WO2001078068A2 - Support d'information optique - Google Patents

Support d'information optique Download PDF

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Publication number
WO2001078068A2
WO2001078068A2 PCT/US2001/011359 US0111359W WO0178068A2 WO 2001078068 A2 WO2001078068 A2 WO 2001078068A2 US 0111359 W US0111359 W US 0111359W WO 0178068 A2 WO0178068 A2 WO 0178068A2
Authority
WO
WIPO (PCT)
Prior art keywords
layer
servo
data
recording
medium
Prior art date
Application number
PCT/US2001/011359
Other languages
English (en)
Other versions
WO2001078068A3 (fr
Inventor
Toshiki Aoi
Tokuyuki Honda
Mark E. Mcdonald
Michael V. Morelli
Andrew J. Daiber
Sanjoy Ghose
Lambertus Hesselink
Shunichi Nishimura
Sergei Sochava
Original Assignee
Siros Technologies, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/549,075 external-priority patent/US6574174B1/en
Application filed by Siros Technologies, Inc. filed Critical Siros Technologies, Inc.
Priority to AU2001256991A priority Critical patent/AU2001256991A1/en
Priority to EP01930455A priority patent/EP1281175A4/fr
Publication of WO2001078068A2 publication Critical patent/WO2001078068A2/fr
Publication of WO2001078068A3 publication Critical patent/WO2001078068A3/fr

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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
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
    • 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
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0938—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following servo format, e.g. guide tracks, pilot signals
    • 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
    • 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
    • G11B7/244—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 organic materials only
    • 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
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0009—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage
    • G11B2007/0013—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage for carriers having multiple discrete 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
    • G11B7/007—Arrangement of the information on the record carrier, e.g. form of tracks, actual track shape, e.g. wobbled, or cross-section, e.g. v-shaped; Sequential information structures, e.g. sectoring or header formats within a track
    • 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
    • G11B7/252—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
    • G11B7/253—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 substrates
    • G11B7/2533—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 substrates comprising resins
    • G11B7/2534—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 substrates comprising resins polycarbonates [PC]
    • 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
    • G11B7/258—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 reflective layers
    • G11B7/2595—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 reflective layers based on gold

Definitions

  • This invention relates to a multi-layer information medium which has at least two data layers such as recording layer.
  • DVD Digital Versatile Disk
  • the DVD has a storage capacity of about 4.7 GB per single side which is about 7 times larger than the compact disk. Technologies enabling further increase in the amount of information recorded are under active development.
  • JP-A 255374/1996 discloses a medium wherein a rewritable information storage layer and a read only information storage layer are laminated.
  • the optical pickup In the reading of a multi -layer recording medium including a plurality of recording layers by using an optical pickup which irradiates a reading beam, the optical pickup receives the beam reflected from the recording layer on which the reading beam had focused, and in addition, the beam reflected from the recording layer(s) other than the recording layer to which the reading beam had focused.
  • noise is introduced in the read out signal.
  • the influence of the beam reflected from the recording layer other than the target recording layer reduces inversely with the square of the distance between the recording layers. Therefore, increase in the distance between the adjacent recording layers is effective in reducing the noise induced.
  • the recording layers are disposed at a mutual distance of at least 30 m, and preferably at least 70 m to realize the signal quality of practically acceptable level.
  • the transparent resin layer provided between the recording layers is also associated with a difficulty.
  • formation of a transparent resin layer with a consistent thickness is difficult in spite of various attempts in forming the transparent resin layer by spin coating, resin sheet disposition and the like when the transparent resin layer formed is as thick as, for example, 30 m or more, and in particular, 70 m or more.
  • the thick resin layer also suffers from increased internal stress and the medium is subject to warping. As a consequence, reliable provision with the optical disk of the required mechanical precision has been difficult.
  • the shape of the grooves (guide grooves) formed in the resin substrate will be transferred to the recording layer.
  • formation of the grooves in the transparent resin layer by photopolymerization (2P) process will be required as described, for example, in the JP-A 198709/1997 and eminent increase in the production cost is invited.
  • An object of the present invention is to realize a highly accurate tracking servo with no increase in the production cost in a multi-layer information medium wherein a plurality of data layers such as recording layers are disposed. Another object of the present invention is to suppress the cross talk associated with the decrease in the distance between the data layers. SUMMARY OF THE INVENTION Such objects are attained by the present invention.
  • the invention comprises, in general terms, an optical information medium comprising at least two data layers for bearing recorded information, and a servo layer for bearing tracking servo information which is independently formed from the data layers; wherein the medium is used with a recording or reading system wherein a data beam for recording or reading the data in the data layer and a servo beam for reading the tracking servo information in the servo layer are used, and the servo layer is read by the servo beam that had passed through the data layer; and a filter layer is disposed between the data layer and the servo layer, and the filter layer exhibits higher absorption to the data beam than to the servo beam.
  • the filter layer exhibits an abso ⁇ tion of at least 80% to said data beam and an abso ⁇ tion of up to 20% to said servo beam.
  • the filter layer may comprise a resin layer formed by UN curing a composition containing a UN-curable composition and a photoinitiator.
  • the filter layer may contain a dye.
