JPH025237A - Optical information recording/reproducing/erasing member and optical disk - Google Patents

Abstract

PURPOSE:To obtain a member that can perform the crystallization with a short circle spot by choosing a specific recording thin film and forming this film on a substrate. CONSTITUTION:A mixture of GeTe and Ge (mol ratio X set as 0<X<0.3) is used as a thin film material and formed on a substrate. A GeTe alloy has a high melting point and is turned into a thin film for acquisition of an amorphous film. This film is irradiated by the laser light and heated and cooled to secure the recording actions for acquisition of an amorphous state and the crystallization. Such a composition matter has a high crystallizing speed and is crystallized with a short laser spot or circle spot. On the other hand, said composition matter receives the limitation of the cooling speed at formation of an amorphous mark owing to the high crystallizing speed. Therefore the crystallizing speed is controlled by mixing Ge having a higher melting point. Thus it is possible to suppress the change of sensitivity due to the diameters of crystallized grains in the recording and erasing cycles and to improve the cycle characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information recording/reproducing/erasing member and an optical disk that are capable of recording, reproducing, and erasing information with high density and large capacity using a laser beam or the like.

Conventional technology Regarding optical disk memory, Te and Tea.

There is a write-once type disk using a thin film of TeOx (0<x<2.0) whose main component is TeOx (0<x<2.0). Furthermore, varnish is a material that can record information by heating a thin film with laser light, melting it, and rapidly cooling it, and then crystallizing and erasing information by heating and slowly cooling it.・
Earl Ovshinsky (S, R, Ovshinsky)
) et al.'s chalcogen material Ge15Te81sbz St
etc. are known. Also, As! S3 or A3 = Se
3 or Sb, 3e.

Thin films made of a combination of an isochalcogenic element and an element from group Ⅰ of the periodic table or a group ① element such as Ge are widely known. In order to record information on these thin films with laser light and erase that information, the thin film is crystallized in advance, and a laser light focused on a diameter of 1 μm is intensity-modulated in accordance with the information, for example. A disc-shaped recording disk is rotated and irradiated, and the area irradiated with the laser beam is heated to a temperature higher than the melting point of the thin film and rapidly cooled, so that information can be recorded as an amorphous mark. A known method for erasing this information is to irradiate a long spot light in the direction of the rotating track of the disk to heat the thin film to raise its temperature, and then crystallize it again by the slow cooling effect of the long spot light.

Problems to be Solved by the Invention The first problem with information recording and erasable recording media that uses means of heating a thin film to raise its temperature, melting and quenching it into an amorphous state, and heating and heating it to crystallize it is that the first problem is that long spots are created during crystallization. This requires a slow cooling effect using light. The second problem is that the signal quality fluctuates in response to heating cycles.

Factors contributing to this variation include thermal and mechanical damage to the substrate material due to repeated stimulation of rapid heating and cooling of 400° C. or higher by the recording spot light and the erasing spot light many times. Furthermore, there is thermal and mechanical damage to the recording thin film. Regarding the recording thin film, depending on its composition, local changes in the composition and components in the film, so-called segregation, may occur.

If the substrate or recording film undergoes any of the above changes,
In the recording/reproducing/erasing cycle, there is a problem in that noise increases and cycle characteristics deteriorate.

The first object of the present invention is to provide a member that can perform crystallization in a short, circular spot.

The second purpose is to provide a member with stable cycle characteristics.

Means for Solving the Problems The present invention provides a member for recording and erasing information by thermally changing the state of the thin film through irradiation with laser light, etc. The thin film material is a mixture of GeTe and Ge. and GeTe, where X is the molar ratio of
The present invention provides an optical information recording/reproducing/erasing member characterized in that eTe is selected to satisfy 0<X<0.3 and is formed on a substrate.

Function GeTe alloy has a high melting point of Tm=725°C, and by making it into a thin film, an amorphous film can be obtained.By irradiating this film with laser light and melting and rapidly cooling it at an elevated temperature, or by slowly cooling it at an elevated temperature. It has a recording effect of amorphization and crystallization.

