CA1299286C - Data storage device having a phase change memory medium reversible by direct overwrite - Google Patents
Data storage device having a phase change memory medium reversible by direct overwriteInfo
- Publication number
- CA1299286C CA1299286C CA000568330A CA568330A CA1299286C CA 1299286 C CA1299286 C CA 1299286C CA 000568330 A CA000568330 A CA 000568330A CA 568330 A CA568330 A CA 568330A CA 1299286 C CA1299286 C CA 1299286C
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- Prior art keywords
- data storage
- phase change
- layer
- dielectric
- tlle
- Prior art date
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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
- G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
- G11B7/0045—Recording
- G11B7/00454—Recording involving phase-change effects
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
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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
- G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
- G11B7/0055—Erasing
- G11B7/00557—Erasing involving phase-change media
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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
- G11B7/242—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
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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
- G11B7/257—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B9/00—Recording or reproducing using a method not covered by one of the main groups G11B3/00 - G11B7/00; Record carriers therefor
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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
- G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
- G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
- G11B2007/24302—Metals or metalloids
- G11B2007/24314—Metals or metalloids group 15 elements (e.g. Sb, Bi)
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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
- G11B7/257—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers
- G11B2007/25705—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials
- G11B2007/2571—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials containing group 14 elements except carbon (Si, Ge, Sn, Pb)
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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
- G11B7/257—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers
- G11B2007/25705—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials
- G11B2007/25715—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials containing oxygen
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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
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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
- G11B7/253—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
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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
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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
Abstract
1524.1 ABSTRACT OF THE DISCLOSURE
Disclosed is method and apparatus for direct, single beam, overwrite of new data over existing date in a phase change optical data storage device. This eliminates the need for an intermediate erase step.
0110r
Disclosed is method and apparatus for direct, single beam, overwrite of new data over existing date in a phase change optical data storage device. This eliminates the need for an intermediate erase step.
0110r
Description
l524 ~ 6 D~T~ 5TORr~GE ~EVICE IIAVING A Pi~SE CHANGE
MEMORY tlEDlUM REVERSI~LE BY DIRECT OVERWRITE
AND METHOD OF DIRECT OVEI~RITE
FIELD OF T~E IN~ENIIUN
The invention disclosed herein relates to data storage devices, where data is stored in a material that is reversibly switchdble between detectable states by the application of projected bealn energy thereto.
BACKGI~OUNU UF TllE INVENllUN
.
' Non-ablative state changeable data storage systems, for example, optical data storage systems, record information in a state changeable material that is switchable between at least two detectable states by the application of projected beam eneryy thereto, for example, optical energy.
State changeable data storage material is incorporated in a data storage device having a structure such that the data storage material is supported by a substrate and encapsulated in encapsulants. In the case of optical data storage devices tlle encapsulants include, for example, anti-ablation materials and layers, thermal insulation materials and layers, anti-reflection materials and layers, reflective layers, and ctlelnical isolation layers. Moreover, various layers may perform more~
tllan one of these functions. For example, anti-reflection layers may also be anti-at)lation layers and therlllal insulating layers. The thicknesses of the layers, including the layer of state changeable data storage rnaterial, are optimized to minimize the 15~4.1 energy necessary for state change and optimize the high contrast ratio, hiyh carrier to noise ratio, and high stability of state changeable data storage materials.
The state changeable material is a materidl capable of being switched from one detectable state to another detectable state or states by the appl;cation of projected bearn energy thereto. State cllangeable materials are sucll that the detectable states may differ in their morphology, surface topography, relative degree of order, relative degree of disorder, electrical properties, optical properties including the absorption coefficient, the indices of refraction and reflectivity, or combinations of one or more of these properties. The state of state changeable material is detectable by the electrical conductivity, electrical resistivity, optical transmissivity, optical absorption, optical refraction, optical reflectivity, or combinations thereof.
Formation of the data storage device includes deposition of the individual layers, for example by evaporative deposition, chemical vapor deposition, and/or plasma deposition. As used l~erein plasma deposition includes sputtering, glow discharge, and plasma assisted chemical vapor deposition.
Tellurium based materials have been utilized as state changeable materials for data storage where the state change is a structural change evidenced by a change in reflectivity. This effect is described, for example, in J. Feinleib, J. deNeufville, S.C. Moss, and S.R. Ovsllinsky, "Rapid llever5it)1e Light-lnduced Crystallization of Amorphous Semiconductors," Appl.
Phys. Lett., Vol. 18(~), pages 254-257 (March 15, 1971), and in U.S. Patent 3,530,~41 to S.R. Ovsllinsky for Method and Apparatus For Storin~ And Retrieving Of Information. A recent description of 1 5 2 4 . 1 1~9 telluriu~ germdniuln-tin systems, witl10ut oxygen, is in M. Chen, K.A. Rubin, V. Marrello, U.G. Gerber, and V.B. Jipson, "Reversibility And Stability of Tellurium Alloys for Optical Data Storage," Appl. Phys. Lett., 5 Vol. 46(8), pages 734-736 (April 15, 1~53. A recent description of telluriuln-gerlnaniulll-tin systems witi oxygen is in M. Takenaga, N. Yamada, S. ~hara, K.
Nishiciuchi, M. Nagashi11la~ T. Kas~ ara, S. Nakam~lra, and T. Yamasllita, "New Opttcal Erasable ~ledium Usiny Tellurium Suboxide Thin Filn1," Proceedinys, SPIE
Conference on Optical Data Storage, Arlington, VA, 1983, pages 173-177.
Tellurium based state cllallgeahle nlaterials, - in general, are single or multi~pl1ased systems (lJ
where the ordering pllenolnena include a nucleation and growth process (including both or eitller homogeneous and heterogeneous nucleations) to convert a system of disordered materials to a system of ordered and disordered materials, and (Z) wllere the vitrification phenomenon includes melting and rapid quenchirlg of ttle phase challgeab1e material to transform a system of disordered and ordered materials to a system of largely disordered materials. Tlle above phase charlyes and separations occur over relative1y small distances, with intimate interlocking of the phases and gross structural discrimination, and can be higl1ly sensitive to local variations in stoichiometry.
A serious limitation to the rate of data transfer is the slow cycle time, wllich is, in turn, limited by the crystallizing or erasir1g time. Pllase change data storage systems suffer from a deficiency not encountered in magnetic data storage systems. In magnetic data storage systems, a new recording is made over an existing recording, simultalleously erasing the existing recording. This is not possible with phase change media optical data storane systel1ls. To the contrary, phase cllange optical data storage systems require separate erase (crystallize) and write (vitrify) steps in the "write" cycle in order to enter data where data already exists.
s An important operational aspect of this problem is that tlle long duratioll of the erasing or crystallization process un(iuly lengtllells the time required for tl~e erase-rewrite cycle. In priol art systenls, the phase change materials llave an erase lo (crystallization) time of 0.5 micro seconds or larger. Tllis has necessitated sucll expedients as an elliptic laser beam spot to lengthen tlle irradiation time. Ilowever, for reading and fur writing (vitrifying) anotller spot, e.g., a round spot, is necessary. This required two optical systenls. Thus, in prior art phase change systems a two laser erase-write cycle is utilized. Tllis requires a two laser head. This is a complex system, and difficult to keep aligned. The first laser erases (crystallized) a data segment or sector. Thereafter, the data segment or sector is written by the second laser, e.g., by programnled vitrification.
In tlle case of nlagneto-optic systems, two complete disc revolutiolls are required per cycle, one for erasing and one for writing. Tllis particularly limits the ability to use these prior art erasable discs in real time recording of long data streams.
