The smallest wires ever developed in silicon - just one atom tall and four atoms wide - have been shown by a team of researchers from the University of New South Wales, Melbourne University and Purdue University to have the same current-carrying capability as copper wires.
Experiments and atom-by-atom supercomputer models of the wires have found that the wires maintain a low capacity for resistance despite being more than 20 times thinner than conventional copper wires in microprocessors.
The discovery has several implications, including:
* 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 shows that a single dense row of phosphorus atoms embedded in silicon will be the ultimate limit of downscaling.
* For computer scientists, it places donor-atom based silicon quantum computing closer to realisation.
* And for physicists, the results show that Ohm's Law, which demonstrates the relationship between electrical current, resistance and voltage, continues to apply all the way down to an atomic-scale wire.
Bent Weber, the paper's lead author and a graduate student in the Centre of Excellence for Quantum Computation and Communication Technology at the University of New South Wales, was thrilled with the finding.
"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," he says.
The innovation of the Australian group was to build the circuits up atom by atom, instead of the current method of building microprocessors, in which material is stripped away, says Gerhard Klimeck, a Purdue professor of electrical and computer engineering and director of the Network for Computational Nanotechnology.
"Typically we chip or etch material away, which can be very expensive, difficult and inaccurate," Klimeck says. "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 a wire that conducts just as well as metal."
The goal of the research is to develop future quantum computers in which single atoms are used for the computation, says Michelle Simmons, director of the Centre of Excellence for Quantum Computation and Communication Technology at the University of New South Wales and the project's principal investigator.
"We are on the threshold of making transistors out of individual atoms," Simmons says. "But to build a practical quantum computer we have recognised that the interconnecting wiring and circuitry also needs to shrink to the atomic scale."
Purdue University
