Determination of the thermoelectric figure of merit of doped polysilicon thin films by micromachined test structures

This paper reports on the determination of the thermoelectric figure of merit ZT of doped polysilicon (poly-Si) thin films. For the extraction of accurate thermal properties, micromachined membrane test structures for the Seebeck coefficient S and the thermal conductivity κ of poly-Si were developed. The electrical resistivity ρ is measured using van-der-Pauw structures. From the results the temperature dependent value of ZT = S²Tk^-l ρ^-1 is extracted. The material parameters were measured in the temperature range from 90 to 370 K. A ZT of (10.08±0.14)×10^-3 and (10.29±0.12)×10^-3 was obtained at 290 K for n- and p-doped poly-Si thin films. The corresponding material parameters for n-doped material are k = 25.0 Wm^-1K^-1, S = -81 μVK^-1 and ρ = 7.58 μΩm. For p-doped poly-Si the values are found to be κ = 40.6 Wm^-1K^-1, S = 240 μVK^-1 and ρ = 40.1 μΩm.