JP2000195113A - Initialization method of phase transition type optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent thermal deformation of a substrate, a UV resin layer and the like due to heat generated from a recording layer as well as preventing chamber and crack due to thermal deflection of a formed film by specifying the range of the ratio of the crystallization of the recording layer and irradiating the recording layer with a light beam having specific power density at a specified linear velocity to perform initialization. SOLUTION: In the initialization method in which a recording layer of a phase transition type optical recording medium is changed from an amorphous state to a crystallized state using a heat source or a light beam, the ratio Z of the crystallization is desirably set in the range of 0.50 to 0.85. In addition, in the case of the phase transition type optical storage medium of one beam overwrite method, the linear density v (m/s) is 3.0 to 12.0, and desirably 5.0 to 10.0. Furthermore, the power density P (mW/μm2) of the optimum light beam at such linear velocity varies depending on the material and the layer constitution of the phase transition type optical storage medium, however, the P is set 3.0 to 15.0, and desirably 4.0 to 12.0, and the initialization is performed by irradiating the recording layer with the light beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat source or a light beam for a phase change type optical recording medium for recording, reproducing and erasing information utilizing a change in phase structure of a recording layer caused by light irradiation. And an initialization method for crystallizing the recording layer using the method.

[0002]

2. Description of the Related Art A phase change type optical recording medium records information by reversible structural change (phase change) between an amorphous state and a crystalline state of a substance caused by light irradiation, mainly laser light irradiation. We use for. Such a phase-change optical recording medium has a large recording capacity in addition to a high-speed information processing capability. Under such circumstances, a performance of erasing information recorded at high speed at higher speed is required for a phase change type optical recording medium. For this purpose, a stable operation of repeating recording and erasing, in which once recorded information is erased and further information is recorded thereon, is indispensable. It is preferable that the number of repetitions of the recording / erasing is large.

The recording layer of such a phase-change type optical recording medium is formed by a vacuum process such as a sputtering method or a vacuum evaporation method. Immediately after, it is in an amorphous state, and when used as a phase-change optical recording medium, it is necessary to perform a so-called initialization process in which the recording layer of the entire recording area is once changed to a crystalline state prior to recording. For this purpose, the conventional method of initializing a phase-change optical recording medium has been to irradiate a large power heat source or continuous emission laser light widely to initialize the entire recording area in a short time with uniform reflectance. Was used.

[0004]

However, in the above-mentioned conventional initialization method, when a plastic substrate such as a polycarbonate resin or a polymethacrylate resin is used as the substrate of the phase change type optical recording medium, the substrate is formed by vapor deposition or sputtering. Thermal stress is generated due to the difference in thermal expansion between the film and the substrate, and the UV resin layer itself for protection is thermally deformed. There were issues such as doing. In addition, in some cases, minute cracks occur in the formed film, resulting in defects, and subsequent growth of recording / erasing repeatedly or in a high-temperature, high-humidity environment greatly increases the life of the phase-change optical recording medium. There was a problem that. Therefore, if initialization is performed under such conditions as to reduce the thermal load on the phase-change optical recording medium in order to solve these problems, there arises a problem that the erasing rate of the recording / erasing characteristics, especially at the initial stage of repetition, becomes low. did.

Alternatively, the irradiation power density P (m
W / μm ² ) and irradiation time T (nsec) have been attempted to control the crystal state, and 0.5 ≦ P ≦
5.0 and 1 ≦ T ≦ 100 (Japanese Unexamined Patent Publication No.
78338) and 5.0 ≦ P ≦ 25.0 and 20
≦ T ≦ 1000 (Japanese Unexamined Patent Publication No. 04-216323)
JP-A-2002-157, there is a report that the recording / erasing characteristics are more excellent. However, according to the study of the present inventors, it has been confirmed that under these conditions, the control of the reflectivity of the phase change type optical recording medium is insufficient, and as a result, the repetition characteristics of recording / erasing are adversely affected. .

