JPS61168144A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the title optical recording medium wherein information is rewritable and having improved sensitivity to light, contrast, etc. by providing an optical recording layer composed of In and Bi in specified composition, and incorporating, if necessary, specified elements such as Al and P into the optical recording layer in a specified ratio. CONSTITUTION:An alloy layer 2 contg., by atomic ratio, 30-90% In and 10-70% Bi is formed on a substrate 1 of glass, plastics, etc. Into the alloy layer 2, 0-20%, by atomic ratio and based on the whole alloy, >= 1 kind of metal selected from Al, Si, P, S, Zn, Ga, Ge, As, Se, Ag, Cd, An, Sb, Te, Ta and Pb is incorporated to improve the sensitivity. A protective layer 3 of an inorg. material such as SiO2, polystyrene, etc. can be furnished on the layer 2. Then layers 4 and 5 of SiO2, SnO2, etc. are provided on both sides of the optical recording layer 2, and the effect of moisture at the outside can be eliminated, when the substrate 1 is formed with an acrylic sheet. An optical storage device wherein information can be rewritten repeatedly and many times and whose shelf life of information is stabilized 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 coated on the substrate by vapor deposition or the like, for example, Te.
, Se, Ge, Sb, Sn, S, or other metals or semimetals or alloys thereof, such as Ge+5Tes+5z
It is composed of an optical recording layer made of Pz, and in order to protect the optical recording layer from oxidation etc., for example, 5iOz
, has a protective film made of metal oxide such as AIZ03 above. Using such an optical recording medium, information can be written or erased, for example, as follows: First, the entire surface of the optical recording medium is irradiated with a light beam to heat it, and the optical recording layer is made into a crystalline layer. A high state B (a state in which crystals are regularly arranged/a stable low resistance state; hereinafter, this state will be referred to as a "crystal state") is achieved. Next, in order to write information, short intense pulsed light is irradiated to heat and rapidly cool. Then,
The crystallinity of the part irradiated with the pulsed light decreases, resulting in a state of low crystallinity (state with a disordered crystal structure/stable high resistance state; hereinafter,
This state is called an "amorphous state"). In this state, the reflectance is low (and the transmittance is high), so information has been 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 changes in the reflectance or transmittance of the irradiated area caused by changing between crystalline states by irradiating light pulses under two conditions with different powers and irradiation times. An optical recording medium having a thin film-like optical recording layer capable of recording, reproducing, erasing, and re-recording information, wherein the optical recording layer is made of an alloy of indium and bismuth; It has been found that the above-mentioned problems can be solved by an optical recording medium whose composition is 30-90% indium and 10-70% bismuth in atomic ratio.

In one preferred aspect, the optical recording layer of the present invention contains aluminum, silicon, phosphorus, sulfur, zinc, gallium, germanium, arsenic, selenium, silver, cadmium, and tin in an atomic ratio of 0 to 20% with respect to the entire alloy. , antimony, tellurium, thallium, and lead. When such metals are used as additives, as detailed below,
It is possible to prevent segregation of indium, which occurs when indium accounts for a large proportion, to increase contrast, and to increase sensitivity.

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 indium and bismuth, which are evaporation sources, separately or in the form of an alloy with a predetermined composition ratio. can be advantageously formed. In addition, when using indium-bismuth 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 the optical recording layer 2 is generally as follows:
Advantageously there are about 300 to 2000 people.

The optical recording layer 2 thus formed 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□, Al2O3, etc. Examples include metal nitrides. Usually, the thickness of the protective film 3 is preferably about 500 to 3000.

The optical recording medium of the present invention may 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 Sing, 5nOz, and the like.

The thickness of the film is several hundred at most.

〔Example〕

Example 1: A disk-shaped acrylic substrate (polymethyl methacrylate) with an outer diameter of 3001 mm and a thickness of 1.2 mm was prepared and thoroughly cleaned. This substrate was set in a vacuum deposition machine, and indium and bismuth were deposited from independent deposition sources. During this vacuum deposition, indium and bismuth were uniformly mixed by rotating the substrate, and the deposition rate was controlled to be constant. Although the ratio of indium and bismuth was varied as shown below, the thickness of the optical recording layer formed was 1200 mm in each case. Further, on this optical recording layer, polystyrene was applied as a protective film at 1,000 ml.
Spincoded by humans.

Example 2: 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 applied to a collimator lens and an objective lens. Irradiation was performed using an optical head focused to a beam diameter of 1 μm. 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. First, in order to write information, the bar is 7-7-2O and the pulse width is 20.
When the medium was irradiated with pulsed light of 0 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. An erasing pulse is added to this part, i.e., power 5mW, pulse width 500n.
When the pulsed light of s was irradiated, the structure of the irradiated part changed and the reflectance became low. Moreover, this reflectance changed reversibly, and the reflectance increased after laser irradiation with high power and short pulse width, and the fouling rate 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 indium and bismuth 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 bismuth in the alloy ranges from 5% to 70% in terms of atomic ratio. However, bismuth is 10
If it is less than %, the proportion of indium in the alloy will increase and segregation of indium will tend to occur, so this range is inappropriate for practical use.

