CROSS-REFERENCE TO RELATED APPLICATIONS
BACKGROUND OF THE INVENTION
This application is a continuation of copending international application PCT/DE99/01655, filed Jun. 7, 1999, which designated the United States.
1. Field of the Invention
The present invention relates to a method for producing structured electrodes and especially organic electro-luminescent components with structured electrodes. The components are used in displays and the like and further comprise structured metal electrodes, The electrode is supported by multiple layers of varying widths and heights such that in combination with other supports, active organic layers may be tightly packed into a display area. A possible arrangement includes the active layers layered below a top electrode.
2. Description of Related Art
Thin layers, in particular those with a thickness of 1 nm to 10 μm, find diverse technological applications in for example: semiconductor production; and microelectronic, sensory and display technologies. Production of the organic electro-luminescent components almost always includes the structuring of necessary layers; whereas the necessary structure sizes go from the sub-μ-area to the entire substrate area. In addition, the required component form varieties are practically unlimited.
In general, there are many available lithographic processes available for structuring electrodes. That which most all the processes have in common, is that the layers to be structured come into contact with more or less caustic chemicals, including photoresists, solvents, developing fluids, and corrosive gases. Such contact leads, during some applications, to corrosion or at least damage of the layers to be structured. This is often the case for organic light emitting diodes.
Organic Light Emitting Diodes (OLEDs), i.e. electro-luminescent diodes, are predominately used in displays. Examples of such applications are set out in U.S. Pat. Nos. 4,356,429 and 5,247,190. An example method of producing electrodes in general is set out in German patent registration reference 197 45 610.3. The structure and production of OLED displays typically occurs as follows.
A substrate, for example glass, is coated entirely with a transparent electrode—bottom electrode, anode. The bottom electrode comprises for example indium-tin-oxide (ITO). To produce pixel-matrix-displays, the transparent bottom electrode as well as later formed top electrode (cathode), must be structured. Accordingly, both electrodes are usually structured in the form of parallel strip conductors. The strip conductors of the bottom and top electrodes tend to run vertically with respect to each other, The structuring of the bottom electrode occurs via a photolithographic process which includes wet chemical etching methods, the details of which are known to one skilled in the art. The etched final structure, which is obtainable with this method, is essentially limited by the photolithographic steps and the consistency of the bottom electrode. According to the current state of the art, pixel sizes as well as non-emitting spaces between the pixels can be realized to a size of few micrometers. The lengths of the strip shaped strip conductors of the bottom electrode can be up to many centimeters. According to current lithographic masking, emitting areas up to several square centimeters can also be produced. The sequence of each emitting area can be regular (pixel-matrix-display) or variable (symbol presentations).
One or more organic layers are applied on a substrate, the substrate including the structured transparent bottom electrode. These organic layers may comprise polymers, oligomers, and low molecular combinations or mixtures thereof. To apply polymers, for example polyanilin, poly (p-phylenvinylen) and poly (2-methoxy-5-(2′ethyl) hexyloxy-p-phenylenvinylen), generally liquid phase processes are used (application of a solution by spin coating or blading); while for low molecular and oligomer combinations a gas phase deposition is preferred (Evaporation or Physical Vapor Deposition, PVD). Examples of preferred low molecular layers include the following combinations transported by positive charge carriers: N,N′-to-(3-methylphenyl)-N,N′-to′(phenyl)benzidin (m-TPD), 4,4′,4″-Tris-(N-3-methylphenyl-N-phenylamino)-triphenylamin (m-MTDATA) and 4,4′,4″-Tris-(carbazol-9-yl)-triphenylamin (TCTA). Hydroxychinoline-aluminium-III-salt (Alq) is used, for example as an emitter, which can be remunerated with suitable chromophores (Chincridon-derivates, aromatic hydrocarbons, etc.). If necessary, exemplary existing additional layers which influence the electro-optical characteristics as well as the long-term characteristics may be copper-phthalocyanine. The entire thickness of the layer sequence can be between 10 nm and 10 μm, typically lying in the range of 50 to 200 nm.
The top electrode usually comprises a metal which is generally applied by gas phase deposition (thermic deposition, sputtering or cathode rays deposition). Preferred compositions are base and therefore reactive metals, especially to water and oxygen, and include lithium, magnesium, aluminum and calcium as well as alloys of these metals. For the production of a pixel-matrix-order structure having metal electrodes, the structure is obtained generally by the metal being applied through a mask opening.
