RU2127915C1 - Information medium for optical storage device - Google Patents

Abstract

FIELD: computer engineering. SUBSTANCE: device has substrate and recording medium. Substrate is made from transparent material, which is covered with sequence of reflecting and protection layers. Reflecting layer is made from aluminum; recording medium from alloy of tellurium, arsenic and selenium. Composition content is the following, %: tellurium, 10-35; arsenic, 2-15; selenium, 50-88. EFFECT: increased reliability of information storage, increased contrast of writing. 2 dwg

Description

 The present invention relates to techniques for recording and reproducing information by optical radiation and is intended for use in optical memory devices for single recording and multiple reading of information by infrared lasers.

 Known information carrier for optical recording, consisting of a substrate and a recording medium made of an alloy of tellurium, arsenic, germanium and selenium with the following ratio of components, at.%: Te 50-88, As 10-25, Ge 0-10, Se 0 -40 (1). Information is recorded by local destruction of the material of the recording medium by laser radiation from the side of the recording layer. The device has the following disadvantage: low reliability of information recording due to contamination by the vaporized substance of the recording layer and laser optics.

A prototype of the present invention is a carrier for optical recording by infrared lasers, consisting of a substrate made of a transparent material and a recording medium, with a reflective and protective layer successively applied to it (2). Sb ₂ Se _{3 was} chosen as the material of the recording medium, and Bi ₂ Te _{3 was the} reflective layer. When recording information in the device according to the prototype, the material of the recording medium passes from the amorphous state to the crystalline state, which leads to an increase in the reflection coefficient from 10 to 40%. To ensure reliable operation of the laser tracking mechanism for marking in a transparent disk substrate and high recording contrast, the highest possible reflection coefficient (more than 60%) is required, and the prototype device provides an information carrier reflection coefficient of not more than 40%. The relatively high temperature of the phase transition of the recording medium 160 ^o C requires an increase in laser power when recording information.

 Thus, the main disadvantage of the device of the prototype is the relatively small reflection coefficient.

 Another disadvantage of the prototype device is the higher phase transition temperature of the material of the recording medium, which requires increased laser power when recording.

 In connection with the indicated technical and technological results of using the device according to the prototype, there is a problem of creating an information storage medium of an optical storage device intended for use in information storage systems with write-once and multiple reads, in particular in household ones, and having an increased reflection coefficient, lower softening temperature recording environment and increased reliability of information storage.

 The problem is solved by the author as follows. In a known storage medium of an optical storage device, consisting of a substrate made of a transparent material, and a recording medium, with a reflective layer and a protective layer successively applied to it, the reflective layer is made of aluminum, and the recording medium is made of an alloy of tellurium, arsenic and selenium with the following the composition of the components: tellurium 10-35 at. %, arsenic 2-15 at.%, selenium 50-88 at.%.

 The technical result from the application of the proposed device is to increase the reliability of information storage while maintaining its sensitivity.

 The main technical advantage of the present invention compared to the prototype is the increase in reflectance due to the presence of a reflective layer with a high reflectance. This increases the contrast of the recording information.

 The invention is illustrated by the drawings of FIG. 1 and FIG. 2, in which: FIG. 1 is a table of compositions of the recording medium, on the basis of which information carriers for recording by infrared lasers can be prepared, FIG. 2 - storage medium of an optical storage device.

 In FIG. Figure 1 shows the compositions of a recording medium with a low glass transition temperature, on the basis of which information carriers can be prepared for recording by infrared lasers. The recording medium should have a relatively small absorption coefficient to increase the reflection coefficient of the information carrier. To maintain the sensitivity of the information carrier, the softening temperature of the recording medium should be relatively low. Information is recorded by the method of local photothermal destruction of the recording medium. The combination of low absorption and low softening temperature allows for the recording of information on the proposed information carrier. An increase in tellurium content in excess of the specified range leads to an increase in the crystallization ability of the recording medium and the rapid aging of the information carrier and its degradation over several months. A decrease in tellurium content reduces the absorption coefficient of the medium and makes it weakly sensitive to radiation by a semiconductor laser. An increase in the content of arsenic increases the glass transition temperature of the recording medium, which complicates the formation of a unit of information. Information is recorded by the method of local photothermal destruction of the recording medium. A decrease in arsenic leads to an increase in the crystallization ability of the recording medium. The content of arsenic and tellurium is optimal and provides a high resistance of the medium to aging and degradation, on the one hand, and the ability to record information by near-infrared semiconductor lasers, on the other.

