JPS61168145A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the title highly durable optical recording medium wherein information is rewritable and whose recording signals are not deteriorated by forming an optical recording layer contg. Ga and Sb in specified composition. CONSTITUTION:An optical recording layer 2 contg., by atomic ratio, 10-60% Ga and 40-90% Sb is formed on a substrate 1 made of plastics such as polymethyl methacrylate, glass, etc. Then a protective film 3 of synthetic resins, SiO2, Al2O3, etc. is furnished on the layer 2 to obtain an optical recording medium. Into the layer 2, if necessary, 0 20%, by atomic ratio, >= 1 kind of metal selected from Al, Si, P, S, Zn, Ge, As, Se, In, Sn, Te, Bi and Pb is incorporated to prevent the segregation of Ga and further improve the contrast and sensitivity to light. The protective layer 3 consisting of an UV ray-curing resin, and SiO2 film, etc. is provided on the layer 2 and used. A highly durable optical recording medium having excellent C/N, etc. and wherein information can be rewritten is thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to optical recording technology. More specifically, the present invention aims to irradiate an optical recording layer with a light pulse, such as a laser beam, under two conditions of different power and irradiation time to change the reflectance or transmittance in the irradiated portion of the layer. The present invention relates to a type of optical recording medium, such as an optical disk, that causes a change in optical properties and uses this change in optical properties to record, reproduce, erase, and re-record information. This type of optical recording medium is generally called an optical recording medium in which information can be rewritten, in other words, it can be used repeatedly.

[Conventional technology]

The conventionally widely used rewritable optical recording media are
For example, a substrate made of glass or a plastic material (for example, an acrylic resin such as polymethyl methacrylate) and a material such as Te, which is coated on the substrate by vapor deposition or the like, can be used.
Se, Qe, 3b.

It is composed of an optical recording layer made of a thin film of a metal such as Sn or S, or a metalloid or an alloy thereof, such as Gel5Tea+5zPz.In order to protect the optical recording layer from oxidation, it is made of a thin film of a metal such as SiO□, Al2O3, etc. It has a protective film made of oxide above.

Using such an optical recording medium, information can be written or erased in the following manner, for example.

First, the entire surface of the optical recording medium is irradiated with a light beam to heat it, and the optical recording layer is brought into a highly crystalline state (a state in which crystals are regularly arranged/a stable low resistance state; hereinafter, this state is referred to as a "crystalline state"). call). Next, to write information,
It is heated and rapidly cooled by irradiation with short, strong pulsed light. As a result, the crystallinity of the area irradiated with the palace light decreases, resulting in a state of low crystallinity (
A state in which the crystal structure is disordered/a stable high-resistance state; hereinafter, this state will be referred to as an "amorphous state"). In this state,
The reflectance is low (and the transmittance is high), so
The information will be written. The information written in this manner can then be erased by irradiating the information recording portion with long weak pulsed light and heating and slowly cooling it. That is, as a result of the irradiation with such weak pulsed light, the optical recording layer, which was in an amorphous state, returns to its original state, which is a crystalline state. In short, in this optical recording medium, information can be written or erased using phase transformation (reversible change from crystalline state to amorphous state) of the optical recording layer.

[Problem that the invention seeks to solve]

However, since the above-mentioned type of optical recording medium uses a disordered crystal structure (orientation) when writing information, it has the disadvantage that information retention is inherently unstable. This is because the amorphous state is a metastable state leading to the crystalline state, and can easily transition to the crystalline state as a result of application of thermal energy or chemical energy. In fact, it is widely recognized that information once written is likely to be lost due to such instability in information retention. The present invention, therefore, aims to solve the problems of the conventional techniques and provide an improved optical recording medium that is capable of stably retaining information.

[Means for solving problems]

The present inventors have recently discovered that crystal U
, -g ~ An optical recording medium having a thin film-like optical recording layer that allows information to be recorded, reproduced, erased, and re-recorded from changes in the fouling rate or transmittance of the irradiated part caused between crystal states. By an optical recording medium, the optical recording layer is made of an alloy of gallium and antimony, and the composition of the alloy is 10 to 60% gallium and 40 to 90% antimony in atomic ratio. It has been found that the above-mentioned problems can be solved.

