Development of thick-film thermoelectric microcoolers using electrochemical deposition

Advanced thermoelectric microdevices integrated into thermal management packages and low power, electrical source systems are of interest for a variety of space and terrestrial applications. By shrinking the size of the thermoelements, or legs, of these devices, it becomes possible to handle much higher heat fluxes, as well as operate at much lower currents and higher voltages that are more compatible with electronic components. The miniaturization of state-of-the-art thermoelectric module technology based on Bi₂Te₃ alloys is limited due to mechanical and manufacturing constraints for both leg dimensions (100-200 μm thick minimum) and the number of legs (100-200 legs maximum). We are investigating the development of novel microdevices combining high thermal conductivity substrate materials such as diamond, thin film metallization and patterning technology, and electrochemical deposition of thick thermoelectric films. It is anticipated that thermoelectric microcoolers with thousands of thermocouples and capable of pumping more than 200 W/cm² over a 30 to 60 K temperature difference can be fabricated. In this paper, we report on our progress in developing an electrochemical deposition process for obtaining 10-50 μm thick films of Bi₂Te₃ and its solid solutions. Results presented here indicate that good quality n-type Bi₂Te₃, n-type Bi₂Te_2.95Se_0.05 and p-type Bi_0.5Sb_1.5Te₃ thick films can be deposited by this technique. Some details about the fabrication of the miniature thermoelements are also described.