Method for producing organic electroluminescent components

Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device

Reexamination Certificate

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C430S315000, C430S320000, C430S324000, C313S494000, C313S504000

Reexamination Certificate

active

06582888

ABSTRACT:

BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for producing organic electroluminescent components having a structured electrode, in particular displays having a structured metal electrode.
With an increasing interchange of data and information, their visualization, particularly in communications technology terminals, is becoming ever more important. That information presentation normally takes place through the use of pixel matrix display apparatuses which may have additional, permanently specified symbol displays (“icons”). Known technologies of pixel matrix apparatuses are, for example, cathode ray tubes although, due to space requirement, electrical power consumption and weight, they are not suitable for use in mobile and portable electronic equipment. Flat screens (“flat panel displays”) are considerably more suitable for that purpose and, nowadays, are predominantly based on liquid crystal display (LC display) technology.
Simple, monochrome, passive-matrix-operated LC displays offer the advantage of cost-effective producibility as well as low electrical power consumption, low weight and small space requirement. However, the use of such displays is also linked to serious disadvantages. Specifically, the displays are not self-emitting due to the technological/physical principle, that is to say they can only be read and identified reliably in particularly favorable ambient lighting conditions. A further major constraint is the severely limited viewing angle of the display.
The problem of the lack of contrast in ambient lighting conditions that are not optimal can admittedly be improved by additionally fitting back-lighting, but that improvement is linked to a number of disadvantages. For example, back-lighting greatly increases the thickness of the LC flat screen. Specifically, while LC displays without back-lighting can be manufactured with a thickness of <1 mm, the total thickness of back-lit LC displays is typically several millimeters. In addition to the lamps or fluorescent tubes, the light-conducting plastic (“diffuser”) required for homogeneous illumination of the display area in particular contributes to increasing the thickness. A further major disadvantage of back-lighting is that the great majority of the electrical power consumption is required for the lighting. Furthermore, a higher voltage which is required to operate the light sources (lamps and fluorescent tubes), is normally produced with the aid of “voltage-up converters” from batteries or rechargeable batteries.
Active matrix LC displays can achieve better performance than with LC displays driven in the passive mode. In that case, each of the three primary colors in each pixel is assigned its own thin-film transistor (TFT). However, TFT technology is very costly and stringent requirements are placed on the substrates that are used, due to the high process temperatures that occur. The price for active matrix LC displays is correspondingly high.
The switching time of a single liquid crystal pixel is typically several milliseconds due to the physical principle of reorientation of a molecule in the electrical field, and furthermore is very highly temperature-dependent. The slow and delayed formation of the image, for example in traffic equipment (navigation systems in motor vehicles), thus has a particularly disturbing effect at low temperatures. LC technology can therefore be used only to a limited extent in the case of applications in which rapidly changing information and images are displayed, for example in video applications.
Other display technologies have either not yet reached the level of maturity for technical applicability, for example flat panel CRTs (CRT=cathode ray tube), or their use, particularly in portable electronic equipment, is subject to serious disadvantages resulting from specific characteristics: high operating voltage for vacuum fluorescence displays and inorganic thin-film electroluminescent displays, and high costs for displays based on inorganic light-emitting diodes.
Those disadvantages can be overcome by using displays based on organic light-emitting diodes (OLEDs). That new technology has a large number of advantages over LC displays, of which the major advantages are as follows:
Due to the principle of self-emissivity, there is no necessity for back-lighting, which considerably reduces the space requirement, power consumption and weight.
The typical switching times of pixels are in the order of magnitude of 1 &mgr;s and thus allow rapid image sequences to be displayed without any problems.
The switching times have no disturbing inertia at low temperatures.
The reading angle is considerably greater than in the case of LC displays, and is virtually 180°.
There is no need for the polarizers required for LC displays, so that increased brightness can be achieved even with a multiplexed display.
In contrast to other display technologies, organic light-emitting diodes can also be produced on flexible substrates and with non-planar geometries.
The production and layout of displays based on organic light-emitting diodes is much easier, and thus more cost-effective to achieve, than LC displays. Layout and production are typically carried out as follows.
The substrate, for example glass, is coated over the entire surface with a transparent electrode that is composed, for example, of indium tin oxide (ITO). Both the transparent electrode and the top electrode must be structured to produce pixel matrix displays. In that case, both electrodes are normally structured in the form of parallel conductor tracks, with the conductor tracks of the transparent electrode and top electrode running at right angles to one another. The structuring of the transparent electrode is carried out by a photolithographic process including wet-chemical etching methods, the details of which are known to the person skilled in the art. The resolution that can be achieved by using those methods is essentially limited by the photolithographic steps and the nature of the transparent electrode. Based on the prior art, both pixel sizes and non-emitting intermediate spaces between the pixels of a few micrometers in size can be achieved in that case. The length of the conductor tracks (which are in the form of strips) of the transparent electrode may be up to many centimeters. Depending on the lithography mask being used, emitting surfaces with a size of up to several square centimeters can also be produced. The sequence of the individual emitting surfaces may be regular (pixel matrix display) or variable symbol displays).
One or more organic layers are applied to the substrate with the structured transparent electrode. Those organic layers may be composed of polymers, oligomers, low molecular-weight compounds or mixtures thereof. Liquid-phase processes (application of a solution through the use of spin coating or wiping) are normally used for applying polymers, for example polyanline, poly(p-phenylene-vinylene) and poly(2-methoxy-5-(2′-ethyl)-hexyloxy-p-phenylene-vinylene), while gas-phase deposition (vapor deposition or “physical vapor deposition”, PVD) is preferred for low molecular-weight and oligomer compounds. Examples of low molecular-weight compounds, which preferably transport positive charge carriers, are: N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine (m-TPD), 4,4′,4″-tris-(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA) and 4,4′,4″-tris-(carbazol-9-yl)triphenylamine (TCTA).
Hydroxyquinoline aluminum III salt (Alq) is used, for example, as an emitter, which can be doped with suitable chromophores (quinacridon derivatives, aromatic hydrocarbons etc.). Additional layers, which influence the electrooptical characteristics as well as the long-term characteristics, may also be present and may be composed, for example, of copper phthalocyanine. The total thickness of the layer sequence may be between 10 nm and 10 &mgr;m, typically being in the range between 50 and 200 nm.
The top electrode is normally composed of

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