Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
1999-12-06
2001-08-21
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064200, C428S064400, C428S913000, C430S270120, C430S945000, C369S283000, C369S288000
Reexamination Certificate
active
06277462
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P10-350536 filed Dec. 9, 1998 which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical recording medium in which information writing and/or readout is effected using the light, and a method for manufacture thereof. More particularly, it relates to a magneto-optical disc in which information writing and/or readout is effected using the light illuminated from an opposite side of a substrate, and a method for manufacture thereof.
2. Description of the Related Art
Recently, an optical recording medium in which a heat diffusion layer, a dielectric layer or an information recording layer are formed on a substrate and in which the information is written or read out by the light illuminated on the information recording layer, has come in popular use.
In such optical recording medium, researches are underway for raising the recording density in order to record as much information as possible.
In keeping up with the tendency towards the higher recording density for the optical recording medium, attempts have been made to reduce the diameter of the light spot illuminated on the information recording layer for an optical head configured for writing or reading out signals for the optical recording medium.
In particular, there have recently been conducted researches for constituting a flying optical head by having an objective lens mounted on a slider by application of the technique of the flying magnetic head as used in a hard disc device etc. This flying optical head is flown for facing the layered films on the substrate of the optical recording medium to write or read out information signals from the layered film side of the optical recording medium.
By having the flying optical head flown for facing the layered films on the substrate of the optical recording medium to write or read out information signals, it becomes possible to reduce the distance between the objective lens and the information recording layer of the optical recording medium appreciably in comparison with that in case the light from the optical head is illuminated on the information recording layer via the substrate. This renders it possible to increase the numerical aperture (NA) of the objective lens to reduce the size of the light spot formed on the information recording layer.
If the flying type optical head is flown for facing the layered films on the substrate of the optical recording medium to write or read out the information as described above, the light from the optical head is illuminated from the layered film side. Thus, the layering sequence of the layered films on the substrate in this type of the optical recording medium is reversed from that in the optical recording medium of the type in which the light is illuminated via the substrate.
Meanwhile, if, in the optical recording medium in which the layered films on the substrate are formed in the reverse sequence from that in the optical recording medium irradiated with light via the substrate, the respective layers of the layered films are formed under the conditions similar to those of an optical recording medium of the type illuminated by the light via the substrate, the optical recording medium produced suffers from excessive noise and is lowered in the C/N ratio such that optimum recording and/or reproducing characteristics cannot be achieved.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical recording medium of the type in which a heat diffusion layer, a dielectric layer and an information recording layer are formed on a substrate and the information is written and/or read out by the light illuminated from the layered film side, wherein optimum recording and/or reproducing characteristics can be achieved.
The present inventors have conducted perseverant researches towards solving the above problem, and found that surface properties of a heat diffusion layer constituting a layered film structure appreciably influence recording and/or reproducing characteristics of the optical recording medium, and that, by improving surface properties of the heat diffusion layer, surface properties of the dielectric layer or the information recording layer are improved to achieve optimum recording and/or reproducing characteristics.
The present invention has been brought to completion on the basis of the above information. In one aspect, the present invention provides an optical recording medium in which at least a heat diffusion layer, a first dielectric layer, an information recording layer and a second dielectric layer are formed in this order on a substrate and signals are recorded and/or reproduced by the light illuminated from the side of the second dielectric layer, wherein an under layer for optimizing surface properties of the heat diffusion layer is formed between the substrate and the heat diffusion layer.
In this optical recording medium, the surface properties of the heat diffusion layer are optimized by the under layer provided between the substrate and the heat diffusion layer. In the present optical recording medium, since the surface properties of the heat diffusion layer are optimized, those of the first dielectric layer, information recording layer and the second dielectric layer, formed on the heat diffusion layer, are also optimized. This reduces the noise to realize a high C/N and optimum recording and/or reproducing characteristics.
In another aspect, the present invention provides a method for preparing an optical recording medium in which at least a heat diffusion layer, a first dielectric layer, an information recording layer and a second dielectric layer are formed in this order on a substrate and signals are recorded and/or reproduced by the light illuminated from the side of the second dielectric layer, wherein the method includes forming an under layer for optimizing surface properties of the heat diffusion layer, and subsequently forming the heat diffusion layer on the under layer.
In this manufacturing method for the optical recording medium, in which the heat diffusion layer is formed after forming the under layer on a substrate, the heat diffusion layer having optimum surface properties is formed to optimize the surface properties of the first dielectric layer, information recording layer and the second dielectric layer formed on the heat diffusion layer. Thus, with the manufacturing method of the optical recording medium, an optical recording medium may be provided which has a reduced noise and a high C/N to realize optimum recording and/or reproducing characteristics.
In the optical recording medium according to the present invention, in which an under layer is formed between the substrate and the heat diffusion layer, surface properties of the heat diffusion layer may be optimized to optimize the surface properties of the first dielectric layer, information recording layer and the second dielectric layer formed on the heat diffusion layer. Thus, with the present optical recording medium, optimum recording and/or reproducing characteristics are achieved with the reduced noise and the high C/N.
In the manufacturing method for the optical recording medium according to the present invention, in which the under layer is formed on a substrate and subsequently the heat diffusion layer is formed, it is possible to optimize surface properties of the heat diffusion layer and hence the first dielectric layer, information recording layer and the second dielectric layer formed on the heat diffusion layer. Thus, with the manufacturing method for the optical recording medium, it is possible to produce an optical recording medium having reduced noise and a high C/N to realize optimum recording and/or reproducing characteristics.
REFERENCES:
patent: 5639563 (1997-06-01), Ohnuki
patent: 5965286 (1999-10-01), Ohnuki
Miyata Kazutomo
Watanabe Makoto
Evans Elizabeth
Sonnenschein Nath & Rosenthal
Sony Corporation
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