CA2194227A1 - Dual layer optical medium having partially reflecting thin film layer - Google Patents
Dual layer optical medium having partially reflecting thin film layerInfo
- Publication number
- CA2194227A1 CA2194227A1 CA002194227A CA2194227A CA2194227A1 CA 2194227 A1 CA2194227 A1 CA 2194227A1 CA 002194227 A CA002194227 A CA 002194227A CA 2194227 A CA2194227 A CA 2194227A CA 2194227 A1 CA2194227 A1 CA 2194227A1
- Authority
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- Canada
- Prior art keywords
- reflective layer
- layer
- partially reflective
- medium
- pit pattern
- Prior art date
- Legal status (The legal status 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 status listed.)
- Abandoned
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-
- 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
- G11B7/24062—Reflective layers
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- 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
-
- 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
- G11B7/252—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
-
- 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]
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- 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
- G11B7/254—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 protective topcoat layers
- G11B7/2548—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 protective topcoat layers consisting essentially of inorganic materials
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- 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
- G11B7/2585—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 aluminium
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- 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
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S428/00—Stock material or miscellaneous articles
- Y10S428/913—Material designed to be responsive to temperature, light, moisture
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- 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
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
- Y10S430/146—Laser beam
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- 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
Abstract
A dual layer pre-recorded optical disc (12) includes a transparent substrate (14), a partially reflective layer (16), a transparent spacer layer (18), and a highly reflective layer (20). One pattern of data pits (15) is provided on the substrate, adjacent the partially reflective layer, and another pattern of data pits (19) is provided on the spacer layer, adjacent the highly reflective layer. The partially reflective layer may be made of silicon carbide. A
substrate-incident beam can be used to read data encoded in either data pit pattern depending on which layer the laser (30) is focused upon. The dual layer disc has twice the data storage capacity of conventional single layer discs.
substrate-incident beam can be used to read data encoded in either data pit pattern depending on which layer the laser (30) is focused upon. The dual layer disc has twice the data storage capacity of conventional single layer discs.
Description
W0 96104650 2 1 9 4 2 2 7 PCT~Us9sl07096 DUAL LAYER OPTICAL MEDIUM HAVlNG
PART~Al .1 .Y RE~ECl~G T~l EILM LAYER
Field of the Invention The present invention relates generally to the field of optical media, and more specifically to the area of optical media which employ two or more '- storage layers.
Back~round of the Invention There is a seemingly never-ending demand in the field of data storage for media having increased storage capacity and p r.... ---, e In the field of pre-recorded optical &scs, such as compact discs and video discs, increased storage 15 capacity is usuaUy achieved by increasing the storage density per unit area of the disc. However, the maximum data storage density achievable in an optical recording system is limited by the smallest feature that the optical system can resolve. For .,~,.... ' far-field imaging systems, the smallest resolvable feature size is limited by difflaction effects to alJp~ the ~ . ' , ' of the available light source, usually a solid state laser diode. Thus, one method of increasing disc storage capacity is to decrease the wavelength of the laser diode. However, while the ~YD~.~ ,,' available from laser &odes have been steadily decreasing, the decreases have not been dramatic due to limitations in solid state technology and materials.
A number of other techniques for increasing storage capacity of optical recordmg systems have been proposed. These include: (1) higher efflciency data coding schemes, e.g., I ' ..;J~I. ' ' , (2) optical and/or magnetic super-resolution; (3) zoned recording at constant angular velocity; (4) advanced data channel detection methods, such as partial I~D~OOnS;~/III~IIIUIII likelihood detection, 30 and (5) recording on both the grooves and land areas of the disc.
While the preceding methods for increasing storage capacity all rely upon increasing the storage density per unit area of the disc, an alternative method for w0 96io46s0 2 1 9 4 2 2 7 r~l,., . . L
increasing the capacity of an optical disc is to employ additional storage layers on the disc which can be L 1~ . L .~lly recorded or reproduced. Thus, the approach in this case is to increase the add.~le area of the disc. This approach is attractive because it has the potential to ' ~l~ increase media storage capacity with only a modest increase in media and recording system complexity.
Tf multiple storage layers, e.g., 2, are to be reproduced by optical beam(s) provided on one side of the disc, then one of the storage layers of the disc must be reflective enough so that it may be reproduced by the optical beam(s), but transparent enough so that the beam(s) may penetrate the first storage layer andpass on to a second storage layer. However, such a disc has proved to be difficult to construct, especially, where only a single laser is employed.
.~nmrr ~y of th~ InvPnti~m Accordingly, the present invention provides an optical disc having a partially rerdecting layer and a transparent spacer layer that allows a single .~q,.-' _ optical beam to focus on either of two different plames within the disc. The disc includes a tr~msparent substrate having a pattem of pits in one of its sides. A
partially reflective layer adjacent the pit pattem has an index of refraction having a real component (n) between 2.6 and 3.2 and an imaginary component (K) less than 0.4, measured at any wavelength within the range of from 500 to 850 nm. A
transparent polymer spacer layer is provided over the partially reflective layer, and a highly reflective layer is provided over the spacer layer.
In one '-" of the present invention, the substrate comprises pcl~l and the spacer layer comprises a PI~ JVI~ . A second pattem of pits may be provided in the side of the spacer layer adjacent the highly reflective layer. The internal surface reflectivity of the partially reflective layer preferably varies by less than +0.03 over variations in thickness in the partially reflective layer of _10~/~. The spacer layer has a thickness of from about 5 to 100 ~Lm.
In another; b~ " of the present invention, the partially reflective layer includes silicon carbide. One preferred ratio of the silicon to the carbon in the partially reflective layer is 1:1.3. In yet another ~i I ' t, the partially reflective 2 l 9 4 2 2 7 r~
layer includes silicon carbide containing from about 5 to 15 atomic % oxygen. The partially reflective layer is preferably 30 to 80 nm thick.
The present invention also includes optical storage systems which include the media described above. The systems further include a focused laser beam positioned to enter the medium through the substrate, means for adjusting the focal position of the laser beam on either the partiaUy reflective or highly reflective layer, and a l' ' positioned to detect the reflected laser beam exiting the medium.
As used herein, the terms "silicon carbide" or "SiC" mean mixtures of silicon and carbon ranging in cu ~ from 30-50 atomic % silicon, 35-60 atomic %
carbon, and 0-20 atomic % oxygen, as measured by x-ray ,uLùLù~le.,l~un ~ ,L~u~,u~)y~ and having silicon-carbon ' ranging from SiCog to SiC~
Brief Descrigtion of the Drawing FIGURE I shows an optical data storage system according to the present invention.
FIGURE 2 is a computer-generated graph of internal interface reflectivity at 650 nm as a function of thickness for various materials.
FIGURE 3 is a computer-generated graph of internal surface reflectivity at 650 nm as a function of thickness for silicon carbide according to the present invention.
FIGURE 4 is a computer-generated graph of apparent reflectivity at 780 nm as a function of thickness for silicon carbide according to the present invention.
FIGURE 5 is a graph of the real component of the index of refraction (n) as a function of wavelength for various materials according to the present invention.
FIGIJRE 6 is a graph of the imaginary component of the index of refraction ~K) as a function of wavelength for various materials according to the present invention.