  • the optical information medium typically comprises at least two data layers for bearing recorded information, and a servo layer for bearing tracking servo information which is independently formed from said data layers, wherein the medium is used with a recording or reading system wherein a data beam for recording or reading the data in the data layer and a servo beam for reading the tracking servo information in the servo layer are used, and the servo layer is read by the servo beam that had passed through the data layer, and the servo layer exhibits lower reflectivity to the data beam than to servo beam.
  • the servo layer may comprise a metal or a semimetal.
  • the data layer may be a flat layer, and the servo layer may be a layer formed with surface projections and depressions for bearing the tracking servo information.
  • the data layer may be readable by using a confocal optical system.
  • the data layers are separately formed from the servo layer, and there is no need to form the tracking servo pattern on each data layer. Therefore, the data layer can be formed as a smooth layer, and highly accurate tracking servo is enabled with no increase in the production cost of the medium. Formation of the smooth data layer also results in the merits as described above.
  • a filter layer is disposed between the data layer and the servo layer, and adverse effects on the tracking servo induced by the data beam reflected from the servo layer is thereby avoided.
  • FIG. 1 is a partial cross-sectional view showing an embodiment of the optical information medium according to the present invention.
  • FIG. 2 is a view showing an embodiment of the optical pickup used for recording and reading of the optical information medium according to the present invention.
  • a "data layer” is the layer wherein record marks and pits carrying the recorded information are present
  • a servo layer is the layer formed with a tracking servo pattern comprising projections and depressions such as grooves and pits.
  • the term “information-bearing layer” may be used to designate both the data layer and the servo layer.
  • the "optical information medium” of the present invention includes both an optical recording medium and a read only medium.
  • the data layer of an optical recording medium at least includes a recording layer. In the case of a read only medium, data-bearing pits or record marks are preliminarily formed in the data layer.
  • the beam used in the reading of the data layer and the recording of the data layer is designated “data beam” and the beam used in the reading of the servo layer is designated “servo beam”.
  • the "recording/reading beam” of the present invention is a concept including the data beam and the servo beam.
  • the "multi-layer information medium" of the present invention is a medium comprising a plurality of information -bearing layers, and wherein the recording or the reading of an information-bearing layer is conducted by the recording/reading beam which has passed through other information-bearing layer(s).
  • a filter layer FL On the transparent layer TL-5 is formed a filter layer FL, a servo layer SL, and a servo substrate 20 in this order.
  • the servo substrate 20 is formed with a tracking servo pattern comprising grooves and/or pits, and on the surface on the side of the recording/reading beam incidence of this servo substrate 20 is formed a reflective layer which functions as the servo layer SL.
  • the data layers and the servo layer are independently formed in the present invention because of the difficulty in forming the tracking servo pattern on each of the two or more data layers, and in particular, on each of the three or more data layers at a high accuracy.
  • a servo layer SL is formed independently from the data layer, there will be no need to form the tracking servo pattern on the data layers, and formation of the data layers as a smooth layer will be enabled. Then, the production cost will be reduced since there is no need to provide the tracking servo pattern on each of the multiple data layers by 2P (photopolymerization) process as described above.
  • the data layer formed is a smooth layer
  • the data layer DL will exhibit an increased reflectivity, and no interference will be induced by the steps of the tracking servo pattern. Generation of the noise due to irregularity such as deformation of the tracking servo pattern such as winding of the groove will also be avoided.
  • the servo layer SL is read with or addressed by the servo beam having a wavelength different from that of the data beam.
  • the data beam and the servo beam are irradiated from the bottom side of the medium in FIG. 1, and therefore, the servo beam reaches the servo layer after passing through the data layer.
  • the distance between the adjacent data layers is preferably reduced. Such reduction in the distance between the data layers, however, is associated with the problem of cross talk by the light reflected from other data layers.
  • an optical pickup equipped with a confocal optical system which utilizes the principle of a confocal microscope for the reading of each data layer.
  • An optical pickup equipped with a confocal optical system has a very high resolution in the thickness direction of the medium, and cross talk between the data layers can be greatly reduced.
  • Confocal optical systems which may be used in the reading of a multi -layer information medium are described, for example, in JP-A 222856/1998 and ISOM '94 Technical digest (1994) 19.
  • An embodiment of the optical pickup which is equipped with a confocal optical system and which can be used in the recording and reading of a multi-layer information medium is shown in FIG. 2 together with the medium. The medium shown in FIG.
  • the data beam which addresses the data layers is emitted from a laser diode LD1.
  • the data beam then goes through a lens LI to become collimated, and after going through a polarizing beam splitter PBS 1 , the beam is focused by lens L2.
  • a pin- hole plate PHP formed with a pin hole is arranged at the focal point, and the data beam which passes through the pin hole is collimated by lens L3, and after passing through quarter-wave plate QWP1 and dichroic mirror DCM which is transparent to the data beam, the beam enters objective lens L4 to be focused at the data layer DL-1 on the lower side of the multi-layer information medium.
  • the data beam reflected by the data layer DL-1 goes back along the same pathway as the incidence into the medium, and the beam is then reflected by the polarizing beam splitter PBSl to be focused by a lens L5 to a photodetector PD 1.
  • the focus servo to the data layer DL-1, or the focus servo and detection of the readout signal is thereby accomplished.
