JP2572091B2 - Optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium for writing information by a structural change of a recording layer due to light or heat energy and optically reading the information by a laser beam.

(Prior art)

Conventionally, as the optical recording medium as described above,
As described in US Pat. No. 5,538,884, it is known to use glassy carbon as a recording layer. In the present invention, by polishing the surface of the glassy carbon obtained by carbonizing the thermosetting resin, a Raman spectrum of 1360 cm ^-1 that was not detected before polishing can be detected, and this is set to the initial state. It is assumed that. By irradiating a laser beam, a change in Raman spectrum is used for writing information. In general, a Raman spectrum is observed at 1580 cm ^-1 for carbon materials (of graphite structure).
The recorded information is read out by measuring the Raman spectrum intensity ratio to 1360 cm ^-1 which is reduced by laser light irradiation. Normally, a carbon material (other than diamond) has a graphite-like bond and exhibits an E ₂ g mode Raman spectrum at 1580 cm ⁻¹ . The Raman band of 1360 cm ^-1 is forbidden in graphite crystal, but when the domain of graphite crystal becomes minute, the forbidden is broken and 13
The observation of a Raman spectrum at 60 cm ^-1 has been reported in a paper and is well known. Therefore, when irradiating a laser beam to a Raman line of 1360 cm ^-1 which is strongly expressed by polishing a glassy carbon material with graphite structure
It is considered that the phenomenon that the Raman line at 1360 cm ^-1 is weakened is because the domain of the carbon material is enlarged by annealing with the laser beam. As described above, optical recording media for writing and reading information by changing the Raman intensity of the glassy carbon material have attracted attention because they are lightweight, chemically stable, and do not have the drawbacks of magneto-optical recording media.

However, a problem with the invention described in Japanese Patent Application Laid-Open No. Sho 62-53884 is that the glassy carbon material is polished to obtain an initial state. In fact, it is very difficult to damage the surface of the glassy carbon material by polishing and to mirror-finish it so that the same domain size always occurs.

〔Purpose〕

The present invention solves the above-mentioned conventional problems, eliminates the need for surface polishing, enables a large area, has high productivity, and uses a hard amorphous carbon thin film as a recording layer capable of recording with high hardness and high density. It is an object of the present invention to provide a conventional optical recording medium.

〔Constitution〕

A feature of the present invention resides in that the recording layer formed on the substrate is a hard amorphous carbon thin film formed by a plasma CVD method.

As described above, in the present invention, the above object has been achieved by utilizing the Raman spectrum of a hard amorphous carbon (hereinafter referred to as i-carbon) thin film mainly composed of carbon atoms and some hydrogen atoms formed by the plasma CVD method. Things. That is, i-carbon film is plasma CVD
It can be formed as a thin film on a substrate in the gas phase by the gas method, so that it is possible to increase the area and reduce the thickness, which is extremely advantageous in terms of productivity, etc. 4,000 or more), and there are almost no defects such as pinholes, and it is very excellent as a recording medium.

Such an i-carbon film has a thickness of 3000 to 9000 on a substrate.
The film is formed by Å. One example of deposition conditions in the i- carbon film, the gas flow rate CH ₄ 5SCCM, H ₂ 5SCCM, pressure 0.03 Torr, RF
The test is performed at a power of 100 W and a substrate temperature of room temperature. As the substrate, glass, inexpensive organic polymer resin, film or the like is used. As the organic polymer, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate,
Many examples include polymethyl methacrylate, polyvinyl chloride, polyacrylonitrile, polyethylene, and polystyrene.

FIG. 1A shows a Raman spectrum of the i-carbon film formed under the above conditions. That is, this is the initial state. FIG. 1 (b) and FIG. 1 (c) show the results of writing information with a laser beam or heat and measuring the Raman spectrum at that point. First
FIG. 1 (b) is a graph heated to 600 ° C. by writing, and FIG. 1 (c) is a Raman spectrum in a state heated to 800 ° C. In the initial state of i-carbon in FIG. 1 (a), there is a wide Raman band near 1500 cm ^-1 and 1365 cm ^-1.
Signal is small. On the other hand, as shown in (b) to (c), as heating is performed, spectra are generated at ₁₅₈₀ cm ^-1 and 1365 cm ^-1 , and the intensity ratio I ₁₃₆₅ / I ₁₅₈₀ tends to increase with temperature. It is in. This relationship is shown in FIG.

The physical meaning of these developments is that the i-carbon thin film locally has sp ³ bonds, but most of the amorphous structure mainly composed of sp ² bonds, This is a phase transition to a microcrystalline graphite film having a domain structure.

After recording the optical information in this way, 1580 cm ^-1
The intensity ratio of the Raman spectrum of ₁₃₆₅ cm ^-1 , that is, I ₁₃₆₅ /
Information can be read by measuring I ₁₅₈₀ . Since the measurement of the intensity ratio of the Raman spectrum is performed by irradiating a minute beam such as 4880 ° of an argon ion laser, it is possible to sufficiently detect a phase change in a minute region, which corresponds to high density recording.

〔effect〕

According to the present invention as described above, it is possible to obtain an optical recording medium which is easy to increase in area and thin, has high hardness and is chemically stable.

[Brief description of the drawings]

FIG. 1 is a Raman spectrum of the optical recording medium according to the present invention. Figure 2 is a relation diagram showing the temperature dependence of the Raman intensity ratio between 1365cm ^-1 and 1580 cm ^-1 in the case of writing to an optical recording medium according to the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuji Kimura 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (72) Inventor Hitoshi Kondo 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (56) References JP-A-62-35888 (JP, A)

Claims (1)

(57) [Claims] A recording layer formed on a substrate is formed by a plasma CVD method in an optical recording medium in which writing is performed by changing the structure of the recording layer by light or thermal energy and reading is performed optically by laser light. An optical recording medium comprising a hard amorphous carbon thin film.