CA2430941C - Cesium dispensers and process for the use thereof - Google Patents
Cesium dispensers and process for the use thereof Download PDFInfo
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- CA2430941C CA2430941C CA002430941A CA2430941A CA2430941C CA 2430941 C CA2430941 C CA 2430941C CA 002430941 A CA002430941 A CA 002430941A CA 2430941 A CA2430941 A CA 2430941A CA 2430941 C CA2430941 C CA 2430941C
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/02—Manufacture of electrodes or electrode systems
- H01J9/12—Manufacture of electrodes or electrode systems of photo-emissive cathodes; of secondary-emission electrodes
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B33/00—Electroluminescent light sources
- H05B33/10—Apparatus or processes specially adapted to the manufacture of electroluminescent light sources
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
- C23C14/24—Vacuum evaporation
- C23C14/243—Crucibles for source material
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
- C30B23/02—Epitaxial-layer growth
- C30B23/06—Heating of the deposition chamber, the substrate or the materials to be evaporated
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B33/00—Electroluminescent light sources
- H05B33/12—Light sources with substantially two-dimensional [2D] radiating surfaces
- H05B33/22—Light sources with substantially two-dimensional [2D] radiating surfaces characterised by the chemical or physical composition or the arrangement of auxiliary dielectric or reflective layers
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
- H10K71/30—Doping active layers, e.g. electron transporting layers
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
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- Chemical Kinetics & Catalysis (AREA)
- Mechanical Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Electroluminescent Light Sources (AREA)
- Physical Vapour Deposition (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
- Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)
- Nitrogen And Oxygen Or Sulfur-Condensed Heterocyclic Ring Systems (AREA)
- Luminescent Compositions (AREA)
- Compounds Of Unknown Constitution (AREA)
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Abstract
Cesium dispensers based on the use of a mixture between a reducing agent and a cesium compound selected among molibdate, tungstate, niobate, tantalate, silicate and zirconate are described. Some processes for the use of these dispensers are also described.
Description
"CESIUM DISPENSERS AND PROCESS FOR THE USE THEREOF"
The present invention relates to cesium dispensers and a process for using them.
Cesium has been used for a long time in the electronic field. In particular this metal has been used in the past for the production of photosensible surfaces, for example of image intensifiers or photomultiplier tubes.
A novel application field for cesium is in the OLED (Organic Light Emitting Display) screens.
In short, an OLED is formed of a first transparent planar support (of glass or plastics); a second, not necessarily transparent support that may be realized in glass, metal or plastics, essentially planar and parallel to the first support and secured along the perimeter thereof, so as to form a closed space; and a structure in said space that is active in forming an image. The active structure is formed in turn by a first set of linear and reciprocally parallel, transparent electrodes, deposited on the first support; a multilayer of different electroluminescent organic materials comprising at least one layer of electron-conductive material and one layer of an electronic vacancies (also defined in the field as "holes") conductive material deposited on the first set of electrodes; a second set of linear and reciprocally parallel electrodes that are orthogonally oriented with respect to those of the first set and in contact with the opposite side of the multilayer of organic materials, so that the latter is comprised between the two sets of electrodes.
For a more detailed description of the structure and operation of OLED screens one can refer for instance to patent applications EP 0 845 924 A2, filed November 27, 1997, EP 0 949 696 A2, filed April 7, 1999, JP 9078058 A, filed September 8, 1995 and patent US 6, 013,384, issued January 11, 2000. Recently it has been ascertained that the doping of one or more layers of the organic multilayer with little amounts of electron-donor metals, in particular cesium, enables to reduce the potential difference to be applied to the sets of electrodes for the functioning of screens, and thus the energy consumption of the latter.
Due to its high reactivity to atmospheric gases and moisture, cesium is not usually used in industry as pure metal, but rather in the form of its compounds stable to air at room temperature.
Some cesium compounds release the metal by simple heating. Among these compounds, alloys with silicon or germanium may be cited as described for example in patent application EP 0 360 317, filed August 30, 1989 and patent US
5,066,888, issued November 19, 1990 as well as the intercalation compound of cesium with graphite, having formula CsCg, cited in patent application EP 0 803 A2, filed June 28, 1984. These compounds have however no practical application at industrial level.
Cesium dichromate, CssCr207, or more commonly cesium chromate, Cs2CrO4 are normally used in the industry in mixture with a reducing agent. By heating these mixtures at temperatures generally over 500 C, and usually between 550 and 650 C, a reaction takes place wherein chromium is reduced to a lower valence as a consequence of which cesium is released in vapor form. As reducing agents aluminum, silicon or getter alloys, i.e. alloys based on titanium or zirconium with aluminum or one or more transition elements, are generally used.
The use of these mixtures is described for example in patent US 2,117,735, issued May 17, 1938.
These compounds are generally introduced into suitable dispensers that are able to retain solid particles of the compounds, but have at least a portion of the surface permeable to cesium vapors. Various forms of dispensers are the object for instance of patents US 3,578,834, issued May 18, 1971, US 3,579,459, issued May 18, 1971, US 3,598,384, issued October 14, 1980, US 3,636,302, issued January 18, 1972, US 3,663,121, issued May 16, 1972, and US 4,233,936, issued November 18, 1980. A further property required for cesium dispensers is not to release gases that are detrimental to the operation of devices wherein cesium is used during their production.
Cesium chromate and dichromate suffer however the disadvantage of containing hexavalent chromium, that may cause irritations by contact, ingestion or inspiration and may be carcinogenic in case of protracted exposures.