  • the data beam also reaches the data layer DL-2 after passing through the data layer DL-1 the data of which is to be read, and a light is also reflected from the data layer DL-2 back to the optical pickup.
  • This data beam is out of focus at the data layer DL-2, and the light reflected from the data layer DL-2 is not focused to the pinhole position of the pinhole plate PHP.
  • the beam which is unfocused at the pinhole is substantially blocked by the pinhole plate PHP.
  • the cross talk between the data layers is thereby suppressed by the optical pickup equipped with the confocal optical system.
  • the servo beam is irradiated from a laser diode LD2.
  • the beam is then reflected by a polarizing beam splitter PBS 2, and goes through a lens L6 and a quarter- wave plate QWP2 to be reflected by a dichroic mirror DCM.
  • the beam then enters the obj ective lens L4 and become focused on the servo layer SL.
  • the servo beam is then reflected by the servo layer SL to go back along the same pathway as its incidence into the medium, and the beam passes through the polarizing beam splitter PBS 2 to be focused on a photodetector PD2.
  • the tracking servo and the focus servo to the servo layer are thereby accomplished.
  • the data layer should be irradiated with the recording beam, namely, with a data beam of high intensity.
  • Servo tracking using the light reflected from the servo layer is also conducted during the recording, and if the data beam of high intensity is directed to a medium having a transparent layer instead of the filter layer FL, the data beam will pass through the data layer to reach the servo layer, and a part of the data beam reflected therefrom will reach the dichroic mirror DCM.
  • the data beam will not fully pass through the dichroic mirror DCM, and a part of the data beam will be reflected by the dichroic mirror DCM.
  • the data beam will partly reach the photodetector PD2 provided for the servo pu ⁇ ose and the tracking servo will be adversely affected.
  • the influence on the tracking servo is not negligible even if the reflection by the dichroic mirror DCM was only partial.
  • the reading data beam of low intensity is also associated with the same problem since a part of the reading data beam may reach the photodetector PD2 provided for the servo pu ⁇ ose to adversely affect the tracking servo.
  • a filter layer FL is provided in the present invention between the servo layer SL and the adjacent data layer (DL-4 in FIG. 1, and DL-2 in FIG. 2), and this filter layer exhibits higher abso ⁇ tion of the data beam compared to the abso ⁇ tion of the servo beam.
  • the data beam is considerably attenuated on the way and back through the filter layer FL, and the adverse effects on the tracking servo caused by the data beam are thereby greatly suppressed.
  • the filter layer is a layer which exhibits higher abso ⁇ tion of the data beam compared to the abso ⁇ tion of the servo beam.
  • the filter layer preferably exhibits an abso ⁇ tion of the data beam of about 80% or more, and more preferably, at least 90%. When the abso ⁇ tion is too low, the merits of the present invention will not be sufficiently realized.
  • the filter layer preferably exhibits an abso ⁇ tion of the servo beam of less than about 20%, and more preferably, less than about 10%. When the abso ⁇ tion is too high, reading of the servo layer by the servo beam entering through the filter layer will be difficult to detract from the tracking servo.
  • the filter layer is configured to selectively absorb light at the data beam wavelength, and to selectively pass light at the servo b earn wavelength.
  • the material used for the filter layer is not particularly limited, and an adequate material may be selected from the materials exhibiting the desired spectral abso ⁇ tion characteristics, for example, from the dyes comprising an organic material or an inorganic material.
  • Use of an organic dye is preferable, and use of an organic dye further comprising a resin is more preferable.
  • Exemplary preferable resin is a resin cured by UN or other active energy ray. Formation of the filter layer is facilitated by such admixture of the resin component compared to the use of the dye alone. For example, a uniform, relatively thick filter layer can be formed in a short period when a mixture of a UV-curable composition an a dye is spin coated and UV cured.
  • the dye used for the filter layer is not particularly limited, and an adequate dye may be selected from the dyes exhibiting the desired spectral abso ⁇ tion characteristics, for example, from cyanine, phthalocyanine, and azo organic dyes.
  • the dye may be modified as desired, for example, by introducing a substituent in the side chain of the dye in consideration of the compatibility with the resin.
  • the filter layer may also be constituted from two or more dye layers each having different spectral abso ⁇ tion characteristics for ease of controlling the spectral abso ⁇ tion characteristics.
  • the filter layer contains a dye and a resin
  • the dye is not limited for its content, and the content may be determined depending on the type of the resin employed and to satisfy the required spectral abso ⁇ tion characteristics.
  • the content is typically 1 to 10 mass%.
  • An excessively low dye content is undesirable since increase in the thickness of the filter layer is required.
  • excessively large content will result in the shortening of the pot life.
  • the filter layer may be constituted from a UV-curable resin layer free from the dye.
  • the UV- curable resin layer may be formed by coating a composition containing a UV-curable composition and a photoinitiator, and UV curing the coated film.
  • the photoinitiator exhibits high abso ⁇ tion near the wavelength of the light beam used for the curing, and the thus cured film also exhibits high abso ⁇ tion near such wavelength. This is believed to be due to the condition that the photoinitiator is not completely decomposed in the course of curing and a part of the photoinitiator remains in intact or modified state after the curing. As a consequence, such layer can be used as a filter layer which exhibits selectively high abso ⁇ tion at the short wavelength region.
