Information recording medium and method for manufacturing the same

Abstract

An information recording medium having such a recording material layer on a substrate where reversible phase change between electrically or optically detectable states can be caused by electric energy or electromagnetic energy. The recording material forming the recording layer is either a material having a crystal structure including lattice defects in one phase of the reversible phase change or a material having a complex phase composed of a crystal portion including a lattice defect in one phase of the reversible phase change and an amorphous portion. Both portions contain a common element. A part of the lattice defects are filled with an element other than the element constituting the crystal structure. The recording medium having a recording thin film exhibits little variation of the recording and reproduction characteristics even after repetition of recording and reproduction, excellent weatherability, strong resistance against composition variation, and easily controllable characteristics.

Description

TECHNICAL FIELD The present invention relates to an information recording medium that can record, reproduce, erase and rewrite high-density information by means of irradiation of laser beams and application of a high electric field. The present invention relates to also a method for manufacturing the information recording medium. BACKGROUND ART It is well known to apply as a memory a change in optical characteristics caused by reversible phase change of a substance, and a technique using this has come into practice as phase change optical disks such as DVD-RAM. Specifically, recording, reproducing and rewriting of signals will be available by rotating a disk medium comprising a substrate on which a recording thin film for generating reversible phase change is provided, and by irradiating the disk medium with a laser beam drawn to a sub-micron size. In the case of a phase change optical disk, overwriting by means of a single laser beam is carried out. That is, irradiation is perfor...

AI Technical Summary

Benefits of technology

To solve the above-mentioned problems, a first purpose of the present invention is to provide a phase change memory material that will increase a number of repetitions of rewriting and enables rewriting at a high speed. The memory device can be constituted with either an optical memory or an electric memory. The present invention aims to provide a recording medium comprising a recording thin film formed on a substrate. Due to the above-mentioned excellent characteristics of stoichiometric composition, the recording thin film provides less influence on the characteristics regardless of some composition variation. That is, the recording thin film comprises a composition exhibiting easy controllability of the characteristics. The present invention provides also a method for manufacturing a recording medium comprising such a recording thin film.

The element composing the rock-salt type crystal preferably contains Ge and Te as its base materials, and further preferably, it contains at least one element selected from Sb and Bi. It is particularly preferable that the base material composition of the rock-salt type crystal substantially corresponds to a GeTe—Sb2Te3 quasibinary system composition, a GeTe—Bi2Te3 quasibinary system composition or a mixture thereof. When an element composing the rock-salt type crystal contains Ge, Te, and Sb, or it contains Ge, Te, and Bi, the element to fill the lattice defects is at least one selected from Al, Ag, Pb, Sn, Cr, Mn and Mo. It is also preferable that the base material composition of the rock-salt type crystal substantially corresponds with (GeTe)1−x(M2Te3)x, in which 0.2≦x≦0.9 (M denotes at least one element selected from Sb, Bi and Al, or an arbitrary mixture of these elements). It is further preferable that 0.5≦x≦0.9. For improving recording sensitivity, it is further preferable that the recording film contains nitrogen (N) or oxygen (O). Preferably, the concentration of the N atom (Dn) is 0.5 atom %≦Dn≦5 atom % since the range provides higher effects.

Filling Al, Cr or Mn in lattices is preferable to improve repeatability, and addition of Ag is preferable to increase changes in optical characteristics (signal amplitude change) between the crystalline phase and the amorphous phase. Filling Sn or Pb is effective in improving crystallization speed.

It is further effective to fill plural elements at the same time in lattice defects for improving the characteristics. When the material is based on Ge—Sb—Te or Ge—Bi—Te, both the crystallization speed and the repeatability can be improved preferably at the same time by, for example, using simultaneously at least one of Sn and Pb together with Al, Cr or Mn. Otherwise, simultaneous use of either Sn or Pb together with Ag is preferable to improve the crystallization speed and the signal amplitude at the same time. Using at least one of Al, Cr and Mn together with Ag is preferable to improve repeatability and signal amplitude at the same time. Furthermore, addition of at least one of Al, Cr and Mn, at least either Sn or Pn together with Ag is preferable in improving crystallization speed, signal amplitude and repeatability at the same time.

An optical information recording medium according to the present invention can comprise a single layer medium prepared by forming the above-mentioned recording material thin film on a substrate. However, it is desirable to use a multilayer including the recording layer. For example, it is preferable that a protective layer is provided between the substrate and the recording layer in order to reduce thermal damage in the substrate or to utilize its optical interference effect. It is also preferable to provide a protective layer to the opposing surface of the recording layer as well in order to prevent deformation of the recording layer and to utilize its optical interference effect. The protective layer is made of a material that is stable thermally and chemically, and transparent optically, such as an oxide, a sulfide, a nitride, a nitride-oxide, a carbide, and fluoride. Examples of the materials include ZnS, SiO2, ZnS—SiO2, SiNO, SiN, SiC, GeN, Cr2O3, and Al2O3. It is preferable to provide a reflecting layer over the protective layer in order to increase efficiency for laser beams or the like used for recording. The reflecting layer can be a metallic material film or a multilayer film combined with a dielectric material. The metallic material can be Au, Al, Ag or an alloy based on these metals.

Problems solved by technology

However, these materials would cause a problem.

That is, when the crystallization temperature is raised, the crystallization speed is lowered remarkably, and this would make rewriting difficult.

Alternatively, when the crystallization speed is increased, the crystallization temperature is lowered sharply, and thus, the amorphous state will be unstable at a room temperature.

Though this material is reported to be excellent in the erasing performance, it has been found that the characteristics deteriorate due to the phase separation as a result of repeated overwriting.

Similarly, characteristic deterioration caused by repetition may be observed even if a stoichiometric composition is used.

As a result, the film thickness will be uneven at some parts after a big repetition.

Namely, during a repeated recording, even a slight variation that may have not caused a trouble in a conventional process will lead to errors in reading, and thus, the number of available repetitions of rewriting is decreased substantially.

This problem can be noticeable in the a case of so-called land-groove recording, in which a concave-convex-shaped groove track is formed on a substrate and information is recorded on both the groove (a region closer to the light-incident side) and the land portion (spacing between the grooves) in order to guide a laser beam for recording and reproducing.

Specifically, since the thermal and optical conditions are different between the land and groove, the repeatability will deteriorate easily, especially in the land region.

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