Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
  • H10K59/30—Devices specially adapted for multicolour light emission
  • H10K59/35—Devices specially adapted for multicolour light emission comprising red-green-blue [RGB] subpixels
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/917—Electroluminescent

Definitions

• the invention relates to multi-colour EL displays and a method of manufacture thereof .
• Organic electroluminescent devices are made from materials that emit light when a suitable voltage is applied across electrodes deposited on either side of the organic layer(s) .
• One class of such materials is semiconductive conjugated polymers which have been described in our earlier Patent US 5,247,190, the contents of which are herein incorporated by reference.
• the metal electrodes can be patterned to form a matrix of rows and columns so that matrix addressing can take place.
• This second layer covers the first emitting area and in that area of overlap acts as a transport layer. Thus no patterning above the first layer is required.
• This approach requires that the overlayers act as hole transport layers as well as emitters, so there is some compromise that must be made on their properties.
• the simplest structure would be made up of laterally-defined and separated LEP areas but it is not obvious how to pattern such a structure . Direct printing techniques (e.g. gravure) would be possible but the alignment tolerances required between different colours is probably beyond the resolution achievable in printing processes. Summary of the Invention
• the present invention provides a method of fabricating a multi ⁇ colour electroluminescent display, comprising the steps of: forming on a substrate a plurality of first electrode regions; forming over a first selected group of said first electrode regions a first layer of a precursor for a first material for emitting radiation of a first colour, said precursor for said first material being susceptible to patterning; at least partially converting said precursor for said first material into said first material which is substantially resistant to subsequent patterning steps; depositing over said first layer and over at least a second selected group of said first electrode regions a second layer of a precursor for a second material for emitting radiation of a second colour, said precursor for said second material being susceptible to patterning; patterning said second layer to remove said second layer from above said first layer and leaving said second layer over said second selected group of said first electrode regions; at least partially converting said precursor for said second material into said second material; converting any unconverted precursors into said respective materials; forming a plurality of second electrode regions over said layers in such a manner that said materials for emitting
• said step of forming a plurality of first electrode regions comprises the steps of: depositing a layer of a conductive material on a substrate; and patterning said layer of said conductive material to form a plurality of first electrode regions .
• said step of forming a first layer of a precursor for a first material comprises the steps of: depositing a layer of a precursor for a first material for emitting radiation of a first colour over said first electrode regions; and patterning said layer of said precursor for said first material to form a layer of said precursor for said first material over a first selected group of said first electrode regions.
• said step of forming a plurality of second electrode regions comprises the steps of: depositing a layer of a conductive material over said layers; and patterning said layer of conductive material to form a plurality of second electrode regions .
• said steps of at least partially converting said precursor for said second material into said second material and converting any unconverted precursors for said first and second materials into said first and second materials are performed in a single step.
• said second material is substantially resistant to subsequent patterning steps
• said method further comprises, after said step of at least partially converting said precursor for said second material, the steps of: depositing over said first and second layers and over a third selected group of said first electrode regions a third layer of a precursor for a third material for emitting radiation of a third colour, said precursor for said third material being susceptible to patterning; patterning said third layer to remove said third layer from over said first and second layers and leaving said third layer over said third selected group of said first electrode regions; and at least partially converting said precursor for said third material into said third material .
• said steps of at least partially converting said precursor for said third material into said third material and converting any unconverted precursors for said first, second and ⁇ resort endeavour, respectively., «
• third materials into said first, second and third materials are performed in a single step.
• said method further comprises the step of depositing an electron transport layer prior to said step of forming said plurality of second electrode regions.
• said electron transport layer is a conjugated polymer layer.
• the thickness of said electron transport layer is from 5 to 200 nm.
• said method further comprises the step of depositing a hole blocking layer prior to said step of forming said plurality of second electrode regions.
• said hole blocking layer is a dielectric layer.
• the thickness of said hole blocking layer is from 1 to 10 nm.
• said first electrode regions are composed of a light- transmissive conductive material.
• said first electrode regions are composed of indium-tin oxide, tin oxide or zinc oxide.
• said second electrode regions are composed of Al or an alloy thereof.
• the thickness of said first electrode regions is from 10 to 500 nm.
• the thickness of said second electrode regions is from 10 to 1000 nm.
• each of said first and second electrode regions comprises a line.
• the width of each of said lines of said first electrode regions is from 10 to 5000 ⁇ m.
