
Under the condition (1), as can be seen from the reproduced waveform in FIG. 6, the erase rate is high because the reflectance of the initialization section and the reflectance of the crystal section are almost equal, but the temperature rise during laser irradiation is the same as that of the initialization section. Since the amorphous portion is different, the jitter is polarized and increased. Under the condition that the initialization power is 10 mW, the difference in reflectance between the initialized portion and the amorphous portion is large, so that the C / N ratio is high. However, since the temperature rise amount during laser irradiation is different between the initialized portion and the erased portion, Jitter is divided into two polarities. On the other hand, under the condition of the initialization power of 6 mW where A _i > A _a , the reflectance of the initialization section is lower than the reflectance of the erasure section, so the erasure rate is slightly low, but the temperature rise during laser irradiation is small. Since the initialization section and the erasing section have the same jitter, the jitter is not divided into two poles and has a low value from the initial stage to the repeated stage.

A TEM observation of a track in which a 2.12 MHz signal was overwritten once with a 1.06 MHz signal was carried out to examine the relationship between the initialization condition and the mark length. In the track initialized under the condition of the initialization power of 6 mW that causes less increase in jitter, the mark length M _i of the mark recorded on the initialization part is
There 2.34Myuemu, mark length M _a mark formed by overwriting on the amorphous portion was 2.38 .mu.m. On the other hand, under the condition of the initialization power of 8 mW that the jitter increase is large,
M _i was 2.31 μm and the difference from M _a was 0.07 μm. Similarly, under the condition of initialization power of 10 mW in which the jitter is greatly increased, M _i is 2.26 μm, and M _{a is}
Was 0.12 μm.

[0017] Example 2 polycarbonate (PC) was used as the substrate 1, 250 nm and ZnS-SiO ₂ as the lower protective layer 2, 15 nm _of Ge ₂ Sb ₂ Te ₅ as the recording layer 3, ZnS-SiO ₂ as the upper protective layer 4 18 nm, and Si as a reflection layer 5 is 65 nm.
nm was sequentially laminated by sputtering.

A flash lamp was used for the initialization, the irradiation lamp intensity was changed, and the initialization was performed. Then, the change of the overwrite characteristic with the repetition was examined. The absorptance of the initialization part changed as shown in FIG. 7 depending on the energy supplied by the flash lamp. On the other hand, the absorptance of the amorphous portion was 58%.

Using a semiconductor laser having a wavelength of 830 nm, a linear velocity of 20 m / s, 2.12 MHz, duty = 45
% And a signal of 3.39 MHz, duty = 45% were alternately overwritten to measure the jitter. As shown in FIG. 8, when the initialization is performed at 2.6 KJ that satisfies A _i > A _a , the jitter is low from the initial stage to the repeated stage. On the other hand, when the initialization was performed at 2.9 KJ where A _i = A _a , the initial overwrite resulted in high jitter.

Initialization conditions and mark lengths were examined by TEM observation of a track in which a 2.39 MHz signal was overwritten with a 3.39 MHz signal once. In the track which was initialized under the condition of 2.6 KJ with little increase in jitter, the mark length M _i of the mark recorded on the initialized portion was 2.97 μ.
m, the mark length M _a mark formed by overwriting on the amorphous portion was 2.95Myuemu. On the other hand, under the condition of a large increase in jitter of 2.9 KJ, M _i is 2.88 μm.
The difference with M _a was 0.07 μm.

[0021] Example 3 Polycarbonate (PC) is used as the substrate 1, 200 nm and ZnS-SiO ₂ as the lower protective layer 2, 10 nm _of Ge ₂ Sb ₂ Te ₅ as the recording layer 3, ZnS-SiO ₂ as the upper protective layer 4 18 nm, and Si as the reflection layer 5 of 60
nm was sequentially laminated by sputtering.

Using the above disk, the initialization power was changed to perform initialization, and the error rate in the initial overwrite was measured.

