CA2004708A1 - Erasable phase change optical recording elements and methods - Google Patents
Erasable phase change optical recording elements and methodsInfo
- Publication number
- CA2004708A1 CA2004708A1 CA002004708A CA2004708A CA2004708A1 CA 2004708 A1 CA2004708 A1 CA 2004708A1 CA 002004708 A CA002004708 A CA 002004708A CA 2004708 A CA2004708 A CA 2004708A CA 2004708 A1 CA2004708 A1 CA 2004708A1
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- optical recording
- alloy
- recording
- layer
- laser
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Links
- 230000003287 optical effect Effects 0.000 title claims abstract description 32
- 238000000034 method Methods 0.000 title claims abstract description 25
- 230000008859 change Effects 0.000 title abstract description 4
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 42
- 239000000956 alloy Substances 0.000 claims abstract description 42
- 239000010409 thin film Substances 0.000 claims abstract description 6
- 230000007613 environmental effect Effects 0.000 abstract description 3
- 230000007704 transition Effects 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 31
- 239000000463 material Substances 0.000 description 31
- 239000010408 film Substances 0.000 description 13
- 239000000203 mixture Substances 0.000 description 13
- 230000007797 corrosion Effects 0.000 description 8
- 238000005260 corrosion Methods 0.000 description 8
- 230000008569 process Effects 0.000 description 8
- 239000000758 substrate Substances 0.000 description 6
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 230000005855 radiation Effects 0.000 description 3
- 238000002310 reflectometry Methods 0.000 description 3
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- 230000008025 crystallization Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005499 laser crystallization Methods 0.000 description 2
- 230000005415 magnetization Effects 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 239000003973 paint Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 238000004544 sputter deposition Methods 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 229910052714 tellurium Inorganic materials 0.000 description 2
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 description 2
- 238000001771 vacuum deposition Methods 0.000 description 2
- 229910005900 GeTe Inorganic materials 0.000 description 1
- 229910017629 Sb2Te3 Inorganic materials 0.000 description 1
- 229910018321 SbTe Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 229910001215 Te alloy Inorganic materials 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 238000005280 amorphization Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
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- 238000001816 cooling Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000009499 grossing Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000004093 laser heating Methods 0.000 description 1
- 238000001755 magnetron sputter deposition Methods 0.000 description 1
- 239000000382 optic material Substances 0.000 description 1
- 239000012782 phase change material Substances 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 229920003229 poly(methyl methacrylate) Polymers 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000004417 polycarbonate Substances 0.000 description 1
- -1 polyethylene terephthalate Polymers 0.000 description 1
- 229920000139 polyethylene terephthalate Polymers 0.000 description 1
- 239000005020 polyethylene terephthalate Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000004926 polymethyl methacrylate Substances 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- DDJAGKOCVFYQOV-UHFFFAOYSA-N tellanylideneantimony Chemical compound [Te]=[Sb] DDJAGKOCVFYQOV-UHFFFAOYSA-N 0.000 description 1
- BPDQXJZWVBPDSN-UHFFFAOYSA-N tellanylideneantimony;tellurium Chemical compound [Te].[Te]=[Sb].[Te]=[Sb] BPDQXJZWVBPDSN-UHFFFAOYSA-N 0.000 description 1
- 230000002123 temporal effect Effects 0.000 description 1
- 238000007736 thin film deposition technique Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
- G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
- G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
- G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
- G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
- G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
- G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
- G11B7/2433—Metals or elements of Groups 13, 14, 15 or 16 of the Periodic Table, e.g. B, Si, Ge, As, Sb, Bi, Se or Te
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
- G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
- G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
- G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
- G11B2007/24302—Metals or metalloids
- G11B2007/24314—Metals or metalloids group 15 elements (e.g. Sb, Bi)
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
- G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
- G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
- G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
- G11B2007/24302—Metals or metalloids
- G11B2007/24316—Metals or metalloids group 16 elements (i.e. chalcogenides, Se, Te)
Landscapes
- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Thermal Transfer Or Thermal Recording In General (AREA)
- Optical Record Carriers And Manufacture Thereof (AREA)
Abstract
ERASABLE PHASE CHANGE OPTICAL RECORDING
ELEMENTS AND METHODS
Abstract An optical recording element comprising a thin film optical recording layer of an alloy is disclosed. The alloy is represented by the formula Sbx Te1-x, wherein x is between about 0.58 and 0.75. The alloys have short erasure times (amorphous to crystalline transition) and excellent environ-mental stability.
