JPH06103545B2 - Information recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel information recording medium. More specifically, the present invention relates to a medium for recording information by irradiating a recording layer provided on a substrate with active light such as laser light and recording information by utilizing the change in reflectance of the irradiated portion. The present invention relates to an information recording medium having excellent properties.

2. Description of the Related Art Hitherto, as recordable information recording media, a recording medium is provided on a substrate and a laser beam is irradiated to form holes corresponding to information. There is known a system in which characteristics are changed and a change in reflectance caused by the change in optical characteristics is used.

The latter method utilizing changes in optical characteristics does not require the process of melting, dispersing or evaporating the recording layer, as compared with the method of forming holes, and therefore the shape of the recording pit can be controlled easily. It has the advantage of

By the way, in this type of information recording medium, in order to improve the contrast relating to the reflectance between the portion to be recorded by the laser beam and the unrecorded portion, a reflective layer is laminated on the recording layer to form a two-layer structure. Is often done.

However, in the information recording medium in which the reflective layer is laminated on the recording layer, the element contained in the recording layer gradually moves into the reflective layer under high temperature and high humidity conditions, and the reflectance and sensitivity of the recording medium are reduced. There was a practical problem that various characteristics were adversely affected.

In a laminated structure having a recording layer composed of a single element or multiple elements and a reflective layer, element migration is likely to occur due to diffusion due to heat or electrochemical action due to humidity. If left in the atmosphere for a long time,
It was unavoidable that the composition of the recording layer and the reflective layer changed immediately after the recording medium was produced, and had a great influence on various characteristics such as reflectance.

Problems to be Solved by the Invention Under the circumstances, the object of the present invention is at least 1
In an information recording medium having a recording layer and a reflective layer composed of different elements, it is an object to provide an information recording medium excellent in long-term stability by suppressing migration of the element from the recording layer to the reflective layer. .

Means for Solving the Problems The inventors of the present invention have found that the cause of migration of the elements constituting the recording layer to the reflective layer is due to thermal diffusion or difference in electronegativity based on the concentration difference between the recording layer and the reflective layer. As a result of intensive studies, it was easy for the element constituting the recording layer to move to the surface opposite to the surface in contact with the recording layer, and electronegative. By stacking thin film layers containing elements with a low degree of influence, it is possible to suppress the transfer of constituent elements of the recording layer to the reflective layer, and to maintain the composition of the recording layer even when left under high temperature and high humidity conditions for a long time. It can be kept constant, and the deterioration of the reflective layer can be significantly suppressed, and for that purpose, the recording layer should be a layer containing at least Ge and Te, and the surface of the reflective layer opposite to the surface in contact with the recording layer. See that it is sufficient to provide a thin film layer containing Ge on the side surface. The present invention has been completed based on this finding.

That is, the present invention provides a recording layer containing at least Ge and Te, and an information recording medium having a reflective layer, a thin film layer containing Ge is provided adjacent to the reflective layer and on the side opposite to the recording layer. The present invention provides an information recording medium characterized by:

The recording layer in the recording medium of the present invention is composed of a system containing at least Ge and Te, which has a relatively small electronegativity and is easy to move. These are not limited to holes, phase transformations, magneto-optical methods, information recording methods, and the like.

Further, the film thickness of the recording layer varies depending on the kind of the material of the reflective layer, but is usually preferably in the range of 200 to 1000Å.

The material used for the reflective layer is not particularly limited, but G
e, Al, Ti, Cr, Co, Ni, Se, Zr, Ag, In, Sn, Sb, Te, Pt, Au, Pb, Bi
Metals or alloys thereof are preferred, especially Ge, Al, S
b, Bi and Bi ₂ Te ₃ are preferred. The thickness of this reflective layer is 100
It is preferably Å or more, and particularly preferably from 100 to 1000 Å from the viewpoint of sensitivity.

The thin film layer in the recording medium of the present invention contains a small electronegativity Ge as a constituent element component of the recording layer,
It is provided adjacent to the reflective layer and on the side opposite to the recording layer. The film thickness is preferably 500 Å or less, but a range of 10 to 100 Å is particularly suitable in order to prevent heat dissipation during information recording.

Next, the structure of the information recording medium of the present invention will be described with reference to the accompanying drawings. 1 and 2 (A), (B), (C)
FIG. 3 is a schematic cross-sectional view showing different examples of the structures of the recording medium of the present invention. When recording and reproducing information through a substrate, as shown in FIG. The basic structure is a structure in which 2 and the reflective layer 3 are sequentially stacked, and the thin film layer 4 according to the present invention is further stacked on the reflective layer 3.

Further, as shown in FIG. 2, a protective layer 5 made of a metal oxide or a metal nitride is provided between the substrate 1 and the recording layer 2 [FIG. 2 (A)], or the protective layer 5 is provided. By providing it on the thin film layer 4 according to the present invention [FIG. 2 (B)], or by providing the protective layer 5 both on the substrate 1 and on the thin film layer 4 [FIG. )], The long-term stability of the information recording medium can be further improved.