A produced OLED-display, according to this method, may additional contain electro-optical features such as: UV-filters, polarization filters, anti-reflex-coatings, and (micro-cavities) known installations such as color conversion and color correctional filters. In addition, a hermetically sealed packaging may be provided by which the organic electro-luminescent displays are protected from external environmental influences such as humidity and mechanical strains. In addition, thin film transistors for individual picture elements (pixel) can be present.
For high resolution displays for which the presentation of large informational content is possible, a fine structuring of the metal electrodes in the form of strip conductors is necessary, i.e. the width of the strip conductors as well as the spacing therebetween must be structured in keeping with narrow tolerances in the microns. Herein, the width of a strip conductor can lie between 10 μm and several hundred micrometers, preferably between 100 and 300 μm. To reach a high filling factor (share of the active light emitting area versus the entire display area) it is additionally necessary that the spaces between the metallic strip conductors as well as the spaces between the strip conductors of the transparent bottom electrode are only a few micrometers. Established structuring techniques can not be used here because the existing active organic layers, i.e. the electro-luminescent materials, are not resistant to the necessary chemicals for such fine structuring.
By so called shadow masking, i.e. thin metals or segments with correspondingly formed openings for a desired structure, only layers can be structured and produced according to CVD or PVD (chemical vapor deposition, physical vapor deposition) methods. Furthermore, the obtainable dissolution produces (based on the finite distance between masking and substrate) relatively inferior results and large areas (as a result of a bending of the shadow masking) which cannot be realized in view of production engineering.
A lift off method for the production of structured metallizations by use of two separate photoresist layers is known from German reference DE-A44 01 590. Relatively thick metal structures on semiconductor components can be produced by this method.
- BRIEF SUMMARY OF THE INVENTION
Furthermore European reference EP-A-0 732 868 shows a method for the production of an organic electro-luminescent display device. For this, on a multiple number of first display electrodes, electrically insulated overhanging structures are produced, which are built up from a first layer, for example of polyamide, and a second layer of for example SiO2. Afterwards, organic functional layers for different color components or also an only color component are applied in the areas between the electrically insulated structures by use of (shadows) masks, and following this the material for the second display electrode is precipitated on the organic functional layers and the electrically insulated structures.
It is an object of the invention to provide a generally applicable structuring technique for electrodes, i.e. a technique which is subject, as little as possible, to limitations regarding geometry (structure size, forms, areas) and production (CVD and PVD methods, solvent processes). In particular, the instant method allows for suitable mass production of structured electrodes in organic electro-luminescent components, and in particular of fine structured metallic top electrodes for highly dissolvent displays wherein the electrodes to be structured are not damaged by chemicals.
With the foregoing and other objects in view, there is provided in accordance with the invention a method of producing structured electrodes for organic electro-luminescent displays, comprising the steps of: forming a first layer on a substrate, said first layer having a first width and a first solvent rate; forming a protective layer over said first layer; forming a second layer on said protective layer, said second layer having a second width and a second solvent rate; etching said first and second layer with at least one solvent such that said second width is greater than said first width; and forming an electrode on said second layer.
The present invention may further comprises a method of producing structured electrodes for organic electro-luminescent displays, comprising the steps of: first forming a bottom electrode on a semiconductor substrate, second forming a first layer on said bottom electrode, said first layer having a first width and a first solvent rate; third forming an electrically insulating protective layer over said first layer; fourth forming a second layer on said protective layer, said second layer having a second width and a second solvent rate; fifth etching said first and second layer with at least one solvent such that said second width is greater than said first width; sixth forming an organic active layer on said second layer; and seventh forming a top electrode on said second layer. And in addition, the method may be applied where only one solvent is used and said first and second layers are reactive to said one solvent.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
By this invention, a new method for a maskless production of structured electrodes, especially for organic electro-luminescent components, is realized. This method especially enables the production of structured metal electrodes, particularly for organic-electro-luminescent displays. By this method, structures can be produced which are suitable for wide area displays and in addition the possibility of the structuring of metal electrodes on electro-luminescent polymers. The instant method is also especially suitable for lithographic applications.
DETAILED DESCRIPTION OF THE INVENTION
The FIGURE depicts a schematic cross section of an example embodiment of an organic light emitting diode produced in accordance with the instant method.
