Patent Application
20080227361
The invention relates to a method and a device for the production of an electroluminescent light-emitting element according to the preamble of independent claims.
Light-emitting elements on the basis of electroluminescence are known. Besides light-emitting diodes, the so-called LEDs, light-emitting elements with large areas on rigid as well as on flexible carriers are known. In practice, film elements, produced on the basis of thick-film technology, and excited with alternating voltage fields, have proved to be value. In such elements, the luminous pigments are embedded in a transparent, organic or ceramic, binding agent. The luminous pigments usually contain binary compounds. The electric field is supplied through structured electrodes, of which, the front electrode, from which the electroluminescent radiation is emitted, consists of a transparent, electrically conducting material layer, for instance a very thin metal layer, or a transparent semiconductor, such as indium oxide or indium tin oxide (ITO). The rear electrode consists of a conducting metal layer. The luminous pigment layer, arranged between the front electrode and the rear electrode, possibly with an additional insulating layer, forms, together with its embedding device, the dielectric of a capacitor, for which reason the term “light-emitting capacitor” is oftentimes used for it. The light-emitting elements are nonlinear components, whose parameters are a function of the applied voltage and the frequency as well as also of the ambient conditions such as humidity and temperature.
The transparent electrode is frequently made of a synthetic material (for example polyester) coated with indium oxide or indium tin oxide. The luminous pigment can, for instance, be made of zinc sulfide, doped with different metals like Au, Ag, Cu, Ga or Mn. The color of the emitted light and the conductivity of the luminous pigment layer are determined by the strength and the composition of the doping. By varying the doping, color tones, ranging from blue to yellow, corresponding to the wavelengths of about 480 nm to 580 nm, can be generated, and by mixing the doping materials, compound colors resulting from it, such as, for instance, the compound color white, can be obtained. An insulation layer, for instance made of barium nitrate, applied on this luminous pigment layer, acts at the same time as a reflector. After that, the rear electrode, containing aluminum, carbon or silver lacquer for instance, is applied on it. Since zinc sulfide is heavily hygroscopic, an encapsulation, consisting of an intensively water-repelling material, is provided. However, raw pigment materials, in which zinc sulfide molecules are microencapsulated, are already available, so that the hygroscopic properties come less prominently to expression. Due to the large molecular distance, the luminance is slightly lower and not quite homogeneous. Film-like light-emitting elements of this type are sliceable, extremely thin, highly flexible and economical. Lamination is no longer absolutely necessary as such, but if done, it additionally increases the protection against moisture.
Since it is desirable that light-emitting elements have large surface areas, the structuring of the transparent front electrodes is particularly difficult. At the same time, the large surface area is however of advantage especially in serial manufacture.
The task of the invention is to provide an improved method and an improved device for the production of that type of flat electroluminescent light-emitting elements.
This task is resolved according to the invention by the features of the independent claims. Advantageous embodiments and advantages of the invention follow from the other claims and the description.
In the method of production of an electroluminescent light-emitting element according to the invention, in which a transparent electrode layer is deposited on a carrier and a luminous pigment layer and a counter-electrode layer are deposited on the transparent electrode layer, a roller electrode, impregnated with an acid, is brought in physical contact, in particular in rotary physical contact, with the transparent electrode. With that a local etching of the transparent electrode layer takes place. A preceding structuring, for instance using a mask technique during the deposition of the transparent electrode layer, or an elaborate masking and etching of the coated carrier in an etching bath, in which the carriers with large surface areas can be handled only with difficulty and in which the etching method is difficult to control, can be dispensed with. The transparent electrode layer must be removed from some areas of the carrier due to reasons related to the functioning of the light-emitting element, in order, for instance, to prevent appearance of an electric field outside the luminous pigment layer between the front electrode and the rear electrode. The roller electrode can be of equal size or longer than the width of the carrier and it should be possible to guide it lengthwise. However, alternatively, the roller electrode can also be shorter than the width of the carrier. Thinkable is further a roller electrode with a structured surface, with which it is possible to etch a strip-shaped pattern in the electrode layer.
