Inkjet Printing of Light-Emitting Polymer Displays
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Inkjet Printing of
Light-Emitting Polymer Displays
Tatsuya Shimoda, Katsuyuki Morii, Shunichi Seki, and Hiroshi Kiguchi Abstract Based on the concept of a microliquid process, we have developed an organic electroluminescent display using conductive polymers, including light-emitting polymers. The technology of inkjet printing has progressed enough to be used for the microliquid process. First, we describe the process used to form a patterned thin film. This involves inkjet-related technologies, the self-patterning behavior of a microliquid on the substrate, and the drying process that defines the thickness profile and film properties. Some microliquid behaviors and related phenomena, along with properties of the resulting film, were identified as distinct from those coming from a macroscopic liquid, as a result of size effects. By fully utilizing these unique properties of microliquids, we have succeeded in fabricating color-pixel arrays by direct patterning of polymer solutions. As a result, an organic electroluminescent display with a vivid full-color image has been developed. Keywords: chemical synthesis, electrical properties, electro-optical materials, inkjet printing, liquids, polymers, solution processing.
Introduction:The Microliquid Process Modern industry has produced many kinds of electronic devices using thin-film device technology, in which the constituent thin film is deposited by a vacuum deposition process and then patterned as desired using a photolithography process. Although this technology is excellent for fabricating submicron-sized devices, and the applications for it are still expanding, it has an inherent shortcoming: a long, complex production process that is inefficient in its use of energy and material. In the vacuum deposition process, the yield ratio of the material from the source to the deposited film is low (10%). Moreover, the subsequent photolithography process removes the greater part of the film (sometimes exceeding 90%). Consequently, the total yield ratio of the constituent material is usually in the neighborhood of a few percent. Supplemental materials in the photolithography process, such as photoresist, are also inefficiently used. A new process, based on a liquid phase instead of a gas phase and on direct pat-
MRS BULLETIN/NOVEMBER 2003
terning rather than photolithography, offers various advantages over conventional technology. The material in a solution is usually more concentrated by several orders of magnitude than in the gas phase, in terms of the number of molecules in a given volume; this would allow less source material to be used. Direct patterning would allow a great reduction in the size of machines and factories, which would in turn lead to a reduction in the energy required for production by a factor of from 10 to 100. The new process consists of two major parts: the use of a functional liquid material as a source material, and the direct patterning of microfabricated devices with an accuracy equaling that provided by the conventional process. We call thi
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