Examples of the metal oxide or nitride used for the protective layer 5 include Al, Cr, Si, Ge, Zr, Ti, V, Hf, Ce, Sn, La, Sm, Y, Sb, Ta, Pb,
Preferred are oxides or nitrides of elements selected from Bi, Se, Te and the like. By providing the protective layer made of these metal oxides or metal nitrides, invasion of water or oxygen that permeates the recording layer or the reflective layer from the air or the substrate is prevented, and the protective layer of the recording layer or the reflective layer is prevented. Deterioration is greatly suppressed. Among the metal oxides, oxides of Si are preferable, especially Si
Low oxides as indicated by Ox (0 <x ≦ 2) are preferred. On the other hand, among metal nitrides, nitrides of Si, Al, Ti and Zr are suitable.

When recording and reproducing information from the recording layer side opposite to the substrate, the order of the recording layer, the reflection layer and the thin film layer according to the present invention shown in FIGS. 1 and 2 is reversed.

As the substrate in the present invention, glass, a substrate provided with a photocurable resin on glass, a plastic substrate such as polycarbonate, acrylic resin, epoxy resin or polystyrene, or a metal plate such as Al alloy is used.

When the recording medium of the present invention is actually used as an information recording medium, two identical discs having a recording material provided on a substrate are placed with a spacer in between with the surfaces provided with the recording material facing each other. The so-called air-sandwich structure or two identical discs that are bonded and integrated with each other are bonded and integrated on the entire surface without a spacer, with the surfaces provided with the recording materials facing each other. A so-called whole-surface adhesive structure, or a structure different from these, such as a structure in which a recording material is provided on a film-like sheet and the sheet is rolled, may be adopted.

EFFECTS OF THE INVENTION The information recording medium of the present invention has a structure in which a thin film layer containing an element that constitutes the recording layer and has a low electronegativity is provided adjacent to the reflective layer, and therefore, at a high temperature. The composition of the recording layer is maintained constant even when left for a long time under high humidity conditions, and the deterioration of the reflective layer is significantly suppressed, resulting in excellent long-term stability and reliability.

EXAMPLES Next, the present invention will be described in more detail with reference to examples.

Example 1 GeTe (Ge: Te atomic ratio ≈ 1: 1) was formed as a recording layer on a polymethylmethacrylate (hereinafter abbreviated as PMMA) substrate by 400 V by vacuum deposition, and then Sb was provided by 500 L as a reflective layer. A sample was prepared by stacking Ge50Å and 100Å on this Sb layer.

A semiconductor laser beam having a wavelength of 8300 Å was used to measure the reflectance of the sample just after the production through the substrate,
After leaving it in an atmosphere of 90% RH (relative humidity) for a long time,
The reflectance was measured. The results are shown in Table 1.

For samples left at 60 ° C and 90% RH for 1000 hours, SI
As a result of investigating the composition in the film thickness direction using MS (Secondary Ion Mass Spectroscopy), in the sample in which the Ge layer was not provided on the Sb reflective layer, Ge moved into the Sb reflective layer and the GeTe layer
It was confirmed that the concentration of Ge decreased. However, when Ge was provided on the Sb reflective layer, the composition of the GeTe layer was almost constant.

In addition, the sample left at 60 ° C and 90% RH for 1000 hours was ESCA
As a result of investigating the oxidization rate of the Sb reflective layer by (Electron Spectroscopy for Chemical Analysis), Ge on the Sb reflective layer
Oxidation proceeded to a depth of about 250 Å in the sample without the layer, whereas it was about 100 in the sample with the Ge layer.
Å and deterioration of the reflective layer was suppressed.

As can be seen from Table 1, when the Ge layer is not provided on the Sb reflective layer, the reflectance changes greatly. This is because the oxidation of the Sb reflective layer progressed in addition to the change in the optical characteristics of the GeTe layer,
This is because the metal Sb layer is substantially thin.

In addition, the reduction of the Ge content in the GeTe layer not only affects the reflectance but also causes a serious problem in sensitivity during information recording because it essentially changes the phase transformation characteristics.

On the other hand, when a Ge thin film is provided on the Sb reflective layer, the change in reflectance is suppressed as shown in Table 1, and
The composition of the GeTe layer is also kept almost constant.

Example 2 Similar to Example 1, Sb-Te was used as a recording layer on a PMMA substrate.
-Sample (Sb: Te: Ge ≒ 15:40:45) of 330 Å was formed by vacuum deposition method, and then 500 Å Sb was provided as a reflection layer
A sample was prepared by stacking Ge50Å and 100Å on the layer.

After measuring the reflectances of the above three types of samples with light having a wavelength of 8300Å, the samples were left in an atmosphere of 60 ° C and 90% RH for a long time, and then the reflectances were measured. The results are shown in Table 2.

As can be seen from Table 2, when the Ge thin film is provided, the rate of change is small with respect to the reflectance change in the sample in which the Ge thin film is not provided.

In addition, the analysis results by SIMS and ESCA are similar to those in the first embodiment.
It was found that when the e thin film was laminated on the Sb reflective layer, the movement of Ge from the Sb-Te-Ge layer was suppressed, and the deterioration of the Sb reflective layer due to oxidation was reduced.

[Brief description of drawings]

1 and 2 (A), (B), and (C) are schematic cross-sectional views of different examples of the information recording medium of the present invention, in which reference numeral 1 is a substrate and 2 is a recording layer. 3 is a reflective layer, 4 is a thin film layer according to the present invention, and 5 is a protective layer.

Claims (1)

[Claims] 1. A recording layer containing at least Ge and Te,
An information recording medium having a reflective layer, characterized in that a thin film layer containing Ge is provided adjacent to the reflective layer and on the side opposite to the recording layer.