JPH0725208B2 - Information recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel information recording material, more specifically, a recording layer provided on a predetermined substrate is irradiated with an energy beam such as a laser beam to expose an irradiated portion. The present invention relates to a medium for recording and reading information by utilizing a change in reflectance.

2. Description of the Related Art Conventionally, as a recordable information recording medium, for example, a predetermined recording layer is provided on a substrate, a laser beam is irradiated to form a hole corresponding to information, and a difference in reflectance depending on the presence or absence of this hole. There is known a recording medium for reading out information by utilizing.

In this case, Te or Bi having a low melting point and an alloy or compound containing them are often used as the recording layer.

Further, a recording layer has also been proposed which changes the optical characteristics by irradiating a laser beam and utilizes the change in reflectance caused by the change in the optical characteristics. As such a recording layer, for example, Te particles in TeO ₂ are used. Dispersed system (Japanese Patent Laid-Open No. 59-18
No. 5048), a two-layer structure such as Sb ₂ Se ₃ \ Bi ₂ Te ₃ (Japanese Patent Laid-Open No. 59-35988), and a chalcogenite glass containing Te as a main component (Japanese Patent Publication No. 47-26897). Gazette) is known.

However, in the above-mentioned perforation method, since the process of melting, dispersion, or evaporation in addition to heating is involved in forming the holes, the viscosity at the time of melting and the surface tension at the time of dispersion have a delicate influence. However, there is a drawback that it is difficult to control the shape of the hole, and a residue is generated inside the hole to increase noise and errors.

On the other hand, in the method of utilizing the change in optical characteristics caused by heating by laser light irradiation, the process of melting, dispersing or evaporating the recording layer is not required, so that the shape of the bit can be easily controlled, and The problem of residue generation in the holes also disappears. However, the conventional recording material using this method has poor thermal stability, which has been a practical obstacle.

By the way, the compound Sb ₂ Te ₃ has been considered to be used as an information recording material because the transmittance greatly changes by heating, but since the temperature change is low and it lacks thermal stability, It was considered impossible to use for practical purposes ("Journal of Applied Physics (J.
Appl.Phys) ", Volume 54 (No.3), pages 1256-1260].

SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to provide an information recording medium that utilizes a change in optical characteristics due to laser irradiation.
It is to provide a recording material that is thermally stable and is superior to conventional recording materials in terms of sensitivity, S / N ratio and bit error rate.

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the inventors have found that at least three elements of Sb, Te and Ge are present on the substrate, and the ratio of these three elements is at least three. It was found that by providing a recording layer in a specific range, the thermal stability can be significantly improved without substantially changing the change itself in the optical characteristics that are a characteristic of the Sb-Te binary system. The present invention has been completed based on the above.

That is, the present invention provides an information recording medium in which a recording layer made of a material whose light absorption coefficient changes by heating 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 at least S
A recording layer made of a material, which is composed of three elements b, Te and Ge, and whose light absorption coefficient is changed by heating, is provided on the substrate, and information is recorded by a change of light reflectance caused by the change of the absorption coefficient. In the information recording medium, the recording layer consists of at least three elements of Sb, Te and Ge, and
In the triangular coordinate graph with the apexes of each of these elements, the atomic ratio of the elements is the straight line (a) connecting the point (Sb _0.8 Te ₀ Ge _0.2 ) and the point (Sb ₀ Te _0.8 Ge _0.2 ), and the point (Sb A straight line (b) connecting _0.4 Te ₀ Ge _0.6 ) and a point (Sb ₀ Te _0.4 Ge _0.6 ), and a straight line (c) connecting a point (Sb _0.2 Te ₀ Ge _0.8 ) and a point (Sb _0.2 Te _0.8 Ge ₀ ). , Within a region surrounded by a straight line (d) connecting the point (Sb ₀ Te ₀ Ge _1.0 ) and the point (Sb _0.05 Te _0.95 Ge ₀ ), where the straight line (a) (b) (c) (d) is included , A line (e) connecting the point (Sb _0.4 Te _0.6 Ge ₀ ) and the point (Sb ₀ Te _0.5 Ge _0.5 ), and a point (Sb ₀ Te _0.5 Ge _0.5 ) and the point (Sb _1.0 Te ₀ Ge ₀ ). Except for the straight line (f)].

