Stock material or miscellaneous articles – Circular sheet or circular blank
Patent
1999-04-01
2000-09-05
Evans, Elizabeth
Stock material or miscellaneous articles
Circular sheet or circular blank
428 644, 428 645, 428 646, 428913, 43027013, 4304951, 430945, 369283, 369288, B32B 300
Patent
active
061140015
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention is concerned with a novel optical information recording medium. In particular, it relates to an optical information recording medium of excellent reliability capable of optically recording, reading and erasing information at a high speed and at a high density.
BACKGROUND ART
A phase change type optical disc as a sort of optical information recording media uses a material which causes reversible phase change between crystalline and amorphous states as a recording layer, so as to conduct recording and erasing of information by utilizing the nature of the recording layer. The phase change type optical disc is capable of recording new information while erasing preceding information (hereinafter referred to as "overwriting") by merely changing the power of an irradiated laser beam corresponding to new recording information.
As the recording material for the phase change type optical disc capable of overwriting, chalcogen alloys, for example, In--Se series alloys (Appl. Phys. Lett. vol. 50, page 667, 1987) or In--Sb--Te alloy (Appl. Phys. Lett. vol. 50, page 16, 1987) and Ge--Te--Sb alloy have been mainly employed. Recording and erasing on the phase change type optical disc are conducted as described below. That is, upon recording, a laser beam at a high power focused through a lens is at first irradiated to a recording layer to melt the recording layer by raising the temperature to higher than a melting point (about 500 to 600.degree. C.). Successively, the recording layer is quenched by lowering the power of the laser beam. As a result of such rapid heating and quenching, the recording layer becomes amorphous and is in a stable state at a room temperature. An amorphous portion, for example, of about 1 .mu.m is thus formed on the recording layer (recording mark).
Upon erasing, a laser beam at a low power is at first irradiated to the amorphous portion to heat the same to a crystallizing temperature lower than the melting point. Subsequently, the amorphous portion is crystallized by gradual cooling to erase the recording mark.
As described above, since the laser beam at a high power is irradiated to the phase change type optical disc upon recording, a protection layer of high thermal resistance is disposed to both or either one of surfaces of the recording layer in order to prevent thermal damage (for example, deformation of a substrate, oxidation of a recording layer and movement of material along guide grooves).
As the material for the protection layer, materials comprising at least one of oxides, carbides, fluorides, sulfides and nitrides of metals or semi-metals are used. For example, Japanese Patent Laid-Open publication SHO No. 63-103453 proposes use of a mixture comprising, for example, ZnS and SiO.sub.2 as the material for the protection layer. It has been known that the protection layer comprising the mixture has higher thermal resistance than the protection layer only consisting of ZnS.
Further, a phase change type optical disc having high recording and erasing characteristics, which is also excellent in overwrite cyclability has been obtained by using a mixture comprising ZnS and SiO.sub.2 as the material for the protection layer and optimizing the thickness for each of the layers.
However, since the protection layer present on both surfaces of the recording layer is also repeatedly heated rapidly and quenched by overwriting cycles, there is a danger that the protection layer itself is deformed as the number of cycles increases extremely. If the protection layer itself suffers from deformation as described above, a problem results in that the recording layer is damaged causing a deterioration of the recording and erasing characteristics.
In order to solve the foregoing problem, Japanese Patent Laid-Open publication HEI No. 3-263627 proposes a method of depositing a first protection layer (a protection layer disposed to the recording layer on the side of the substrate) and a second protection layer (a protection layer disposed to the recording layer on the side
REFERENCES:
patent: 4847132 (1989-06-01), Takao et al.
patent: 5622607 (1997-04-01), Yamazaki
patent: 5812182 (1998-09-01), Kawai
patent: 5989654 (1999-11-01), Yoshioka
Appl. Phys. Lett., vol. 50, No. 1, Jan. 5, 1987, A. Ogura et al. (pp. 16-18).
Appl Phys. Lett., vol. 50, No. 11, Mar. 16, 1987 Nishida et al. (pp. 667-669).
Ohyama Akihiko
Suzuki Masaru
Asahi Kasei Kogyo Kabushiki Kaisha
Evans Elizabeth
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