Method of designing a phase-change optical recording medium, and

Details Method of designing a phase-change optical recording medium, and Method of designing a phase-change optical recording medium, and

1998-08-28

2000-11-21

Evans, Elizabeth

Stock material or miscellaneous articles

Circular sheet or circular blank

428 644, 428 645, 428 646, 428913, 43027013, 4304951, 430945, B32B 300

Patent

active

061499994

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention is concerned with a phase-change optical recording medium for recording, erasing and reading information by utilizing a reversible phase-change in a recording layer by irradiation of laser beam and, more in particular, it relates to a phase-change optical recording medium capable of recording information at a high density and excellent in recording and erasing characteristics.


BACKGROUND ART

In recent years, along with progress of the semiconductor technology, digitalization of information has been progressed rapidly and, along with digitalization of information, particularly, digitalization of image information such as static or moving picture, the amount of information to be treated has become enormous. In such a situation, it is necessary to store the information temporarily or quasi-permanently. As means for recording the enormous information, optical recording media such as optical discs are considered to be promising and research and development have been conducted vigorously for increasing the capacity.
Particularly, a so-called phase-change optical recording medium, which records and erases information by utilizing a material that conducts reversible phase change between two states, namely, a crystalline state and an amorphous state, is highly expected as an image recording medium, since it has an excellent feature capable of recording and erasing information by a simple optical system and easily so-called overwriting, which conducts recording new information while erasing already recorded information simultaneously.
As a recording material for the phase-change recording medium, chalcogenide alloys such as Ge--Te--Sb series alloys (refer to Japanese Patent Laid-Open Sho 62-53886 and Japanese Patent Laid-Open Sho 61-258787), In--Sb--Te alloys (refer to Japanese Patent Laid-Open Sho 62-241145) or oxide series materials such as Te--Ge--Sn--O have been used mainly. Upon overwriting, a portion of a recording layer irradiated by a laser beam with a recording power is made amorphous by being heated to higher than the melting point and then quenched to form a recording mark, whereas a portion of the recording layer irradiated by a laser beam with an erasing power is crystallized to erase the recording mark by being heated to higher than the crystallizing temperature.
When recording and erasing of information are actually conducted by using the recording material described above, a protection layers are usually located just beneath and just above the recording layer for preventing the recording layer from oxidation or deformation. Further, a structure of disposing a reflection layer through a protection layer on a recording layer is often used as a more preferred layer structure for picking up an optical change in the recording layer as a great change of reflectance by utilizing the interference effect of light.
As the material for the protection layer, oxides, carbides, nitrides, flouorides and sulfides of metals or semimetals, and the like have been known and, among them, ZnS has been known to provide a strong adhesion with the recording layer. However, a protection layer consisting only of ZnS was insufficient for the heat resistance since crystalline grains of ZnS becomes coarser by repetitive recording and erasing by overwriting. Japanese Patent Laid-Open Sho 63-103453 discloses an optical disc enhanced with the heat resistance of the protection layer and improved with respect to deterioration of cyclability caused by thermal deformation or the like of the recording layer, by the addition of a glass-forming material such as Sio.sub.2 to ZnS. Such existent material for the protection layer as described above is usually transparent to a light used for recording, erasing and reading.
On the other hand, as a method of increasing the recording density, in a case of existent mark position recording of corresponding a recording signal to a central position of a recording mark, there is a method of increasing the density in the direction of a recording track (linear de

REFERENCES:
patent: 5424106 (1995-06-01), Yamada et al.
patent: 5545454 (1996-08-01), Yamada et al.

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