Single-atom transistor is ‘end of Moore’s Law’ and ‘beginning of quantum computing’

February 20, 2012

A controllable transistor engineered from a single phosphorus atom. The atom, shown here in the center of an image from a computer model, sits in a channel in a silicon crystal. The atomic-sized transistor and wires might allow researchers to control gated qubits of information in future quantum computers. (Credit: Purdue University)

The smallest transistor ever built has been created using a single phosphorous atom by an international team of researchers at the University of New South Wales, Purdue University and the University of Melbourne.

The latest Intel chip, the “Sandy Bridge,” uses a manufacturing process to place 2.3 billion transistors 32 nanometers apart.

A single phosphorus atom, by comparison, is just 0.1 nanometers across, which would significantly reduce the size of processors made using this technique, although it may be many years before single-atom processors are manufactured.

“To me, this is the physical limit of Moore’s Law,” Gerhard Klimeck, who directed the Purdue group that ran the simulations, claims. “We can’t make it smaller than this.”

According to University of New South Wales Prof. Michelle Simmons, “We made a single-atom transistor roughly 8 to 10 years ahead of where the industry’s going to be,” consistent with Moore’s law, in 2020.

Basis for a quantum computer

The researchers used use a combination of scanning tunneling microscopy and hydrogen-resist lithography. Although single atoms serving as transistors have been observed before, this is the first time a single-atom transistor has been controllably engineered with atomic precision. The structure even has markers that allow researchers to attach contacts and apply a voltage, says Martin Fuechsle, a researcher at the University of New South Wales and lead author on the journal paper.

The single-atom transistor could lead the way to building a quantum computer that works by controlling the electrons and thereby the quantum information, or qubits. Some scientists, however, have doubts that such a device can ever be built.

The single-atom transistor does have one serious current limitation: It must be kept very cold, at least as cold as liquid nitrogen, or minus 391 degrees Fahrenheit (minus 196 Celsius).

“The atom sits in a well or channel, and for it to operate as a transistor the electrons must stay in that channel,” Klimeck says. “At higher temperatures, the electrons move more and go outside of the channel. For this atom to act like a metal you have to contain the electrons to the channel.

The same research team announced in January that it had developed a wire of phosphorus and silicon just one atom tall and four atoms wide that behaved like copper wire.

Ref.: Martin Fuechsle et al., A single-atom transistor, Nature Nanotechnology, 2012 [DOI: 10.1038/nnano.2012.21] (open access)

See also: Single-atom transistor created