ELEMENTS AND METHODS
Abstract An optical recording element comprising a thin film optical recording layer of an alloy is disclosed. The alloy is represented by the formula Sbx Te1-x, wherein x is between about 0.58 and 0.75. The alloys have short erasure times (amorphous to crystalline transition) and excellent environ-mental stability.
Description
~()04~n~
ERASABLE PHASE CHANGE OPTICAL RECORDING
ELEMENTS AND METHODS
Technical Field This invention relates to antimony-tellurium alloys that are useful in optical recording.
Background Art Optical recording, a technique utilizing a focused laser beam to make micron size marks in an appropriate medium for high density information recording, has been extensively studied in recent years. There are basically two types of optical recording; write-once and the erasable. In write-once recording, the media can only be recorded once, but the recorded information can be read many times. In erasable recording, the recorded information can be erased and new information can be recorded over the same area of the media.
There are several commercially available write-once optical recording products, but the introduction of erasable products has been plagued with delays. One of the major difficulties has been the availability of good media.
The technique most widely studied for erasable recording has been based on magneto-optic materials. This technique relies on the thermal-magnetic recordin~ process. A focused laser beam is used to heat a spot on a magneto-optical material 80 that its coercivity is reduced and the magnetization within the spot can be switched by an applied field. The readout is accomplished by sensing the Kerr rotation of a reading laser beam induced by the magnetization in the media. Good recording performance has been reported by many working in the field. However, all reports are based on rare-earth/transition metal alloys, notably TbFeCo, and these alloys have some fundamental problems.
~ 4~
First of all, these materials are corrosion prone. Various approaches to solve the problem have been investigated, including the addition of a fourth element and the use of protecting layers on both 5 sides of the alloy layer. The success of the first method in reducing the corrosion rate has been very limited; and it is also difficult to obtain defect free protecting layers to provide protection over the entire alloy layer. The compatibility of protecting 10 layers with the alloy layers, in terms of adhesion, differential thermal expansion, etc., has been a problem alæo. Another problem with the alloys is that the properties critical to the optical recording process are extremely sensitive to the composition of 15 the alloys. A few percent deviation from the optimum composition can degrade the performance significantly.
An alternative technique for erasable recording uses amorphous-crystalline phase-change materials. In this technique, a focused laser beam is used to switch the material between the amorphous state and the crystalline state. As is commonly done, a high power laser is used to heat a spot on the material to above its melting point to randomize the atomic arrangement in the material. When the laser beam is switched off, the material is left in the metastable amorphous state because of the high cooling rate. A low power laser, in many cases of longer duration, is then used to heat the material to below the melting point. The increased mobility of 30 the atoms at the elevated temperature then allows the material to go to the more stable crystalline state.
Thus by varying the power and duration of the laser beam, the material can be switched between the amorphous state and the crystalline state, and 35 erasable recording is thus accomplished.
The major problem in the development of this technique haæ been the lack of appropriate ~n~
materials. In particular, it has been difficult to find materials which have crystallization rate high enough under laser heating to allow high rate recording (erasure time c 1 ~s), and yet slow enough at room temperature to ensure data i~tegrity.
With slower erasing materials, the erase beam spot is normally made elliptical. This means that two lasers are needed in the recorder head.
With faster erasing materials, only one laser, providing a circular spot, is needed in the recording head. The simplicity and c03t advantage of a one-laser head over a two-laser head is apparent.
Also, lower power laser pulse means lower laser cost and shorter laser pulse means higher data rate. In addition, low power laser pulse is less likely to damage the substrate. It is evident from the above discussions that super-sensitive media will of~er many advantages.
EP-Al-0-212-336 describes a method of erasable recording using single-phase phase-change alloys. Whereas the crystallization rate of the preferred material, (GeTe)~5Snl5, appeared to be high (erasure time < 55 ns), the laser power required for write and erase was also high (18 mW and 10 mW, respectively). Whi~e there was no mention of the corrosion resistance of the material, it contains a high concentration of corrosion prone tellurium.