In one preferred aspect, the optical recording layer of the present invention comprises aluminum, silicon, phosphorus, sulfur, zinc, germanium, arsenic, selenium, indium, tin, tellurium, bismuth in an atomic ratio of 0 to 20% with respect to the entire alloy. It may further contain one or more metals selected from the group consisting of lead and lead. The use of such metals as additives can prevent gallium segregation that occurs when gallium is present in large proportions, increase contrast, and increase sensitivity, as detailed below. can do.

The optical recording medium of the present invention can have a structure as shown in cross section in FIG. 1, for example.

1 in the figure is a substrate, and an optical recording layer 2 and a protective film 3 are sequentially coated on this substrate. Note that it should be understood in advance that the illustrated film thicknesses are for convenience and do not represent accurate ratios.

The substrate 1 can be made of a material commonly used in this technical field, such as acrylic resin such as polymethyl methacrylate, glass, or the like.

The optical recording layer 2 on the substrate 1 is formed by a vacuum evaporation method, a sputtering method, etc. by arranging gallium and antimony, which are vapor deposition sources, separately or in the form of an alloy with a predetermined composition ratio. can be advantageously formed. In addition, when using gallium-antimony alloy as a vapor deposition source,
Care must be taken in advance that there will be a difference in composition between the deposition source and the deposited film. The thickness of this optical recording layer 2 is generally as follows:
Advantageously, there are about 300 to 200 people.

The formed optical recording layer 2 can be coated with a protective film 3 by a spin coating method, a vapor deposition method, a sputtering method, etc., as is widely practiced in this technical field. Examples of such protective films include organic polymer materials such as thermoplastic resins such as polymethyl methacrylate and polystyrene, ultraviolet curing resins (so-called 2P resins), metal oxides such as SiO□, A7!203, etc. Depending on the case, metal nitrides can be used. Normally, the thickness of the protective film 3 is preferably about 500 to 300.

The optical recording medium of the present invention can also have a structure as shown in FIG. The structure of this medium is the same as that shown in FIG. 1 above, except that thin inorganic material layers 4 and 5 are newly provided between the optical recording layer 2. As a result of sandwiching the optical recording layer 2 with the layers 4 and 5, it is possible to prevent problems such as the optical recording layer 2 being affected by moisture in the air when an acrylic substrate is used, for example. Examples of inorganic materials forming these layers include SiO□, SnO□, and the like.

The film thickness is usually on the order of several hundred layers.

〔Example〕

Example 1: A disc-shaped acrylic substrate (polymethyl methacrylate) with an outer diameter of 300 mm and a thickness of 1.2 In was prepared and thoroughly cleaned. This substrate was set in a vacuum deposition machine, and gallium and antimony were deposited from independent deposition sources. During this vacuum deposition, gallium and antimony were mixed uniformly by rotating the substrate, and the deposition rate was controlled to be constant. Although the ratio of gallium and antimony was varied as shown below, the thickness of the optical recording layer formed was 1800 mm in each case. moreover,
A protective film of polystyrene is placed on this optical recording layer to a thickness of 1
000 people made a spin code.

%] - A sample of the optical recording medium produced as described in Example 1 above was placed on a spindle, and with the substrate stationary, light from a semiconductor laser (wavelength 830 nm) was irradiated with a collimating lens. Irradiation was performed using an optical head that focused the beam diameter to 1 μm using an objective lens.

As a result of this irradiation, the portion of the medium that was irradiated with the focused beam of semiconductor laser light changed into a crystalline state.

Next, in order to evaluate the rewritability of this medium, the medium was alternately irradiated with two types of laser light pulses with different powers and pulse widths. Changes in reflectance were measured using light. First, to write information, the power was 10 mW and the pulse width was 1.
When the medium was irradiated with pulsed light of 00 ns, the irradiated portion was heated and rapidly cooled, and as a result, the structure of the irradiated portion changed and the reflectance became high. Add an erase pulse to this part, i.e., power 5mW, pulse width 500
When irradiated with ns pulsed light, the structure of the irradiated portion changed and the reflectance became low. Moreover, this reflectance changed reversibly; it increased after laser irradiation with high power and similar pulse width, and decreased after laser irradiation with low power and long pulse width.