As depicted, the diode comprises a substrate 1, with a structured bottom electrode 2 layered thereon. Electrode 2 may be transparent. The electrode 2 may further comprise a non-planar geometry of glass, metal, silicon or polymer (in the form of a foil). Electrode 2 may further comprise an ITO electrode (ITO=Indium Tin Oxide). Atop the electrode 2, a first layer 3 is formed, the details of which are set out below. A protective layer is formed on layer 3 (not shown). The layer may be electrically insulating and comprise any properties known to one skilled in the art to accomplish the same. Likewise, the layer may prevent intermixing, as discussed below, and further comprise any suitable materials for the same. Atop the protective layer, a second layer 4 is formed. Thereon, an active organic layer 5 is formed and still further a top electrode 6. The top electrode may be a metal. As set out in more detail below, the first and second layers are formed such that the second layer overhangs the first layer. In the spaces between the above-described structure, a second active organic layer 5 and top electrode 6 may be formed—second formation, The first and second active organic layers and top electrodes may be identical, different and/or related in composition and function. The height and width of the second formation is engineered so as to maximize exposure of the active organic layer, in the top direction, from between adjacent structured electrode formations or along side at least one electrode formation.
By way of more detail, according to the instant method, two layers are preferably applied on a bottom electrode, itself positioned on a substrate. On a second of the two layers, (after structuring, structure transmission and integration) at least one active organic layer is applied. Then on the active organic functional layer a top electrode is deposited.
The top electrode, which preferably includes few escaping electrons, functions as an electron-receiving electrode, and comprises a metal or a metallic coating. In addition, this electrode may also include a layered arrangement, wherein on a thin dielectrical layer (<5 nm), which for example comprises lithiumfluoride or aluminiumoxide, a metal or ITO layer as a (transparent) electrode.
According to the present inventive method, it is essential that the first lower electrode, which can be a structured or applied layer, is not damaged by applying the second upper layer and as such between both layers a defined boundary is maintained. The first and/or second layer preferably comprises an organic film developing material, such as a photoresist.
Photoresists are radiation sensitive film developing materials whose solubility changes with exposure to radiation. Herein, it is distinguished between use of positive and negative photoresists. When the upper and lower layers comprise a photoresist and each are sensitive to approximately the same radiation wavelength, the lower photoresist may not be a negative photoresist.
According to a preferred embodiment of the present invention, wherein an essential characteristic of the embodiment includes a photolithographic process, at least two layers are selectively applied on a transparent bottom electrode, wherein the first layer comprises a resist or photoresist and the second layer comprises a positive or negative photoresist layer, and in the case where the first layer comprises a photoresist layer, the first layer with be exposed to radiation prior to the application of the second layer. The layers are then structured in such a way that the active organic layers and top electrodes may be respectively applied and/or deposited on the second layer. The layers are structured in a vertical direction with respect to the length of the bottom electrode. The application of the active organic layers on the second layer can generally occur by thermic deposition processes as well as by solvent applications, such as spinning or blading following drying.
At the photolithographic method step, the first of the two layers must be overcoatable or overcoated with a protective layer. This means, that both layers can be applied on top of each other without a so called intermixing, i.e. applied coatings dissolvable in different solvents, such that the (photo)resist of the first layer is not affected by the solvent for the photoresist of the second layer. Accordingly, the applied first layer is preserved during application of the second layer. Likewise, between the two layers a defined boundary is effected.
For the photolithographic method step it is additionally recommended, that the first layer has a higher developing rate than the second layer. As such, after the exposure, by the necessary structuring treatment of the photoresist layers, the first layer dissolves faster with a developing solvent than the second layer. It is of advantage here, if both layers can be treated i.e. developed, with the same developer, preferably a watery-alkaline developer.
In general, for the lower layer, electrical insulating organic and inorganic materials are used. Suitable inorganic materials include: silicondioxide; siliconnitrite; and aluminiumoxide. But the lower layer may for example also comprise an alkaline developing non-photo sensitive polyamide. It is advantageous if the lower layer is photosensitive and preferably comprises a positive photoresist on the basis of polyglutarimide or polybenzoxazol.
The upper layer is preferably also a photoresist. This layer comprises a positive photoresist (Positivresist) of a Novolak/Diazochinon-basis or a negative photoresist (Negativresist) on the basis of Novolak/Integrater/photo acid. For the positiveresist polymethylmethacrylate (PMM) may be used, and as negativeresist an integratable polysilpheylensiloxanes may be used.
However, it is also possible to indirectly structure the upper layer. An amorphous carbon (a-C) or amorphous hydrogen carbon (a-C:H) serves, for example, as a coating material. Such layers are structured in an oxygen plasma, whereas a corrosive masking is used in the form of a silicon photoresist layer, particularly a so-called CARL-resist (CARL=Chemical Amplification of Resist Line) or a TSI system (TSI=Top Surface Imaging).
