Nanoscale Wiring Technology May Open Doors To Quantum Computing

At just four atoms thick, a new nanoscale wire could extend the life of Moore’s law and open new possibilities in computer technology, according to reports.

The atomic-scale silicon wires, which have the carrying capacity of copper, were created by scientists at the University of New South Wales in Australia (UNSW), according to nature.com. The wires were made using a technique where a silicon crystal is covered with a layer of hydrogen atoms and then several-nanometre-wide channels are carved into the hydrogen using the tip of a scanning tunnelling microscope. Phosphorous atoms are absorbed onto the exposed silicon and after heating covered with crystalline silicon, creating wires of phosphorous-doped silicon in which the phosphorous provides the extra electrons needed to generate a current.

Resistance is futile

According to UNSW PhD student Bent Weber, who led the work, the continuous downscaling of transistors and wiring means that “Pretty soon you reach a few atoms but building components that small is something the industry can’t achieve at the moment.”

This new development would extend Moore’s Law, which has been predicted to fail in the next decade. Described in a 1965 paper, Moore’s Law predicts that number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years. The law’s limits relate to the problems that arise as components shrink to the molecular level.

Scientists have previously argued conductive wires smaller than 10 nanometres, would no longer obey Ohm’s Laws of resistance due to the unpredictable effects of quantum physics, but this experiment has shown otherwise; since the wires were not impeded by an exponential rise in resistance at low temperatures, but followed Ohm’s law of classical electronics, even at thicknesses on only 1.5 nanometres.

Transistor gate lengths are now about 22 nanometres, which is about 100 times the spacing of the individual silicon atoms.

David Ferry, condensed-matter physicist at Arizona State University told  physicsworld.com that this experiment was a valuable demonstration that, in principle, the miniaturisation of classical electronics can continue for several years. “Firms such as Intel have been worried about making their devices so small that they become quantum mechanical in their behaviour. There’s a concern about how small these devices can become before quantum effects take over, and this suggests they still have a few more generations,” Ferry said. “When you have quantum coherence the transistor doesn’t turn on and off like you expect it to,” he explains, “and if the transistor doesn’t work like it ought to then Moore’s law is ended.”

Michelle Simmons, director of the Centre for Quantum Computation and Communication Technology at UNSW, said that while the team’s approach could not be used alongside current techniques for mass-producing computer chips, this breakthrough would pave the way for single-atom device architectures for both classical and quantum information processing.