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  • New Thin-Film Method Developed
Mar 2004
YORKTOWN HEIGHTS, N.Y., March 17 -- Researchers at IBM say they have developed a simple, low-cost process to make extraordinarily thin films of semiconducting materials that allows electrical charges to move through them about 10 times more easily than had been reported for similar approaches.

The researchers said the technique will significantly accelerate progress toward the widespread use of thin-film electronics made by the family of fast, inexpensive, high-throughput "solution processes," such as spin coating, printing, stamping, nanoimprinting, inkjet printing and dipping.

While advances in high-performance microelectronics are typically aimed at making ever-smaller features in intricate and precisely defined patterns on perfectly formed silicon crystals -- a task that is becoming increasingly difficult as the feature dimensions decrease and the cost of manufacturing equipment increases -- researchers are also seeking extremely low-cost methods for making massive numbers of relatively simple electronic devices for use in many potential applications.

Spin coating is one of the simplest and cheapest of such techniques: Several drops of a liquid solution are simply placed onto a spinning platter in a high-tech version of a carnival paint spinner. Centripetal forces then spread the liquid to a uniform thickness over the entire surface. The film's thickness is usually determined by the solution's viscosity (its resistance to flow) and the rate and duration of spinning. The liquid is then cured into a solid thin film upon which transistors and other various electronic devices can be made.

Until now, the only semiconducting materials that could be made using spin coating had limited usefulness due to their low charge "mobility" -- a measure of how fast electronic circuits made with a semiconductor can operate. Better semiconductors could not be dissolved in any liquid that would result in a thin film that retained the desired mobility. Mitzi's team developed a way to dissolve such higher-mobility materials in a liquid that could be used in a spin-coating process, leaving a very uniformly controlled film. Moreover, in a transistor made on the films, the materials exhibited 10 times the charge mobility of any previously spin-coated semiconductor.

Applications for solution-processed electronics include advanced displays, flexible devices, high-function smart cards and RFID tags, photovoltaic solar cells and phase-change solid-state memories.

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