Semiconductor ceramics for NTC thermistors: the reliability aspects

Thermally induced processes in ceramic–electrode interfaces of CuxNi1–x–yCo2yMn2–yO4-based NTC thermistors as a function of their chemical compositions and quantitative parameters of low-temperature annealing at 400–800° C are studied. Thermal treatment of thermistors at 400-600° C during 15 h leads to degradation of the metallization layers for the majority of the investigated samples owing to the migration of electrode material (silver) into ceramic body. An accompanying anomalous increase of thermistorsʹ electrical conductivity is observed. The following thermal treatment during 15 h at 800°C leads to an electrical conductivity regeneration to, approximately, the initial values. The reversible nature of this phenomenon is confirmed by Auger-spectroscopy method. Some of the studied NTC thermistors appear to be stable to low-temperature thermal treatment. These compositions are proposed for applications in devices operating at the temperatures up to 530° C.