The electrode layer can be applied over the entire area of the carrier and can be provided thereafter with a suitable structuring. The carrier can be rigid or it can be embodied as a film, in particular as a PET (PET=polyethylene terephthalate) film. The transparent electrode can be embodied as a very thin metal layer, which is only a few tenths of a nanometer thick, or can be made of a transparent semiconductor. Preferably indium oxide or indium tin oxide is used as the transparent semiconductor, which has adequate transparency even with layer thickness of several hundred nanometers. To improve the conductivity of the electrode layer, the semiconductor can also be doped. Preferably the electrode layer is deposited with CVD or PVD method (CVD=chemical vapor deposition, PVD=physical vapor deposition). It is particularly preferable if the electrode layer is prepared with cathode sputtering. Cathode sputtering has the advantage that the thermal stress of the carrier is smaller compared with the vapor deposition method and better adhesion of the layer is obtained due to the higher kinetic energy of the sputtered layer components. Further the sputtering can take place in a reactive atmosphere in order to induce oxide formation during the sputtering process, so that, for example, indium tin oxide forms on the carrier during the condensation.
If the roller electrode is displaced relatively to the transparent electrode layer, while an electric voltage is applied between the transparent electrode layer and the roller electrode, the carrier in a flat laminar pattern can be freed from the transparent electrode layer. The roller electrode can slide or roll above the carrier.
In an advantageous step of the method, the roller electrode can be rolled on the carrier during the etching. With that a homogeneous utilization of the acid or the acid layer carried along by the roller electrode can be achieved. The cauterized material gets distributed over the surface of the roller electrode and can for instance be delivered over an acid bath and/or cleaning bath. Larger areas can be treated before the acid gets exhausted due to the too high concentration of the cauterized material.
Preferably an electric voltage between 10 and 50 volts, preferably between 12 and 40 volts, can be applied. It is of advantage if the voltage is adjusted by a person skilled in the art in dependence of the type of the acid, type of the material to be cauterized, concentration, temperature and, where applicable, other processing parameters.
It is of advantage if the roller electrode can be impregnated with acid between the etching steps. This is especially meaningful with larger areas and/or in a serial process.
If the surface of the roller electrode is structured, on contact with roller electrode the carrier can be freed at the same time from the transparent electrode layer at areas provided specifically with recesses, and can produce, for instance, a strip-like pattern in a single processing step. The processing time for the treatment of large areas is shortened. Conceivable is also to provide several paths in the carrier material side by side and treat them with a single roller electrode.
It is advantageous if the carrier with the structured transparent electrode layer can be cleaned with water after the etching.
It is especially advantageous, if the roller electrode can be soaked with citric acid. In which case the waste disposal can take place without problems.
In a device for application of a method for the production of an electroluminescent light-emitting element according to the invention, a roller electrode is provided that can be impregnated with acid, with which the transparent electrode layer in some areas can be removed in course of its electrochemical path. Several roller electrodes can also be provided, in order to treat several parallel strip-shaped carriers, in particular films, in through-feed method.
It is of advantage if the roller electrode is arranged in a rotatable manner.
Devices that can actuate relative motion between the roller electrode and the carrier can also be provided.
In a suitable embodiment, the roller electrode can have a homogeneous surface. Alternatively, the roller electrode can have a structured surface with flat areas spaced by gaps. On contact with the coated carrier, the flat areas etch the transparent electrode layer, while the electrode layers in the gap areas remain intact.
It is of advantage if an acid is provided in which the roller electrode can be dipped for soaking.
It is of advantage if several roller electrodes are provided for parallel treatment of several carriers. Alternatively or additionally, several roller electrodes can be provided for parallel treatment of the carrier. With that, the processing time can be shortened in case of large number of units and/or large areas.