Further, in the conventional research of the present inventors, the crystallization ratio Z is controlled to be 0.37 ≦ Z ≦ 0.46, and the power density P (mW / μm ² ) is 7.5 ≦ P ≦ 20. 2.0 light beam, a constant linear velocity v (m / s) of 3.0 ≦ v ≦
By performing the initialization at 12.0, there is no unevenness in the initialization, and the occurrence of warping and cracks due to the thermal deformation of the substrate or the UV resin layer and the thermal distortion of the formed film due to the heat generated from the recording layer is excellent. It was reported that the recording / erasing / reproduction characteristics after initial and repeated recording can be obtained at high speed.

However, as the storage density has been greatly increased year by year and the size of the recording mark has been reduced, the unevenness in the reflectance of a minute area, which has not been a problem in the past, has caused the reliability of the recording / erasing / reproducing characteristics to increase. It is starting to have an adverse effect. Therefore, it has become necessary to more strictly control the non-uniformity of the reflectance caused by the unevenness in initialization.

The present invention solves the problems of the prior art, and does not cause warping or cracks due to thermal deformation of a substrate or a UV resin layer due to heat generated from a recording layer and thermal distortion of a formed film. Also suppresses reflectivity unevenness,
It is an object of the present invention to provide a method for initializing a phase-change optical recording medium, which can realize high-speed, good recording / erasing / reproducing initial and initialization showing repetitive characteristics.

[0009]

According to the present invention, there is provided a method for initializing a phase change type optical recording medium, comprising the steps of recording, reproducing, and erasing information by utilizing a change in phase structure of a recording layer caused by light irradiation. In the initialization method for changing the recording layer of the phase-change optical recording medium from an amorphous state to a crystalline state using a heat source or a light beam when the changeable optical recording medium is initialized, the crystallization ratio Z In a range of 0.50 ≦ Z ≦ 0.85.

If the crystallization ratio is less than 0.50, the reflectivity of the phase-change type optical recording medium is too low, or the reflectivity of a minute area becomes uneven, so that the servo of the drive becomes unstable or the defect is not obtained. The characteristics are bad. On the other hand, if the crystallization ratio is larger than 0.85, coarse crystal grains are likely to be generated, causing large reflectance unevenness, and defects such as film distortion of the recording layer are likely to occur. It may cause a deterioration in the life of the device. Here, the crystallization ratio Z is determined according to the literature “E. Huber et al.,
Physical Review B, 36
(3), 1595 (1987) ". R = (0.65-Ra) {Z ⁴ / (Z ⁴ + α ⁴ )} + Ra Here, R and Ra are the crystallization ratios Z, respectively.
Is the reflectivity of the recording layer in the case of (1), and the reflectivity of the recording layer in the amorphous state, and α is a shape parameter of 0.5.

By the way, the linear velocity v of the irradiation when the recording layer is initialized by irradiation with a light beam means the speed at which the full width at half maximum of the light beam passes through a certain point of the phase change type optical recording medium. The higher the linear velocity, the less the thermal load on the substrate and the UV resin layer. However, it is necessary to increase the power of the light beam in order to provide sufficient phase transition heat. In addition, in order to crystallize the recording layer of the phase-change optical recording medium, it is necessary to heat the recording layer to a temperature region equal to or higher than the crystallization temperature, and then hold the recording layer for a time necessary for crystallization, and to achieve an appropriate linear velocity. Must be set.

Therefore, in the case of the phase change type optical recording medium of the one-beam overwrite system, the linear velocity v (m / s) is 3.
The range is preferably 0 ≦ v ≦ 12.0, more preferably 5.0 ≦ v ≦ 10.0. If the speed is higher than 12.0 m / s, the crystallization tends to be uneven, and it is difficult to perform highly reliable initialization once. If it is less than 3.0 m / s, the initialization time becomes longer and the productivity decreases, and the thermal load on the substrate and the UV resin layer due to the thermal diffusion from the recording layer increases, and the thermal deformation of the phase change optical recording medium and This may cause cracks in the formed film.