Initialization was performed by using a semiconductor laser having a wavelength of 830 nm and a focused beam diameter of 1.5 μm, and changing the initialization power to 4, 6, 8 mW at a linear velocity of 7.5 m / s. After the initialization, a semiconductor laser having a wavelength of 690 nm was used to record at a linear velocity of 10 m / s under the conditions of (1-7) modulation and the shortest mark length of 0.7 μm, and the error rate was measured. As shown in FIG. 9, after repeated overwriting, the error rate is 10 ⁻⁴ or less regardless of the initialization condition. On the other hand, under the condition that the initialization power is 4 mW, the error rate is 10 ⁻⁴ or less from the initial value, but the initialization power 6
Under the conditions of mW and initialization power of 8 mW, it can be seen that the error rate deteriorates in the initial overwrite.

In order to investigate the relationship between the sensitivity difference between the amorphous part and the initialized part and the error rate fluctuation, first, 1.05 MHz, d at a linear velocity of 10 m / s for each initialization condition.
After recording the signal of duty = 50%, 2.12 MHz,
A signal of duty = 50% was overwritten and TEM observation was performed. The mark length M _i of the mark recorded on the initialized portion is 2.36 μm, and the error rate is over the amorphous portion under the condition of the initialization power of 4 mW where the error rate is stable at 10 ⁻⁴ or less from the initial stage. Mark length M of the mark formed by writing
_a was 2.38 μm. On the other hand, under the condition of the initialization power of 6 mW in which the error rate fluctuates, M _i is 2.32.
The difference from M _{a in} μm was 0.06 μm. Similarly, under the condition of initialization power of 8 mW in which the error rate fluctuates, M _i is 2.25 μm, and the difference from M _a is 0.11.
It was μm.

In the above embodiments, polycarbonate (PC) is used as the substrate and ZnS-Si is used as the protective layer.
Although O ₂ and Ge ₂ Sb ₂ Te ₅ are used as the recording layer, the present invention is not limited to this. Further, although the semiconductor laser and the flash lamp are used for the initialization, the present invention is not limited to this.

[0026]

As described above, according to the present invention, it is possible to provide a medium in which the jitter at the mark edge recording is small from the initial recording to the repeated overwriting, so that the high density can be realized.

Further, since the temperature rise amount at the time of laser irradiation is the same in the initialization portion and the erasing portion, the mark length does not change with repetition, and stable recording can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing optical characteristics of a phase change optical disc according to the present invention.

FIG. 2 is a diagram showing a cross section of an example of a medium configuration of a phase change optical disc according to the present invention.

FIG. 3 is a diagram showing a state change of a phase change optical disc.

FIG. 4 is a diagram showing the relationship between the initialization power and the reflectance and absorptance in the example of the present invention.

FIG. 5 is a diagram showing the relationship among the number of repeated overwrites, the erase rate, and the jitter in the example of the present invention.

FIG. 6 is a diagram showing a reproduced waveform and a jitter distribution in the example of the present invention.

FIG. 7 is a diagram showing the relationship between the initialization energy and the absorptance in the example of the present invention.

FIG. 8 is a diagram showing the relationship between the number of repeated overwrites and jitter in the example of the present invention.

FIG. 9 is a diagram showing the relationship between the number of repeated overwrites and the error rate in the embodiment of the present invention.

[Explanation of symbols]

 1 substrate 2 lower protective layer 3 recording layer 4 upper protective layer 5 reflective layer

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[Procedure amendment]

[Submission date] October 25, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Delete

Claims (4)

[Claims] 1. A method of initializing a phase-change optical disk for recording / erasing / reproducing information by using mark edge recording, wherein an absorptance A _i of an initialized part and an absorptivity A _{a of an} amorphous part irradiated with light. The method for initializing a phase-change optical disk is characterized in that optical energy is supplied to the phase-change optical disk so as to satisfy the relationship of A _i > A _a . 2. A method of initializing a phase change optical disk for recording / erasing / reproducing information using mark edge recording, wherein a length M _i of a recording mark recorded on a light-irradiated initializing portion and an amorphous state. relationship between the length M _a recording mark recorded by overwriting on the quality _{portion, | M a -M i | <} 0.0
An initialization method for a phase-change optical disk, which comprises supplying light energy to a phase-change optical disk so as to satisfy 5 μm for initialization. 3. The method for initializing a phase change optical disk according to claim 1, wherein a laser beam is used for initialization. 4. A method for initializing a phase change optical disk according to claim 1, wherein a flash lamp is used for initialization.