Carbon Valley

the microelectronic revolution is based on the remarkable properties of a single element: silicon. Researchers have been trying to design and build circuits using carbon, an element very similar to silicon, but with little luck. Carbon circuits will be faster, more robust and could operate at higher temperatures. Some German scientists could be a step closer to realising the carbon circuit. They have successfully grown very high quality thin films of diamond.

It is said that diamond, a pure form of carbon, could replace silicon as the material of choice for the next generation of electronic circuits. This is because diamond circuits would be smaller and faster than silicon ones, and would be able to operate at 500C. Interestingly, while silicon is a semiconductor -- which makes it useful -- diamond in its pure form is an insulator. It has to be doped with impurities (such as boron or nitrogen) to become a semiconductor and hence be useful in circuits.

Scientists first deposited diamond films on surfaces doped with impurities in the 1960s. But these films, though useful for making cutting tools, were not of the quality required for circuits. What was needed is a technique to grow smooth, defect-free films on silicon substrates, as silicon will continue to be used in circuits for some time to come.

Now, L Ley and colleagues from the University of Erlangen in Germany have developed a method for making such films smooth and relatively free of defects. The essential point is to lay down a thin film of diamond using microwaves to assist the formation of carbon vapour and then use a hot filament to make the vapour instead. The microwave method is best for starting the film off on the bare silicon surface with all the diamond crystals in the same orientation, but the hot-filament method is best for ensuring that it stays that way as it grows subsequently ( Applied Physics Letters , Vol 75, p2094).

The researchers claim that the quality of films so obtained is good enough to make it useful in fabricating silicon and diamond circuits.

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