Phase change optical disk

Details Phase change optical disk Phase change optical disk

1999-09-28

2002-03-12

Evans, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064500, C428S064600, C428S457000, C428S913000, C430S270130, C369S288000

Reexamination Certificate

active

06355326

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to a phase change optical disk; and, more particularly, to a rewritable phase change optical disk comprising a double-layered reflection layer and having an excellent corrosion resistance, cyclability and signal fidelity.
BACKGROUND OF THE INVENTION
An optical disk generally has the structure shown in
FIG. 1
, and in the information recording area (
1
), digital information forming pits(
11
) are formed on the track of a substrate(
10
). A reflection layer(
12
) and a protection layer(
13
) are then sequentially formed thereon, as shown in FIG.
2
.
With the advent of CD-ROMs, there have been increasing demands for rewritable recording media that can effectively accommodate multi-media related software such as video images, still images and animations. As a result, there have been developed CD-RWs(compact disks-rewritable) which can be recorded and erased repeatedly. The CD-RWs include magneto optical type disks, phase change type optical disks, and the like. A phase change optical disk makes use of a recording material which is capable of undergoing a phase change between crystalline and amorphous phases in response to light, e.g., a laser beam, and this type of optical disk is compatible with the information reading mechanism used in conjunction with conventional CDs.
In a phase change disk, information can be recorded on or erased off a recording layer by way of interconverting the phase of the recording pits between crystallin/amorphous phases with a controlled laser beam irradiation. As shown in
FIG. 3
, a conventional phase change disk has a first dielectric layer(
21
), a recording layer(
22
), a second dielectric layer(
23
), a reflection layer(
24
) and a protection layer(
25
), which are sequentially formed on a transparent substrate (
20
). The tracks in the recording layer contain recorded signals formed thereon when a laser beam is irradiated so as to convert the phase of a specific area of the recording layer from crystalline to amorphous state, or vise versa.
This type of phase change optical disk, with which a short-wavelength laser beam and a single optical system can be employed, is applicable to next generation high density rewritable optical disk such as DVD-RAMs(digital video disk random access memory).
In conventional phase change optical disks, an Al alloy or Ag is used in forming a relatively thick reflection layer having limited performance characteristics. The use of a reflection layer made of a thin Al alloy film, however, may lead to a disk having unsatisfactory recording properties, and a reflection layer made of a thin Ag film tends to exhibit poor corrosion resistance.
Therefore, there has existed a need to develop a phase change optical disk comprising a thin reflection layer which is corrosion resistant and possessed with improved recording properties.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide a phase change optical disk having excellent recording properties as well as corrosion resistance.
In accordance with the present invention, there is provided a phase change optical disk having a first dielectric layer, a recording layer, a second dielectric layer, a reflection layer and a protection layer, characterized in that the reflection layer comprises a first reflection layer made of a metal or an alloy thereof having an electronegativity ranging from 1.9 to 3.0 and a second reflection layer made of Cu, Ag or an alloy thereof, the first reflection layer being in closed contact with the second dielectric layer, and the second reflection layer, with the first reflection layer and the protection layer.


REFERENCES:
patent: 5439752 (1995-08-01), Yoshiko
patent: 6042921 (2000-03-01), Yoshinari
patent: 6177166 (2001-01-01), Ohno

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