FIGURES 7A-7C show I ' u~ hs of various layers of the optical recording medium ~,u~l ~Llu~,Lcd according to Example I .
PART~Al .1 .Y RE~ECl~G T~l EILM LAYER
Field of the Invention The present invention relates generally to the field of optical media, and more specifically to the area of optical media which employ two or more '- storage layers.
Back~round of the Invention There is a seemingly never-ending demand in the field of data storage for media having increased storage capacity and p r.... ---, e In the field of pre-recorded optical &scs, such as compact discs and video discs, increased storage 15 capacity is usuaUy achieved by increasing the storage density per unit area of the disc. However, the maximum data storage density achievable in an optical recording system is limited by the smallest feature that the optical system can resolve. For .,~,.... ' far-field imaging systems, the smallest resolvable feature size is limited by difflaction effects to alJp~ the ~ . ' , ' of the available light source, usually a solid state laser diode. Thus, one method of increasing disc storage capacity is to decrease the wavelength of the laser diode. However, while the ~YD~.~ ,,' available from laser &odes have been steadily decreasing, the decreases have not been dramatic due to limitations in solid state technology and materials.
A number of other techniques for increasing storage capacity of optical recordmg systems have been proposed. These include: (1) higher efflciency data coding schemes, e.g., I ' ..;J~I. ' ' , (2) optical and/or magnetic super-resolution; (3) zoned recording at constant angular velocity; (4) advanced data channel detection methods, such as partial I~D~OOnS;~/III~IIIUIII likelihood detection, 30 and (5) recording on both the grooves and land areas of the disc.
While the preceding methods for increasing storage capacity all rely upon increasing the storage density per unit area of the disc, an alternative method for w0 96io46s0 2 1 9 4 2 2 7 r~l,., . . L
increasing the capacity of an optical disc is to employ additional storage layers on the disc which can be L 1~ . L .~lly recorded or reproduced. Thus, the approach in this case is to increase the add.~le area of the disc. This approach is attractive because it has the potential to ' ~l~ increase media storage capacity with only a modest increase in media and recording system complexity.
Tf multiple storage layers, e.g., 2, are to be reproduced by optical beam(s) provided on one side of the disc, then one of the storage layers of the disc must be reflective enough so that it may be reproduced by the optical beam(s), but transparent enough so that the beam(s) may penetrate the first storage layer andpass on to a second storage layer. However, such a disc has proved to be difficult to construct, especially, where only a single laser is employed.
.~nmrr ~y of th~ InvPnti~m Accordingly, the present invention provides an optical disc having a partially rerdecting layer and a transparent spacer layer that allows a single .~q,.-' _ optical beam to focus on either of two different plames within the disc. The disc includes a tr~msparent substrate having a pattem of pits in one of its sides. A
partially reflective layer adjacent the pit pattem has an index of refraction having a real component (n) between 2.6 and 3.2 and an imaginary component (K) less than 0.4, measured at any wavelength within the range of from 500 to 850 nm. A
transparent polymer spacer layer is provided over the partially reflective layer, and a highly reflective layer is provided over the spacer layer.
In one '-" of the present invention, the substrate comprises pcl~l and the spacer layer comprises a PI~ JVI~ . A second pattem of pits may be provided in the side of the spacer layer adjacent the highly reflective layer. The internal surface reflectivity of the partially reflective layer preferably varies by less than +0.03 over variations in thickness in the partially reflective layer of _10~/~. The spacer layer has a thickness of from about 5 to 100 ~Lm.
In another; b~ " of the present invention, the partially reflective layer includes silicon carbide. One preferred ratio of the silicon to the carbon in the partially reflective layer is 1:1.3. In yet another ~i I ' t, the partially reflective 2 l 9 4 2 2 7 r~
layer includes silicon carbide containing from about 5 to 15 atomic % oxygen. The partially reflective layer is preferably 30 to 80 nm thick.
The present invention also includes optical storage systems which include the media described above. The systems further include a focused laser beam positioned to enter the medium through the substrate, means for adjusting the focal position of the laser beam on either the partiaUy reflective or highly reflective layer, and a l' ' positioned to detect the reflected laser beam exiting the medium.
As used herein, the terms "silicon carbide" or "SiC" mean mixtures of silicon and carbon ranging in cu ~ from 30-50 atomic % silicon, 35-60 atomic %
carbon, and 0-20 atomic % oxygen, as measured by x-ray ,uLùLù~le.,l~un ~ ,L~u~,u~)y~ and having silicon-carbon ' ranging from SiCog to SiC~
Brief Descrigtion of the Drawing FIGURE I shows an optical data storage system according to the present invention.
FIGURE 2 is a computer-generated graph of internal interface reflectivity at 650 nm as a function of thickness for various materials.
FIGURE 3 is a computer-generated graph of internal surface reflectivity at 650 nm as a function of thickness for silicon carbide according to the present invention.
FIGURE 4 is a computer-generated graph of apparent reflectivity at 780 nm as a function of thickness for silicon carbide according to the present invention.
FIGURE 5 is a graph of the real component of the index of refraction (n) as a function of wavelength for various materials according to the present invention.
FIGIJRE 6 is a graph of the imaginary component of the index of refraction ~K) as a function of wavelength for various materials according to the present invention.
FIGURES 7A-7C show I ' u~ hs of various layers of the optical recording medium ~,u~l ~Llu~,Lcd according to Example I .
wo 96/046s0 2 ~. 9 4 2 2 7 I~ 6 n ~ ~ Descriptiorl ~.
An optical data storage system 10 according to the present invention is shown in FIGURE 1. Optical storage medium 12 comprises a transparent substrate 14, a partially reflective thin film layer 16 on a first data pit pattern 15, a transparent spacer layer 18, and a highly reflective thin film layer 20 on a second data pitpattern 19. An optical laser 30 en~its an optical beam toward medium 12, as shown in FIGURE 1. Light from the optical beam which is reflected by either thin film layer 16 or 20 is sensed by detector 32, which senses ' ' - in light intensity 0 based on the presence or absence of a pit in a particular spot on the thin film layers.
Although patterns 15 and 19 are referred to as "data pit pattems," pit patterns 15 and 19 may be any pattern of pits or grooves that is capable of storing '- , be it data, servo or tracking r ' , format r ~ ~ etc.
The capabilit,v for ' ~" ' 1~, reading either the first or second pit pattern 15 or 19 is based on the ~,u~u~ iv~l~ limited focal depth ~.Lvv~ , of typical optical disc readout systems. The lenses employed in typical optical c~,uld~ L.~_.v to form a diflfraction limited laser radiation spot on the media storage layer have moderately large (0.4 to 0.6) numerical apertures to improve resolution and increase storage density. Such lenses exhibit focal depths (i.e., the range of focus variation over which the focused spot size remains ~
diflraction limited) of about 2 llm; for large focus variations the size of the illuminated spot grows rapidly. C~ , if partially reflective thin film layer 16 exhibits adequate and the distance separating the two data pit pattems 15 and 19 is large relative to the optical system focal depth, it is possible to 2s focus the laser 30 on either data pi~ pattern with acceptably low "cross-talk" from the other data pit pattern. Thus, although the light from laser 30 will be reflected back toward detector 32 by both layers 16 and 20, only the layer upon which lhe laser is focused will strongly modulate the reflected light intensity, thereby enabling data readout.
