Cooling large items with little chips

June 2, 2005
Chip-sized refrigerators have been used for the first time to chill objects to the 100-mK range, according to engineers at the National Institute of Standards and Technology.

A colorized scanning micrograph shows a germanium cube sitting on a silicon nitrate membrane. The cooling chips are the four small light blue rectangles at the midsections of the membrane perimeter.

The devices consist of a layer each of insulation and superconducting metal sandwiched between normal metal. Voltage applied across the sandwich sends the hottest electrons from the metal tunneling through to the insulator and superconductor. This drops the temperature of the normal metal and drains electronic and vibrational energy from objects being cooled.

Researchers used four pairs of these sandwiches hooked to a silicon nitrate membrane to cool a germanium cube 240 m on a side, or about 11,000 times as large as the combined volume of the chips. This is roughly analogous to a refrigerator the size of a human cooling an object the size of the Statue of Liberty. The germanium cube was cooled to 200 mK.

The chips are made using standard lithography methods so production and integration with other microscale devices should be straightforward. They will likely be used to cool cryogenic sensors down to 100 mK, the sensors' working environment. Such sensors let scientists study small differences in X-rays emitted by nanoscale particles.

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