Information recording medium

Details Information recording medium Information recording medium

2001-04-11

2002-08-20

Mulvaney, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064500, C428S064600, C430S270130

Reexamination Certificate

active

06436504

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an information recording medium used for an optical disk.
BACKGROUND ART
Various principles are known for recording information in a thin film (recording film) by radiating a laser beam on it. Among them, a method utilizing the change of the atomic arrangement by the radiation of the laser beam such as the phase transition (also called the phase change) of the film material or the photo darkening is not substantially accompanied by the deformation of the thin film, and therefore has the advantage that an information recording medium of a two-side disk structure can be obtained by attaching two disk members directly to each other.
Generally, these information recording media are configured of a substrate, and a protective layer, a recording film of GeSbTe group, etc., a protective layer and a reflective layer formed on the substrate, and the reflectance is higher in crystal state than in amorphous state. Therefore, the absorption of a recording film is larger for amorphus. The recording mark portion in amorphous state is liable to increase in temperature more easily than the crystal. In the case where an overwrite operation is performed in this state, therefore, a newly recorded mark is increased excessively, thereby causing the reproduction signal to be distorted.
In order to prevent this inconvenience, an effort has been made to increase the absorption coefficient of the recording film in crystal state as compared with that of the recording film in amorphous state. For example, reference 1 “Yamada and three others, Shingaku Giho MR92-71, CPM92-148, December 1992, p.37” describes a structure formed with an Au reflective layer as thin as 10 nm to reverse the absorption coefficient.
Also, reference 2 “Okada and six others, Shingaku Giho MR93-53, CPM93-105, December 1993, p. 1” describes a structure in which Si of 65 nm is used for the reflective layer thereby to reverse the absorption coefficient.
In this specification, the term “phase change” is defined to include not only the phase change between crystal and amorphus but also between melting (change to liquid phase) and recrystallization and between crystal states.
DISCLOSURE OF INVENTION
In all the conventional information recording media used as a high-density rewritable information recording media of phase transition type using a mark edge recording, the erase characteristic is improved by reversing the absorption coefficient (the absorption coefficient of amorphus is lower than that of crystal). These media use a material with a thin reflective layer or a material of a reflective layer through which light is transmitted or has a structure allowing light to transmit therethrough. This method poses the problem that each absorption coefficient is smaller than that of the normal disk with the absorption coefficient not reversed, resulting in a small recording sensitivity. The laser used for recording having a wavelength shorter than about 680 nm is still low in output, and if the linear speed is increased for increasing the transfer rate, the recording sensitivity tends to deteriorate. Therefore a medium of high recording sensitivity is required.
Further, the use of a thin material of a low heat conductivity for the reflective layer poses the problem that heat generated at the time of recording is not easily diffused often causing an increased jitter after a multiplicity of overwrite cycles.
Accordingly, an object of the present invention is to solve these problems and to provide an information recording medium which has a superior recording/reproduction characteristic without increasing the jitter as compared with the prior art even after the overwrite cycle for high-density recording and reproduction.
Means for solving the problems will be described below.
(1) There is provided an information recording medium comprising an information recording thin film as a recording layer formed on a substrate for recording and/or reproducing information by the change in atomic arrangement caused by the radiation of light, and at least one protective layer, wherein the protective layer and the recording layer are formed in that order from the light incidence side, followed by being formed with at least one absorption control layer.
(2) There is provided an information recording medium as described in (1), characterized in that the thickness of the absorption control layer is in the range of not less than 10 nm but not more than 50 nm. The thickness of not less than 10 nm but not more than 40 nm is more preferable.
(3) There is provided an information recording medium as described in (1), wherein at least 95% of the total number of atoms of the absorption control layer is composed of a mixture or a compound of a dielectric material and a metal element.
(4) There is provided an information recording medium as described in (1), wherein the absorption control layer is made of a material having n (refractive index) of not less than 1.2 but not more than 6, and k (extinction coefficient) not less than 0.5 but not more than 3.3. If n is not less than 1.8 but not more than 5.5, and k is not less than 0.8 but not more than 3, it is more preferable.
(5) There is provided an information recording medium as described in (1), wherein the absorption control layer is made of a material having a melting point of not less than 600° C.
(6) There is provided an information recording medium as described in (1), characterized in that in the case where information is recorded on the recording film, the reflectance in amorphous state is lower than that in crystal state, the reflectance in amorphous state is lower than the reflectance in crystal state, and the mark size with the shortest mark recorded on a material in amorphous state is equal to or smaller than the mark size with the shortest mark recorded on a material in crystal state under the same conditions.
(7) There is provided an information recording medium as described in (1), wherein at least a heat diffusion layer is formed between the substrate and the protective layer.
(8) There is provided an information recording medium comprising an information recording thin film as a recording layer formed on a substrate for recording and/or reproducing information by the change in atomic arrangement caused by the radiation of light, at least a protective layer, at least a heat diffusion layer and at least a heat diffusion layer, characterized in that the heat diffusion layer, the protective layer and the recording layer are formed in that order from the light incidence side, followed by being formed with at least one reflective layer.
(9) There is provided an information recording medium as described in any one of (7) and (8), characterized in that at least 90% of the total number of atoms of the heat diffusion layer is composed of Al—O.
(10) There is provided an information recording medium as described in any one of (7) and (8), characterized in that the heat diffusion layer has a layer in which at least 90% of the total number of atoms has a composition similar to any one of (SiO
2
), (Al
2
O
3
), (Ta
2
O
5
), (Al
2
O
3
)—(SiO
2
), (Ta
2
O
5
)—(SiO
2
), (Al
2
O
3
)—(Ta
2
O
5
) and (Al
2
O
3
)—(SiO
2
)—(Ta
2
O
5
) or a mixture composition thereof.
(11) There is provided an information recording medium as described in any one of (7) to (8), wherein the heat diffusion layer has a layer in which at least 90% of the total number of atoms has a composition similar to any one of Be—O, B—N, Si—C and Mg—O or a mixture composition thereof.
(12) There is provided an information recording medium as described in (1), characterized by having a structure wherein a reflection layer composed of at least one layer of a Cu alloy, an Al alloy and an Au alloy is formed on the absorption control layer.
(13) There is provided an information recording medium as described in (1) or (8), characterized in that at least one surface protect layer is formed in the boundary of the recording film.
(14) There is provided an information recording medium as described in (1) or (8), character

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