30The data pit patterns 15 and 19 on medium 10 can be reproduced most easily by first focusing on one of the reflective layers 16 or 20, and then w096l04650 ~ 1 9 4 2 ~7 Y~
IqJI~ ~U ' ,, the data on that entire layer before switching focal position to focus on the other reflective layer. In the alternative, it may be desirable to switch focus position one or more times before completely ltlJluJuv;llg the data contained m one of data pit patterns 15 and 19. In either case, use of two data pit patterns separated 5 by transparent layer 18 effectively doubles the data storage capacity of optical recording medium 10.
T . , substrate 14 may be a polymeric materiai suitable for opticai disc substrates which supports moldmg of data pit pattern 15 with sufficient fidelity, such as pol~ or amorphous polyolefin. Al ~ it is possible to use o a flat substrate of, for example, glass or pGl~l...,Ll.J' ' ~iale~ and form data pit pattern 15 by means of pl-V~U~/GI,r..l~l replication, as will be described for the formation of data pit pattern 19.
T ,, spacer layer 18 may be a polymer, such as a pl,~,l.. ,.l11.
polymer, which has a complex refractive index with a reai r r t, n, ranging from about 1.45 to 1.6 and an imaginary , t, K, of less than 10~ and more preferably less than 105. Transparent spacer iayer 18 should be thick enough to ailow laser 30 to focus on either of data pit patterns 15 and 19 with a minimum of cross-talk. This translates into a thicicness that is preferably within the range of from about 5 to 100 llm, and more preferably from about 30 to 5ollm Highiy reflective layer 20 may be a metailic layer which exhibits high reflectivity at the laser vvv~L,..,~ used to reproduce the data. Currently available laser diode sources radiate at ~ ' ranging from about 600 to 850 nm.
Aiuminum, gold, silver, copper and their alloys can exhibit suitably high reflectivity in this ~vvv, ' . ' range. Highiy reflective layer 20 preferably has a reflectance of at least 70~/0, and more preferably at least 80%
In order to minimize the complexity and cost of optical data storage system 10, it is desirable that the average readout signai levels from each of the data pit patterns 15 and 19 be vlJyl~ 1~, equal. Thus, the apparent l~Li~,~,Liv;l;.,v from layers 16 and 20, as seen by detector 32, should also be vp~ , equai As used herein, the term "apparent ~ ,livity" refers to the fraction of opticai power incident upon transparent substrate 14 which, when focused to a spot wo961046s0 2 1 9 4 22 7 . ~IIU~ S _ v G
~n a flat region of either layer 16 or 20, could, in principle, be sensed by a in an optical readout device. It is assumed that the readout device comprises a laser, an a~ ulJl;vLcl~ designed opticai path, and a ~ t n~ . It is further assumed that the optical eiement in the opticai path which is in closest5 proximity to transparent substrate 14 is a high (>0.4) numerical aperture objective lens. As used herein, the terms "intemai surface lcn~,~,LiviLy" or "intemai interface c,n~~ " refer to the fraction of opticai power incident upon an interface withinthe media structure (e.g., the interface betveen transparent substrate 14 and partiaily reflecting layer 16 or the interface between spacer layer 18 and highiy lo reflecting layer 20) which is reflected.
In order to estimate the necessary reflectivity from partially reflective layer 16, we assume that highiy reflective layer 20 consists of aluminum, which reflects about 80 to 85% of the light incident on the intemai interface between spacer layer 18 and highiy reflective layer 20. It is further assumed that the refractive index reai 1S : . t, n, of spacer layer 18 is 1.5, that substrate 14 is pul~,al~ with a refractive index real ç/~mnr~n~nt~ n, of 1.57, and that reflections at the air-substrate interface do not contribute to the readout signal. If we further assume that partially reflecting layer 16 is an ideal materiai which exhibits no absorption, it can be shown that a reflectivity of about 0.35, as observed at the intemal interface between 20 substrate 14 and the partially reflecting layer will yield a balance in the apparent ~-,n~,~,LiviLi~,v from layers 16 and 20. While a partially reflecting iayer 16 which exhibits no absorption is ideal, reai partiaily reflecting layer materials are iikely to exhibit some absorption. If we choose a h~u~h~,ti~.ai partially reflective layer which absorbs 25% of the iight it does not reflect and define this as an upper limit for 2s acceptable absorption, we find that an intemal surface reflectivity of about 0.25 is required to baiance the reflectivity of layers 16 and 20. In this case, the apparent ~cll.,~L;viLi.,D from both layers is about 30% less than for the case of a partially reflecting layer which exhibits no absorption. Thus, the preceding examples define a range for the intemai surface reflectivity at the interface between the substrate 14 and layer 16 of from about 0.25 to 0.35 Taking into account the attenuation due to ~ W096104650 2 1 9 ~ ~7 PCTIUSgS/07096 reflections at the substrate-air interface, the above range CUIIG~)UIIdS to am apparent ~ reflectivity seen by an opticai readout device of about 0.24 to û.33.
Candidate materiais for partiaily reflecting layer 16 include metais, ~ ' and dielectrics. Metais, however, are generally strongly absorbing and may be expected to cause excessive signai at~pn~ on Ful~h~ u~ the reflectivity of metaiiic fiims typically is a very strong function of film thickness.
FIGURE 2 is a computer-generated graph based on optical modeling showing intemai surface reflectivity for incident iight of ~va~ ll 650 nm as a fiunction of thickness caiculated for films of gold (Au), aiuminum (Ai), and siiicon (Si) films 10 sall;i~ ~i between a 1.2 mm thick pOly~al~ substrate and a slab of n= 1.5, I~ = û material, which a~ u~;lllatl~D the effect of transparent spacer layer 18.r - of FIGW~E 2 reveals that the reflectivity of an Ai or Au partially reflecting layer chamges very rapidly with thickness, making control of film thickness and unifomlity during lllal.ura~,tul~: very difficult. An amorphous layer of 15 the ! ' ~ S; exhibits behavior which is similar to that of Au over the desired reflectivity range of û.24 to U.33; i.e., small changes in film thickness result in substantiai changes in reflectivity. r...Lh~....ul~, films with l~iu~,~iviL.,i~ in the desired 0.24 to U.33 range would be oniy about 4 nm thick for Ai and about 15-2ûrlm thick for Au and Si. Such relatively thin films may exhibit poor ~,.,~;.~ ' stabiiity.
In contrast to the behavior depicted in FIGURE 2, I have found that a partiaily reflective film comprising amorphous siiicon carbide exhibits reflectivity vs.
tbickness behavior which is much more desirable. As shown in FIGURE 3, which is a computer-generated graph based on opticai modeiing, the intemai surface reflectivity at 650 mm lies within the desirable range of from about 0.24 to 0.33 for amorphous siiicon carbide fihm thicknesses ranging from about 35 nm to 65 nm.
Smail changes in thickness within this range have a much less p~ u~luu.l~ d effect on reflectivity than is observed for the materials depicted in FIGURE 2. C~r-~q~
*e r ' ~ / of a duai layer disc comprising a siiicon carbide partiaily reflecting layer is greatly improved relative to that of a dual layer disc comprising partiaily reflecting layers with ~,La~ a~ Lh~ such as those depicted rn FIGURE 2.