Shogo Yagi, et al (Crystalliæation of Amorphous Marks in SbTe Erasable Optical Storage Media, Japanese Journal of Applied Physics, Vol 26, Supplement 26-4, 51(1987)), studied SbxTel_x erasable optical storage alloy. The composition range they reported were from x = 0.19 to 0.55. They found that Sb2Te3 thin film was the best composition due to its long amorphous life time at room temperature and short erasure time (~ 1 ~s).
Yagi' 8 data indicate that when Sb content is higher than 55% the amorphizing threshold increases abruptly (Fig.4 in Yagi's paper), and when Sb content i8 more than 44% the erasure time shows a trend of rapid increase (Fig.8 in Yagils paper).
The problem with the compositions of Yagi et al is that the time required for erasure are longer than desired and that the environmental stability of the composition iR less than desired. The present invention i8 directed to a solution to these problems.
Discloæure of the Invention In accordance with the present invention, there is provided an optical recording element comprising a thin film optical recording layer of an alloy, eaid alloy represented by the formula SbxTel_x, wherein x i8 between about 0.58 and 0.75.
In preferred embodiments, x i5 between about 0.65 and 0.73.
Brief Description of the Drawings Figure 1 i8 a plot of the erasure time versus alloy composition for several alloys useful in the invention.
Detailed Descrigtion of the Invention The alloy that is useful in the present invention is similar to the SbxTel_x alloy of Yagi et al. To our surprise however, we found that the films with composition near Sb70Te30 performed exceptionally well as optical recording media. The films have a much shorter erasure time (~ 100 ns), and a better environmental stability than that of Sb2Te3 studied by Yagi et al. The content of corrosion prone tellurium is also considerably less, which leads to improved corrosion resistance.
The alloys u~eful in the invention have fast write-erase rates, improved sensitivity, thermal stability, and corrosion resistance. At Sb70Te30 composition, the medium can be cycled at \< 100 ns and < 12 mW.
The media can be prepared by conventional vacuum deposition processes, such as evaporation and ~puttering, onto a variety of substrates. The layer thickness is preferably between 10 and 300 nm. An overcoat layer is preferably applied over the alloy layer to reduce any alloy deformation as a result of the recording processes. Such deformation can result in residual signals that can not be erased by the erasing process. Common overcoat materials are polymer coatings such aR those described in United 1 States Patent 4,340,655 issued July 20, 1982 to Hollister et al and dielectric coatings such as SiOx, ZnS and A1203. A commercially available acrylic spray paint such as clear Krylon~ can be used.
After the alloy is deposited, the recording layer is preferably initialized. The layer that is deposited by vacuum deposition is amorphous. For optimum performance, it is desirable to crystallize at least tho~e portions of the layer that are to be used for recording. The layer can be crystallized by heating, for example in an oven or by other conventional means such a~ with a laser or a high power flash lamp.
Optical recording layers can be prepared by conventional thin film deposition techniques such as RF (radio frequency) and DC (direct current) sputtering from an alloy target using the alloys of the invention. Enhancement of sputtering processes by applying magnetic fields (magnetron sputtering) can also be used.
Supports which can be used include plastic plates, such as polyethylene terephthalate, polymethyl methacrylate, and polycarbonate, a glass plate, paper and metallic plates such as aluminum.
Erasable recording is achieved by varying the power of the laser pulses. A high power, short duration (e.g., 100 ns, 12 mW) pulse changes the material to a low reflectivity amorphous state and a low power long duration (e.g., 100 ns, 6 mW) pulse changes the material to a high reflectivity crystalline state.
Thus, according to another aspect of the invention, there is provided a method of recording and erasing information on an optical recording element, said element comprising a thin film optical recording layer of an alloy in a crystalline form, said alloy represented by the formula SbxTel_x, wherein x is between about 0.58 and 0.75, ~aid method comprising the steps of:
a) recording said information by focusing an information modulated laser beam on said crystalline alloy recording layer at a power and for a time sufficient to form a pattern of amorphous areas in said layer of alloy, said pattern corresponding to said information, and b) focusing a laser beam on said recorded layer for a time and at a power sufficient to crystallize at least a portion of the amorphous areas formed in step a), thereby erasing the information in the amorphous areas.
