Synthetic diamond films herald carbon electronics.
Step aside silicon: the carbon chip is coming. Researchers have made films of synthetic diamond that have electrical properties approaching those of silicon1.
"These results could be a watershed for carbon electronics," says Gehan Amaratunga a materials scientist at the University of Cambridge, UK.
The electrons and holes that carry electrical currents in semiconducting materials are twice as mobile in these new films as in their forerunners. Devices based upon them, such as transistors, might work fast enough to compete with silicon.
Jan Isberg of the ABB Group Services Center in Västerås, Sweden, and co-workers tweaked a technique, known since the 1980s, called microwave plasma chemical-vapour deposition (CVD). Carbon-rich methane molecules are broken into fragments and allowed to settle on a surface. The carbon atoms join up to form diamond.
The new CVD technique produces thick, high-quality diamond films. Previously, CVD generated a jumbled patchwork of tiny crystallites in which the boundaries between grains disrupted the flow of an electrical current.
Pure diamond conducts electricity very poorly; it is a good insulator. But, like silicon, it can be turned into a semiconductor by mixing in small amounts of impurities such as boron or nitrogen. Isberg's team makes boron-doped diamond by adding diborane, a boron-hydrogen compound, to the CVD mixture of methane and hydrogen.
Crucially, the researchers grow their films on small crystals of industrial diamond (made by the older, brute-force method of squeezing and heating graphite). This support helps the films' carbon atoms to line up properly.
There's little prospect of diamond microelectronics ousting silicon totally, however, even when the remaining fabrication problems are overcome. Rather, it's hoped that diamond devices will function in situations where silicon electronics fails.
For example, diamond chips could still work at temperatures of several hundred degrees, whereas silicon devices generally fail above 150 oC. Also, diamond can carry much more power than silicon, so diamond-based devices could be smaller than silicon ones.
Advantages such as these are driving intense research into diamond electronics. Several prototype diamond transistors and light-emitting diodes have already been made. High-mobility films should enable such devices to start approaching the performance the market-place demands.
Isberg, J. et al. High carrier mobility in single-crystal plasma-deposited diamond. Science, 297, 1670 - 1672, (2002).