JPH0399884A - Information recording medium - Google Patents

Abstract

PURPOSE:To improve the contrast and recording and erasing sensitivities of the title medium and to lengthen its life by including two kinds of more of components of stable compounds, alloy and elements in a recording layer and by making the crystallizing transition point of the component with the lowest crystallizing transition point by not less than specific temperature higher than that in the case, where the component exists singly. CONSTITUTION:Two kinds or more of components out of singly stable compounds, alloy and elements are included all together in the recording layer of an information-recording medium and the crystallizing transition point of the component with the lowest crystallizing transition point is by not less than 30 deg.C higher than that in the case, where the component exists singly. In this case, a substance having a high crystallizing transition point is considered to influence the rise in the crystallizing transition point of a substance having a low crystallizing transition point. As the substance having a high crystallizing transition point, there can be cited Ib-IIIb-VIb2 and IIb-IVb-Vb2 chalcopyrite type compounds typified by AgInTe2, etc. As the substance having a low crystal lizing transition point, there can be cited chalcogen elements such as Te and Se, chalcogenides such as GeTe, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an information recording medium, particularly a phase change type information recording medium, in which a phase change is caused in a recording layer material by irradiation with a light beam, It relates to an information recording medium on which information can be recorded, reproduced, and rewritable, and is applied to optical memory-related equipment.

[Prior Art] As one of the optical memory media that can record, reproduce, and erase information by irradiation with electromagnetic waves, especially laser beams, it utilizes transition between crystal-amorphous phase or crystal-crystal phase.
So-called phase change recording media are well known. In particular, it is possible to override with a single beam, which is difficult to do with magneto-optical memory, and the optical system on the drive side is also simpler, so research and development on this topic has been active recently. As a typical material example, USP 3,530,441
Ge-Te, Ge-Te-8S as disclosed in
Ge-Se-8s Ge-5e'-Sb, Ge-As-
8e, In-Te.

Examples include so-called chalcogen alloy materials such as 5e-Te and 5e-As. In addition, for the purpose of improving stability, high-speed crystallization, etc., Au (Japanese Patent Application Laid-Open No. 61-219892) is added to the Ge-Te system.
Ge-Te-5e was proposed for the purpose of proposing materials added with Sn and Au (Japanese Unexamined Patent Publication No. 81-270190), Pd (Japanese Unexamined Patent Publication No. 82-19490), etc., and improving the repeatability of recording/erasing.
- Material with specified composition ratio of Sb (Japanese Unexamined Patent Publication No. 62-7343
8) has also been proposed.

However, none of these can satisfy all of the characteristics required of a phase change type rewritable optical memory medium.

In particular, the most important issues to be solved are improving contrast, recording sensitivity, and erasing sensitivity, preventing a decrease in erasing ratio due to unerased parts during overwriting, and extending the lifespan of recorded and unrecorded areas.

The biggest factor hindering improvement in contrast is that a single recording material has its own maximum contrast ratio. A method of providing a reflective layer behind the recording film has been devised, but when using a crystal-amorphous transition, the contrast ratio decreases depending on the material because the reflectance in the amorphous state, which has high transmittance, increases. Resulting in. Furthermore, it is extremely difficult to simultaneously improve the contradictory properties of recording sensitivity and erasing sensitivity with a single-phase recording material. In many cases, additives or impurities are added to promote amorphization or crystallization. However, this method increases the number of phases contained in the recording film, which causes phase separation, aggregation, and accompanying oxidation. These significantly deteriorate the properties as a recording material, leading to a significant deterioration in the service life.

[Problems to be Solved by the Invention] The present invention seeks to provide an information recording medium that has higher contrast and recording/erasing sensitivity than conventional information recording media, and has a longer lifespan for recorded and unrecorded areas. It is something.

[Means for Solving the Problems] The basic configuration of the present invention for solving the above problems is as follows.

The recording layer of an information recording medium simultaneously contains at least two or more components selected from independently stable compounds, alloys, and elements, and the crystallization transition point of the component with the lowest crystallization transition point among them is the component. 30°C than when present alone
Information recording media in a state where the increase is above.

There are various possible reasons for the increase in crystallization transition of materials with low crystallization transition points, but they can be broadly classified into the following two reasons.

First, substances with a low crystallization transition point in the parent phase (matrix) that make up the recording layer are called fine particles (microclusters) that are smaller than the size that allows them to maintain their bulk properties.
Or if they are confined in similar conditions. In this case, the energy difference between forming a crystal lattice and remaining in an amorphous state is not very large, so crystallization does not occur even if the original crystallization transition point is reached. As atoms move when the matrix crystallizes at higher temperatures, microclusters bond together,
As a result, it transforms into a more energetically stable crystal.

Next, there is a case where microclusters of compounds, alloys, or elements in the recording phase are chemically bonded at a portion thereof. In this case as well, until the bond between different types of microclusters (between microclusters of a material with a high crystallization transition point and microclusters of a material with a low crystallization transition point) is dissolved due to the rearrangement of the parent phase with a higher crystallization transition point. , crystallization of substances with low crystallization transition points is suppressed. In any case, it is thought that a substance with a high crystallization transition point greatly influences the increase in the crystallization transition point of a substance with a low crystallization transition point.

Ib-I represented by Ag1nTe2 has a high crystallization transition point.
I[b-Vlbz, IIb-rVb-vb2 series, chalcopyrite-type compounds, Ge-3b-Te-based compounds and alloys, In-3b-Te-based compounds and alloys, Ib-V
Examples include b-VTb2 type compounds. Examples of materials that can be used as having a low crystallization transition point include chalcogen-based elements such as T e S S e and chalcogenides such as GeTe.

