The World's Smallest Refrigerator

Scientists have developed the world's tiniest refrigerator - and it's pretty cold too. Even smaller than a college dorm fridge, the microchip sized fridge can cool objects down to -459 degrees Fahrenheit.

The National Institute of Standards and Technology-designed refrigerators, each 25 by 15 micrometers, are sandwiches of a normal metal, an insulator and a superconducting metal. When a voltage is applied across the sandwich, the hottest electrons "tunnel" from the normal metal through the insulator to the superconductor. The temperature in the normal metal drops dramatically and drains extra heat energy from the objects being cooled.

The researchers used four pairs of these sandwiches to cool the contents of a silicon nitrate membrane that was 450 micrometers on a side and 0.4 micrometers thick. A cube of germanium 250 micrometers on a side, about 11,000 times larger than the combined volume of the fridges was glued on top of the membrane. This is roughly equivalent to having a refrigerator the size of a person cool an object the size of the Statue of Liberty. Both objects were cooled down to about -459° F.

The refrigerators are made using common chip-making lithography methods, which makes it easy to integrate them in production of other micro scale devices. These tiny fridges are much smaller and less expensive than conventional equipment. The fridges have applications such as cooling cryogenic sensors in highly sensitive instruments for semiconductor analysis and astronomical research.

The work is featured in the April 25, 2005, issue of Applied Physics Letters.

Bjorn Carey

Credit: N. Miller, A. Clark/NIST