JPH0877596A - Optical information recording medium - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an optical information recording medium with small overwrite jitter in mark edge recording using an optical head having a wavelength of 670 to 690 nm. [Structure] The reflective layer is Si, and the thickness of each layer is
The lower protective layer is 180 to 260 nm, and the recording layer is 10 to 13 nm.
nm, upper protective layer 13-25 nm, reflective layer 55-6
5 nm. In the vicinity of the wavelength of 690 nm, it is possible to make the absorptance of the crystal higher than the absorptivity of the amorphous while maintaining a large change in the reflectivity of the amorphous and the crystal. It is possible to provide an optical information recording medium whose increase is small. Also,
Since the light absorption in the reflective layer is also small, a good amorphous mark can be formed without slowing the cooling rate of the recording layer after laser irradiation.

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 disk, 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 is recorded / erased by heating with laser light
This is performed by utilizing the phase change between the amorphous and crystalline of the recording layer which is induced by the difference in thermal history of cooling. That is, the recording layer is melted and rapidly cooled to be amorphized for recording, and the recording layer is kept at a crystallization temperature or higher for a certain time to be crystallized and erased. 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 viewpoint of sensitivity, C / N, erasing rate, rewritable repetition count, and the like.

[0005] To increase the recording density, mark edge recording in which information is provided at both ends of a recording mark is effective. However, in a phase-change optical disk that utilizes the difference in reflectance between crystalline and amorphous to reproduce a signal, the absorptance in the crystalline state and the absorptance in the amorphous state are often different. The absorptance of the state is higher than that of the crystalline state. In such a case, the width and length of the mark to be formed are affected by whether the state before 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 absorptance of the amorphous state equal to that of the crystalline state. Considering that the latent heat associated with melting is higher in the crystalline state, it is desirable to design the absorptance of the crystalline state to be higher than that of the amorphous state. As a means for providing such a medium, it is known that the absorptance control method using a transmissive reflective layer such as Si described in JP-A-2-218334 is effective. Also, a phase change optical disc in which overwrite jitter is reduced at a wavelength of 830 nm using this method has been reported (ISOM / O
DS '93 Conference Digest p.72).

[0004]

Wavelengths of 780 to 830 are currently used as optical head light sources for optical disks that are currently being commercialized.
nm laser diodes are used. In order to further improve the recording density, the wavelength of the laser diode has been shortened, and a high power red laser diode with a wavelength of about 690 nm is being put to practical use. The optical constants of the recording layer and the reflective layer of the phase change optical disc are 780 to 830 nm.
And 690 nm have different values. Therefore, 780
In the medium having the conventional structure suitable for 830 nm, it is difficult to secure a good overwrite characteristic for the optical head of 690 nm, and there is a problem that the jitter increases due to the overwrite. The present invention has a wavelength of 690n
In mark edge recording using an optical head near m,
An object of the present invention is to provide a phase change optical disk that can obtain good overwrite characteristics.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to recording / recording information.
An erasing / reproducing phase change optical disc has a structure in which a lower protective layer, a recording layer, an upper protective layer, and a reflective layer made of Si are sequentially formed on a substrate, and the lower protective layer has a thickness of 180 to 260 nm. , The thickness of the recording layer is 10 to 1
3 nm, the thickness of the upper protective layer is 13 to 25 nm, and the thickness of the reflective layer is 55 to 65 nm. Here, it is preferable that the phase change optical disc is one that records / erases / reproduces information by using mark edge recording by using an optical head having a wavelength of 670 to 695 nm.

According to the present invention, in the vicinity of a wavelength of 690 nm, it is possible to make the absorptance of the crystal higher than the absorptivity of the amorphous while maintaining a large change in the reflectivity of the amorphous and the crystal. It is possible to provide an optical information medium having a high rate and a small increase in jitter due to overwriting.

[0007]

Function: GeSbT generally used as a recording layer
The change of e with the phase change of the optical constant in the vicinity of 690 nm is smaller than that in the vicinity of 780 to 830 nm. For example, with Ge ₂ Sb ₂ Te ₅ , the optical constant (n, k) at a wavelength of 830 nm is (4.6, 1.06) in the amorphous state and (5.89, 3.47) in the crystalline state. On the other hand, at a wavelength of 690 nm, (4.36, 1.7
2), the crystal has (4.46, 4.0), and the change of n is small. Therefore, in order to control the absorptance by utilizing the transmitted light, the film thickness of the recording layer must be made smaller than that in the case of 780 to 830 nm. However, from the viewpoint of sensitivity and film quality, 10 nm or more is necessary. Also, the wavelength 690
The optical constants (n, k) of Si in nm are slightly different depending on the manufacturing method, but are (4.0 to 4.6, 0.1 to 0.
4), and the extinction coefficient k becomes larger than that of 780 to 830 nm. Light absorption in the Si reflection layer slows down the cooling rate of the recording layer after the laser light reflection and hinders the formation of a good amorphous mark. Therefore, it is necessary to reduce the thickness of Si in the vicinity of 690 nm.