4a SUMMARY OF THE INVENT ON
The present invention is used in an optical data storage memory device comprising a substrate, a dielectric first encapsulating layer on the substrate, a memory layer on the dielectric first encapsulating layer, and a dielectric second encapsulating layer atop the memory layer, the improvement wherein the memory layer is a non-ablative, reversible, phase change m~mory layer comprising a solid solution of antimony, selenium, and tellurium, the solid solution being single phase in the amorphous and crystalline states, having a crystallization temperature above 120 degrees Centigrade, and having the composition:
( Sb2Te3 ) l-X ( Sb2 Se3 ) x where x is from 0.18 to 0.43.
According to the invention herein contemplated there is provided an apparatus for direct single beam overwrite.
By direct overwrite is meant rewriting, i.e., vitrifying, without first erasing (crystallizing in phase change systems) any pre-existing data. The 1nvention described herein ~: rn/
1 5 2 4 . 1 provides optical data entl^y in a manner analogous to that oF magnetic discs i.e. direct overwrite witht)ut a first separate discrete erasure (crystallization) step.
According to the inverltion there is provided a local therlllal envirolllllent that allows the laser pulse that is the ;ntensity the duratiorl or the integral of the intensity witl\ respect to time to be tlle determinant of the state of the phase change datd lo storage material. This may be accomplished by meltirlg the phase change material with superlleating of the molten phase change material with tlle superheat heating adjacent material and allowing the phase change material and the layers in contact therewith to act as a thermal capacitance to reduce the tl)e cooling rate dTemperature/dTilne of the solidifyiny phase cllange material in crystalli~ation while permitting a higher cooling rate dTemperature/dTillle of the solidifying phase change material to obtain an amorphous material.
According to a preferred eYemplificatiorl of the invention erasure (crystalli~ation in the case of phase change systems) is affected by heating both a memory cell of phase change material and the surrounding therlrlal envirolllllellt to a high enouyh temperature to slowly cool the molten phase chanqe matérial and form a crystalline solid thereof and writing (vitrification in the case of phase ch~nge systems) is affected by heating a melrlory cell of phase changè material higll enougll to melt the materi~l while avoiding significant heating of tlle surrounding thermal envirorlment so that the aforementioned surrounding thermal environmént acts as a heat sink for the molten phase change material to rapidly cool the molten phase change material and form an amorphous solid thereof. As useli herein the 52~
l5~4.l ~6--thermal environmerlt' refers primarily to adjacent layers.
For exalnple during the record or vitrification step at a first relatively low puwer level Pl the energy incident upon a melilory cell and absorbed by the phase chanye material is enougll to melt a memory cell of the phase change material but insufficient to significantly heat surroundillg and adjacent layers and memory cells. Thus the cooliny rate dTemperature/dTime of tl,e solidifying phase change material is relatively high and the phase change material cools and solidifies into the amorphous state.
By way of contrast during the erase or crystallization step at a second relatively higil power level, P2, the energy incident upon d mernory cell and absorbed by the phase change material is enough to hoth melt the phase change material and heat the surrounding therlllal environment high enough to slow or retard the cooling rate dTemperature/dTime of the solidifying phase change material to an extent that permits the phase change materidl to solidify into a crystalline state.
According to the invention, the optical reflectivities and optical absorptiolls of each state of the phase change recording mediulll are tailored such that the anlount of tlle energy absorbed per unit volume of the phase change material is indepelldent of the state of the phase change rnaterial. Ihis results in the same temperature-tirlle profile for both states for any yiven incident power level.
In the practice of the inverltion a data storage device is utilized for exanll)le havirlg a chalcogenide compound or mixture of chalcoyenide compounds as the data storage mediurn. The material exhibits crystallization tirnes of undPr l microsecnnd ~ ~S ~8 1524.1 .
~1000 nanoseconds), direct overwrite capability, and preferably a long cycle life. A suhstrate supl)orts t!le mediurll, and dielectric films enrapsulate the phase cllange material data stordge mediulll.
s In order to take greatest advantage of direct, single beam, overwrite, the data storage mediuln should be one that can un-iergo structural transformation with minimal compositional change so as to exhibit rapid ordering phenomenon, e.g., lo crystallization. Thus, the data storage material itself should be one that chemically and morphologically provides reduced time for switching from tlle less ordered detectable state to the more ordered detectable state.
The preferred data storage media are those that have a fast enough crystallization time to avoid damage or degradation of the substrate, and to allow the use of relatively inexpensive solid state lasers for writing and erasing, but high enollgh to provide a measure of archival thernlal stability. Preferably the crystallization temperature is from above about 120 degrees Centigrade and even above e.g. to about 200 degrees Centigrade or even higher. I'referably, in order to take advantage of direct, single beam, overwrite, e.g., for real time data entry the data storage medium composition has a switching time, i.e., an "erase" time or "crystallization" time of less thar 1 microsecond, and preferably less then 500 nanoseconds.
In a further exemplification, one or more of writing data into a data storage device, reading data out of the data storage device, or erasing data from the data storage device is perforllled. The metllod comprises writing data into tl1e data storage mediunl with electromagnetic energy of a first energy derlsity and duration, reading the state of tbe dlta storage l5~4.l medium with electromagnetic energy of a second enertJy density and duration, and direct ovelwriting of new data into the data storage medium atop the unerased data already present with electrornagnetic energy of a proper energy density and duration, for example of the same energy density and duration as tlle first write, or at a different energy density and duration.
The data storage mediuln may be formed by depositing the materials to form a substantially uniform deposit thereof. Generally, the deposit llas a thickness of an even multiple of one quarter of the product of the optical index of refraction of the material and the laser wavelength.
Accordiny to a further exemnlificatioll of the invention herein comtelnplated tllere is provided a data storage device having a chalcogenide compound or mixture oF chalcogenide compounds as the data storaye medium. Ihe material exhibits crystallization times of under l microsecond (lO00 nanoseconds), direct overwrite capability, and a long cycle life. A
substrate supports the medium, and a dielectric film encapsulates the chalcogenide COIllpOUlld data storage medium.
It is believed that tlle chalcogen data storage medium undergoes structural transforlnation with minimal compositiorlal change so as to exhibit rapid ordering phenolllenon, e.g., crystallization.
Thus, the chalcogen data storage material provides reduced time for switclling from tlle less ordered detectable state to the more ordered detectable state.
The chalcogenide data storage medium is a miscible solid solution of a telluride and a selenide, as arsenic telluride-arsenic selenide, antimony telluride-antimony selenide, or bismuth telluride-bismuth selenide. Especially preferred is the composition antimorly tellllride-.lrltilllonY selPrlide.
15~ cJ~
The telluride-selenide composition appear to be substantially miscible and substantial1y single phase ti.e. it is believed to be iso-structural) in each of the amorI)Ilous and crystalline states.
Preferably the telluride-selenide composition has a crystallization temperature low enough and a fast enough crystallization time to avoid damage or degradation of the substrate and to allow the use of relatively inexpensive solid state lasers for writing and erasing but high enough to pruvide a measure of archival thermal stability. Preferably the crystallization temperature is from above about 1~0 degrees Centigrade and even above e.g. to about ~0 degrees Centigraie or even higher. Preferably the telluride-selenide composition llas a switchirlg time i.e., an "erase" time or "crystallization" time of less than 1 microsecond, and preferably less then 3~0 nanoseconds.
In a particularly preferred exemplification the telluride-selenide composition is (sb2Te3)l-x(sb2se3)x~ where x is froIn ~ 1 to 0.43 and preferably from 0.2~ to 0.3S.
TIIE DI~WINGS
The invention may be particuIarly understood by reference to the drawings appended hereto.
Figure 1 is a partial cut away isometric view, not to scale, with exaggerated latitudinal dimensions and vertical scale, of an optical data storage device.
Figure 2 is a detailed section of the part of the optical data storage device of Figure 1 showing the relationship of the various layers thereof.
