Scientists at the NIST (National Institute of Standards and Technology) have designed microscopic refrigerators, that are capable of reaching temperatures as low as 0.1 Kelvin (-273.06°C). These chip-sized refrigerators have been used to cool a cube of Germanium. The solid-state refrigerators have applications such as cooling cryogenic sensors in highly sensitive instruments for semiconductor defect analysis and astronomical research. The work is presented in the April 25, 2005, issue of Applied Physics Letters.

Cool Germanium! (Courtesy: NIST)The refrigerators are 25 microns x 15 microns (1 micron = 0.0001 cm) in size, and 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 electronic and vibrational energy from the objects being cooled. Tunneling is a quantum mechanical phenomenon, which allows the electrons to jump the insulator barrier, and directly go to the superconductor.
Four pairs of such sandwiches were used to cool a cube of Germanium (250 microns on a side), which was in placed on a Silicon Nitrate membrane (450 microns size). Both the membrane and the cube were cooled down to about 0.1 Kelvin. The cube is about 1,000 times larger than the combined volume of the refrigerators. This is equivalent to having a refrigerator the size of a person cool an object the size of the Statue of Liberty :D.
The refrigerators are made using common lithography techniques (used to 'print' circuits on a semiconductor chip), which makes a large-scale production very much possible in the near future. Such refrigerators might also have applications in draining heat from high-speed chips, and cauterizing small nerves/blood vessels during operations :).