Following the above described method, a structure as shown in the figure is created, wherein the second layer shows a larger structure width than the first layer (overhanging structure). The second layer, which consists preferably of a film developing organic material, is cross-linked, whereby the mechanical stability and the thermic resistance is elevated. The overhanging structure will not be impaired by the cross-linking.
Based on the cross-linking, the overhanging of the second layer will be stabilized, so that larger areas, especially long borders, can be realized and the layer production can take place by solvent processes. The stable overhanging then produces the structure of the following applied layers because at the border of the overhanging by, CVD- or PVD as well as from liquid phase processes, applied layers are cut off and therefore separated in to different zones, i.e. structured. In particular, these are active organic layers, i.e. electro-luminescent layers, and electrodes.
As discussed above, the upper layer shows a wider structuring width after the structuring than the lower layer. The difference in the structuring width (overhanging) is preferably between 1 and 10 μm. Preferably, the thickness of the lower layer is 0.1 to 30 μm and in particular 0.5 to 10 μm, and the thickness of the upper layer 0.1 to 30 μm and in particular 0.5 to 5 m.
- EXAMPLE 1
Production of an OLED Display
The following are two examples of implementing the above-described method.
The production of a display proceeds according to the following method steps:
1. An entire area of a glass sheet is coated with indium-tin-oxide (ITO) and then structured according to a photolithographic method followed by wet chemical etching, in such a way that parallel conductor strips with a width of approximately 200 μm and a space of approximately 50 μm are formed. The photoresist used during structuring is then completely removed. The conductor strips are each approx. 2-cm long and include at their outer ends additions for external contacting if applicable,
2. The glass sheet will be heated approximately 1 hour at a temperature of 250° C., then a commercial photoresist on the basis of polyglutarimide will be spun on (application for a duration of 10 seconds at 700 rotations/minute, then spun off for 30 seconds at 3000 rotations/minute). The received layer will be dried for 15 minutes at 150° C. and then 30 minutes at 250° C. in a circulating air oven. A streaming exposure at a wavelength of 248 nm (polychromatic) with a dose of 100 mJ/cm2 is created afterwards. Then a commercial photoresist on the basis of Novolak/Diazochinone (10:1 thinned with (1-mehtoxy-2-propyl)acetate) will be spun on at 2000 rotations/minute for 20 seconds. Both layers will be dried 60 seconds at 100° C., and afterwards with a radiation dose of 62 mJ/cm2 at a wavelength of 365 nm (polychromatic) via lithographic masking. Then with a commercial developer which contains tetramethylammoniumhydroxyde, the structure is developed for 20 seconds. Afterwards the glass sheet will be put into a 100° C. preheated air circulating oven and annealed for 45 minutes at 230° C.; thereby cross-linking the upper photoresist. Then the described developer develops twice more for 70 seconds; thereby an overhanging of the upper layer of approximately 5 μm is created. The layer thickness of the lower layer is approximately 2.6 μm; both layers together are approx. 4.3 μm thick. Afterwards, resist remnants will be removed for 90 seconds from the ITO surface by oxygen plasma (RF capacity: 70 W, gas flux: 30 sccm),
3. At a pressure of 10−5 mbar, a layer of N,N′-(3methylpheyle)-N,N′-(phenyl)-benzidin (m-TPD) will be applied by conventional vapor deposition (layer thickness: 135 nm, deposition rate: 0.2 nm/s).
- EXAMPLE 2
Production of an OLED Display
4. Without the use of a mask, a 100 nm thick layer of magnesium will be applied on the active surface of the display by thermic deposition (deposition rate: 1 nm/s, pressure:10−5 mbar), Interrupting the vacuum, a 100 nm thick layer of silver nm will be applied, also by vapor deposition, on the active display area (deposition rate: 1 nm/s, pressure: 10−5 mbar). The resulting display flashes are clearly visibly in the day light and the emission color is greenish-yellow.
A 1% solvent of an electro-luminescent polymer on the basis of fluorines in Xylole is spun on (4000 rotations/min, 30 s) a glass sheet with a produced layer build up corresponding to example 1. Afterwards, it is dried for 60 seconds at 85° C. Without the use of masking, a 100 nm thick layer of calcium will be applied on the active area of the display by vapor deposition (deposition rate: 1 nm/s, pressure: 10−5 mbar). Without interrupting the vacuum, a 100 nm thick layer of silver will also be applied on the active display area by vapor deposition (deposition rate; 1 nm/s, pressure: 10−5 mbar).
The display flashes are clearly visibly in the day light and the emission color is greenish-yellow. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications would be obvious to one skilled in the art intended to be included within the scope of the following claims,