Feasibility of preparing patterned molybdenum coatings on bismuth telluride thermoelectric modules

Abstract

Molybdenum electrical interconnects for thermoelectric modules were produced by air plasma spraying a 30µm size molybdenum powder through a laser-cut Kapton tape mask. Initial feasibility demonstrations showed that the molybdenum coating exhibited excellent feature and spacing retention (~170µm), adhered to bismuth-telluride, and exhibited electrical conductivity appropriate for use as a thermoelectric module interconnect. A design of experiments approach was used to optimize air plasma spray process conditions to produce a molybdenum coating with low electrical resistivity. Finally, a molybdenum coating was successfully produced on a fullscale thermoelectric module. After the addition of a final titanium/gold layer deposited on top of the molybdenum coating, the full scale module exhibited an electrical resistivity of 128Ω, approaching the theoretical resistivity value for the 6mm module leg of 112Ω. Importantly, air plasma sprayed molybdenum did not show significant chemical reaction with bismuth-telluride substrate at the coating/substrate interface. The molybdenum coating microstructure consisted of lamellar splats containing columnar grains. Air plasma sprayed molybdenum embedded deeply (several microns) into the bismuth-telluride substrate, leading to good adhesion between the coating and the substrate. Clusters of round pores (and cracks radiating from the pores) were found immediately beneath the molybdenum coating. These pores are believed to result from tellurium vaporization during the spray process where the molten molybdenum droplets (2623°C) transferred their heat of solidification to the substrate at the moment of impact. Substrate cooling during the molybdenum deposition process was recommended to mitigate tellurium vaporization in future studies.

BibTeX

@techreport{2013_sarobol_patterned_molybdenum_coatings,
  title     = {Feasibility of preparing patterned molybdenum coatings on bismuth telluride thermoelectric modules},
  author    = {Sarobol P and Hall A and Miller S and Knight M and LePage W and Sobczak C and Wesolowski D},
  institution = {Sandia National Laboratories, SAND2013-7962},
  year      = {2013},
}

Vancouver

Sarobol P, Hall A, Miller S, Knight M, LePage W, Sobczak C, et al. Feasibility of preparing patterned molybdenum coatings on bismuth telluride thermoelectric modules. Sandia National Laboratories, SAND2013-7962. 2013.

Version and rights

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Sandia National Laboratories technical report, approved for unlimited public release.