  • the photoinitiator used in the filter layer is not particularly limited, and an adequate photoinitiator may be selected from conventional photoinitiators such as benzoates, benzophenone derivatives, benzoin derivatives, thioxanthone derivatives, acetophenone derivatives, propiophenone derivatives, and benzyls depending on the wavelength of beam to be absorbed.
  • conventional photoinitiators such as benzoates, benzophenone derivatives, benzoin derivatives, thioxanthone derivatives, acetophenone derivatives, propiophenone derivatives, and benzyls depending on the wavelength of beam to be absorbed.
  • the thickness of the filter layer may be adequately determined to satisfy the required spectral abso ⁇ tion characteristics.
  • the filter layer containing a resin wherein a dye or a photoinitiator is used for the abso ⁇ tion material is preferably formed to a thickness in the range of 1 to 30 m.
  • the filter layer is too thin, sufficient abso ⁇ tion characteristics is less likely to be obtained.
  • the filter layer is too thick, number of the data layers included in the medium will be limited in view of the total thickness of the medium and this is not preferable.
  • a metal layer containing at least one metal (including semimetal) element may be used for the filter layer.
  • the type of the metal included and the thickness of the filter layer may be selected so that sufficient abso ⁇ tion and sufficient - transmittance are reliably achieved at the target wavelength regions of abso ⁇ tion and transmittance, respectively.
  • the metals which may be preferably used in the filter layer include Au, Pt, Cu and the like.
  • the filter layer may also comprise two or more different metal layers each having different spectral abso ⁇ tion characteristics.
  • the thickness of the metal layer used as the filter layer may vary by the type of the metal used. However, the thickness of such layer is preferably in the range of 10 to 200 nm, and more preferably 20 to 100 nm. When the metal layer is too thin, the layer will fail to exhibit sufficient abso ⁇ tion at the target abso ⁇ tion wavelength region while excessively thick metal layer results in an insufficient transmittance at the target transmittance wavelength region.
  • the filter layer may also comprise an interference filter. Exemplary interference filters which may be used include a dielectric multi-layer film and a dielectric film sandwiched between two metal thin films comprising Ag or the like.
  • the reflective layer (servo layer SL) formed on the servo substrate 20 can be used instead of providing the filter layer FL.
  • the servo layer SL should exhibit a relatively high reflectivity to the servo beam and a relatively low reflectivity to the data beam.
  • the data beam and the servo beam are not particularly limited for their wavelength.
  • difference in the wavelength of these beams is preferably 50 to 700 nm, and more preferably 100 to 400 nm.
  • the filter layer will be required to have steep spectral abso ⁇ tion characteristics and selection of the material used for the filter layer will be difficult.
  • the wavelength difference is too large, difficulty is encountered in increasing the recording density of the entire medium or in obtaining sufficient servo accuracy.
  • the wavelength region wherein the data beam and the servo beam are present is preferably the wavelength region of 300 to 1000 nm, and more preferably 400 to 800 nm.
  • a semiconductor laser oscillating a laser beam having a wavelength shorter than such range is associated with difficulty in availability while use of a laser beam having a wavelength longer than such range is associated with difficulty in high density recording as well as difficulty in the reading of the information recorded at a high density.
  • the transparent layer preferably comprises a material which exhibits high transmittance to the recording/reading beam.
  • the material used for the transparent layer is not limited.
  • the transparent layer is preferably formed from a resin since the transparent layer should be deposited to a considerable thickness.
  • the process used for the formation of the transparent layer is not limited.
  • the transparent layer is preferably formed from a resin, and in particular, from a UN-curable resin or other active energy beam-curable resin.
  • the transparent layer may be formed from a resin sheet.
  • the transparent layer formed from a UV-curable resin will exhibit a relatively steep abso ⁇ tion in the short wavelength region due to the influence of the photoinitiator as described above in the section of the "Filter layer ".
  • an adequate type of photoinitiator should be selected depending on the wavelength of the recording/reading beam used.
  • the transparent layer When the transparent layer is provided in contact with the substrate 2, it should be noted that the difference between the refractive index of the transparent layer and the refractive index of the substrate is up to 0.1 at the wavelength of the recording/reading beam in order to suppress the reflection at the boundary between the transparent layer and the substrate.
  • the transparent layer is not particularly limited for its thickness, and the thickness may be adequately determined so that the cross talk between the data layers is within acceptable limits.
  • the transparent layer has a thickness of at least 30 m when an optical pickup of conventional type is used. An excessively thick transparent layer is likely to result in an unduly increased inconsistency in the thickness as well as increased internal stress, and such a thick transparent layer is also likely to invite increase in the total thickness of the medium. Accordingly, the transparent layer preferably has a thickness of up to 100 m.
  • the thickness of the transparent layer is determined depending on the resolution of the confocal optical system in the depth direction so that the cross talk between the data layers is within acceptable limits.
  • the preferable thickness of the transparent layer is 5 m or more when the data beam has a wavelength of about 300 to about 1000 nm although such thickness may vary with the wavelength of the data beam and the constitution of the confocal optical system.
  • Use of a confocal optical system enables provision of a transparent layer with a reduced thickness of less than 30 m, and no problem is induced even when the thickness is reduced to 20 m or less.
