Down to the wire
9 Feb 2012 by Evoluted New Media
A silicon wire just four atoms wide and one atom thick containing a string of phosphorus atoms has the same current-carrying capability as copper wires say American and Australian researchers.
The aim of the research – published in Science – is to develop future quantum computers in which single atoms are used for computation.
“We are on the threshold of making transistors out of individual atoms,” said Michelle Simmons, principal investigator from the University of New South Wales. “To build a practical quantum computer we have recognised that the interconnecting wiring and circuitry also needs to shrink to the atomic scale.”
The Australian group – which included researchers from Melbourne University – built circuits atom by atom, instead stripping material away as in the current method of building microprocessors. Material is etched or chipped away, which is expensive, difficult and inaccurate said Gerhard Klimeck, professor of electrical and computer engineering at Purdue University.
“Once you get to 20 atoms wide you have atomic fluctuations that make scaling difficult. But this experimental group built devices by placing atomically thin layers of phosphorus in silicon and found that with densely doped phosphorus wires just four atoms wide it acts like wire that conducts just as well as metal,” Klimeck said.
Experiments and atom-by-atom supercomputer models have found the wires maintain a low capacity for resistance – around 0.3milliohm-cm – despite being more than 20 times thinner than conventional copper wires.
The research has several implications. For engineers it could provide a roadmap to future nanoscale computational devices where atomic sizes are at the end of Moore’s law. The theory suggests a single dense row of phosphorus atoms embedded in silicon will be the ultimate limit of downscaling. For computer scientists it brings donor-atom based silicon quantum computer closer.
For physicists, it means that Ohm’s Law – which demonstrates the relationship between electrical current, resistance and voltage – continues to apply to atomic-scale wire.
“It’s extraordinary to show that Ohm’s Law, such a basic law, still holds even when constructing a wire from the fundamental building blocks of nature – atoms,” said Bent Webber, lead author from the University of New South Wales.