W096/04650 2 19 4 2 2 7 r_l,.S . .~ ~
The complex refractive index used to generate the graph shown in FIGURE
3 was determined for an amorphous silicon carbide film having a~.y~ , 42 atomic % silicon, 53 atomic % carbon, amd 5 atomic % oxygen, as measured by x-ray, ' ' ua D~ LluDcu~Jy. The highly dcsirable behavior shown in FIGURE 3 5 results from the complex refractive index ~ ul~ L;u of amorphous silicon carbide. The relatively low value of K (~0.19 at 650 nm) results in acceptably low attenuation of the signal from second data pit pattern 20, and in . ' with the relatively large value of n (~3.07at 650nm), yields a first maximum in reflectivity as a function of thickness that lies within the desired range for the lo FIGURE I media ..o..~.u, The small rate of change in reflectance versus thickness on either side of the maximum yields the highly desired viLy of the reflectance to variations in the thickness of partially reflecting layer 16.
As noted previously, in addition to having a partially reflective layer for which reflectance changes only slowly with thickness variations, it is also desirable 15 that the apparent ~;n~LiviLi~D from layers 16 and 20 be ~ Jlwd~ LulJ equal, and it is most desirable that both . ~ n. ~ occur over the same range of partiallyreflectmg layer i' ' Stated differently, it is most desirable to have a media CUIIDLIU~LiUII for which the apparent ~r~ iviLkD from layers 16 and 20 are both ".~, equal and insensitive to layer 16 thickness variations. This situation is 20 depicted ' '1~ in a computer-generated graph based on optical modeling shown in FIGURE 4 . Inspection of FIGllRE 4 reveals that the apparent ~t n~ ~Livi~ D from layers 16 and 20 differ from one another by less than about _ 0.03 for partially reflecting layer thicknesses ranging from about 50 to about 80 nrn, i.e., a thickness variation from a nominal value of 65 nm of more than + 20%.
25 It can be shown that the absolute values of apparent reflectivity for both layers 16 and 20 depend upon both the real and imaginary r~ - ~~ of the partiaOy reflecting layer complex reflractive index, and that the behavior shown in FIGURE 4 occurs for only a narrow range of complex refractive index values.
Using the previously described ~ . regarding the reflectsmce of the 30 highly reflective layer and the optical properties of the substrate 14 and ~LUL~ U /~ Iayer 18, it can be shown that a SiC partially reflective layer (similar ~ W0 96/046~0 2 1 9 4 2 ~ 7 P~ v. E
in . . to the film used in FIGURE 3) will exhibit behavior ' 'ly identical to that depicted in FIGURE 4 when used at a ~4a~,L l.~,LIl of 780 nm, i.e., the ~a~lul~ Il used by currently available compact disc players. Amorphous silicon carbide, thus, is close to an ideal material for use at this ~a~' ,,"
5 However, K varies as a function of ~av. ' ,," Use of amorphous silicon carbide- containing no more than 5 atomic % oxygen at ~a~ .S~ho in the 600-650 mm range is some,vhat less ideal, however, as K has increased from about 0.12 at 780 nm to about 0.24 at 600 nm.
The a~ lu~ hlldt~ doubling of K results in less light i through o partially reflecting layer 16, which reduces the apparent reflectivity from highly re'decting layer 20. C.. l ~ly, the apparent ~cn~Livi~h,s from layers 16 and 20 will not be ' 'l~ equal over the desired range of partially refiecting layer thi~ l-n.~cc~c Accordingly, it may be desirable to alter the physical properties of the SiC to reduce K This may be , ' ' ' by the use of a dopant, such as silicon dioxide.
The real and imaginary r ' of complex refractive index for three different amorphous silicon carbide: . are shown in FIGURES 5 and 6 as a function of ~ ' These three specimens were prepared by UUv~UI ' ~, from a silicon carbide target and a silicon dioxide target and changing the power levels, resulting in three different amorph~us silicon carbide c ~ ~u~ -- - The first CUIIIIJI "' contained about 42 atomic % silicon, 53 atomic % carbon, and 5 atomic % oxygen. The second and third amorphous silicon carbide l u~
contained about 8 and 12 atomic ~/0 oxygen, ,.,v~ ,Li~ . As shown in FIGURES 5 and 6, the complex refractive index of these materials varies with ~a~lul~5 h.
FIGURES 5 and 6 show that addition of oxygen to the amorphous SiC
reduces both n and K of the resulting mixture. As the reduction in n will decrease the magnitude of the maximum refiectivity from the internal interface between substrate 14 and layer 16 while the reduction in K manifests itself as increasedof light through layer 16, it is apparent that relatively small additions of oxygen into SiC can be used to tune the optical properties of the resulting mixture such that the highly desirable behavior ' "!~ depicted in FIGURE 4 can be wo 96/0465~) 2 1 9 4 2 2 7 r~
obtained for ' '1~ any ~n~ ~ for which media operation is desired within the 500 to 850 mm ~n~ range.
Those skilled in the art will appreciate that me&um 12 of the present invention is not restricted to pre-recorded media. For example, second data pit 5 pattem 19 could be replaced with a grooved or pitted pattem which provides tracking '' to the drive. If a highly refiective, recordable material were used for highly reflective thin film layer 20, medium 12 could contain pre-recorded '- in first data pit pattem 15 while allowing data to be recorded by the user into layer 20. Thus, in this case, medium 12 would have one layer of pre-10 recorded data and one layer of user recordable The present invention will now be further illustrated by the following non-limiting examples. (All ~ are n~ u~di~ Le.) Example 1 A medium 10 as shown in FTGURE I was CU.. ~.lUl,ltl;] as follows. A
nominally 1.2 mm thick pul~l,, substrate 14 having a data pit pattem 15 was injection molded. Substrate 14 was placed under vacuum for at least 8 hours to remove absorbed water. Amorphous silicon carbide was used for the partially re'dective layer 16. The silicon carbide was sputter deposited from a silicon carbide 20 target onto data pit pattem 15 on substrate 14 using an inner diameter (ID) and outer diameter (OD) mask.
The &sc was then placed in a spin coater. Transparent spacer layer 18 was deposited by dispersing via syringe about I ml of W curable ~ Lul~ul~ having a nominal viscosity of 1350 centipoise in a "donut", 6,, dLiUII near the disc ID25 while the disc was rotating at about 50 ~vuluL;uns/ ~ (rpm). The rotational speed of the disc was then quickly (i.e., in less than one second), ramped up to 3000 rpm for at least 10 seconds.
The disc was then removed from the spin coater using a vacuum wand and was positioned on a replicator platen. The disc was covered with an inert 30 a , ' c; (nitrogen) and was cured using ultraviolet (W) radiation from a medium pressure mercury arc lamp.
~ wo 961046s0 2 l 9 4 2 2 ~ PCT/USgS/07096 A second pl.~"opol.~ Iayer was deposited and cured on the previous layer in the same manner described above to create a nominal I ~ l spacer layer 18 of 34-37 llm between the data pit pattern molded into the substrate and the s ' . ~v deposited i ' . ~ . Iayer into which the second data pit pattern was replicated.
Second data pit pattern 19 was formed by first depositing a third layer as described above, but without performing the W cure step.
