The first experimental demonstration of a transistorless approach to computing, called quantum-dot cellular automata (QCA), is reported by University of Notre Dame researchers in the Aug. 15 issue of Science.
In this experiment, a single electron was used for the first time to control the position of another electron. "We are trying to bring information storage down to the molecular level," said Gregory L. Snider, assistant professor of electrical engineering, who headed the research team.
Conventional microelectronic technology has relied on shrinking transistors to produce increasingly smaller, faster and more powerful computers. But, because the laws of physics prevent conventional devices from working below a certain size, that method is nearing its physical limits.
QCA leapfrogs that barrier with an entity known as the "quantum dot," a tiny structure in which an electron can be confined. These quantum dots can be created and arranged into cells through microelectronic techniques, and in turn these cells can be lined up end to end to form "binary wires" or arrayed to form switches and various computer logic devices.
If successful, a 4-inch-square QCA chip could contain as many as 40 trillion devices, as opposed to the 6 million devices in the most advanced conventional chip. And since it does not rely on flowing electrons to transmit a signal, no electric current is produced and heat problems are avoided.
In this first demonstration of a basic cell, the device studied was made of four metal dots, connected with tunnel junctions and capacitors and operated at a temperature less than 50 mK, very near absolute zero.
"Our particular challenge is that our device requires such painfully cold temperatures," said Snider. "We now need to scale our device down to a size that can operate at room temperature."
According to Snider, it will be another 20 years before computers and other electronic equipment will incorporate QCA.
Other members of the research team include Gary H. Bernstein, associate professor of electrical engineering; Craig S. Lent, professor of electrical engineering; Wolfgang Porod, professor of electrical engineering; and James L. Merz, Friemann professor of engineering and vice president of graduate studies and research.
This research was funded by Defense Research Projects Agency (DARPA)/Office of Naval Research (ONR).
For more information, contact Snider in his office at (219) 631-4148; Bernstein, 631-6269; Lent, 631-6992; Porod, 631-6376; and Merz, 631-6291.
A web page containing more information about Quantum-dot Cellular Automata is located at http://www.nd.edu/~lent/QCAhome.html
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Science