Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Patent
1995-11-22
1998-11-24
Angebranndt, Martin
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
4302751, 4302731, 430945, 458 645, 458 646, 369283, 369288, G11B 724
Patent
active
058404660
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a optical recording medium wherein the recording, erasing, and reading of data are carried out applying a light beam, and production methods thereof. The invention particularly relates to phase-change type rewritable optical recording medium, such as optical disks, wherein recorded data can be erased or overwritten and wherein data can be recorded with high speed and high density, and production methods thereof.
BACKGROUND OF THE INVENTION
Techniques for conventional phase-change type rewritable optical recording media are as follows.
Those optical recording media have a recording layer consisting mainly of telluride, which, for recording, is partially melted by applying a converged pulsed laser beam to the crystalline-state recording layer for a short period of time. The melted portion is rapidly cooled and solidified due to thermal diffusion, resulting in the formation of an amorphous record mark. With an optical reflectivity lower than that for the crystalline state, the record mark can be read to produce a signal.
To erase the data, a laser beam is applied to the record mark to heat the recording layer up to a temperature that is lower than the melting point but higher than the crystallization temperature so that the amorphous record mark portion is crystallized to allow that portion of the layer to recover its unrecorded state.
Known materials for the recording layer of such phase-change type rewritable optical recording media include some alloys such as Ge.sub.2 Sb.sub.2 Te.sub.5 (N. Yamada et al., Proc. Int. Symp. on Optical Memory 1987 pp. 61-66).
These optical recording media with layers recording layer consisting of a Te alloy has a high crystallization rate to allow high-speed overwriting to be performed by varying the power of the beam which has a circular cross-section. In the optical recording media with such a recording layer, a heat-resistant transparent dielectric layer is provided on both sides of the recording layer to prevent deformation and opening formation from occurring on the recording layer during the recording process. In addition, there are other known techniques which use a reflecting metal layer, of Al etc., provided over the dielectric layer so that some optical interference is caused to improve the signal contrast during reading and so that the recording layer is cooled efficiently to facilitate the formation of amorphous record marks and to improve the erasing characteristics and repeated use characteristics. In particular, a structure where the recording layer and the dielectric layer between the recording layer and the reflection layer are about 20 nm or less in thickness (rapid cooling structure) is small in the deterioration of recording characteristics due to repeated erasing and writing and wide in erasing power margin as compared to ones with a dielectric layer with an about 200 nm or more thickness (moderate cooling structure). (T. Ohta et al., SPIE Proc. Vol. 1316 (1990) pp.367-373).
These conventional phase-change type rewritable optical recording media of a rapid cooling structure have such problems as follows:
The conventional disk structure requires a large-power laser beam to produce record marks. Thus a disk drive for recording and reading has to be provided with laser equipment that produces a high-power beam, leading to large costs.
SUMMARY OF THE INVENTION
An object of the present invention is to solve said problems with conventional optical recording media and to provide high-sensitivity optical recording media.
Another object of the invention is to provide optical recording media that are high in stability for long-term storage and are long in service life.
Another object of the invention is to provide optical recording media that are high in resistance to repeated use.
Another object of the invention is to provide methods that can produce said optical recording media easily.
These objects are achieved by the following features of the invention. The invention provides optical recording media,
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patent: 5346740 (1994-09-01), Ohno et al.
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patent: 5378527 (1995-01-01), Nakanishi et al.
patent: 5395669 (1995-03-01), Kawahara et al.
CRC Handbook of Chemistry and Physics, 63rd ed., pp. F-76, .COPYRGT. 1982.
Ohta et al., "Phase Change Disk Media Having Rapid Coling Structure", vol. 28, Suppl. 28-3, pp. 123-128 (.COPYRGT. 1898).
Hirota Kusato
Nonaka Toshihisa
Ohbayashi Gentaro
Angebranndt Martin
Toray Industries Inc.
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