 In FIG. 2 shows the layered structure of the storage medium. The information carrier consists of a substrate (1) made of a transparent material, a recording medium (2), a reflective layer of aluminum (3) and a protective layer (4). The laser beam (5) passes through a fission prism (6), the transparent substrate (1), which records the medium (2), is reflected from the reflective layer (3), passes in the opposite direction, and enters the radiation registration device (7). When recording information, a laser with a higher power is used, which causes an increase in optical density due to photothermal destruction of the recording medium. The laser power when reading is insufficient to change the optical density of the recording layer. Due to the difference in the magnitude of the reflected signal in the recorded and unrecorded areas, the information of the proposed information medium is recorded. The application of a reflective layer allows to increase the reflection coefficient of the information carrier. In addition, the isolation of the recording medium between the substrate and the reflective layer significantly reduces the crystallization ability of the recording medium, which increases the reliability of information storage. The material of the reflective layer must have a high reflectance and be chemically passive with respect to the recording medium. Aluminum fully meets these requirements. The protective layer protects the storage medium from external influences. A protective layer of a UV curable polymer is preferred.

Example. The storage medium of the optical storage device is made as follows. For the synthesis of the alloy of the recording medium, 3.39 g of tellurium, 0.50 g of arsenic and 6.11 g of selenium are taken. A sample is placed in a quartz glass ampoule, the ampoule is evacuated and soldered. The mixture is heated to 600 ^o C and incubated for 3 hours with stirring of the melt. The melt is cooled in air. An alloy of the composition Te ₂₄ Se ₇₀ As ₆ is applied to a polycarbonate substrate with a thickness of 1.2 mm and a diameter of 120 mm by thermal ion sputtering with a layer with a thickness of 120 nm. A 60 nm thick reflective layer of aluminum is applied from the side of the recording medium by cathodic sputtering. A protective layer with a thickness of 10-20 μm from a photocurable polymer is applied to aluminum by centrifugation in air followed by hardening under the influence of ultraviolet radiation.

The reflection coefficient of the information carrier is 71%, the absorption coefficient of the recording medium is 19% at a wavelength of 790 nm. The carrier is operable at a temperature of from -20 to 40 ^o C; withstands temperatures of 50 ^o C for a long time (10 to 20 days) without deterioration, temperature 30 ^o C at a relative humidity of 95% for 10 days.

The recording layer has a thickness of 50-300 nm. At a thickness less than 50 nm, the energy sensitivity decreases due to the small absorption of optical radiation in the recording layer. With a thickness greater than 300 nm, the resolution decreases. Glass, polycarbonate, polymethyl methacrylate with a thickness of 0.6-2 mm can be used as the material of the information substrate carrier. For applying the material of the recording medium, methods of high-frequency magnetron and thermionic sputtering using special form evaporators can be used. The deposition rate of 0.5-5 nm / s, the pressure of the residual gases in the chamber 10 ^-5 mm RT.article

 Aluminum is deposited by cathodic sputtering in vacuum with a thickness of 40-80 nm. As the material of the protective layer, photo-curing polymers based on epoxy acrylates are used. The protective layer is applied by centrifugation in air with a thickness of 10-20 microns, followed by hardening under the influence of ultraviolet radiation.

Sources of information;
1. French patent N 2363857, cl. G 11 B 7/00, 1978.

 2. French Patent N 2536197 A, CL G 11 B 7/24, 05/18/84.

Claims (1)

An information storage medium of an optical storage device consisting of a substrate made of a transparent material and a recording medium with successively applied reflective and protective layers, characterized in that the reflective layer is made of aluminum, and the recording medium is made of an alloy of tellurium, arsenic and selenium with the following composition of components, ab.%:
Tellurium - 10 - 35
Arsenic - 2 - 15
Selenium - 50 - 88

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