1524.1 Figure 3 is a representation of (a) tlle switching time, and (b) the crystallization temperature measured at a heating rate of 1 degree centigrade per second, both versus the variable x in the formula (Sbzle3)l x(Sb2Se3)x, i-e., as a function of Se and Te contents.
DETAILED DE~CR~PTION UF IHE I~IVENII~N
IO According to tlle inventioll described llereirl, there is provided a method and apparatus for direct, single beam, overwrite of data into a projected beam storage device havirlg a phase cllarlge data storage medlulll swltchable between detectable states by the application of projected beam energy tllereto.
Figures 1 and 2 show a projected beam (lata storage device 1 having a substrate, for example a plastic substrate 11, a first encapsulating dielectric layer 21, for example a first germalliuln oxide encapsulating layer, a chalcogenide pllase change compound data storage medium layer 31, a second dielectric layer 41, e.g., a second germanillln oxide layer 41, and a second substrate, e.g., plastic substrate 51.
Figure 2 shows a section o~ the data storage device 1 of Figure 1 in greater detail. As there shown, the substrate 11 is a polymeric sheet, for example a polymethyl methacrylate sl1eet. The substrate 11 is an optically invariant, optically isotropic, transparent sheet. The preferred thickness is of from about 1 mm to about 1.5 m~
Atop the substrate 11 may be a film, sheet, or layer 13, e.g., a polymerized acrylic slleet.
Polymerized, molded, injection molded~ or cast into the polymeric sheet 13 may be grooves. Alternatively, the grooves may be in the substit~lte 11~ in whicll casP
1524.1 ~ 6 tlle film, sheet, or layer 13 may be omitted. WherI
grooves are present they may hdve a tllickness from about 500 to about 1000 Angstroms. The film, sheet, or layer 13 may act as an adllesive, holding the substrate 11 to the encapsulants. It has a thickness of from about 30 to about ~00 microns and preferably from about 50 to about 100 microns.
Deposited atop the polymerized sheet 13 is a dielectric barrier layer 21. The dielectric barrier Io layer 21, for example, of gerInaniulll oxide, is fron1 about 500 to about 2000 angstroms thick. Preferably it has a thickness of lU30 Angstroms and arl optical thickness of one-quarter times the laser wavelenyth times the index of refraction of the material fornliIlg the dielectric layer 21. The iielectric barrier layer 21 has one or more functiolls. It serves to prevent oxidizing agents from getting to the chalcogen active layer 31 and prevents the plastic substrate from deforming due to local heating of the chalcogellide layer 31, e.g., during recording or erasing. The barrier layer 21 also serves as an anti-reflective coating, increasing the optical sensitivity of the chalcogenide active layer 31.
Other dielectrics may provide the encapsulating layers 21, 41. For example, the encapsulating layers may be silicon nitride, layered or graded to avoid diffusion of silicon into the chalcogenide layer 31. Alternatively, the encapsulating dielectric layers 21, 41 may be silica, alumina, silicon nitride, or other dielectric.
The compound data storage me~ In 31 has an optical thickness of one half of the laser waveIength times the index of refraction of the data storage material, i.e., about 800 Angstroms ~top the 31 and in contact with the opposite surface thereof is a second dielectric layer 41, e.g., a gerIllanilllll oxide 1';24.1 ~ 2~2~6 layer. Tlle second dielectric layer 41 mdy but need not be of equal thickness as tlle first layer 21.
Preferably it has a thickl)ess of one half times the laser wavelerlgth times the index of refraction.
second polymer layer q9 and a second substrate layer 51 may be in contact with tlle opposite surface of the encapsulatitlg layer 41 alternatively an air sandwicl structure nlay be utilized.
Tlle cllalcogenide coml)oulld data storage mediu behaves as a miscible solid solution of the telluride and the selenide. That is tlle selenide and the telluride are substantially capable of being mixed in substantially all proportions e.g. a single pllase in botn the crystalline and the amorpllous states.
The telluride-selenide cllalcogellide conlpoullds are telluride-selenides of one Ot' more Group VB
elements i.e. one or more As Sb or Bi. Especially preferred is the telluride-selenide of antimolly ( 2 e3)1 x(Sb2Se3)x. The value of x is determined by the balance of the switcing speed (crystallization time or erase time) and tlle crystallization temperature.
As shown in Figure 3 the switchirlg speed is a relative minumllnl in the vicini~y of x betweell ~.lU
and 0.43 witl7 values of x from 0.20 to ~.35 yieldiny the fastest erase times.
As futher shown in Figure 3 tlle crystallization temperature increases witll increasillg selenium content. Thus for archival stability higller selenium contents are indicated. Preferably the crystallization temperature is above 120 deyrees centigrade e.g. up to 200 degrees centigrade or even higher.
The switching times of tlle ( 2 e3)1 x(Sb2Se3)x especially when x is from about 0.20 to about 0.35 result in an erase 4.1 (crystallization) time of less thell U.5 microsecollds.
This permits the use of a circular laser beam spot for eras;ng rather than the elliptical laser beam erase spot of prior art material5. As a result, erasure can be accomplislled simultaneously with writing by sinyle beam overwrite.
The polyacrylate layers 13, 49, when present, are cast or moldecl in place. These layers 13, 49 can be photo-polyrnerized in place, e.g., by the application of ultra-violet light. The barrier layers 21, 41, are deposited, by evaporation, for example, of germanium and germanium oxide materials, or by sputtering, including reactive sputtering where the content of the reactive gas used in reactive sputtering is controlled. The chalcogerli(le film 31 may be prepared by evaporation, or by sputtering, or by chemical vapor deposition.
According to the invention tllere is provided a local thermal environment that allows the laser pulse, that is tlle intensity, the duration, or the integral of the intensity with respect to time, to be the determinant of tne state of the phase change data storage material 31. This may be accomplisl)ed by melting the phase change material 31, with superheating of the molten phase chanye material 31, witll the superheat ileating adjacent material,as the encapsulating dielectrics 21 and 41, and allowing the phase change material 31, and the layers, 21 and 41, in contact therewith, to act as a tllerlllal capacitance to reduce the the cooling rate, dTemperature/dTime, of the solidifying phase change material 31 in crystallization, while permitting a higller cooling rate, dTemperature/dTilne, of the solidifying phase change material 31 to obtain an amorl)hous material.
According to a preferred exemplification of the invention, erasure (crystallization) is affected 1524.1 ~ 2~
by heating both a melllory cell of phase change material 31 and tlle surroullding therlnal environlllent, as tile dielectric layers ~1 and 41, as well as other layers, for exannple thernlal insulation layersl heat sink layers, reflector layers, hermetic seal layers, an(l the like, to a high enough temperature to allow slow cooling of the molten phase change material 31 and form a crystalline solid thereof, and writing (vitrification) is affected by heating a memory cell lo of phase cllange material 31 high enough to melt tlle material while avoiding significant lleatillg of the surrounding therlllal envirorllllerlt so that the aforementioned surrounding therlnal environlllent acts as a heat sink for the molten phase change material 31 to force rapid cooling of the molten phase change materjal 31 and form an amorphous solid thereof.
For example, during the record or vitrification step, at a first, relatively lo~ power level, Pl, tlle energy incident upon a melnory cell and absorbed by the phase change material 31 is enough to melt 2 melnory cell of the phase change material 31, but insufficient to to significantly heat surrounding and adjacent layers e.g., layers 21 and 41, and melnory cells. Thus, the cooling rate, dlemperature/drillle, of the solidifying phase change material 31 is relatively high, and the phase change material 31 cools and solidifies into the amorphous state.
