Coating processes – Electrical product produced – Fluorescent or phosphorescent base coating
Reexamination Certificate
1999-07-15
2002-05-28
Yamnitzky, Marie (Department: 1774)
Coating processes
Electrical product produced
Fluorescent or phosphorescent base coating
C428S917000, C313S504000, C257S089000
Reexamination Certificate
active
06395328
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to multi-colour EL displays and a method of manufacture thereof.
BACKGROUND OF THE INVENTION
The most popular flat panel display technology currently in use is based on liquid crystal devices, which are effectively light shutters used in combination with illumination sources. In graphic displays there are many different pixels that must be independently driven. Typically this is achieved through matrix addressing, where each pixel is addressed by application of a suitable switching voltage applied between row and column conducting tracks on either side of the liquid crystal. Each row is selected by applying. a voltage to the row track, and individual pixels within the row selected by application of column data voltages to the column tracks. The rows are addressed sequentially, each for a line address time such that the whole frame is addressed within the Frame time. However, because the speed of switching of the liquid crystals is slow relative to the line addressing time, when video frame rates are required (<20 ms), special circuitry has to be typically added to each pixel. This arrangement is called active matrix addressing and often involves the use of thin-film transistors at each pixel. Because of the increased complexity of the active matrix displays they are much more expensive to make than passive matrix devices.
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 U.S. Pat. No. 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. There are several potential advantages over liquid crystal graphic displays. Because the polymers are directly emissive, no backlight is required. Also polymers of different colours can be fabricated so that a suitably patterned matrix of polymers can be used for a colour display (multi-colour or full-colour RGB) without the use of colour filters as required by a liquid crystal display.
Our earlier applications (EP-A-94924916.3 and GB 9507862.2) show ways to achieve patterned emission of different colours. In these different embodiments the polymer materials are not themselves patterned and the emission patterns are defined by the intersection of the injecting electrodes. Multiple colour emission is possible through stacking of the emitting layers on top of each other in a vertical fashion. This approach results in a device fabrication process with many steps, but with low complexity for each step. Another U.S. Pat. No. 5,424,560 recently disclosed an approach for producing Organic LEDs where the emission areas are themselves patterned, avoiding the requirement for multiple electrode depositions. In this approach an emitting area of one colour is first patterned, and subsequently a material of different colour emission is deposited and patterned to form a separate emission area. 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 problem can be solved if, as described herein, layers could be patterned to form emitting areas, but without disturbing previously patterned emitting areas of a different colour.
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; finally converting any partially-converted precursors into said respective materials; forming a plurality of second electrode regions over said layers in such a manner that said materials for emitting radiation can be selectively excited to emit radiation by applying an electric field between said first and second electrode regions.
Preferably, 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.
Preferably, 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.
Preferably, 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.
In one embodiment, said steps of at least partially converting said precursor for said second material into said second material and finally converting any partially-converted precursors for said first and second materials into said first and second materials are performed in a single step.
In another embodiment, said second material is substantially resistant to subsequent patterning steps, and 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.
Preferably, said steps of at least partially converting said precursor for said third material into said third material and finally converting any partially-converted precursors for said first, second and third materials into said first, second and third materials are performed in a single step.
Preferably, said method further comprises the step of depositing an electron transport layer prior to said step of forming said plurality of second electrode regions.
Preferably, said electron transport layer is a conjugated polymer layer.
Preferably, the thickness of said electron transport layer
Cambridge Display Technology Limited
Finnegan Henderson Farabow Garrett & Dunner
Yamnitzky Marie
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