Evolution of ruthenate-based thick film cermet resistors

An experimental investigation has been carried out to study variations of microstructure, composition and electrical properties (sheet resistance and its temperature coefficient) occurring in thick film (cermet) resistors during the annealing process which transforms the initial ink into a resistive layer. Resistors based on Bi₂Ru₂O₇ and a lead silica glass have been studied. Analyses have been performed on the inks using thermogravimetric measurements, and on annealed (fired) layers by means of X-ray diffraction, atomic absorption, electron microscopy, microprobe analysis and other complementary techniques. The results point out the role of exchange reactions and redox reactions inside the resistor body and emphasise the complexity of the phenomena which concur to define the final electrical properties of these resistive systems. Interrelations between microstructure, composition and electrical properties have been found and tentative explanations proposed.