A stamper containing a negative of the second data pit pattern was brought into contact with the uncured 1 ' . 1~ . The third polymer was then W cured and 0 the stamper carefully removed. The disc was then subjected to a post-W cure.
The disc was then placed under vacuum for at least 8 hours to remove absorbed water and other vacuum ~~ Using an ID mask, highly reflective layer 20 comprising about 97 atomic % alummum was vacuum deposited to a thickness of about 100 nm.
A pl ~lu~ P sealcoat was then deposited over highly reflective layer 20 to protect it, and was W cured as described above. As a final step, the disc wasfinished by abrasive polishing around its outer ..;. ~ ~ .,.,ce to remove any excess 1' ' r-l~lll~.l from the spin coating and replication processes. The abrasive finishing step was ,- . ' ' ' by holding the disc in a center-hole chuck, rotating it at about 500 to 1000 rpm, and gently holding the edge against sandpaper attached to a firm surface.
ExamDle 2 Discs made in the manner described above were then placed in a Nkon model UM-2 measuring ~. '_,uscu~,~;. P; ~ ' u~a~LD of the two reflective layers are shown in FIGURES 7A and 7B. Fl[GURE 7A shows data pit pattern 15 for partially reflective layer 16. FIGURE 7B shows data pit pattern 19 for highly reflective layer 20. Note that even though light from the ~.u.,.u~,op., must pass through partially reflective layer 16 to reach highly reflective layer 20 (and then must pass back through layer 16 upon refiection from layer 20), the ~ u~,ul~, was still able to focus on highly reflective layer 20. The ~ ' ~ u~sla~JL~ shown in w0 96/04650 2 1 9 4 2 2 7 ~ c FIGURES 7A and 7B show good contrast between land and pit regions, which would be expected to lead to adequate read-back signals from a laser focused on either layer. FIGURE 7C is a r~ - u~lvph taken where the ll~ivlU~vOpe was focused at a point midway between reflective layers 16 and 20. The 5 1 ' ~ u~;.v.~,hv d ...~ that it is possible for a drive to focus on and distinguish between the two data pit patterns.
An optical data storage system 10 according to the present invention is shown in FIGURE 1. Optical storage medium 12 comprises a transparent substrate 14, a partially reflective thin film layer 16 on a first data pit pattern 15, a transparent spacer layer 18, and a highly reflective thin film layer 20 on a second data pitpattern 19. An optical laser 30 en~its an optical beam toward medium 12, as shown in FIGURE 1. Light from the optical beam which is reflected by either thin film layer 16 or 20 is sensed by detector 32, which senses ' ' - in light intensity 0 based on the presence or absence of a pit in a particular spot on the thin film layers.
Although patterns 15 and 19 are referred to as "data pit pattems," pit patterns 15 and 19 may be any pattern of pits or grooves that is capable of storing '- , be it data, servo or tracking r ' , format r ~ ~ etc.
The capabilit,v for ' ~" ' 1~, reading either the first or second pit pattern 15 or 19 is based on the ~,u~u~ iv~l~ limited focal depth ~.Lvv~ , of typical optical disc readout systems. The lenses employed in typical optical c~,uld~ L.~_.v to form a diflfraction limited laser radiation spot on the media storage layer have moderately large (0.4 to 0.6) numerical apertures to improve resolution and increase storage density. Such lenses exhibit focal depths (i.e., the range of focus variation over which the focused spot size remains ~
diflraction limited) of about 2 llm; for large focus variations the size of the illuminated spot grows rapidly. C~ , if partially reflective thin film layer 16 exhibits adequate and the distance separating the two data pit pattems 15 and 19 is large relative to the optical system focal depth, it is possible to 2s focus the laser 30 on either data pi~ pattern with acceptably low "cross-talk" from the other data pit pattern. Thus, although the light from laser 30 will be reflected back toward detector 32 by both layers 16 and 20, only the layer upon which lhe laser is focused will strongly modulate the reflected light intensity, thereby enabling data readout.
30The data pit patterns 15 and 19 on medium 10 can be reproduced most easily by first focusing on one of the reflective layers 16 or 20, and then w096l04650 ~ 1 9 4 2 ~7 Y~
IqJI~ ~U ' ,, the data on that entire layer before switching focal position to focus on the other reflective layer. In the alternative, it may be desirable to switch focus position one or more times before completely ltlJluJuv;llg the data contained m one of data pit patterns 15 and 19. In either case, use of two data pit patterns separated 5 by transparent layer 18 effectively doubles the data storage capacity of optical recording medium 10.
T . , substrate 14 may be a polymeric materiai suitable for opticai disc substrates which supports moldmg of data pit pattern 15 with sufficient fidelity, such as pol~ or amorphous polyolefin. Al ~ it is possible to use o a flat substrate of, for example, glass or pGl~l...,Ll.J' ' ~iale~ and form data pit pattern 15 by means of pl-V~U~/GI,r..l~l replication, as will be described for the formation of data pit pattern 19.
T ,, spacer layer 18 may be a polymer, such as a pl,~,l.. ,.l11.
polymer, which has a complex refractive index with a reai r r t, n, ranging from about 1.45 to 1.6 and an imaginary , t, K, of less than 10~ and more preferably less than 105. Transparent spacer iayer 18 should be thick enough to ailow laser 30 to focus on either of data pit patterns 15 and 19 with a minimum of cross-talk. This translates into a thicicness that is preferably within the range of from about 5 to 100 llm, and more preferably from about 30 to 5ollm Highiy reflective layer 20 may be a metailic layer which exhibits high reflectivity at the laser vvv~L,..,~ used to reproduce the data. Currently available laser diode sources radiate at ~ ' ranging from about 600 to 850 nm.
Aiuminum, gold, silver, copper and their alloys can exhibit suitably high reflectivity in this ~vvv, ' . ' range. Highiy reflective layer 20 preferably has a reflectance of at least 70~/0, and more preferably at least 80%
In order to minimize the complexity and cost of optical data storage system 10, it is desirable that the average readout signai levels from each of the data pit patterns 15 and 19 be vlJyl~ 1~, equal. Thus, the apparent l~Li~,~,Liv;l;.,v from layers 16 and 20, as seen by detector 32, should also be vp~ , equai As used herein, the term "apparent ~ ,livity" refers to the fraction of opticai power incident upon transparent substrate 14 which, when focused to a spot wo961046s0 2 1 9 4 22 7 . ~IIU~ S _ v G
~n a flat region of either layer 16 or 20, could, in principle, be sensed by a in an optical readout device. It is assumed that the readout device comprises a laser, an a~ ulJl;vLcl~ designed opticai path, and a ~ t n~ . It is further assumed that the optical eiement in the opticai path which is in closest5 proximity to transparent substrate 14 is a high (>0.4) numerical aperture objective lens. As used herein, the terms "intemai surface lcn~,~,LiviLy" or "intemai interface c,n~~ " refer to the fraction of opticai power incident upon an interface withinthe media structure (e.g., the interface betveen transparent substrate 14 and partiaily reflecting layer 16 or the interface between spacer layer 18 and highiy lo reflecting layer 20) which is reflected.
