Organic Transistors That Assemble Themselves

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Near the electrodes, the semiconductor crystals assemble themselves in an ordered way so that they carry current well. Away from the electrodes, however, crystals are randomly oriented so that the material acts as an insulator. "Now we can make circuits without patterning [the semiconductor] at all," says Thomas Jackson, an electrical engineering professor at Pennsylvania State University, who was involved in the work. "We simply spin it on and we're done. We don't have to go through the step of removing the material where we don't want it."

Getting rid of this step makes the manufacturing process significantly simpler, says John Kymissis, an electrical engineering professor at Columbia University. Patterning the semiconductor layer is one of the most delicate steps in making an organic electronic circuit, he says. If any semiconductor material accidentally spans the electrodes of two adjacent transistors, that could allow current to flow between transistors, making the circuit dysfunctional. In a display, for instance, two pixels might go on instead of one. "Even if you print the electrodes, if you don't have to pattern the organic semiconductor, [the process] is going to be faster," says Kymissis. "It is a huge advantage."

Compared with current techniques, the simplicity of the new method should make it more practical to manufacture organic electronic circuits on a large scale, says Natalie Stingelin-Stutzmann, a materials-science researcher at Queen Mary, University of London. "Inkjet is simple, but if you can cover large areas with a simple coating technique, it will be cheaper," she says. "At the end, it is the cost which will determine if organic electronics makes it or not."