JP2538915B2 - How to record and erase information - Google Patents

Description

The present invention relates to a method for recording and erasing information, and more specifically,
The present invention relates to a method for recording and erasing information signals at high density and high speed by using laser lights having different powers.

2. Description of the Related Art A technique for recording and reproducing high-density information using a laser beam is known, and is now being put to practical use for document files, still image files, and the like.

Also, some recording materials have been proposed for rewritable recording media. These techniques mainly record and erase information by utilizing the state change between an amorphous state and a crystalline state in an alloy. That is,
Amorphous state is formed by high power laser light irradiation with short irradiation time, while a crystalline state is formed by low power laser light irradiation with long irradiation time. Information recording or recording is performed by the difference in optical constant between these two states. Erase is performed.

As a recording material utilizing such a state change, for example, a Ge-Te system ["Appl. Phys. Lett.", Vol. 49, p. 502 (1986)
Year)], Te-Ge-Sn-Au system ["SPIE"] 69th
Volume 5, page 79 (1986)] and the like are known.

However, in these alloys, since the crystallization time is long, in order to crystallize the amorphous state,
It is necessary to keep the recording medium at the temperature required for crystallization for a long time. In order to realize such a situation with a disc rotating at a constant speed, it is necessary to use an oval laser beam. Therefore, in such a case, it is necessary to use both the circular beam for amorphization and the elliptical beam for crystallization, which inevitably complicates the drive device, which is not preferable in practice.

On the other hand, if a recording material with a short crystallization time is used,
Since it can be crystallized by laser irradiation for a short time, it can be amorphized and crystallized with a normal circular beam. The amorphous state is obtained by heating the recording film to a melting point or higher and then rapidly cooling it, while crystallization may be performed by heating the recording film to a crystallization temperature (<melting point) or higher. Therefore, an amorphous state and a crystalline state can be obtained only by changing the intensity of one laser beam, so that so-called single-beam overwriting is possible, in which already recorded information is erased and simultaneously recorded.

As described above, as a recording material having a short crystallization time and capable of single beam overwriting, for example, an In-Se alloy [“Applied Physical Letters (Appl. Phys.
tt.) ”, Volume 50, Page 667 (1987)] is proposed. However, in this In-Se alloy, although the crystallization time was short, the sensitivity was not sufficient and there was a problem in practical use.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention overcomes the drawbacks of the conventional recording materials, uses a recording material having a short crystallization time and excellent sensitivity, and has a high density and high speed of an information signal. The purpose of the present invention is to provide a method of recording and erasing.

Means for Solving Problems So far, regarding the recording material using the Ge-Te alloy,
Although the composition range of Ge 50 mol% or less has been vigorously investigated, the crystallization time is long and the sensitivity is insufficient with such a composition.

The present inventors have conducted extensive studies on a recording material having a short crystallization time and excellent sensitivity, and for a binary alloy of Ge-Te to the light, if the composition of Ge is 50 mol% or more, the crystal is formed. It was found that the conversion time was extremely short, but this was difficult to form into amorphous form. Therefore, as a result of further research by the present inventors, it has been confirmed that at least Sb is contained in the binary alloy of Ge—Te and the ratio of the number of atoms of the three elements of Ge—Te and Sb is within a specific range. It was found that the added material has a short crystallization time, is reversible, and has good sensitivity, and therefore an information recording medium having a recording layer made of this material can meet the above purpose, The present invention has been completed based on this finding.

That is, the present invention is a method for recording and erasing information by changing the light reflectance of a recording layer made of a material whose optical constant is changed by heating provided on a substrate. In at least three elements of Sb, Te and Ge, and the ratio of the number of atoms of these three elements is A in the triangular coordinates with Sb, Te and Ge as vertices.
(Sb ₂₁ Te ₁₉ Ge ₆₀ ), B (Sb ₂₁ Te ₉ Ge ₇₀ ), C (Sb ₀ Te ₂₀ Ge ₆₀ ).
₈₀ ) and D (Sb ₀ Te ₄₀ Ge ₈₀ ), a recording layer having a composition within the range surrounded by four points (excluding the composition in which Sb is 0) is used, and the recording layer has a single power of different power. The present invention provides a method for recording and erasing information, which is characterized by irradiating a laser beam to perform crystallization and amorphization.

 Hereinafter, the present invention will be described in detail.