FIG. 1 shows the composition range of the present invention, including 3 of Sb, Te and Ge.
3 is a triangular coordinate graph having elements as vertices, and the present invention has a composition range excluding the points on the straight lines (e) and (e) in the range indicated by diagonal lines.

As a heating means at this time, irradiation with an energy beam such as an electron beam of laser light is suitable. When information is recorded by irradiation with an energy beam such as a laser beam or an electron beam, two kinds of recording can be performed depending on the heating temperature by irradiation with the energy beam and the cooling rate after irradiation. That is, recording can be performed by changing from a state with a small absorption coefficient to a state with a large absorption coefficient, or by changing from a state with a large absorption coefficient to a state with a small absorption coefficient.

The recording layer in the information recording medium of the present invention is at least S
It consists of three elements, b, Te, and Ge, and their composition ratio is such that when expressed by the general formula (SbxTe _1- x) yGe _1- x, x is 0.
05-0.7, preferably 0.1-0.6, y is 0.4-0.8, preferably 0.5-0.7, and Te and Ge are equal, and Ge _1- xSb ₂ xTe _{1 + 2} x (0 <x < 1.0) is excluded. If the value of x is less than 0.05, the change in the absorption coefficient due to heating is small, sufficient contrast cannot be obtained, and the stability against temperature and humidity is low, and if it exceeds 0.7, the contrast becomes extremely low. The / N ratio will also be low. On the other hand, if the value of y exceeds 0.8, the change of the absorption coefficient due to heating will occur at low temperature, and the thermal stability will decrease, and if it is less than 0.4, the contrast will decrease significantly and the S / N method will also decrease. . If sensitivity is important,
The value of x is preferably in the range of 0.1 to 0.35.

Furthermore, from a practical point of view, it may occur that the information reading beam is continuously applied to the same location for a long time,
During such a long-time reproduction, heat due to the read beam is accumulated, and due to the heat, the unrecorded part gradually approaches the same state as the recorded part, and as a result, the amplitude of the reproduced signal decreases, and the S / N ratio and elastomer are reduced. Tend to decline gradually. Therefore, in order to balance the sensitivity and the S / N ratio in consideration of such stability for long-term reproduction, the value of x is set to 0.15 to 0.4 and the value of y is set to the range of 0.5 to 0.7. It is most preferable for practical use.

In addition, the amount of Sb is 20 atom% based on the total amount of Sb, Te, and Ge.
It is the following.

In the information recording material of the present invention, Sb as a recording layer,
It is practically sufficient to use only the elements consisting of the three elements Te and Ge, but other elements can be contained if necessary.

The (SbxTe _1- x) yGe _1- y recording layer is formed by a vapor deposition method such as vacuum vapor deposition or sputtering. To control the composition, in the case of vacuum vapor deposition, it is preferable to perform the ternary co-evaporation method or the flash vapor deposition method of the deposit of a specific composition, and depending on the desired composition, the binary co-evaporation method. You can also

On the other hand, in the case of sputtering, it is advantageous to use a target material having a specific composition or to place fragments of another element or alloy on a target material of one element or alloy.

When the film is formed by the vacuum evaporation method, the degree of vacuum is 10
^It is preferably in the range of ^-5 to 10 ^-6 Torr and the vapor deposition rate is in the range of 0.5 to 20 Å / sec. The substrate temperature is not particularly limited, so room temperature is desirable. In the case of one method or the sputtering method, the substrate temperature is likely to rise, so that it is necessary to cool the substrate.

In general, the reflectance when a thin film is laminated on a substrate is uniquely determined by the refractive index, the absorption coefficient and the thickness of the substrate and the thin film. By determining the reflectance at 1, the range of the film thickness for increasing the reflectance change before and after heating is naturally determined. On the other hand, when recording is actually performed by irradiation with laser light or the like, the absorptivity of the laser light and the heat dissipation state differ depending on the film thickness of the recording layer and the reflection layer, and therefore the recording sensitivity also differs. The preferable film thickness range of the recording layer and the reflective layer is mainly determined by the above two factors.