By the way, the above-mentioned reversible change in reflectance, in other words, rewriting of information, is possible only when the ratio of gallium and antimony is within a certain range, and outside that range, there is no difference in reflectance. , it turns out that it cannot be rewritten. Experiments have confirmed that a reversible change in reflectance can occur when the proportion of gallium in the alloy ranges from 10% to 70% in terms of atomic ratio. However, gallium is 6
If it exceeds 0%, a striped pattern appears on the medium, which is thought to be caused by segregation of gallium, which is not practical. In addition, in areas where gallium is less than 20%, the film bulges in the laser beam irradiation area, probably due to the formation of bubbles.
The level at which the reflectance changes becomes unstable, which again poses a practical problem. Therefore, in the practice of the present invention, gallium in an atomic ratio of 20 to 60% is particularly suitable.

Next, in order to compare the crystal states of the recorded and unrecorded portions of the medium, the diffraction patterns were observed using a transmission electron microscope. When the protective film was peeled off from the medium and the state of the optical recording layer was observed from a diffraction pattern, a halo pattern characteristic of an amorphous film was observed in the unrecorded portion (the portion not irradiated with laser light).

On the other hand, in the recorded area (laser beam irradiated area), spots were formed that were diffracted by the crystal in both the high reflectance state and the low reflectance state, and it was confirmed that both states were in the crystal state.

Example 3: In this example, an optical recording medium according to the invention was tested for durability.

The following three types of optical recording media were manufactured according to the method described in Example 1: Sample 1 (Control) Ga655b3 was placed on an acrylic substrate of the same shape as a slide glass.
5 alloys (same for the other two samples) were deposited. This layer was not heat treated and was not coated with a protective film.

Sample 2 (present invention) Gab5Sb+ on an acrylic substrate of the same shape as the slide glass
The s-alloy was deposited and the layer was heat treated at 80° C. for 2 hours to crystallize. This sample was also not coated with a protective film.

Sample 3 (Invention) While rotating Sample 2 at 600 rpm, the medium was irradiated with a concentric beam of semiconductor laser light to record a 2 MHz signal.

This sample was also not coated with a protective film.

Each of the above samples 1.2 and 3 was heated at a temperature of 70°C.
Changes in reflectance over time by holding in an atmosphere with a relative humidity (RH) of 85%, and C/N ratio (carrier to noise)
The change in was measured. The results plotted in FIGS. 3 and 4 were obtained.

Sample 1 exhibited a significant decrease in reflectance over time, as shown by the curve ■ in FIG. However, in contrast to this, Sample 2, which is an example of the medium of the present invention, exhibits very stable reflectance with almost no change over time, as shown by the curve ■ in Figure 3. did. In fact, sample 2
There was almost no change in the reflectance even after 3 months. Also,
The change in reflectance of the recorded portion of Sample 3 was also almost the same as that of Sample 2.

The recording portion of Sample 3 showed a change in C/N ratio as shown by the curve ■ in FIG. That is, as is clear from the figure, this sample showed only a slight decrease in the C/N ratio of 3 dB or less even after 3 months.

Example 4: In this example, the improvement in stability when a metal additive was added to the optical recording layer of the optical recording medium according to the present invention was evaluated.

An optical recording medium of the present invention was produced as described in Example 1 above. However, the composition of the optical recording layer of this medium is GabsSb.
3s, and in addition to this, atomic ratio of 5% and 1
It contained 0% and 15% selenium (Se), respectively. When each of these media was evaluated for rewritability using the method described in Example 2 above, it was found that in each case, segregation of gallium was less likely to occur than in the case without selenium addition, and it was useful for stabilization. It turns out. In fact, segregation could be prevented even with a gallium-rich composition. In FIG. 5, regions where gallium segregation does not occur are indicated by diagonal lines.

Furthermore, other metal additives, AA, in place of Se.

A similar effect could be obtained by adding Si, Zn, Ge, and As.

Example 5: In this example, the increase in contrast when metal additives were added to the optical recording layer of the optical recording medium according to the present invention was evaluated.

An optical recording medium of the present invention was produced as described in Example 1 above. However, in the case of this example, the composition of the optical recording layer of this medium is Gab5Sb3S, and it does not contain tin (Sn) or contains 5% or 10% of the atomic ratio of the entire alloy.
and 20% tin, respectively. Each of these media was evaluated for contrast between the high and low reflectance states and was found to have increased contrast in each case. The results are listed in the table below.

