JPH0477968B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to optical reflective or transmissive video discs, digital audio discs, etc., and particularly to an information recording medium suitable for writing arbitrary information onto the disc. Regarding.

[Background of the invention]

2. Description of the Related Art As an information recording medium on which information can be written and read by irradiation with laser light, a method has been proposed in which information is recorded as a change in optical characteristics, such as reflectance, transmittance, refractive index, etc. Among them, information recording media in which the recording film is composed of two layers: a light absorption layer that has good light absorption properties for laser light and has the effect of converting light into heat, and a phase change layer whose optical properties change when heated. has high sensitivity and enables high-density recording. As such a recording film,
For example, selenium Se or Se as a phase change layer.
Bismuth Bi, tellurium Te, or a compound thereof is used as the light absorption layer, each having a thickness of 50 to 1500 Å. When putting an information recording medium having this recording film into practical use, it is essential to protect the thin recording film as described above.

Conventionally, as shown in FIG. 1, a phase change layer 1 is formed on a transparent substrate 3 made of glass or acrylic resin, a light absorption layer 2 is formed on the phase change layer 1, and a protective layer made of SiO ₂ , Al ₂ O ₃ or resin is formed on the phase change layer 1. 4 is formed and information is recorded by irradiating laser light from the substrate side, thereby increasing the stability and reliability of the information recording film. but,
By forming the protective layer 4, the recording sensitivity is reduced to less than half, and writing information requires more than twice the laser power as in the case without the protective layer. There is a limit to the output of a semiconductor laser, which is normally used as a laser light source, and the recording sensitivity decreases, making it impossible to write information. As described above, the conventional technology has the disadvantage that it is not possible to form an effective protective layer without significantly reducing recording sensitivity.

[Object of the Invention] An object of the present invention is to improve the above-mentioned drawbacks of the prior art and to provide an information recording medium with high recording sensitivity and good stability.

[Summary of the invention]

The present invention focuses on the fact that in conventional information recording films, heat from the light absorption layer is used only on the side in contact with the phase change layer, and the heat escaping from the opposite side in contact with the protective film is effectively used. , by sequentially forming a first phase change layer, a light absorption layer, and a second phase change layer on a substrate, and forming a protective layer thereon, the heat utilization rate from the light absorption layer is doubled; It is characterized by improved recording sensitivity.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

FIG. 2 shows the structure of the recording film in the present invention.
Write light, for example, at a wavelength of 830 nm, is applied onto a light-transmissive glass substrate or a resin substrate 3 made of acrylic resin.
A first phase change layer 1 is provided, which has a small optical absorption rate with respect to the semiconductor laser light and whose optical properties such as reflectance, transmittance, and refractive index change by 10% or more mainly due to heat. A light absorption layer 2 having a high light absorption rate for the laser beam and having the effect of converting the light into heat by absorption is provided on top of the light absorption layer 2, and a second phase change layer similar to the first layer is provided on top of the light absorption layer 2. 5,
The recording film has a three-layer structure. This recording film is made of SiO ₂ ,
It is protected by a protective layer 4 made of Al ₂ O ₃ or resin. The first and second phase change layers include materials whose optical properties change upon heating;
For example, Se, or Sb ₂ Se ₃ , TeSe ₂ , TnSe,
Se compounds such as CdSe or Se alloys are used as the light absorption layer, and undesirable physical properties such as melting or softening at temperatures (e.g. 200°C) that can change the optical properties of the first and second phase change layers are required. Bi, Te, or their alloys, etc., which do not undergo any chemical changes are used.

To write information on such an information recording medium, semiconductor laser light (wavelength: 830 nm) with an output of about 10 mW is scanned relatively from the transparent substrate 3 side according to the recording pattern. At this time, most of the laser light passes through the first phase change layer and reaches the light absorption layer 2, but since the absorption rate here is high, the light is absorbed and converted into heat, and the laser light irradiation area The temperature of the light absorption layer rises to about 200° C., and the first and second phase change layers in contact with this portion are locally heated. The heated first and second phase change layers change their optical properties, such as their reflectance, so that a difference in reflectance occurs between the portions that are irradiated with the laser beam and the portions that are not irradiated with the laser beam, resulting in optical information recording. It will be done. To read this, like writing, a semiconductor laser is used. In this case, the reading power is sufficiently lower than the writing power, for example, 1 mW, and reading with this low power prevents rewriting.