Other advantages and details of the invention are explained further in the following with the help of a preferable exemplary embodiment described in the drawing, though not limited to the case of this exemplary embodiment. Shown are:
a-f Several processing steps in the production of a light-emitting element; and
a, b Schematic view of a device with a roller electrode (a) and a detail with the set-up roller electrode during the etching (b)
In the figures, same elements or elements with similar action are numbered with the same reference symbols.
As one can see in the sectional view in
The luminous pigment layer 13 is embedded in an insulation layer 14, on which the metallic electrode layer 15, forming the rear electrode is deposited. In an area 20 in which the metallic electrode layer 15 is not covered, the transparent electrode layer 12 is removed, so that no capacitive interference due to an arrangement outside the electroluminescent area can arise.
Besides the insulation layer 14, a conductor structure 16 is provided, which is in electrical contact with the transparent electrode layer 12 and serves the purpose as a bus-bar structure.
The electrode layer 15 is covered with a protective layer 17 and is accessible from outside only at a contact area 18 in a recess of the protective layer 17. The conductor structure 16 exhibits just such a contact area 19 (
a to 2f represent individual steps of coating in the production of such a light-emitting element 10. For the sake of better overview, only the new upcoming layers are indicated with the reference symbols. A transparent carrier 11, preferably made of PET film, is coated over its entire surface area with a transparent electrode layer 12 formed from indium zinc oxide (
A device for electrochemical structuring of a transparent electrode layer 12 on a carrier 11 before the deposition of a luminous pigment layer 13 as done in a tampon method is shown in
The carrier 11 is fixed on a depositing rack 25 and is brought in physical contact at its desired areas with a roller electrode 21 impregnated with an acid. A typical size of the carrier 11 is about 610 mm×1000 mm. Thinkable is, however, also a roller material. The roller electrode 21 is arranged in a displaceable manner relative to the transparent electrode layer 12, so that the roller electrode 21 preferably moves above the carrier 11. This is indicated by the double arrow.
A power supply unit 29 supplies the electric voltage, which is applied between the transparent electrode layer 12 and the roller electrode 21. The method can be employed both as a potentiostatic method with a constant voltage, or as a galvanostatic method with a constant current. Thereby the roller electrode 21 forms the cathode 27, while the transparent electrode layer 12 forms the anode. In the areas, in which the roller electrode 21 comes in contact with the transparent electrode layer 12, the latter is electrochemically cauterized. Thereby it is of advantage to roll the roller electrode 21 on the carrier 11 during the etching, as indicated in the front part of the roller electrode 21.
The roller electrode 21 can be impregnated with the acid between the etching steps by dipping it in an acid reservoir 26.
Preferably citric acid is used for impregnation of the roller electrode 21. The processing takes place preferably at room temperature. Citric acid with a concentration commercially available for domestic use has been found to be suitable. Voltage range found suitable for the etching is 10 to 50 volts with direct current, in particular 12 to 40 volts. The etching rate depends on different parameters, such as the contact pressure of the roller electrode 21, the conductivity of the transparent electrode layer 12, the concentration of the acid, the temperature and so on. The lower the resistance of the electrode layer 12, the higher is the observed etching rate. The roller electrode 21 can be moved above the carrier 11 with a velocity that is adjusted to the other processing parameters.
b illustrates the etching process in detail. The roller electrode 21 comprises an impregnable roller body 23 on a shaft 22. The roller body 23 consists for example of an acid-resistant textile or fleece, as known for instance in the conventional, so-called tampon coating method, in which the coats can be deposited on the substrates electrochemically.
If the roller electrode 21 is moved with the voltage applied and with its surface 24 in physical contact above the carrier 11, the acid in the roller body 23 cauterizes the transparent electrode layer 12 and leaves behind an exposed area 20 in the carrier 11.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2005-033-714.7 | Jul 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP06/06530 | 7/5/2006 | WO | 00 | 1/25/2008 |
