JPS63153737A - Optical recording medium - Google Patents

Abstract

PURPOSE:To make recording by which >=3 discriminations can be made in one bit by controlling temp. by using an alloy which has >=3 kinds of different crystal structures according to a thermal change and contains the low melting metal exhibiting different light reflectivities in the respectively crystal states. CONSTITUTION:Ge and Se metal pieces are disposed on a Te target at ratios of, for example, 85 Te, 10 Ge and 5 Sn to form an optical recording medium alloy by sputtering. The single film exhibits the plural light reflectivities when the temp. of the medium is controlled by projecting a laser beam to such medium 3. The medium which is formed of the alloy contg. such low melting metal, has >=3 kinds of the different crystal structures including the amorphous structure according to thermal changes and exhibits the different light reflectivities in the respective crystal states is used as the optical recording medium. The multi-value memory medium which permits >=3 recordings in the single film by controlling the temp. of the medium is thus obtd.

Description

[Detailed Description of the Invention] Further Fields of Use> The present invention aims to provide an optical recording medium on which information can be recorded, reproduced, and erased.

<Prior Art and its Problems> Optical recording media are in the form of disks, and write-once memories have been developed first, followed by the widespread development of magneto-optical media and phase change media.

Optical recording media have the advantage of being capable of higher density recording than magnetic recording media, but in the future, even higher densities will be needed. For this reason, research has recently been carried out on multilayer memory materials and media that can record multiple bits (multilevel memory media), such as photochemical hole/light/burning (PHB), but the former In this case, it is necessary to superimpose a large number of recording films and intermediate layers, and there are difficulties in the process of film formation, which is complicated, and in the technique of focusing laser light on different recording layers. The latter method requires extremely low temperatures such as 11 um to maintain the memory, and is therefore less practical.

<Purpose of the Invention> As a result of various studies in order to provide a multi-level memory medium with fewer practical problems as described above, the present inventors have found that by alloying low-melting point metals, multiple levels of recording can be achieved. They discovered that the value can be taken, and completed the present invention.

<Structure of the Invention> The gist of the present invention is to make an alloy containing a low melting point metal,
An optical recording medium characterized in that it hardens as a recording material using an alloy that has three or more different crystal structures (including an amorphous structure) and exhibits different light reflectance in each crystalline state in response to thermal changes. Exists.

The present inventor conducted research on phase-change recording media that change upon reflection due to amorphous ψ crystal transition, and found that
We have discovered a recording film medium whose reflectance changes stepwise at different temperatures. By controlling the power and irradiation time of light (heat) such as a laser beam, the temperature of the medium is controlled and a single film takes on multiple reflective states. This makes it possible to record distinguishable records.

As alloys having such properties, To-Sn alloy,
Te-Ge-Sn alloy, TO-Ge-8b alloy, Te-
Examples include Ge-An alloy and Te-Go-Cu alloy.

It is not clear why these alloys have three or more different crystal structures (including amorphous structures), but
According to the observations of the inventors, this seems to be because a crystalline state, which can also be called a comparatively stable quasicrystalline state, clearly appears between the amorphous state and the crystalline state. This quasicrystalline state is
This clearly appeared in the binary or ternary alloys mentioned above.

Therefore, in these alloys, the amorphous state -
Three types of crystalline states, quasicrystalline state and crystalline state, are recognized and it is possible to optically distinguish between them, so it is possible to record a plurality of values in a single bit.

In other words, if the recording layer is made into an amorphous state and then irradiated with a weak laser beam and cooled, a quasi-crystalline state is obtained, and if it is irradiated with a strong laser beam and cooled, a crystalline state is obtained. Due to the difference, multi-level memory can be constructed.

The alloys that can be used as such multivalued memories are described above. Although there are probably other factors besides the composition, the composition ratios for the alloys mentioned above are shown below.

