Unlike conventional compressor-based refrigerators, thermoelectric coolers made from semiconductors have no moving mechanical parts and can be miniaturized. However, they require a lot of energy, and their performance--which is quantified as "ZT"--isn't as good as conventional cooling technology.

Despite years of research, ZT of thermoelectric coolers as measured at room temperature has barely exceeded 1, notes Rama Venkatasubramanian, senior program director of Research Triangle Institute's (RTI) Center for Semiconductor Research. But according to Ali Shakouri, an assistant professor of electrical engineering at UC Santa Cruz who studies thin-film thermoelectric coolers, Venkatasubramanian and his colleagues have now achieved "an important breakthrough. They improved room-temperature ZT" significantly for the first time in almost 40 years.

The RTI researchers achieved a ZT of 2.4 in p-type lattices built by alternating engineered thin films of bismuth telluride and antimony telluride and a ZT of 1.4 in n-type lattices of bismuth telluride and bismuth telluride selenide [Nature, 413, 597 (2001)]. The ZT of a thermoelectric device can be approximated by averaging the ZT of its n- and p-type components. Once the average ZT reaches 1.5, Venkatasubramanian says, it "opens the door to a huge number of applications." These include temperature control for a lab on a chip, automotive heating and cooling applications, and cooling of computer chips. Because the production temperature for these thermoelectric devices is below 300 °C, they can be built on silicon chips after the chips have been processed. They can also be used for high-speed cooling for applications such as fiber-optic switches.

Shakouri cautions that reliability of the system must be tested, "since very high current densities are needed to operate thin-film coolers."

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