Stock material or miscellaneous articles – Circular sheet or circular blank
Patent
1999-02-08
2000-04-25
Evans, Elizabeth
Stock material or miscellaneous articles
Circular sheet or circular blank
428 644, 428 645, 428913, 43027013, 4304951, 430945, 3692754, 369283, B32B 300
Patent
active
060541997
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical recording medium for optically recording and reproducing information thereon. In particular, the present invention relates to an optical recording medium formed with a wide-width groove as a data-recording area.
BACKGROUND ART
FIG. 8 shows an outline of a surface structure of a conventional magneto-optical recording medium. The magneto-optical recording medium comprises a multi-layered film 26 composed of at least one layer of a magnetic recording film and a reflective film or the like formed on a transparent substrate 10 via an insulative film. The substrate 10 includes grooves 22 and prepits 24 which are previously formed in a direction along the track by means of injection molding. Lands (projections) 28 are defined between the grooves 22. The land 28 includes a data-recording area for recording information thereon, and a header area in which, for example, an address signal is recorded in a form of prepit 24. The track position control (tracking) is performed as follows when data are recorded and reproduced. That is, for example, the push-pull system is adopted, in which the groove 22 is irradiated with a light spot to detect diffracted light beams subjected to diffraction from the groove 22 in a divided manner in right and left directions perpendicular to the track respectively, and the track position is controlled so that the diffracted light beams have an equal intensity. The tracking must be correctly performed in order to write data at a desired position. For this purpose, it is necessary to highly accurately process the grooves 22 and the lands 28.
The substrate, which has the grooves 22 and the prepits 24 as described above, is usually formed in accordance with the following procedure. At first, a flat base disk made of glass, to which a photoresist is applied to give a predetermined thickness, is prepared. A master disk exposure apparatus is used to expose portions corresponding to the grooves and the prepits with a laser spot while rotating the glass base disk at a constant speed. The exposed base disk is subjected to a development process to remove the exposed portions so that a master disk is produced. A stamper is formed on the basis of the master disk. Further, the stamper is installed in a molding mold to perform injection molding for a plastic material with the mold. Thus, the substrate for the optical recording medium having the predetermined grooves and the prepits is reproduced.
An optical recording medium, which makes it possible to perform high density recording, is demanded as the amount of information to be processed is increased. In the case of the optical recording medium having the structure as shown in FIG. 8, the track pitch should be made narrow in order to achieve a high density. For this reason, when the groove portion is subjected to exposure by using the master disk exposure apparatus, an optical blur occurs at the land 28 adjacent to the groove 22. That is, the laser beam for exposure usually has an intensity distribution which follows the Gaussian distribution curve. The diameter of the laser spot for exposure is substantially determined by the half value width. Therefore, the outside of the portion corresponding to the groove (edge of the land) is also subjected to exposure. Accordingly, the portion corresponding to the land tends to cause surface roughness during the development process. The width and the height of the land are decreased due to the surface roughness, resulting in decrease in S/N ratio of the data signal.
An optical recording medium, for example, a so-called wide-width groove type magneto-optical disk is known concerning a structure of the optical recording medium for dissolving the problem described above, in which grooves 12 having a wide width are formed as shown in FIG. 1, and data are written in the grooves 12. In the case of the optical recording medium having such a structure, the recording signal is recorded on the groove 12 having the wide width, not on the land on which the optic
REFERENCES:
patent: 5583847 (1996-12-01), Takeshima et al.
patent: 5856969 (1999-01-01), Nishiyama
patent: 5898663 (1999-04-01), Miyamoto et al.
patent: 5970027 (1999-10-01), Narita et al.
Kinoshita Shinitsu
Suenaga Masashi
Sugiyama Hisataka
Sugiyama Toshinori
Sukeda Hirofumi
Evans Elizabeth
Hitachi , Ltd.
Hitachi Maxell Ltd.
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