Optical recording medium and sputtering target for...

Details Optical recording medium and sputtering target for... Optical recording medium and sputtering target for...

2001-05-24

2003-07-15

Mulvaney, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064500, C428S064600, C430S270130, C419S035000

Reexamination Certificate

active

06592958

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording medium suitable for application to optical memory devices, in particular, a rewritable compact disk (CD-rewritable). More specifically, the present invention relates to a phase-change optical recording medium comprising a recording material in a recording layer thereof, which recording material is capable of causing a change in the phase thereof by the application of a light beam thereto, thereby recording, reading, erasing, and overwriting information therein.
In addition, the present invention also relates to a sputtering target for fabricating a recording layer of the above-mentioned optical recording medium.
2. Discussion of Background
A phase-change optical recording medium utilizing the phase changes between a crystalline phase and an amorphous phase or between one crystalline phase and another crystalline phase is well known as one of the optical recording media capable of recording, reading, and erasing information by the application thereto of electromagnetic waves, such as a laser beam.
This kind of phase-change optical recording medium enables the overwriting of information to be performed using a single beam, while it is difficult for the magneto-optical memory to conduct such an overwriting operation. An optical system of a drive unit for the phase-change optical recording medium can be made simpler than that for a magneto-optical recording medium, so that research and development of the phase-change optical recording medium has been actively conducted recent years.
As disclosed in U.S. Pat. No. 3,530,441, chalcogen-based alloys, such as Ge—Te, Ge—Te—Sn, Ge—Te—S, Ge—Se—S, Ge—Se—Sb, Ge—As—Se, In—Te, Se—Te, and Se—As are conventionally used as recording materials for the phase-change optical recording medium.
In addition, it is proposed to add an element of Au to the above-mentioned Ge—Te based alloy to improve the stability and to increase the rate of crystallization of the recording material as disclosed in Japanese Laid-Open Patent Application 61-219692. Furthermore, the addition of Sn and Au to the Ge—Te based alloy, and the addition of Pd to the same are respectively proposed in Japanese Laid-Open Patent Applications 61-270190 and 62-19490 for the same purposes as mentioned above. Furthermore, Ge—Te—Se—Sb and Ge—Te—Sb materials with the specific composition ratios of the constituent elements are proposed in order to improve the recording and erasing repetition properties, as respectively disclosed in Japanese Laid-Open Patent Applications 62-73438 and 63-228433.
However, none of the above-mentioned conventional optical recording media satisfies all the requirements for the rewritable phase-change optical memory medium. In particular, improvement of recording and erasing sensitivities, prevention of a decrease in erasability that results from imperfect erasure at the time of overwriting operation, and extension of the life of a recorded portion and a non-recorded portion are the most significant problems to be solved.
A recording medium is proposed in Japanese Laid-Open Patent Application 63-251290, which is provided with a recording layer comprising a compound of a multi-component system composed of substantially three or more components in a single crystalline phase. In this case, the recording layer is defined as a layer comprising a compound of a multi-component system composed of three or more components with a stoichiometric composition, for example, In
3
SbTe
2
, in an amount of 90 atom % or more. It is mentioned that recording and erasing characteristics can be improved to some extent by the provision of this kind of recording layer. However, there are the shortcomings that the erasability is low and the laser power necessary for recording and erasing cannot be sufficiently reduced.
Furthermore, Japanese Laid-Open Patent Application 1-277338 discloses an optical recording medium which comprises a recording layer comprising an alloy with a composition represented by formula of (Sb
a
Te
1-a
)
1-b
M
b
, wherein 0.4≦a<0.7, b≦0.2, and M is one element selected from the group consisting of Ag, Al, As, Au, Bi, Cu, Ga, Ge, In, Pb, Pt, Se, Si, Sn, and Zn. The basic system of the aforementioned alloy is Sb
2
Te
3
, and the addition of a large excess of Sb to this composition in terms of atomic percentage achieves high-speed erasing performance and improves the repetition properties. The addition of the element M can further enhance the high-speed erasing performance. In addition to the above advantages, this reference asserts that the erasability is high when direct current (DC) light is used. However, this reference does not show any specific erasability obtained at the overwriting operation. According to the investigation conducted by the inventors of the present invention, imperfect erasure is recognized in the course of the overwriting operation. Further, the recording sensitivity is insufficient.
Japanese Laid-Open Patent Application 60-177446 discloses an optical recording medium which comprises a recording layer comprising an alloy with a composition represented by the formula of (In
1-x
Sb
z
)
1-y
M
y
, wherein 0.55≦x≦0.80, 0≦y≦0.20, and M is one element selected from the group consisting of Au, Ag, Cu, Pd, Pt, Al, Si, Ge, Ga, Sn, Te, Se, and Bi. Japanese Laid-Open Patent Application 63-228433 discloses a recording layer of an optical recording medium, which comprises an alloy with a composition of GeTe—Sb
2
Te
3
—Sb (excess). However, any recording layers do not satisfy the requirements such as the sensitivity and the erasability.
In addition, Japanese Laid-Open Patent Application 4-163839 discloses an optical recording medium, which is provided with a recording thin layer prepared by adding nitrogen to a Te—Ge—Sb alloy. A recording thin layer of a recording medium disclosed in Japanese Laid-Open Patent Application 4-52188 is made of a Te—Ge—Se alloy, with at least one element of Te, Ge, or Se forming a nitride. Japanese Laid-Open Patent Application 4-52189 discloses a recording thin layer that is made of a Te—Ge—Se alloy, with nitrogen atom being adsorbed thereby.
However, any of these conventional optical recording media cannot exhibit satisfactory performance.
As mentioned above, to enhance the recording and erasing sensitivities, to prevent a decrease in erasability which is caused by imperfect erasure in the overwriting operation, and to increase the life of a recorded portion and that of a non-recorded portion are the most important research topics in the conventional phase-change optical recording media.
With the rapid spread of a compact disk (CD), a write-once compact disk (CD-R) capable of writing data therein only once has been developed and put on the market. However, even one error in the course of data recording makes the CD-R unavailable because it is impossible to correct the recorded data. There is no choice but to discard such a disk. The practical use of a rewritable compact disk that can compensate the above-mentioned shortcoming is desired.
For example, research and development of a rewritable compact disk has been conducted based on the magneto-optical recording disk. However, there are difficulties in performing the overwriting operation and ensuring the compatibility with the CD-ROM or CD-R. In contrast to this, a phase-change optical recording medium is considered to ensure the compatibility with the CD-ROM or CD-R more favorably in principle when compared with the above-mentioned rewritable compact disk of a magneto-optical type. The application of the phase-change optical recording medium to the rewritable compact disk has been thus actively researched and developed recent years.
Papers on the rewritable compact disk obtained from the phase-change optical disk are read, for instance, as Furuya et al., “Proceedings of the 4th Symposium on Phase-Change Recording” p.70 (1992); Jinno et al., “Proceedings of the 4th Symposium on Phase-Change Recording” P.76 (1992); Kawanishi et al., “Proceedings of the 4t

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