By way of contrast, during the erase or crystallization step, at a second, relatively high power level, P2, the energy incident upon a memory cell and absorbed by the phase change material 31 is enough to both melt the pllase change material 31 and heat the surrounding thermal environlnent, e.g., layers 21 and 41, as well as other layers, not shown, high enough to retard the cooling rate, dTemperature/dTime, of the solidifying phase change material to an extent 1524.1 that perrllits tlle phase change material to solidify into a crystalline state.
A cooling rate, dTemperature/dTilne, low enough to obtain a crystallized phase challge rnaterial 31 may be obtained by heating the therltlal environment surrounding the memory cell hot enough to retard the cooling rate thereof, so that phase change continues long after the laser has gone on to subsequent mellloly cells. This effectively increases the crystallization Io time in terms of structural pllenolllena within the device, i.e, the phase cllange material layer 31, and surrounding layers, 21 and 41, wllile acceleratiny tlle erase speed in terms of tl-e laser pulse, the disc rotation, and the rate of data entry. In this way crystallization time is effectively decoupled from data entry rate.
The optical reflectivities and optical absorptions of the states of the pllase change recording medillnl are tailored such that tlle amount of the energy absorbed per unit volulne of tlle phase change material is independent ot the state of tlle phase change material. This results in the same temperature-time profile for both states for any given incident power level. Generally, this means that the state having the higher reflectivity also llas a higller absorption coefficient, such that higller energy losses caused by higher reflectivity in one state are balanced by higher losses in the other state caused by lower absorption. This provides for the same portion of the incident beam energy to be absorbed by the memory material in each state.
In one alternatlve exempllflcation the non-ablative, phase change memory material 31 is a miscible telluride-selenide solid solution, for example a telluride-selenide solid solution of arsenic, antimony, or bismutll. Preferred is antimonY
~5~4.1 ttelluride-selerlide) which is single phase in both the amorphous (written) and crystalline (erased) states and has a crystallization temperature above about 120 degrees Centigrade. One pdrticularly preferred composition for the phase change material is (sb2se3)l-x(sb2Te3)x w~ere x is from U.18 to 0.43 as described above.
In a further exemplificatioll one or more of writing data into a data storage device reading data Io out of the data storage device or erasing data from the data storage devtce ls perforlned. the method comprises writing data into the data storage medium with electromagnetic energy of a first energy density and duration, reading the state of the data storagemediuln with electromagnetic energy of a second energy density and duration and direct overwriting of new data into the data storage mediuln atop the unerased data already present with electromagnetic energy of a proper energy density and duration for example of the same energy density and duration as the first write or at a different energy density and duration.
In order to take greatest advantage of direct, single beam overwrite the data storage medium should be one that can undergo structural transformation with minimal compositional change so as to exhibit rapid ordering phenomenon e.g.
crystalli~ation. Thus the data storage material itself should be one that chelnically and morphologically provides reduced time for switching from the less ordered detectable state to the more ordered detectable state.
~ Ihile the invention has been described with respect to certain preferred exemplifications and embodiments thereof it is not intended to be bound thereby but solely by the claims appellded llereto.
MEMORY tlEDlUM REVERSI~LE BY DIRECT OVERWRITE
AND METHOD OF DIRECT OVEI~RITE
FIELD OF T~E IN~ENIIUN
The invention disclosed herein relates to data storage devices, where data is stored in a material that is reversibly switchdble between detectable states by the application of projected bealn energy thereto.
BACKGI~OUNU UF TllE INVENllUN
.
' Non-ablative state changeable data storage systems, for example, optical data storage systems, record information in a state changeable material that is switchable between at least two detectable states by the application of projected beam eneryy thereto, for example, optical energy.
State changeable data storage material is incorporated in a data storage device having a structure such that the data storage material is supported by a substrate and encapsulated in encapsulants. In the case of optical data storage devices tlle encapsulants include, for example, anti-ablation materials and layers, thermal insulation materials and layers, anti-reflection materials and layers, reflective layers, and ctlelnical isolation layers. Moreover, various layers may perform more~
tllan one of these functions. For example, anti-reflection layers may also be anti-at)lation layers and therlllal insulating layers. The thicknesses of the layers, including the layer of state changeable data storage rnaterial, are optimized to minimize the 15~4.1 energy necessary for state change and optimize the high contrast ratio, hiyh carrier to noise ratio, and high stability of state changeable data storage materials.
The state changeable material is a materidl capable of being switched from one detectable state to another detectable state or states by the appl;cation of projected bearn energy thereto. State cllangeable materials are sucll that the detectable states may differ in their morphology, surface topography, relative degree of order, relative degree of disorder, electrical properties, optical properties including the absorption coefficient, the indices of refraction and reflectivity, or combinations of one or more of these properties. The state of state changeable material is detectable by the electrical conductivity, electrical resistivity, optical transmissivity, optical absorption, optical refraction, optical reflectivity, or combinations thereof.
Formation of the data storage device includes deposition of the individual layers, for example by evaporative deposition, chemical vapor deposition, and/or plasma deposition. As used l~erein plasma deposition includes sputtering, glow discharge, and plasma assisted chemical vapor deposition.
Tellurium based materials have been utilized as state changeable materials for data storage where the state change is a structural change evidenced by a change in reflectivity. This effect is described, for example, in J. Feinleib, J. deNeufville, S.C. Moss, and S.R. Ovsllinsky, "Rapid llever5it)1e Light-lnduced Crystallization of Amorphous Semiconductors," Appl.
Phys. Lett., Vol. 18(~), pages 254-257 (March 15, 1971), and in U.S. Patent 3,530,~41 to S.R. Ovsllinsky for Method and Apparatus For Storin~ And Retrieving Of Information. A recent description of 1 5 2 4 . 1 1~9 telluriu~ germdniuln-tin systems, witl10ut oxygen, is in M. Chen, K.A. Rubin, V. Marrello, U.G. Gerber, and V.B. Jipson, "Reversibility And Stability of Tellurium Alloys for Optical Data Storage," Appl. Phys. Lett., 5 Vol. 46(8), pages 734-736 (April 15, 1~53. A recent description of telluriuln-gerlnaniulll-tin systems witi oxygen is in M. Takenaga, N. Yamada, S. ~hara, K.
Nishiciuchi, M. Nagashi11la~ T. Kas~ ara, S. Nakam~lra, and T. Yamasllita, "New Opttcal Erasable ~ledium Usiny Tellurium Suboxide Thin Filn1," Proceedinys, SPIE
Conference on Optical Data Storage, Arlington, VA, 1983, pages 173-177.
Tellurium based state cllallgeahle nlaterials, - in general, are single or multi~pl1ased systems (lJ
where the ordering pllenolnena include a nucleation and growth process (including both or eitller homogeneous and heterogeneous nucleations) to convert a system of disordered materials to a system of ordered and disordered materials, and (Z) wllere the vitrification phenomenon includes melting and rapid quenchirlg of ttle phase challgeab1e material to transform a system of disordered and ordered materials to a system of largely disordered materials. Tlle above phase charlyes and separations occur over relative1y small distances, with intimate interlocking of the phases and gross structural discrimination, and can be higl1ly sensitive to local variations in stoichiometry.
A serious limitation to the rate of data transfer is the slow cycle time, wllich is, in turn, limited by the crystallizing or erasir1g time. Pllase change data storage systems suffer from a deficiency not encountered in magnetic data storage systems. In magnetic data storage systems, a new recording is made over an existing recording, simultalleously erasing the existing recording. This is not possible with phase change media optical data storane systel1ls. To the contrary, phase cllange optical data storage systems require separate erase (crystallize) and write (vitrify) steps in the "write" cycle in order to enter data where data already exists.
s An important operational aspect of this problem is that tlle long duratioll of the erasing or crystallization process un(iuly lengtllells the time required for tl~e erase-rewrite cycle. In priol art systenls, the phase change materials llave an erase lo (crystallization) time of 0.5 micro seconds or larger. Tllis has necessitated sucll expedients as an elliptic laser beam spot to lengthen tlle irradiation time. Ilowever, for reading and fur writing (vitrifying) anotller spot, e.g., a round spot, is necessary. This required two optical systenls. Thus, in prior art phase change systems a two laser erase-write cycle is utilized. Tllis requires a two laser head. This is a complex system, and difficult to keep aligned. The first laser erases (crystallized) a data segment or sector. Thereafter, the data segment or sector is written by the second laser, e.g., by programnled vitrification.