In order to estimate the necessary reflectivity from partially reflective layer 16, we assume that highiy reflective layer 20 consists of aluminum, which reflects about 80 to 85% of the light incident on the intemai interface between spacer layer 18 and highiy reflective layer 20. It is further assumed that the refractive index reai 1S : . t, n, of spacer layer 18 is 1.5, that substrate 14 is pul~,al~ with a refractive index real ç/~mnr~n~nt~ n, of 1.57, and that reflections at the air-substrate interface do not contribute to the readout signal. If we further assume that partially reflecting layer 16 is an ideal materiai which exhibits no absorption, it can be shown that a reflectivity of about 0.35, as observed at the intemal interface between 20 substrate 14 and the partially reflecting layer will yield a balance in the apparent ~-,n~,~,LiviLi~,v from layers 16 and 20. While a partially reflecting iayer 16 which exhibits no absorption is ideal, reai partiaily reflecting layer materials are iikely to exhibit some absorption. If we choose a h~u~h~,ti~.ai partially reflective layer which absorbs 25% of the iight it does not reflect and define this as an upper limit for 2s acceptable absorption, we find that an intemal surface reflectivity of about 0.25 is required to baiance the reflectivity of layers 16 and 20. In this case, the apparent ~cll.,~L;viLi.,D from both layers is about 30% less than for the case of a partially reflecting layer which exhibits no absorption. Thus, the preceding examples define a range for the intemai surface reflectivity at the interface between the substrate 14 and layer 16 of from about 0.25 to 0.35 Taking into account the attenuation due to ~ W096104650 2 1 9 ~ ~7 PCTIUSgS/07096 reflections at the substrate-air interface, the above range CUIIG~)UIIdS to am apparent ~ reflectivity seen by an opticai readout device of about 0.24 to û.33.
Candidate materiais for partiaily reflecting layer 16 include metais, ~ ' and dielectrics. Metais, however, are generally strongly absorbing and may be expected to cause excessive signai at~pn~ on Ful~h~ u~ the reflectivity of metaiiic fiims typically is a very strong function of film thickness.
FIGURE 2 is a computer-generated graph based on optical modeling showing intemai surface reflectivity for incident iight of ~va~ ll 650 nm as a fiunction of thickness caiculated for films of gold (Au), aiuminum (Ai), and siiicon (Si) films 10 sall;i~ ~i between a 1.2 mm thick pOly~al~ substrate and a slab of n= 1.5, I~ = û material, which a~ u~;lllatl~D the effect of transparent spacer layer 18.r - of FIGW~E 2 reveals that the reflectivity of an Ai or Au partially reflecting layer chamges very rapidly with thickness, making control of film thickness and unifomlity during lllal.ura~,tul~: very difficult. An amorphous layer of 15 the ! ' ~ S; exhibits behavior which is similar to that of Au over the desired reflectivity range of û.24 to U.33; i.e., small changes in film thickness result in substantiai changes in reflectivity. r...Lh~....ul~, films with l~iu~,~iviL.,i~ in the desired 0.24 to U.33 range would be oniy about 4 nm thick for Ai and about 15-2ûrlm thick for Au and Si. Such relatively thin films may exhibit poor ~,.,~;.~ ' stabiiity.
In contrast to the behavior depicted in FIGURE 2, I have found that a partiaily reflective film comprising amorphous siiicon carbide exhibits reflectivity vs.
tbickness behavior which is much more desirable. As shown in FIGURE 3, which is a computer-generated graph based on opticai modeiing, the intemai surface reflectivity at 650 mm lies within the desirable range of from about 0.24 to 0.33 for amorphous siiicon carbide fihm thicknesses ranging from about 35 nm to 65 nm.
Smail changes in thickness within this range have a much less p~ u~luu.l~ d effect on reflectivity than is observed for the materials depicted in FIGURE 2. C~r-~q~
*e r ' ~ / of a duai layer disc comprising a siiicon carbide partiaily reflecting layer is greatly improved relative to that of a dual layer disc comprising partiaily reflecting layers with ~,La~ a~ Lh~ such as those depicted rn FIGURE 2.
W096/04650 2 19 4 2 2 7 r_l,.S . .~ ~
The complex refractive index used to generate the graph shown in FIGURE
3 was determined for an amorphous silicon carbide film having a~.y~ , 42 atomic % silicon, 53 atomic % carbon, amd 5 atomic % oxygen, as measured by x-ray, ' ' ua D~ LluDcu~Jy. The highly dcsirable behavior shown in FIGURE 3 5 results from the complex refractive index ~ ul~ L;u of amorphous silicon carbide. The relatively low value of K (~0.19 at 650 nm) results in acceptably low attenuation of the signal from second data pit pattern 20, and in . ' with the relatively large value of n (~3.07at 650nm), yields a first maximum in reflectivity as a function of thickness that lies within the desired range for the lo FIGURE I media ..o..~.u, The small rate of change in reflectance versus thickness on either side of the maximum yields the highly desired viLy of the reflectance to variations in the thickness of partially reflecting layer 16.
As noted previously, in addition to having a partially reflective layer for which reflectance changes only slowly with thickness variations, it is also desirable 15 that the apparent ~;n~LiviLi~D from layers 16 and 20 be ~ Jlwd~ LulJ equal, and it is most desirable that both . ~ n. ~ occur over the same range of partiallyreflectmg layer i' ' Stated differently, it is most desirable to have a media CUIIDLIU~LiUII for which the apparent ~r~ iviLkD from layers 16 and 20 are both ".~, equal and insensitive to layer 16 thickness variations. This situation is 20 depicted ' '1~ in a computer-generated graph based on optical modeling shown in FIGURE 4 . Inspection of FIGllRE 4 reveals that the apparent ~t n~ ~Livi~ D from layers 16 and 20 differ from one another by less than about _ 0.03 for partially reflecting layer thicknesses ranging from about 50 to about 80 nrn, i.e., a thickness variation from a nominal value of 65 nm of more than + 20%.
25 It can be shown that the absolute values of apparent reflectivity for both layers 16 and 20 depend upon both the real and imaginary r~ - ~~ of the partiaOy reflecting layer complex reflractive index, and that the behavior shown in FIGURE 4 occurs for only a narrow range of complex refractive index values.
Using the previously described ~ . regarding the reflectsmce of the 30 highly reflective layer and the optical properties of the substrate 14 and ~LUL~ U /~ Iayer 18, it can be shown that a SiC partially reflective layer (similar ~ W0 96/046~0 2 1 9 4 2 ~ 7 P~ v. E
in . . to the film used in FIGURE 3) will exhibit behavior ' 'ly identical to that depicted in FIGURE 4 when used at a ~4a~,L l.~,LIl of 780 nm, i.e., the ~a~lul~ Il used by currently available compact disc players. Amorphous silicon carbide, thus, is close to an ideal material for use at this ~a~' ,,"
5 However, K varies as a function of ~av. ' ,," Use of amorphous silicon carbide- containing no more than 5 atomic % oxygen at ~a~ .S~ho in the 600-650 mm range is some,vhat less ideal, however, as K has increased from about 0.12 at 780 nm to about 0.24 at 600 nm.
The a~ lu~ hlldt~ doubling of K results in less light i through o partially reflecting layer 16, which reduces the apparent reflectivity from highly re'decting layer 20. C.. l ~ly, the apparent ~cn~Livi~h,s from layers 16 and 20 will not be ' 'l~ equal over the desired range of partially refiecting layer thi~ l-n.~cc~c Accordingly, it may be desirable to alter the physical properties of the SiC to reduce K This may be , ' ' ' by the use of a dopant, such as silicon dioxide.
