Micro thermoelectric cooler fabrication: growth and characterization of patterned Sb2Te3 and Bi2Te3 films
L.W. da Silva, M. Kaviany
Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125, USA
A column-type micro thermoelectric cooler is designed and the fabrication, including growth, characterization, and patterning of p-type Sb2Te3 and n-type Bi2Te3 thick (approximately 4mm) films, are presented. These films are grown by thermal co-evaporation of the elements and patterned on Cr/Au/Ti/Pt (hot) connectors, which are deposited onto a silicon wafer with a silicon dioxide layer for electrical insulation. The Au and Pt layers are 200 nm and 20 nm thick respectively (Cr and Ti are seed layers). The Pt allows for an acceptable adhesion to columns, while preventing diffusion of Au. The columns height is limited by control of Te deposition rate, which becomes compromised with the depletion of Te inside the evaporation boat. Electroplated copper is planned for the top (cold) connectors. Their photoresist patterning is affected by the height of the columns and distance between them. The substrate temperature during thermoelectric films deposition is limited by the photoresist used for patterning. The Seebeck coefficient and electrical resistivity of Sb2Te3 films deposited with substrate temperature of 350 K are 105 mV/K and 3.5x10-5 ohm-m and are reproducible. The preliminary results show that excess tellurium increases the Seebeck coefficient. The characteristics of the Bi2Te3 films are also reported.