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
1999-04-05
2001-04-03
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S270110, C430S945000, C428S064200, C428S064400
Reexamination Certificate
active
06210860
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a recording medium which comprises a first substance and a second substance at least, and whose optical characteristics are varied to record information by applying an external energy for reaction to at least one of the first and second substances.
2. Description of the Related Art
As a conventional optical recording medium, for example, Japanese Unexamined Patent Publication (KOKAI) No. 62-226,442 discloses an optical recording medium in which a mixture film (a single-layered film) is used as a recording film. The mixture film is composed of a low-melting point metal (e.g., In or Zn) and sulfide (e.g., GeS
x
). Japanese Unexamined Patent Publication (KOKAI) No. 2-152,029 discloses another optical recording medium in which a layered film is used as a recording film. The layered film is composed of a metallic layer (i.e., a first layer), which includes Al, Cu or Ag, and the other layer (i.e., a second layer), which includes S, Se or mixtures thereof.
These recording films are formed by a vapor deposition method or a sputtering method. Since the recording films exhibit reactivity, the recording films are modified chemically and/or physically by irradiating with a recording laser beam (or by applying an external energy). Accordingly, the optical characteristics of the recording films, such as the reflectance, are varied, thereby recording information.
Japanese Unexamined Patent Publication (KOKAI) No. 62-226,442 discloses to form the mixture film of the low-melting point metal (e.g., In, etc.) and the sulfide (e.g., GeS) by a co-vapor deposition method, or the like, in the preferred embodiments. However, according to the investigations carried out by the inventors of the present invention, the reaction proceeds considerably between the metal and the sulfide during the formation of the mixture film. As a result, there is a possibility that the entire reflectance of the optical recording medium decreases significantly, and this causes problems in applying the optical recording medium to practical uses.
Japanese Unexamined Patent Publication (KOKAI) No. 2-152,029 discloses the laminated construction in which the metal of high reactivity (e.g., Ag, etc.) are laminated on S. However, according to the investigations carried out by the inventors of the present invention, it can be readily judged that such a system suffers from severe chronological degradations, for instance, the layers react with each other even when information is not being recorded. Hence, it is believed that, the optical recording medium suffers from problems in practical uses. Moreover, in the preferred embodiments, the values of C/N (Carrier to Noise ratio, i.e., output level ratio of carrier to noise) are listed, but do not imply the favorable characteristics.
Thus, in the conventional optical recording media, unnecessary reactions, such as the reactions in the formation of the films and the chronological degradations, are allowed, because they use reactive recording films. Hence, the conventional optical recording media have problems in that the recording characteristics, such as the reflectance, degrade in the formation of the films and during the ordinary service.
SUMMARY OF THE INVENTION
The present invention has been developed in view of the aforementioned problems. It is therefore an object of the present invention to suppress the reactions degrading the recording characteristics of a recording medium which comprises a first substance and a second substance at least, and whose optical characteristics are varied to record information by applying an external energy to at least one of the first and second substances to react the first and second substances.
The inventors of the present invention investigated into recording films in which information was recorded by irradiating with a recording laser beam. The inventors considered that it is easier to control the reactions in laminated constructions than in single-layered films. In the laminated constructions, the laminated layers react with each other by irradiating with a laser beam, and vary the optical characteristics to record information. Based on the idea, the inventors diligently studied the laminated constructions. Then, the inventors thought of providing a threshold level at which the reaction occurs between the mutual layers, and which differs between the case where the recording laser beam is irradiated and the case where the recording laser beam is not irradiated (including during a film making process). Thus, the inventors completed a first aspect of the present invention.
The first aspect of the present invention is a recording medium which comprises a first substance and a second substance, wherein an external energy is applied to at least one of the first and second substances to react them in order to change the optical characteristics of the substances for recording information, the recording medium comprising:
a first layer composed of a first substance including at least one of S and Se,
a second layer composed of a second substance including a metal, and
a barrier layer being disposed between the first and second layers, which allows the reaction between the first and second layers when laser beam for recording is irradiated as an external energy, and suppresses the reaction between the first and second layers when laser beam for recording is not irradiated.
In the first aspect of the present invention, when the laser beam for recording is irradiated, namely when information is recorded, the first layer and/or the second layer go over (pass through) the barrier layer and/or destroy (break through) the barrier layer at portions which are irradiated with the laser beam. The first layer and the second layer undergo a chemical reaction, thereby forming reaction products (e.g., sulfide, selenide or mixtures thereof). Accordingly, at these portions, the optical characteristics (e.g., reflectance, etc.) are varied so that information can be recorded. On the other hand, when the laser beam for recording is not irradiated (i.e., when the films are formed or when the present recording medium is put in the ordinary service), the interposing barrier layer suppresses the reaction between the first layer and the second layer. Consequently, the reaction of a recording film itself is suppressed. Hence, it is possible to inhibit the recording characteristics of the present recording medium from degrading.
According to the investigations carried out by the inventors of the present invention, the following were found to be appropriate for the first layer, the second layer and the barrier layer.
The first layer can preferably be composed of Ge and S. Specifically, the first layer can preferably be composed of at least one member selected from the group consisting of GeS
x
(0<x≦2), a Ge—Zn—S compound and a Ge—S—O compound. In the GeS
x
, the value “x” can further preferably fall in the range of more than 1 to 2 or less (i.e., 1<x≦2) because the GeS
x
exhibits enhanced transparency in the visible-ray region and because a recording laser power can be decreased.
The second layer can preferably be composed of at least one member selected from the group consisting of Sn, In, Sb, Bi, Pb, Cr, Mn, Fe, Ni, Cu, Zn and Ag. Specifically, the second layer can preferably be composed of at least one member selected from the group consisting of the simple substance of In, the simple substance of Cr, an In—Sn alloy and an Au—Cu alloy.
The barrier layer can preferably be composed of at least one member selected from the group consisting of a metal, sulfide, nitride, boride, carbon (C), carbide, oxide and phosphide. Specifically, the barrier layer can preferably be composed of at least one member selected from the group consisting the simple substance of C, ZnS, the simple substance of Si and SiO
2
. Moreover, depending on the material qualities, etc., the thickness of the barrier layer can preferably be 2 nm or more, further preferably fall in the range of from 2 to 5 nm.
The in
Fukano Tatsuo
Kato Naohiko
Motohiro Tomoyoshi
Takeda Yasuhiko
Takeichi Akihiro
Kabushiki Kaisha Toyota Chuo Kenkyusho
McPherson John A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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