In production processes of common devices in which cesium is used (image intensifiers or photomultipliers) high temperatures are reached, and only by using chromate and diclll omate one can avoid the release of cesium in an early stage of the process. In addition, in these cases limited productions are obtained and consequently the amounts of chromate that are used are limited too.
The temperatures of production processes of OLEDs are on the contrary lower, and for these screens productions on very large scale are foreseen, in.
the order of tens of millions of pieces per year. With these production volumes, the safety problems linked with the transportation and use of chromates become outstandiuig. In the production of OLEDs it is thus possible and highly desirable not to resort to the use of Cs2CrO4 or CsZCr2O7 to evaporate cesium.
The object of the present invention is to provide cesium dispensers particularly suitable for the production of OLED screens, wherein cesiuni is not present in the form of a chromium salt.
A further object of this invention is to provide a process for the use of cesium dispensers in the production of OLED screens.
These objects are achieved by the present invention, which in a first respect relates to cesium dispensers formed by a container able to retain solid particles but having at least a part of the surface pernieable to cesiuin vapors and containing a nlixture of at least a cesium compound and at least a reducing agent, characterized in that the cesium compound is selected among molibdate, tungstate, niobate, tantalate, silicate and zirconate.
The invention will be described below with reference to the drawings ui which:
- Figure 1 shows, in a perspective view, a first possible cesium dispenser according to the invention;
- Figure 2 shows a sectional view aloxig line II-II' in Fig. 1 of the saine dispenser;
- Figure 3 shows a perspective, partially cut-away view of another possible dispenser of the invention;
- Figure 4 shows a top plan view of a fitrther possible dispenser of the invention; and - Figure 5 shows a sectional view along line V-V' of the dispenser in Fig. 4.
The inventors have found that mixtures of one or more reducing agents and one or more compounds selected among cesium molibdate, Cs2MoO4, cesium tungstate, CszWO4, cesium niobate, CsNbO3, cesium tantalate, CsTaO3, cesium silicate, Cs2SiO3 and cesium zirconate, CsZZrO3, are compatible with the production process of OLEDs, in that they are able to evaporate cesium at lower temperatures than the corresponding chromates without practically releasing gases potentially harmful for OLEDs, mainly comprising water vapor. In particular the evaporation teniperatures of cesium from these inixtures are generally lower than 450 C: these temperatures can easily be locally reached on the cesium dispenser in the purification chainbers of OLEDs.
The mixtures used in the dispensers of the invention may comprise more than one cesium compound and more than one reducing element or compound, but geiierally a single component per each kind is used.
As a reducing agent it is possible to use one of the already lu-iown components used in dispensers based on chromates, such as aluminum, silicon, zirconium or titaiiium, or alloys containing zirconiuln or titanitun, such as for example the alloy having percent composition by weight Zr 84% - Al 16%, produced and sold by the Applicant under the trade name St 101 , or the alloy having percent composition by weight Zr 76,5% - Fe 23,5%, produced and sold by the Applicant under the trade naine St 1980.
In order to promote the contact between cesium compound and reducing agent, these are preferably used in the form of powders. Both components of the nlixture have generally a particle size lower than 1 mm, preferably lower than zn; even inore preferably the particle size is comprised between about 10 and m. Powders with grains smaller than 10 m are generally difficult to be treated in production and retained in the dispenser; furthermore, in case of the reducing agent, powders too fine may become pyrophoric, thus causing safety problems in the production plant. On the contrary, with powders having sizes higher than those named, the contact between the mixture components get worse, and the reaction causing the release of cesium slows down.
The weight ratio between cesium compound and reducing agent can vary between wide limits. Said ratio is preferably comprised between 10:1 and 1:10.
The use of cesiunl compound in great excess with respect to the reducing agent does not offer practical advantages; on the contrary, mainly when the reducing agent is a getter alloy, such as the named alloy St 101 , its excess in the mixture may becoine useful since the portion not ulvolved in the reaction witli cesium compound can carry out an. absorbing action on the gases that may get free during the reaction.
5 The mixture can be used in the form of free powders, or it is possible to preform pellets of the same; the use of pellets bears the advantage of further iinproving the contact between the coinponents of the mixture, and facilitating the charging operations of the container.
The container can be realized in every material and shape compatible with the specific application.
In particular, with reference to the material, this must be cheinically inert witll respect to the worlcing atniosphere and cesium releasing mixture in the wlzole temperature range foreseen for the use, generally between the room temperature and about 450 C; in the same temperature range, the material forming tlie container inust not undergo noticeable physical changes, such as to modify its lnechanical resistance or shape, and must have the lowest possible values of gas emission. Materials having these properties are for instance metals or metallic alloys, ceramics, graphite and boron nitride, BN. The use of metals is preferred due to their easier workability and formability. A fiirther advantage in using metals, graphite and BN is that the dispenser can be heated up to the cesium evaporation temperature by siinple passing of current through the container walls.
Preferred metals and alloys for manufacturing the container are molybdenum, tantalum, tungsten, niclcel, steel and niclcel-chromium alloys.
The shape of the container may be any of those known from the previously named patents US 3,578,834, US 3,579,459, US 3,598,384, US 3,636,302, US
3,663,121 and US 4,233,936. Containers of various shapes and materials are also available on sale, for example from the Austrian company Plansee or from the USA company Midwest Tungsten Service.
In figures 1 and 2 is represented, in perspective and sectional views respectively, a possible dispenser using the mixtures of the invention; in particular figure 2 shows the sectional view of the dispenser along line II-II' of figure 1.
