Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1998-08-10
2003-01-07
Angebranndt, Martin (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S945000, C428S064500, C428S064600, C369S275200, C369S275400
Reexamination Certificate
active
06503690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information recording medium on which information can be recorded at a high density and high speed by using optical techniques such as irradiation of laser beams, a method for producing such an optical information recording medium and a method for recording and reproducing optical information with such an optical information recording medium.
2. Description of the Prior Art
An optical magnetic recording medium or a phase-changeable recording medium is known as a medium on which information can be recorded in large capacity and reproduced and rewritten at a high speed. Such a transportable optical recording medium is expected to be more important in a highly information-oriented society. The improvements in the function of applications and in the quality of graphic information require larger capacity and higher-speed recording or reproducing of the medium.
These optical recording media utilize a difference in the optical characteristics of the recording material created by locally irradiating the recording material with laser beams. For example, for the optical magnetic recording medium, a difference in the angle of rotation on a plane of polarization of a reflected light, which is created by a difference in the magnetized state, is utilized for recording. Furthermore, for the phase-changeable recording medium, an amount of reflected light in the crystalline state different from that in the amorphous state when light with a specific wavelength is used is utilized for recording. The phase-changeable recording medium is advantageous because erasing recorded information and overwriting information can be simultaneously performed by adjusting the output power of the laser, so that it is possible to rewrite information signals at a high speed.
FIGS. 5 and 6
show exemplary structures of layers of conventional optical information recording media. A resin such as polycarbonate, polymethyl methacrylate (PMMA) or glass can be used for a substrate
101
. The substrate
101
may have a guide groove.
A recording layer
103
is formed of a material that has states having different optical characteristics and can change between the different states reversibly. In the case of a rewritable phase change type optical disk, a chalcogenide such as a material containing Te and Se as a main component can be used for the recording layer
103
.
Protecting layers
102
,
104
and
106
serve to protect the recording layer in such a manner that the recording layer material is prevented from being oxidized, evaporated or distorted. Furthermore, it is possible to adjust the absorption of the optical information recording medium or a difference in the reflectance between a recorded portion and a erased portion by adjusting the thickness of the protective layers. Thus, the protective layers also serve to adjust the optical characteristics of the medium. Moreover, a material for the protective layer is required to have good adhesiveness with a material forming the recording layer and the substrate, and good weather resistance so that the protective layer itself is not cracked.
Examples of the material for the protective layer include a dielectric such as a sulfide such as ZnS, an oxide such as SiO
2
, Ta
2
O
5
or Al
2
O
3
, a nitride such as Si
3
N
4
or AlN, a nitrogen oxide such as SiON or AlON, a carbide, a fluoride or the like, or suitable combinations thereof. Especially, ZnS—SiO
2
has been generally used, because the layer composed of the material has less stress and good adhesiveness to the recording layer.
As shown in
FIG. 5
, in general, the protecting layers
102
,
104
are formed on both sides of the recording layer
103
. It has been proposed to produce a layered structure composed of two protective layers
102
,
106
including different materials from the other, as shown in
FIG. 6
, so that the adhesiveness with the substrate and the characteristics in repetitive recording of information are improved.
A reflection layer
105
can be formed on the protecting layer
104
for the purpose of radiating heat and allowing the recording layer to absorb light effectively, but the reflection layer is not necessarily provided. The reflection layer is generally formed of a metal such as Au, Al, Cr or the like, or an alloy of these metals.
In general, an overcoating layer or a dummy substrate is located on the reflection layer
105
so that the optical recording information medium is not oxidized and dust or the like does not become attached to the medium, although those are not shown in
FIGS. 5 and 6
. The dummy substrate can be bonded with an ultraviolets-curing resin.
As a material for the recording layer, a Ge—Sb—Te-based material has been investigated extensively, because the material is excellent in weather resistance and the characteristics in repetitive recording of information.
For example, Japanese Laid-Open Patent Publication (Tokkai-Sho) No. 61-89889 discloses a material for recording represented by Ge
(1−x)
Sb
4x
Te
(1−5x)
(0<x<1). The material provides a substantial change of reflectance with a phase-change between an amorphous state and a crystalline state by irradiation of light beams. The material also can make the sensitivity to recording higher, because the material has a lower crystallization temperature to eliminate energy for crystallization. However, this investigation takes no account of a repetitive recording of information which involves a phase change between an amorphous state and a crystalline state.
Japanese Laid-Open Patent Publication (Tokkai-Sho) No. 62-53886 discloses a material for recording represented by (Sb
x
Te
(1−x)
)
y
Ge
(1−y)
(x=0.05-0.7, y=0.4-0.8), and an example in which the irradiation of laser beams to a recording layer composed of the material can change the transmittance of the layer. However, this investigation takes no account of reversibility of the change and a repetitive recording of information.
Japanese Laid-Open Patent Publication (Tokkai-Sho) No. 62-196181 discloses a rewritable medium including a Ge—Sb—Te-based material. A recording layer is composed of Ge
23
Sb
46
Te
31
or the like, and has a protecting layer of SiO
2
, AlN or the like on the recording layer. The reflectance of the recording layer can vary reversibly by changing the power level of a semiconductor laser beam having a wavelength of 830 nm. However, this investigation takes no account of a repetitive recording of information and a preferable composition of the recording layer for irradiation of laser beams having a short wavelength of 680 nm or less.
The difference in an optical constant of a recording layer composed of a Ge—Sb—Te-based material between an amorphous state and a crystalline state becomes narrower as the wavelength of the laser beams shortens for high-density recording. The narrower difference in optical characteristics such as reflectance makes the degree of signal change smaller, which restricts the density of recording.
Conventionally, a material having a composition ratio obtainable by adding some Sb to a stoichiometric composition ratio of Ge
2
Sb
2
Te
5
, or ones that are close to the composition ratio, has been used for a Ge—Sb—Te-based material. It is believed that excellent characteristics in repetitive recording can be obtained, only because such a composition ratio is used for the recording layer. On the other hand, a composition ratio in the near side to GeTe on the GeTe—Sb
2
Te
3
line can enlarge the difference in an optical constant between the two states. However, such a composition ratio is not suitable for a rewritable medium, because the characteristics in repetitive recording of information deteriorate. The composition ratio far from the stoichiometric ratio is generally believed to cause the deterioration in repetitive recording.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is the object of the present invention to provide an optical information recording medium having sufficie
Kawahara Katsumi
Uno Mayumi
Yamada Noboru
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