Therefore, in the practice of the present invention, it is appropriate that bismuth be present in an atomic ratio of 10 to 70%.

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 substrate 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 area (the area that was 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.

(2) Main: In this example, the durability of the optical recording medium according to the present invention was tested.

The following three types of optical recording media were manufactured according to the method described in Example 1 above: Sample 1 (Control) Ino, 7B was placed on an acrylic substrate of the same shape as a slide glass.
io, 3 alloy (same for the other two samples) was deposited. This layer was not heat treated and was not coated with a protective film.

Sample 2 (invention) Ino, 7 old on an acrylic substrate of the same shape as the slide glass.

, 3 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 60 rpm, the medium was irradiated with a concentric beam of semiconductor laser light to record a 2 Mn2 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 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 change in reflectance over time, as shown by curve I in FIG. However, in contrast, Sample 2, which is an example of the medium of the present invention,
As shown by the curve ■ in the figure, very stable reflectance was exhibited. In fact, the reflectance of Sample 2 hardly changed even after three months. Further, the change in reflectance of the recorded portion of Sample 3 was 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. As is clear from this figure, even after 3 months, this sample still shows only 3 dB
It only showed the following decrease in C/N ratio.

Base: 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 Ino,
Bio, 3, and contained arsenic (As) in an atomic ratio of 5%, 10%, and 20%, respectively, based on the entire alloy. 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 indium was less likely to occur than when no arsenic was added, which helped stabilize the media. It turns out.

Furthermore, other metal additives, AI, Si
.

Zn, Ge, Ag, Sb, Se,
A similar effect can be obtained by adding Te.

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 Ino, 7Bio, 3, and 68(Sn).
5 in atomic ratio to the entire alloy.
%, 10% and 20% tin, respectively. Each of these media was evaluated for contrast between high reflectance and low reflectance areas and was found to increase contrast, particularly when containing 5% or 10% tin. The results are listed in the table below.

-$-μ (%) pn Trust (X) 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 in the high reflectance state. It is multiplied by 100.

Furthermore, other metal additives such as As and Cd may be used instead of Sn.
.

A similar effect could be obtained by adding TI and Pb.

Nawari Ichimoxibustion: In this example, an increase in sensitivity 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, in the case of this example, the composition of the optical recording layer of this medium is Ino, 7B+ O, 3, and gallium (
Ga) is not included or I5 is not included in the entire alloy.
) gallium was contained in an atomic ratio of 5%, 10%, and 20%, respectively. For each of these media, in terms of contrast between parts of the high reflectance state and parts of the low reflectance state,
However, when the irradiation power of high-power, short-pulse-width laser light was varied and evaluated, it was found that the contrast increased as gallium was added. The results are shown in Figure 5.

Furthermore, from the results shown in FIG. 5, it is obvious that the addition of gallium increases the sensitivity. In addition, in Fig. 5, curve a represents 0% Ca, curve a represents 5% Ga,
Curve C represents GalO%, and curve d represents Ga2O%.
Represent each.

Furthermore, other metal additives, p, and s may be used instead of Ga.

A similar effect could be obtained by adding 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 the drawing]

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 graph showing the relationship between irradiation power and contrast. In the figure, 1 is a substrate, 2 is an optical recording layer, and 3 is a protective film. Figure 1 Figure 2 Figure 5 Irradiation power (mW) Figure 3 Elapsed time (months) Figure 4 Elapsed time (months) Procedural amendment (voluntary) August 1985-1θ Commissioner of the Japan Patent Office U Ka Michibe 1, Indication of the case 1985 Patent Application No. 006670 2, Name of the invention Optical recording medium 3, Person making the amendment Relationship to the case Patent applicant name (522) Fujitsu Ltd. 4, Agent address 5-8-1o Toranomon-chome, Minato-ku, Tokyo 105,
Column 6 of “Detailed Description of the Invention” of the specification to be amended, content of amendment (1) Specification, page 3, lines 10-11, “[hereinafter, this state will be referred to as one crystal state”] has been changed to the so-called “ Correct to crystalline state "j". (2) In the specification, page 3, lines 15-16, ``Hereafter, this state will be referred to as the ``amorphous state'''' is referred to as ``the so-called ``amorphous state.''
Correct to.

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, characterized in that the optical recording layer is made of an alloy of indium and bismuth, and the composition of the alloy is 30 to 90% indium and 10 to 70% bismuth in atomic ratio. optical recording medium. 2. From the group consisting of aluminum, silicon, phosphorus, sulfur, zinc, gallium, germanium, arsenic, selenium, silver, cadmium, tin, antimony, tellurium, thallium, and lead in an atomic ratio of 0 to 20% based on the entire alloy. The optical recording layer further contains one or more selected metals.
An optical recording medium according to claim 1.