Optical recording medium and recording method

Details Optical recording medium and recording method Optical recording medium and recording method

2002-05-20

2004-08-03

Mulvaney, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064500, C430S270130

Reexamination Certificate

active

06770346

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to phase-change optical recording medium recordable and reproducible of information by optically changing a recording layer material by optical beam irradiation, and also rewritable, and a recording method thereof.
2. Description of the Related Art
As one of optical information recording media which is recordable, reproducible, and erasable of information by irradiation of laser beam, a so-called phase-change optical recording medium utilizing transition between crystal-amorphous phase or crystal—crystal phase is well known. Such recording medium has been utilized as recording medium for computers or image and sound related devices for its capability of overwriting with single beam and for its simple structure compared to an optical system of a drive unit.
The recording materials thereof include GeTe, GeTeSe, GeTeS, GeSeS, GeSeSb, GeAsSe, InTe, SeTe, SeAs, Ge—Te—(Sn, Au, Pd), GeTeSeSb, GeTeSb, Ag—In—Sb—Te, and the like. Particularly, Ag—In—Sb—Te has characteristic of high sensitivity and a clear profile of amorphous part, and is developed as a recording layer for mark edge recording.
In Japanese Patent Application Laid-Open No. 3-231889, for example, a recording layer represented by an I·(III1−&ggr;V &ggr;)·VI type general formula wherein I is an element of the group I, III is an element of the group III, V is an element of the group V, and VI is an element of the group VI is disclosed. However, such a recording layer has a problem in repetitive recording property.
The recording layer used in information recording medium disclosed in Japanese Patent Application Laid-Open No. 4-191089 has a problem also in repetitive recording property although improvement in erasing ratio and high-speed recording can be attained.
The unrecorded part (crystallized part) of the recording layer used in information recording medium disclosed in Japanese Patent Application Laid-Open No. 4-232779 has a structure including a stable phase (AgSbTe
2
) and an amorphous phase present around the stable phase. Therefore, a minute grain boundary is present in the crystallized part, causing noises, although the repetitive recording property can be improved. This does not have a serious adverse effect on the recording property of optical recording medium having relatively low recording density such as CD-RW (Compact Disk-Rewritable) using a laser beam of recording and reproducing wavelength about 780 nm, but is an obstacle to the realization of high-density recording in DVD (Digital Versatile Disk)-RAM using a laser beam of 680 nm or less and having a recording density about 4 times CD-RW, further high-density DVD-RW, and the like. A problem is left also for repetitive recording property.
The structure of the crystallized part of the recording layer utilized in Japanese Patent Application Laid-Open No. 4-267192 is in the multi-phase state of AgSbTe
2
phase separated from a uniform amorphous phase and the other phase (stable phase or amorphous phase). When the other phase above mentioned is the amorphous phase, it has the similar problem with the information recording medium in Japanese Patent Application Laid-Open No. 4-232779 described above, and when the other phase is the stable crystal phase, the problem arises in that the satisfying recording property cannot be obtained.
In Japanese Patent Application Laid-Open No. 1-277338, a composition expressed by the composition formula (SbxTe1−x) are disclosed as the recording material, wherein M is at least one element selected from Ag, Al, As, Au, Bi, Cu, Ga, Ge, In, Pb, Pt, Se, Si, Sn and Zn with composition range of 0.4≦x<0.7 and y≦0.2. The structure of this composition range is based on Sb
2
Te
3
. The recording layer of this structure has a problem in repetitive recording property in the region where y is 0.7 or more.
In Japanese Patent Application Laid-Open No. 1-303643, it is taught that a single &ggr;-phase was obtained and satisfying repetition property was obtained for the information recording media disclosed therein. However, it does not refer to the crystalline structure of this &ggr;-phase, and thus has a problem in realizing a recording media conformable to high linear velocity and high density in the future.
In Japanese Patent Application Laid-Open No. 2000-79761, a recording layer approximating SbTe eutectic composition is disclosed. The recording layer disclosed therein utilizes the phase separation of Sb phase and Sb
2
Te
3
phase. Sb is determined in the range of 0.5 or more and 0.7 or less, thus it is not conformable to high-linear velocity recording.
Recording medium utilizing a reversible phase change between a crystalline phase and an amorphous phase has been internationally utilized in rewritable recording media (CD-RW, etc.). For use in CD-RWs, speeding up in recording has been required accompanying the wide use, and the high-speed recording became also indispensable for the phase-change recording medium.
In high-speed recording, or in recording at a high linear velocity, the reference clock of the emitting pulse of laser beam is shortened in accordance with the increase in recording density. Therefore, in order to form a mark (amorphous phase), both the emitting (heating) time of one optical pulse and the time of emitting a lower power necessary for cooling (or often emitting no power) are shortened, compared to the recording at a lower linear velocity.
Further, in an optical recording which utilizes LD (laser diode), since the rise time and the fall time of the LD are limited, it is difficult to form a mark by heating and cooling at one optical pulse. For this reason, the heating can be performed by emission of higher recording power, however the recording power has a limit in recording. Also a certain cooling time should be considered for rapid quenching to be carried out after heating, however, the cooling time cannot be assigned too long. It is thus difficult to control the heating and cooling within the reference clock to record a mark of a prescribed length at a higher linear velocity.
On the other hand, it is also required to optimize the recording material of the phase-change recording layer and the medium structure.
In order ensure the repetitive recording property in high-speed recording, the crystallization rate (or crystallization speed) must be increased to raise the erasing ratio, and it is necessary to optimize the recording layer material and the composition ratio of each constituting element.
When the crystallization rate (or crystallization speed) is too high, however, the amorphous phase is difficult to form. In this case, the medium structure may be arranged to form a quench structure, but the recording power is also required. In Ag—In—Sb—Te series and Sb—Te eutectic series, although the crystallization rate can be increased by increasing Sb quantity, it makes difficult to form the amorphous phase, and also deteriorates the storage property under high-temperature environment of mark, if an increase in the quantity is too much. When the medium structure is arranged to form the quench structure, a problem of deficiency in sensitivity arises. The causes of the deterioration in repetitive recording property in the high-speed recording include deterioration of not only the recording layer but also the upper protection layer located between the recording layer and the reflection layer, or dispersion of the constituting elements in the recording film or cracking of the protection layer by thermal impact, due to repetition of heating under high temperature and cooling in a short time. To cope with the speed up, studying of recording layer material, protection layer material and reflection layer material are required. For the same reason, study of recording method is also necessary.
Known recording layer materials conformable to high-linear velocity recording include for example, the one disclosed in Japanese Patent Application Laid-Open No. 2000-313170. Namely, it is expressed by the formula [(SbxTe1−x)yGe1&mi

Affiliated with

Also associated with

Rating

Optical recording medium and recording method does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical recording medium and recording method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical recording medium and recording method will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3344863