Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
1999-02-19
2001-06-12
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064200, C428S064400, C428S064500, C428S064600, C428S913000, C428S457000, C430S270130, C430S495100, C430S945000, C369S283000, C369S288000
Reexamination Certificate
active
06245404
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P10 045904 filed Feb. 26, 1998 which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc comprising on a substrate a recording layer including at least a phase change film changing between a crystalline state and amorphous state, so that this recording layer is heated by a ray radiation so as to cause a phase change for recording and deleting an information. More specifically, the present invention relates to an improvement of materials constituting a light reflection film formed on the recording layer.
2. Description of the Prior Art
As an optical disc for recording and/or reproducing information signals by applying a laser beam, there can be exemplified an optical disc in which an information signal is written beforehand by an emboss pit; a phase change optical disc for writing an information signal by utilizing a phase change between a crystalline state and an amorphous state of a recording layer; and a magneto-optical disc for writing an information signal by utilizing the magneto-optical effect of a recording layer. These optical discs have function films such as a recording layer and a light reflection film on a transparent substrate made from a plastic such as polycarbonate or glass.
In the case of the phase change optical disc, recording, erase, and reproduction are performed as follows. Firstly, this phase change optical disc is subjected to an initialization treatment by applying a predetermined laser beam so that the recording layer is uniformly made into a crystalline state. When recording an information signal on this optical disc, a laser beam of a high-level power (hereinafter, referred to as a recording power) is applied to the recording layer so as to increase the temperature of the recording layer equal to or above its melting point, after which the recording layer is suddenly cooled down so that the portion of the recording layer to which the laser beam has been applied becomes a record mark of the amorphous state.
Moreover, when erasing an information signal which has been recorded on the recording layer, a laser beam of a weaker power than the record power is applied to at least the record mark so that the portion to which the laser beam is applied is heated equal to or above the crystallization temperature but below the melting temperature, after which the portion is suddenly cooled down so that the record mark of the amorphous state becomes crystalized.
Furthermore, in this phase change optical disc, the reflection factor differs between the crystalline state and the amorphous state of the material constituting the recording layer. Accordingly, when reproducing the information signal, the weakest laser beam is applied to the recording layer so as to detect the reflection factor change in the respective states.
Thus, the phase change optical disc does not require means for generating an external magnetic field and accordingly, the size of a recording/reproduction apparatus can be reduced. Moreover, the phase change optical disc can be re-written and produced. This phase change optical disc attracts much attention now.
The recording layer of this phase change optical disc may be made from a phase change material such as a chalcogen compound containing Ge such as Ge—Sb—Te (hereinafter, referred to as Ge chalcogen compound) and a chalcogen compound containing Ag such as Ag—In—Sb—Te (hereinafter, referred to as Ag chalcogen compound). Especially, a phase change optical disc having a recording layer made from the Ge chalcogen compound is known to exhibit a preferable repeated recording characteristic and an excellent repeat durability.
However, even in this phase change optical disc, a further quality improvement is desired as a recording medium of the next generation and there arises following problems.
The phase change optical disc using the Ge chalcogen compound as the material of the recording layer shows a tendency to have a high jitter value of a reproduction signal. Although the phase change disc using the Ge chalcogen compound as, the material of the recording layer has a durability superior to the phase change optical disc using the Ag chalcogen compound, the jitter value suddenly increases as the recording layer is deteriorated after repeated recording of several tens of thousand times. For this, in this phase change optical disc, after repetition of recording a number of times, only a very narrow recording power margin can be obtained for suppressing the jitter value of the reproduction signal below the reproduction limit level.
That is, in this phase change optical disc, after repetition of recording a number of times, the recording power margin enabling to obtain a preferable reproduction signal becomes very narrow.
As a result, in this phase change optical disc, after repetition of recording a number of times, the recording/reproduction failure is easily caused by the recording power fluctuation and the ambient temperature change.
SUMMARY OF THE INVENTION
It is therefore and object of the present invention to provide an optical disc capable of exhibiting a preferable recording/reproduction characteristic by effectively reducing the reproduction signal jitter value and providing a wider recording power margin by assuring a reproduction limit jitter value even after repetition of recording a number of times.
The optical disc according to the present invention includes: a recording layer having at least a phase change film whose phase is changed between a crystalline state and an amorphous state thereby to record an information signal; and a light reflection film formed on the recording layer and constituted by an Al alloy containing Cu in a range from 0.1 to 1.0 atomic %.
In the optical disc according to the present invention having the aforementioned configuration, the light reflection film can have a preferable level of heat conductivity, which in turn enables to obtain an optimal cooling efficiency of the recording layer, so that the phase change film subjected to a beam can change its phase accurately and effectively for an information signal. This reduces the reproduction signal jitter value, and it is possible to obtain a wide record power margin capable of assuring a reproduction limit jitter value even after a repeated recording, thus enabling to obtain a stable recording/reproduction characteristic.
Moreover, in the optical disc according to the present invention, the light reflection film is constituted by an Al alloy containing Cu in the aforementioned range. This enables to obtain an excellent weather resistance of the optical disc.
Consequently, the optical disc according to the present invention can have a preferable recording/reproduction characteristic even after a repeated recording as well as an excellent weather resistance.
REFERENCES:
patent: 5368986 (1994-11-01), Terao
patent: 5674659 (1997-10-01), Yoshioka et al.
patent: 5958649 (1999-09-01), Hirotsune
patent: 5965229 (1999-10-01), Zhou
patent: 6004646 (1999-12-01), Ohno
patent: 0 356 064 A2 (1990-02-01), None
patent: 0 574 025 A2 (1993-12-01), None
patent: 0 822 543 A1 (1998-02-01), None
Akimoto Yoshihiro
Kikuchi Minoru
Saito Nobuhiro
Takase Fuminori
Evans Elizabeth
Sonnenschein Nath & Rosenthal
Sony Corporation
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