The real and imaginary r ' of complex refractive index for three different amorphous silicon carbide: . are shown in FIGURES 5 and 6 as a function of ~ ' These three specimens were prepared by UUv~UI ' ~, from a silicon carbide target and a silicon dioxide target and changing the power levels, resulting in three different amorph~us silicon carbide c ~ ~u~ -- - The first CUIIIIJI "' contained about 42 atomic % silicon, 53 atomic % carbon, and 5 atomic % oxygen. The second and third amorphous silicon carbide l u~
contained about 8 and 12 atomic ~/0 oxygen, ,.,v~ ,Li~ . As shown in FIGURES 5 and 6, the complex refractive index of these materials varies with ~a~lul~5 h.
FIGURES 5 and 6 show that addition of oxygen to the amorphous SiC
reduces both n and K of the resulting mixture. As the reduction in n will decrease the magnitude of the maximum refiectivity from the internal interface between substrate 14 and layer 16 while the reduction in K manifests itself as increasedof light through layer 16, it is apparent that relatively small additions of oxygen into SiC can be used to tune the optical properties of the resulting mixture such that the highly desirable behavior ' "!~ depicted in FIGURE 4 can be wo 96/0465~) 2 1 9 4 2 2 7 r~
obtained for ' '1~ any ~n~ ~ for which media operation is desired within the 500 to 850 mm ~n~ range.
Those skilled in the art will appreciate that me&um 12 of the present invention is not restricted to pre-recorded media. For example, second data pit 5 pattem 19 could be replaced with a grooved or pitted pattem which provides tracking '' to the drive. If a highly refiective, recordable material were used for highly reflective thin film layer 20, medium 12 could contain pre-recorded '- in first data pit pattem 15 while allowing data to be recorded by the user into layer 20. Thus, in this case, medium 12 would have one layer of pre-10 recorded data and one layer of user recordable The present invention will now be further illustrated by the following non-limiting examples. (All ~ are n~ u~di~ Le.) Example 1 A medium 10 as shown in FTGURE I was CU.. ~.lUl,ltl;] as follows. A
nominally 1.2 mm thick pul~l,, substrate 14 having a data pit pattem 15 was injection molded. Substrate 14 was placed under vacuum for at least 8 hours to remove absorbed water. Amorphous silicon carbide was used for the partially re'dective layer 16. The silicon carbide was sputter deposited from a silicon carbide 20 target onto data pit pattem 15 on substrate 14 using an inner diameter (ID) and outer diameter (OD) mask.
The &sc was then placed in a spin coater. Transparent spacer layer 18 was deposited by dispersing via syringe about I ml of W curable ~ Lul~ul~ having a nominal viscosity of 1350 centipoise in a "donut", 6,, dLiUII near the disc ID25 while the disc was rotating at about 50 ~vuluL;uns/ ~ (rpm). The rotational speed of the disc was then quickly (i.e., in less than one second), ramped up to 3000 rpm for at least 10 seconds.
The disc was then removed from the spin coater using a vacuum wand and was positioned on a replicator platen. The disc was covered with an inert 30 a , ' c; (nitrogen) and was cured using ultraviolet (W) radiation from a medium pressure mercury arc lamp.
~ wo 961046s0 2 l 9 4 2 2 ~ PCT/USgS/07096 A second pl.~"opol.~ Iayer was deposited and cured on the previous layer in the same manner described above to create a nominal I ~ l spacer layer 18 of 34-37 llm between the data pit pattern molded into the substrate and the s ' . ~v deposited i ' . ~ . Iayer into which the second data pit pattern was replicated.
Second data pit pattern 19 was formed by first depositing a third layer as described above, but without performing the W cure step.
A stamper containing a negative of the second data pit pattern was brought into contact with the uncured 1 ' . 1~ . The third polymer was then W cured and 0 the stamper carefully removed. The disc was then subjected to a post-W cure.
The disc was then placed under vacuum for at least 8 hours to remove absorbed water and other vacuum ~~ Using an ID mask, highly reflective layer 20 comprising about 97 atomic % alummum was vacuum deposited to a thickness of about 100 nm.
A pl ~lu~ P sealcoat was then deposited over highly reflective layer 20 to protect it, and was W cured as described above. As a final step, the disc wasfinished by abrasive polishing around its outer ..;. ~ ~ .,.,ce to remove any excess 1' ' r-l~lll~.l from the spin coating and replication processes. The abrasive finishing step was ,- . ' ' ' by holding the disc in a center-hole chuck, rotating it at about 500 to 1000 rpm, and gently holding the edge against sandpaper attached to a firm surface.
ExamDle 2 Discs made in the manner described above were then placed in a Nkon model UM-2 measuring ~. '_,uscu~,~;. P; ~ ' u~a~LD of the two reflective layers are shown in FIGURES 7A and 7B. Fl[GURE 7A shows data pit pattern 15 for partially reflective layer 16. FIGURE 7B shows data pit pattern 19 for highly reflective layer 20. Note that even though light from the ~.u.,.u~,op., must pass through partially reflective layer 16 to reach highly reflective layer 20 (and then must pass back through layer 16 upon refiection from layer 20), the ~ u~,ul~, was still able to focus on highly reflective layer 20. The ~ ' ~ u~sla~JL~ shown in w0 96/04650 2 1 9 4 2 2 7 ~ c FIGURES 7A and 7B show good contrast between land and pit regions, which would be expected to lead to adequate read-back signals from a laser focused on either layer. FIGURE 7C is a r~ - u~lvph taken where the ll~ivlU~vOpe was focused at a point midway between reflective layers 16 and 20. The 5 1 ' ~ u~;.v.~,hv d ...~ that it is possible for a drive to focus on and distinguish between the two data pit patterns.
Claims (10)
1. An optical storage medium (12), comprising, in order:
a transparent substrate (14) having a pattern of pits (15) in one major surface thereof;
a partially reflective layer (16) adjacent the pit pattern, having an index of refraction having a real component, n, wherein 2.6 <
n < 3.2, and an imaginary component, K, less than 0.4, measured at any wavelength within the range 500 to 850 nm;
a transparent polymer spacer layer (18) having a thickness within the range of from about 5 to 100 µm; and a highly reflective layer (20).
a transparent substrate (14) having a pattern of pits (15) in one major surface thereof;
a partially reflective layer (16) adjacent the pit pattern, having an index of refraction having a real component, n, wherein 2.6 <
n < 3.2, and an imaginary component, K, less than 0.4, measured at any wavelength within the range 500 to 850 nm;
a transparent polymer spacer layer (18) having a thickness within the range of from about 5 to 100 µm; and a highly reflective layer (20).