Dispenser 10 is formed of two metal foils 11 and 12. A depression 13, obtained for instance by cold forming the foil is arranged in the central part of foil 12. Foil 11 has, in its central zone 14 (bordered by the broken line in figure 1), a set of small through holes 15. In the assembled dispenser, zone 14 corresponds to depression 13; the latter contains a mixture 16 of at least one cesium compound and at least one reducing agent according to the invention. Foils 11 and 12 can be secured to each other, outside depression" 13, in any way assuring powders tightness; for example, a mechanical fixing can be obtained in the form-of "tongues" in a foil folded on the other, or a fixing by continuous or spotted welding, or combinations of these methods. Finally, dispenser 10 has two lateral projections 17 and 17' useful for the handling with mechanical means in the production line and for connection to electric terminals in order to heat it.
In figure 3 another possible dispenser 30 according to the invention is represented partially cut away. In this case the container of mixture 16 is formed by a foil 31 (for instance metallic) similar to foil 12 of figures 1 and 2, whereas the surface portion of the container permeable to cesium vapors is formed by a porous body 32 comprising or formed of a getter material. Body 32 can be maintained in position by any method; for example only, in figure 3 a retaining element 33 is shown secured to foil 31 by means of welding spots 34; body 32 can be maintained in the desired position by means of any other retaining element, fixed to foil 31 in any suitable way. Body 32 may be formed of sintered getter material only; such a getter body can be obtained for example according to the method described in patent EP 0 719 609 B1, issued February 9, 2000 in the name of the Applicant. Alternatively, body 32 may be formed of getter material deposited according to various methods on a supporting open structure, such as for instance a wire net having meshes of suitable dimensions; similar open structures are described for example in patent US 4,146,497, issued March 27, 1979 in the name of the Applicant, or may be produced by depositing getter particles on a wire net through the electrophoretic technique, as described for example in patent US 4,628,198, issued December 9, 1986. By this structure, the getter body 32 fulfils the double service of allowing the passage of cesium vapors yet retaining the particles of mixture 16, and avoiding the pollution of the atmosphere in the process chamber, where the dispenser is used, by gases such as water, carbon oxides, etc. that can be released by the components of said mixture.
Finally, figures 4 and 5 represent a further possible form of dispenser using the mixtures of the invention, that is useful when is necessary to evaporate little amounts of cesium; this dispenser has the structure described in patent US
3,598,384. Figure 4 shows the dispenser in a top plan view, and figure 5 shows a sectional view along line V-V' of figure 4. Dispenser 40 is formed of a container 41 having an extended structLu-e with a trapezoidal section and a longitudinal slit 42 blocked by a wire 43 that allows the evaporation of cesium but prevents the powdery mixture 44 from escaping; container 41 is tapered at its ends about two teiminals 45, 45' that fulfill the double service of closing said ends and as electric terininals for heating the assembly.
In a second aspect, the invention relates to a process for using the above-described dispensers in the production of screens of OLED sort.
The structure of an OLED (briefly described above) is produced, by means of techniques that are typical in the inicroelectronic industry, by prearranging the first transparent support and depositing in sequence thereon the various forming layers. The electrodes are generally deposited according to techniques such as the screen printing; the layers of organic materials are obtained in general by means of evaporation or the technique known as "spin coating", consisting in the deposition of a drop of liquid material on the support and swift rotation of the latter.
As the used organic materials and especially the second set of electrodes (generally made of metals such as barium) are extreinely sensitive to the atmospheric agents and in particular to water vapor, at least the arranging steps of these layers and the subsequent ones must take place in proper chambers, under vacuum or inert atniosphere. The cesium dispensers of the invention are especially suitable for introducing the element into the active structure during these treatments in the chamber.
In particular the process of the iiivention comprises the steps of:
- introducing a cesiuin dispenser into a chainber having a controlled atmosphere and being provided with means for heating it;
- arranging in said chamber the production intermediate of OLED screen as obtained after having formed the organic multilayer;
- causing the evaporation of cesium from the dispenser by heating the latter;
and - carrying out the subsequent production phases of the OLED screen up to its sealing with the second support.
For the objects of the invention, it is not required that these phases are carried out in the above order; in addition, the cesium evaporation operation may be accomplished in different production times of the OLED. Possible changes in the process of the invention will be described below in inore detail.
The chamber with controlled atinosphere can be one of those already provided for carrying out the other production process steps of the OLEDs, or can be a chamber dedicated to the cesium evaporation operation. This chamber inust be provided with means for heating the dispenser, that can be radiative (infrared lamps) or, in the case of a dispenser witll metallic or grapliitic container, of inductive type; the heating can alternatively be carried out by direct passage of current, by prearranging a heatable support for the dispenser or even, in the case of containers in graphite, boron nitride and metal (for instance of the type previously described with reference to figures 1 and 2), by heating the dispenser through direct passage of current in the container walls; in this latter case the heating means in the chamber will be simply electric through means with suitable terminals for connection to the container.
In the case where the cesium evaporation chamber is a chamber in which also other process operations are effected, the dispenser will be introduced prior to the evaporation phase and thermally activated at a convenient time. If on the contrary the chamber is used exclusively for evaporating cesium, in the chamber where the dispenser is already present there is introduced a production intermediate of the OLED. Cesium is then evaporated from the dispenser by heating it with the previously named means at a temperature between about 250 and 450 C, according to the specific cesium compound used therein.
The evaporation of cesium can be effected in various intermediate production phases of the OLED. For example, the production of OLED may comprise the following main operations:
- production of the first set of electrodes on the first transparent support;
- production of the organic multilayer on the first set of electrodes;
- evaporation of cesiuin on the organic multilayer;
- production of the second set of electrodes on the organic multilayer;
- other possible operations and sealing along the perimeters of the first and second supports.
