Scientists have demonstrated methods that could see higher-performance computer chips made from tiny straws of carbon called nanotubes. Carbon nanotubes have long been known to have electronic properties superior to current silicon-based devices.
But difficulties in manipulating them have hampered nanotube-based chips.
The race is on in the semiconductor chip industry to replace current silicon technology - methods to make smaller and therefore faster devices will soon come up against physical limits on just how small a silicon device can be. Though single nanotubes have shown vastly superior speed and energy characteristics in lab demonstrations, the challenge has been in so-called integration - getting billions of them placed onto a chip with the precision the industry now demands.
Current chips are made using lithography, in which large wafers of silicon are layered with other materials of different electronic properties and then devices are simply "etched" out using a focused beam of electrons or charged atoms. To address the integration challenge, Dr Hannon and his colleagues came up with a solution - two of them in fact. The first was a chemical that coats nanotubes and makes them soluble in water. The second was a solution that binds to the first chemical and to the element hafnium, but not to silicon. Then they simply "double-dipped" the chip into the two solutions - one chemical stuck to the hafnium, and the other chemical acted as the second part of a two-part epoxy, tightly binding nanotubes to the hafnium regions on the chip but not to silicon. The result was a series of neatly aligned nanotube devices, already wired up within the pattern, at a density of a billion per square centimeter.
"That's one nanotube every 150 or 200 nanometer or so," explained Dr Hannon. "That's not good enough to make a microprocessor yet - it's a factor of 10 away. "But it's a factor of 100 better than has been done previously."