Background of Invention
The present invention relates to a new manufacturing process for the low speed formats of re-writable compact disc. Discs manufactured through this process exhibit excellent electrical performance before and after environmental stressing at 70°C and 85% of relative humidity, when kept for longer period of 300hrs (more than ISdays). Produced discs through invented process are suitable to read, write and store data for more than 1000 times of overwriting even when they are kept in the harass environmental conditions. Quality parameters including mechanical, optical and electrical are well within media specifications as provided in the books of international standards and thereby suitable for general purposes in the vast consumer market. This process invention is an outcome of our innovative experiments, which we carried out during course of regular production of low speed rewritable compact discs, while in the way of improving the quality performances.
Prior Art
In current scenarios, enormous emphasis has been drawn on optical media due to their huge demand and capacity to store data. Re-writable formats of compact disc have attained special attention due to their high data transfer rate, ability to read, write and erase data for many times and of course, for their interesting phase change technology based on chalcogenide materials. After commercialization of re-writable formats, numerous process technology have been adopted to prepare discs both from academic and commercial end, however, all processes differ from each other due to variation in stamper geometry, thickness of layer stacks and composition of
phase change chalcogenide materials. In such a race, many contradictory perceptions have been reported. As an offshoot, scientific research literatures have been cited describing details of method for re-writable compact discs including different processes and variation in composition of phase change chalcogenide materials, however, improvement in electrical quality with its attribution to environmental stressing has neither been reported. We hereby claim a new manufacturing process, which enhances electrical quality of low speed re-writable compact disc before and after environmental soaking.
Statement of Invention
The present invention relates to a novel process for the manufacturing of low speed re-writable version of compact disc with improved electrical performance, before and after environmental stressing at an elevated temperature of 70°C and relative humidity of 85% for 300 hours. By way of example and without employing any limitation thereto, low speed rewritable compact discs with different percentage doping of ultra pure nitrogen gas have been prepared. As for vast and wide consumer sake, discs must should have excellent write and erase capabilities along with performance stability in harassed environmental conditions. Discs therefore, unambiguously show optimum and moderate value of jitter and Block Error Rate (BLER) at an elevated temperature and humidity for longer period with no failure in recording characteristics e.g., E32 is zero.
As per the present invention, low speed re-writable compact disc doped with 2.0 seem content of nitrogen exhibits excellent electrical performance:
Wherein,
BLER and Jitter reduced significantly after 1000 times of overwriting
No recording failure is observed e.g., E32 is zero, always
BLER and Jitter reduced to an optimum level after direct overwriting of 0 and 1, which are primary quality requisite for re-writable discs
Electrical behavior is in close conformity with specifications provided in media specification book (Orange book)
Characteristics quality parameters are in accordance with media specification even after stressing the disc at an elevated temperature of 70°C and 85% of relative humidity for more than 300 hrs (ISdays)
Detailed Description of the Invention
Re-writable compact disc, which is based on the principle of phase change technology has attracted immense interest in recent years due to their overwrite capability of data, more than 1000 times. As the process technology is based on the principle of phase change reversibility of materials, chalcogenide group materials have been found suitable in lieu, composition differs in many cases due to inherent effect of elements. Most investigated chalcogenide groups are Ag-In-Sb-Te and Ge-Sb-Te quaternary and ternary soft metal alloys, respectively.
Suitable Ag-In-Sb-Te quaternary soft metal alloy has been selected and sputtered in form of thin film on polycarbonate circular substrates. Ultra pure nitrogen as a foreign material was introduced during the process of sputtering of Ag-In-Sb-Te metal alloy. The concentration of nitrogen was varied from 0.0 seem to 4.5 seem.
Discs made with various percentages doping of nitrogen were subjected to go for detailed investigation before and after environmental aging (300hrs). Investigation of quality parameters was carried out at room temperature using dedicated and recommended equipments. It has been found that discs with 2.0 seem content of nitrogen exhibit excellent electronic properties, with reduction in Jitter, BLER and E22. The most prodigious recording failure error (E32) is also zero after 0, 1, 500 and 1000 times of overwriting. In the continuation, similar behavior has been predicted for discs after stressing them in environment at 70°C and 85% humidity for 300hrs. In order to foregoing, however, environmental stability of re-writable disc varies from material to material, it is now apparent that N2 plays a crucial role while determining the quality of re-writable compact disc. Defining the findings as an example leads to
Example
Polycarbonate circular subsfrate of thickness 1.2mm and diameter 120.00mm was fabricated using an injection molding.
Substrate was cooled to an optimum temperature and accordingly dielecfric material (ZnS+Si02) was sputtered so as to protect the subsfrate from excessive heat produced by high power laser used in the way of writing and reading.
Suitable composition of Ag-In-Sb-Te chalcogenide material was sputtered along with varying concenfration of ulfra pure N2 from 0.0 seem to 4.5sccm.
Dielecfric material (ZnS+Si02) was re-sputtered in the similar fashion above the Ag-In-Sb-Te chalcogenide film.
Al was coated on the top as a reflective layer. Disc was finally protected by coating with lacquer. Lacquer coating enables the disc to have resistant from dust and scratches.
Proceeding according to the method described above and using 2.0 seem of ultra pure N2, it has been found that overwrite capability of low speed rewritable compact disc improved tremendously. Electrical parameters like Jitter, BLER, E22 are quite low which are preliminary requisite for the best quality compact disc. It is also professed that recording failure (E32) is virtually zero and thus disc is able to attract attention in the consumer market.
The most detrimental aspect of enhanced jitter, BLER, E22 and E32 after suitably treating the disc with 85% of relative humidity for 300hrs and at elevated temperature of 70°C is also ruled out for 2,0 seem concentration of N2 doping into phase change chalcogenide material during process of sputtering.
Reproducibility in the properties of low speed compact discs manufactured through this process has also been established. Hence, the new manufacturing process developed in the present invention enables to provide excellent quality low speed re-writable compact disc suitable for commercial applications.

We claim
1. A novel manufacturing process for obtaining low speed re-writable compact disc
Wherein, Overwrite performance improved to more than 1000 times
Initial overwrite performances are better than other manufacturing methods on commercial scale
Error concepts of jitter, BLER, E22 reduce significantly and thereby improve overall quality
Recording failure error (E32) tends to always zero even after overwriting the disc for more than 1000 times.
Production yield increases significantly
2. A new process as claimed in claim 1
Wherein,
Direct overwrite performance is far superior than other methods even
after soaking the disc at harassed environmental condition
No recording failure of disc after stressing environmentally
3. A process for improvement in electrical quality of low speed
writable compact disc before and after environmental soaking
substantially as herein described