Composition and temperature coefficient of resistance of Ni-Cr thin films

Abstract

Thin films of Ni-Cr have previously been found to have an anomalous maximum in the temperature coefficient of resistance (TCR) values in the thickness range 100–150 Å. The region of high TCR on the higher thickness side (170–230 Å) of this maximum was studied. Films were evaporated from a given amount of the evaporant material under high vacuum ((1–8) × 10 −4 Pa) in series of depositions at 0.5–1.5 Å s −1. Their thickness-composition profiles were analysed using Auger electron spectroscopy in conjunction with sputtering and their TCR and electrical resistivity values were compared. It was shown that under certain conditions the anomalous TCR maximum could be avoided. Thinner films and films deposited at slower rates had higher resistivities and higher total contents of oxygen and carbon. Ni-Cr films of low (less than 100 ppm °C −1) TCR were obtained at all thicknesses studied when the sum of the total atomic contents of chromium, oxygen and carbon reached 50–55%. This effect is attributed to potential barriers due to chromium oxide and carbide in the grain boundary region.