  • the transparent layer is preferably formed by spin coating since the spin coating is a process which is capable of forming a relatively uniform transparent layer.
  • the transparent layer formed by the spin coating process suffers from the problem that the layer is thicker in the outer periphery region of the disk compared to the inner periphery region, and in other words, from the problem of inconsistent thickness in the radial direction of the disk.
  • the number of the transparent layers increase with the number of the data layers, and such thickness inconsistency is accumulated with the increase in the number of the data layers.
  • the data beam entered the substrate 2 in the outer periphery region of the disk at a normal direction the data beam reflected at the surface of the data layer will not be normal to the substrate 2, and the quantity of the light returning to the optical pickup will be reduced.
  • the medium will then exhibit different read-out outputs in the inner periphery region and in the outer periphery region.
  • a pinhole is provided in the optical system and the reading is accomplished by using the beam that had passed thorough this pinhole. Accordingly, when an optical pickup equipped with a confocal optical system is used, the tracking range of the focus servo will be narrower, and therefore, a higher thickness consistency is required for the transparent layer.
  • difference between the maximum thickness and minimum thickness of the transparent layer between recorded information-bearing areas (area where the recording tracks are present) of two adjacent data layers or between the recorded information-bearing area of the data layer and the servo layer is preferably up to 3 m, and more preferably up to 2 m.
  • the difference between the maximum and minimum thickness of the transparent layer is reduced to the lowest possible value, reduction of such difference to zero is difficult as long as the transparent layer is formed by spin coating, and the fluctuation in the read-out output is sufficiently reduced when the thickness difference is within the above- specified range. Therefore, the thickness difference need not be reduced to less than 1 m.
  • the recorded information-bearing area is typically an annular area having a width of about 20 to about 50 mm.
  • the resin layers other than the transparent layer for example, the filter layer comprising a resin or a resin and a dye, a protective layer which is often provided on the surface of the medium, an adhesive layer, and the like may be formed by spin coating.
  • the servo layer is a reflective layer formed on the servo substrate 20, and the servo layer is formed with the projections and depressions carrying the tracking servo information.
  • the servo layer carries tracking servo information corresponding to the projections and depressions. Grooves and/or pits are typically used for the projections and depressions.
  • the reflective layer constituting the servo layer is not particularly limited for its constitution, and the reflective layer formed may be similar to those formed in conventional optical information media.
  • the reflective layer may typically comprise a metal or semimetal such as Al, Au, Ag, Pt, Cu, Ni, Cr, Ti, or Si as a simple substance or as an alloy containing at least one of such metals and semimetals.
  • the reflective layer is typically formed to a thickness of 10 to 300 nm. A thickness below such range is likely to result in an insufficient reflectivity while the thickness in excess of such range is not advantageous in cost since increase in the thickness does not result in significant increase of the reflectivity.
  • the reflective layer is preferably formed by vapor deposition such as sputtering and evaporation.
  • the data layer includes at least a recording layer comprising a recording material.
  • the optical recording medium to which the present invention is applied is not limited particular type, and applicable media include a rewritable medium or a write once medium employing a phase change recording material, a rewritable medium employing a magnetooptical recording material, a write once medium employing an organic dye.
  • use of a phase change recording material is preferable in view of high light transmittance compared to other recording materials, and accordingly, capability of increasing the number of recording layers.
  • the composition of the phase change recording material is not particularly limited, and the material is preferably the one containing at least Sb and Te.
  • crystallization temperature of the recording layer containing Sb and Te as the only components is as low as about 130°C and the storage reliability is insufficient, and therefore, the recording layer may preferably comprise elements other than Se and Te.
  • Such element is preferably element M (element M is at least one element selected from In, Ag, Au, Bi, Se, Al, P, Ge, H, Si, C, V, W, Ta, Zn, Ti, Ce, Tb, Sn, Pb, Pd, and Y), and among these, the preferred is Ge in view of the high effect in improving the storage reliability.
  • phase change recording medium is generally used as a rewritable medium.
  • the phase change recording medium may be used as a write once medium.
  • the "write once medium" used herein designates a medium which is recordable but wherein erasure of the once recorded record mark is not ensured, and in the case of a write once medium, overwriting of the record marks recorded in the recording track by erasing the record marks is not intended.
  • Advantages associated with the use of a phase change recording medium for the write once medium are as described below.
  • a multi -layer recording medium In the case of a multi -layer recording medium, a plurality of recording layers are disposed one on another, and this structure is accompanied with an increased loss in the light quantity of the recording/reading beam. Therefore, use of a thinnest possible recording layer is desired. Decrease in the thickness of the recording layer, however, invites an increase in the cooling speed of the recording layer after the recording beam irradiation. Crystallization is less likely to take place at a higher cooling speed, and use of a composition which easily undergo crystallization is required to ensure the erasability. In other words, considerable increase in the crystallization speed of the recording layer will be required. A recording layer of high crystallization speed, however, is associated with the problem of higher occurrence of the self erase as described below.
  • the recording heat dissipates from the beam spot of the recording beam in the lateral direction of the recording layer, and cooling of the record marks is inhibited by this heat.