In the present invention, the film thicknesses of the first and second phase change layers and absorption layer described above are important. That is, in order to efficiently read out optical property changes in the first and second phase change layers using the thin film interference effect, it is necessary to set the film thickness of each layer to an appropriate value. When Sb ₂ Se ₃ is used for the phase change layer and Bi is used for the light absorption layer, the thickness of each layer and the reflectance 10 before information writing and the reflectance 20 after writing are shown in FIGS. 3 to 5. Figure 3 shows a Bi layer of 200 Å and a second Sb ₂ Se ₃ layer.
400 Å and a change in reflectance with respect to the thickness of the first Sb ₂ Se ₃ layer when a resin layer with a thickness of 30 μm is provided as a protective layer. The reflectance changes with the film thickness of the first Sb ₂ Se ₃ layer due to the interference effect of the film, and when the film thickness is around 500 Å, the reflectance before writing is 5% and after writing it is 30%. If this film thickness is selected, extremely good readout of recorded information becomes possible. Also, the first
and the thickness of the second Sb ₂ Se ₃ layer is 500 Å, respectively.
Figure 4 shows the change in reflectance with respect to the change in the thickness of the Bi layer when the thickness was set to 400 Å. When the Bi layer has a thickness of 400 Å or more, light absorption is large, so the Bi layer does not have an interference effect as a film, and the reflectance does not depend on the film thickness. In the present invention, in order to utilize the interference effect from the second _three Sb ₂ Se layers, the thickness of the Bi layer is
The thickness is selected to be 400 Å or less, for example 200 to 300 Å. Furthermore, the thickness of the first Sb ₂ Se ₃ layer and Bi layer is
FIG. 5 shows the change in reflectance with respect to the thickness change of the second Sb ₂ Se ₃ layer when the thickness is 500 Å and 200 Å. Second
When the thickness of the Sb ₂ Se ₃ layer is 100 to 800 Å, the reflectance 20 after writing is more than twice the reflectance 10 before writing, and good information can be written and read. As described above, the first
An information recording medium in which a _{three-layer recording film is formed with three Sb 2 Se} layers of 400 to 700 Å, a Bi layer of 100 to 400 Å, and a second Sb ₂ Se _three layer of 100 to 800 Å, and this is protected by a resin layer, has good performance. It can be seen that a change in reflectance can be obtained, making it suitable for writing with laser light.

On the other hand, FIG. 6 shows the relationship between the reflectance ratio (after writing/before writing) with respect to the laser power of the above three-layer recording film 40 and the conventional two-layer recording film 30. Figure 6 shows the reflectance ratio to the laser power when the above recording medium was made into a disk shape, rotated at 1800 rpm, and a signal of a constant level was written at a radius of 130 mm, and the thickness of each layer was first
Sb ₂ Se ₃ 500 Å, Bi 200 Å, and a second Sb ₂ Se ₃ 400
It is Å. As shown in FIG. 6, 3 according to the present invention
It can be seen that the layered recording film can obtain a constant reflectance ratio with a smaller laser power than the conventional two-layered recording film, that is, has a high recording sensitivity.

As described above, the three-layer recording film according to the present invention has high recording sensitivity during writing even with the formation of a protective film, and a large reflectance ratio can be obtained, so it can be used for optical video discs, digital audio discs, etc. It has a great effect on improving performance and reliability.

In the above embodiments, a reflective type information recording medium has been described, but it is easy to understand that the configuration of the present invention can be used as is for a transmissive type.

Furthermore, as an effect of the present invention, in addition to the above-mentioned improvement in recording sensitivity, in a reflective type double-sided laminated disk as shown in FIG. 7, it has a great effect in reducing noise due to backside reflection. That is, in the conventional two-layer recording film shown in FIG. 1, for example, Sb ₂ Se ₃ as the phase change layer,
When Bi is used as the light absorption layer, the thickness of the Bi layer is
Even at a thickness of about 400 Å, the transmittance of the recording film is more than 10%, and the surface reflectance of the Bi layer is high (50 to 60 Å).
%), when reading information by irradiating laser light, a portion of the read light was reflected back by the Bi layer of the reflective disk, becoming noise and degrading the performance of the disk. However, in the three-layer recording film according to the present invention, the optical absorption layer is almost optically symmetrical, and as can be inferred from Fig. 3, the reflectance on the second Sb ₂ Se ₃ side is kept below 10%. It's easy to do. Therefore, it is possible to significantly reduce the return light from the opposite disk, which has a great effect on noise reduction.

In the above embodiments, the protective layer and disk adhesive layer were used as both, but it is clear that the present invention can be applied even if an independent protective layer and adhesive layer are used as long as each layer is transparent.

〔Effect of the invention〕

According to the present invention, it is possible to significantly improve the sensitivity of an information recording medium on which a protective film is formed, which has a great effect on improving the performance and reliability of the information recording medium.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a cross section of a conventional information recording medium, Fig. 2 is a schematic diagram showing a cross section of an information recording medium according to the present invention, and Fig. 3 is a diagram showing the film thickness and reflection of the first Sb ₂ Se ₃ layer. Figure 4 is a diagram showing the relationship between Bi layer thickness _and reflectance, Figure 5 is a diagram showing the relationship between Bi layer thickness and reflectance, and Figure 5 is a diagram showing the relationship between Bi layer thickness and reflectance _.
FIG. 6 is a diagram showing the relationship between layer thickness and reflectance ratio, FIG. 6 is a diagram showing the relationship between laser power and reflectance ratio, and FIG. 7 is a schematic diagram showing a cross section of a double-sided laminated disk according to the present invention. DESCRIPTION OF SYMBOLS 1...First phase change layer, 2...Light absorption layer, 3...
...Transparent substrate, 4...Protective layer, 5...Second phase change layer

Claims (1)

[Claims] 1. In an information recording medium formed by forming an information recording film and its protective film on a substrate, the information recording film consists of a first, second, and third layer, and the first and third layers have optical properties by heating. Se or Se where changes
An information recording medium characterized in that the second layer is made of an alloy material, and the second layer is made of Bi, Te, or an alloy material thereof, which has light absorption property for writing light.