We have investigated the electrical characteristics of three different stacks of ohmic contacts (TiW/Ti/Pt, TiW, and Ni/TaSix/Pt) on highly doped n-type 4H-silicon carbide for harsh environment operation gas sensor applications such as automotive and space aircraft applications. The first two samples were tested at 500 ~ 600 oC in a vacuum chamber for up to 300 hours. From our TLM measurement, TiW contacts with a Ti glue layer and a Pt capping layer have stable specific contact resistance at high temperature in a vacuum chamber. The long-term reliability tests of ohmic contacts in an oxidizing environment (20 % O2/N2) for up to 520 hours showed that TiW/Ti/Pt had the better stability and the lower contact resistance while Ni/TaSix/Pt ohmic contacts had a severe contact degradation due to the oxidation at the interface. Therefore, we believe that our TiW based metallization schemes can be applied to gas sensor operating in a harsh environment such as an oxidizing ambient.
Keywords: Silicon carbide, Ohmic contacts, TLM structure, 4H-SiC, Long-term stability
pISSN 0374-4914
eISSN 2289-0041