In tlle case of nlagneto-optic systems, two complete disc revolutiolls are required per cycle, one for erasing and one for writing. Tllis particularly limits the ability to use these prior art erasable discs in real time recording of long data streams.
4a SUMMARY OF THE INVENT ON
The present invention is used in an optical data storage memory device comprising a substrate, a dielectric first encapsulating layer on the substrate, a memory layer on the dielectric first encapsulating layer, and a dielectric second encapsulating layer atop the memory layer, the improvement wherein the memory layer is a non-ablative, reversible, phase change m~mory layer comprising a solid solution of antimony, selenium, and tellurium, the solid solution being single phase in the amorphous and crystalline states, having a crystallization temperature above 120 degrees Centigrade, and having the composition:
( Sb2Te3 ) l-X ( Sb2 Se3 ) x where x is from 0.18 to 0.43.
According to the invention herein contemplated there is provided an apparatus for direct single beam overwrite.
By direct overwrite is meant rewriting, i.e., vitrifying, without first erasing (crystallizing in phase change systems) any pre-existing data. The 1nvention described herein ~: rn/
1 5 2 4 . 1 provides optical data entl^y in a manner analogous to that oF magnetic discs i.e. direct overwrite witht)ut a first separate discrete erasure (crystallization) step.
According to the inverltion there is provided a local therlllal envirolllllent that allows the laser pulse that is the ;ntensity the duratiorl or the integral of the intensity witl\ respect to time to be tlle determinant of the state of the phase change datd lo storage material. This may be accomplished by meltirlg the phase change material with superlleating of the molten phase change material with tlle superheat heating adjacent material and allowing the phase change material and the layers in contact therewith to act as a thermal capacitance to reduce the tl)e cooling rate dTemperature/dTilne of the solidifyiny phase cllange material in crystalli~ation while permitting a higher cooling rate dTemperature/dTillle of the solidifying phase change material to obtain an amorphous material.
According to a preferred eYemplificatiorl of the invention erasure (crystalli~ation in the case of phase change systems) is affected by heating both a memory cell of phase change material and the surrounding therlrlal envirolllllellt to a high enouyh temperature to slowly cool the molten phase chanqe matérial and form a crystalline solid thereof and writing (vitrification in the case of phase ch~nge systems) is affected by heating a melrlory cell of phase changè material higll enougll to melt the materi~l while avoiding significant heating of tlle surrounding thermal envirorlment so that the aforementioned surrounding thermal environmént acts as a heat sink for the molten phase change material to rapidly cool the molten phase change material and form an amorphous solid thereof. As useli herein the 52~
l5~4.l ~6--thermal environmerlt' refers primarily to adjacent layers.
For exalnple during the record or vitrification step at a first relatively low puwer level Pl the energy incident upon a melilory cell and absorbed by the phase chanye material is enougll to melt a memory cell of the phase change material but insufficient to significantly heat surroundillg and adjacent layers and memory cells. Thus the cooliny rate dTemperature/dTime of tl,e solidifying phase change material is relatively high and the phase change material cools and solidifies into the amorphous state.
By way of contrast during the erase or crystallization step at a second relatively higil power level, P2, the energy incident upon d mernory cell and absorbed by the phase change material is enough to hoth melt the phase change material and heat the surrounding therlllal environment high enough to slow or retard the cooling rate dTemperature/dTime of the solidifying phase change material to an extent that permits the phase change materidl to solidify into a crystalline state.
According to the invention, the optical reflectivities and optical absorptiolls of each state of the phase change recording mediulll are tailored such that the anlount of tlle energy absorbed per unit volume of the phase change material is indepelldent of the state of the phase change rnaterial. Ihis results in the same temperature-tirlle profile for both states for any yiven incident power level.
In the practice of the inverltion a data storage device is utilized for exanll)le havirlg a chalcogenide compound or mixture of chalcoyenide compounds as the data storage mediurn. The material exhibits crystallization tirnes of undPr l microsecnnd ~ ~S ~8 1524.1 .
~1000 nanoseconds), direct overwrite capability, and preferably a long cycle life. A suhstrate supl)orts t!le mediurll, and dielectric films enrapsulate the phase cllange material data stordge mediulll.
s In order to take greatest advantage of direct, single beam, overwrite, the data storage mediuln should be one that can un-iergo structural transformation with minimal compositional change so as to exhibit rapid ordering phenomenon, e.g., lo crystallization. Thus, the data storage material itself should be one that chemically and morphologically provides reduced time for switching from tlle less ordered detectable state to the more ordered detectable state.
The preferred data storage media are those that have a fast enough crystallization time to avoid damage or degradation of the substrate, and to allow the use of relatively inexpensive solid state lasers for writing and erasing, but high enollgh to provide a measure of archival thernlal stability. Preferably the crystallization temperature is from above about 120 degrees Centigrade and even above e.g. to about 200 degrees Centigrade or even higher. I'referably, in order to take advantage of direct, single beam, overwrite, e.g., for real time data entry the data storage medium composition has a switching time, i.e., an "erase" time or "crystallization" time of less thar 1 microsecond, and preferably less then 500 nanoseconds.
In a further exemplification, one or more of writing data into a data storage device, reading data out of the data storage device, or erasing data from the data storage device is perforllled. The metllod comprises writing data into tl1e data storage mediunl with electromagnetic energy of a first energy derlsity and duration, reading the state of tbe dlta storage l5~4.l medium with electromagnetic energy of a second enertJy density and duration, and direct ovelwriting of new data into the data storage medium atop the unerased data already present with electrornagnetic energy of a proper energy density and duration, for example of the same energy density and duration as tlle first write, or at a different energy density and duration.
The data storage mediuln may be formed by depositing the materials to form a substantially uniform deposit thereof. Generally, the deposit llas a thickness of an even multiple of one quarter of the product of the optical index of refraction of the material and the laser wavelength.
Accordiny to a further exemnlificatioll of the invention herein comtelnplated tllere is provided a data storage device having a chalcogenide compound or mixture oF chalcogenide compounds as the data storaye medium. Ihe material exhibits crystallization times of under l microsecond (lO00 nanoseconds), direct overwrite capability, and a long cycle life. A
substrate supports the medium, and a dielectric film encapsulates the chalcogenide COIllpOUlld data storage medium.
It is believed that tlle chalcogen data storage medium undergoes structural transforlnation with minimal compositiorlal change so as to exhibit rapid ordering phenolllenon, e.g., crystallization.
Thus, the chalcogen data storage material provides reduced time for switclling from tlle less ordered detectable state to the more ordered detectable state.
The chalcogenide data storage medium is a miscible solid solution of a telluride and a selenide, as arsenic telluride-arsenic selenide, antimony telluride-antimony selenide, or bismuth telluride-bismuth selenide. Especially preferred is the composition antimorly tellllride-.lrltilllonY selPrlide.
15~ cJ~
The telluride-selenide composition appear to be substantially miscible and substantial1y single phase ti.e. it is believed to be iso-structural) in each of the amorI)Ilous and crystalline states.