When (SbxTe _1- x) yGe _1- y is used as a recording layer in an information recording medium, this recording layer may be a single layer, but in that case, in order to obtain sufficient contrast, the thickness of the recording layer should be 700 Å or more. , Preferably in the range of 800 to 2000Å. However, if the film thickness is made too thick, it becomes difficult to uniformly cause a physicochemical state change for changing the light absorption coefficient in the film thickness direction, which corresponds to the original high contrast.
It becomes impossible to obtain the S / N ratio. On the other hand, when the reflective layer is provided above or below the recording layer, sufficient contrast can be obtained even in a region where the film thickness of the recording layer is thin, and as a result, a high S / N ratio can be obtained, which is advantageous. Is. When such a reflective layer is provided, the film thickness of the recording layer depends on the material and film thickness of the reflective layer, but in general, the range of 20 to 1000Å is preferable.

As a material that can be used for the reflective layer, a substance having a high absorption coefficient for an information reading beam is preferable, and examples of such a material include Al, Ti, Cr, Co, Ni, and S.
Examples thereof include metals such as e, Ge, Zr, Ag, In, Sn, Sb, Te, Pt, Au, Pb and Bi, or alloys thereof. Among these, Sb, Te and Bi, or alloys thereof, are particularly excellent in sensitivity. The reflective layer may be a single element or an alloy of these elements, or may be a laminate of two or more elements or alloys. The film thickness of this reflective layer is preferably 100Å or more,
Particularly, from the viewpoint of sensitivity, it is preferably in the range of 100 to 1000Å. In the following description, when the structure provided with the reflective layer is described, both the recording layer and the reflective layer are collectively referred to as an information carrier layer.

Like the recording layer, the reflective layer in the present invention can be formed by a vapor deposition method such as vacuum vapor deposition or sputtering.

As the substrate in the present invention, glass, a substrate provided with a photocurable resin on glass, a plastic substrate such as polycarbonate, acrylic resin, epoxy resin, polystyrene, or a metal plate such as an aluminum alloy is used.

1 and 2 are sectional views showing a structural example of the recording medium of the present invention, in which 1 is a substrate, 2 is a recording layer, and 3 is a reflective layer.

When the recording medium of the present invention is actually used as an information recording medium, two identical discs each having a recording layer provided on a substrate are placed with a spacer in between with the recording material-provided surfaces facing each other. In this state, the so-called air sandwich structure or two identical discs, which are adhered and integrated together, are adhered and integrated over the entire surface without the spacers, with the surfaces provided with the recording materials facing each other. It may have any structure such as a full-surface adhesive structure, or a structure different from those, in which a recording material is provided on a film-like sheet and the sheet is rolled. In addition, in the embodiment, the case where recording is performed by changing from a state with a small absorption coefficient to a state with a large absorption coefficient has been described, but the reverse case can be similarly performed.

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 On a glass slide having a thickness of 1.2 mm, by the resistance heating method, S
From three vapor deposition boats containing b, Te and Ge, a film having a composition shown in Table 1 was formed to a thickness of 300 Å by ternary co-evaporation. As a comparative example, Sb ₂ Te ₃ alloy was vapor-deposited from one vapor deposition boat to form a film having a thickness of 300 Å.

These samples were subjected to heat treatment for about 10 minutes in the temperature range of 50 ° C. to 250 ° C., and the light transmittance at each temperature was measured at a wavelength of 830 nm. The rate of change of this transmittance is shown in FIG.

Analysis of changes in the optical characteristics of Samples A and B revealed that
It was found that the extinction coefficient, that is, the absorption coefficient changed largely before and after the heat treatment.

Those samples that have not been heat-treated at 80 ° C
After being left for 7 days in the drier, the transmittance was measured.
The change in transmittance after 7 days is shown in FIG.

As shown in Fig. 4, the transmissivity greatly changes in the example containing no Ge, whereas the transmissivity hardly changes in the example containing 20 atomic% or more of Ge, and therefore is very thermally stable. I understand.

Example 2 In the same manner as in Example 1, a Sb, Te and Ge film having a composition shown in Table 2 and a thickness of 300 Å was formed on a 1.2 mm-thick glass slide by a ternary co-evaporation method. Let X and y in Table 2 represent the composition of the formed film by the formula (SbxTe _1- x) yGe _1- y
(X and y are atomic ratios) are the corresponding values.

The light transmittance at a wavelength of 830 nm was measured for these samples in an untreated state and a state in which they were heat-treated in an oven heated to 200 ° C. for about 10 minutes. The rate of change in transmittance before and after heating is shown in FIG. As is clear from this figure, the change in transmittance is large in all the samples.

