Synthesis and characterization of CaRuO3 and SrRuO3 for resistor paste application

Resistors used in Hybrid Micro Circuits are essentially cermet composites consisting of an intimate mixture of an insulating phase and a suitable conducting phase, the relative proportions of which determine the nominal resistivity of the resultant resistor paste. Resistor pastes were formulated by using ruthenium based perovskites of Ca and Sr. The ruthenates of alkaline earth elements (Ca and Sr) have high metallic conductivity (28-300 microohm.cm) and have been extensively used in superconducting and ferroelectric systems. Ca and Sr ruthenates were prepared by heating the physical admixtures of the respective carbonates of Ca/Sr and RuO2 at 500, 800 and 900 C for 15 h. The resultant powders were characterised by TGA/DTA, SEM-EDX and XRD. Solid-state reactions occurred between 700 and 800 C, but the powder thus obtained contained carbonate and hence the powders were heated again at 900 C for 15 h to eliminate the detrimental effect of carbonate in the resistor paste. Microstructural studies revealed that the average particle size was about 200-400 nm. Resistor paste was formulated by using powder admixtures heated at 800 and 900 C. A preliminary account is given of the synthesis and physico-chemical, electrical and microstructural properties of powders and fired thick film resistors. 15 refs.