Phase-change information recording medium and optical...

Details Phase-change information recording medium and optical... Phase-change information recording medium and optical...

1999-10-27

2001-08-28

Evans, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064400, C428S064500, C428S064600, C428S457000, C428S913000, C430S270130, C430S495100, C430S945000, C369S283000, C369S288000

Reexamination Certificate

active

06280810

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a phase-change information recording medium and an optical recording method which records information to the phase-change information recording medium.
(2) Description of the Related Art
A phase-change information recording medium which utilizes a phase change of a recording layer made of a phase-change alloy, between the crystalline phase and the amorphous phase is known as one of optical information recording media that are capable of reading, writing and erasing of information by the application of light, such as a laser beam, to the recording layer. In the phase-change information recording medium, the entire recording layer is initially set in the crystalline phase. The laser beam is locally emitted to a portion of the recording layer in the recording medium, and the recording layer portion is heated above the melting point of the recording layer by the light energy, and rapidly cooled so that the recording layer portion is set in the amorphous phase.
In a conventional recoding method for the information recording media of the above type, a data signal is supplied to a semiconductor laser of an optical pickup through pulsewidth modulation (PWM), so that the laser is operated in accordance with a controlled power supplied to the laser so as to emit a laser beam to the recording layer of the recording medium. In this manner, a sequence of amorphous/crystalline phases is created along the track of the recording medium so that the data signal is encoded in the recording medium.
The standard requirements for rewritable compact disk have been provided by the so-called orange book, part III. The rewritable compact disk is a type of the above-mentioned information recording media. According to the standard requirements, the linear rotation rate of the rewritable compact disk is to be in a range from 2.4 m/s to 2.8 m/s. This linear rotation rate is only twice as large as the basic linear rotation rate which is in a range from 1.2 m/s to 1.4 m/s.
However, with recent development of personal computers with high-speed data processing performance, there is an increasing demand for an improved phase-change information recording medium for use in the recent personal computers which can achieve the reading, writing and overwriting of information at higher rotation rates than those achieved by a conventional phase-change information recording medium. In addition, it is desirable to establish an optical recording method which can achieve the reading, writing and overwriting of information for the improved phase-change information recording medium at the higher rotation rates without significant degradation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved phase-change information recording medium and the optical recording method thereof in which the above-described problems are eliminated.
Another object of the present invention is to provide a phase-change information recording medium which can achieve the reading, writing and overwriting of information, without significant degradation, at higher rotation rates than those achieved by a conventional phase-change information recording medium.
Another object of the present invention is to provide an optical recording method which can achieve the reading, writing and overwriting of information for the improved phase-change information recording medium at the higher rotation rates without significant degradation.
The above-mentioned objects of the present invention are achieved by an information recording medium which includes a substrate, a first protective layer formed on the substrate, a recording layer formed on the first protective layer, and a second protective layer formed on the recording layer, the first protective layer having a thickness in a range from 65 nm to 130 nm, the second protective layer having a thickness in a range from 15 nm to 45 nm, the recording layer having a thickness in a range from 15 nm to 35 nm and being composed of a phase-change alloy with the composition in terms of atomic percentage being represented by the formula
Ag
a
In
b
Sb
c
Te
d
where 0<
a≦
6, 3≦
b≦
15, 50≦
c≦
65, 20≦
d≦
35, 9
+b+c+d=
100,
the recording medium being configured to provide capabilities of reading, writing and overwriting of information at linear rotation rates ranging from 1.2 m/s to 11.2 m/s.
The above-mentioned objects of the present invention are achieved by an optical recording method for writing or overwriting of information to an information recording medium through a pulsewidth modulation PWM conversion, the optical recording method including the steps of: providing an information recording medium which comprises a substrate, a first protective layer formed on the substrate, a recording layer formed on the first protective layer, and a second protective layer formed on the recording layer, the first protective layer having a thickness in a range from 65 nm to 130 nm, the second protective layer having a thickness in a range from 15 nm to 45 nm, the recording layer having a thickness in a range from 15 nm to 35 nm and being composed of a phase-change alloy with the composition in terms of atomic percentage being represented by the formula
Ag
a
In
b
Sb
c
Te
d
where 0<
a≦
6, 3≦
b≦
15, 50≦
c≦
65, 20≦
d≦
35, and
a+b+c+d=
100,
the recording medium being configured to provide capabilities of reading, writing and overwriting of information at linear rotation rates ranging from 1.2 m/s to 11.2 m/s; and supplying a data signal to a semiconductor laser via a PWM converter so that the laser is operated in accordance with a controlled power supplied by the PWM converter and the data signal is encoded in the recording layer of the recording medium by a laser beam emitted by the laser, wherein the data signal has a waveform of power-control pulses with a fixed clock duration, the controlled power supplied to the laser including at least three power levels including a write power level Pw, an erase power level Pe and a biased power level Pb, where Pw>Pe>Pb, the waveform of power-control pulses including a multi-pulse portion with a number of cycles, each cycle including a selected one of either the write power level Pw for a pulse duration t
on
and the biased power level Pb for a pulse duration t
off
, or the erase power level Pe for a pulse duration t
on
and the biased power level Pb for a pulse duration t
off
, wherein each of the linear rotation rates of the recording medium is set to an integer multiple of a basic linear rotation rate Vmin which ranges from 1.2 m/s to 1.4 m/s, and wherein a duty ratio of the multi-pulse portion in the data signal represents a ratio of an on-time of the semiconductor laser to a multi-pulse duration and is given by t
on
/(t
on
+t
off
), and the duty ratio is set to one of a plurality of ranges of 0.05 to 0.4, 0.1 to 0.6, 0.2 to 0.8, 0.25 to 1.0, and 0.3 to 1.0 for the linear rotation rates Vmin,
2
Vmin,
4
Vmin,
6
Vmin, and
8
Vmin, respectively.
In a preferred embodiment of the phase-change information recording medium of the invention, the recording characteristics of the recording medium have been verified from the experimental results which indicate that the recording medium of the invention can achieve the reading, writing and overwriting of information, without significant degradation, at higher rotation rates than those achieved by a conventional phase-change information recording medium.
In a preferred embodiment of the optical recording method of the invention, the recording characteristics of the recording medium as the result of execution of the optical recording method have been verified which indicate that the optical recording method of the invention can achieve the reading, writing and overwriting of information for the phase-change information recording medium at the higher rotation rates without significant degradation.


REFERENCES:
patent: 5681632 (1997-10-01)

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