A useful recording material comprises, starting from the outside surface of the recording material, an overcoat layer, a thin film optical recording layer as described and a substrate. In response to a drive signal, the intensity of a diode recording beam focused on the recording layer is modulated in accordance with information to be recorded.
During recording, the recording material is spun at a constant rate, e.g., 1800 rotations per minute (rpm). As a result, a track of information is Z00470~
recorded on the optical recording layer in the form of selected amorphized areas. As recording continues, the recording spot is caused to scan radially inward across the recording material, thereby causing information to be recorded along a spiral or concentric track. The ~izes and spacings of the recorded information markæ vary in accordance with the information content of the recording laser drive signal, as well as with radial position on the recording material.
During the readback process, the thus recorded information bearing recording material is spun at the same rate as it was spun during the recording process. The optical path of a readout laser beam is focused to a ~layback 8pot on the recording material by a high numerical aperture lens. The recording material is of the reflective type so that the radiation forming the playback spot is reflected back through the high numerical aperture lens after interacting with the information marks recorded on the optical recording material. A lens directs reflected laser radiation onto a detector which produces an electrical playback signal in responæe to temporal variations (contrast) in the ; 25 irradiance of the reflected laser radiation falling on the detector.
Other types of recording materials are also useful. For example, a reflective substrate such as aluminum can be provided with a recording layer comprising an alloy of the invention on both sides of the substrate. A useful recording material is thus, aluminum coated on both sides with a smoothing layer, a layer of the phase change alloy of the invention and a layer of a clear protective overcoat. In a ~imilar embodiment, the alloy is provided on a clear subætrate which is then adhered to both sides of the subætrate with an adhesive. In yet another ~7 ~ ~
embodiment, the alloy as described is provided on a transparent substrate to form the recording layer.
The optical recording layer is then adhered to the recording layer of an identical recording material with an adhesive layer. The thickness of the adhesive layer provides for the optical separation of the two recording layers.
The following examples are presented for a further understanding of the invention.
E~ample 1:
A range of SbxTel-x compositions, 0.58 x ~ 0.75, were investigated. The deposited alloys were overcoated with a clear acrylic spray paint. Some areas of the as-deposited amorphous films were initially irradiated by laser pulses at 30 ~s, 2 mW. The irradiated spots were therefore crystallized. The center of the crystallized spots were followed by laser irradiation at 50 ns, 12 mW in order for them to be re-amorphorized.
The alloys were then subjected to a variety of conditions to recrystallize designated areas. The areas were ~ubjected to a laser pulse irradiation (power ~ 12 mW). The shortest required pulse lengths (erasure time> to erase several compositions are shown in Fig. 1. The erasure time of the present alloy is generally less than 1 ~s.
The above amorphous films with laser crystallized spots were kept in a humidity chamber at 70~C and 70% relative humidity for 3 weeks. No corrosion or crystal growth was observed. This test shows that these films are thermally and environmentally stable.
Example 2:
We also investigated the compositional dependence of erasure time for thermally crystallized films. The method was the same as in Example 1, except that the first laser crystallization step was , ~O~t7n~
not needed. The results were ~imilar to those in Example 1.
Example 3:
The phase transformation kinetics (PTK) diagrams were constructed for a number of compositions according to the method of Chen et al, Appl. Phys. Lett. 46, 734 (1985). Amorphous Sb70Te30, thermally crystallized Sb70Te30, amorphous Sb72Te28, and amorphous Sb63Te37 were tested.
The amorphized region, for as-deposited film, was determined by firstly laser crystallizing (30 ~s, 2 mW) some spots and then re-amorphizing them at proper laser power-pulse duration combinations The amorphized region, for thermally pre-crystallized film, was determined by laser amorphizing some spots with proper laser power-pulse duration combinations.
The crystallized region, for as-deposited film, ~as determined by laser crystallization (30 ~s, 2 mW) followed by re-amorphization (50 ns, 12 mW), and then re-cryætallizing them at proper power-pulse duration combinations.
The crystallized region, for thermally pre-crystallized film, was determined by laser crystallizing the laser-amorphized spots with proper power-pulse duration combinations.
