Thermo-electric characterization of APCVD PolySi0.7Ge0.3 for IC-compatible fabrication of integrated lateral Peltier elements

The performance of poly-Si_0.7Ge_0.3 as a thermo-electric material that is process compatible with IC fabrication in silicon has been analyzed and fully characterized using on-chip MEMS-based test structures. The application is in on-chip thermal stabilization of a micromachined platform in silicon containing a reference component. A CMOS process has been adapted to include SiGe thermo-electric elements. The results are a Seebeck coefficient α_n=-179 μV/K and α_p=131 μV/K at 295 K with a TC of 0.2 μV/K², and -0.1 μV/K², respectively. High-dose implantation and appropriate anneal have been used to achieve an electrical resistivity of 28.9 μΩ·m for p-doped material and 29.2 μΩ·m for n-doped material. Thermal conductivity was measured λ=5 Wm^-1·K^-1, which is close to the theoretical minimum. The contact resistance is identified as an important performance limiting parameter. The resulting figure of merit z_dev=168×10^-6K^-1, which would enable a temperature difference for Peltier cooling of ΔT_max=7.3 K. Parasitic thermal conductance limits ΔT_max to 2.1 K in this work. Peltier heating and cooling offers superior dynamic performance of temperature control close to ambient temperature, as compared to passive cooling. A response time τ=2 ms has been found.