Cool computer chips reach hot speeds

Habif (left) and Bocko (right) at work on the superconducting circuit.

hough Intel has unveiled its 1-gigahertz Pentium chip to great fanfare, inside a frozen canister of liquid helium in a small laboratory at the University, a prototype of a superconducting circuit silently cruises along 50 times faster.

The near-absolute-zero-temperature chip--powered by a new kind of "transistor" capable of a searing 750 gigahertz--may be a crucial link to the future of computers.

"Superconductors are a realistic alternative to semiconductors for future electronics," says Mark Bocko, professor of electrical and computer engineering.

Bocko and his collaborators, professor Marc Feldman and doctoral student Jonathan Habif, are testing the speed of new chips, which at their heart contain "transistors" known as Josephson junctions.

The junctions switch between "on" and "off" states like traditional transistors, but they do so in just 2 trillionths of a second--thousands of times faster than conventional transistors.

That furious speed creates a mountainous hurdle that Bocko and his collaborators have overcome. Until recently, the clock running on a 50-gigahertz chip ran so fast that researchers couldn't keep up to measure its stability--its ability to consistently keep proper time. With no way to govern the clock's stability, the rest of the chip was gridlocked.

Bocko found an answer from an unlikely source: gravity.

Working for years on gravity wave detectors, devices meant to sense the warping of space created by binary black holes and colliding neutron stars, Bocko and his colleagues designed extraordinarily sensitive transducers to detect the vibrations of a cryogenically cooled multi-ton bar of aluminum.

Much of Bocko's contribution to the project was in detecting the tiny irregularities in the hypersensitive clock, and tracking down whether the gravity wave detector signals were due to a passing gravity wave, or just to clock noise.

"We have designed a simple tool that allows us to directly measure the variation of the time interval separating the ticks of a superconducting clock," says Bocko. "If it fails to be as accurate as we need, this diagnostic tool guides our design changes so we can fine-tune the design of the clock until we have exactly what we need."

The Rochester group worked with their collaborators at Hypres, Inc., a small superconducting electronics company in Elmsford, New York, which is looking to apply the group's work to superconducting wireless communications equipment.

Together, they worked to figure out a way to uncover any irregularities in the network that distributes the clock's "ticks" around the chip.

By comparing the known time the clock sent its signal with the time it emerged from any point on the network, Bocko can tell what quirky roadblocks and irregularities litter the network.

"This information is crucial to building superconducting circuits," says Bocko. "Engineers need to know exactly how the clock, basic building blocks such as gates, and the clock distribution network perform before they can even begin designing an entire microchip."

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