Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1999-09-07
2001-09-11
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C428S064400, C430S270130
Reexamination Certificate
active
06288997
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk medium for optically recording and reproducing information by using an optical disk device, and in particular to a phase change optical disk medium for recording information with a high density by using phase changes of a thin layer for recording information from its crystal phase to its amorphous phase and reproducing the information.
With development of the computer technology, it has become possible to process audio data and moving picture data by using a personal computer, besides text data processed conventionally. Large-capacity information storage devices capable of coping with various kinds of information media have become necessary. As an optical disk satisfying such a demand, there is a DVD (Digital Video Disk). A DVD-ROM dedicated for reproduction having a user capacity of 4.7 GB/surface has already been put into production. A rewritable DVD-RAM is also under development. As a draft of specifications of optical disks for DVD-RAM, “DVD Specifications for Rewritable Disc (DVD-RAM) Version 1.0; July 1997” is open to the public.
According to the draft of specifications of optical disks for DVD-RAM, a phase change recording layer on which information marks are recorded by phase changes from the crystal phase to the amorphous phase and vice versa is used as an information recording layer, with a capacity of 2.6 GB/surface, a track pitch of 0.74 &mgr;m, and a minimum mark length of 0.614 &mgr;m. Its track structure takes a shape of concave portions that alternate with convex portions. Each groove has a width nearly equal to that of each land portion. Using both groove and land portions as tracks, information marks can be recorded. In addition, cross-talk from adjacent tracks can be canceled. The so-called land/groove structure is thus adopted.
Furthermore, the draft of specifications of optical disks for DVD-RAM described that a test of disks should be conducted by recording and reproducing with a laser spot obtained by focusing a laser beam having a wavelength of approximately 650 nm by a lens having a numerical aperture of 0.6. A reproduced signal of a 14T mark having a mark length of approximately 2.87 &mgr;m should have an amplitude equivalent to at least 43% of the reproduced signal level of unrecorded portions. A reproduced signal of a 3T mark having a mark length of approximately 0.614 &mgr;m should have an amplitude equivalent to at least 40% of that of the reproduced signal of the 14T mark. Assuming that the reproduced signal level of the unrecorded portions is 100% in the case of a disk yielding the smallest reproduced signal, the amplitude of the reproduced signal of the 3T mark is 43%×40%&rlarr2;17%. If a phase change optical disk is capable of yielding at least 17% as the reproduced signal amplitude of the shortest 3T mark when a laser beam having a wavelength of approximately 650 nm and a lens having a numerical aperture of 0.6, information reproduction processing of the phase change optical disk can be conducted by using a drive for DVD-RAM.
For compiling and preserving data recorded on a DVD-ROM disk, a capacity nearly equivalent to that of the DVD-ROM disk or a capacity exceeding that is needed. However, the user capacity of an optical disk for DVD-RAM conforming to the above described draft of specifications is 2.6 GB/surface, which is approximately half of the capacity 4.7 GB/surface of the DVD-ROM. Therefore, the optical disk for DVD-RAM conforming to the draft of specifications is insufficient in capacity. It thus becomes difficult to compile and preserve various data including data recorded on the DVD-ROM disk.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a phase change optical disk medium which has a capacity larger than that of the DVD-RAM conforming to the above described draft of specifications, and which has a performance suitable for test conditions of optical disks stated in the draft of specifications of optical disks for DVD-RAM and thereby which can be subjected to reproduction processing even in a DVD-RAM drive now under development.
Another object of the present invention is to provide a phase change optical disk medium having a user capacity of 4.7 GB/surface equivalent to that of the DVD-ROM or having a larger capacity.
In accordance with a first aspect of the present invention, the above described objects are achieved by a phase change optical disk medium including a disklike substrate and a recording layer formed by a laminate of a plurality of thin layers including a phase change layer, information marks being recorded on the phase change layer by phase changes from a crystal phase to an amorphous phase and vice versa, tracks for recording information marks in groove portions and land portions being formed on the recording layer so as to take a grooved shape having concave portions that alternate with convex portions, wherein the tracks have an interval in the range of 0.54 to 0.64 &mgr;m, and wherein the recording layer has a ratio of the optical reflectance of 0.35 or less when the phase change layer has changed to the amorphous phase in case where the optical reflectance of the recording layer is 1 when the phase change layer is in the crystal phase.
In accordance with a second aspect of the present invention, the tracks have an interval of approximately 0.59 &mgr;m and the recording layer has a ratio of optical reflectance of approximately 0.2 or less when the phase change layer has changed to the amorphous phase in the case where an optical reflectance of the recording layer is 1 when the phase change layer is in the crystal phase.
In accordance with a third aspect of the present invention, the recording layer has a ratio of optical reflectance of approximately 0.1 or less when the phase change layer has changed to the amorphous phase in the case where an optical reflectance of the recording layer is 1 when the phase change layer is in the crystal phase.
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Standard ECMA-272, Standardizing Information and Communication Systems, 120 mm DVD Rewritable Disk (DVD-RAM), Feb. 1998.
DVD Specifications for Rewritable Disc (DVD-RAM) Version 1.0, Jul. 1997.
Miyamoto Makoto
Nakamura Shigeru
Nishida Tetsuya
Dinh Tan
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
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