Alternatively, the cesium evaporation operation can be subsequent to the production of the second set of electrodes.
The invention will be furtller illustrated in the following examples relating to some cesium compounds of the invention, and in particular the molibdate and tungstate, in addition to a comparison exainple with the chromate of the prior art.
EX.AMPLE 1 A cesiuin dispenser is produced, wherein as a compound of said element the inolibdate, Cs2MoO4, is used.
The dispenser is of the lcind described in the specification with reference to figures 4'and 5. Container, wire and terminals are, made in niclcel-chromium alloy.
The portion filled with the mixture has a section of about 1 nun x 1,5 mm and a length of 25 inm. This container is filled with a mixture of one part by weight of cesium molibdate in powder form and five parts by weight of the named St 101 alloy; the powders have a particle size between 10 and 125 m. The linear charging of the container is of about 40 mg of mixture per centimeter.
The so produced dispenser is sample 1.
A cesium dispenser as described in example 1 is produced, by using however as cesium compound the tungstate Cs2WO4. This dispenser is sample 2.
(COMPARATIVE) EXAMPLE 3 A cesium dispenser as described in example 1 is produced for comparison, by using as cesium coinpound the chromate Cs2CrO4. This dispenser is sample 3.
This example relates to the cesium evaporation tests from the dispensers produced in the previous examples.
Samples 1-3 are assembled within a chamber that is then evacuated, are 5 connected to electric loops and fed by a current generator. The current is gradually increased with a slope of 0.1 A/min. The temperature of the sample is measured by a thermocouple welded on the oii.ter wall of the container, and the current value is registered that produces the start of cesium evaporation, taken by the aid of a triode sensor mounted near the evaporation slit. The thus taken temperature values 10 of evaporation start are given in the following table.
Cs compound Temperature of evaporation start ( C) CsZMoO4 (invention) 295 Cs2WO4 (invention) 250 Cs2CrO4 (comparison) 625 Based on the test results, it stands out that mixtures using the coinpounds of the invention are able to release cesium vapors in current, and thus teinperature, conditions that are lower with respect to cesium chromate.
The present invention relates to cesium dispensers and a process for using them.
Cesium has been used for a long time in the electronic field. In particular this metal has been used in the past for the production of photosensible surfaces, for example of image intensifiers or photomultiplier tubes.
A novel application field for cesium is in the OLED (Organic Light Emitting Display) screens.
In short, an OLED is formed of a first transparent planar support (of glass or plastics); a second, not necessarily transparent support that may be realized in glass, metal or plastics, essentially planar and parallel to the first support and secured along the perimeter thereof, so as to form a closed space; and a structure in said space that is active in forming an image. The active structure is formed in turn by a first set of linear and reciprocally parallel, transparent electrodes, deposited on the first support; a multilayer of different electroluminescent organic materials comprising at least one layer of electron-conductive material and one layer of an electronic vacancies (also defined in the field as "holes") conductive material deposited on the first set of electrodes; a second set of linear and reciprocally parallel electrodes that are orthogonally oriented with respect to those of the first set and in contact with the opposite side of the multilayer of organic materials, so that the latter is comprised between the two sets of electrodes.
For a more detailed description of the structure and operation of OLED screens one can refer for instance to patent applications EP 0 845 924 A2, filed November 27, 1997, EP 0 949 696 A2, filed April 7, 1999, JP 9078058 A, filed September 8, 1995 and patent US 6, 013,384, issued January 11, 2000. Recently it has been ascertained that the doping of one or more layers of the organic multilayer with little amounts of electron-donor metals, in particular cesium, enables to reduce the potential difference to be applied to the sets of electrodes for the functioning of screens, and thus the energy consumption of the latter.
Due to its high reactivity to atmospheric gases and moisture, cesium is not usually used in industry as pure metal, but rather in the form of its compounds stable to air at room temperature.
Some cesium compounds release the metal by simple heating. Among these compounds, alloys with silicon or germanium may be cited as described for example in patent application EP 0 360 317, filed August 30, 1989 and patent US
5,066,888, issued November 19, 1990 as well as the intercalation compound of cesium with graphite, having formula CsCg, cited in patent application EP 0 803 A2, filed June 28, 1984. These compounds have however no practical application at industrial level.
Cesium dichromate, CssCr207, or more commonly cesium chromate, Cs2CrO4 are normally used in the industry in mixture with a reducing agent. By heating these mixtures at temperatures generally over 500 C, and usually between 550 and 650 C, a reaction takes place wherein chromium is reduced to a lower valence as a consequence of which cesium is released in vapor form. As reducing agents aluminum, silicon or getter alloys, i.e. alloys based on titanium or zirconium with aluminum or one or more transition elements, are generally used.
The use of these mixtures is described for example in patent US 2,117,735, issued May 17, 1938.
These compounds are generally introduced into suitable dispensers that are able to retain solid particles of the compounds, but have at least a portion of the surface permeable to cesium vapors. Various forms of dispensers are the object for instance of patents US 3,578,834, issued May 18, 1971, US 3,579,459, issued May 18, 1971, US 3,598,384, issued October 14, 1980, US 3,636,302, issued January 18, 1972, US 3,663,121, issued May 16, 1972, and US 4,233,936, issued November 18, 1980. A further property required for cesium dispensers is not to release gases that are detrimental to the operation of devices wherein cesium is used during their production.
Cesium chromate and dichromate suffer however the disadvantage of containing hexavalent chromium, that may cause irritations by contact, ingestion or inspiration and may be carcinogenic in case of protracted exposures.
