Dynamic information storage or retrieval – Storage medium structure – Layered
Reexamination Certificate
2001-04-09
2003-10-21
Cao, Allen (Department: 2652)
Dynamic information storage or retrieval
Storage medium structure
Layered
Reexamination Certificate
active
06636477
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an information-recording medium in which information is recorded through radiation of an energy beam, and the information-recording medium, and more particularly a phase change optical disk or a rewritable optical disk such as an optical-magnetic disk. Further, the present invention relates to an information recording apparatus in which either reproduction or recording for the information recording medium is carried out in a superior manner.
In the description of the present invention, the information-recording medium is sometimes expressed as a phase change optical disk, an optical magnetic disk, or merely an optical disk. In addition, if the information-recording medium is a medium in which radiation of energy beam may generate heat and this heat may generate a certain variation in atomic arrangement or magnetic momentum to perform information recording operation, the present invention can be applied to this medium, so that the present invention may also provide a certain effect against information recording medium other than a disk-like information recording medium such as an optical card and the like.
In addition, although the energy beam is sometimes expressed as a laser beam or merely as a laser light, if the energy beam can generate heat on the information recording medium as described above, the present invention can be applied to the information recording medium in which information is generally recorded with energy beam such as an electron beam, an ion beam or the like that are not normally meant by light.
BACKGROUND OF THE INVENTION
In the case of rewritable optical disk, there was provided in general a method in which some groove or land (groove shape) type steps are set on a plastic substrate as a laser beam tracking and information is recorded at the groove or land. However, in order to improve a density in recording (a narrow track pitch), a method for recording information at each of groove and land under utilization of the groove and land shapes has been developed in recent years. In this case, the protruded shape in the groove and land is called as a land and the notch shape of the groove and land is defined as a groove. In general, in the case that a track pitch in the information recording medium is changed into a narrow track pitch down to about 80% of a laser beam spot and information is recorded at both land and groove, a leakage of reproducing signal is produced from the adjacent track (either the groove against the land or the land against the groove). For example, when information recorded at the land is reproduced, the reproducing signal from information recorded at the groove is leaked to generate a problem that information recorded at the land cannot be accurately reproduced. The leakage of the reproduced signal from information recorded in the adjacent track is called as a cross-talk.
In order to solve this problem, it is well known in the art to provide a method in which a plurality of magnetic layers are arranged to act as a recording layer and information only at the high temperature section is reproduced under utilization of temperature distribution at the recording layer when the laser beam is radiated (the prior art 1: Japanese Patent Laid-Open No.Hei 8-249737, the prior art 2: Japanese Patent Laid-Open No.Hei 9-293286). In accordance with these methods, since a temperature at the recording layer in the adjacent track becomes a low temperature as compared with the temperature at the recording layer of the center track, no leakage of the reproducing signal from information recorded in the adjacent track is generated. However, such a recording system as above does not provide any sufficient measure against a method for restricting a phenomenon (a so-called cross-erase) in which information (a recording mark) recorded in the adjacent track (the adjacent groove at the time of recording at the land or the adjacent land at the time of recording at the groove) is erased. For example, although the prior art 1 has a heat sink layer with a high thermal conductivity at a side opposite to the laser beam incident side, a distance between the magnetic layer and the heat sink layer is short with 20 nm or less, so that heat is easily dispersed at the adjacent track through the heat sink layer. In addition, although the distance between the magnetic layer and the heat sink layer in the prior art 2 is relatively thick of 80 nm, there are provided three metal magnetic layers as the recoding layer (a functional thin film changing in atomic arrangement or changing in electronic state under application of radiation of the laser beam and a total film thickness of the three layers has a quite thick thickness of 145 nm. Due to this fact, it has been found that heat is dispersed within the recording layer to delete information recorded in the adjacent track.
Accordingly, it has become a substantial problem that a technology for reducing a cross-erase is developed.
However, a step (a groove depth) between a center of the groove and a center of the land in the groove and land shape is usually set to &lgr;/8, where &lgr; is a wavelength of laser forming a laser beam. A reason why this value is set consists in the fact that the largest tracking error signal can be attained when the groove depth is &lgr;/8. However, there sometimes occurs a case that the groove depth is &lgr;/7 or more and &lgr;/5 or less due to the fact that a land groove recording system has been developed recently (prior art 3: Japanese Patent Laid-Open No. Hei 6-338064). A feature of this system consists in the fact that a cross-talk from an adjacent track (a leakage of signal from an adjacent track) can be cancelled even if a track pitch is made to be narrow by about 60% of that of the laser beam spot. However, this recording system does not provide a sufficient measure about a method for restricting a phenomenon (a so-called cross-erase) for deleting a recording mark recorded in the adjacent track (the adjacent groove at the time of land recording or the adjacent land at the time of groove recording). For example, in the prior art 3, although GeSbTe phase change recording material with a low thermal conductivity as compared with metal is used as a recording layer and further the film thickness of the recording layer is 5 to 50 nm, so that it has been found to generate a problem that a distance between the recording layer and the heat sink layer (a reflective layer) has a low value of 18 nm to cause heat to be dispersed into the adjacent track through the heat sink layer at the time of recording of information and a cross-erase is easily generated.
For example, under the standard of DVD-RAM with 2.6 GB/screen, since laser with a laser wavelength (&lgr;) being 645 to 660 nm is metered with a lens having a number of aperture (NA) of lens of 0.6, it is possible to perform a recording and a reproduction under application of the laser beam spot of 0.97 to 0.99 &mgr;m (0.9 &lgr;/NA). Due to this fact, it is also possible to cancel the cross-talk even in the case that the track pitch is set to 0.7 &mgr;m or less. To the contrary, the track pitch under the standard of DVD-RAM with 2.6 GB/screen is set to 0.74 &mgr;m. Its reason consists in the fact that a cross-erase is generated in the case that the track pitch is made narrower than this value.
Accordingly, development of a technology for reducing the cross-erase is a substantial problem.
Additionally, a film structure of rewritable type optical disk is a multi-interference structure in which a dielectric member protective layer (hereinafter called as an under protective layer) such as Si
2
N
4
, ZnS—SiO
2
, a recording layer represented by TbFeCo type magnetic film or a chalcogenide type phase change film such as GeSbTe and the like, a dielectric member protective layer similar to the under protective layer (hereinafter called as a heat sink control layer) are laminated in sequence on a transparent substrate made of the plastic material and further there is provided a metal reflection film
Ando Keikichi
Anzai Yumiko
Hirotsune Akemi
Miyamoto Makoto
Miyamoto Mitsuhide
Antonelli Terry Stout & Kraus LLP
Cao Allen
Hitachi , Ltd.
LandOfFree
Information recording medium and information recording device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Information recording medium and information recording device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Information recording medium and information recording device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3164144