Flexible electronics are organic

IBM scientists have made an advance in material science that could lead to the development of organic electronics for use in flexible computer screens, watches, smart cards and theatre tickets.

Previously, the promise of organic electronics has faced a key limitation - the poor electrical characteristics of small crystal grains. But now, researchers at IBM have found that by carefully preparing the surface on which an organic semiconductor is deposited, electronic thin films with crystal grains 20 to 100 times larger than previously observed can be produced.

These have semiconductor characteristics good enough to build low-cost, low-power organic transistors and light-emitters.

While still far from a commercial product, the discovery in organic chemistry could make it easier to build computing devices by 'printing' or 'spraying' a thin-film of semiconductors onto plastic and other materials.

Over the last few years, Pentacene molecules have been deposited on a wide variety of materials to build flexible electronics. And scientists have found that the highest quality devices (including transistors and lasers) can be fabricated on a single, high quality crystal of pentacene, a molecule comprising carbon and hydrogen atoms (C22H14).

However, unlike thin films, a single crystal takes too long to prepare and is too expensive for large-scale manufacturing. The IBM scientists have now found a way to grow large pentacene thin films which can be manufactured at low cost and have performance characteristics similar to single crystals. This new growth technique could lead to a practical way to manufacture flexible transistors.

Using an electron microscopy technique, the IBM team shot high resolution videos which captured pentacene molecules in the early stages of crystal growth. The researchers found that when pentacene is grown on a silicon substrate, it tends to stick to surface impurities, resulting in erratic growth and grain sizes too small for building high-quality devices.

To grow larger grains, the IBM team first applied a 'molecular buffer' - a single layer of molecules called cyclohexene - on top of the silicon substrate. This layer covers the 'sticky sites' on the silicon, resulting in a surface that is clean and allows the pentacene to grow very large grains, which could be useful for future manufacturing of flexible transistors on a mass scale.

The next steps toward commercial production are to fabricate improved devices in these new large-grain films.