In production processes of common devices in which cesium is used (image intensifiers or photomultipliers) high temperatures are reached, and only by using chromate and diclll omate one can avoid the release of cesium in an early stage of the process. In addition, in these cases limited productions are obtained and consequently the amounts of chromate that are used are limited too.
The temperatures of production processes of OLEDs are on the contrary lower, and for these screens productions on very large scale are foreseen, in.
the order of tens of millions of pieces per year. With these production volumes, the safety problems linked with the transportation and use of chromates become outstandiuig. In the production of OLEDs it is thus possible and highly desirable not to resort to the use of Cs2CrO4 or CsZCr2O7 to evaporate cesium.
The object of the present invention is to provide cesium dispensers particularly suitable for the production of OLED screens, wherein cesiuni is not present in the form of a chromium salt.
A further object of this invention is to provide a process for the use of cesium dispensers in the production of OLED screens.
These objects are achieved by the present invention, which in a first respect relates to cesium dispensers formed by a container able to retain solid particles but having at least a part of the surface pernieable to cesiuin vapors and containing a nlixture of at least a cesium compound and at least a reducing agent, characterized in that the cesium compound is selected among molibdate, tungstate, niobate, tantalate, silicate and zirconate.
The invention will be described below with reference to the drawings ui which:
- Figure 1 shows, in a perspective view, a first possible cesium dispenser according to the invention;
- Figure 2 shows a sectional view aloxig line II-II' in Fig. 1 of the saine dispenser;
- Figure 3 shows a perspective, partially cut-away view of another possible dispenser of the invention;
- Figure 4 shows a top plan view of a fitrther possible dispenser of the invention; and - Figure 5 shows a sectional view along line V-V' of the dispenser in Fig. 4.
The inventors have found that mixtures of one or more reducing agents and one or more compounds selected among cesium molibdate, Cs2MoO4, cesium tungstate, CszWO4, cesium niobate, CsNbO3, cesium tantalate, CsTaO3, cesium silicate, Cs2SiO3 and cesium zirconate, CsZZrO3, are compatible with the production process of OLEDs, in that they are able to evaporate cesium at lower temperatures than the corresponding chromates without practically releasing gases potentially harmful for OLEDs, mainly comprising water vapor. In particular the evaporation teniperatures of cesium from these inixtures are generally lower than 450 C: these temperatures can easily be locally reached on the cesium dispenser in the purification chainbers of OLEDs.
The mixtures used in the dispensers of the invention may comprise more than one cesium compound and more than one reducing element or compound, but geiierally a single component per each kind is used.
As a reducing agent it is possible to use one of the already lu-iown components used in dispensers based on chromates, such as aluminum, silicon, zirconium or titaiiium, or alloys containing zirconiuln or titanitun, such as for example the alloy having percent composition by weight Zr 84% - Al 16%, produced and sold by the Applicant under the trade name St 101 , or the alloy having percent composition by weight Zr 76,5% - Fe 23,5%, produced and sold by the Applicant under the trade naine St 1980.
In order to promote the contact between cesium compound and reducing agent, these are preferably used in the form of powders. Both components of the nlixture have generally a particle size lower than 1 mm, preferably lower than zn; even inore preferably the particle size is comprised between about 10 and m. Powders with grains smaller than 10 m are generally difficult to be treated in production and retained in the dispenser; furthermore, in case of the reducing agent, powders too fine may become pyrophoric, thus causing safety problems in the production plant. On the contrary, with powders having sizes higher than those named, the contact between the mixture components get worse, and the reaction causing the release of cesium slows down.
The weight ratio between cesium compound and reducing agent can vary between wide limits. Said ratio is preferably comprised between 10:1 and 1:10.
The use of cesiunl compound in great excess with respect to the reducing agent does not offer practical advantages; on the contrary, mainly when the reducing agent is a getter alloy, such as the named alloy St 101 , its excess in the mixture may becoine useful since the portion not ulvolved in the reaction witli cesium compound can carry out an. absorbing action on the gases that may get free during the reaction.
5 The mixture can be used in the form of free powders, or it is possible to preform pellets of the same; the use of pellets bears the advantage of further iinproving the contact between the coinponents of the mixture, and facilitating the charging operations of the container.
The container can be realized in every material and shape compatible with the specific application.
In particular, with reference to the material, this must be cheinically inert witll respect to the worlcing atniosphere and cesium releasing mixture in the wlzole temperature range foreseen for the use, generally between the room temperature and about 450 C; in the same temperature range, the material forming tlie container inust not undergo noticeable physical changes, such as to modify its lnechanical resistance or shape, and must have the lowest possible values of gas emission. Materials having these properties are for instance metals or metallic alloys, ceramics, graphite and boron nitride, BN. The use of metals is preferred due to their easier workability and formability. A fiirther advantage in using metals, graphite and BN is that the dispenser can be heated up to the cesium evaporation temperature by siinple passing of current through the container walls.
Preferred metals and alloys for manufacturing the container are molybdenum, tantalum, tungsten, niclcel, steel and niclcel-chromium alloys.
The shape of the container may be any of those known from the previously named patents US 3,578,834, US 3,579,459, US 3,598,384, US 3,636,302, US
3,663,121 and US 4,233,936. Containers of various shapes and materials are also available on sale, for example from the Austrian company Plansee or from the USA company Midwest Tungsten Service.
In figures 1 and 2 is represented, in perspective and sectional views respectively, a possible dispenser using the mixtures of the invention; in particular figure 2 shows the sectional view of the dispenser along line II-II' of figure 1.