  • the recording layer has a high crystallization speed, the record marks are partly recrystallized due to such cooling inhibition, and the size of the record mark formed will be reduced.
  • the phenomenon often encountered is erasure of the leading edge of the record mark (the part first irradiated with the beam spot) or the trailing edge of the record mark. Such phenomenon is referred in the present invention as the "self erase”.
  • the self erase is associated with decrease in the C/N or increase in the jitter.
  • the recording is conducted only once with no overwriting operation, it will be possible to conduct the recording at a high linear velocity, for example, at a linear velocity of about 10 m/s in a recording layer having a relatively slow crystallization speed with reduced likeliness of self erase, and a high data transfer rate is easily realized.
  • the medium of the present invention has a plurality of recording layers disposed one on another and loss of the light quantity of the recording/reading beam is thereby increased. Therefore, use of a thinnest possible recording layer is preferable with the function of the recording layer maintained. However, an excessively thin recording layer can no longer function as a recording layer, and the recording layer preferably has a thickness of 2 to 50 nm, and more preferably, 4 to 20 nm.
  • the data layer may preferably have the structure as shown for DL-1 in FIG. 1.
  • This data layer has a structure wherein the recording layer 4 is sandwiched between the first dielectric layer 31 and the second dielectric layer 32.
  • the recording layer and the dielectric layers are preferably formed by sputtering.
  • the dielectric material used in the dielectric layers may be a compound containing at least one metal component selected from Si, Ge, Zn, Al, and rare earth metals, and the compound is preferably an oxide, a nitride, a sulfide, or a fluoride. A mixture containing two or more such compounds may be also used.
  • Each dielectric layer may preferably have a thickness of 10 to 500 nm.
  • the recording layer with a reduced thickness is preferable in order to reduce the loss in the light quantity of the recording/reading beam.
  • Decrease in the thickness of the phase change recording layer is associated with a decrease in the degree of modulation, namely, with a decrease in the difference in reflectivity between the amo ⁇ hous record mark and the crystalline region.
  • the dielectric layer is preferably formed as a laminate of two or more layers each having different refractive index.
  • Such multi-layer structure also results in an increased flexibility of optical design, and increase in the light transmittance of the entire data layer can be realized.
  • An exemplary dielectric layer of multi-layer structure is a laminate of at least one layer selected from magnesium fluoride layer, manganese fluoride layer, germanium nitride oxide layer, and silicon oxide layer with a ZnS-SiO 2 layer.
  • recording sensitivity of the recording layer is preferably adjusted corresponding to the intensity of the recording beam reaching to the particular recording layer.
  • increase in the thickness of the recording layer results in an increase in heat storage, and hence, in an increase in the recording sensitivity.
  • the thickness of the recording layer remote from the surface of the recording beam incidence may be increased as required compared to the recording layer near the surface of the recording beam incidence.
  • adjacent two recording layers may have an identical thickness.
  • the recording/reading beam used in the recording layer remote from the surface of the recording beam incidence is the recording/reading beam which has passed through other recording layers, and for the pu ⁇ ose of leveling the reading properties of the recording layers, a recording layer near the surface of the recording beam incidence may preferably have a higher light transmittance. In consideration of such light transmittance, it is also preferable that the recording layer remote from the surface of the recording beam incidence has an increased thickness.
  • the adjustment of the recording sensitivity and the transmittance can also be accomplished through control of the composition of the recording layer.
  • all recording layers may be formed to an identical thickness, or alternatively, control of the composition can be combined with the control of the thickness.
  • the present invention is also applicable to a read only medium.
  • the data layers of such medium may comprise either a layer formed with pits carrying the recorded information or a layer of a write once medium carrying the preliminarily recorded data.
  • the pits are generally formed in the transparent layer or the filter layer, and a translucent reflective layer is formed on the surface of the layer formed with the pits.
  • the reflective layer will then serve as the data layer. Examples of such translucent reflective layers are an extremely thin metal layer and a silicon layer.
  • reflectivity of the data layer may be controlled for the leveling of the read-out signal.
  • the reflectivity may be controlled such that the data layer with the smaller quantity of light reached exhibits higher reflectivity.
  • number of the data layers included in the medium is not limited as long as two or more data layers are included. An excessive number of data layers, however, results in unduly increased thickness of the medium and the effect of the thickness inconsistency of the transparent layer formed by spin coating will also su ⁇ ass the acceptable level. Accordingly, the number of the data layers is preferably up to 10, and more preferably up to 6.
  • the information-bearing layer When a plurality of information-bearing layers are disposed one on another, quantity of the light reflected from the information-bearing layer will be reduced. However, it has been found that sufficient C/N at the data layer and sufficient servo signal at the servo layer are attained when the maximum reflectivity of the information-bearing layer is 5% or less. However, sufficient C/N and servo signal strength will not be ensured when the reflectivity is excessively low, and the information-bearing layer may preferably have a maximum reflectivity of at least 0.1%.
  • the substrate 2 preferably comprises a material which is substantially transparent to the recording/reading beam such as a resin or glass since the recording/reading beam is irradiated through the substrate 2.
  • a resin is preferable in view of the handling convenience and the low price
  • exemplary resins include acrylic resins, polycarbonates, epoxy resins, and polyolefins.
