THERMOELECTRIC THIN-FILMS FOR MICROCOOLERS AND ENERGY SCAVENGING MICROSYSTEMS

The present work reports on the fabrication and characterization of the first planar Peltier microcooler (Fig. 1) on a flexible substrate. The microcooler was fabricated on flexible Kapton© polyimide substrate, 25 μm in thickness, using Bi2Te3 and Sb2Te3 thermoelectric elements deposited by thermal co-evaporation. The cold area of the device (4 mm2) is cooled using four pair of thermoelectric elements, connected in series with aluminum/nickel contacts (Fig. 3). Flexible substrates add uncommon mechanical properties to the composite film-substrate and enable their integration with many novel types of electronic devices. Kapton was chosen as substrate because of its low thermal conductivity (0.16 W.m−1.K−1), thus allowing for higher performance of cooler devices. The value of thermal expansion coefficient of Kapton (12×10-6 K−1), which closely matches the thermal expansion coefficient of the telluride films, reduces residual stress and increases adhesion of thermoelectric films. Films were deposited by co-evaporation of Bismuth and Tellurium or Antimony and Tellurium to obtain Bi2Te3 or Sb2Te3 compounds (Fig. 2), respectively. The performance of thermoelectric devices depends on figure of merit (ZT) of the film, given by ZT = α2T/(κρ), where α, T, κ and ρ are the Seebeck coefficient, absolute temperature, therma