JPH0380635B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention is a novel information recording material, more specifically, an energy beam such as a laser beam is irradiated onto a recording layer provided on a predetermined substrate, and changes in the reflectance of the irradiated portion are utilized. The present invention relates to a medium for recording and reading information. BACKGROUND ART Conventionally proposed recordable information recording media include, for example, providing a predetermined recording layer on a substrate, irradiating it with laser light, and forming holes according to information.
A recording medium is known in which information is read out using the difference in reflectance depending on the presence or absence of holes. In this case, materials such as Te and Bi, which have low melting points, and alloys or compounds containing them are well known as the memory layer used. In addition, a recording layer has been proposed in which the optical properties are changed by laser light irradiation and the change in reflectance caused by this change in _optical properties is utilized. A system in which fine particles are dispersed (Japanese Unexamined Patent Publication No. 185048/1983),
Those with a two-layer structure such as Sb ₂ Se ₃ Bi ₂ Te ₃ (JP-A-59
-35988) and chalcogenide glass containing Te as a main component (Japanese Patent Publication No. 47-26897). However, in the above hole-forming method, in addition to heating, the formation of holes involves the process of melting, dispersion, or evaporation, so the viscosity at the time of melting and the surface tension at the time of dispersion have subtle effects. It is difficult to control the shape of the hole, and residues are generated inside the hole, resulting in increased noise and errors. On the other hand, the method that utilizes the change in optical properties caused by heating by laser beam irradiation does not require the process of melting, dispersing, or evaporating the recording layer, so it is easy to control the shape of the pits. Moreover, the problem of residue generation in the holes is also eliminated. However, conventional recording materials using this method have poor thermal stability, which is a practical disadvantage. By the way, the transmittance of the compound Sb ₂ Te ₃ changes greatly when heated, so its use as an information recording material has been considered, but it has a low temperature change and lacks thermal stability. Therefore, it was considered impossible to use it for practical purposes [J.Appl.
Phys.), Volume 54 (No. 3), Pages 1256-1260]. Problems to be Solved by the Invention In view of the above circumstances, an object of the present invention is to provide an information recording medium that is thermally stable and has a sensitivity S/
The object of the present invention is to provide a recording material that is superior to conventional recording materials in terms of N ratio and bit error rate. Means for Solving the Problems As a result of intensive research to achieve the above object, the present inventors have found that at least Sb, Te and Ge are present on the substrate.
By providing a recording layer consisting of three elements and having a ratio of these three elements within a specific range,
We have discovered that thermal stability can be significantly improved without changing the optical property change itself, which is a characteristic of the Sb-Te binary system, and based on this knowledge, we have completed the present invention. . That is, the present invention provides an information recording medium in which a recording layer made of a material whose light absorption coefficient changes when heated is provided on a substrate, and information is recorded by a change in light reflectance caused by the change in the absorption coefficient. , the recording layer is composed of at least three elements, Sb, Te, and Ge, and the atomic ratio of the three elements is expressed as a point (Sb _0.8 Te ₀ Ge _0.2 ) and point (Sb ₀ Te _0.8
Straight line A connecting point (Sb _0.7 Te _0.3 Ge ₀ ) and point (Sb ₀ Te ₀ Ge _1.0 ) Straight line B connecting point (Sb _0.7 Te 0.3 Ge 0 ) and point (Sb _{0.2 )}
Straight line c connecting point (Te ₀ Ge _0.8 ) and point (Sb _0.2 Te _0.8 Ge ₀ ), point (Sb _0.4 Te ₀ Ge _0.6 ) and point (Sb ₀ Te _0.4 Ge _0.6 )
Within the area surrounded by the straight line D connecting the and the straight line E connecting the point (Sb _0.4 Te _0.6 Ge ₀ ) and the point (Sb ₀ Te _0.5 Ge _0.5 ) [However, points on the lines C and E are not included. The present invention provides an information storage medium characterized by having the following composition. As a heating means at this time, irradiation with an energy beam such as a laser beam or an electron beam is suitable. When recording information by irradiation with an energy beam such as a laser beam or an electron beam, two types of recording can be performed depending on the heating temperature caused by the energy beam irradiation and the cooling rate after irradiation. That is, recording can be performed by changing the absorption coefficient from a small state to a large state, or by changing the absorption coefficient from a large state to a small state. The recording layer in the information recording medium of the present invention comprises a first
