PolySi0.7Ge0.3 for IC-Compatible Fabrication of Integrated Lateral Thermo-Electric Components

Professor Reinoud R. Wolffenbuttel,
Delft University of Technology, Faculty EEMCS,
Dept. ME/EI,
Mekelweg 4, NL-2628 CD Delft, THE NETHERLANDs

The performance of lateral thermo-electric components (TEC's) in silicon MEMS is discussed and compared to the more conventional discrete transversal devices. It is demonstrated that the Seebeck effect, the Peltier effect and the Thomson effect have to be included for a realistic analysis. The presentation focuses on poly-Si0.7Ge0.3 as a thermo-electric material that is process compatible with IC fabrication in silicon. The material has been analyzed and fully characterized recently using on-chip MEMS-based test structures. Applications are in uncooled bolometers, on-chip auxiliary electrical power generation and room-temperature thermal stabilization of a micromachined platform in silicon containing a reference component.
A CMOS process can relatively easily be adapted to include SiGe TEC's. Typcical results are: Seebeck coefficient _n= -179 _V/K and _p= 131 _V/K at 295 K with a TC of 0.2 _V/K2 and -0.1 _V/K2, respectively. Contact resistance and parasitic thermal conductance are limiting factors in lateral on-chip TEC's. High-dose implantation and appropriate anneal have been used to achieve an electrical resistivity of 28.9 ©m for p-doped material and 29.2 ©m for n-doped material. Thermal conductivity was measured ā= 5 Wm-1K-1, which is close to the theoretical minimum. The resulting figure of merit zdev= 168×10-6 K-1, which would enable a maximum temperature difference for Peltier cooling of ÎTmax= 7.3 K. Thermal conductance of metal interconnect limits ÎTmax to smaller values. In the application of temperature stabilization close to ambient temperature, Peltier heating and cooling offers superior dynamic performance, as compared to passive cooling.

Reinoud F. Wolffenbuttel received a M.Sc. degree in 1984 and a Ph.D. degree in 1988, both from the Delft University of Technology. Between 1986 and 1993, he has been an assistant professor, and since 1993, he has been an associate professor at the Department of Microelectronics, Faculty of Information Technology and Systems of the Delft University of Technology. He is involved in instrumentation and measurement in general and on-chip functional integration of microelectronic circuits and silicon sensor, IC process compatible MEMS fabrication and silicon microsystems in particular. He was a visitor at the University of Michigan, Ann Arbor, USA in 1992, 1999, and 2001, Tohoku University, Sendai, Japan in 1995, and EPFL, Lausanne, Switzerland in 1997. He is the recipient of a 1997 NWO pioneer award. He served as general chairman of the Dutch national sensor conference in 1996, Eurosensors in 1999 and the MicroMechanics Europe workshop in 2003.