2. An optical storage disc (12), comprising, in order:
a transparent substrate (14) having a first data pit pattern (15) in one major surface thereof;
a partially reflective layer (16) adjacent the first data pit pattern, having an index of refraction having a real component, n, wherein 2.6<n<3.2, and an imaginary component, K, less than 0.4, measured at a wavelength of 650 nm;
a transparent spacer layer (18) having a second data pit pattern (19) in one major surface thereof, said major surface being on a side of the spacer layer opposite the partially reflective layer, the spacer layer having a thickness within the range from about 5 to 100 µm; and a highly reflective layer (20) provided adjacent the second data pit pattern.
a transparent substrate (14) having a first data pit pattern (15) in one major surface thereof;
a partially reflective layer (16) adjacent the first data pit pattern, having an index of refraction having a real component, n, wherein 2.6<n<3.2, and an imaginary component, K, less than 0.4, measured at a wavelength of 650 nm;
a transparent spacer layer (18) having a second data pit pattern (19) in one major surface thereof, said major surface being on a side of the spacer layer opposite the partially reflective layer, the spacer layer having a thickness within the range from about 5 to 100 µm; and a highly reflective layer (20) provided adjacent the second data pit pattern.
3. An optical storage medium (12), comprising, in order:
a transparent substrate (14) having a pattern of pits (15) in one major surface thereof, a partially reflective layer (16), adjacent the pit pattern, comprising silicon carbide;
a transparent polymer spacer layer (18); and a highly reflective layer (20).
a transparent substrate (14) having a pattern of pits (15) in one major surface thereof, a partially reflective layer (16), adjacent the pit pattern, comprising silicon carbide;
a transparent polymer spacer layer (18); and a highly reflective layer (20).
4. The medium of claims 1, 2, or 3, wherein the partially reflective layer has an internal surface reflectivity which varies by less than ~0.03 over thickness variations in the partially reflective layer of ~10%.
5. The medium of claims 1 or 2, wherein the partially reflective layer comprises silicon carbide.
6. The medium of claims 3 or 5, wherein the silicon carbide comprises from about 5 to 15 atomic % oxygen.
7. The medium of claims 1, 2, or 3, wherein the partially reflective layer is from 30 to 80 nm thick.
8. The medium of claims 3 or 5, wherein the ratio of silicon to carbon in the partially reflecting layer is about 1:1.3.
9. An optical storage system (10), comprising:
an optical storage medium (12), comprising, in order:
a transparent substrate (14) having a pattern of pits (15) in one major surface thereof;
a partially reflective layer (16) comprising silicon carbide;
a transparent polymer spacer layer (18); and a highly reflective layer (20);
a focused laser beam (30) positioned to enter the medium through the substrate;
means for adjusting focal position of the laser beam, whereby the beam may be focused on either the partially reflective layer or the highly reflective layer; and a photodetector (32) positioned to detect the reflected laser beam exiting the medium.
an optical storage medium (12), comprising, in order:
a transparent substrate (14) having a pattern of pits (15) in one major surface thereof;
a partially reflective layer (16) comprising silicon carbide;
a transparent polymer spacer layer (18); and a highly reflective layer (20);
a focused laser beam (30) positioned to enter the medium through the substrate;
means for adjusting focal position of the laser beam, whereby the beam may be focused on either the partially reflective layer or the highly reflective layer; and a photodetector (32) positioned to detect the reflected laser beam exiting the medium.
10. A pre-recorded optical disc storage system (10), comprising:
a pre-recorded optical disc (12), comprising, in order:
a transparent substrate (14) having a first data pit pattern (15) in one major surface thereof;
a partially reflective layer (16), adjacent the first data pit pattern, having an index of refraction having a real component, n, wherein 2.6 < n < 3.2, and an imaginary component, K, less than 0.4, measured at a wavelength of 650 nm;
a transparent spacer layer (18) having a second data pit pattern (19) in one major surface thereof, said major surface being on a side of the spacer layer opposite the partially reflective layer; and a highly reflective layer (20) provided adjacent the second data pit pattern;
a focused laser beam (30) positioned to enter the disc through the substrate;
means for adjusting focal position of the laser beam, whereby the beam may be focused on either the partially reflective layer or the highly reflective layer; and a photodetector (32) positioned to detect the reflected laser beam exiting the disc.
a pre-recorded optical disc (12), comprising, in order:
a transparent substrate (14) having a first data pit pattern (15) in one major surface thereof;
a partially reflective layer (16), adjacent the first data pit pattern, having an index of refraction having a real component, n, wherein 2.6 < n < 3.2, and an imaginary component, K, less than 0.4, measured at a wavelength of 650 nm;
a transparent spacer layer (18) having a second data pit pattern (19) in one major surface thereof, said major surface being on a side of the spacer layer opposite the partially reflective layer; and a highly reflective layer (20) provided adjacent the second data pit pattern;
a focused laser beam (30) positioned to enter the disc through the substrate;
means for adjusting focal position of the laser beam, whereby the beam may be focused on either the partially reflective layer or the highly reflective layer; and a photodetector (32) positioned to detect the reflected laser beam exiting the disc.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/286,289 US5540966A (en) | 1994-08-05 | 1994-08-05 | Dual layer optical medium having partially reflecting thin film layer |
| US08/286,289 | 1994-08-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2194227A1 true CA2194227A1 (en) | 1996-02-15 |
Family
ID=23097924
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002194227A Abandoned CA2194227A1 (en) | 1994-08-05 | 1995-06-05 | Dual layer optical medium having partially reflecting thin film layer |
Country Status (9)
| Country | Link |
|---|---|
| US (3) | US5540966A (en) |
| EP (1) | EP0775357B1 (en) |
| JP (1) | JPH10503872A (en) |
| KR (1) | KR970705136A (en) |
| CN (1) | CN1134774C (en) |
| CA (1) | CA2194227A1 (en) |
| DE (1) | DE69508258T2 (en) |
| MX (1) | MX9700859A (en) |
| WO (1) | WO1996004650A1 (en) |
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-
1994
- 1994-08-05 US US08/286,289 patent/US5540966A/en not_active Expired - Lifetime
-
1995
- 1995-06-05 KR KR1019970700735A patent/KR970705136A/en not_active Application Discontinuation
- 1995-06-05 DE DE69508258T patent/DE69508258T2/en not_active Expired - Fee Related
- 1995-06-05 MX MX9700859A patent/MX9700859A/en unknown
- 1995-06-05 CA CA002194227A patent/CA2194227A1/en not_active Abandoned
- 1995-06-05 JP JP8506475A patent/JPH10503872A/en active Pending
- 1995-06-05 EP EP95922964A patent/EP0775357B1/en not_active Expired - Lifetime
- 1995-06-05 WO PCT/US1995/007096 patent/WO1996004650A1/en not_active Application Discontinuation
- 1995-06-05 CN CNB951944819A patent/CN1134774C/en not_active Expired - Fee Related
-
1996
- 1996-06-07 US US08/660,241 patent/US5679429A/en not_active Expired - Lifetime
-
1998
- 1998-08-21 US US09/138,066 patent/US5993930A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| KR970705136A (en) | 1997-09-06 |
| US5993930A (en) | 1999-11-30 |
| WO1996004650A1 (en) | 1996-02-15 |
| EP0775357B1 (en) | 1999-03-10 |
| EP0775357A1 (en) | 1997-05-28 |
| JPH10503872A (en) | 1998-04-07 |
| US5540966A (en) | 1996-07-30 |
| DE69508258D1 (en) | 1999-04-15 |
| US5679429A (en) | 1997-10-21 |
| DE69508258T2 (en) | 1999-09-09 |
| MX9700859A (en) | 1997-04-30 |
| CN1134774C (en) | 2004-01-14 |
| CN1155347A (en) | 1997-07-23 |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Discontinued |