Preferably the telluride-selenide composition has a crystallization temperature low enough and a fast enough crystallization time to avoid damage or degradation of the substrate and to allow the use of relatively inexpensive solid state lasers for writing and erasing but high enough to pruvide a measure of archival thermal stability. Preferably the crystallization temperature is from above about 1~0 degrees Centigrade and even above e.g. to about ~0 degrees Centigraie or even higher. Preferably the telluride-selenide composition llas a switchirlg time i.e., an "erase" time or "crystallization" time of less than 1 microsecond, and preferably less then 3~0 nanoseconds.
In a particularly preferred exemplification the telluride-selenide composition is (sb2Te3)l-x(sb2se3)x~ where x is froIn ~ 1 to 0.43 and preferably from 0.2~ to 0.3S.
TIIE DI~WINGS
The invention may be particuIarly understood by reference to the drawings appended hereto.
Figure 1 is a partial cut away isometric view, not to scale, with exaggerated latitudinal dimensions and vertical scale, of an optical data storage device.
Figure 2 is a detailed section of the part of the optical data storage device of Figure 1 showing the relationship of the various layers thereof.
1524.1 Figure 3 is a representation of (a) tlle switching time, and (b) the crystallization temperature measured at a heating rate of 1 degree centigrade per second, both versus the variable x in the formula (Sbzle3)l x(Sb2Se3)x, i-e., as a function of Se and Te contents.
DETAILED DE~CR~PTION UF IHE I~IVENII~N
IO According to tlle inventioll described llereirl, there is provided a method and apparatus for direct, single beam, overwrite of data into a projected beam storage device havirlg a phase cllarlge data storage medlulll swltchable between detectable states by the application of projected beam energy tllereto.
Figures 1 and 2 show a projected beam (lata storage device 1 having a substrate, for example a plastic substrate 11, a first encapsulating dielectric layer 21, for example a first germalliuln oxide encapsulating layer, a chalcogenide pllase change compound data storage medium layer 31, a second dielectric layer 41, e.g., a second germanillln oxide layer 41, and a second substrate, e.g., plastic substrate 51.
Figure 2 shows a section o~ the data storage device 1 of Figure 1 in greater detail. As there shown, the substrate 11 is a polymeric sheet, for example a polymethyl methacrylate sl1eet. The substrate 11 is an optically invariant, optically isotropic, transparent sheet. The preferred thickness is of from about 1 mm to about 1.5 m~
Atop the substrate 11 may be a film, sheet, or layer 13, e.g., a polymerized acrylic slleet.
Polymerized, molded, injection molded~ or cast into the polymeric sheet 13 may be grooves. Alternatively, the grooves may be in the substit~lte 11~ in whicll casP
1524.1 ~ 6 tlle film, sheet, or layer 13 may be omitted. WherI
grooves are present they may hdve a tllickness from about 500 to about 1000 Angstroms. The film, sheet, or layer 13 may act as an adllesive, holding the substrate 11 to the encapsulants. It has a thickness of from about 30 to about ~00 microns and preferably from about 50 to about 100 microns.
Deposited atop the polymerized sheet 13 is a dielectric barrier layer 21. The dielectric barrier Io layer 21, for example, of gerInaniulll oxide, is fron1 about 500 to about 2000 angstroms thick. Preferably it has a thickness of lU30 Angstroms and arl optical thickness of one-quarter times the laser wavelenyth times the index of refraction of the material fornliIlg the dielectric layer 21. The iielectric barrier layer 21 has one or more functiolls. It serves to prevent oxidizing agents from getting to the chalcogen active layer 31 and prevents the plastic substrate from deforming due to local heating of the chalcogellide layer 31, e.g., during recording or erasing. The barrier layer 21 also serves as an anti-reflective coating, increasing the optical sensitivity of the chalcogenide active layer 31.
Other dielectrics may provide the encapsulating layers 21, 41. For example, the encapsulating layers may be silicon nitride, layered or graded to avoid diffusion of silicon into the chalcogenide layer 31. Alternatively, the encapsulating dielectric layers 21, 41 may be silica, alumina, silicon nitride, or other dielectric.
The compound data storage me~ In 31 has an optical thickness of one half of the laser waveIength times the index of refraction of the data storage material, i.e., about 800 Angstroms ~top the 31 and in contact with the opposite surface thereof is a second dielectric layer 41, e.g., a gerIllanilllll oxide 1';24.1 ~ 2~2~6 layer. Tlle second dielectric layer 41 mdy but need not be of equal thickness as tlle first layer 21.
Preferably it has a thickl)ess of one half times the laser wavelerlgth times the index of refraction.
second polymer layer q9 and a second substrate layer 51 may be in contact with tlle opposite surface of the encapsulatitlg layer 41 alternatively an air sandwicl structure nlay be utilized.
Tlle cllalcogenide coml)oulld data storage mediu behaves as a miscible solid solution of the telluride and the selenide. That is tlle selenide and the telluride are substantially capable of being mixed in substantially all proportions e.g. a single pllase in botn the crystalline and the amorpllous states.
The telluride-selenide cllalcogellide conlpoullds are telluride-selenides of one Ot' more Group VB
elements i.e. one or more As Sb or Bi. Especially preferred is the telluride-selenide of antimolly ( 2 e3)1 x(Sb2Se3)x. The value of x is determined by the balance of the switcing speed (crystallization time or erase time) and tlle crystallization temperature.
As shown in Figure 3 the switchirlg speed is a relative minumllnl in the vicini~y of x betweell ~.lU
and 0.43 witl7 values of x from 0.20 to ~.35 yieldiny the fastest erase times.
As futher shown in Figure 3 tlle crystallization temperature increases witll increasillg selenium content. Thus for archival stability higller selenium contents are indicated. Preferably the crystallization temperature is above 120 deyrees centigrade e.g. up to 200 degrees centigrade or even higher.
The switching times of tlle ( 2 e3)1 x(Sb2Se3)x especially when x is from about 0.20 to about 0.35 result in an erase 4.1 (crystallization) time of less thell U.5 microsecollds.
This permits the use of a circular laser beam spot for eras;ng rather than the elliptical laser beam erase spot of prior art material5. As a result, erasure can be accomplislled simultaneously with writing by sinyle beam overwrite.
The polyacrylate layers 13, 49, when present, are cast or moldecl in place. These layers 13, 49 can be photo-polyrnerized in place, e.g., by the application of ultra-violet light. The barrier layers 21, 41, are deposited, by evaporation, for example, of germanium and germanium oxide materials, or by sputtering, including reactive sputtering where the content of the reactive gas used in reactive sputtering is controlled. The chalcogerli(le film 31 may be prepared by evaporation, or by sputtering, or by chemical vapor deposition.
According to the invention tllere is provided a local thermal environment that allows the laser pulse, that is tlle intensity, the duration, or the integral of the intensity with respect to time, to be the determinant of tne state of the phase change data storage material 31. This may be accomplisl)ed by melting the phase change material 31, with superheating of the molten phase chanye material 31, witll the superheat ileating adjacent material,as the encapsulating dielectrics 21 and 41, and allowing the phase change material 31, and the layers, 21 and 41, in contact therewith, to act as a tllerlllal capacitance to reduce the the cooling rate, dTemperature/dTime, of the solidifying phase change material 31 in crystallization, while permitting a higller cooling rate, dTemperature/dTilne, of the solidifying phase change material 31 to obtain an amorl)hous material.
According to a preferred exemplification of the invention, erasure (crystallization) is affected 1524.1 ~ 2~
by heating both a melllory cell of phase change material 31 and tlle surroullding therlnal environlllent, as tile dielectric layers ~1 and 41, as well as other layers, for exannple thernlal insulation layersl heat sink layers, reflector layers, hermetic seal layers, an(l the like, to a high enough temperature to allow slow cooling of the molten phase change material 31 and form a crystalline solid thereof, and writing (vitrification) is affected by heating a memory cell lo of phase cllange material 31 high enough to melt tlle material while avoiding significant lleatillg of the surrounding therlllal envirorllllerlt so that the aforementioned surrounding therlnal environlllent acts as a heat sink for the molten phase change material 31 to force rapid cooling of the molten phase change materjal 31 and form an amorphous solid thereof.
