Contact resistance in PTC thermistors

Abstract

The electrode resistance of semiconducting PTC BaTiO/sub 3/ ceramic was studied in same detail. Commercial In-Ag paste, In-Ga alloy, and electroless plated Ni as well as evaporated Al with and without Pt overcoat layer mere chosen as electrode. The contact resistance of electroded samples at or above room temperature was determined using both dc resistance and ac impedance measurements. The aging of contact resistance under cyclic loading from -10 to 85/spl deg/C was also monitored for the prolonged period of time. The effect of heat treatment and protective coating on the stability of Al electrode was determined. Commercial In-Ag paste showed the excellent stability against contact resistance degradation. However, the contact resistance of Al electrode during aging was strongly dependent on the annealing condition and the presence of protective layer.