In the triangular coordinate graph shown in the figure with Sb, Te, and Ge as three vertices, it is necessary that the structure be within the shaded range. If the proportion of Sb is lower than this, the change in the absorption coefficient due to heating will be small, and not only will sufficient contrast not be obtained, but stability against temperature and humidity will decrease, and if the proportion is higher than this, the contrast will be extremely Therefore, the S/N ratio also becomes low. On the other hand, if the proportion of Ge is small, changes in the absorption coefficient due to heating will occur at low temperatures, resulting in a decrease in thermal stability.If the proportion of Ge is too large, the contrast will be extremely reduced and the S/N ratio will be low. Become. In the information recording medium of the present invention, it is practically sufficient to use a recording layer consisting of only the three elements of Sb, Te, and Ge, but other elements may be included if necessary. The recording layer in the present invention is formed by a vapor deposition method such as vacuum vapor deposition or sputtering. In the case of vacuum evaporation, it is preferable to control the composition by a ternary co-evaporation method, or by a flash evaporation method for deposits of a specific composition; It can also be performed by a vapor deposition method. In the case of sputtering, on the other hand, it is advantageous to use a target material of a specific composition or to place fragments of one element or alloy on top of a target material of another element or alloy. When forming a film by vacuum evaporation, the degree of vacuum is in the range of 10 ^-5 to 10 ^-6 Torr, and the deposition rate is 0.5
A range of ~20 Å/sec is preferable, and there is no particular restriction on the substrate temperature, so room temperature is preferable. On the other hand, when using the sputtering method, the substrate temperature is particularly likely to rise, so cooling is required. In general, when thin films are stacked on a substrate, the reflectance is uniquely determined by the refractive index, absorption coefficient, and thickness of the substrate and thin film. By determining the reflectance at each film thickness, the range of film thickness for increasing the change in reflectance before and after heating is automatically determined. On the other hand, when recording is actually performed by irradiation with laser light, etc., the absorption rate of the laser light and the state of heat dissipation vary depending on the thickness of the recording layer and reflective layer, so the recording sensitivity is affected. It comes differently. The preferred thickness range of the recording layer and reflective layer is mainly determined by the two factors mentioned above. When the above-described Sb-Te-Ge material is used as a recording layer in an information recording medium, the thickness of the recording layer is preferably 700 Å or more, preferably in the range of 800 to 2000 Å in order to obtain sufficient contrast. but,
If the film thickness is made too thick, it becomes difficult to uniformly cause physicochemical state changes in the film thickness direction to change the light absorption coefficient, making it difficult to obtain an S/N ratio that corresponds to the original high contrast. become unable to do so. On the other hand, when a reflective layer is provided above or below the recording layer, sufficient contrast can be obtained even in areas where the recording layer is thin, and as a result, a high S/N ratio can be obtained, which is advantageous. It is. When such a reflective layer is provided, the thickness of the recording layer depends on the material and thickness of the reflective layer, but is generally preferably in the range of 20 to 1000 Å. The material that can be used for the reflective layer is preferably a substance that has a high absorption coefficient for the information readout beam, such as Al, Ti, Cr, Co, Ni, Se, Ge, Zr, Ag,
Metals such as In, Sn, Sb, Te, Pt, Au, Pb, Bi,
Alternatively, alloys thereof can be mentioned. Among these, Sb, Te, Bi, or alloys thereof are particularly excellent in sensitivity. The reflective layer is
These elements or alloys may be used alone, or two or more elements or alloys may be stacked. The thickness of this reflective layer is preferably 100 Å or more, and particularly preferably in the range of 100 to 1000 Å from the viewpoint of sensitivity.
