OHMIC STABILITY AND LOW-TEMPERATURE COEFFICIENT OF RESISTANCE OF CU-NI-AU-NI MULTILAYERS OBTAINED IN ULTRAHIGH-VACUUM BY CONTROLLED CO-EVAPORATION

For compositions around 43 at.% Ni, thin films of CuNi alloys more than 1200 Å thick deposited in ultrahigh vacuum (UHV) onto a fused silica substrate by controlled co-evaporation from two separate copper and nickel sources show low negative temperature coefficients of resistance (TCRs) (-10-4 to -10-6 °C-1) and a satisfactorily high stability in the temperature range 20-300 °C in UHV. In the atmosphere, however, the ohmic behaviour of the films shows hysteresis and appreciable instability due to oxidation. Thin Au-Ni films (38 at.% Ni) have a higher positive TCR (+2 × 10-4 °C-1) but they have the advantage of being less oxidized in atmospheric air up to 150 °C. In order to obtain unoxidizable multilayers with a low TCR we prepared CuNi films 1300 Å thick and stabilized them by annealing. AuNi films 200 Å thick were then deposited onto the CuNi films by controlled co-evaporation. After the annealing process the TCR was about -3 × 10-6 °C-1 from 20 to 150 °C. The ohmic stability tested from 20 to 150 °C in nitrogen and then in the atmosphere showed no appreciable zero balance drift or ohmic instability. © 1979.