Optical recording medium

Details Optical recording medium Optical recording medium

1999-02-12

2001-05-08

Evans, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064400, C428S064800, C428S457000, C428S913000, C430S270160, C430S270180, C430S270200, C430S945000, C369S283000, C369S288000

Reexamination Certificate

active

06228455

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 87113547, filed Aug. 18, 1998, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical recording medium, and more particularly, to a recordable optical recording medium.
2. Description of Related Art
Since the growth of multi-media applications for computers is raised according to the increasingly advanced computer hardware, recording media that are capable of storing a mass of data are needed. An optical compact disc (CD) has been currently utilized as a medium for storing a mass of data, such as multi-media programs and files because of its capacity and data-retrieving rate.
CDs can be divided into three categories, read-only CD, recordable CDs, and rewritable CDs mainly. The read-only CD, or a ca-called CD read-only memory (CD-ROM), is developed based on CD digital audio (CD-DA) and is capable of storing 650-Megabyte (MB) data. Because the data stored on a CD-ROM is burned onto a surface of the CD-ROM during the fabrication process, users are not allowed to modify and edit the stored data. Hence, a recordable optical recording medium, CD-recordable or CD-R, was introduced into the market in 1988.
The structure of a CD-R is similar to what of a traditional CD as shown in FIG.
1
. Referring to
FIG. 1
, a conventional CD-R consists of a 1.2-mm grooved polycarbonate (PC) substrate
12
, a 0.2-&mgr;m dye layer
14
, a metallic reflective layer
16
, and a protective layer
18
. The metallic reflective layer
16
is gold or silver formed by a vacuum sputtering process, and the protective layer
18
is an ultraviolet-cured resin formed by spin-coating. The dye layer
14
, which is not present in a conventional CD-ROM, reacts with laser beams to record data on the CD-R. Compared with a conventional CD-R, besides the lack of a dye layer
14
, a conventional CD-ROM has pre-formed data pits on the substrate
12
before the formation of other components.
The dye layer
14
of a CD-R has certain requirements including:
1. capability of absorbing the laser beam and converting the laser beam into heat, wherein the heat is then used to heat the dye layer
14
, melt and dissolve the dye layer, and form data pits on the substrate
12
;
2. property of a excellent process resolvability for a spin-coating process; and
3. stability on environment to keep the stored data for a long period of time.
The dye layer in most currently available CD-Rs include cyanine, phthalocyanine, and azo-metal complex, wherein cyanine is the most common material used to form a dye layer in a CD-R because of its advantages include non-toxicity, metal-likeness, film-formability, and excellent resolvability. In the fabrication process of a conventional CD-R with a cyanine dye layer, a quencher is normally added to enhance the poor lightfastness of cyanine. Even though the method, which is provided in U.S. Pat. No. 5,328,741, U.S. Pat. No. 5,328,802 and U.S. Pat. No. 5,336,584, is able to last the lifetime of dye layers of CD-R by adding a quencher, there are still drawbacks. The added quencher costs several times than the cyanine, so that the fabrication cost is increased. Since the volatility and the resolvability of quencher are relatively poor, that makes it difficult to processed. In addition, the crystallization of quencher occurring in the dye layer due to an improper process degrades the recording capability of the dye layer.
According to the foregoing, a conventional method that increases the lightfastness of a dye layer by adding quencher is not cost effective and cost competitive, and tends to damaging the dye layer.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a method and a structure for fabricating an optical recording medium that includes forming an additional dielectric layer, instead of adding a quencher, to increase the lifetime of a dye layer. The additional dielectric layer is capable of preventing the dye layer from oxygen and moisture to enhance the lightfastness of the dye layer. The method of the invention is also able to reduce the fabrication cost by not adding expensive quencher.
In accordance with the foregoing and other objectives of the present invention, the invention provides a structure of an optical recording medium that includes a dielectric layer, a dye layer, and a reflective layer formed on a substrate in sequence. The dielectric layer isolates the dye layer from oxygen and moisture to improve the lightfastness and the thermostability of the dye layer. Furthermore, the dielectric layer further increases the lifetime of the dye layer.
In addition, another dielectric layer can be added between the reflective layer and the dye layer to prevent the dye layer from being evaporated by a long-term illumination.
A method for fabricating the forgoing optical recording medium of the invention is also porvided.


REFERENCES:
patent: 5817389 (1998-10-01), Ono
patent: 5871882 (1999-02-01), Schmidhalter
patent: 5879772 (1999-03-01), Morishima
patent: 5879773 (1999-03-01), Hatwar

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