The Effect of Surface Morphology of Substrates Upon Electrical Stability of Nichrome Thin Film Resistors

The effect of substrate surface roughness on the thermal stability of nichrome thin film resistors is presented. This investigation was confined primarily to glass- and alumina-type substrates. Electron microscope surface morphology examinations made of alumina substrates, obtained from different sources, revealed some differences in microstructure. No particular microdefect or combination of defects could be rigorously related to the thermal aging data for alumina. Comparative results between glass and alumina, where differences in roughness were quite pronounced, gave corresponding large differences in stability during thermal aging. Oxidation based on surface roughness is suggested as the mechanism to account for the increase in resistance obtained on the nichrome films supported on alumina during thermal aging.