Radiation imagery chemistry: process – composition – or product th – Erasable imaging
Patent
1989-06-21
1991-06-18
Bowers, Jr., Charles L.
Radiation imagery chemistry: process, composition, or product th
Erasable imaging
430270, 430495, 430945, 428 64, 3461351, G03C 100
Patent
active
050249100
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to optical information recording mediums which enable information to be recorded, reproduced and erased by means of laser beams in high density and in large capacity.
TECHNICAL BACKGROUND
There is known as an optical disk memory a disk of the write-once type using a thin film of TeO.sub.x (0<x<2.0) mainly composed of Te and TeO.sub.2. A chalcogen material, Ge.sub.15 Te.sub.81 Sb.sub.2 S.sub.2, is also known as reported by S. R. Ovshinsky. This material is utilizable for recording information by heating and melting it by application of a laser beam and quenching for amorphization. The recorded information can be erased by heating by irradiation with a laser beam and subsequent gradual cooling for crystallization. Moreover, thin films made of combinations of chalcogens and the elements of the Group V or VI of the Periodic Table such as Ge, e.g. As.sub.2 S.sub.3, As.sub.2 Se.sub.3 or Sb.sub.2 S.sub.3, are widely known.
One of procedures of recording information on these thin films by means of a laser beam and erasing the information is described. A thin film is initially crystallized and a laser beam with about 1 .mu.m.phi. whose intensity is modulated according to information is applied, for example, to a recording disk having a thin film thereon under conditions of rotation of the disk. Portions where irradiated with the laser beam are heated to a temperature higher than the melting point of the thin film and then quickly cooled, thereby causing the information to be recorded as amorphous dots. For the erasure of the information, a spot beam which is elongated along the direction of rotating track or tracks of the disk is irradiated, so that the thin film is heated and is then recrystallized by the effect of gradual cooling with the elongated spot beam.
In recording mediums where information is recorded and erased through heating, temperature rise, melting, quenching and heating, temperature rise, gradual cooling, respectively, by laser beam irradiation of the thin film, the quality of signals may vary in correspondence with the heating cycle. The variation is considered to result from thermal, mechanical damages of a material for substrate which are produced by repetition of a number of cycles of rapid heating over 400.degree. C. by application of a recording spot beam and an erasing spot beam and cooling. In addition, the recording thin film may suffer thermal, mechanical damages. Depending on the composition, the recording thin film may undergo a local change in the composition, component of the film or so-called segregation.
A problem has been involved in that where the substrate or recording film undergoes such a change as mentioned above, an increasing number of noises generate and the cycle characteristic deteriorates during the recording, reproducing and erasing cycles.
DISCLOSURE OF THE INVENTION
This invention relates to the art of recording and erasure of optical information by thermally changing the state of thin film by irradiation, for example, of a laser beam and has for its object the improvement in the cycle characteristics of recording and erasure. The invention is characterized in that the thin film used is formed of three components of GeTe, Sb.sub.2 Te.sub.3 and Sb and that when the molar ratio of Sb/Sb.sub.2 Te is taken as b, 0.3<b<0.8 (wherein b=excess Sb/Sb2Te3).
When Sb.sub.2 Te.sub.3 (melting point: 622.degree. C.) is converted into a thin film, an amorphous film is obtained. This film undergoes a change between amorphization and crystallization and is usable for recording. However, its blackening (involving crystallization) temperature is as low as 100.degree. C. and is thus thermally unstable. Mixing of GeTe having a high melting point, Tm=725.degree. C., can raise the blackening (crystallization) temperature over 180.degree. C. Although the thin film of the mixture has good thermal stability, the quality of signal is liable to lower when repeating the cycle of recording (amorphization), erasure (crystallization) or the cy
REFERENCES:
patent: 4499178 (1985-02-01), Wada et al.
patent: 4670345 (1987-06-01), Morimoto et al.
Bordas, S.; M. T. Clavaguera-Mora, B. Lengendre, Chhay Hancheng, "Phase Diagram of the Ternary System Ge-Sb-Te", Thermochimica Acta, vol. 107, (1986), pp. 239-265.
Kotera Koichi
Matsubara Kunihiro
Ohta Takeo
Uchida Masami
Bowers Jr. Charles L.
Matsushita Electric - Industrial Co., Ltd.
Pezzner Ashley I.
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