The optimum light beam pattern at such a linear velocity
Power density P (mW / μm^Two) Is the material of the phase change optical recording medium
3.0 ≦ P ≦ 15, depending on the material and the layer structure.
0 is preferable, and more preferably 4.0 ≦ P ≦ 1.
2.0. 3.0mW / μm^TwoIf less than, crystallization is likely
The reflectivity is not constant and adversely affects the recording / erasing characteristics.
Or it takes time to crystallize
15.0mW / μm ^TwoLarger and recording layer due to heat
Defects such as film distortion of the
Recording and erasing characteristics may deteriorate.
No.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of a phase change type optical recording medium is as follows: a first transparent dielectric protective layer, a recording layer,
Providing a second transparent dielectric protective layer and a reflective layer in this order;
Further, a resin protective layer such as an ultraviolet (UV) curable resin layer is further laminated thereon, so that more preferable effects can be expected by applying the initialization method of the present invention, and thus it is desirable. Further, a material in which an adhesive layer is provided on the protective layer and bonded to another substrate may be used.

When recording / erasing is performed from the substrate side, it is preferable to use a material through which laser light is transmitted. For example, a polymer resin such as polymethyl methacrylate resin, polycarbonate resin, epoxy resin, polyolefin resin, or the like is used. Glass etc. are mentioned.

The protective layer includes a deformation preventing layer for preventing the substrate and the recording layer from being deformed by heat due to the recording and deteriorating the recording and erasing characteristics, a protective layer for providing the moisture and heat resistance and the oxidation resistance of the recording layer, In addition, it plays a role of a diffusion prevention layer for preventing diffusion of atoms from the recording layer to the reflection layer. Examples of such a protective layer include ZnS, SiO ₂ , Ta ₂ O ₅ , IT
An inorganic film such as O, Si ₃ N ₄ , TiO ₂ , ZnO, GeN, Cr ₂ O ₃ or a mixed film thereof can be used. In particular, a mixed film of ZnS and SiO ₂ is preferable because it has excellent wet heat resistance and suppresses deterioration of the recording layer due to repeated recording / erasing.

As the recording layer, one having a high crystallization speed is preferable as a phase-change type optical recording medium for performing recording / erasing of the one-beam overwrite method. For example, GeSbTe
-Based thin films, InSbTe-based thin films, and the like. In particular, a recording layer containing GeSbTe having excellent repetition characteristics is preferable.

The reflective layer facilitates the formation of amorphous marks by facilitating thermal diffusion from the protective layer 14 and increasing the cooling rate of the recording layer melted during recording. In addition, there is an effect of preventing the protective layer and the like from being thermally deformed, and an effect of improving the contrast of a reproduced signal due to optical interference. As such a reflective layer, a mixture of a metal or a metal oxide, a metal nitride, a metal carbide, or the like, which has light reflectivity and absorptivity at the wavelength of laser light and has higher thermal conductivity than the protective layer. For example, Zr, Hf, Ti, Ta, Mo, S
Metals such as i, Al, Au, Cr and the like, alloys thereof, and mixtures thereof with Si oxides, Si nitrides, Al nitrides and the like can be used. In particular, Al, Au, Ta, their alloys, and the like have a high light reflectivity and a high thermal conductivity by selecting a material.

[0019]

Examples 1-2 and Comparative Examples 1-4 Transparent substrate / first transparent dielectric protective layer / recording layer / second transparent dielectric protective layer /
A phase-change optical recording medium having a configuration of a reflective layer / an ultraviolet (UV) curable protective layer / a transparent substrate was produced. Here, the transparent substrate has a groove for tracking, a diameter of 120 mm,
Use was made of polycarbonate having a thickness of 0.6 mm and a land and groove having a pitch of 0.74 μm and recordable on grooves.
The first transparent dielectric protection layer is made of ZnS—SiO ₂ (film thickness 1).
00 nm) and was formed on a transparent substrate by magnetron sputtering. The recording layer is Ge ₂ Sb ₂ Te ₅
(Film thickness 20 nm). The second transparent dielectric protective layer is
A ZnS-SiO ₂ (thickness of 15nm). The reflective layer
Al (film thickness 150 nm). The ultraviolet (UV) curing type protective layer has a thickness of 2 μm. Further, a polycarbonate transparent substrate having a thickness of 0.6 mm was bonded to the disk so that the warpage of the disk did not adversely affect the initialization. Thus, a phase change type optical recording medium to which the initialization method of the present invention was applied was obtained.

