Electrodeposition and Characterization of Bi-Te-Se Thermoelectric Thick Films

Thermoelectric materials can convert heat into electricity, and vice versa. Bi2Te2.7Se0.3 is considered to be one of the most efficient n-type thermoelectric materials near room temperature. The current tendency to miniaturization has provoked interest in thick film thermoelectric devices. Among the methods to deposit thick films, electrochemical deposition is a promising method due to its vacuum-free system, higher deposition rate, and complete integration with MEMS. In fact, nitric acid system was studied well, so further investigation of hydrochloric acid system has to be conducted. In this research, electrodeposition of n-type Bi2Te2.7Se0.3 was studied, followed by the measurement of thermoelectric properties and the preparation of MEMS devices. Firstly, in order to understand the differences between the nitric acid and the hydrochloric acid system, cyclic voltammetry was conducted. According to the results, with the introduction of chloride ions, reduction potential for BiIII and SeIV would shift toward negative direction; a positive shift of reduction potential for TeIV was observed. Furthermore, by adding selenium ions in the binary system, the reduction peaks shifted toward positive direction. Secondly, compact deposits of Bi1.88Te2.80Se0.32 with 27 μm and Bi1.89Te2.82Se0.29 with 43 μm were obtained, respectively, after potentiostatic deposition for 3 and 6 hours. Thirdly, deposits were flipped from substrates by epoxy resin prior to the measurement of thermoelectric properties. The resistivity and mobility of the deposits were better than other researches, but slight deviation of composition may lead to low Seebeck coefficient. Last but not least, compact and stoichiometric n-type deposits with 20 μm were successfully produced on MEMS.