Excess noise and refiring processes in thick-film resistors

Excess noise in thick-film resistors (TFRs) fired from one to ten times under the same firing profile has been investigated. The changes in structure and composition, which are responsible for variations in sheet resistivity and TCR, affect also the noise index of TFRS, sometimes in a substantial way, and the changes in noise index depend both on the resistor composition and the nature of the substrate. Moreover, the excess noise appears to be correlated to physico-chemical phenomena induced by refiring in the bulk of the resistors, much more than to changes in the density of microdefects (or microvoids) in the resistors investigated.