For example, during the record or vitrification step, at a first, relatively lo~ power level, Pl, tlle energy incident upon a melnory cell and absorbed by the phase change material 31 is enough to melt 2 melnory cell of the phase change material 31, but insufficient to to significantly heat surrounding and adjacent layers e.g., layers 21 and 41, and melnory cells. Thus, the cooling rate, dlemperature/drillle, of the solidifying phase change material 31 is relatively high, and the phase change material 31 cools and solidifies into the amorphous state.
By way of contrast, during the erase or crystallization step, at a second, relatively high power level, P2, the energy incident upon a memory cell and absorbed by the phase change material 31 is enough to both melt the pllase change material 31 and heat the surrounding thermal environlnent, e.g., layers 21 and 41, as well as other layers, not shown, high enough to retard the cooling rate, dTemperature/dTime, of the solidifying phase change material to an extent 1524.1 that perrllits tlle phase change material to solidify into a crystalline state.
A cooling rate, dTemperature/dTilne, low enough to obtain a crystallized phase challge rnaterial 31 may be obtained by heating the therltlal environment surrounding the memory cell hot enough to retard the cooling rate thereof, so that phase change continues long after the laser has gone on to subsequent mellloly cells. This effectively increases the crystallization Io time in terms of structural pllenolllena within the device, i.e, the phase cllange material layer 31, and surrounding layers, 21 and 41, wllile acceleratiny tlle erase speed in terms of tl-e laser pulse, the disc rotation, and the rate of data entry. In this way crystallization time is effectively decoupled from data entry rate.
The optical reflectivities and optical absorptions of the states of the pllase change recording medillnl are tailored such that tlle amount of the energy absorbed per unit volulne of tlle phase change material is independent ot the state of tlle phase change material. This results in the same temperature-time profile for both states for any given incident power level. Generally, this means that the state having the higher reflectivity also llas a higller absorption coefficient, such that higller energy losses caused by higher reflectivity in one state are balanced by higher losses in the other state caused by lower absorption. This provides for the same portion of the incident beam energy to be absorbed by the memory material in each state.
In one alternatlve exempllflcation the non-ablative, phase change memory material 31 is a miscible telluride-selenide solid solution, for example a telluride-selenide solid solution of arsenic, antimony, or bismutll. Preferred is antimonY
~5~4.1 ttelluride-selerlide) which is single phase in both the amorphous (written) and crystalline (erased) states and has a crystallization temperature above about 120 degrees Centigrade. One pdrticularly preferred composition for the phase change material is (sb2se3)l-x(sb2Te3)x w~ere x is from U.18 to 0.43 as described above.
In a further exemplificatioll one or more of writing data into a data storage device reading data Io out of the data storage device or erasing data from the data storage devtce ls perforlned. the method comprises writing data into the data storage medium with electromagnetic energy of a first energy density and duration, reading the state of the data storagemediuln with electromagnetic energy of a second energy density and duration and direct overwriting of new data into the data storage mediuln atop the unerased data already present with electromagnetic energy of a proper energy density and duration for example of the same energy density and duration as the first write or at a different energy density and duration.
In order to take greatest advantage of direct, single beam overwrite the data storage medium should be one that can undergo structural transformation with minimal compositional change so as to exhibit rapid ordering phenomenon e.g.
crystalli~ation. Thus the data storage material itself should be one that chelnically and morphologically provides reduced time for switching from the less ordered detectable state to the more ordered detectable state.
~ Ihile the invention has been described with respect to certain preferred exemplifications and embodiments thereof it is not intended to be bound thereby but solely by the claims appellded llereto.
Claims (2)
1. In an optical data storage memory device comprising a substrate, a dielectric first encapsulating layer on the substrate, a memory layer on the dielectric first encapsulating layer, and a dielectric second encapsulating layer atop the memory layer, the improvement wherein the memory layer is a non-ablative, reversible, phase change memory layer comprising a solid solution of antimony, selenium, and tellurium, said solid solution being single phase in the amorphous and crystalline states, having a crystallization temperature above 120 degrees Centigrade, and having the composition:
(Sb2Te3)1-x(Sb2Se3)x where x is from 0.18 to 0.43.
(Sb2Te3)1-x(Sb2Se3)x where x is from 0.18 to 0.43.
2. In an optical data storage memory device comprising a substrate a dielectric first encapsulating layer on the substrate, a memory layer on the dielectric first encapsulating layer, and a dielectric second encapsulating layer atop the memory layer, the improvement wherein:
(a) the memory layer has a nominal thickness of 800 Angstroms, in a non-ablative, reversible, phase change memory layer comprising a solid solution of antimony, selenium, and tellurium, said solid solution being single phase in the amorphous and crystalline states, having a crystallization temperature above 120 degrees Centigrade, and having the composition:
(Sb2Te3)1-x(Sb2Se3)x where x is from 0.20 to 0.35;
(b) the dielectric first encapsulating layer has a nominal thickness of 1030 Angstroms and comprises germanium oxide;
(c) the dielectric second encapsulating layer has a nominal thickness of 2060 Angstroms and comprises germanium oxide; and (d) the memory device has a crystallization time of less than 300 nanoseconds at 8300 Angstrom incident laser radiation.