The recording layer in the information recording medium of the present invention is composed of at least three elements of Sb, Te and Ge, and the ratio of the number of atoms of these three elements is Sb, Te and Ge as shown in FIG. In the triangulated coordinates, A (Sb ₂₁ Te ₁₉ Ge ₆₀ ), B
(Sb ₂₁ Te ₉ Ge ₇₀ ), C (Sb ₀ Te ₂₀ Ge ₈₀ ), and D (Sb ₀ Te ₄₀ G
It is necessary to use a material having a composition within the range surrounded by the four points of (e ₈₀ ), that is, the composition of the shaded area surrounded by the four points of A, B, C and D in FIG. . Sb
Content of 21 mol% or less, preferably 15% or less.
When the amount of Sb is 0 mol%, that is, when the composition is only Ge-Te, the crystallization time is short, but it does not exhibit reversibility and is difficult to form into amorphous form, so that it is unsuitable as a recording material.
When it exceeds 21 mol%, the crystallization time becomes long and the effects of the present invention are not sufficiently exhibited. Further, the Ge content is in the range of 60 to 80 mol%, and if this amount exceeds 80 mol%, crystallization becomes extremely difficult.

From the above, it is considered that the effect of Sb has a function of hindering the crystallization of Ge—Te and promoting amorphization.

The recording material according to the present invention can be sufficiently used practically even if it is composed of only three elements of Sb, Te and Ge. However, if necessary, other elements may be added within a range not impairing the purpose of the present invention. Good.

To provide a recording layer made of these materials on the substrate, a method conventionally used for forming the recording layer, for example, a method such as vacuum deposition or sputtering is used. The composition can be controlled by a ternary co-evaporation method or the like in vacuum vapor deposition, and by using a target having a specific composition or by placing a chip on an alloy target in sputtering. The recording layer thus formed preferably has a film thickness in the range of 20 to 200 nm in order to obtain sufficient contrast.

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

FIG. 2 is a cross-sectional view showing an example of the configuration of the information recording medium of the present invention, showing a structure in which a recording layer 2 composed of at least three elements of Sb, Te and Ge is provided on a substrate 1. There is.

The method of the present invention has a short crystallization time of a specific composition,
Since the recording material having excellent sensitivity is used, it is possible to record and erase the information signal at a high density and at a high speed only by irradiating the recording material with a single laser beam having a different power.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

Example 1 A 100-nm-thick recording layer made of Sb-Te-Ge was formed on a 1.2 mm-thick polycarbonate substrate by a ternary co-evaporation method at a vacuum degree of 1.0 * 10 < ^-5 > Torr. That is, Ge and Te were skipped from a W boat by a resistance heating method and Sb was skipped by an electric beam evaporation method to form a recording layer having a composition of Sb ₁₀ Te ₂₄ Ge ₆₆ to prepare a sample.

On the other hand, by the same method, a thin film having a film thickness of 50 nm made of the composition Sb ₁₀ Te ₂₄ Ge ₆₆ was formed on a 1.2 mm-thick glass slide. A sample with a thin film formed on this slide glass was heat-treated in an oven in the temperature range of 50 ° C to 300 ° C for about 10 minutes, and the light transmittance at each temperature was measured at a wavelength of 830n.
It was measured in m. From the results, the temperature at which the transmittance decreased by 10% compared to the initial state (this is defined as the crystallization temperature) is about
It was 160 ° C.

A sample in which a thin film was formed on polycarbonate was irradiated with laser light in a stationary state, and then the change in reflectance was measured. FIG. 3 shows the configuration of the laser light irradiation device in a stationary state. The light emitted from the semiconductor laser 3 is collimated by the first lens 4 and then is collimated by the objective lens 7 through the second lens system, the prism 5 and the λ / 4 plate 6, and is condensed on the recording medium. Is irradiated. The reflected light follows a path opposite to the incident light, is bent by the prism 5, is condensed by the lens 8, and is detected by the photodetector 9. The results of crystallization and amorphous conversion of the sample using this device
Shown in the figure. As is clear from this figure, pulse width 0.2 μs
In ec, it was crystallized at 1.5 mW and amorphized at 5 mW, and the crystallization time was short and the sensitivity was high.

Reference Example A sample having the composition shown in Table 1 was formed in a thickness of 100 nm on a polycarbonate substrate in the same manner as in Example 1. Table 1 shows the pulse width required for crystallization when these samples were irradiated with a laser beam of 2 mW in a stationary state. In Table 1, the pulse widths required for crystallization are all as short as 1.5 μsec or less, and especially in the composition of Sb ₁₀ Te ₂₄ Ge ₆₆ and Sb ₃ Te ₂₅ G ₆₂ , it is 0.
The value was 2 μsec, which was a sufficient value for practical use.