In the following, when describing a configuration in which a reflective layer is provided, both the recording layer and the reflective layer are collectively referred to as an information carrier layer. The reflective layer in the present invention, like the recording layer, can be formed using a vapor deposition method such as vacuum vapor deposition or sputtering. As the substrate in the present invention, glass, a photocurable resin on glass, a plastic substrate made of polycarbonate, acrylic resin, epoxy resin, polystyrene, etc., a metal plate made of aluminum alloy, etc. are used. 2 and 3 are cross-sectional views showing structural examples of the recording medium of the present invention, in which 1 is a substrate, 2 is a recording layer,
3 is a reflective layer. When the recording medium of the present invention is actually used as an information recording medium, two identical disks each having a recording material provided on a substrate are placed with the surfaces provided with the recording material facing each other with a spacer interposed therebetween. integrated with adhesive,
The so-called air sandwich structure, or the so-called full-surface adhesive structure, in which two identical discs are bonded together over the entire surface without a spacer, with the recording material facing each other. Alternatively, completely different from these, any structure may be used, such as a structure in which a recording material is provided on a film-like sheet and this sheet is wound into a roll. EXAMPLES Next, the present invention will be explained in further detail by reference examples and examples. In this embodiment, a case will be described in which recording is performed by changing the absorption coefficient from a small state to a large state, but the reverse case can be performed in the same manner. Reference Example 1 A film having the composition shown in Table 1 was deposited on a slide glass with a thickness of 300 Å by binary co-evaporation from two evaporation boats containing Sb and Te using a resistance heating method on a slide glass with a thickness of 1.2 mm. were formed respectively.

[Table] These samples were tested in the untreated state and at 200℃.
The light transmittance at a wavelength of 830 nm was measured after heat treatment was performed for about 10 minutes in an oven heated to .
FIG. 4 shows the rate of change in transmittance before and after this heat treatment. From FIG. 4, it can be seen that the change in transmittance due to heat is large in the range where the atomic percentage of Sb is 20% or more and 70% or less. When the Sb content is less than 20%, the transmittance increases with heating, but this was confirmed by X-ray diffraction analysis.
It was confirmed that this was due to the oxidation of Te. Reference Example 2 A film having the composition shown in Table 2 was formed on a slide glass with a thickness of 1.2 mm by ternary co-evaporation from three evaporation boats containing Sb, Te, and Ge using the resistance heating method. Each was formed to a thickness of 300 Å.
As a comparative example, an Sb ₂ Te ₃ alloy was deposited from one deposition boat to form a film with a thickness of 300 Å.

[Table] These samples were subjected to heat treatment for about 10 minutes at a temperature range of 50°C to 250°C, and the light transmittance at each temperature was measured at a wavelength of 830nm. The rate of change in transmittance is shown in FIG. From Figure 5, in the range where the number of Ge atoms is 60% or less, as the amount of Ge increases, the temperature at which the transmittance begins to change shifts to higher temperatures, but the change in transmittance at 250℃ The rate is largely independent of the amount of Ge;
A large change in transmittance has occurred. When we analyzed the changes in the optical properties of Sample D, we found that the refractive index and extinction coefficient before treatment were each 4.4.
The refractive index and extinction coefficient after heat treatment at 250°C were 4.2 and 4.0, respectively. Therefore, there is almost no change in the refractive index, but a large change in the extinction coefficient, that is, a large change in the absorption coefficient. These samples without heat treatment were left in a dryer at 80° C. for 7 days, and then the transmittance was measured. The change in transmittance after 7 days is shown in FIG. From FIG. 6, it can be seen that those containing 20% or more of Ge have almost no change in transmittance and are therefore very thermally stable. Reference Example 3 In the same manner as in Reference Example 1, Sb, Te, and
A Ge film was formed to a thickness of 300 Å with the composition shown in Table 3. x and y in Table 3 are equivalent values when the composition of the formed film is expressed by the formula (Sb _x Te _1-x ) _y Ge _1-y (x and y indicate the atomic ratio) It is.

[Table] These samples were tested in the untreated state and at 200℃.
The light transmittance at a wavelength of 830 nm was measured after heat treatment was performed for about 10 minutes in an oven heated to . The rate of change in transmittance before and after this heat treatment is calculated as
As shown in the figure. As is clear from Figure 7, in a system containing Ge,
Unlike a binary system containing only Sb and Te, the change in transmittance is large in all regions where x is 0.7 or less. These samples that were not heat-treated were left in a constant temperature and humidity chamber at 50°C and 90% RH for 10 days, and the transmittance was measured.The transmittance of samples A and G was initially In comparison, they increased by about 2 times and about 1.5 times, respectively. This increase in transmittance is presumed to be due to the oxidation of Te. On the other hand,
For samples other than A and G, almost no change in transmittance was observed. From the above, it can be seen that when the value of x is in the range of 0.05 to 0.7, the change in transmittance due to heating is large and the film is stable even in a high temperature and high humidity environment. Example 1 Grooves (700 Å deep,
Using a resistance heating method, it was placed on an acrylic substrate with a thickness of 1.5 mm and a diameter of 305 mm, with a width of 0.5 μm and a pitch of 1.6 μm.
