JPH0355892B2 - - Google Patents

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. A type of optical recording medium that causes a change in optical properties and uses this change in optical properties to record, reproduce, erase, and re-record information.
For example, it relates to optical disks. 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]

Rewritable optical recording media, which have been widely used in the past, include a substrate made of, for example, glass or plastic material (for example, acrylic resin such as polymethyl methacrylate), and a material coated on the substrate by vapor deposition or the like. Te, Se, Ge, Sb, Sn,
It is composed of an optical recording layer made of a thin film of a metal such as S, a metalloid, or an alloy thereof, such as Ge ₁₅ Te ₈₁ S ₂ P _2. Also, in order to protect the optical recording layer from oxidation, it is made of, for example, SiO _{2 .} , a protective film made of a metal oxide such as Al ₂ O ₃ is provided 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 and heated to bring the optical recording layer into a highly crystalline state (a state in which crystals are regularly arranged/a stable low resistance state; the so-called "crystalline state"). , in order to write information, a short strong pulse of light is irradiated and the area is heated and rapidly cooled.Then, the crystallinity of the part irradiated with the pulsed light decreases, resulting in a state of low crystallinity (a state with a disordered crystal structure/a stable high resistance state). State; so-called “amorphous state”)
becomes. In this state, the reflectance is low (and the transmittance is high), and therefore information has been written. The information written in this way can then be erased by irradiating the information recording area with long weak pulsed light and slowly heating and 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, the optical recording layer undergoes phase transformation (from crystalline state to
Information can be written and erased using the reversible change in the amorphous state.

[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 demonstrated that the reflectance or transmittance of the irradiated area caused between crystalline states by irradiating light pulses under two conditions with different power and irradiation time is Recording information from changes,
An optical recording medium having a thin film-like optical recording layer capable of reproducing, erasing, and re-recording, wherein the optical recording layer is made of an alloy of gallium and antimony, and in this case, the composition of the alloy is atomic. It has been found that the above-mentioned problems can be solved by an optical recording medium having a ratio of 10 to 60% gallium and 40 to 90% antimony.

In one preferable aspect, the optical recording layer of the present invention has an atomic ratio of 0 to 20% based on the entire alloy.
It may further contain one or more metals selected from the group consisting of aluminum, silicon, phosphorus, sulfur, zinc, germanium, arsenic, selenium, indium, tin, tellurium, bismuth, and lead. The use of such metals as additives can prevent the segregation of gallium that occurs when gallium accounts for a large proportion, as detailed below.
Contrast can be increased or sensitivity can be increased.

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 arranging gallium and antimony, which are evaporation sources, separately or in the form of an alloy with a predetermined composition ratio, using a vacuum evaporation method, a sputtering method, etc. Therefore, it can be formed advantageously. Note that when using a gallium-antimony alloy as a vapor deposition source, care must be taken in advance that there will be a difference in composition between the vapor deposition source and the vapor deposited film. Advantageously, the thickness of this optical recording layer 2 is generally about 300 to 2000 Å.

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 ₂ and Al ₂ O ₃ , and in some cases metal nitrides. be able to. Normally, the thickness of the protective film 3 is preferably about 500 to 3000 Å.

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 substances forming these layers include SiO ₂ and SnO ₂ .
The film thickness is usually on the order of several 100 Å.

〔Example〕

Example 1 A disc-shaped acrylic substrate (polymethyl methacrylate) with an outer diameter of 300 mm and a thickness of 1.2 mm 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 Å in all cases. Furthermore, a protective film of polystyrene is applied on this optical recording layer to a thickness of
Spin coated at 1000 Å.

