Micromachined Polycrystalline Sige-Based Thermopiles for Micropower   Generation on Human Body
  This paper presents a polycrystalline silicon germanium (poly-SiGe) thermopile specially designed for thermoelectric generators used on human body. Both the design of the single thermocouple and the arrangement of the thermocouple array have been described. A rim structure has been introduced in order to increase the temperature difference across the thermocouple junctions. The modeling of the thermocouple and the thermopile has been performed analytically and numerically. An output power of about 1 $\mu$W at an output voltage of more than 1 V is expected from the current design of thermopiles in a watch-size generator. The key material properties of the poly-SiGe have been measured. The thermopile has been fabricated and tested. Experimental results clearly demonstrate the advantage of the rim structure in increasing output voltage. In presence of forced convection, the output voltage of a non-released thermopile can increase from about 53 mV/K/cm2 to about 130 mV/K/cm2 after the rim structure is formed. A larger output voltage from the thermopile is expected upon process completion. 
Z. Wang, V. Leonov, P. Fiorini, C. Van Hoof