A film with a composition ratio of Sb _0.25 Te _0.45 Ge _0.3 was formed to a thickness of 300 Å by ternary co-evaporation from three evaporation boats containing Sb, Te, and Ge, and then a film was deposited on top of it.
A 200 Å film of Al was also deposited using the resistance heating method. This recording medium is rotated at 900 rpm, and a semiconductor laser (wavelength 830 nm) is transmitted through the transparent substrate.
A 1.5MHz signal was written by concentrating the light and irradiating it. At this time, the laser power required to record a signal on a 140 mm diameter point on the disk was 7.0 mW on the recording film surface. Next, when the signal was regenerated at 1.2 mW using a semiconductor laser beam of the same wavelength, the C/N ratio of the signal was
It was 60dB. FIG. 8 shows the reflectance of this sample before and after heat treatment. FIG. 9 shows the reflectance of a sample similarly formed on a slide glass before and after heat treatment. 8th
Figure 9 and Figure 9 are calculation curves for the case where the Al reflective layer is 500 Å thick and the recording layer thickness is 300 Å, respectively, and the calculations were performed based on the refractive index and extinction coefficient obtained in Reference Example 2. be. Even when these samples were left in a dryer at 60° C. for 10 days, no change was observed in sensitivity, C/N ratio, or reflectance. Example 2 On an acrylic substrate similar to Example 1, 200 Å of Sb ₂ Te ₃ and 200 Å of Ge were deposited by binary co-evaporation from two evaporation boats containing Sb ₂ Te ₃ and Ge using a resistance heating method.
The equivalent of 100 Å was provided. Further, a 200 Å thick Sb film and a 200 Å thick Bi ₂ Te ₃ film were formed thereon by electron beam evaporation. In addition, as a comparative example, a 300 Å thick film was similarly placed on the substrate.
After forming a Sb ₂ Te ₃ film of 200 Å thick on top of it,
An Sb film was prepared. In terms of the composition ratio of the films formed in each sample, the Ge content was approximately 40%. These three recording media were evaluated in the same manner as in Example 1, except that the recorded signal was 3MHz, and the reflectance was
The one with Sb has a sensitivity of 5mW and the C/N ratio of 60dB, and the one with the reflective layer of Bi ₂ Te ₃ has a sensitivity of 3.5mW and a C/N ratio.
Obtained 57dB. In addition, the comparative example has a sensitivity of 4.5 mW,
A C/N ratio of 60 dB was obtained. When these recording media were left in a dryer at 60°C for 7 days, the sensitivity, C/N ratio,
There was no change in reflectance, but the initial reflectance of the recording medium of the comparative example changed from 25% to 40%.
The C/N ratio was significantly reduced to 20 dB. Example 3 Grooves (depth 700 Å, width
Sb ₂ Te ₃ was deposited on the substrate on which 0.6 μm, pitch 1.6 μm) was formed using a resistance heating method at a vacuum level of 2×10 ^-6 Torr.
A recording layer with a thickness of 600 Å was formed by co-evaporating two elements: Further, on top of this film, a 100 Å thick Al layer was provided using a similar resistance heating method. When evaluated in the same manner as in Example 1, the sensitivity
Obtained 6.5 mW and C/N ratio of 60 dB. This medium at 80℃
Sensitivity and C/N remain unchanged even after being left in a dryer for 10 days.
No change was observed in the ratio or reflectance. By the way, the reflectance at this time was 31%. Example 4 Grooves were prepared in advance by injection molding (depth
700Å, width 0.65μm, pitch 1.6μm) Sb ₂ Te ₃ and
Binary co-evaporation was carried out from two evaporation boats containing Ge to deposit Sb ₂ Te ₃ equivalent to 200 Å and Ge equivalent to 100 Å.