Dispenser 10 is formed of two metal foils 11 and 12. A depression 13, obtained for instance by cold forming the foil is arranged in the central part of foil 12. Foil 11 has, in its central zone 14 (bordered by the broken line in figure 1), a set of small through holes 15. In the assembled dispenser, zone 14 corresponds to depression 13; the latter contains a mixture 16 of at least one cesium compound and at least one reducing agent according to the invention. Foils 11 and 12 can be secured to each other, outside depression" 13, in any way assuring powders tightness; for example, a mechanical fixing can be obtained in the form-of "tongues" in a foil folded on the other, or a fixing by continuous or spotted welding, or combinations of these methods. Finally, dispenser 10 has two lateral projections 17 and 17' useful for the handling with mechanical means in the production line and for connection to electric terminals in order to heat it.
In figure 3 another possible dispenser 30 according to the invention is represented partially cut away. In this case the container of mixture 16 is formed by a foil 31 (for instance metallic) similar to foil 12 of figures 1 and 2, whereas the surface portion of the container permeable to cesium vapors is formed by a porous body 32 comprising or formed of a getter material. Body 32 can be maintained in position by any method; for example only, in figure 3 a retaining element 33 is shown secured to foil 31 by means of welding spots 34; body 32 can be maintained in the desired position by means of any other retaining element, fixed to foil 31 in any suitable way. Body 32 may be formed of sintered getter material only; such a getter body can be obtained for example according to the method described in patent EP 0 719 609 B1, issued February 9, 2000 in the name of the Applicant. Alternatively, body 32 may be formed of getter material deposited according to various methods on a supporting open structure, such as for instance a wire net having meshes of suitable dimensions; similar open structures are described for example in patent US 4,146,497, issued March 27, 1979 in the name of the Applicant, or may be produced by depositing getter particles on a wire net through the electrophoretic technique, as described for example in patent US 4,628,198, issued December 9, 1986. By this structure, the getter body 32 fulfils the double service of allowing the passage of cesium vapors yet retaining the particles of mixture 16, and avoiding the pollution of the atmosphere in the process chamber, where the dispenser is used, by gases such as water, carbon oxides, etc. that can be released by the components of said mixture.
Finally, figures 4 and 5 represent a further possible form of dispenser using the mixtures of the invention, that is useful when is necessary to evaporate little amounts of cesium; this dispenser has the structure described in patent US
3,598,384. Figure 4 shows the dispenser in a top plan view, and figure 5 shows a sectional view along line V-V' of figure 4. Dispenser 40 is formed of a container 41 having an extended structLu-e with a trapezoidal section and a longitudinal slit 42 blocked by a wire 43 that allows the evaporation of cesium but prevents the powdery mixture 44 from escaping; container 41 is tapered at its ends about two teiminals 45, 45' that fulfill the double service of closing said ends and as electric terininals for heating the assembly.
In a second aspect, the invention relates to a process for using the above-described dispensers in the production of screens of OLED sort.
The structure of an OLED (briefly described above) is produced, by means of techniques that are typical in the inicroelectronic industry, by prearranging the first transparent support and depositing in sequence thereon the various forming layers. The electrodes are generally deposited according to techniques such as the screen printing; the layers of organic materials are obtained in general by means of evaporation or the technique known as "spin coating", consisting in the deposition of a drop of liquid material on the support and swift rotation of the latter.
As the used organic materials and especially the second set of electrodes (generally made of metals such as barium) are extreinely sensitive to the atmospheric agents and in particular to water vapor, at least the arranging steps of these layers and the subsequent ones must take place in proper chambers, under vacuum or inert atniosphere. The cesium dispensers of the invention are especially suitable for introducing the element into the active structure during these treatments in the chamber.
In particular the process of the iiivention comprises the steps of:
- introducing a cesiuin dispenser into a chainber having a controlled atmosphere and being provided with means for heating it;
- arranging in said chamber the production intermediate of OLED screen as obtained after having formed the organic multilayer;
- causing the evaporation of cesium from the dispenser by heating the latter;
and - carrying out the subsequent production phases of the OLED screen up to its sealing with the second support.
For the objects of the invention, it is not required that these phases are carried out in the above order; in addition, the cesium evaporation operation may be accomplished in different production times of the OLED. Possible changes in the process of the invention will be described below in inore detail.
The chamber with controlled atinosphere can be one of those already provided for carrying out the other production process steps of the OLEDs, or can be a chamber dedicated to the cesium evaporation operation. This chamber inust be provided with means for heating the dispenser, that can be radiative (infrared lamps) or, in the case of a dispenser witll metallic or grapliitic container, of inductive type; the heating can alternatively be carried out by direct passage of current, by prearranging a heatable support for the dispenser or even, in the case of containers in graphite, boron nitride and metal (for instance of the type previously described with reference to figures 1 and 2), by heating the dispenser through direct passage of current in the container walls; in this latter case the heating means in the chamber will be simply electric through means with suitable terminals for connection to the container.
In the case where the cesium evaporation chamber is a chamber in which also other process operations are effected, the dispenser will be introduced prior to the evaporation phase and thermally activated at a convenient time. If on the contrary the chamber is used exclusively for evaporating cesium, in the chamber where the dispenser is already present there is introduced a production intermediate of the OLED. Cesium is then evaporated from the dispenser by heating it with the previously named means at a temperature between about 250 and 450 C, according to the specific cesium compound used therein.
The evaporation of cesium can be effected in various intermediate production phases of the OLED. For example, the production of OLED may comprise the following main operations:
- production of the first set of electrodes on the first transparent support;
- production of the organic multilayer on the first set of electrodes;
- evaporation of cesiuin on the organic multilayer;
- production of the second set of electrodes on the organic multilayer;
- other possible operations and sealing along the perimeters of the first and second supports.
