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
  • G11B7/26—Apparatus or processes specially adapted for the manufacture of record carriers
• • 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
  • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
  • G11B7/257—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers
  • G11B7/2578—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials
• • 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
  • G11B7/2403—Layers; Shape, structure or physical properties thereof
  • G11B7/24056—Light transmission layers lying on the light entrance side and being thinner than the substrate, e.g. specially adapted for Blu-ray® discs
  • G11B7/24059—Light transmission layers lying on the light entrance side and being thinner than the substrate, e.g. specially adapted for Blu-ray® discs specially adapted for near-field recording or reproduction
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/21—Circular sheet or circular blank

Definitions

• the invention relates to an optical storage medium comprising a mask layer with a super resolution near field structure and to a method for manufacturing of a respective optical storage medium.
• Storage media of this kind may be used for example for storage and recording of data as used with consumer electronic appliances.
• Optical storage media with a super resolution near field structure offer the possibility to increase the data density of the optical recording medium by a factor of three in one dimension as compared with regular optical recording media. This is possible by a so-called super RENS structure, which is placed above a data layer of the optical recording medium, and which significantly reduces the effective size of a light spot used for reading from and/or writing to the optical storage medium.
• the super resolution layer corresponds also, in a simplified picture, with a mask layer, because it is placed above the data layer and only the high intensity center part of a laser beam can penetrate the Super-RENS layer.
• other types of Super-RENS layers are known where the reflectivity in the center point of the laser beam is increased.
• the Super-RENS layers at present under development for future optical storage media have the drawback that a high laser power is needed to heat the mask layer and the respective surrounding protection layers.
• an optical disc comprising a Super-RENS mask layer
• a Super-RENS mask layer comprising a semiconductor film which can have a contamination or a matrix material mixed into the semiconductor which is not more than 20 at %.
• the Super-RENS detection is based on an increase of the transmittance of the mask layer, which the transmittance being increased by absorption saturation of the semiconductor layer upon radiation with an incident laser beam.
• the mask layer may include impurities, which allows to shift the energy gap such that efficient absorption is obtained for a certain wavelength.
• An embodiment is described for which a GaP layer can be utilized as a Super-RENS layer when doping the GaP layer with Be, which provides an acceptor level, or Te, which provides a donor level.
• a comparatively high laser power is required, for example 1,3 mW when using a pulsed laser source.
• the optical storage medium according to the invention uses a mask layer as a super resolution near field structure, which comprises a doped semiconductor material.
• the semiconductor material is in particular n- doped such that the reflectivity of the semiconductor material is increased, for providing a high reflectivity factor when irradiated with a laser beam, in accordance with the Drude model of free electrons in solids.
• an indium alloy and as a doping material selenium or tellurium can be used.
• Measured data show that a reflectivity change of typically about a factor of 2 can be obtained with increasing laser power, when using a selenium or tellurium doped semiconductor mask layer.
• Other doped semiconductor materials may even provide higher reflectivity changes.
• a sputtering method for depositing the doped semiconductor as a mask layer can be used, wherein the doped semiconductor material is in a preferred InSb and the dopant is included already in the semiconductor sputtering target.
• the optical storage medium is in particular an optical storage disc comprising a super resolution near field structure (Super-RENS) as a mask layer.
• Super-RENS super resolution near field structure
• Such a mask layer can be easily manufactured, when using a doped semiconductor material, and by using a suitable donation, a lower laser power seems to be possible for writing and reading of data in comparison with other Super-RENS storage media.
• Fig. 1 a calculated reflectivity factor as a function of the free carrier concentration for an InSb layer
• Fig. 2 a calculation of the absorption coefficient in dependency of the free carrier concentration for an InSb layer
• Fig. 3 calculation of the reflectivity of an n-doped semiconductor in dependency of the laser power and the doping concentration of the semiconductor
• Fig. 4 a simplified cross section of an optical storage medium comprising a doped semiconductor layer as a mask layer
• Fig. 5 reflectivity measurements as a function of the laser power for doped semiconductor mask layers with different tellurium concentrations
• Fig. 6 reflectivity measurements as a function of the laser power for doped semiconductor mask layers with different selenium concentrations.
• the reflectivity R of a thin semiconductor layer is a function of the free carrier concentration and the thickness.
• the free carrier concentration can be calculated by using the Drude model of free electrons in solids.