The amorphized and crystallized regions in the PTK diagrams indicate that the Sb70Te30 alloys can be amorphized at 100 ns, >/ 10 mW and crystallized at 100 ns, 6-9 mW.
Example 4:
Films with various compositions were used to write (100 ns, 12 mW) and erase (100 ns, 6 mW) for 1000 cycles. As-deposited and thermally crystallized films were tested. The reflectivity difference (~
x~ nh 6%) between write state and erase state doe3 not show any sign of degradation after 1000 cycles. This indicates that these films are good erasable materials.
Industrial Applicaabilitv The present invention provides optical recording elements which are erasable.
ERASABLE PHASE CHANGE OPTICAL RECORDING
ELEMENTS AND METHODS
Technical Field This invention relates to antimony-tellurium alloys that are useful in optical recording.
Background Art Optical recording, a technique utilizing a focused laser beam to make micron size marks in an appropriate medium for high density information recording, has been extensively studied in recent years. There are basically two types of optical recording; write-once and the erasable. In write-once recording, the media can only be recorded once, but the recorded information can be read many times. In erasable recording, the recorded information can be erased and new information can be recorded over the same area of the media.
There are several commercially available write-once optical recording products, but the introduction of erasable products has been plagued with delays. One of the major difficulties has been the availability of good media.
The technique most widely studied for erasable recording has been based on magneto-optic materials. This technique relies on the thermal-magnetic recordin~ process. A focused laser beam is used to heat a spot on a magneto-optical material 80 that its coercivity is reduced and the magnetization within the spot can be switched by an applied field. The readout is accomplished by sensing the Kerr rotation of a reading laser beam induced by the magnetization in the media. Good recording performance has been reported by many working in the field. However, all reports are based on rare-earth/transition metal alloys, notably TbFeCo, and these alloys have some fundamental problems.
~ 4~
First of all, these materials are corrosion prone. Various approaches to solve the problem have been investigated, including the addition of a fourth element and the use of protecting layers on both 5 sides of the alloy layer. The success of the first method in reducing the corrosion rate has been very limited; and it is also difficult to obtain defect free protecting layers to provide protection over the entire alloy layer. The compatibility of protecting 10 layers with the alloy layers, in terms of adhesion, differential thermal expansion, etc., has been a problem alæo. Another problem with the alloys is that the properties critical to the optical recording process are extremely sensitive to the composition of 15 the alloys. A few percent deviation from the optimum composition can degrade the performance significantly.
An alternative technique for erasable recording uses amorphous-crystalline phase-change materials. In this technique, a focused laser beam is used to switch the material between the amorphous state and the crystalline state. As is commonly done, a high power laser is used to heat a spot on the material to above its melting point to randomize the atomic arrangement in the material. When the laser beam is switched off, the material is left in the metastable amorphous state because of the high cooling rate. A low power laser, in many cases of longer duration, is then used to heat the material to below the melting point. The increased mobility of 30 the atoms at the elevated temperature then allows the material to go to the more stable crystalline state.
Thus by varying the power and duration of the laser beam, the material can be switched between the amorphous state and the crystalline state, and 35 erasable recording is thus accomplished.
The major problem in the development of this technique haæ been the lack of appropriate ~n~
materials. In particular, it has been difficult to find materials which have crystallization rate high enough under laser heating to allow high rate recording (erasure time c 1 ~s), and yet slow enough at room temperature to ensure data i~tegrity.
With slower erasing materials, the erase beam spot is normally made elliptical. This means that two lasers are needed in the recorder head.
With faster erasing materials, only one laser, providing a circular spot, is needed in the recording head. The simplicity and c03t advantage of a one-laser head over a two-laser head is apparent.
Also, lower power laser pulse means lower laser cost and shorter laser pulse means higher data rate. In addition, low power laser pulse is less likely to damage the substrate. It is evident from the above discussions that super-sensitive media will of~er many advantages.
EP-Al-0-212-336 describes a method of erasable recording using single-phase phase-change alloys. Whereas the crystallization rate of the preferred material, (GeTe)~5Snl5, appeared to be high (erasure time < 55 ns), the laser power required for write and erase was also high (18 mW and 10 mW, respectively). Whi~e there was no mention of the corrosion resistance of the material, it contains a high concentration of corrosion prone tellurium.