• the width of each of said lines of said second electrode regions is from 10 to 5000 ⁇ m.
• the spacing between each of said lines of said first electrode regions is from 10 to 5000 ⁇ m.
• the spacing between each of said lines of said second electrode regions is from 10 to 5000 ⁇ .
• said first electrode regions are one of columns or rows and said second electrode regions are the other of columns or rows.
• said layers of precursor for each of said materials are formed to a thickness of from 10 to 500 nm.
• said materials for emitting radiation are polymer materials .
• said polymer materials are selected from poly(p- phenylene vinylene) for a green colour, poly(p-phenylene) or poly(p-phenylene vinylene) co-polymer with non-conjugated sections for a blue colour, and poly(1, 4-napthylene vinylene) or a dialkoxy substituted poly(p-phenylene vinylene) for a red colour;
• X denotes -SR 3 , -SO-R 3 , -S0 2 -R ⁇ -COOR 3 , -NO.,, -CN,
• R ⁇ ⁇ 3 are the same or different and denote -H, -R' 1 or -X
• R 4 denotes a straight chain or branched alkyl group with 1 to 20 carbon atoms, phenyl or benzyl, either of which can be substituted once or twice with -R', -OR 1 , -N0 2 , -CN, -Br, -Cl or -F
• Ar denotes an aromatic system, comprising from 4 to 20 carbon atoms which can optionally be substituted; (iii) a thiophene, furan, pyrrole or pyridine analogue of (i) or (ii) ; and
• the poly(p-phenylene vinylene) precursor comprising: (i) poly(p-xylylene- ⁇ -dialkyl sulphonium halide) ; (ii) poly(p-xylylene- ⁇ -cycloalkyl sulphonium halide) ; (iii)poly(p-xylylene- ⁇ -halide) ;
• X denotes -SR 3 , -SO-R 3 , -S0 2 -R 3 , -COOR ⁇ -NO ? , -CN,
• R R 2 ,R 3 are the same or different and denote -H, -R 4 or -X, R 4 denotes a straight chain or branched alkyl group with
• X denotes -SR 3 , -SO-R 3 , -S0 2 -R ⁇ -COOR 3 ,-N0 2 , -CN,
• R ⁇ RYR 3 are the same or different and denote -H, -R 4 or -X, R 4 denotes a straight chain or branched alkyl group with
• Ar denotes an aromatic system, comprising from 4 to 20 carbon atoms which can optionally be substituted.
• said steps of patterning said precursor materials comprise steps of etching. ⁇ mntt . ..
• said conversion steps comprise at least one of heat treatment, chemical treatment, electron beam exposure or radiation exposure.
• said conversion steps comprise a heat treatment at a temperature of from 50 to 300 * C in an inert atmosphere.
• said heat treatment is performed at about 150'C.
• said layers of said materials for emitting radiation are formed to cover said first electrode regions so as to electrically insulate said first electrode regions from said second electrode regions.
• said layers of said materials for emitting radiation each comprise a plurality of areas, each area overlying a respective one of said first electrode regions.
• said areas of material each comprise a plurality of discrete sub-areas and said second electrode regions are formed to overlie selected ones of said sub-areas.
• the present invention also provides a multi-colour electroluminescent display, comprising: a substrate; a plurality of first electrode regions formed over said substrate; a plurality of discrete, laterally-spaced areas of light- emissive material formed over said first electrode regions, wherein selected groups of said plurality of areas are each formed of a material for emitting radiation of a different colour and each individual first electrode region has only a material for emitting radiation of one colour formed thereover; and a plurality of second electrode regions formed over said plurality of light-emissive areas; wherein said light-emissive areas can be selectively excited to emit radiation by applying an electric field between said first and second electrode regions.
• said device comprises a plurality of areas of a first material for emitting radiation of a first colour formed over a first selected group of said first electrode regions, a plurality of areas of a second material for emitting radiation of a second colour formed over a second selected group of said first electrode regions, and a plurality of areas of a third material for emitting radiation of a third colour formed over a third selected group of said first electrode regions.
• said plurality of areas of said first, second and third materials are arranged such that each area of said plurality of areas of said second material is adjacent a respective one of said plurality of areas of said first material and a respective one of said plurality of areas of said third material .
• said device further comprises an electron transport layer between said plurality of light-emissive areas and said plurality of said second electrode regions.
• said electron transport layer is a conjugated polymer layer.
