Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-09-03
2004-11-23
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S945000, C369S275500, C369S275200, C428S064600
Reexamination Certificate
active
06821707
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information recording medium provided with an optically detectable information recording layer, the producing method thereof and a method of recording/erasing/reproducing information.
2. Description of the Prior Art
A recording material thin film layer comprising a metal thin film and an organic thin film is formed on a disc-shaped or a card-shaped substrate. A high energy beam focused on a micro light spot having a submicron order diameter is irradiated onto the recording material layer, thereby a local variation is generated on recording material layer. Thereby, such a technique so that an information signal is stored is already well known. More specifically, when an optical magnetic material thin film and a phase change material thin film are used for a recording layer, it is easy to rewrite the signal. Accordingly, this technique has been actively studied and developed. For example, in case of the optical magnetic recording medium, a difference of a rotating angle on a polarized surface of a reflected light generated due to the difference of a magnetization state is used as the record. Furthermore, in case of the phase change recording medium, an amount of a reflected light relative to a light having a specific wavelength in a crystalline state is different from that in an amorphous state, thereby the difference is used as the record. A laser output is modulated between a record level having a relatively higher power and an erasure level having a relatively lower power, and the modulated output is only irradiated on a recording medium. Thereby similarly to a magnetic disk, there is such a characteristic that the record erasure and the record of a new signal can be simultaneously performed (it is possible to overwrite the record). The information signal can be rewritten for a short time.
Usually, the optical magnetic recording medium and the phase change recording medium comprise, for example, a multi-layer film shown in FIG.
1
. That is, on a substrate
1
comprising a resin plate of a polycarbonate and PMMA (polymethyl-methacrylate), a glass plate, or the like, usually, a recording layer
3
having an optical absorption comprising the phase change material and the optical magnetic material inserted between protective layers
2
and
4
comprising a dielectric material is formed. Furthermore, a metallic reflecting layer
5
comprising an alloy of Au and Al for increasing an optical absorption efficiency on the recording layer
3
and for acting as a thermal diffusion layer is formed on the protective layer
4
. These layers are sequentially laminated by a sputtering method, a vacuum deposition method, or the like. Furthermore, an overcoat layer
6
is formed on an uppermost layer in such a manner that a scratch and dusts are not attached to these layers. Usually, a laser beam is incident from a side of the substrate
1
. In many cases, a front surface of the substrate
1
is provided with a concave-convex groove track or a concave-convex pit sequence as guide means for guiding the laser beam to a predetermined position on the disk.
A function of each layer and a concrete example of materials forming each layer are as follows.
In case of the recording layer
3
, when the phase change material is used, chalcogenite thin film whose base comprises Te and Se, for example, a Ge—Sb—Te alloy thin film, a Ge—Sb—Te—Se alloy thin film, an In—Sb—Te alloy thin film, an Ag—In—Sb—Te alloy thin film, an In—Se alloy thin film, and the like are reported. In the medium using such phase change materials, the laser beam is irradiated, thereby the signal is recorded and reproduced. As already described, while the power of the laser beam is being modulated at a strong level and a weak level, the laser beam is irradiated onto a revolving recording medium. A portion irradiated with the strong power is locally melt in an instant, thenceforth, the portion is quenched. Thereby the portion is amorphized, and the signal is recorded. Furthermore, at the portion irradiated with a relatively weak power, the amorphous-state portion is annealed, thereby the portion is crystallized, and the recorded signal is erased. In order to reproduce the signal, the power of the laser beam is reduced enough in such a manner that the recording film is not changed, and the laser beam is irradiated. At this time, a strength of the reflected light is detected, and whether the portion irradiated with the laser beam is in the crystalline state or the amorphous state is judged, thereby the signal is reproduced.
The functions of the protective layers
2
and
4
comprising a dielectric material are, for example, as follows:
1) the recording layer is protected from an external mechanical damage;
2) a thermal damage such as a roughness on the surface of the substrate, a break of the recording layer and an evaporation, etc. occurred due to repeatedly rewriting the signal are reduced, thereby a repetition of rewriting the signal can be increased;
3) an interference effect of a multipath reflection is used so that an optical change can be enhanced;
4) an influence from an outside air is intercepted so that a chemical change can be prevented.
As the material comprising the protective layer for satisfying the above objects, heretofore, an oxide such as SiO
2
, Al
2
O
3
or the like, a nitride such as Si
3
N
4
, AlN or the like, an acid nitride such as Si—O—N or the like (for example, disclosed in Japanese Patent Application Laid-open No. 3-104038), a sulfide such as ZnS or the like, a carbide such as SiC or the like, or a mixed material such as ZnS—SiO
2
or the like (disclosed in Japanese Patent Application Laid-open No. 63-103453) is proposed, and one part of them is practically used.
Two layers are provided to the protective layer, thereby the characteristic thereof can be enhanced. The example of the phase change recording medium is disclosed in Japanese Patent Application Laid-open No. 5-217211. That is, the dielectric layer comprising the nitride (SiN, AlN) and the carbide (SiC) is used at the side contacted to the optical recording layer as the protective layer of the optical recording layer including Ag, and ZnS or a compound including ZnS is used as the outer layer of the dielectric layer. The above SiN, SiC, AlN layer is used, thereby a combination of Ag included in the recording layer and S in the protective layer is prevented. As disclosed in Japanese Patent Application Laid-open No. 5-217211, a film thickness of the SiN, AMN, SiC layer is ranging from 5 nm to 50 nm. Furthermore, as disclosed in Japanese Patent Application Laid-open No. 6-195747, the protective layer has two layers inserted between the recording layer and the substrate, where one layer contacted to the recording layer comprises Si
3
N
4
layer and the other layer contacted to the substrate comprises ZnS—SiO
2
layer, thereby two dielectric layers are formed. The Si
3
N
4
layer facilitates a crystallization of the phase change material layer.
The example of the optical magnetic recording medium is disclosed in Japanese Patent Application Laid-open No. 4-219650. Here, the dielectric layer contacted to the substrate has two layers, and one layer contacted to the substrate is a silicon oxide film, thereby an addhesiveness of the substrate and the dielectric layer is enhanced. Furthermore, the other layer contacted to the recording layer comprises the compound of the carbide and the nitride, thereby it is possible to prevent a corrosion of the magnetic recording layer occurred due to that oxygen from the silicon oxide layer and water passing through the substrate are penetrated into the recording layer. As disclosed in Japanese Patent Application Laid-open No. 4-219650, preferably, the nitride comprises Sn—N, In—N, Zr—N, Cr—N, Al—N, Si—N, Ta—N, V—N, Nb—N, Mo—N and W—N, and the film thickness thereof is ranging from 10 nm to 20 nm. Furthermore, as disclosed in Japanese Patent Application Laid-open No. 4-321948, in the same view of Japanese Patent Application Laid
Kawahara Katsumi
Nagata Ken'ichi
Ohno Eiji
Ohta Hiroyuki
Uno Mayumi
Angebranndt Martin
Merchant & Gould P.C.
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