50 of these samples without heat treatment
After leaving it in a constant temperature and humidity chamber at 90 ° C and 90% RH for 10 days, the transmittance was measured.
Compared to the initial period, they increased by about 2 times and about 1.5 times, respectively. It is speculated that this increase in transmittance is due to the oxidation of Te. On the other hand, almost no change in transmittance was observed in the samples other than A and D.

From the above, it can be seen that in the region where the value of x is 0.05 or more, the change in transmittance due to heating is large and the stability is high even in a high temperature and high humidity environment.

Example 3 On a slide glass having a thickness of 1.2 mm, by resistance heating, S
_Films with composition ratios of Sb _0.12 Te _0.48 Ge _0.4 were formed with three compositional vapor deposition boats containing b, Te, and Ge to 200 Å, 350 Å, and 600 Å, respectively, and further resistance heating was performed on them. An Sb film having a thickness of 1000 Å was formed by the method.

The reflectance of these samples from the side of the slide glass at a wavelength of 830 nm was measured in an untreated state and a state where the sample was heat-treated in an oven heated to 200 ° C. for about 10 minutes. The reflectance before and after this heat treatment is shown in FIG. The solid line in the figure is before heating, and the broken line is after heating (same below). From FIG. 6, it can be seen that when Sb is used for the reflective layer, the contrast is highest when the film thickness of the recording layer is around 350 Å.

Next, on a disk-shaped acrylic substrate obtained by an injection molding method with a diameter of 305 mm and a thickness of 1.5 mm and a slide glass of 1.2 mm, a film having a composition ratio of Sb _0.12 Te _0.48 Ge _0.4 by a ternary co-evaporation method. Was formed to a thickness of 350 Å, and then Sb was formed thereon to a resistance of 200 Å and 500 Å, respectively. Similarly, with respect to the sample formed on the slide glass, the reflectance before and after the heat treatment measured from the slide glass side is shown in FIG. The calculation curves in Fig. 6 and Fig. 7 show the refractive index (4.4) and extinction coefficient (1.6) before heat treatment.
And calculated based on the refractive index (4.2) and extinction coefficient (4.0) after heat treatment. The sample with the film formed on the acrylic substrate was rotated at 900 rpm, and the light of the semiconductor laser (wavelength 830 nm) was focused and irradiated through the transparent substrate, and the area of 140 mm in diameter on the disk was 1.5 MHz. I wrote the signal. The signal was reproduced with a semiconductor laser beam of the same wavelength and 1.2 mW. Signal C / N ratio has a bandwidth of 30
Measured in KHz. At this time, the laser power required to record a signal at a location with a diameter of 140 mm on the disk was 4 mW and 5.5 mW on the recording mirror surface, respectively, and the C / N ratio was 60 dB and 58 dB, which is practically sufficient sensitivity. And C / N ratio. But Sb
However, the 500 Å had less sensitivity than the 200 Å due to the large heat dissipation, and had a slightly lower C / N ratio. Even if these samples were left in a dryer at 60 ° C for 10 days, no change was observed in the sensitivity, C / N ratio and reflectance.

Example 4 A hardened glass disk having a thickness of 1.5 mm and a diameter of 305 mm was preliminarily formed with a groove (depth 700 Å, width 0.6 μm) using a photocurable resin.
m, pitch 1.6 μm) on the substrate formed by resistance heating method, from the three vapor deposition boats containing Sb, Te and Ge by ternary co-evaporation, a film with a composition ratio of Sb _0.15 Te _0.35 Ge _0.5 , The film was formed to a thickness of 400 Å, and a 300 Å Bi film was further formed thereon by the same resistance heating method.

Evaluation was made in the same manner as in Example 3 except that the signal recorded on this recording medium was set to 3 MHz, and the sensitivity was 6 mW and the C / N ratio was
I got 58 dB.

Even if it is left in a dryer at 80 ° C for 10 days, the sensitivity and C / N
No change was observed in the ratio and reflectance.

Example 5 A groove (depth 700Å, width 0.5 μm) was previously prepared by injection molding.
m, pitch 1.6 μm) and a composition ratio (SbxTe _1- x) yGe ₁ by co-evaporating three elements of Sb, Te and Ge on an acrylic substrate with a thickness of 1.5 mm and a diameter of 305 mm by a resistance heating method. _- and a film of y is formed in a thickness of 300 Å. Here, y = 0.6, and the value of x is
Three kinds of samples were prepared as 0.1, 0.2 and 0.3. For all three samples, (SbxTe _1- x) yGe
An Sb film having a thickness of 200Å was further formed on the _1- y film.