The information recording medium of the present invention may be provided with auxiliary layers such as a heat-resistant protective layer, a surface protective layer, a reflective layer, and an adhesive layer, if necessary.

The substrate used in the present invention is usually made of glass, ceramics, or resin, and resin substrates are preferable in terms of moldability, cost, and the like. Typical examples of resins include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, etc. Polycarbonate resins and acrylic resins are preferred in terms of processability, optical properties, and the like. Further, the shape of the substrate may be a disk, a card, or a sheet.

Materials for the heat-resistant protective layer include 5iO1Si02, Zn
O, 5nOz, Al2O3, Ti0z, In203, M
Metal oxides such as g0SZ r02, S i 3N4, A
IN, TiN.

Nitride such as BN, ZrN, SiCST a CsB4
Examples include carbides such as C, WC, TiC, and ZrC, diamond-like carbon, and mixtures thereof. Further, it may contain impurities as necessary. Such a heat-resistant protective layer can be formed by various vapor phase deposition methods, such as vacuum evaporation, sputtering, plasma CVD, photoCVD, ion blating, and electron beam evaporation.

The thickness of the heat-resistant protective layer is preferably 200 to 5000×, preferably 500 to 3000×. When the thickness is less than 200, it does not function as a heat-resistant protective layer, and on the other hand, when it is thicker than 5,000, sensitivity decreases and interfacial peeling is likely to occur.

Moreover, the protective layer can be multi-layered if necessary.

The phase change material may be not only a single layer but also a multilayer film.

The thickness of the recording layer is 200 to 10,000 times, preferably 500 to 3,000 times, and most preferably 700 to 2,000 times.

Various types of electromagnetic waves can be used for recording, reproducing, and erasing, such as laser light, electron beams, X-rays, ultraviolet rays, visible light, infrared rays, and microwaves. A solid semiconductor laser beam is optimal.

Hereinafter, the present invention will be explained by citing the characteristics of the recording medium that was actually produced. These examples do not limit the invention in any way.

[Example] Te (tellurium) was selected as a substance with a low crystallization transition point and dispersed in Ag1nTez. RF for recording film production
Using magnetron sputtering method, the target is Ag2.
An Ag-In-Te ternary system target was used in which the molar ratio of Te and In2Te3 was adjusted to be 48:52.

The film thickness was 7800X. The film immediately after film formation is in an amorphous state as determined by X-ray diffraction.

FIG. 1 shows the X-ray diffraction pattern after heat treatment at 300° C. for 1 hour. Ag1nTe with chalcopyrite structure
2 (c-AgInTez) and zinc blend structure A
Peaks due to g1nTe2 (z -AglnTez) and Te are observed.

FIG. 2 shows the crystallization process measured with a differential scanning calorimeter (DSC). Measurements were performed in a nitrogen atmosphere, and the temperature increase rate was 1O
℃/1n. Three consecutive exothermic peaks are observed at approximately 200°C.

Since no crystalline peaks are observed in X-ray diffraction even if heat treatment is performed below this temperature, these three exothermic peaks are
two phases (C-AgInTe2, z-AglnTe2.T
It can be said that this corresponds to the crystallization of e). That is, the crystallization peak of Te in this film is when Te alone (Tc=
This is an increase of more than 100°C compared to the previous year (=80°C). Moreover, even after crystallization, it remains stably in the film without being oxidized. There is an endothermic peak around 420°C, which corresponds to the melting point of Te.

These are because Te, which has a low melting point (s, p,: 450°C) but cannot be used alone because the crystallization transition point is too low (80°C in Tc), can be replaced with Ag1nTez, which has a high crystallization transition point.
It has been shown that by mixing these in the layer, it is possible to raise the crystallization transition point by more than 100°C to around 200°C while maintaining a low melting point.

By using such a film as a recording layer, a recording medium with high sensitivity recording (amorphous) and long recording life can be obtained. Furthermore, Ag1nT, which is the matrix
The crystal structure of ez is a tetragonal one, which is simple and isotropic, which is advantageous in terms of improving the erasure (crystallization) speed.

[Effects of the Invention] The effects of the present invention as explained above are summarized as follows.

Longer life can be achieved by stably existing a substance with a low crystallization point in the matrix.

Since the phase transition of a substance having a low crystallization point with good recording sensitivity can be stably utilized, recording sensitivity and erasing sensitivity are improved.

Since the number of phases that undergo phase change increases, recording with high contrast can be achieved.

[Brief explanation of drawings]

FIG. 1 is an X-ray diffraction pattern of the recording film of Example 1 of the present invention, and FIG. 2 is a graph showing the results of differential scanning calorimetry of the crystallization process of the recording film.

Claims (4)

[Claims] (1) A compound that is stable alone in the recording layer of an information recording medium,
Contains at least two or more components selected from alloys and elements at the same time, and the crystallization transition point of the component with the lowest crystallization transition point among them is 30°C or more higher than when the component exists alone. An information recording medium characterized by being in a state where (2) The information recording medium according to claim (1), wherein the component having the lowest crystallization transition point is tellurium. (3) Claim (1) characterized in that at least one of the components having a high crystallization transition point has a chalcopyrite structure.
) or the information recording medium described in (2). (4) The information record according to any one of claims (1) to (3), characterized in that during crystallization, a component having the lowest crystallization transition point and other components are successively crystallized. Medium.