• the absorption coefficient ⁇ is much higher and because the free carrier generation N 0 is correspondingly also higher, the reflectivity of the semiconductor layer is enhanced therefore.
• the free carrier concentration can be enhanced in particular by laser absorption from an initial intrinsic carrier concentration N to a concentration N' when irradiated. This is shown in figure 3, where the reflectivity R is plotted as a function of the laser power for several doping concentrations.
• the semiconductor material is in particular n-doped for increasing the number of free electrons representing the free carrier concentration N.
• N free carrier concentration
• the laser power for reading data from the optical storage medium can be adjusted such that only for a small center part of the laser beam a high reflectivity is obtained, hence having a low reflectivity of the outer parts of the laser beam.
• This has the effect, that only the center beam interacts with the data layer by means of the super resolution near-field effect, which allows therefore to reduce the readout spot size considerably below the diffraction limit of the applied laser beam. It is therefore expected that already a laser power below 1 mW is sufficient for reading a Super-RENS optical storage medium at a moderate linear speed.
• the laser power and therefore the heat dissipation of the optical storage medium can be considerably reduced. This is in particular the case because the Super-RENS effect is provided by a change of the reflectivity of the mask layer for the inner laser beam part with regard to the outer laser beam, and not by heating effects of the mask layer, as necessary for prior art Super-RENS optical storage media.
• a simplified structure of a respective optical recording medium is shown in a cross section in figure 4.
• Data information with marks and spaces is embossed as a pit structure into a plastic substrate 1.
• a Super-RENS layer as a mask layer 2 is arranged, comprising for example an indium-antimonide alloy, InSb, semiconductor, which is n-doped.
• a first protective layer 3 and above the mask layer 2 a second protective layer 4 may be arranged comprising the material: ZnS:SiO2.
• a cover layer 5 is arranged above the protection layer 4 arranged.
• the indium-antimonide layer 2 for example selenium, SE, or tellurium, Te
• InSb instead of InSb also other Indium-alloy semiconductor materials, for example InN, InP, InAs, or InSb, being doped respectively, can be used.
• Advantageous are in particular materials of the III-V semiconductor family having a bandgap of below 1 eV, which is the case in particular for InAs (0,354 eV) , InSb (0,17 eV) and GaSb (0,726 eV) .
• the low bandgap provides a high free carrier concentration and therefore a high reflectivity factor when irradiated with a laser beam, as explained before.
• An optical storage medium as shown in figure 4 can be manufactured by the following steps: In case of a read only data disc, a ROM disc, a pit structure is embossed or molded into the plastic substrate 1. Then the layers 3, 2 and 4 are deposited on the layer 1 as a multilayer by sputtering the materials ZnS:SiO2, n-doped InSb, and again ZnS:SiO2. In a following step the cover layer 5 is applied for the optical storage medium.
• the doping material can be included already into the semiconductor sputtering target, for example an InSb sputtering target. The doping concentration selected for the sputtering target can be transmitted then easily to the mask layer 2.
• the laser power is adjusted such, that only the center part of the laser beam has an intensity, which is sufficient to increase the reflectivity of the mask layer 2 substantially. Then only the increased number of carriers according to the center beam generate a near field interaction with the marks and spaces of the track of the data layer 1, which is arranged closely to the mask layer 2. The near field interaction is strongly dependant on the pit and land structure of the substrate 1 below the mask layer 2. The reflectivity of the center part of the laser beam is therefore modulated by the pit structure of the corresponding track.
• the Super-RENS effect of the mask layer 2 is based on a change of the reflectivity of the doped semiconductor material, no substantial heating of the mask layer 2 is necessary, respectively takes place.
• This has the advantage, that the lifetime of the disk and also of the laser is increased, and that the power consumption of a respective optical data reader or data recorder can be decreased accordingly.
• the generation of free carriers providing the high reflectivity of the semiconductor material can be substantially increased.

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Manufacturing Optical Record Carriers (AREA)
• Optical Record Carriers And Manufacture Thereof (AREA)
• Optical Recording Or Reproduction (AREA)

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• 2006
  • 2006-10-13 EP EP06122288A patent/EP1912216A1/en not_active Withdrawn
• 2007
  • 2007-10-11 CN CN2007800381181A patent/CN101523492B/zh not_active Expired - Fee Related
  • 2007-10-11 JP JP2009531852A patent/JP5202533B2/ja not_active Expired - Fee Related
  • 2007-10-11 US US12/311,716 patent/US8067079B2/en not_active Expired - Fee Related
  • 2007-10-11 KR KR1020097006650A patent/KR101413211B1/ko not_active Expired - Fee Related
  • 2007-10-11 AT AT07821221T patent/ATE500589T1/de not_active IP Right Cessation
  • 2007-10-11 DE DE602007012926T patent/DE602007012926D1/de active Active
  • 2007-10-11 WO PCT/EP2007/060854 patent/WO2008043824A1/en not_active Ceased
  • 2007-10-11 EP EP07821221A patent/EP2084706B1/en not_active Not-in-force

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