• the thickness of said electron transport layer is from 5 to 200 nm.
• said device further comprises a hole blocking layer between said plurality of light-emissive areas and said plurality of said second electrode regions .
• said hole blocking layer is a dielectric layer.
• the thickness of said hole blocking layer is from 1 to 10 nm.
• esp ⁇ ⁇ the thickness of said hole blocking layer is from 1 to 10 nm.
• said first electrode regions are composed of a light- trans issive conductive material.
• said first electrode regions are composed of indium-tin oxide, tin oxide or zinc oxide.
• said second electrode regions are composed of Al or an alloy thereof.
• the thickness of said first electrode regions is from 10 to 500 nm.
• the thickness of said second electrode regions is from 10 to 1000 nm.
• each of said first and second electrode regions comprises a line.
• the width of each of said lines of said first electrode regions is from 10 to 5000 ⁇ m.
• the width of each of said lines of said second electrode regions is from 10 to 5000 ⁇ m.
• the spacing between each of said lines of said first electrode regions is from 10 to 5000 ⁇ m.
• the spacing between each of said lines of said second electrode regions is from 10 to 5000 ⁇ .
• said first electrode regions are one of columns or rows and said second electrode regions are the other of columns or rows.
• said areas of light-emissive material are each formed to a thickness of from 10 to 500 nm.
• said materials for emitting radiation are polymer materials .
• said polymer materials are selected from poly (p- phenylene vinylene) for a green colour, poly (p-phenylene) or poly(p-phenylene vinylene) co-polymer with non-conjugated sections for a blue colour, and poly(1 , 4-napthylene vinylene) or a dialkoxy substituted poly(p-phenylene vinylene) for a red colour.
• said areas of material for emitting radiation cover said first electrode regions so as to electrically insulate said first electrode regions from said second electrode regions.
• said areas of material for emitting radiation each comprise a plurality of sub-areas, each sub-area overlying a respective one of said first electrode regions.
• said sub-areas of material each comprise a plurality of further discrete sub-areas and said second electrode regions are formed to overlie selected ones of said further sub- areas .
• a precursor of a material is to be construed broadly as encompassing any precursor from which the material can in any way be formed.
• a method of manufacture of a colour polymer EL display is described herein wherein two or more precursor polymer materials are used to define the emitting areas and are deposited in sequence onto one electrode of the device, patterned and converted to their final form before deposition of the next polymer layer such that the converted polymers are not in any way damaged by the deposition, patterning or conversion of subsequent precursor layers .
• one colour is first deposited then lithographically defined, and finally converted to its final form. Subsequently other colours are deposited and lithographically defined before conversion. Conversion of the precursor occurs through heat treatment or chemical treatment or electron beam exposure or radiation exposure (including electromagnetic radiation) or some combination of these techniques .
• the underlying electrode and/or the subsequently deposited top electrode are patterned to define areas of emission from the converted polymers, and the area of overlap between the electrodes is chosen to ensure that there is always an emitting polymer layer between the two electrodes .
• a further unpatterned layer is deposited on top of the patterned electroluminescent polymers and prior to the deposition of the final electrode, such layer being either a charge transport layer or a very thin dielectric layer whose thickness and constitution is chosen to increase the overall efficiency of the EL device; the area of overlap between the electrodes is chosen to ensure that there is always an emitting polymer layer between the two electrodes.
• the underlying mechanism that causes the precursor polymer to be changed into its final robust form can include scission of solubilising side groups or cross-linking of side groups on different polymer chains.
• Lithographic definition can take place through the use of compatible photoresists (i.e. that can be put down without disturbing the underlying layer) followed by masked exposure and development. Also possible is partial conversion using masked UV exposure prior to development and removal of the unwanted areas followed by a full conversion. The full conversion can be performed prior to the deposition of the next precursor polymer, or after any subsequent polymers have been patterned depending on the effect of subsequent solvents on the partially converted material.
• the final form of the polymers is insoluble in subsequent solvents. A final unpatterned layer can be subsequently deposited over all the emitting areas to improve efficiency.
• Figure 1 is a schematic section through part of a multi ⁇ colour device
• Figure 2 is formulae of side-group leaving precursor materials for red, green and blue precursors and final polymer forms at a conversion temperature of 200°C;
• Figure 3 is an energy band diagram
• Figure 4 is a RGB dot-matrix architecture.
• the structure comprises a glass substrate 2 with patterned regions of a transparent electrode, which in the preferred embodiment is indium tin oxide.