Te-Sn alloy...Sn:j~/j atomic%Te
-Ge-Sn alloy...Ge:/j%% or less (
(excluding 0) Eln:j~/! Atomic % Te-()θ-sb alloy...Ge:/jO not included below the original atomic mass)SbNio~/! Atomic % TeC) θ-A-u alloy...Ge: /! r
atomic% or less (not including 0) Au: 10 atomic% or less (not including 0) Te-Ge-Cu alloy...Ge: /j original atomic mass or less (not including 0) Oa: 10 atoms % or less (not including 0) <Example> Although actual examples are shown below, the present invention is not limited to the following examples as long as they do not exceed the gist of the invention.

Example / A thickness of 10 coated and hardened with ultraviolet curable resin on the surface
Using a glass substrate with a μm undercoat layer, a SiO
It was provided to have a thickness of about 00λ.

Next, a recording layer 2BF was provided on the protective undercoat layer by sputtering.

The recording layer is formed by placing Oa gold pieces and Sn metal pieces on the Te target. , Ge 10 , and Snj were arranged in the same proportions and sputtered. The film formation rate was approximately 10λ/S.

Next, a 5i02 layer was formed as a protective layer by test sputtering.

As a result of X-ray diffraction of the composition of the obtained alloy thin film, no peaks corresponding to specific crystal planes appeared, indicating that it was an amorphous phase.

Local crystallization of the amorphous phase was performed using the heat of focused semiconductor laser light.

Figure/ shows a diagram of the equipment for this purpose. In this device, light from a semiconductor laser (wavelength: 30 nm) is focused onto the surface of the recording medium by a lens, and is crystallized by rectangular wave light whose irradiation power and irradiation time are controlled by a pulse generator. have them do it.

FIG. 2 shows a typical example of the waveform of the applied laser power and the change in reflectance of the recording medium due to the laser light pulse irradiation. As is clear from the figure, the reflectance changes stepwise as the laser pulse irradiation time increases.

FIG. 3 shows the change in permeability of the sample with respect to temperature when the sample was heated at io° C./mm in an electric furnace. You can understand how the transmission changes at different temperatures. Generally, when a change in transmittance occurs, a change in reflection also occurs, indicating that the above-mentioned change in reflection as the irradiation time of the laser pulse increases is dependent on the medium temperature.

In this embodiment, the increase in medium temperature is controlled by changing the pulse irradiation time, but it is also possible to control by changing the laser pulse light intensity while keeping the irradiation time constant.

Also, although we used the phase transition of amorphous≠crystal as an example, crystal≠
Three or more polymorphs exist in crystal phase transition as well, and by changing the medium temperature, the same thing can be expected in a medium that has light reflection corridors corresponding to the polymorphs.

In the example, the reflective states are R1s R2, R,
In addition to the three states shown in FIG. 2, there are also cases where a large number of states exist in a stepwise manner.

<Effects of the Invention> According to the present invention, optical recording with a larger capacity than conventional optical recording can be realized.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an apparatus for irradiating a recording film with a laser beam according to the present invention. / is a servo DC power supply for focusing the laser beam onto the recording medium, ko is a mirror that reflects the laser beam, 3 is a sample, ≠ is a light beam splitter, j is a lens, O is a semiconductor laser element,
7 represents a pulse generator, ♂ represents a PIN type optical sensor, and 2 represents a synchroscope. Figure 2 shows the applied laser beam pulse (a) and -
A typical diagram of the reflection of the recording film accompanying the laser beam irradiation is shown when the reflectance is converted into voltage output. If the initial reflection is R1, as the beam irradiates, R2s
L and the reflection top change in a step-like manner. FIG. 3 is a diagram showing the change in transmittance of the recording film as the temperature rises.

Claims (3)

[Claims] (1) An alloy that is made of an alloy containing a low-melting point metal, has three or more different crystal structures (including an amorphous structure) depending on thermal changes, and exhibits different light reflectance in each crystal state is used as a recording material. An optical recording medium characterized in that it is used. (2) The optical recording medium according to claim 1, wherein the low melting point metal is chalcogen. (3) The alloy containing low melting point metal is Te-Sn, Te
-Ge-Sn, Te-Ge-Sb, Te-Ge-Au
The optical recording medium according to claim 1, wherein the optical recording medium is a Te-Ge-Cu alloy.