Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
  • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
  • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
  • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
  • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
  • G11B7/2433—Metals or elements of Groups 13, 14, 15 or 16 of the Periodic Table, e.g. B, Si, Ge, As, Sb, Bi, Se or Te
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
  • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
  • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
  • G11B2007/24302—Metals or metalloids
  • G11B2007/24314—Metals or metalloids group 15 elements (e.g. Sb, Bi)
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
  • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
  • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
  • G11B2007/24302—Metals or metalloids
  • G11B2007/24316—Metals or metalloids group 16 elements (i.e. chalcogenides, Se, Te)

Definitions

• This invention relates to antimony- tellurium alloys that are useful in optical recording.
• Optical recording a technique utilizing a focused laser beam to make micron size marks in an appropriate medium for high density information recording, has been extensively studied in recent years. There are basically two types of optical recording; write-once and the erasable. In write-once recording, the media can only be recorded once, but the recorded information can be read many times. In erasable recording, the recorded information can be erased and new information can be recorded over the same area of the media.
• the technique most widely studied for erasable recording has been based on magneto-optic materials. This technique relies on the thermal-magnetic recording process. A focused laser beam is used to heat a spot on a magneto-optical material so that its coercivity is reduced and the magnetization within the spot can be switched by an applied field. The readout is accomplished by sensing the Kerr rotation of a reading laser beam induced by the magnetization in the media. Good recording performance has been reported by anv working in the field. However, all reports are based on rare-earth/transition metal alloys, notably TbFeCo, and these alloys have some fundamental problems . First of all, these materials are corrosion prone.
• An alternative technique for erasable recording uses amorphous-crystalline phase-change materials.
• a focused laser beam is used to switch the material between the amorphous state and the crystalline state.
• a high power laser is used to heat a spot on the material to above its melting point to randomize the atomic arrangement in the material.
• the laser beam is switched off, the material is left in the metastable amorphous state because of the high cooling rate.
• a low power laser in many cases of longer duration, is then used to heat the material to below the melting point.
• the increased mobility of the atoms at the elevated temperature then allows the material to go to the more stable crystalline state
• the material can be switched between the amorphous state and the crystalline state, and erasable recording is thus accomplished.
• EP-A1-0-212-336 describes a method of erasable recording using single-phase phase-change alloys. Whereas the crystallization rate of the preferred material, GeTe) g5 Sn 15 , appeared to be high (erasure time ⁇ 55 ns) , the laser power required for write and erase was also high (18 W and 10 mW, respectively). While there was no mention of the corrosion resistance of the material, it contains a high concentration of corrosion prone tellurium.
• compositions of Yagi et al The problem with the compositions of Yagi et al is that the time required for erasure are longer than desired and that the environmental stability of the composition is less than desired.
• present invention is directed to a solution to these problems. Disclosure of the Invention
• an optical recording element comprising a thin film optical recording layer of an alloy, said alloy represented by the formula Sb Te , , wherein x is between about 0.58 and 0.75.
• x is between about 0.65 and 0.73.
• Figure 1 is a plot of the erasure time versus alloy composition for several alloys useful in the invention.
• the alloy that is useful in the present invention is similar to the Sb Te, allov of
• the alloys useful in the invention have fast write-erase rates, improved sensitivity, thermal stability, and corrosion resistance.
• Sb Te Sb Te
• the recordin g layer i s preferably initialized.
• the layer that is depos i ted by vacuum deposition is amorphous
• the layer can be crystallized by h eat i ng, for example in an oven or by other conventional means such as with a laser or a hie h power flash lamp.
• Optical recording layers can be prepared bv conventional thin film deposition techniques such as RF ( rad i o frequency) and DC (direct current ) sputtering from an alloy target usin * the allo y s of the i nvention. Enhancement of sputtering processes by applying magnetic fields (magnetron sputtering can also be used.
• RF rad i o frequency
• DC direct current
• Supports which can be used include plastic plates, such as polyethylene terephthalate polymethyl methacrylate, and polycarbonate,' a glass Plate, paper and metallic plates such as aluminum. Erasable recording is achieved by varying the power of the laser pulses.
• a high power, short duration (e.g., 100 ns, 12 mW) pulse changes the material to a low reflectivity amorphous state and a low power long duration (e.g., 100 ns , 6 mW ) pulse changes the material to a high reflectivity crystalline state.
• a method of recording and erasing information on an optical recording element comprising a thin film optical recording layer of an alloy in a crystalline form, said alloy represented by the formula Sb Te wherein x is between about 0.58 and 0.75 X si ⁇ d'method comprising the steps of: a ) recording said information by focusing an information modulated laser beam on said crystalline alloy recording layer at a power and for a time sufficient to form a pattern of amorphous areas in said layer of alloy, said pattern corresponding to said information, and b ) focusing a laser beam on said recorded layer for a time and at a power sufficient to crystallize at least a portion of the amorphous areas formed in step a), thereby erasing the information in the amorphous areas.