The entire surface of the sample of the phase change type optical recording medium thus manufactured is initialized under the respective conditions.
The rate of crystallization and the envelope variability were measured. Here, the envelope fluctuation rate is an amount defined as follows. Consider a case where a reproduced signal waveform is observed with a digital oscilloscope, with the vertical axis set to a voltage value and the horizontal axis set to time. At this time, the voltage value on the vertical axis is relatively light irradiation,
This corresponds to a difference in reflectance mainly due to a reversible structural change (phase change) between an amorphous state and a crystalline state of a substance caused by laser light irradiation. The horizontal axis depends on the rotation speed of the disk. No peeling or cracking of the film
Alternatively, a normal reproduction signal waveform of a disk having a uniform reflectance shows a stable waveform having a constant voltage value (reflectance) in each of the amorphous state and the crystalline state. On the other hand, in a reproduced signal waveform of a disk in which film peeling or cracking occurs or reflectance is uneven, the voltage value (reflectance) in an amorphous state or a crystalline state is correspondingly disturbed. The difference (fluctuation width) between the maximum value and the minimum value caused by the disturbance of the voltage value (reflectance) is normalized by the average value of the voltage value (reflectance) with respect to the ground level. In order for the drive to stably perform good recording / reproducing, it is usually desirable for the drive to be 5.0% or less.

Further, recording / reproducing / erasing was performed on the sample of the phase change type optical recording medium manufactured as described above as follows. A phase change type optical recording medium is rotated at a linear velocity of 6 m / s by a driving device for evaluation, and a semiconductor laser having a wavelength of 680 nm is used to overwrite a random pattern in RLL (2, 10) modulation with a peak power of 11 mw and a bias power of 5 mW. Was repeated, and the jitter measurement and the reproduction signal waveform were observed after the first and 150,000 rewrite operations at a read power of 1 mW.

Here, the jitter indicates the signal quality after recording and reproduction, and is obtained by standardizing the time axis fluctuation of the reproduction signal with the reproduction reference clock. The reproduced waveform has variations in the reproduced waveform curve due to various fluctuation factors such as disc rotation fluctuation and recording mark non-uniformity, and when this is sliced into a binary signal, it appears as a fluctuation in the time axis direction. . Since the binarized data is reproduced based on the reproduction reference clock, if the jitter is large, the probability of a data error increases. In order to perform good recording and reproduction, it is usually desirable that the content is 8.0% or less.

Table 1 summarizes the results of the evaluation of the initialization conditions, initialization characteristics, and recording / reproduction characteristics. From these results, it was found that good characteristics were obtained when the crystallization ratio Z was in the range of 0.50 ≦ Z ≦ 0.85. The power density P (mW / μm ² ) is 3.0 ≦ P ≦ 15.
0 and the linear velocity v (m / s) is 3.0 ≦ v ≦ 1
It was found that good characteristics were obtained in the range of 2.0.

[0024]

[Table 1]

[0025]

As described above, according to the method for initializing a phase-change optical recording medium of the present invention, by controlling the rate of crystallization after initialization, there is no unevenness in initialization even in a minute area, and the recording layer By suppressing the occurrence of warping and cracks due to the thermal deformation of the substrate or the UV resin layer and the thermal distortion of the formed film due to the heat generated from the above, good initial and repeated recording / erasing / reproducing characteristics after repeated recording can be obtained. Further, the phase change type optical recording medium having a long life can be obtained because the initialization can be performed with few defects.

Continued on the front page (72) Inventor Kenji Nakatani 4-3-2 Asahigaoka, Hino-shi, Tokyo Teijin Limited, Tokyo Research Center F-term (reference) 5D090 AA01 BB05 CC11 DD03 EE05 KK03 KK18 5D121 AA01 GG02 GG07 GG26

Claims (2)

[Claims] 1. A recording layer using a heat source or a light beam for a phase change type optical recording medium in which information is recorded, reproduced, and erased by utilizing a change in phase structure of the recording layer caused by light irradiation. In the initialization method for crystallization, the crystallization ratio Z
Is set to 0.50 ≦ Z ≦ 0.85. 2. The crystallization of the recording layer is performed at a power density P (mW
/ Μm ² ) by irradiating the recording layer with a light beam having 3.0 ≦ P ≦ 15.0 at a constant linear velocity v (m / s), and the linear velocity v is 3.0 ≦ P 2. The method for initializing a phase-change optical recording medium according to claim 1, wherein v ≦ 12.0.