Researchers at the Massachusetts Institute of Technology (MIT) have developed a chip with built-in superconducting circuits. These circuits exhibit zero electrical resistance, and are 100 times more energy-efficient than today’s chips.
A type of superconducting circuit called the Josephson junction was developed several years ago, but devices using this effect are bulky, difficult to manufacture, and use minute amounts of current that are difficult to measure. Experiments with these junctions have shown clocking rates of 770 GHz, or 500 times faster than a modern smart phone. Current applications for these devices are limited.
Graduate student Adam McCaughan and his doctoral advisor, Professor Karl Berggren, developed a new type of circuit that will make fabrication of superconducting circuits easier and cheaper. They call their device the nanocryotron (nTron, for short). A paper published in the Nano Letters online magazine describes the details of this research. The nTron is a three-terminal, nanowire, electrothermal device that can be built from a single thin film of niobium-nitride using conventional lithography, patterned in the shape of a capital letter T.
A square-centimeter chip containing the nTron, which performed the first computation using the MIT’s new superconducting circuit. © Adam N McCaughan
"The superconducting-electronics community has seen a lot of devices come and go, without any real-world application," McCaughan says. "But in our paper, we have already applied our device to applications that will be highly relevant to future work in superconducting computing and quantum communications."
The T-shaped nTron can be operated as a switch, so it can be used as the switching element in digital computers. The device is built so that the upright of the T, at the point where it joins the crossbar, narrows to only one-tenth of its original width. Electrons move unimpeded (no resistance) through the upright of the T, where they are eventually collide with each other in the narrowed portion. This produces heat and destroys the niobium superconductivity. Thus, when a current is applied to the upright of the T, the current flowing through the crossbar is turned off. The researchers found that currents, even smaller than those used in Josephson junctions, can switch the nTron Crossbar from a conductive to a nonconductive state. The crossbar can carry currents large enough to drive other devices.
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