Robust Electrical Contacts for Sensors and Electronics in Space Flight

During my time as a NASA Space Technology Research Fellow, I studied metalsemiconductor interfaces both at Penn State University and NASA Glenn Research Center. This project has focused on studying tungsten-nickel contacts to the silicon carbide for high temperature electronics. Select alloy compositions form simultaneous ohmic contacts to both ptype and n-type silicon carbide after equivalent processing steps and annealing between 1000– 1150 °C. The ohmic contacts have low specific contact resistances (10-6–10-5 Ωcm2) to both conductivity types. Materials characterization of these contacts indicates an important phase transformation into a tungsten-nickel-carbide occurring in all the ohmic contacts. A tungsten carbide and nickel silicide also form at the higher temperatures. I also studied diffusion barriers for these contacts, high-temperature reliability, and the effect of polarity on the kinetics of reaction between metals and a different polar semiconductor, indium nitride From the present work, the formation of WxNiyC seems linked to formation of lowresistance, W:Ni ohmic contacts to SiC. Knowledge gained from further annealing will help quantitatively judge their lifetimes under various conditions. Future work in this area should focus on stable diffusion barriers for long-term protection from the environment at high temperatures. Other future work should investigate polarity’s impact on ohmic contact performance. At present, the W:Ni alloys with an atomic concentration of nearly 50:50 have shown the formation of ohmic contacts with low specific contact resistances to both conductivity types of SiC. Industries from drilling to aerospace will demand the availability of electronics for high temperatures, requiring further development of these materials for achieving the desired goals.