Example 2 On a disc-shaped polycarbonate substrate having a diameter of 5 1/4 inch and a thickness of 1.2 mm and obtained by an injection molding method, Sb ₁₀ Te ₂₈ Ge ₆₂ was prepared in the same manner as in Example 1. Thickness of thin film with composition ratio of
It was formed to 100 nm. The substrate was rotated at 900 rpm, and light of a semiconductor laser (wavelength 830 nm) was emitted through the substrate for one rotation of the disk at an output of 4 mW to crystallize one track at a radius of about 30 mm. A 1 MHz signal was then recorded on this crystallized track. At this time, the laser power required for recording was 7 mW, and the power required to erase the signal was 4 mW, which was a sensitivity sufficient for practical use.

Example 3 On the same polycarbonate substrate as in Example 2, Sb ₁₃ Te
A thin film with a composition ratio of ₂₂ Ge ₆₅ was formed with a sputtering pressure of 1.0 × 10 ⁻³ Torr and a thickness of 100 nm by the RF sputtering method while rotating the substrate. This sample was evaluated in the same manner as in Example 2. The laser power required to record a 1 MHz signal at a position where the substrate rotation was 900 rpm and the radius was 30 mm was 8 mW, and the laser power required for erasing was 6.5 mW, which was a sufficient sensitivity.

Comparative Example In the same manner as in Example 1, Ge-Te having the composition shown in Table 2 was used.
A thin film with a thickness of 100 mm on a 1.2 mm thick polycarbonate substrate.
formed to nm.

On the other hand, a thin film having the same composition was formed in a thickness of 50 nm on a slide glass having a thickness of 1.2 mm. This sample is heat-treated for about 10 minutes in the temperature range from 50 ° C to 300 ° C,
The light transmittance at each temperature was measured at a wavelength of 830 nm to determine the crystallization temperature. Table 2 shows the results. As is clear from Table 2, the crystallization temperature rises as the amount of Ge increases.

Further, a sample in which a thin film was formed on polycarbonate was irradiated with laser light in a stationary state, and the laser power and pulse width required for crystallization were measured. Results are shown in FIG. As is clear from this figure, crystallization begins to occur even in a short time of 0.2 μsec or less. However, even in the stationary state, it was impossible to make amorphous form at 8 mW or less, which was not practical.

[Brief description of drawings]

FIG. 1 is a triangular coordinate diagram showing the composition range of the material used for the recording layer of the information recording medium in the method of the present invention, and FIG. 2 is a sectional view showing an example of the configuration of the information recording medium of the present invention.
FIG. 4 is a block diagram of an example of a laser light irradiation device for irradiating a laser beam on a recording medium in a stationary state, and FIG. 4 is an amorphous threshold for crystallization and a crystallization threshold of a recording layer in the embodiment in a stationary state. FIG. 5 is a graph showing the values, and FIG. 5 is a graph showing the crystallization threshold of the recording layer in the stationary state in the comparative example. In the formula, reference numeral 1 is a substrate, 2 is a recording layer, 3 is a semiconductor laser, 4 and 8 are lenses, 5 is a prism, 7 is an objective lens, and 9 is a photodetector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-2594 (JP, A) JP-A-61-89889 (JP, A) JP-A-62-73438 (JP, A) JP-A-62- 196181 (JP, A) JP 62-209742 (JP, A) JP 63-100632 (JP, A) JP 63-142542 (JP, A)

Claims (1)

(57) [Claims] 1. A method for recording and erasing information by changing the reflectance of light in a recording layer made of a material whose optical constant changes by heating provided on a substrate in response to a change in the optical constant. , At least three elements of Sb, Te, and Ge, and the atomic ratio of these three elements is Sb,
In triangular coordinates with Te and Ge as vertices, A (Sb ₂₁ Te ₁₉
Ge ₆₀ ), B (Sb ₂₁ Te ₉ Ge ₇₀ ), C (Sb ₀ Te ₂₀ Ge ₈₀ ), and D
(Sb ₀ Te ₄₀ Ge ₈₀ ) A recording layer having a composition within a range surrounded by four points (excluding a composition in which Sb is 0) is used,
A method for recording and erasing information, characterized in that the recording layer is irradiated with a single laser beam of different power to perform crystallization and amorphization.