Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1999-05-18
2001-05-01
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S064400, C428S064500, C428S064600, C428S913000, C430S270130, C430S495100, C430S945000, C369S283000, C369S288000
Reexamination Certificate
active
06224960
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to phase-change recording medium which is particularly suitable for write-once read-many times (WORM) applications.
BACKGROUND OF THE INVENTION
Optical recording has been increasingly used in recent years to publish, distribute, store, and retrieve digital information. This is done by focusing a laser beam to write and/or read information on an optical recording media usually in the form of a spinning disk. In the read only memory (ROM) format, the information is prefabricated at the factory in the form of encoded small features on the disk and the laser beam is used to read back the information. In the writable formats, the laser beam is used to create the small encoded marks through a variety of physical recording mechanisms. This permits the user to record their own data on the disk. Some recording physical mechanisms are reversible. The recorded marks can be erased and remade repeatedly. Disks that utilize these mechanisms are called Erasable or Re-writable disks. Some of these physical mechanisms are one way, once the marks are made they cannot be reversed or altered without leaving a clearly identifiable trace that can be detected. Disks that utilize these mechanisms are called WORM disks. Each of these formats is suitable for certain practical applications.
The present invention focuses on WORM disks. The popularity of compact disk recordable (CD-R), which is a WORM disk, in recent years suggests that the demand of WORM disks is very strong. This format is suitable for many applications where the data are to be stored in such a form that any modification to the content is not possible without leaving a easily detectable trace. The format is also suitable for many applications where rewriteability is not needed such as those for publishing and distribution. In these applications the WORM disks are desirable if they can be provided at lower costs than the rewritable.
Many physical mechanisms have been used for WORM recording. The first practical WORM disks utilized ablative recording where the pulsed laser beam is used to create physical pits in the recording layer. This mechanism requires the disks to be in an air-sandwiched structure to leave the surface of the recording layer free from any physical obstruction during the pit formation process. The other mechanism is to use the laser beam to cause the fusing or chemical interaction of several layers into a different layer. This mechanism suffers from the requirement of relatively high laser power and from the difficulty in manufacturing the multi-layered structure. The other mechanism is to use organic dye as the recording layer. Although used successfully in CD-R disks, this mechanism suffers from its strong wavelength dependence. The optical head used in the DVD devices operating at 650 nm, for example, is not able to read the CD-R disks designed to work at the CD wavelength of 780 nm. Yet another mechanism is to use phase-change recording media. In contrast to the more popular erasable phase-change media, these WORM media are designed to record data via laser crystallization of the as-deposited amorphous phase. The materials are designed such that it is practically impossible to reverse the laser crystallized state back into the amorphous state. Whereas this mechanism is able to minimize or eliminate most of the problems mentioned above, it is unique in its recording polarity. The crystalline recorded marks have higher reflectivity than the amorphous background, opposite to most other recording mechanisms. This makes it difficult to produce multi-function drive devices.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved WORM media that can avoid the above mentioned problems.
It is a further object to provide WORM media with an intrinsic low-cost structure so that those applications for which WORM functionality is not a necessity can benefit from having these media.
These object are achieved in a recording medium comprising:
(a) a transparent substrate;
(b) a crystalline phase-change layer provided over the transparent substrate;
(c) a dielectric layer provided over the phase-change layer;
(d) a metallic reflector layer provided over the dielectric layer; and
(e) the crystalline phase-change layer having a thickness and phase-change material selected so that data can be recorded in it on a first write, but on second or subsequent writes the written data results in at least a 50% increase in data jitter.
Quite unexpectedly it has been discovered that if the disk structure and materials are properly chosen, a WORM disk can be fabricated using erasable phase-change materials. These materials can be cycled between the amorphous and crystalline phases and are normally used to produce rewritable disks. Specifically, it has been discovered that by choosing the phase-change material and disk structure that produce a detectable irreversible change during recording than any attempts to rewrite the data will still leave a detectable residue even if the recording layer itself is undergoing a completely reversible change. To qualify as a WORM media, however, the detectable residue has to be large enough so that it can be unmistakenly distinguished from other possible causes of data degradation. For one skilled in the art the data-to-clock jitter is a parameter normally used to describe the quality of the read-back data. For DVD-ROM disks, for example, the specification for the data-to-clock jitter is 8% of the detection timing window of 38.23 ns. If the data-to-clock jitter is degraded by 50% of this value to above 12%, the change can be easily detected.
The present invention is particularly suitable for providing a WORM recording medium using phase-change materials that can be cycled between the amorphous and the crystalline state by the application of a laser beam. The present invention is also suitable for providing the WORM media with physical and recording properties very similar to rewritable media so that it is easier to provide a multifunction read/write drives that can handle both types of media. The present invention also provides the WORM media with a simpler layer structure so that it is easier to manufacture and lower cost than the rewritable media. A feature of the present invention is the provision of the WORM media using the same materials as those used for a re-writable media so that the two types of media can share the same production equipment to reduce cost.
REFERENCES:
patent: 5719006 (1998-02-01), Ohkubo
patent: 5912103 (1999-06-01), Ebina
patent: 5978349 (1999-11-01), Yoshinari
patent: 6094405 (2000-07-01), Ogawa
Cushman Thomas R.
Farruggia Guiseppe
Olin George R.
Primerano Bruno
Tyan Yuan-Sheng
Eastman Kodak Company
Evans Elizabeth
Owens Raymond L.
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