RUTHENIUM CLUSTERS IN LEAD-BOROSILICATE GLASS IN THICK-FILM RESISTORS

An interparticle glass matrix in ruthenium dioxide-based thick film resistors has been studied intensively by means of analytical and high resolution transmission electron microscopy. The ruthenium dioxide phase interacts with lead-borosilicate glass at high temperature by dissolving ruthenium ions and incorporating a small number of lead and aluminum ions on the surface. Ruthenium ions diffuse through the glass network at least over a distance of 1 mum during firing, but are accommodated in the glass structure by an amount only less than 7 at. % at room temperature. High resolution electron microscopy reveals numerous ruthenium-pyrochlore crystallites in high-lead glasses, but hardly any Ru-based clusters/crystallites in low-lead glasses, where lead-rich glass clusters due to glass immiscibility and reduced lead metal clusters are more commonly observed instead of ruthenium clusters. Lead oxide is prone to reduction both in high- and low-lead glasses upon irradiating with a high-energy incident electron beam. Comparison with gold-based resistor and estimation of average dispersion length of ruthenium clusters, 2 to 4 nm, prefer the model of electron hopping via ruthenium clusters/crystallites as a dominant conduction mechanism in thick film resistors.