Origin of the enhanced electrical characteristics of BaTiO₃-based thermistors by sputtered Al and Ni-Cu buffer electrode films

Significant improvements in the characteristics of positive temperature coefficient of resistance for BaTiO₃/Ag-based temperature sensors are reported by utilizing buffer electrode films of Al and Ni-Cu. The Ni-Cu buffer layer was more effective in reducing room temperature electrical resistance than the Al layer, which results in a significant increase in the resistance jump ratio. As a promising example, the use of a 541 nm thick Ni-Cu buffer film demonstrated a substantially increased log(R_max/R_min) value of 3.15, compared to 1.80 for only the Ag electrode without the buffer layer. Origin of the enhancement by Ni-Cu is attributed due to the improved ohmic behavior with a lowered Schottky barrier potential at the ceramic-electrode interfaces. The thicker layer is preferred regardless of the type of buffer layer since it demonstrates a lower interfacial electrical resistance as confirmed by the impedance analysis.