Flexible circuitry

11 December 2007

Scientists at the Georgia Institute of Technology have fabricated high-performance field effect transistors with thin films of Carbon 60.

The development is said to represent another advance toward practical applications for large-area, low-cost electronic circuits on flexible organic substrates.

Such devices could encourage designers to work on circuitry for displays, active electronic billboards, RFID tags or any application that uses flexible substrates.

Researchers have long been interested in making field-effect transistors (devices that use an electric field to control the shape and conductivity of a 'channel' in a semiconductor material) from organic semiconductors that can be processed onto various substrates, including flexible plastic materials.

As an organic semiconductor material, C60 is capable of yielding electron mobility as high as 62 cm per volt-second (6cm2/V/s).

This figure was achieved using a hot-wall epitaxy process requiring processing temperatures of 250º C.

Though the transistors produced by Kippelen's research team display slightly lower electron mobility — 2.7 to 5cm2/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 150ºC,' Kippelen said.

'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 anticipates addressing that limitation by using other fullerene molecules and by properly packaging the devices.