A room temperature semiconductor process developed by researchers at the Georgia Institute of Technology could be another step on the road toward practical applications for flexible electronic circuits on organic substrates.

The team has fabricated field effect transistors which have electron-mobility values higher than amorphous silicon, low threshold voltages, large on-off ratios and high operational stability.

The process uses thin films of Carbon 60, also known as fullerene. The significance is that this has been achieved at room temperatures.

"If you open a textbook and look at what a thin-film transistor should do, we are pretty close now," said Bernard Kippelen, a professor in Georgia Tech's School of Electrical and Computer Engineering and the Center for Organic Photonics and Electronics.

As an organic semiconductor material, C60 is attractive because it can provide high electron mobility, and so will support fast current flow. But previously this has required a epitaxy process at temperatures of 250[deg]C which is too hot for plastic substrates.

"Now that we have shown very nice single transistors, we want to demonstrate functional devices that are combinations of multiple components. We have everything ready to do that," said Kippelen.

Though the transistors display slightly lower electron mobility, in the range 2.7 to 5cm sq/V/s, they can be produced at room temperature.

"If you want to deposit transistors on a plastic substrate, you really can't have any process at a temperature of more than 150 degrees Celsius," said Kippelen. "With room temperature deposition, you can be compatible with many different substrates. For low-cost, large area electronics, that is an essential component."

Because they are sensitive to contact with oxygen, the C60 transistors must operate under a nitrogen atmosphere.

Kippelen expects to address that limitation by using other fullerene molecules, and properly packaging the devices.