  • a polycarbonate substrate will exhibit an excessively high abso ⁇ tion of the recording/reading beam
  • use of a material such as an amo ⁇ hous polyolefin exhibiting lower optical abso ⁇ tion to a short wavelength beam is preferable.
  • the substrate 2 is not limited for its shape and dimension.
  • the substrate 2 is typically a disk having a thickness of at least 5 m and preferably about 30 m to 3 mm and a diameter of about 50 to 360 mm.
  • the servo substrate 20 shown in FIG 1 may comprise a resin or a glass as in the case of the substrate 2. Use of a resin, however, is preferable in view of the ease of forming the servo information-carrying projections and depressions by injection molding. It should be noted that the servo substrate 20 is not necessary transparent.
  • the servo substrate 20 is also not limited for its thickness, and an adequate thickness may be selected, for example, from the range described for the substrate 2. However, when the substrate 2 has a relatively low rigidity, the rigidity of the entire medium is preferably ensured by increasing the thickness of the servo substrate 20 to a considerable degree.
  • Samples of optical recording disk having the structure as shown in FIG. 1 were produced by the procedure as described below.
  • the transparent layers were formed by spin coating a UN-curable resin (SK-5110 manufactured by Sony Chemicals Co ⁇ oration) at a rotation speed of 1500 ⁇ m for 2 seconds and UV curing the coated resin.
  • the transparent layer after the curing had a thickness of 15 m. It should be noted that this thickness is a value measured at the radially central position of the area where recorded information is carried (the area at a radial distance of 20 mm to 58 mm from the center of the disk).
  • the recording layer 4 included in each data layer had a composition (atomic ratio) of:
  • the recording layers 4 were formed to a thickness of 5 nm, 5 nm, 7 nm, and 13 nm, respectively, from the side of the data beam incidence.
  • the recording layer 4 was formed by magnetron sputtering system and the thickness was adjusted by controlling the power, pressure, and time of the sputtering.
  • the first dielectric layer 31 and the second dielectric layer 32 included in each data layer was adjusted to the range of 75 to 271 nm to thereby ensure abso ⁇ tion of the recording layer and simultaneously increase the light transmittance of the entire data layer.
  • These dielectric layers were formed by magnetron sputtering system and the composition of the layers was ZnS (80 mole%)-SiO 2 (20 mole%).
  • a servo substrate 20 comprising a disk having a thickness of 1.2 mm and a diameter of 120 mm was prepared by injection molding a polycarbonate. This disk had a groove having a width of 0.76 m and a depth of 183 nm formed therewith. On the surface of the servo substrate 20 where the groove had been formed, a gold layer was deposited as a servo layer SL to a thickness of 100 nm by sputtering.
  • this reflective layer On the surface of this reflective layer was formed a filter layer FL, and the filter layer FL was formed by spin coating a mixture (dye content, 3 mass%) of a phthalocyanine dye (Blue-N manufactured by Nippon Kayaku Co., Ltd.) and a UV-curable resin at a rotation speed of 2500 ⁇ m for 5 seconds and UV curing the layer.
  • the filter layer FL after curing had a thickness of 11 m.
  • the filter layer FL exhibited an abso ⁇ tion of 95% at a wavelength of 660 nm, and 8% at a wavelength of 780 nm. It should be noted that the abso ⁇ tion is a value evaluated by forming the filter layer alone on a transparent plate, and conducting the evaluation for this sample.
  • UV-curable resin (DVD-003 manufactured by Nippon Kayaku Co., Ltd.) was dripped on the top surface of the laminate including the substrate 2 (surface of the uppermost data layer DL-4), and the laminate including the servo substrate 20 was aligned on the laminate including the substrate 2.
  • the laminates were rotated at 5000 ⁇ m for 2 seconds, and the UV-curable resin was cured by UV irradiation through the substrate 2 to thereby adhere the laminate including the substrate 2 and the laminate including the servo substrate 20 by an intervening transparent layer TL-5 of 35 m thick.
  • a sample of the optical recording disk having the structure shown in FIG. 1 was thereby produced. The recording layers of this sample were initialized (crystallized) with a bulk eraser.
  • the data layers and the servo layer were evaluated for their maximum reflectivity at a wavelength of 660 nm, with reflectivities of: DL-1: 1.1%; DL-2: 0.7%; DL-3: 0.9%; DL-4: 0.5%; and SL: 0.05%.
  • the sample was rotated, and single signal comprising pulses of the same length continuing at a constant interval was recorded in the data layers of the sample, and the recorded signal was read to measure the C/N.
  • the recorded pulses were at a duty ratio of 50%.
  • a data beam having a wavelength of 660 nm was used for the recording and the reading.
  • tracking servo was also conducted by reading the servo layer SL with a servo beam having a wavelength of 780 nm.
  • the results are shown in Table 2.
  • the recording density shown in Table 2 is the value determined by converting the mark length of the single signal as described above to the bit linear density of the 1-7 modulation signal containing the signal of the same mark length as its minimum signal.
  • the disk was rotated at a rotation speed of 2000 ⁇ m (CAV), and the recording density was changed by changing the frequency of the single signal as described above.
  • CAV rotation speed of 2000 ⁇ m
  • the recording track measured was at a radial position measured from the sample center of 42.5 mm, and the linear velocity was about 8.9 m/s.
