Process development and material characterization of polycrystalline Bi2Te3, PbTe, and PbSnSeTe thin films on silicon for millimeter-scale thermoelectric generators

Boniche, I.; Morgan, B. C.; Taylor, P. J.; Meyer, C. D.; Arnold, D. P.

doi:doi:10.1116/1.2841522

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Journal of Vacuum Science & Technology A / Volume 26 / Issue 4 / PAPERS FROM THE 54TH INTERNATIONAL SYMPOSIUM OF AVS / MEMS and NEMS

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J. Vac. Sci. Technol. A 26, 739 (2008); http://dx.doi.org/10.1116/1.2841522 (6 pages)

Process development and material characterization of polycrystalline Bi₂Te₃, PbTe, and PbSnSeTe thin films on silicon for millimeter-scale thermoelectric generators

I. Boniche¹, B. C. Morgan², P. J. Taylor², C. D. Meyer¹, and D. P. Arnold¹

¹Interdisciplinary Microsystems Group, University of Florida, 229 Benton Hall, Gainesville, Florida 32611–6200
²U.S. Army Research Laboratory, Adelphi, Maryland 20783

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(Published online 30 June 2008)

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In this work, deposition, patterning, and metallization of vapor-deposited polycrystalline thermoelectric (TE) thin films of Bi₂Te₃, PbTe, and PbSnSeTe on silicon (Si) substrates are investigated. These fundamental microfabrication methods are intended for use in integrating TE films into thermally powered micro-electro-mechanical systems (MEMS)-based power generators. P-type polycrystalline Bi₂Te₃, PbTe, and PbSnSeTe films were successfully deposited on thermally oxidized (100) Si substrates to thicknesses ranging from 0.4 to 9 μm. Dry etch rates of about 0.6−0.7 μm/min were achieved for Bi₂Te₃ and PbTe/PbSnSeTe using methane-based gases. Wet etch rates of ∼ 3 μm/min were achieved using various acid wet chemistries. Films were electrically characterized using van der Pauw and transfer length method (TLM) test structures. Postdeposition resistivities were measured as low as 23 mΩ cm for Bi₂Te₃, 134 mΩ cm for PbTe, and 52 mΩ cm for PbSnSeTe. The Seebeck coefficients were measured at up to 94 μV/K for undoped Bi₂Te₃, and 160 and 42 μV/K for doped PbTe and PbSnSeTe, respectively. Metal contact resistivities (0.18−42 mΩ cm²) were also extracted for a variety of thin film metals (Pt, Au, Cu, Ni, Cr/Pt/Au, Ti/Pt). Various postdeposition annealing treatments were explored for reducing film resistivity that would enable higher power delivery for TE generator applications. Rapid thermal annealing in nitrogen at 400 °C was shown to reduce the resistivity of PbTe and improve film adhesion to oxidized silicon substrates. Also, after successive heatings in air at 200 °C, the resistivity of the PbTe films remained stable while that of the PbSnSeTe increased up to 10×.

ACKNOWLEDGMENTS

This research was sponsored by the Army Research Laboratory (ARL) and was accomplished under Cooperative Agreement No. W911NF-06-2-0004. The authors appreciate the support of the staff at ARL and the University of Florida Nanofabrication Facilities (UFNF).

Article Outline

INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
1. Film microstructure
2. Etch studies
3. Electrical and thermoelectric performance of Bi₂Te₃ , PbTe, and PbSnSeTe
4. Thermal stability of PbTe and PbSnSeTe
CONCLUSIONS

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KEYWORDS and PACS

Keywords

bismuth compounds, electrical resistivity, etching, lead compounds, metallisation, micromechanical devices, rapid thermal annealing, Seebeck effect, thermoelectric devices, thin films, vapour deposition, Materials terms: lead telluride, bismuth telluride, bromine, hydrobromic acid, methane, hydrochloric acid, nitric acid, silicon dioxide, polyimide, photoresist, silicon

PACS

85.40.Ls

Metallization, contacts, interconnects; device isolation
73.40.Ns

Metal-nonmetal contacts
81.05.Hd

Other semiconductors

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History

Received 1 October 2007
Accepted 14 January 2008
Published online 30 June 2008

Digital Object Identifier

http://dx.doi.org/10.1116/1.2841522

PUBLICATION DATA

ISSN

0734-2101 (print)

1520-8559 (online)

Publisher

American Vacuum Society

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