| AVS 54th International Symposium | |
| MEMS and NEMS | Monday Sessions |
| Session MN-MoM |
| Session: | Materials Processing, Characterization and Fabrication Aspects |
| Presenter: | I. Boniche, University of Florida |
| Authors: | I. Boniche, University of Florida B.C. Morgan, U.S. Army Research Laboratory P.J. Taylor, U.S. Army Research Laboratory C.D. Meyer, University of Florida D.P. Arnold, University of Florida |
| Correspondent: | Click to Email |
Numerous opportunities exist in commercial and military applications for thermoelectric (TE) energy scavengers to act as integrated power sources. Bulk TE materials and modules are commercially available but are often tailored for heating/cooling applications, rather than power generation. Additionally, these bulk technologies limit the miniaturization of TE modules. This work seeks to develop and characterize vapor-deposited polycrystalline TE thin films on Si substrates for integration with MEMS devices, specifically investigating Bi2Te3 and PbTe alloys for both room and high-temperature applications. P-type polycrystalline Bi2Te3 and PbTe films from 0.4 µm to 9 µm thick have been successfully deposited on bare and etched Si, thermally oxidized Si, and Si/SiO2 substrates with patterned metal traces. The films were vapor-deposited in UHV using congruent sublimation of the solid-source parent compounds. Fundamental microfabrication techniques for Bi2Te3 films, such as patterning and metallization, have recently been developed to augment previous work on PbTe alloys.1 Dry etch rates of 0.4 µm/min and 0.7 µm/min were obtained for Bi2Te3 and PbTe, respectively. Wet etch rates of ~3 µm/min were achieved using bromine-based chemistries, but at the expense of mask undercut. Films have been characterized electrically using van der Pauw and transfer length method test structures. As-deposited resistivity was 23 mΩ-cm for Bi2Te3, and 126 mΩ-cm for PbTe films. Contact resistivities of 2x10-4 Ω-cm2 were achieved for Cr/Pt/Au on Bi2Te3, and 4x10-4 Ω-cm2 for Cr/Au on PbTe. The Seebeck coefficient was measured to be 94 μV/K for Bi2Te3 and ~100 μV/K for PbTe alloys. Analytical modeling of in-plane MEMS TE generators showed that film resistivity is a limiting factor for power generation. Various post-deposition annealing treatments were explored to reduce film resistivity, and thus enable higher power delivery. The results show that successive rapid thermal annealing in nitrogen at 400°C can reduce the resistivity of PbTe. The integration of these materials into prototype generator structures will also be discussed, particularly towards developing fabrication compatible TE, heat exchanger, and mechanical MEMS structures.
1I. Boniche, et al, PowerMEMS Conf., Nov. 2006.