• a useful recording material comprises, starting from the outside surface of the recording material, an overcoat layer, a thin film optical recording layer as described and a substrate.
• ⁇ n response to a drive signal, the intensity of a diode recording beam focused on the recording layer is modulated in accordance with information to be recorded.
• the recording material is spun at a constant rate, e.g., 1800 rotations per minute ( rpm ) .
• a track of information is recorded on the optical recording layer in the form of selected amorphized areas.
• the recording spot is caused to scan radially inward across the recording material thereby causing information to be recorded along a spiral or concentric track.
• the sizes and spacings of the recorded information marks vary in accordance with the information content of the recording laser drive signal, as well as with radial position on the recording material.
• the thus recorded information bearing recording material is spun at the same rate as it was spun during the recording process.
• the optical path of a readout laser beam is focused to a playback spot on the recording material by a high numerical aperture lens.
• the recording material is of the reflective type so that the radiation forming the playback spot is reflected back through the high numerical aperture lens after interacting with the information marks recorded on the optical recording material.
• a lens directs reflected laser radiation onto a detector which produces an electrical playback signal in response to temporal variations (contrast) in the irradiance of the reflected laser radiation falling on the detector.
• a reflective substrate such as aluminum can be provided with a recording layer comprising an alloy of the invention on both sides of the substrate.
• a useful recording material is thus aluminum coated on both sides with a smoothing layer a layer of the phase change alloy of the invention and a layer of a clear protective overcoat, in a similar embodiment, the alloy is provided on a clear substrate which is then adhered to both sides of the substrate with an adhesive.
• the alloy as described is provided on a transparent substrate to form the recording layer. The optical recording layer is then adhered to the recording layer of an identical recording material with an adhesive layer. The thickness of the adhesive layer provides for the optical separation of the two recording layers.
• Example 1 The following examples are presented for a further understanding of the invention.
• Example 1 The following examples are presented for a further understanding of the invention.
• a range of Sb x Te ⁇ _ x compositions 0.58 ⁇ x ⁇ 0.75, were investigated.
• the deposited alloys were overcoated with a clear acrylic spray paint. Some areas of the as—deposited amorphous films were initially irradiated by laser pulses at 30 ⁇ s, 2 mW. The irradiated spots were therefore crystallized. The center of the crystallized spots were followed by laser irradiation at 50 ns , 12 W in order for them to be re—amorphorized.
• the alloys were then subjected to a variety of conditions to recrystallize designated areas. The areas were subjected to a laser pulse irradiation (power ⁇ 12 mW).
• the shortest required pulse lengths (erasure time) to erase several compositions are shown in Fig. 1.
• the erasure time of the present alloy is generally less than 1 ⁇ s.
• Example 2 The above amorphous films with laser crystallized spots were kept in a humidity chamber at 70 ⁇ C and 70% relative humidity for 3 weeks. No corrosion or crystal growth was observed. This test shows that these films are thermally and environmentally stable.
• Example 2
• Example 3 We also investigated the compositional dependence of erasure time for thermally crystallized films. The method was the same as in Example 1, except that the first laser crystallization step was not needed. The results were similar to those in Example 1.
• Example 3 The results were similar to those in Example 1.
• phase transformation kinetics (PTK) diagrams were constructed for a number of compositions according to the method of Chen et al Appl. Phys. Lett. 46, 734 (1985).
• Amorphous Sb 70 Te 30 thermally crystallized Sb 7Q Te 30 , amorphous Sb 72 Te 2g , and amorphous Sb ⁇ Te- were tested.
• the amorphized region, for as-deposited film, was determined by firstly laser crystallizing ( 30 ⁇ s, 2 mW) some spots and then re-amorphizing them at proper laser power-pulse duration combinations .
• the amorphized region, for thermally pre-crystallized film, was determined by laser amorphizing some spots with proper laser power-pulse duration combinations.
• the crystallized region, for as-deposited film, was determined by laser crystallization (30 ⁇ s, 2 mW) followed by re-amorphization (50 ns , 12 mW), and then re-crystallizing them at proper power-pulse duration combinations.
• the crystallized region for thermally pre-crystallized film, was determined by laser crystallizing the laser-amorphized spots with proper power—pulse duration combinations.
• the present invention provides optical recording elements which are erasable.

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)
• Optical Record Carriers And Manufacture Thereof (AREA)

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• 1989
  • 1989-12-06 CA CA002004708A patent/CA2004708A1/en not_active Abandoned
  • 1989-12-07 EP EP90901285A patent/EP0406378A1/de not_active Withdrawn
  • 1989-12-07 WO PCT/US1989/005435 patent/WO1990007181A1/en not_active Application Discontinuation
  • 1989-12-07 KR KR1019900701789A patent/KR910700522A/ko not_active Application Discontinuation
  • 1989-12-07 JP JP2501363A patent/JPH03502787A/ja active Pending

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