  • Bit Error Rate The sample was recorded with a random signal of 1-7 modulation (marklength, 2T to 8T), and the signal was read to measure the bit error rate(BER). The results are shown in Table 3. Table 3
  • Samples of optical recording disk were produced by repeating the procedure of Example 1 except that the filter layer FL was formed by the procedure as described below.
  • the filter layer FL of this sample was formed by spin coating a mixture (dye content, 3 mass%) of a yellow dye (Yellow-2G manufactured by Nippon Kayaku Co., Ltd.) and a UV-curable resin at a rotation speed of 2500 ⁇ m for 5 seconds and UV curing the resin.
  • the filter layer FL after curing had a thickness of 10 m.
  • the filter layer FL exhibited an abso ⁇ tion of 95% at a wavelength of 405 nm, and 7% at a wavelength of 650 nm. It should be noted that the abso ⁇ tion was measured by repeating the procedure of Example 1.
  • the sample was evaluated for its recording/reading properties by repeating the procedure of Example 1 except for the wavelength of the data beam and the servo beam which were 405 nm and 650 nm, respectively. The properties were sufficient as in the case of Example 1.
  • Samples of optical recording disk were produced by repeating the procedure of Example 1 except that the filter layer FL was formed by the procedure as described below.
  • the filter layer FL of this sample was formed by spin coating a UV-curable resin admixed with 3 mass% of Irgacure 819 (a photoinitiator, manufactured by Ciba Specialty Chemicals Co ⁇ oration) at a rotation speed of 2500 ⁇ m for 5 seconds and UV curing the resin.
  • the filter layer FL after curing had a thickness of 10 m.
  • the filter layer FL exhibited an abso ⁇ tion of 93% at a wavelength of 405 nm, and 5% at a wavelength of 650 nm. It should be noted that the abso ⁇ tion was measured by repeating the procedure of Example 1.
  • the sample was evaluated for its recording/reading properties by repeating the procedure of Example 1 except for the wavelength of the data beam and the servo beam which were 405 nm and 650 nm, respectively. The properties were sufficient as in the case of Example 1.
  • the data layers are separately formed from the servo layer, and there is no need to form the tracking servo pattern on each data layer. Therefore, the data layer can be formed as a smooth layer, and highly accurate tracking servo is enabled with no increase in the production cost of the medium. Formation of the smooth data layer also results in the merits as described above.
  • a filter layer is disposed between the data layer and the servo layer, and adverse effects on the tracking servo induced by the data beam reflected from the servo layer is thereby avoided.

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Abstract

Support d'information optique comprenant au moins deux couches de données servant à supporter un enregistrement d'information et une couche asservie servant à porter des informations asservies de centrage et constituée de façon indépendante par rapport aux couches de données. On utilise ce support avec un système d'enregistrement ou de lecture mettant en application un faisceau de données afin d'enregistrer ou de lire les données de la couche de données et un faisceau asservi afin de lire les informations asservies de centrage de la couche asservie. Ce faisceau asservi lit la couche asservie après avoir traversé la couche de données et une couche filtrante est placée entre la couche de données et la couche asservie, cette couche filtrante présentant une absorption plus importante du faisceau de données que du faisceau asservi.
PCT/US2001/011359 2000-04-07 2001-04-05 Support d'information optique WO2001078068A2 (fr)

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AU2001256991A AU2001256991A1 (en) 2000-04-07 2001-04-05 Optical information medium
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US19577200P 2000-04-07 2000-04-07
US60/957,720 2000-04-07
US09/549,075 US6574174B1 (en) 2000-04-15 2000-04-15 Optical data storage system with multiple layer media
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EP1965376A1 (fr) * 2005-12-21 2008-09-03 FUJIFILM Corporation Support d'enregistrement d'informations optique, procédé et système d'enregistrement d'informations
EP2006848A3 (fr) * 2007-06-12 2009-05-27 Sony Corporation Dispositif à disque optique et procédé de correction de la position convergente

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JPH09198709A (ja) 1996-01-23 1997-07-31 Sony Corp 多層光ディスク及び記録再生装置
JPH10222856A (ja) 1997-02-07 1998-08-21 Olympus Optical Co Ltd 光学式情報記録再生装置

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EP1760707A3 (fr) * 2005-09-06 2007-12-05 FUJIFILM Corporation Support d'enregistrement optique, procédé de fabrication de celui-ci, procédé d'enregistrement optique et procédé de reproduction optique
US7894319B2 (en) 2005-09-06 2011-02-22 Fujifilm Corporation Optical recording medium, method of producing the same, and, optical recording method and optical reproducing method
EP1965376A1 (fr) * 2005-12-21 2008-09-03 FUJIFILM Corporation Support d'enregistrement d'informations optique, procédé et système d'enregistrement d'informations
EP1965376A4 (fr) * 2005-12-21 2009-02-04 Fujifilm Corp Support d'enregistrement d'informations optique, procédé et système d'enregistrement d'informations
EP2006848A3 (fr) * 2007-06-12 2009-05-27 Sony Corporation Dispositif à disque optique et procédé de correction de la position convergente
US7948840B2 (en) 2007-06-12 2011-05-24 Sony Corporation Optical disc device and converging position correction method

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