This composition has a fast crystallization rate and has the property of crystallizing in a short laser spot or circle spot. However, on the contrary, since the crystallization rate is fast, the formation of amorphous marks is limited by the cooling rate. Therefore, T with a high melting point
The crystallization rate is controlled by mixing Ge at m=936°C. As the amount of Ge mixed increases, the crystallization speed decreases, and conversely, the formation of amorphous marks becomes easier. In the process of crystallization and amorphization, this Ge
It has the effect of inhibiting the growth of the crystallized grain size of eTe, suppresses sensitivity changes due to the crystallized grain size during recording and erasing cycles, and improves cycle characteristics.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

As the substrate on which the thin film serving as the recording layer is formed, a resin substrate made of polycarbonate or the like, or a glass plate, on which grooves or pit rows for guiding laser light are formed in advance is used. On this surface, a first inorganic dielectric layer such as ZnS or SIO, which has excellent heat resistance, is formed in advance.

This dielectric layer is 510! A ZnS dielectric layer containing 15 mol % or more of ZnS is preferred.

On top of this, a mixed thin film consisting of a GeTe alloy and excess Ge is formed. Furthermore, heat resistance can be improved by providing a second inorganic dielectric layer on this recording thin film layer. As a method for forming a thin film, vacuum evaporation or a vacuum deposition method can be used. Sensitivity can also be improved by providing a reflective layer on the second inorganic dielectric layer.

80n+++ is selected as the thickness of this thin film. Furthermore, a polycarbonate plate is attached with adhesive as a protective plate.

As a disk of φ130 vna, a signal of fl = 3.43 MHz at 1800 rpm rotation and f 2 = 1.0
Measure the overwrite characteristics of a MHz signal. Override is a modulation between a high power level of 18IIW and a low power level of 101 using a laser beam with a circle spot of 1 μm in diameter, forming an amorphous mark at a high power level and forming an amorphous mark at a low power level. This is a simultaneous erasure method that crystallizes and erases the quality marks.

FIG. 1 shows the relationship between the composition of the recording thin film and its recording and erasing characteristics. The composition of the recording thin film is X-Ge/GeT
Hail e. The recording characteristics are C/N. The erasure characteristic is expressed as the erasure rate. In other words, when there is no excess Ge, the recording C/N is low, which corresponds to the fact that amorphous marks are less likely to be formed. When only a small amount of Ge is added, the recording C/N suddenly increases and becomes 50 dB or more when X=0.1 or more. However, the erasure rate is x = 0, that is, the excess G
It is higher when there is no e, and decreases as the amount of Ge increases. It becomes 20dB or less at X-0.4 or higher. The cycle characteristics have a limit due to a decrease in recording amplitude in a region where Ge is small. In regions with a lot of Ge, a limit arises due to an increase in the noise level. When X=0.2, the C/N and erasure rate are high, and furthermore, it is stable for IE+5 cycles or more.

Effects of the invention In a member that performs recording, reproducing and erasing using a laser beam,
The following effects can be obtained by using a recording thin film made of a GeTe alloy mixed with excess Ge.

(11 Amorphous recording and crystallization erasure are easy, and one-spot circle beam overwriting is possible.

(2) C/N in multi-cycle recording and erasing.

Excellent erasure rate characteristics.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the composition of the recording thin film and the laser recording and erasing characteristics of an optical information recording/reproducing/erasing member in one embodiment of the present invention. ■... Recording characteristics C/N, 2... Erasing characteristics, erasing rate.

Claims (3)

[Claims] (1) GeTe can be used as a recording thin film that has the property of absorbing the energy of laser light, heating up, melting, rapidly cooling, and becoming amorphous, and the property of crystallizing by heating the amorphous state. Alloys and excess Ge
, and the molar ratio of Ge/GeTe is X, 0
An optical information recording/reproducing/erasing member formed on a substrate selected to satisfy <X<0.3. (2) A dielectric layer is formed on the substrate in advance, a thin film made of GeTe-excess Ge is formed on it, a dielectric layer is further formed on it, and a reflective layer is further formed on the dielectric layer. The optical information recording/reproducing/erasing member according to claim 1, wherein the optical information recording/reproducing/erasing member is formed of: (3) An optical disc using a material consisting of GeTe-excess Ge as a recording thin film.