Development of a micro-generator based on Bi2Te3 thin films

In this study, we fabricated in-plane thermoelectric micro-generators (4 mm times 4 mm) based on bismuth telluride thin films by using flash evaporation method. The thermoelectric properties of as-grown thin films are lower than those of bulk materials. Therefore the as-grown thin films were annealed in hydrogen at atmospheric pressure for 1 hour in a temperature range of 200 degC. to 400degC. By optimizing the annealing temperature, thin films with high thermoelectric power factors of 8.8 muW/(cmldrK²) in n-type and 13.8 muW/(cmldr K²) in p-type are obtained. To evaluate the figure of merit of the thin film, the thermal conductivity of the n-type thin film is measured by the 3omega method. The thin film annealed at 200degC exhibited a cross-plane thermal conductivity of 1.2 W/(mldrK). Micro-generators of flash-evaporated bismuth-telluride thin films are fabricated using three shadow masks. The shadow masks are prepared by standard micro-fabrication processes such as nitridation of Si, dry etching, and wet etching. Thermoelectric power of the as-grown thin film devices with 16 pairs of p-n legs are measured by YAG laser heating at the center of the devices. The maximum open circuit voltage is 6.7 mV under 2.5 K temperature difference.