Thermal Aging of ThickFilm Resistors

The paper reports the results of a systematic study of the effects of thermal ageing in thick-film resistors (TFRs) over a wide temperature range (from 125°C to 4O0°C). The relative change of resistance ?>R/R was studied as a function of ageing temperatures and times. TCR and excess noise index before and after ageing processes were also measured. These electrical properties were investigated on samples prepared in the same way, except for the substrate, the latter being in all cases 96% alumina, taken from five different suppliers. A systematic difference in ?>R/ R for the same ageing conditions is observed in samples on different substrates.

The relative change of resistance is positive after ageing at lower temperatures up to very long times; it follows a square-root dependence and is thermally activated. At higher temperatures ?>R/R is negative and follows a linear time dependence.

Resistors with different thicknesses were also analysed; the thinner the sample, the larger is the ?>R/R observed under the same ageing conditions.

All these experimental findings must be considered in a comprehensive interpretative scheme of ageing mechanisms of TFRs on alumina substrates.