New cryogenic refrigerator to deep-freeze chips

Researchers at the National Institute of Standards and Technology (NIST) have developed a compact, solid-state refrigerator capable of reaching very low temperatures (as low as 100 milliKelvin). The refrigerator works using a "sandwich" of normal- metal/insulator/superconductor junctions. When a voltage is applied across the "sandwich," high-energy (hot) electrons leave the normal metal and go through the insulator and into the superconductor. Removing the hot electrons allows the temperature of the normal metal to drop. This refrigerator can be made in a wide range of sizes and shapes, as well as readily integrated with other cryogenic devices ranging in size from nano-meters to millimeters. As current equipment capable of cooling to these temperatures is bulky and expensive, this refrigerator could, when combined with an X-ray sensor, reduce the weight and cost of such equipment, used in semiconductor manufacturing for identifying trace contaminants and in the astronomical community for X-ray telescopes. A report of the work is featured on the cover of the January 26, 2004, issue of Applied Physics Letters. "The idea is to use a solid-state refrigerator for on-chip cooling of these cryogenic sensors," says Anna M. Clark, the report's lead author. "We have a working refrigerator that reduces temperatures low enough to be used with highly sensitive X-ray detectors. These detectors require subKelvin temperatures to minimize thermal noise and maximize their resolution."