Furthermore, by using a similar resistance heating method,
Sb film formed with a thickness of 200 Å and Bi ₂ Te ₃
Each film was prepared with a thickness of 200 Å. As a comparative example, on a similar substrate,
A Sb ₂ Te ₃ film was formed to a thickness of 300 Å, and then an Sb film was formed to a thickness of 200 Å on top of the Sb 2 Te 3 film. In both samples, the composition ratio of the film is Sb:
The Te ratio was approximately 2:3, and the Ge content was approximately 40% for the two types to which Ge was added. The signal for recording these three recording media is 3MHz
When evaluated in the same manner as in Example 1 except that the reflection layer was Sb, the sensitivity was 5 mW,
The C/N ratio is 60dB and the reflection layer is Bi ₂ Te ₃ .
3.5 mW and C/N ratio of 57 dB were obtained. Moreover, the comparative example obtained a sensitivity of 4.5 mW and a C/N ratio of 60 dB. When these recording media were left in a dryer at 60°C for 7 days, the sensitivity, C/N ratio,
There was no change in reflectance, but in the recording medium of the comparative example, the reflectance changed from an initial value of 25% to 40%, and the C/N ratio significantly decreased to 20 dB. Example 5 On the same acrylic substrate as in Example 4, the three elements Sb, Te, and Ge were co-evaporated by a resistance heating method, and at the composition ratio (Sb _x Te _1-x ) _y Ge _1-y , x =
Two types of samples were prepared in which films of y=0.4, y=0.7, and 0.9 were formed with a thickness of 300 Å. For all of these two types of samples, Sb was further formed to a thickness of 200 Å on top of the Sb _x Te _1-x ) _y Ge _1-y . When each medium was evaluated in the same manner as in Example 4, the sensitivity and C/N ratio were (5.5 mW, 58 dB), (5 mW, 60 dB), (4.5 mW,
60dB). These disks at 60℃, 82%
When the signal was reproduced after 7 days of acceleration testing under RH conditions, the contrast decreased and the C/N ratio decreased in the medium with a y value of 0.9.
However, no change in the C/N ratio was observed for those with y of 0.5 and 0.7. Effects of the Invention According to the present invention, it is possible to provide a mutually reliable information recording medium that records information with high sensitivity and high S/N ratio, is extremely stable against temperature and humidity, and is highly reliable.

[Brief explanation of drawings]

FIG. 1 is a triangular coordinate graph showing the composition of the recording layer of the information recording medium of the present invention, FIGS. 2 and 3 are cross-sectional views showing different examples of the information recording medium of the present invention, and FIG. 4 is a reference example. 5 is a graph showing the transmittance change due to heating of Reference Example 2, FIG. 6 is a graph showing the thermal stability of Reference Example 2, and FIG. 7 is a graph showing the thermal stability of Reference Example 3. Graphs showing changes in transmittance, FIGS. 8 and 9, are for Example 1, respectively.
1 is a graph showing the reflectance of a sample, in which reference numeral 1 indicates a substrate, 2 indicates a recording layer, and 3 indicates a reflective layer.

Claims (1)

[Claims] 1. Information recording in which a recording layer made of a material whose light absorption coefficient changes when heated is provided on a substrate, and information is recorded by a change in light reflectance caused by the change in the absorption coefficient. In the medium, the recording layer is composed of at least three elements, Sb, Te, and Ge, and the atomic ratio of these three elements is such that the point (Sb _0.8
Straight line A connecting point (Te ₀ Ge _0.2 ) and point (Sb ₀ Te _0.8 Ge _0.2 ) Straight line B connecting point (Sb _0.7 Te _0.3 Ge ₀ ) and point (Sb ₀ Te ₀ Ge _1.0 ) Point (Sb _0.2 Te ₀ Ge _0.8 ) and point (Sb _0.2
Line c connecting point (Te _0.8 Ge ₀ ) and point (Sb _0.4 Te ₀ Ge _0.6 )
Within the area surrounded by the straight line D connecting the point (Sb ₀ Te _0.4 Ge _0.6 ) and the straight line E connecting the point (Sb _0.4 Te _0.6 Ge ₀ ) and the point (Sb ₀ Te _0.5 Ge _0.5 ) 1. An information recording medium characterized by having a composition which does not include points on the lines C and E.