Alternatively, the cesium evaporation operation can be subsequent to the production of the second set of electrodes.
The invention will be furtller illustrated in the following examples relating to some cesium compounds of the invention, and in particular the molibdate and tungstate, in addition to a comparison exainple with the chromate of the prior art.
EX.AMPLE 1 A cesiuin dispenser is produced, wherein as a compound of said element the inolibdate, Cs2MoO4, is used.
The dispenser is of the lcind described in the specification with reference to figures 4'and 5. Container, wire and terminals are, made in niclcel-chromium alloy.
The portion filled with the mixture has a section of about 1 nun x 1,5 mm and a length of 25 inm. This container is filled with a mixture of one part by weight of cesium molibdate in powder form and five parts by weight of the named St 101 alloy; the powders have a particle size between 10 and 125 m. The linear charging of the container is of about 40 mg of mixture per centimeter.
The so produced dispenser is sample 1.
A cesium dispenser as described in example 1 is produced, by using however as cesium compound the tungstate Cs2WO4. This dispenser is sample 2.
(COMPARATIVE) EXAMPLE 3 A cesium dispenser as described in example 1 is produced for comparison, by using as cesium coinpound the chromate Cs2CrO4. This dispenser is sample 3.
This example relates to the cesium evaporation tests from the dispensers produced in the previous examples.
Samples 1-3 are assembled within a chamber that is then evacuated, are 5 connected to electric loops and fed by a current generator. The current is gradually increased with a slope of 0.1 A/min. The temperature of the sample is measured by a thermocouple welded on the oii.ter wall of the container, and the current value is registered that produces the start of cesium evaporation, taken by the aid of a triode sensor mounted near the evaporation slit. The thus taken temperature values 10 of evaporation start are given in the following table.
Cs compound Temperature of evaporation start ( C) CsZMoO4 (invention) 295 Cs2WO4 (invention) 250 Cs2CrO4 (comparison) 625 Based on the test results, it stands out that mixtures using the coinpounds of the invention are able to release cesium vapors in current, and thus teinperature, conditions that are lower with respect to cesium chromate.
Claims (18)
1. A cesium dispenser formed of a container capable of retaining solid particles, but having at least a portion of the surface permeable to cesium vapors, and containing a mixture of:
at least one cesium compound selected among molibdate, tungstate, niobate, tantalite, silicate and zirconate; and at least one reducing agent for reducing the at least one cesium compound.
at least one cesium compound selected among molibdate, tungstate, niobate, tantalite, silicate and zirconate; and at least one reducing agent for reducing the at least one cesium compound.
2. The cesium dispenser according to claim 1, wherein said mixture comprises a single cesium compound and a single reducing agent.
3. The cesium dispenser according to claim 1, wherein the reducing agent is selected among aluminum, silicon, zirconium, titanium or alloys containing zirconium or titanium.
4. The cesium dispenser according to claim 3, wherein the reducing agent is an alloy having a percent composition by weight Zr 84% -Al 16%.
5. The cesium dispenser according to claim 3, wherein the reducing agent is an alloy having a percent composition by weight Zr 76,5% - Fe 23,5%.
6. The cesium dispenser according to claim 1, wherein the materials forming said mixture are in powder form.
7. The cesium dispenser according to claim 6, wherein said powders have a particle size lower than 1 mm.
8. The cesium dispenser according to claim 7, wherein said powders have a particle size lower than 500 µm.
9. The cesium dispenser according to claim 8, wherein said powders have a particle size between and 125 µm.
10. The cesium dispenser according to claim 1, wherein the weight ratio between the materials forming said mixture is from 10:1 to 1:10.
11. The cesium dispenser according to claim 1, wherein the container is made of a material selected among metals, metal alloys, graphite, boron nitride and ceramics.
12. The cesium dispenser according to claim 11, wherein said material is selected among molybdenuan, tantalum, tungsten, steel and nickel-chromium alloys.
13. The cesium dispenser according to claim 1, wherein said container is formed by joining two metal foils , the first foil having in its central zone a plurality of holes having size suitable for retaining solid particles and the second foil having in its corresponding central zone a depression for containing the mixture of at least one cesium compound and at least one reducing agent; the junction between said two foils being made so as not to allow solid particles from escaping; and said cesium dispenser having two lateral extensions for handling with mechanical means and connection to electric terminals.
14. The cesium dispenser according to claim 1, composed by a container formed of a foil in a depression of which is contained the mixture of at least one cesium compound and at least one reducing agent, and of a porous body comprising or formed of getter material, maintained in position on said depression by means of a retaining element secured on said foil by welding spots.
15. The cesium dispenser according to claim 1, composed by a container having extended structure with trapezoidal section and an longitudinal slit blocked by a wire that allows the evaporation of cesium but prevents the mixture of at least one cesium compound and at least one reducing agent present in the container from escaping, said container being tapered at the ends around two terminals that close said ends and form electric contacts for heating the dispenser.
16. A process for the production of OLED screens formed of a first transparent support, a first set of electrodes, an organic multilayer, a second set of electrodes and a second support, comprising the steps of:
introducing the cesium dispenser according to any one of claims 1 to 15 in a chamber with controlled atmosphere and provided with means for heating said cesium dispenser;
arranging in said chamber a production intermediate of the OLED screen as obtained after having formed the organic multilayer;
causing the evaporation of cesium from said cesium dispenser by heating the latter; and carrying out the subsequent production steps of the OLED screen up to its sealing with the second support.
introducing the cesium dispenser according to any one of claims 1 to 15 in a chamber with controlled atmosphere and provided with means for heating said cesium dispenser;
arranging in said chamber a production intermediate of the OLED screen as obtained after having formed the organic multilayer;
causing the evaporation of cesium from said cesium dispenser by heating the latter; and carrying out the subsequent production steps of the OLED screen up to its sealing with the second support.