Contrast (%) - The contrast (%) in this table is calculated by dividing the difference in reflectance between the high reflectance state and the low reflectance state by the reflectance of the high reflectance state, and adding 10
It is multiplied by 0.

Furthermore, other metal additives, As, may be used instead of Sn.

Similar effects could be obtained by adding Pb and Zn.

Example 6: In this example, the increase in sensitivity when metal additives were added to the optical recording layer of the optical recording medium according to the present invention was evaluated.

An optical recording medium of the present invention was produced as described in Example 1 above. However, in the case of this example, the composition of the optical recording layer of this medium is Gabs 5b3s, which does not contain tellurium (Te) or contains 5% by atomic ratio of the entire alloy.
, 10% and 20% tellurium, respectively. Each of these media is compared with respect to the contrast between parts of the high-reflectance state and parts of the low-reflectance state, with the exception of high power,
When the irradiation power of short pulse width laser light was varied and evaluated, it was found that the contrast increased as tellurium was added. The results are shown in Figure 6.

Furthermore, from the results shown in FIG. 6, it is obvious that the sensitivity increases when tellurium is added. In addition, in Fig. 6,
Curve a represents Te 0%, curve A represents Te 5%, curve C represents TeIO%, and curve d represents Te 20%.

Furthermore, other metal additives such as In and P may be used instead of Te.

Similar effects could be obtained by adding S, Se, and Sn.

〔Effect of the invention〕

According to the present invention, the durability of a rewritable optical recording medium can be increased, and information retention can be stably maintained. Furthermore, there is no deterioration in signal quality in the medium of the present invention. As a result, according to the present invention, the reliability of the optical storage device can be significantly improved.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing preferred configuration examples of the optical recording medium according to the present invention, FIG. 3 is a graph showing the relationship between elapsed time and reflectance, and FIG. 4 is a graph showing the relationship between elapsed time and reflectance. , a graph showing the relationship between elapsed time and C/N ratio, FIG. 5 is a phase diagram showing the region where Ga segregation does not occur in a Ga-3b-Se ternary alloy film, and FIG. 6 is a graph showing the relationship between irradiation power and It is a graph showing the relationship of contrast. In the figure, 1 is a substrate, 2 is an optical recording layer, and 3 is a protective film. Fig. 1 Fig. 20 Fig. 3 Elapsed time (months) Fig. 40 Elapsed time (months) Fig. 5 e. Uga Michibe 1, Indication of the case 1985 Patent Application No. 006,671 2, Name of the invention Optical recording medium 3, Relationship with the person making the amendment Name of the patent applicant (522) Fujitsu Limited 4, Agent address: 5-8-10 Toranomon-chome, Minato-ku, Tokyo 105
“Detailed Description of the Invention” column 66 of the specification subject to amendment Contents of the amendment (1) Specification, page 3, lines 9-10 “Hereinafter, this state will be referred to as “
``Crystalline state'' is corrected to ``So-called ``crystalline state.'' (2) In the specification, page 3, lines 14-15, ``J, hereinafter referred to as ``amorphous state,'' is corrected to ``so-called ``amorphous state.'''' (3) Specification, page 7, line 4 (7) r200^'20
Correct to 00AJ. (4) In the specification, page 7, line 14, "3ookyu" is changed to '3000'.
Correct to AJ.

Claims (1)

[Claims] 1. A thin-film optical recording layer capable of recording, reproducing, erasing, and re-recording information from changes in reflectance or transmittance of the irradiated portion caused by irradiation with a light pulse. An optical recording medium, wherein the optical recording layer is made of an alloy of gallium and antimony, and the composition of the alloy is 10 to 60% gallium and 40 to 90% antimony in atomic ratio. Characteristic optical recording media. 2. Aluminum, silicon, phosphorus, sulfur, zinc, germanium in an atomic ratio of 0 to 20% with respect to the entire alloy,
The optical recording medium according to claim 1, wherein the optical recording layer further contains one or more metals selected from the group consisting of arsenic, selenium, indium, tin, tellurium, bismuth, and lead. .