Shogo Yagi, et al (Crystalliæation of Amorphous Marks in SbTe Erasable Optical Storage Media, Japanese Journal of Applied Physics, Vol 26, Supplement 26-4, 51(1987)), studied SbxTel_x erasable optical storage alloy. The composition range they reported were from x = 0.19 to 0.55. They found that Sb2Te3 thin film was the best composition due to its long amorphous life time at room temperature and short erasure time (~ 1 ~s).
Yagi' 8 data indicate that when Sb content is higher than 55% the amorphizing threshold increases abruptly (Fig.4 in Yagi's paper), and when Sb content i8 more than 44% the erasure time shows a trend of rapid increase (Fig.8 in Yagils paper).
The problem with the compositions of Yagi et al is that the time required for erasure are longer than desired and that the environmental stability of the composition iR less than desired. The present invention i8 directed to a solution to these problems.
Discloæure of the Invention In accordance with the present invention, there is provided an optical recording element comprising a thin film optical recording layer of an alloy, eaid alloy represented by the formula SbxTel_x, wherein x i8 between about 0.58 and 0.75.
In preferred embodiments, x i5 between about 0.65 and 0.73.
Brief Description of the Drawings Figure 1 i8 a plot of the erasure time versus alloy composition for several alloys useful in the invention.
Detailed Descrigtion of the Invention The alloy that is useful in the present invention is similar to the SbxTel_x alloy of Yagi et al. To our surprise however, we found that the films with composition near Sb70Te30 performed exceptionally well as optical recording media. The films have a much shorter erasure time (~ 100 ns), and a better environmental stability than that of Sb2Te3 studied by Yagi et al. The content of corrosion prone tellurium is also considerably less, which leads to improved corrosion resistance.
The alloys u~eful in the invention have fast write-erase rates, improved sensitivity, thermal stability, and corrosion resistance. At Sb70Te30 composition, the medium can be cycled at \< 100 ns and < 12 mW.
The media can be prepared by conventional vacuum deposition processes, such as evaporation and ~puttering, onto a variety of substrates. The layer thickness is preferably between 10 and 300 nm. An overcoat layer is preferably applied over the alloy layer to reduce any alloy deformation as a result of the recording processes. Such deformation can result in residual signals that can not be erased by the erasing process. Common overcoat materials are polymer coatings such aR those described in United 1 States Patent 4,340,655 issued July 20, 1982 to Hollister et al and dielectric coatings such as SiOx, ZnS and A1203. A commercially available acrylic spray paint such as clear Krylon~ can be used.
After the alloy is deposited, the recording layer is preferably initialized. The layer that is deposited by vacuum deposition is amorphous. For optimum performance, it is desirable to crystallize at least tho~e portions of the layer that are to be used for recording. The layer can be crystallized by heating, for example in an oven or by other conventional means such a~ with a laser or a high power flash lamp.
Optical recording layers can be prepared by conventional thin film deposition techniques such as RF (radio frequency) and DC (direct current) sputtering from an alloy target using the alloys of the invention. Enhancement of sputtering processes by applying magnetic fields (magnetron sputtering) can also be used.
Supports which can be used include plastic plates, such as polyethylene terephthalate, polymethyl methacrylate, and polycarbonate, a glass plate, paper and metallic plates such as aluminum.
Erasable recording is achieved by varying the power of the laser pulses. A high power, short duration (e.g., 100 ns, 12 mW) pulse changes the material to a low reflectivity amorphous state and a low power long duration (e.g., 100 ns, 6 mW) pulse changes the material to a high reflectivity crystalline state.
Thus, according to another aspect of the invention, there is provided a method of recording and erasing information on an optical recording element, said element comprising a thin film optical recording layer of an alloy in a crystalline form, said alloy represented by the formula SbxTel_x, wherein x is between about 0.58 and 0.75, ~aid method comprising the steps of:
a) recording said information by focusing an information modulated laser beam on said crystalline alloy recording layer at a power and for a time sufficient to form a pattern of amorphous areas in said layer of alloy, said pattern corresponding to said information, and b) focusing a laser beam on said recorded layer for a time and at a power sufficient to crystallize at least a portion of the amorphous areas formed in step a), thereby erasing the information in the amorphous areas.