17. The process according to claim 16, comprising the following series of operations:
production of the first set of electrodes on the first transparent support;
production of the organic multilayer on the first set of electrodes;
evaporation of cesium on the organic multilayer;
production of the second set of electrodes on the organic multilayer; and sealing of the first and second support along their perimeter.
production of the first set of electrodes on the first transparent support;
production of the organic multilayer on the first set of electrodes;
evaporation of cesium on the organic multilayer;
production of the second set of electrodes on the organic multilayer; and sealing of the first and second support along their perimeter.
18. The process according to claim 16, comprising the following series of operations:
production of the first set of electrodes on the first transparent support;
production of the organic multilayer on the first set of electrodes;
production of the second set of electrodes on the organic multilayer;
evaporation of cesium on the second set of electrodes; and sealing of the first and second support along their perimeter.
production of the first set of electrodes on the first transparent support;
production of the organic multilayer on the first set of electrodes;
production of the second set of electrodes on the organic multilayer;
evaporation of cesium on the second set of electrodes; and sealing of the first and second support along their perimeter.
Applications Claiming Priority (3)
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| ITMI2001A000995 | 2001-05-15 | ||
| IT2001MI000995A ITMI20010995A1 (en) | 2001-05-15 | 2001-05-15 | CESIUM DISPENSERS AND PROCESS FOR THEIR USE |
| PCT/IT2002/000301 WO2002093664A2 (en) | 2001-05-15 | 2002-05-07 | Cesium dispensers and process for the use thereof |
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| CA2430941A1 CA2430941A1 (en) | 2002-11-21 |
| CA2430941C true CA2430941C (en) | 2009-12-29 |
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| CA002430941A Expired - Fee Related CA2430941C (en) | 2001-05-15 | 2002-05-07 | Cesium dispensers and process for the use thereof |
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| ITMI20021904A1 (en) * | 2002-09-06 | 2004-03-07 | Getters Spa | ACCESSORY ELEMENT FOR ALKALINE METAL DISPENSERS |
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| EP1585159A4 (en) * | 2003-01-17 | 2006-12-13 | Hamamatsu Photonics Kk | Alkali metal generating agent, alkali metal generator, photoelectric surface, secondary electron emission surface, electron tube, method for manufacturing photoelectric surface, method for manufacturing secondary electron emission surface, and method for manufacturing electron tube |
| CN100521037C (en) | 2003-01-17 | 2009-07-29 | 浜松光子学株式会社 | Alkali metal generator |
| JP4312555B2 (en) * | 2003-09-18 | 2009-08-12 | 富士フイルム株式会社 | Vacuum deposition crucible and phosphor sheet manufacturing apparatus |
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| DE502005009415D1 (en) | 2005-05-27 | 2010-05-27 | Novaled Ag | Transparent organic light emitting diode |
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- 2002-05-07 DE DE60210478T patent/DE60210478T2/en not_active Expired - Lifetime
- 2002-05-07 EP EP02735976A patent/EP1419542B1/en not_active Expired - Lifetime
- 2002-05-07 WO PCT/IT2002/000301 patent/WO2002093664A2/en not_active Ceased
- 2002-05-07 AT AT02735976T patent/ATE322744T1/en not_active IP Right Cessation
- 2002-05-07 KR KR1020037000536A patent/KR100742424B1/en not_active Expired - Lifetime
- 2002-05-07 AU AU2002309256A patent/AU2002309256A1/en not_active Abandoned
- 2002-05-07 CA CA002430941A patent/CA2430941C/en not_active Expired - Fee Related
- 2002-05-13 MY MYPI20021724A patent/MY132034A/en unknown
-
2003
- 2003-06-19 US US10/465,004 patent/US6753648B2/en not_active Expired - Lifetime
-
2004
- 2004-05-10 US US10/842,352 patent/US20040206205A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| US20040206205A1 (en) | 2004-10-21 |
| CN1531839A (en) | 2004-09-22 |
| KR100742424B1 (en) | 2007-07-24 |
| CN100459219C (en) | 2009-02-04 |
| TWI284001B (en) | 2007-07-11 |
| US6753648B2 (en) | 2004-06-22 |
| CA2430941A1 (en) | 2002-11-21 |
| JP4087715B2 (en) | 2008-05-21 |
| JP2004532932A (en) | 2004-10-28 |
| WO2002093664A8 (en) | 2003-03-06 |
| WO2002093664A2 (en) | 2002-11-21 |
| AU2002309256A1 (en) | 2002-11-25 |
| EP1419542A2 (en) | 2004-05-19 |
| ITMI20010995A0 (en) | 2001-05-15 |
| ATE322744T1 (en) | 2006-04-15 |
| KR20030038666A (en) | 2003-05-16 |
| HK1068495A1 (en) | 2005-04-29 |
| WO2002093664A3 (en) | 2003-02-06 |
| ITMI20010995A1 (en) | 2002-11-15 |
| DE60210478T2 (en) | 2006-10-05 |
| EP1419542B1 (en) | 2006-04-05 |
| MY132034A (en) | 2007-09-28 |
| DE60210478D1 (en) | 2006-05-18 |
| US20040001916A1 (en) | 2004-01-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20160509 |