Reliability and effective signal-to-noise ratio of RuO2-based thick film strain gauges: The effect of conductive and glass particle size

For RuO₂-based thick film resistors used in high-sensitivity and -reliability strain gauges, crucial quality indicator besides long-term stability is the effective signal-to-noise ratio, which incorporates both piezoresistive strain response and current noise produced in the resistive film. Previous research in this field has shown an influence of both conductive and glass particle sizes on the microstructure and electrical properties of the films, however, most of these studies did not account for effects on resistor reliability and effective noise behaviour. The aim of this work is a systematic approach to revealing correlations between strain sensitivity, current noise and stability of resistance on one side and resistor microstructure on the other. For this purpose, various thick film resistor pastes have been prepared from RuO₂- and glass powders of different particle size distributions and concentrations. It has been shown that the conductive and insulating particle sizes effect resistance and its temperature behaviour, the effective signal-to-noise ratio and the ageing stability of resistance, and that the development of a thick film paste suitable for strain gauges requires an application dependent tradeoff between these properties.