Single-atom transistor built with precise control

Seeking to keep Moore's Law on pace, researchers have developed a repeatable technique for assembling a single-atom version of the transistor--the building block of semiconductors and computers.

Researchers were able to make a single-atom transistor with a scanning tunneling microscope that includes the  single red phosphorous atom and electrical leads for control gates and electrodes.
Researchers were able to make a single-atom transistor with a scanning tunneling microscope that includes the single red phosphorous atom and electrical leads for control gates and electrodes. University of New South Wales

Researchers are getting down to the atomic level in the pursuit of smaller and more powerful computers.

The University of New South Wales in Australia today announced it has made a single-atom transistor using a repeatable method, a development that could lead to computing devices that use these tiny building blocks.

About two years ago, a team of researchers from the Helsinki University of Technology, the University of New South Wales, and the University of Melbourne in Australia announced the creation of a single-atom transistor designed around a single phosphorus atom in silicon.

Now a new paper published in the journal "Nature Nanotechnology" describes a technique for making this type of transistor with very precise control. That opens up the possibility that the method can be automated and single-atom transistors could be manufactured, according to the group at the University of New South Wales.

"The thing that's unique about the work that we've done is that we have, with atomic precision, positioned this single atom within our device," said Martin Fuechsle from the lab. That level of control is important in order to fabricate the other components, including control gates and electrodes, needed for a working transistor, the building block of microprocessors and computers.

The lab members used a scanning tunneling microscope to manipulate atoms at the surface of a silicon crystal. Then with a lithographic process, they laid phosphorous atoms onto the silicon substrate.

"Our group has proved that it is really possible to position one phosphorus atom in a silicon environment--exactly as we need it--with near-atomic precision, and at the same time register gates," Fuechsle said in a statement.

The technique, which uses liquid nitrogen-cooled equipment, can only be done at very low temperatures of minus 391 degrees Fahrenheit, noted Purdue University researchers who did computer simulations of the transistors for the project. But despite that limitation, the work shows how small electronics can be done, said Gerhard Klimeck from Purdue.

"To me, this is the physical limit of Moore's Law," Klimeck said in a statement. "We can't make it smaller than this."

Work on alternatives to traditional microprocessor designs has been going on for years to maintain the pace of Moore's Law, which predicts that the number of transistors on a semiconductor doubles every 18 months. Intel last year announced it would start using three-dimensional transistors for its 22-nanometer process, a move designed to avoid the leakage of current that occurs at this very small scale. Other groups have pursued carbon nanotubes or graphene rather than silicon in the pursuit of miniaturization.

The University of New South Wales team hopes that its method of manipulating at the atomic scale can form the basis for quantum computers, machines that use the effects of quantum mechanics, specifically the spin of electrons around an atom, to represent digital information.

"This individual position (of a phosphorus atom in silicon) is really important...because it turns out that if you want to have precise control at this level, you need to position individual atoms with atomic precision with respect to control gates and electrodes," Fuechsle said.

Michelle Simmons, the director of the ARC Centre for Quantum Computation and Communication at the University of New South Wales, said that even with this development, it's still not clear that a quantum computer can ever be built.

"The answer to this lies in whether quantum coherence can be controlled over large numbers of qubits. The technique we have developed is potentially scalable, using the same materials as the silicon industry, but more time is needed to realize this goal," she said in a statement.

Updated on February 21 with more details from Purdue University.

 

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