When each medium was evaluated by the same method as in Example 4, the sensitivity C / N ratio was (3.5 mW, 60 dB), (4 m
W, 6 dB), (4.5 mW, 60 dB) was obtained. These disks were subjected to an accelerated test for 7 days under the conditions of 60 ° C. and 82% RH, and then the signals were reproduced. No change in C / N ratio was observed in any of the samples.

Example 6 Pre-grooved by injection molding (depth 700Å,
Width 0.65 μm, pitch 1.6 μm) and thickness 1.5 mm on an acrylic substrate, Sb ₂ Te ₃ and Ge targets were used to simultaneously sputter by the high frequency sputtering method to obtain a composition.
A 500 Å-thick recording layer of Sb ₂₀ Te ₃₅ Ge ₄₅ was provided, and a 100 Å Sb film was further provided thereon by a resistance heating method. A semiconductor laser beam (wavelength: 830 nm) was collected and irradiated through the substrate of this medium, and a signal of 1.5 MHz was recorded at a substrate rotation speed of 600 rpm. The laser power required for recording is 5 m on the recording surface.
It was W.

A 1.2 mW semiconductor laser beam was used to reproduce the signal, and C / N
A ratio of 58 dB was obtained. This medium was subjected to an acceleration test for 7 days under the conditions of 60 ° C. and 80% RH, but no change was observed in the sensitivity and the C / N ratio.

Example 7 On the same acrylic substrate as in Example 6, three elements of Sb, Te and Ge were co-deposited by a resistance heating method, and the composition ratio (SbxT
e ₁₋ x) yGe ₁₋ y, a film with x = 0.4 and y = 0.5 was formed with a thickness of 300 Å. Then add another Sb film on this 200 Å
Was formed. The sensitivity of this product was 5.5 mW, and the C / N ratio was 58 dB. These discs were subjected to an acceleration test for 7 days under the conditions of 60 ° C. and 82% RH, and when the signals were reproduced, no change in C / N ratio was observed.

EFFECTS OF THE INVENTION According to the present invention, an information recording medium with high sensitivity and high C / N ratio, which is extremely stable against temperature and humidity and has high reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a triangular coordinate graph showing the elemental composition of the recording layer of the present invention, FIGS. 2 and 3 are sectional views showing a structural example of the information recording medium of the present invention, and FIG. 4 is an embodiment of the present invention. 5 is a graph showing changes in transmittance due to heating, FIG. 5 is a graph showing changes in transmittance over time in Examples of the present invention, FIG. 6 is graphs showing changes in transmittance in Examples of the present invention, and FIGS. FIG. 9 is a graph showing the relationship between the change in reflectance due to heating and the film thickness in the example of the present invention. In the figure, 1 is a substrate, 2 is a recording layer, and 3 is a reflective layer.

Claims (1)

[Claims] 1. An information recording medium in which a recording layer made of a material whose light absorption coefficient is changed by heating is provided on a substrate, and information is recorded by a change of light reflectance caused by the change of the absorption coefficient. Recording layer is at least Sb, Te and Ge
Of the three elements, and the atomic ratio of these three elements is
In a triangular coordinate graph with these elements as vertices, a straight line (a) connecting the point (Sb _0.8 Te ₀ Ge _0.2 ) and the point (Sb ₀ Te _0.8 Ge _0.2 ) and the point (Sb _0.4 Te ₀ Ge _0.6 ) Straight line (b) connecting point (Sb ₀ Te _0.4 Ge _0.6 ), line (c) connecting point (Sb _0.2 Te ₀ Ge _0.8 ) and point (Sb _0.2 Te _0.8 Ge ₀ ), point (Sb ₀ Te ₀ Ge _1.0 ) and a point (Sb _0.05 Te _0.95 Ge ₀ ) within a region surrounded by a straight line (d) [however, the lines (a), (b), (c), and (d) are included, but the point (Sb _0.4 Te _0.6 Except for the straight line (e) connecting Ge ₀ ) and the point (Sb ₀ Te _0.5 Ge _0.5 ), and the straight line (f) connecting the point (Sb ₀ Te _0.5 Ge _0.5 ) and the point (Sb _1.0 Te ₀ Ge ₀ )] An information recording medium having the following composition.