A useful recording material comprises, starting from the outside surface of the recording material, an overcoat layer, a thin film optical recording layer as described and a substrate. In response to a drive signal, the intensity of a diode recording beam focused on the recording layer is modulated in accordance with information to be recorded.
During recording, the recording material is spun at a constant rate, e.g., 1800 rotations per minute (rpm). As a result, a track of information is Z00470~
recorded on the optical recording layer in the form of selected amorphized areas. As recording continues, the recording spot is caused to scan radially inward across the recording material, thereby causing information to be recorded along a spiral or concentric track. The ~izes and spacings of the recorded information markæ vary in accordance with the information content of the recording laser drive signal, as well as with radial position on the recording material.
During the readback process, the thus recorded information bearing recording material is spun at the same rate as it was spun during the recording process. The optical path of a readout laser beam is focused to a ~layback 8pot on the recording material by a high numerical aperture lens. The recording material is of the reflective type so that the radiation forming the playback spot is reflected back through the high numerical aperture lens after interacting with the information marks recorded on the optical recording material. A lens directs reflected laser radiation onto a detector which produces an electrical playback signal in responæe to temporal variations (contrast) in the ; 25 irradiance of the reflected laser radiation falling on the detector.
Other types of recording materials are also useful. For example, a reflective substrate such as aluminum can be provided with a recording layer comprising an alloy of the invention on both sides of the substrate. A useful recording material is thus, aluminum coated on both sides with a smoothing layer, a layer of the phase change alloy of the invention and a layer of a clear protective overcoat. In a ~imilar embodiment, the alloy is provided on a clear subætrate which is then adhered to both sides of the subætrate with an adhesive. In yet another ~7 ~ ~
embodiment, the alloy as described is provided on a transparent substrate to form the recording layer.
The optical recording layer is then adhered to the recording layer of an identical recording material with an adhesive layer. The thickness of the adhesive layer provides for the optical separation of the two recording layers.
The following examples are presented for a further understanding of the invention.
E~ample 1:
A range of SbxTel-x compositions, 0.58 x ~ 0.75, were investigated. The deposited alloys were overcoated with a clear acrylic spray paint. Some areas of the as-deposited amorphous films were initially irradiated by laser pulses at 30 ~s, 2 mW. The irradiated spots were therefore crystallized. The center of the crystallized spots were followed by laser irradiation at 50 ns, 12 mW in order for them to be re-amorphorized.
The alloys were then subjected to a variety of conditions to recrystallize designated areas. The areas were ~ubjected to a laser pulse irradiation (power ~ 12 mW). The shortest required pulse lengths (erasure time> to erase several compositions are shown in Fig. 1. The erasure time of the present alloy is generally less than 1 ~s.
The above amorphous films with laser crystallized spots were kept in a humidity chamber at 70~C and 70% relative humidity for 3 weeks. No corrosion or crystal growth was observed. This test shows that these films are thermally and environmentally stable.
Example 2:
We also investigated the compositional dependence of erasure time for thermally crystallized films. The method was the same as in Example 1, except that the first laser crystallization step was , ~O~t7n~
not needed. The results were ~imilar to those in Example 1.
Example 3:
The phase transformation kinetics (PTK) diagrams were constructed for a number of compositions according to the method of Chen et al, Appl. Phys. Lett. 46, 734 (1985). Amorphous Sb70Te30, thermally crystallized Sb70Te30, amorphous Sb72Te28, and amorphous Sb63Te37 were tested.
The amorphized region, for as-deposited film, was determined by firstly laser crystallizing (30 ~s, 2 mW) some spots and then re-amorphizing them at proper laser power-pulse duration combinations The amorphized region, for thermally pre-crystallized film, was determined by laser amorphizing some spots with proper laser power-pulse duration combinations.
The crystallized region, for as-deposited film, ~as determined by laser crystallization (30 ~s, 2 mW) followed by re-amorphization (50 ns, 12 mW), and then re-cryætallizing them at proper power-pulse duration combinations.