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, a semiconductor laser (wavelength
830 nm) was irradiated by an optical head that was focused to a beam diameter of 1 μm using a collimator lens and 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 a low power laser beam of ~0.2 mW. First, when a medium was irradiated with pulsed light with a power of 10 mW and a pulse width of 100 ns to write information, the irradiated area was heated and rapidly cooled, resulting in a change in the structure of the irradiated area, resulting in a high reflectance state. It became. When this portion was further irradiated with an erasing pulse, that is, pulsed light with a power of 5 mW and a pulse width of 500 ns, the structure of the irradiated portion 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 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 turned out that it was impossible to rewrite. Experiments have shown that the proportion of gallium in the alloy is 10 in terms of atomic ratio.
It was confirmed that a reversible change in reflectance can occur from % to 70%. However, gallium is 60
%, a striped pattern appears on the medium that is thought to be caused by segregation of gallium, which is not practical. Also,
In areas where gallium is less than 20%, the film bulges in the laser beam irradiation area, likely due to the formation of bubbles, making the level at which the reflectance changes unstable, which is still 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 crystalline 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 above: Sample 1 (control) On an acrylic substrate of the same shape as a slide glass.
A Ga ₆₅ Sb ₃₅ 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) On an acrylic substrate of the same shape as a slide glass
A Ga ₆₅ Sb ₃₅ 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 (present invention) While rotating the sample 2 at 600 rpm,
This medium was irradiated concentrically with a focused beam of semiconductor laser light to record a 2MHz signal. This sample was also not coated with a protective film.

Each of the above samples 1, 2, and 3 was held in an atmosphere with a temperature of 70°C and a relative humidity (RH) of 85%, and changes in reflectance over time and changes in C/N ratio (carrier to noise) were measured. did. 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, showed very stable reflectance with almost no change over time, as shown by the curve in FIG. In fact, the reflectance of sample 2 is 3
Even after several months, little had changed. 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. That is,
As is clear from the figure, this sample showed only a slight decrease in C/N ratio of 3 dB or less even after 3 months.

Example 4 In this example, the improvement in stability 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, the composition of the optical recording layer of this medium was Ga ₆₅ Sb ₃₅ , which contained selenium (Se) in an atomic ratio of 5%, 10%, and 15%, 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 gallium was less likely to occur than in the case without selenium addition, and it was useful for stabilization. I found out. actual,
Segregation could be prevented even with a composition rich in gallium. In FIG. 5, regions where gallium segregation does not occur are indicated by diagonal lines.

Furthermore, other metal additives such as Al, Si,
Similar effects could be obtained by adding Zn, Ge, and As.

Example 5 In this example, an increase in contrast when a metal additive was added to the optical recording layer of an 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 Ga ₆₅ Sb ₃₅ , and tin (Sn) is added to this.
Either no tin was contained or tin was contained in an atomic ratio of 5%, 10%, and 20%, respectively, based on the entire alloy. 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.

Sn (%) Contrast (%) 0 19 5 24 10 29 20 26 The contrast (%) in this table is the difference in reflectance between the high reflectance state and the low reflectance state with the reflectance of the high reflectance state. Divide and multiply this by 100.

Furthermore, other metal additives, As,
A similar effect 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 Ga ₆₅ Sb ₃₅ , and either it does not contain tellurium (Te) or it contains 5%, 10%, and 20% by atomic ratio of the entire alloy. % tellurium. When each of these media was evaluated with respect to the contrast between the high reflectance state and the low reflectance state, however, the irradiation power of high power, short pulse width laser light was changed, and it was found that as tellurium was added, It was found that the contrast was increased. 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%, and curve b represents Te 5%.
%, curve c is Te 10%, and curve d is Te
Each represents 20%.

Furthermore, other metal additives, In, P,
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 a region where Ga segregation does not occur in a Ga-Sb-Se ternary alloy film,
FIG. 6 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.

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 comprising: the optical recording layer made of an alloy of gallium and antimony, and
An optical recording medium characterized in that the composition of the alloy is 10 to 60% gallium and 40 to 90% antimony in atomic ratio. 2 0 to 20% in atomic ratio to the entire alloy,
A patent in which the optical recording layer further contains one or more metals selected from the group consisting of aluminum, silicon, phosphorus, sulfur, zinc, germanium, arsenic, selenium, indium, tin, tellurium, bismuth, and lead. An optical recording medium according to claim 1.