Synthesis and characterization of CaRuO sub(3) and SrRuO sub(3) for resistor paste application

Resistors are used in Hybrid Micro Circuits (HMC) are essentially cermet composites consisting of an intimate mixture of an insulating phase (the glass binder or glass frit) and suitable conducting phase, the relative proportions of which to a greater degree, determine the nominal resistivity of the resultant resistor paste. In this paper, we report resistor pastes formulated by using ruthenium based perovskites of Ca and Sr. Though the ruthenates of alkaline earth elements (Ca and Sr) have high metallic conductivity (28-300 mu Omega cm) and have been extensively used in superconducting and ferroelectric systems, their usage in thick film resistor pastes has rarely been reported. Ca and Sr ruthenates were prepared by air-heating the physical admixtures of respective carbonates of Ca/Sr and RuO sub(2) at three different temperatures, viz., 500, 800 and 900 degree C. In each case, heating was carried out for 15 h. The resultant powders were characterized by TGA/DTA, SEM-EDX and XRD techniques. The solid-state reactions were found to occur between 700-800 degree C. But the powder, thus obtained, contained certain amount of carbonate and hence the powders were heated again at 900 degree C for 15 h to eliminate detrimental effect of carbonate in resistor paste. The microstructural studies of powders revealed that the average particle size is around 200-400 nm. The resistor paste was formulated by using powder admixtures heated at two different temperatures, viz., 800 and 900 degree C. In this paper, we are presenting the preliminary account on synthesis and physico-chemcial, electrical and microstructural properties of powders and fired TFRs.