The crystallized region, for thermally pre-crystallized film, was determined by laser crystallizing the laser-amorphized spots with proper power-pulse duration combinations.
The amorphized and crystallized regions in the PTK diagrams indicate that the Sb70Te30 alloys can be amorphized at 100 ns, >/ 10 mW and crystallized at 100 ns, 6-9 mW.
Example 4:
Films with various compositions were used to write (100 ns, 12 mW) and erase (100 ns, 6 mW) for 1000 cycles. As-deposited and thermally crystallized films were tested. The reflectivity difference (~
x~ nh 6%) between write state and erase state doe3 not show any sign of degradation after 1000 cycles. This indicates that these films are good erasable materials.
Industrial Applicaabilitv The present invention provides optical recording elements which are erasable.
Claims (5)
1. An optical recording element comprising a thin film optical recording layer of an alloy, said alloy represented by the formula SbxTe1-x, wherein x is between about 0.58 and 0.75.
2. An optical recording element according to claim 1 wherein x is between 0.65 and 0.73.
3. An optical recording element according to claim 1 further comprising an overcoat layer.
4. An optical recording element according to claim 1 wherein x is 0.70.
5. A method of recording and erasing information on an optical recording element, said element comprising a thin film optical recording layer of an alloy in a crystalline form, said alloy represented by the formula SbxTe1-x, wherein x is between about 0.58 and 0.75, said method comprising the steps of:
a) recording said information by focusing an information modulated laser beam on said crystalline alloy recording layer at a power and for a time sufficient to form a pattern of amorphous areas in said layer of alloy, said pattern corresponding to said information, and b) focusing a laser beam on said recorded layer for a time and at a power sufficient to crystallize at least a portion of the amorphous areas formed in step a), thereby erasing the information in said amorphous areas.
a) recording said information by focusing an information modulated laser beam on said crystalline alloy recording layer at a power and for a time sufficient to form a pattern of amorphous areas in said layer of alloy, said pattern corresponding to said information, and b) focusing a laser beam on said recorded layer for a time and at a power sufficient to crystallize at least a portion of the amorphous areas formed in step a), thereby erasing the information in said amorphous areas.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US28600388A | 1988-12-19 | 1988-12-19 | |
| US286,003 | 1988-12-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2004708A1 true CA2004708A1 (en) | 1990-06-19 |
Family
ID=23096629
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002004708A Abandoned CA2004708A1 (en) | 1988-12-19 | 1989-12-06 | Erasable phase change optical recording elements and methods |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0406378A1 (en) |
| JP (1) | JPH03502787A (en) |
| KR (1) | KR910700522A (en) |
| CA (1) | CA2004708A1 (en) |
| WO (1) | WO1990007181A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| LU87571A1 (en) * | 1989-08-23 | 1991-05-07 | Glaverbel | OPTICALLY READABLE INFORMATION RECORDING MEDIUM |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5935988A (en) * | 1982-08-23 | 1984-02-27 | Sony Corp | Information recording medium |
| JPS59214449A (en) * | 1983-04-18 | 1984-12-04 | ノ−ウツド・インダストリ−ズ・インコ−ポレ−テツド | Foreskin care material |
| JPS6070536A (en) * | 1983-09-28 | 1985-04-22 | Nippon Columbia Co Ltd | Optical information recording medium |
| GB8422492D0 (en) * | 1984-09-06 | 1984-10-10 | Smith & Nephew Ass | Adhesive dressing |
| JPS61253058A (en) * | 1985-05-01 | 1986-11-10 | 帝人株式会社 | Bandage |
-
1989
- 1989-12-06 CA CA002004708A patent/CA2004708A1/en not_active Abandoned
- 1989-12-07 JP JP2501363A patent/JPH03502787A/en active Pending
- 1989-12-07 WO PCT/US1989/005435 patent/WO1990007181A1/en not_active Ceased
- 1989-12-07 EP EP90901285A patent/EP0406378A1/en not_active Withdrawn
- 1989-12-07 KR KR1019900701789A patent/KR910700522A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| WO1990007181A1 (en) | 1990-06-28 |
| KR910700522A (en) | 1991-03-15 |
| EP0406378A1 (en) | 1991-01-09 |
| JPH03502787A (en) | 1991-06-27 |
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