FIG. 1 shows an example of optical characteristics at 690 nm of a phase change optical disk having Si as a reflection layer. The medium composition is Si (60 nm) reflective layer / ZnS—SiO ₂ (18
nm) upper protective layer / GeSbTe (13 nm) recording layer /
A ZnS-SiO ₂ lower protective layer / polycarbonate substrate. In the figure, Ac represents a crystal absorption rate, Aa represents an amorphous absorption rate, Rc represents a crystal reflectance, and Ra represents an amorphous reflectance. By making the recording layer as thin as 13 nm, it is possible to make the absorptance of crystals higher than the absorptivity of amorphous over a wide thickness range of the lower protective layer.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 FIG. 2 is a diagram showing a cross section of an optical information recording medium according to the present invention. In this configuration, 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. Polycarbonate (PC) is used as the substrate 1, ZnS—SiO ₂ is 240 nm as the lower protective layer 2, and Ge ₂ S is as the recording layer 3.
b ₂ Te ₅ of 12 nm, ZnS-Si as the upper protective layer 4
O ₂ having a thickness of 18 nm and Si having a thickness of 60 nm as the reflection layer 5 were sequentially laminated by sputtering. In this structure, the absorptance of the recording layer in the amorphous state and the absorptance of the recording layer in the crystalline state were 50% and 63%, respectively. The disk was rotated at a linear velocity of 10 m / s, and recording / erasing was performed using a semiconductor laser having a wavelength of 690 nm. 1.88MHz, du
3.03 MHz for duty = 50% signal, duty = 50
% Signal was overwritten, and C / N, erasure rate, and jitter were measured. As shown in FIG. 3, the jitter was a good value of 3 ns or less even after overwriting.

Comparative Example 1 Using a disk showing good characteristics at a wavelength of 830 nm, the overwrite characteristics at a wavelength of 690 nm were measured. The disk has ZnS-Si as the lower protective layer 2.
O ₂ is 250 nm, and Ge ₂ Sb ₂ Te ₅ is used as the recording layer 3.
ZnS-SiO ₂ as the upper protective layer 4 having a thickness of 5 nm
m, and the reflective layer 5 has a structure in which Si having a thickness of 65 nm is sequentially laminated by sputtering. In this configuration, the wavelength 69
Both the absorptance in the amorphous state and the absorptance in the crystalline state at 0 nm were 60%, and the absorptance in the crystalline state could not be made higher than that in the amorphous state. FIG. 4 shows the result of measuring the overwrite characteristics of the above-mentioned disk under the same conditions as in Example 1. It was confirmed that the jitter was 4 ns, which was significantly larger than the jitter of 2 ns at the time of initial recording.

Comparative Example 2 In order to investigate the influence of the film thickness of the recording layer on the overwrite jitter, a disk having a recording layer film thickness of 15 nm was prepared with almost the same structure as in Example 1, and the overwrite characteristics were evaluated. It was measured. FIG. 5 shows the results of measurement of C / N, erasure rate, and jitter under the same conditions as in Example 1. The erasing rates are almost the same and the C / N is improved. However, the jitter is greatly increased, and it is difficult to increase the density.

Comparative Example 3 In order to investigate the influence of the film thickness of the Si reflective layer on the reproduced signal quality, the Si film thickness was set to 70 n in the same configuration as in Example 1.
A disk with m and 80 nm was prepared and the reproduced waveform was observed. FIG. 6 shows the result, and FIG.
0 nm, 70 nm in FIG. 6 (b), 80 nm in FIG. 6 (c)
Is the case. As shown in the same figure, as the film thickness of the Si reflective layer increases, the distortion of the reproduced waveform increases. It was confirmed from TEM observation that this distortion was due to recrystallization in the central portion of the recorded amorphous mark caused by a decrease in cooling rate.

Example 2 In order to investigate the optimum film thickness of the lower protective layer, a disk having the same structure as in Example 1 in which the film thickness of the lower protective layer was changed between 150 and 300 nm was prepared, and the disc with the overwrite characteristics was prepared. The measurement was performed. When the dependency of the absorptance in the amorphous state and the crystalline state on the thickness of the lower protective layer was measured, it was as shown in FIG. In FIG. 7, ◯ indicates the absorption rate in the crystalline state, and □ indicates the absorption rate in the amorphous state. In the range of 180 to 260 nm, the absorptance in the crystalline state was higher than that in the amorphous state. Each disk was overwritten under the same conditions as in Example 1 and the dependence of the jitter on the thickness of the lower protective layer was measured. As a result, as shown by the ● mark in FIG. 7, the absorptance in the crystalline state is that in the amorphous state. Low jitter in the higher range.

[0014]

As described above, according to the present invention,
In mark edge recording using an optical head with a wavelength in the vicinity of 670 to 695 nm, it is possible to reduce overwrite jitter and achieve higher density.

[Brief description of drawings]

FIG. 1 is a diagram showing the dependency of absorptance and reflectance on the thickness of a lower protective layer of an example of the optical information recording medium according to the present invention.

FIG. 2 is a basic configuration diagram of an optical information recording medium according to the present invention.

FIG. 3 is an optical characteristic diagram of an example of an optical information recording medium according to the present invention.

FIG. 4 is an optical characteristic diagram of an example of a conventional optical information recording medium.

FIG. 5 is an optical characteristic diagram of an example of a conventional optical information recording medium.

FIG. 6 is a diagram showing the dependence of a reproduced waveform on the thickness of a Si reflective layer.

FIG. 7 is a diagram showing dependency of absorptance and jitter in a crystalline state and an amorphous state on a thickness of a lower protective layer.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. A phase change optical disk for recording / erasing / reproducing information, which has a structure in which a lower protective layer, a recording layer, an upper protective layer and a reflective layer made of Si are sequentially formed on a substrate, The thickness of the protective layer is 180 to 260 nm,
The recording layer has a film thickness of 10 to 13 nm, the upper protective layer has a film thickness of 13 to 25 nm, and the reflective layer has a film thickness of 55 to 65.
An optical information recording medium characterized by having a thickness of nm. 2. The phase change optical disk has a wavelength of 670 to 69.
2. Information recording / erasing / reproducing is performed by using mark edge recording using a 5 nm optical head.
The optical information recording medium described.