(a) the memory layer has a nominal thickness of 800 Angstroms, in a non-ablative, reversible, phase change memory layer comprising a solid solution of antimony, selenium, and tellurium, said solid solution being single phase in the amorphous and crystalline states, having a crystallization temperature above 120 degrees Centigrade, and having the composition:
(Sb2Te3)1-x(Sb2Se3)x where x is from 0.20 to 0.35;
(b) the dielectric first encapsulating layer has a nominal thickness of 1030 Angstroms and comprises germanium oxide;
(c) the dielectric second encapsulating layer has a nominal thickness of 2060 Angstroms and comprises germanium oxide; and (d) the memory device has a crystallization time of less than 300 nanoseconds at 8300 Angstrom incident laser radiation.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US064,645 | 1987-06-22 | ||
| US07/064,645 US4876667A (en) | 1987-06-22 | 1987-06-22 | Data storage device having a phase change memory medium reversible by direct overwrite |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1299286C true CA1299286C (en) | 1992-04-21 |
Family
ID=22057350
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000568330A Expired - Lifetime CA1299286C (en) | 1987-06-22 | 1988-06-01 | Data storage device having a phase change memory medium reversible by direct overwrite |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4876667A (en) |
| CA (1) | CA1299286C (en) |
Families Citing this family (49)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2680039B2 (en) * | 1988-06-08 | 1997-11-19 | 株式会社日立製作所 | Optical information recording / reproducing method and recording / reproducing apparatus |
| US5335219A (en) * | 1991-01-18 | 1994-08-02 | Ovshinsky Stanford R | Homogeneous composition of microcrystalline semiconductor material, semiconductor devices and directly overwritable memory elements fabricated therefrom, and arrays fabricated from the memory elements |
| US5373491A (en) * | 1991-05-30 | 1994-12-13 | Hitachi, Ltd. | Wavelength-multiple optical recording medium |
| US6821707B2 (en) * | 1996-03-11 | 2004-11-23 | Matsushita Electric Industrial Co., Ltd. | Optical information recording medium, producing method thereof and method of recording/erasing/reproducing information |
| US7260051B1 (en) | 1998-12-18 | 2007-08-21 | Nanochip, Inc. | Molecular memory medium and molecular memory integrated circuit |
| US20020101816A1 (en) * | 1999-05-20 | 2002-08-01 | Michael F. Braitberg | Removable optical storage device and system |
| US6569705B2 (en) * | 2000-12-21 | 2003-05-27 | Intel Corporation | Metal structure for a phase-change memory device |
| US6924538B2 (en) | 2001-07-25 | 2005-08-02 | Nantero, Inc. | Devices having vertically-disposed nanofabric articles and methods of making the same |
| US6643165B2 (en) | 2001-07-25 | 2003-11-04 | Nantero, Inc. | Electromechanical memory having cell selection circuitry constructed with nanotube technology |
| US7259410B2 (en) | 2001-07-25 | 2007-08-21 | Nantero, Inc. | Devices having horizontally-disposed nanofabric articles and methods of making the same |
| US6911682B2 (en) | 2001-12-28 | 2005-06-28 | Nantero, Inc. | Electromechanical three-trace junction devices |
| US6919592B2 (en) | 2001-07-25 | 2005-07-19 | Nantero, Inc. | Electromechanical memory array using nanotube ribbons and method for making same |
| US7566478B2 (en) | 2001-07-25 | 2009-07-28 | Nantero, Inc. | Methods of making carbon nanotube films, layers, fabrics, ribbons, elements and articles |
| US6574130B2 (en) | 2001-07-25 | 2003-06-03 | Nantero, Inc. | Hybrid circuit having nanotube electromechanical memory |
| US6706402B2 (en) | 2001-07-25 | 2004-03-16 | Nantero, Inc. | Nanotube films and articles |
| US6835591B2 (en) | 2001-07-25 | 2004-12-28 | Nantero, Inc. | Methods of nanotube films and articles |
| US7176505B2 (en) | 2001-12-28 | 2007-02-13 | Nantero, Inc. | Electromechanical three-trace junction devices |
| US6784028B2 (en) | 2001-12-28 | 2004-08-31 | Nantero, Inc. | Methods of making electromechanical three-trace junction devices |
| US7335395B2 (en) | 2002-04-23 | 2008-02-26 | Nantero, Inc. | Methods of using pre-formed nanotubes to make carbon nanotube films, layers, fabrics, ribbons, elements and articles |
| US6985377B2 (en) | 2002-10-15 | 2006-01-10 | Nanochip, Inc. | Phase change media for high density data storage |
| US7233517B2 (en) | 2002-10-15 | 2007-06-19 | Nanochip, Inc. | Atomic probes and media for high density data storage |
| US6969868B2 (en) * | 2002-12-28 | 2005-11-29 | Intel Corporation | Method of storing a data bit including melting and cooling a volume of alloy therein |
| US7560136B2 (en) | 2003-01-13 | 2009-07-14 | Nantero, Inc. | Methods of using thin metal layers to make carbon nanotube films, layers, fabrics, ribbons, elements and articles |
| US7075141B2 (en) * | 2003-03-28 | 2006-07-11 | Nantero, Inc. | Four terminal non-volatile transistor device |
| US7113426B2 (en) * | 2003-03-28 | 2006-09-26 | Nantero, Inc. | Non-volatile RAM cell and array using nanotube switch position for information state |
| US7294877B2 (en) * | 2003-03-28 | 2007-11-13 | Nantero, Inc. | Nanotube-on-gate FET structures and applications |
| US6995046B2 (en) * | 2003-04-22 | 2006-02-07 | Nantero, Inc. | Process for making byte erasable devices having elements made with nanotubes |
| US7045421B2 (en) * | 2003-04-22 | 2006-05-16 | Nantero, Inc. | Process for making bit selectable devices having elements made with nanotubes |
| US7274064B2 (en) | 2003-06-09 | 2007-09-25 | Nanatero, Inc. | Non-volatile electromechanical field effect devices and circuits using same and methods of forming same |
| US7280394B2 (en) * | 2003-06-09 | 2007-10-09 | Nantero, Inc. | Field effect devices having a drain controlled via a nanotube switching element |
| US7528437B2 (en) * | 2004-02-11 | 2009-05-05 | Nantero, Inc. | EEPROMS using carbon nanotubes for cell storage |
| US7330369B2 (en) | 2004-04-06 | 2008-02-12 | Bao Tran | NANO-electronic memory array |
| US20050218398A1 (en) * | 2004-04-06 | 2005-10-06 | Availableip.Com | NANO-electronics |
| US7301887B2 (en) | 2004-04-16 | 2007-11-27 | Nanochip, Inc. | Methods for erasing bit cells in a high density data storage device |
| US20050232061A1 (en) | 2004-04-16 | 2005-10-20 | Rust Thomas F | Systems for writing and reading highly resolved domains for high density data storage |
| US7379412B2 (en) | 2004-04-16 | 2008-05-27 | Nanochip, Inc. | Methods for writing and reading highly resolved domains for high density data storage |
| US7709880B2 (en) * | 2004-06-09 | 2010-05-04 | Nantero, Inc. | Field effect devices having a gate controlled via a nanotube switching element |
| US6955937B1 (en) | 2004-08-12 | 2005-10-18 | Lsi Logic Corporation | Carbon nanotube memory cell for integrated circuit structure with removable side spacers to permit access to memory cell and process for forming such memory cell |
| US7671398B2 (en) * | 2005-02-23 | 2010-03-02 | Tran Bao Q | Nano memory, light, energy, antenna and strand-based systems and methods |
| US7479654B2 (en) * | 2005-05-09 | 2009-01-20 | Nantero, Inc. | Memory arrays using nanotube articles with reprogrammable resistance |
| US7394687B2 (en) | 2005-05-09 | 2008-07-01 | Nantero, Inc. | Non-volatile-shadow latch using a nanotube switch |
| TWI324773B (en) | 2005-05-09 | 2010-05-11 | Nantero Inc | Non-volatile shadow latch using a nanotube switch |
| US7367119B2 (en) | 2005-06-24 | 2008-05-06 | Nanochip, Inc. | Method for forming a reinforced tip for a probe storage device |
| US7463573B2 (en) | 2005-06-24 | 2008-12-09 | Nanochip, Inc. | Patterned media for a high density data storage device |
| US7309630B2 (en) | 2005-07-08 | 2007-12-18 | Nanochip, Inc. | Method for forming patterned media for a high density data storage device |
| US7525117B2 (en) * | 2005-08-09 | 2009-04-28 | Ovonyx, Inc. | Chalcogenide devices and materials having reduced germanium or telluruim content |
| KR101330769B1 (en) * | 2005-12-12 | 2013-11-18 | 오보닉스, 아이엔씨. | Chalcogenide devices and materials having reduced germanium or telluruim content |
| DE102006004218B3 (en) * | 2006-01-30 | 2007-08-16 | Infineon Technologies Ag | Electromechanical storage device and method for manufacturing an electromechanical storage device |
| DE102018203241A1 (en) | 2018-03-05 | 2019-09-05 | Carl Zeiss Smt Gmbh | Optical element, and method for correcting the wavefront effect of an optical element |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60155495A (en) * | 1984-01-26 | 1985-08-15 | Sony Corp | Information-recording medium |
| US4719594A (en) * | 1984-11-01 | 1988-01-12 | Energy Conversion Devices, Inc. | Grooved optical data storage device including a chalcogenide memory layer |
| US4660175A (en) * | 1985-07-08 | 1987-04-21 | Energy Conversion Devices, Inc. | Data storage device having novel barrier players encapsulating the data storage medium |
| US4744055A (en) * | 1985-07-08 | 1988-05-10 | Energy Conversion Devices, Inc. | Erasure means and data storage system incorporating improved erasure means |
-
1987
- 1987-06-22 US US07/064,645 patent/US4876667A/en not_active Expired - Lifetime
-
1988
- 1988-06-01 CA CA000568330A patent/CA1299286C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| US4876667A (en) | 1989-10-24 |
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