Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-03-16
2002-05-14
Hindi, Nabil (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C475S047000
Reexamination Certificate
active
06388978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an optical recording method for recording information on an optical recording medium such as a rewritable compact disc (CD-RW) or a rewritable digital video disc (DVD-RW) and, more particularly, to an optical recording method for recording information on a rewritable phase-change optical recording medium by projecting an optical beam onto the rewritable phase-change optical recording medium so as to cause a change of phase in a recording layer of the optical recording medium.
2. Description of the Related Art
A phase-change optical recording medium is known as an optical memory medium onto which information is recorded or information recorded thereon is reproduced or erased by projecting a laser beam onto the optical memory medium. The phase-change optical recording medium utilizes a transformation between a crystal phase and a noncrystal phase or between a crystal phase and a different crystal phase. Development of the phase-change optical recording medium has become active since information recorded on the phase-change optical recording medium can be overwritten by using a single laser beam and an optical system of a drive unit can be a relatively simple structure.
A typical phase-change optical recording medium is disclosed in U.S. Pat. No. 3,530,441. The phase-change optical recording medium disclosed in this patent document is made of a so-called chalcogenic alloy such as Ge—Te, Ge—Te—Sn, Ge—Te—S, Ge—Se—Sb, Ge-As—Se, In—Te, Se—Te or Se—As. Each of Japanese Laid-Open Patent Applications No. 61-219692, No. 61-270190 and No. 62-19490 suggests a material in which Au and Sn or Au and Pd are added to a Ge—Te alloy for improving a stability and a high-speed crystalization of the material. Additionally, each of Japanese Laid-Open Patent Applications No. 62-73438 and No. 63-228433 suggests a Ge—Te—Se—Sb material or a Ge—Te—Sb material having a composition ratio which is specifically defined for improving a repetition characteristic of recordings and erasures. However, none of the materials suggested in the above-mentioned patent documents can satisfy all of the characteristics required for a rewritable phase-change optical recording medium. An important issues to be solved are 1) improvement in recording sensitivity and erasing sensitivity, 2) prevention of decrease in an erasure ratio due to incomplete erasure during an overwriting operation and 3) extension of a service life of a recordable part and a nonrecordable part.
Additionally, Japanese Laid-Open Patent Application No. 63-251290 suggests a recording medium provided with a recording layer comprising a single, multi-state composite layer of which crystal state can be substantially more than three different states. Such a multi-state composite layer which can be more than three different states is defined as a composite layer which includes more than 90 atomic percentage of a composite material (for example, In
3
SbTe
2
) having a chemical composite of more than three states. By using such a recording layer, a recording and erasing characteristic may be improved. However, there still exist problems in that an erasure ratio is small and a laser power used for recording and erasure is not sufficiently reduced.
Further, Japanese Laid-Open Patent Application No. 1-277338 suggests an optical recording medium having a recording layer made of an alloy having a composite represented by (Sb
a
Te
1-a
)
1-y
M
y
, where 0.4:≦a≦0.7, y≦=0.2 and M is at least one element selected from a group consisting of Ag, Al, As, Au, Bi, Cu, Ga, Ge, In, Pb, Pt, Se, Si, Sn and Zn. The basic material of this system is Sb
2
Te
3
. A high-speed erasure characteristic and a repetition characteristic are improved by providing an excessive amount of Sb, and the high-speed erasure characteristic is promoted by adding the element M. Additionally, it is explained that a large erasure ratio by a DC light can be achieved. However, this patent document does not teach an erasure ratio during an overwriting operation, and a recording sensitivity is insufficient.
Additionally, Japanese Laid-Open Patent Application No. 60-177446 suggests an optical recording medium including a recording layer made of an alloy having a composite represented by (In
1-x
Sb
x
)
1-y
M
y
, where 0.4≦a≦0.7, y≦0.2 and M is at least one element selected from a group consisting of Au, Ag, Cu, Pd, Pt, Al, Si, Ge, Ga, Sn, Te, Se and Pi. Japanese Laid-Open Patent Application No. 63-228433 teaches a Ge—Te—Sb
2
Te
3
—Sb(excessive) alloy used for a recording layer. However, the recording layer disclosed in each of the above-mentioned two patent documents does not satisfy a sensitivity characteristic and an erasure ratio.
Further, Japanese Laid-Open Patent Application No. 4-16383 discloses an optical recording medium provided with a recording thin film formed of a Te—Ge—Sb alloy containing N. Japanese Laid-Open Patent Application No. 4-52188 discloses an optical recording medium provided with a recording thin film formed of a Te—Ge—Se alloy containing a nitride of at least one of the component elements of the alloy. Japanese Laid-Open Patent Application No. 4-52189 discloses an optical recording medium provided with a recording thin film formed of a Te—Ge—Se alloy which is caused to adsorb N. However, none of the above-mentioned optical recording media can provide sufficient characteristics.
As discussed above, in a conventional optical recording medium, the most important issues to be solved are 1) improvement in recording sensitivity and erasing sensitivity, 2) prevention of decrease in an erasing ratio due to incomplete erasure during an overwriting operation and 3) extension of a service life of a recordable part and a nonrecordable part.
On the other hand, in association with a rapid spread of a compact disc (CD), a recordable compact disc (CD-R), which is recordable only once, was developed and has become popular. However, the CD-R cannot correct recorded information when a recording operation has failed. Accordingly, the failed disc is not reusable and must be discarded. Thus, it is desirous to develop a rewritable compact disc so as to eliminate such a drawback.
A rewritable compact disc which utilizes a magneto-optical disc has been developed. However such a rewritable compact disc has drawbacks in that an overwriting operation is difficult to perform and there is no compatibility with a CD-ROM and a CD-R. Accordingly, instead of the rewritable compact disc utilizing a magneto-optical disc, development of a phase-change optical disc has become active.
The following technical documents are related to a rewritable compact disc utilizing a phase-change optical disc:
1) Fourth phase change recording study symposium preceding, 70 (1992), K. Furuya et al., “Disk structure and composition of Ge—Te—Sb recording film suitable for low linear velocity”
2) Fourth phase change recording study symposium preceding., 76 (1992), S. Jinno et al., “Erasable Phase Change Optical Disks for Recording at Low linear Velocity”
3) Fourth phase change recording study symposium preceding, 82 (1992), Y. Kawanishi et al., “Write, Read and Erase Characteristic of InSe Phase Change CD”
4) Jpn. J. Appl. Phys., 32 (1993), T. Handa et al.
5) Fifth phase change recording study symposium preceding, 9 (1993), S. Maita et al., “Erasable Phase Change Optical Disks”
6) Fifth phase change recording study symposium preceding, 5 (1993), J. Tominaga et al., “Overwrite Properties of V doped In—Ag—Te—Sb Optical Phase Change Media at CD Velocity”
However, none of the phase-change optical discs satisfies the desirous characteristics such as compatibility with a CD-ROM and a CD-R, a recording and erasing performance, a recording sensitivity, a number of times of repetition of overwriting, a number of times of reproduction, a stability for storage or a total performance. The drawbacks are mainly caused by a small erasure ratio due to a composition and structure of a material of the optical disc.
Accordingly, it is desirou
Aihara Kenichi
Iwasaki Hiroko
Nakamura Yuki
Noda Eiji
Ogawa Ippei
Dickstein , Shapiro, Morin & Oshinsky, LLP
Hindi Nabil
Ricoh & Company, Ltd.
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