• the strips define columns of the RGB dot-matrix architecture. As can be appreciated from the view of Figure 4, in the final structure these represent strips of indium tin oxide.
• the strips are denoted in Figure 1 by the reference numerals 4a, 4b and 4c.
• On top of each strip of indium tin oxide is a strip of a li- t emitting polymer. The polymers atop the strips 4a, 4b and 4c respectively emit light of different wavelengths, red, green and blue as illustrated.
• the red emitting polymer strip 6a lies on top of ITO strip 4a.
• the green emitting polymer 6b lies on top of ITO strip 4b.
• the blue emitting polymer strip 6c lies on top of ITO strip 4c.
• the respective wavelengths of emission are - 15 - indicated by the capital letters on the arrows.
• An optional electron transport/hole blocking layer extends crosswise and over the strips 4a, 4b and 4c. When the electron transport/hole blocking layer 8 is present the polymer strips can be narrower than the ITO strips. Atop this, lie a plurality of aluminium electrode strips 10. Once again, as can be seen from Figure 4 the aluminium electrode strips 10 and the electron transport/hole blocking layer extend crosswise to define rows of the dot matrix architecture.
• Each of the light emitting polymer strips 6a, 6b, 6c is derived from a respective precursor.
• Figure 1 The structure of Figure 1 is manufactured in accordance with the following steps.
• a layer of indium tin oxide is patterned on the glass substrate 2 to form the indium tin oxide strips 4a, 4b and 4c.
• a layer of a first precursor is formed over a first selected group of the ITO portions, that is those which are to excite emission of a first colour.
• the precursor to the red emitting polymer could be put down first. That precursor is susceptible to patterning, for example by etching, in its precursor form but, when converted or partially converted into its final polymer is substantially resistant to subsequent patterning steps. After being put down over the first selected group of ITO portions, the precursor is at least partially converted into its red emitting polymer.
• a second precursor material is deposited over the first layer and over a second selected group of ITO portions.
• the precursor to the green emitting polymer could next be deposited.
• That precursor is also susceptible to patterning, for example by etching, in its precursor form but is substantially resistant to patterning when at least partially converted.
• the second layer can be patterned while in its precursor form to remove it from above the first layer, but leaving the second layer over the second selected group of ITO portions.
• the second precursor is at least partially converted into the green emitting polymer. Similar steps are carried out for the blue emitting polymer. Finally, any unconverted precursors are converted into their respective polymers .
• precursors can be fully converted after being deposited and patterned.
• the order in which the precursors are put down may not be significant, though the materials with the most severe conversion conditions should be processed first (i.e. to minimize the damage to previously deposited emitting areas) .
• the three precursors are shown in Figure 2 (Formulae I, II and III) .
• the green emitter precursor is a polyphenylenevinylene (PPV) polymer with a tetrahydrathiophene leaving group and bromine counter ion. Conversion in an inert atmosphere can be effected at between 150 and 200°C.
• the blue emitter (Formula II) is a block copolymer which limits the conjugation length of the PPV monomer and thereby shifts the emission wavelength into the blue.
• the blue copolymer is a PPV copolymer with non- conjugated sections. Similar conversion conditions to the green emitter are required.
• a red emitting precursor (Formula III) is shown based on a polynaphthalene polymer with a tetrahydrathiophene leaving group and bromine counter ion. Again, similar conversion conditions to the green emitter are required.
• the ITO is patterned as lines (columns of a passive matrix display) and the subsequent precursor polymers are patterned as parallel lines each associated with a single ITO line, and each slightly wider so that the ITO lines are completely covered as in Figure 4. Finally the top electrode (e.g. aluminium) is deposited as orthogonal rows .
• Such a display can be addressed by applying data voltages to the columns and by sequential row selection so that within each selected row the required pixel/colour combinations are switched on.
• the optional second layer 8 above the RGB emitters can be added, both to help prevent shorting of the top contact to the ITO at the edge of the top electrode, and to increase the efficiency of emission.
• a conjugated polymer electron transport layer with a bandgap E qA as shown in Figure 3 can be used but may cause differential efficiency from each of the RGB areas.
• E gA >E g B >E g G >E g R where E g BRG represents the energy gap of the blue red or green polymers respectively.
• LUMO represents the lowest unoccupied molecular orbital and HOMO represents the highest occupied molecular orbital.

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• 1997
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