Semiconductor ceramics for NTC thermistors: the reliability aspects

Thermally induced processes in ceramic-electrode interfaces of CuxNi1-x-yCo 2yMn2-yO4-based NTC thermistors as a function of their chemical composition s and quantitative parameters of low-temperature annealing at 400-800 degre es C are studied. Thermal treatment of thermistors at 400-600 degrees C dur ing 15 h leads to degradation of the metallization layers for the majority of the investigated samples owing to the migration of electrode material (s ilver) into ceramic body. An accompanying anomalous increase of thermistors ' electrical conductivity is observed. The following thermal treatment duri ng 15 h at 800 degrees C leads to an electrical conductivity regeneration t o, approximately, the initial values. The reversible nature of this phenome non is confirmed by Auger-spectroscopy method. Some of the studied NTC ther mistors appear to be stable to low-temperature thermal treatment. These com positions are proposed for applications in devices operating at the tempera tures up to 530 degrees C. (C) 2001 Elsevier Science Ltd. All rights reserv ed.